Carbonylation of Polyfluorinated 1-Arylalkan-1-ols and Diols in Superacids

We describe the carbonylation of a series of mono and dihydroxy derivatives of polyfluorinated alkylbenzenes and benzocycloalkenes with OH groups at benzylic positions using carbon monoxide in the presence of a superacid (TfOH, a TfOH–SbF5 mixture, or a FSO3H–SbF5 mixture). It was shown that the superacid-catalyzed addition of CO to various primary and secondary polyfluorinated alcohols and diols gives the corresponding mono- and dicarboxylic acids or lactones. The efficiency of various superacids depending on alcohol structure was evaluated, and FSO3H–SbF5 yielded the best results in most transformations. The addition of CO to secondary 1-arylalkan-1-ols containing vicinal fluorine atoms was found to be accompanied by elimination of HF with the formation of α,β-unsaturated aryl-carboxylic acids. In contrast to primary and secondary alcohols, conversion of tertiary perfluoro-1,1-diarylalkan-1-ols into carbonylation products is not complete, and the resulting carboxylic acids are easily decarboxylated after water treatment of the reaction mixture.


Introduction
Organofluorine compounds are important for basic research in organic chemistry and for its applications, particularly to materials science, biomedicine, and agriculture [1][2][3][4][5][6][7][8][9][10]. Therefore, the development of new approaches to their synthesis is of obvious interest. Currently in hydrocarbon chemistry, there are many known acid-catalyzed carbonylation reactions of alcohols, alkyl halides, and other compounds proceeding via CO addition to carbocations generated from these compounds in acidic systems and leading to the formation of carboxylic-acid derivatives [11][12][13]. In spite of the variety of reactions of fluorinated cations, acid-catalyzed carbonylation of polyfluorinated compounds had not been known before our recent reports [14][15][16][17], and a reverse reaction-decarbonylation of fluorinated acyl halides under the action of Lewis acids-is commonly observed [18][19][20]. Known examples of acid-catalyzed carbonylation of organofluorine compounds (structures where a fluorine atom or polyfluoroalkyl group is separated from the reaction center by no more than 4-5 bonds and can influence it) are limited to reactions of alcohols Ar 2 RCOH (R = H, CH 3 ) containing no more than two fluorine atoms [21] as well as mono-(polyfluoroalkyl)-substituted adamantyl halides [22,23] with a mixture of formic and sulfuric acids resulting in carboxylic acids.
In our previous research, we have found that perfluorinated alkyl-and phenylbenzocyclobutenes [14,15] and their carbonyl derivatives [17] undergo carbonylation/ four-membered-ring opening tandem reactions under the action of carbon monoxide at atmospheric pressure in the presence of SbF 5 . In these reactions, irreversible four-memberedring transformations promote the conversion of polyfluorobenzocyclobutenes into the desired products. In the CO-SbF 5 system, the possibility of carbonylation of per-and polyfluorinated indanes and tetralins giving rise to fluorocarbonyl derivatives and corresponding acids after hydrolysis has been demonstrated too [16], and the transformation proceeds as an equilibrium process without skeletal rearrangements, while the degree of conversion substantially depends on the substrate structure. The discovered transformations are first examples of the functionalization of perfluorinated compounds via a carbonylation reaction.
In this research field, we have studied the possibility of H + -catalyzed carbonylation of polyfluorinated alcohols. The current work describes the carbonylation of a series of mono and dihydroxy derivatives of polyfluorinated alkylbenzenes and benzocycloalkenes with OH groups at benzylic positions by means of carbon monoxide in the presence of such a superacid as TfOH, a TfOH-SbF 5 mixture, or an FSO 3 H-SbF 5 mixture as a way to transform the above compounds into carboxy derivatives. Polyfluorinated α-aryl-substituted aliphatic carboxylic acids are of interest because this class of compounds with fluorine atoms in both aliphatic and aromatic moieties has been investigated as bioactive compounds or used for synthesis thereof [49][50][51][52][53][54], as is the case for halogenated derivatives of benzocycloalkene-1-carboxylic acids [55][56][57][58][59]. The presence of a polyfluorinated aromatic ring in the molecule gives an opportunity for further synthetic modification via S n Ar substitution. Additionally, the perfluorinated aryl group has unique physicochemical properties that can be used in the design of materials. For instance, derivatives of pentafluorophenyl acetic acid have been utilized to create semiconductor and photoluminescent materials [60,61], gas sensors [62], and supramolecular associates for biological applications [63,64].

Results and Discussion
2.1. Carbonylation of Primary and Secondary Alcohols C 6 F 5 CH(OH)R (R = H, C 6 F 5 , CF 3

), and Selection of a Superacid
It was shown that 1-phenylalkan-1-ols 1a-c (Table 1) can be converted to corresponding acids 2 by carbonylation in superacids using carbon monoxide under atmospheric pressure, followed by water treatment of the reaction mixture. In TfOH, pentafluorobenzyl alcohol 1a adds CO, and heating to 50 • C is required for a fast and complete reaction, whereas diphenylmethanol 1b easily reacts at room temperature (r.t.). In contrast, alcohol 1c failed to be carbonylated in TfOH, and its acidity is apparently insufficient to generate the respective CF 3 -substituted intermediate carbocation. The use of a mixture of TfOH and SbF 5 (1:1), which has higher acidity, made it possible to obtain the carbonylation product, acid 2c, at r.t. Two equiv. of this mixture allowed to achieve 95% conversion of the starting alcohol into acid 2c in 2 h. As the reaction time was extended, the conversion approached 100%. Reducing the amount of the acid mixture to 1.5 equiv. considerably reduced the content of acid 2c. An FSO 3 H-SbF 5 mixture (1:1) compared to TfOH-SbF 5 (1:1) in the amount of 2 equiv. worked more efficiently, yielding complete conversion of alcohol 1c to acid 2c in 2 h, probably due to its higher acidity [65]. Table 1. Carbonylation of primary and secondary alcohols C 6 F 5 CH(OH)R 1a-c in superacids.
the starting alcohol into acid 2c in 2 h. As the reaction time was extended, the conversion approached 100%. Reducing the amount of the acid mixture to 1.5 equiv. considerably reduced the content of acid 2c. An FSO 3 H SbF 5 mixture (1:1) compared to TfOH-SbF 5 (1:1) in the amount of 2 equiv. worked more efficiently, yielding complete conversion of alcohol 1c to acid 2c in 2 h, probably due to its higher acidity [65].

Carbonylation of Tertiary Perfluorinated 1,1-Diarylalkan-1-ols
Alcohols 1d-f ( Table 2) did not react with CO in TfOH at r.t. despite the presence of two aryl moieties that can stabilize the intermediate cation. With an increase in the reaction temperature, the substitution of fluorine atoms in the aryl moiety began to occur instead of carbonylation. It was noted that TfOH-SbF 5 (1:1) enables us to carry out the carbonylation of alcohol 1d; however, after hydrolysis of the reaction mixture, the resulting acid 2d was easily decarboxylated, giving hydro derivative 3d and alkene 4d (see Scheme 2). Replacing the hydrolysis with treatment of the reaction mixture with methanol led to the formation of methyl ester 2dMe; however, decarboxylation products 3d and 4d also formed. Another difference from the carbonylation of alcohols 1a-c was the incomplete conversion of tertiary alcohol 1d into carbonylation products: the reaction mixtures also contained perfluorodiphenylethane 5d and the starting alcohol. The highest conversion of compound 1d to carbonylation products in the TfOH-SbF 5 medium was achieved with the help of 2 equiv. of the superacid (total content of products 3d and 4d:~30%). Extension of the reaction time from 5 to 24 h barely changed the reaction outcome, whereas an increase in the amount of the superacid to 4 equiv. or its decrease to 1.2 equiv. substantially diminished the concentration of products 3d and 4d in the reaction mixture. Using 2 equiv. of the mixture of FSO 3 H and SbF 5 (1:1) instead of TfOH-SbF 5 afforded a slightly higher conversion of alcohol 1d to carbonylation products (~45%); in this case, the introduction of a solvent (C 6 F 6 ) was required to reduce the viscosity of the reaction mixture for efficient mixing. The results on carbonylation of compound 1d can be explained (Scheme 1) by the presence (in the TfOH-SbF5 medium) of an equilibrium between noncarbonylated forms (alcohol 1d or/and its triflate: fluoro derivative 5d) and carbonylation products (acid 2d, the corresponding acyl fluoride 2dF, or/and acyl triflate). The feasibility of carbonylation of perfluorodiphenylethane 5d in this medium was confirmed by a separate experiment. The equilibrium state depended on the amount of the superacid: its excess shifted the equilibrium toward decarbonylation, whereas its deficit hindered the generation of cation 6, which interacts with CO. After water treatment of the reaction mixture, all carbonylation products were hydrolyzed into acid 2d. In an aqueous medium, its deprotonation was possible, and the resulting carboxylate anion-owing to steric hindrance and the electron-withdrawing effect of substituents-easily eliminated CO2 with the formation of carbanion 7. The latter either added a proton or eliminated a fluoride ion, thereby yielding 3d and 4d, respectively. The formation of alkene 4d as a result of the transformation of hydro derivative 3d during treatment of the reaction mixture is unlikely; it was found that such elimination of HF, even in the presence of a base, is possible only under forcing conditions (NEt3, CaH2, 130 °C). The emergence of acid 2d and acyl fluoride 2dF, along with compounds 3d and 4d, could be detected after water treatment during the extraction of products with a mixture of CH2Cl2 and Et2O; the concentration of acid 2d in the extract gradually declined with time, while the concentration of products 3d and 4d went up. Extraction with pure Et2O gave only compounds 3d and 4d. Scheme 1. Transformations of compound 1d in the reaction with CO in TfOH-SbF 5 followed by water treatment.  the concentration of products 3d and 4d in the reaction mixture. Using 2 equiv. of the mixture of FSO3H and SbF (1:1) instead of TfOH-SbF5 afforded a slightly higher conversion of alcohol 1d to carbonylation products (~45% in this case, the introduction of a solvent (C6F6) was required to reduce the viscosity of the reaction mixture for efficient mixing. (1:1) instead of TfOH-SbF5 afforded a slightly higher conversion of alcohol 1d to carbonylation products (~45%); in this case, the introduction of a solvent (C6F6) was required to reduce the viscosity of the reaction mixture for efficient mixing.  The results on carbonylation of compound 1d can be explained (Scheme 1) by the presence (in the TfOH-SbF5 medium) of an equilibrium between noncarbonylated forms (alcohol 1d or/and its triflate: fluoro derivative 5d) and carbonylation products (acid 2d, the corresponding acyl fluoride 2dF, or/and acyl triflate). The feasibility of carbonylation of perfluorodiphenylethane 5d in this medium was confirmed by a separate experiment. The equilibrium state depended on the amount of the superacid: its excess shifted the equilibrium toward decarbonylation, whereas its deficit hindered the generation of cation 6, which interacts with CO. After water treatment of the reaction mixture, all carbonylation products were hydrolyzed into acid 2d. In an aqueous medium, its deprotonation was possible, and the resulting carboxylate anion-owing to steric hindrance and the electronwithdrawing effect of substituents-easily eliminated CO2 with the formation of carbanion 7. The latter either added a proton or eliminated a fluoride ion, thereby yielding 3d and 4d, respectively. The formation of alkene 4d as a result of the transformation of hydro derivative 3d during treatment of the reaction mixture is unlikely; it was found that such elimination of HF, even in the presence of a base, is possible only under forcing conditions (NEt3, CaH2, 130 °C). The emergence of acid 2d and acyl fluoride 2dF, along with compounds 3d and 4d, could be detected after water treatment during the extraction of products with a mixture of CH2Cl2 and Et2O; the concentration of acid 2d in the extract gradually declined with time, while the concentration of products 3d and 4d went up. Extraction with pure Et2O gave only compounds 3d and 4d. The results on carbonylation of compound 1d can be explained (Scheme 1) by the presence (in the TfOH-SbF5 medium) of an equilibrium between noncarbonylated forms (alcohol 1d or/and its triflate: fluoro derivative 5d) and carbonylation products (acid 2d, the corresponding acyl fluoride 2dF, or/and acyl triflate). The feasibility of carbonylation of perfluorodiphenylethane 5d in this medium was confirmed by a separate experiment. The equilibrium state depended on the amount of the superacid: its excess shifted the equilibrium toward decarbonylation, whereas its deficit hindered the generation of cation 6, which interacts with CO. After water treatment of the reaction mixture, all carbonylation products were hydrolyzed into acid 2d. In an aqueous medium, its deprotonation was possible, and the resulting carboxylate anion-owing to steric hindrance and the The reaction of phenylindanol 1e with CO in FSO3H-SbF5 ( Table 2) followed by hydrolysis of the reaction mixture also generated products 3e and 4e; the conversion of 1e into carbonylation products was slightly higher than that for compound 1d (the total content of products 3e and 4e: ~60%) but also incomplete. In a similar reaction of phenyltetralinol 1f, the total level of products 3f and 4f was much lower (~20%), which can be explained by large steric hindrances for CO addition. The conversion to carbonylation products 3e and 4e for alcohol 1e was close to that obtained in the carbonylation of perfluorophenylindane 5e in SbF5 (55% conversion). On the other hand, for alcohol 1f, the conversion to carbonylation products was substantially higher than that in the reaction of perfluorophenyltetralin 5f with CO-SbF5 (5%) [16]. Aside from compounds 3f and 4f, the reaction of alcohol 1f generated lactone 8 as another carbonylation product (Scheme 2). The content of lactone 8 went up with increasing reaction time, temperature, and amount of the superacid. On the contrary, the concentration of products 3f and 4f strongly decreased ( Table 2). Lactone 8 emerged via the cyclization of acid 2f; apparently, cation 9 generated from it in the FSO3H-SbF5 medium undergoes an intramolecular attack by the oxygen atom of the carboxyl group. In the carbonylation of phenylindanol 1e, lactone formation was not observed.

Carbonylation of Secondary Polyfluorinated 1-Arylalkan-1-ols and Concomitant Elimination of HF
It was demonstrated that carbonylation of secondary polyfluorinated 1-arylalkan-1ols with fluorine atoms at the β-position toward the hydroxyl group (in superacid FSO3H-SbF5 or TfOH-SbF5) can be accompanied by partial or complete elimination of HF, thus giving rise to α,β-unsaturated carboxylic acids 10 (Table 3). For instance, the reaction of phenylpropanol 1g with CO in TfOH-SbF5 at r.t., followed by hydrolysis of the reaction mixture, produced acid 2g with a small admixture of unsaturated acid 10g. A higher reaction temperature promoted more complete elimination of HF; acid 10g became the main product at 70 °C. In the FSO3H-SbF5 medium, the proportion of elimination product 10g was higher than that in TfOH-SbF5. An important factor is also the nature of the substituents at the nascent double bond; this nature affects the energy of its formation and accordingly the ease of elimination. Thus, in contrast to phenylpropanol 1g, carbonylation of phenylethanol 1c after heating under similar conditions did not give appreciable amounts The results on carbonylation of compound 1d can be explained (Scheme 2) by the presence (in the TfOH-SbF 5 medium) of an equilibrium between noncarbonylated forms (alcohol 1d or/and its triflate: fluoro derivative 5d) and carbonylation products (acid 2d, the corresponding acyl fluoride 2dF, or/and acyl triflate). The feasibility of carbonylation of perfluorodiphenylethane 5d in this medium was confirmed by a separate experiment. The equilibrium state depended on the amount of the superacid: its excess shifted the equilibrium toward decarbonylation, whereas its deficit hindered the generation of cation 6, which interacts with CO. After water treatment of the reaction mixture, all carbonylation products were hydrolyzed into acid 2d. In an aqueous medium, its deprotonation was possible, and the resulting carboxylate anion-owing to steric hindrance and the electronwithdrawing effect of substituents-easily eliminated CO 2 with the formation of carbanion 7. The latter either added a proton or eliminated a fluoride ion, thereby yielding 3d and 4d, respectively. The formation of alkene 4d as a result of the transformation of hydro derivative 3d during treatment of the reaction mixture is unlikely; it was found that such elimination of HF, even in the presence of a base, is possible only under forcing conditions (NEt 3 , CaH 2 , 130 • C). The emergence of acid 2d and acyl fluoride 2dF, along with compounds 3d and 4d, could be detected after water treatment during the extraction of products with a mixture of CH 2 Cl 2 and Et 2 O; the concentration of acid 2d in the extract gradually declined with time, The reaction of phenylindanol 1e with CO in FSO 3 H-SbF 5 ( Table 2) followed by hydrolysis of the reaction mixture also generated products 3e and 4e; the conversion of 1e into carbonylation products was slightly higher than that for compound 1d (the total content of products 3e and 4e:~60%) but also incomplete. In a similar reaction of phenyltetralinol 1f, the total level of products 3f and 4f was much lower (~20%), which can be explained by large steric hindrances for CO addition. The conversion to carbonylation products 3e and 4e for alcohol 1e was close to that obtained in the carbonylation of perfluorophenylindane 5e in SbF 5 (55% conversion). On the other hand, for alcohol 1f, the conversion to carbonylation products was substantially higher than that in the reaction of perfluorophenyltetralin 5f with CO-SbF 5 (5%) [16].
Aside from compounds 3f and 4f, the reaction of alcohol 1f generated lactone 8 as another carbonylation product (Scheme 1). The content of lactone 8 went up with increasing reaction time, temperature, and amount of the superacid. On the contrary, the concentration of products 3f and 4f strongly decreased ( Table 2). Lactone 8 emerged via the cyclization of acid 2f; apparently, cation 9 generated from it in the FSO 3 H-SbF5 medium undergoes an intramolecular attack by the oxygen atom of the carboxyl group. In the carbonylation of phenylindanol 1e, lactone formation was not observed.

Carbonylation of Secondary Polyfluorinated 1-Arylalkan-1-ols and Concomitant Elimination of HF
It was demonstrated that carbonylation of secondary polyfluorinated 1-arylalkan-1-ols with fluorine atoms at the β-position toward the hydroxyl group (in superacid FSO 3 H-SbF 5 or TfOH-SbF 5 ) can be accompanied by partial or complete elimination of HF, thus giving rise to α,β-unsaturated carboxylic acids 10 (Table 3). For instance, the reaction of phenylpropanol 1g with CO in TfOH-SbF 5 at r.t., followed by hydrolysis of the reaction mixture, produced acid 2g with a small admixture of unsaturated acid 10g. A higher reaction temperature promoted more complete elimination of HF; acid 10g became the main product at 70 • C. In the FSO 3 H-SbF 5 medium, the proportion of elimination product 10g was higher than that in TfOH-SbF 5 . An important factor is also the nature of the substituents at the nascent double bond; this nature affects the energy of its formation and accordingly the ease of elimination. Thus, in contrast to phenylpropanol 1g, carbonylation of phenylethanol 1c after heating under similar conditions did not give appreciable amounts of the corresponding unsaturated acid 10c with two fluorine atoms at the double bond.
Some structural features can improve the efficiency of conjugation of the resulting double bond with the aryl moiety, for example, its fixation in the plane of the aryl moiety probably contributed to the elimination; as a result, carbonylation of tetralinol 1h gave considerable amounts of acid 10h already at r.t. A greater amount of the superacid caused more complete elimination (Table 3, entries 5 and 7), whereas extension of the time of the process had little effect (Table 3, entries 5 and 6).
A decrease in the size of the aliphatic ring from the six-membered to five-membered hindered the elimination; for example, carbonylation of indanol 1i in the FSO 3 H-SbF 5 medium did not give HF elimination products at r.t., in contrast to its homolog 1h. On the other hand, under these conditions, a partial transformation of the CF 2 group into a carbonyl group was observed; as a consequence, the reaction mixture also containedalongside acid 2i-keto acid 2j and apparently other 3-R-2,2,4,5,6,7-hexafluorindan-1-ones (R = F, OSO 2 F), which are not carbonylation products. Previously, carbonylation of 1,1,2,2,3,4,5,6,7-nonafluoroindane was conducted in a CO-SbF 5 system, and acid 2i was the only product obtained [16]. The transformation of the CF 2 group of indanol 1i or of products of its transformation into a carbonyl group is mediated by elimination of the fluoride ion in the superacid and a reaction of the emerging carbocation with O-nucleophiles contained in the reaction medium (for example, RCOOH [66]), thereby leading to the carbonyl derivatives. Lower stability of polyfluorinated tetralin-1-yl cations compared to respective indan-1-yl cations [67] explains the absence of transformations of the benzyl Molecules 2022, 27, 8757 6 of 31 CF 2 group during the carbonylation of tetralinol 1h at r.t. When the temperature of the reaction of indanol 1i with CO in the FSO 3 H-SbF 5 medium was raised to 70 • C, both the carbonylation and transformation of the CF 2 group into the carbonyl group proceeded completely; futher, the elimination of HF also occurred, which produced a mixture of acids 2j and 10j. A mixture of acids 2j and 10j also formed in the reaction of hydroxyketone 1j with CO in the FSO 3 H-SbF 5 medium at 70 • C. Table 3. Carbonylation of secondary polyfluorinated 1-arylalkan-1-ols 1g-n in superacids.
product at 70 °C. In the FSO3H-SbF5 medium, the proportion of elimination product 10g was higher than that in TfOH-SbF5. An important factor is also the nature of the substituents at the nascent double bond; this nature affects the energy of its formation and accordingly the ease of elimination. Thus, in contrast to phenylpropanol 1g, carbonylation of phenylethanol 1c after heating under similar conditions did not give appreciable amounts of the corresponding unsaturated acid 10c with two fluorine atoms at the double bond.
Some structural features can improve the efficiency of conjugation of the resulting double bond with the aryl moiety, for example, its fixation in the plane of the aryl moiety probably contributed to the elimination; as a result, carbonylation of tetralinol 1h gave considerable amounts of acid 10h already at r.t. A greater amount of the superacid caused more complete elimination (Table 3, entries 5 and 7), whereas extension of the time of the process had little effect (Table 3, entries 5 and 6). Table 3. Carbonylation of secondary polyfluorinated 1-arylalkan-1-ols 1g-n in superacids. mixture, produced acid 2g with a small admixture of unsaturated acid 10g. A higher reaction temperature promoted more complete elimination of HF; acid 10g became the main product at 70 °C. In the FSO3H-SbF5 medium, the proportion of elimination product 10g was higher than that in TfOH-SbF5. An important factor is also the nature of the substituents at the nascent double bond; this nature affects the energy of its formation and accordingly the ease of elimination. Thus, in contrast to phenylpropanol 1g, carbonylation of phenylethanol 1c after heating under similar conditions did not give appreciable amounts of the corresponding unsaturated acid 10c with two fluorine atoms at the double bond. Some structural features can improve the efficiency of conjugation of the resulting double bond with the aryl moiety, for example, its fixation in the plane of the aryl moiety probably contributed to the elimination; as a result, carbonylation of tetralinol 1h gave considerable amounts of acid 10h already at r.t. A greater amount of the superacid caused more complete elimination (Table 3, entries 5 and 7), whereas extension of the time of the process had little effect (Table 3, entries 5 and 6). Table 3. Carbonylation of secondary polyfluorinated 1-arylalkan-1-ols 1g-n in superacids. product at 70 °C. In the FSO3H-SbF5 medium, the proportion of elimination product 10g was higher than that in TfOH-SbF5. An important factor is also the nature of the substituents at the nascent double bond; this nature affects the energy of its formation and accordingly the ease of elimination. Thus, in contrast to phenylpropanol 1g, carbonylation of phenylethanol 1c after heating under similar conditions did not give appreciable amounts of the corresponding unsaturated acid 10c with two fluorine atoms at the double bond. Some structural features can improve the efficiency of conjugation of the resulting double bond with the aryl moiety, for example, its fixation in the plane of the aryl moiety probably contributed to the elimination; as a result, carbonylation of tetralinol 1h gave considerable amounts of acid 10h already at r.t. A greater amount of the superacid caused more complete elimination (Table 3, entries 5 and 7), whereas extension of the time of the process had little effect (Table 3, entries 5 and 6). Table 3. Carbonylation of secondary polyfluorinated 1-arylalkan-1-ols 1g-n in superacids. ingly the ease of elimination. Thus, in contrast to phenylpropanol 1g, carbonylation of phenylethanol 1c after heating under similar conditions did not give appreciable amounts of the corresponding unsaturated acid 10c with two fluorine atoms at the double bond. Some structural features can improve the efficiency of conjugation of the resulting double bond with the aryl moiety, for example, its fixation in the plane of the aryl moiety probably contributed to the elimination; as a result, carbonylation of tetralinol 1h gave considerable amounts of acid 10h already at r.t. A greater amount of the superacid caused more complete elimination (Table 3, entries 5 and 7), whereas extension of the time of the process had little effect (Table 3, entries 5 and 6). Table 3. Carbonylation of secondary polyfluorinated 1-arylalkan-1-ols 1g-n in superacids. was higher than that in TfOH-SbF5. An important factor is also the nature of the substituents at the nascent double bond; this nature affects the energy of its formation and accordingly the ease of elimination. Thus, in contrast to phenylpropanol 1g, carbonylation of phenylethanol 1c after heating under similar conditions did not give appreciable amounts of the corresponding unsaturated acid 10c with two fluorine atoms at the double bond. Some structural features can improve the efficiency of conjugation of the resulting double bond with the aryl moiety, for example, its fixation in the plane of the aryl moiety probably contributed to the elimination; as a result, carbonylation of tetralinol 1h gave considerable amounts of acid 10h already at r.t. A greater amount of the superacid caused more complete elimination (Table 3, entries 5 and 7), whereas extension of the time of the process had little effect (Table 3, entries 5 and 6). Table 3. Carbonylation of secondary polyfluorinated 1-arylalkan-1-ols 1g-n in superacids. The results on carbonylation of compound 1d can be explained (Scheme 1) by the presence (in the TfOH-SbF5 medium) of an equilibrium between noncarbonylated forms (alcohol 1d or/and its triflate: fluoro derivative 5d) and carbonylation products (acid 2d, the corresponding acyl fluoride 2dF, or/and acyl triflate). The feasibility of carbonylation of perfluorodiphenylethane 5d in this medium was confirmed by a separate experiment. The equilibrium state depended on the amount of the superacid: its excess shifted the equilibrium toward decarbonylation, whereas its deficit hindered the generation of cation 6, which interacts with CO. After water treatment of the reaction mixture, all carbonylation products were hydrolyzed into acid 2d. In an aqueous medium, its deprotonation was possible, and the resulting carboxylate anion-owing to steric hindrance and the electronwithdrawing effect of substituents-easily eliminated CO2 with the formation of carbanion 7. The latter either added a proton or eliminated a fluoride ion, thereby yielding 3d and 4d, respectively. The formation of alkene 4d as a result of the transformation of hydro derivative 3d during treatment of the reaction mixture is unlikely; it was found that such elimination of HF, even in the presence of a base, is possible only under forcing conditions (NEt3, CaH2, 130 °C). The emergence of acid 2d and acyl fluoride 2dF, along with compounds 3d and 4d, could be detected after water treatment during the extraction of products with a mixture of CH2Cl2 and Et2O; the concentration of acid 2d in the extract gradually declined with time, while the concentration of products 3d and 4d went up. Extraction with pure Et O gave only compounds 3d and 4d. A decrease in the size of the aliphatic ring from the six-membered to five-membered hindered the elimination; for example, carbonylation of indanol 1i in the FSO3H-SbF5 medium did not give HF elimination products at r.t., in contrast to its homolog 1h. On the other hand, under these conditions, a partial transformation of the CF2 group into a car-  A decrease in the size of the aliphatic ring from the six-membered to five-membered hindered the elimination; for example, carbonylation of indanol 1i in the FSO3H-SbF5 medium did not give HF elimination products at r.t., in contrast to its homolog 1h. On the other hand, under these conditions, a partial transformation of the CF2 group into a carbonyl group was observed; as a consequence, the reaction mixture also contained-along-  A decrease in the size of the aliphatic ring from the six-membered to five-membered hindered the elimination; for example, carbonylation of indanol 1i in the FSO3H-SbF5 medium did not give HF elimination products at r.t., in contrast to its homolog 1h. On the other hand, under these conditions, a partial transformation of the CF2 group into a carbonyl group was observed; as a consequence, the reaction mixture also contained-along-  A decrease in the size of the aliphatic ring from the six-membered to five-membered hindered the elimination; for example, carbonylation of indanol 1i in the FSO3H-SbF5 medium did not give HF elimination products at r.t., in contrast to its homolog 1h. On the other hand, under these conditions, a partial transformation of the CF2 group into a carbonyl group was observed; as a consequence, the reaction mixture also contained-alongside acid 2i-keto acid 2j and apparently other 3-R-2,2,4,5,6,7-hexafluorindan-1-ones (R =  A decrease in the size of the aliphatic ring from the six-membered to five-membered hindered the elimination; for example, carbonylation of indanol 1i in the FSO3H-SbF5 medium did not give HF elimination products at r.t., in contrast to its homolog 1h. On the other hand, under these conditions, a partial transformation of the CF2 group into a carbonyl group was observed; as a consequence, the reaction mixture also contained-alongside acid 2i-keto acid 2j and apparently other 3-R-2,2,4,5,6,7-hexafluorindan-1-ones (R = F, OSO2F), which are not carbonylation products. Previously, carbonylation of The presence of hydrocarbon groups in the aliphatic part of the molecule in some cases required lower acidity of the medium for successful carbonylation. For instance, for indanol 1m, carbonylation generating acid 2m in the FSO 3 H-SbF 5 medium was accompanied by considerable resinification, which could be avoided in TfOH-SbF 5 (5:1) at 50 • C; in pure TfOH, almost no carbonylation of indanol 1m occurred.

Entry
The formation of an aromatic system through the elimination of HF accompanying the carbonylation could ensure rapid and complete elimination even at r.t. For example, in the reaction of heterocyclic alcohol 1n with CO in the FSO 3 H-SbF 5 medium (in the TfOH-SbF 5 medium, the outcome was similar), after hydrolysis of the reaction mixture, benzofurancarboxylic acid 10n arose, and acid 2n was not detectable. The formation of a cationic species with a benzofuran moiety (acid 10n protonated at carbonyl oxygen or its acyl cation) was registered before the water treatment of the reaction mixture, thus confirming that the elimination of HF took place in the FSO 3 H-SbF 5 medium.
It should be noted that in most of the carbonylation reactions mentioned above and involving the concomitant elimination of HF, there was no full conversion to elimination product 10; furthermore, in contrast to some factors such as reaction temperature or the amount of the superacid, the increase in the reaction time had little effect on the ratio of acids 2 and 10. It can be theorized that the elimination of HF is a reversible process, but when we introduced product 10j into the reaction mixture obtained after the carbonylation of alcohol 1n and kept the resulting mixture either at r.t. or at 70 • C, we failed to detect (after water treatment) acid 2j as an HF addition product.
The interaction of tetralinol 1h with CO in FSO 3 H-SbF 5 at 70 • C (Scheme 3), in contrast to the analogous reaction of indanol 1i (Table 3, entry 9), did not generate the corresponding ketoacids. The main product was naphthalenecarboxylic acid 11; in addition, the reaction mixture contained acids 2h and 10h, perfluorotheralin (12), and tetralon 13. Acid 11 was isolated as dimethylated derivative 11Me after treatment of the reaction mixture with diazomethane. Carbonylation of hydroxyketone 1o under similar conditions resulted in a complex mixture of compounds, among which acid 11 was the main one as well (Scheme 3).
To explain the simultaneous formation of naphthalenecarboxylic acid 11 and tetralin 12 in the reaction of alcohol 1h with CO in FSO 3 H-SbF 5 at 70 • C, the following sequence of transformations can be proposed (Scheme 3). Acid 10h under the reaction conditions is partially converted to carbonyl derivative 10o through the generation of the corresponding cation and its reaction with the O-nucleophiles contained in the reaction medium. Protonation of compound 10o gives naphthalinonium cation 14, the reaction of which with the enol form of acyl fluoride 2hF (or mixed anhydride RCO 2 SO 2 F)-as a consequence of a redox process with the transfer of a fluorine atom-gives acid 11 and perfluorinated acyl fluoride 15. The latter is decarbonylated under these reaction conditions, thereby yielding tetralin 12. The possibility of decarbonylation of compound 15 is consistent with the finding that tetralin 12 did not give a carbonylation product in the CO-SbF 5 system because the equilibrium of this reaction is shifted toward the starting tetralin [16]. The lower concentration of tetralin 12 in the reaction mixture compared to acid 11 can be attributed to its low solubility in the inorganic superacid in combination with its appreciable volatility; accordingly, it can be partially carried away by the CO flow. To explain the simultaneous formation of naphthalenecarboxylic acid 11 and tetralin 12 in the reaction of alcohol 1h with CO in FSO3H-SbF5 at 70 °C, the following sequence of transformations can be proposed (Scheme 3). Acid 10h under the reaction conditions is partially converted to carbonyl derivative 10o through the generation of the corresponding cation and its reaction with the O-nucleophiles contained in the reaction medium. Protonation of compound 10o gives naphthalinonium cation 14, the reaction of which with the enol form of acyl fluoride 2hF (or mixed anhydride RCO2SO2F)-as a consequence of a redox process with the transfer of a fluorine atom-gives acid 11 and perfluorinated acyl fluoride 15. The latter is decarbonylated under these reaction conditions, thereby yielding tetralin 12. The possibility of decarbonylation of compound 15 is consistent with the finding that tetralin 12 did not give a carbonylation product in the CO-SbF5 system because the equilibrium of this reaction is shifted toward the starting tetralin [16]. The lower concentration of tetralin 12 in the reaction mixture compared to acid 11 can be attributed to its low solubility in the inorganic superacid in combination with its appreciable volatility; accordingly, it can be partially carried away by the CO flow. Tetralone 13 seems to come from another kind of transformation of acid 10h (Scheme 3, bottom pathway). It is possible that the reaction of the acyl cation deriving from acid 10h with O-nucleophiles present in the reaction medium (RCO2H and FSO3H) drives the replacement of the fluorine atom by

Carbonylation of Diols
Carbonylation of benzylic dihydroxy derivatives of polyfluorinated arylalkanes and benzocycloalkenes, depending on the structure, led to the addition of one or two CO molecules. The reaction of indanediol 17a with CO in FSO 3 H-SbF 5 selectively gave diacid 18a as a mixture of cisand trans-isomers (Scheme 4); no HF elimination products formed at r.t., as in the case of other indanols tested above. On the other hand, in the reaction of tetralindiol 17b with CO in the presence of 5 equiv. of FSO 3 H-SbF 5 , the addition of two CO molecules was accompanied by the elimination of two HF molecules already at r.t., resulting in a mixture of acids 18b and 19. Products of the elimination of one HF molecule were absent; apparently, the elimination of the second HF molecule proceeded faster than that of the first one because this led to the aromatic naphthalene system. An increase in the reaction temperature to 70 • C caused complete elimination of HF with the formation of diacid 19; the reaction mixture also contained admixtures of naphthalenecarboxylic acids 20 and 21 arising in side reactions; they were isolated and characterized after esterification as a mixture of ethyl esters 20Et and 21Et. Acid 20 apparently is a consequence of OH group replacement by fluorine in the monocarbonylation product (or in the starting diol) and the elimination of two HF molecules. The pathway to hydro derivative 21 is not clear; it was demonstrated that diacid 19 does not transform into it under the reaction conditions in question.
were absent; apparently, the elimination of the second HF molecule proceeded faster than that of the first one because this led to the aromatic naphthalene system. An increase in the reaction temperature to 70 °C caused complete elimination of HF with the formation of diacid 19; the reaction mixture also contained admixtures of naphthalenecarboxylic acids 20 and 21 arising in side reactions; they were isolated and characterized after esterification as a mixture of ethyl esters 20Et and 21Et. Acid 20 apparently is a consequence of OH group replacement by fluorine in the monocarbonylation product (or in the starting diol) and the elimination of two HF molecules. The pathway to hydro derivative 21 is not clear; it was demonstrated that diacid 19 does not transform into it under the reaction conditions in question. After a reduction in the amount of FSO 3 H-SbF 5 to 2.2 equiv. in the reaction of diol 17b at r.t., it was possible to achieve selective monocarbonylation, which was accompanied by the assembly of a lactone ring involving the second OH group leading to lactone 22. Hydroxy acid 23 was also present in the reaction mixture, along with dicarbonylation products 18b and 19. In contrast to diacid 18b, hydroxy acid 23 was present in the mixture as a single diastereomer, which apparently has cis-configuration and arises via partial hydrolysis of lactone 22 during water treatment of the reaction mixture. Hydrolysis of lactone 22 by dilute sulfuric acid caused selective formation of the same diastereomer of acid 23. For indandiol 17a, selective preparation of the monocarbonylation product was not achieved.
Monocarbonylation affording lactones also occurred when diols 17c-e were reacted with CO in the presence of a superacid ( Table 4). Carbonylation of diol 17c in FSO 3 H-SbF 5 (1:1), as in the case of indanol 1m, was accompanied by considerable resinification. The use of less acidic system TfOH-SbF 5 (6:1) helped the carbonylation to generate lactone 24c. Of note, carbonylation of diols 17c-e required more forcing conditions as compared to respective alcohols 1a-c. For instance, diol 17c, carbonylation in pure TfOH proceeded with difficulty, even when heated. Pentafluorophenyl-substituted diol 17d did not react with CO either in TfOH at 50 • C or even in TfOH-SbF 5 (7:2) at r.t., giving only the corresponding phthalane as a diol cyclization product. By contrast, in the FSO 3 H-SbF 5 medium at r.t., diol 17d easily added CO, thereby yielding a mixture of isomeric lactones 24d and 25d in a ratio close to 1:1. Carbonylation of diol 17e in FSO 3 H-SbF 5 took place upon heating to 50 • C, and the destabilizing effect of the CF 3 group on the cationic center induced regioselective carbonylation in the CH 2 OH moiety, giving rise to lactone 24e. For ortho-substituted diols 17c-e, products of addition of two CO molecules were not observed, while corresponding diacids 18f and 18g formed from metaand para-substituted diols 17f and 17g. Meta-isomer 17f readily reacted with CO in TfOH-SbF 5 (7:1), whereas para-isomer 17g required the use of FSO 3 H-SbF 5 . Table 4. Carbonylation of polyfluorinated diols 17c-g in superacids.
Molecules 2022, 27, 8757 13 of 41 FSO 3 H-SbF 5 medium at r.t., diol 17d easily added CO, thereby yielding a mixture of isomeric lactones 24d and 25d in a ratio close to 1:1. Carbonylation of diol 17e in FSO 3 H-SbF 5 took place upon heating to 50 °C, and the destabilizing effect of the CF 3 group on the cationic center induced regioselective carbonylation in the CH 2 OH moiety, giving rise to lactone 24e. For ortho-substituted diols 17c-e, products of addition of two CO molecules were not observed, while corresponding diacids 18f and 18g formed from meta-and para-substituted diols 17f and 17g. Meta-isomer 17f readily reacted with CO in TfOH-SbF 5 (7:1), whereas para-isomer 17g required the use of FSO 3 H-SbF 5 .

Esterification and Elimination Reactions of the Carbonylation Products
In some cases, esterification was performed to isolate and purify carboxylic acids obtained in carbonylation reactions. Furthermore, the feasibility of conversion of several acids and esters into α,β-unsaturated derivatives by elimination of HF was tested. Thus, mixtures of esters 2gMe+10gMe and 2hMe+10hMe were obtained by the reaction of the respective acid mixtures with diazomethane (Scheme 5). Ester 2gMe could be smoothly converted into product 10gMe under the influence of NEt 3 in chloroform; elimination in ester 2hMe proceeded fully, even during column chromatography on silica gel. Esterification of a mixture of diacids 18b and 19 with methanol in the presence of H 2 SO 4 made it possible to selectively obtain ester 18bMe because acid 19 became esterified much more slowly. Nonetheless, the purification of ester 18bMe by silica gel chromatography afforded a mixture of esters 18bMe and 19Me, owing to partial elimination of HF; treatment of the obtained mixture with NEt 3 in chloroform led to ester 19Me as the only product.

Esterification and Elimination Reactions of the Carbonylation Products
In some cases, esterification was performed to isolate and purify carboxylic acids obtained in carbonylation reactions. Furthermore, the feasibility of conversion of several acids and esters into α,β-unsaturated derivatives by elimination of HF was tested. Thus, mixtures of esters 2gMe + 10gMe and 2hMe + 10hMe were obtained by the reaction of the respective acid mixtures with diazomethane (Scheme 5). Ester 2gMe could be smoothly converted into product 10gMe under the influence of NEt 3 in chloroform; elimination in ester 2hMe proceeded fully, even during column chromatography on silica gel. Esterification of a mixture of diacids 18b and 19 with methanol in the presence of H 2 SO 4 made it possible to selectively obtain ester 18bMe because acid 19 became esterified much more slowly. Nonetheless, the purification of ester 18bMe by silica gel chromatography afforded a mixture of esters 18bMe and 19Me, owing to partial elimination of HF; treatment of the obtained mixture with NEt 3 in chloroform led to ester 19Me as the only product.
Esterification of acids 2c and 2i with methanol in the presence of H 2 SO 4 gave corresponding esters 2cMe and 2iMe (Scheme 6). The reaction of ester 2iMe with NEt 3 in chloroform generated compound 10iMe as the main product, but complete conversion of the starting compound with the increasing reaction time was not achieved. This finding is probably due to the reversibility of this process. When K 2 CO 3 was used as a base, the eliminated HF produced insoluble salts, which helped to achieve full conversion of ester 2iMe. respective acid mixtures with diazomethane (Scheme 5). Ester 2gMe could be smoothly converted into product 10gMe under the influence of NEt3 in chloroform; elimination in ester 2hMe proceeded fully, even during column chromatography on silica gel. Esterification of a mixture of diacids 18b and 19 with methanol in the presence of H2SO4 made it possible to selectively obtain ester 18bMe because acid 19 became esterified much more slowly. Nonetheless, the purification of ester 18bMe by silica gel chromatography afforded a mixture of esters 18bMe and 19Me, owing to partial elimination of HF; treatment of the obtained mixture with NEt3 in chloroform led to ester 19Me as the only product. Scheme 5. Esterification of acids 2g, 2h, 10g, 10h, and 18b in reaction mixtures generated by the carbonylation procedures and HF elimination from esters 2gMe, 2hMe, and 18bMe.
Esterification of acids 2c and 2i with methanol in the presence of H2SO4 gave corresponding esters 2cMe and 2iMe (Scheme 6). The reaction of ester 2iMe with NEt3 in chloroform generated compound 10iMe as the main product, but complete conversion of the starting compound with the increasing reaction time was not achieved. This finding is probably due to the reversibility of this process. When K2CO3 was used as a base, the eliminated HF produced insoluble salts, which helped to achieve full conversion of ester 2iMe.

Scheme 5.
Esterification of acids 2g, 2h, 10g, 10h, and 18b in reaction mixtures generated by the carbonylation procedures and HF elimination from esters 2gMe, 2hMe, and 18bMe. An attempt to carry out the conversion of ester 2cMe into product 10cMe in a reaction with NEt3 in chloroform was utterly unsuccessful: ester 2cMe mostly did not change, giving only a small amount of ester 2aMe without a CF3 group (probably owing to a reaction with traces of water). These data are also consistent with the presumed reversibility of the HF elimination process; the equilibrium in the case of ester 2cMe almost completely shifted toward the starting compound because the formation of compound 10cMe with two fluorine atoms at the double bond is thermodynamically less favorable. Nonetheless, it can act as an intermediate in nucleophilic reactions involving CF3 group transformation. The reaction of 2cMe with K2CO3 in chloroform afforded ester 10cMe, but at r.t., it was too slow. When the temperature was raised to 55 °C, ester 2aMe became the main product, which is apparently a consequence of further transformations of compound 10cMe in the reaction with O-nucleophiles.
For acid 2l, it was feasible to implement selective elimination of HF with the formation of acid 10l in the reaction with NEt3 without esterification of the carboxyl group beforehand (Scheme 7). This process is apparently facilitated by the steric effect of the two bulky perfluoroethyl groups, which, on one hand, promotes elimination (because this effect reduces their repulsion from other substituents in the five-membered cycle) and, on the other hand, prevents subsequent nucleophilic addition to the nascent double bond. Attempts to carry out similar selective elimination under the action of NEt3 with a number of other carboxylic acids obtained in this work were futile. The reactions are complicated by concomitant decarboxylation with or without HF elimination. For example, the interaction of acid 2c with NEt3 in Et2O at r.t. or in chloroform at 55 °C predominantly gave Scheme 6. Synthesis of esters 2cMe and 2iMe and HF elimination under the action of NEt 3 and K 2 CO 3 .
An attempt to carry out the conversion of ester 2cMe into product 10cMe in a reaction with NEt 3 in chloroform was utterly unsuccessful: ester 2cMe mostly did not change, giving only a small amount of ester 2aMe without a CF 3 group (probably owing to a reaction with traces of water). These data are also consistent with the presumed reversibility of the HF elimination process; the equilibrium in the case of ester 2cMe almost completely shifted toward the starting compound because the formation of compound 10cMe with two fluorine atoms at the double bond is thermodynamically less favorable. Nonetheless, it can act as an intermediate in nucleophilic reactions involving CF 3 group transformation. The reaction of 2cMe with K 2 CO 3 in chloroform afforded ester 10cMe, but at r.t., it was too slow. When the temperature was raised to 55 • C, ester 2aMe became the main product, which is apparently a consequence of further transformations of compound 10cMe in the reaction with O-nucleophiles.
For acid 2l, it was feasible to implement selective elimination of HF with the formation of acid 10l in the reaction with NEt 3 without esterification of the carboxyl group beforehand (Scheme 7). This process is apparently facilitated by the steric effect of the two bulky perfluoroethyl groups, which, on one hand, promotes elimination (because this effect reduces their repulsion from other substituents in the five-membered cycle) and, on the other hand, prevents subsequent nucleophilic addition to the nascent double bond. Attempts to carry out similar selective elimination under the action of NEt 3 with a number of other carboxylic acids obtained in this work were futile. The reactions are complicated by concomitant decarboxylation with or without HF elimination. For example, the interaction of acid 2c with NEt 3 in Et 2 O at r.t. or in chloroform at 55 • C predominantly gave ethylbenzene 26 and styrene 27.

Structural Analysis of Compounds
The structures of the compounds were established by means of high-resolution mass spectrometry (HRMS), elemental analysis, and spectral characteristics. Signals in NMR Scheme 7. Transformation of acids 2c and 2l under the influence of NEt 3 .

Structural Analysis of Compounds
The structures of the compounds were established by means of high-resolution mass spectrometry (HRMS), elemental analysis, and spectral characteristics. Signals in NMR Scheme 8. Synthesis of starting alcohols 1j,o and diols 17c-g.
Structures of Eand Z-isomers of compounds 10g and 10gOMe were determined by means of through-space J F,F values between closely located fluorine atoms. For instance, for the Z-isomers, J CF3,F(ortho) = 2 Hz, whereas for the E-isomers, it is not observed; on the other hand, J 3,ortho < 2 Hz for the Z-isomers and 11-12 Hz for the E-isomers. The position of the substituent (C 6 F 5 or CF 3 ) in lactones 24d, 25d, and 24e was identified with the help of 1 H NMR spectra. Chemical shifts of CH 2 protons in the Ar F CH 2 CO moiety of compounds 24d and 24e were found to not exceed 4 ppm, whereas in the Ar F CH 2 O moiety of compound 25d, they are more than 5 ppm.

Materials and Methods
Analytical measurements and spectral analyses were carried out at the Multi-Access Chemical Research Center SB RAS. IR spectra were acquired on a Bruker Vector 22 IR spectrophotometer. 19 F, 1 H, and 13 C NMR spectra were recorded on a Bruker AV 300 instrument (282.4 MHz, 300 MHz, and 75.5 MHz, respectively). Chemical shifts are given in δ ppm from CCl 3 F ( 19 F) and TMS ( 1 H, 13 C). C 6 F 6 ( 19 F, −162.9 ppm), CHCl 3 ( 1 H, 7.24 ppm), acetone-d 5 ( 1 H, 2.04 ppm), DMSO-d 5 ( 1 H, 2.50 ppm), and CDCl 3 ( 13 C, 76.9 ppm) served as internal standards. Gas chromatography coupled with mass spectrometry (GC-MS) was performed on Hewlett Packard G1081A combined with Hewlett Packard 5890 with mass selective detector HP 5971 (EI 70 eV). Molecular masses of the compounds were determined by HRMS with a Thermo Electron Corporation DFS instrument (EI 70 eV). The progress of reactions and levels of products in reaction mixtures were monitored with the help of 19 F NMR spectroscopic data.
FSO 3 H and TfOH were purchased from commercial sources (99% purity); antimony pentafluoride was distilled under atmospheric pressure (bp 142-143 • C); carbon monoxide was prepared by decomposition of formic acid in concentrated sulfuric acid and was additionally dried by passing it through a layer of concentrated sulfuric acid. Et 2 O and CHCl 3 for HF elimination reactions were dehydrated over 3A molecular sieves.

A Typical Carbonylation Procedure
A mixture of an alcohol and superacid was intensively stirred in a round-bottom glass flask (10 mL) in a slow flow of CO under atmospheric pressure. The mixture was poured into 10-15 mL of 5% hydrochloric acid and extracted three times with 4 mL of a CH 2 Cl 2 -Et 2 O mixture (3:1) (if not specified otherwise). The extract was dried over MgSO 4 and analyzed by 19 F NMR spectroscopy. Reagent amounts, reaction conditions, and procedures for separation of mixtures and product isolation are detailed in the experiments below.
b. Alcohol 1i (0.413 g, 1.49 mmol), FSO 3 H (0.452 g, 4.52 mmol), and SbF 5 (0.984 g, 4.55 mmol) (molar ratio 1:3:3), according to the typical procedure (Section 3.1) (6 h, 70 • C), gave a mixture of compounds containing 63% of 2j and 34% of 10j. The solvent was evaporated, and the residue was dissolved in Et 2 O (10 mL), after which the solution was saturated with gaseous ammonia until precipitation of yellow crystals stopped. Crystals of an ammonium salt of acid 10j were filtered off and washed with Et 2 O (5 mL). Next, 5% hydrochloric acid (5 mL) and Et 2 O (5 mL) were added to the crystals, the organic layer was separated and dried over MgSO 4 ; evaporation and recrystallization from CCl 4 -acetone gave 0.100 g (yield 25%) of acid 10j. The ether solution obtained after the filtration of crystals of the ammonium salt of acid 10j was washed with 5% hydrochloric acid (10 mL) and dried over MgSO 4. Evaporation of the solvent and sublimation (130 • C, 1 Torr) afforded 0.170 g of acid 2j (yield 40%).