New Nitrogen, Sulfur-, and Selenium-Donating Ligands Derived from Chiral Pyridine Amino Alcohols. Synthesis and Catalytic Activity in Asymmetric Allylic Alkylation

Although many chiral ligands for asymmetric catalysis have been developed, there is still a need for new structures allowing the modular approach. Recently, easy synthesis of chiral pyridine-containing β-amino alcohols has been elaborated by opening respective epoxides with enantiomeric 1-phenylethylamine. This paper reports the synthetic transformation of β-amino alcohols into the new complexing pyridine-containing seleno- and thioethers. The amino alcohols were effectively converted to cyclic sulfonamidates, which were reacted with thiolates or phenyl selenide nucleophile. The reaction was diastereoselective, and its outcome depended on the configuration at the substitution center. The problem was discussed considering DFT optimized structures of both diastereomeric sulfonamidates. New amino-aldimine ligands were also synthesized from chiral pyridine-containing diamines. Nine new chiral ligands were tested in the Tsuji-Trost allylic alkylation resulting in the enantiomerically enriched product in up to 75% ee. The observed stereochemical induction agrees with the prevailing nucleophilic attack at the allylic carbon laying opposite to the complexing nitrogen of pyridine in η3-allylic intermediate complexes.


Introduction
Catalytic properties of metal complexes used in asymmetric reactions depend on the coordinated metal and the topology of the chiral ligand. Also, an electronic character of the donating (metal-binding) groups is of primary importance [1,2]. Their σ-donating and πaccepting (back-bonding) properties influence the reactivity of the key catalytic complexes. The chiral sulfur [3][4][5] and selenium [6,7], in addition to the foremost used phosphorus and nitrogen [1, 2,8] donating ligands play an important role in asymmetric catalysis. In particular, the asymmetric allylic alkylations catalyzed by Pd (the Tsuji-Trost reaction) [9][10][11][12][13][14][15][16][17] have been carried out in the presence of the ligands with sulfide, selenide, and diselenide groups, as exemplified by chiral ligands 1-5, [18][19][20][21] (Figure 1). Though, the literature reports a moderate number of similar catalysts used in the Tsuji-Trost reaction [22][23][24]. In particular, the interplay between the pyridine nitrogen and sulfide-or selenide-donating site seems to deserve further investigation. Thus, the direct enantioselective transformation of the easily available chiral β-amino alcohols containing pyridine unit [25] to the new S and Se derivatives was attempted. However, the nucleophilic substitution of the corresponding oxophosphonium-activated hydroxyls resulted in the epimerization at the substitution center. In other cases, the respective internal reaction led to the corresponding aziridines. Thus, to achieve our task, we adopted the synthetic procedure via cyclic sulfonamidates. Interestingly, also outcomes of these reactions depended on the stereochemistry of the epimeric substrates. For comparison, the previously obtained chiral diamines [26] were transformed into amino-aldimine derivatives, analogous to the well-known salen-type obtained chiral diamines [26] were transformed into amino-aldimine derivatives, analogous to the well-known salen-type ligands. The obtained chiral ligands were examined in the palladium-catalyzed Tsuji-Trost reaction, giving up to 75% ee. The absolute configuration of the product explains the preferred direction of the nucleophilic attack and suggests a stronger π-accepting character of pyridine nitrogen over chalcogen ethers.

Synthesis of Sulfur and Selenium Derivatives
To prepare chiral N, S donating ligands, we applied the Hata reaction conditions (Bu3P, (PhS)2, in toluene under Ar, in a sealed tube at 65 °C) [27,28]. When the reaction was run with the amino alcohol (1S,1′S)-6, the respective phenylsulphanyl derivative 7 resulted in good yield (Scheme 1), but the product was obtained as a mixture of both diastereomers (ca. 2:1). Though, when we used the pyridine amino alcohol (1S,2S,1′S)-9, we couldn't obtain the desired sulfur-containing compounds. The reaction resulted in a very small amount of the corresponding aziridines only (Scheme 1). We also used the Grieco procedure (Bu3P, PhSeCN, in toluene under Ar, at 25 °C) [28,29] to obtain the corresponding chiral selenide (Scheme 1). The hydroxyl group was again activated as the oxyphosphonium salt and reacted with the phenylselenide anion, giving a mixture of diastereomeric direct substitution products 8 (4:1). However, when we used amino alcohol (1S,2S,1′S)-9 in this reaction, we obtained aziridine (2R,3S,1′S)-10 in 88% yield instead the selenium compound. Scheme 1. Attempted synthesis of chiral sulfur and selenium derivatives.
Due to the lack of selectivity in the method described above, the procedure was changed. To develop the enantioselective transformation of chiral β-amino alcohols to new phenylsulfanyl derivatives, we have adopted the synthetic procedure via cyclic sulfonamidates, which were obtained earlier in our laboratory [26]. The cyclic amidates could be prepared by a simple reaction with thionyl chloride followed by the in situ oxidation of the product. So the corresponding sulfonamides were used as the starting material in the reaction with a sulfur nucleophile in the presence of diisopropylethylamine (DIEA).

Synthesis of Sulfur and Selenium Derivatives
To prepare chiral N, S donating ligands, we applied the Hata reaction conditions (Bu 3 P, (PhS) 2 , in toluene under Ar, in a sealed tube at 65 • C) [27,28]. When the reaction was run with the amino alcohol (1S,1 S)-6, the respective phenylsulphanyl derivative 7 resulted in good yield (Scheme 1), but the product was obtained as a mixture of both diastereomers (ca. 2:1). Though, when we used the pyridine amino alcohol (1S,2S,1 S)-9, we couldn't obtain the desired sulfur-containing compounds. The reaction resulted in a very small amount of the corresponding aziridines only (Scheme 1). We also used the Grieco procedure (Bu 3 P, PhSeCN, in toluene under Ar, at 25 • C) [28,29] to obtain the corresponding chiral selenide (Scheme 1). The hydroxyl group was again activated as the oxyphosphonium salt and reacted with the phenylselenide anion, giving a mixture of diastereomeric direct substitution products 8 (4:1). However, when we used amino alcohol (1S,2S,1 S)-9 in this reaction, we obtained aziridine (2R,3S,1 S)-10 in 88% yield instead the selenium compound. es 2021, 26, x FOR PEER REVIEW 2 of 12 obtained chiral diamines [26] were transformed into amino-aldimine derivatives, analogous to the well-known salen-type ligands. The obtained chiral ligands were examined in the palladium-catalyzed Tsuji-Trost reaction, giving up to 75% ee. The absolute configuration of the product explains the preferred direction of the nucleophilic attack and suggests a stronger π-accepting character of pyridine nitrogen over chalcogen ethers.

Figure 1.
Examples of nitrogen-sulfur and selenium chiral ligands.

Synthesis of Sulfur and Selenium Derivatives
To prepare chiral N, S donating ligands, we applied the Hata reaction conditions (Bu3P, (PhS)2, in toluene under Ar, in a sealed tube at 65 °C) [27,28]. When the reaction was run with the amino alcohol (1S,1′S)-6, the respective phenylsulphanyl derivative 7 resulted in good yield (Scheme 1), but the product was obtained as a mixture of both diastereomers (ca. 2:1). Though, when we used the pyridine amino alcohol (1S,2S,1′S)-9, we couldn't obtain the desired sulfur-containing compounds. The reaction resulted in a very small amount of the corresponding aziridines only (Scheme 1). We also used the Grieco procedure (Bu3P, PhSeCN, in toluene under Ar, at 25 °C) [28,29] to obtain the corresponding chiral selenide (Scheme 1). The hydroxyl group was again activated as the oxyphosphonium salt and reacted with the phenylselenide anion, giving a mixture of diastereomeric direct substitution products 8 (4:1). However, when we used amino alcohol (1S,2S,1′S)-9 in this reaction, we obtained aziridine (2R,3S,1′S)-10 in 88% yield instead the selenium compound. Due to the lack of selectivity in the method described above, the procedure was changed. To develop the enantioselective transformation of chiral β-amino alcohols to new phenylsulfanyl derivatives, we have adopted the synthetic procedure via cyclic sulfonamidates, which were obtained earlier in our laboratory [26]. The cyclic amidates could be prepared by a simple reaction with thionyl chloride followed by the in situ oxidation of the product. So the corresponding sulfonamides were used as the starting material in the reaction with a sulfur nucleophile in the presence of diisopropylethylamine (DIEA). Due to the lack of selectivity in the method described above, the procedure was changed. To develop the enantioselective transformation of chiral β-amino alcohols to new phenylsulfanyl derivatives, we have adopted the synthetic procedure via cyclic sulfonamidates, which were obtained earlier in our laboratory [26]. The cyclic amidates could be prepared by a simple reaction with thionyl chloride followed by the in situ oxidation of the product. So the corresponding sulfonamides were used as the starting material in the reaction with a sulfur nucleophile in the presence of diisopropylethylamine (DIEA). The reaction was carried out in toluene for 4 days at 60 • C to give the corresponding products 15-16 in yields 5-49% (Scheme 2, Method 1) ( Table 1). The slow progress of the reaction was observed for the pyridine derivatives; therefore, the reaction conditions were changed. Thioles or selenide derivatives were mixed with cyclic sulfonamidates in the presence of 1.5 eq of NaOH suspension in ethanol, which gave products 16-19 in higher yields. This procedure allowed to shorten the reaction time from 4 days to 4 h-Method 2 (Table 1). Interestingly, when we used (4S,5S,1 S)-13, the significant drop in yield was observed in Method 1, the product (1S, 2R,1 S)-16 was only formed in just 5% yield (identified by 1 H NMR), and the starting material could be recovered from the reaction mixture. Method 2 resulted in an elimination reaction, and the inseparable mixture containing enamine product was obtained (identified by 1 H NMR, see SI: Figure S25). To explain these phenomena, we modeled both epimeric cyclic sulfonamidates 13 using the DFT geometry optimization at the B3LYP/CC-pVDZ level of theory utilizing Gaussian code ( Figure 2) [30]. The obtained structures clarify the observed diastereoselectivity. Thus, for (4R,5R,1 S)-13, the observed nucleophilic attack on the C-5 could take place, while for (4S,5S,1 S)-13, the respective substitution product was formed in a very small amount (5% only), because of the steric hindrance ( Figure 2). Moreover, the trans-location of the leaving group at the C-5 and the hydrogen atom at C-4 in the reaction in the presence of NaOH caused the observed elimination.
The obtained phenylsulfanyl derivatives (1R, 2S,1 S)-16 and (1S, 2R,1 S)-16 were subjected to the DFT geometry optimization at the B3LYP/CC-pVDZ level of theory with Gaussian code [30] (Figure 3). GIAO isotropic shielding values were calculated and converted to chemical shifts for the most stable conformations using linear scaling factors [31]. The calculated δ values were compared with the experimental data for the very well-resolved aliphatic region. They showed a good qualitative agreement, which allowed confirming stereochemistry at the substitution center for both diastereomers (Figure 3 and SI, Table S1).
presence of 1.5 eq of NaOH suspension in ethanol, which gave products 16-19 in high yields. This procedure allowed to shorten the reaction time from 4 days to 4 h-Method (Table 1). Interestingly, when we used (4S,5S,1′S)-13, the significant drop in yield was o served in Method 1, the product (1S, 2R,1′S)-16 was only formed in just 5% yield (iden fied by 1 H NMR), and the starting material could be recovered from the reaction mixtur Method 2 resulted in an elimination reaction, and the inseparable mixture containin enamine product was obtained (identified by 1 H NMR, see SI: Figure S25). To expla these phenomena, we modeled both epimeric cyclic sulfonamidates 13 using the DFT g ometry optimization at the B3LYP/CC-pVDZ level of theory utilizing Gaussian code (Fi ure 2) [30]. The obtained structures clarify the observed diastereoselectivity. Thus, f (4R,5R,1′S)-13, the observed nucleophilic attack on the C-5 could take place, while f (4S,5S,1′S)-13, the respective substitution product was formed in a very small amount (5 only), because of the steric hindrance ( Figure 2). Moreover, the trans-location of the lea ing group at the C-5 and the hydrogen atom at C-4 in the reaction in the presence of NaO caused the observed elimination.  ometry optimization at the B3LYP/CC-pVDZ level of theory utilizing Gaussian code (Figure 2) [30]. The obtained structures clarify the observed diastereoselectivity. Thus, for (4R,5R,1′S)-13, the observed nucleophilic attack on the C-5 could take place, while for (4S,5S,1′S)-13, the respective substitution product was formed in a very small amount (5% only), because of the steric hindrance ( Figure 2). Moreover, the trans-location of the leaving group at the C-5 and the hydrogen atom at C-4 in the reaction in the presence of NaOH caused the observed elimination.   The obtained phenylsulfanyl derivatives (1R, 2S,1′S)-16 and (1S, 2R,1′S)-16 were subjected to the DFT geometry optimization at the B3LYP/CC-pVDZ level of theory with Gaussian code [30] (Figure 3). GIAO isotropic shielding values were calculated and converted to chemical shifts for the most stable conformations using linear scaling factors [31]. The calculated δ values were compared with the experimental data for the very well-resolved aliphatic region. They showed a good qualitative agreement, which allowed confirming stereochemistry at the substitution center for both diastereomers (Figure 3 and SI, Table S1).

Synthesis of Nitrogen Derivatives (Chiral Schiff Base)
We have synthesized a library of the amino-aldimine ligands from chiral diamines [26]. Although the Schiff bases have been extensively studied [32], there is still a group of unsymmetrical ligands with unexplored catalytic applications. For this reason, we obtained appropriate derivatives containing pyridine fragments. The reaction was run in toluene with salicylaldehydes in the presence of molecular sieves 4 Å . The products 22-24 were obtained in 60-70% yield ( Table 2).

Synthesis of Nitrogen Derivatives (Chiral Schiff Base)
We have synthesized a library of the amino-aldimine ligands from chiral diamines [26]. Although the Schiff bases have been extensively studied [32], there is still a group of unsymmetrical ligands with unexplored catalytic applications. For this reason, we obtained appropriate derivatives containing pyridine fragments. The reaction was run in toluene with salicylaldehydes in the presence of molecular sieves 4 Å. The products 22-24 were obtained in 60-70% yield ( Table 2).

Application of Chiral S, Se, and N derivatives in the Tsuji-Trost Reaction
The  (Table 3). Then, the reaction temperature was optimized for reaction with (1R,2S,1′S)-16 ligand, for 0-4 °C we observed an increase in enantioselectivity to 70% (S), and for −18 °C-75% ee (S), respectively. Further lowering the temperature did not affect the enantiomeric excess ( Table 4). The stereochemistry of the product (enantiomeric excess and configuration) was determined by HPLC, comparing the obtained results with the literature data [32]. In the absence of pyridine moiety (as for the ligands 15), the most opposite product was formed. We also run the reaction catalyzed by (1R,2S,1′S)-16 between rac-1,3-diphenyl-2-propenyl acetate and acetylacetone and obtained the respective product in only 14% yield, 20% ee for S enantiomer. A similar reaction with ethyl acetoacetate gave a mixture of both diastereomers (ca. 1:1) in 95% yield and 20% ee for each diastereomer.   (Table 3). Then, the reaction temperature was optimized for reaction with (1R,2S,1 S)-16 ligand, for 0-4 • C we observed an increase in enantioselectivity to 70% (S), and for −18 • C-75% ee (S), respectively. Further lowering the temperature did not affect the enantiomeric excess ( Table 4). The stereochemistry of the product (enantiomeric excess and configuration) was determined by HPLC, comparing the obtained results with the literature data [32]. In the absence of pyridine moiety (as for the ligands 15), the most opposite product was formed. We also run the reaction catalyzed by (1R,2S,1 S)-16 between rac-1,3-diphenyl-2-propenyl acetate and acetylacetone and obtained the respective product in only 14% yield, 20% ee for S enantiomer. A similar reaction with ethyl acetoacetate gave a mixture of both diastereomers (ca. 1:1) in 95% yield and 20% ee for each diastereomer.

Application of Chiral S, Se, and N derivatives in the Tsuji-Trost Reaction
The  (Table 3). Then, the reaction temperature was optimized for reaction with (1R,2S,1′S)-16 ligand, for 0-4 °C we observed an increase in enantioselectivity to 70% (S), and for −18 °C-75% ee (S), respectively. Further lowering the temperature did not affect the enantiomeric excess ( Table 4). The stereochemistry of the product (enantiomeric excess and configuration) was determined by HPLC, comparing the obtained results with the literature data [32]. In the absence of pyridine moiety (as for the ligands 15), the most opposite product was formed. We also run the reaction catalyzed by (1R,2S,1′S)-16 between rac-1,3-diphenyl-2-propenyl acetate and acetylacetone and obtained the respective product in only 14% yield, 20% ee for S enantiomer. A similar reaction with ethyl acetoacetate gave a mixture of both diastereomers (ca. 1:1) in 95% yield and 20% ee for each diastereomer.  The observed stereochemical outcome of the (1R, 2S,1 S)-16 catalyzed allylic alkylation, i.e., formation mainly of the (S)-configured product, can be accounted for the preferred nucleophilic attack at the trans position [33] of the allylic part of the intermediate   The observed stereochemical outcome of the (1R, 2S,1′S)-16 catalyzed allylic alkylation, i.e., formation mainly of the (S)-configured product, can be accounted for the preferred nucleophilic attack at the trans position [33] of the allylic part of the intermediate  Thus, for both M-and W-shaped η 3 -allylic intermediate complexes, the nucleophilic addition led to the obtained (S)-product. Generally, the enantioselectivity in the Tsuji-Trost reaction depends on both, steric and electronic properties of the η 3 palladium allylic complexes [9][10][11][12][13][14][15][16][17]. An attacking nucleophile favorably approaches the complexed allylic system from the site opposite to the more π-accepting ligand center. Thus, in the case of heterobidentate N (sp 2 )-chalcogen ether ligands, the nucleophile approaches trans to the more π-accepting imine donor (here: pyridine nitrogen) [33,34]. For strongly σ-donating N (sp 3 ) and weakly π-accepting chalcogen atoms, the attack trans to chalcogen is generally favored [35,36]. This last tendency may be responsible for the observed stereochemical result of the reaction catalyzed by (2S,1′S)-15. Also, the imino-amines lacking pyridine moiety (23 and 24) gave mostly the Tsuji-Trost product of (R)-configuration, while the respective pyridine derivative (1S,2R,1′S)-22 afforded (S)-product with considerable ee.

General
Solvents were distilled, and other reagents were used as received. Reactions were monitored by thin-layer chromatography (TLC) on silica gel 60 F-254 precoated plates, and spots were visualized with a UV lamp (A.Krüss Optronic GmbH, Hamburg, Germany) and/or Dragendorff reagent. Separation of products by chromatography was carried out on silica gel 60 (230-400 mesh). Observed rotations at 589 nm were measured using an Optical Activity Ltd. Model AA-5 automatic polarimeter (Huntington, UK). 1 H and 13 C NMR spectra (400, 600 MHz, and 100, 151 MHz, respectively) were collected on Jeol 400 yh and Bruker Avance II 600 instruments (Karlsruhe, Germany). The spectra were Thus, for both M-and W-shaped η 3 -allylic intermediate complexes, the nucleophilic addition led to the obtained (S)-product. Generally, the enantioselectivity in the Tsuji-Trost reaction depends on both, steric and electronic properties of the η 3 palladium allylic complexes [9][10][11][12][13][14][15][16][17]. An attacking nucleophile favorably approaches the complexed allylic system from the site opposite to the more π-accepting ligand center. Thus, in the case of heterobidentate N (sp 2 )-chalcogen ether ligands, the nucleophile approaches trans to the more π-accepting imine donor (here: pyridine nitrogen) [33,34]. For strongly σ-donating N (sp 3 ) and weakly π-accepting chalcogen atoms, the attack trans to chalcogen is generally favored [35,36]. This last tendency may be responsible for the observed stereochemical result of the reaction catalyzed by (2S,1 S)-15. Also, the imino-amines lacking pyridine moiety (23 and 24) gave mostly the Tsuji-Trost product of (R)-configuration, while the respective pyridine derivative (1S,2R,1 S)-22 afforded (S)-product with considerable ee.

General
Solvents were distilled, and other reagents were used as received. Reactions were monitored by thin-layer chromatography (TLC) on silica gel 60 F-254 precoated plates, and spots were visualized with a UV lamp (A.Krüss Optronic GmbH, Hamburg, Germany) and/or Dragendorff reagent. Separation of products by chromatography was carried out on silica gel 60 (230-400 mesh). Observed rotations at 589 nm were measured using an Optical Activity Ltd. Model AA-5 automatic polarimeter (Huntington, UK). 1 H and 13 C NMR spectra (400, 600 MHz, and 100, 151 MHz, respectively) were collected on Jeol 400 yh and Bruker Avance II 600 instruments (Karlsruhe, Germany). The spectra were recorded in CDCl 3 referenced to the respective residual signals of the solvent. Chemical shifts are given in parts per million (ppm) and coupling constants (J) are in Hertz (Hz). High-resolution mass spectra were recorded using electrospray ionization on Waters LCT Premier XE TOF instrument (Milford, MA, USA). Melting points were determined using a Boëtius hotstage apparatus (PHMK VEB Analytic, Dresden, Germany). The enantiomeric ratios of the samples were determined by chiral high-performance liquid chromatography (HPLC) measurements (Thermo Fisher Scientific, Waltham, MA, USA) using Chiracel ADH chiral column.

General Procedure for the Synthesis of Cyclic Sulfonamidates
The synthesis of S,S-dioxides was performed according to a modified literature procedure [26,37,38]. To a solution of amino alcohol 6, 9 or 11 (1 mmol) and triethylamine (3 mmol, 0.42 mL) in dry dichloromethane (3.5 mL) was added a solution of thionyl chloride (0.8 mmol, 58 µL) in dry dichloromethane (0.25 mL) at −78 • C for 20 min. The mixture was stirred at −78 • C for 20 min and 0 • C for the next 20 min. The reaction mixture was partitioned between ether and water, the organic layer was washed with brine and dried over anhydrous sodium sulfate, filtered, and the filtrate was concentrated in vacuo. The residue was dissolved in acetonitrile (4 mL), cooled to 0 • C, and NaIO 4 (1.2 mmol, 257 mg), RuCl 3 ·3H 2 O (ca. 2 mg), and water (4 mL) were added. The reaction mixture was stirred at room temperature for 1 h and then extracted 3 × Et 2 O. The combined organic extracts were washed with brine and dried over sodium sulfate. The residue was purified by column chromatography (SiO 2 , 10% AcOEt in hexane) to provide the cyclic sulfamidate. The same eluent was used for TLC; the respective R f value is given below.
1 H and 13

General Procedure for the Synthesis of S and Se Derivatives
Method 1: Sulfonamide (0.2 mmol) was dissolved in toluene (1 mL), then diisopropylethylamine (0.3 mmol, 0.055 mL) and thiophenol (0.25 mmol, 0.024 mL) were added. The mixture was stirred at 60 • C under argon for 4 days. The crude mixture was then applied to a chromatography column (SiO 2 , 30% AcOEt in hexane) for product isolation. The same eluent was used for TLC; the respective R f values are given below.
Method 2: Sulfonamide (0.2 mmol or 0.5 mmol for reaction with Se derivatives) was dissolved in EtOH (0.5 mL), then a suspension of NaOH (15 mg) in EtOH (1 mL) and the appropriate sulfur or selenium derivative (0.25 mmol or 0.55 mmol for Se derivatives) were added. The mixture was stirred at 60 • C under argon for 4 h. Then, ethanol was evaporated, 1 mL of H 2 O was added, followed by extraction with 3 × 5 mL of Et 2 O, dried over Na 2 SO 4 . The product was isolated in the same way as in method 1. To a solution of the diamine (0.15 mmol) in dry toluene (1 mL) were added a solution of the aldehyde (0.15 mmol) in the dry toluene (0.5 mL) and Activated molecular sieves 4 Å under argon atmosphere. The reaction was carried out at RT for 6h, and then the crude mixture was separated by column chromatography (SiO 2 , 20% AcOEt in hexane) to give a pure product. The same eluent was used for TLC; the respective R f values are given below.
The reaction was carried out at room temperature for 1-4 days (monitored by TLC) [18]. After the reaction was complete, the crude mixture was filtered by SiO 2 , and then the solvent was evaporated to give the crude product as yellow oil. Enantiomeric excess was determined using a Chiralpak AD-H column (n-hexane/isopropanol 90/10, 1.0 mL/min, 254 nm) t R 12.4 and t S 17.2 min. Configuration assignment was based on the literature data [32].

Conclusions
Concluding, we successfully converted chiral pyridine-containing amino alcohols into the respective thioethers, selenoethers, and the mono-Schiff bases of the corresponding diamines. These new chiral compounds were tested in the Tsuji-Trost allylic alkylation resulting in the enantiomeric enrichment of product in up to 75%. The resulting stereochemical induction agrees with the nucleophilic attack at the allylic carbon located trans to the complexing nitrogen of pyridine in η 3 -allylic intermediate complexes.
Supplementary Materials: The following are available online, Figures S1-S25: copies of 1 H and 13 C NMR spectra, Figures S26-S28: HPLC plots for the Tsuji-Trost reaction outcomes, Table S1: