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Catalysts 2016, 6(9), 142; https://doi.org/10.3390/catal6090142

Article
Solventless Synthesis of Quaterphenyls and Terphenyls from Chalcones and Allylsulfones under Phase Transfer Catalysis Conditions
1
Department of Chemistry, Università degli Studi di Milano, via Golgi 19, Milano 20133, Italy
2
Centre for Synthesis and Chemical Biology, Royal College of Surgeons in Ireland, 123 St. Stephen’s Green, Dublin 2, Ireland
*
Author to whom correspondence should be addressed.
Academic Editor: Keith Hohn
Received: 15 July 2016 / Accepted: 7 September 2016 / Published: 13 September 2016

Abstract

:
Easily available chalcones and allyl sulfones along with cheap solid NaOH and polyethyleneglycol (PEG) 1000 have been used to directly generate the meta-terphenyl or quaterphenyl motifs under Phase Transfer Catalysis solventless conditions. The new approach provides an economic and environmentally friendly solution to removal of hazardous bases as well as organic solvents.
Keywords:
terphenyls; quaterphenyls; Phase Transfer Catalysis; PEG; green chemistry; solventless

1. Introduction

The synthesis of polysubstituted aromatic compounds relies on various strategies involving multistep approaches using organometallic species [1,2,3,4,5] or cycloadditions [6,7], or under acid or basic reaction conditions [8].
The synthesis of terphenyls has recently aroused a great deal of interest since this skeleton has been found in many natural products, for example fungi, exhibiting diverse bioactivity [9]. Moreover, meta-terphenyls have been used as ligands [10], as intermediates for the synthesis of covalent nanostructures [11] and as electron transporting material [12]. For example, 5′,5′′′′-sulfonyl-di-[1,1′:3′,1′′]-terphenyl (BTPS, Scheme 1), bearing two meta-terphenyl subunits, has been recently prepared from bis(3,5-dichlorophenyl)sulfone [13] by Suzuki-Miyaura coupling in order to develop new highly efficient organic light emitting diodes (OLED) [14].
Although several procedures allow the synthesis of the terphenyl skeleton, the development of alternative methods is still an issue since the regioselective construction of carbon–carbon bonds is a goal not always easy to be achieved.
A more practical approach to terphenyls has been realized by direct procedures capable of generating the central benzene ring with a single reaction involving easily available reagents.
For example, the Morita-Baylis-Hillman reaction of nitroalkenes 1 and alkylidene malono nitriles 2 gave good yields of the desired substituted terphenyls 3 under mild conditions (Scheme 2). However, this approach suffers from the need for additional steps to prepare reactants and the formation of toxic HCN during annulation [15].
On the other hand, a mixture of meta-terphenyl 6a along with sulfonyl-meta-terphenyl 8a has been obtained by reacting allylsulfone 4a with chalcone 5a in the presence of excess of NaH in THF at 50 °C (Scheme 3) [16]. By the same approach, 1,2,4-quaterphenyls 7a can also be obtained by using an aryl substituted allyl sulfone 4b [17].
The aryl groups in the 1,3-position of meta-terphenyls 6 derive from the starting chalcones 5; therefore, a variety of substituted terphenyls can be prepared by using substituted chalcones, easily accessed by the Claisen-Schmidt condensation of methylketones with aldehydes. Sulfones are versatile intermediates used in many different applications [18,19,20,21]. Sulfones 4a and 4c have been prepared by alkylation of the proper sulfinic acid with allyl bromide or cinnamyl chloride under Phase Transfer Catalysis (PTC) conditions.
However, this approach requires the use of excess NaH (4 equiv) in order to deprotonate the allylsulfone, thus triggering the reaction cascade leading to terphenyls [16]. Moreover, the hydrogen evolution and the need to remove THF before aqueous work-up of the crude reaction mixture constitute additional drawbacks. Under such reaction conditions huge amounts of sulfonyl-meta-terphenyls (30%–53% yield) are generated along with the desired products (40%–53% yield).
In order to develop a more practical approach and increase the selectivity, we planned to carry out this reaction under PTC conditions [22,23,24,25,26,27]. In fact, PTC represents a powerful tool to replace hazardous and relatively expensive reactants such as NaH with cheap and practical bases such as alkaline carbonates and hydroxides [28]. In addition, mild reaction conditions, safety, operational simplicity, and high selectivity are widely accepted typical features of PTC processes that allow an easy scale-up of reactions.

2. Results and Discussion

Here we report that the synthesis of a variety of meta-terphenyls and quaterphenyls can be carried out in a chemoselective fashion by using NaOH as base under solid-liquid (SL) PTC conditions.
A preliminary set of reactions using allylsulfone 4a and chalcone 5a showed that solid NaOH was capable to promote the reaction, whereas solid K2CO3 or K3PO4 were less effective. On the other hand, no conversion was observed by using 1,5-diazabiciclo[5.4.0]undec-5-ene (1.5 equiv) as base under homogeneous conditions in THF as solvent. Although similar selectivity was observed by using stoichiometric or excess NaOH, it was preferred to use excess NaOH since higher yields of terphenyls could be obtained (Table 1, entries 1 and 2).
The reaction did not proceed significantly in the presence of 10% of base only, and various quaternary ammonium salts such as triethylbenzylammonium chloride (TEBA), Aliquat and tetrabutylammonium hydrogensulfate (TBAHSO4) gave similar results both as regards the yield and chemoselectivity.
In toluene the main product was sulfonyl-meta-terphenyl 8a whereas nearly equimolar amounts of meta-terphenyl 6a and 8a were obtained in CH3CN (Table 1, entries 1–3).
When the reaction has been carried out in the presence of a molar excess of allylsulfone 1a, the sulfonyl-meta-terphenyl 8a was isolated as the major compound (Table 1, entry 4). It was also found that an excess of chalcone 5a provided higher yields of products 6a and 8a, although with the same selectivity (Table 1, entry 5). A good selectivity favoring the desired meta-terphenyl was obtained in DMSO (Table 2, entry 6). Similar results have been obtained by using substituted chalcones 5b and 5c (Table 1, entries 7 and 8).
Since the results suggested a possible positive influence of solvent polarity on the selectivity to 6a, more practical alternatives to DMSO were sought.
When a stoichiometric amount of (C3H7)4NOH was used as base and catalyst in toluene, a good selectivity towards the desired meta-terphenyl was observed (Table 1, entry 9). On the other hand, a reversed selectivity was obtained by working under liquid-liquid PTC conditions using 50% aq. NaOH/toluene biphasic system (Table 1, entry 10).
The well-known metal cation coordination ability of polyethyleneglycols (PEG) [29], and the appropriate physical and solvent properties of low molecular weight liquid/low melting solid PEG, suggested us to use PEG 1000 as a Phase Transfer Catalyst. In fact, it is a low melting solid (mp 37–40 °C) easier to manipulate than viscous PEG 400. We were indeed delighted to find that the best result as regards to the selectivity was achieved when the reaction was carried out in the presence of PEG 1000 as catalyst, without any other solvent (Table 1, entry 11). Indeed the desired terphenyl 6a was isolated as a single compound, although in modest yield.
Higher yields of the desired terphenyl 6a can be obtained by working under unselective conditions in CH3CN as solvent (Table 1, entry 5) affording good yields of the combined terphenyls mixture (6a + 8a), followed by desulfonylation in order to convert 8a to the desired 6a. Thus, the mixture of 6a and 8a was dissolved in THF, cooled to −80 °C, and dropwise added to a stirred THF solution of freshly prepared sodium naphthalenide solution at −80 °C. The meta-terphenyl 6a was isolated in a 72% overall yield by quenching with water after 40 min, followed by usual work-up and chromatographic purification.
In order to determine the influence of the sulfone on the outcome of the reaction, the (cinnamylsulfonyl)benzene (4c) was reacted with chalcone 5a under the previously optimized reaction conditions (Table 2).
When the reaction was carried out in the presence of Aliquat as catalyst in DMSO, only the desired 1,2,4-triphenylbenzene 7a was recovered in 65% yield (Table 2, entry 1). When the temperature was increased to 100 °C a slight drop of the yield of 7a was observed along with the formation of 5% of the sulfonyl derivative 9a (Table 2, entry 2). Lower yield of 7a was obtained by using 1.1 equiv of NaOH, whereas a sharp decrease in selectivity was observed without Aliquat (Table 2, entries 3 and 4). A completely chemoselective reaction was obtained in the presence of PEG 1000 (0.4 equiv) without organic solvent (Table 2, entry 5). Lower yields were obtained when lower or higher amounts of PEG were used (Table 2, entries 6 and 7).
Although the two chemoselective methods gave similar results (Table 2, entries 1 and 5) the reaction scope was investigated using the method employing PEG 1000 since it is more practical and economic. In fact, PEG 1000 is a cheap, easy to handle solid that successfully replace both Aliquat, a viscous liquid, and DMSO, a dipolar aprotic solvent that is difficult to remove completely from the reaction mixture. Moreover, 160 mg of PEG 1000 only are used to promote the reaction instead of 16 mg of Aliquat along with 1.1 g of DMSO.
A variety of substituted chalcones 5bh afforded the corresponding 1,2,4-triphenylbenzenes 7bh in 51%–71% yield (Table 3).
Good yields were obtained with electronwithdrawing or electrondonating groups on the benzene ring of chalcones 5b, 5c and 5h (Table 3, entries 1, 2 and 8). Heteroaromatic chalcones 5f and 5g were also shown to be good substrates for the reaction (Table 3, entries 6 and 7), whereas (E)-4-phenylbut-3-en-2-one (5d), bearing a methyl group instead of a benzene ring also provided good yield of the terphenyl 7d (Table 3, entry 3).
The polycyclic aromatic hydrocarbon 7e, bearing seven benzenic rings could be isolated, although in low yield, when the bifunctional enone 5e was used as starting material. Similar results have been obtained by using a stoichiometric or 0.5 equiv of the sulfone 4c (Table 3, entries 4 and 5).
In summary, in this paper we have described a new, practical and chemoselective environmentally friendly method for the assembly of meta-terphenyl and 1,2,4-tetraphenyl skeleton under PTC conditions. The method uses allyl sulfones 4 and chalcones 5 as easily available starting materials along with cheap, solid NaOH and PEG 1000. Moreover, no organometallic species or inert atmosphere are required. In particular, the use of PEG 1000 as a PTC catalyst enables to avoid the use of any organic solvent thus adding value to the procedure. The choice of PEG 1000 was found to be crucial in order to develop a completely chemoselective method generating the desired compounds 6 and 7 without formation of the corresponding sulfonylated byproducts 8 and 9.
Further work is in progress in order to increase the yield of meta-terphenyls 6 involving the use of allylsulfone 4a and ascertain the role of PTC in the chemoselective reaction.

3. Experimental Section

3.1. Materials and Methods

Reagents and solvents were purchased from commercial suppliers and used as received, without further purification. Melting points were determined with a BÜCHI 535 melting point apparatus (BÜCHI, Flawil, Switzerland) and are corrected. NMR spectra were recorded with a Bruker Fourier 300 spectrometer (Bruker Billerica, Massachusetts, MA, USA). Chemical shifts are reported by using CHCl3 as an external standard (δ = 7.24 ppm for 1H NMR and 77.0 for 13C NMR). APT experiments were used in the assignment of carbon spectra. Mass spectra (electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI)) were measured with a LCQ Advantage Thermo-Finnigan LLC spectrometer (Thermo-Finnigan LLC San Jose, California, CA, USA). Column chromatography on silica gel (230–400 mesh) was performed by the flash technique. Petroleum ether (PE) refers to the fraction boiling in the range of 40–60 °C.

3.2. Synthesis of Sulfones 4 and Chalcones 5

Allyl sulfones 4a and 4c were prepared by alkylation of the proper commercially available sodium arylsulfinate under PTC conditions. The following detailed procedure for 4a is typical.
1-(Allylsulfonyl)-4-methylbenzene (4a): in a two-neck flask provided with a reflux condenser and calcium chloride drying tube sodium 4-methylbenzenesulfinate (8.91 g, 50 mmol) and TEBA (1.14 g, 5 mmol) were dissolved in CH3CN (50 mL). Allyl bromide (4.23 g, 35 mmol) was added and the mixture was heated and magnetically stirred at 70 °C for 21 h. Some solid material formed during reaction was dissolved by adding H2O (5 mL) and the reaction mixture was then extracted with AcOEt (3 × 20 mL). The organic layer was dried (MgSO4) and evaporated at reduced pressure. The crude product was purified through a small silica plug (AcOEt/PE = 1:1) to give 5.36 g of the title compound (78% yield). The analytical data match those reported in the literature [30].
3-Benzenesulfonylpropenylbenzene (4c). The title compound was generated in a 75% yield (6.78 g, white solid, mp 110.6–112.0 °C) with the same protocol described above for 4a and using cinnamyl chloride (4.08 g, 35 mmol) instead of allyl bromide. The analytical data of 4c are consistent with those reported in the literature [31].
Chalcones 5a and 5c are commercially available. Other chalcones have been prepared by the Claisen-Schmidt condensation of methylketones with aldehydes [32] and their spectroscopic and physical properties matched those reported in literature:
(E)-3-(4-bromophenyl)-1-phenylprop-2-en-1-one (5b) [33], (E)-4-phenylbut-3-en-2-one (5d) [34], (2E,2′E)-3,3′-(1,4-phenylene)bis(1-phenylprop-2-en-1-one) (5e) [35], (E)-3-(3-methylthio phen-2-yl) -1-phenylprop-2-en-1-one (5f) [36], (E)-3-(5-methylfuran-2-yl)-1-phenylprop-2-en-1-one (5g) [37], (E)-1-(4-Chlorophenyl)-3-phenylprop-2-en-1-one (5h) [38].

3.3. General Procedure for the Synthesis of meta-Terphenyls 6ac under PTC Conditions

In a screw cap vial allylsulfone 4a (79 mg, 0.40 mmol) and chalcone 5 (0.40 mmol) were dissolved in DMSO (1 mL). Solid NaOH (1.6 mmol, 64 mg) and TEBA (0.04 mmol, 9 mg) were added and the resulting mixture was stirred at 70 °C until completion. The reaction mixture was quenched with sat NH4Cl solution and extracted with AcOEt (3 × 5 mL). The combined organic solution was dried and evaporated to dryness. The pure compounds were obtained by column chromatography (AcOEt/hexane from 1:20 to 1:3).
1,1′:3′,1′′-terphenyl (6a): yield 22%; mp 86.5–87 °C, lit. [16] mp 86–88 °C. 1H NMR (300 MHz, CDCl3): δ 7.82 (m, 1H), 7.67–7.26 (m, 13 H). 13C NMR (300 MHz, CDCl3): δ 141.7 (C), 141.1 (C), 129.0 (CH), 128.6 (CH), 127.2 (CH), 127.1 (CH), 126.0 (CH).
4′-sulfonyl-1,1′:2′,1′′-terphenyl (8a): 1H NMR (300 MHz, CDCl3): δ 8.46 (m, 1H), 7.78–6.99 (m, 16H), 2.34 (s, 3H).
4-bromo-1,1′:3′,1′′-terphenyl (6b): yield 23%; mp 91–92 °C, lit. [39] mp 91.5–92 °C. 1H NMR (300 MHz, CDCl3): δ 7.78 (s, 1H), 7.61 (m,5H), 7.51 (m, 6H), 7.39(m, 1H). 13C NMR (300 MHz, CDCl3): δ 142.0 (C), 141.0 (C), 140.6 (C), 140.1 (C), 131.9 (CH), 129.3 (CH), 128.8 (CH), 127.5 (CH), 127.2 (CH), 126.5 (CH), 125.9 (CH), 125.9 (CH), 121.7 (C). 4-methoxy-1,1′:3′,1′′-terphenyl (6c): yield 39%, mp 122–123 °C, lit. [40] mp 123–124 °C. 1H NMR (300 MHz, CDCl3): δ 7.76 (m, 1H), 7.66–7.374 (m, 10H), 7.00 (d, 2H, J = 9 Hz), 3.86(s, 3H). 13C NMR (300 MHz, CDCl3): δ 159.2 (C), 141.6 (C), 141.3 (C), 141.2 (C), 133.6 (C), 129.0 (CH), 128.6 (CH), 18.1 (CH), 127.2 (CH), 127.1 (CH), 125.6 (CH), 125.4 (CH), 114.2 (CH), 55.2 (CH3).

3.4. General Procedure for the Solventless Synthesis of Quaterphenyls 8 under PTC Conditions

A screw cap vial was charged with allylsulfone 4c (0.40 mmol, 103 mg), chalcone 5 (0.40 mmol), solid NaOH (1.6 mmol, 64 mg) and PEG 1000 (0.16 mmol, 162 mg). After stirring at 70 °C until completion, the reaction mixture was quenched with sat NH4Cl solution and extracted with AcOEt (3 × 5 mL). The combined organic solution was dried and evaporated to dryness. The pure compounds were obtained by column chromatography (AcOEt/hexane from 1:20 to 1:3).
4′-phenyl-1,1′:2′,1′′-terphenyl (7a): yield 66%, mp 120.5–121 °C, lit. [41] mp 121–122 °C. 1H NMR (300 MHz, CDCl3): δ 7.75–7.69 (m, 4H), 7.59–7.48 (m, 3H), 7.44–7.40 (m, 1H), 7.28–7.24 (m, 10H).
4-bromo-5′-phenyl-1,1′:2′,1′′-terphenyl (7b): yield 71%, mp 210.5–211.2 °C. 1H NMR (300 MHz, CDCl3): δ 7.63–7.50 (m, 7H), 7.26–7.16 (m, 10H). 13C NMR (300 MHz, CDCl3): δ 141.3 (C), 141.2 (C), 141.0 (C), 140.0 (C), 139.5 (C), 139.1 (C), 131.9 (CH), 131.2 (CH), 129.8 (CH), 129.2 (CH), 128.7 (CH), 127.9 (CH), 126.7 (CH), 126.6 (CH), 125.9 (CH), 121.7 (C).
4-methoxy-5′-phenyl-1,1′:2′,1′′-terphenyl (7c): yield 69%, mp 165.4–166.0 °C. 1H NMR (300 MHz, CDCl3): δ 7.66 (m, 4H), 7.53 (m, 1H), 7.25 (m, 10H), 7.04 (m, 2H), 3.90 (s, 3H). 13C NMR (300 MHz, CDCl3): δ 159.4 (C), 141.6 (C), 141.2 (C), 141.0 (C), 140.0 (C), 139.0 (C), 133.1 (C), 131.1 (CH), 129.9 (CH), 129.9 (CH), 129.0 (CH), 128.2 (CH), 127.9 (CH), 127.9 (CH), 126.6 (CH), 126.5 (CH), 125.7 (CH), 114.3 (CH), 55.4 (CH3).
2′-methyl-1,1′:4′,1′′-terphenyl (7d): yield 70%, mp 84.5–86.8 °C. 1H NMR (300 MHz, CDCl3): δ 7.64 (m, 2H), 7.51–7.26 (m, 11H), 2.36 (s, 3H). 13C NMR (300 MHz, CDCl3): δ 141.6 (C), 141.0 (2C), 140.2 (C), 135.8 (C), 130.3 (CH), 129.2 (CH), 129.1 (CH), 128.8 (C), 128.1 (CH), 127.2 (CH), 127.1 (CH), 126.9 (CH), 124.6 (CH), 20.7 (CH3).
4′,5′′′-diphenyl-1,1′:2′,1′′:4′′,1′′′:2′′′,1′′′′-quinquephenyl (7e): yield 15%, mp 255.6–258.1 °C. 1H NMR (300 MHz, CDCl3): δ 7.79–7.06 (m, 30H). 13C NMR (300 MHz, CDCl3): δ 141.5, 141.1, 139.7, 131.2, 131.1, 130.4, 129.9, 129.3, 128.8, 127.9, 127.5, 127.2, 126.6, 126.2, 126.0, 125.9. APCI–MS: m/z = 535.3 [M + H]+.
2-(2′-1,1′:4′,1′′-terphenyl)-3-methyl-thiophene (7f): yield 63%, mp 111.8–114.3 °C. 1H NMR (300 MHz, CDCl3): δ 7.46–7.37 (m, 4H), 7.17–7.07 (m, 10H), 6.64 (d, 1H), 2.33 (s, 3H). 13C NMR (300 MHz, CDCl3): δ 141.2 (C), 141.1 (C), 140.7 (C), 139.4 (C), 137.3 (C), 134.0 (C), 133.4 (C), 131.1 (CH), 130.8 (CH), 129.90 (CH), 129.8 (CH), 127.9 (CH), 126.6 (CH), 126.6 (CH), 123.6 (CH), 15.1 (CH3).
2-(2′-1,1′:4′,1′′-terphenyl)-3-methyl-furan (7g): yield 51%, oil. 1H NMR (300 MHz, CDCl3): δ 7.7–7.2 (m, 13H), 6.61 (d, 1H, J = 3.2), 6.08 (d, 1H, J = 3.2), 2.39 (s, 3H). 13C NMR (300 MHz, CDCl3): δ 152.2 (C), 151.9 (C), 141.5 (C), 141.2 (C), 140.9 (C), 138.9 (C), 137.9 (C), 131–125 (13CH), 107.8 (CH2), 106.2 (CH2), 13.7 (CH3).
4-chloro-3′-phenyl-1,1′:4′,1′′-terphenyl (7h): yield 63%, mp 206.4–208.6 °C. 1H NMR (300 MHz, CDCl3): δ 7.60–7.63 (m, 4H), 7.50–7.53 (m, 1H), 7.42–7.45 (m, 2H), 7.15–7.26 (m, 10H). 13C NMR (300 MHz, CDCl3): δ 141.3 (C), 141.2 (C), 140.9 (C), 139.9 (C), 139.1 (C), 139.0 (C), 133.6 (C), 131.2 (CH), 129.8 (CH), 129.2 (CH), 129.0 (CH), 128.4 (CH), 128.0 (CH), 128.0 (CH), 126.7 (CH), 126.6 (CH), 125.9 (CH).

3.5. Desulfonation of the meta-Terphenyl (6a) and Sulphonyl-meta-terphenyl (8a) Mixture

The mixture of compounds 6a (0.152 mmol, 35 mg) and 8a (0.144 mmol, 55.4 mg), as recovered after usual work-up of reaction carried out under condition reported in Table 1 (entry 5), was dissolved in anhydrous THF (1 mL), cooled to −80 °C and subsequently added to a stirred THF solution of freshly prepared sodium naphthalenide (0.86 mmol) at −80 °C. After 40 min at the same temperature the reaction was quenched by water addition. The reaction mixture was allowed to come to room temperature and was extracted with CH2Cl2 (3 × 5 mL). The organic phase was dried over Na2SO4, evaporated under reduced pressure and purified by column chromatography (AcOEt/PE) to give 66 mg of meta-terphenyl (3a), overall yield 72%.

Author Contributions

Domenico C. M. Albanese conceived and designed the experiments; Selene Brunialti and Dario Destro performed the experiments; Domenico C. M. Albanese analyzed the data; Domenico C. M. Albanese and Selene Brunialti wrote the paper.

Conflicts of Interest

The authors declare no conflict of interest.

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Scheme 1. Synthesis of 5′,5′′′′-sulfonyl-di-[1,1′:3′,1′′]-terphenyl (BTPS).
Scheme 1. Synthesis of 5′,5′′′′-sulfonyl-di-[1,1′:3′,1′′]-terphenyl (BTPS).
Catalysts 06 00142 sch001
Scheme 2. Morita-Baylis-Hillman route to meta-terphenyls.
Scheme 2. Morita-Baylis-Hillman route to meta-terphenyls.
Catalysts 06 00142 sch002
Scheme 3. Base promoted route to meta-terphenyls. The red and green benzenic rings are used to highlight the position of aryl groups of the starting chalcone in the produced meta-terphenyl.
Scheme 3. Base promoted route to meta-terphenyls. The red and green benzenic rings are used to highlight the position of aryl groups of the starting chalcone in the produced meta-terphenyl.
Catalysts 06 00142 sch003
Table 1. Synthesis of meta-terphenyls 6 under Phase Transfer Catalysis (PTC) conditions a.
Table 1. Synthesis of meta-terphenyls 6 under Phase Transfer Catalysis (PTC) conditions a.
Catalysts 06 00142 i001
EntryBase (equiv)Catalyst (equiv)ChalconeSolventt (h)6 (%)8 (%)
1NaOH (1)TEBA (0.1)5aToluene31323
2NaOH (4)TEBA (0.1)5aToluene32028
3NaOH (4)TEBA (0.1)5aCH3CN31417
4 bNaOH (4)TEBA (0.1)5aCH3CN3529
5 cNaOH (4)TEBA (0.1)5aCH3CN33836
6NaOH (4)TEBA (0.1)5aDMSO1318
7NaOH (4)TEBA (0.1)5bDMSO3236
8NaOH (4)TEBA (0.1)5cDMSO3392
9(C3H7)4NOH 1M (1)5aToluene3318
1050% NaOH (4.1)Bu4N+HSO4 (0.1)5aToluene211126
11NaOH (4)PEG 1000 (0.4)5a122
a Reaction conditions: 4a (0.4 mmol), 5a (0.4 mmol), TEBA (0.04 mmol), 70 °C; b 4a (0.8 mmol); c 5a (0.8 mmol).
Table 2. Synthesis of quaterphenyls 7 under PTC conditions a.
Table 2. Synthesis of quaterphenyls 7 under PTC conditions a.
Catalysts 06 00142 i002
EntryBase (equiv)Catalyst (equiv)ChalconeSolventt (h)7a (%)9a (%)
1NaOH (4)Aliquat (0.1)5aDMSO165
2 bNaOH (4)Aliquat (0.1)5aDMSO1605
3NaOH (1.1)Aliquat (0.1)5aDMSO3489
4NaOH (4)5aDMSO14224
5NaOH (4)PEG 1000 (0.4)5a166
6NaOH (4)PEG 1000 (1.2)5a158
7NaOH (4)PEG 1000 (0.1)5a141
a Reaction conditions: 4c (0.4 mmol), 5 (0.4 mmol), 70 °C; b at 100 °C.
Table 3. Synthesis of quaterphenyls under solventless PTC conditions a.
Table 3. Synthesis of quaterphenyls under solventless PTC conditions a.
EntryCalchone 5Quaterphenyl 7Yield (%)
1 Catalysts 06 00142 i003 Catalysts 06 00142 i00471
2 Catalysts 06 00142 i005 Catalysts 06 00142 i00669
3 Catalysts 06 00142 i007 Catalysts 06 00142 i00870
4 b Catalysts 06 00142 i009 Catalysts 06 00142 i01019
5 c5e7e15
6 Catalysts 06 00142 i011 Catalysts 06 00142 i01263
7 Catalysts 06 00142 i013 Catalysts 06 00142 i01451
8 Catalysts 06 00142 i015 Catalysts 06 00142 i01663
a Reaction conditions: 4c (0.4 mmol), 5 (0.4 mmol), PEG 1000 (0.16 mmol), 1 h, 70 °C; b 4c (0.4 mmol), 5e (0.2 mmol); c 4c (0.4 mmol), 5e (0.4 mmol).
Catalysts EISSN 2073-4344 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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