5-aryl-2,2-bithiophenes

In the reactions of (2-furyl)- and (2-thienyl)diphenylmethanols, the heteroaryl groups have also been found to be eliminated selectively [48]. This maybe attributed to the coordination ability of the internal heteroatoms. It has been applied to the synthesis of 5-aryl-2,2 -bithiophenes (Eq. 27) [51]. 

A variety of 2- or 3-substituted thiophenes, as well as benzothiophenes, have been subjected to the catalytic direct arylation [3, 9, 10]. As expected, 2,2 -bithio-phene can be diarylated at the 5,5 -positions (Equation 10.47) [72], although the use of a bulky phosphine is of key importance for this reaction. 2,2 -Bithiophene protected by benzophenone at the 5-position reacts with aryl bromides, initially with liberation of the ketone (see Scheme 10.6, to give 5-aryl-2,2 -bithiophene, which is then arylated at the 5 -position (Equation 10.48) [72]. 5-Bromo-2,2 -bithio-phenes undergo oxidative homocoupling in the presence of a palladium complex and a silver salt (Equation 10.49) [73]. 

This report summarizes some analogs of a-terthienyl 2-aryl-5-dihalovinylthiophenes, 5-aryl-2,2 -bithiophenes and diarylthiazoles. These compounds are light-activated miticides. The synthesis, activity and structure-activity relationship of each class of compounds will be discussed. 

Table IV. Activity of 5-aryl-2,2 -bithiophenes (2) on Two-spotted Mites.

Thienylstannanes were also coupled with a series of reagents other, than conventional aryl halides. 2,2 -Bithiophene was prepared from the thienyliodonium salt shown in 6.34. and 2-tributylstannylthiophene. The activity of the iodonium salt allows for the room temperature coupling of the reagents in the presence of only 0.5 mol% palladium dichloride in a coordinating solvent mixture to give an excellent yield of the desired product.48... 

The dithienophospholes 74 are obtained in good yields by lithiation of dibromo-bithiophenes 73, followed by addition of dihalo (aryl) phosphines (Scheme 4.22) [57]. The Lewis basicity of the P center of 74 enables a broad range of facile chemical modifications to be undertaken, as exemplified with the synthesis of derivatives 75-77 (Scheme 4.22) [57]. 

The regioselectivity observed with many nucleophilic arenes is moderate to excellent, and generally follows the pattern expected for aromatic electrophilic substitution (e.g., nitration, bromination, etc.) of the arenes. 3-Methoxythiophene reacts first at the 2-position but double arylation at the 2- and 5-positions is achieved in the absence of DME additive. 2-Ethylthiophene, 2,3-dimethylfuran, and 2,2 -bithiophene react at the expected 5-position and, similarly, thiophene reacts at the 2-position. 1,3-Dimethoxybenzene reacts exclusively at the 4-position while... 

Transition metal catalyzed processes are useful tools for the synthesis of functionalized thiophenes. Thus for instance, a phosphine-free, palladium catalyzed coupling protocol for the synthesis of 2-arylbenzo[d]thiophenes from various 3-substituted benzo[6]thiophenes and aryl bromides or iodides has been reported <04T3221>. Likewise, 2,2 -bithiophenes have been 5,5 -diarylated directly with aryl bromides in the presence of Pd(OAc)2, bulky phosphine ligands and CS2CO3 <04T6757>. A series of electron-deficient and relatively electron-rich benzo[6]thienyl bromides have been shown to participate in palladium catalyzed amination reactions, as exemplified by the interesting conversion of 63 to the tetracyclic system 64 upon reaction with 2-aminopyridine 65 <04EJO3679>. 

The selective monoarylation of unsubstituted thiophene and furan can be made by using an excess amount of the substrate [ 130]. It has been demonstrated that the use of AgF and DMSO as base and solvent, respectively, enables the reaction at 60 °C [ 135]. Various 2- or 3-substituted thiophenes andbenzothiophenes have been subjected to the catalytic arylation [8,128,130,134-139]. 2,2 -Bithiophene can be arylated at the 5 and 5 positions (Eq. 55) [137]. 

Cu-TC promoted homo-couplings of aryl halides are presented in the Table 11. Among heteroaryl halides, 2-iodothiophene (97) was coupled to 2,2 -bithiophene (98) with a 77% yield [73], respectively, Scheme 20. 

Among intermolecular reactions, an interesting example is arylation of thiophene with diiodopyrrole 519 where the respective bithiophene 520 was obtained in 78% yield [93], respectively. Scheme 49. 

Several additional homo-, co-, and terpolymers based on P3ATs have been synthesized recently. Monomers that incorporate two or three thiophenes such as the 4,4-dialkyl-2,2 -bithiophenes or 3,3-dialkyl-2,2 -bithiophenes with various substituent groups such as alkyl, oxyalkyl, )3-aryl have been prepared by chemical and electrochemical methods (134-137). 

A series of terthiophenes substituted with an aryl group at the central thiophene ring (3 position) were polymerized, and the properties of the monomers and the polymers were studied [523, 524], An improvement of the properties compared with the unsubstituted PTT is achieved. The best results are obtained with electron-withdrawing substituents, especially with a 4-cy-anophenyl substituent [524], The redox potentials of PBT derivatives decrease the order poly(3,3 -dibromo-2,2 -bithiophene) > poly(3,3 -dichloro-2,2 -... 

The general structure-activity relationship for the bithiophenes, 2, appears identical to that for the dihalovinyl derivatives, 1. For example, 3,4-diaryl-2,2 -bithiophenes would be inactive due to steric crowding of the aryl and thiophene rings causing non-planarity of the pi-system. Also, a substituent in the 4-position of the central thiophene ring of 2 causes a decrease in activity. 

Twofold reaction based on bisthiophene product is 5 -bis(4-hexylphenyl)-2,2 -bithiophene Twofold reaction based on aryl bromide product is 4,4 -di(thiophen-2-yl)-l,l -biphenyl... 

Bithiophene and a-terthiophene monomers containing jS-aryl substituents have also been polymerized. A material derived from XL has been used in blends with other poly(3-substituted thiophene)s to afford electroluminescent devices whose emission color depended on the applied voltage [62]. Monomers in which the central ring of a-terlhiophene has been substituted with phenyl-157,63], p-cyanophenyl-, p-methoxyphenyl-, p-pyridyl-, 2-thienyl-, or 3-methyl-2-thienyl [63] have been electro-chemically oxidized to yield mixtures of oligomers in all cases [63]. 

J. Kuwabara, Y. Nohara, S. J. Choi, Y. Fujinami, W. Lu, K. Yoshimura, J. Oguma, K. Suenobu and T. Kanbara, Direct arylation polycondensation for the synthesis of bithiophene-based alternating eopolymers, Polym. Chem., 2013,4(4), 947-953. 

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