Synthesis of Conjugated F-Polyenes Containing Thienyl Ring Systems

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Abstract

Novel 1-substituted F-1,3-butadienes ThioAr−CFCFCFCF2, ThioAr = 2-thienyl and 2-benzo[b]thienyl, and symmetrically 1,4-disubstituted F-1,3-butadienes ThioAr-CFCFCFCF−ThioAr, ThioAr = 5-R‘-2-thienyl (R‘ = Me, SiMe3, CFCFCl), 3-thienyl, and 4-dibenzo[b,d]thienyl, inclusive of the above-named substituents, were prepared by the reaction of organolithium derivatives with F-1,3-butadiene (PFBD). Monothioaryl-substituted F-1,3-butadienes were used as intermediates in subsequent reactions with other (thioaryl)organolithium derivatives for the synthesis of a new series of unsymmetrically substituted α,ω-bis(thioaryl)-F-polyenes ThioAr−(CFCF)n−ThioAr‘, where n = 2, ThioAr, ThioAr‘ = 4-RC6H4 (R = H, Me, OC6H11, NMe2), 2-thienyl, 5-methyl-2-thienyl, 2-benzo[b]thienyl, 4-dibenzo[b,d]thienyl, and for n = 3, ThioAr = 2-thienyl, ThioAr‘ = 5-methyl-2-thienyl. The reaction of 2,5-dilithiothiophene with 1-(2-thienyl)-F-1,3-butadiene affords 2,5-bis[4-(2-thienyl)-1,2,3,4-tetrafluoro-1,3-butadienyl]thiophene (5). 2,5-Thienylene-F-polyenylene polymers were prepared by the reaction of 2,5-dilithio- and 2,5-bis(bromomagnesio)thiophene derivatives with PFBD and F-ethylene. The oligomers 5 and 2,5-bis[2-(2-thienyl)-1,2-difluoroethylenyl]thiophene (16) were found to possess liquid crystalline properties. The reaction of 1,4-bis(2-thienyl)-F-1,3-butadiene with nitric acid led to substitution in one or in both thienyl rings at position 5. NMR, electronic spectra, and structural aspects of the title compounds are discussed.

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