Thiophene-2-boronic acid, bromination

In the presence of zero-valent palladium complexes as the catalyst, 2,4-di-tert-butoxypyrimidine-5-boronic acid (244) reacts with the bromine derivatives of thieno[2,3-Z)]- (142) and thieno[3,2-Z)]thiophene (145) (90JHC2165, 91JHC1623). This reaction was used to introduce fragments of isomeric thienothiophenes at position 5 of 2,4-di-tert-butoxypyrimidine. The resulting compounds 245 were transformed into uracils 246 in quantitative yields. 

Reactions.—All the mono- and poly-bromo-derivatives, as well as iodo-derivatives, of thieno[2,3-h]thiophen have been prepared by direct bromination or iodination, or from the lithium compounds, and characterized by their n.m.r. spectra. Boronic acids were obtained from several alkyl- and aryl-thienothiophens via lithiation and were converted by hydrogen peroxide oxidation into the tautomeric hydroxy-derivatives. It was shown by n.m.r. that all thieno[2,3-h]-thiophen systems exist as thieno[2,3-h]thiophen-2(3 )-ones, while in the case of... 

Successive cycles of thiophene terminal bromination and Suzuki-type coupling reactions with 3-hexylthiophene-2-boronic ester gave intermediate ter- and quaterthiophenes. Formylation of these intermediates and final condensation with cyanoacetic acid in basic medium afforded corresponding oligothiophenes in 70-90% yields. UV-Vis absorption spectra of 2.82 (n = 1, 2) showed maxima at 463 and 473 nm, respectively. Fabrication of DSSCs based on 2.82 (n = 1, 2) showed a high incident photon-to-current conversion efficiency (IPCE) of 70 % in the range 400-650 nm and good maximum power conversion efficiencies of 7.7 and 5.6% under AM 1.5 illumination. 

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