Synthesis of Naturally Occurring Bithiophenes: A Photochemical Approach

Article abstract of DOI:10.1021/jo00232a034

A photochemical approach to the synthesis of six naturally occurring bithiophenes is described.The irradiation of 5-iodo-2-tiophenecarbaldehyde (3) in the presence of 2-bromothiophene (4) or 2-methylthiophene (15) furnishes 5-bromo- (5) and 5-methyl-2,2'-bithiophene-5'-carbaldehyde (16) in 99 and 69 percent yields respectively> Compounds 5 and 16 are used in the synthesis of 5-(1-propynyl)-2,2'-bithiophene-5'-methanol (7),5'-propynyl-2,2'-bithiophene-5-carbaldehyde (8), 5-ethynyl-5'-(1-propynyl)-2,2'-bithiophene (9), 5-ethenyl-5'-(1-propynyl)-2,2'-bithiophene (11),5'-<(isovaleryloxy)methyl>-5-<4-(isovaleryloxy)but-1-ynyl>-2,2'-bithiophene (14), and 5-methyl-5'-<1-(buta-1,3-dienyl)>-2,2'-bithiophene (17) through known reactions.In particular, the most important synthetic methodology used in an alkynylation procedure accomplished in the presence of Pd(0) in phase-transfer conditions.