Photochemical coupling between halogenoheterocyclic and heterocyclic derivatives

Abstract

The photochemical reaction between 5-iodo- heteroaryl derivatives 1a–d and both 3-heteroaryl allylic alcohols (2a–b) and acetates (3a–b) have been investigated. The presence of an alcoholic function was not compatible with photochemical coupling since compounds 1a–d were photoreduced in the presence of an alcohol. In contrast, the acetates 3a, b gave the expected coupling products. The presence of a weak electron-withdrawing group on the alkene induced an inverted regiochemistry giving only aryl–aryl coupling products. The same behaviour was observed using 2-(3-acetoxyprop-1-ynyl)thiophene 8, in which case only the product deriving from aryl–aryl coupling was again observed. When 2-prop-1-ynylthiophene 11 was used as starting material, the some product resulting from attack on the methyl group 13 was observed. Photochemical coupling between 2-thienylacetonitrile (14) and halogenothienyl derivatives 1b, c gave no reaction product. In contrast, the irradiation of methyl 2-thienylacetate 15 and methyl 2-(2-thienyl)propionate (17) in the presence of 1b, c did give the corresponding coupling products.