Synthesis of benzimidazolyl selenophenes

Abstract

Benzimidazol-2-ylmethaneselenol (5a) and its sodium salt (5b) have been prepared and treated in situ with α,β-unsaturated ketones to give the β-seleno ketones (3). In the absence of a α,β-CC double bond, the seleno ketones appeared highly prone to retro-Michael type decomposition. Thus, cyclisation to give the tetrahydro- and dihydro-selenophene derivatives (1) and (2) was found to be efficient only in the case of compound (3c) which has an α,β-CC bond. Some peculiar but not unprecedented reactions such as selenium extrusion from the diselenide (8) and reductive cyclisation of the bis(benzimidazolylmethyl) selenides (9), (10), and (11) were encountered.