Radical annulation route to the synthesis of lignans: An account.

Abstract

Hydroxybenzo[b]thiophene is an important benzo[b]thiophene derivative because of its role as an intermediate in the synthesis of condensed sulfur heterocycles. The hydroxyl group can be converted into O-carbamate and the latter utilized in the regiocontrolled introduction of substituents through directed metallation. In the present review, synthesis, properties and reactions of various hydroxybenzo[b]thiophenes are described.the pyranoxanthone (14) and its prenylated derivative (31) followed by a Claisen rearragement leading to the target substrate (7).