Studies on sulphur heterocycles. Reactions of 6,7‐dihydrobenzo[b]thiophen‐4(5H)one derivatives and their conversion to 7‐substituted thieno[2,3‐h][1]benzopyran‐8‐ones

Cyclization of γ‐(2‐thienyl)butryic acid with acid anhydrides gives 2‐acyl derivatives as well as the expected 6,7‐dihydrobenzo[b]thiophen‐4(5H)one. Several reactions of these ketones have been studied including their conversion to 0,0‐diethyl thiophosphonohydrazones. 7‐Substituted thieno[2,3‐h][1]benzopyran‐8‐ones have been prepared via 4‐hydroxybenzo[b]thiophen‐5‐carbaldehydes.