Synthesis and reactions of 3-benzo[b]thienyl-lithium

Abstract

(Phenylthio)acetone on cyclodehydration with polyphosphoric acid or phosphorus pentoxide at 160—180° gave a mixture of 2-(15—18 mole%) and 3-methylbenzo[b]thiophen (82—85 mole%). Pure 3-Bromobenzo[b]thiophen was obtained in high yield by hydrolysis of 3-bromo-2-benzo[b]thienyl-lithium and by debromination of 2,3-dibromobenzo[b]thiophen with zinc dust and acetic acid. It was treated with n-butyl-lithium in ether at –70° to give 3-benzo[b]thienyl-lithium which was used to synthesize a number of 3-substituted benzo[b]thiophens. 1-(3-Benzo[b]thienyl) ethanol was oxidized with potassium dichromate and sulphuric acid to give 3-acetylbenzo[b]-thiophen and Wolff–Kishner reduction of benzo[b]thiophen-3-carboxaldehyde afforded 3-methylbenzo[b]thiophen.