Condensed thiophen ring systems. Part VI. Synthesis and some reactions of 5-methyl- and 5-chloro-3-benzo[b]thienyl-lithium

Abstract

3-Bromo-5-methyl- and 3-bromo-5-chloro-2-benzo[b]thienyl-lithium were prepared and treated (i) with carbon dioxide, to give the corresponding 2-carboxylic acid, and (ii) with acid, to give the 3-bromo-derivatives of 5-methyl-and 5-chloro-benzo[b]thiophen, respectively. With n-butyl-lithium in ether at –70°C the 3-bromo-derivatives gave 5-methyl- and 5-chloro-3-benzo[b]thienyl-lithium, which reacted with carbon dioxide, NN-dimethylformamide, and dimethyl sulphate to give the corresponding 3-carboxylic acid, 3-carbaldehyde, and 3-methyl derivative, respectively. 3,5-Dimethylbenzo[b]thiophen was also prepared by Huang-Minlon reduction of 5-methylbenzo-[b]thiophen-3-carbaldehyde.