Substitution reactions of benzo[b]thiophen derivatives. Part I. Bromination and nitration of 2,3-dibromobenzo[b]thiophen and its 5-methyl derivative

Abstract

Bromination of 2,3-dibromobenzo[b]thiophen in chloroform or acetic acid gives the 2,3,6-tribromo-derivative; nitration gives a mixture of 2,3,6-tribromo-(25%), 2,3,4-tribromo-(3%), 2,3-dibromo-6-nitro-(32%), and 2,3-dibromo-4-nitrobenzo[b]thiophen (36%). Analogous results are obtained for the bromination and nitration of 2,3-dibromo-5-methylbenzo[b]thiophen, except that the presence of the 5-methyl group increases the proportion of the 4-substituted product in each case. The structures assigned are supported by a detailed analysis of their ¹H n.m.r. spectra.