Synthesis of 3-alkoxybenzo[c]thiophen-1(3H)-ones by hydrolysis of N-substituted 3-alkoxybenzo[c]thiophen-1(3H)-imines derived from 1-bromo-2-(dialkoxymethyl)benzenes and isothiocyanates

Abstract

A convenient procedure for the preparation of a new type of thiophthalides, 3-alkoxybenzo[c]thiophen-1(3H)-ones 4 and 9 has been developed. Thus, 1-(dialkoxymethyl)-2-lithiobenzenes, generated by Br/Li exchange between 2-bromo-1-(dialkoxymethyl)benzenes 1 and 6, and BuLi, react with isothiocyanates to afford N-substituted 2-(dialkoxymethyl)benzothioamides 2 and 7, which, on treatment with a catalytic amount of TsOH×H2O, give N-substituted 3-alkoxybenzo[c]thiophen-1(3H)-imines 3 and 8. The latter are hydrolyzed under acidic conditions to the desired products 4 and 9, respectively. Copyright © 2013 Verlag Helvetica Chimica Acta AG, Zürich.