On the Vilsmeier formylation of N-aryl-substituted 2-aminothiophenes - a simple route to new thieno[2,3-b]quinolinium salts

The Vilsmeier reaction of N-substituted 2-arylamino-thiophenes-5-carboxylic acid or their alkyl derivatives gives rise, depending on the substitution pattern at the thiophene moiety, to the formation of either N-substituted 2-arylamino-thiophene-5-carbaldehydes, corresponding imminium salt precursors, or novel thieno[2,3-b]quinolinium salts. These salts are highly reactive towards nucleophiles and can be easily transformed by reduction into the corresponding 4,9-dihydro derivatives.