Fused Heterocycles From Pyrrolethiols. Thieno[2,3-B]Pyrroles, Thieno[3,2-B]Pyrroles and Thiazolo[3,2-a]Pyrroles From Pyrrol-2-Yl Phenacyl Sulfides

Abstract

A reinvestigation of the cyclization of pyrrol-2-yl phenacyl sulfides in polyphosphoric acid has shown that the major product is a thieno[3,2-b]pyrrole, where rearrangement of the sulfur substituent from position 2 to position 3 has preceded cyclization. When TiCl₄ is used as cyclocondensation reagent minimal rearrangement is observed and the product obtained is either a thiazolo[3,2-a]pyrrole when the pyrrole nitrogen is unsubstituted, or a thieno[2,3-b]pyrrole where an N-substituent is present.