Iso‐anellated thienopyrroles: The chemistry of 5,6‐dihydro‐4H‐thieno[2,3‐c]pyrroles and 5H‐thieno[2,3‐c]pyrroles

Abstract

AbstractThe ring closure reaction of methyl 2,3‐bis(chloromethyl)thiophene‐5‐carboxylate with several primary amines gives a series of 5,6‐dihydro‐4H‐thieno‐[2,3‐c]pyrroles. Oxidation of some of these dihydro compounds, using aqueous hydrogen peroxide in methanol, furnishes the corresponding N‐oxides. When the nitrogen atom possesses an aromatic substituent and the oxidation is carried out with aqueous hydrogen peroxide in formic acid, Meisenheimer 1 rearrangement products instead of N‐oxides are formed. The structure of one of the Meisenheimer products was elucidated by an independent synthesis of its degradation product.5H‐Thieno[2,3‐c]pyrroles are prepared by three separate methods: (a) dehydration of the N‐oxides; (b) autoxidation of the dihydrothieno[2,3‐c]‐pyrroles; (c) dehydrogenation of the dihydro compounds with chloranil.