Regioselective competitive synthesis of 3,5-bis(het) aryl pyrrole-2-carboxylates/carbonitriles vs. β-enaminones from β-thioxoketones

Abstract

An easily adaptable protocol for the synthesis of 3,5-bis(het)aryl-2-carboxylate/nitrile pyrroles and the related 2,3,5-tri(het)aryl-pyrroles with complementary regioselectivity from the corresponding 1,3-bis(het)aryl-1,3-monothio diketones or β-enaminone precursors has been reported. Initially, regioselective base catalyzed condensation of glycine ethyl/methyl esters or aminoacetonitrile with 1,3-bis(het)aryl-1,3-monothio diketones give β-enaminones, which then in-situ undergoes cyclization to form 3,5-bis(het)aryl-2-carboxylate/nitrile pyrroles. The synthesis of 2,3,5 tri substituted pyrroles with full control over 3rd & 5th position on pyrrole ring is the noteworthy feature of this protocol. Although the product yields are moderate to good, the method offers a facile regioselective entry to 2,3,5 trisubstituted pyrroles without the aid of transition metal.