Microwave-assisted Paal-Knorr reaction. A rapid approach to substituted pyrroles and furans

An array of tetrasubstituted pyrroles (and trisubstituted furans) was obtained using a simple three-step procedure. Functional homologation of beta-ketoester with an aldehyde followed by oxidation gave a series of differently substituted 1,4-dicarbonyl compounds that can be rapidly cyclized with the Paal-Knorr procedure carried out under microwave irradiation.