An acyl-Claisen/Paal-Knorr approach to fully substituted pyrroles

Abstract

The synthesis of fully substituted pyrroles using the Paal-Knorr reaction on acyl-Claisen derived 2,3-syn-disubstituted-1,4-diketones is reported. The use of the acyl-Claisen rearrangement allows the synthesis of wide variety of syn-substituted 1,4-diketones which are shown to be better substrates for pyrrole condensation than their corresponding anti isomers. When the reaction was performed open to air the use of nucleophilic amines in the pyrrole forming step leads to auto-oxidation of the 5-methyl group giving exclusively 5-formyl pyrroles.