Synthesis of 2,5-Disubstituted Pyrroles and Pyrrolidines by Intramolecular Cyclization of 6-Amino-3-keto Sulfones

Abstract

Wittig reaction of 4-[(4-methylphenyl)sulfonyl]-1-(triphenylphosphoranylidene)butan-2-one (1) with N-protected α-amino aldehydes furnished N-protected γ-amino-α,β-unsaturated keto sulfones which have been conveniently utilized as precursors of both aromatic and non-aromatic 2,5-disubstituted five-membered heterocyclic compounds. While 2,5-disubstituted pyrroles are efficiently formed by cyclodehydration of the starting materials, 2,5-disubstituted pyrrolidines and pyrrolenines could be obtained by prior reduction of the conjugated double bond followed by acid- or base-mediated cyclization. The ready availability of the materials required for the whole sequence makes this methodology a convenient way to generate both aromatic and saturated 2,5-disubstituted five-membered heterocyclic compounds.