Synthesis of Angularly Fused (Homo)triquinane-Type Hydantoins as Precursors of Bicyclic Prolines

Abstract

An efficient strategy for a four-step synthesis of angularly fused tricyclic hydantoins as suitable precursors of cis-fused bicyclic α-amino acids is developed by combining a highly diastereoselective Bucherer–Bergs reaction of 2-alkenylcycloalkanones and a regiospecific selenium-induced closure of pyrrolidine ring. This methodology was applied in a five-step synthesis of bicycloproline derivatives in high overall yield. The method could be used for the multigram preparation of free conformationally constrained bicyclic α-amino acids with two points of diversity (size of cycloalkyl ring and substituent at the pyrrolidine ring).