Stereoselective Synthesis of New Chiral N-Tertiary Tetrasubstituted β-Enamino Ester Piperidines through an Ammonia-Catalyzed Process

Abstract

We report here two approaches for the preparation of new N-substituted beta-enamino ester piperidines featuring an exocyclic tetrasubstituted double bond, based either on the direct alkylation of piperidine beta-enamino esters bearing an exocyclic trisubstituted double bond or on the intramolecular cyclization of linear amino beta-keto esters. The target compounds were obtained as unusual (Z)-stereoisomers in high yields. The key role of ammonia as reagent, acting both as a nucleophile and a base, was underlined. The diastereoselective formation of the products was rationalized on the basis of an ammonia addition-syn elimination catalytic process.