Boron Tribromide-Assisted Chiral Phosphoric Acid Catalyst for a Highly Enantioselective Diels–Alder Reaction of 1,2-Dihydropyridines

Abstract

BBr₃–chiral phosphoric acid complexes are highly effective and practical Lewis acid-assisted Brønsted acid (LBA) catalysts for promoting the enantio­selective Diels–Alder (DA) reaction of α-substituted acroleins and α-CF₃ acrylate. In particular, the DA reaction of α-substituted acroleins with 1,2-dihydro­pyridines gave the corresponding optically active isoquinuclidines with high enantio­selectivities. Moreover, transformations to the key intermediates of indole alkaloids, catharanthine and allocatharanthine, are demonstrated