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

BBr3-chiral phosphoric acid complexes are highly effective and practical Lewis acid-assisted Bronsted acid (LBA) catalysts for promoting the enantioselective Diels-Alder (DA) reaction of a-substituted acroleins and alpha-CF3 acrylate. In particular, the DA reaction of alpha-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.