Acid or Salt? New Insights into ‘Phosphoric Acid Catalysis’

Significance

Ishihara and co-workers found that not only chiral phosphoric acids, but also their calcium salts catalyze the asymmetric Mannich reaction of aryl imines and 1,3-dicarbonyl compounds. Interestingly, catalyst types 1 and 2 complement each other in substrate scope and even the absolute configuration of the products obtained was ­inverted in some cases. The Mannich products were obtained in high yields and enantioselectivities. Furthermore, plausible transition states are discussed and the versatility of the products was demonstrated by converting them into synthetically useful compounds, such as β-amino alcohols or β-amino ketones.