Which Is the Actual Catalyst: Chiral Phosphoric Acid or Chiral Calcium Phosphate?

Abstract

Both catalysts work: A highly enantioselective direct Mannich-type reaction of N-Boc-protected aldimines with 1,3-dicarbonyl compounds has been developed with the use of a chiral phosphoric acid in the presence or absence of CaII. The absolute stereoselectivity of the phosphoric acid catalysis was found to be opposite to that of the calcium phosphate catalysis (see scheme; Boc=tert-butoxycarbonyl).