Proline‐Catalyzed Mannich Reaction of Aldehydes with N‐Boc‐Imines

A curious cat.: The proline-catalyzed Mannich reaction between aldehydes and N-Boc-imines (Boc=tert-butoxycarbonyl) gives crystalline β-amino aldehydes with exceptionally high diastereoselectivities and enantioselectivities (see scheme). The products of this reaction typically precipitate from the reaction mixture and are useful intermediates in the synthesis of α- and β-substituted β-amino acids.