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Abstract

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.