Asymmetric Addition of Chiral 1,3,2‐Benzoxazaphosphinine 2‐Oxides to Aldehydes: Diastereoselective Synthesis of α‐Substituted β‐Hydroxyphosphonic Acids

The addition of stabilized phosphorus anions to aldehydes leads to α‐substituted β‐hydroxyphosphonates. The diastereoselectivity of the process is strongly influenced by the substitution of the phosphorus atom. Whereas P ‐ethyl derivatives provide a mixture of three isomers, the presence of a benzyl group enhances the stereocontrol, providing two diastereomers in ratios of up to 5:1. Elimination of the aminomenthol appendage produces enantiopure α‐phenyl‐β‐hydroxyphosphonic acids in high yields.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)