The asymmetric synthesis of alpha-substituted alpha-methyl and alpha-phenyl phosphonic acids: Design, carbanion geometry, reactivity and preparative aspects of chiral alkyl bicyclic phosphonamides

The design, preparation, structural and spectroscopic analyses of topologically unique and enantiomerically pure alkyl phosphonamides are described. In the case of alpha-ethyl and alpha-benzyl phosphonamides, the geometry of both the secondary and tertiary carbanions was determined to be planar through deprotonation/deuteration/alkylation experiments. Stereoselective alkylations of such systems proceeded in good yields and with high diastercoselectivities. The resulting alpha,alpha-alkylated phosphonamides were hydrolyzed to give the corresponding alpha,alpha-alkyl phosphonic acids with high degrees of enantiomeric purity. Copyright (C) 1996 Elsevier Science Ltd.