Efficient stereodivergent synthesis of cis-(2R,4S)- and trans-(2R,4R)-4-phosphonomethyl-2-piperidinecarboxylic acids from the same chiral imine derived from (R)-glyceraldehyde

Abstract

Two diastereomeric 4-phosphonomethyl-2-piperidinecarboxylic acids have been prepared in ca. 20% overall yield starting from the easily accessible N-[(S)-1-phenylethyl]-(S)-2,3-di-O-benzylglyceraldimine. The key step for the stereodivergent synthesis is the asymmetric reduction of an exocyclic C=C double bond on a highly functionalized chiral intermediate. This intermediate is ­obtained by Horner-Wadsworth-Emmons (HWE) reaction of a ­piperidone derived from the cycloadduct obtained in the aza ­Diels-Alder reaction between N-[(S)-1-phenylethyl]-(S)-2,3-di-O-benzylglyceraldimine and Danishefsky's diene. In these synthetic routes two new stereogenic centres are created on the piperidine ring with very good or excellent stereoselectivity.