Reduction of α-diazo-β-hydroxy esters to β-hydroxy esters: application in one of two convergent syntheses of a (22S)-22-hydroxy bile acid from fish bile and its (22R)-epimer

Abstract

α-Diazo-β-hydroxy esters (3) prepared by condensation of aldehydes (1) with ethyl (lithio) diazoacetate (2) are reduced with 5% palladium over charcoal in methanol into the corresponding β-hydroxy esters (5) in high yield. This sequence is applied to a new synthesis of haemulcholic acid (14c), a (22S)-22-hydroxy bile acid from fish bile and its (22R)-epimer (14d). A convergent synthesis of (14c), a (22S)-22-hydroxy bile acid from fish bile and its (22R)-epimer (14d). A convergent synthesis of (14c) and (14d) involves, as a key step, the dirhodium (II) tetra-acetate conversion of (12) into the corresponding β-keto ester (13).