Diastereoselective synthesis of enantiomerically pure syn- or anti-β-alkyl γ-alkoxyesters by addition of organometallic compounds to α-alkoxy isopropylidene alkylidenemalonates

Abstract

The stereochemistry of the conjugate additions of organometallic compounds R²M (M = Li or Mg) to O-protected α-hydroxy alkylidene isopropylidenemalonates is highly dependent on the nature of the protecting group; in the case of the MEM group, syn-compounds were obtained almost exclusively with Grignard compounds whereas the use of a non-chelating protecting group such as Bu^tPh₂Si afforded nearly pure anti-compounds with organolithium compounds in the presence of 12-crown-4.