Asymmetric synthesis of β-substituted δ-ketoesters via michael-additions of samp/ramp-hydrazones to α,β-unsaturated esters, virtually complete 1.6-asymmetric induction
Asymmetric synthesis of β-substituted δ-ketoesters via michael-additions of samp/ramp-hydrazones to α,β-unsaturated esters, virtually complete 1.6-asymmetric induction
A simple and efficient enantioselective synthesis of 2-substituted 4-oxosulfones 5 in 40 – 71% overall chemical yield and enantiomeric excesses of 86->97% is described. The key step is an asymmetric Michael-addition of lithiated methylketone -SAMP-/RAMP-hydrazones 3 to α,β-unsaturated phenylsulfones 2. The absolute configuration is determined by X-ray structure analysis of a crystalline hydrazone Michael