Examination was made of 1,2-asymmetric induction in the addition of alkyl radicals to gamma-oxy-alpha,beta-unsaturated ester derivatives 1 and 2 prepared from ethyl lactate and (R)-2,3-0-isopropylideneglyceraldehyde 3, respectively. The addition reactions of hexyl, cyclohexyl and 3-phenylpropyl radicals to (Z)-2 derived from aldehyde 3 gave beta-addition products with syn-stereoselectivity (syn:anti = 8.6:1-syn only). The reactions of (E)-2 were non-stereoselective. Based on allylic strain, a transition-state model for the syn-stereoselectivity is proposed. 1,2-Asymmetric induction was carried out in radical cyclisation to synthesize optically active cyclohexane derivatives.
Highly Selective Synthesis of <i>Z</i>-Unsaturated Esters by Using New Horner−Emmons Reagents, Ethyl (Diarylphosphono)acetates
作者:Kaori Ando
DOI:10.1021/jo970057c
日期:1997.4.1
New Horner-Emmons reagents, ethyl (diarylphosphono)acetates 1, were prepared from triethyl phosphonoacetate, PCl(5), and the corresponding phenols. The reaction of 1 with several kinds of aldehydes in the presence of Triton B or NaH in THF solvent revealed that these reagents are useful for the synthesis of Z-unsaturated esters. Among the reagents examined, ethyl(di-o-tolylphosphono)-, [bis(o-ethylphenyl)phosphono]-