Horner-Wadsworth-Emmons Reagents [Olefination]

　Horner-Emmons reagents are efficient olefinating reagents for the preparation of α-β-unsaturated esters. Generally, their reaction with aldehydes affords the E-isomer of the related olefins preferentially. So, to obtain the E-isomer selectively, it is required to investigate the reaction conditions and other effective olefinating reagants.
　Ando had studied the Z-preferential Horner-Emmons reaction on the basis of detailed analysis of its reaction mechanism, and resultantly it was found that the Z-isomer of α-β-unsaturated esters was given with high stereoselectively by use of ethyl (diaryl)phosphonoacetates as olefinating reagents.¹⁾ In this synthetic method, quaternary ammonium hydroxides stable to water are available as a base, and it doesn’t require any special experimental-equipment/-technique. In addition, this method gives Z-α-β-unsaturated esters with extremely high stereoelectivity, so ethyl (diaryl)phosphonoacetates are the practical Horner-Emmons reagents.