Z-selective Horner－Emmons Reagents

Ethyl diphenylphosphonoacetate and ethyl di-o-tolylphosphonoacetate are new Horner—Emmons reagents developed by Ando. They form preferentially Z-unsaturated esters in high yields. The reaction condition is very mild and quaternary ammonium hydroxides or NaH used in this reaction as bases are inexpensive.