Stereoselectivity in the Wittig‐Horner‐Emmons Synthesis of Vinylphosphonates by the Reaction of Acylphosphonates with Acyclic or Heterocyclic Phosphonoacetates

A new synthetic approach to vinylphosphonates is presented. The reaction of diethyl benzoylphosphonate ( 1 ) with diethyl methoxycarbonyl‐methyl‐phosphonate ( 2 ) gives diethyl 2‐methoxycarbonyl‐l‐styrylphosphonate ( 3 ) as a mixture of geometrical isomers ( Z ‐3) and ( E ‐3) in the ratio of 83:17. In contrast, reaction of 1 with the heterocyclic phosphonate reagent, 2‐methoxycarbonyl‐methyl‐2‐oxo‐4,5‐dimethyl [1,3,2] dioxaphospholane ( 4 ) leads to a mixture of the isomers ( Z ‐3) and ( E ‐3) in the ratio of 20:80.