Efficient Approach to 4-Oxo-2-alkenylphosphonates via Regiospecific Friedel−Crafts Acylation

Treatment of allylic and vinylic phosphonates with excess LiHMDS, followed by addition of chlorotrimethylsilane, afforded α- and γ- silylated allylic phosphonate mixtures. Without separation, these mixtures underwent the Friedel−Crafts reaction and base-promoted isomerization to give 4-oxo-2-alkenylphosphonates, which can serve as building blocks for the construction of polyethylenic chains.