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 alpha- and gamma- 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.