Synthesis of allenes by double Horner–Wadsworth–Emmons reaction

LDA treatment of aldehydes or ketone with alkenylphosphonates , prepared by Horner–Wadsworth–Emmons (HWE) reaction of methylenebisphosphonate with aldehydes, afforded Baylis–Hillman reaction-type products in high yields. HWE olefination of with KH or KH-18-crown-6 as a base provided allenes in good yields. One-flask procedure was successfully developed starting from to afford an allene in a reasonably good yield.