A Simple Synthesis of New Phosphaalkenes

Abstract Upon treatment of phosphanylsubstituted phosphorus ylides like la-c with two equivalents BF3 *OEt2 the compounds 2a-d are obtained almost quantitatively. In them a phosphonium-and a phosphenium ion compete for the electron density at the bridgeing carbon atom. A X-ray analysis of 2a and the reactivity of transient 3a,b so far studied reveal the olefinic character corresponding to phosphonium substituted phosphaalkenes.