Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 1. Preparation of aliphatic and terminal alkynes

Thermal extrusion of Ph(3)PO from beta-oxoalkylidenetriphenylphosphoranes 4 to give the alkynes 5, which under conventional pyrolysis conditions is restricted to cases in which R(1) is an electron withdrawing group, has been successfully achieved for R(1) = H or alkyl by using FVP. The method allows convenient construction of multigram quantities of the alkynes 5 from alkyl halides 1 and acid chlorides 3 in three steps with good overall yields. Under the conditions used the ylides with R(2) = cyclobutyl also undergo loss of ethene to provide convenient access to the vinylalkynes 6.