Reactions of phosphine alkylenes

Alkylidenephosphoranes have recently achieved great importance by their use in Wittig olefination. The manifold applications of that reaction are supplemented by the reactions involving introduction of acyl or alkyl groups the latter have been reviewed by Bestmann.455-457 It should be noted that, 

The procedures for acylation, mainly due to Bestmann and his collaborators, consist in their simplest form of treatment of an alkylidenephosphorane with an acid halide, normally a chloride 456,458 

A second molecule of the ylide is consumed in binding of the halogen acid formed (transylidation) instead of this, another base, such as triethylamine, may be added, but this must then be a stronger base than the ylide used. The following details describe the general synthetical technique  

Most of the acylalkylidenetriphenylphosphoranes can be recrystallized from ethyl acetate. The solubility in this solvent increases with increasing number of methyl groups in the molecule. A small amount of ether often hastens a slow crystallization. Many acylalkylidenetriphenyl-phosphoranes retain the solvent tenaciously. 

It is not essential to isolate the acylated product before using it in further reactions the residue obtained on evaporating the benzene solution may be used directly or, if the further reaction is to be effected in benzene, the acylation solution itself may be used after removal of the phosphonium salt. 

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