TRIPHENYLALLENYLLEAD - A FACILE PREPARATION AND ITS USE AS A PROPARGYLATING REAGENT

Triphenylallenyllead, which is easily prepared by reaction of the readily available Ph3PbMgBr (in situ, via 3 PhMgBr + PbCl2 in THF) with propargyl bromide, reacts with aldehydes in the presence of a Lewis acid (BF3.OEt2 or TiCl4) to give homopropargylic alcohols, RCH(OH)CH2C=CH, in good yield. Propargylation of ketones requires transmetalation of Ph3PbCH=C=CH2 with PhLi to CH2=C=CHLi and reaction of the latter with the ketone.