Reactive phosphonium ylides based on 3-phenyl-3-chloro-2-aza-2-propen-1-yl(triphenyl)phosphonium chloride

Treatment of the accessible phosphonium salt PhCCl=NCH2P+Ph3Cl- with trieth ylamine yields a solution of biphilic ylide PhCCl=NCH=PPh3, which along wit h the nucleophilic center of the P=C bond contains an electrophilic imidoyl chloride group and therefore enters cyclocondensations with carboxylic aci d chlorides, carbon disulfide, and acyl isothiocyanates. The latter cycliza tion is of particular significance because it yields previously inaccessibl e (5-acylimino-2-phenyl-4,5-dihydrothiazol-4-ylidene)triphenylphosphoranes, which, in turn, were used to prepare a series of new derivatives of 5-benz oylamino-2-phenylthiazole. Reaction of the above-mentioned phosphonium salt with sodium thiocyanate in the presence of triethylamine apparently yields the unstable intermediate ylide PhC(NCS)=NCH=PPh2, which is stabilized by intramolecular cyclization to give 5(4)-thioxo-2-phenyl-4,5-dihydroimidazol -4(5)-ylidenetriphenylphosphorane.