Triphenylphosphoranylidene ketene

An improved route to fluorinated 4-hydroxycoumarins has been reported, based on a facile decarboxylation-deacetylation of their 3-(3-oxopropanoic acid) derivatives <96TL15S1>. The reaction of methyl salicylates with triphenylphosphoranylidene ketene, Ph3P=C=C=0, affords 4-methoxycoumarins <96JCS(P1)2799> and the formation of coumarin 3-phosphonates from salicylaldehydes and phosphonoacetates, Et02CCH2P(0)(0R)2, has been investigated <96T12597>. 

Fig. 1 Phosphacumulenes (triphenylphosphoranylidene)ketene (2), sodium cyanomethyl-enetriphenylphosphorane (3), and (diethoxyvinylidene)triphenylphosphorane (4)...

Chiral stabilized ylides were prepared by the reaction of the Bestmann ylide ((triphenylphosphoranylidene)ketene) with camphor-derived lactams that were used directly or after modification by alkylation in Wittig olefinations. Representative examples are shown in Scheme 92. The products can be regarded as chiral building blocks. ... 

The interaction of dibenzoyldiazine with (triphenylphosphoranylidene)ketene furnished a novel cyclic adduct with phosphorane function (Scheme 97). ... 

The tautomeric form of l-methyl-2-thiohydantoin added easily to the C=C double bond of (triphenylphosphoranylidene)ketene. A subsequent intramolecular cyclization afforded a thioxo-(triphenylphosphoranylidene-)hexahydro-furo-[2,3-d]imidazol-5-one (Scheme 99). ... 

Other heterocycles prepared using iminophosphoranes include novel py-rimidinone and quinazoline derivatives, obtained from in situ aza-Wittig reactions of N aryl-iV-(triphenylphosphoranylidene)carboxidamides (114) and ketenes, and pyridothienopyridazines and pyrimidothienopyridazines, accessed from aza-Wittig/electrocyclic-ring closure reactions between phos-phoranes (115) and (116) and heterocumulenes. ... 

Pyrolysis of the keten-A t-butylimines (39) and (40), prepared by reaction of bis(trifluoromethyl)keten with iV-(triphenylphosphoranylidene)-t-butyl-amine and from perfluorobut-2-yne and t-butyl isocyanide (see p. 52), respectively, yields isobutene and a nitrile " ... 

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