Phosphines, with carbon tetrahalides

The first isolable product in the reaction of triphenylphosphine and carbon tetrachloride is the salt (73), which reacts rapidly with further phosphine to give the stable phosphorane (74).62 In contrast, tris-t-butylphosphine reacts with germanium and tin tetrahalides to form the salts (75) 3 compounds of the latter type have long been postulated as arising from the reactions of phosphines with carbon tetrahalides but so far have defied detection. 

The second group of the reactions resulting in the formation of phosphorylated ketenes is based on the specific properties of trivalent phosphorus compounds (2 -- ).The Phosphines bearing an activated hydrogen atom in oC -position readily react with carbon tetrahalides... 

Ylids are produced by reaction with a-bromosulphones (6.91). Initial attack at halogen is probably also involved in the reactions between tertiary phosphines and carbon tetrahalides (6.92). 

Phosphonium ylids are formed in reactions between phosphines and carbenes (6.97) and between phosphines and carbon tetrahalides (6.85). Phosphines also react with aliphatic diazo compounds to give ylids, provided cuprous chloride is present to prevent the formation of phosphinazines (6.107). 

A halogenating system related to the preceding case is formed by the reaction of triphenylphosphine with molecular bromine or chlorine. The system is not as sensitive to moisture as the phosphine-carbon tetrahalide system (see preceding section), but it suffers from the disadvantage that hydrohalic acids are produced as the reaction proceeds. Nevertheless, sensitive compounds can be successfully halogenated by the system, as exemplified by the preparation of cinnamyl bromide from the alcohol. 

Treatment of N-acylated a-aminonitriles 1077 with PPh3 and a carbon tetrahalide affords 2,4-disubstituted 5-halo-17/-imidazoles 1078 in good yields. A variety of alkyl and aryl substituents (R and R ) are tolerated. A possible mechanism involves the formation of a novel seven-membered ring intermediate and then elimination of triphenyl-phosphine oxide, as illustrated in Scheme 261 <20040L929>. 

Cyclohexanedione and triethylamine added to a suspension of triphenyl-phosphine dichloride in benzene, and stirred 1 hr. at room temp. 3-chloro-2-cyclohexen-l-one. Y 91%. F. e. s. E. Piers and I. Nagakura, Synth. Commun. 5, 193 (1975) with triphenylphosphine and carbon tetrahalides s. L. Gruber, I. Tomoskozi, and L. Radies, Synthesis 1975, 708 with oxalyl chloride, also from -ketoaldehydes, s. R. D. Clark and C. H. Heathcock, J. Org. Chem. 41, 636 (1976). 

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