Triphenylphosphine-carbon tetrahalide

I. Halides from Alcohols by Triphenylphosphine-Carbon Tetrahalide... 

Triphenylphosphine-carbon tetrahalides. 13, 331-332 15, 352 16, 366-368 Acid halides. The relatively mild conditions of converting acids to halides by Ph3P-CX4 can be exploited for a one-flask synthesis of A-methoxy imidoyl bromides, which give rise to nitriles on photolysis. In the presence of EtsN the PhsP-CX4 combination converts amines and CF3COOH to trifluoroacetimidoyl halides. ... 

Triphenylphosphine carbon tetrahalide m-1,2-Dihalides from oxido compds. 

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. 

Like tellurophene the fused compound forms 1,1-addition products with halogens (73BSF2468), but further bromination of such a 1,1-dibromo species gave 1,1,2-tribromobenzo[/>]tellurophene, which was able to be reduced to 2-bromobenzo[b]tellurophene. The 3-chloro and -bromo compounds were isolated following reaction of triphenylphosphine and the appropriate carbon tetrahalide with 2,3-dihydro-3-oxobenzo[b]telluro-phene (80BSB763). 

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. 

Although the use of N,N-dimethylformamide permits satisfactory chlorination or bromination of primary positions at room temperature, side reactions can occur between carbon tetrahalides, triphenylphosphine, and JV,N-dimethylformamide that can, in some cases, result in low yields of halogenated products (see also, Section II, 2c p. 230). 

A variety of phosphorus-coutaining reagents have been employed in sugar chemistry in the direct SN2 replacement of hydroxy groups mainly by halide ions [35], Most of these reagents used a combination of triphenylphosphine with an electrophilic halogen source such as /V-halosuccinimide [36,37], carbon tetrahalides [38-41], and more recently, tri-haloimidazole or iodine and imidazole [42-45] or related reagents [46J. The Mitsunobu... 

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). 

For example, alcohols can be converted into the related bromides and chlorides through treatment with triphenylphosphine and a carbon tetrahalide. The alkyl halide is generally formed with inversion, and a rough mechanism involving a series of Sn2 reactions is sketched out in Figure 7.45. 

FIGURE 7.45 Halides are formed from the reaction of alcohols with the intermediate produced from triphenylphosphine and a carbon tetrahalide. 

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