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35.1.1.5.8.1 Variation 1: Using Triphenylphosphine and Tetrachloromethane

DOI: 10.1055/sos-SD-035-00055

Margaretha, P.Science of Synthesis, (20073579.

This variation is now generally used for converting alcohols into chlorides, the reactions taking place under mild, essentially neutral conditions. Because it proceeds with inversion of configuration, it is a simple device for converting optically active alcohols into chiral chlorides in high optical purity. Tetrachloromethane generally serves both as solvent and halogen source, but in some instances the tetrachloride has been replaced by hexachloroethane or by trichloroacetic acid derivatives (when ester or nitrile groups are present).[‌65‌,‌66‌] The byproduct, triphenylphosphine oxide, usually precipitates completely and is easily removed by filtration. On occasion, a difficulty may be encountered in separating the alkyl halide from the accompanying phosphine oxide, but this is usually resolved by adding an inert solvent such as pentane to ensure precipitation of the phosphine oxide. Because triphenylphosphine reacts with tetrachloromethane in the absence of alcohols, the success of this variation depends critically on the initial presence of an alcohol to avoid the formation of triphenylphosphine dichloromethylene ylide. In a representative example, 1-chloro-3,7-dimethylocta-2,6-diene (geranyl chloride, 30) is obtained by heating geraniol (29) in tetrachloromethane at reflux with triphenylphosphine (Scheme 25).[‌67‌] After distillation, the chloro compound is obtained in 7581% yield. This same variation can be used for the (stereoselective) preparation of enantiomerically pure pheromone precursors. Thus, all four enantiomers of 1-chloro-2,4-dimethyloctane and of 1-chloro-2,6-dimethyloctane can be obtained in very good yields from the corresponding (C2 inverted) alcohol precursors.[‌68‌,‌69‌] Similarly, racemic 1-chloro-2-methylheptane is obtained in >90% yield,[‌70‌] whereas 1-chloro-4-methyldodecane (31) is obtained from 4-methyldodecan-1-ol in 85% yield (Scheme 25).[‌71‌]

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8-Meeeee-8-eeeeeeeeeeeeee (88):[‌88‌]

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