Factors in the formation of isomerically and optically pure alkyl halides. Part XI. Vilsmeier reagents for the replacement of a hydroxy-group by chlorine or bromine

Vilsmeier reagents, [Me2NCHX]+X–(X = Cl or Br), interact with alcohols to give good yields of the corresponding alkyl halides. Isolation of the product is facilitated by the use of water-soluble solvents. Little or no rearrangement of the alkyl group occurs, except in the case of a branched-chain secondary alcohol, e.g. 3-methylbutan-2-ol. In dioxan or acetonitrile, (+)-octan-2-ol yields the optically pure chloride with inversion of configuration, although some racemisation occurs in dimethylformamide. 2-Bromo-octane is obtained with no detectable rearrangement and with an optical purity of ca. 75% by reaction in dioxan.