Alkenes reaction with hypohalous acids

The critical intermediate (64) for this route (Scheme 65) can be reached in several ways. The commonest is by the reaction of an alkene with hypohalous acid (Scheme 66) which proceeds with overall retention. 

Yet another example of an electrophilic addition is the reaction of alkenes with the hypohalous acids HO—Cl or HO-Br to yield 1,2-halo alcohols, called halohydrins. Halohydrin formation doesn t take place by direct reaction of an alkene with HOBr or HOC1, however. Rather, the addition is done indirectly by reaction of the alkene with either Br2 or Cl2 in the presence of water. 

This section will begin with a simple method for producing epoxides that uses the reaction of alkenes and hypohalous acids (generated by the reactions CI2 + H2O HOCl or Br2 + H2O HOBr) to give the trans-(or anti-) halohydrin as the major product. An example is the conversion of cyclohexene to bromohydrin 149 (sec. 2.10.C). Subsequent treatment with a base such as sodium hydride generates the alkoxide (150), which is anti- to the adjacent bromine, which anti- orientation leads to displacement of halide... 

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