Transformation of Alcohols into Chlorides

Activated alcohols are unstable, at least at high temperature, when the corresponding radicals are able to stabilize carbocations, for example in the case of allylic alcohols. The thermal decomposition of activated allylic alcohols leads to the formation of allylic chlorides. This decomposition can 

Sometimes, the transformation of allylic alcohols into chlorides, by the action of activated DMSO, is so quick that it competes with a normal oxidation.234 

No oxidation of the allylic alcohol occurs, because the intermediate activated alcohols evolve very quickly to the corresponding allylic chlorides. 

Nonetheless, very often activated allylic alcohols are persistent enough at low temperature, so as to allow a normal Swern oxidation with an added base.235 

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In fact, Corey-Kim conditions offer a good method for the regioselec-tive transformation of allylic and benzylic alcohols into chlorides, in the presence of other alcohols.252 The use of A-bromosuccinimide in spite of /V-chIorosuccini mide, quite expectedly, allows the preparation of allylic and benzylic bromides. It must be mentioned that when the transformation of alcohols into chlorides is desired, the activated alcohol is allowed to decompose in the absence of triethylamine whereas, when an oxidation is desired, triethylamine must be added as soon as the alcohol is activated. That is why, some benzylic alcohols can be efficiently oxidized under Corey Kim conditions,253 while others can be transformed into benzylic bromides with NBS and Me2S.252... 

The above transformation of alcohols into chlorides does not occur for simple alcohols unless a catalytic amount of DMSO is added. Thus, addition of the catalyst into a mixture of 1-propanol and TMSCl (2 equiv) at rt provides 1-chloropropane in 93% yield in only 10 min (eq 54). The reaction also works for other primary and tertiary alcohols, but not for secondary alcohols. The reaction of secondary alcohols with TMSCl and a stoichiometric amount of DMSO follows a procedure similar to that of the Swem oxidation and the corresponding ketones are produced. ... 

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