Side Reactions in Which Several of the Above Principles Operate

Side Reactions in Which Several of the Above Principles Operate 

Sometimes, the action of PCC on alcohols leads to products that can be explained by complex mechanism, in which several of the reactivity principles mentioned above act in a sequential manner.334 

This mechanistically fascinating product can be explained by the initial formation of a cyclic chromate ester, facilitated by the formation of a five-membered ling and the (cis) relationship in the 1,2-diol. Interestingly, this stable chromate does not evolve resulting in the oxidation of the secondary alcohol, but it suffers elimination producing a very electron-rich benzyloxy alkene that is easily epoxidized intramolecularly by chromium. Observe that the epoxide oxygen enters from the same face than the secondary alcohol. 

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