Allyl alcohols oxidative rearrangement with pyridinium

The allyl alcohol in the seven-membered ring is oxidized to the corresponding a,P-unsaturated ketone as expected, whereas the allyl alcohol in the five-membered ring is oxidized to afford the transposed a,P-unsaturated ketone after [3,3]-sigmatropic rearrangement. This behavior is only observed with cyclic, tertiary allyl alcohols upon treatment with one equivalent of pyridinium chlorochromate. The desired oxidation product 34 is obtained in 90 % over two steps. [Pg.108]

A useful application of chromium-based oxidants, especially pyridinium chlorochromate, is in the conversion of allylic tertiary alcohols to their transposed a,(3-unsaturated ketones. For example, treatment of the allylic alcohol 24 with PCC gave the a,p-unsaturated ketone 25 (6.23). The reaction is thought to proceed by rearrangement of the chromate ester of the allylic alcohol to give a new allyl chromate ester that is oxidized to the ketone. [Pg.381]