Photooxygenation of α‐Ionone and Oxygen Transfer Reactions of the Resulting Allylic Hydroperoxides

The photooxygenation of α‐ionone ( 4 ) in different solvents leads, with higher than 90% regioselectivity, to a mixture of two diastereomeric allylic hydroperoxides 5a and 5b (diastereomeric ratio 77:23). These compounds are transformed in the presence of Ti(OiPr) 4 into the corresponding epoxy alcohols 8a and 8b ( cis selectivity) and the allylic alcohols 7a and 7b with high diastereoselectivity. In these cases the substrate configuration exhibits a pronounced control of type selectivity: the cis allylic hydroperoxide 5a is preferentially reduced to the allylic alcohol 7a , whereas the diastereomeric trans compound 5b is preferentially ( syn selectivity) converted to the epoxy alcohol 8b . Epoxidation of the allylic alcohol 7a with meta ‐chloroperbenzoic acid leads, in contrast to the Ti(IV)‐catalyzed reaction, to a mixture of diastereomeric epoxy alcohols 8a and 8c , with the anti product 8c as major diastereomer (diastereomeric ratio 28:72). These reactions serve as a route to three of the four possible diastereomeric epoxides of 3‐hydroxy‐γ‐ionone.