Photoinduced Hydrogen Atom Abstraction by Carbonyl Compounds

Hydrogen atom abstraction by photoexcited carbonyl compounds has played a central role in the development of a general picture of how photochemical reactions occur. Environmental effects on hydrogen transfer have been used to determine information about the structures of organized media. Synthetic organic chemists have begun to utilize photorearrangements initiated by hydrogen transfers. With the current intense interest in synthetic applications of intramolecular radical reactions, it is almost a certainty that initiation by hdyrogen abstraction will be used more routinely for natural products synthesis. Y. Kanaoka first discovered that N-alkylimides undergo photoinduced intramolecular hydrogen abstractions when he observed the photo-cyclization of N-(o-tolyl)phthalimide. The initial hydrogen abstraction reaction is known to be a rare example of rotational control of triplet reactivity. In o-alkylphenyl alkyl ketones, some reaction may occur from n, π* singlets; in o-alkylbenzophenones, the reaction occurs only from triplets.