PHOTOCHEMICAL REACTIONS .53. PHOTOCHEMICAL ADDITION OF ALKYL AROMATICS TO ARYL CARBONYL COMPOUNDS

In the preceding paper [1] a novel primary photochemical process of triplet excited α,β‐conjugated cycloalkenones in toluene solution has been reported: the abstraction of a benzylic hydrogen from the solvent by the β‐carbon (cf. 1 → 2 + 3 + 4). The reaction has been attributed to the π,π* triplet. Aromatic aldehydes and ketones (5–11a), the triplet state reactivity of which is known to be mostly π,π* in nature, have now been examined under the same irradiation conditions. However, a reaction similar to that of cycloalkenones — expected to result in the addition of hydrogen to the ortho and para positions of the aryl moiety and the formation of benzylcyclohexa‐1,3‐and 1,4‐diene derivatives — could not been found. Compounds 5–10 remained essentially unchanged. 4‐Methoxyacetophenone (11a) reacted slowly to form the same type of products [tert‐carbinol 12a, pinacol 13a and dibenzyl (4)] as the aromatic carbonyl compounds 11b‐d, benzophenone and cyclopropylphenylketone, which exhibit typical n,π* triplet reactivity (hydrogen abstraction by the carbonyl oxygen). Copyright © 1969 Verlag GmbH & Co. KGaA, Weinheim