EXPLORATORY STUDIES OF H-ATOM ABSTRACTION AND SILYL-TRANSFER PHOTOREACTIONS OF SILYLALKYL KETONES AND (SILYLALKYL)PHTHALIMIDES

Exploratory studies have been conducted to probe competitive H-atom ab straction and SET-promoted, silyl-transfer reactions of excited states of silylalkyl ketones and (silylalkyl)phthalimides. Photochemical inv estigations with the (silylalkyl)phthalimides have demonstrated that t ypical gamma-H atom abstraction reactions occur upon irradiation in le ss polar and less silophilic solvents. In contrast, irradiation of the se substances in polar-protic-silophilic solvents results in product f ormation via pathways involving SET-induced desilylation. Photoreactio ns of silylamido-aryl ketones in either nonsilophilic or silophilic so lvents take place almost exclusively by sequential SET silyl-transfer routes to produce azetidine products. Finally, the chemical selectivit ies of photochemical reactions of silylpropyl-aryl ketones appear to d epend on medium polarity and silophilicity. Irradiation of these subst rates in less polar-nonsilophilic solvents leads to almost exclusive f ormation of acetophenone and vinyltrimethylsilane in essentially equal yields by a reaction pathway initiated by gamma-H atom abstraction an d 1,4-biradical fragmentation. However, irradiation of these substance s in polar-silophilic solvents produces acetophenone and vinyltrimethy lsilane in an ca. 1.7:1 ratio reflecting the fact that a silyl-transfe r pathway competes with H-atom abstraction under these conditions.