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 abstraction and SET-promoted, silyl-transfer reactions of excited states of silylalkyl ketones and (silylalkyl)phthalimides. Photochemical investigations with the (silylalkyl)phthalimides have demonstrated that typical gamma-H atom abstraction reactions occur upon irradiation in less polar and less silophilic solvents. In contrast, irradiation of these substances in polar-protic-silophilic solvents results in product formation via pathways involving SET-induced desilylation. Photoreactions of silylamido-aryl ketones in either nonsilophilic or silophilic solvents take place almost exclusively by sequential SET silyl-transfer routes to produce azetidine products. Finally, the chemical selectivities of photochemical reactions of silylpropyl-aryl ketones appear to depend on medium polarity and silophilicity. Irradiation of these substrates in less polar-nonsilophilic solvents leads to almost exclusive formation of acetophenone and vinyltrimethylsilane in essentially equal yields by a reaction pathway initiated by gamma-H atom abstraction and 1,4-biradical fragmentation. However, irradiation of these substances in polar-silophilic solvents produces acetophenone and vinyltrimethylsilane in an ca. 1.7:1 ratio reflecting the fact that a silyl-transfer pathway competes with H-atom abstraction under these conditions.