Photoreactions of (2-Acetoxyphenyl)pentamethyldisilane

Abstract

It is well known that the photoreactions of aryldisilanes show four reaction patterns 1 since the first report on the photolysis of phenylpentamethyldisilane and (p-tolyl)pentamethyldisilane by Ishikawa et al.2 in 1975 : (path a) formation of a silene compound via elimination of a trimethylsilane 3 , (path b) formation of a silene compound arising from 1,3-shift of trimethylsilyl radical, which is formed via homolytic cleavage of silicon-silicon bond [4][5][6][7][8][9] , (path c) formation of a trimethylsilyl compound via elimination of a silylene 10,11 , (path d) formation of a direct solvolysis compound via elimination of a trimethylalkoxysilane or pentamethylalkoxydisilane. 12,13Silenes having the C=Si moiety are regarded as highly interesting intermediates. Consequently the synthesis and reactions of silenes as useful intermediates have been extensively investigated.14,15 The intermolecular reactions between highly unstable silenes and the compounds containing functional groups such as OH [16][17][18][19][20][21][22] , C=O 23-26, and C=C 27-31 bonds resulted in the formation of the addition products.In connections with the photolysis of aryldisilanes, we recently disclosed the intramolecular reactions between the silene intermediates resulted from the photoreactions of ortho-substituted aryldisilanes and ortho-substituents to give the novel silicon-containing heterocyclic compounds such as the photoinduced intramolecular reactions of (2-substitutedphenyl)pentamethyldisilanes 32 , (2-alkoxymethylphenyl)pentamethyldisilanes 33 , 2-(pentamethyldisilanyloxy)phenylpentamethyldisilane 34 and (2-hydroxyethoxyphenyl)pentamethyldisilane. 35 We have also investigated the synthesis of siliconcontaining heterocyclic compounds through the intramolecular reactions of silacyclopropene or 1-silaallene moiety with ortho-substituents in ortho-substituted-phenylethynylpentamethyldisilanes 36. As a part of our continuous studies utilizing the silenes as reaction intermediates for the synthesis of silicon-containing heterocyclic compounds, we investigated the photoreactions of (2-acetoxyphenyl)pentamethyldisilane which has the acetoxy group as ortho substituent to phenylpentamethyldisilane because it was expected that the novel photoproducts could be formed from the intramolecular reaction of ortho-substituted acetoxy group with the silene intermediate. In this note, we would like to report the detailed photochemical study of (2-acetoxyphenyl)pentamethyldisilane.The starting (2-acetoxyphenyl)pentamethyldisilane 2 was prepared from the reaction of (2-hydroxyphenyl)pentamethyldisilane 1 35 with acetyl chloride using triethylamine as base in tetrahydrofuran at room temperature (Scheme 1).In order to investigate a possibility that the C=O bond as ortho substituent in 2 reacts intramolecularly with a silene, the photolysis of 2 was performed.Irradiation of 2 in deaerated benzene with 254nm UV light afforded two photo-Fries rearrangement products 4 (18% yield) and 5 (10% yield) along with some decomposition products of unknown structu...

Aryl–Cl vs heteroatom–Si bond cleavage on the route to the photochemical generation of σ,π-heterodiradicals

“…The photochemistry of compound 6 can be in part explained by the typical behavior of disubstituted phenyl pentamethyldisilane upon excitation in polar solvents. In fact, when the aromatic ring of the disilane is substituted with a more photolabile moiety, as the OCOMe group in (2-acetoxyphenyl)pentamethyldisilane, the disilane structure remains untouched after the reaction [88]. However, other substituted phenyldisilanes showed a varied photoreactivity including the formation of a silylene intermediate or the nucleophilic attack of a protic solvent (e.g., an alcohol) at the β-silicon atom or the photohomolytic cleavage of the Si-Si bond [89][90][91][92][93].…”