A Novel Photoreaction of (2-Hydroxypropoxyphenyl)pentamethyldisilane

Abstract

Since the first reports on the photoreactions of 1-phenyl-2-(pentamethyldisilanyl)ethyne 1 and phenylpentamethyldisilane 2 by Ishikawa et al., the intermolecular photolysis of these compounds and their derivatives has been extensively investigated. It is well known that the photolysis of 1-phenyl-2-(pentamethyldisilanyl)ethyne afforded silacyclopropene 3-10 and 1-sila-1,2-propadiene 11-13 intermediate and the photoreaction of phenylpentamethyldisilane gave silatriene 14-20 intermediate. However, relatively little is known about the intramolecular photoreactions of ortho-substituted 1-phenyl-2-(pentamethyldisilanyl)ethynes and ortho-substituted phenylpentamethyldisilanes.Recently, we have found that the photolysis of orthosubstituted 1-phenyl-2-(pentamethyldisilanyl)ethynes 21 and ortho-substituted phenylpenta methyldisilanes 22,23 afforded the novel intramolecular photoproducts via silacyclopropene, 1-sila-1,2-propadiene, and silatriene intermediates.Very recently, we have found that the photoreaction of (2-hydroxymethylphenyl)pentamethyldisilane 24 and (2-hydroxyethoxyphenyl)pentamethyldisilane 25 afforded the novel intramolecular photoproducts via silatriene intermediates.In connection with our ongoing studies for the utility of silacyclopropenes, 1-sila-1,2-propadiene, and silatriene as reaction intermediates in organic synthesis of silicon-containing heterocyclic compounds, we were now interested in the synthesis of silicon-containing large ring compounds via the photolysis of ortho-substituted phenylpentamethyldisilanes. And, we have investigated the photoreactions of (2-hydroxypropoxyphenyl)pentamethyldisilane 2, since novel photoproducts from the intramolecular reaction of orthosubstituted group with the silatriene intermediate are expected and we would like to report the detailed photochemical study of 2.The starting material 2 was prepared by the reaction of (2-hydroxyphenyl)pentamethyldisilane 25 (1) with 3-chloro-1-propanol in the presence of sodium hydroxide and tetra-nbutyl ammonium iodide using microwave reactor, Micro-SYNTH in water as a solvent as shown in Scheme 1.To investigate whether or not the hydroxypropoxy group as ortho-substituent in 2 reacts intramolecularly with silatriene moiety in the reaction intermediate 3 formed in the photoexcited state of 2, the photoreaction of 2 in benzene was studied.Photolysis of 2 in deaerated benzene with 254 nm UV light gave a novel photoproduct 6 (32% yield) along with some decomposition products of unknown structure as shown in Scheme 2, when 95% of 2 was photolyzed but the expected intramolecular photoproduct was not obtained. The formation of a novel photoproduct 6 can best be explained in terms of the initial formation of silatriene intermediate 3 arising from1,3-migration of trimethylsilyl radical, which is formed via the homolytic cleavage of silicon-silicon bond of pentamethyldisilanyl group in the photoexcited state of 2 to the C6 position of benzene ring as shown in Scheme 2. The intramolecular reaction to form a oxirane ring in this silatriene ...

A Novel Photoreaction of (2‐Propargyloxyphenyl)pentamethyldisilane

“…The other study afforded the compound 5 from a C–H bond activation‐based borylation and then C–C bond formation by using Pd(OAc) 2 and 1,1′‐bis(diphenylphosphino)‐ferrocene. The spectroscopic data ( 1 H and 13 C NMR) of the compound 5 obtained from the photoreaction of 2 in benzene were exactly the same with them obtained from the earlier studies by our study and Olsson et al .’s study . The formation of a compound 6 having allenyloxy group was explained by the hydride shift at the photoexcited state of a compound 2 as shown in Scheme .…”

“…Finally, the rearrangement of the oxirane intermediate 13 to the more stable compound gave a novel conjugated photoproduct 5 as shown in Scheme . Indeed, there are already three papers which were published concerning the formation of (3E, 5E)‐6‐(1,1,1‐trimethylsilyl)‐3,5‐hexadien‐2‐one 5 . In two cases by our photolysis research, starting materials for the photoreactions were different but it is thought that the same photoproduct was formed via the same reaction intermediate 13 .…”

“…Indeed, there are already three papers which were published concerning the formation of (3E, 5E)‐6‐(1,1,1‐trimethylsilyl)‐3,5‐hexadien‐2‐one 5 . In two cases by our photolysis research, starting materials for the photoreactions were different but it is thought that the same photoproduct was formed via the same reaction intermediate 13 . The other study afforded the compound 5 from a C–H bond activation‐based borylation and then C–C bond formation by using Pd(OAc) 2 and 1,1′‐bis(diphenylphosphino)‐ferrocene.…”

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

“…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]. In the latter examples, the fate of the reaction depends on the structure of the disilane in combination with the media used albeit the Si-Si bond was always photocleaved.…”