Reactions of Stable N-Heterocyclic Silylenes with Ketones and 3,5-Di-tert-butyl-o-benzoquinone

Silylenes are silicon analogues of carbenes and exist with neutral divalent silicon atoms. The first stable N-heterocyclic silylene (NHSi) was reported byWest et al., in 1994. Since then, many stable NHSis d,3 and other silylenes have been isolated. The reactivity pattern of NHSis is quite comparable with that of the N-heterocyclic carbenes (NHCs), where the latter led to many applications in chemistry. Silylenes have two nonbonding electrons in the HOMO which possess nucleophilic character, and an empty 3p-orbital as the LUMO which causes electrophilic properties. They possess both nucleophilic and electrophilic reactive sites at the same silicon atom, therefore they are ambiphilic and behave as Lewis acids as well as Lewis bases. Owing to this, there is an extensive research activity going on in the chemistry of NHSis, which is very challenging (insertion: C H, N H, O H, S H, P P, N Si, C F, C X (Cl, Br, I), Si Cl, P H, As H, addition, metal complexes, Lewis acids). In addition, the reactions of silylenes with organic substrates lead to a number of interesting new organosilicon compounds, which are otherwise difficult to achieve. Recently, we became interested in the reactivity studies of silylenes L [PhC(NtBu)2SiCl] and L0 [CH{(CdCH2)(CMe)(2,6-iPr2C6H3N)2}Si] toward organic substrates. 3b,9b 9d,13,19 Inspired by the diverse reactivity shown by silylenes with ketones, we report herein the reactions of silylenes L and L0 with 2-adamantanone, 3,5-di-tert-butyl-o-benzoquinone, and acylferrocene. The reaction of L with 2-adamantanone favors a [1 + 2] cycloaddition product 1, whereas with 3,5-di-tert-butyl-o-benzoquinone leads to [1 + 4] cycloaddition product 2. Treatment of L0 with 3,5-di-tertbutyl-o-benzoquinone affords the [1 + 4] cycloaddition product 3, and the reaction with acylferrocene gives compound 4.