The stable exocyclic silenolates 2a–c (2a, R = Mes; 2b, R = o-Tol; 2c, R = 1-Ad) were fully characterized by NMR and UV–vis spectroscopy. According to spectroscopic and structural features, 2a–c are best described as acyl silyl anions (tautomeric structure I) in solution. This behavior is also reflected by the reaction of 2a,c with MeI. Both alkylation reactions take place at the corresponding silicon atom and lead to the formation of the methylated structures 4a,b in nearly quantitative yields. Furthermore, the thermal stability of exocyclic silenolates 2a,c was investigated. In the case of 2a, a thermally induced intramolecular sila-Peterson alkenation was observed at 60 °C. This transformation allowed straightforward access to 2-oxahexasilabicyclo[3.2.1]octan-8-ide 5 as a structurally complex, bicyclic silicon framework. In contrast to that, heating of 2c, as an example of an alkyl-substituted silenolate, led to an unexpected degradation to uncharacterized polymers. However, we were able to isolate the 1-adamantyl-substituted, bicyclic compound 8, which is structurally closely related to 5, by the treatment of 1,4-dipotassium-1,4-bis(trimethylsilyl)cyclohexasilane with 1 equiv of 1-adamantoyl chloride. Again an intramolecular sila-Peterson alkenation is responsible for the formation of 8. The mechanism for this highly selective reaction sequence is outlined and supported by density functional theory (DFT) calculations, which highlight the thermodynamic driving force and the low activation barriers of this multistep transformation.

中文翻译：

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再谈环状硅酸盐的反应性

稳定的环外硅酸盐2a – c（2a，R = Mes; 2b，R = o- Tol; 2c，R = 1-Ad）已通过NMR和UV-vis光谱进行了全面表征。根据光谱和结构特征，2a - c最好描述为溶液中的酰基甲硅烷基阴离子（互变异构结构I）。2a，c与MeI的反应也反映了这种行为。两种烷基化反应均发生在相应的硅原子处，并导致形成甲基化结构4a，b以几乎定量的产量。此外，研究了环外硅酸盐2a，c的热稳定性。在2a的情况下，在60°C时观察到热诱导的分子内sila-Peterson烯化。这种转变允许直接进入2-氧杂六硅双环[3.2.1] octan-8-ide 5，作为结构复杂的双环硅骨架。与此相反，加热2c（作为烷基取代的硅烷基化物的一个例子）导致意外降解为未表征的聚合物。但是，我们能够分离出1-金刚烷基取代的双环化合物8，该化合物在结构上与5密切相关通过用1当量的1-金刚烷酰氯处理1,4-二钾-1,4-双（三甲基甲硅烷基）环己硅烷。再次，分子内sila-Peterson链负责8的形成。密度泛函理论（DFT）计算概述并支持了这种高度选择性的反应序列的机理，该机理突出了​​这种多步转化的热力学驱动力和低活化势垒。