1,2-disilacyclobut-2-enes: Donor-free four-membered cyclic silenes from reaction of disilenides with vinylbromides
1,2-disilacyclobut-2-enes: Donor-free four-membered cyclic silenes from reaction of disilenides with vinylbromides
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DOI：
10.1002/chem.200800919
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发表时间：
2008-01-01
影响因子：
4.3
通讯作者：
Scheschkewitz, David
中科院分区：
文献类型：
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作者：
Bejan, Iulia;Inoue, Shigeyoshi;Scheschkewitz, David
1981年，Brook等人报道了第一个稳定的硅烯1，[1]，即具有SiO2 C双键的化合物，改变了硅作为较重的主族元素不会参与多重键的范式。[2]1的出乎意料的长Si= C键归因于释放电子的甲硅烷氧基的影响（方案1）。随后合成的Si-C距离明显较短的无供体2 [3]进一步支持了SiO2 C π键的电子和拓扑特征对取代基性质的强烈依赖性，这后来被置于坚实的理论基础上。[2c正如Ottosson和Steel最近指出的，[2a]迄今为止报道的许多稳定和瞬态的硅烯的通用反应性的应用仍然受到限制，这是由于它们产生的特殊（有时是强制）条件：高温或辐照，[1，5]使用强碱，[3，6]或形成亲核的次级产物。[7]我们最近报道了通过在非常温和的条件下与羧酸氯化物反应，将乙烯基阴离子的二硅类似物二硅烯3a，B [8]定量转化为具有内环氧原子的环状硅烯4a-c（方案1）。[9]基于DFT计算，我们证明了双键的硅原子的前所未有的显著的非线性化不完全是由于在双键的碳原子旁边存在释放电子的氧原子，而且还由于Si= C部分并入四元环。然而，早期的理论计算预测了相关的1，4-二氢-1，2-二硅酸酯的平面拓扑结构，其中4的氢取代母体的内环氧原子形式上被CH 2部分取代。[10]这些1，2-二硅杂环丁烯是特别令人感兴趣的合成目标，因为它们的饱和同类物，即1，2-和1，3-二硅杂环丁烷，在光解或热条件下断裂成瞬时的硅烯，因此对于SiO2 C双键化学的整体发展是关键的。[11]最近通过二硅烯3a与弱亲电芳基碘的反应成功地将Si= Si部分转移到芳族底物[12]，这鼓励我们研究3a，B对溴乙烯的反应性。我们推测，中间形成的乙烯基取代的二硅烯可能不稳定，因此重排为所需的环状衍生物。
In 1981 the report by Brook et al. on the first stable silene 1,[1] that is, a compound with a SiÀC double bond, contributed to the change of the paradigm that silicon as a heavier main group element would not engage in multiple bonding.[2] The unexpectedly long Si= C bond of 1 was attributed to the influence of the electron-releasing siloxy group (Scheme 1). The subsequent synthesis of donor-free 2 with a considerably shorter Si–C distance [3] further supported a strong dependency of the electronic and topological character of the SiÀC π bond on the nature of the substituents, which was later put on a firm theoretical basis.[2c, 4] As Ottosson and Steel pointed out recently,[2a] the application of the resulting versatile reactivity of the numerous stable and transient silenes reported to date is still limited due to the particular (sometimes forcing) conditions for their generation: high temperatures or irradiation,[1, 5] use of strong bases,[3, 6] or formation of nucleophilic secondary products.[7] We recently reported the quantitative conversion of disilenides 3a, b, disila analogues of vinyl anions,[8] into cyclic silenes 4a–c featuring an endocyclic oxygen atom by reaction with carboxylic acid chlorides under very mild conditions (Scheme 1).[9] On grounds of DFT calculations we demonstrated that the unprecedented significant pyramidalisation of the silicon atom of the double bond was not entirely due to the presence of the electron-releasing oxygen atom next to the carbon atom of the double bond, but also to the incorporation of the Si= C moiety into a four-membered ring. Early theoretical calculations, however, predicted a planar topology in case of the related 1, 4-dihydro-1, 2-disiletes, in which the endocyclic oxygen atom of the hydrogen substituted parent of 4 is formally replaced by a CH2 moiety.[10] These 1, 2-disilacyclobutenes are particularly interesting synthetic targets in view of the rich cycloreversion chemistry of their saturated congeners, that is, 1, 2-and 1, 3-disilacyclobutanes, which under photolytic or thermal conditions fragment into transient silenes and were therefore pivotal for the development of SiÀC double bond chemistry as a whole.[11]The recent successful transfer of Si= Si moieties to aromatic substrates by reaction of disilenide 3a with the weakly electrophilic aryl iodides [12] encouraged us to investigate the reactivity of 3a, b towards vinyl bromides. We speculated that intermediately formed vinyl substituted disilenes would likely not be stable and therefore rearrange to the desired cyclic derivatives.