A New Entry into Cyclo[n]carbons: [2 + 2] Cycloreversion of Propellane-Annelated Dehydroannulenes
A New Entry into Cyclo[n]carbons: [2 + 2] Cycloreversion of Propellane-Annelated Dehydroannulenes
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环[n]碳的新进入：[2 2]丙烷环合脱氢轮烯的环化
DOI：
10.1021/ja952801l
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发表时间：
1996
影响因子：
15
通讯作者：
Tomonari Wakabayashi
中科院分区：
文献类型：
--
作者：
Y. Tobe;T. Fujii;H. Matsumoto;K. Naemura;Y. Achiba;Tomonari Wakabayashi
人们对环碳的兴趣与日俱增，这是碳团簇中最稳定的形式，在C10到C20的相对较窄的尺寸范围内。1对富勒烯形成的机理研究表明，单环物种在碳笼的形成中起着关键作用。2p轨道的新拓扑，由两组垂直的p轨道的循环阵列组成，激发了许多关于Hückel规则的理论研究。3例如，关于C18最稳定的几何构型，无论是D9h或C9h对称性的聚炔，还是D9h或D18h对称性的异丙苯，都存在争议。3B-f作为一种从具有明确环结构的有机前体合成环[n]-碳的方法，Diederich合成了三种类型的脱氢环烯，它们可以通过[4+2]环逆转、氧化分解或脱羰基生成相应的全碳分子。3B，4通过激光解吸飞行时间(LD-TOF)质谱学观察到其中一些前驱体形成了环-C18、环-C24和环-C30，它们产生了富勒烯阳离子(C60+和C70+)，表明单环物种与富勒烯的形成机理有关。然而，尚未实现对任何环碳分子结构的光谱测定。在这一点上，我们设计了十二氢[18]轮烯1和十六氢[24]轮烯2。2]螺三烯单元分别作为环[18]碳和环[24]碳的新的可行前体。基于我们以前对二乙炔取代的光解反应的研究结果[4.3。2]螺三烯、61和2应通过消除吲哚分子进行光化学[2+2]环还原反应，生成相应的环碳化合物。此外，螺旋桨单元的加入将极大地稳定固有的不稳定(爆炸性)脱氢轮烯核心。7在此COM中-
Increasing interest has been focused on cyclocarbons, the most stable form of carbon clusters in the relatively narrow size range from C10 through C20. 1 Mechanistic studies on the formation of fullerenes suggest that the monocyclic species play a key role in the formation of carbon cages. 2 The novel topology of the p orbitals, composed of two sets of cyclic arrays of perpendicular p orbitals, stimulated a number of theoretical studies concerned with the Hückel rule. 3 For example, there are controversies regarding the most stable geometry of C18, whether it is a polyyne of D9h or C9h symmetry or a cumulene of D9h or D18h symmetry. 3b-f As an approach to the synthesis of cyclo [n]-carbons from organic precursors of well-defined cyclic structure, Diederich synthesized three types of dehydroannulenes which would generate the corresponding all-carbon molecules by [4+ 2] cycloreversion, oxidative decomplexation, or decarbonylation. 3b, 4 The formation of cyclo-C18, cyclo-C24, and cyclo-C30 was indeed observed by the laser-desorption time of flight (LD-TOF) mass spectra of some of these precursors, which generated fullerene cations (C60+ and C70+), indicating the relevance of monocyclic species to the mechanism of fullerene formation. 5 However, spectroscopic determination of the molecular structure of any cyclocarbon has not yet been achieved. In this connection, we designed dodecadehydro [18] annulene 1 and hexadecadehydro [24] annulene 2 annelated by [4.3. 2] propellatriene units as new viable precursors of cyclo [18] carbon and cyclo [24] carbon, respectively. On the basis of our previous results on the photolysis of diethynyl-substituted [4.3. 2] propellatrienes, 6 1 and 2 should undergo photochemical [2+ 2] cycloreversion by elimination of indan molecules to produce the corresponding cyclocarbons. Moreover, the incorporation of the propellane units would considerably stabilize the inherently unstable (explosive) dehydroannulene core. 7 In this com-