Substituent effects in [2.sigma. + 2.sigma. + 2.sigma.] thermal decarbonylation of cage ketones. Remarkably effective elongation of strained carbon-carbon bond by through-bond coupling
Substituent effects in [2.sigma. + 2.sigma. + 2.sigma.] thermal decarbonylation of cage ketones. Remarkably effective elongation of strained carbon-carbon bond by through-bond coupling
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[2.sigma 中的取代基效应。
DOI：
10.1021/ja00399a029
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发表时间：
1981
影响因子：
15
通讯作者：
K. Kanematsu
中科院分区：
文献类型：
--
作者：
K. Harano;T. Ban;M. Yasuda;E. Ōsawa;K. Kanematsu
7V-乙氧羰基氮杂卓与取代环庚烯酮的[4+ 2]环加成反应高产率地合成了应变五环酮（5a-d）。通过X-射线分析证实笼酮之一（5d）的结构为1，2-二苯基-5，7-双（甲氧羰基）-11-（乙氧羰基）-11-氮杂五环[5.5. 0.02 '5.03，12.04' 8]-十二碳-9-烯-6-酮。该分子的（Pty-C（Ph））键非常长（1.657（5）π）。无论是机械应变，也不是传统的通过键的相互作用的苯基系统是令人满意的解释这种伸长率。我们认为，最初由5的变形碳骨架引起的预应变Q-C2键的高能级和低 * 能级导致了与苯基轨道的有效混合。结合分子力学和MNDO计算模型结构，包括1，4-二苯基双环[2.2]。0]己烷。在观察到的5d的结构中也不寻常的是与酮基相邻的甲氧羰基的构象，其中三个羰基偶极子以几乎顺式平行的方式排列。化合物5a-d在180 ℃下迅速脱羰基，以定量产率得到三环三烯6a-d。5的热不稳定的长C [-C2]键被认为在开环中起关键作用。通过将与5a的羰基相邻的甲基改变为烷氧基羰基（5d，e），脱羰基速率增加100倍。这一速率的提高解释前线轨道和立体理论。
Strained pentacyclicketones (5a-d) were prepared in high yields by photoinduced [4+ 2] cycloadduct of7V-(ethoxycarbonyl) azepine with substitutedcyclopentadienones. The structure of one of the cage ketones (5d) was confirmed by X-ray analysis to be l, 2-diphenyl-5, 7-bis (methoxycarbonyl)-ll-(ethoxycarbonyl)-ll-azapentacyclo [5.5. 0.02'5.03, 12.04'8]-dodeca-9-en-6-one. The QfPty-C^ Ph) bond of this molecule is extraordinarily long (1.657 (5) Á). Neither mechanical strain nor conventional through-bond interaction of phenyl systems was satisfactory to interpret this elongation. We propose that the heightened level and lower* level of the prestrained Q-C2 bond, originally caused by thedeformed carbon skeleton of 5, leadto efficient mixing with the phenyl orbitals. The enhanced “through-bond” interactions involving strained bond were demonstrated with combined molecular mechanics and MNDO calculations of model structures including 1, 4-diphenylbicyclo [2.2. 0] hexane. Also unusual in the observed structure of 5d is the conformation of methoxycarbonyl groups adjacent to keto group, wherein three carbonyl dipoles align in nearly syn-parallel fashion. Compounds 5a-d decarbonylate rapidly at 180 C to give tricyclic trienes 6a-d in quantitative yields. The thermally labile, long C [-C2 bond of 5 is suggested to play a key role in the ring opening. Decarbonylation rate increased 100-fold by changing the methyl group adjacent to carbonyl of 5a to alkoxycarbonyls (5d, e). This rate enhancement was explained in terms of frontier orbital and steric theories.