Enediynes in 11-membered rings. Synthesis, structure, and reactivity of highly strained but unusually stable macrocycles.
Enediynes in 11-membered rings. Synthesis, structure, and reactivity of highly strained but unusually stable macrocycles.
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11 元环烯二炔。
DOI：
10.1021/jo0106041
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
O. Wiest
中科院分区：
文献类型：
--
作者：
Holger Wandel;O. Wiest
报道了用双Wittig缩合、溴化和二脱氢溴化合成了两个新的芳香族环二炔1a和1b。用X-射线单晶衍射法测定了它们的结构。观察到的含氧和含硫十一元环中烯二炔部分的C(1)-C(6)距离很短，分别为3.44和3.50A，表明这些化合物具有高度应变的性质。在B3LYP/6-31G理论水平上的等温线计算表明，应变能分别为8.2和5.8千卡/摩尔。尽管存在高度紧张的环系，但化合物在热、光化学和电子转移条件下都是稳定的。通过BLYP/6-311+G/BLYP/6-31G计算，这种异常稳定性的起源可追溯到通过Bergman环化生成的1，4苯并二自由基的高能。对于自由基阳离子，先前报道的1的非环类似物的C(1)-C(6)和C(1)-C(5)环化模式都被发现是能量受阻的。
The synthesis of two new aromatic cyclic enediynes 1a and 1b using a double Wittig condensation, followed by bromination and di-dehydrobromination, is reported. The structures were determined using X-ray crystallography. The observed C(1)-C(6) distances of the enediyne moiety in the oxygen- and sulfur-containing eleven-membered rings are quite short with 3.44 and 3.50 A, respectively, indicating the highly strained nature of these compounds. Isodesmic calculations at the B3LYP/6-31G level of theory indicate a strain energy of 8.2 and 5.8 kcal/mol, respectively. Despite the highly strained ring system, the compounds were found to be stable under thermal, photochemical, and electron-transfer conditions. Using BLYP/6-311+G/BLYP/6-31G calculations, the origin of this unusual stability was traced to the high energy of the 1,4 benzyne diradicals formed via Bergman cyclization. For the radical cation, both the C(1)-C(6) and the C(1)-C(5) cyclization mode previously reported for acyclic analogues of 1 were found to be energetically prohibitive.