Wu Hai-Shun, Jiao Haijun, Wang Zhi-Xiang, Schleyer Paul v R
Department of Chemistry, Shanxi Normal University, Linfen 041004, China.
J Am Chem Soc. 2003 Sep 3;125(35):10524-5. doi: 10.1021/ja036403r.
Isolobal substitution of CH units by boron carbonyl groups (BCO) at C2,6 and C2,8,4,6 in semibullvalene favors the delocalized neutral bishomoaromatic systems substantially. The homoaromaticity is documented by the computed diatropic nucleus independent chemical shifts (NICS). In addition, BCO substitution can result in low-lying triplet and open-shell singlet states. In contrast, substitution at C1,5 more than doubles the related Cope rearrangement barrier. The C2,6 and C2,8,4,6 BCO-substituted barbaralanes, barbaralones, and bullvalenes have substantially reduced barriers.
在半富烯的C2,6和C2,8,4,6位置用硼羰基（BCO）对CH单元进行等瓣取代，极大地有利于离域的中性双高芳香体系。同芳香性通过计算得到的抗磁核独立化学位移（NICS）得以证明。此外，BCO取代可导致低能三重态和开壳单重态。相比之下，在C1,5位置进行取代会使相关的Cope重排势垒增加一倍多。C2,6和C2,8,4,6位被BCO取代的双环[3.3.0]辛烷、双环[3.3.0]辛烯和富烯的势垒大幅降低。
