Helical-chiral analogues of imidazopyridine-2-yilidene were synthesized from 2-aza[6]helicene. The energies of their frontier orbitals were analyzed by the density functional theory calculations. The exceedingly large extension of NHC’s π system by helicene annelation significantly enhanced the π electron-accepting properties of the carbene center while the strong σ electron-donating properties of imidazopyridine-2-yilidenes were retained.

中文翻译：

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基于氮杂庚烯的亲电N-杂环卡宾的合成

由2-氮杂[6]螺旋烯合成咪唑并吡啶-2-乙叉基的螺旋手性类似物。通过密度泛函理论计算分析了其前沿轨道的能量。NHC的π螺旋扩展极大地增强了NHC的π系统，同时保留了咪唑并吡啶-2-亚基的强σ供电子特性，从而显着增强了卡宾中心的π电子接受性能。