Department of Chemistry, Graduate School of Science and Integrated Research Consortium on Chemical Sciences (IRCCS), Nagoya University, Furo, Chikusa, Nagoya, 464-8602, Japan.
Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo, Chikusa, Nagoya, 464-8602, Japan.
Angew Chem Int Ed Engl. 2017 Mar 13;56(12):3270-3274. doi: 10.1002/anie.201611344. Epub 2017 Jan 9.
Pentalenes represent highly reactive Hückel antiaromatics with 8π electrons. Usually, pentalenes are stabilized by incorporation of two benzene rings in a fused fashion. In dibenzo[a,e]pentalenes, however, the high aromaticity of the fused benzene rings compromises the inherent antiaromaticity of the pentalene core. Herein, we disclose that this forfeited antiaromaticity can be restored by fusing four additional aromatic rings onto the peripheral positions of dibenzo[a,e]pentalenes. Such polycyclic pentalenes were prepared by successive transannular cyclizations via in situ-generated tetrakisdehydro[16]annulenes. The thus obtained compounds showed intriguing properties, for example, characteristic absorptions in the visible-to-near-infrared (NIR) region and low reduction potentials. These results hence afford a design principle to produce highly antiaromatic yet stable pentalenes. The antiaromaticity of the pentalene core can be widely tuned via the degree of aromaticity of the peripherally fused rings.
戊搭烯是一类具有 8π 电子的高度反应性的休克尔反芳香体系。通常，戊搭烯通过以稠合方式并入两个苯环来稳定。然而，在二苯并[a,e]戊搭烯中，稠合苯环的高芳香性会损害戊搭烯核心的固有反芳香性。在此，我们揭示了通过将四个额外的芳环融合到二苯并[a,e]戊搭烯的外围位置，可以恢复这种丧失的反芳香性。这些多环戊搭烯是通过在原位生成的四脱氢[16]轮烯的连续跨环环化反应制备的。所得到的化合物表现出有趣的性质，例如在可见光到近红外（NIR）区域的特征吸收和低还原电位。这些结果为制备高反芳香性但稳定的戊搭烯提供了一个设计原则。通过外围稠合环的芳香度，可以广泛调节戊搭烯核心的反芳香性。
