Department of Chemistry, Graduate School of Science and ‡Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University , Furo, Chikusa, Nagoya 464-8602, Japan.
J Am Chem Soc. 2014 Jun 18;136(24):8738-45. doi: 10.1021/ja503499n. Epub 2014 Jun 6.
The transannular cyclization of dehydroannulenes bearing several alkyne moieties in close proximity is a powerful synthetic method for producing polycyclic aromatic hydrocarbons. We report that the reactivity can be switched by the aromaticity of the ring skeletons fused with the dehydroannulene core. Thus, while thiophene-fused bisdehydro[12]annulene 1 was handled as a stable compound in the air at room temperature, the oxidation with m-chloroperbenzoic acid from the aromatic thiophene rings to the nonaromatic thiophene-S,S-dioxides induced the transannular cyclization, even at room temperature, which was completed within 1 day to produce the formal [2 + 2] cycloadduct 3. This is in stark contrast to the fact that the thermal cyclization of 1 itself required heating at 80 °C for 9 days for completion. Experimental and theoretical studies indicate that the oxidation of even one thiophene ring in 1 sufficiently decreases the activation barrier for the transannular cyclization that proceeds through the 8π and 4π electrocyclic reaction sequence. The thiophene-S,S-dioxide-fused biphenylene 3 thus produced exhibits a set of intriguing properties, such as a higher electron affinity (E1/2 = -1.17 V vs Fc and Fc(+)) and a stronger fluorescence (ΦF = 0.20) than the other relevant biphenylene derivatives, which have electron-donating and nonfluorescent characteristics.
具有多个炔基部分的去氢并环芳烃的跨环环化是一种合成多环芳烃的有效方法。我们报道了通过与去氢并环芳烃核心融合的环骨架的芳香性可以切换反应性。因此，尽管噻吩并双去氢[12]并环烯 1 在室温下的空气中作为稳定化合物处理，但用间氯过苯甲酸从芳香噻吩环氧化到非芳香噻吩-S，S-二氧化物诱导了跨环环化，即使在室温下，也在 1 天内完成，生成了形式上的[2 + 2]环加成产物 3。这与 1 本身的热环化需要在 80°C 加热 9 天才能完成的事实形成鲜明对比。实验和理论研究表明，1 中即使一个噻吩环的氧化也足以降低通过 8π和 4π 电环反应序列进行的跨环环化的活化能垒。因此，生成的噻吩-S，S-二氧杂并联苯 3 表现出一系列有趣的性质，例如比其他相关联苯衍生物更高的电子亲和力（E1/2 = -1.17 V 与 Fc 和 Fc(+)）和更强的荧光（ΦF = 0.20），因为后者具有供电子和非荧光的特性。
