Dearomatization-Induced Transannular Cyclization: Synthesis of Electron-Accepting Thiophene-S,S-Dioxide-Fused Biphenylene

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• 作者：Aiko Fukazawa ; Hiroya Oshima ; Soji Shimizu ; Nagao Kobayashi ; Shigehiro Yamaguchi
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：June 18, 2014
• 年：2014
• 卷：136
• 期：24
• 页码：8738-8745
• 全文大小：575K
• 年卷期：v.136,no.24(June 18, 2014)
• ISSN：1520-5126

文摘

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 掳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 8蟺 and 4蟺 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 (E_1/2 = 鈭?.17 V vs Fc and Fc⁺) and a stronger fluorescence (桅_F = 0.20) than the other relevant biphenylene derivatives, which have electron-donating and nonfluorescent characteristics.