Synthesis of 1,2-Bis(2-aryl-1H-indol-3-yl)ethynes via 5-exo-Digonal Double Cyclization Reactions of 1,4-Bis(2-isocyanophenyl)buta-1,3-diyne with Aryl Grignard Reagents

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• 作者：Rino Ishikawa ; Ryosuke Iwasawa ; Yuichiro Takiyama ; Tomokazu Yamauchi ; Tetsuo Iwanaga ; Makoto Takezaki ; Motonori Watanabe ; Naozumi Teramoto ; Toshiaki ShimasakiMitsuhiro Shibata
• 刊名：Journal of Organic Chemistry
• 出版年：2017
• 出版时间：January 6, 2017
• 年：2017
• 卷：82
• 期：1
• 页码：652-663
• 全文大小：652K
• ISSN：1520-6904

文摘

New π-conjugated 1,2-bis(2-aryl-1H-indol-3-yl)ethynes 1a–j having various substituents on the two aryl groups were efficiently synthesized via unusual 5-exo-digonal double isocyanide-acetylene cyclization reactions of 1,4-bis(2-isocyanophenyl)buta-1,3-diyne 3 and aryl Grignard reagents (R-MgBr, R = C₆H₅ (1a), 4-H₃CC₆H₄ (1b), 2-H₃CC₆H₄ (1c), 3-MeOC₆H₄ (1d), 3-(CH₃)₂NC₆H₄ (1e), 4-F₃CC₆H₄ (1f), 4-FC₆H₄ (1g), 3-FC₆H₄ (1h), 4-PhOC₆H₄ (1i), and 2-Naph (1j)) in 19–85% yields. The UV–vis spectra were rationalized in detail using time-dependent DFT and single point calculations. The fluorescence emission peaks for 1a–j were observed at around 450 nm. Especially for 1f and 1j, those spectra displayed broad emission bands and relatively large Stokes shifts (3977–4503 cm^–1), indicating the contribution of an intramolecular charge transfer. The absolute quantum yields (0.50–0.62) of 1a–j were higher than those of parent 8 (0.19) and 2-phenyl-1H-indole (0.11). The electrochemical features for 1a–j were investigated by cyclic voltammetry. The frontier molecular orbital levels for 1a–j were estimated based on the combination of oxidation potentials, UV–vis, and DFT calculated data. The structural property of 1,2-bis(2-phenyl-1H-indol-3-yl)ethyne 1a was characterized by several spectroscopic methods and finally determined by X-ray analysis of a single crystal of 1a recrystallized from ethyl acetate. The structural features of 1a–j were also supported by DFT calculations.