Imidazo[1,2-a]pyridines Susceptible to Excited State Intramolecular Proton Transfer: One-Pot Synthesis via an Ortoleva鈥揔ing Reaction

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• 作者：Anton J. Stasyuk ; Marzena Banasiewicz ; Micha艂 K. Cyra艅ski ; Daniel T. Gryko
• 刊名：The Journal of Organic Chemistry
• 出版年：2012
• 出版时间：July 6, 2012
• 年：2012
• 卷：77
• 期：13
• 页码：5552-5558
• 全文大小：263K
• 年卷期：v.77,no.13(July 6, 2012)
• ISSN：1520-6904

文摘

A short and efficient route to a broad range of imidazo[1,2-a]pyridines from 2-aminopyridines and acetophenones is achieved by a tandem, one-pot process starting with an Ortoleva鈥揔ing reaction. Optimal conditions for the first step were established after examining various reaction parameters (solvent, reagent ratios, and temperature). The conditions identified (1st step, neat, 2.3 equiv of 2-aminopyridine, 1.20 equiv of I₂, 4 h, 110 掳C; 2nd step, NaOH_aq, 1 h, 100 掳C) resulted in the formation of imidazo[1,2-a]pyridines in 40鈥?0% yields. The synthesis is compatible with various functionalities (OH, NMe₂, Br, OMe). Products containing a 2-(2鈥?hydroxyphenyl) substituent undergo excited state intramolecular proton transfer (ESIPT) in nonpolar and polar-aprotic solvents. Although ESIPT-type emission in nonpolar solvents is weak, the Stokes shifts are very high (11000 cm^鈥?). The comparison of the properties of six ESIPT-capable imidazo[1,2-a]pyridines shows the influence of various substituents on emission characteristics. All of them also display strong, solid-state emission in blue鈥揼reen鈥搚ellow region. 2-Aryl-imidazo[1,2-a]pyridines not capable of ESIPT emit in the blue region, displaying high fluorescence quantum yield.