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Facile synthesis of alkynyl-, aryl- and ferrocenyl-substituted pyrazoles via Sonogashira and Suzuki-Miyaura approaches

2016-10-01
KARABIYIKOĞLU, Sedef
Zora, Metin
A concise and efficient synthesis of densely substituted novel pyrazoles with alkynyl, aryl and ferrocenyl functionalities is reported, providing a platform for biological studies. The general strategy involves Sonogashira and Suzuki-Miyaura cross-coupling reactions of easily obtainable 5-ferrocenyl/phenyl-4-iodo-1-phenylpyrazoles with terminal alkynes and boronic acids, respectively. The starting 4-iodopyrazoles were synthesized by electrophilic cyclization of alpha,beta-alkynic hydrazones with molecular iodine. Sonogashira reactions have been achieved by employing 5 mol% PdCl2(PPh3)(2), 5 mol% CuI, excess Et3N and 1.2 equiv. of terminal alkyne, relative to 4-iodopyrazole, in tetrahydrofuran at 65 degrees C, while Suzuki-Miyaura reactions have been accomplished using 5 mol% PdCl2(PPh3)(2) and 1.4 equiv. of both boronic acid/ester and KHCO3, with respect to 4-iodopyrazole, in 4:1 dimethylformamide-H2O solution at 110 degrees C. Both Sonogashira and Suzuki-Miyaura coupling reactions have proven effective for the synthesis of alkynyl-, aryl- and ferrocenyl-substituted pyrazoles and demonstrated good tolerance to a diverse range of substituents, including electron-donating and electron-withdrawing groups. These coupling approaches could allow for the rapid construction of a library of functionalized pyrazoles of pharmacological interest. Copyright (C) 2016 John Wiley & Sons, Ltd.