Copper-mediated oxidative [3+2]-annulation of nitroalkenes and pyridinium imines: efficient synthesis of 3-fluoro- and 3-nitro-pyrazolo[1,5-a]pyridinesстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 15 апреля 2020 г.
Аннотация:An efficient route to pyrazolo[1,5-a]pyridines by Cu(OAc)2∙H2O-promoted oxidative [3+2]-annulation of nitroalkenes with in situ generated pyridinium imines was developed. The reaction with α-fluoronitroalkenes provides the first preparative synthesis of 3-fluoro-pyrazolo[1,5-a]pyridines. The cycloaddition with α-unsubstituted nitroalkenes opens access to 3 nitro-pyrazolo[1,5-a]pyridines in excellent yields. Broad scope of transformation was demonstrated. Both electron-rich and electron-deficient nitroalkenes as well as different aminopyridinium salts can be used for the assembly of target pyrazolo[1,5-a]pyridines. The related aza-heterocycles, namely, pyrazolo[1,5-a]-pyrazines and pyrazolo[1,5-b]pyridazines were successfully prepared via the present methodology. Possible mechanism of the reaction is discussed.