Synthesis of 2H‐benzofuro/thieno/pyrroloindazoles via Intramolecular Dehydrogenation Photocyclization

Main observation and conclusionA catalyst‐, acid‐ and base‐free, environmental‐friendly method for synthesis of 2H‐benzo[g]furo[2,3‐e]indazoles, 2H‐benzo[g]thieno[2,3‐e]indazoles and 2H‐benzo[g]pyrrolo[2,3‐e]indazoles via UV light irradiation of 3‐phenyl‐4‐(2‐heteroaryl)pyrazoles (aryl = furanyl, th...

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Published inChinese journal of chemistry Vol. 39; no. 8; pp. 2213 - 2219
Main Authors Zhang, Wei, Wang, Ping, Zhang, Xi, Wang, Rui, Wang, Tao, Liu, Zhicun, Zhang, Zunting
Format Journal Article
LanguageEnglish
Published Shanghai Wiley Subscription Services, Inc 01.08.2021
Subjects
Argon
Catalysts
Dehydrogenation
Irradiation
Light irradiation
Pyrazole
Pyrazoles
Room temperature
Selectivity
Tautomerism
Ultraviolet radiation
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Summary:Main observation and conclusionA catalyst‐, acid‐ and base‐free, environmental‐friendly method for synthesis of 2H‐benzo[g]furo[2,3‐e]indazoles, 2H‐benzo[g]thieno[2,3‐e]indazoles and 2H‐benzo[g]pyrrolo[2,3‐e]indazoles via UV light irradiation of 3‐phenyl‐4‐(2‐heteroaryl)pyrazoles (aryl = furanyl, thiophenyl and N‐methylpyrrolyl) in EtOH/H2O at room temperature under argon atmosphere was described. Irradiation of 3‐(2‐hydroxyphenyl)‐4‐(2‐heteroaryl)pyrazoles showed a high chemo‐selectivity to obtain dehydrogenation product 2H‐benzo[g]furo/ thieno/pyrrolo[2,3‐e]indazols‐10‐ol. The mechanism of photocyclization was expounded through the process of 6π‐electroncyclization, [1,5]‐hydrogen shift, pyrazole tautomerism, 1,3‐eneamine tautomerism and evolution of H2.
ISSN:1001-604X
1614-7065
DOI:10.1002/cjoc.202100103