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Copper‐ or Thermally Induced Divergent Outcomes: Synthesis of 4‐Methyl 2 H ‐Chromenes and Spiro‐4 H ‐Pyrazoles
Author(s) -
Zheng Yang,
Qiu Lihua,
Hong Kemiao,
Dong Shanliang,
Xu Xinfang
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201704759
Subject(s) - cycloaddition , pyrazole , copper , catalysis , chemistry , substrate (aquarium) , combinatorial chemistry , single crystal , cascade , medicinal chemistry , organic chemistry , crystallography , oceanography , chromatography , geology
An unprecedented divergent outcome transformation of alkyne tethered N ‐sulfonyl hydrazones is reported, which provides a direct and effective access to 4‐methyl 2 H ‐chromene derivatives and spiro‐4 H ‐pyrazoles in the presence of copper catalyst or under thermal conditions, respectively. The notable features of this process include readily available starting materials, an inexpensive copper catalyst, mild reaction conditions, broad substrate scope, diverse transformations and potential applications of these generated products. Mechanistic studies indicate that the 3 H ‐pyrazole, which is generated via direct [3+2] cycloaddition, is the communal key intermediate of these two divergent transformations. To the best of our knowledge, this is the only example of sulfonation reaction that goes through a cascade process involving 3 H ‐pyrazole, which was isolated and confirmed by single crystal X‐ray diffraction analysis for the first time.