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Synthesis of New 1 H ‐Indazoles through Diels–Alder Transformations of 4‐Styrylpyrazoles under Microwave Irradiation Conditions
Author(s) -
Silva Vera L. M.,
Silva Artur M. S.,
Pinto Diana C. G. A.,
Elguero José,
Cavaleiro José A. S.
Publication year - 2009
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200900513
Subject(s) - chemistry , dehydrogenation , cycloaddition , microwave irradiation , microwave heating , diels–alder reaction , solvent , irradiation , microwave , photochemistry , nuclear magnetic resonance spectroscopy , medicinal chemistry , organic chemistry , catalysis , physics , quantum mechanics , nuclear physics
Microwave irradiation under solvent‐free conditions induces 1‐acetyl‐4‐styrylpyrazoles to undergo Diels–Alder cycloaddition reactions with N ‐methyl‐ or N ‐phenylmaleimide to give tetrahydroindazoles in good yields and with high selectivities. With conventional heating, these reactions either do not occur or afford only traces of the cycloadducts. These cycloadducts were then converted into the corresponding 1 H ‐indazoles by dehydrogenation with DDQ in dry 1,2,4‐trichlorobenzene under microwave irradiation or classical heating conditions. The structures of all new derivatives and the stereochemistries of the cycloadducts were assigned by NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)