N-Acetyl-styrylpyrazoles undergo Diels-Alder cycloaddition reactions with N-methylmaleimide under solvent-free conditions to give the corresponding tetrahydroindazoles in good yields and high selectivity. On heating, these reactions do not occur or afford only traces of the cycloadducts. The stereochemistry of obtained cycloadducts was assigned by NMR. Oxidation of the tetrahydroindazoles with DDQ gave the expected indazoles and was accompanied by N-deacylation.
Synthesis of New 1<i>H</i>-Indazoles through Diels-Alder Transformations of 4-Styrylpyrazoles under Microwave Irradiation Conditions
作者:Vera L. M. Silva、Artur M. S. Silva、Diana C. G. A. Pinto、José Elguero、José A. S. Cavaleiro
DOI:10.1002/ejoc.200900513
日期:2009.9
Microwaveirradiationunder 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