Efficient Microwave-Assisted Synthesis of Tetrahydroindazoles and their Oxidation to Indazoles

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.