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.
在无溶剂条件下,N-乙酰基
苯乙烯基
吡唑与 N-甲基马来
酰亚胺发生 Diels-Alder 环加成反应,生成相应的四氢
吲唑,产率高,选择性强。加热时,这些反应不会发生或仅产生微量的环加成物。所得到的环加合物的立体
化学结构是通过核磁共振来确定的。用
DDQ 氧化四氢
吲唑可得到预期的
吲唑,并伴随 N-脱酰基反应。