Isoxazoles and Isoxazolines by 1,3-Dipolar Cycloaddition: Base-Catalysed Condensation of Primary Nitro Compounds with Dipolarophiles
作者:Fabrizio Machetti、Luca Cecchi、Elena Trogu、Francesco De Sarlo
DOI:10.1002/ejoc.200700276
日期:2007.9
1,4-Diazabicyclo[2.2.2]octane (DABCO) or other suitable N-bases cause primaryactivatednitrocompounds to condense with alkenes to yield isoxazolines or with alkynes to give isoxazoles. As the molar ratio of the base with respect to the dipolarophile decreased, the reaction became slower, but the nitrocompound became more resistant to hydrolytic cleavage. The best results were achieved with a molar
1,4-二氮杂双环 [2.2.2] 辛烷 (DABCO) 或其他合适的 N-碱导致初级活化硝基化合物与烯烃缩合生成异恶唑啉或与炔烃缩合生成异恶唑。随着碱与偶极体的摩尔比降低,反应变慢,但硝基化合物对水解裂解的抵抗力更强。碱的摩尔比在 0.05-0.1 范围内时获得最佳结果。反应在氯仿中于 60 °C 下进行;对于硝基乙酸乙酯和苯基硝基甲烷,可以使用 80 °C 的乙醇获得更好的结果和更短的反应时间。建议采用催化循环: