An efficient approach has been described for the synthesis of 3,5-disubstituted isoxazoles from propargylic alcohols. The strategy involves a one-pot p-TSA-catalyzed N-propargylation of protected hydroxylamines followed by a TBAF-mediated detosylative 5-endo-dig cyclization. The method was successfully used for the synthesis of various 3,5-disubstituted isoxazoles.
Tandem reaction of propargyl alcohols and N-tosyl hydroxylamine: switchable synthesis of 2,5-dihydroisoxazoles and 4-halo-2,5-dihydroisoxazoles
作者:Yuanxun Zhu、Guangwei Yin、Lang Sun、Ping Lu、Yanguang Wang
DOI:10.1016/j.tet.2012.09.092
日期:2012.12
2,5-Dihydroisoxazoles, 4-iodo-2,5-dihydroisoxazoles, and 4-bromo-2,5-dihydroisoxazoles were efficiently constructed from propargylic alcohols and N-tosyl hydroxylamine using ytterbium triflate, iodine and N-bromosuccinimide, respectively. N-sulfonylallenamide is postulated to be the key intermediate for these tandem transformations. Moreover, the resulting 4-iodo-2,5-dihydroisoxazoles could be elaborated by palladium-catalyzed carbonylation to generate 4-methoxycarbonyl-4,5-dihydroisoxazoles. (C) 2012 Elsevier Ltd. All rights reserved.