Diastereoselectivity-Switchable and Highly Enantioselective 1,3-Dipolar Cycloaddition of Nitrones to Alkylidene Malonates
journal contributionposted on 13.05.2004, 00:00 by Zheng-Zheng Huang, Yan-Biao Kang, Jian Zhou, Meng-Chun Ye, Yong Tang
Trisoxazoline 1/Co(ClO4)2·6H2O catalyzed the 1,3-cycloaddition between nitrones 3 with alkylidene malonates 2 at 0 °C to give the isoxazolidines with both high enantioselectivity and high exo selectivity. However, when the temperature was lowered from 0 to −40 °C, the same cycloaddition afforded endo isomers as the major products with good to high enantioselectivity. A mechanism is provided.