A Lewis acid promotes the E- to Z-isomerization of carbonyl-conjugated nitrones. The MgBr2•Et2O-catalyzed cycloadditions to allylic alcohols lead to the exclusive formation of the exo-stereoisomers of isoxazolidine-5-methanols. Participation of the Z-nitrone/MgBr2 complexes is suggested.
路易斯酸促进了羰基共轭硝基的 E- 到 Z- 异构化。MgBr2-Et2O 催化的烯丙基醇环加成反应导致
异噁唑烷-5-
甲醇外异构体的形成。这表明 Z-硝酮/MgBr2 复合物参与了反应。