1,3-Dipolar Cycloadditions ofN-Benzyl-2,3-O-isopropylidene-D-glyceraldehyde Nitrone to Methoxyallene – Control of Site- and Diastereoselectivity of Isoxazolidine Formation by Lewis Acids
D-glyceraldehyde-derived nitrone 1 and methoxyallene (2) is strongly influenced by Lewis acids. The uncatalyzed reaction results in the formation of isomeric isoxazolidines 3a–3d and 4a–4c, whereas in the presence of different Lewis acids exclusive formation of 4-methylene-substituted isoxazolidines 4a–4d is observed. Furthermore, the diastereofacial selectivity of the methoxyallene addition to nitrone 1 can be controlled