Asymmetric [1,3]-dipolar cycloaddition reactions : synthesis of highly substituted proline derivatives

The asymmetric [1,3]-dipolar cycloaddition reactions of azomethine ylides derived from (SR,6S)-2,3,5,6-tetrahydro-5,6-diphenyl-1,4-oxazin-2-one with various aldehydes and methyl maleate is described. The reactions prove to be highly endo-selective, installing three contiguous stereogenic centers in the newly formed five-membered ring with essentially complete stereochemical control