[3+2] CYCLOADDITION OF CHIRAL AZOMETHINE YLIDES FROM AMINOSUGAR N-OXIDES - ENANTIOSELECTIVE SYNTHESIS OF 3,4-DISUBSTITUTED PYRROLIDINES

The base deprotonation method, applied to amino-sugar N-oxides prepared from methyl 2,3-anhydro-4,6-O-benzylidene-alpha-D-mannopyranoside (8) and methyl 2,3-anhydro-4,6-O-benzylidene-alpha-D-allopyranoside (9), allows the easy generation of complex and very reactive sugar azomethine ylides. Fair yields of the major diastereomeric pyrrolidines resulting from [3+2] cycloaddition to stilbene are thus obtained with good asymmetric induction. The easy elimination of the chiral appendage as starting epoxides gives access to the enantiomerically enriched 3,4-diphenylpyrrolidines.