DIASTEREO-AND ENANTIOSELECTIVE SYNTHESIS OF (#DELTA#~2)-1,2,4-OXADIAZOLINES BY ,1,3-DIPOLAR CYCLOADDITION OF NITRILE OXIDES WITH CHIRAL HYDRAZONES

摘要

Abstract-Diastereo-and enantioselective,1,3-dipolar cycloadditions of nitrile oxides(3) with (#alpha#),(#beta#)-unsaturated hydrazones(2)gave spiro oxadiazolines (4) in good yields and low to excellent diastereomeric excesses(de=5->=98%).Open chain hydrazones (6)afforded 5,5-disubstituted #DELTA#-1,2,4-oxadiazolines (7) .A subsequent N-N bond cleavage to remove the chiral auxiliary was achieved with formic acid and gave the oxadiazolines (8)(ee=0-91%).