Diastereo- and enantioselective synthesis of Delta(2)-1,2,4-oxadiazolines by 1,3-dipolar cycloaddition of nitrile oxides with chiral hydrazones

Diastereo- and enantioselective 1,3-dipolar cycloadditions of nitrile oxide s (3) with alpha,beta-unsaturated hydrazones (2) gave spiro oxadiazolines ( 4) in good yields and low to excellent diastereomeric excesses (de = 5 - gr eater than or equal to 98%). Open chain hydrazones (6) afforded 5,5-disubst ituted Delta(2)-1,2,4-oxadiazolines (7). A subsequent N-N bond cleavage to remove the chiral auxiliary was achieved with formic acid and gave the oxad iazolines (8) (ee = 0 - 91%).