Formal [3+2] Cycloaddition with in situ Generated N-Carbamoyl Nitrones

Significance

An asymmetric formal [3+2] nitrone cycloaddition with glutaconates 3 giving access to N-Boc- and N-Cbz-protected isoxazolidines 4 is described. Nitrones A are generated in situ from N-Boc- and N-Cbz-protected N-hydroxy-α-amido sulfones 2. Cinchona alkaloid derived phase-transfer catalyst 1 delivered the products with three contiguous stereocenters as single diaste­reomers in generally high yields and with high enantioselectivity. Attempted differentiation of ester groups in 3 (OMe and Ot-Bu) resulted in a low regioselectivity. The synthetic utility of the products was demonstrated by chemoselective Boc deprotection and N-O cleavage.