1,3-dipolar cycloadditions of D-erythrose- and D-threose-derived nitrones to maleimides

The nitrones derived from cyclic acetals of D-erythrose 1a,b and D-threose 2a,b react with N-phenylmaleimide (3) to afford the corresponding diastereo meric isoxazolidines. The stereoselectivity is dependent on the steric hind rance of the nitrone. In the case of D-erythro-derived nitrones 1a,b the cy cloaddition is exo-selective. The major products are in the C-3/C-4 erythro - and C-3/C-3a transconfiguration. This finding can be rationalized by a le ss hindered exo-attack of the (Z)-nitrone in an antiperiplanar manner with respect to the largest group of the cyclic acetal. The cycloaddition to the chiral maleimides 12 and 13 is less stereoselective.