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 Nphenylmaleimide (3) to afford the corresponding diastereomeric isoxazolidines.The stereoselectivity is dependent on the steric hindrance of the nitrone.In the case of D-erythroderived nitrones 1a,b the cycloaddition is exo-selective.The major products are in the C-3/C-4 erythroand C-3/C-3a trans-configuration.This finding can be rationalized by a less 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.

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