Diastereofacial selectivity in the cycloaddition of nitrones to(E)-gamma-oxygenated alpha,beta-unsaturated esters

The 1,3-dipolar cycloadditions of nitrones 1 and 2 to a series of 1,2-disubstituted electron-deficient olefins bearing an allylic stereocenter, 4-8, are reported. The synlanti stereochemistry of the major endo adducts may be rationalized through the Houk transition-state model, but the possibility of intramolecular hydrogen bonding must be taken into account. In the case of the minor exo adducts the syn stereochemistry always predominates.