The stereochemistry of 1,3-dipolar cycloaddition of internally H-bonded chiral methylenenitrones

A study of diastereoselectivity in the cycloaddition reactions of a series of mono- and disubstituted alkenes with two chiral, internally H-bonded methylenenitrones has been carried out. The high degree of stereochemical control in the presence of anhydrous magnesium bromide has been explained in terms of a metal chelated transition state. Intramolecular cycloaddition involving a methylenenitrone containing an alkene moiety linked to a nitrogen gave a stereoselective addition product.