Diastereoselectivity of nitrone 1,3-dipolar cycloaddition to Baylis-Hillman adducts

Abstract

1,3-Dipolar cycloadditions of C-phenyl-N-methylnitrone to Baylis-Hillman adducts (-hydroxy-methylene esters) proceed with complete regioselectivity in good yields to afford the corresponding diastereomeric 3,5,5-trisubstituted isoxazolidines. Attack of the dipole from the less sterically hindered side of the dipolarophiles affords C-3/C-5 cis isoxazolidines as the predominant isomers. Addition of Lewis acids and microwave irradiation produce only a small effect on the diastereoisomeric product ratio. Microwave irradiation accelerates the reaction.