Diastereoselective thermal [3+2] cycloaddition reactions of nitrone possessing an amide functional group as hydrogen bond donor/acceptor

Abstract

High diastereoselectivity in the [3+2] cycloaddition reactions of a series of maleimides with a nitrone capable of hydrogen bonding have been carried out. The cycloaddition reaction proceeded in highly diastereoselective manner leading to novel pyrrolo[3,4-d]isoxazolidines with good yields. NMR studies revealed that in the performed cycloaddition reactions, a pair of diastereomers are formed in all cases and the cis-diastereomeric product is the favorite cycloadduct with de values up to 90%. It would appear that the presence of amide functionality at the phenyl moiety of nitrone can influence the diastereomeric ratio in the cycloaddition reactions and cis stereoselectivity is most likely dependent on the presence of this group. The nature of the cycloadddition process was interpreted in the framework of the Molecular Electron Density Theory.