Preparation and Stereoselectivity of 1,3-Dipolar Cycloaddition of C-Glycosyl Nitrones to N-Arylmaleimides

Article abstract of DOI:10.1007/BF00810931

The cycloaddition of 3'-hydroxyglycosyl-N-methylnitrone (1) to N-arylmaleimides gave the syn isoxazolidines 6, whereas 3'-acetoxyglycosyl-N-methylnitrone (2) afforded the anti isoxazolidines 8 and 10.The formation of 6 was rationalized by an exo attack, stereoelectronically preferred through the hydrogen bond between the pentose hydroxyl group and one of the carbonyl groups of N-arylmaleimide.The sterically preferred endo attack avoiding the repulsions between N-arylmaleimide and sugar moiety was proposed for addition of 2.The structure and steric configuration of the products have been assigned on the basis of 1H- and 13C-NMR spectroscopy, mainly by nuclear Overhauser effect difference spectroscopy.AM1 calculations of the nitrones and MM2 calculations of the adducts were performed. Keywords: 1,3-Dipolar cycloaddition of chiral nitrones; 3'-Hydroxy- and 3'-acetoxyglycosyl-N-methylnitrones; Stereoselectivity of 1,3-dipolar cycloaddition; AM1 calculations.