Preparation and stereoselectivity of 1,3-dipolar cycloaddition of C-glycosyl nitrones to N-arylmaleimides

摘要

The cycloaddition of 3′-hydroxyglycosyl-N-methylnitrone (1) to N-arylmaleimides gave thesynisoxazolidines6, whereas 3′-acetoxyglycosyl-N-methylnitrone (2) afforded theantiisoxazolidines8and10. The formation of6was rationalized by anexoattack, stereoelectronically preferred through the hydrogen bond between the pentose hydroxyl group and one of the carbonyl groups of N-arylmaleimide. The sterically preferredendoattack avoiding the repulsions between N-arylmaleimide and sugar moiety was proposed for addition of2. The structure and steric configuration of the products have been assigned on the basis of1H- and13C-NMR spectroscopy, mainly by nuclear Overhauser effect difference spectroscopy. AM1 calculations of the nitrones and MM2 calculations of the adducts were perfor