Regio- and stereoselectivity in the 1,3-dipolar cycloaddition of C,N-diarylnitrones to 3,3-methylene-5,5-dimethyl-2-pyrrolidinone
摘要:
Regio- and stereoselectivity of the nitrone cycloaddition with 3,3-methylene-5,5-dimethyl-2-pyrrolidinone ((1) is discussed. Nitrones react regioselectively with 1 to give a mixture of diastereoisomeric spiro-cycloadducts 3 and 4, in which 3 always dominates. Both 3 and 4 result from the approach which binds the carbon of the nitrone with the exocyclic carbon of 1 and the oxygen to the spiro carbon. The structure and steric configuration of the adducts have been assigned on the basis of H-1- and C-13-NMR spectroscopy, mainly by nuclear Overhauser effect difference spectroscopy. AM1 calculations of the reactants were performed, the regio- and stereochemistry of the cycloaddition seems to be controlled by steric effects.
Regio- and stereo-selective synthesis of carbohydrate isoxazolidines by 1,3-dipolar cycloaddition of nitrones to 5,6-di-deoxy-1,2- O -isopropylidene-α- d - xylo -hex-5-enofuranose
The synthesis of 2-phenyl-3-aryl and 2-phenyl-3-aroyl derivatives 5-(1,2-O-isopropylidene-alpha-D-xylo-tetrofuranos-4-yl)isoxazolidi ne (3) from nitrones and 5,6-dideoxy-1,2-O-isopropylidene-alpha-D-xylo-hex-5- enofuranose (1) is described. The 1,3-dipolar cycloaddition reactions given mainly anti adducts 3 and 4 (greater than or equal to 95% pi-facial stereoselectivity). The cycloadducts 3 with H-3