REGIOSELECTIVITY IN THE 1,3-DIPOLAR CYCLOADDITION OF NITRILE OXIDES TO N-(3,5-DICHLOROPHENYL)ITACONIMIDE

The regioselectivity of the nitrile oxide cycloaddition with 3,3-methylene-1-(3,5-dichlorophenyl)-2,5-pyrrolidindione (1) is discussed. Arylnitrile oxides add regioselectively to the carbon-carbon double bond of 1, giving exclusively spiro-isoxazolines 3a-k, whereas acetonitrile oxide gives both adducts 31 and 41. AMI calculations of the reactants and cycloadducts were performed, the regiochemistry of the cycloaddition seems to be controlled by steric effects. Reduction of 3a with NaBH4 in the presence of magnesium perchlorate at -20-degrees-C was regio- and stereoselective to yield the hydroxylactams 9a and 10a, whereas hydroxymethylisoxazoline 14a was obtained in the absence of Mg(ClO4)2.