STUDIES ON CYCLOADDITION REACTIONS OF 2,2-DIMETHYL-3,4-DIHYDRO-2H-PYRROLE N-OXIDE AND N-(BENZYLIDENE)METHYLAMINE N-OXIDE WITH ALPHA,BETA-UNSATURATED LACTONES AND ESTERS

Intermolecular asymmetric 1,3-dipolar cycloaddition of 2,2-dimethyl-3, 4-dihydro-2H- pyrrole N-oxide and N-(benzylidene)methylamine N-oxide w ith optically active alpha,beta-unsaturated esters 1,2,4 and 7-9 provi ded the corresponding diastereomers while chiral sugar lactones gave s tereoselectively the cycloadducts 17a and 17b (in the case of dipolaro phile 3) and 18 in (the case of the dipolarophile 6) with the acyclic nitrone B. The stereochemistry of the products has been established us ing high field nmr techniques. The regioselectivities of these reactio ns are inconsistent with FMO coefficients and are explained on the bas is of charge distribution obtained through AM1 calculations. (C) 1997 Elsevier Science Ltd.