REGIOSELECTIVE AND STEREOSELECTIVE REDUCTION OF 3,5-DISUBSTITUTED -DIHYDRO-4H-PYRROLO[3,4-D]ISOXAZOLE-4,6(5H)-DIONES WITH SODIUM-BOROHYDRIDE

The reduction of condensed imides 1 with sodium borohydride proceeds r egio- and stereoselectively to yield the hydroxylactams 2, 3 and 4. AM 1 calculations of the reactants and products reveal that the regiochem istry of the reductions seems to be controlled by both electronic and steric effects. The regio- and stereoselectivity of the reductions are dramatically improved by the presence of magnesium perchlorate. This is interpreted in terms of a chelate complex formation between the car bonyl group, isoxazoline oxygen atom and magnesium ion. The presence o f p-toluenesulfonic acid (p-TsOH) also improves the regioselectivity, but lowers the chemoselectivity.