ENANTIOMERICALLY PURE ISOXAZOLINES BY STEREOSELECTIVE 1,3-DIPOLAR CYCLOADDITION OF SILYL NITRONATES

The cycloaddition reactions of in situ generated silyl nitronates 3 to chiral enone 1a or enoate 1b proceed with high stereoselectivity to g ive enantiomerically pure N-silyloxyisoxazolidines 4, which can easily be transformed into Delta(2)-isoxazolines 5. Based on an X-ray analys is the major diastereomers were assigned as the syn-derivatives, thus differing from diastereofacial selectivity found with nitrile oxides. The base-catalyzed ring-opening reaction of isoxazoline 5a affords the chiral beta-hydroxy nitrile 6, which was cyclized to the sugar-lire t etrahydrofuran 7. Copyright (C) 1996 Elsevier Science Ltd