ENANTIOMERICALLY PURE 3,7-DIOXA-2-AZABICYCLO[3.3.0]OCTANES BY INTRAMOLECULAR 1,3-DIPOLAR CYCLOADDITION OF NITRONES

Starting with chiral non-racemic esters of lactic acid 7 and mandelic acid 8, respectively, chiral nitrones 4 have been prepared. They spontaneously undergo an intramolecular cycloaddition which proceeds with asymmetric induction by the chiral center yielding exclusively the bicyclic compounds 5 in enantiomerically pure form. Reductive opening of the isoxazolidine ring affords tetrahydrofuran derivatives 13 with an gamma-amino alcohol group. Reaction of 13 with (-)-camphanoyl chloride gives the esters 14. Their H-1-NMR spectra reveal a diastereomeric purity of at least 98%.