Straightforward synthesis of enantiomerically pure (3S,4R)- and (3R,4S)-3,4-isopropylidenedioxypyrroline 1-oxide, precursors of functionalized cis-dihydroxy azaheterocycles, by a novel "one-pot" procedure.

The enantiomerically pure nitrone 3, a valuable precursor of mono- and bicyclic azaheterocycles, has been synthesized in 57% yield by a novel "one-pot" process starting from lactol 1, in turn readily available from D-arabinose. The same process, consisting of reaction with a O-silyl-protected hydroxylamine followed by mesylation in pyridine, furnished ent-3 in 55% yield when applied to L-arabinose.