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Dihydroxylation-Based Approach for the Asymmetric Syntheses of Hydroxy-γ-butyrolactones
A method of preparing enantiopure hydroxy-γ-butyrolactones
containing multiple contiguous stereocenters in high yield with good
diastereoselectivity has been developed. Osmium tetroxide mediated
dihydroxylation of a range of β-alkenyl-β-hydroxy-<i>N</i>-acyloxazolidin-2-ones results in formation of triols that
undergo spontaneous intramolecular 5-<i>exo</i>-trig cyclization
reactions to provide hydroxy-γ-butyrolactones. The stereochemistry
of these hydroxy-γ-butyrolactones has been established using
NOE spectroscopy, which revealed that 1-substituted, 1,1-disubstituted,
(<i>E</i>)-1,2-disubstituted, (<i>Z</i>)-1,2-disubstituted,
and 1,1,2-trisubstituted alkenes undergo dihydroxylation with <i>anti</i>-diastereoselectivity, while 1,2,2-trisubstituted systems
afford <i>syn</i>-diastereoisomers. The synthetic utility
of this methodology has been demonstrated for the asymmetric synthesis
of the natural product 2-deoxy-d-ribonolactone