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DOI: 10.1055/s-2007-983802
A Stereoselective Access to Dihydroxylated Pyrrolidines by Reductive Ring Contraction of 1,2-Oxazines
Publication History
Received
30 March 2007
Publication Date:
24 July 2007 (online)


Abstract
Protected dihydroxylated 1,2-oxazine derivatives such as rac-4 were converted into tetrahydro-1,2-oxazines rac-7 by employing BH3·THF for the stereoselective reduction of the C=N bond. Compound 7a underwent a reductive ring contraction on hydrogenation in the presence of palladium on charcoal to provide rac-5 in good yield. Enantiopure 1,2-oxazine derivatives 13 and 14 were prepared using (-)-menthol as chiral auxiliary. Their diastereoselective dihydroxylation and BH3·THF reduction furnished enantiopure tetrahydro-2H-1,2-oxazine derivatives 17 and 18 in good overall yield. Enantiomers (6R)-18 and (6S)-18 were transformed into the two enantiomeric hydroxylated pyrrolidine derivatives 5 in moderate yield.
Key words
cycloaddition - 1,2-oxazines - pyrrolidines - hydrogenation - ring contraction