Subsequent oxidation occurred at the alkyl group, selectively affording the corresponding C-phenyl- and C-unsubstituted N-glycosylnitrones. C-phenyl-N-glycosylnitrones 10 and 13 underwent highly stereoselective 1,3-dipolar cycloaddition with dimethyl maleate, with the sugar moiety acting as a chiral auxiliary. Final removal of the glycosyl moiety afforded enantiopure enantiomeric isoxazolidines 17 and
Access to Piperidine Imino-<i>C</i>-glycosides via Stereoselective Thiazole-Based Aminohomologation of Pyranoses
作者:Alessandro Dondoni、Andrea Nuzzi
DOI:10.1021/jo060890m
日期:2006.9.1
with the NH group is described. The key process involves the stereoselective addition of 2-thiazolylmagnesium bromide to an N-glycosylhydroxylamine, i.e., a hidden open-chain sugar nitrone. The N-thiazolylalkylhydroxylamine formed in this way is reduced to amine, and this transformed into a substituted piperidine via intramolecularcyclization by an SN2 process. Cleavage of the thiazole residue attached
A practical synthesis of N-benzyl-N-glycosylhydroxylamines 3 (R = CH2Ph) is reported. The ability of these compounds to act as versatile synthetic intermediates is demonstrated by their oxidation followed by cycloaddition to N-glcosyl isoxazolidines and by the novel direct cycloaddition as masked acyclic. highly functionalized chiral nitrones. (C) 2002 Elsevier Science Ltd. All rights reserved.