Steric and conformational effects in the dehalogenation of 2-halo sugar derivatives with tributylstannane
摘要:
The stereochemistry of dehalogenation of 2-halo sugars with tributyltin hydride has been investigated in terms of the influence of steric and conformational effects using deuterium-labeling techniques. Detailed analysis of the results (Tables I-III) demonstrates that the size and orientation of the ring substituents are a determining factor in the stereochemical outcome of the reaction' However, some results can only be explained considering reduction of two equilibrating radical conformers.
New thiophilic polymer-bound haloate(l) complexes are presented which are well suited for the polymer-assisted solution-phase activation of 2-deoxythioglycosides. In the presence of alcohols 2-deoxyglycosides are obtained in yields between 60 and 95%. Isolation of the target glycosides is further simplified by removing the byproduct diphenyldisulfide by reductive work-up. Here also a polymer-bound reagent, namely borohydride exchange resin, served as a tool for sequestering the sulfur-containing impurities. (C) 2003 Elsevier Science Ltd. All rights reserved.