Synthesis of 7-Oxabicyclo[2.2.1]heptanes and 8-Oxabicyclo[3.2.1]octanes from C-Glycosides via an Intramolecular Cyclization
作者:Wei Zou、Kannan Vembaiyan
DOI:10.1021/jo3024973
日期:2013.3.15
A simple and effective method for the synthesis of 7-oxabicyclo[2.2.1]heptanes and 8-oxabicyclo[3.2.1]octanes from acetonyl C-glycoside substrates is described, which involves an intramolecular cyclization reaction through a nucleophilic substitution at C-5 or C-6 of C-glycosides by a 2′-enamine intermediate formed in the presence of pyrrolidine. Because anomeric epimerization occurs under these conditions
2'-Carbonyl 5-S-acetyl-C-glycofuranosides and 2'-carbonyl 4-S-acetyl-C-glycopyranosides were converted in good yields to respective 5-thio-C-glycopyranosides and 4-thio-C-glycofuranosides under base treatment. The transformation was resulted from beta-elimination on 2'-carbonyl C-glycoside to form alpha,beta-conjugated aldehyde (or ketone) and following intramolecular hetero-Michael addition by the thiol group. Crown Copyright (C) 2003 Published by Elsevier Science Ltd. All rights reserved.