Synthesis of 7‑Oxabicyclo[2.2.1]heptanes and 8‑Oxabicyclo[3.2.1]octanes from C‑Glycosides via an Intramolecular Cyclization

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, C-glycoside substrates with either anomeric configuration were converted to the same product(s) in same stereoselectivity and similar chemical yield.