Unexpected Anomeric Selectivity of a 1-C-Arylglycal Donor in Kdo Glycoside Synthesis

A novel class of 1-C-arylglycals was developed and subjected to N-iodosuccinimide-mediated glycosylations with alcohols. Unexpectedly, all reactions provided 2-iodo-β-d-ketopyranosides in high yields and excellent stereoselectivity. After removal of the 2-iodide by radical conditions, the aryl group was smoothly oxidized to provide the corresponding β-Kdo glycosides. A mechanism for the stereoselective formation of β-d-ketopyranosides was proposed, which was supported by evidence from X-ray crystallography.