Differentially Substituted Galactosyl Chlorides Reveal Unusual Reactivity Trends under the 4K Reaction Conditions

Recently, it was discovered that the addition of a catalytic (Lewis) acid to a silver salt-promoted glycosylation reaction (Koenigs-Knorr reaction) has a dramatic effect on the reaction rates and yields. Under these reaction conditions (the 4K reaction), an unusual reactivity trend among glycosyl bromide donors of the d-gluco and d-manno series was observed. Reported herein are the synthesis and glycosidation of differently protected galactosyl chlorides. Also presented is a preliminary overview of the reactivity and reaction time discrepancy with respect to those commonly known in the field. A preliminary attempt to rationalize the unusual reactivity trends is also presented.