Stereoselective Cycloaddition on Carbohydrates for the Synthesis of New Bicyclic Oxazolidines Bearing a Quaternary Bridgehead

A new carbohydrate nitrone intramolecular cycloaddition reaction is described for the enantioselective synthesis of bicyclic oxazolidines. By choice of the precursor, the products possess a chiral quaternary bridgehead aryl substitution. Also described is the diverse synthesis of 6-keto and 6-alkenyl carbohydrates by a general approach. The overall protocol provides versatility through the possibility of introducing diverse reagents at several entry points.