Pyridinium Ions Adjacent to Oxirane Rings: Useful Intermediates for the Stereospecific Synthesis of β‐Hydroxy Ketones

α,β‐Epoxytriflates like epoxytriflate pyranoside 1 undergo rearrangement in a one‐pot reaction after treatment with pyridine. The epoxy ring is opened giving N ‐vinylpyridinium derivatives such as 2 , which can be reduced with NaBH 4 and hydrolyzed under acidic conditions to give β‐hydroxy ketones. This generally applicable procedure can be used to convert easily accessible epoxypyranoses into deoxyketo sugars like 3 in high yields.