Introduction of a sulfonatomethyl moiety into the primary position of thioglycosides by nucleophilic displacement of the corresponding 6‐O‐triflate is described. The 1→6 migration of the anomeric group, which inevitably occurs through a bicyclic sulfonium ion intermediate, from conformationally flexible β‐thioglycosides was prevented by using an α‐thioglycoside or conformationally locked β‐thioglycoside as the starting material. The thioglycoside 6‐sulfonic acids showed excellent α‐selectivity during synthesis of uronic acid containing heparinoid trisaccharides.

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