Attempted Synthesis of the Imidazylate of an α-Hydroxylactone Results in Unexpected Chlorination: Synthesis and X-Ray Crystal Structure of 5-Chloro-5-deoxy-1,2-O-isopropylidene-β-<scp>l</scp>-idurono-6,3-lactone

Attempted synthesis of the imidazylate derivative of 1,2-O-isopropylidene- α-D-glucurono-6,3-lactone (2) via treatment with sulfuryl chloride in the presence of excess imidazole in DMF at either -40&#176;C or -70&#176;C resulted in the unexpected formation of 5-chloro-5-deoxy-1,2-O-isopropylidene-β-l- idurono-6,3-lactone (7). Chloride 7 presumably forms via the rapid S N2 displacement by a chloride ion of an initially formed chlorosulfate ester intermediate, which is evidently unusually reactive. The identity of the product was confirmed by a single-crystal X-ray structure determination.