Approaches to the synthesis of sugar thiolactones

Evidence is presented that aldonolactones undergo “alkyl-oxygen” fission when attacked by thionucleophiles. The reaction of 2,3-O-isopropylidene-d-ery-throno-1,4-lactone with potassium thioacetate gives 2,3-O-isopropylidene-4-thio-d-erythrono-1,4-lactone, the first example of a thiolactone of an aldonic acid. Deacetylation of 5-S-acetyl-2,3-O-isopropylidene-5-thio-d-ribono-1,4-lactone is accompanied by partial migration of sulphur from C-5 to C-4; a mechanism involving an intermediate 5,6-episulphide is suggested.