“…in 50 % yield. 386 Similarly, 1,2-0-isopropylidene-a-o-glucofuranur-ono-6.3-lactone (339) on treatment with manganese dioxide in acetone was converted into the 5-ulose-6,3-lactone (340) in 28% yield,387 and 2',3'-O-isopropylidene-6,S' (S) cyclouridine (341) was oxidized to 2,3' -O-isopropylidene-S' -oxo-6,S' -cyclouridine (342) …”