A new method of acetonation. Synthesis of 4,6-O-isopropylidene-D-glucopyranose

Ethyl isopropenyl ether reacts with D-glucose in N,N-dimethylformamide containing a trace of p-toluenesulfonic acid to give crystalline 4,6-O-isopropylidene-α,β-D-glucopyranose (2) in near-quantitative yield. The structure of 2 was established by n.m.r. spectroscopy of it and of its β-triacetate 3, and by conversion of 3 through deacetonation and subsequent acetylation into β-D-glucopyranose pentaacetate (5). The acetonation reagent operates under kinetic control, with favored attack at primary hydroxyl groups, instead of by the thermodynamic control associated with conventional acetonation methods. The reagents converts methyl α-D-glucopyranoside (7) into the 4,6-isopropylidene acetal 8, and D-mannitol (9) into a 2:1 mixture of the 1,2:5,6-di-isopropylidene acetal 10 and the 1,2:3,4:5,6-tri-isopropylidene acetal 11.