Acetolysis of 1,6-anhydro sugars can be achieved by treatment with acetic anhydride and triethylsilyl trifluoromethanesulphonate at 0 "C for 5-15 minutes, under which conditions a wide variety of protecting groups are unaffected, and even the trisulphonate is cleaved, albeit in six hours. TBDPSO 7c OAc 8c Complex mixture TBDPSO 9 L O A c AGO S O Ac OAc 85 13 14 a Typical experimental procedure. The anhydro sugar is dissolved in Ac20 and cooled to 0°C with stirring under argon. Two drops (-20-30 pl) of triethylsilyl trifluoromethanesulphonate are added to the solution. The reaction is followed by TLC and generally requires 5-15 min for completion. A solution of saturated sodium bicarbonate is then added and after being stirred for 30 min, the aqueous mixture is extracted three times with ethyl acetate. The organic extracts are combined and washed with saturated sodium hydrogen carbonate solution followed by brine. The mixture is then dried over sodium sulphate, filtered and the solvents removed under reduced pressure. Percolation through silica gel removes any trace of acetic anhydride affording clean product. b This reaction required 6 hours for completion; Ts = p-tolylsulphonyl. c p: CY = 3 : 1. d TBDPS = tert-butyldiphenylsilyl.
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