p-Toluenesulfonic acid → Methyl 2,3:4,6-Di-O-benzylidene-alpha-D-mannopryanoside

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Reaction Steps

A mixture of methyl α-D-mannopyranoside (Compound I, 50 g, 258 mmoles), α,α-dimethoxytoluene (92 g, 600 mmoles), and anhydrous p-toluene-sulfonic acid (1 g) in N,N-dimethylformamide (300 ml), in a 1-liter flask fitted with an air condenser attached to a water aspirator, was stirred magnetically and heated in an oil bath for 3 hours at 65°-75° C. None of the starting Compound I remained after this time (t.l.c., 4:1 ether-petroleum ether). The mixture was poured with vigorous stirring into 1 liter of ice-water containing sodium hydrogen carbonate (30 g). The resultant precipitate was filtered off, resuspended in ice-water, filtered off again, and dried in air and finally in vacuo over phosphorus pentaoxide; yield 90.6 g (95%), m.p. 120°-160° C, [α]D23 -33° (c 1, chloroform).

Provenance & Evidence