p-Toluenesulfonic acid → 2,3:5,6-Di-O-isopropylidene-L-gulonolactone

Beteiligte Stoffe

Reaktionsschritte

L-Gulonolactone (20.00 g, 112.3 mmol) was stirred with acetone (160 ml), 2,2-dimethoxypropane (40 ml) and a catalytic amount of p-toluenesulphonic acid under dry nitrogen for 36 h when t.l.c. (ethyl acetate) revealed no starting material (Rf 0.0) and one product (Rf 0.9). The reaction mixture was stirred with an excess of sodium bicarbonate and the solvent removed under reduced pressure. The residue was dissolved in dichloromethane (200 ml) and washed with water (3×200 ml). The organic extracts were dried (magnesium sulphate) and the solvent removed under reduced pressure to give a solid which was recrystallized from ethyl acetate to yield 2,3:5,6-di-O-isopropylidene-L-gulonolactone, (22.89 g, 79%), m.p. 151°-153° C. [α]D20 +68.4° (c, 1 in acetone) [lit. m.p. 153°-154° C. [α]D20 +91.5°]. δC (CDCl3), 173.3 (s, C-1), 114.7 (s), 110.5 (s), 80.9, 76.0, 75.7 and 75.2 (4×d, C-2, C-3, C-4 and C-5), 65.1 (d, C-6), 26.5 (q), 25.7 (q), 25.0 (q).

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