D-glycero-D-gulo-Heptono-1,4-lactone (6) (10 g, 48.08 mmol) and imidazole (4.98 g, 1.5 equiv) were added to dry DMF (25 ml) and the mixture stirred at 0° C. under nitrogen. tert-Butylchlorodiphenylsilane (13.74 ml, 1.1 equiv) was added slowly, after which the reaction mixture was allowed to warm up to room temperature over three hours. After 22 hours, t.l.c. (eluant ethyl acetate) indicated that the mixture contained the desired monosilyl derivative (Rf 0.65) and a smaller amount of another carbohydrate derivative (Rf 0.9). The crude reaction mixture was shaken with water (50 ml), causing a white precipitate to form. Ethyl acetate (90 ml) was added and the layers separated after shaking. The aqueous layer was back-extracted with more ethyl acetate (25 ml). The combined organic extracts were washed with saturated aqueous sodium chloride (4×25 ml) and dried (magnesium sulphate). Evaporation of the solvent followed by dry column chromatography (eluant hexane ethyl: acetate, 2:1, increasing the eluant polarity with each fraction), yielding 7-O-tert-butyldiphenylsilyl-D-glycero-D-gulo-heptono-1,4-lactone (7) (11.02 g, 55%) as a white solid, m.p. 54°-57° C. (Found: C, 61.58; H, 6.86%. C23H30O7Si requires: C, 61.87; H, 6.77%); [α]d20 -10.56° (c, 0.99 in CHCl3); vmax (CHCl3) 3410 (broad, OH) and 1790 cm-1 (γ-lactone); and 2,7-di-O-tert-butyldiphenylsilyl-D-glycero-D-gulo-heptono-1,4-lactone (8) (5.94 g, 18%) as a colorless, viscous oil [α]D20 -4.08° (c, 1.20 in CHCl3); vmax (CHCl3) 3440 (broad, OH) and 1790 cm-1 (γ-lactone).
