Preparation of 2,3-Epoxyaldonolactones and their Conversion into 2-Fluoro-2-deoxy-aldonolactones and -sugars.

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Abstract
Treatment of the 2-bromo-2-deoxylactones 1, 2 and 8 with potassium fluoride in acetonitrile or acetone gives the corresponding 2,3-epoxylactones 4,5 and 10, respectively. The .gamma.-lactones 5 and 10 were in equilibrium with the corresponding .delta.-lactones 7 and 12. The 2,5-dibromo-2,5-dideoxypentonolactones 3 and 9 gave the 2,3-epoxylactones 6 and 11, respectively, when treated with potassium carbonate in acetone. By treatment of the 2,3-epoxylactones with Et3N.cntdot.3HF at 70.degree.C for 3-13 days the 2-fluoro-2-deoxylactones 13, 15 and 18 were obtained in 57-69% yield; 15 and 18 were converted into 2-fluoro-2-deoxy-D-xylose (17) and -D-arabinose (19), respectively. Hydrolysis of 13 gave crystalline 2-fluoro-2-deoxy-L-threonic acid.