Stereocontrolled halofluorination of glycals with silicon tetrafluoride, leading to a facile synthesis of glycosyl fluorides
作者:Makoto Shimizu、Yuko Nakahara、Hirosuke Yoshioka
DOI:10.1016/s0022-1139(99)00026-3
日期:1999.7
Bromofluorination of glycals was carried out with SiF4, 1,3-dibromo-5,5-dimethylhydantoin (DBH), and H2O in 1,4-dioxane in the presence of HMPA to give bromofluoro sugars in good yields with good selectivities. Subsequent debromination with n-Bu3SnH gave 2-deoxy sugars in good yields. Furthermore, hydroxyfluorination of glycal was also successfully conducted using SiF4-PhI(OAc)2-H2O to give fluoroglucose
derivatives display intramolecular stabilization of the glycosyl cations. Introducing a strongly electron-withdrawing fluorine atom at C2 exerts considerable influence on the oxocarbenium ion reactivity. In a superacid, these oxocarbenium ions are quenched by weakly coordinating SbF6 - anions, thereby demonstrating their highly electrophilic character and their propensity to interact with poor nucleophiles