The key steps include protection of the uracil base with methoxyethoxymethyl (MEM) chloride, conversion to the corresponding 2'-C-alpha-epoxide, and regioselective opening of the oxirane ring with potassium fluoride/hydrogenfluoride. Subsequent acetylation of the 3'- and 5'-hydroxyl groups enables MEM removal using B-bromocatecholborane. Deacetylation generates the parent nucleoside, 2'-C-beta-flurormethyluridine
Ring-opening fluorinationreactions of epoxides using tetrabutylammonium bifluoride (TBABF)-KHF2, or Et3N-3HF under microwave irradiation were applied for the introduction of a fluorineatom into the carbohydrate molecules. When TBABF-KHF2 was used as the fluorination reagent, a fluorineatom was introduced regioselectively and various functional groups can tolerate the conditions. When Et3N-3HF was