Uracil, 3- 2,2 -anhydride from

Epoxide ring-formation has not yet been observed from fluorine derivatives, but 3-(2-deoxy-2-fluoro-/3-n-ribosyl)uracil forms the 2,2 -anhydride... 

A useful method for preparing enol-acetates from uracil 4-keto-nucleosides uses dimethyl formamide diethyl acetal followed by acetic anhydride 2-keto isomers, or N-3-substituted analogues, did not react. Further studies supported a mechanism involving 0-4 esterification of the nucleoside followed by enoliza-tion, which is intramolecularly catalysed by the dimethylamino group, as illustrated in (63). 

A solution of 5.0 g 2, 3 -(9-(methoxymethylene) uridine (17.5 mmol) in 50 mL acetic anhydride was stirred for 3 h at 132°C. The reaction mixture was cooled to room temperature and evaporated. Chloroform (50 mL) was added, and the mixture was washed with 50 mL aqueous NaHCOs. Aqueous layer was extracted with 50 mL CHCI3, and the combined organic layers were dried over Na2S04, concentrated, and purified by silica gel column chromatography (CHCb/MeOH, 10 1) to give 1.87 g l-(5-0-acetyl-2, 3 -dideoxy)-/3-D-glycero-pent-2-enofuranosyl)uracil, in a yield of 42%, m.p. 128-128.5°C (recrystallized from EtOH). 

The D-g/wco-pentitol-l-yl substituted uracil 96 and its D-galacto-isomer were synthesized from tri-O-benzyl-D-glucal and -o-galactal, respectively, by [2+2]cy-cloaddition of trichloroacetyl or chlorosulfonyl isocyanate, cleavage of the p-lactam rings in the products with methanol after AT-carbamoylation, and cycliza-tion of resulting glycosylureas. Tosylation of 4-(D-ga/acro-pentitol-l-yl)-2-phenyl-2/f-l,2,3-triazole led to the 3,6-anhydride 97 and two partially tosylated derivatives. ... 

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