Studies on Tetrahydrofuryl-5-fluorouracils. IV. Mode of Reaction of 5-Fluorouracil with 2-Acetoxytetrahydrofuran

The mechanism of the condensation of 5-fluorouracil and 2-acetoxytetrahydrofuran (3), giving 1-(tetrahydro-2-furyl)-5-fluorouracil, was studied. An equilibrium between 2-acetoxytetrahydrofuran (3) and 2, 3-dihydrofuran (4) was observed at 120-170°C in dimethylformamide. It was found by the use of 1, 3-dideuterio-5-fluorouracil that the condensation of 5-fluorouracil with 3 occurred both by direct substitution and by the formation of 4 from 3 followed by addition of the uracil to it. The contribution of the latter path increased with increase of the reaction temperature.