I, R= F 11, R= CH, zine-2, 6 (3H)-dione dissolved in anhydrous acetone with fluoroxytrifluoromethane at-55 to-60" C. The rapid disappearance of UV absorption at 260 nm indicated the formation of an adduct, as was previously reported to occur upon the interaction of this reagent with pyrimidine bases and nucleosides. 12