6-Ethyl-5-fluoro-2-methoxypyrimidin-4(3H)-one

In the title compound, C7H9FN2O2, the methoxy and ethyl groups form dihedral angles of 1.4 (2) and 73.5 (3)°, respectively, with the mean plane of the pyrimidine ring. In the crystal structure, two molecules are linked by a pair of N—H⋯O hydrogen bonds, forming a centrosymmetric dimer.

In the title compound, C 7 H 9 FN 2 O 2 , the methoxy and ethyl groups form dihedral angles of 1.4 (2) and 73.5 (3) , respectively, with the mean plane of the pyrimidine ring. In the crystal structure, two molecules are linked by a pair of N-HÁ Á ÁO hydrogen bonds, forming a centrosymmetric dimer.

Related literature
For fluoro-containing pyrimidines as intermediates for the synthesis of some anticancer and antifungal drugs, see: Bergmann et al. (1959) Table 1 Hydrogen-bond geometry (Å , ).

Comment
The fluoro-containing pyrimidines have been used as a kind of important intermediates for the synthesis of some anticancer drugs and antifungal drugs (Bergmann et al., 1959;Butters et al., 2001). In the synthesis of the novel antifungal drug-Voriconazole, we have prepared the title compound 6-ethyl-5-fluoro-2-methoxypyrimidin-4(3H)-one as an intermediate, which was synthesized by reacting methyl 2-fluoro-3-oxopentanoate with o-methylisourea sulfate in a solution of sodium methylate in methanol.
The molecular structure of the title compound, (I), is illustrated in Fig. 1. The bond lenghth of C4-O2 and C1-O1 are 1.238 (3) and 1.321 (2) Å, respectively, corresponding to a double C=O bond and a Csp 2 -O single bond. In the sixmembered pyrimidine ring, the even bond lengths of C-N and C-C are 1.361 (3) and 1.380 (3) Å, respectively, indicating these bond forming a conjugating system. The atoms in the pyrimidine ring (C1-C4/N1/N2) form a good plane with a mean deviation of 0.006 Å. An intermolecular N-H···O hydrogen bond was found to link two molecules as a pair ( Fig. 2 and Table 1).

Experimental
To a 250 ml flask was added a 80 ml solution of 25% sodium methylate in methanol. The solution was cooled to 278 K, and then 40 g o-methylisourea sulfate and 20 g methyl 2-fluoro-3-oxopentanoate were added. After the addition, the mixture were stirred at 298 K for half an hour and refluxed for three hours. The mixture was concentrated under reduced pressure, and the residue was dissolved with 200 ml water. The aqueous solution was treated with 6M hydrochloric acid to pH3 and cooled in refrigerator for three hours. The resulted precipitate was filtered, to give 12.5 g product as white powder (yield 53.8%; m.p. 447-449 K). Since the product was not found to be suitable for X-ray diffraction studies, a few samples were dissolved in absolute ethanol, which was allowed to evaporate slowly to give colourless crystals of (I) suitable for X-ray diffraction studies.

Refinement
H atoms were placed in calculated positions (C-H = 0.96-0.97 Å and N-H = 0.86 Å) and refined using a riding model, with U iso (H) = 1.2U eq (C, N) or 1.5U eq (methyl C).
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of (I) with 30% probability displacement ellipsoids. Refinement. Refinement using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 σ(F 2 ) is used only for calculating R-factor (gt).