CIF access Acta Cryst. (1998). C54, IUC9800030 [ doi:10.1107/S0108270198099533 ] 5-[Bis(trimethylsilyl)amino]-2-methoxy-3-methyl-6-(trimethylsilylamino)pyrimidin-4(3H)-one S. Molina, J. Cobo, M. Nogueras, A. Sanchez, G. Ferguson and J. N. Low Abstract The analysis establishes the structure of the title compound, C 15 H 34 N 4 O 2 Si 3 . There is disorder of one of the SiMe 3 groups, otherwise dimensions are normal. The N—H group of the molecule forms an intramolecular N—H···N hydrogen bond [N···N 2.836 (3) Å] and is shielded from possible intermolecular acceptors by the SiMe 3 groups. Comment The title compound was prepared as an intermediate in the synthesis of other heterocyclic compounds. We wished, in this case, to modify the 4,5-diamino-2-methoxy-3-methylpyrimidin-4(3H)-one heterocyclic nucleus using an electron-deficient reactant, and used trimethylsilyl to protect the amino group from unwanted reactions. Experimental The title compound was prepared by refluxing a mixture of 5,6-diamino-2-methoxy-3-methylpyrimidin-4(3H)-one (2 g, 11.7 mmol) in hexamethyldisilazane (HMDS, 30 ml) in the presence of ammonium sulfate (50 mg) for 20 h. The resulting mixture was cooled to 253 K and produced several crystalline fractions of the title compound; these were filtered off and washed with hexane (yield: 3.726 g, 83%). Refinement The title compound crystallized in the monoclinic system; space group P2 1 /n from the systematic absences. H atoms were treated as riding atoms (C—H 0.96 and N—H 0.86 Å). It was clear from the elongated anisotropic displacement ellipsoid shapes that the methyl groups at Si52 were disordered. This was modelled by employing two equal-occupancy SiMe 3 groups (six 0.5 occupancy methyl groups) with appropriate restraints. Computing details Data collection: CAD-4-PC (Enraf-Nonius, 1992); cell refinement: SET4 and CELDIM in CAD-4-PC; data reduction: DATRD2 in NRCVAX96 (Gabe et al., 1989); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: NRCVAX96 and SHELXL97 (Sheldrick, 1997b); molecular graphics: NRCVAX96, ORTEPII (John- son, 1976) and PLATON (Spek, 1998); software used to prepare material for publication: NRCVAX96, SHELXL97 and WORDPERFECT macro PRPCIF97 (Ferguson, 1997). 5-Bis(trimethylsilyl)amino-2-methoxy-3-methyl-6-(trimethylsilylamino)- pyrimidin-4(3H)-one