Nam Sook Cho

Synthesis of silyl and stannyl pyrimidines

Abstract 2,4-Dimethoxy- and 2,4-dibenzyloxy-5-lithiopyrimidines, obtained from the corresponding substituted 5-bromopyrimidines, react with trimethylsilyl chloride or trimethylstannyl chloride to give the appropriate 5-trimethylsilyl or 5-trimethylstannyl derivatives. The following compounds were synthesized by this reaction sequence: 2,4-dimethoxy-5-trimethylsilylpyrimidine (2), 2,4-dibenzyloxy-5-trimethylsilylpyrimidine (3), 2,4-dimethoxy-5-trimethylstannylpyrimidine (4), and 2,4-dibenzyloxy-5-trimethylstannylpyrimidine (5). Similarly, 6-chloro-2,4-dimethoxypyrimidine was converted into the 5-lithio derivative which subsequently gave 6-chloro-2,4-dimethoxy-5-trimethylsilylpyrimidine (6) and 6-chloro-2,4-dimethoxy-5-trimethylstannylpyrimidine (7). In a new modified synthesis of 5-trimethylsilyluracil (1), 2,4-dibenzyloxy-5-trimethylsilylpyrimidine (3) was smoothly converted into 1 by reaction with trimethylsilyl iodide.

5-Amino-1,3,4-thia-diazol-2(3H)-one.

The asymmetric unit of the title compound, C2H3N3OS, contains three independent molecules which are essentially planar, with r.m.s. deviations of 0.011 (2)–0.027 (2) Å from the mean plane defined by the seven non-H atoms. In the crystal, N—H⋯N and N—H⋯O hydrogen bonds link the molecules into a sheet parallel to the (111) plane.

5-Eth-oxy-1,3,4-thia-diazole-2(3H)-thione.

In the title compound, C4H6N2OS2, the dihedral angle between the five-membered heterocyclic ring and the plane of the ethoxy group is 4.9 (2)°. The 1,3,4-thiadiazole-2-thione unit is planar, with an r.m.s. deviation of 0.011 Å from the corresponding squares plane defined by the seven constituent atoms. In the crystal, pairs of N—H⋯S hydrogen bonds link the molecules into inversion dimers.

Ethyl N-[(benz-yloxy)thio-carbon-yl]carbamate.

In the title compound, C11H13NO3S, the dihedral angle between the benzyl and carbamate groups is 12.67 (10)°. The S atom and the carbonyl O atom are positioned anti to each other. In the crystal, pairs of N—H⋯S hydrogen bonds link molecules into inversion dimers.

N-(5-Eth­oxy-1,3,4-thia­diazol-2-yl)benzamide

In the title compound, C11H11N3O2S, the dihedral angle between the thiadiazole and phenyl rings is 28.08 (7)°. In the crystal, molecules are linked into an inversion dimer by a pair of intermolecular N—H⋯N hydrogen bonds with an R 2 2(8) graph-set motif.

Synthetic and tautomeric studies of 5-amino-2,3-dihydro-1,2,4-oxadiazol-3-one

5-Amino-2,3-dihydro-1,2,4-oxadiazol-3-one 2 was synthesized as an analogue of cytosine. Among the possible four tautomers it was established by spectroscopic methods and ab initio calculations that it exists as a lactam form 2b like cytosine. The NH is more acidic than NH2, thus it could be regioselectively mesylated and acetylated under basic conditions.

5,5′-[1,4-Phenyl­enebis(methyl­enesulfanedi­yl)]bis­[1,3,4-thia­diazol-2(3H)-one] dimethyl sulfoxide disolvate

The asymmetric unit of the title compound, C12H10N4O2S4·2C2H6OS, contains one half of the p-xylene molecule and one dimethyl sulfoxide molecule. The p-xylene molecule is located about a crystallographic inversion centre. In the molecule, the thiadiazole and benzene rings are almost perpendicular to one another, with a dihedral angle of 88.95 (6)°. In the crystal, an N—H⋯O hydrogen bond is observed between the two components. The dimethyl sulfoxide molecule is disordered over two orientations with an occupancy ratio of 0.879 (1):0.121 (1).

N-(5-Sulfanyl­idene-4,5-dihydro-1,3,4-thia­diazol-2-yl)acetamide dimethyl sulfoxide disolvate

In the title compound, C4H5N3OS2·2C2H6OS, the five-membered heterocyclic ring and the N—(C=O)—C plane of the acetamide group are essentially co-planar, with a dihedral angle of 1.25 (3)°. Intermolecular N—H⋯O hydrogen bonds between the acetamide compound and the dimethyl sulfoxide molecules stabilize the crystal structure. The two dimethyl sulfoxide molecules are each disordered over two positions with occupancy ratios of 0.605 (2):0.395 (2) and 0.8629 (18):0.1371 (18).

5-({3-[(5-Amino-1,3,4-thia-diazol-2-yl)sulfanylmeth-yl]benz-yl}sulfan-yl)-1,3,4-thia-diazol-2-amine.

In the title compound, C12H12N6S4, the two terminal thiadiazole rings are twisted with respect to the central benzene ring, making dihedral angles of 54.28 (4) and 76.56 (3)°. The dihedral angle between the two thiadiazole rings is 27.77 (4)°. Intermolecular N—H⋯N hydrogen bonds stabilize the crystal packing, linking the molecules into a tape along the b axis.

4,17,25,26-Tetraaza-6,9,12,15-tetra­oxa-2,19,21,24-tetrathiatricyclo[18.4.11,4.117,20]hexacosa-1(25),20(26)-diene-3,5,16,18-tetraone

The title compound, C14H16N4O8S4, has crystallographic C2 symmetry with half a molecule in the asymmetric unit and a dihedral angle of 58.7 (1)° between the two planar 1,3,4-thiadiazole five-membered rings of the macrocyclic, giving the molecule a twisted conformation.