Reaction of cyclooctatetraene dianion with halosilanes: Preparation of 3,4-(tetramethyldisiloxy)-1,3,5-cyclooctatriene and 5,8-bis(trimethylsilyl)-1,3,6-cyclooctatriene

The dipotassium salt of cyclooctatetraene dianion, COT^2?, reacts at ?35° with dimethyldichlorosilane, followed by aqueous workup, to give C₈H₈[Si(CH₃)₂]₂O (I) in 4.4% yield. On the basis of spectroscopic (IR, mass, ¹H and ¹³C NMR spectra) and chemical data, compound 1 is formulated as 3,4-(tetramethyldisiloxy)-l,3,5-cyclooctatriene. Reaction of COT^2? with trimethylchlorosilane yields the compound C₈H₈[Si(CH₃)₃]₂ in 50% yield, which is shown to be 5,8-bis(trimethylsilyl)-1,3,6-cyclooctatriene.     

Kinetic and equilibrium study of gas-phase interconversions of 1,3,6-cyclooctatriene, 1,3,5-cyclooctatriene and bicyclo[4.2.0]octa-2,4-diene

The gas-phase equilibrium and rate constants for the isomerizations of 1,3,6-cyclooctatriene (136COT) to 1,3,5-cyclooctatriene (135COT) [reaction (1)] and bicyclo[4.2.0]octa-2,4-diene (BCO) to 135COT [reaction (-2)] have been measured between 390 and 490 K and between 330 and 475 K, respectively. The rate constant of reaction (1) obeys the Arrhenius equation The corresponding equilibrium constant is given by the van′t Hoff equation The strain energy of the 136COT ring is calculated to be 31.7 kJ/mol, based on the known value of 37.2 kJ/mol for 135COT, and ΔH(298 K) for gaseous 136COT is 196.3 kJ/mol. The rate constant of reaction (-2) obeys the Arrhenius equation The equilibrium constant for 135COT ? BCO fits the van′t Hoff equation The strain energy of the BCO skeleton is calculated to be 108.3 kJ/mol, and ΔH(298 K) for gaseous BCO is 183.3 kJ/mol.     

Chemistry of Ru(eta6-1,3,5-cyclooctatriene)(eta2-dimethyl fumarate)2

The chemistry of a novel zerovalent Ru complex, Ru(eta6-cot)(eta2-dmfm)2 (1) (cot=1,3,5-cyclooctatriene; dmfm=dimethyl fumarate), is reviewed with a focus on its reactivity toward phosphines, amines, and H2O, as well as arenes and p-quinones. A variety of novel zerovalent Ru complexes were synthesized from Ru(eta6-cot)(eta2-dmfm)2 (1), and it was shown that the complexes preferably bear both electron-donating and -accepting ligands simultaneously to exhibit thermodynamic stability. The first isolable zerovalent Ru aqua complexes were successfully prepared, and in these complexes, the generation of a chiral center on the O atom of the coordinated H2O was disclosed. In addition, the characteristic catalytic activity of 1 in organic synthesis was considered by reviewing recently developed novel reactions: (i) dimerization of 2,5-norbornadiene to pentacyclo[6.6.0.0(2,6).0(3,13).0(10,14)]tetradeca-4,11-diene (PCTD), (ii) intramolecular hydroamination of aminoalkynes to cyclic imines, (iii) formal [4+2] cycloaddition of alkynes with dmfm to trans-4-cyclohexene-1,2-dicarboxylates, and (iv) co-dimerization of dihydrofurans with alpha,beta-unsaturated esters to 2-alkylidenetetrahydrofurans. The products obtained here are expected to be used as novel functional organic monomers.     

Chemistry of new dimethyl-benzo,-1,3,6-oxadiazepine and 1,3,5-triazepine derivatives as anticancer agents

A series of novel substituted 2,4-dimethyl-benzo[f][1,3,5] triazepine, such as 2-thioxopyrimidinone(4), 2-oxopyridine-3-carbonitrile(6), benzamide(8), N’-(6-oxopyrimidine)benzohydrazide(10), 1-(4-(1,3,4-oxadiazole)thiophene)ethan-one(12), 1-(4-methylthiophene-3-carbonyl)pyrazolidine-dione(14), 1-(4-(pyrazole-carbonyl)-3-methylthiophene)ethanone(16), ethyl dimethylthieno[2,3-b]pyridine-2-carboxylate (18), and 2-thioxo-thieno[2,3-d]pyrimidinone(20) derivatives, were synthesized from 2,4-dimethyl benzo[d] [1,3,6] oxadiazepine (2). The structures of these newly synthesized compounds were established on the basis of their spectral data and elemental analysis. These compounds were also screened for their anti-tumor activities. Some of the prepared compounds showed promising activities for example; benzotriazepine, thienopyrimidine, oxadiazole, and thiophene moiety displayed cytotoxic activity.     

CBS-QB3 computational examination of substituent effects on the interconversion of 1,3,5-cyclooctatriene and bicyclo[4.2.0]-2,4-octadiene

The position of equilibrium between 7-substituted and 7,8-disubstituted 1,3,5-cyclooctatrienes (1) and the corresponding valence isomeric bicyclo[4.2.0]-2,4-octadienes (2) is highly sensitive to the nature of substituents. In particular, the difference between trans and cis-7,8 isomers in this regard has never been explained. These differences have been clarified by computational means. The CBS-QB3 hybrid quantum chemical computational method reproduces the experimental free energy differences between a series of cyclooctatrienes (1) and the corresponding valence isomers (2) with excellent accuracy; the MAD and root mean square (rms) differences are 0.54 kcal/mol and 0.58 kcal/mol, respectively. The energy barriers between several derivatives of 1 and 2 were computed with good accuracy (MAD=1.3 kcal/mol and rms=1.5 kcal/mol) by the same procedure. The dihedral angle between the substituents increases upon electrocyclic conversion of trans-7,8-disubstituted cyclooctatrienes to the bicyclic isomer and decreases for the corresponding cis isomers. This differential effect explains both the higher bicyclic proportion at equilibrium and the faster rate of cyclization in the trans series compared to cis.     

The stereodynamics of 3,5-bis(trifluoromethylsulfonyl)-1,3,5-oxadiazinane and 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane—an experimental and theoretical study

Multinuclear dynamic NMR spectroscopy of 3,5-bis(trifluoromethylsulfonyl)-1,3,5-oxadiazinane (3) revealed the existence of two conformers with differently oriented CF₃ groups with respect to the ring, and two dynamic processes: ring inversion and restricted rotation about the N-S bond. Two transition states connecting the two conformers and corresponding to clockwise and counterclockwise rotations about the N-S bond were found; the calculated activation barriers of about 12 kcal/mol are in excellent agreement with those measured experimentally for the related molecule 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane (1). X-ray analysis proved the existence of the symmetric isomer of 3, which is the minor isomer in solutions but the only one in the crystal due to packing effects. The normal Perlin effect (JCH_ax<JCH_eq) was observed for 2(6)-CH₂ in 3, whereas the reversed Perlin effect was found for the 4-CH₂ group in 3 as well as for all CH₂ groups in 1 both experimentally and theoretically. The latter effect in compounds 1, 3, and 1-(methylsulfonyl)-3,5-bis(trifluoromethylsulfonyl)-1,3,5-triazinane (2) can be considered as a genuine reverse Perlin effect since larger values of ¹J_CH are observed for longer C-H bonds.     

Ru(η-1,3,5-cyclooctatriene)(η-dimethyl fumarate)2: a novel, versatile zerovalent ruthenium complex with electron-deficient olefinic ligands

The reactivity of a novel zerovalent ruthenium complex, Ru(η⁶-cot)(η²-dmfm)₂ (cot = 1,3,5-cyclooctatriene, dmfm, =dimethyl fumarate), which is readily prepared from Ru(η⁴-cod)(η⁶-cot) (cod = 1,5-cyclooctadiene) and dmfm was examined. The reaction with monodentate phosphine or amine ligands gave Ru(η⁶-cot)(dmfm)(L) (L = ligand) via dissociation of dmfm. Among bidentate phosphines, dppm (dppm = bis(diphenylphosphino)methane) reacted to give Ru(η⁴-cot)(dmfm)(dppm) along with releasing a dmfm ligand. In the case of dppe (dppe = 1,2-bis(diphenylphosphino)ethane), two types of complexes were obtained depending on the reaction conditions, Ru(dmfm)(dppe)₂ and an alkyl alkenyl complex; in the formation of the latter complex, sp² C-H bond activation of dmfm occurred. Ru(η⁴-cot)(dmfm)(N^?N) and Ru(dmfm)₂ (N^?N^?N) were formed by reacting with bidentate and tridentate nitrogen ligands. The reactions with arenes gave π-coordinated complexes, Ru(η⁶-arene)(dmfm)₂. p-Quinones and a p-biqunone reacted to give Ru(η⁶-cot)(p-quinone) and {Ru(η⁶-cot)}₂(p-biquinone), respectively, along with the dissociation of two dmfm ligands. It was found that low-valent ruthenium complexes preferably bear both electron-donating and accepting ligands simultaneously to be thermodynamically stable.     

[f]-Fused purine-2,6-diones: Synthesis of new [1,3,5]- and [1,3,6]-thiadiazepino-[3,2-f]-purine ring systems

Summary 6-Phenyl-1,3-dimethyl-2,4-dioxo-1,2,3,4,8,9-hexahydro-[1,3,5]-thiadiazepino-[3,2-f]-purine (5) was obtained by a three-step synthesis from 8-mercapto-1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione (1) and 2-(benzoylamino)-ethyl chloride (2)via 8-(benzoylaminoethylthio)-1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione (3) and its chloromido derivative4. The analogous 9-phenyl-1,3-dimethyl-2,4-dioxo-1,2,3,4,6,7-hexahydro-[1,3,6]-thiadiazepino-[3,2-f]-purine (7) was synthesized either from compound1 and N-(2-chloroethyl)-benzimido chloridevia N-(chloroethyl)-S-(1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydro-7H-purin-8-yl)-benzothioimide (6), or alternatively from 7-(2-benzoylaminoethyl)-8-bromo-1,3-dimethyl-3,7-dihydro-1H-purine-2,6-dione (9), its 8-mercapto derivative10 and the corresponding chloroimido compound11 being the intermediates.Part of this paper was presented as a preliminary report at the Congress of Czech and Slovak Chemical Societies, Olomouc, Czech Republic, September 13–16, 1993     

Condensed 1,3,5-triazines: 1,3,4-Thiadiazolo[3,2-a]-1,3,5-triazines and isoxazolo[2,3-a]-1,3,5-triazines

A convenient route is reported for the synthesis of substituted 1,3,4-thiadiazolo[3,2-a]-1,3,5-triazine-5,7-diones and isoxazolo[2,3-a]-1,3,5-triazines. Condensation of the appropriately substituted 2-amino-1,3,4-thiadiazole and 3-aminoisoxazole with phenoxycarbonyl isocyanate provides the desired target compounds in fair yield.     

Molecular conformation of cyclenes: Part IX. Asymmetrical 1,3,6-cyclononatriene and 1,3,6-cyclodecatriene

The strain energy of the most probable conformers of 1,3,6-cyclononatriene and 1,3,6-cyclodecatriene, which are asymmetrical compounds, has been calculated as a function of various geometrical parameters by means of the semiempirical Hendrickson's treatment, partially modified. The most stable conformation of 1,3,6-cyclononatriene is a member of the all-cis family, while a transcis-trans structure is the most stable among the 1,3,6-cyclodecatriene conformations. In this latter compound however, the energy minima of the all-cis, trans-cis-cis, and cis-cis-trans conformers also appear to be close to each other. Some possible interconversions are also discussed.     

Stereodynamics of 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane: experimental and theoretical analysis

Dynamic NMR of 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane reveals two dynamic processes: ring inversion leading to equilibrium between two degenerate rotamers of C_s symmetry (ΔG^≠ = 13.5 kcal/mol), and rotation about the S-N bond leading to equilibrium between the C_s (more stable) and C_3v (2.12 kcal/mol less stable) rotamers (ΔG^≠ = 13.0 kcal/mol).