Yuri V. Gatilov

Stereochemistry of hydrogen peroxide-acetic acid oxidation of ursolic acid and related compounds

Abstract Stereochemistry of a number of oxidized derivatives of ursolic acid was established using NMR data and X-ray analysis. Full signal assignments were made in 1H and 13C NMR spectra of 26 natural and synthetic ursane type triterpenoids. Possible mechanisms of oxidation of ursolic acid and related compounds by peracids, as well as mechanisms of secondary processes, were formulated basing on chemical behavior and molecular mechanics calculations of the starting materials and certain intermediate species.

Cyclic aryleneazachalcogenenes—VI. Synthesis, crystal and molecular structure of 5,6,7,8-tetrafluoro-1,3,2,4-benzodithiadiazine, a formally antiaromatic stable compound

Abstract 1-Pentafluorophenyl-4-trimethylsilyl-2,4-diaza-1,3-dithia-2,3-butadiene is cyclized by CsF in acetonitrile to 5,6,7,8-tetrafluoro-1,3,2,4-benzodithiadiazine (54% yield), a thermodynamically stable formally antiaromatic 12Π-electron compound having an almost planar molecular geometry, as shown by the X-ray structure analysis data. The crystal and molecular structure of the polyfluorinated derivative appreciably differ from those of its hydrocarbon analogue, 1,3,2,4-benzodithiadiazine.

Interaction of 1,2,5-Chalcogenadiazole Derivatives with Thiophenolate: Hypercoordination with Formation of Interchalcogen Bond versus Reduction to Radical Anion

According to the DFT calculations, [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazole (4), [1,2,5]selenadiazolo[3,4-c][1,2,5]thiadiazole (5), 3,4-dicyano-1,2,5-thiadiazole (6), and 3,4-dicyano-1,2,5-selenadiazole (7) have nearly the same positive electron affinity (EA). Under the CV conditions they readily produce long-lived π-delocalized radical anions (π-RAs) characterized by EPR. Whereas 4 and 5 were chemically reduced into the π-RAs with thiophenolate (PhS(-)), 6 did not react and 7 formed a product of hypercoordination at the Se center (9) isolated in the form of the thermally stable salt [K(18-crown-6)][9] (10). The latter type of reactivity has never been observed previously for any 1,2,5-chalcogenadiazole derivatives. The X-ray structure of salt 10 revealed that the Se-S distance in the anion 9 (2.722 Å) is ca. 0.5 Å longer than the sum of the covalent radii of these atoms but ca. 1 Å shorter than the sum of their van der Waals radii. According to the QTAIM and NBO analysis, the Se-S bond in 9 can be considered a donor-acceptor bond whose formation leads to transfer of ca. 40% of negative charge from PhS(-) onto the heterocycle. For various PhS(-)/1,2,5-chalcogenadiazole reaction systems, thermodynamics and kinetics were theoretically studied to rationalize the interchalcogen hypercoordination vs reduction to π-RA dichotomy. It is predicted that interaction between PhS(-) and 3,4-dicyano-1,2,5-telluradiazole (12), whose EA slightly exceeds that of 6 and 7, will lead to hypercoordinate anion (17) with the interchalcogen Te-S bond being stronger than the Se-S bond observed in anion 9.

Planar 1,3λ4δ2,2,4‐Benzodithiadiazine and Its Nonplanar 5,6,7,8‐Tetrafluoro Derivative: Gas‐Phase Structures Studied by Electron Diffraction and Ab Initio Calculations

The gas-phase molecular structures of 1,3lambda4delta2,2,4-benzodithiadiazine and 5,6,7,8-tetrafluoro-1,3lambda4delta2,2,4-benzodithiadiazine have been investigated by ab initio calculations and electron diffraction using the SARACEN method of structural analysis. Important structural parameters (r(h1) structure) for the parent compound were found to be: 1.546(3), r(S-N) 1.697(5), r(C-S) 1.784(5), and r(C-N) 1.393(6) A. For the tetrafluoro derivative, these are (r(h1) structure): 1.552(3), r(S-N) 1.723(8), r(C-S) 1.812(9), and r(C-N) 1.396(7) A. Furthermore, the GED experiment (Gas Electron Diffraction) quite convincingly demonstrates the nonplanarity of the former and the planarity of the latter in agreement with DFT calculations; but the results contradict calculations at the MP2 level. The effect of the fluorine atoms on the conformations of the molecules is discussed.

1,2,3-benzodithiazolyl radicals formed by thermolysis and photolysis of 1,3,2,4-benzodithiadiazines

Mild thermolysis (at 110–150°C) of 1,3,2,4-benzodithiadiazine 1 and its carbocyclic substituted derivatives 2–15 in hydrocarbon solvents quantitatively yields stable 1,2,3-benzodithiazolyl π-radicals 1•–15•. Kinetics of this reaction can be described as a first-order process. Arrhenius parameters of the effective rate constant are Ea = 80 ± 8 kJ mol−1, k0 = 106.4 ± 1.1 s−1 for 1 in squalane. Room-temperature photolysis of 1 in hydrocarbon solvents also affords radical 1• in nearly quantitative yield. Quantum yield of photolysis is wavelength dependent and is equal to 0.08 ± 0.01 at 313 nm in benzene. Experimental hyperfine coupling (hfc) constants in the ESR spectra of 1•–15• agree fairly well with those calculated at the B3LYP/CC-pVDZ level of theory. Spin density distribution in 1•–15• is in striking contrast to that of isomeric 1,3,2-benzodithiazolyls but resembles the distribution in correspondingly substituted benzyl radicals. ESR linewidths of radicals 1•-15• display some features likely related to spin-rotational relaxation.

Synthesis of new chiral heterocycles of the pyrazole and 2-isoxazoline types from (+)-3-carene.

Abstract Preparation of chiral heterocyclic compounds of the pyrazole and 2-isoxazoline types starting from natural monoterpene hydrocarbon (+)-3-carene is described. Stereochemical assignment of the compounds synthesized is made by NMR spectroscopy and X-ray analysis together with the data obtained by molecular mechanics and quantum chemical calculations.

Optically active ZnII and PtII complexes of the 3-carene type α-amino oxime

Abstract (1S,3S,6R)-3- N,N- Dimethylaminocaran-4-one E-oxime forms stable 1:1 chelate complexes with ZnCl2 and PtCl2 whose structures are supported by X-ray, 1H, 13C, 14N and 195Pt NMR data. The conformation of the six-membered carbon cycle in the complexes was found to be changed as compared to the starting compound.

Molecular complexes of octafluoronaphthalene with acyclic and heterocyclic sulfur–nitrogen compounds

Abstract Mismatched molecular 1:1 complexes were prepared from C10F8 and sulfur diimides ArNSNAr 1 and ArNSN–SiMe3 2, 3 (1, 2: Ar=2,6–dimethylphenyl; 3: Ar=phenyl). In the case of 2, the complexation is accompanied by the unexpected cyclization of 2 into 7-methyl-2,1-benzisothiazole 4. The X-ray molecular structures of C10F8·1, C10F8·3 and C10F8 are presented; in C10F8·4 the 7-methyl-2,1-benzisothiazole 4 is highly disordered. The complexes provide very rare examples of markedly bent (C10F8·1), polyheteroatom (C10F8·3) and heterocyclic (C10F8·4) molecules involved in non-covalent arene-polyfluoroarene π-stacking interactions.

Study of chiral β-enaminones prepared from pyrrolidine, cytisine, salsoline and 2-amino-1-(4-nitrophenyl)propane-1,3-diol: resolution of salsoline via diastereomeric modified carane-type β-enaminones

Abstract A series of novel optically active β-enaminones have been prepared regio- and stereoselectively from primary and secondary amines (pyrrolidine, cytisine salsoline and 2-amino-1-(4-nitrophenyl)propane-1,3-diol) and (+)-3-carene-derived β-chlorovinylketone. Resolution of the isoquinoline alkaloid salsoline has been demonstrated as well as isolation of a single diastereomeric adduct from racemic 2-amino-1-(4-nitrophenyl)propane-1,3-diol.

Synthesis of extended acyclic azathienes. Crystal and molecular structure of two compounds, Ar(SNSN)nSiMe3 (Ar 2-O2NC6H4; n 1,2)

Abstract The 1:1 reaction of (Me3SiNSN)2S with ArSCl gives Ar(SNSN)2SiMe3, while the 1:2 reaction gives (ArSN)2S and (SN)4 if Ar = Ph, and (ArSNSN)2S if Ar = nitrophenyl. Thus, the aromatic nitro groups inhibit spontaneous shortening of azathiene chains of (ArSNSN)2S, but they do not stabilize the compounds containing a chain of 17 alternating nitrogen and sulphur atoms [Ar(SNSN)2SiMe3 + SCl2, 2:1] which are shortened to (ArSNSN)2S. As shown by X-ray structure analysis, the configuration of the azathiene chains in the compounds Ar(SNSN)nSiMe3 (Ar = 2- O2NC6H4; n = 1, 2) is similar to that of (SN)x macromolecules: Z, E, n = 1; Z, E, Z, E, n = 2. At n = 1 the molecule is planar, at n = 2 (the longest oligomer azathiene chain with established real geometry) the non-hydrogen atoms lie on the cylindrical surface with a radius of ca 50 A.