Theoretical study of cyclization of 2′-hydroxychalcone

The isomerization mechanism of 2′(OH)chalcone (1) in flavanone (2) was studied. The calculations were performed with the semiempirical method AM1, using totally optimized molecular geometries. A 6-step mechanism including several equilibrium states was proposed. It was concluded that: (a) At the conformational equilibrium of 1 there could be 43.9% of s-cis conformer; (b) The acid dissociation of 1 trans-s-trans is considerable; (c) The E_E, ΔH_f and net charges show that the rotation of ring A of 1 and the formation of ring C of 2 occurs without greater impairments; (d) Although the keto structure is the most stable one, the enolate of 2 is present in the reaction medium; (e) The conversion of enol of 2 in the keto form would be the limiting step of the analyzed isomerization rate.     

Synthesis, X-ray structure and properties of a new nitrite-bound copper(II) complex with 2-(3,5- dimethylpyrazol-1-ylmethyl)pyridine in a CuN4(O) coordination

Synthesis and characterization of a nitrite-bound copper(II) compound [CuL⁴)₂(ONO)]ClO₄ have been achieved (L⁴ = 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine]. The bidentate ligand L⁴ provides a pyridine and a pyrazole donor site; however, they are separated by a methylene spacer. The complex has been structurally characterized and it belongs to only a handful of complexes having nitrito-bound mononuclear copper(II) centre. The metal atom has a distorted square pyramidal geometry with the copper atom displaced from the equatorial plane by 0.25 Å. In MeCN solution the green complex exhibits a broad ligand-field transition at 655 nm with a shoulder at 675 nm and in dichloromethane-toluene glass (80 K) it exhibits an EPR spectral feature characteristic of the unpaired electron in the d_x²−y² orbital. Variable-temperature (80–300 K) magnetic susceptibility measurements in the solid state as well as room temperature measurement in MeCN solution reveal mononuclear magnetically dilute copper(II) centre. When examined by cyclic voltammetry (MeCN solution) it displays electrochemically irreversible Cu^II---Cu^I response [cathodic peak potential, E_pc (V vs saturated calomel electrode (SCE)): −0.32]. An oxidative response is observed at 1.14 V, probably due to bound-nitrite oxidation and is partially removed to generate a solvated complex at the electrode surface. The latter species gives rise to reversible Cu^II---Cu^I redox response [ ].     

Reinvestigation of the Nazarov cyclization of 1-(3-hydroxypropynyl)cyclododecan-1-ol to bicyclo[10.3.0]pentadec-1(12)-en-13-one

Reinvestigation of the acid-catalyzed cyclization of 1-(3-hydroxypropynyl)cyclododecan-1-ol under the conditions of the Nazarov reaction demonstrated that this conversion yields two isomeric bicyclic ketones, namely, bicyclo[10.3.0]pentadec-1(12)-en-13-one and bicyclo[10.3.0]pentadec-1-en-3-one. The latter compound is thermodynamically less stable. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1325–1327, July, 1997.     

Correlation NMR spectroscopy of 1,1-dichloro-2,3,4,5-tetraphenyl-1-germacyclopenta-2,4-diene

Assignment of all of the signals in the¹H and¹³C NMR spectra of 1,1-dichloro-2,3,4,5-tetraphenyl-l-germacyclopenta-2,4-diene has been carried out using two-dimensional NMR spectroscopy. Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya, No. 3, pp. 623–625, March, 1997.     

Stereocontrolled synthesis of (+)- and (−)-iridomyrmecin from citronellene enantiomers

Natural (+)-iridomyrmecin and its unnatural enantiomer (−)-iridomyrmecin were synthesized by intramolecular [3+2] dipolar cycloaddition of silyl nitronates that had been generated from the nitro derivatives of (+)- and (−)-citronellenes, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1683–1687, September, 1997.     

205T1-NMR and UV-Visible spectroscopic determination of the formation constants of aqueous thallium(I) hydroxo-complexes

The hydrolysis of T1(I) has been studied at 25°C using²⁰⁵T1-NMR spectroscopy and UV-Vis spectrophotometry in aqueous solutions with ionic strengths maintained by NaC10₄ at 2, 4, 6, and 8M. The formation constant and the spectral characteristics for the hydroxo complex, T10Hℴ have been determined. At high hydroxide ion concentrations there is clear evidence from the UV-Vis data for the formation of a T1(OH)₂-species. The spectrum and an estimated formation constant for this second hydroxo complex are also reported.     

Reaction ofo-aminobenzohydroxamic acid with aldehydes

The reaction of o-aminobenzohydroxamic acid with aliphatic, aromatic, or heterocyclic aldehydes leads to the formation of derivatives of 3-hydroxy-1,2-dihydroquinazolin-4-one. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 115–117, January, 1997.     

Conversion ofn-hexane over Pt?Sn/γ-Al2O3 catalyst

Conversion ofn-hexane has been applied as a test reaction to study differences between the series of Pt−Sn/γ-Al₂O₃ catalysts obtainedvia different methods of preparation. Preliminary results of catalytic experiments have been compared with some changes occurring on the catalysts surfaces as the results of the preparation technique applied. It has been found that catalysts with the second metal (Sn) introduced to the support by the coprecipitation technique were much more stable in comparison to the catalysts where the tin component has been added by the impregnation method, however, we have not observed large differences in catalytic activity.     

Oxidation of γ-stannyl sulfides by monochloramine CB and hydrogen peroxide

The first γ-trimethylstannyl sulfimide, Me³Sn(CH₂)₃S(=NSO₂Ar)C₅H₁₁-n, was synthesized by oxidative imination of Me₃Sn(CH₂)₃SC₅H₁₁-n with ArSO₂(Na)Cl (Ar=C₆H₄Cl-4). Oxidation of γ-trimethylstannyl sulfimide by an alkaline solution of H₂O₂ gave γ-trimethylstannyl sulfoximide, Me₃Sn(CH₂)₃S(O)(=NSO₂Ar)C₅H₁₁-n, and γ-trimethylstannyl sulfone, Me₃Sn(CH₂)₃SO₂C₅H₁₁-n, the latter compound resulting from hydrolysis of the arylsulfimide group. Oxidation of stannyl sulfide by hydrogen peroxide yielded γ-trimethylstannyl sulfoxide, Me₃Sn(CH₂)₃S(O)C₅H₁₁-n (under mild conditions) or γ-trimethylstannyl sulfone (under more severe conditions). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 371–374, February, 1997.     

A convergent synthesis of octadeca-2E, 13Z-dienyl acetate, a pheromone component ofSynanthedon tipuliformis C.

A convergent synthesis of octadeca-2E, 13Z-dienyl acetate, a pheromone component ofSynanthedon tipuliformis C., has been developed. The synthesis is based on cross-coupling of 8-iodooct-2E-en-I-ol THP ether with dec-5Z-enyl bromide catalyzed by CuBr. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1529–1531, August, 1997.