Spectroscopic studies of 1,2-diphenyl-3,3,4,4-tetramethylcyclobutene and 3,4-diphenyl-2,5-dimethyl-2,4-hexadiene radical cations and their possible interconversion

In order to study radical cation rearrangements, the species generated by γ-irradiation of 1,2-diphenyl-3,3,4, 4-tetramethylcyclobutene (CB) and 3,4-diphenyl-2,5-dimethyl-2,4-hexadiene (BD) in frozen Freon solutions were studied by monitoring their EPR and visible absorption spectra. The optical and EPR spectra are indicative of CB⁺ and BD⁺ Conversion of CB⁺ to BD⁺ is not a dominant process at low temperatures in CFCl₃ or the Freon mixture (50:50 CFCl₃:CF₂BrCF₂Br) but can be assisted photochemically.     

Structure of 3,4-dinitro-3,4-dimethyl-1,1-diphenyl-1-silacyclopentane

Conclusions 3,4-Dinitro-3,4-dimethyl-1,1-diphenyl-1-silacyclopentane in the liquid phase has a half-chair conformation, and in the solid phase, its conformation is described by a form intermediate between the half-chair and the envelope conformation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2731–2736, December, 1985.     

1,3-Dimethoxy-1,3-dimethyl-1,3-diphenyl- and 1,3-dimethoxy-1,3-tetraphenyldisiloxanes: synthesis and structure

Russian Chemical Bulletin - 1,3-Dimethoxy- 1,3-dimethyl- 1,3-diphenyl- and 1,3-dimethoxy- 1,3-tetraphenyldisiloxanes were synthesized. Their structures were confirmed by IR and NMR spectroscopy....     

Conformational analysis and selective hydrolysis of 2,5-disubstituted-1,3-dioxane-2-carboxylic acid esters

5-Alkyl-2-methyl-2-carbomethoxy-1,3-dioxanes were found to have a cis preferential configuration in the equilibrium state, and the ester hydrolysis rate of the trans-isomers was faster than that of the cis-isomers. Conformational analysis and charge calculation of the carbomethoxy group in both dioxanes elucidated this selectivity.     

Influence of medium acidity upon the luminescence properties of 2,5-diphenyl-1,3,4-oxadiazole and 2,5-diphenyl-1,3-oxazole

The luminescence properties of 2,5-diphenyl-1,3,4-oxadiazole and 2,5-diphenyl-1,3-oxazole in aqueous solutions of sulfuric acid (pH 7 to H_o − 10) were studied. The spectral parameters are essentially acidity dependent, which is due to the acid-base equilibria of these heterocycles both in the ground and in the first excited singlet states. The difference between these two compounds is governed by their dissimilar solvation. The basicity constants of 2,5-diphenyl-1,3,4-oxadiazole in the S₀ state (pK_BH+ = − 2.49) and 2,5-diphenyl-1,3-oxazole in the S₀ and S₁ states (pK_BH+ = −1.93, pK_BH+^* = 1.95) were experimentally obtained. The enthalpies of formation, electron charge density, and geometry of the bases and corresponding conjugate acids in the S₀ and S₁ states were calculated by the MNDO method.     

Reaction of 2,5-diphenyl-3,4-diazacyclopentadien-1-one 3,4-dioxide with trialkyl phosphites

Conclusions The trimethyl and triethyl phosphite react with 2,5-diphenyl-3,4-diazacyclopentadien-1-one 3,4-dioxide to give 1-alkyl-3,5-diphenyl-4-pyrazolyl dialkyl phosphates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1422–1424, June, 1972.     

Study of the reaction of bulky aryllithium reagents with 3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidine-2-borane derived from ephedrine

The ring opening of enantiomerically pure 3,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidine-2-borane (1) with a variety of bulky aryllithium reagents was studied. Our results are not in total agreement with those obtained by others. In fact, several 2,6-disubstituted aryl groups were successfully appended to the phosphorus atom, furnishing the corresponding (N-ephedrino)phosphine boranes 2a-g with dr>99:1. However, when the attack on the phosphorus atom is hindered, deprotonation on the benzylic position occurs, leading to the formation of enantiomerically pure trans-(N-methylamino)(phenyl)(1-phenyl-1-propenyloxy)phosphine-P-borane (3). While the attack of 2,2'-dilithio-1,1'-biarenes leads to the corresponding (P-phenyl)phosphole derivatives (4i,j) and to [bis(N-ephedrino)](phenyl)phosphine-P-borane (5), the attack of 1,1'-dilithiometallocenes (M=Fe, Ru) leads to a separable diastereomeric mixture of 1,1'-bis[(N-ephedrino)(phenyl)phosphino-P-borane]metallocenes (2k,l/2k',l') with dr approximately 80:20.     

Esters of 2,5-multisubstituted-1,3-dioxane-2-carboxylic acid: their conformational analysis and selective hydrolysis

The carbomethoxy group at the C2 position of the 2,5-multisubstituted 1,3-dioxanes prefers the axial conformation rather than the equatorial one due to an anomeric effect. The trans isomers of the 5-monosubstituted compounds are more selectively hydrolyzed than the cis isomers. Based on the calculated results, hydrolysis to the trans isomers is attributed to the larger carbonyl charges of the trans than those of the cis isomers. The anomeric and homoanomeric effects will explain the axial preference of the carbomethoxy group and selective hydrolysis to the trans isomers. Furthermore, the calculated stability between the cis and trans isomers is in good agreement with the experimental results in the equilibrium state.     

Crystal structure analysis of 3,4-dimethyl-2,5-dihydrothiophen-1,1-dioxide

The geometry of 3,4-dimethyl-2,5-dihydrothiophen-1,1-dioxide was determined by X-ray diffraction: cell dimensions are reported together with bond lengths and bond angles. While bond lengths are smaller than those for the homologue 3-methyl-2,5-dihydrothiophen-1,1-dioxide, bond angles are similar. TheMe-C₃-C₄-Me torsion angle is 5.1±0.5°. These results are consistent with its relatively slow rate of decomposition.

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Kristallstrukturanalyse von 3,4-Dimethyl-2,5-dihydrothiophen-1,1-dioxid

Zusammenfassung Die Geometrie von 3,4-Dimethyl-2,5-dihydrothiophen-1,1-dioxid wurde mittels Röntgendiffraktion bestimmt. Es werden die Dimensionen der Einheitszelle zusammen mit Bindungslängen und Bindungswinkeln berichtet. Die Bindungswinkel sind sehr ähnlich denen des homologen 3-Methyl-2,5-dihydrothiophen-1,1-dioxids, die Bindungslängen sind jedoch kürzer. DerMe-C 3-C 4-Me Torsionswinkel ist 5.1±0.5°. Diese Ergebnisse sind mit der relativ langsamen Zersetzungsgeschwindigkeit im Einklang.

     

Reaction of 3,4-diiodo-2,5-dimethyl-1H-pyrrole with thioamides

3,4-Diiodo-2,5-dimethyl-1H-pyrrole reacted with thioacetamide in polar solvents or under solvent-free conditions to give 2,4,6-trimethyl-5H-pyrrolo[3,4-d][1,3]thiazole. The major product in the reaction of the title compound with thiobenzamide was 3,5-diphenyl-1,2,4-thiadiazole.     

Synthesis of new spiropyrans from 2,5-dimethyl-1,3-benzodithiolium salts

New spiropyrans that have thermochromic properties were obtained by the condensation of 2,5-diniethyl-1,3-benzodlthiolium perchlorate with o-hydroxy aromatic aldehydes and subsequent treatment of the resulting 2-styryl derivatives with ammonia in ether.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 318–320, March, 1972.     

Consequences of the formation of 3,4-dimethyl-5-phenyl-1,3-oxazolidine on the analysis of ephedrines in urine by gas chromatography and a new method for confirmation as N-trifluoroacetyl-O-t-butyldimethylsilyl ether derivatives

The compound 3,4-dimethyl-5-phenyl-1,3-oxazolidine can appear as an artifact during the gas chromatographic analysis of ephedrines. Its presence is a risk for doping control and forensic analyses. An evaluation about the consequences of its formation showed the possibility of a false positive for ephedrine, a false negative for pseudophedrine and increased uncertainty in the quantitative approach. Misinterpretations can be avoided with the observation of fragments m/z 56 and 71 in the ephedrine mass spectrum during GC-MS analysis and also by the formation of N-TFA-O-TBDMS derivatives prior to GC analysis. These N-TFA-O-TBDMS derivatives lead to an increase in the number and mass of diagnostic ions, meet the identification criteria, and provide an improvement in chromatographic resolution, allowing the separation of the ephedrines.     

Synthesis of 3,4-bis(2,5-dimethyl-3-thienyl)furan-2,5-dione from mucobromic acid

Palladium-catalyzed cross-coupling between 2,5-dimethyl-3-thienylboronic and mucobromic acids under phase transfer catalysis (PTC) conditions gave the expected 3,4-bis(2,5-dimethyl-3-thienyl)-5-hydroxyfuran-2-one in 32% yield. The by-product was 2,2’,5,5’-tetramethyl-3,3’-bithiophene. The oxidation of the obtained hemiacylal with potassium permanganate under PTC conditions afforded 3,4-bis(2,5-dimethyl-3-thienyl)furan-2,5-dione in high yield.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2238–2240, October, 2004.     

Intermediates of chemical assembling of oligoorganosiloxanes in hydrolysis of organochlorosilanes

The mechanism of the formation of oligoorganosiloxanes during the hydrolysis of organochlorosilanes was considered. A comparative estimation of a relationship of the degree of conversion of the monomer vs. degree of conversion of functional groups in the homo- and heterofunctional condensation and partial hydrolysis of organochlorosilanes was performed for the first time. In the hydrolysis of diorganodichlorosilanes with either an excess or a deficiency of water, the homofunctional condensation of diorganosilanediols is not the main mode for the chemical assembling of oligoorganosiloxanes. The main intermediates in the route of oligoorganosiloxane formation during organochlorosilane hydrolysis are the incomplete hydrolysis products (organochlorohydroxysilanes). Experimental data suggest that the chemical assembling of oligoorganosiloxanes occurs via the mechanism of organochlorohydroxysilane heterocondensation under usually used conditions of organochlorosilane hydrolysis.     

Molecular structure of 1-dichloroacetyl-3,5-dimethyl-4,6-diphenyl-2-oxoperhydro-1,3-5-triazine

A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 5, pp. 189–192, September–October, 1989.     

Mass spectroscopic study of 2,5-dimethyl-4-benzoyl- and 2,5-dimethyl-4-benzylpyridine derivatives

The dissociative ionization of sixteen 4-benzoyl- and 4-benzylpyridine derivatives and their deuteroanalogs has been studied. An ortho effect, due to the benzoyl and benzyl radicals in the methyl group in the 5-position of the pyridine ring, has been detected. It has also been established that fragmentation of 4-benzoylpyridines substituted with a nitro group in the benzene ring leads to [M-OH]⁺ ions, due to the ortho effect, whereas fragmentation of 4-benzylpyridines leads to [M-C₆H₅R]⁺ ions. The probability of a given process depends on the position and nature of any substituent in the benzene ring; this makes it possible to identify different isomers in a given series of compounds.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 810–816, June, 1987.     

Reduction of 4,7-diphenyl-1,2,5-thia(oxa)diazolo[3,4-c]pyridines affording 2,5-diphenyl-3,4-diaminopyridines and ring closure of the diamines to fluorescent azaheterocycles

Reduction of 4,7-diphenyl-1,2,5-thia- ( 1a-i ) and 1,2,5-oxadiazolo[3,4-c]pyridines ( 3a and c-e ) gave 3,4-diamino-2,5-diphenylpyridines ( 2a-g ), which were converted into the fluorescent triazolo[4,5-c]-( 5 ), 1,2,5-selenadiazolo[3,4-c]- ( 6 ), imidazolo[4,5-c]pyridines ( 8 ), and pyrido[5,6-c]pyridines ( 11 ). In the reduction of 3a, c and e , 4,5-dihydro[1,2,5]oxadiazolo[3,4-c]pyridines ( 4a-c ) were obtained.