Conformational Analysis of 5-Ethyl-5-hydroxymethyl-2,2-dimethyl-1,3-dioxane

Russian Journal of Organic Chemistry - Computer simulation of conformational transformations of 5-ethyl-5-hydroxymefhyl-2,2-dimefhyl-1,3-dioxane in the gas phase, as well as in mixtures with...     

The regioselective mono-deprotection of 1,3-dioxa-2,2-(di-tert-butyl)-2-silacyclohexanes with BF3*SMe2

The selective mono-deprotection of di-tert-butylsilylene ethers prepared from substituted 1,3-pentanediols and 2,4-hexanediols has been achieved with BF3*SMe2. The reaction conditions are compatible with esters, allyl ethers, and TIPS ethers. The resulting di-tert-butylfluorosilyl ethers are stable to various conditions including low pH aqueous solutions and silica gel chromatography; the di-tert-butylfluorosilyl ethers are readily cleaved with HF-pyridine. Substrate stereochemistry and conformation influences the efficiency of the deprotection, while the deprotection regiochemistry is consistent with coordination of boron to the sterically more accessible oxygen prior to intramolecular delivery of fluoride.     

Synthesis and Stereochemistry of Substituted 1,3-Dioxa-2-silacyclohexanes: VII. Synthesis and Stereochemistry of Substituted 2-Vinyl-2-methyl-1,3-dioxa-2-silacyclohexanes

The stereochemistry of substituted 2-vinyl-2-methyl-1,3-dioxa-2-silacyclohexanes was studied by ^1Hand ^13C NMR spectroscopy. The configurational and conformational assignment of a mixture of 2-vinyl-2,4-dimethyl-1,3-dioxa-2-silacyclohexane diastereomers with various ratios of the cis and trans forms was made. The molecules of both conformers occur chiefly in the chair conformartion with equatorial location of the methyl group at the C⁴ atom. The experimental data were confirmed by AM1 and MM+ optimization of the molecular geometry.     

Spatial structure of 2,2-dimethyl-5-alkyl-1,3,2,5-dioxasilaphosphorinanes

Conclusions A study was made of the IR spectra and dipole moments of some heterocycles that simultaneously contain phosphorus and silicon atoms. The preferential conformation of the dioxasilaphosphorinanes is discussed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2129–2131, September, 1978.The authors are indebted to A. B. Remizov for the IR spectral study of 2,2,5-trimethyl-1,3,2,5-dioxasilaphosphorinane.     

N-(2-Thenyl)derivatives of aminoalkyltriethoxysilanes,-silatranes and 2,2-dimethyl-1,3-dioxa-6-aza-silacyclooctane

The reactions of aminoalkylethoxysilanes and 2,2-dimethyl-1,3-dioxa-6-aza-2-silacyclooctane with 2-(chlormethyl)thiophene and its 5-chloroderivative lead to the correspondingN-(2-thenyl) derivatives. TheN-methyl-N-(2-thenyl)aminomethyltriethoxysilane and 5-chlorothyenyl derivative formed are converted by triethanolamine into silatranes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 384–386, February, 1995.     

Reactions of 1,4-dioxa-2-silacyclohexanes with acetyl chloride

The reactions of 1,4-dioxa-2-silacyclohexanes with acetyl chloride lead to the cleavage of the Si−O bond to form chlorotriorganosilanes containing the acetoxy group in the organic radical at the silicon atom. Hydrolysis of these chlorosilanes affords bis(acetoxy-alkoxy(aryloxy)methyl)disiloxanes, while the reactions with cage copper sodium phenylsiloxane give dodecaphenyl[dodeca(acetoxyorganodimethylsilyloxy)]cyclododecasiloxanes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2527–2529, December, 1998.     

Conformational analysis of 2-methyl-5-alkyl- and 5-aryl-1,3,2-dioxaborinanes

Quantum chemical study of conformational isomerization of 2-methyl-5-alkyl- and 5-aryl-1,3,2-dioxaborinanes using RHF/6-31G(d) method led to the conclusion that the equilibrium between equatorial and axial sofa conformers is shifted to the latter form. Based on the experimental and theoretically calculated vicinal coupling constants J _HH the quantitative conformational composition and the values of ΔG ⁰ for substituents at the C⁵ ring atom were established.     

Mass spectra and stereochemistry of alkylsubstituted 2,2-diphenyl-1,3-dioxa-2-germacyclohexanes

The correlations between electron impact induced formation of fragment [M ? C₆H₆]⁺˙ from alkyl-substituted 2,2-diphenyl-1,3-dioxa-2-germacyclohexane (1) and the peculiarities of the molecular structures were found. Benzene elimination is regiospecific and stereoselective, resulting from the abstraction of an axial phenyl group and a hydrogen atom from the C-4 or C-6 position of the ring.     

2,2-Diamino-1,3-dimethyl-1,3,2-diazaphospholaniumchlorid

Ohne Zusammenfassung     

Thermal stability of 2,2-Diaryl/dialkyl-4,4,5,5-tetraaryl-1,3-dioxa-2-siloles

Fully substituted 1,3-dioxa-2-siloles contain a strained carbon–carbon bond that will undergo thermolysis at modest temperatures to generate a diradical capable of initiating vinyl polymerization. If the substituents contain flame-retarding moieties, e.g., halogen or phophorus-containing groups, the use of such compounds as initiators serves to incorporate a flame-retarding unit into the polymer mainchain. Both 2,2-dialkyl- and 2,2-diaryl-4,4,5,5-tetra(3,5-dibromophenyl)-1,3-dioxa-2-siloles may be prepared from the appropriate tetra(bromoaryl)-1,2-ethanediol and are obtained as white solids. Thermal decomosition (thermogravimetry) of these materials occurs in two stages. Initial decomposition is observed at about 250 °C and corresponds to the loss of nearly half of the initial sample mass.     

Stereochemical features of transesterification (N-B)-perhydro-2-isopropyl-1,3-dioxa-6-aza-2-boracine by 2-alkyl-1,3-butanediols

The stereoisomeric composition of 2,4,5-substituted 1,3,2-dioxaborinanes, products of transesterification of the diethanolamine ester of isopropylboric acid by 2-alkyl-1,3-butanediols, are shown by GLC not to correspond to the ratio of erythrothreo-forms of the starting diols. The fraction of trans-isomer of 2,4,5-substituted 1,3,2-dioxaborinane which is elevated by comparison with that expected is explained by stereoselective reaction of the erythro-form of the 1,3-diol with diethalnolaminoborate.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 994–996, July, 1989.     

Structure and Conformational Analysis of 5-Methyl-2,2-diphenyl-1,3-dioxane

Russian Journal of Organic Chemistry - The structure of 5-methyl-2,2-diphenyl-1,3-dioxane has been studied by1H and 13C NMR spectroscopy and X-ray analysis. Its molecules in crystal, as well as in...     

Germa-2-dioxa-1,3-cycloalcanes

The action of the α-, β- and γ-diols on the dialkyl(aryl)-bis(dialkylamino) germanes R₂Ge(NR'₂)₂ leads, in high yields, to the dialkyl(aryl)-2,2-germa-2-dioxa-1,3-cycloalkanes. The IR. and NMR. spectral study in the presence of Eu(Dpm)₃ allowed to demonstrate a dimerisation by coordination in some of these heterocycles. In this complex, the germanium is hexacoordinated by association with the two oxygens of the second associate molecule. Its hybridation state is sp₃d₂ or spd₄ (D_3h symmetry, prismatic structure). These low energy association are ruptured in solution at moderate temperatures; these heterocycles are monomers by ebulliometry in benzene. This association is disfavoured by the presence of substituents on the cycle and by hindering substituents with donor effect on the germanium. The diminution of nucleophilicity of the oxygens by mesomeric effect with neighbouring π systems also prevents any association.     

Conformational analysis of 5-substituted 1,3-dioxanes

Quantum-chemical study on the potential energy surface of 5-alkyl- and 5-phenyl-1,3-dioxanes at the RHF/6-31G(d) level of theory revealed two pathways for conformational isomerizations of the equatorial and axial chair conformers. Potential barriers to this process were estimated. The Gibbs conformational energies ΔG° of substituents at C⁵ in the 1,3-dioxane ring were determined on the basis of experimental (¹H NMR) and theoretical vicinal coupling constants, which turned out to be consistent with published data.