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The conformational equilibria of 1-phenyl-1-silacyclohexane 1, 3-phenyl-1,3-thiasilacyclohexane 2, 1-methyl-1-phenyl-1-silacyclohexane 3, and 3-methyl-3-phenyl-1,3-thiasilacyclohexane 4 have been studied for the first time by low temperature 13C NMR spectroscopy at 103 K. Predominance of the equatorial conformer of compound 1 (Ph eq/Ph ax=78%:22%) is much less than in its carbon analog, phenylcyclohexane (nearly 100% of Ph eq). And in contrast to 1-methyl-1-phenylcyclohexane, the conformers with the equatorial Ph group are predominant for compounds 3 and 4: at 103 K, Ph eq/Ph ax ratios are 63%:37% (3) and 68%:32% (4). As the Si-C bonds are elongated with respect to C-C bonds, the barriers to ring inversion are only between 5.2-6.0 (ax→eq) and 5.4-6.0 (eq→ax) kcal mol -1. Parallel calculations at the DFT and MP2 level of theory (as well as the G2 calculations for compound 1) show qualitative agreement with the experiment. The additivity/nonadditivity of conformational energies of substituents on cyclohexane and silacyclohexane derivatives is analyzed. The geminally disubstituted cyclohexanes containing a phenyl group show large deviations from additivity, whereas in 1-methyl-1-phenyl-1-silacyclohexane and 3-methyl-3-phenyl-1,3-thiasilacyclohexane the effects of the methyl and phenyl groups are almost additive. The reasons for the different conformational preferences in carbocyclic and heterocyclic compounds are analyzed using the homodesmotic reactions approach. © 2011 Elsevier B.V. All rights reserved. Source

Shainyan B.A.,Favorsky Irkutsk Institute of Chemistry | Kleinpeter E.,University of Potsdam

Stereochemical studies on silaheterocyclohexanes is a 'hot topic' as evidenced by the growing number of publications. During last 10 years a substantial number of substituted silacyclohexanes and heterocyclohexanes containing sulfur, oxygen or nitrogen as the second (or third) heteroatom have been synthesized and studied by variable temperature dynamic NMR spectroscopy, gas-phase electron diffraction, variable temperature IR, Raman, microwave spectroscopy with respect to thermodynamic (frozen conformational equilibria) and kinetic (barrier to ring inversion) information. As the stereochemistry of cyclohexane and its N-, O-, P-, S-hetero analogues is one of keystones of modern theoretical and synthetic organic and heterocyclic chemistry, the stereochemistry of silacyclohexane and its hetero analogs is an important element of theoretical and synthetic organosilicon chemistry. The various classes of saturated six-membered rings were critically compared and studied in detail with respect to differences in their stereochemistry and dynamic behavior. © 2013 Elsevier Ltd. All rights reserved. Source

Lazareva N.F.,Favorsky Irkutsk Institute of Chemistry
Russian Chemical Bulletin

The data on biological activity of the compounds with the geminal fragment N-C-Si are systematized. The examples of using N-(silylmethyl)amines and related compounds in syntheses of biologically active substances, including natural compounds, are considered. © 2011 Springer-Verlag. Source

Rusakov Yu.Yu.,Favorsky Irkutsk Institute of Chemistry | Krivdin L.B.,Favorsky Irkutsk Institute of Chemistry
Russian Chemical Reviews

The modern quantum chemical methods for calculating spin-spin coupling constants in NMR spectra are reviewed. The theoretical basis of these methods and author's vision of the prospects of their development and practical applications in structural and stereochemical studies are presented. The bibliography includes 288 references. © 2013 Russian Academy of Sciences and Turpion Ltd. Source

Rulev A.Y.,Favorsky Irkutsk Institute of Chemistry
Russian Chemical Reviews

Data published in the last 10 years on the use of the aza-Michael reaction in organic synthesis are described systematically. The attention is focused on environmentally friendly processes following green chemistry principles and on methods for the synthesis of compounds that are difficult to access by other routes. The bibliography includes 269 references. © 2010 Russian Academy of Sciences and Turpion Ltd. Source

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