Liquid-Phase Oxidation of Pentamethyldisilane with Oxygen

Russian Journal of General Chemistry -     

In search of efficient 5-endo-dig cyclization of a carbon-centered radical: 40 years from a prediction to another success for the Baldwin rules

Despite being predicted to be stereoelectronically favorable by the Baldwin rules, efficient formation of a C-C bond through a 5-endo-dig radical cyclization remained unknown for more than 40 years. This work reports a remarkable increase in the efficiency of this process upon beta-Ts substitution, which led to the development of an expedient approach to densely functionalized cyclic 1,3-dienes. Good qualitative agreement between the increased efficiency and stereoselectivity for the 5-endo-dig cyclization of Ts-substituted vinyl radicals and the results of density functional theory analysis further confirms the utility of computational methods in the design of new radical processes. Although reactions of Br atoms generated through photochemical Ts-Br bond homolysis lead to the formation of cyclic dibromide side products, the yields of target bromosulfones in the photochemically induced reactions can be increased by recycling the dibromide byproduct into the target bromosulfones through a sequence of addition/elimination reactions at the exocyclic double bond. Discovery of a relatively efficient radical 5-endo-dig closure, accompanied by a C-C bond formation, provides further support to stereoelectronic considerations at the heart of the Baldwin rules and fills one of the last remaining gaps in the arsenal of radical cyclizations.     

Theory of thermostimulated currents in layered crystals

A mathematical model is proposed for layered crystals, based on a system of kinetic equations describing the change in charged relaxation oscillators with time. An analytical solution of this system is found and a theory constructed, which allows determination of the type and parameters of relaxation oscillators, as well as the properties of the crystals. A calculation of the thermostimulated depolarization current spectrum is confirmed by experiment.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 68–72, January, 1991.     

Tandem radical and non-radical reactions mediated with thiols--a new method of cleavage of allylic amines

Thiyl radical promotes the isomerisation of allylic amines into enamines via two consecutive hydrogen atom abstraction steps, and the subsequent polar addition of the corresponding thiol to the enamine results in the cleavage of the C-N bond via a thioaminal intermediate: this reaction provides a mild, metal-free methodology for the deprotection of allylated primary and secondary amines.     

Brønsted base-modulated regioselectivity in the aerobic oxidative amination of styrene catalyzed by palladium

Palladium(II)-catalyzed aerobic oxidative amination of styrene with oxazolidinone proceeds with catalyst-controlled regioselectivity: (CH3CN)2PdCl2 (1) and (Et3N)2PdCl2 (2) catalyze formation of the anti-Markovnikov and Markovnikov enecarbamate products, 3 and 4, respectively. Kinetic studies and deuterium kinetic isotope effects demonstrate that these two reactions possess different rate-limiting steps, and the data indicate that the product regiochemistry arises from the presence or absence of an effective Br?nsted base in the reaction. In the presence of a Br?nsted base such as triethylamine or acetate, the kinetically preferred Markovnikov aminopalladation adduct of styrene is trapped via rapid deprotonation of a zwitterionic intermediate and leads to formation of 4. In the absence of an effective Br?nsted base, however, slow deprotonation of this adduct enables aminopalladation to be reversible, and product formation proceeds through the thermodynamically preferred anti-Markovnikov aminopalladation adduct to yield 3.     

Comparative study of oxochlorides of molybdenum,tungsten and element 106

An isotope of element 106, namely²⁶³106, detected by its spontaneous fission, has been chemically isolated by thermochromatography of oxochlorides. The last one has been compared with short- and long-lived isotopes of Mo and W. Two chemical species were observed, presumably MO₂Cl₂ and MOCl₄ (M=Mo,W). A kinetic dependence of these two species has been discussed and a chemical form [106]O₂Cl₂ has been described for the registered atoms of element 106.     

Dynamic chain system with seismic damper: reduction of nonlinear model

The efficiency of model reduction via balancing for a multimass system with a nonlinear inertial link is demonstrated. As an example, a three-mass dynamic system with a seismic damper is examined. The constraints of the seismic damper are assumed to be ideal. The order of the system of differential equations is reduced by one. It is pointed out that the difference between the numerically analyzed dynamic processes in the original and reduced systems is minor, which makes it possible to use the method for justified simplification of nonlinear systems     

Modification of Rissanen’s Method in Linear Memory

The problem of solving a linear system with a Hankel or block-Hankel matrix, as well as Rissanen’s algorithm and its generalization to the block case, are considered. Modifications of these algorithms that use less memory (O(n) against O(n²)).     

Spectral manifestations of intramolecular interactions in acid chlorides of unsaturated acids of phosphorus

The mutual effect of atomic groups in acid chlorides of threeand four-coordination phosphorus was investigated by the nuclear quadrupole resonance of Cl³⁵ (NQR Cl³⁵) and Raman spectroscopy methods. On the basis of the NQR data it is suggested that in the ground state the interaction of unshared pairs of chlorine with the d orbitals of phosphorus is displayed weakly and the interaction of the indicated atoms is accomplished predominantly by an inductive mechanism. The integral intensities of the Raman lines of vibrations of the P-Cl and P=Cl bonds were measured. The Raman scattering data and the results of quantummechanical calculations by the molecular orbital method indicate some additional multiplicity of the P-Cl bond.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 75–80, December, 1972.The authors thank V. T. Aleksanyan and G. Kuz'yants for help in measuring the depolarization ratio.