K. A. Chernyshev

Quantum-Chemical Calculations of NMR Chemical Shifts of Organic Molecules: I. Phosphines, Phosphine Oxides, and Phosphine Sulfides

The accuracy in the calculation of 31P NMR chemical shifts in the series of the simplest phosphines, phosphine oxides, and phosphine sulfides was estimated in terms of the Hartree-Fock self-consistent final perturbation theory and density functional theory with different basis sets. The best agreement between the calculated and experimental data was achieved at the DFT/B3LYP/IGLO-III level of theory.

A regio- and stereospecific reaction of tellurium tetrachloride with (trimethyl)(propargyl)silane

 Halovinyl tellurides are used in cross coupling reac tions for the synthesis of functionalized alkenes.1 A com mon route to these compounds involves addition of tellu rium tetrahalides to alkynes followed by reduction to tellurium(II) products.1 Our systematic investigations2—5 of the addition of se lenium and tellurium halides to alkynes have yielded un expected results in the case of trimethylsilyl containing alkynes. For instance, a reaction of SeCl2 with (tri methyl)(propargyl)silane (1) proceeds regio and ste reospecifically to form Z,E bis[2 chloro 3 (trimethyl silyl)prop 1 enyl] selenide in quantitative yield.3 We have assumed3 that the reaction begins with anti addition of SeCl2 to one molecule of silane 1 followed by syn addition of the resulting monoadduct to a second molecule of si lane 1. No reaction of TeCl4 with compound 1 has been documented; however, it is known4 that TeCl4 reacts with (ethynyl)(trimethyl)silane to give Z 2 chloro 1 (trimeth ylsilyl)vinyltellurium trichloride, an anti Markownikoff adduct. It turned out that the bulky trimethylsilyl group substantially influences the regio and stereochemical out comes of the reaction.4 We were the first to study a reaction of TeCl4 with propargylsilane 1. We found that the reaction proceeds regio and stereospecifically to give a Markownikoff ad duct, namely, Z 2 chloro 3 (trimethylsilyl)prop 1 enyl tellurium trichloride (2), in 96% yield (Scheme 1). The reaction is performed by adding a solution of an equimolar amount of propargylsilane 1 in benzene to a cooled (5 C) solution of TeCl4 in benzene; the reaction mixture is stirred at 5 C for 3 h and then at room temper ature for 12 h. If no cooling is used, the room temperature reaction yields compound 2 contaminated with small amounts of by products. We failed to obtain the bisadduct Z,Z bis[2 chloro 3 (trimethylsilyl)prop 1 enyl]tellurium dichloride by a re action of TeCl4 with an excess of reactant 1 in benzene or chloroform at room temperature or at 60 C. This may probably be due to the poor stability of monoadduct 2, which decomposes partially when heated in solution or in the solid state to 45—48 C. At room temperature, mono adduct 2 does not react with a second molecule of com pound 1, while heating results in the decomposition of both monoadduct 2 and, probably, the bisadduct formed. Reduction of compound 2 with the system Na2S2O5— H2O—C6H6 at room temperature gave the novel com pound Z,Z bis[2 chloro 3 (trimethylsilyl)prop 1 enyl] ditelluride (3) in 94% yield. Despite the presence of water, no desilylation occurs. So the silyl group, as well as the Z configuration, is retained in the final product 3. The structures of products 2 and 3 were proved by 1H and 13C NMR spectroscopy (with a NOESY experiment used to determine the stereoconfiguration) and confirmed by elemental analysis. The spin spin coupling between the Te atom and the carbon atom of =CH is characterized by coup ling constants of 260 and 328 Hz (for 2 and 3, respectively), which correspond to direct constants JTe,C. 5 This sug gests the attachment of the Te atom to the terminal C atom of silane 1 and the formation of a Markownikoff adduct. To sum up, in contrast to the reaction of TeCl4 with (ethynyl)(trimethyl)silane, the addition of TeCl4 to prop argylsilane 1 gives a Markownikoff adduct. The resulting organotellurium compounds 2 and 3 are of interest as semi finished products for fine organic synthesis.

A novel regiospecific cascade synthesis of sulfonamide derivatives from N-(2-polychloroethyl)sulfonamides via chloroaziridine intermediates in the presence of mercaptoethanol

N-(1-Aryl-2-polychloroethyl)arenesulfonamides obtained on the basis of N,N-dichlorosulfoamides and polychloroethenes or phenylacetylene undergo a reaction cascade in the presence of mercaptoethanol. The reaction cascade opens a new route to the series of cyclic or open-chain sulfonamide derivatives. The process includes cyclization to aziridine intermediates, their further recyclization, and isomerization to imidoylchlorides or chloroimines, followed by substitution or reduction under the action of mercaptoethanol or hydrolysis. The final sulfonamide structures depend on the starting N-(polychloroethyl)sulfonamides. N-(2,2-Dichloroethyl)sulfonamides were transformed into sulfonamide-containing 1,4-oxathians while N-(2,2,2-trichloroethyl)sulfonamides were converted to N-(2-arylacetyl)arenesulfonamides. N-(2-Phenyl-2,2-dichloroethyl)sulfonamides form enamide derivatives that were transformed into aromatic ketones.

Quantum-chemical calculations of NMR chemical shifts of organic molecules: VIII. Solvation effects on 15N NMR chemical shifts of nitrogen-containing heterocycles

Effect of solvation on the accuracy of DFT quantum-chemical calculations of 15N NMR chemical shifts of pyrrole, N-methylpyrrole, and pyridine was studied. The use of continuum model is sufficient to obtain consistent theoretical σN values for weakly polar aprotic solvents, whereas solvation effects in strongly polar and protic solvents should be taken into account in the explicit form.

N-(2,2-Dichloro-2-phenylethylidene)arenesulfonamides in reactions with secondary amines

N-(2,2-Dichloro-2-phenylethylidene)arenesulfonamides were synthesized by a modified procedure, and their reactions with secondary amines were studied for the first time. Reactions of imines with dialkylamines proceed at room temperature to afford α,α-dichloromethylbenzene and N,N-dialkyl-N′-(arenesulfonyl)formamidines arising from the haloform cleavage of the initially formed unstable N-(1-dialkylamino-2,2-dichloro-2-phenylethyl)arenesulfonamides. When the reaction is carried out upon cooling to 0°C, the products of the nucleophilic addition of secondary amines to azomethines, N-(1-dialkylamino-2,2-dichloro-2-phenylethyl) are formed in yields of no higher than 5%. Nonempirical calculations of 13C-1H spin-spin coupling constants and their experimental measurements for the series of the synthesized N-arenesulfonamides were performed to show that these compounds exist in solutions exclusively as E isomers. Preferable conformations of the investigated compounds and the relative energies of their E and Z isomers in the gas phase were determined by quantum-chemical calculations at the MP2/6-311G** level of theory. The NMR spectral data revealed restricted rotation of the N,N-dialkylamino group about the partially double C-NAlk2 bond in the molecules of N-arenesulfonylformamidines.

Configurational Assignment and Conformational Study of Methylglyoxal Bisdimethylhydrazones Derived from the 2-Ethoxypropenal Precursor

A configurational assignment of the isomeric methylglyoxal bisdimethylhydrazones derived from the 2-ethoxypropenal precursor has been performed based on experimental measurements and high-level ab initio calculations of 1J(C,C) and 1J(C,H) couplings. The results reveal the marked stereochemical dependence upon the orientation of the lone pairs of both nitrogen atoms in different isomers. Methylglyoxal bisdimethylhydrazone is shown to exist in a mixture of the EE and ZE isomers (ca. 75:25), both of which adopt predominant s-trans conformations with minor (up to 8°) out-of-plane deviations.

Quantum-Chemical Calculations of NMR Chemical Shifts of Organic Molecules: II.* Influence of Medium, Relativistic Effects, and Vibrational Corrections on Phosphorus Magnetic Shielding Constants in the Simplest Phosphines and Phosphine Chalcogenides

The influence of solvent nature, relativistic effects, and vibrational corrections on the accuracy of calculation of 31P chemical shifts of the simplest phosphines, phosphine oxides, phosphine sulfides, and phosphine selenides was studied. Consideration of the above factors at the stage of both geometry optimization and calculation of magnetic shielding constants was found to appreciably improve the accuracy of calculation of 31P NMR chemical shifts in the series of phosphines and phosphine chalcogenides.

Quantum-chemical calculations of NMR chemical shifts of organic molecules: X. Dynamic equilibrium effects in the 29Si NMR spectra of silacycloalkanes

Dynamic equilibria related to change of the coordination number of the silicon atom in bis[N-(dimethylamino) imidato-N′,O]silacycloalkanes in solution were studied by theoretical calculations and experimental measurement of the 29Si NMR chemical shifts. Silacyclopentane derivatives were found to exist in solution as mixtures of species with six- and five-coordinate silicon atoms, and silacyclohexane derivatives, as mixtures of five- and four-coordinate silicon compounds.

The effects of intramolecular and intermolecular coordination on 31P nuclear shielding: phosphorylated azoles

The effects of intramolecular and intermolecular coordination on 31P nuclear shielding have been investigated in the series of tetracoordinated, pentacoordinated and hexacoordinated N‐vinylpyrazoles and intermolecular complexes of N‐vinylimidazole and 1‐allyl‐3,5‐dimethylpyrazole with phosphorous pentachloride both experimentally and theoretically. It was shown that either intramolecular or intermolecular coordination involving phosphorous results in a dramatic 31P nuclear shielding amounting to approximately 150 ppm on changing the phosphorous coordination number by one. A major importance of solvent effects on 31P nuclear shielding of intramolecular and intermolecular complexes involving N → P coordination bond has been demonstrated. It was found that the zeroth‐order regular approximation–gauge‐including atomic orbital–B1PW91/DZP method was sufficiently accurate for the calculation of 31P NMR chemical shifts, provided relativistic corrections are taken into account, the latter being of crucial importance in the description of 31P nuclear shielding. Copyright

Reactions of N-(Polychloroethylidene)arene-and - trifluoromethanesulfonamides with indoles

N-(Polychloroethylidene)arene-and -trifluoromethanesulfonamides reacted with indole and N-substituted indoles to give the corresponding N-[2,2-dichloro(or 2,2,2-trichloro)-1-(1H-indol-3-yl)ethyl]-substituted sulfonamides. Unlike N-(2,2,2-trichloroethylidene)trifluoromethanesulfonamide, less electrophilic N-(poly-chloroethylidene)arenesulfonamides failed to react with 1-(4-nitrophenyl)-1H-indole. Previously unknown N,N’-bis(2,2-dichloroethylidene)biphenyl-4,4’-disulfonamide reacted with 1-benzyl-1H-indole at both azomethine fragments. Likewise, reactions of 1,6-bis(1H-indol-1-yl)hexane and 1,4-bis(1H-indol-1-ylmethyl)-benzene with N-sulfonyl trichloroacetaldehyde imines involved both indole rings in the former.