Center for Magnetic Resonance

I.S. Ignatyev, T.A. Kochina, V.V. Avrorin, V.V. Gurzha, I.M. Fundamensky

“Molecular and crystal structure of 2-phenyl-2-hydro-6-methyl-1,3-dioxa-6-aza-2-silacyclooctane”

J. Molec. Struct., 2015, 1094, 169-173
DOI:10.1016/j.molstruc.2015.03.061

The crystal structure of 2-phenyl-2-hydro-6-methyl-1,3-dioxa-6-aza-2-silacyclooctane [HPhSi(OCH₂CH₂)₂NMe – phenylhydrosilocane (I)] is determined by single-crystal X-ray diffraction at 100 K. The unit cell consists of four molecules connected only by Van-der-Waals interactions. Each molecule has an eight-membered heterocycle with a phenyl group in the axial position. The Si⋯N transannular bond has a short (2.206 Å) interatomic distance which exceeds only this distance in ocanes with highly electronegative fluorine substituents at Si. Since there exist experimental data on the occurrence of different conformers of I in the liquid phase, the PES of the molecule was analyzed by DFT B3LYP and MP2 methods with the aug-cc-pVDZ basis set. The energy minimum belongs to the boat–chair conformation with the axial position of the phenyl group. Rotation of the phenyl ring around the SiC bond has a barrier ca. 1 kcal/mol. The conformer with the equatorial position of this group lies 6 kcal/mol higher. Interconversion of this conformers which was observed in experiment proceeds through the chair–chair configuration in which the Si⋯N transannular bond is absent and coordination at silicon is tetrahedral, rather than trigonal bipyramidal one observed in other conformers.

D.V. Kurandina, E.V. Eliseenkov, T.S. Khaibulova, A.A. Petrov, V.P. Boyarskiy

“Copper-catalyzed C-N bond cross-coupling of aryl halides and amines in water in the presence of ligand derived oxalyl dihydrazide: scope and limitation”

Tetrahedron, 2015, 71, 7931-7937
DOI:10.1016/j.tet.2015.07.071

An efficient and convenient method has been developed for the copper-catalyzed C–N bond cross-coupling of aryl bromides with electron-donor substituents and aliphatic amines in water. The new ligand system N-phenyloxalyl bishydrazide/hexane-2,5-dione has been shown to be considerably more efficient in the copper-catalyzed C–N bond cross-coupling reaction as compared to the ligands described in the literature and allowed decreasing of the catalyst amount (up to 2 mol %) to achieve acceptable yields of isolated products (46–84%). Acceptor substituted aryl bromides, aryl bromides with substituents in the ortho-position, and some aryl dichlorides can undergo the C–N cross-coupling under the developed conditions, but their reactivity is lower.

Yu.B. Koptelov, D.O. Antuganov, A.P. Molchanov, R.R. Kostikov

“Steric Hindrances to the Cycloaddition of (Z)-1-Arylmethylidene-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ides to N-Arylmaleimides”

Russ. J. Org. Chem., 2015, 7, 972-981
DOI:10.1134/S1070428015070143

Sterically hindered cycloaddition of (Z)-1-arylmethylidene-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ides to 4-mono- and 2,6-disubstituted N-arylmaleimides requires prolonged heating (40–60 h) at ~150–155°C and yields mixtures of diastereoisomeric cycloadducts. The observed diastereoselectivity is determined by both electronic and steric interactions, depending on the nature and position of substituents in the azomethine imine and maleimide. The reactions of (Z)-1-(2,6-dichlorobenzylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide with 4-substituted N-arylmaleimides give mainly the corresponding cis adducts as a result of preferential exo attack by the dipolarophile, whereas trans adducts predominate in the cycloaddition of (Z)-1-(4-X-benzylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide and (Z)-1-(2,6-dichlorobenzylidene) -5,5-dimethyl-3-oxopyrazolidin- 1-ium-2-ide to 2,6-disubstituted N-arylmaleimides.

S.A. Timofeeva, M.A. Kinzhalov, V.P. Boyarskiy, T.M. Buslaeva, E.A. Valishina, M. Haukka, K.V. Luzyanin, V.Yu. Kukushkin

“Application of palladium complexes bearing acyclic amino(hydrazido)carbene ligands as catalysts for copper-free Sonogashira cross-coupling”

J. Catalysis, 2015, 329, 449-456
DOI:10.1016/j.jcat.2015.06.001

Metal-mediated coupling of one isocyanide in cis-[PdCl₂(CNR¹)₂] (R¹ = C₆H₁₁ (Cy) 1, tBu 2, 2,6-Me₂C₆H₃ (Xyl) 3, 2-Cl-6-MeC₆H₃4) and various carbohydrazides R²CONHNH₂ [R² = Ph 5, 4-ClC₆H₄6, 3-NO₂C₆H₄7, 4-NO₂C₆H₄8, 4-CH₃C₆H₄9, 3,4-(MeO)₂C₆H₃10, naphth-1-yl 11, fur-2-yl 12, 4-NO₂C₆H₄CH₂13, Cy 14, 1-(4-fluorophenyl)-5-oxopyrrolidine-3-yl 15, (pyrrolidin-1-yl)C(O) 16, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propane-1-yl 17, EtNHC(O) 18] or sulfohydrazides R3SO2NHNH2 [R³ = Ph 19, 4-MeC₆H₄20] led to a series of (hydrazido)(amino)carbene complexes cis-[PdCl₂{C(NHNHX)double bond; length as m-dashN(H)R¹}(CNR¹)]; X = COR², SO₂R³ (21–48, isolated yields 60–96%). All prepared species were characterized by elemental analyses (C, H, N), HR ESI+-MS, IR, ¹H and ¹³C{¹H} NMR spectroscopy, and by a single-crystal X-ray diffraction for 38. Complexes 21–48 demonstrated excellent activity as catalysts in copper-free Sonogashira coupling of aryl iodides and a variety of aromatic terminal alkynes. Catalytic system runs in environmentally benign EtOH ensuring product yields of up to 75–96% and TONs of up to 104. Mechanism of the copper-free Sonogashira catalytic cycle involving 21–48 as catalysts was proposed upon identification of key intermediates using HRESI-mass.