On the interaction of silyl triflates with enamines: iminium ion formation versus silylation

The interaction of Me₃SiOTf and (C₆F₅)₃SiOTf with enamines generating α-silyl-substituted iminium ions is investigated. A trimethylsilyl iminium cation is formed as a long-lived species observable by NMR spectroscopy, whilst the tris(pentafluorophenyl)silyl analogue is very labile and prone to the loss of a proton. On the basis of the latter phenomenon, a method for the synthesis of β-silyl enamines is proposed.     

The effects of the nature of catalyst and of the solvent on the stereoselectivity in amine-catalyzed asymmetric synthesis of substituted cyclohexa-1,3-dienes from prenal and monoesters of ylidenemalonic acids

In the amine-catalyzed reactions of prenal with (Z)-5-methyl-2-(methoxycarbonyl)hexa-2,4-dienoic or (Z)-3-phenyl-2-(ethoxycarbonyl)prop-2-enoic acid chiral β-amino alcohols provide for higher enantiomeric purity of the resulting alkyl 4-methyl-6-(2-methylprop-1-enyl)-and 4-methyl-6-phenylcyclohexa-1,3-dienoates than that provided by related chiral amines without hydroxy group. The values ofee attained in nonpolar solvents are higher than those observed in the polar ones. Substituting stoichiometric amounts of a chiral 1-amino-3-methylbuta-1,3-diene for a combination of prenal with 0.1 equiv. of the corresponding chiral amine results in the products of much lower enantiomeric purity. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 84–92, January, 1998.     

Reactions of salicylaldehyde with tris(pentaf luorophenyl)silanes and secondary amines

Reactions of tris(pentafluorophenyl)silanes RSi(C₆F₅)₃ with salicylaldehyde and secondary amines were studied. The reactions afforded α-pentafluorophenyl-substituted amines. Silanes RSi(C₆F₅)₃ (R = Me, Ph, C₆F₅, CH₂CH=CH₂, and CH=CH₂) were found to be efficient reagents for transfer of the C₆F₅ group to the iminium cation generated from salicylaldehyde and amine. However, tris(pentafluorophenyl)phenylethynyl-and tris(pentafluorophenyl)silanes were not able to serve as a source of a fluorinated substituent because of competitive transfer of acetylenide fragment or hydride. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 498–503, March, 2006.     

1H and13C NMR spectra of 1,5-disubstituted 1,3,4-oxadiazoles

The¹H and¹³C NMR spectra of 2, 5-disubstituted 1,3,4-oxadiazoles with aliphatic, aromatic, and hetero-aromatic substituents have been described and interpreted. The electronic effect of the 1,3,4-oxadiazole group as a benzene ring substituent was evaluated using¹³C NMR spectroscopy.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 834–842, June, 1994. Original article submitted April 8, 1994.     

Tantalum(v) oxoalkoxides. Synthesis and structure

Anodic oxidation of tantalum in isopropyl alcohol or prolonged reflux of an alcohol solution of Ta(OPrⁱ)₅ afford crystalline oxoisopropoxide Ta₂O(OPrⁱ)₈ · PrⁱOH (1). In its molecule, two octahedra about Ta atoms are linkedvia the shared edge [(OPrⁱ)O]. Compound1 is the first example of oxoalkoxide containing such a small number of metal atoms. Unlike the known polynuclear molecules M _n O _m (OR) _p , oxoalkoxide1 is stable in solutions; on transition to the gas phase, this compound is desolvated to form a very stable molecule Ta₂O(OPrⁱ)₈ (apparently, consisting of two octahedra with a shared edge). According to the data of mass spectrometry, analogous molecules exist in the gas phase over Ta(OAlk)₅ (Alk = Me, Et, Prⁱ, or Bu¹¹). When compound1 is heated invacuo (10^–2–10^–3 Torr), Ta(OPrⁱ)₅ is sublimated. Crystals of Ta₇O₉(OPrⁱ)₁₇ (2) were formed upon prolonged storage of solutions of1 in PrⁱOH. Heptanuclear molecule2 consists of two [Ta₄] tetrahedra with a shared vertex. These tetrahedra are additionally linked togethervia one ₃-oxo and two ₂-OPrⁱ groups. Complex2 is a representative of heptameric oxoalkoxides of a new structural type.Deceased in I995.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 125–131, January, 1996.     

Furazan-containing bromoarenes in the Suzuki-Miyaura reaction

The palladium-catalyzed cross-coupling reactions of 3-[bromo(het)aryl]furazans and bromobenzofurazans with arylboronic acids afford target biaryls in good yields. 3-Bromo-4-phenylfurazan containing a bromine atom in the furazan ring undergoes decomposition under the reaction conditions.     

Synthesis of N,N′-bis[4-(1H-1,2,3-triazol-1-yl)furazan-3-yl]-methylenediamine derivatives

[3+2] Cycloaddition of azide groups of N,N′-bis(4-azidofurazan-3-yl)methylenediamine to 1,3-dicarbonyl compounds and malonodinitrile was shown to proceed regioselectively with the formation of the corresponding N,N′-bis[4-(1H-1,2,3-triazol-1-yl)furazan-3-yl]methylenediamine derivatives. The reactions of N,N′-bis(4-azidofurazan-3-yl)methylenediamine with cyanoacetic acid ethyl ester and amide led to the formation of the product of transformation of the azide group in the starting compound to the amino groups.