Biogenetically patterned synthesis of Δ8(9-capnellene

In a biogenetically patterned synthesis, treatment of the cycloocta-1,5-diene (3$\text{3}$) or its $\text{oxo}$-methylene isomer (4), with boron trifluoride etherate is shown to lead to Δ⁸(⁹)-capnellene (8).     

13C NMR spectroscopy of tautomeric conversions in imidazole compounds

A study has been made of¹³C NMR spectra of several series of imidazoles and their salts in solution and in the solid state. It has been shown that in compounds containing a pyridine ring, prototropic tautomerism on the NMR time scale may be retarded. The possible mechanism of these processes is discussed.V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 11795 Moscow. Torino University, Italy. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 299–308, February, 1992.     

Hexamethyldilead: III. Reaction with metal salts and organomercurials

Hexamethyldilead reacts with various metal salts very rapidly in comparison with the rate of mixing of the reactants so that the product composition depends upon the order of addition and the competition between rapid reactions rather than any fundamental differences in mechanism.     

Transformations of C-adducts of 1,4-diazinium salts with dicarbonyl compounds into polycyclic systems

C-Adducts of 5-(het)aryl-2,3-dicyano-1-pyrazinium salts containing a residue of a 1,3-dicarbonyl compound at position 6 can be involved in the cyclization with hydrazine hydrate giving rise to pyrazino[2,3-c]pyridazines along with the expected pyrazole derivatives. The reactions of the same σ^H-adducts with hydroxylamine unexpectedly afforded triazacyclopenta[a]indene derivatives. The crystallographic data on the three-dimensional structures of new polycyclic compounds were obtained. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 639–643, March, 2008.     

Electron transfer-II: Accumulation of 5-ethyl-3-methyllumiflavin radical by spontaneous conversions of 5-ethyl-3- methyllumiflavinium salts

5-Ethyl-3-methyllumiflavinium salts 3 (Scheme 1 ; 5-EtFl⁺_ox⁺, A^- in Scheme 2) may arise in situ on adding an acid (HA) to solutions of the 4^a-flavin adducts 5 in low polar solvents. The acidified solutions were kept under N₂ at 25° in the dark to give spontaneous accumulations of the 5-ethyl-3-methyllumiflavin radical 6 (5-EtFl· and/or 5-EtFlH⁺·) and of some 3-methyllumiflavin 10 (Scheme 3) in dependence on the nature of the solvent and, on the nature and the concentration of the acid.The use of TFA;TCA;AcOH;α-ketoglutaric and salicyclic aci (Table 1) gave 6 and 10 in yields of 60–90% and 6–21%, respectively. The anaerobic production of 10 limits the formation of 6 to a theoretical yield of 66.7%. On suppressing the limiting pathway (eqn 3) the formation of 6 is increased which, however, will not always be revealed by an increased accumulation of 6. In a radical termination, 6 could react with another radical to give a 4^a-flavin adduct. The use of TCA in MeCN gave a decrease of 10 coupled with the increased occurrence of Cl₃CCOO· and Cl₃C· radicals as appeared from the spontaneous generation of CO₂ (eqns 3+7). 5-EtFl· was probably trapped by Cl₃,C· to give 5-ethyl-3-methyl-4^a-trichloromethyllumiflavin (eqn 8). In contrast, the use of HCOOH promised the achievements of quantitative accumulations of 6 which was indeed realized (Table 2 ; Figs 2 and 3).     

Nitropyridines: III. Synthesis of meta-terphenyls by recyclization of nitropyridinium salts

A two-component Hantzsch synthesis was applied to preparation of nitropyridines and their quaternary salts from various enamines and chalcones based on nitroacetophenone. The recyclization of nitropyridinium quaternary salts under the treatment with an aqueous-alcoholic alkali led to preparation of 5′-methylamino-2′-nitro-m-terphenyl derivatives.     

Precipitation of surfactant salts III. Metal perfluoroalkanecarboxylates

Precipitation of perfluorocarboxylic acids (n-C₃H₇OOH, n-C₇H₁₅COOH, and n-C₉F₁₉COOH) in aqueous solutions of different metal nitrates (K⁺, Ag⁺, Ca²⁺, Ba²⁺, Zn²⁺, Al³⁺, La³⁺) was studied by solubility and calorimetric measurements. The free energy of precipitation per single surfactant chain was found to depend on the chain length but not on the charge of the reacting cation. It was shown that the precipitation of perfluorocarboxylates of multivalent cations was governed by positive entropy change and a low enthalpic contribution, whereas the soaps of monovalent cations exhibited the opposite behavior. The entropy of precipitation was not affected by the chain length of the surfactants in the presence of monovalent cations, but it increased for cations of higher charge.Supported by the NSF Grant CHE-8619509.This paper is dedicated to Professor Armin Weiss on the occasion of his 60th birthday. One of the authors (E. M.) particularly appreciates many years of cooperation with Professor Weiss in editing Colloid and Polymer Science, as well as in many other scientific interactions.     

Diterpene chemistry—IV : Transformations of 8(17),14-labdadien-13-ol

The origin of the long range coupling in exocyclic epoxides with quasi-axial methylenes has been established by the synthesis of specifically deuterated analogues. Use was made of paramagnetic shift reagents in distinguishing between the epoxide protons.     

Recyclable synthesis of mesityl iodonium(III) salts

An efficient protocol for C–H condensation of hypervalent iodine compounds toward arenes in fluoroalcohols has been applied to the recyclable preparation of mesityl iodonium(III) salts. The electrophilicities of [hydroxy(tosyloxy)iodo]mesitylene (MesI(OH)OTs) and iodomesitylene diacetate (MesI(OAc)₂) are suitably enhanced in 2,2,2-trifluoroethanol. A series of nucleophilic aromatic compounds react smoothly with MesI(OH)OTs and MesI(OAc)₂ or in situ hypervalent iodine(III) species, generated from iodomesitylene, to provide the target mesityl iodonium(III) salts in good yields at room temperature with broad functional group tolerance. This C–H condensation strategy merits high para-regioselectivities during the diaryliodonium(III) salt formation, but the major limitation in the case of low-reactive aromatic substrates is byproduct formation resulting from the self-condensation of the nucleophilic mesitylene ring in MesI(OH)OTs and MesI(OAc)₂.     

5-Arylidene aminouracils: III. Kinetics and mechanism of sodium salts formation

It extension of the studies on the search for the new biologically active 5-aminouracyl derivatives, we synthesized by the reaction of dialkylphosphites with arylideneuracils respective aminomethylphosphonates. The high level of the antiviral and anti-mycobacterial activity of the target compounds correlates well with the physicochemical parameters characterizing their structure.     

Diterpene chemistry : Transformations of 8(17), 14-labdadien-13-ol—Part 2

Aqueous permanganate oxidation of 8(17)-labden-13-ol gave two novel oxidation products by functionalisation of an unactivated carbon atom. The structures have been confirmed by degradative studies and a mechanism to account for their formation is proposed.     

13C NMR spectra of azolopyridines and their quaternary salts

¹³ C NMR spectra of some azole series have been investigated: 2-pyridylbenzimidazoles, 2-pyridylimidazo [4,5-b]-pyridines, 2-pyridylimidazo[4,5-c]-pyridines, analogous oxazole compounds, as well as their mono- and bisquaternary salts. Some problems, related to the structure of these compounds in solution, have been discussed.V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow 117975. Torino University, Italy. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 866–872, April, 1992.