(Alk-1-ynyl)organylthiocarbenes: generation and reactions with olefins

1-Substituted 1-chloro-3-organylthiopropa-1,2-dienes 1a–f belonging to previously unknown type of allenic compounds were synthesized by chlorination of 1-organylthioalk-1-ynes 3a–f with N-chlorosuccinimide. The reactions of compounds 1a–f with Bu^tOK in hexane at –20 °C are accompanied by -elimination of HCl to give new alk-1-ynyl(organylthio)carbenes 2a–f, which add to olefins to form the corresponding 1-(alk-1-ynyl)-1-organylthiocyclopropanes 5 in yields of up to 60%. The electrophilic properties of carbenes 2 were confirmed experimentally.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2440–2447, November, 2004.     

New synthesis of 3,3-disubstituted piperidin-2-ones from esters and 1-(3-halopropyl)-2,5-dimethylpyrroles

Russian Chemical Bulletin - 3,3-Disubstituted piperidin-2-ones were obtained by alkylation of carboxylic acid esters with 1-(3-halopropyl)-2,5-dimethylpyrroles using lithium diisopropylamide as a...     

The electronic structure of 5-methylhexa-1,2,4-triene-1,3-diyl, the first representative of highly delocalized triplet ethynylvinylcarbenes, from ESR spectroscopy data and quantum chemical calculations

The ESR spectrum of the first representative of highly conjugated triplet ethynylvinylcarbenes, 5-methylhexa-1,2,4-triene-1,3-diyl (1), was recorded in solid argon matrix. The zero-field splitting (ZFS) parameters of carbene 1 (D = 0.5054±0.0006 cm^?1 and E = 0.0045±0.0002 cm^?1) determined from the experimental ESR spectrum are in between the corresponding parameters of ethynylcarbene C3H2 (2) and vinylcarbene C₃H₄ (3): D(3) < D(1) < D(2) and E(2) < E(1) < E(3). Quantum chemical calculations of the ZFS parameters of 1, 2, and 3 have been carried out for the first time using two DFT-based approaches, RODFT and UDFT. An analysis of the experimental and theoretical ZFS parameters shows that carbene 1 is characterized by a greater extent of delocalization of the spin density of unpaired electrons than carbenes 2 and 3. The characteristic structural fragments of carbene 1 possess the principal features of the electronic structure of both ethynylcarbene (2) and vinylcarbene (3), respectively. Magnetic spin-spin interactions are identical in carbenes 1 and 2. The dominant contribution to D in 1 and 2 results from the one-center spin-spin interactions on carbon atoms in the propynylidene group, which are subjected to strong spin polarization.     

Lithiation of 1-alkynyl-1-chlorocyclopropanes and subsequent reactions with electrophilic reagents: synthesis of functionalized alkynyl- and vinylidenecyclopropanes

1-Alkynyl-1-chlorocyclopropanes undergo chlorine-lithium exchange on treatment with BuⁿLi in THF at -40—0 °C. Thus generated organolithium species react with carbon dioxide (dry ice) and acetone to give selectively hitherto unknown 1-alkynylcyclopropanecarboxylic acids and the corresponding alcohols in up to 74% yields. Similar reactions involving methyl chloroformate result in the mixtures of cyclopropylacetylenic and vinylidenecyclopropanic esters, while the use of aliphatic aldehydes as electrophiles provides secondary allenic alcohols in up to 64% yields.

     

New selective cyclizations of alk-4-ynals with primary amines and azoles:one-pot synthesis of 2-azolylpyrrolidines and 3-iminocyclopentenes

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Measurements of neutron fluxes with energies from thermal to several MeV in near-Earth space: SINP results

Neutron measurement results obtained at SINP MSU since 1970 are presented. These measurements were made using techniques based on neutron moderation and subsequent detection in a Li6I(Eu) crystal or a He3 coronal counter. The measurements were mainly carried out in orbits with inclination of 52 degrees and altitudes of 200-450 km. The spatial and angular distributions of the measured neutron fluxes were studied. The albedo neutron flux was estimated according to the count rate difference for opposite detector orientations towards Earth and away from it. This flux is comparable to the local neutron flux outside the Brazil anomaly region, where local neutrons dominate. Neutron fluxes, generated by solar protons, were detected during a solar flare on June 6, 1991 for the first time. Their spectrum was estimated as a power law with alpha>2.