Yu. N. Bubnov

Determination of the activation parameters of permanent allylic rearrangement in allyl- and methallylboranes and in 1,1-bis(dipropylborylmethyl)ethylene by dynamic NMR spectroscopy

Abstract The activation parameters were determined for the permanent allylic rearrangement (PAR) in five organoboranes of allylic type by means of complete line shape analysis for the dynamic NMR spectra. The introduction of the second boron atom into the allylborane molecule leads to a significant decrease in the activation barrier of the PAR.

Cage complexes of transition metals in biochemistry and medicine

The review presents the following main trends and the perspectives of application of the transition metal clathrochelates in medicine and biochemistry: encapsulation of radioactive metal ion for diagnostics and therapy; imaging agents for MRI; antidotes and prolonged pharmaceuticals; pharmaceuticals for boron neutron capture therapy; antihelminthic and antiparasitic detergents; antioxidants; membrane transport of the metal ions; interaction of the cage metal complexes with nucleic acids and the potential of their self-assembling reactions in immunology and molecular biology (recognition of antibodies, antigens and DNA sites); design of HIV inhibitors for the therapy.

Organoboron compounds. Allylboration of carbonyl compounds with allyl(alkyl)boranes

Abstract A convenient procedure for the synthesis of homoallylic alcohols from carbonyl compounds and allylboranes is described. Allyl-, 2-methylallyl-, crotyl- and 3,3-dimethylallyl(dialkyl)boranes, as well as diallyl(alkyl)boranes and derivatives of 3-allyl- and 3-metallyl-3-borabicyclo[3.3.1]non-6-ene are effective reagents for allylation of carbonyl compounds (aldehydes, ketones, esters, carboxylic acids and others) offering, in a number of cases, considerable advantages over use of corresponding allylmagnesium halides. Allylboration of carbonyl compounds is attended by the allylic rearrangement; while reacting crotyl- and 3,3-dimethyl-allylboranes are changed to homoallylic alcohols with terminal double bonds.

Organoboron compounds, synthesis of allyl(dialkyl)boranes and diallyl(alkyl)boranes

Abstract Highly reactive allyl(dialkyl)-, crotyl(dialkyl)-, 3,3-dimethylallyl(dialkyl)-(= prenyl(dialkyl), and diallyl(alkyl)-boranes were prepared by allylation of esters R2BOR′, RB(OR′)2 or thioesters R2BSR′ (R = alkyl) using allylic derivatives of aluminium, magnesium or boron in exchange reactions. The titled compounds are stable up to 100°C and do not symmetrize even on heating at 100°C for a long time. PMR spectroscopy data show that the characteristic feature of these compounds is a permanent allyl rearrangement, the rate of which increases with an increase in temperature. For allyl(diethyl)-borane at 100°C and 125°C the rates are equal to 2500 and 5000 sec−1 respectively; activation energy of the rearrangement amounts to 11.8±0.2 kcal mol−1. The boronallyl bonds in unsymmetrical allyl(alkyl)boranes readily split under the action of water and alcohols, protonolysis being accompanied by allyl rearrangement, crotyl and prenyl compounds are converted into 1-butene or 3-methyl-1-butene, respectively.

A novel method of synthesis of 1-azaadamantane from 1-boraadamantane

Abstract A novel and convenient method for the synthesis of 1-azaadamantane (I) from the 1-boraadamantane-tetrahydrofuran complex (XIII) is described. This is based on an intramolecular reaction of organic azides with organoboron compounds. Treatment of the boron cage compound XIII with iodine and an excess of sodium azide followed by oxidation (H 2 O 2 , OH − ) affords 7α-hydroxymethyl-3-azabicyclo[3.3.1]nonane (VII), cyclization of which leads to I in 40% overall yield. Some new boron cage compounds were also isolated, diazidoborane (XIV) being of particular interest.

Organoboranes-atmospheric oxygen systems as unconventional initiators of radical polymerization

This paper provides the first generalization and analysis of our results and published data about a new type of pseudoliving process: radical polymerization mediated by boroxyl radicals generated through the oxidation of organoboranes by atmospheric oxygen. The kinetics and mechanism of polymerization of methyl methacrylate and vinyl acetate in the presence of ammonia-organoboranes and boracyclanes are studied. Methods of practical use of polymerization initiated by organoborane-oxygen systems for macromolecular design are discussed.

Synthesis of 1,4-dienes and α-alkoxystyrene derivatives via allyl- and benzylboronation of acetylenic compounds

Abstract The addition of allylboranes to monosubstituted acetylenic compounds followed by protolysis of the resulting vinylboranes is a general method for synthesis of 1,4-substituted pentadienes. α-Alkoksystyrenes are obtained via the reaction of benzylboranes with alkoxyacetylenes.

An Unusual Mechanism of Polymerization of MMA Initiated by Ammonia—Triisobutyl Borane and Atmospheric Oxygen

The kinetics of polymerization of methyl methacrylate in vacuum initiated by ammonia-triisobutyl borane (iso-Bu3B · NH3) oxidized in air is studied. It is shown that the rate of reaction shows the first order with respect to the monomer concentration and a variable order with respect to the initiator concentration; the process is characterized by a low activation energy. It is demonstrated that polymerization proceeds according to a two-step mechanism. The mechanism of polymerization initiation and reinitiation is investigated via ESR spectroscopy, and it is found that one primary radical generated during initiation can form up to 200 substantial chains during the subsequent chain-transfer process.

Construction of nitrogen bicyclic and cage compounds with the use of allylic organoboranes

It is shown that reactions of triallylborane with pyrrole, pyridines, isoquinolines, lactams, 1-pyrroline, and acetylenes offer versatile methodology for the construction of various bicyclic and polycyclic nitrogen compounds, some of which are skeletally related to important classes of alkaloids. Optically active 3-borabicyclo[3.3.1]non-6-enes are useful precursors for synthesis of chiral 3-aza- and 3-thiabicyclo[3.3.1]non-6-enes, as well as derived chiral cyclohexenoid systems. The convenient methodology for the transformation of 1-boraadamantanes into 1-azaadamantanes is also discussed.

Reductive allylation of pyrrole with allylboranes. Synthesis oftrans- andcis-2,5-disubstituted pyrrolidines

Pyrrole undergoes reductive mono- and diallylation on successive treatment with β,γ-unsaturated organoboron derivatives (triallylborane, allyl(dipropyl)borane, and triprenylborane) and alcohols to give 2-allylated 3-pyrrolines andtrans-2,5-diallylated pyrrolidines. The addition of both the first and second boron-allylic fragment to the heterocycle proceeds with rearrangement. A method for transformation of thetrans-2,5-diallylpyrrolidine into thecis-isomer (heating with triallylborane at 190 °C) was developed and a series ofN-substituted derivatives of these pyrrolidines was synthesized. A method for the preparative synthesis of nonsymmetrically substitutedtrans- andcis-2-alkyl(phenyl)-5-allylpyrrolidines, based on reductive allylboration of pyrrole followed by 1,2-addition of RLi to the 5-allyl-1-pyrroline that formed, was also developed. A direct confirmation of intermediate formation of 2H- and 3H-pyrrole tautomers under the action of allylboranes was obtained. The adduct of 2H-pyrrole with BF3 was detected by NMR spectroscopy.