V. P. Boyarskii

Steric effect of substituents in haloarenes on the rate of cross-coupling reactions

The relative reactivity of ortho- and para-methyl-substituted iodoarenes in the Sonogashira reaction and palladium-catalyzed methoxycarbonylation, as well as of similarly substituted bromoarenes in the Suzuki reactions and cobalt-catalyzed methoxycarbonylation, was studied. Introduction of a methyl group into the para position of aryl halide slows down the cross-coupling. o-Methylhaloarenes are less reactive in palladiumcatalyzed reactions as compared to both unsubstituted haloarene and para-substituted analog. The presence of a methyl group in the ortho position with respect to the reaction center accelerates cobalt-catalyzed methoxycarbonylation.

Application of copper(I) halides to modifying reactivity of polyhalomethanes and arenesulfonyl chlorides in free-radical addition. Cross-halogenation reaction

In the free-radical addition of a number of organohalogen reagents to cyclic alkenes and dienes in the presence of copper(I) halides the composition of the reaction products is governed by the stage of a fast halogen transfer from the copper derivative to the alkyl radical. Under these conditions in contrast to the free-radical addition reactions initiated by UV light or peroxide initiators the intramolecular rearrangements are suppressed, the stereoselectivity of the reaction changes, and also some adducts contain halogen atoms different from those present in the organohalogen reagent employed.

Catalytic activity of palladium(II) diaminocarbene complexes in the Sonogashira and Suzuki reactions

Palladium(II) complexes with chelating and non-chelating diaminocarbene ligands were assessed as catalysts in the cross-coupling reactions of haloarenes with oct-1-yne (Sonogashira reaction) and phenylboronic acid (Suzuki reaction). Both complexes exhibited a higher catalytic activity than traditional phosphine ligandbased systems in the Sonogashira reaction, and they ensured cross-coupling not only with iodoarenes but also with bromoarenes activated by electron-withdrawing substituents. The catalytic activities of the examined complexes in the Suzuki reaction were appreciably different: the palladium(II) complex with the chelating ligand turned out to be considerably less active than the complex with the non-chelating ligand.

Comparative activity of aryl, alkyl, and cycloalkyl halides in the suzuki reaction catalyzed with acyclic diaminocarbene complex of palladium

Relative activity of halogenated arenes, alkanes, and alkanes in the Suzuki reaction catalyzed with acyclic diaminocarbene complex of palladium has been investigated. Under all the investigated conditions, 4-iodoanisole has been more active than the alkyl halides. The reaction with 4-methyl-1-(chloromethyl)benzene has afforded the target 4-methyl-1-(phenylmethyl)benzene along with significant amount of by-products; other alkyl and cycloalkyl halides do not participate into the cross-coupling reaction. Ethanol has been found the most suitable solvent for the reaction. The reaction in acetonitrile provides noticeable yield of the products only in the presence of polyethylene glycol and water.

Addition of Bromotrichloromethane and Tetrachloromethane to cis-Cyclooctene, Cyclohexene, and Norbornadiene in the Presence of Palladium(II) Complexes

Addition of bromotrichloromethane and tetrachloromethane to alkenes in the presence of palladium(II) complexes begins with single-electron transfer from the palladium atom to polyhalomethane molecule, followed by fragmentation of the radical anion thus formed and generation of trichloromethyl radical. Halogen transfer to a carbon-centered radical arising from addition of trichloromethyl radical at the double bond occurs both from the polyhalomethane molecule and from halide palladium complex.

Catalysis of the Suzuki reaction by acyclic diaminocarbene palladium complexes generated in situ

Acyclic diaminocarbene palladium complexes generated in situ by nucleophilic attack of morpholine, 4-nitrophenylhydrazine, or benzhydrazide on bis(isocyanide) palladium(II) complexes catalyzed the Suzuki reaction of 4-iodo- or 4-bromoanisole with phenylboronic acid. Morpholine turned out to be the best catalyst modifier. The cross coupling reaction under fairly mild conditions (reflux in ethanol in the presence of potassium carbonate) in 2 h afforded 4-methoxybiphenyl whose yield was insignificantly lower than in the presence of preliminarily prepared catalyst. Neither preliminary degassing nor protection from atmospheric moisture and oxygen was necessary.

Theoretical study of the structure of acyclic diaminocarbene ligands in Pd(II) complexes

The electronic and steric features of acyclic aminohydrazinocarbene ligands in palladium(II) complexes are studied by the DFT method. It was found that most of the studied complexes prefer an amphi-2 conformation over all the other possible conformations. At the same time, in the ligand containing a hydrazide fragment more stable is a syn conformation. The basicity and nucleophilicity of the title ligands are much higher compared to the respective characteristics of the triphenylphosphine ligand and close to those of bis-(diisopropylamino)carbene.

New synthesis of aryl β-bromoalkyl sulfones from arenesulfonyl chlorides via cross halogenation

A new procedure has been proposed for the synthesis of aryl β-bromoalkyl sulfones by radical addition of arenesulfonyl chlorides at the double bond of alkenes in the presence of copper(I) halides, sodium bromide, and phase-transfer catalyst. The key stage of the process is bromide ion insertion into intermediate copper(II) derivative formed in the initiation stage. The subsequent bromine atom transfer from copper to alkyl radical yields the addition product.

New promising porphyrazine-based agents for optical theranostics of cancer

New porphyrazine bases containing peripheral benzyloxyphenyl groups have been synthesized by the template method. The procedure includes condensation of aromatic aldehydes with malononitrile, transformation of arylmethylidenemalononitriles to arylethenetricarbonitriles, template assembly of porphyrazine macrocycle on bis(indenyl)ytterbium(II) complex, and removal of the central metal ion. Luminescence properties of the synthesized porphyrazines and their dependence on the viscosity of the medium were studied, and the light and dark toxicities of the porphyrazines have been estimated. The obtained results suggest the possibility of using these porphyrazines as optical theranostic agents of new generation.

Sonogashira reaction catalyzed by palladium isocyanide complex modified in situ

Palladium isocyanide complex modified in situ by addition of benzohydrazide as nucleophile was shown to catalyze Sonogashira reactions of phenylacetylene with iodobenzenes in refluxing ethanol in the presence of potassium carbonate. The reactions were complete in 2 h, and neither preliminary degassing nor protection from atmospheric moisture and oxygen was necessary. The yields of the cross-coupling products, unsymmetrical diarylacetylenes were only slightly lower than those obtained with the preliminarily prepared catalyst. The proposed procedure was used to synthesize a series of diarylacetylenes containing both electrondonating and electron-withdrawing substituents in the benzene rings.