Oxidative coupling of arylboronic acids with arenes via Rh-catalyzed direct C-H arylation

Oxidative coupling of three different arenes and a thiophene derivative with various arylboronic acids was achieved with a [RhCl(C2H4)2]2/P[p-(CF3)C6H4]3 catalyst system. Commercially available 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO) was used as a stoichiometric oxidant. A 2-pyridyl group and an imine functional group served as ortho-directing groups to mediate the direct C-H arylation by a Rh complex. Moderate to excellent yields were obtained for the coupling reactions.     

Palladium-catalyzed ortho-selective C–H bond chlorination of aromatic ketones

A palladium-catalyzed ortho-selective C–H bond chlorination reaction for the preparation of 2-chloro aromatic ketones was described. Both electron-withdrawing and electron-donating groups on the aromatic rings are well tolerated under the optimized conditions. The 2-chloro aromatic ketones obtained by our method could be applied to synthesize the derivatives of 1H-indazole or benzo[d]isoxazole.     

Pd-catalyzed oxidative ortho-C-H borylation of arenes

The development of a Pd-catalyzed oxidative ortho-C-H borylation with N-arylbenzamides is reported. A modified dibenzylideneacetone (dba) ligand, a weak base, and a strong oxidant are critical for obtaining good yields. The reaction is tolerant of electron-deficient and electron-rich benzamides derived from readily available benzoic acids. The borylated products can be converted to various synthons via diverse transformations.     

Ruthenium-catalyzed regiospecific borylation of methyl C-H bonds

We report the regiospecific, ruthenium-catalyzed borylation of saturated terminal C-H bonds. Alkylboronates were obtained in 78-98% yields. The borylations of alkanes, trialkylamines, protected alcohols, and fluoroalkanes occurred regiospecifically at the methyl group that is least sterically hindered. In contrast to most organometallic C-H activation, the reactions of alkanes occurred in higher yields than the reactions of arenes. Reactions were conducted that probed steric and electronic effects on the alkyl borylation. These reactions showed that the borylation occurred preferentially at the methyl group that is least sterically hindered and most electron-deficient. Ruthenium compounds containing boryl ligands were synthesized, and one was characterized by X-ray crystallography. One of these compounds contained a rare bridging boryl ligand and served as a catalyst precursor for the borylation of octane.     

Sterically directed functionalization of aromatic C-H bonds: selective borylation ortho to cyano groups in arenes and heterocycles

Ir-catalyzed borylations of 4-substituted benzonitriles are described. In contrast to electrophilic aromatic substitutions and directed ortho metalations, C-H activation/borylation enables functionalization at the 2-position, adjacent to the cyano group, when the 4-subsitutent is larger than cyano. When an excess of borane reagent is used, diborylation can be achieved with a single regioisomer being formed in certain cases. Extension of sterically directed borylation to cyano-substituted, five- and six-membered ring heterocycles is also reported.     

Asymmetric hydrogenation of aromatic ketones with new P-chirogenic monophosphine ligands

Novel P-chirogenic anisylphenyl-HMOP derivatives have been synthesised from (R)-2,2′-bis-(trifluoromethanesulfonyloxy)1,1′-binaphthyl. Preliminary results concerning the asymmetric hydrogenation of acetophenone and 3,5-bis(trifluoromethyl)acetophenone with Ru(II)-HMOP complexes in combination with various diamines was also tackled.     

Palladium-catalyzed C-H perfluoroalkylation of arenes

A new Pd-catalyzed reaction for the coupling between perfluoroalkyl iodides (R(F)I) and simple aromatic substrates is described. The perfluoroalkylated arene products are obtained in good to excellent yields in the presence of a phosphine-ligated Pd catalyst and Cs(2)CO(3) as a base. The development, optimization, scope, and preliminary mechanistic studies of these transformations are reported.     

Regioselectivity of the borylation of alkanes and arenes

The borylation of alkanes and arenes has become some of the most practical C-H bond functionalization chemistry. Most striking is the high regioselectivity of these reactions. Rhodium and ruthenium complexes catalyze with exquisite selectivity the borylation of methyl C-H bonds over methylene or methine C-H bonds. Iridium complexes catalyze, with high steric control, the borylation of one aromatic C-H bond over another. In contrast, iridium-catalyzed borylation of heteroaromatic C-H bonds is more controlled by electronic effects. Detailed information on these selectivities and mechanistic information on the origins of this regioselectivity will be described in this critical review (95 references).     

Direct oxidative coupling of arenes with olefins by Rh-catalyzed C-H activation in air: observation of a strong cooperation of the acid

A [{RhCl(cod)}(2)]/CCl(3) COOH system was developed for the oxidative coupling of non-chelate-assisted arenes with olefins in the presence of catalytic amounts of Cu(OAc)(2) ?H(2) O as a co-oxidant and oxygen as the terminal oxidant. The acid was an indispensable component in this system and played a very important role in the coupling reaction. This catalytic system was applied to the direct oxidative coupling of a series of arenes and olefins and the corresponding products were afforded in high yields with special chemo- and regioselectivity. This reaction provides an atom-efficient route to vinylarenes, which are widely used in various fine chemicals.     

Development of recyclable iridium catalyst for C-H borylation

Aromatic C-H borylation using [IrCl(COD)]₂ and 2,2′-bipyridinedicarboxylic acids was studied. 2,2′-Bipyridine-4,4′-dicarboxylic acid was complexed with [IrCl(COD)]₂ in the presence of bis(pinacolato)diboron. The resulting iridium catalyst could be readily separated from the reaction mixture by simple filtration, and the recovered catalyst under a nitrogen atmosphere was still active and could be reused more than 10 times.     

Palladium-catalyzed borylation of sterically demanding aryl halides with a silica-supported compact phosphane ligand

Immobile but active: A silica-supported "compact" phosphane, Silica-SMAP, can be used in the Pd-catalyzed borylation of aryl chlorides or bromides with bis(pinacolato)diboron. The Silica-SMAP/Pd system significantly expands the substrate scope of the borylation toward sterically and electronically challenging aryl halides.     

Unsaturated iridium pyridinedicarboxylate pincer complexes with catalytic activity in borylation of arenes

Unsaturated σ,π-cyclooctenyl and hydrido Ir(III) complexes bearing an unusual tridentate dianionic ONO pincer-type ligand have been straightforwardly obtained from 2,6-pyridinedicarboxylic acid and standard Ir(I) starting materials. These complexes efficiently catalyzed the arene C-H borylation under thermal conditions.     

Palladium-catalyzed monoselective C-H borylation of acetanilides under acidic conditions

A practical Pd-catalyzed reaction was developed to achieve C-H activation/C-B cross-coupling of acetanilides under acidic conditions. The new reaction shows a good functional group tolerance and an exclusive mono-selectivity. This C-H borylation method may provide a generally applicable route for the conversion of C-H moieties into many other types of bonds.     

Iridium-catalyzed, substrate-directed C-H borylation reactions of benzylic amines

The iridium-catalyzed arene C-H borylation reaction of benzylic amines has been developed, which inverts the typical steric-controlled product distribution to provide ortho-substituted boronate esters. Picolylamine was found to be an ideal ligand to replace 4,4'-di-tert-butylbipyridine to induce the directing effect. Preliminary experiments are consistent with a mechanism involving dissociation of one amine of the hemilabile diamine ligand.     

Copper-mediated C-H bond arylation of arenes with arylboronic acids

A new copper-mediated cross-coupling of arenes and arylboronic acids is described. Under the influence of Cu(OCOCF 3) 2, the C-H bond arylation of electron-rich arenes with arylboronic acids takes place to afford a range of biaryls in good yields. The reaction is selective for cross-coupling; no homocoupling product arising from arenes or arylboronic acids is detected. Multiple C-H bond arylation is possible with indoles and pyrroles furnishing interesting extended pi-systems.     

Synthetic and structural studies of the diiron toluenedithiolate carbonyl complexes with monophosphine ligands

Four diiron toluenedithiolate complexes 2–5 with monophosphine ligands are reported. Treatment of [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₆ (1) with tris(3-chlorophenyl)phosphine, tris(4-chlorophenyl)phosphine, tris(4-methylphenyl)phosphine or 2-(diphenylphosphino)benzaldehyde, and Me₃NO?2H₂O in MeCN resulted in the formation of [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₅[P(3-C₆H₄Cl)₃] (2), [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₅[P(4-C₆H₄Cl)₃] (3), [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₅[P(4-C₆H₄CH₃)₃] (4), and [μ-SC₆H₃(CH₃)S-μ]Fe₂(CO)₅[Ph₂P(2-C₆H₄CHO)] (5) in 64–82% yields. Complexes 2–5 have been characterized by elemental analysis, IR, ¹H NMR, ³¹P{¹H} NMR, ¹³C{¹H} NMR and further confirmed by single crystal X-ray diffraction analysis. The molecular structures show that 2–5 contain a butterfly diiron toluenedithiolate cluster coordinated by five terminal carbonyls and an apical monophosphine.     

Transition metal-catalyzed borylation of alkanes and arenes via C---H activation

Since 1999, direct borylation of hydrocarbons catalyzed by a transition metal complex has been extensively studied by several groups and has become an economical, efficient, elegant, and environmentally benign protocol for the synthesis of a variety of organoboron compounds. Re-, Rh-, Ir- and Pd-catalyzed C---H borylation of alkanes, arenes and benzylic positions of alkylarenes by bis(pinacolato)diboron or pinacolborane provide alkyl-, aryl-, heteroaryl- and benzylboron compounds, respectively. In this review, seminal early works and exciting recent developments in the area of direct borylation of hydrocarbons via C---H activation are summarized.