Rhodium-catalyzed selective olefination of arene esters via C-H bond activation

A new catalytic procedure of ortho-olefination of benzoates and benzaldehydes has been developed. Ester and carboxaldehyde units were revealed to be effective chelating groups in focusing the activation of aryl C-H bonds ortho to the directing moieties under the Rh-catalyzed oxidative conditions. The reaction is highly regioselective with a range of benzoates and benzaldehydes enabling the efficient olefination with acrylates, acrylic acid, and styrenes.     

Rhodium-catalyzed direct ortho C-H olefination of phenol derivatives

Cationic rhodium complex-catalyzed olefination of phenol derivatives for the direct introduction of an α,β-unsaturated ester appendage is described. In addition, deuterium labelling and kinetic isotope effect studies were performed to probe the reaction mechanism.     

Rhodium-catalyzed C-H activation and conjugate addition under mild conditions

An efficient rhodium(III)-catalyzed C-H activation and subsequent conjugate addition was achieved under mild conditions. The reaction utilized inert arenes to replace stoichiometric organometallic reagents and can tolerate various functional groups as well as air and water.     

Ligand-promoted C-3 selective C-H olefination of pyridines with Pd catalysts

Pd-catalyzed C-3 selective olefination of pyridines is developed for the first time using 1,10-phenanthroline as the ligand. This finding provides a novel disconnection for the synthesis of pyridine-containing alkaloids and drug molecules as well as a new approach for developing Pd-catalyzed C-H functionalizations of pyridines.     

Rhodium-catalyzed alkylation of aromatic azines with alkenes via C-H bond activation

The aromatic azines reacted with terminal alkenes under a rhodium catalyst [RhCl(coe)₂]₂ and Cy₃P to give the alkylated products with good to high isolated yields. The azines bearing H and o-CH₃, p-CH₃ and p-CH₃O groups have high reactivities, but m-CH₃O, p-Cl, p-F exhibit low reactivities.     

Rhodium-catalyzed alkylation of terephthaldialdimine with terminal alkenes via C-H bond activation

Terephthaldialdimine 1a reacted with alkenes to give 2,6-dialkylated products selectively in moderate to high isolated yields. In the case of terephthaldialdimine 1b having a substituent at site 2 in the phenyl ring, the alkylation takes place selectively at site 6 in the phenyl ring. In this alkylation, a meta-substituent affected the reactivity significantly because of the steric hindrance.     

Rhodium-catalyzed regioselective C-H functionalization via decarbonylation of acid chlorides and C-H bond activation under phosphine-free conditions

Efficient rhodium(I)-catalyzed regioselective functionalization of aromatic C-H bonds has been realized with acid chlorides as the coupling partners via decarbonylation and C-H activation under phosphine-free conditions.     

Rhodium-catalyzed C-H bond activation/[4 + 2] annulation/aromatization cascade to produce phenol, naphthol, phenanthrenol, and triphenylenol derivatives

It has been established that a cationic rhodium(I)/dppp complex catalyzes the aldehyde C-H bond activation/[4 + 2] annulation/aromatization cascade to produce phenol, naphthol, phenanthrenol, and triphenylenol derivatives from readily available conjugated alkynyl aldehydes and alkynes.     

Rhodium-catalyzed regioselective olefination directed by a carboxylic group

The ortho-olefination of benzoic acids can be achieved effectively through rhodium-catalyzed oxidative coupling with alkenes. The carboxylic group is readily removable to allow ortho-olefination/decarboxylation in one pot. α,β-Unsaturated carboxylic acids such as methacrylic acid also undergo the olefination at the β-position. Under the rhodium catalysis, the cine-olefination of heteroarene carboxylic acids such as thiophene-2-carboxylic acid proceeds smoothly accompanied by decarboxylation to selectively produce the corresponding vinylheteroarene derivatives.     

Rhodium-catalyzed intermolecular amidation of arenes with sulfonyl azides via chelation-assisted C-H bond activation

We report the direct amidation of arene C-H bonds using sulfonyl azides as the amino source to release N(2) as the single byproduct. The reaction is catalyzed by a cationic rhodium complex under external oxidant-free conditions in the atmospheric environment. A broad range of chelate group-containing arenes are selectively amidated with excellent functional group tolerance, thus opening a new avenue to practical intermolecular C-N bond formation.     

Rhodium-catalyzed intramolecular C-H insertion of alpha-aryl-alpha-diazo ketones

Direct diazo transfer proceeds smoothly with alpha-aryl ketones. The derived alpha-aryl-alpha-diazo ketones cyclize efficiently with Rh catalysis to give the corresponding alpha-aryl cyclopentanones.     

N-acylsulfonamide assisted tandem C-H olefination/annulation: synthesis of isoindolinones

A tandem C-H olefination/annulation sequence directed by N-acylsulfonamides affords a variety of isoindolinones. This transformation is compatible with aliphatic alkenes as well as conjugated alkenes. Notably, molecular oxygen can be used as the sole, eco-friendly oxidant.     

Mechanistic rationalization of unusual kinetics in Pd-catalyzed C-H olefination

Detailed kinetic studies and novel graphical manipulations of reaction progress data in Pd(II)-catalyzed olefinations in the presence of mono-N-protected amino acid ligands reveal anomalous concentration dependences (zero order in o-CF(3)-phenylacetic acid concentration, zero order in oxygen pressure, and negative orders in both olefin and product concentrations), leaving the catalyst concentration as the sole positive driving force in the reaction. NMR spectroscopic studies support the proposal that rate inhibition by the olefinic substrate and product is caused by formation of reversible off-cycle reservoirs that remove catalyst from the active cycle. NMR studies comparing the interaction between the catalyst and substrate in the presence and absence of the ligand suggest that weak coordination of the ligand to Pd prevents formation of an inactive mixed acetate species. A fuller understanding of these features may lead to the design of more efficient Pd(II) catalysts for this potentially powerful C-H functionalization reaction.     

Rh catalyzed C-H activation and oxidative olefination without chelate assistance: on the reactivity of bromoarenes

A Rh catalyzed, no-chelate-assisted C-H activation/oxidative olefination reaction of bromoarenes has been discovered, in which the latter ones seem to act as a substrate, terminal oxidant, and catalyst modifier.     

Rhodium catalyzed C-H olefination of N-benzoylsulfonamides with internal alkenes

An annulation via tandem rhodium catalyzed C-H olefination of N-benzoylsulfonamides with internal olefins followed by C-N bond formation is disclosed. A N-substituted quaternary center is formed during the reaction thus providing efficient access to a series of 3,3-disubstituted isoindolinones.     

Palladium-catalyzed direct olefination of urea derivatives with n-butyl acrylate by C-H bond activation under mild reaction conditions

Pd(II)-catalyzed aromatic C-H bond activation using urea as a directing group was achieved in a p-TsOH/AcOH medium under mild reaction conditions. The direct olefination products of various urea derivatives were produced from aryl urea derivatives and butyl acrylate in moderate to good yields.