New palladium(II)-catalyzed asymmetric 1,2-dibromo synthesis

[reaction: see text] The oxidation of olefins by chiral monometallic and bimetallic Pd(II)-Cu(II) catalysts in bromide-containing aqueous-THF reaction mixtures produced chiral 1,2-dibromides. With alpha-olefins, the ee's were about 95% while most of the internal alkenes gave somewhat lower enantioselectivities ( approximately 80%).     

Pd(0)-catalyzed intramolecular Heck reaction: a versatile route for the synthesis of dibenzoazocinone derivatives

Two efficacious synthetic methodologies for the construction of medium-sized nitrogen heterocycles dibenzoazocinones have been developed. The phosphine-assisted protocol afforded better yields of the dibenzoazocinones (73-82%).     

Pd(0)-catalyzed intramolecular Heck reaction: A general route for fused oxepine derivatives

A simple and facile approach for the synthesis of various structurally different tricyclic bent oxepine frameworks from a readily accessible precursor has been introduced. The synthesis of substituted oxepine derivative involved Pd(0)-catalyzed Heck reaction. This methodology enriches the literature for the large ring formation.     

Short and versatile route to a key intermediate for lactacystin synthesis

[reaction: see text] A key intermediate 14 for the synthesis of lactacystin 1 has been constructed in four steps and 33% overall yield. The key steps involve cyclization of a suitably functionalized glutamic acid derivative and concomitant alkylation of the resulting beta,beta-diketoester system, C-acylation of the cyclic alpha-amidoketone 9, and decarboxylbenzylation of 12. Alkylation of a related beta,beta-diketoester 5 was additionally achieved with several electrophiles.     

Intramolecular Pd(II)-catalyzed oxidative biaryl synthesis under air: reaction development and scope

New reaction conditions for intramolecular palladium(II)-catalyzed oxidative carbon-carbon bond formation under air are described. The use of pivalic acid as the reaction solvent, instead of acetic acid, results in greater reproducibility, higher yields, and broader scope. This includes the use of electron-rich diarylamines as illustrated in the synthesis of three naturally occurring carbazole products: Murrayafoline A, Mukonine, and Clausenine. A variety of side products have also been isolated, casting light on competing reaction pathways and revealing new reactivity with palladium(II) catalysis.     

Tandem-type Pd(II)-catalyzed oxidative Heck reaction/intramolecular C-H amidation sequence: a novel route to 4-aryl-2-quinolinones

A novel catalytic method for synthesizing 4-aryl-2-quinolinones is reported. The process involves two mechanistically independent, sequential Pd(II)-catalyzed reactions--the oxidative Heck reaction and the intramolecular C-H amidation--both of which smoothly proceed in the presence of a single catalytic system in a one-pot manner.     

The novel approach to indole alkaloids by using Pd(II)-catalyzed cyclization

The synthesis of indole skeleton by using Pd(II)-catalyzed cyclization of the urethane has been achieved. The urethanes with allylic alcohol were converted into vinyl indolines in good yield. The vinyl indoline was transformed into some intermediates of indole alkaloids.     

Triphenylphosphine chalcogenides as efficient ligands for room temperature palladium(II)-catalyzed Suzuki-Miyaura reaction

A simple catalytic system based on PdCl₂ and triphenylphosphine chalcogenides (PPh₃X; X = O, S, Se) is found to be highly effective (up to 97% isolated yield) in the room temperature Suzuki-Miyaura reactions. Under the same experimental conditions, triphenylphosphine chalcogenides as ligands show superior activities compared to free triphenylphosphine.     

A Rh(II)-catalyzed cycloaddition approach toward the synthesis of komaroviquinone

Using a rhodium(II)-catalyzed cyclization/cycloaddition sequence as the key reaction step, the icetexane core of komaroviquinone was constructed by an intramolecular dipolar-cycloaddition of a carbonyl ylide dipole across a tethered π-bond. The ylide was arrived at by cyclization of a rhodium carbenoid intermediate onto a proximal ester group. Efforts toward the preparation of the required precursor for elaboration to the natural product are discussed.     

Pd(II)-catalyzed ortho trifluoromethylation of arenes and insights into the coordination mode of acidic amide directing groups

A Pd(II)-catalyzed trifluoromethylation of ortho C-H bonds with an array of N-arylbenzamides derived from benzoic acids is reported. N-Methylformamide has been identified as a crucial promoter of C-CF(3) bond formation from the Pd center. X-ray characterization of the C-H insertion intermediate has revealed a rare coordination mode of acidic amides as directing groups and the origin of their capacity in directing C-H activation.     

Cationic palladium(II)-catalyzed addition of arylboronic acids to nitriles. One-step synthesis of benzofurans from phenoxyacetonitriles

[Structure: see text] A cationic palladium complex catalyzed addition of arylboronic acids to nitriles to yield aryl ketones with moderate to good yields was developed. A one-step synthesis of benzofurans from phenoxyacetonitriles under the catalysis of [(bpy)Pd+(micro-OH)]2(-OTf)2 or [(bpy)Pd2+(H2O)2](-OTf)2 was developed which showed that the cationic palladium catalyst is highly active for these addition reactions.     

Chiral Palladium(II)-catalyzed asymmetric glyoxylate-Ene reaction: alternative approach to the enantioselective synthesis of alpha-hydroxy esters

An effective chiral palladium catalyst [Pd(CH(3)CN)(2)(S)-Tol-BINAP](SbF(6))(2) (2b) is developed for asymmetric glyoxylate-ene reactions. This palladium dicationic catalyst provides a simple but efficient approach to the asymmetric synthesis of alpha-hydroxy esters in excellent yields with high enantioselectivities at relatively higher reaction temperature (60 degrees C).     

Tandem Pd(II)-catalyzed vinyl ether exchange-Claisen rearrangement as a facile approach to gamma,delta-unsaturated aldehydes

A sequential allyl vinyl ether formation-Claisen rearrangement process catalyzed by a palladium(II)-phenanthroline complex is reported. The effects of allylic alcohol structure, type of vinylating agent, and palladium catalysts are discussed. This method provides a convenient approach to gamma,delta-unsaturated aldehydes under mild conditions that avoid the use of toxic Hg(II) catalysts. The new methodology has been successfully demonstrated on the kilogram scale.     

Pd(II)-catalyzed oxidative dimeric cyclization-coupling reaction of 2,3-allenoic acids: an efficient synthesis of bibutenolide derivatives

Three sets of convenient catalytic systems have been developed for the oxidative dimeric cyclization coupling of differently substituted 2,3-allenoic acids catalyzed by Pd(II), affording bibutenolides that are not otherwise readily available. The advantages and disadvantages of these systems are discussed. Although the diastereoselectivity for the bicyclization of racemic 2,3-allenoic acids is low, excellent diastereoselectivity was realized in the bicyclization reaction of optically active 2,3-allenoic acids, leading to the optically active bibutenolides in high yields and ee. Based on a mechanistic study, it is believed that the reaction may proceed by means of a double oxypalladation and reductive elimination to yield butenolide 3 and Pd(0) species, which may be reoxidized to the catalytically active Pd(II) species in the presence of alkyl iodide/air, metallic iodide/air, or benzoquinone.     

Cationic Pd(II)-catalyzed arylative cyclization of N-(2-formylaryl)alkynamides: An efficient route to 2-quinolinones

A cationic palladium complex catalyzed arylative cyclization reaction of N-(2-formylaryl)alkynamides with arylboronic acids was developed. This new process provides an efficient way for the synthesis of functionalized 2-quinolinones in good to excellent yields under mild conditions. Some control experiments were conducted to explain the possible mechanism for the formation of the products.     

Enantioselective Pd(II)-catalyzed aerobic oxidative amidation of alkenes and insights into the role of electronic asymmetry in pyridine-oxazoline ligands

Enantioselective intramolecular oxidative amidation of alkenes has been achieved using a (pyrox)Pd(II)(TFA)(2) catalyst (pyrox = pyridine-oxazoline, TFA = trifluoroacetate) and O(2) as the sole stoichiometric oxidant. The reactions proceed at room temperature in good-to-excellent yields (58-98%) and with high enantioselectivity (ee = 92-98%). Catalyst-controlled stereoselective cyclization reactions are demonstrated for a number of chiral substrates. DFT calculations suggest that the electronic asymmetry of the pyrox ligand synergizes with steric asymmetry to control the stereochemical outcome of the key amidopalladation step.