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.     

Palladium-catalyzed synthesis of 2-allylindole and 2-allylbenzofuran derivatives from 2-((trimethylsilyl)ethynyl)arenes

A new protocol for the synthesis of 2-allylindole and 2-allylbenzofuran derivatives has been developed from readily accessible starting material, 2-((trimethylsilyl)ethynyl)arenes via Pd-catalysis. The presence of trimethylsilyl group in the alkyne is vital for this reaction. Stereoselectivity of 2-allylindole derivatives is controlled by the use of different nitrogen-protecting groups for 2-((trimethylsilyl)ethynyl)aniline. The CO₂Me protection gives Z-isomers, whereas acetyl protection gives E-isomers.     

Palladium-catalyzed cross-coupling reactions of 2-diazonaphthoquinones with arylboronic acids

Palladium-catalyzed cross-coupling reactions of 2-diazonaphthoquinones and arylboronic acids proceeded by the treatment with Pd(OAc)₂ in acetic acid to afford 2-aryl-1-naphthols.     

Palladium-catalyzed acetoxylation of arenes by 1,2,3-triazole-directed CH activation

A facile and efficient method for the regioselective acetoxylation of 1,4-disubstituted 1,2,3-triazoles via Pd-catalyzed C$\text{<mglyph src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"></mglyph>}$H bond activation was developed. The cheap acetic acid was applied as the acetoxyl source to convert aromatic sp² C$\text{<mglyph src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"></mglyph>}$H bonds into C$\text{<mglyph src="https://sdfestaticassets-eu-west-1.sciencedirectassets.com/shared-assets/16/entities/sbnd"></mglyph>}$O bonds in high regioselectivity, employing 1,2,3-triazole as an elegant directing group and K₂S₂O₈ as the oxidant. A range of 1,2,3-triazoles bearing acetoxyl group can be synthesized with the reaction facilely.     

Palladium-catalyzed benzylic direct arylation of benzyl sulfones with aryl halides

An effective palladium catalyst system for the direct arylation of benzyl sulfones with aryl halides has been developed. The catalytic reaction provides a facile route to diarylmethyl sulfones. The products can be transformed further via desulfonylative functionalization mediated by aluminum compounds.     

Palladium-catalyzed oxime ether directed regioselective C-H alkoxylation of arenes

A palladium-catalyzed highly regioselective ortho-C(sp²)-H alkoxylation of oxime ethers with PhI(OAc)₂ as the oxidant and alcohols as the alkoxylation reagents has been developed. Mono-alkoxylated and acetoxylated products could be selectively obtained via tuning the reaction conditions. A series of oxime ethers were tolerated, affording the corresponding products in moderate to good yields. Both primary and secondary alcohols survived the reaction conditions. Moreover, the directing group can be easily removed, thereby providing a straightforward access to substituted aryl ketones.     

Palladium-catalyzed cyclization of vinyl iodide-tethered allensulfonamide

This Letter describes a palladium-catalyzed cyclization of vinyl iodide-tethered allensulfonamide in the presence of alkylol, which provides a facile access to 2-alkoxy-3-methylene-tetrahydropyridine. The asymmetric version of this reaction has also been preliminarily realized with up to 81% enantioselectivity when chiral bisphosphine ligands were used.     

Palladium-catalyzed, asymmetric Baeyer-Villiger oxidation of prochiral cyclobutanones with PHOX ligands

Described in this report is a general method for the conversion of prochiral 3-substituted cyclobutanones to enantioenriched γ-lactones through a palladium-catalyzed Baeyer-Villiger oxidation using phosphinooxazoline ligands in up to 99% yield and 81% ee. Lactones of enantiopurity ≥93% could be obtained through a single recrystallization step. Importantly, 3,3-disubtituted cyclobutanones produced enantioenriched lactones containing a β-quaternary center.     

Palladium-catalyzed and samarium-promoted coupling of stereochemically-biased allylic acetates with carbonyl compounds

Stereochemically-biased bicyclic allylic acetates endo- and exo-1 were shown as being allyl donors for Pd-catalyzed carbonyl allylation using stoichiometric quantities of samarium diodide. Cyclopentenyl acetate and bicyclic derivatives 1 react with cyclic ketones in the presence of SmI₂ without requirement of palladium catalysis. Use of enantiomerically enriched substrate suggests that the reaction goes through a π-allyl samarium complex. However, this reactivity appears to be restricted to strained cyclopentenyl acetates since other linear and cyclic allylic acetates do not give the carbonyl allylation product.     

Palladium-catalyzed diastereoselective synthesis of homoaldol equivalent products

A palladium-catalyzed reaction of easily accessible 3-(pinacolatoboryl)allyl acetates and aldehydes provides facile access to synthetically useful homoaldol equivalent products with high diastereoselectivity. The reaction presumably proceeds via allylation of aldehydes with α-acetoxy allylboronates that produced in situ by reductive elimination from allylic gem-palladium/boryl intermediates.     

Palladium-catalyzed cross-couplings of allylic phosphates

A range of palladium-catalyzed cross-coupling reactions can be performed using allylic phosphates as electrophiles. Both conventional heating and microwave irradiation can be used.     

Palladium-catalyzed asymmetric allylic alkylation using chiral hydrazone ligands with ferrocene skeleton

Palladium-catalyzed asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate (4) with a dimethyl malonate-BSA-LiOAc system has been successfully carried out in the presence of chiral phosphine-hydrazone ligands such as 3a in good yields with good enantioselectivities (up to 84% ee).     

Palladium-catalyzed direct arylation of 4-hydroxycoumarins with arylboronic acids via C-OH bond activation

Operationally simple PdCl₂-catalyzed direct arylation of 4-hydroxycoumarins with arylboronic acids via C-OH bond activation under mild conditions is described, which gave rise to the corresponding 4-arylcouamrins in good to excellent yields.     

Palladium-catalyzed alkenation of thiophenes and furans by regioselective C-H bond functionalization

A palladium-catalyzed direct alkenation of thiophenes and furans has been developed in the presence of AgOAc and pyridine. A variety of olefinic substrates such as acrylates, acrylamides, and acrylonitrile can perform the direct oxidative coupling reactions with various thiophenes and furans to give the mono-alkenylated products in good yields. In most cases, the (E)-isomers were isolated as the major products.     

Palladium-catalyzed cross-coupling of polyfluoroarenes with simple arenes

The most efficient method to construct biaryls is the direct dehydrogenative cross-coupling of two different aromatic rings. Such an ideal cross arylation starting from distinct polyfluoroarenes and simple arenes was presented. The selectivity of the cross-coupling was controlled by both of the electronic property of fluoroarenes and steric hindrance of simple arenes. Diisopropyl sulfide was essential to promote the efficacy.     

Palladium-catalyzed asymmetric tandem allylic substitution using chiral 2-(phosphinophenyl)pyridine ligand

Palladium-catalyzed asymmetric tandem allylic substitution of (Z)-1,4-diacyloxy- and (Z)-1,4-bis(alkoxycarbonyloxy)-2-butene (2a-c) using 2-(phosphinophenyl)pyridine 1 as chiral ligand provided optically active six-membered 2-vinyl-1,4-diheterocyclic compounds with good to high enantioselectivity. For example, the reactions with catechol, 2-(benzylamino)phenol, or 1,2-bis(benzylamino)ethane as a nucleophile gave 2-vinyl-1,4-benzodioxane (71% ee), 4-benzyl-2-vinyl-1,4-benzoxazine (86% ee), and 1,4-dibenzyl-2-vinylpiperazine (86% ee), respectively.     

Palladium-catalyzed C-N bond formation via direct C-H bond functionalization. Recent developments in heterocyclic synthesis

The formation of carbon-nitrogen bonds by reaction between a nitrogen atom and an unactivated carbon-hydrogen bond is a highly atom-economical process that attracted the attention of the chemists in the last two decades. The widely useful amination and hydroamination reactions, which furnish acyclic or cyclic products, give access to various nitrogen-containing basic and fine chemicals. This review highlights recent progress in the development of palladium-catalyzed reactions that occur by direct functionalization of simple carbon-hydrogen bonds to give heterocyclic products. Pd(0)- and Pd(II)-catalyzed reactions are described separately, emphasizing the different behavior of the metal in these two oxidation states.     

Palladium-catalyzed heteroannulation of cyclic alkenes by functionally substituted aryl iodides

Indolines and 2,3-dihydrobenzofurans are produced in good yields by the Pd(0)-catalyzed heteroannulation of cyclic and bicyclic alkenes by o-amino- and o-hydroxyaryl iodides. These processes are only successful with cyclic olefins in which the key alkylpalladium intermediate cannot undergo facile palladium β-hydride elimination. These reactions appear to involve: (1) oxidative addition of the aryl iodide to the palladium catalyst, (2) arylpalladation of the olefin, (3) possible coordination of the internal nucleophile to the palladium, (4) formation of a six-membered palladacycle, and (5) reductive elimination of the organopalladium intermediate to give the heteroannulation product and regenerate Pd(0).