Aerobic intramolecular oxidative amination of alkenes catalyzed by NHC-coordinated palladium complexes

[reaction: see text] Palladium(II) complexes bearing a single N-heterocyclic carbene ligand serve as effective catalysts for the aerobic oxidative cyclization of alkenes with pendant sulfonamides. The use of carboxylic acid cocatalysts (AcOH and PhCO(2)H) often leads to significant improvements in catalyst stability and product yield and enables catalytic turnover to be achieved with air, rather than pure oxygen gas, as the source of O(2).     

Intramolecular Pd(II)-catalyzed aerobic oxidative amination of alkenes: synthesis of six-membered N-heterocycles

Use of a base-free Pd(DMSO)(2)(TFA)(2) catalyst system enables the synthesis of six-membered nitrogen heterocycles via a Wacker-type aerobic oxidative cyclization of alkenes bearing tethered sulfonamides. Various heterocycles, including morpholines, piperidines, piperazines, and piperazinones, are accessible by this method.     

Aerobic oxidative amination of unactivated alkenes catalyzed by palladium

The first examples of palladium-catalyzed oxidative amination of unactivated alkyl olefins have been identified. To be successful, these reactions must be conducted under cocatalyst-free conditions that involve direct dioxygen-coupled turnover of the palladium catalyst. The oxidative amination products of norbornene and other cyclic alkenes implicate a cis-aminopalladation mechanism.     

Acetalization of alkenes catalyzed by Pd(OAc)2/NPMoV supported on activated carbon under a dioxygen atmosphere

[reaction: see text] The acetalization of terminal alkenes such as ethyl acrylate and acrylonitrile with alcohols under O2 was efficiently achieved by Pd(OAc)2 supported on activated carbon combined with molybdovanadophosphate (NPMoV). For example, ethyl acrylate was subjected to acetalization with EtOH acidified by CH3SO3H under O2 (1 atm) in the presence of [8 wt%Pd(OAc)2/C] and NPMoV to form ethyl 3,3-diethoxypropionate in quantitative yield.     

Pd(II)-catalyzed enantioselective intramolecular oxidative amination utilizing (+)-camphorsulfonic acid

An enantioselective Pd(II)-catalyzed intramolecular oxidative amination reaction was developed utilizing the commercially available chiral X-type ligand (1S)-(+)-camphorsulfonic acid. The Wacker-type cyclization produced chiral indoline products with enantioselectivies up to 45% ee. Electronic structure calculations employing density functional theory support a trans-aminopalladation mechanism.     

Mechanistic characterization of aerobic alcohol oxidation catalyzed by Pd(OAc)(2)/pyridine including identification of the catalyst resting state and the origin of nonlinear [catalyst] dependence

The Pd(OAc)(2)/pyridine catalyst system is one of the most convenient and versatile catalyst systems for selective aerobic oxidation of organic substrates. This report describes the catalytic mechanism of Pd(OAc)(2)/pyridine-mediated oxidation of benzyl alcohol, which has been studied by gas-uptake kinetic methods and (1)H NMR spectroscopy. The data reveal that turnover-limiting substrate oxidation by palladium(II) proceeds by a four-step pathway involving (1) formation of an adduct between the alcohol substrate and the square-planar palladium(II) complex, (2) proton-coupled ligand substitution to generate a palladium-alkoxide species, (3) reversible dissociation of pyridine from palladium(II) to create a three-coordinate intermediate, and (4) irreversible beta-hydride elimination to produce benzaldehyde. The catalyst resting state, characterized by (1)H NMR spectroscopy, consists of an equilibrium mixture of (py)(2)Pd(OAc)(2), 1, and the alcohol adduct of this complex, 1xRCH(2)OH. These in situ spectroscopic data provide direct support for the mechanism proposed from kinetic studies. The catalyst displays higher turnover frequency at lower catalyst loading, as revealed by a nonlinear dependence of the rate on [catalyst]. This phenomenon arises from a competition between forward and reverse reaction steps that exhibit unimolecular and bimolecular dependences on [catalyst]. Finally, overoxidation of benzyl alcohol to benzoic acid, even at low levels, contributes to catalyst deactivation by formation of a less active palladium benzoate complex.     

Efficient Stille cross-coupling reaction catalyzed by the Pd(OAc)2/Dabco catalytic system

[reaction: see text] An efficient Pd(OAc)2/Dabco-catalyzed Stille cross-coupling reaction procedure has been developed. In the presence of Pd(OAc)2 and Dabco (triethylenediamine), various aryl halides including aryl iodides, aryl bromides, and activated aryl chlorides were coupled efficiently with organotin compounds to afford the corresponding biaryls, alkene, and alkynes in good to excellent yields. Furthermore, high TONs [turnover numbers, up to 980,000 TONs for the coupling reaction of 1-bromo-4-nitrobenzene and furan-2-yltributyltin] for the Stille cross-coupling reaction were observed.     

Pd(OAc)2 promoted bis-N-heterocyclic carbene-catalyzed oxidative transformation of aldehydes

The bis-N-heterocyclic carbene-catalyzed (bis-NHC-catalyzed) oxidative transformation of aldehydes was successfully studied in water under air. The reaction rate increased through the use of Pd(OAc)₂ as an additive. Notably, the catalytic system exhibited good tolerance toward aliphatic and aromatic aldehydes bearing halide and alkyl functional groups. In addition, gram-scale reaction was also tested in this study. The use of water and operational simplicity make this methodology environmentally benign and cost-effective.     

Oxidative cross-coupling of acrylates with vinyl carboxylates catalyzed by a Pd(OAc)2/HPMoV/O2 system

Oxidative cross-coupling of acrylates with vinyl carboxylates was first successfully achieved by the use of a Pd(OAc)(2)/HPMoV/O(2) system in fair to good yields. For instance, the reaction of n-butyl acrylate with vinyl acetate in the presence of catalytic amounts of Pd(OAc)(2) and H(4)PMo(11)VO(40).nH(2)O under O(2) in acetic acid at 70 degrees C for 12 h afforded the corresponding cross-coupling product, n-butyl 5-(acetoxy)-2,4-pentadienoate, in 70% yield.     

An efficient Stille cross-coupling reaction catalyzed by Pd(OAc)2/DAB-Cy catalytic system

An efficient palladium-catalyzed Stille cross-coupling reaction has been developed. In the presence of 3 mol% of Pd(dba)₂ and 6 mol% of DAB-Cy (1,4-dicyclohexyl-diazabutadiene), various aryl halides (iodides and bromides) were coupled with organotin compounds to afford the corresponding biaryls and alkyne in good to excellent yields. Furthermore, high TONs [turnover numbers, TONs up to 950,000 for the reaction of 1-iodo-4-nitrobenzene and tributyl(phenyl)stannane] for the Stille cross-coupling reaction were observed.     

Pd(OAc)_2/HQ/FePc、Pd(OAc)_2/FePc 催化烯烃氧化合成酮的研究

考察了在乙腈酸性水溶液中Ｐｄ（ＯＡｃ）２／氢醌（ＨＱ）／酞青铁（ＦｅＰｃ）和Ｐｄ（ＯＡｃ）２／ＦｅＰｃ对环己烯、环戊烯、苯乙烯、正癸烯氧化合成相应酮的催化活性．实验结果表明，两类催化体系对环戊烯的酮基化均呈现出较高的催化活性，环戊酮收率可达９８％．在其它烯烃的氧化反应中，三元催化体系Ｐｄ（ＯＡｃ）２／ＨＱ／ＦｅＰｃ的催化活性高于二元的Ｐｄ（ＯＡｃ）２／ＦｅＰｃ．这表明，在Ｗａｃｋｅｒ类催化体系中，电子传递体的作用是很重要的．对催化体系中各组分的作用进行了讨论，并给出了可能的催化作用机理．     

Carboxylation of anisole derivatives with CO and O2 catalyzed by Pd(OAc)2 and molybdovanadophosphates

Anisole and its homologues were carboxylated under the influence of CO and O2 catalyzed by Pd(OAc)2 combined with molybdovanadophosphates (HPMoV) under mild conditions to give the corresponding carboxylic acids in fair to good yields; for instance, anisole underwent the carboxylation under a mixed gas of CO (0.5 atm) and O2 (0.5 atm) in the presence of Pd(OAc)2 (5 mol%) and H5PMo10V2O40.nH2O (2 mol%) to form an isomeric mixture of anisic acids in good yield.     

Efficient aerobic oxidative synthesis of 2-aryl quinazolines via benzyl C-H bond amination catalyzed by 4-hydroxy-TEMPO

A novel and efficient aerobic protocol for the oxidative synthesis of 2-aryl quinazolines via benzyl C-H bond amination by a one-pot reaction of arylmethanamines with 2-aminobenzoketones and 2-aminobenzaldehydes has been carried out using the 4-hydroxy-TEMPO radical as the catalyst, without any metals or additives.     

Kinetics of homogeneous acetoxylation of cyclododecene and 1,5,9-cyclododecatriene catalyzed by Pd(OAc)2

The kinetics of acetoxylation of cyclododecene and (E,E,E)-1,5,9-cyclododecatriene catalyzed by Pd(OAc)₂ has been studied in glacial acetic acid solutions at 323–343 K and atmospheric pressure. The experimental data were described by kinetic equations of the Michaelis-Menten type.     

Efficient homo-coupling reactions of heterocyclic aromatic bromides catalyzed by Pd(OAc)2 using indium

Homo-coupling reactions of heterocyclic aromatic bromides smoothly proceeded with cat-Pd(OAc)₂, indium, and LiCl in DMF to afford exclusively symmetric biaryls possessing heterocyclic aromatic ring in good to excellent yields.     

Stereoselective synthesis of cis-2,5-disubstituted pyrrolidines via Wacker-type aerobic oxidative cyclization of alkenes with tert-butanesulfinamide nucleophiles

Palladium(II)-catalyzed aerobic oxidative cyclization of alkenes with tethered tert-butanesulfinamides furnishes enantiopure 2,5-disubstituted pyrrolidines, originating from readily available and easily diversified starting materials. These reactions are the first reported examples of metal-catalyzed addition of sulfinamide nucleophiles to alkenes.     

Enantioselective synthesis of N-heterocycles via intramolecular Pd(0)-catalysed allylic amination

An efficient and stereoselective synthesis of pyrrolidine-, piperidine-, and azepane-type N-heterocycles is described by the intramolecular Pd(0)-catalysed cyclisation of amino allylic carbonates. The use of chiral ligands gave the corresponding heterocyclic derivatives having er values that were from moderate to good.     

Kinetic models of the cyclohexene hydromethoxycarbonylation catalyzed by the Pd(OAc)2/trans-2,3-bis(diphenylphosphinomethyl)norbornane/p-toluensulfonic acid

Operating over the entire length from the region of initial rates to deep conversions of cyclohexene, hydromethoxycarbonylation kinetic models have been obtained in the temperature range of 358–378 K. At 378 K, a conclusion on a higher stability of the diphosphine complex [HPd(TBDPN)(CH₃OH)]OTs compared to [HPd(CO)₂OTs] under hydromethoxycarbonylation conditions has been made based on the comparison of the kinetic model constant values.     

Palladium-catalyzed aerobic oxidative amination of alkenes: development of intra- and intermolecular aza-Wacker reactions

Palladium-catalyzed methods for the aerobic oxidative coupling of alkenes and oxygen nucleophiles (e.g., water and carboxylic acids) have been known for nearly 50 years. The present account summarizes our development of analogous aerobic oxidative amination reactions, including the first intermolecular aza-Wacker reactions compatible with the use of unactivated alkenes. The reactions are initiated by intra- or intermolecular aminopalladation of the alkene. The resulting alkylpalladium(II) intermediate generally undergoes beta-hydride elimination to produce enamides or allylic amide products, but in certain cases, the Pd-C bond can be trapped to achieve 1,2-difunctionalization of the alkene, including carboamination and aminoacetoxylation. Mechanistic studies have provided a variety of fundamental insights into the reactions, including the effect of ancillary ligands on palladium catalysts, the origin of the Br?nsted-base-induced switch in regioselectivity in the oxidative amination of styrene, and evidence that both cis- and trans-aminopalladations of alkenes are possible. Overall, these reactions highlight the potential utility of an "organometallic oxidase" strategy for the selective aerobic oxidation of organic molecules.