Presence Of Palladium Catalyst Research Articles

Palladium-catalyzed ring-opening/defluorinative coupling of gem-DFCPs with pyranones/pyridones

The monofluoroalkenes are found widespread applications in areas such as bioactive molecules, materials science and synthetic organic chemistry, therefore, investigating efficient methodologies to construct monofluoroalkenes is still in demand. In this paper, we reported an efficient synthesis of monofluoroalkenyl substituted pyranones/pyridones by using the gem-difluorocyclopropanes (gem-DFCPs) as monofluoroalkenyl precursors. In the presence of Palladium catalyst, the monofluoroalkenyl group was introduced into the C3 positions of pyranones/pyridones successfully. The reaction was featured with high regioselectivity, mild conditions, broad substrate scope, easy to scale up synthesis, which provided a novel avenue for the late-stagy modification of pyranones/pyridones.

Palladium-Catalyzed Triple Suzuki-Miyaura Reactions Using Cyclic (Vinyl Triflate)iodonium Salts.

By using cyclic (vinyl triflate)iodonium salts, a novel triple Suzuki-Miyaura reaction was accomplished for the synthesis of polyaromatic ethylene derivatives in the presence of palladium catalysts. The reaction exhibits extensive compatibility with a wide range of readily available arylboronic acids, giving triaryl-substituted ethylenes in good yields.

Alkoxycarbonylation of Unsaturated Substrates of Plant Origin in the Presence of Palladium Catalysts as a Route to Synthesize Ester Products

Alkoxycarbonylation of Unsaturated Substrates of Plant Origin in the Presence of Palladium Catalysts as a Route to Synthesize Ester Products

Isocyanide‐Based One‐Pot Cascade Synthesis of 3‐Acyl Isoindolinones†

Comprehensive SummaryA series of 3‐acyl‐substituted isoindolinone derivatives were synthesized in a one‐pot manner via the reaction of o‐bromobenzaldehydes, isocyanides, and carboxylic acids in the presence of palladium catalyst and base. The reaction employing easily available starting materials features simple operation and high efficiency. The mechanistic study showed that the reaction might undergo 1) Pd‐catalyzed [3+2] cyclization of o‐bromobenzaldehyde with isocyanide and the re‐insertion of another molecule of isocyanide, 2) addition of carboxylic acid to in situ formed ketenimine followed by a rearrangement relay to give 3,3‐diacyl‐substituted isoindolinone derivative. Further transformations of the obtained products through decarbonylation could also be realized.

Palladium-Catalyzed C-N Coupling in the Synthesis of 1,4-Benzodiazepines Fused with 5-Membered Carbo- and Heterocycles

Abstract: In this review, we have focused our attention on Pd-catalyzed amination and arylation reactions for the construction of various benzodiazepine scaffolds. It includes numerous types of synthetic strategies like C-H arylation, Pd-catalyzed carbonylation, and Buchwald Hartwig coupling. To synthesize different functionalized benzodiazepines, the domino processes as intra- or intermolecular reactions are developed as an eco-friendly and effective tool. Benzodiazepines exhibit several biological activities and play a valuable role in medicinal and pharmaceutical chemistry. This review article mainly focuses on synthesizing a 1,4- benzodiazepine nucleus fused with 5-membered carbo- and heterocycles in the presence of palladium catalysts.

Catalytic synthesis of N-substituted allylarylamines

Some N-substituted allylarylamines, for example, N-(1-methyl-2-butenyl) aniline (N-MBA) form, upon isomerization, not only ortho-, but also para- and 2,6-disubstituted derivatives, which does not fit into generally accepted theory. The amino-Claisen rearrangement (ACR) of N-MBA is catalyzed by Lewis acids, cationites, and arylamine hydrochlorides. This work presents the results of studies of ACR N-MBA in solutions of mineral acids. It was found that the reaction must be carried out in dilute solutions. At H2SO4 concentrations of 0.5 mol/L and below, three parallel reactions are observed with the formation of aniline, 2-(1-methyl-2-butenyl) aniline (2-MBA) and 4-(1-methyl-2-butenyl) aniline (4-MBA). The main product in all cases is 2-MBA, the content of which in the reaction mixture exceeds the amount of 4-MBA and aniline by 7 times, which are formed in approximately equal amounts. Prolonged refluxing of 2-MBA under the reaction conditions does not lead to its isomerization to 4-MBA, i.e., the para-isomer is formed directly from N-MBA. The formation of 2,6-di-(1-methyl-2-butenyl) aniline (DMBA) was not observed. In the presence of palladium catalysts, 2-MBA cyclizes to 2,4-methyl quinoline, which indicates the ortho-arrangement of its substituents; 4-MBA does not cyclize under these conditions. The obtained compounds are of interest in the synthesis of nitrogen-containing heterocycles and other polyfunctional organic compounds.

Engaging Diastereomeric syn‐ and anti‐6‐Bromo‐4a‐isopropyl‐2‐methyl‐2,3,4,4a‐tetrahydro‐1H‐carbazoles in Suzuki Coupling Reaction: Synthesis, Spectral Characterization and DFT Studies

AbstractSuzuki coupling reaction is one of the useful methods for carbon‐carbon bond formation. In the present study, the aforementioned method is used to expand an aryl appendage on the indolenine nucleus of diastereomeric syn‐ and anti‐6‐bromo‐4a‐isopropyl‐2‐methyl‐2,3,4,4a‐tetrahydro‐1H‐carbazole analogs. Therefore, two sets of new diastereomeric Suzuki‐coupled products (16 compounds) were prepared. For this, diastereomeric syn‐ and anti‐6‐bromo‐4a‐isopropyl‐2‐methyl‐2,3,4,4a‐tetrahydro‐1H‐carbazole analogs were treated with arylboronic acids in the presence of palladium catalyst under thermal catalysis. Structures of synthesized compounds were inferred using spectroscopic studies. DFT‐based quantum chemical calculations were used to decipher structural attributes and stability of diastereomeric bromo‐2,3,4,4a‐tetrahydro‐1H‐carbazoles and their Suzuki‐coupled products, which revealed chair conformation for methylcyclohexane ring of syn‐compound while twist‐boat conformation for diastereomeric anti‐compound. syn‐Compound was found more stable than its anti‐isomer based on DFT‐calculations. Also, results demonstrated agreement between experimental and theoretical chemical shift values in NMR spectra with some deviations. Thus, structural elucidation based on computational advances in combination with the spectroscopic method can provide a powerful method for studying and comparing the structural attributes of diastereomeric compounds.

Palladium-Catalyzed Sonogashira Coupling of a Heterocyclic Phosphonium Salt with a Terminal Alkyne.

An efficient Sonogashira coupling of a heterocyclic phosphonium salt with a terminal alkyne via C-P bond cleavage was developed. The reactions proceeded smoothly in the presence of palladium catalyst, copper(I) iodide, and N,N-diisopropylethylamine (DIPEA) in N-methyl-2-pyrrolidone (NMP) at 100 °C for 12 h, producing the corresponding alkynyl-substituted pyridine, quinoline, pyrazine, and quinoxaline in moderate to good yields with wide substrate scope and broad functional group tolerance. In addition, gram-scale synthesis could also be achieved, and the reaction could be applied to the functionalization of alkyne-containing complex molecules derived from sugars and pharmaceutical and naturally occurring products (e.g., estrone, d-galactopyranose, menthol, and ibuprofen).

Palladium‐Catalyzed Intramolecular C−H Heteroarylation to Access Fused Tricyclic Oxazolo[4,5‐c]Quinolines

AbstractSynthesis of fused tricyclic oxazolo[4,5‐c]quinolines from 2‐iodo‐N‐((2‐phenyloxazol‐4‐yl)methyl)anilines via intramolecular C−H heteroarylation in the presence of palladium catalyst under ligand free conditions has been disclosed. Various substituted 2‐iodo‐N‐((2‐phenyloxazol‐4‐yl)methyl)anilines are well tolerated and furnished the products in good yields. The synthetic utility of the resulting molecules has been demonstrated. This method features broad substrate scope, mild reaction conditions, good functional group tolerance, and scalability.

Valorization of a CO2‐Derived Lactone by Acyclic Diene Metathesis Polymerization

AbstractThe exploitation of carbon dioxide (CO2) as a feedstock for the chemical processes has been an evasive venture due to its thermodynamic stability. The synthesis of highly functionalized metastable δ‐lactone (3‐ethylidene‐6‐vinyltetrahydro‐2H‐pyran‐2‐one) was reported in 1970s which is formed by the condensation of CO2 and 1,3‐butadiene in the presence of palladium catalyst. Several attempts have been made to utilize the intermediate for the polymerization processes, however, only a few have been successful. Here, we report a novel mechanism of metathesis polymerization of the metastable monomer by the action of a transition metal carbene complex (Hoveyda Grubb's II generation catalyst) to yield a new class of materials. The reaction mechanism for the polymerization has been proposed and substantiated by nuclear magnetic spectroscopic analysis. The obtained polymeric species consist of a complex unit structure where the cyclic lactone groups are connected by the olefin groups in different combinations.

Palladium‐Catalyzed Annulation of Arylbenzamides with Diaryliodonium Salts

AbstractBy using diaryliodonium salts, a cylization has been accomplished in the synthesis of N‐aryl phenanthridinone derivatives via a cascade of ortho‐arylation and Csp2‐N bond formation in the presence of palladium catalyst. The reaction exhibits a broad compatibility of readily available N‐arylnaphthamides.magnified image

DFT (density functional theory) studies on cycloisomerization of 15-membered triazatriacetylenic macrocycle.

The mechanism as well the stereochemistry of cascade cycloisomerization of 15–membered triazatriacetylenic macrocycle was investigated theoretically by using M062X/6–31+G(d,p) and M062X/LANL2DZ calculations. The results showed that the mechanism and outcome of the reaction depended on the absence and presence of a transition metal catalyst. So that, in thermal-induced condition, the reaction had to experience several suprafacial concerted reactions including Ene-reaction (DG#=35.38 kcal/mol), Diels–Alder cycloaddition (DG# = 17.16 kcal/mol), and sigmatropic H-shift rearrangement (DG# = 56.21 kcal/mol) to produce diastereoselective fused cis–tetracyclic aromatic bearing a pyrrole moiety by following kinetic considerations. Also, the [2+2+2] cycloaddition mechanism was neglected in thermal–induced conditions because of high activation free Gibbs energy (DG# = 63.90 kcal/mol). In the presence of palladium catalyst, Pd(0) formed an adduct by coordinating to C = C bonds and decreased the DG# of the process to 29.58 kcal/mol, and consequently provided a facilitated media for the reaction to follow the [2+2+2] to produce more stable fused tetracyclic benzenoid aromatic by passing through the lower energy barrier.

Microwave-assisted cross-coupling synthesis of aryl functionalized MWCNTs and investigation of hydrogen storage properties

In recent years, nanostructures have attracted the attention of many scientists due to their unique properties. Many properties of nanostructures can be improved by changing the surface. For this purpose, multi-walled carbon nanotubes (MWCNTs) were covalently modified using Suzuki-cross coupling reactions with microwave-assisted synthesis. First, the MWCNTs were brominated. Aryl functionalized MWCNTs were synthesized from the reaction of brominated MWCNTs with aryl boronic acid derivatives in the presence of palladium catalyst. Synthesized compounds were characterized by the techniques of Fourier-Transform Infrared Spectroscopy, Nuclear Magnetic Resonance, Thermogravimetric Analysis and Transmission Electron Microscopy. The hydrogen storage properties of the synthetic compounds were determined. The example with the highest hydrogen storage capacity was N2 and its hydrogen storage capacity was determined as 0.45 wt%. The hydrogen storage capacity of functionalized MWCNTs was consistent with the results of carbon nanomaterials in the literature.

Palladium-Catalyzed sp3 C–H Benzoxylation of Alanine Derivatives Using Aldehydes under Ambient Conditions

AbstractThe Pd(II)-catalyzed sp3 C–H bond benzoxylation of N-phthaloylalanine derivatives possessing an 8-aminoquinolyl group as a directing group with aldehydes under ambient conditions is reported. When a solution of an alanine derivative and an aldehyde in a toluene/water co-solvent was reacted in the presence of palladium catalyst and tert-butyl hydroperoxide at room temperature, a benzoxylated product was formed in up to 68% yield. The protecting group of the obtained benzoxylated product was smoothly removed to afford a free amide in high yield.

Synthesis of Axially Chiral Carboxamides via Aminocarbonylation of Aryl and Vinyl Iodides with 2,2’‐Diamino‐1,1’‐binaphthalene in the Presence of Palladium Catalysts

AbstractPalladium‐catalysed aminocarbonylation of iodobenzene and 1‐iodocyclohexene with both enantiomerically pure and racemic 2,2’‐diamino‐1,1’‐binaphthalene (BINAM) as N‐nucleophile was carried out. The mono‐ and dicarboxamide enantiomers possessing axial chirality were synthesised using (Sax)‐BINAM. In the possession of these reference compounds the partial chiral kinetic resolution of racemic BINAM was carried out using various optically active bidentate ligands such as (2S,4S)‐BDPP, (2S,3S)‐CHIRAPHOS and (R)‐BINAP. It was revealed by chiral HPLC measurements that up to 10 % enantiomeric excess of carboxamides can be achieved in this way. Although with low enantioselection, enantioselectve aminocarbonylation was carried out for the first time.

Palladium-Catalyzed Site-Selective Benzocylization of Aromatic Acids with o-Fluoro-Substituted Diaryliodonium Salts toward 3,4-Benzocoumarins.

By using 2-fluoro-substituted diaryliodonium salts, a novel benzocylization has been accomplished for the synthesis of 3,4-benzocoumarin derivatives via a cascade of ortho-arylation and defluorination in the presence of palladium catalysts. The reaction exhibits a broad compatibility of readily available aromatic acids with an excellent level of site-selectivity. Mechanistic investigations revealed a unique reactivity of carboxylic acid directed arylation by followed nucleophilic substitution of aromatic fluoride in the present system.

Unusual Side Transformation of Spiro[2,4]hepta‐4,6‐dienes into Fulvene Derivatives During Pd‐Catalyzed Cyclopropanation with Diazomethane

AbstractThe catalytic cyclopropanation of spiro[2.4]hepta‐4,6‐diene and 1,1,2,2‐tetradeutero‐, 1‐methyl‐, and 1,1‐dimethylspiro[2.4]hepta‐4,6‐dienes on treatment with excess diazomethane in the presence of palladium catalysts, which gives products of double bond dicyclopropanation, is also accompanied by an unusual transformation of the three‐membered ring of the spiro moiety with elimination of the unsubstituted methylene group in the form of ethylene to give the corresponding 5‐methylidenetricyclo[4.1.0.02,4]heptanes (bishomofulvenes). The putative mechanism of the reactions is considered.

The unsteady investigation of methane-air premixed counterflow flame into newly proposed plus-shaped channel over palladium catalyst

In this paper, the time dependent study of methane-air premixed counterflow flame into a newly proposed plus-shaped channel, in order to obtain effects of palladium catalyst surfaces on the flame structure and pollutant emissions, is described. The results are presented at non-catalytic and catalytic conditions with considering effects of reaction time and various equivalence ratios, from lean to rich combustion, on flame characteristics and pollutant emissions. The governing equations are composed of continuity, momentum, energy and mass fraction equations are numerically solved considering a coupled Piso scheme and Simple algorithm. The comparison between the presented model and published data shows an acceptable agreement that confirms the accuracy of this solution. The average values of CH4 mass fraction over the geometry at the presence of palladium catalyst is nearly decreased 25% relative to non-catalytic case. The existence of Palladium catalyst has great impact, mostly 34% decrease, on CO formation but the catalyst leads to increment of CO2 formation 5%. At different values of equivalence ratio, the average temperature of non-catalytic flame is about 16% lower than catalytic one.

Rapid Construction of Fused Heteropolycyclic Aromatics via Palladium-Catalyzed Domino Arylations of Imidazopyridine Derivatives.

By using diaryliodonium salts, a novel approach of a palladium-catalyzed cascade of diarylation/intramolecular dehydrogenative coupling reaction has been developed in the synthesis of phenanthro-imidazopyridine fused heteropolycycles. The method can tolerate various substrates, and the target products were rapidly constructed in one pot. Furthermore, studies of the detailed reaction mechanism provide an insight into the C-H functionalization of 2-aryl-imidazopyridine derivatives and the C-C bond formations in the presence of palladium catalyst.

Palladium catalyzed cross-dimerization of terminal acetylenes and acrylates

A palladium catalyzed oxidative cross-coupling reaction between terminal alkynes and acrylates was developed. In the presence of palladium catalyst and copper(II) acetate as oxidant, the cross dimerization products with were formed. This protocol provides a novel method to construct the tetrasubstituted functionalized alkenes.