An efficient method for the synthesis of N-(quinolin-2-yl)sulfonamides is described. The intermolecular amidation of quinoline N-oxides with sulfonamides proceeded smoothly in the presence of PhI(OAc)2 and PPh3 to afford N-(quinolin-2-yl)sulfonamides in satisfactory to excellent yields.

Palladium-catalyzed remote sp2–sp3 coupling reaction of chloromethylarenes with allyltrimethoxysilane is described in this work. The allylation reaction regioselectively occurred on the para-positions of 1-(chloromethyl)naphthalenes and benzyl chlorides to form new C(sp2)–C(sp3) bonds. The reaction proceeds smoothly under mild conditions to produce allyl arenes in moderate to excellent yields.

We report the highly chemoselective and stereoselective semihydrogenation of alkynes to Z-internal and terminal alkenes by using unsupported nanoporous palladium (PdNPore) as a heterogeneous catalyst under mild reaction conditions (room temperature and 1 atm of H2). The semihydrogenation of various terminal/internal and aromatic/aliphatic alkynes afforded the corresponding alkenes in good chemical yields with high selectivities. PdNPore further showed high chemoselectivity toward terminal alkynes in the presence of internal alkynes, which has not yet been achieved using supported palladium nanoparticle catalysts. H–H heterolysis of H2 on the surface of PdNPore was strongly suggested by deuterium labeling experiments. No Pd leached from PdNPore during the reaction, and the catalyst was easily recovered and reused without a loss of activity.Keywords: alkyne; heterogeneous catalysis; nanoporous palladium; no leaching; semihydrogenation;

AbstractA straightforward, highly chemoselective hydrogenation of α,β-unsaturated aldehydes was developed using unsupported nanoporous gold (AuNPore) as a heterogeneous catalyst with bio-renewable formic acid (HCO2H) as hydrogen source. Various α,β-unsaturated aldehydes were reduced to their corresponding allylic alcohols in good to high chemical yields with excellent selectivity. AuNPore offers several attractive features as a catalyst, such as high activity and selectivity, easy recyclability, and no leaching.

•Acidic deep eutectic solvents were synthesized by mixing choline chloride with different organic acids.•The concise control of DESs' acidity was realized successfully.•The density, electrical conductivity, dynamic viscosity and refractive index of the four DESs were determined.•The acidity of the four DESs was detected by Hammett acidic functions.Four deep eutectic solvents (DESs) based on different acids as hydrogen bond donors (HBDs), namely p-toluenesulfonic acid (PTSA), trichloroacetic acid (TCA), monochloroacetic acid (MCA), and propionic acid (PA) with hydrogen bond acceptor (HBA) choline chloride (ChCl) are synthesized with a mole ratios of HBD to HBA is 2:1. The density, electrical conductivity, dynamic viscosity and refractive index of the four DESs were determined at atmospheric pressure and temperatures from (288.15 to 338.15) K at an interval of 5 K. The results show that the temperature has great influences on the physical properties of DESs. The thermal expansion coefficient, molecular volume, standard molar entropy, and lattice energy were calculated by empirical equation. The molar conductivity was determined from the data of density.and conductivity. The temperature dependence of electrical conductivities and dynamic viscosities for the DESs were fitted by Vogel–Fulcher–Tamman (VFT) and Arrhenius equation. The relationship of the molar conductivity and viscosity was determined using the Walden rule. The acidities of the above DESs were measured by Hammett acidic functions. The present study will help to understand the properties of DESs and provide a guide for further applications of DESs.The density, dynamic viscosity, electrical conductivity, refractive index and acidity of DESs were characterized.Download high-res image (107KB)Download full-size image

Subnano-MoO3 supported on ultrasmall mesoporous silica nanoparticles (UMSN, ca. 14 nm) has been successfully synthesized by a reverse microemulsion method. The obtained subnano-MoO3/UMSN exhibited superior catalytic activity for the oxidative desulfurization of model diesel. The dibenzothiophene can be oxidized to dibenzothiophene sulfone and removed simultaneously by adsorbing on the catalyst. The superiority in catalytic performance of subnano-MoO3/UMSN can be attributed to the subnanometer size and the mesoporosity of the ultrasmall support. The origin of the unusual catalytic properties of the subnanoclusters was also explored preliminarily.

An efficient method for the synthesis of 5-vinyl-2-norbornene from cyclopentadiene and 1,3-butadiene was developed. The Diels–Alder reaction of cyclopentadiene with 1,3-butadiene proceeded smoothly in supercritical carbon dioxide in the absence of any polymerization inhibitor to produce the corresponding 5-vinyl-2-norbornene in satisfactory yield with high selectivity.Download high-res image (55KB)Download full-size imageThe Diels–Alder reactions of cyclopentadiene with 1,3-butadiene proceeded smoothly in supercritical carbon dioxide in the absence of any polymerization inhibitor to produce the 5-vinyl-2-norbornene in satisfactory yield (25% yield) with high selectivity (52% selectivity).

The inside cover picture, provided by Ming Bao and co-workers, illustrates the unprecedented remote allylation of chloromethyl(hetero)arenes with allyl pinacolborate. The palladium-catalyzed regioselective allylation reaction between chloromethyl(hetero)arenes and allyl pinacolborate proceeded smoothly via η3-benzylpalladium intermediates to provide para-allylated dearomatization products or para-allylated arenes in satisfactory to good yields; the formation of traditional Suzuki coupling products was not observed at all. This novel protocol exhibits good tolerance for various functional groups linked to (hetero)arene rings. Details of this work can be found in the communication on pages 2723–2728 (S. Zhang, A. Ullah, Y. Yamamoto, M. Bao, Adv. Synth. Catal. 2017, 359, 2723–2728; DOI: 10.1002/adsc.201700350).

AbstractThe palladium-catalyzed regioselective allylation reaction between chloromethyl(hetero)arenes and allyl pinacolborate is reported in this work. Chloromethylarenes smoothly reacted with allyl pinacolborate, producing para-allylated dearomatization products or para-allylated arenes in satisfactory to good yields. 2-(Chloromethyl)thiophenes and 2-(chloromethyl)furans bearing substituents on the 5-positions also smoothly reacted with allyl pinacolborate, producing the 5-allylated dearomatization products in satisfactory yields.

Mix'em all together: A straightforward, highly chemoselective hydrogenation of α,β-unsaturated aldehydes was developed using unsupported nanoporous gold (AuNPore) as a heterogeneous catalyst with bio-renewable formic acid (HCO2H) as hydrogen source. Various α,β-unsaturated aldehydes were reduced to their corresponding allylic alcohols in good to high chemical yields with excellent selectivity. AuNPore offers several attractive features as a catalyst, such as high activity and selectivity, easy recyclability, and no leaching. More information can be found in the Full Paper by Xiujuan Feng, Ming Bao and co-workers on page 867 in Issue 7, 2017 (DOI: 10.1002/ajoc.201700130).

A convenient and efficient method for the synthesis of 5H-dibenzo[c,e]azepine-5,7(6H)-diones from simple and readily available benzamides is described in this work. The palladium-catalyzed homocoupling of benzamides occurred via ortho-selective double C–H bond activation using the simplest amide CONH2 as a directing group. The subsequent intramolecular condensation reaction proceeded smoothly to produce 5H-dibenzo[c,e]azepine-5,7(6H)-diones in satisfactory to excellent yields in one pot.

Uniform Au particles with a mean size of 1.9 nm were initially synthesized with polyvinyl alcohol (PVA) as protecting agent, and then deposited on MgO, Al2O3, TiO2, Fe2O3, Co3O4, ZnO and In2O3. After calcinations at 300 °C in air to remove PVA, Au particles were highly dispersed and immobilized on all the supports, displaying narrow diameter distributions and almost identical mean sizes of 2.5–3.2 nm. The Au-oxides catalysts were further used to catalyze selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL). It was found that the selectivity of COL was tightly related to the acidity/basicity of the Au/oxides catalysts. The catalyst with only acidic sites such as the Au/Al2O3 catalyst gave very low selectivity of COL of 15%. The catalysts with only basic sites such as Au/MgO catalyst displayed medium selectivity of COL of 52%. Interesting, the Au catalysts with both acidic and basic sites such as the Au/In2O3 and Au/ZnO catalyts exhibited the highest selectivity of COL of around 86%. The synergistic cooperation of acidic sites and basic sites should be responsible for preferential adsorption and activation of the C=O group than C=C group in CAL, and then preferential hydrogenation of C=O to COL.

For the first time, H–H dissociation on an unsupported nanoporous gold (AuNPore) surface is reported for chemoselective hydrogenation of C≡C, C═C, C═N, and C═O bonds under mild conditions (8 atm H2 pressure, 90 °C). Silver doping in AuNPore, which was inevitable for its preparation through a process of dealloying of Au–Ag alloy, exhibited a remarkable difference in catalytic activity between two catalysts, Au>99Ag1NPore and Au90Ag10NPore.The former was more active and the latter less active in H2 hydrogenation, while the reverse tendency was observed for O2 oxidation. This marked contrast between H2 reduction and O2 oxidation is discussed. Further, Au>99Ag1NPore showed a high chemoselectivity toward reduction of terminal alkynes in the presence of internal alkynes which was not achieved using supported gold nanoparticle catalysts and other previously known methods. Reductive amination, which has great significance in synthesis of amines due to its atom-economical nature, was also realized using Au>99Ag1NPore, and the Au>99Ag1NPore/H2 system showed a preference for the reduction of aldehydes in the presence of imines. In addition to this high chemoselectivity, easy recovery and high reusability of AuNPore make it a promising heterogeneous catalyst for hydrogenation reactions.

Rhodium-catalyzed oxidative benzannulation of N-adamantyl-1-naphthylamines with internal alkynes to produce highly substituted anthracenes in satisfactory to good yields was developed. The annulation reaction proceeded smoothly under mild conditions in the presence of [Cp*RhCl2]2 as the precatalyst and Cu(OAc)2 as the oxidant.

A new halogenation method to construct halogen-substituted quinoline moieties is described. The Cu-catalyzed intramolecular aza-Diels–Alder reaction and halogenation reaction proceeded smoothly under mild conditions to produce the corresponding 7-chloro-6H-chromeno[4,3-b]quinolines and 7-chloro-6H-thiochromeno[4,3-b]quinolines in satisfactory yields.

•Selective synthesis of δ-lactone via palladium nanoparticles-catalyzed teleomerization of CO2 with 1,3-butadiene.•Gives the desired product δ-lactone in satisfactory yield with high selectivity.•Avoids the use of air-sensitive phosphine ligand.•The catalyst could be easily recovered and reused.An efficient method for the selective synthesis of δ-lactone from carbon dioxide and 1,3-butadiene was developed using palladium nanoparticles as the catalyst without any additional ligand. The highest yield (51% with 94% selectivity) was achieved using Pd(acac)2 as the precatalyst in the presence of TBAAc as both reducing and stabilizing agent in acetonitrile at 70 °C. The palladium nanoparticles generated in situ could be easily recovered through a simple extraction process and reused three times without an obvious loss in activity. The TEM image showed the presence of (3.8 ± 1.1) nm-sized palladium nanoparticles in the reaction mixture.An efficient method for the selective synthesis of δ-lactone from CO2 and 1,3-butadiene was developed with palladium nanoparticles as catalyst and without any additional ligand.

Palladium-catalyzed a solvent-dependent product distribution in the propargylative and allenylative dearomatization reaction of 2-(chloromethyl)thiophenes with allenyltributylstannane under mild conditions is reported in this study. In the coordinating solvent acetonitrile, the propargylative dearomatization reaction selectively occurred to produce only the propargylic compounds with satisfactory to good yield. In the uncoordinating solvent dichloromethane, allenic compounds were obtained as major products with a small amount of propargylic compounds.The reaction selectivity could be easily controlled by the use of different solvents. The use of a coordinating solvent led to the formation of a propargylic compound as the sole product, whereas the use of an uncoordinating solvent led to the generation of an allenic compound as the major product.

Two-step one-pot transformation of primary halides into corresponding nitriles is successfully achieved. Nucleophilic substitution of primary halides with sodium azide and subsequent palladium-catalyzed hydrogen transfer proceeds smoothly in the presence of sterically bulky ligand dicyclohexyl(2′,4′,6′-triisopropylbiphenyl-2-yl)phosphine (XPhos) in acetone to produce nitriles in satisfactory to good yields.

Palladium-catalyzed allylation reactions of 2-(chloromethyl)thiophenes, 2-(chloromethyl)furans, and N-protected 2-(chloromethyl)-1H-pyrroles with allyltributylstannane were described in this study. This type of allylation reaction regioselectively occurred on the heteroarene rings to produce allylated dearomatization products or allylated heteroarenes with satisfactory yields.

The palladium-catalyzed three-component coupling reaction of five-membered (chloromethyl)heteroarenes, allyltributylstannane, and carbon dioxide (carboxylative Stille coupling reaction) was successfully conducted to produce β,γ-unsaturated esters in satisfactory to good yields. The carboxylative Stille coupling reaction occurred smoothly under mild conditions in the presence of palladium nanoparticles through the formation of π-allylpalladium chloride intermediates.Palladium-catalyzed chemical fixation of CO2 is successfully achieved using the π-allyl group related to heterocycles as a carbon-based ligand. The PdNPs generated in situ played a key role for the success in the carboxylative Stille coupling reaction.

An efficient method for the synthesis of isoquinolones through base KOtBu-promoted SNAr reaction of 2-halobenzonitriles with ketones followed by Lewis acid Cu(OAc)2-catalyzed cyclization is described. Isoquinolone derivatives were obtained in satisfactory to good yields.

The remarkable effect of an unsupported nanoporous gold catalyst (AuNPore) on chemoselective hydrogenation of α,β-unsaturated aldehydes using silane has been described. Enals can be reduced with excellent selectivity, giving the corresponding allylic alcohols in good to high chemical yields.

Brønsted acid catalyzed cyclization reactions of 2-amino thiophenols/anilines with β-diketones under oxidant-, metal-, and radiation-free conditions are described. Various 2-substituted benzothiazoles/benzimidazoles are obtained in satisfactory to excellent yields. Different groups such as methyl, chloro, nitro, and methoxy linked on benzene rings were tolerated under the optimized reaction conditions.

Aldimines (R1HC═NR2) were reduced in the coexistence of aldehydes (R1CHO) with 100% chemoselectivity by the use of AuNPore giving corresponding amines (R1H2C-NHR2) in high chemical yields.

Organic synthesis using gold has gained tremendous attention in last few years, especially heterogeneous gold catalysis based on gold nanoparticles has made its place in almost all organic reactions, because of the robust and green nature of gold catalysts. In this context, gold nanopore (AuNPore) with a 3D metal framework is giving a new dimension to heterogeneous gold catalysts. Interestingly, AuNPore chemistry is proving better than gold nanoparticles based chemistry. In this review, along with recent advances, major discoveries in heterogeneous gold catalysis are discussed.

Palladium-catalyzed carbonylative addition of aryl bromides to terminal arylalkynes was carried out to produce chalcones in satisfactory to excellent yields. The unprecedented carbonylation reaction proceeded smoothly under mild conditions in the presence of a simple palladium catalyst system (PdCl2/DPPB/iPr2NEt) in N,N-dimethyl formamide.

Cyclization reactions of 2-aminophenols with β-diketones catalyzed by a combination of Brønsted acid and CuI are presented. Various 2-substituted benzoxazoles were obtained through these reactions. Different substituents such as methyl, chloro, bromo, nitro, and methoxy on 2-aminophenol are tolerated under the optimized reaction conditions.

An efficient method for the synthesis of enaminones is described. The aldol-type addition of ketones to aromatic nitriles proceeded smoothly in the presence of a simple copper catalyst system (CuI–2,2′-bipyridine–NaOtBu) in N,N-dimethylformamide. Enaminones in satisfactory to excellent yields were produced using this technique.

Palladium-catalyzed carboxylative coupling of benzyl chlorides with allyltributylstannane was successfully conducted to produce benzyl but-3-enoates in satisfactory to good yields. The carboxylative coupling reaction occurred smoothly under mild conditions in the presence of palladium nanoparticles in tetrahydrofuran.

The palladium-catalyzed three-component reactions of benzyl halides, activated olefins, and allyltributylstannane were successfully conducted to produce the corresponding benzylallylation products in satisfactory to high yields. The benzylallylation reaction proceeded smoothly under mild conditions in the presence of palladium nanoparticles in tetrahydrofuran.

An efficient method for the synthesis of 3,5-disubstituted pyrazoles is described. The reactions of 1,3-dialkynes with hydrazine proceeded smoothly in dimethyl sulfoxide under mild reaction conditions to produce 3,5-disubstituted pyrazoles in satisfactory to excellent yields. A one-pot procedure of the transformation has been developed.

Palladium-catalyzed amination of chloromethylnaphthalene and chloromethylanthracene derivatives to produce naphthylamines and anthrylamines in satisfactory to good yields has been developed. The unprecedented amination reactions proceeded smoothly under mild conditions in the presence of Pd(PPh3)4 as a catalyst.

An efficient method for the synthesis of aryl and heteroaryl chlorides is described. The reactions of aryl and heteroaryl bromides with tetramethylammonium chloride proceeded smoothly in the presence of a copper catalyst under mild reaction conditions to produce the corresponding chlorides in satisfactory to excellent yields.

An efficient method for the synthesis of 3,5-disubstituted isoxazoles is described. The reactions of 1,3-dialkynes with hydroxylamine proceeded smoothly in DMSO under mild reaction conditions to produce 3,5-disubstituted isoxazoles in satisfactory to excellent yields.

An efficient method for the synthesis of indolylglycine derivatives is described. The oxidative coupling reactions of ethyl 2-(disubstituted amino)acetates with indoles proceeded smoothly in the presence of meta-chloroperoxybenzoic acid (mCPBA) under ambient conditions to produce indolylglycine derivatives in satisfactory to excellent yields.

Palladium-catalyzed nucleophilic dearomatization of chloromethyl naphthalene derivatives to produce ortho- or para-substituted carbocycles in satisfactory to excellent yields has been developed. The unprecedented dearomatization reactions proceeded smoothly under mild conditions via η3-benzylpalladium intermediates.

A new method for the preparation of SBA-15-supported palladium catalyst for Heck reaction in supercritical carbon dioxide was presented. The newly formed SBA-15-supported palladium catalyst (Ph-SBA-15-PPh3-Pd) exhibited high catalytic activity for the Heck reaction of 4-nitrobromobenzene with methyl acrylate. The catalyst can be reused several times without a loss of activity.

An efficient method for synthesizing N,N-dimethylpropargylamines is described. The synthesis exploited the Cu(II)-catalyzed oxidative alkynylation reaction of trimethylamine N-oxides with alkynes in the absence of external oxidant. Both aromatic and aliphatic alkynes were utilized to achieve the corresponding products in moderate to excellent yields. The reaction conditions tolerated ester, hydroxy, and aldehyde groups.

The external and internal surfaces of SBA-15 were modified by (MeO)3SiPh and a phosphine ligand, (MeO)3SiCH2CH2CH2SCH2C6H4PPh2, before and after the template Pluronic P123 copolymer was removed, respectively. Palladium was then tethered within the cavity of the mesoporous material Ph-SBA-15-PPh3via a ligand-exchange reaction to provide a new supported palladium catalyst Ph-SBA-15-PPh3-Pd. This catalyst was demonstrated to be a robust and active catalyst in Suzuki reaction of a wide range of aryl bromides with arylboronic acids in supercritical carbon dioxide. After the reaction mixtures were treated at 90 °C for 24 h, the crude coupling products were obtained as crystalline solids when the reaction temperature was lowered to room temperature and the carbon dioxide was then slowly released. The pure products can be obtained by simple recrystallization in good to excellent yields. The Ph-SBA-15-PPh3-Pd catalyst has low leaching loss and can be reused at least 7 times without loss of activity.

A new method for the preparation of microcapsule-supported palladium catalyst was described. The highly monodisperse cross-linked polystyrene microcapsules containing phosphine ligand were synthesized by the self-assembling of phase separated polymer (SaPSeP) method using diphenyl(4-vinylphenyl)phosphine and divinylbenzene as a monomer and crosslinking agent, respectively, and 2,2′-azobisisobutyronitrile (AIBN) as an initiator within the droplets of oil-in-water (O/W) emulsions, which were prepared by using the Shirasu Porous Glass (SPG) membrane emulsification technique. The prepared microcapsule-supported palladium catalyst exhibited high catalytic activity for Heck reaction and can be reused several times without loss of activity.

Suzuki reaction of bromoallenes with arylboronic acids was successfully performed by using an air-stable hemilabile P–O coordinated cyclopalladated complex Pd(Ph2PCH2CO2)2 as a precatalyst, and the corresponding coupling products were obtained in satisfactory to excellent yields. All products are unknown compounds which were characterized by 1H NMR, 13C NMR, IR, and HRMS.

Two-step one-pot transformation of primary halides into corresponding nitriles is successfully achieved. Nucleophilic substitution of primary halides with sodium azide and subsequent palladium-catalyzed hydrogen transfer proceeds smoothly in the presence of sterically bulky ligand dicyclohexyl(2′,4′,6′-triisopropylbiphenyl-2-yl)phosphine (XPhos) in acetone to produce nitriles in satisfactory to good yields.

Palladium-catalyzed allylation reactions of 2-(chloromethyl)thiophenes, 2-(chloromethyl)furans, and N-protected 2-(chloromethyl)-1H-pyrroles with allyltributylstannane were described in this study. This type of allylation reaction regioselectively occurred on the heteroarene rings to produce allylated dearomatization products or allylated heteroarenes with satisfactory yields.

An efficient method for the synthesis of enaminones is described. The aldol-type addition of ketones to aromatic nitriles proceeded smoothly in the presence of a simple copper catalyst system (CuI–2,2′-bipyridine–NaOtBu) in N,N-dimethylformamide. Enaminones in satisfactory to excellent yields were produced using this technique.

The remarkable effect of an unsupported nanoporous gold catalyst (AuNPore) on chemoselective hydrogenation of α,β-unsaturated aldehydes using silane has been described. Enals can be reduced with excellent selectivity, giving the corresponding allylic alcohols in good to high chemical yields.

An efficient method for the synthesis of aryl and heteroaryl chlorides is described. The reactions of aryl and heteroaryl bromides with tetramethylammonium chloride proceeded smoothly in the presence of a copper catalyst under mild reaction conditions to produce the corresponding chlorides in satisfactory to excellent yields.

Palladium-catalyzed carbonylative addition of aryl bromides to terminal arylalkynes was carried out to produce chalcones in satisfactory to excellent yields. The unprecedented carbonylation reaction proceeded smoothly under mild conditions in the presence of a simple palladium catalyst system (PdCl2/DPPB/iPr2NEt) in N,N-dimethyl formamide.

Organic synthesis using gold has gained tremendous attention in last few years, especially heterogeneous gold catalysis based on gold nanoparticles has made its place in almost all organic reactions, because of the robust and green nature of gold catalysts. In this context, gold nanopore (AuNPore) with a 3D metal framework is giving a new dimension to heterogeneous gold catalysts. Interestingly, AuNPore chemistry is proving better than gold nanoparticles based chemistry. In this review, along with recent advances, major discoveries in heterogeneous gold catalysis are discussed.

The palladium-catalyzed three-component reactions of benzyl halides, activated olefins, and allyltributylstannane were successfully conducted to produce the corresponding benzylallylation products in satisfactory to high yields. The benzylallylation reaction proceeded smoothly under mild conditions in the presence of palladium nanoparticles in tetrahydrofuran.