Carboxylate-Directed Addition of Aromatic C–H Bond to Aromatic Aldehydes under Ruthenium Catalysis

Ru-Catalyzed Switchable Reactions of Acrylic Acids with Glyoxylate: Access to Functionalized γ-Butenolides

We herein report a switchable coupling of acrylic acids with ethyl glyoxylate under ruthenium catalysis enabling the synthesis of diverse functionalized γ-butenolides. The carboxyl-directed vinylic C-H cleavage and dual nucleophilic addition to aldehyde are achieved to deliver hydroxymethylated butanolides under mild and oxidant-free conditions. Alternatively, a controlled and unprecedented tandem C-H cyclization/oxidative homocoupling reaction is realized by using silver salt as the oxidant to generate a range of dimeric butenolides bearing vicinal all-carbon quaternary centers.

Theoretical Study on the Mechanism of Ru(II)-Catalyzed Intermolecular [3 + 2] Annulation between o-Toluic Acid and 3,5-Bis(trifluoromethyl)benzaldehyde: Octahedral vs Trigonal Bipyramidal

Density functional theory was utilized to investigate the mechanism of Ru(II)-catalyzed aromatic C-H activation and addition of aromatic aldehydes. The proposed catalytic cycle consists of C-H bond activation, aldehyde carbonyl insertion for C-C coupling, lactonization for the formation of the final product, product separation, and catalyst recovery. Our calculations suggest that Ru(OAc)2(PCy3) (referred to as CAT) is the most favorable active catalyst, facilitating the C-H bond activation to form a five-membered ring cycloruthenium intermediate (INT2). Subsequently, the aromatic aldehyde reactant 2a enters the Ru coordination sphere, accelerating the C-C coupling and lactonization for the formation of the final product. The involvement of acetate assists in the final product separation, while INT1 re-enters the Ru coordination sphere to initiate a new catalytic cycle. Utilizing the energetic span model, the apparent activation free energy barrier was computed to be 34.3 kcal mol-1 at 443 K. Furthermore, exploration of the reaction mechanism in the absence of phosphine ligands identified Ru(OAc)2(p-cymene) as the most favorable active catalyst. The derived apparent activation free energy barrier offers a comprehensive explanation for the experimentally observed yields. Additionally, we have examined the disparities between the octahedral and trigonal bipyramidal structures of the catalysts concerning their effects on the reaction mechanisms and apparent activation free energy barriers.

Ionic liquid post-modified carboxylate-rich MOFs for efficient catalytic CO2 cycloaddition under solvent-free conditions

The synthesis of cyclic carbonates through cycloaddition reactions between epoxides and carbon dioxide (CO2) is an important industrial process. Metal-Organic Frameworks (MOFs) have functional and ordered pore structures, making them attractive catalysts for converting gas molecules into valuable products. One approach to enhance the catalytic activity of MOFs in CO2 cycloaddition reactions is to create open metal sites within MOFs. In this study, the amino-functionalized rare earth Gd-MOF (Gd-TPTC-NH2) and its ionic liquid composite catalysts (Gd-TPTC-NH-[BMIM]Br) were synthesized using 2'-amino-[1,1':4',1''-terphenyl]-3,3'',5,5''-tetracarboxylic acid (H4TPTC-NH2) as the ligand. The catalytic performance of these two catalysts was observed in the cycloaddition reaction of CO2 and epoxides. Under the optimized reaction conditions, Gd-TPTC-NH-[BMIM]Br can effectively catalyze the cycloaddition reaction of a variety of epoxide substrates with good to excellent yields of cyclic carbonate products. Comparatively, epichlorohydrin and epibromohydrin, which possess halogen substituents, promote higher yields of cyclic carbonates due to the electron-withdrawing nature of Cl and Br substituents. Additionally, the Gd-TPTC-NH-[BMIM]Br catalyst demonstrated good recyclability and reproducibility, maintaining its catalytic activity without any changes in its structure or properties after five reuse cycles.

Asymmetric Ruthenium-Catalyzed C-H Activation by a Versatile Chiral-Amide-Directing Strategy

A versatile and readily available chiral amide directing group has been developed for the ruthenium(II)-catalyzed asymmetric C-H activation. Asymmetric C-H activation of the related chiral benzamides with various olefins, aldehydes and propargylic alcohols has been accomplished with high stereoselectivities, affording a series of chiral products including 3,4-dihydroisocoumarins (up to 96 % ee), isocoumarins (up to 92 % ee), phthalides (up to 99 % ee), chiral bicyclo[2.2.1]heptanes (>20 : 1 dr), 4-alkylidene-3,4-dihydroisocoumarins (up to 97 % ee) and allenes (>20 : 1 dr). Importantly, our methodologies enabled concise syntheses of many biologically active compounds and natural products (e.g., Montroumarin, Cyclosporone E, Cyclosporone Q, Concentricolide, Chuangxinol, and Eleutherol).

Electroreductive coupling of 2-acylbenzoates with α,β-unsaturated carbonyl compounds: density functional theory study on product selectivity

The electroreductive coupling of 2-acylbenzoates with acrylonitrile in the presence of TMSCl and successive treatment with 1 M HCl gave 2-cyanonaphthalen-1-ols or 3-(3-cyanoethyl)phthalides. On the other hand, the reaction of 2-acylbenzoates with methyl vinyl ketone under the same conditions produced 3-(3-oxobutyl)phthalides as the sole products. What determines the product selectivity was studied using DFT calculations.

Synthesis of Pyranones: Ru-Catalyzed Cascade Reaction via Vinylic C-H Addition to Glyoxylate

The efficient synthesis of pyranones is presented by a three-component cascade reaction from readily available acrylic acids, ethyl glyoxylate, and p-toluenesulfonamide under ruthenium catalysis. For the first time, the nucleophilic addition of the vinylic C-H bond of acrylic acids across aldehyde is achieved, and the intramolecular cyclization as well as subsequent second insertion to aldehyde form the substituted butenolides. The elimination of sulfonamides occurs at higher temperature to give the pyranones.

DFT study on ruthenium-catalyzed N-methylbenzamide-directed 1,4-addition of the ortho C–H bond to maleimide via C–H/C–C activation

B3LYP-D3a+IDSCRF/tzp-dkh(-dfg) calculations indicate that CO as a directing group is much more favourable than the N–H group, and the real active catalyst is an ionic type with one [SbF6]− group.

Palladium Catalyzed Regioselective Cyclization of Arylcarboxylic Acids via Radical Intermediates with Diaryliodonium Salts

Palladium-catalyzed C₂-arylation/intramolecular acylation with arylcarboxylic acids was developed by using diaryliodonium salts. The protocol has the advantage of good step-economy by two chemical bonds formation in one pot.

Cobalt-Catalyzed Vinylic C-H Addition to Formaldehyde: Synthesis of Butenolides from Acrylic Acids and HCHO

A carboxyl-assisted C-H functionalization of acrylic acids with formaldehyde to give butenolides is described. It is the first time that the addition of an inert vinylic C-H bond to formaldehyde has been achieved via cobalt-catalyzed C-H activation. The unique reactivity of the cobalt species was observed when compared with related Rh or Ir catalysts. γ-Hydroxymethylated butenolides were produced by the treatment of Na₂CO₃ after the catalytic reaction in one pot.

Ru-Catalyzed (E)-Specific ortho-C-H Alkenylation of Arenecarboxylic Acids by Coupling with Alkenyl Bromides

In the presence of [p-cymene)RuCl₂]₂, (E)-configured alkenyl bromides couple with aromatic carboxylates to form ortho-vinylbenzoic acids. This C-H vinylation proceeds in high yields without any activating phosphine ligands and has an excellent functional group tolerance. Starting from commonly available (E/Z )-mixtures of alkenyl bromides, (E)-configured vinyl arenes or dienes are formed exclusively. Mechanistic studies show that this selectivity is achieved because the (E)-configured alkenyl bromides undergo a smooth coupling, whereas the (Z)-isomers are rapidly eliminated with the formation of alkynes.

Preparation of Neutral trans - cis [Ru(O2CR)2P2(NN)], Cationic [Ru(O2CR)P2(NN)](O2CR) and Pincer [Ru(O2CR)(CNN)P2] (P = PPh3, P2 = diphosphine) Carboxylate Complexes and their Application in the Catalytic Carbonyl Compounds Reduction

The diacetate complexes trans-[Ru(κ¹-OAc)₂(PPh₃)₂(NN)] (NN = ethylenediamine (en) (1), 2-(aminomethyl)pyridine (ampy) (2), 2-(aminomethyl)pyrimidine (ampyrim) (3)) have been isolated in 76-88% yield by reaction of [Ru(κ²-OAc)₂(PPh₃)₂] with the corresponding nitrogen ligands. The ampy-type derivatives 2 and 3 undergo isomerization to the thermodynamically most stable cationic complexes [Ru(κ¹-OAc)(PPh₃)₂(NN)]OAc (2a and 3a) and cis-[Ru(κ¹-OAc)₂(PPh₃)₂(NN)] (2b and 3b) in methanol at RT. The trans-[Ru(κ¹-OAc)₂(P₂)₂] (P₂ = dppm (4), dppe (5)) compounds have been synthesized from [Ru(κ²-OAc)₂(PPh₃)₂] by reaction with the suitable diphosphine in toluene at 95 °C. The complex cis-[Ru(κ¹-OAc)₂(dppm)(ampy)](6) has been obtained from [Ru(κ²-OAc)₂(PPh₃)₂] and dppm in toluene at reflux and reaction with ampy. The derivatives trans-[Ru(κ¹-OAc)₂P₂(NN)] (7-16; NN = en, ampy, ampyrim, 8-aminoquinoline; P₂ = dppp, dppb, dppf, (R)-BINAP) can be easily synthesized from [Ru(κ²-OAc)₂(PPh₃)₂] with a diphosphine and treatment with the NN ligands at RT. Alternatively these compounds have been prepared from trans-[Ru(OAc)₂(PPh₃)₂(NN)] by reaction with the diphosphine in MEK at 50 °C. The use of (R)-BINAP affords trans-[Ru(κ¹-OAc)₂((R)-BINAP)(NN)] (NN = ampy (11), ampyrim (15)) isolated as single stereoisomers. Treatment of the ampy-type complexes 8-15 with methanol at RT leads to isomerization to the cationic derivatives [Ru(κ²-OAc)P₂(NN)]OAc (8a-15a; NN = ampy, ampyrim; P₂ = dppp, dppb, dppf, (R)-BINAP). Similarly to 2, the dipivalate trans-[Ru(κ¹-OPiv)₂(PPh₃)₂(ampy)] (18) is prepared from [Ru(κ²-OPiv)₂(PPh₃)₂] (17) and ampy in CHCl₃. The pincer acetate [Ru(κ¹-OAc)(CNN^OMe)(PPh₃)₂] (19) has been synthesized from [Ru(κ²-OAc)₂(PPh₃)₂] and HCNN^OMe ligand in 2-propanol with NEt₃ at reflux. In addition, the dppb pincer complexes [Ru(κ¹-OAc)(CNN)(dppb)] (CNN = AMTP (20), AMBQ^Ph (21)) have been obtained from [Ru(κ²-OAc)₂(PPh₃)₂], dppb, and HAMTP or HAMBQ^Ph with NEt₃, respectively. The acetate NN and pincer complexes are active in transfer hydrogenation with 2-propanol and hydrogenation with H₂ of carbonyl compounds at S/C values of up to 10000 and with TOF values of up to 160000 h^-1.

Palladium-Catalyzed Site-Selective Benzocyclization of Naphthoic Acids with Diaryliodonium Salts: Efficient Access to Benzanthrones

Dual activation of both C-I and vicinal C-H bonds of diaryliodonium salts allowing for diarylation is a subject of rapid construction of π-extended frameworks. Here, we report palladium-catalyzed cascade of C₈-arylation/intramolecular Friedel-Crafts acylation of α-naphthoic acids in the synthesis of benzanthrone derivatives. The step-economical protocol tolerates various substrates, which resulted in a potential molecular library for developing functional polycyclic scaffolds. The approach relies on the synergistic action of strong acid with palladium catalysts to form two bonds in a one-pot procedure.

Rh-Catalyzed Annulation of Benzoic Acids, Formaldehyde, and Malonates via ortho-Hydroarylation to Indanones

A three-component reaction from readily available low-cost materials of benzoic acids, formaldehyde, and malonates for the preparation of indanones by rhodium catalysis is reported. The annulation is initiated by an ortho-hydroarylation of benzoic acids, and a Lewis acid is not required. The solvent has a significant influence to the reaction, and 2-substituted or nonsubstituted indanones are obtained by the change of solvent.

Ru(II)-Catalyzed C-H Hydroxyalkylation and Mitsunobu Cyclization of N-Aryl Phthalazinones

Ruthenium(II)-catalyzed C(sp²)-H functionalization of N-aryl phthalazinones with a range of aldehydes and activated ketone is described. Initial formation of hydroxyalkylated phthalazinones and subsequent Mitsunobu cyclization provided facile access to biologically relevant indazolophthalazinones. The utility of this method is highlighted by synthetic transformations into a series of potentially bioactive scaffolds.