Efficient alkylation of ketones with primary alcohols catalyzed by ruthenium(II)/P,N ligand complexes

Alcohols as Substrates in Transition-Metal-Catalyzed Arylation, Alkylation, and Related Reactions

Alcohols are abundant and attractive feedstock molecules for organic synthesis. Many methods for their functionalization require them to first be converted into a more activated derivative, while recent years have seen a vast increase in the number of complexity-building transformations that directly harness unprotected alcohols. This Review discusses how transition metal catalysis can be used toward this goal. These transformations are broadly classified into three categories. Deoxygenative functionalizations, representing derivatization of the C-O bond, enable the alcohol to act as a leaving group toward the formation of new C-C bonds. Etherifications, characterized by derivatization of the O-H bond, represent classical reactivity that has been modernized to include mild reaction conditions, diverse reaction partners, and high selectivities. Lastly, chain functionalization reactions are described, wherein the alcohol group acts as a mediator in formal C-H functionalization reactions of the alkyl backbone. Each of these three classes of transformation will be discussed in context of intermolecular arylation, alkylation, and related reactions, illustrating how catalysis can enable alcohols to be directly harnessed for organic synthesis.

Synthesis of Thiophene-Substituted Ketones via Manganese-Catalyzed Dehydrogenative Coupling Reaction

This study reports an efficient and green one-step method for synthesizing thiophene-substituted ketones from 2-thiophenemethanol and ketones via dehydrogenative coupling using manganese complexes as catalysts. The manganese complex demonstrated a broad applicability under mild conditions and extended the range of usable substrates. Utilizing this strategy, we carried out an efficient and diverse reaction of ketones with 2-thiophenemethanol, and successfully synthesized a series of thiophene-substituted saturated ketones and α, β-unsaturated ketones in good isolated yields.

Ruthenium Complexes Bearing α-Diimine Ligands and Their Catalytic Applications in N-Alkylation of Amines, α-Alkylation of Ketones, and β-Alkylation of Secondary Alcohols

New Ru(II) complexes encompassing α-diimine ligands were synthesized by reacting ruthenium precursors with α-diimine hydrazones. The new ligands and Ru(II) complexes were analyzed by analytical and various spectroscopic methods. The molecular structures of L₁ and complexes 1, 3, and 4 were determined by single-crystal XRD studies. The results reveal a distorted octahedral geometry around the Ru(II) ion for all complexes. Moreover, the new ruthenium complexes show efficient catalytic activity toward the C-N and C-C coupling reaction involving alcohols. Particularly, complex 3 demonstrates effective conversion in N-alkylation of aromatic amines, α-alkylation of ketones, and β-alkylation of alcohols.

Selective Synthesis of Ketones and Chiral Allylic Alcohols from the Addition of Arylboronic Acids to α,β-Unsaturated Aldehydes Mediated by a Transition Metal/Monophosphorus Ligand System

Here, we demonstrated a transition metal-mediated/monophosphorus ligand system for the selective synthesis of ketones or chiral allylic alcohols in high yields/enantiomeric excess from the 1,2-addition of arylboronic acids to α,β-unsaturated aldehydes. Notably, isomerization of the chiral allylic alcohols to ketones was suppressed by the Ru-catalyzed/monophosphorus ligand system. The asymmetric catalytic system provides an alternative and efficient method of preparing chiral allylic alcohols.

RuII complexes of 1,2,3-triazole appended tertiary phosphines, [P(Ph){(o-C6H4)(1,2,3-N3C(Ph)CH}2] and [P(Ph){o-C6H4(CCH)-(1,2,3-N3-Ph)}2]: highly active catalysts for transfer hydrogenation of carbonyl/nitro compounds and for α-alkylation of ketones

The synthesis of two new 1,2,3-triazole appended monophosphines [P(Ph){(o-C₆H₄)(1,2,3-N₃C(Ph)CH}₂] (1) and [P(Ph){o-C₆H₄(CCH)(1,2,3-N₃-Ph)}₂] (2) and their Ru^II complexes is described. The reactions of 1 and 2 with [Ru(PPh₃)₃Cl₂] in a 1 : 1 molar ratio produced cationic complexes 3 and 4, respectively. Both the complexes showed very high catalytic activity towards transfer hydrogenation, nitro reduction, and α-alkylation reactions and afforded the corresponding products in good to excellent yields. The free energy of β-hydride elimination from the respective Ru-alkoxide intermediates, a key mechanistic step common to all the three catalytic pathways, was calculated to be close to ergoneutral by density functional theory-based calculations, which is posited to rationalize the catalytic activity of 3. The reduction of aromatic nitro compounds was found to be highly chemoselective and produced the corresponding amines as major products even in the presence of a carbonyl group. The triazolyl-N2 coordinated Ru^II-NPN complex 3 showed better catalytic activity compared to the triazolyl-N3 coordinated complex 4.

A heterogeneous cobalt catalyst for C–C bond formation by a borrowing hydrogen strategy

Co–MgO/TiO2 exhibited high activity for α-alkylation of ketones with alcohols through a borrowing hydrogen strategy without the addition of bases which were utilized in reported heterogeneous catalytic systems.

Unveiling the catalytic nature of palladium-N-heterocyclic carbene catalysts in the α-alkylation of ketones with primary alcohols

We report herein the synthesis of four new Pd-PEPPSI complexes with backbone-modified N-heterocyclic carbene (NHC) ligands and their application as catalysts in the α-alkylation of ketones with primary alcohols using a borrowing hydrogen process and tandem Suzuki-Miyaura coupling/α-alkylation reactions. Among the synthesized Pd-PEPPSI complexes, complex 2c having 4-methoxyphenyl groups at the 4,5-positions and 4-methoxybenzyl substituents on the N-atoms of imidazole exhibited the highest catalytic activity in the α-alkylation of ketones with primary alcohols (18 examples) with yields reaching up to 95%. Additionally, complex 2c was demonstrated to be an effective catalyst for the tandem Suzuki-Miyaura-coupling/α-alkylation of ketones to give biaryl ketones with high yields. The heterogeneous nature of the present catalytic system was verified by mercury poisoning and hot filtration experiments. Moreover, the formation of NHC-stabilized Pd(0) nanoparticles during the α-alkylation reactions was identified by advanced analytical techniques.

Choline Chloride-Based Deep Eutectic Systems in Sequential Friedländer Reaction and Palladium-Catalyzed sp3 CH Functionalization of Methyl Ketones

A volatile organic solvent-free and choline chloride (ChCl)-based deep eutectic system (DES)-mediated sp³-CH functionalization of acetophenones 1 with benzyl alcohols 2 to the corresponding α, β-saturated ketones 3 is accounted for. The domino dehydrogenation-aldol condensation (hydrogenation borrowing concept) has been successfully attempted with palladium-tetrakis(triphenylphosphine) [Pd(PPh₃)₄] catalyst-xantphos ligand combination. Furthermore, a sequential Friedländer reaction of 2-aminobenzophenone 4 and palladium-catalyzed α-alkylation of the quinolinyl methyl ketone with benzyl alcohols 2 in ChCl-based DES have been successfully investigated. The C-C bond formation through sp³-CH functionalization involves a wide scope of the substrates, high atom efficiency, chemoselectivity, and environmentally friendly strategy.

Effects of water on a catalytic system for preparation of N-(1,4-dimethylamyl)-N′-phenyl-p-phenylenediamine by reductive alkylation

Effects of water on a catalytic reaction system for reductive alkylation of p-aminodiphenylamine (p-ADPA) with 5-methyl-2-hexanone (MIAK) was studied. Platinum nanoparticles supported on activated carbon with high specific surface area were used as catalysts for reductive alkylation reaction under different water content conditions. Schiff base forming data, catalytic activity and stability of the catalysts were investigated under the aforementioned reaction conditions. Fresh and used catalysts were characterized by TEM, SEM, XRD, ICP, laser particle size analysis, N₂ physical adsorption and CO chemical adsorption to explore the effects of water on the catalytic reaction system for the ketone/amine reductive alkylation reaction. The characterization results indicated that catalyst support pulverization and Pt loss occurred in the reused catalyst, and the trend was more obvious under the conditions of higher water content. Water in the reaction system could also aggravate the decrease of the catalyst's specific surface area and pore volume, which should be a major reason of the lower catalytic performance.

Water could restrain the formation of a Schiff base, reducing the selectivity of 7PPD and aggravating the decrease of catalytic performance.