Manganese(I)-Catalyzed β-Methylation of Alcohols Using Methanol as C1 Source

Nickel-catalyzed coupling of R2P(O)Me (R = aryl or alkoxy) with (hetero)arylmethyl alcohols

α-Alkylation of methyldiarylphosphine oxides with (hetero)arylmethyl alcohols was performed under nickel catalysis. Various arylmethyl and heteroarylmethyl alcohols can be used in this transformation. A series of methyldiarylphosphine oxides were alkylated with 30-90% yields. Functional groups on the aromatic rings of methyldiarylphosphine oxides or arylmethyl alcohols including OMe, NMe2, SMe, CF3, Cl, and F groups can be tolerated. The conditions are also suitable for the α-alkylation reaction of dialkyl methylphosphonates.

Alcohol-Assisted Hydrogenation of Carbon Monoxide to Methanol Using Molecular Manganese Catalysts

Alcohol-assisted hydrogenation of carbon monoxide (CO) to methanol was achieved using homogeneous molecular complexes. The molecular manganese complex [Mn(CO)2Br[HN(C2H4P i Pr2)2]] ([HN(C2H4P i Pr2)2] = MACHO- i Pr) revealed the best performance, reaching up to turnover number = 4023 and turnover frequency 857 h-1 in EtOH/toluene as solvent under optimized conditions (T = 150 °C, p(CO/H2) = 5/50 bar, t = 8-12 h). Control experiments affirmed that the reaction proceeds via formate ester as the intermediate, whereby a catalytic amount of base was found to be sufficient to mediate its formation from CO and the alcohol in situ. Selectivity for methanol formation reached >99% with no accumulation of the formate ester. The reaction was demonstrated to work with methanol as the alcohol component, resulting in a reactive system that allows catalytic "breeding" of methanol without any coreagents.

Tungsten-Catalyzed Direct N-Alkylation of Anilines with Alcohols

The implementation of non-noble metals mediated chemistry is a major goal in homogeneous catalysis. Borrowing hydrogen/hydrogen autotransfer (BH/HA) reaction, as a straightforward and sustainable synthetic method, has attracted considerable attention in the development of non-noble metal catalysts. Herein, we report a tungsten-catalyzed N-alkylation reaction of anilines with primary alcohols via BH/HA. This phosphine-free W(phen)(CO)₄ (phen=1,10-phenthroline) system was demonstrated as a practical and easily accessible in-situ catalysis for a broad range of amines and alcohols (up to 49 examples, including 16 previously undisclosed products). Notably, this tungsten system can tolerate numerous functional groups, especially the challenging substrates with sterically hindered substituents, or heteroatoms. Mechanistic insights based on experimental and computational studies are also provided.

Enantioselective direct, base-free hydrogenation of ketones by a manganese amido complex of a homochiral, unsymmetrical P–N–P′ ligand

Base-free direct hydrogenation of ketones using a Mn(PNP′)(CO)₂ complex is more enantioselective than that of a related base-activated iron complex.

Installing the “magic methyl” – C–H methylation in synthesis

Following notable cases of remarkable potency increases in methylated analogues of lead compounds, this review documents the state-of-the-art in C–H methylation technology.

Visible-light-promoted α-methoxymethylation and aminomethylation of ketones with methanol as the C1 source

Visible-light-promoted α-methoxymethylation and aminomethylation of ketones using methanol as a sustainable C1 source have been developed. With rose bengal as the photosensitizer and air as the green oxidant, the methoxymethylation reactions proceeded smoothly under visible light irradiation at ambient temperature. Additionally, a one-pot one-step α-aminomethylation of ketones was achieved by adding N-nucleophiles. Preliminary mechanism studies suggest that the reaction mainly proceeds via a radical pathway.

Manganese catalyzed C-alkylation of methyl N-heteroarenes with primary alcohols

C-Alkylations of nine different classes of methyl-substituted N-heteroarenes are disclosed using a bench stable Mn(i)-catalyst under borrowing hydrogen conditions.

Nickel-catalyzed defluorinative alkylation of C(sp2)–F bonds

A nickel-catalyzed defluorinative alkylation of unactivated C(sp²)–F electrophiles using commercially available trialkylaluminum reagents, thus forming the C(sp²)–C(sp³) bonds is reported.

Recent advances in sustainable organic transformations using methanol: expanding the scope of hydrogen-borrowing catalysis

Recent progress relating to sustainable approaches using methanol as a C1-alkylating agent for C–Me and N–Me bond formation is discussed.

C(sp3)-H Monoarylation of Methanol Enabled by a Bidentate Auxiliary

With the assistance of a practical directing group (COAQ), the first catalytic protocol for the palladium-catalyzed C(sp³)-H monoarylation of methanol has been developed, offering an invaluable synthesis means to establish extensive derivatives of crucial arylmethanol functional fragments. Furthermore, the gram-scale reaction, broad substrate scope, excellent functional group compatibility, and even the practical synthesis of medicines further demonstrate the usefulness of this strategy.

Alcohols as Fluoroalkyl Synthons: Ni-catalyzed Dehydrogenative Approach to Access Polyfluoroalkyl Bis-indoles

An acceptorless dehydrogenative strategy for the synthesis of polyfluoroalkylated bis-indoles is described by employing an earth-abundant nickel-based catalytic system under air. The notable feature of the present transformation is the use of bench stable and easily affordable polyfluorinated alcohols without any pre-functionalization for the introduction of precious polyfluoroalkyl groups. The developed straightforward protocol accomplished biologically relevant fluoroalkyl bis-indoles in a sustainable fashion. Extensive DFT study predicts the unique role of indole molecules which stabilizes the transition states during the dehydrogenation process of polyfluorinated alcohols, presumably through non-covalent π⋅⋅⋅π and H-bonding interactions.

Carbon monoxide and hydrogen (syngas) as a C1-building block for selective catalytic methylation

A catalytic reaction using syngas (CO/H2) as feedstock for the selective β-methylation of alcohols was developed whereby carbon monoxide acts as a C1 source and hydrogen gas as a reducing agent. The overall transformation occurs through an intricate network of metal-catalyzed and base-mediated reactions. The molecular complex [Mn(CO)2Br[HN(C2H4P i Pr2)2]] 1 comprising earth-abundant manganese acts as the metal component in the catalytic system enabling the generation of formaldehyde from syngas in a synthetically useful reaction. This new syngas conversion opens pathways to install methyl branches at sp3 carbon centers utilizing renewable feedstocks and energy for the synthesis of biologically active compounds, fine chemicals, and advanced biofuels.

Asymmetric Synthesis of 1,2-Dihydronaphthalene-1-ols via Copper-Catalyzed Intramolecular Reductive Cyclization

We describe a copper-catalyzed intramolecular reductive cyclization of easily accessible benz-tethered 1,3-dienes containing a ketone moiety. This process provided biologically active 1,2-dihydronaphthalene-1-ol derivatives in good yields with excellent enantio- and diastereoselectivity. Mechanistic investigations using density functional theory revealed that (Z)- and (E)-allylcopper intermediates formed in situ from the diene and copper catalyst undergo isomerization and selective intramolecular allylation of the (E)-allylcopper form of the major product through a six-membered boatlike transition state. The resulting products were further transformed to fully saturated naphthalene-1-ols by reactions of the olefin moiety.

Synthesis of Tetrahydroquinolines via Borrowing Hydrogen Methodology Using a Manganese PN3 Pincer Catalyst

A straightforward and selective synthesis of 1,2,3,4-tetrahydroquinolines starting from 2-aminobenzyl alcohols and simple secondary alcohols is reported. This one-pot cascade reaction is based on the borrowing hydrogen methodology promoted by a manganese(I) PN³ pincer complex. The reaction selectively leads to 1,2,3,4-tetrahydroquinolines thanks to a targeted choice of base. This strategy provides an atom-efficient pathway with water as the only byproduct. In addition, no further reducing agents are required.

Sustainable and Selective Alkylation of Deactivated Secondary Alcohols to Ketones by Non-bifunctional Pincer N-heterocyclic Carbene Manganese

A sustainable and green route to access diverse functionalized ketones via dehydrogenative-dehydrative cross-coupling of primary and secondary alcohols is demonstrated. This borrowing hydrogen approach employing a pincer N-heterocyclic carbene Mn complex displays high activity and selectivity. A variety of primary and secondary alcohols are well tolerant and result in satisfactory isolated yields. Mechanistic studies suggest that this reaction proceeds via a direct outer-sphere mechanism and the dehydrogenation of the secondary alcohol substrates plays a vital role in the rate-limiting step.

Manganese-Catalyzed β-Methylation of Alcohols by Methanol

We report an earth-abundant-metal-catalyzed double and single methylation of alcohols. A manganese catalyst, which operates at low catalyst loadings and short reaction times, mediates these reactions efficiently. A broad scope of primary and secondary alcohols, including purely aliphatic examples, and 1,2-aminoalcohols can be methylated. Furthermore, alcohol methylation for the synthesis of pharmaceuticals has been demonstrated. The catalyst system tolerates many functional groups among them hydrogenation-sensitive examples and upscaling is easily achieved. Mechanistic investigations are indicative of a borrowing hydrogen or hydrogen autotransfer mechanism involving a bimetallic K-Mn catalyst. The catalyst accepts hydrogen as a proton and a hydride from alcohols efficiently and reacts with a chalcone via hydride transfer.

Manganese(I)-Catalyzed β-Methylation of Alcohols Using Methanol as C1 Source

Highly selective β-methylation of alcohols was achieved using an earth-abundant first row transition metal in the air stable molecular manganese complex [Mn(CO)2 Br[HN(C2 H4 Pi Pr2 )2 ]] 1 ([HN(C2 H4 Pi Pr2 )2 ]=MACHO-i Pr). The reaction requires only low loadings of 1 (0.5 mol %), methanolate as base and MeOH as methylation reagent as well as solvent. Various alcohols were β-methylated with very good selectivity (>99 %) and excellent yield (up to 94 %). Biomass derived aliphatic alcohols and diols were also selectively methylated on the β-position, opening a pathway to "biohybrid" molecules constructed entirely from non-fossil carbon. Mechanistic studies indicate that the reaction proceeds through a borrowing hydrogen pathway involving metal-ligand cooperation at the Mn-pincer complex. This transformation provides a convenient, economical, and environmentally benign pathway for the selective C-C bond formation with potential applications for the preparation of advanced biofuels, fine chemicals, and biologically active molecules.

Electrochemical α-methoxymethylation and aminomethylation of propiophenones using methanol as a green C1 source

We have developed an efficient and convenient strategy for the straightforward α-methoxymethylation and aminomethylation of a series of propiophenones.