Nickel-catalyzed C-alkylation of thioamide, amides and esters by primary alcohols through a hydrogen autotransfer strategy

Iron-Catalyzed sp3 C-H Alkylation of Fluorene with Primary and Secondary Alcohols: A Borrowing Hydrogen Approach

The utilization of earth-abundant, cheap, and nontoxic transition metals in important catalytic transformations is essential for sustainable development, and iron has gained significant attention as the most abundant transition metal. A mixture of FeCl2 (3 mol %), phenanthroline (6 mol %), and KOtBu (0.4 eqivalent) was used as an effective catalyst for the sp3 C-H alkylation of fluorene using alcohol as a nonhazardous alkylating partner, and eco-friendly water was formed as the only byproduct. The substrate scope includes a wide range of substituted fluorenes and substituted benzyl alcohols. The reaction is equally effective with challenging secondary alcohols and unactivated aliphatic alcohols. Selective mono-C9-alkylation of fluorenes with alcohols yielded the corresponding products in good isolated yields. Various postfunctionalizations of C-9 alkylated fluorene products were performed to establish the practical utility of this catalytic alkylation. Control experiments suggested a homogeneous reaction path involving borrowing hydrogen mechanism with the formation and subsequent reduction of 9-alkylidene fluorene intermediate.

Iron- and base-catalyzed C(α)-alkylation and one-pot sequential alkylation-hydroxylation of oxindoles with secondary alcohols

The utilization of economical and environmentally benign transition metals in crucial catalytic processes is pivotal for sustainable advancement in synthetic organic chemistry. Iron, as the most abundant transition metal in the Earth's crust, has gained significant attention for this purpose. A combination of FeCl2 (5 mol%) in the presence of phenanthroline (10 mol%) and NaOtBu (1.5 equivalent) proved effective for the C(α)-alkylation of oxindole, employing challenging secondary alcohol as a non-hazardous alkylating agent. The C(α)-alkylation of oxindole was optimized in green solvent or under neat conditions. The substrate scope encompasses a broad array of substituted oxindoles with various secondary alcohols. Further post-functionalization of the C(α)-alkylated oxindole products demonstrated the practical utility of this catalytic alkylation. One-pot C-H hydroxylation of alkylated oxindoles yielded 3-alkyl-3-hydroxy-2-oxindoles using air as the most sustainable oxidant. Low E-factors (3.61 to 4.19) and good Eco-scale scores (74 to 76) of these sustainable catalytic protocols for the alkylation and one-pot sequential alkylation-hydroxylation of oxindoles demonstrated minimum waste generation. Plausible catalytic paths are proposed on the basis of past reports and control experiments, which suggested that a borrowing hydrogen pathway is involved in this alkylation.

Copper-Catalyzed Borrowing Hydrogen Reaction for α-Alkylation of Amides with Alcohols

We report the first example of copper-catalyzed α-alkylation of acetamides with alcohols via a borrowing hydrogen strategy. Catalyzed by the in situ-generated copper particles, acetamides and various substituted benzyl or alkyl alcohols were transformed into functionalized amides in good yields with excellent selectivity. Compared with previous work, this process is simple using commercially available Cu(OAc)2 as a precatalyst, without an additional ligand or a metal complex, and easier. Mechanistic studies revealed that aldehyde and α,β-unsaturated amides were the intermediates of this reaction and also disclosed the role of copper in alcohol dehydrogenation and C═C bond hydrogenation.

Quinoline-derived NNP-manganese complex catalyzed α-alkylation of ketones with primary alcohols

An air-stable quinoline-derived NNP ligand chelated Mn catalyst was developed for the efficient α-alkylation of ketones with primary alcohols via a hydrogen auto-transfer methodology. The sole by-product formed is water, rendering the protocol atom efficient. A wide range of ketone and alcohol substrates were employed, providing the α-alkylated ketones with isolated yields up to 94%. This system was also efficient for the green synthesis of quinoline derivatives while using (2-aminophenyl)methanol as an alkylating reagent.

Nickel-Catalyzed α-Alkylation of Arylacetonitriles with Challenging Secondary Alcohols

Nickel(II) complex 1 was utilized as a sustainable catalyst for α-alkylation of arylacetonitriles with challenging secondary alcohols. Arylacetonitriles with a wide range of functional groups were tolerated, and various cyclic and acyclic secondary alcohols were utilized to yield a large number of α-alkylated products. The plausible mechanism involves the base-promoted activation of precatalyst 1 to an active catalyst 2 (dehydrochlorinated product) which activates the O-H and C-H bonds of the secondary alcohol in a dehydrogenative pathway.

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.

Dehydrogenative Electrochemical Synthesis of N-Aryl-3,4-Dihydroquinolin-2-ones by Iodine(III)-Mediated Coupling Reaction

Electrochemically generated hypervalent iodine(III) species are powerful reagents for oxidative C-N coupling reactions, providing access to valuable N-heterocycles. A new electrocatalytic hypervalent iodine(III)-mediated in-cell synthesis of 1H-N-aryl-3,4-dihydroquinolin-2-ones by dehydrogenative C-N bond formation is presented. Catalytic amounts of the redox mediator, a low supporting electrolyte concentration and recycling of the solvent used make this method a sustainable alternative to electrochemical ex-cell or conventional approaches. Furthermore, inexpensive, readily available electrode materials and a simple galvanostatic set-up are applied. The broad functional group tolerance could be demonstrated by synthesizing 23 examples in yields up to 96 %, with one reaction being performed on a 10-fold higher scale. Based on the obtained results a sound reaction mechanism could be proposed.

Nickel-Catalyzed Alkylation of Oxindoles with Secondary Alcohols

Herein, we have demonstrated a simple nickel-catalyzed C-3-selective alkylation of 2-oxindoles using a wide variety of secondary alkyl alcohols. As a special highlight, functionalization of the cholesterol derivative was reported. Control experiments, initial mechanistic studies, and deuterium-labeling experiments were performed for the alkylation process.

Divergent upgrading pathways of sulfones with primary alcohols: nickel-catalyzed α-alkylation under N2 and metal-free promoted β-olefination in open air

We report here our findings on the diverse reaction results of sulfones and alcohols. In the presence of NiCl₂/P(t-Bu)₃ and under a N₂ atmosphere, α-C-alkylation of sulfones with alcohols occurs through a borrowing-hydrogen mechanism; when the reaction was carried out in the open air without nickel, the product was not the predicted α,β-unsaturated sulfone, but the β-alkenyl sulfone, which is a useful building block in organic synthesis.

A Journey from June 2018 to October 2021 with N,N-Dimethylformamide and N,N-Dimethylacetamide as Reactants

A rich array of reactions occur using N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAc) as reactants, these two amides being able to deliver their own H, C, N, and O atoms for the synthesis of a variety of compounds. This account highlights the literature published since June 2018, completing previous reviews by the author.

Borrowing Hydrogen for Organic Synthesis

Borrowing hydrogen is a process that is used to diversify the synthetic utility of commodity alcohols. A catalyst first oxidizes an alcohol by removing hydrogen to form a reactive carbonyl compound. This intermediate can undergo a diverse range of subsequent transformations before the catalyst returns the "borrowed" hydrogen to liberate the product and regenerate the catalyst. In this way, alcohols may be used as alkylating agents whereby the sole byproduct of this one-pot reaction is water. In recent decades, significant advances have been made in this area, demonstrating many effective methods to access valuable products. This outlook highlights the diversity of metal and biocatalysts that are available for this approach, as well as the various transformations that can be performed, focusing on a selection of the most significant and recent advances. By succinctly describing and conveying the versatility of borrowing hydrogen chemistry, we anticipate its uptake will increase across a wider scientific audience, expanding opportunities for further development.

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.

Nickel-catalyzed C3-alkylation of indoles with alcohols via a borrowing hydrogen strategy

An efficient Ni-catalyzed C3-alkylation of indoles with alcohols via a borrowing hydrogen pathway was achieved utilizing an N,O-donor coordinated nickel complex as the precatalyst.