Rhodium(I)-Catalyzed Borylation of Nitriles through the Cleavage of Carbon–Cyano Bonds

Copper/O2-Mediated Oxidative C-C Activation of Nitriles for Selective Acylation-Bromination of Anilines

This study reports selective dual amino acylation and C-H bromination of aniline compounds enabled by Cu/O2 catalyst systems. This method involves crucial oxidation-induced C-CN bond cleavage of α-methylene nitriles to generate an acylcyanide intermediate that is facilely intercepted by anilines. After amino acylation, the Cu(II) precatalyst in combination with NBS generates Cu(III)-Br in situ that engages in selective electrophilic para- or ortho-C-H bromination. The substrate scope, mechanistic aspects, and late-stage functionalization of biologically active anilines are studied. This study shows the synthetic potential of oxidative C-CN bond activation of nitriles for the development of valuable reactions.

Synthesis of Tetrasubstituted Alkenes by Rhodium-Catalyzed Regioselective Cyano Transfer

We describe herein a novel, general, and robust approach to structurally diversified alkenyl nitriles through a Rh-catalyzed cyano transfer reaction between alkynyl-malononitrile derivatives and aryl/alkenyl boronic acids. This reaction exhibits high chemo- and regioselectivity and a broad substrate scope. The tetrasubstituted alkenyl dinitriles (34 examples, average 58% yield) are obtained through substrate tuning and ligand control.

Direct transformation of nitriles to cyanide using chloride anion as catalyst

A simple method is explored for the scission of C-CN bonds into aldehyde and CN- in air. The transformation was mediated by chloride anions. The cyanide anions were extracted from the reaction solution to form (Et4N)2[Zn(CN)4] and (Et4N)2[Ni(CN)4]. A chloride-induced reaction mechanism is proposed based on experimental studies and DFT calculations. This work might guide the study of halogen catalysts for C-C bond cleavage.

Recent Expedition in Pd- and Rh-Catalyzed C(Ar) -B Bond Formations and Their Applications in Modern Organic Syntheses

Transition metal-catalyzed borylation has emerged as a powerful and versatile strategy for synthesizing organoboron compounds. These compounds have found widespread applications in various aspects, including organic synthesis, materials science, and medicinal chemistry. This review provides a concise summary of the recent advances in palladium- and rhodium-catalyzed borylation from 2013 to 2023. The review covers the representative examples of catalysts, substrates scope and reaction conditions, with particular emphasis on the development of catalyst systems, such as phosphine ligands, NHC-carbene, and more. The diverse array of borylative products obtained for further applications in Suzuki-Miyaura coupling, and other transformations, are also discussed. Future directions in this rapidly evolving field, with the goal of designing more efficient, selective borylation methodologies are highlighted, too.

Bis(neopentylglycolato)diboron (B2nep2) as a bidentate ligand and a reducing agent for early transition metal chlorides giving MCl4(B2nep2) complexes

We found that bis(neopentylglycolato)diboron (B2nep2) served as a bidentate ligand and a one-electron reducing agent for early transition metal chlorides to afford MCl4(B2nep2). Treatment of B2nep2 with MCl5 (M = Nb and Mo) produced MCl4(B2nep2) via two successive reactions, coordination of B2nep2 to the metal center and one-electron reduction from M(V) to M(IV), while coordination of B2nep2 to MCl4 (M = Zr, Ti) was observed without reduction of the central metals. DFT studies for the reduction of NbCl5 by B2nep2 clarified the initial formation of seven-coordinated and B2nep2-ligated Nb(V) species, NbCl5(B2nep2), and one chloride on niobium(V) moves to the Lewis acidic boron center to generate NbCl4[(B2nep2)Cl]. The chloride on the boron atom of NbCl4[(B2nep2)Cl] is trapped by the second B2nep2 to give [NbCl4(B2nep2)][ClB2nep2]. After the formation of [ClB2nep2]- as an anionic sp2-sp3 diboron adduct, one-electron reduction of the niobium(V) center produces NbCl4(B2nep2) along with [ClB2nep2]˙ as a plausible diboron species, whose decomposition affords ClBnep and B2nep2. The reduction of metal halides in the presence of B2nep2 was exemplified by green LED irradiation of TiCl4(B2nep2), producing chloride-bridged titanium(III) species, (B2nep2)TiCl2(μ-Cl)2TiCl2(B2nep2).

Relativistic quantum calculations to understand the contribution of f-type atomic orbitals and chemical bonding of actinides with organic ligands

The nuclear waste problem is one of the main interests of rare earth and actinide element chemistry. Studies of actinide-containing compounds are at the frontier of the applications of current theoretical methods due to the need to consider relativistic effects and approximations to the Dirac equation in them. Here, we employ four-component relativistic quantum calculations and scalar approximations to understand the contribution of f-type atomic orbitals in the chemical bonding of actinides (Ac) to organic ligands. We studied the relativistic quantum structure of an isostructural family made of Plutonium (Pu), Americium (Am), Californium (Cf), and Berkelium (Bk) atoms with the redox-active model ligand DOPO (2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazin-9-olate). Crystallographic structures were available to validate our calculations for all mentioned elements except for Cf. In short, state-of-the-art relativistic calculations were performed at different levels of theory to investigate the influence of relativistic and electron correlation effects on geometrical structures and bonding energies of Ac-DOPO₃ complexes (Ac = Pu, Am, Cf, and Bk): (1) the scalar (sc) and spin-orbit (so) relativistic zeroth order regular approximation (ZORA) within the hybrid density functional theory (DFT) and (2) the four-component Dirac equation with both the Dirac-Hartree-Fock (4c-DHF) and Lévy-Leblond (LL) Hamiltonians. We show that sr- and so-ZORA-DFT could be used as efficient theoretical models to first approximate the geometry and electronic properties of actinides which are difficult to synthesize or characterize, but knowing that the higher levels of theory, like the 4c-DHF, give closer results to experiments. We also performed spin-free 4c calculations of geometric parameters for the Americium and Berkelium compounds. To the best of our knowledge, this is the first time that these kinds of large actinide compounds (the largest contains 67 atoms and 421 electrons) have been studied with highly accurate four-component methods (all-electron calculations with 6131 basis functions for the largest compound). We show that relativistic effects play a key role in the contribution of f-type atomic orbitals to the frontier orbitals of Ac-DOPO₃ complexes. The analysis of the results obtained applying different theoretical schemes to calculate bonding energies is also given.

Mechanistic Investigation of the Nickel-Catalyzed Metathesis between Aryl Thioethers and Aryl Nitriles

Functional group metathesis is an emerging field in organic chemistry with promising synthetic applications. However, no complete mechanistic studies of these reactions have been reported to date, particularly regarding the nature of the key functional group transfer mechanism. Unraveling the mechanism of these transformations would not only allow for their further improvement but would also lead to the design of novel reactions. Herein, we describe our detailed mechanistic studies of the nickel-catalyzed functional group metathesis reaction between aryl methyl sulfides and aryl nitriles, combining experimental and computational results. These studies did not support a mechanism proceeding through reversible migratory insertion of the nitrile into a Ni-Ar bond and provided strong support for an alternative mechanism involving a key transmetalation step between two independently generated oxidative addition complexes. Extensive kinetic analysis, including rate law determination and Eyring analysis, indicated the oxidative addition complex of aryl nitrile as the resting state of the catalytic reaction. Depending on the concentration of aryl methyl sulfide, either the reductive elimination of aryl nitrile or the oxidative addition into the C(sp²)-S bond of aryl methyl sulfide is the turnover-limiting step of the reaction. NMR studies, including an unusual ³¹P-²H HMBC experiment using deuterium-labeled complexes, unambiguously demonstrated that the sulfide and cyanide groups exchange during the transmetalation step, rather than the two aryl moieties. In addition, Eyring and Hammett analyses of the transmetalation between two Ni(II) complexes revealed that this central step proceeds via an associative mechanism. Organometallic studies involving the synthesis, isolation, and characterization of all putative intermediates and possible deactivation complexes have further shed light on the reaction mechanism, including the identification of a key deactivation pathway, which has led to an improved catalytic protocol.

Cascade of C(sp2)-H Addition to Carbonyl and C(sp2)-CN/C(sp2)-H Coupling Enabled by Brønsted Acid: Construction of Benzo[a]carbazole Frameworks

Herein, we report an unprecedented cascade reaction of C(sp²)-H addition to carbonyl and the C(sp²)-CN/C(sp²)-H coupling of 2-(2-oxo-2-arylethyl)benzonitriles with indoles enabled by commercially available TsOH·H₂O. The protocol represents the first metal-free C(sp²)-CN/C(sp²)-H coupling, affording a new route for the synthesis of various benzo[a]carbazole derivatives with a broad substrate scope, high yields, and simple conditions.

Palladium-Catalyzed Cascade Carbonylation to α,β-Unsaturated Piperidones via Selective Cleavage of Carbon-Carbon Triple Bonds

A direct and selective synthesis of α,β-unsaturated piperidones by a new palladium-catalyzed cascade carbonylation is described. In the presented protocol, easily available propargylic alcohols react with aliphatic amines to provide a broad variety of interesting heterocycles. Key to the success of this transformation is a remarkable catalytic cleavage of the present carbon-carbon triple bond by using a specific catalyst with 2-diphenylphosphinopyridine as ligand and appropriate reaction conditions. Mechanistic studies and control experiments revealed branched unsaturated acid 11 as crucial intermediate.

Nickel-Catalyzed Thiolation of Aryl Nitriles

A nickel-catalyzed thiolation of aryl nitriles has been developed to access functionalized aryl thioethers. The ligand dcype (1,2-bis(dicyclohexylphosphino)ethane) as well as the base KOt Bu (potassium tert-butoxide) are essential to achieve this transformation. This scalable and practical process involves both a C-C bond activation and a C-S bond formation. Furthermore, this reaction shows a high functional-group tolerance and enables the late-stage functionalization of important molecules.

N-Heterocyclic Carbene-Catalyzed Truce-Smiles Rearrangement of N-Arylacrylamides via the Cleavage of Unactivated C(aryl)-N Bonds

We report on the N-heterocyclic carbene (NHC)-catalyzed Truce-Smiles rearrangement of aniline derivatives, in which an unactivated C(aryl)-N bond is cleaved, leading to the formation of a new C(aryl)-C bond. The key to the success of this reaction is the utilization of a highly nucleophilic NHC, which enables the formation of a highly nucleophilic ylide intermediate that is generated from an α,β-unsaturated amide.

Ni-catalyzed reductive decyanation of nitriles with ethanol as the reductant

Ethanol, as an environmentally friendly and renewable reagent, was applied as a hydride donor to convert C–CN to C–H bonds in this nickel-catalyzed protocol.

Cleavage of the Inert C(sp2)-Ar σ-Bond of Alkenes by a Spatial Constrained Interaction with Phosphinidene

[1 + 2] cycloaddition is a classical reaction between the electrophilic phosphinidene and an alkene. However, a spatial constraint blocks this well-known reaction and enables an unprecedented chemoselective C(sp²)-Ar σ-bond insertion of the alkene. The theoretical calculations demonstrate that this C-C bond cleavage is energetically feasible and thermodynamically favored through an electrophilic rearrangement and concomitant 1,9-aryl migration without involving any strained intermediate.

Combined Cyanoborylation, C-H Activation Strategy for Styrene Functionalization

A one-pot multicomponent copper-catalyzed protocol for borylation/ortho-cyanation of styrene derivatives followed by a Suzuki-Miyaura coupling provides a platform to explore the factors that control the selectivity between distal or proximal functionalization of arenes. The development of divergent nitrile-directed C-H functionalization (acetoxylation, pivalation, and methoxylation) offers an effective approach to rapidly increase synthetic complexity. Finally, the development of a mild reductive decyanation allows a traceless method to access functionalized biaryl motifs.

Methodologies and Strategies for Selective Borylation of C-Het and C-C Bonds

Organoborons have emerged as versatile building blocks in organic synthesis to achieve molecular diversity and as carboxylic acid bioisosteres with broad applicability in drug discovery. Traditionally, these compounds are prepared by the substitution of Grignard/lithium reagents with electrophilic boron species and Brown hydroboration. Recent developments have provided new routes for the efficient preparation of organoborons by applying reactions using chemical feedstocks with leaving groups. As compared to the previous methods that used organic halides (I, Br, and Cl), the direct borylation of less reactive C-Het and C-C bonds has become highly important to get efficiency and functional-group compatibility. This Review aims to provide a comprehensive overview of this topic, including (1) C-F bond borylation, (2) C-O bond borylation, (3) C-S bond borylation, (4) C-N bond borylation, and (5) C-C bond borylation. Considerable attention is given to the strategies and mechanisms involved. We expect that this Review will inspire chemists to discover more efficient transformations to expand this field.

Lewis Acid Mediated Electrophilic Cyanation of 2,2'-Biphenols

A Lewis acid mediated electrophilic cyanation of 2,2'-biphenols with a trifluoromethanesulfonyl (Tf) protecting group is reported. The cyanation reactions with less toxic, commercially available MeSCN as a cyanating reagent afforded a range of 3-cyan-2,2'-biphenols in moderate to high yields. The use of trifluoromethanesulfonyl (Tf) as a protecting group is crucial to the success of this transformation. Moreover, the cyanated products were readily transformed into various synthetically useful molecules. This protocol features high efficiency, excellent regioselectivity, and good functional group compatibility and may provide a practical tool for the synthesis and modification of biologically active compounds, catalysts, and ligands.

An umpolung reaction of α-iminonitriles and its application to the synthesis of aminomalononitriles

An umpolungN-alkylation reaction of α-iminonitriles with Grignard reagents gaveN-alkylated α-aminonitriles in good yields.

Indolylboronic Acids: Preparation and Applications

Indole derivatives are associated with a variety of both biological activities and applications in the field of material chemistry. A number of different strategies for synthesizing substituted indoles by means of the reactions of indolylboronic acids with electrophilic compounds are considered the methods of choice for modifying indoles because indolylboronic acids are easily available, stable, non-toxic and new reactions using indolylboronic acids have been described in the literature. Thus, the aim of this review is to summarize the methods available for the preparation of indolylboronic acids as well as their chemical transformations. The review covers the period 2010-2019.

Cyano-borrowing reaction: nickel-catalyzed direct conversion of cyanohydrins and aldehydes/ketones to β-cyano ketone

A direct nickel-catalyzed, high atom- and step-economical reaction of cyanohydrins with aldehydes or ketones via an unprecedented “cyano-borrowing reaction” has been developed.

A direct nickel-catalyzed, high atom- and step-economical reaction of cyanohydrins with aldehydes or ketones via an unprecedented “cyano-borrowing reaction” has been developed. Cleavage of the C–CN bond of cyanohydrins followed by aldol condensation and conjugate addition of cyanide to α,β-unsaturated ketones proceeded to deliver a range of racemic β-cyano ketones with good to high yields. The practical procedure with the use of a commercial and less-toxic CN source bodes well for wide application of this protocol.

Direct synthesis of 8-acylated quinoline N-oxidesviapalladium-catalyzed selective C–H activation and C(sp2)–C(sp2) cleavage

An efficient method for the synthesis of 8-acylated quinoline N-oxides from the reaction of quinoline N-oxides with α-diketonesviaC–C bond cleavage was developed. A variety of quinoline N-oxides and α-diketones with different groups was well tolerated in this system.

Base induced C–CN bond cleavage at room temperature: a convenient method for the activation of acetonitrile

Acetonitrile was activated to form formaldehyde and cyanide in air. Utilization of the product [Cu^II–CN] for catalytic cyanation was investigated.

Palladium(ii)-mediated rapid 11C-cyanation of (hetero)arylborons

A palladium(ii)-mediated rapid ¹¹C-cyanation of (hetero)arylborons with [¹¹C]NH₄CN/NH₃ has been developed using bench-stable and readily available reagents. The method showed excellent functional-group tolerance, and allowed the highly efficient synthesis of a wide range of [¹¹C]cyanoarenes, including PET tracers for aromatase imaging. A mechanistic study of the ¹¹C-cyanation suggests the instantaneous formation of a mono[¹¹C]cyanopalladium(ii) complex that reacts smoothly with arylborons.

Palladium-Catalyzed Cyanothiolation of Internal Alkynes Using Organic Disulfides and tert-Butyl Isocyanide

Despite the availability of selective synthetic approaches to multifunctionalized substituted olefins, the cyanothiolation of internal alkynes has been much less explored. Herein, we show that nonactivated internal alkynes can be successfully cyanothiolated with diaryl disulfides and tert-butyl isocyanide in the presence of a Pd catalyst (e.g., Pd(PPh₃)₄) with the release of isobutene and arenethiol to afford β-thiolated alkenyl cyanides in yields of 34-89%.

Palladium-catalyzed C(carbonyl)–C bond cleavage of amides: a facile access to phenylcarbamate derivatives with alcohols

A sulfur-containing auxiliary enabled palladium-catalyzed C(carbonyl)–C bond activation of amides was reported to form phenylcarbamate derivatives with alcohols.

Featuring Xantphos

This review highlights the use of the bisphosphine ligand group in homogeneous catalysis.

Theoretical investigations of the Ir-catalyzed direct borylation of B(3,6)–H of o-carborane: the actual catalyst, mechanism, and origin of regioselectivity

The Ir^III species is proved to be the actual catalyst. The electron-delocalized structure and the inductive effects of the carbon centers is account for the regioselectivity.

1,4-Refunctionalization of β-diketones to γ-keto nitriles via C–C single bond cleavage

The 1,4-refunctionalization of β-diketones to γ-keto nitriles was realized via an Fe-catalyzed cascade radical process.