Rhodium-Catalyzed Cyanation of C(sp2)–H Bond of Alkenes

Catalyst and transition-metal free 1,6-conjugate addition of azobisisobutyronitrile: access to isobutyronitrile containing diarylmethanes

A catalyst and transition-metal free 1,6-conjugate addition of azobisisobutyronitrile to para-quinone methides for the synthesis of isobutyronitrile containing diarylmethanes has been achieved. This protocol enables the synthesis of isobutyronitrile containing diarylmethanes in good yields and with a broad substrate scope. This is the first example wherein azobisisobutyronitrile has been used as a cyanide source for 1,6-conjugate addition under catalyst and metal-free conditions.

DNDMH enabled C(sp3)-H nitration of aryl alkenes

C(sp3)-H bond nitration provides facile access to nitro compounds that are inaccessible through traditional nitration pathways. This work describes a C(sp3)-H bond nitration of aryl alkenes using DNDMH, a nitration reagent developed previously in our lab. Notably, this novel nitration process presents excellent regioselectivity and chemoselectivity between C(sp3)-H nitration and C(sp2)-H nitration.

Ni-catalyzed reductive cyanation of alkenyl tosylates and triflates

Herein, we disclose the nickel-catalyzed reductive cyanation of alkenyl tosylates and triflates. Both cyclic and acyclic alkenyl nitriles are produced in moderate to good yield using 2-(4-methoxyphenyl)-2-methylmalononitrile (MeO-MPMN), a novel transnitrilation, or nitrile transfer, reagent. A robustness screen was undertaken to demonstrate the functional group tolerance of this method.

Green and efficient synthesis of dibenzyl cyanamides and ureas with cyanamide as a block

A method for the two-step synthesis of dibenzyl cyanamide and dibenzyl urea via cyanamide is presented. This approach is both efficient and environmentally friendly. Various N,N-dibenzyl ureas could be obtained by reactions of N,N-dibenzyl cyanamides and N,N-dibenzyl cyanamides as intermediates formed from cyanamide. In the absence of metal, ligand and hydrogen peroxide as the oxidant, products with moderate yields have been obtained under mild conditions. Key features include the use of widely available and easily handled cyanamide sources as starting materials.

tert-Butylhydroperoxide mediated radical cyanoalkylation/cyanoalkenylation of 2-anilino-1,4-naphthoquinones with vinylarenes/arylalkynes and azobis(alkylcarbonitrile)s

A novel sustainable methodology based on one-pot cyanoalkylation/cyanoalkenylation of 2-anilino-1,4-naphthoquinones with vinylarenes/arylalkynes and azobis(alkylcarbonitrile)s involving a three-component radical cascade pathway has been achieved. Here, tert-butylhydroperoxide (TBHP) acts as an efficient oxidant, and it smoothly drives the reaction, producing the three-component products in very good to excellent yields. This cascade reaction eliminates the use of any base, additive, metal and hazardous cyanating agent. Additionally, this protocol exclusively delivers a stereospecific product in the case of arylalkynes. The involvement of radicals is evidenced through various radical trapping experiments.

One-Step Protocol for the Synthesis of Cyanoacrylates Promoted by Elemental Sulfur from p-Quinone Methides and Cyanoacetates under Basic Conditions

Cyanoacrylates have a wide range of biological activities and are extensively applied in production and daily life. Classic synthetic routes to cyanoacrylates have many limitations. Herein, we demonstrate an elemental sulfur-promoted method for the synthesis of β,β-diaryl cyanoacrylates by a tandem 1,6-Michael addition/oxidation/elimination process from p-QMs and cyanoacetates under optimal conditions. The effective protocol has good substrate scopes and yields, and the ratio of inseparable E/Z isomers of cyanoacrylates is also determined by 1HNMR.

Functionality-Directed Regio- and Enantio-Selective Olefinic C-H Functionalization of Aryl Alkenes

Aryl alkenes represents one of the most widely occurring structural motif in countless drugs and natural products, and direct C-H functionalization of aryl alkenes provides atom- step efficient access toward valuable analogues. Among them, group-directed selective olefinic α- and β-C-H functionalization, bearing a directing group on the aromatic ring, has attracted remarkable attentions, including alkynylation, alkenylation, amino-carbonylation, cyanation, domino cyclization and so on. These transformations proceed by endo- and exo-C-H cyclometallation and provide aryl alkene derivatives in excellent site- stereo-selectivity. Enantio-selective α- and β- olefinic C-H functionalization were also covered to synthesis axially chiral styrenes.

Directed Lithiation of Protected 4-Chloropyrrolopyrimidine: Addition to Aldehydes and Ketones Aided by Bis(2-dimethylaminoethyl)ether

Pyrrolopyrimidines are important scaffolds for the preparation of bioactive molecules. Therefore, developing efficient and flexible ways for selective functionalization of the pyrrolopyrimidine skeleton is of interest. We have investigated lithiation-addition at C-6 of protected 4-chloro-7H-pyrrolo [2,3-d]pyrimidine as a route to new building blocks for medicinal chemistry. It was found that bis(2-dimethylaminoethyl) ether as an additive increased the yield in the additional reaction with benzaldehyde. Deuterium oxide quench experiments showed that this additive offered both a higher degree of lithiation and increased stability of the lithiated intermediate. The substrate scope of the protocol was investigated with 16 aldehydes and ketones, revealing the method to be excellently suited for reaction with aldehydes, cyclohexanone derivatives and 2,2,2-trifluoroacetophenone, while being less efficient for acetophenones. Yields in the range of 46-93% were obtained.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Aryl acrylonitriles synthesis enabled by palladium-catalyzed α-alkenylation of arylacetonitriles with vinyl halides/triflates

Aryl acrylonitriles are an important subclass of acrylonitriles in the medicinal chemistry and pharmaceutical industry. Herein, an efficient synthesis of aryl acrylonitrile derivatives using a Palladium/NIXANTPHOS-based catalyst system was developed. This approach furnishes a variety of substituted and functionalized aryl acrylonitriles (up to 95% yield). The scalability of the transformation and the synthetic versatility of aryl acrylonitrile were demonstrated.

Catalytic Direct Cyanomethylenation of C(sp3)-H Bonds via a One-Step Double C-C Bond Formation

An elegant and catalytic procedure for the one-step cyanomethylenation of C(sp³)-H bonds adjacent to benzazoles and ketones is described herein using DMF as a C-1 unit and TMSCN as the cyanide source. The copper-mediated reaction between DMF and TMSCN gives a cyanomethylene radical intermediate that reacts with 2-alkylbenzazoles or alkylketones to furnish desired cyanomethylenated compounds under palladium catalysis. Subsequent interconversion of cyanomethylenated products makes the protocol synthetically attractive.

Synthesis of Unsymmetrical Diarylfumaronitriles via Tandem Michael Addition and Oxidation under K3Fe(CN)6/O2 System

An efficient formal alkenyl C-H cyanation reaction has been developed for the general synthesis of unsymmetrical diarylfumaronitriles in good to excellent yields. The reaction was achieved through tandem Michael addition and an oxidative process. The merits of this transformation include the use of K₃Fe(CN)₆ as a safe and nontoxic cyanide source, without an external noble metal catalyst, oxygen-involved reactions, easily available raw materials, good functional group tolerance, high stereoselectivity, and potential further application of the products.

Metal-free three-component cyanoalkylation of quinoxalin-2(1H)-ones with vinylarenes and azobis(alkylcarbonitrile)s

A K2S2O8-mediated C3 cyanoalkylation of quinoxalin-2(1H)-ones via a three-component radical cascade reaction with vinylarenes and azobis(alkylcarbonitrile)s has been achieved.

Cyanide-Free Cyanation of sp2 and sp-Carbons by Oxazole based Masked CN Source Using Flow Microreactors

We herein report a cyanide-free continuous-flow process for cyanation of sp 2 and sp carbons to synthesize aryl, vinyl and acetylenic nitriles from (5-methyl-2-phenyloxazol-4-yl) boronic acid [OxBA] reagent as a sole source of carbon-bound masked -CN source. Non-toxic and stable OxBA reagent is generated by lithiation-borylation of bromo-oxazole, and the consecutive Suzuki-Miyaura cross-coupling with aryl, vinyl, or acetylenic halides and demasking [4 + 2]/retro-[4 + 2] sequence were successfully accomplished to give the desired cyano compounds with reasonably good yields in a four-step flow manner. A unique feature of this cyanation protocol in flow enables to cyanate a variety of sp 2 and sp carbons to produce a broad spectrum of aryl acetonitrile. It is envisaged that the OxBA based cyanation would replace existing unstable and toxic approaches as well as non-toxic cyanation using two different sources of "C" and "N" to incorporate the -CN group.

Insights into the chemistry and therapeutic potential of acrylonitrile derivatives

Acrylonitrile is a fascinating scaffold widely found in many natural products, drugs, and drug candidates with various biological activities. Several drug molecules such as entacapone, rilpivirine, teriflunomide, and so forth, bearing an acrylonitrile moiety have been marketed. In this review, diverse synthetic strategies for constructing desired acrylonitriles are discussed, and the different biological activities and medicinal significance of various acrylonitrile derivatives are critically evaluated. The information gathered is expected to provide rational guidance for the development of clinically useful agents from acrylonitriles.

Rhodium-Catalyzed Annulation of N-Acetoxyacetanilide with Substituted Alkynes: Conversion of Nitroarenes to Substituted Indoles

A general and efficient rhodium-catalyzed redox-neutral annulation of N-acetoxyacetanilides, readily accessible from nitroarenes, with alkynes has been accomplished for the synthesis of substituted indole derivatives. A wide range of substituted 2,3-diarylindoles were achieved from various substituted N-acetoxyacetanilides and symmetrical/unsymmetrical alkynes in good to excellent yields. The developed method was successfully integrated with the synthesis of N-acetoxyacetanilides for the efficient one-pot synthesis of indoles from nitroarenes. The important features are the introduction of N-acetoxyacetamide as a new directing group, redox-neutral annulation, an additive-free approach, wide functional group tolerance, an intramolecular version, and a one-pot reaction of nitroarenes. The method was further extended to the synthesis of potent higher analogues of indole, viz., pyrrolo[3,2-f]indoles and dibenzo[a,c]carbazoles. In addition, a plausible mechanism was proposed based on the isolation and stoichiometric study of a potential aryl-Rh intermediate.

Aromatic C-H Methylation and Other Functionalizations via the Rh(III)-Catalyzed Migratory Insertion of Bis(phenylsulfonyl)carbene and Subsequent Transformations

The Rh(III)-catalyzed migratory insertion of bis(phenylsulfonyl)carbene into aromatic C-H bonds has been developed. A variety of bis(phenylsulfonyl)methyl derivatives were prepared with good yields under mild conditions. The methylated products were readily obtained after reductive desulfonylation. Furthermore, the diverse transformations of bis(phenylsulfonyl)methyl to trideuteriomethyl, aldehyde, and other functional groups were demonstrated.

C–CN bond formation: an overview of diverse strategies

Aim for cyanation: a comprehensive overview on various approaches on C–CN bond formation in arenes/heteroarenes by activated halides/pseudohalide, directed, non-directed, electro-catalyzed, photoredox-catalyzed, and radical approaches.

Recent advances in chelation-assisted site- and stereoselective alkenyl C–H functionalization

This review highlights recent advances in vicinal- and geminal-group-directed alkenyl C–H functionalizations which proceeded by endo- and exo-cyclometallation.

Stereospecific cyanation of the olefinic C–H bond enabled by 1,4-rhodium migration

Rhodium-catalyzed stereospecific cyanation of the olefinic C–H bond for the synthesis of β,β-disubstituted acrylonitriles has been developed.

Directing group strategies in catalytic sp2 C–H cyanations: scope, mechanism and limitations

Directing group strategy in transition metal catalyzed sp² C–H bond cyanation has contributed to the direct conversion of hydrocarbons to cyano-containing compounds. Recent developments in transition metal-mediated sp² C–H bond cyanation using this strategy are reviewed.

Transition-metal-free direct C-3 cyanation of quinoxalin-2(1H)-ones with ammonium thiocyanate as the “CN” source

A practical protocol for TBHP-mediated oxidative C–H cyanation of quinoxalin-2(1H)-ones utilizing ammonium thiocyanate as the cyanide source has been developed under metal free conditions.

Functionalized Acrylonitriles with Aggregation-Induced Emission: Structure Tuning by Simple Reaction-Condition Variation, Efficient Red Emission, and Two-Photon Bioimaging

Acrylonitriles with aggregation-induced emission (AIE) characteristics have been found to show promising applications in two-photon biomedical imaging. Generally, elaborate synthetic efforts are required to achieve different acrylonitriles with distinct functionalities. In this work, we first reported the synthesis of two different group-functionalized AIE-active acrylonitriles (TPAT-AN-XF and 2TPAT-AN) obtained simply by mixing the same reactants at different temperatures using a facile and transition metal-free synthetic method. These two AIE luminogens (AIEgens) exhibit unique properties such as bright red emission in the solid state, large Stokes shift, and large two-photon absorption cross section. Water-soluble nanoparticles (NPs) of 2TPAT-AN were prepared by a nanoprecipitation method. In vitro imaging data show that 2TPAT-AN NPs can selectively stain lysosome in live cells. Besides one-photon imaging, remarkable two-photon imaging of live tumor tissues can be achieved with high resolution and deep tissue penetration. 2TPAT-AN NPs show high biocompatibility and are successfully utilized in in vivo long-term imaging of mouse tumors with a high signal-to-noise ratio. Thus, the present work is anticipated to shed light on the preparation of a library of AIE-active functionalized acrylonitriles with intriguing properties for biomedical applications.

Ligand-Promoted Non-Directed C-H Cyanation of Arenes

This article reports the first example of a 2-pyridone accelerated non-directed C-H cyanation with an arene as the limiting reagent. This protocol is compatible with a broad scope of arenes, including advanced intermediates, drug molecules, and natural products. A kinetic isotope experiment (k_H /k_D =4.40) indicates that the C-H bond cleavage is the rate-limiting step. Also, the reaction is readily scalable, further showcasing the synthetic utility of this method.

Rhodium(iii)-catalyzed aromatic C–H cyanation with dimethylmalononitrile as a cyanating agent

Safe, bench-stable, and commercially available DMMN was used as a cyanating reagent in Rh(iii)-catalyzed aromatic C–H bond direct cyanation in the presence of copper oxide as a promotor.

Cu(OAc)2-Mediated benzimidazole-directed C–H cyanation using 2-(4-methylpiperazin-1-yl)acetonitrile as the cyano source

The C–H activation catalytic system was originally applied to the C(sp²)–H cyanation of aryls/heteroaryls to synthesize 2-(1H-benzo[d]imidazol-2-yl)aryl nitriles.

Ligand-accelerated, branch-selective oxidative cyanation of alkenes

A ligand-accelerated, branch-selective oxidative cyanation of alkenes has been developed in the presence of catalytic Cu₂O. Both styrenes and aliphatic alkenes with directing groups are well tolerated in this inexpensive protocol. The mild condition allows for a good tolerance of functional groups, enabling facile access to a diverse array of simple and complex branched vinyl nitriles. The wide synthetic utility of this methodology has been further demonstrated via the efficient scaleup in both batch and continuous flow processes.

Divergent Functionalization of N-Alkyl-2-alkenylanilines: Efficient Synthesis of Substituted Indoles and Quinolines

An efficient divergent functionalization of N-alkylated ortho-alkenylanilines to substituted indoles and quinolines has been accomplished by employing rhodium-catalyzed cross-dehydrogenative coupling and silver-mediated oxidative cyclization, respectively. The developed methods tolerate various functional groups and allow the synthesis of substituted indoles and quinolines in good to excellent yield. Synthetic utility is demonstrated through conversion to an indole with antimicrobial activity and C-H bond functionalization of 2-arylquinolines. Furthermore, a plausible mechanism was proposed based on preliminary mechanistic investigations.

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation. In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate. Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it. Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure. The schemes feature typical substrates used, the products obtained as well as the required reaction conditions. Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness. The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them. Accordingly, this review should be of particular interest also for scientists from industrial R&D sector. Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date.

Rhodium-Catalyzed Direct C-H Bond Cyanation in Ionic Liquids

A Cp*Rh(III)/IL-based direct C-H bond cyanation system was developed for the first time. The system is a mild, efficient, and recyclable method for the synthesis of aryl nitriles. Many different directing groups can be used in this cyanation, and the reaction tolerates a variety of functional groups.

Metal-Free Direct C-H Cyanation of Alkenes

A metal‐free and direct alkene C−H cyanation is described. Directing groups are not required and the mechanism involves electrophilic activation of the alkene by a cyano iodine(III) species generated in situ from a [bis(trifluoroacetoxy)iodo]arene and trimethylsilyl cyanide as the cyanide source. This C−H functionalization can be conducted on gram scale, and for noncyclic 1,1‐ and 1,2‐disubstuted alkenes high stereoselectivity is achieved, thus rendering the method highly valuable.

Selective Synthesis of Aryl Nitriles and 3-Imino-1-oxoisoindolines via Nickel-Promoted C(sp2)-H Cyanations

An efficient nickel-promoted selective monocyanation of benzamides with TMSCN via 8-aminoquinoline directed ortho C-H activation has been developed. Varieties of functionalized ortho-cyanated (hetero)aryl nitriles can be selectively synthesized in moderate to good yields. These cyanation products can be easily transformed into various 3-imino-1-oxoisoindolines in a one-pot procedure. The mild reaction conditions, use of cheap and commercially available reagents, wide functional group tolerance, and operational convenience make this protocol practical to the synthetic community.

Cp*Co(iii)-catalysed selective alkylation of C–H bonds of arenes and heteroarenes with α-diazocarbonyl compounds

Cp*Co(iii)-catalysed selective alkylation of directed C–H bonds of arenes and heteroarenes has been accomplished employing donor–acceptor carbenes, derived from α-diazocarbonyl compounds.

Copper catalyzed cyanation through CC bond cleavage of gem-aryl dibromide followed by second cyanation of iodoarene by a released CN unit

A new approach for the synthesis of aryl cyanides through CC cleavage of styrenyl gem-dibromide has been achieved.

Recent developments and applications of cyanamides in electrophilic cyanation

This review summarizes the recent developments and applications of readily accessible cyanamides in the electrophilic cyanation of various nucleophiles.