Palladium-catalyzed site-selective functionalization of unactivated alkenes with vinylcyclopropanes aided by weakly coordinating native amides

Herein, we have demonstrated a palladium-catalyzed regioselective allylation of unactivated alkenes with vinylcyclopropanes assisted by weak-coordinating native amides. The reaction exhibits wide substrate scope and excellent β-selectivity. Substrate diversification was performed to demonstrate the synthetic utility of the reaction. Mechanistic investigations were carried out to provide an insight into the reaction mechanism.

Synthesis of 1H-Isoindoles via Ruthenium(II)-Catalyzed Cyclization of Benzimidates with Alkenes

A Ru(II)-catalyzed efficient synthesis of 1H-isoindoles via the cyclization of benzimidates with alkenes has been demonstrated. This methodology exhibits high compatibility with various functionalized activated and unactivated olefins containing different sensitive functional groups. This protocol provides an effective method for synthesizing various 1H-isoindole derivatives in decent to excellent yields. Notably, the ortho-alkenylation of benzimidates with unactivated alkenes was achieved. A potential reaction mechanism has been suggested that involves C-H activation, 1,2 insertion, and β-hydride elimination subsequent to aza-Michael addition.

Controlling Reactivity and Selectivity in the Mizoroki-Heck Reaction: High Throughput Evaluation of 1,5-Diaza-3,7-diphosphacyclooctane Ligands

We report a high throughput evaluation of the Mizoroki-Heck reaction of diverse olefin coupling partners. Comparison of different ligands revealed the 1,5-diaza-3,7-diphosphacyclooctane (P2N2) scaffold to be more broadly applicable than common "gold standard" ligands, demonstrating that this family of readily accessible diphosphines has unrecognized potential in organic synthesis. In particular, two structurally related P2N2 ligands were identified to enable the regiodivergent arylation of styrenes. By simply altering the phosphorus substituent from a phenyl to tert-butyl group, both the linear and branched Mizoroki-Heck products can be obtained in high regioisomeric ratios. Experimental and computational mechanistic studies were performed to further probe the origin of selectivity, which suggests that both ligands coordinate to the metal in a similar manner but that rigid positioning of the phosphorus substituent forces contact with the incoming olefin in a π-π interaction (for P-Ph ligands) or with steric clash (for P-tBu ligands), dictating the regiocontrol.

Palladium-Catalyzed Cascade Endo-dig Cycloisomerization and Olefination with Alkenes to Access Fused Oxatricyclic Compounds

A novel cascade Pd(II)-catalyzed endo-dig cycloisomerization and olefination reaction of 2-benzyl-3-alkynyl chromones with activated/unactivated alkenes has been developed for the synthesis of fused oxatricyclic compounds. This concise one-pot synthetic approach was applied to the difunctionalization of unbiased alkynes based on 2-benzyl-3-(alkynyl)-4H-chromen-4-one via O-attack endo-dig cycloisomerization, followed by olefination with both activated and unactivated alkenes.

Chiral Transient Ligand Enabled Enantioselective Synthesis of Atropisomers Decorated with Unactivated Olefins via a Palladium-Catalyzed C-H Olefination

Herein, atroposelective synthesis of axially chiral biaryls with unactivated olefins by a palladium-catalyzed C-H olefination using a chiral transient directing group strategy has been disclosed. This protocol is well compatible with a variety of biaryl-2-aldehydes as well as various olefins such as allyl sulfonamides and allyl sulfones to provide the atroposelective olefinated products in synthetically useful yields with excellent enantioselectivities up to >99% ee. In addition, a wide number of axially chiral biaryl alcohols were synthesized by the simple diversification of the products in excellent enantioselectivity.

Dehydrogenative Cross-Coupling of α,β-Unsaturated Compounds with Unactivated Olefins via Co(III) Catalysis

An oxidative cross-coupling of α,β-unsaturated compounds with unactivated alkenes via cobalt-catalyzed vinylic C-H activation has been developed. The present catalytic reaction was examined with various differently functionalized unsaturated compounds and unactivated olefins. In these reactions, highly valuable amide functionalized butadienes and indenones were prepared in good to excellent yields. A possible reaction mechanism is proposed involving directed olefinic C-H activation through a base-assisted deprotonation pathway.

Ru(II)-Catalyzed C-H Alkenylation of Benzimidates with Unactivated Olefins: A Route to ortho-Alkenylated Benzonitriles

A Ru(II)-catalyzed C-H alkenylation of benzimidates with unactivated alkenes providing ortho-alkenylated benzonitriles in good to excellent yields in a highly regio- and stereoselective manner is described. In the reaction, an imidate group converted into a nitrile under the reaction conditions. The alkenylation reaction was compatible with various substituted benzimidates as well as functionalized unactivated olefins, including ibuprofen-, neproxen-, coumarin-, and cholesterol-substituted alkenes. A feasible reaction mechanism was proposed to account for the present alkenylation reaction.

Denitrative Mizoroki–Heck reaction of unactivated alkenes

A general palladium-catalyzed denitrative Mizoroki–Heck reaction of unactivated alkenes has been developed with high E/Z selectivity.

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.

Palladium-Catalyzed Regioselective Diarylation/Deamination of Homoallylamines: Modular Assembly of 1,1,4,4-Tetraaryl-1,3-butadienes

Herein, a novel palladium-catalyzed regioselective diarylation/deamination of homoallylamines is described. During the process, a ubiquitous free amine (NH₂) was used as the directing group to accomplish the regioselective δ,δ-diarylation and it was removed in situ to form the privileged 1,1,4,4-tetraaryl-1,3-butadiene motif. This chelate-controlled Heck-type approach eliminates the traditional need of preinstalled and hard removable directing groups, proceeds under simple conditions, and exhibits good tolerance to a wide range of synthetically useful functional groups.

Rh(III)-Catalyzed Enone Carbonyl/Ketone-Directed Aerobic C-H Olefination of Aromatics with Unactivated Olefins

A Rh(III)-catalyzed weak enone carbonyl/ketone-assisted aerobic oxidative C-H olefination of aromatics with unactivated alkenes has been developed. This protocol involves cross-dehydrogenative Heck-type olefination reaction of various substituted biologically relevant chalcones and aromatic ketones such as acetophenones and chromones with various functionalized unactivated olefins in moderate to good yields. Further, ortho-alkylation of chalcones with norbornene is also demonstrated. A possible reaction mechanism involving weak chelation-assisted C-H activation/insertion/β-hydride elimination was proposed and supported by the deuterium labeling studies.

Ester-directed orthogonal dual C-H activation and ortho aryl C-H alkenylation via distal weak coordination

An unprecedented orthogonal cross-coupling between aromatic C(sp²) and aliphatic olefinic C(sp²) carbons of two same molecules via dual C-H bond activation in an intermolecular fashion has been developed using a distal ester-directing group. This new coupling reaction led to the synthesis of the highly functionalized 1,3-diaryl molecular architecture in very good yields and with high chemo- and regioselectivities. In addition, using ester as the distal directing group, ortho C-H olefination of α-methyl aryl acrylates and cinnamic esters with various alkenes has been achieved in very good yields and with a wide range of substrate scope.

Palladium-catalyzed oxidative Heck reaction of non-activated alkenes directed by fluorinated alcohol

A new reactivity pattern for the regio- and stereoselective oxidative arylation of non-activated alkenes by introducing a trifluoromethyl group in the substrate enol has been established.

Ruthenium(II)-Catalyzed Redox-Neutral C-H Alkylation of Arylamides with Unactivated Olefins

A Ru(II)-catalyzed weak chelating group-aided ortho-C-H alkylation of arylamides with unactivated olefins in a redox-neutral fashion has been demonstrated. The present alkylation reaction was well-suited for various substituted arylamides and unactivated aliphatic alkenes. In this alkylation reaction, pivalic acid plays dual role in which it delivers the proton source in a protonation step and the corresponding acetate moiety deprotonates the ortho-C-H bond of the arylamides.

Aerobic Oxidative C-H Olefination of Arylamides with Unactivated Olefins via a Rh(III)-Catalyzed C-H Activation

An efficient Rh(III)-catalyzed aerobic oxidative C-H alkenylation of arylamides with unactivated alkenes is described. The olefination reaction was compatible with various substituted arylamides including primary, secondary, and tertiary as well as functionalized unactivated olefins. Meanwhile, ortho mono/bis-alkylated arylamides were synthesized in the reaction of arylamides with norbornene. In the alkenylation reaction, molecular oxygen along with organic acid was used to regenerate the active catalyst for the next catalytic cycle. A possible reaction mechanism involving C-H activation/insertion/β-hydride elimination followed by aerobic oxidation was proposed and supported by the deuterium labeling studies.

Palladium-Catalyzed Regioselective C-H Functionalization/Annulation Reaction of Amides and Allylbenzenes for the Synthesis of Isoquinolinones and Pyridinones

A regioselective C-H functionalization/annulation reaction of N-sulfonyl amides and allylbenzenes through a palladium-catalyzed C(sp²)-H allylation/aminopalladation/β-H elimination/isomerization sequence has been reported. Various aryl and alkenyl carboxamides are found to be efficient substrates to construct isoquinolinones and pyridinones in up to 96% yield. Using ambient air as the terminal oxidant is another advantage regarding environmental friendliness and operational simplicity.

Rhodium(III)-Catalyzed Aerobic Oxidative C-H Olefination of Unsaturated Acrylamides with Unactivated Olefins

A rhodium(III)-catalyzed aerobic oxidative cross-coupling of acrylamides with unactivated alkenes via vinylic C-H activation has been developed. The present cross-coupling reaction was examined with a variety of differently functionalized acrylamides and unactivated olefins. In these reactions, highly valuable amide-functionalized butadienes were prepared in good to excellent yields. This protocol was also compatible with Weinreb amides. A possible reaction mechanism involving the chelation-assisted vinylic C-H activation via a carboxylate-assisted deprotonation pathway is proposed.

Recent development in transition metal-catalysed C-H olefination

Transition metal-catalysed functionalizations of inert C-H bonds to construct C-C bonds represent an ideal route in the synthesis of valuable organic molecules. Fine tuning of directing groups, catalysts and ligands has played a crucial role in selective C-H bond (sp2 or sp3) activation. Recent developments in these areas have assured a high level of regioselectivity in C-H olefination reactions. In this review, we have summarized the recent progress in the oxidative olefination of sp2 and sp3 C-H bonds with special emphasis on distal, atroposelective, non-directed sp2 and directed sp3 C-H olefination. The scope, limitation, and mechanism of various transition metal-catalysed olefination reactions have been described briefly.

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.

Recent Developments in Heck-Type Reaction of Unactivated Alkenes and Alkyl Electrophiles

The Mizoroki–Heck reaction is considered as one of the most ingenious and widely used methods for constructing C–C bonds. This reaction mainly focuses on activated olefins (styrenes, acrylates, or vinyl ethers) and aryl/vinyl (pseudo) halides. In comparison, the studies on unactivated alkenes and alkyl electrophiles are far less due to the low reactivity, poor selectivity, as well as competitive β-H elimination. In the past years, a growing interest has thus been devoted and significant breakthroughs have been achieved in the employment of unactivated alkenes and alkyl electrophiles as the reaction components, and this type of coupling is called as Heck-type or Heck-like reaction, which distinguishes from the traditional Heck reaction. Herein, we give a brief summary on Heck-type reaction between unactivated alkenes and alkyl electrophlies, covering its initial work, recent advancements, and mechanistic discussions.

1 Introduction

2 Intramolecular Heck-Type Reaction of Unactivated Alkenes and Alkyl Electrophiles

2.1 Cobalt-Catalyzed Intramolecular Heck-Type Reaction

2.2 Palladium-Catalyzed Intramolecular Heck-Type Reaction

2.3 Nickel-Catalyzed Intramolecular Heck-Type Reaction

2.4 Photocatalysis and Multimetallic Protocol for Intramolecular Heck-Type Reaction

3 Intermolecular Heck-Type Reaction of Unactivated Alkenes and Alkyl Electrophiles

3.1 Electrophilic Trifluoromethylating Reagent as Reaction Partners

3.2 Alkyl Electrophiles as Reaction Partners

4 Oxidative Heck-Type Reaction of Unactivated Alkenes and Alkyl Radicals

5 Conclusions and Outlook

Traceless directing groups: a novel strategy in regiodivergent C-H functionalization

The use of functional groups as internal ligands for assisting C-H functionalization, termed the chelation assisted strategy, is emerging as one of the most powerful tools for construction of C-C and C-X bonds from inert C-H bonds. However, there are various directing groups which cannot be either removed after functionalization or require some additional steps or reagents for their removal, thereby limiting the scope of structural diversity of the products, and the step and atom economy of the system. These limitations are overcome by the use of the traceless directing group (TDG) strategy wherein functionalization of the substrate and removal of the directing group can be carried out in a one pot fashion. Traceless directing groups serve as the most ideal chelation assisted strategy with a high degree of reactivity and selectivity without any requirement for additional steps for their removal. The present review overviews the use of various functional groups such as carboxylic acids, aldehydes, N-oxides, nitrones, N-nitroso amines, amides, sulfoxonium ylides and silicon tethered directing groups for assisting transition metal catalyzed C-H functionalization reactions in the last decade.

Palladium-catalyzed cross-coupling reaction of alkenyl aluminums with 2-bromobenzo[b]furans

Highly efficient and simple cross-coupling reactions of 2-bromobenzo[b]furans with alkenylaluminum reagents for the synthesis of 2-alkenylbenzo[b]furan derivatives using PdCl₂ (3 mol%)/XantPhos (6 mol%) as catalyst are reported. Excellent yields (up to 97%) were obtained for a wide range of substrates at 80 °C for 4 h in DCE.

PdCl₂ (3 mol%)/XantPhos (6 mol%) complexes was found to be a highly efficient catalyst for the synthesis of 2-alkenylbenzo[b]furans from 2-bromobenzo[b]furans and alkenylaluminums. The reaction was also found to be effective in gram-scale synthesis.

Geminal group-directed olefinic C-H functionalization via four- to eight-membered exo-metallocycles

Great efforts have been made in the activation of a C(alkenyl)-H bond vicinal to the directing group to proceed via five- or six-membered endo-metallocycles. In stark contrast, functionalization of a C(alkenyl)-H bond geminal to the directing group via exo-metallocycle pathway continued to be elusive. Here we report the selective transformation of an olefinic C-H bond that is geminal to the directing group bearing valuable hydroxyl, carbamate or amide into a C-C bond, which proceeds through four- to eight-membered exo-palladacycles. Compared to the reported mechanisms proceeding only through six-membered exo-palladacycles via N,N-bidentate chelation, our weak and O-monodentate chelation-assisted C(alkenyl)-H activations tolerate longer or shorter distances between the olefinic C-H bonds and the coordinating groups, allowing for the functionalizations of many olefinic C-H bonds in alkenyl alcohols, carbamates and amides. The synthetic applicability has been demonstrated by the preparative scale and late-stage C-H functionalization of steroid and ricinoleate derivatives.

Identifying distinct cyclometallation pathways is essential to new types of C-H activation and functionalization in organic synthesis. Here, the authors show the activation of an olefinic C-H bond geminal to the directing group via four- to eight-membered exo-palladacycles with broad substrate scope.

Benzylarylation of N-Allyl Anilines: Synthesis of Benzylated Indolines

An unprecedented benzylic C-H functionalization of methyl arenes across unactivated alkenes is presented. In the presence of MnCl₂·4H₂O and di- tert-butyl peroxide, N-allyl anilines underwent benzylation/cyclization cascade to give benzylated indolines, which are a previously unmet synthetic goal. This protocol features simple operation, broad substrate scope, and great exo selectivity.

PdCl2(CH3CN)2-catalyzed regioselective C-H olefinations of 2-amino biaryls with vinylsilanes as unactivated alkenes

The first example of palladium-catalyzed chelation-assisted C-H olefination of 2-amino biaryls using readily available vinylsilanes as unactivated olefinating reagents has been developed, affording valuable arylated vinylsilane compounds in moderate to excellent yields and with exclusive (E)-selectivities.

Cobalt-catalyzed directed C-H alkenylation of pivalophenone N-H imine with alkenyl phosphates

A cobalt–N-heterocyclic carbene (NHC) catalyst efficiently promotes an ortho C–H alkenylation reaction of pivalophenone N–H imine with an alkenyl phosphate. The reaction tolerates various substituted pivalophenone N–H imines as well as cyclic and acyclic alkenyl phosphates.

Ligand-enabled ortho-C-H olefination of phenylacetic amides with unactivated alkenes

Although chelation-assisted C-H olefination has been intensely investigated, Pd(ii)-catalyzed C-H olefination reactions are largely restricted to acrylates and styrenes. Here we report a quinoline-derived ligand that enables the Pd(ii)-catalyzed olefination of the C(sp2)-H bond with simple aliphatic alkenes using a weakly coordinating monodentate amide auxiliary. Oxygen is used as the terminal oxidant with catalytic copper as the co-oxidant. A variety of functional groups in the aliphatic alkenes are tolerated. Upon hydrogenation, the ortho-alkylated product can be accessed. The utility of this reaction is also demonstrated by the late-stage diversification of drug molecules.

Cross dehydrogenative coupling of sugar enol ethers with terminal alkenes in the synthesis of pseudo-disaccharides, chiral oxadecalins and a conjugated triene

An efficient strategy for the synthesis of C-2 and C-3 branched sugar dienes via cross dehydrogenative coupling of sugar enol ethers with terminal alkenes was developed.

Introducing unactivated acyclic internal aliphatic olefins into a cobalt catalyzed allylic selective dehydrogenative Heck reaction

Unactivated acyclic internal aliphatic olefins are often found to be unreactive in conventional alkenylation reactions. To address this problem, a cobalt catalyzed allylic selective dehydrogenative Heck reaction with internal aliphatic olefins has been developed. The method is highly regio- and stereoselective, the conditions are mild and a wide variety of functional groups can be tolerated. Remarkably, both internal and terminal aliphatic olefins can be employed, thereby significantly expanding the scope of alkenylation chemistry with aliphatic olefins.