Pd-Catalyzed C(sp2)-H/C(sp2)-H Coupling of Limonene

Limonene undergoes a regioselective Pd(II)-catalyzed C(sp2)-H/C(sp2)-H coupling with acrylic acid esters and amides, α,β-unsaturated ketones, styrenes, and allyl acetate, affording novel 1,3-dienes. DFT computations gave results in accord with the experimental results and allowed for the formulation of a plausible mechanism. The postfunctionalization of one of the coupled products was achieved via a large-scale Sonogashira reaction conducted under micellar catalysis.

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.

Transition metal-catalyzed double Cvinyl-H bond activation: synthesis of conjugated dienes

Conjugated dienes have occupied a pivotal position in the field of synthetic organic chemistry and medicinal chemistry. They act as important synthons for the synthesis of various biologically important molecules and therefore, gain tremendous attention worldwide. A wide range of synthetic routes to access these versatile molecules have been developed in the past decades. Transition metal-catalyzed cross-dehydrogenative coupling (CDC) has emerged as one of the utmost front-line research areas in current synthetic organic chemistry due to its high atom economy, efficiency, and viability. In this review, an up-to-date summary including scope, limitations, mechanistic studies, stereoselectivities, and synthetic applications of transition metal-catalyzed double C_vinyl-H bond activation for the synthesis of conjugated dienes has been reported since 2013. The literature reports mentioned in this review have been classified into three different categories, i.e. (a) C_vinyl-C_vinyl bond formation via oxidative homo-coupling of terminal alkenes; (b) C_vinyl-C_vinyl bond formation via non-directed oxidative cross-coupling of linear/cyclic alkenes and terminal/internal alkenes, and (c) C_vinyl-C_vinyl bond formation via oxidative cross-coupling of directing group bearing alkenes and terminal/internal alkenes. Overall, this review aims to provide a concise overview of the current status of the considerable development in this field and is expected to stimulate further innovation and research in the future.

A palladium catalyzed stereo-convergent aminocarbonylation of 1,3-dienes with nitroarenes: synthesis of (E,E)-dienamides

A palladium catalyzed stereo-convergent aminocarbonylation of 1,3-dienes with nitroarenes has been developed. The reaction of mixtrues of E/Z isomers of 1,3-dienes reacted with nitroarenes and produced (E,E)-dienamides with high stereoselectivities.

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 advances in transition metal-catalyzed olefinic C–H functionalization

Recent advances during 2015–2020 in the field of metal-catalyzed olefinic C–H functionalization are organized according to the metal center of the catalyst, with an emphasis on the similarities and differences among different catalysts.

Ruthenium-catalysed oxidative coupling of vinyl derivatives and application in tandem hydrogenation

The first ruthenium-catalyzed oxidative homo- and cross-coupling of exclusive vinyl derivatives giving highly valued 1,3-diene building blocks is reported. In situ ruthenium-catalyzed hydrogenation afforded relevant adipic acid ester derivatives.

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.

Acylsilane directed aromatic C-H alkenylations by ruthenium catalysis

A ruthenium-catalyzed C-H alkenylation of aroylsilanes with electron-deficient alkenes was developed, using acylsilane as the directing group. The mild reaction conditions enable the tolerance of a wide scope of functionalities such as OMe, F, Cl, Br and CF3, providing a convenient and highly effective method for the synthesis of styrene derivatives bearing acylsilane. Steroid and heterocycles such as furan and thiophene were also well tolerated. Furthermore, acylsilane was efficiently converted to the corresponding aldehyde or carboxylic acid.

SO2F2 mediated dehydrative cross-coupling of alcohols with electron-deficient olefins in DMSO using a Pd-catalyst: one-pot transformation of alcohols into 1,3-dienes

A Pd-catalyzed, SO₂F₂ mediated dehydrative cross-coupling of alcohols with electron-deficient olefins for the construction of 1,3-dienes was developed.

Weinreb Amide Directed Versatile C-H Bond Functionalization under (η5 -Pentamethylcyclopentadienyl)cobalt(III) Catalysis

The (η⁵ -pentamethylcyclopentadienyl)cobalt(III) (Cp*Co^III )-catalyzed C-H bond functionalization of aromatic, heteroaromatic, and α,β-unsaturated Weinreb amides was explored. C-H allylation reactions with the use of allyl carbonate and a perfluoroalkene, oxidative alkenylation reactions with the use of ethyl acrylate, iodination reactions with the use of N-iodosuccinimide, and amidation reactions with the use of dioxazolones were catalyzed by Cp*Co(CO)I₂ in the presence of a cationic Ag salt and AgOAc to afford various synthetically useful building blocks. Mechanistic studies of the C-H allylation disclosed that the C-H activation step was rate determining and virtually irreversible.

Highly Stereoselective Synthesis of 1,3-Dienes through an Aryl to Vinyl 1,4-Palladium Migration/Heck Sequence

An efficient aryl to vinyl 1,4-palladium migration/Heck sequence was developed for the stereoselective synthesis of 1,3-dienes. High stereoselectivity was observed not only for 1,3-dienes bearing two similar aryl groups at terminal positions, but also for those with configurations shown to be unfavorable with previous methods.

Palladium-Catalyzed Regioselective C-H Alkenylation of Arylacetamides via Distal Weakly Coordinating Primary Amides as Directing Groups

Herein we disclose the efficient Pd(II)-catalyzed and regioselective ortho C-H alkenylation of arylacetamide derivatives, viz. weakly coordinating aliphatic primary amides. This protocol utilizes ubiquitous free primary amides as the directing group and circumvents two troublesome steps of installation and removal of an external auxiliary. This strategy directly enables the incorporation of a synthetically versatile olefin in the products in moderate to good yields with regio- and distereoselectivity. The alkenylated acetamides can be easily manipulated and further transformed into a variety of useful derivatives.

Efficient synthesis of N-butadiene substituted oxindole derivatives

A novel rhodium(iii)-catalyzed amide carbonyl group directed alkenylation reaction between oxindoles and alkenes has been reported, which provides an efficient method for the synthesis of valuable and versatile functionalized N-(2E,4Z)-butadiene substituted oxindole derivatives.

Copper-Catalyzed Oxidative Cyclization of 2-Amino-azaarenes with Lignin Models: Synthesis of 3-Phenoxy Imidazo Heterocycles

A catalytic oxidative cyclization of 2-aminopyridines or 2-aminobenzothiazole with 2-phenoxyacetophenones (a kind of lignin platform compound) was developed, efficiently providing valuable 3-phenoxy imidazo[1,2-a]pyridines or 3-phenoxy benzo[d]imidazo[2,1-b]thiazoles. The reaction was realized under oxygen by simply using inexpensive CuI as the catalyst.

Palladium-Catalyzed Synthesis of 3-Trifluoromethyl-Substituted 1,3-Butadienes by Means of Directed C-H Bond Functionalization

A palladium-catalyzed C-H bond functionalization of acrylamides was developed to build up stereoselectively trifluoromethylated 1,3-butadienes. Using a tertiary amide as a directing group, olefins were selectively functionalized with 2-bromo-3,3,3-trifluoropropene to access these important fluorinated compounds. The methodology was extended to the construction of pentafluoroethyl-substituted 1,3-dienes. Mechanistic studies supported by density functional theory calculations suggested a redox neutral mechanism for this transformation.

Ruthenium-catalyzed olefinic C–H alkenylation of enol-carbamates: highly stereo-selective synthesis of (Z,Z) and (Z,E)-butadienes

Cross-coupling reactions of enol carbamates with alkynes or alkenes are reported, using an inexpensive ruthenium catalyst.

One step synthesis of γ-alkylidenebutenolides from simple vinyl carboxylic acids and alkenes

A tandem cross-coupling/oxa-Michael addition/dehydrogenation process is described, providing one-step synthesis of γ-alkylidenebutenolides from vinyl carboxylic acids and alkenes.