Palladium(II)-catalyzed direct alkenylation of nonaromatic enamides

An electron donor-acceptor complex-initiated C-H trifluoromethylation and perfluoroalkylation of enamides and quinoxalinones

Facilitated by an electron donor-acceptor (EDA) complex, an efficient β-trifluoromethylation and perfluoroalkylation of enamides with Togni reagent or perfluoroalkyl iodides is presented under transition-metal-free, photocatalyst-free and mild reaction conditions. Notably, using this photocatalyst-free strategy, direct trifluoromethylation and perfluoroalkylation of quinoxalin-2(1H)-one derivatives was also achieved via a photoactive electron donor-acceptor complex.

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.

Rhodium(III)-Catalyzed Switchable β-C(sp2)-H Alkenylation and Alkylation of Acyclic Enamides with Allyl Alcohols

Herein, rhodium(III)-catalyzed β-C(sp2)-H alkenylation and alkylation of enamides are presented using readily accessible allylic alcohols by switching the reaction conditions. This tunable transformation has been applied to a wide range of substrates and typically proceeded with excellent regioselectivity and stereoselectivity as well as with good functional group tolerance. The catalytic system offers an efficient approach for synthesizing various functionalized enamides bearing N-(2Z,4E)-butadiene and (Z)-β-C(sp2)-H alkylated enamides. In addition, mechanistic experiments suggest that Rh(III)-catalyzed C-H activation is not related to the critical step.

Selective Cross-Dehydrogenative Coupling of Various Acyclic Enamides with Heteroarenes via Rh(III)-Catalyzed C-H Activation

The developed methodology describes an efficient Rh(III)-catalyzed oxidative C-H/C-H cross-coupling between acyclic enamides and heteroarenes. This cross dehydrogenative coupling (CDC) reaction offers advantages, including excellent regioselectivity and stereoselectivity, good functional group compatibility, and a broad substrate scope. Mechanistically, Rh(III)-catalyzed β-C(sp2)-H activation of acyclic enamides is proposed to be the critical step.

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 C-H olefination of uridine, deoxyuridine, uridine monophosphate and uridine analogues

The palladium-catalyzed oxidative C-H olefinations of uridine, deoxyuridine, uridine monophosphate and uridine analogues are reported herein. This protocol provides an efficient, atom-economic and environmentally friendly approach to the synthesis of biologically important C5-alkene modified uracil/uridine-containing derivatives and pharmaceutical candidates.

Synthesis of conjugated dienes via palladium-catalysed aerobic dehydrogenation of unsaturated acids and amides

A Pd(II)-catalyzed direct aerobic dehydrogenation of γ,δ-olefinic acids and amides has been demonstrated. The present protocol dehydrogenates the least acidic amides and acids, thus replacing the traditional enolate strategy for dehydrogenation. A broad spectrum of conjugated dienamides and dienoic acids were produced in good to excellent yields. A possible reaction mechanism was proposed and supported by deuterium labelling studies.

Visible-light-initiated regio- and stereoselective C(sp2)–H phosphorylation of enamides under transition-metal-free conditions

A visible-light-induced stereo- and regioselective phosphorylation of enamides with phosphine oxides under transition-metal-free conditions has been disclosed.

K2S2O8-mediated regio- and stereo-selective thiocyanation of enamides with NH4SCN

A direct and straightforward thiocyanation of enamides with NH₄SCN under metal-free conditions has been accomplished. A variety of (E)-β-thiocyanoenamides are readily produced in a regio- and stereo-selective manner. The protocol features mild reaction conditions, good functional group tolerance and operational simplicity. The potential utility of this strategy was further demonstrated by transformation of thiocyanate into thiotetrazole-containing compounds and a Pd-catalyzed cross-coupling reaction to afford six- or seven-membered sulfur-containing heterocycles. Mechanistic insights into the reaction indicate that the reaction may proceed via a radical mechanism.

Modern Synthetic Methods for the Stereoselective Construction of 1,3-Dienes

The 1,3-butadiene motif is widely found in many natural products and drug candidates with relevant biological activities. Moreover, dienes are important targets for synthetic chemists, due to their ability to give access to a wide range of functional group transformations, including a broad range of C-C bond-forming processes. Therefore, the stereoselective preparation of dienes have attracted much attention over the past decades, and the search for new synthetic protocols continues unabated. The aim of this review is to give an overview of the diverse methodologies that have emerged in the last decade, with a focus on the synthetic processes that meet the requirements of efficiency and sustainability of modern organic chemistry.

Visible-light-induced iodine-anion-catalyzed decarboxylative/deaminative C–H alkylation of enamides

An efficient method for photo-induced iodine-anion-catalyzed C–H alkylation of enamides has been developed. Redox-active esters and Katritzky salts of amino acids are amenable, successfully delivering various functionalized enamides.

Photoinitiated stereoselective direct C(sp2)–H perfluoroalkylation and difluoroacetylation of enamides

Photoinitiated regio- and stereoselective C(sp²)–H perfluoroalkylation and difluoroacetylation of enamides are developed, furnishing biologically and physiologically privileged fluoro-containing enamide scaffolds.

Visible-Light-Induced Regio- and Stereoselective C(sp2)-H Trifluoroethylation of Enamides with 2,2,2-Trifluoroethyl Iodide

A photoredox-catalyzed regio- and stereoselective trifluoroethylation reaction of enamides using commercially available 2,2,2-trifluoroethyl iodide as trifluoroethylating agents has been developed, furnishing geometrically defined and synthetically and physiochemically pivotal β-trifluoroethylated enamides bearing a diverse range of functional groups.

Palladium-catalyzed remote C-H functionalization of 2-aminopyrimidines

A straightforward strategy was developed for the arylation and olefination at the C5-position of the N-(alkyl)pyrimidin-2-amine core with readily available aryl halides and alkenes, respectively. This approach was highly regioselective, and the transformation was achieved based on two different (Pd(ii)/Pd(iv)) and (Pd(0)/Pd(ii)) catalytic cycles.

Recent advances in the direct β-C(sp2)–H functionalization of enamides

Recent advances in the direct β-C(sp²)–H functionalization of enamides, mainly including arylation, alkenylation, alkynylation, alkylation, acylation, sulfonylation, phosphorylation, and others, are reported.

Photoredox-catalyzed stereoselective alkylation of enamides with N-hydroxyphthalimide esters via decarboxylative cross-coupling reactions

Stereoselective β-C(sp2)-H alkylation of enamides with redox-active N-hydroxyphthalimide esters via a photoredox-catalyzed decarboxylative cross-coupling reaction is demonstrated. This methodology features operational simplicity, broad substrate scopes, and excellent stereoselectivities and functional group tolerance, affording a diverse array of geometrically defined and synthetically valuable enamides bearing primary, secondary or tertiary alkyl groups in satisfactory yields.

Stereoselective synthesis of alkyl-, aryl-, vinyl- and alkynyl-substituted Z-enamides and enol ethers

Enamides and enol ethers are valuable building blocks in synthetic chemistry, yet their stereoselective synthesis can be challenging. Herein, we report a new stereoselective synthesis of vinyl, aryl, alkynyl, alkyl and thio-substituted Z-enamides and enol ethers based on the use of vinylbenziodoxolone (VBX) reagents. The stable VBX reagents were synthesized by stereoselective addition of N- or O-nucleophiles on the corresponding alkynyl reagents in the presence of a catalytic amount of cesium carbonate. The VBX reagents were used in palladium-catalyzed cross-couplings at room temperature to access Z-enamides and enol ethers.

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.

Iridium-catalyzed α-alkynylation of cyclic nonaromatic eneformamides: application to the synthesis of azapolycyclic architectures

A regioselective and chelation-assisted dehydrogenative alkynylation of cyclic nonaromatic eneformamides with terminal alkynes, under iridium catalysis, is described.

A Sequential Cycloaddition Strategy for the Synthesis of Alsmaphorazine B Traces a Path Through a Family of Alstonia Alkaloids

Driven by a new biogenetic hypothesis, the first total synthesis of alsmaphorazine B and several related indole alkaloids has been achieved. Numerous early approaches proved unsuccessful owing to unproductive side reactivity; nevertheless, they provided important clues that guided the evolution of our strategy. Critical to our success was a major improvement in our Zincke aldehyde cycloaddition strategy, which permitted the efficient gram-scale synthesis of akuammicine. The sequential chemoselective oxidations of akuammicine leading up to the key oxidative rearrangement also yielded several biogenetically related indole alkaloids en route to alsmaphorazine B.

A direct cross-coupling reaction of electron-deficient alkenes using an oxidizing directing group

An oxidant-free cross-coupling reaction of electron-deficient alkenes using an inexpensive ruthenium catalyst is reported. With the assistance of the oxidizing directing group CONH(OMe), this protocol provides a mild, straightforward and efficient method for the preparation of valuable 1,3-butadiene skeletons with excellent Z,E selectivities.

Weinreb amide directed cross-coupling reaction between electron-deficient alkenes catalyzed by a rhodium catalyst

A rhodium-catalyzed Weinreb amide directed cross-coupling reaction between electron-deficient alkenes is reported, which provides an efficient route for the synthesis of valuable and versatile Weinreb amide functionalized (Z,E)-butadienes.

Pd-Catalyzed oxidative annulation of enamides with diazabicyclic olefins: rapid access to cyclopentene fused 2-pyrrolines

A catalytic tandem transformation via C–H activation of enamides for the stereoselective synthesis of cyclopentene fused 2-pyrrolines has been realized.

Copper–Schiff base alumoxane: a new and reusable mesoporous nano catalyst for Suzuki–Miyaura and Stille C–C cross-coupling reactions

For the first time, Cu(ii) supported on Schiff-base alumoxane framework was used as an effective and recyclable nanocatalyst in Suzuki–Miyaura and Stille cross coupling reactions.

Pd(ii)-catalyzed intramolecular oxidative Heck dearomative reaction: approach to thiazole-fused pyrrolidinones with a C2-azaquarternary center

A Pd(ii)-catalyzed intramolecular oxidative Heck dearomative reaction for the construction of thiazole-fused pyrrolidinones was achieved for the first time.

Palladium-Catalyzed Intermolecular Oxyarylation of Vinylacetates with Retention of an Alkenyl Moiety

Palladium-catalyzed intermolecular oxyarylation reaction of vinylacetates with retention of the double bond in the final product is developed. Under the optimized reaction conditions, the desired products of multisubstituted vinylesters could be obtained in moderate to high yields.

One-shot access to α,β-difunctionalized azepenes and dehydropiperidines by reductive cross-coupling of α-selenonyl-β-selenyl enamides with organic bromides

The synthesis of α- and α,β-functionalized azepenes and dehydropiperidines from readily prepared α-selenonyl eneformamides or enecarbamates has been achieved through Fe-catalyzed α-substitutive deselenonation, β-regioselective lithiation/trapping, and Co-catalyzed reductive cross-coupling protocols.

Copper-catalyzed olefinic C-H difluoroacetylation of enamides

Copper-catalyzed olefinic difluoroacetylation of enamides via direct C-H bond functionalization using BrCF2CO2Et is reported for the first time. It constitutes an efficient radical-free method for the regioselective synthesis of β-difluoroester substituted enamides which exhibits broad substrate scope, and thus demonstrates its potent application in a late stage fluorination strategy.