Palladium-Catalyzed Tandem Dehydrogenative [4 + 2] Annulation of Terminal Olefins with N-Sulfonyl Amides via C–H Activations

Photoredox Catalyzed Tandem Denitrogenative [4 + 2] Annulation of 1,2,3-Benzotriazin-4(3H)-ones with Terminal Olefins

The dihydroisoquinolones skeleton is ubiquitous in natural products and biological molecules. Reported strategies for constructing dihydroisoquinolones usually require noble metal catalysts or stoichiometric oxidants, which limit their wide applications. Herein, we developed a photoredox catalyzed tandem denitrogenative [4 + 2] annulation reaction of 1,2,3-benzotriazin-4(3H)-ones with terminal olefins. A variety of dihydroisoquinolones can be accessed in moderate to excellent yield. This protocol features high atom-economy, mild reaction conditions, and is external oxidant-free, enabling the synthesis of various substituted dihydroisoquinolones.

Electrochemical Oxidative (4 + 2) Cyclization of Anilines and o-Phenylenediamines for the Synthesis of Phenazines

Phenazines, crucial constituents of nitrogen-containing heterocycles, widely exist in functional compounds. Herein, we report an anodic oxidative (4 + 2) cyclization between anilines and o-phenylenediamines for the uniform construction of phenazines in a simple undivided cell. Dual C-H amination followed by oxidation represents an outstanding step and atom efficiency. A sequence of phenazines is produced with excellent functional group tolerance at room temperature.

Palladium-Catalyzed C-H Allylation/Annulation Reaction of Amides and Allylic Alcohols: Regioselective Construction of Vinyl-Substituted 3,4-Dihydroisoquinolones

A palladium-catalyzed highly regioselective C-H allylation/annulation reaction of N-sulfonyl amides with secondary or tertiary allylic alcohols has been developed to construct 3,4-dihydroisoquinolones bearing a synthetically valuable vinyl substituent. This cascade cyclization approach of allylic alcohols involving C-H allylation has not been reported previously. The commercially available allylic alcohol substrates, the only by-product of water, and the used terminal oxidant of O₂ provide environmentally benign advantages.

Theoretical investigation of the mechanism of DMAP-promoted [4 + 2]-annulation of prop-2-ynylsulfonium with isatoic anhydride

The mechanism for DMAP-promoted [4 + 2]-annulation of prop-2-ynylsulfonium with isatoic anhydride is investigated using the M06-2X functional. The reaction comprises isomerization of prop-2-ynylsulfonium in stage 1. Stage 2 includes DMAP-promoted deprotonation, nucleophilic addition, ring opening, and decarboxylation. Three steps of intramolecular cycloaddition, DMAP-promoted protonation, and dealkylation occur in stage 3, generating methylated DMAP and neutral thioether, which undergo double-bond isomerization to yield 3-methylthio-4-quinolone. The ability of DMAP to promote the reaction lies in the barrier decrease for alkyne isomerization, deprotonation/protonation of allenes, and dealkylation as effective bases for transferring protons and methyl groups. The roles of prop-2-ynylsulfonium and isatoic anhydride were demonstrated to be C2 and C4 synthons via Multiwfn analysis on the frontier molecular orbital. An alternative path was also confirmed by the Mayer bond order of the vital transition states.

Direct benzylic C–H difluoroalkylation with difluoroenoxysilanes by transition metal-free photoredox catalysis

A visible light promoted direct benzylic C–H difluoroalkylation with difluoroenoxysilanes catalyzed by Na2-eosin Y via a HAT-ORPC pathway has been developed, providing an efficient and atom-economic method for production of α-benzyl-α,α-difluoroketones.

Recent advances in transition metal-catalyzed heteroannulative difunctionalization of alkenes via C-H activation for the synthesis of heterocycles

Heterocyclic compounds are the fundamental structural motifs distributed in natural products, pharmaceuticals and biologically active compounds. Thus, there is increasing interest in the development of novel synthetic strategies for the...

Direct synthesis of indazole derivatives via Rh(III)-catalyzed C-H activation of phthalazinones and allenes

A novel Rh(III)-catalyzed annulation of phthalazinones or pyridazinones with various allenes was developed, leading to the formation of indazole derivatives bearing a quaternary carbon in moderate to good yields. The targeted products were synthesized via sequential C-H activation and olefin insertion, followed by β-hydride elimination and intramolecular cyclization. The synthetic protocol proceeded efficiently with broad functional group tolerance, high atom efficiency and high Z-selectivity. The practicability of this method was proved by synthetic transformation.

Pd-Catalyzed Triple-Fold C(sp2)-H Activation with Enaminones and Alkenes for Pyrrole Synthesis via Hydrogen Evolution

The synthesis of NH-free pyrroles via Pd-catalyzed annulation of enaminones and alkenes is reported. With the catalysis of Pd(II), the activation of triple C(sp²)-H bonds, including one internal C(sp²)-H bond in enaminone, has been activated to provide various pyrroles. The interesting evolution of hydrogen gas from the reactions has been observed by a hydrogen detector.

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.

Rh(iii)-Catalyzed C–H allylation/annulative Markovnikov addition with 5-methylene-1,3-dioxan-2-one: formation of isoquinolinones containing a C3 quaternary centre

Rh(iii)-Catalyzed C–H allylation/annulative Markovnikov addition reaction was disclosed, offering isoquinolinones containing a C3 quaternary centre. By using this method as the key step, the US28 inverse agonist analogs were synthesized.

Vinylogous Elimination/C-H Functionalization/Allylation Cascade Reaction of Allenoate Adducts: Synthesis of Ring-Fused Dihydropyridinones

A palladium-catalyzed cascade reaction of β'-allenoate adducts with aryl/heteroaryl carboxamides through a vinylogous elimination/C-H functionalization/intramolecular allylation reaction sequence has been developed with high Z stereoselectivity. Various ring-fused dihydropyridinones bearing an α,β-unsaturated ester substituent are obtained. It is the first example of application of the allenoate adducts to C-H functionalization annulations as practical precursors of hard-to-get functionalized electron-deficient 1,3-butadienes. Using air as the terminal oxidant also shows a great advantage in environmental friendliness.