Metallfreie radikalische Azidoarylierung von Alkenen: schneller Zugang zu Oxindolen durch kaskadenförmige C-N- und C-C-Bindungsbildung

Recent Advances in 1,2-Amino(hetero)arylation of Alkenes

Alkene amino(hetero)arylation presents a highly efficient and straightforward strategy for direct installation of amino groups and heteroaryl rings across a double bond simultaneously. An extensive array of practical transformations has been developed via alkene difunctionalization approach to access a broad range of medicinally valuable (hetero)arylethylamine motifs. This review presents recent progress in 1,2-amino(hetero)arylation of alkenes organized in three different modes. First, intramolecular transformations employing C, N-tethered alkenes will be introduced. Next, two-component reactions will be discussed with different combination of precursors, N-tethered alkenes and external aryl precursor, C-tethered alkenes and external amine precursor, or C, N-tethered reagents, and alkenes. Last, three-component intermolecular amino(hetero)arylation reactions will be covered.

Minisci aroylation of N-heterocycles using choline persulfate in water under mild conditions

A modified Minisci aroylation of isoquinoline using arylglyoxylic acids in the presence of choline persulfate or pre-composition (choline acetate and K2S2O8) in water at ambient temperature affording aroylated isoquinolines is reported.

Visible-Light-Induced Palladium-Catalyzed Generation of Aryl Radicals from Aryl Triflates

A mild visible-light-induced Pd-catalyzed intramolecular C-H arylation of amides is reported. The method operates by cleavage of a C(sp2 )-O bond, leading to hybrid aryl Pd-radical intermediates. The following 1,5-hydrogen atom translocation, intramolecular cyclization, and rearomatization steps lead to valuable oxindole and isoindoline-1-one motifs. Notably, this method provides access to products with readily enolizable functional groups that are incompatible with traditional Pd-catalyzed conditions.

Mechanism and Origin of MAD-Induced Ni/N-Heterocyclic Carbene-Catalyzed Regio- and Enantioselective C-H Cyclization of Pyridines with Alkenes

This work presents a DFT-based computational study on the regio- and enantioselective C-H functionalization of pyridines with alkenes at the relatively unreactive C4-position, which was successfully achieved by Shi et al. [J. Am. Chem. Soc. 2019, 141, 5628-5634] using Ni⁰ /N-heterocyclic carbene (NHC) catalysis under the assistance of an aluminum-based Lewis acid additive (2,6-tBu₂ -4-Me-C₆ H₂ O)₂ AlMe (MAD). The calculations indicate that the selective functionalization involves a three-step mechanism in which a unique H-migration assisted oxidation metalation (HMAOM) step is identified as the rate- and enantioselectivity-determining step. The newly proposed mechanism can well rationalize the experimental observation that the preferred product is the endo-type (vs. exo-type), R-configuration (vs. S-configuration) product at the C4 (vs. C2) position, and also unveil the reasons that the NHC ligand and the MAD additive can facilitate the reaction.

Photosensitized Intermolecular Carboimination of Alkenes through the Persistent Radical Effect

An intermolecular, two-component vicinal carboimination of alkenes has been accomplished by energy transfer catalysis. Oxime esters of alkyl carboxylic acids were used as bifunctional reagents to generate both alkyl and iminyl radicals. Subsequently, addition of the alkyl radical to an alkene generates a transient radical for selective radical-radical cross-coupling with the persistent iminyl radical. Furthermore, this process provides direct access to aliphatic primary amines and α-amino acids by simple hydrolysis.

Transition-Metal-Free Three-Component Radical 1,2-Amidoalkynylation of Unactivated Alkenes

A transition-metal-free radical 1,2-amidoalkynylation of unactivated alkenes is presented. α-Amido-oxy acids were used as amidyl radical precursors, which were oxidized by an organic photoredox catalyst (4CzlPN). The electrophilic N-radicals chemoselectively reacted with various aliphatic alkenes and the adduct radicals were then trapped by ethynylbenziodoxolone (EBX) reagents to eventually provide the amidoalkynylation products. These transformations, which were conducted under practical and mild conditions, showed high functional group tolerance and broad substrate scope. Mechanistic studies supported the radical nature of these cascades.

Transition-Metal-Free Synthesis of N-Hydroxy Oxindoles by an Aza-Nazarov-Type Reaction Involving Azaoxyallyl Cations

A novel transition-metal-free method to construct N-hydroxy oxindoles by an aza-Nazarov-type reaction involving azaoxyallyl cation intermediates is described. A variety of functional groups were tolerated under the weak basic reaction conditions and at room temperature. A one-pot process was also developed to make the reaction even more practical. This method provides alternative access to oxindoles and their biologically active derivatives.

A Copper-Catalyzed Aerobic [1,3]-Nitrogen Shift through Nitrogen-Radical 4-exo-trig Cyclization

A novel radical [1,3]-nitrogen shift catalyzed by copper diacetate under an oxygen atmosphere (1 atm) has been developed for the construction of a diverse range of indole derivatives from α,α-disubstituted benzylamine. In this reaction, oxygen was used as a clean terminal oxidant, and water was produced as the only by-product. Five inert bonds were cleaved, and two C-N bonds and one C-C double bond were constructed in one pot during this transformation. This unique method demonstrated broad application protential for the late-stage modification of biologically active natural products and drugs. Mechanistic investigations indicate that a unique 4-exo-trig cyclization of an aminyl radical onto a phenyl ring is involved in the catalytic cycle.

Transition-metal-free Chemoselective Oxidative C-C Coupling of the sp3 C-H Bond of Oxindoles with Arenes and Addition to Alkene: Synthesis of 3-Aryl Oxindoles, and Benzofuro- and Indoloindoles

A transition-metal (TM)-free and halogen-free NaOtBu-mediated oxidative cross-coupling between the sp³ C-H bond of oxindoles and sp² C-H bond of nitroarenes has been developed to access 3-aryl substituted and 3,3-aryldisubstituted oxindoles in DMSO at room temperature in a short time. Interestingly, the sp³ C-H bond of oxindoles could also react with styrene under TM-free conditions for the practical synthesis of quaternary 3,3-disubstituted oxindoles. The synthesized 3-oxindoles have also been further transformed into advanced heterocycles, that is, benzofuroindoles, indoloindoles, and substituted indoles. Mechanistic experiments of the reaction suggests the formation of an anion intermediate from the sp³ C-H bond of oxindole by tert-butoxide base in DMSO. The addition of nitrobenzene to the in-situ generated carbanion leads to the 3-(nitrophenyl)oxindolyl carbanion in DMSO which is subsequently oxidized to 3-(nitro-aryl) oxindole by DMSO.

Triiodide-Mediated δ-Amination of Secondary C-H Bonds

The Cδ -H amination of unactivated, secondary C-H bonds to form a broad range of functionalized pyrrolidines has been developed by a triiodide (I3 (-) )-mediated strategy. By in situ 1) oxidation of sodium iodide and 2) sequestration of the transiently generated iodine (I2 ) as I3 (-) , this approach precludes undesired I2 -mediated decomposition which can otherwise limit synthetic utility to only weak C(sp(3) )-H bonds. The mechanism of this triiodide-mediated cyclization of unbiased, secondary C(sp(3) )-H bonds, by either thermal or photolytic initiation, is supported by NMR and UV/Vis data, as well as intercepted intermediates.

[1+1+1] Cyclotrimerization for the Synthesis of Cyclopropanes

The synthesis of small rings by functionalization of C(sp³)−H bonds remains a great challenge. We report for the first time a copper‐catalyzed [1+1+1] cyclotrimerization of acetophenone derivatives under mild reaction conditions. The reaction has a broad scope for the stereoselective synthesis of cyclopropanes by trimerization of acetophenone. The developed transformation is based on an extraordinary copper‐catalyzed cascade process that allows saturated carbocycles to be obtained for the first time by cyclotrimerization through functionalization of C(sp³)−H bonds. The cascade of sixfold C(sp³)−H bond functionalization allows the synthesis of cyclopropanes in a highly stereoselective approach.

Recent Advances in the C-H-Functionalization of the Distal Positions in Pyridines and Quinolines

This review summarizes recent developments in the C-H-functionalization of the distal positions of pyridines, quinolines and related azaheterocycles. While the functionalization of the C2 position has been known for a long time and is facilitated by the proximity to N1, regioselective reactions in the distal positions are more difficult to achieve and have only emerged in the last decade. Recent advances in the transition metal-catalyzed distal C-H-functionalization of these synthetically-important azaheterocycles are discussed in detail, with the focus on the scope, site-selectivity and mechanistic aspects of the reactions.