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Carbon-hydrogen (C−H) functionalization of pyridines is a powerful tool for the rapid construction and derivatization of many agrochemicals, pharmaceuticals, and materials. Because of the inherent electronic properties of pyridines, selective meta -C−H functionalization is challenging. Here, we present a protocol for highly regioselective meta -C−H trifluoromethylation, perfluoroalkylation, chlorination, bromination, iodination, nitration, sulfanylation, and selenylation of pyridines through a redox-neutral dearomatization-rearomatization process. The introduced dearomative activation mode provides a diversification platform for meta-selective reactions on pyridines and other azaarenes through radical as well as ionic pathways. The broad scope and high selectivity of these catalyst-free reactions render these processes applicable for late-stage functionalization of drugs.

The Mizoroki–Heck reaction between alkenes and aryl halides represents one of the most important methods for C−C bond formation in synthetic chemistry. Governed by their electronic and steric nature, alkenes are generally arylated with high regioselectivity, which conversely hampers diversity, in particular, if the regioirregular isomer is targeted. Usually, electron-poor alkenes selectively afford the corresponding β-coupled products, and achieving the opposite regioselectivity to obtain their α-arylated congeners is highly challenging. It would be desirable to access the irregular α-regioisomer by simple variation of the reaction conditions, keeping the standard substrates, thereby significantly enlarging the product space. Herein, we describe an intermolecular α-arylation of electron-poor alkenes through cooperative nickel, photoredox and sulfinate catalysis. This triple catalysis system operates under mild conditions and features excellent functional group tolerance. The orchestration of radical, transition metal and ionic bond-forming and -cleaving reactions in a single process is highly challenging, but certainly opens valuable doors in terms of reactivity. Moreover, the intermolecular α-arylation, α-alkenylation and α-alkynylation of styrenes could also be achieved through a one-pot process.

An intramolecular dearomatizing spirocyclization of indoles by oxidative N-heterocyclic carbene catalysis is reported. C2-iodinated indoles are used as substrates in combination with aroyl azolium ions as acceptors, which provides C2-iodinated indolenines containing an all carbon quaternary stereocenter. The products are readily further C2-functionalized and give access to valuable oxindoles by simple hydrolysis in very good overall yields and excellent enantioselectivities.

Alkynes and cyclopropanes are vital motifs in chemistry. Herein, a photoredox catalyzed 1,3-oxyalkynylation of aryl cyclopropanes with ethylnylbenziodoxolones (EBXs) in an atom-economic fashion is described. This cascade comprises single-electron oxidation of the aryl cyclopropane and nucleophilic ring opening followed by radical alkynylation at the benzylic position. The EBX compounds act as bifunctional reagents providing the nucleophilic acid as well as the alkynyl entity. The introduced method features mild conditions and wide substrate scope.

Carbon-hydrogen (C-H) functionalization of pyridines is a powerful tool for the rapid construction and derivatization of many agrochemicals, pharmaceuticals, and materials. Because of the inherent electronic properties of pyridines, selective

A method for the selective tryptophan modification and labelling of tryptophan-containing peptides is described. Photoirradiation of acylsilanes generates reactive siloxycarbenes which undergo H-N-insertion into the indole moiety of tryptophan to give stable silyl protected hemiaminals. This method is successfully applied to chemically modify various tryptophan containing oligopeptides. The method enables the selective introduction of alkynes to peptides that are eligible for further alkyne-azide click chemistry. In addition, the dansyl fluorophore can be conjugated to a peptide using this approach.

Catalyst‐free 1,2‐carboboration of ynamides is presented. Readily available aryldichloroboranes react with alkyl‐ or aryl‐substituted ynamides in high yields with complete regio‐ and stereoselectivity to valuable β‐boryl‐β‐alkyl/aryl α‐aryl substituted enamides which belong to the class of trisubstituted alkenylboronates. The 1,2‐carboboration reaction is experimentally easy to conduct, shows high functional group tolerance and broad substrate scope. Gram‐scale reactions and diverse synthetic transformations convincingly demonstrate the synthetic potential of this method. The reaction can also be used to access 1‐boraphenalenes, a class of boron‐doped polycyclic aromatic hydrocarbons., The catalyst‐free direct 1,2‐carboboration of ynamides with readily available dichloroboranes is presented. Valuable α,β,β‐trisubstituted alkenylboronates are obtained in high yields with complete regio‐ and stereoselectivity under very mild conditions.

Summary This review illustrates pioneering work and recent advancements on the use of pro-aromatic compounds as carbon- and heteroatom-radical precursors. Pro-aromatic systems such as 1,4-cyclohexadienes, dihydronicotinamides, 1,4-dihydropyridines, 4-substituted Hantzsch esters, pyridinium salts, and benzothiazolines are easily transformed to pro-aromatic radicals and can be used to realize hydrogen atom or radical functional group transfer chemistry. 1,4-dihydropyridines and dihydronicotinamides form complexes with suitable acceptors, and these donor-acceptor complexes engage in intramolecular electron transfer leading to radical pairs that contain a pro-aromatic moiety. We highlight the underlying principle for the generation of reactive radicals in these systems that is gaining aromaticity as the driving force for the fragmentation of the pro-aromatic radicals. Moreover, many pro-aromatic reagents contain weak activated C–H bonds, qualifying them as good H-atom donors in C-radical reductions. Studies from our laboratory along with recent developments from other groups are classified with respect to the structure of the pro-aromatic radical precursor.

Light‐mediated coupling of acylsilanes with indoles is reported. This photo click reaction occurs under mild conditions (415 nm) mostly in quantitative yield and provides stable silylated N,O‐acetals via light mediated siloxycarbene generation with subsequent indole‐N‐H insertion. We show that this very efficient and fully atom economic coupling process can be applied to conjugate complex systems, as documented by the clicking of carbohydrates with indole alkaloids. The method is also applicable to the conjugation of polymer chains. The linking acetal moiety can be readily cleaved and it is also shown that wavelength‐selective coupling and cleavage with acyl silanes bearing a second photoactive moiety is possible. This is documented by a successful polymerization/depolymerization sequence and by a polymer folding/unfolding process., Visible‐light‐mediated coupling of acylsilanes with indoles is reported. This photoreaction occurs under mild conditions mostly in quantitative yield and provides stable silylated N,O‐acetals. The potential of the method is documented by the successful coupling of carbohydrates with indole alkaloids and by the conjugation of polymers.

The reaction of in situ generated arynes with stannylated imines to provide ortho-stannyl-aniline derivatives is reported. The readily prepared trimethylstannyl benzophenone imine is introduced as an efficient reagent to realize the aryne σ-insertion reaction. The imine functionality is an established N-protecting group and insertions proceed with good yields and good to excellent regioselectivities. The product anilines are valuable starting materials for follow-up chemistry thanks to the rich chemistry offered by the trimethylstannyl moiety.

An atom-economic thermal α,β-difunctionalization of various styrenes with readily prepared azodioxy compounds is reported. Mechanistic studies reveal that the starting azodioxy compounds can thermally be cleaved to the corresponding C-nitroso compounds, which under these thermal conditions further homolyze to generate reactive C-radicals along with the persistent NO radical. In the presence of a styrene, C-radical addition with subsequent nitrosylation followed by tautomerization is occurring, resulting in an overall styrene β-alkylation-α-oximation reaction.

While the range of accessible borylenes has significantly broadened over the last decade, applications remain limited. Herein, we present tricoordinate oxy-borylenes as potent photoreductants that can be readily activated by visible light. Facile oxidation of CAAC stabilized oxy-borylenes (CAAC)(IPr

A method for the synthesis of functionalized alternating copolymers by reversible deactivation radical polymerization was developed. Copolymerization by reversible addition-fragmentation chain transfer of hexenyl vinyl ether with a novel fluorinated divinyl monomer yields alternating cyclopolymers that can be chemoselectively modified by three distinct orthogonal functionalization reactions. Along the thiol-ene click reaction and amidation, a third functionalization was achieved via NHC-catalyzed transesterification or acylation resulting in a small library of ABC-type alternating terpolymers.

α-C-H-functionalization of ketones and aldehydes has been intensively explored in organic synthesis. The functionalization of unactivated β-C-H bonds in such carbonyl compounds is less well investigated and developing a general method for their β-C-H arylation remains challenging. Herein we report a method that uses cooperative nickel and photoredox catalysis for the formal β-C-H arylation of aldehydes and ketones with (hetero)aryl bromides. The method features mild conditions, remarkable scope and wide functional group tolerance. Importantly, the introduced synthetic strategy also allows the β-alkenylation, β-alkynylation and β-acylation of aldehydes under similar conditions. Mechanistic studies revealed that this transformation proceeds through a single electron oxidation/Ni-mediated coupling/reductive elimination cascade.

Element–element double bonds of group 14 elements can be formed in solution, but generally only by applying harsh reductive conditions using sterically highly shielded tetryl halides as precursors. The two-dimensional confinement in surface-assisted polymerization represents a valuable alternative to access such reactive compounds, as it allows shielding of the labile entities without requiring bulky residues and catalytic activation of the reactive groups. Here, we demonstrate Si–Si bond formation in on-surface chemistry. Polymerization upon multiple Si–H bond dissociation and subsequent Si–Si bond formation was achieved on Au(111) and Cu(111) surfaces by using two different monomers, each containing two silicon functional groups (CH3SiH2 or SiH3) attached to an aromatic backbone, leading to polymeric disilenes that interact with the surface. A combination of experimental and theoretical studies corroborates the formation of covalent Si–Si bonds between the long, highly ordered polymer chains with high diastereoselectivity. The reactive Si=Si bonds formally generated via double dehydrogenative coupling are stabilized via covalent Si–surface interaction. On-surface dehydrogenative bond formation between sp3-hybridized carbon atoms usually requires high temperatures. Now, it has been shown that the higher homologue, silicon, can undergo dehydrogenative polymerization at room temperature on metal surfaces. This process creates well-ordered structures on Au(111) and Cu(111), with different stereoselectivity depending on the metal.