Copper-Catalyzed Oxidative C-H Amination of Tetrahydrofuran with Indole/Carbazole Derivatives

A simple α-C-H amination of cyclic ether with indole/carbazole derivatives has been accomplished by employing copper(II) chloride/bipy as the catalyst system. In the presence of the di-tert-butyl peroxide oxidant, cyclic ethers such as tetrahydrofuran, 1,4-dioxane, and tetrahydropyran successfully undergo C-H/N-H cross dehydrogenative coupling (CDC) with various carbazole or indole derivatives in good-to-excellent yields.

Dimethylzinc-Initiated Radical Coupling of β-Bromostyrenes with Ethers and Amines

A new coupling reaction has been developed in which β-bromostyrenes react with ethers and tertiary amines to introduce the styryl group in the α-position. The transformation is mediated by Me2 Zn/O2 with 10 % MnCl2 and is believed to proceed by a radical addition-elimination mechanism. The ether and the amine are employed as solvent and the coupling takes place through the most stable α radical for unsymmetrical substrates. The products are obtained in moderate to good yields as the pure E isomers. The coupling can be achieved with a range of smaller cyclic and acyclic ethers/amines as well as various substituted β-bromostyrenes.

Iminoiodane- and Brønsted base-mediated cross dehydrogenative coupling of cyclic ethers with 1,3-dicarbonyl compounds

A one-pot, two-step approach to prepare 2-tetrahydrofuran and -pyran substituted 1,3-dicarbonyl compounds by PhI=NTs-mediated amination/Brønsted base-catalyzed cross dehydrogenative coupling (CDC) reaction of the cyclic ether and 1,3-dicarbonyl derivative under mild conditions is reported. The reaction is compatible with a variety of cyclic ethers and 1,3-dicarbonyl compounds, affording the corresponding coupled products in moderate to good yields of up to 80% over two steps.

Copper-catalyzed oxidative alkenylation of thioethers via Csp(3)-H functionalization

A novel copper-catalyzed oxidative alkenylation of thioethers via Csp(3)-H functionalization to construct allylic thioethers is first demonstrated. Different 1,1-disubstituted olefins could cross-couple with thioethers to generate the corresponding alkenylation products in moderate to excellent yields. This reaction is supposed to proceed via a radical process.

Organocatalytic amination of alkyl ethers via n-Bu4NI/t-BuOOH-mediated intermolecular oxidative C(sp(3))-N bond formation: novel synthesis of hemiaminal ethers

A novel method for constructing the hemiaminal ether framework under metal-free conditions has been developed. It involves direct organocatalytic amination of alkyl ethers through intermolecular oxidative C(sp(3))-N bond formation, with t-BuOOH being the oxidant and n-Bu4NI as the catalyst.

Metal-free oxidative functionalization of C(sp(3))-H bond adjacent to oxygen and radical addition to olefins

A DTBP-promoted oxidative functionalization of a C(sp(3))-H bond adjacent to oxygen and intermolecular radical addition to olefins without use of any metal catalyst or photoredox catalysis is reported. The reaction has a wide scope of olefin, alcohol, and cycloether substrates, which provides an easy way for direct preparation of α,ω-amino alcohols.

Copper-catalyzed oxidative alkenylation of C(sp3)–H bonds via benzyl or alkyl radical addition to β-nitrostyrenes

A new method for the preparation of (E)-β-alkylstyrene derivatives has been developed via the addition of benzyl or alkyl radicals to β-nitrostyrenes using di-tert-butyl peroxide (DTBP) as the oxidant in the presence of Cu powder catalyst.

Palladium-catalyzed direct alkenylation of 2-methyl-4H-pyrido[1,2-a]pyrimidin-4-ones using oxygen as the oxidant

A direct C-3 alkenylation of 2-methyl-4H-pyrido[1,2-a]pyrimidin-4-ones through palladium-catalyzed C–H activation using oxygen as the terminal oxidant has been developed.

Metal-free direct difunctionalization of alkenes with I2O5 and P(O)–H compounds leading to β-iodophosphates

A novel and efficient procedure for direct difunctionalization of alkenes with I₂O₅ and P(O)–H compounds has been developed under metal-free conditions.

Oxidative cross-coupling of pyridine N-oxides and ethers between C(sp2)–H/C(sp3)–H bonds under transition-metal-free conditions

An oxidative cross-coupling of pyridine N-oxides and ethers between C(sp²)–H/C(sp³)–H bonds under transition metal free conditions was developed.

Direct construction of 2-alkylbenzo-1,3-azoles via C–H activation of alkanes for C–C and C–X (X = O, S) bond formation

2-Alkylated benzo(oxa)thiazoles were prepared directly from simple alkanes and aryl isocyanates/isothiocyanates in a one-pot procedure.

Rhenium-catalyzed dehydrogenative olefination of C(sp3)–H bonds with hypervalent iodine(iii) reagents

A dehydrogenative olefination of C(sp³)–H bonds is developed by merging rhenium catalysis with an alanine-derived hypervalent iodine(iii) reagent.

DBU-promoted cyclization of vinyl isocyanides with ethers via the functionalization of a C(sp3)–H bond for the synthesis of isoquinolines

A DBU-promoted cascade functionalization of a C(sp³)–H bond adjacent to oxygen and a radical cyclization reaction of vinyl isocyanides was developed to easily access multi-functionalized isoquinolines.

Olefinic C–H functionalization through radical alkenylation

This tutorial review provides a comprehensive overview of olefinic C–H functionalization through radical addition and following SET oxidation/elimination.

Cu-catalyzed oxidative Povarov reactions between N-alkyl N-methylanilines and saturated oxa- and thiacycles

Cu-catalyzed oxidative Povarov reactions between N,N-dialkylanilines and saturated oxa- or thiacycles with tert-butyl hydroperoxide (TBHP) are described.

Metal-free oxidative C(sp3)–H bond functionalization of alkanes and alkylation-initiated radical 1,2-aryl migration in α,α-diaryl allylic alcohols

A C(sp³)–H bond functionalization of alkanes and 1,2-aryl migration of allylic alcohols was reported with up to 93% yields.

Iron-catalyzed direct α-arylation of ethers with azoles

The direct α-arylation of cyclic and acyclic ethers with azoles has been achieved, which features a novel iron-catalyzed cross-dehydrogenative coupling (CDC) process.

Vanadyl species-catalyzed complementary β-oxidative carbonylation of styrene derivatives with aldehydes

By judicious choice of the counter anions in the vanadyl catalysts, we can achieve β-hydroxylated and t-butyl peroxylated carbonylation of styrenes by aromatic 1° and 2° alkyl aldehydes in a complementary manner.

Recent advances of transition-metal catalyzed radical oxidative cross-couplings

CONSPECTUS: Oxidative cross-coupling reactions between two nucleophiles are a powerful synthetic strategy to synthesize various kinds of functional molecules. Along with the development of transition-metal-catalyzed oxidative cross-coupling reactions, chemists are applying more and more first-row transition metal salts (Fe, Co, etc.) as catalysts. Since first-row transition metals often can go through multiple chemical valence changes, those oxidative cross-couplings can involve single electron transfer processes. In the meantime, chemists have developed diverse mechanistic hypotheses of these types of reactions. However, none of these hypotheses have led to conclusive reaction pathways until now. From studying both our own work and that of others in this field, we believe that radical oxidative cross-coupling reactions can be classified into four models based on the final bond formations. In this Account, we categorize and summarize these models. In model I, one of the starting nucleophiles initially loses one electron to generate its corresponding radical under oxidative conditions. Then, bond formations between this radical and another nucleophile create a new radical, [Nu(1)-Nu(2)](•), followed by a further radical oxidation step to generate the cross-coupling product. The radical oxidative alkenylation with olefin, radical oxidative arylative-annulation, and radical oxidative amidation are examples of this model. In model II, one of the starting nucleophiles loses its two electrons via two steps of single-electron-transfer to generate an electrophilic intermediate, followed by a direct bond formation with the other nucleophile. For example, the oxidative C-O coupling of benzylic sp(3) C-H bonds with carboxylic acids and oxidative C-N coupling of aldehydes with amides are members of this model group. For model III, both nucleophiles are oxidized to their corresponding radicals. Then, the radicals combine to form the final coupling product. The dioxygen-involved radical oxidative cross-couplings between sulfinic acids and olefins or alkynes belong to this bond formation model. Lastly, in model IV, one nucleophile loses two electrons to generate an electrophilic intermediate, while the other nucleophile loses one electron to generate a radical. Then, a bond forms between the cation and the radical to generate a cationic radical, followed by a one-electron reduction to afford the final coupling product. The oxidative coupling between arylboronic acids and simple ethers was classified in this model. At the current stage, there are only a few examples presented for models III and IV, but they represent two types of potentially important transformations. More and more examples of these two models will be developed in the future.

Structurally diverse α-substituted benzopyran synthesis through a practical metal-free C(sp3)-H functionalization

A trityl ion-mediated practical C-H functionalization of a variety of benzopyrans with a wide range of nucleophiles (organoboranes and C-H molecules) at ambient temperature has been disclosed. The metal-free reaction has an excellent functional group tolerance and high chemoselectivity and displays a broad scope with respect to both benzopyran and nucleophile partners, efficiently affording a collection of benzopyrans bearing diverse skeletons and α-functionalities in one step.

Practical and highly selective C-H functionalization of structurally diverse ethers

A trityl ion mediated C-H functionalization of ethers with a wide range of nucleophiles at ambient temperature has been developed. The reaction displays high chemoselectivity and good functional group tolerance. The protocol also exhibits excellent regio- and diastereoselectivities for the unsymmetric ethers, thus stereoselectively generating highly functionalized disubstituted 2,5-trans tetrahydrofurans (THF), 2,6-trans tetrahydropyrans (THP), 2,6-trans dihydropyrans (DHP), and 1,3-trans isochromans, and highlighting the capacity of the protocol in complex molecule synthesis.

Cyclic ethers to esters and monoesters to bis-esters with unconventional coupling partners under metal free conditions via sp3 C–H functionalisation

Oxidative esterification of sp³ C–H bonds in simple solvents has been achieved using latent ArCOO⁻ sources under metal free conditions.

I2-catalyzed oxidative C(sp3)–H/S–H coupling: utilizing alkanes and mercaptans as the nucleophiles

C(sp³)–S bond formation was achieved utilizing C(sp³)–H and S–H as the nucleophile. Methyl arenes, cycloalkanes and aliphatic ketones exhibited reactivity for this transformation. Mechanistic studies revealed that the C(sp³) radical and disulfide were the intermediates in the reaction.

Base-promoted dehydrogenative coupling of benzene derivatives with amides or ethers

Electronically neutral and deficient benzene derivatives are introduced into the dehydrogenative coupling as arenes that couple with amides/ethers.