Metal- and Oxidant-Free Modular Approach To Access N-Alkoxy Oxindoles via Aryne Annulation

An unprecedented metal- and oxidant-free (intermolecular) approach to access N-alkoxy oxindoles via [3 + 2] cycloadition of in situ generated electrophilic species viz. aryne and (putative) aza-oxyallyl cation is reported. This approach is amenable to both C3-unsubstituted as well as C3-substituted oxindoles. A one-pot manipulation further makes this reaction highly practical. The versatility of this approach was demonstrated through valuable synthetic transformations.

Cobalt-catalyzed C(sp3)-H/C(sp2)-H oxidative coupling between alkanes and benzamides

A direct cobalt-catalyzed oxidative coupling between C(sp2)-H in unactivated benzamides and C(sp3)-H in simple alkanes, ethers and toluene derivatives was explored. This protocol achieves direct C-C formation without using alkyl or aryl halide surrogates and exhibits high practicality with ample substrate scope. The method provides a new way to construct linear and five- or six-membered ring moieties in bioactive molecules.

Boryl Radicals-Triggered Selective C-H Functionalization for the Synthesis of Diverse Phenanthridine Derivatives

A boryl radical-triggered C-H functionalization of aliphatic ethers/amines or DMF with isocyanides is developed to deliver diverse phenanthridine derivatives in good to excellent yields. The substrate scope is broad, and a wide range of functional groups are tolerated under the standard conditions. The rapid removal of HBPin species by 4-cyanopyridine 1-oxide provides the driving force for this reaction. This new method should make boryl radicals widely applicable in organic synthesis.

Radical-carbene coupling reaction: Mn-catalyzed synthesis of indoles from aromatic amines and diazo compounds

An unprecedented coupling reaction between aromatic amines and diazo compounds was well developed, which afforded a bridge connecting between radical chemistry and metal carbene chemistry. This Mn-catalyzed tandem reaction also provided a fundamentally different and practical approach to the indole skeleton under mild conditions.

Copper-catalyzed amination of an α-C(sp3)–H bond in inactivated ethers to synthesize α-aminonitriles

A copper-catalyzed functionalization of inert cyclic ethers was developed to provide α-aminonitriles via a cascade oxidation/amination/ring-opening/cyanation reaction.

Transition metal free decarboxylative fluoroalkylation of N-acrylamides with 3,3,3-trifluoro-2,2-dimethylpropanoic acid (TFDMPA)

1,1-Dimethyl-2,2,2-trifluoroethyl substituted oxindoles were prepared by a novel transition metal-free decarboxylative fluoroalkylation of activated alkenes and C–H functionalization cascade process.

Fe-Catalyzed three-component carboazidation of alkenes with alkanes and trimethylsilyl azide

Iron out the difference. Carboazidation of alkenes using cycloalkanes, CH₂Cl₂, CHCl₃ and CCl₄ as alkylating reagents proceeded smoothly in the presence of TMSN₃, DTBP and a catalytic amount of Fe(acac)₃ to afford chain extended alkyl azides and γ-azido chloroalkanes in good to high yields.

Copper-catalyzed oxidative intermolecular 1,2-alkylarylation of styrenes with ethers and indoles

A new copper-catalyzed oxidative three-component intermolecular 1,2-alkylarylation of styrenes with ethers and indoles is disclosed.

Copper-Catalyzed Redox-Neutral Cyanoalkylarylation of Activated Alkenes with Cyclobutanone Oxime Esters

The copper-catalyzed cyclization of activated alkenes with cyclobutanone O-acyl oximes under redox-neutral conditions has been reported. This facile protocol provided an efficient approach to a variety of cyanoalkylated oxindoles and dihydroquinolin-2(1H)-ones with a broad substrate scope and excellent functional group tolerance. In this reaction, sequential C-C bond cleavage, radical addition, and cyclization processes were involved, wherein multiple bonds were constructed in a one-pot reaction. Mechanistic studies suggest that the reaction probably proceeded via a radical pathway.

α-C-H Alkylation of Methyl Sulfides with Alkenes by a Scandium Catalyst

The C-H addition of sulfides to alkenes is an atom-efficient route for the functionalization and modification of sulfide compounds through C-C bond formation, but this transformation is highly challenging. We report here the regioselective α-C(sp³)-H addition of a wide range of methyl sulfides to a variety of olefins and dienes by a half-sandwich scandium catalyst. This protocol provides a unique route for the synthesis of diverse sulfide derivatives through C-C bond formation at a sulfur-adjacent carbon atom in a 100% atom efficient fashion.

Recent Advances in Radical C-H Activation/Radical Cross-Coupling

Research and industrial interest in radical C-H activation/radical cross-coupling chemistry has continuously grown over the past few decades. These reactions offer fascinating and unconventional approaches toward connecting molecular fragments with high atom- and step-economy that are often complementary to traditional methods. Success in this area of research was made possible through the development of photocatalysis and first-row transition metal catalysis along with the use of peroxides as radical initiators. This Review provides a brief and concise overview of the current status and latest methodologies using radicals or radical cations as key intermediates produced via radical C-H activation. This Review includes radical addition, radical cascade cyclization, radical/radical cross-coupling, coupling of radicals with M-R groups, and coupling of radical cations with nucleophiles (Nu).

Transition-metal-free halocarbocyclisation of acrylamides using K2S2O8

A novel and direct transition-metal-free oxidative halocarbocyclisation of acrylamides using inexpensive KX (X = I, Br, Cl) and K2S2O8 has been developed. This methodology not only provides an efficient way to construct valuable halogenated oxindoles in good to excellent yields, but also represents a novel strategy for C–X and C–C bond formation.

Combined Di-tert-butyl Peroxide and Inorganic Base Promoted α-Alkylation of Ethers with Arenesulfonylindoles

The di-tert-butyl peroxide (DTBP) induced coupling of arenesulfonylindoles with ethers such as 1,4-dioxane, tetrahydropyran, tetrahydrofuran, and 1,2-dimethoxyethane was studied. The distinguishing feature of this strategy was characterized by capturing in situ generated vinylogous imine intermediates for the C(sp³)-H bond alkylation of ethers. This general procedure presents the major advantages of its wide substrate scope and good functional group compatibility.

Oxidative 1,2-carboamination of alkenes with alkyl nitriles and amines toward γ-amino alkyl nitriles

Difunctionalization of alkenes has become a powerful tool for quickly increasing molecular complexity in synthesis. Despite significant progress in the area of alkene difunctionalization involving the incorporation of a nitrogen atom across the C-C double bonds, approaches for the direct 1,2-carboamination of alkenes to produce linear N-containing molecules are scarce and remain a formidable challenge. Here we describe a radical-mediated oxidative intermolecular 1,2-alkylamination of alkenes with alkyl nitriles and amines involving C(sp³)-H oxidative functionalization catalysed by a combination of Ag₂CO₃ with iron Lewis acids. This three-component alkene 1,2-alkylamination method is initiated by the C(sp³)-H oxidative radical functionalization, which enables one-step formation of two new chemical bonds, a C-C bond and a C-N bond, to selectively produce γ-amino alkyl nitriles.

Iron-catalyzed boration of allylic esters: an efficient approach to allylic boronates

The first general iron-catalyzed boration of allylic esters has been developed.

Intermolecular cascade annulations of N-(arylsulfonyl)acrylamides with dual C(sp3)–H bonds: divergent access to indanes and pyrrolidin-2-ones

A new divergent cascade annulation reaction of N-(arylsulfonyl)acrylamides and dual alkyl C(sp³)–H bonds for selectively producing indanes and pyrrolidin-2-ones is presented.

Synthesis of oxindole from acetanilide via Ir(iii)-catalyzed C–H carbenoid functionalization

The Ir(iii)-catalyzed intermolecular C–H annulations of acetanilide with diazotized Meldrum's acid furnished the oxindole derivative. Brief synthetic applications of the synthesized oxindole were also demonstrated.

Oxidative bicyclization of N-tethered 1,7-enynes toward polycyclic 3,4-dihydroquinolin-2(1H)-ones via site-selective decarboxylative C(sp3)–H functionalization

A new Ag-catalyzed oxidative bicyclization of N-tethered 1,7-enynes with alkylcarboxylic acids for forming 41 examples of polycyclic 3,4-dihydroquinolin-2(1H)-ones has been established using readily accessible K₂S₂O₈ as an oxidant.

Iron(ii)-catalyzed sulfur directed C(sp3)–H bond amination/C–S cross coupling reaction

An efficient iron(ii)-catalyzed sulfur directed C(sp³)–H bond amination/C–S cross coupling reaction has been developed, and the mechanism corresponds to a Fe(ii)/Fe(iii) catalytic cycle.

Direct alkylheteroarylation of alkenes via photoredox mediated C–H functionalization

The direct alkylheteroarylation of alkenes with cyclic and acyclic ethers via distal heteroaryl ipso-migration has been accomplished through the design of a photoredox-mediated C–H functionalization pathway.

An iron-catalyzed hydroalkylation reaction of α,β-unsaturated ketones with ethers

A general strategy for the hydroalkylation of vinyl ketones using ethers catalyzed by an iron catalyst is described.

Metal-free sequential decarbonylative annulation of N-cyanamides for the construction of 2,3-dihydropyrrolo[2,1-b]quinazolin-9(1H)-ones

A convenient metal-free sequential decarbonylative annulation of unactivated alkenes for the construction of quinazolinones and dihydroisoquinolinones has been developed.

Radical cyclization of benzene-tethered 1,7-enynes with aryldiazonium tetrafluoroborates: a facile route to benzo[j]phenanthridines

A radical cyclization of benzene-tethered 1,7-enynes with aryldiazonium tetrafluoroborates in the presence of copper(ii) acetate and DABCO˙(SO₂)₂ is developed, leading to diverse benzo[j]phenanthridines.

Mechanistic investigation on radical-induced construction of oxindoles: radical versus electrophilic cyclization

A four-step mechanism is established for the title reaction and the radical cyclization is updated to the cationic cyclization.