Synthesis of Functionalized Epoxides by Copper-Catalyzed Alkylative Epoxidation of Allylic Alcohols with Alkyl Nitriles

Selective divergent radical cyclization of 1,6-dienes with alkyl nitriles

An efficient, selective, and step economical radical cyclization of 1,6-dienes with alkyl nitriles initiated by α-C(sp³)-H functionalization under the Sc(OTf)₃ and Ag₂CO₃ system is described here. The selective divergent cyclization relies on the substitution effect at the α-position of the acrylamide moiety and nitriles, which is terminated by hydrogen abstraction, direct cyclization with the aryl ring, or further cyclization with the CN bond and hydrolysis, respectively.

Photoinduced Cross-Coupling of Aryl Iodides with Alkenes

A protocol for photoinduced cross-coupling of aryl iodides having polar π-functional groups or elongated π-conjugation with alkenes has been developed. The radical cascade mechanism involving generation of aryl radicals via C-I bond homolysis of photoexcited aryl iodides and their subsequent addition to alkenes is proposed. The method enables iodide-selective cross-coupling over other halogen leaving groups with functional group compatibility on both arene and alkene motifs.

Radical-mediated alkoxypolyhaloalkylation of styrenes with polyhaloalkanes and alcohols via C(sp3)–H bond cleavage

A radical-mediated alkoxypolyhaloalkylation of styrenes with polychloroalkanes and alcohols for the facile synthesis of complex polyhaloalkanes with excellent functional-group compatibility and a broad substrate scope.

Copper-promoted cyanoalkylation/ring-expansion of vinylcyclopropanes with α-C-H bonds in alkylnitriles toward 3,4-dihydronaphthalenes

A copper-promoted oxidative cyanomethylation/ring-expansion of vinylcyclopropanes with α-C(sp3)-H bonds in alkyl nitriles is established for the generation of 1-cyanoethylated 3,4-dihydronaphthalenes. This cyanomethylation/ring-expansion involves a radical pathway and proceeds via cyanomethyl radical formation, radical addition and ring-expansion. This ring-expansion strategy offers a highly atom-economical route for the construction of nitrile-containing 3,4-dihydronaphthalenes, which can be transformed into other useful products under simple conditions.

Cu/Ni-Catalyzed Cyanomethylation of Alkenes with Acetonitrile for the Synthesis of β,γ-Unsaturated Nitriles

We have developed a protocol for the Cu/Ni-catalyzed cyanomethylation of alkenes with acetonitrile for the synthesis of β,γ-unsaturated nitriles. This is the first example of a direct coupling of the alkene sp² C-H bond and the acetonitrile sp³ C-H bond for the preparation of β,γ-unsaturated nitriles. Acetonitrile, an inexpensive and stable solvent, is demonstrated to be a useful cyanomethyl source. The combination of copper and nickel catalysts resulted in a high reaction efficiency.

Revealing the Iron-Catalyzed β-Methyl Scission of tert-Butoxyl Radicals via the Mechanistic Studies of Carboazidation of Alkenes

We describe here a mechanistic study of the iron-catalyzed carboazidation of alkenes involving an intriguing metal-assisted β-methyl scission process. Although t-BuO radical has frequently been observed in experiments, the β-methyl scission from a t-BuO radical into a methyl radical and acetone is still broadly believed to be thermodynamically spontaneous and difficult to control. An iron-catalyzed β-methyl scission of t-BuO is investigated in this work. Compared to a free t-BuO radical, the coordination at the iron atom reduces the activation energy for the scission from 9.3 to 3.9 ~ 5.2 kcal/mol. The low activation energy makes the iron-catalyzed β-methyl scission of t-BuO radicals almost an incomparably facile process and explains the selective formation of methyl radicals at low temperature in the presence of some iron catalysts. In addition, a radical relay process and an outer-sphere radical azidation process in the iron-catalyzed carboazidation of alkenes are suggested by density functional theory (DFT) calculations.

Free Radical Addition of Nitrile, Ketone, and Ester to Alkyne and the Selectivity Discussion

A general and practical atom transfer radical addition (ATRA) of simple nitriles, ketones, and esters to alkynes was developed. It can allow an efficient access to a wide range of β,γ-unsaturated nitriles, ketones, and esters. The unique chemoselectivity in this system is also discussed.

Remote C(sp3 )-H Arylation and Vinylation of N-Alkoxypyridinium Salts to δ-Aryl and δ-Vinyl Alcohols

The reaction of readily available and bench-stable N-alkoxypyridinium salts with arylboronic and vinylboronic acids afforded δ-aryl and δ-vinyl alcohols, respectively, in the presence of fac-Ir(ppy)₃ and Cu(OTf)₂ dual catalysts. The reaction takes place through a domino process involving the reductive generation of alkoxyl radicals, 1,5-hydrogen atom transfer (1,5-HAT) and the copper-catalyzed cross-coupling reaction of the resulting translocated carbon radicals with boronic acids. Complementary to the Minisci reaction, this method allows for the arylation of nucleophilic alkyl radicals with both electron-rich and electron-poor arenes under mild reaction conditions.

Copper-Promoted Functionalization of Organic Molecules: from Biologically Relevant Cu/O2 Model Systems to Organometallic Transformations

Copper is one of the most abundant and less toxic transition metals. Nature takes advantage of the bioavailability and rich redox chemistry of Cu to carry out oxygenase and oxidase organic transformations using O₂ (or H₂O₂) as oxidant. Inspired by the reactivity of these Cu-dependent metalloenzymes, chemists have developed synthetic protocols to functionalize organic molecules under enviormentally benign conditions. Copper also promotes other transformations usually catalyzed by 4d and 5d transition metals (Pd, Pt, Rh, etc.) such as nitrene insertions or C-C and C-heteroatom coupling reactions. In this review, we summarized the most relevant research in which copper promotes or catalyzes the functionalization of organic molecules, including biological catalysis, bioinspired model systems, and organometallic reactivity. The reaction mechanisms by which these processes take place are discussed in detail.

Synthesis of 3-cyanomethylated coumarins by a visible-light-mediated direct cyanomethylation of aryl alkynoates

A visible-light-promoted, mild, and direct cyanomethylation of aryl alkynoates has been developed.

Iron(ii)-catalyzed C-2 cyanomethylation of indoles and pyrroles via direct oxidative cross-dehydrogenative coupling with acetonitrile derivatives

A novel and efficient approach for the C(sp²)–H/C(sp³)–H oxidative coupling of indoles and pyrroles with acetonitrile derivatives was reported by using the Fe(ii) complex.

Oxidative three-component 1,2-alkylarylation of alkenes with alkyl nitriles and N-heteroarenes

Indium-promoted oxidative three-component 1,2-alkylarylation of alkenes with alkyl nitriles and N-heteroarenes is achieved by C(sp³)–H/C(sp²)–H functionalization.

Transforming Olefins into γ,δ-Unsaturated Nitriles through Copper Catalysis

We have developed a strategy to transform olefins into homoallylic nitriles through a mechanism that combines copper catalysis with alkyl nitrile radicals. The radicals are easily generated from alkyl nitriles in the presence of the mild oxidant di-tert-butyl peroxide. This cross-dehydrogenative coupling between simple olefins and alkylnitriles bears advantages over the conventional use of halides and toxic cyanide reagents. With this method, we showcase the facile synthesis of a flavoring agent, a natural product, and a polymer precursor from simple olefins.

Mild Epoxidation of Allylic Alcohols Catalyzed by Titanium(III) Complexes: Selectivity and Mechanism

A novel methodology for the epoxidation of a broad range of primary, secondary, and tertiary allylic alcohols is described using tert-butyl hydroperoxide as oxidant and Ti(III) species generated by reduction of Ti(IV) complexes, with manganese (0) in 1,4-dioxane under mild reaction conditions. The reaction proceeded with wide substrate scope and high chemo- and diastereoselectivity. A mechanistic pathway for the reaction is also discussed.

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.

Visible-light promoted γ-cyanoalkyl radical generation: three-component cyanopropylation/etherification of unactivated alkenes

A photoredox approach to generate distal cyano-substituted alkyl radicals through C–C bond cleavage of cyclobutanone oximes was developed.

Iron-catalyzed cascade cyanoalkylation/radical dearomatization of N-phenylcinnamamides: access to cyanoalkylated 1-azaspiro[4.5]decanes

An iron-catalyzed tandem cyanoalkylative dearomatization of N-(4-hydroxyphenyl)-cinnamamides via C(sp³)–H functionalization of nitriles with excellent regioselectivity and diastereoselectivity was developed.

Copper-catalysed cyanoalkylative cycloetherification of alkenes to 1,3-dihydroisobenzofurans: development and application to the synthesis of citalopram

A copper-catalysed cyanoalkylative cycloetherification of alkenes was developed. Heating a solution of substituted (2-vinylphenyl)methanol in MeCN/MeOH (v/v 7/3) in the presence of a catalytic amount of copper(ii) tetrafluoroborate hydrate [Cu(BF4)2·6H2O], bathophenanthroline, K3PO4, BnOH and (tBuO)2 afforded 1,3-dihydroisobenzofurans (phthalanes) via formation of one C(sp(3))-C(sp(3)) and one C(sp(3))-O bonds. A concise synthesis of citalopram, a marketed anti-depressant drug, was accomplished by applying this novel synthetic transformation.

Multimetallic catalysed radical oxidative C(sp(3))-H/C(sp)-H cross-coupling between unactivated alkanes and terminal alkynes

Radical involved transformations are now considered as extremely important processes in modern organic synthetic chemistry. According to the demand by atom-economic and sustainable chemistry, direct C(sp³)–H functionalization through radical oxidative coupling represents an appealing strategy for C–C bond formations. However, the selectivity control of reactive radical intermediates is still a great challenge in these transformations. Here we show a selective radical oxidative C(sp³)–H/C(sp)–H cross-coupling of unactivated alkanes with terminal alkynes by using a combined Cu/Ni/Ag catalytic system. It provides a new way to access substituted alkynes from readily available materials. Preliminary mechanistic studies suggest that this reaction proceeds through a radical process and the C(sp³)–H bond cleavage is the rate-limiting step. This study may have significant implications for controlling selective C–C bond formation of reactive radical intermediates by using multimetallic catalytic systems.

Cross coupling via the activation of two carbon-hydrogen bonds avoids the need for organometallic coupling partners and associated waste. Here, the authors report a radical process that allows selective coupling between alkynes and non-activated C(sp³)-H groups via a multimetallic catalytic system.

Radical-promoted site-specific cross dehydrogenative coupling of heterocycles with nitriles

A first free-radical triggered site-specific cross dehydrogenative coupling reaction of heterocycles with simple nitriles is developed. It allows efficient and facile access to various C-2 cyanoalkylated furans, thiophenes, indoles, and pyrroles. The extremely high selectivities in this case indicate that functionalization of an inert C–H bond could be well-controlled by radical initiation.

Copper-mediated radical alkylarylation of unactivated alkenes with acetonitrile leading to fluorenes and pyrroloindoles

A Cu-mediated/catalyzed selective oxidative dual C–H bond cleavage of an arene and alkylnitrile or acetone is reported. This method provides an alternative method for designing new pharmaceutical frameworks and photoelectronic devices.