Based upon a radical polar effect, an intermolecular azidoheteroarylation of simple alkenes via a metal-free radical multicomponent cascade process was achieved. It allows a mild, rapid, and step-economic access to a broad range of azidoalkylated heteroaromatics. Given the diversity in transformations of organic azides and medicinally privileged scaffolds of heteroarenes, this strategy enables efficient synthesis and late-stage derivatization of drugs and candidates.

A free-radical-promoted aryl/heteroaryl C–H silylation using hydrosilane was developed. This cross-dehydrogenative silylation enables both electron-rich and electron-poor aromatics to afford the desired arylsilanes in unique selectivity. A “para-selectivity” was observed by examination of over 54 examples. This exceptional orientation is quite different from that in Friedel–Crafts C–H silylation or transition-metal-catalyzed dehydrogenative silylation.

The carbon–carbon bond formation via autoxidation of organoboronic acid using 1 atm of O2 is achieved in a simple, clean, and green fashion. The approach allows a technically facile and environmentally benign access to structurally diverse heteroaromatics with medicinally privileged scaffolds. The strategy also displays its practicality and sustainability in the resynthesis of marketed drugs Crestor and pyrimethamine.

H-Bonding-induced radical addition of simple alcohols to unactivated olefins was achieved. It effectively solved the long-standing problems of reactivity and selectivity in this type of reaction. The hydroxyalkylation occurred via site-specific cleavage of the α-hydroxyl-C–H bond in alcohols. This method allows a highly atom-economical, operationally simple and environmentally benign access to diverse primary, secondary and tertiary alcohols, diols, and even polyfluorinated alcohols. These useful chemicals are traditionally synthesized by using commercially unavailable organometallics via complex operations. In contrast, they can be facilely obtained through this protocol utilizing widely available starting materials.

A free-radical bromotrifluoromethylation of olefin by using NaSO2CF3 and NaBrO3 has been achieved. Sodium bromate acts not only as a single-electron oxidant but also as a bromine source. A radical-clock experiment and electron-spin-resonance detection support a radical process.

A C–C formation of an electron-rich N-heterocycle with fluorinated alcohol is developed. Through this radical-triggered cross-dehydrogenative coupling strategy, a wide range of useful building blocks such as C3 hydroxyfluoroalkylated indoles and pyrroles can be site-specifically synthesized. Mechanistic studies indicate a single-electron-transfer initiated radical cycle would be involved.

A free-radical mediated highly ordered radical addition/cyclization/(sp3)C–C(sp3) formation domino reaction is developed. Three new C–C bonds are formed one by one in a mixed system. Furthermore, it represents the first example of cascade C–C bond formation via selective functionalization of α-hydroxyl-C(sp3)–H in fluorinated alcohols.

As important and valuable alternatives to transition-metal-catalysis, free-radical strategies for C–Si bond construction via selective C–H/Si–H functionalization have been developed recently. These new reactions along with their suggested mechanisms are summarized and discussed here.

An efficient hydrocyanoalkylation of unactivated alkenes with alkyl nitriles was developed. Through this free-radical-initiated selective activation of the α-C(sp3)–H bond of acetonitriles, an anti-Markovnikov addition of an α-cyano C-centered radical to olefins has been achieved, which allows a facile and convenient access to functionalized nitriles in large scales.

The first example of silylarylation of activated alkenes with silanes is reported via selective activation of the Si–H/C–H bonds, which allows efficient access to silylated oxindoles through a free-radical cascade process.

A scalable, operationally easy intermolecular hydrophosphinylation of various unactivated alkenes with H–P(O) compounds via an Ag(I)-initiated free radical process was developed. Mechanistic studies including electron-spin-resonance (ESR) and radical clock experiments suggest that atom transfer processes were involved in this system.

An I2O5-promoted decarboxylative trifluoromethylation of a series of cinnamic acids and their derivatives by using sodium trifluoromethanesulfinate in aqueous media was demonstrated. This strategy provides a safe and convenient access to various trifluoromethylated (E)-alkenes in a very high selectivity.An I2O5-promoted decarboxylative trifluoromethylation of a series of cinnamic acids and their derivatives by using sodium trifluoromethanesulfinate in aqueous media was demonstrated. This strategy provides a safe and convenient access to various trifluoromethylated (E)-alkenes in a very high selectivity.

We have developed an efficient Co(II)-catalyzed intramolecular C–O bond formation via cross dehydrogenative coupling (CDC) of acids with (sp3)C–H bond by using oxygen as the terminal oxidant. This strategy allows convenient access to a series of ring fused dihydro-benzoxazinones and its derivatives.We have developed an efficient Co(II)-catalyzed intramolecular C–O bond formation via cross dehydrogenative coupling (CDC) of acids with (sp3)C–H bond by using oxygen as the terminal oxidant. This strategy allows convenient access to a series of ring fused dihydro-benzoxazinones and its derivatives.

A free-radical cascade methylation/cyclization of a wide range of N-arylacrylamides and isocyanides is demonstrated by using dicumyl peroxide as the methylating reagent, which provides a convenient and selective access to various methylated N-heterocycles such as oxindoles and phenanthridines.

A scalable, selective, and operationally easy iodotrifluoromethylation of a wide range of alkenes and alkynes by using two simple and safe solids, sodium trifluoromethanesulfinate and iodine pentoxide, in aqueous medium has been developed. Mechanistic studies confirm that free-radical processes are involved in this system since the key radical intermediates such as CF3 and β-CF3 alkyl radicals have been clearly detected by spin trapping and electron spin resonance.

An I2O5-promoted free-radical cascade trifluoromethylation/cyclization of a broad range of N-arylmethacrylamides and enynes with sodium trifluoromethanesulfinate in aqueous medium has been achieved. This strategy allows highly selective access to a variety of CF3-containing oxindoles and pyrrolidines. Electron spin resonance (ESR) studies indicate that atom-transfer processes are involved in this system.

A copper-catalyzed free-radical cascade cyclization of isocyanides with simple alkanes and alcohols was developed, which allowed convenient access to various alkyl-substituted phenanthridines.

A copper-catalyzed alkylarylation of alkenes with simple alkanes was achieved, which not only provided an efficient method to prepare various alkyl-substituted oxindoles, but also represented a novel strategy for selective sp3 C–H functionalization/C–C bond formation via a free-radical cascade process. Additionally, selective activation of unactivated (sp3)C–H and (sp2)C–H bonds by one single step is achieved in this system, which would also provide a novel strategy for raising efficiency in C–H bond functionalization.

A dicumyl peroxide-initiated highly selective activation of the (sp3)C–H bond in dichloromethane (DCM, CH2Cl2) has been achieved, which allows efficient access to dichloronated oxindoles via a free-radical cascade process.

Transition metal-catalyzed oxidative dehydrogenative coupling reactions of Caryl–H bonds with Cvinyl–H bonds to generate a Caryl–Cvinyl bonds have been well developed in recent decades. However, only a few studies have focused on the direct Cvinyl–Cvinyl bond formation via double Cvinyl–H bond activation. Recent developments in this active area have been highlighted in this tutorial review.

A copper-catalyzed decarboxylative trifluoromethylation of various α,β-unsaturated carboxylic acids by using a stable and inexpensive solid, sodium trifluoromethanesulfinate (CF3SO2Na, Langlois reagent), was developed. In addition, an iron-catalyzed difluoromethylation of aryl-substituted acrylic acids by using zinc difluoromethanesulfinate (DFMS, (CF2HSO2)2Zn, Baran reagent) via a similar radical process was also achieved.

A bromo- and chlorodecarboxylation of various aromatic carboxylic acids catalyzed by Pd(II) has been developed in this work. A series of electron-rich arenecarboxylic acids gave the corresponding decarboxylative monohalogenation products under the typical reaction conditions.A bromo- and chlorodecarboxylation of various aromatic carboxylic acids catalyzed by Pd(II) has been developed in this work. A series of electron-rich arenecarboxylic acids gave the corresponding decarboxylative monohalogenation products under the typical reaction conditions.

A copper-catalyzed decarboxylative coupling of vinylic carboxylic acids with simple alcohols, ethers, and hydrocarbons was achieved. In the past decades, most of the sp3 α-C–H activation/C–C bond formation reactions proceeded via an addition of a α-hydroxy carbon-centered radical to heterocycles, alkenes, and alkynes. The present system exhibits a novel pathway for the functionalization of various sp3 C–H bonds via radical addition–elimination of aryl-substituted vinyl carboxylic acids. This strategy allows for rapid and selective access to a variety of (E)-alkenes such as allylic alcohols, allylic ethers, and substituted styrenes. In addition, this procedure could be scaled up to gram level, which would be useful to prepare natural products and pharmaceuticals that contain chromene and its derivatives.

An unexpected Cu-catalyzed oxidative cleavage of the C(sp3)–C(sp3) bond in glycol ethers by using air or molecular oxygen as the terminal stoichiometric oxidant is demonstrated. As a result, the corresponding α-acyloxy ethers and formates of 1,2-ethanediol are formed by direct coupling of carboxylic acids and aldehydes with glycol ethers under the reaction conditions. This method represents the first example of Cu-catalyzed aerobic cleavage of saturated C–C bond in ethers.

This work demonstrates a general and efficient method to prepare conjugated dienes by Pd(II)-catalyzed direct olefination of unactivated alkenes with allylic esters and acrylates via vinylic C–H activation. Various aryl and heteroaryl alkenes as well as aliphatic alkenes all give the desired linear 1,3-butadienes with retention of the traditional leaving groups such as OAc and other carboxylic acid ester groups.

A direct Pd(II)-catalyzed olefination of furans and thiophenes with allyl esters is demonstrated. Under the typical conditions, the dehydrogenative Heck coupling reactions of heteroarenes with allylic esters proceeded via a β-H elimination rather than a β-OAc elimination to give the corresponding γ-substituted allylic esters.

We summarized here the recent developments in the iron-catalyzed C-C bond formation via the polar reactions of alcohols with various carbon-centered nucleophiles. It is composed of three sections according to the categories of the C-centered nucleophiles such as C(sp3), C(sp2), and C(sp).

This work demonstrates an alternative method to prepare allylated arenes and aryl-substituted allylic esters via catalytic decarboxylative C–C bond formation using aromatic carboxylic acids and allylic halides and esters.

This work demonstrates an alternative method to prepare allylated arenes and aryl-substituted allylic esters via catalytic decarboxylative C–C bond formation using aromatic carboxylic acids and allylic halides and esters.

Transition metal-catalyzed oxidative dehydrogenative coupling reactions of Caryl–H bonds with Cvinyl–H bonds to generate a Caryl–Cvinyl bonds have been well developed in recent decades. However, only a few studies have focused on the direct Cvinyl–Cvinyl bond formation via double Cvinyl–H bond activation. Recent developments in this active area have been highlighted in this tutorial review.

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.

A copper-catalyzed decarboxylative coupling of vinylic carboxylic acids with simple alcohols, ethers, and hydrocarbons was achieved. In the past decades, most of the sp3 α-C–H activation/C–C bond formation reactions proceeded via an addition of a α-hydroxy carbon-centered radical to heterocycles, alkenes, and alkynes. The present system exhibits a novel pathway for the functionalization of various sp3 C–H bonds via radical addition–elimination of aryl-substituted vinyl carboxylic acids. This strategy allows for rapid and selective access to a variety of (E)-alkenes such as allylic alcohols, allylic ethers, and substituted styrenes. In addition, this procedure could be scaled up to gram level, which would be useful to prepare natural products and pharmaceuticals that contain chromene and its derivatives.

An efficient hydrocyanoalkylation of unactivated alkenes with alkyl nitriles was developed. Through this free-radical-initiated selective activation of the α-C(sp3)–H bond of acetonitriles, an anti-Markovnikov addition of an α-cyano C-centered radical to olefins has been achieved, which allows a facile and convenient access to functionalized nitriles in large scales.

As important and valuable alternatives to transition-metal-catalysis, free-radical strategies for C–Si bond construction via selective C–H/Si–H functionalization have been developed recently. These new reactions along with their suggested mechanisms are summarized and discussed here.