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

Benzoic Acid Serves as Precursor of Catalytic HAT Reagent in a Two-Molecule Photoredox System

The photoinduced regioselective HAT reactions of acetals, ethers, and alcohols using benzoic acids in a two-molecule photoredox system led to the formation of new C-C bonds with alkenes under mild conditions. Aryl carboxy radicals generated from benzoic acids in a two-molecule photoredox system can function as catalytic HAT reagents, even though an excess amount of a hydrogen donor substrate is required. Various acetals, ethers, alcohols, and alkenes can be employed in the photoreaction to provide both high yields of adducts and high recoveries of benzoic acids.

Visible-Light-Promoted Deoxygenative Alkylation of Quinoxalin-2(1H)-ones with Activated Alcohols

A one-pot strategy for deoxygenative alkylation of alcohols with quinoxalin-2(1H)-ones was developed by using xanthate salts as alcohol-activating groups for radical generation in the presence of tricyclohexylphosphine under visible-light-promoted conditions. The remarkable features of this reaction include a broad substrate scope, excellent functional group tolerance, mild conditions, and simple operation. Moreover, the synthetic utility of this reaction was validated by the success of two-step one-pot reactions, scale-up synthesis, and chemoselective radical monodeoxygenation of diols.

Structure-guided insights into non-catalytic (α-hydroxy)alkylation of olefins with alcohols

New experimental data on the mutual reactivity of alcohols and olefins were obtained at 350 °C and a surrogate for olefins was suggested in return.

C(sp3)–H Bond Functionalization of Alcohols, Ketones, Nitriles, Ethers and Amides using tert-Butyl Hydroperoxide as a Radical Initiator

The C(sp3)–H bond is found widely in organic molecules. Recently, the functionalization of C(sp3)–H bonds has developed into a powerful tool for augmenting highly functionalized frameworks in organic synthesis. Based on the results obtained in our group, the present account mainly summarizes recent progress on the functionalization of C(sp3)–H bonds of aliphatic alcohols, ketones, alkyl nitriles, and ethers with styrene or cinnamic acid using tert-butyl hydroperoxide (TBHP) as a radical initiator.

1 Introduction

2 Oxidative Coupling of Styrenes with C(sp3)–H Bonds

3 Decarboxylative Cross-Couplings of α,β-Unsaturated Carboxylic Acids with C(sp3)–H Bonds

4 Conclusions

Electrochemical oxidative synthesis of 2-benzoylquinazolin-4(3H)-one via C(sp3)–H amination under metal-free conditions

An electrochemically induced C(sp3)–H amination of 2-aminobenzamides with ketones using TBAI as a catalyst was developed, and provided 2-benzoylquinazolin-4(3H)-ones under metal-free conditions.

Azobisisobutyronitrile-Initiated Oxidative C-H Functionalization of Simple Alcohols with Diaryl(arylethynyl)phosphine Oxides: A Metal-Free Approach toward Hydroxymethyl Benzo[b]phosphole Oxides and 6H-Indeno[2,1-b]phosphindole 5-Oxide Derivatives

The first metal-free and facile radical addition/cyclization of simple alcohols with diaryl(arylethynyl)phosphine oxides has been described with azobisisobutyronitrile as a radical initiator, affording an efficient and one-pot procedure to access a new class of hydroxymethyl benzo[b]phosphole oxides and 6H-indeno[2,1-b]phosphindole 5-oxides for potential application in organic materials via sequential C(sp³)-H/C(sp²)-H functionalization. The method employs easily accessible starting materials and is endowed with high regioselectivity and broad functional-group tolerance.

The Ag-promoted α-C-H arylation of alcohols

We herein report the functionalization of α-C-H in alcohols through cross-dehydrogenative coupling reactions. Selectfluor was used as a mild oxidant. In situ-generated HF participated in the reaction and no external strong acid was necessary. A variety of heteroaryl-substituted alcohols were achieved with good yields and with good functional group tolerance.

Recent advances in the direct functionalization of quinoxalin-2(1H)-ones

The direct C3-functionalization of quinoxalin-2(1H)-ones via C-H bond activation has recently attracted considerable attention, due to their diverse biological activities and chemical properties. This review will focus on the recent achievements, mainly including arylation, alkylation, acylation, alkoxycarbonylation, amination, amidation and phosphonation of quinoxalin-2(1H)-ones. Their mechanisms are also discussed.

Visible light-induced direct α C-H functionalization of alcohols

Considering the synthetic value of introducing active alcoholic hydroxyl group, developing C-H functionalization of alcohols is of significance. Herein, we present a photochemical method that under visible light irradiation, selectfluor can effectively promote the oxidative cross-coupling between alcohols and heteroarenes without the external photocatalysis, achieving the selective α sp³ C-H arylation of alcohol, even in the presence of ether. The N-F activation of selectfluor under blue LEDs irradiation is evidenced by electron paramagnetic resonance (EPR) study, which is the key process for the oxidative activation of α sp³ C-H alcohols. The observed reactivity may have significant implications for chemical transformations.

Site-Selective Cu-Catalyzed Alkylation of α-Amino Acids and Peptides toward the Assembly of Quaternary Centers

The Cu^I -catalyzed selective α-alkylation of α-amino acid and peptide derivatives with 2-alkyl-1,3-dioxolanes is reported. This oxidative coupling is distinguished by its site-specificity, high diastereoselectivity, and chirality preservation and exhibits absolute chemoselectivity for N-aryl glycine motifs over other amino acid units. Collectively, the method allows for the assembly of challenging quaternary centers, as well as compounds derived from natural products of high structural complexity, which may provide ample opportunities for late-stage functionalization of peptides.

Metal-free alcohol-directed regioselective heteroarylation of remote unactivated C(sp3)-H bonds

Construction of C–C bonds via alkoxy radical-mediated remote C(sp³)–H functionalization is largely unexplored, as it is a formidable challenge to directly generate alkoxy radicals from alcohols due to the high bond dissociation energy (BDE) of O–H bonds. Disclosed herein is a practical and elusive metal-free alcohol-directed heteroarylation of remote unactivated C(sp³)–H bonds. Phenyliodine bis(trifluoroacetate) (PIFA) is used as the only reagent to enable the coupling of alcohols and heteroaryls. Alkoxy radicals are readily generated from free alcohols under the irradiation of visible light, which trigger the regioselective hydrogen-atom transfer (HAT). A wide range of functional groups are compatible with the mild reaction conditions. Two unactivated C–H bonds are cleaved and one new C–C bond is constructed during the reaction. This protocol provides an efficient strategy for the late-stage functionalization of alcohols and heteroaryls.

Direct remote C–H functionalization of aliphatic alcohols via alkoxy radicals is largely unexplored. Here, the authors report the C(sp³)-heteroaryl bond formation in aliphatic alcohols mediated by alkoxy radicals formed with a hypervalent iodine reagent.

Metal-free α-alkylation of alcohols with para-quinone methides

A metal-free α-alkylation of alcohols with para-quinone methides (p-QMs) for accessing alcohol-containing phenols and dihydroisocoumarins has been developed.

Copper-catalyzed oxidative coupling of quinoxalin-2(1H)-ones with alcohols: access to hydroxyalkylation of quinoxalin-2(1H)-ones

An efficient protocol for the synthesis of hydroxyl-containing quinoxalin-2(1H)-ones has been developed via the copper-catalyzed cross-coupling reaction of quinoxalin-2(1H)-ones with alcohols with moderate to good yields.

Site-specific hydroxyalkylation of chromones via alcohol mediated Minisci-type radical conjugate addition

The metal-free C2-functionalization of chromones with alcohols and ethers via radical sp³ C–H activation was developed.

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).

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.

Cascade alkylarylation of substituted N-allylbenzamides for the construction of dihydroisoquinolin-1(2H)-ones and isoquinoline-1,3(2H,4H)-diones

An oxidative reaction for the synthesis of 4-alkyl-substituted dihydroisoquinolin-1(2H)-ones with N-allylbenzamide derivatives as starting materials has been developed. The radical alkylarylation reaction proceeds through a sequence of alkylation and intramolecular cyclization. The substituent on the C–C double bond was found to play a key role for the progress of the reaction to give the expected products with good chemical yields. Additionally, N-methacryloylbenzamides were also suitable substrates for the current reaction and provided the alkyl-substituted isoquinoline-1,3(2H,4H)-diones in good yield.

Metal-free oxidative functionalization of C(sp3)–H of ketones and alcohols for the synthesis of isoquinolinonediones

A metal-free alkyl radical induced addition/cyclization reaction of acrylamide has been developed.

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.

Direct transformation of amides: a one-pot reductive Ugi-type three-component reaction of secondary amides

An efficient reductive Ugi-type reaction employing common secondary amides as starting materials has been established. The reaction exhibited a broad substrate scope, good chemoselectivity and functional group tolerance.

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.