A new metal‐free radical 5‐exo‐dig cyclization of phenol‐linked 1,6‐enynes with O2, 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO), and tBuONO is described. With this general method, carbonylated ...benzofurans can be accessed through incorporation of two oxygen atoms into the product from O2 and TEMPO through dioxygen activation and oxidative cleavage of the NO bond, respectively.
Benzofurans are obtained by the tBuONO‐initiated radical 5‐exo‐dig cyclization of enynes under mild and metal‐free conditions. The two oxygen atoms that constitute the newly formed carbonyl groups of the benzofuran system originate from O2 and 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO), respectively.
A cobalt‐promoted electrochemical 1,2‐diarylation of alkenes with electron‐rich aromatic hydrocarbons via direct dual C−H functionalizations is described, which employs a radical relay strategy to ...produce polyaryl‐functionalized alkanes. Simply by using graphite rod cathode instead of platinum plate cathode, chemoselectivity of this radical relay strategy is shifted to the dehydrogenative 2+2+2 cycloaddition via 1,2‐diarylation, annulation, and dehydrogenation cascades leading to complex 11,12‐dihydroindolo2,3‐acarbazoles. Mechanistical studies indicate that a key step for the radical relay processes is transformations of the aromatic hydrocarbons to the aryl sp2‐hybridized carbon‐centered radicals via deprotonation of the corresponding aryl radical cation intermediates with bases.
Direct C−H functionalizations enable electrochemical diarylation of alkenes with aromatic hydrocarbons using a radical relay strategy toward polyaryl‐functionalized compounds. Chemoselectivity of the strategy relies on choice of both anode and cathode, which is shifted to the dehydogenative 2+2+2 cycloaddition of alkenes with indoles when using graphite rod as the anode and cathode.
A new metal‐free oxidative radical 2+2+1 carbocyclization of benzene‐linked 1,n‐enynes with two C(sp3)H bonds adjacent to the same heteroatom is described. This method achieves two C(sp3)H ...oxidative functionalizations and an annulation, thus providing efficient and general access to a variety of fused five‐membered carbocyclic hydrocarbons.
An oxidative functionalization of two C(sp3)H bonds adjacent to a same heteroatom for the 2+2+1 carbocyclization with benzene‐linked 1,n‐enynes is presented. This method successfully proceeds using a radical mechanism and provides straightforward access to a variety of fused five‐membered carbocyclic hydrocarbons. TBPB=tert‐butyl perbenzoate.
A new electrochemical intermolecular 1,2‐aminosulfonylation of alkenes with sulfinates and amines is achieved by utilizing balanced three‐component interactions and reactivity differentiation. This ...strategy can be applicable to a wide range of amines, including primary and secondary amines, thus enabling alkene aminosulfonylation for producing diverse functionalized 2‐sulfonylethan‐1‐amines without the need of additive redox catalysts, metal catalysts and chemical oxidants.
Radical‐initiated difunctionalization of alkenes is one of the most important methods in organic synthesis and medicinal chemistry, which can be applied to synthesize value complex compounds as well ...as structural motifs that found in bioactive natural products and pharmaceuticals. In recent years, impressive progress have been made in this area with ideal silver catalysis. Here, we summarize recent advances in silver‐mediated radical difunctionalization of alkenes for the formation of diverse bonds, including 1) two‐component radical difunctionalization reactions enabled by an intramolecular cyclization process toward various cyclic compounds and 2) three‐component radical difunctionalization reactions leading to complex linear compounds. These silver‐mediated radical alkene difunctionalization transformations are general initiated by different radicals, such as carbon‐, oxygen‐, sulfur‐, phosphinyl‐, and halogen‐center radicals, followed by terminated with nucleophiles to form two new bonds in a single reaction.
Ag catalysis: Recent advances in the silver‐mediated intermolecular radical 1,2‐difunctionalization of alkenes are summarized. These reaction are classified by the substrate type and radical regents. Two new C−C/C−C bonds, C−C/C−X bonds (X=F, O, S…) and C−X/C−X bonds (X=O, Br, I…) could be constructed in a single reaction.
The first iron‐catalyzed 1,2‐difunctionalization of styrenes and conjugated alkenes with silanes and either N or C, using an oxidative radical strategy, is described. Employing FeCl2 and ...di‐tert‐butyl peroxide allows divergent alkene 1,2‐difunctionalizations, including 1,2‐aminosilylation, 1,2‐arylsilylation, and 1,2‐alkylsilylation, which rely on a wide range of nucleophiles, namely, amines, amides, indoles, pyrroles, and 1,3‐dicarbonyls, thus providing a powerful platform for producing diverse silicon‐containing alkanes.
Iron clad: By employing FeCl2 and di‐tert‐butyl peroxide (DTBP), divergent alkene 1,2‐difunctionalization reactions, including 1,2‐aminosilylation, 1,2‐arylsilylation, and 1,2‐alkylsilylation, are achieved by using different nucleophiles. The method provides straightforward and practical access to 1‐amino‐2‐silylalkanes and other functionalized silicon‐containing alkanes with broad substrate scope and high selectivity.
We demonstrate a three‐component 1,2‐alkylsulfonylation of alkenes using sodium sulfinates and pyridinium salts through visible light photoredox catalysis, wherein heteroarenium salts are harnessed ...as radical acceptors via dearomatization. This reaction allows the simultaneous incorporation of sulfonyl and 1,4‐dihydropyridine groups across the C=C bonds to access various sulfonyl‐containing 1,4‐dihydropyridine derivatives with a broad substrate scope and represents a mechanistically distinct approach to achieve alkene difunctionalization through reductive single‐electron transfer.
Owing to their easy availability and cheapness, simple alkyl chlorides are good raw materials for introducing complex polychlorinated groups. Polychlorinated hydrocarbons units, such as di‐ or ...trichloromethyl groups, not only widely found in pesticide and bioactive molecule, but also can be as a precursor to converted into different functional groups such as −COOH, −CHO and −CO. The direct polychloroalkylation reaction by using simple alkyl chlrides has been considered to be an important tool for synthesizing complex polychlorinated compounds. This review summarizes recent developments, especially free radical strategies, in the polychloroalkylation of different substrates (such as 2‐acylpyridines, benzyl tertiary amines, alkenes, imine and 1,n‐enynes). We hope that this review provides a new perspective on this field and also provides a reference to develop environmentally friendly and sustainable methods.
We report an unprecedented, efficient nickel‐catalysed radical relay for the remote cross‐electrophile coupling of β‐bromo‐α‐benzylamino acid esters with aryl bromides via 1,4‐aryl ...migration/arylation cascades. β‐Bromo‐α‐benzylamino acid esters are considered as unique molecular scaffolds allowing for aryl migration reactions, which are conceptually novel variants for the radical Truce–Smiles rearrangement. This reaction enables the formation of two new C(sp3)−C(sp2) bonds using a bench‐stable Ni/bipyridine/Zn system featuring a broad substrate scope and excellent diastereoselectivity, which provides an effective platform for the remote aryl group migration and arylation of amino acid esters via redox‐neutral C(sp3)−C(sp2) bond cleavage. Mechanistically, this cascade reaction is accomplished by combining two powerful catalytic cycles consisting of a cross‐electrophile coupling and radical 1,4‐aryl migration through the generation of C(sp3)‐centred radical intermediates from the homolysis of C(sp3)−Br bonds and the switching of the transient alkyl radical into a robust α‐aminoalkyl radical.
A nickel‐catalysed radical relay strategy combines radical rearrangement and cross‐coupling via a C(sp3)‐centred radical, to produce valuable phenylalanine derivatives that are otherwise challenging to access. An N‐benzyl amino acid ester functions as a molecular scaffold for the aryl migration reaction. The synthetic method offers mild reaction conditions, high diastereoselectivity, and broad substrate scope.
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