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 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.
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.
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.
Here we describe the one‐pot construction of the pyrrolo4,3,2‐dequinolinone scaffold by a cascade nitration/cyclization sequence of 1,7‐enynes with tBuONO and H2O. The cascade proceeds through alkene ...nitration, 1,7‐enyne 6‐exo‐trig cyclization, CH nitrations, and redox cyclization, and exhibits excellent functional group tolerance. The mechanism was investigated using in situ high‐resolution mass spectrometry (HR‐MS).
Nitration cascade: The pyrrolo4,3,2‐dequinolinone scaffold was synthesized by a metal‐free reaction of N‐(2‐(ethynyl)aryl)acrylamides, tert‐butyl nitrite and H2O. This cascade reaction is triggered by alkene nitration followed by 1,7‐enyne 6‐exo‐trig cyclization, CH nitrations, and redox cyclization and forms the product in good yields.
Difunctionalization: Inexpensive and environmentally benign FeCl3 catalyzes the oxidative 1,2‐alkylarylation of activated alkenes with an aryl C(sp2)H bond and a C(sp3)H bond adjacent to a ...heteroatom. This reaction is a new strategy for the synthesis of oxindoles and makes use of DBU as ligand and TBHP as oxidant (see scheme, TBHP=tert‐butyl hydrogenperoxide).
A new iron‐facilitated silver‐mediated radical 1,2‐alkylarylation of styrenes with α‐carbonyl alkyl bromides and indoles is described, and two new C−C bonds were generated in a single step through a ...sequence of intermolecular C(sp3)−Br functionalization and C(sp2)−H functionalization across the alkenes. This method provides an efficient access to alkylated indoles with broad substrate scope and excellent selectivity.
Bridging alkene: An intermolecular arene C(sp2)−H functionalization strategy is established for the radical 1,2‐alkylarylation of styrenes with α‐carbonyl alkyl bromides and indoles using iron as the catalyst and silver as the promotor. This method enables the formation of two C−C bonds in a single reaction. acac=acetylacetonate.
A novel copper‐catalyzed oxidative alkylation of α‐amino carbonyl compounds with ethers has been established for the selective synthesis of α‐etherized α‐amino carbonyl compounds. This oxidative ...alkylation is achieved by dual C(sp3)H bond oxidative cross‐coupling, and its scope is expanded to α‐amino ketones, α‐amino esters and α‐amino amides.
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