Oxidative bicyclization of N-tethered 1,7-enynes toward polycyclic 3,4-dihydroquinolin-2(1H)-ones via site-selective decarboxylative C(sp3)–H functionalization

A new Ag-catalyzed oxidative bicyclization of N-tethered 1,7-enynes with alkylcarboxylic acids for forming 41 examples of polycyclic 3,4-dihydroquinolin-2(1H)-ones has been established using readily accessible K₂S₂O₈ as an oxidant.

Radical cascade cyclization of 1,n-enynes and diynes for the synthesis of carbocycles and heterocycles

This review highlights recent advances in radical cascade cyclization of 1,n-enynes and diynes for the construction of carbo- and heterocycles.

Radical cyclization of benzene-tethered 1,7-enynes with aryldiazonium tetrafluoroborates: a facile route to benzo[j]phenanthridines

A radical cyclization of benzene-tethered 1,7-enynes with aryldiazonium tetrafluoroborates in the presence of copper(ii) acetate and DABCO˙(SO₂)₂ is developed, leading to diverse benzo[j]phenanthridines.

Copper-catalyzed cascade annulation of unsaturated α-bromocarbonyls with enynals: a facile access to ketones from aldehydes

A Cu-catalyzed cascade annulation of enynals with alkenyl or alkynyl α-bromocarbonyls for the synthesis of various cyclohexenone-fused polycyclic compounds is described. Up to six new C-C bonds and four new carbocycles can be established in a single reaction, highlighting the high efficiency and step-economics of this protocol. This reaction offers a novel and straightforward entry to the synthesis of ketones featuring the addition of carbon radicals to aldehydes.

Photocatalyst-free hypervalent iodine reagent catalyzed decarboxylative acylarylation of acrylamides with α-oxocarboxylic acids driven by visible-light irradiation

A hypervalent iodine(iii) reagent catalyzed carbonylarylation of acrylamides with α-oxocarboxylic acids driven by visible-light without a photoredox catalyst has been developed. The reactions generate the corresponding products in good yields at room temperature. Experiments indicate that a blue LED (450-455 nm) is the most effective energy for the cleavage of the oxygen-iodine bond to initiate the reaction. Mechanistic studies further demonstrate that the reaction undergoes a cascade decarboxylative radical addition/cyclization process along with releasing CO2 and H2.

Various difunctionalizations of acrylamide: an efficient approach to synthesize oxindoles

In this review, we summarize the advancement and applications in the difunctionalization of acrylamide to synthesize oxindoles based on the mechanism.

Iron-catalyzed addition/cyclization cascade of activated alkenes with alcohols: access to carbonyl substituted quinoline-2,4-diones

Iron-catalyzed radical addition/cyclization cascade of o-cyanoarylacrylamides with alcohols has been developed for the synthesis of carbonyl substituted quinoline-2,4(1H,3H)-diones.

A general route to fluorinated 3,3-disubstituted 2-oxindoles via a photoinduced radical cyclization of N-arylacrylamides under catalyst-free conditions

A catalyst-free radical cyclization of N-arylacrylamides with fluorinated alkyl iodides or the Togni reagent enabled by photoenergy is reported, leading to fluorinated 2-oxindoles in good yields. The broad reaction scope is demonstrated with good functional group tolerance.

Copper-catalyzed alkylarylation of activated alkenes using isocyanides as the alkyl source: an efficient radical access to 3,3-dialkylated oxindoles

A novel copper-catalyzed oxidative cyclization of N-arylacrylamides for the synthesis of 3,3-dialkylated oxindoles is described using isocyanides as alkyl radical precursors.

Synthesis of isoxazoline-featured oxindoles by iminoxyl radical-promoted cascade oxyalkylation/alkylarylation of alkenes

Isoxazoline-featured oxindoles were synthesized by the reaction of β,γ-unsaturated ketoximes with N-arylacrylamides via iminoxyl radical-promoted cascade intra/intermolecular oxyalkylation/alkylarylation of alkenes.

Cyanomethylation of alkenes with C–H bond activation of acetonitrile: in situ generated diazonium salts as promoters without transition-metals

In situ generated diazonium salts were used as radical promoters for the C_sp3–H functionalization of acetonitrile without photocatalyst or transition-metal.

Synthesis of trifluoromethylated 3,4-dihydroquinolin-2(1H)-ones via a photo-induced radical cyclization of benzene-tethered 1,7-enynes with Togni reagent

A photoinduced radical cyclization of benzene-tethered 1,7-enynes with Togni reagent in the presence of sodium iodide is developed. This transformation works well without any metals or photo-redox catalysts at room temperature.

Acyl Radicals from Aromatic Carboxylic Acids by Means of Visible-Light Photoredox Catalysis

Simple and abundant carboxylic acids have been used as acyl radical precursor by means of visible-light photoredox catalysis. By the transient generation of a reactive anhydride intermediate, this redox-neutral approach offers a mild and rapid entry to high-value heterocyclic compounds without the need of UV irradiation, high temperature, high CO pressure, tin reagents, or peroxides.

Ascorbic Acid-Initiated Tandem Radical Cyclization of N-Arylacrylamides to Give 3,3-Disubstituted Oxindoles

An ascorbic acid-promoted and metal-free tandem room temperature cyclization of N-arylacrylamides with 4-nitrobenzenediazonium generated in situ was developed. This reaction proceeds smoothly through a radical mechanism and provides an environmentally friendly alternative approach to biologically active 3-alkyl-3-benzyloxindoles, avoiding the use of excess oxidants and light irradiation.

Iron-Catalyzed Convergent Radical Cyclization of Aldehydes with Two Alkenes to 3,4-Dihydropyrans

A novel convergent radical cyclization of an aldehyde with two alkenes has been developed. With this method, polyfunctionalized 3,4-dihydropyrans are built in an efficient and selective manner. The iron-catalyzed redox radical recombinations are proposed for the formation of a 3,4-dihydropyran skeleton.

Metal-free oxidative decarbonylative coupling of aromatic aldehydes with arenes: direct access to biaryls

A metal-free oxidative decarbonylative coupling of aromatic aldehydes with electron-rich or electron-deficient arenes to produce biaryl compounds was developed. This novel coupling was proposed to proceed via a non-chain radical homolytic aromatic substitution (HAS) type mechanism, based on the substrate scope, ortho-regioselectivity, radical trapping experiments and DFT calculation studies. With the ready availability of aromatic aldehydes and arenes, metal-free conditions should make this coupling attractive for the biaryl synthesis.