Synthesis of O-Heterocycle Spiro-Fused Cyclopentaquinolinones and Cyclopentaindenes through Visible Light-Induced Radical Cyclization Reactions

Electrochemical Aryl(alkyl)thiolation on α-C-H Bond of Ethers to Access O,S-Acetals

The efficient construction of a C-S bond is one of the important topics in organic synthesis. In this work, a cross-dehydrogenative coupling reaction between ether and thiophenols or thiols under electrochemical conditions was studied, and the acetal-O,S products were obtained in moderate to good yields. A free radical coupling mechanism was proposed. The reaction provided a simple protocol for the formation of C(sp3)-S bonds under transition-metal- and chemical oxidant-free conditions, and will have a good application prospect in organic synthesis and drug synthesis.

Copper-Catalyzed 1,4-Alkylarylation of 1,3-Enynes with Ethers and Aryl Boronic Acids Enabled via C(sp3)-H Functionalization

Herein, we present a copper-catalyzed, three-component intermolecular 1,4-alkylarylation of 1,3-enynes with ethers and aryl boronic acids. This method, driven by α-C(sp3)-H functionalization of the oxygen atom in ethers, regioselectively produces various tetrasubstituted allenes from simple, readily available precursors. Key features include mild reaction conditions and a simple catalytic system.

Cu/Pd-Catalyzed Domino Carbonylative Synthesis of Polycyclic Carbonyl-Containing Quinolin-2(1H)-one Scaffolds from α-Bromocarbonyls

A novel Cu/Pd-catalyzed domino radical cyclization and C-H carbonylation of α-bromocarbonyls has been developed, which enables the rapid incorporation of CO unit into polycyclic quinolin-2(1H)-one scaffolds. By using Mo(CO)6 as the CO source, the reaction proceeded smoothly to furnish various polycyclic carbonyl-containing quinolin-2(1H)-one derivatives in high yields. Notably, this method could be used in the late-stage modification of biologically active molecules such as estrone.

Formation of cyclopenta[c]quinolines through visible-light-induced photoredox cascade bis-annulations of 1,7-enynes with sulfoxonium ylides

A novel visible-light-driven photoredox-catalyzed cascade bicyclization of 1,7-enynes with aqueous sulfoxonium ylides is reported. The reaction is highly chemoselective with three new C-C bonds, two new rings, and an all-carbon quaternary stereocenter constructed in a one-pot fashion. This mild protocol features a remarkably broad substrate scope with good functional group tolerance, providing a general and practical approach to access various cyclopenta[c]quinolines.

Radical Cascade Reaction of Heterocyclic Ketene Aminals with Thiocyanates Promoted by Visible Light: Synthesis of Functionalized Fused 2-Iminothiazolines

Herein, a visible-light-promoted radical cascade cyclization of heterocyclic ketene aminals (HKAs) and thiocyanates was developed to access functionalized fused 2-iminothiazolines. This novel cascade reaction can be realized under only visible-light irradiation without the help of external photocatalysts, oxidants, and additives. These multicomponent cascade reactions demonstrate excellent selectivity for the Z-isomers and ensure the formation of the products only in their isomeric form. Preliminary mechanism investigations demonstrated that HKAs and thiocyanates can form electron donor-acceptor complexes for harvesting the energy of visible light to activate substrates and generate reactive radicals. This protocol can be used for synthesizing various natural-like products such as fused 2-iminothiazolines. This approach demonstrates multiple advantages such as commercially available substrates, convenient operation, environmentally friendly, mild conditions, and an efficient multicomponent reaction (2A + B).

Ruthenium and Iodine Anion Cocatalyzed Cascade Dihalogenation and Cyclization of Internal Alkyne-Tethered Cyclohexadienones with 1,2-Dihaloethanes

We have established an efficient ruthenium(II) and iodine anion cocatalyzed dihalogenation and cascade cyclization of internal alkyne-tethered cyclohexadienones, which stereoselectively afforded numerous dihalogenation products with a bioactive hydrobenzofuran skeleton in high yields under mild conditions. In this transformation, the reaction pathway was determined by the concentration of electrophilic iodine reagent, which also provided a strategy for control of the reaction selectivity. Furthermore, this method features the use of 1,2-dihaloroethane as the halogen source via iodine anion catalyst.

Synthesis of Acyl Cyclopentaquinolinones through Simultaneous Construction of the Heterocyclic Scaffold and Introduction of the Acyl Group

Presented herein is an effective and concise synthesis of acyl cyclopentaquinolinone derivatives via the cascade reactions of N-(o-ethynylaryl)acrylamides with α-diazo carbonyl compounds. The formation of product involves a visible light-induced radical formation from α-diazo carbonyl compound followed by its addition onto the acrylamide moiety to trigger double radical annulation, single-electron oxidation, and β-elimination. To our knowledge, this is the first example in which the cyclopentaquinolinone scaffold was constructed along with the introduction of an acyl group under visible light irradiation conditions. Compared with literature methods for similar purpose, this newly developed protocol has advantages such as readily accessible substrates, mild reaction conditions, valuable products, concise synthetic procedure, and high sustainability. With all these merits, this method is expected to find wide applications in the construction of related acyl heterocyclic skeletons.

Cp2Fe-Mediated Electrochemical Synthesis of Phosphorylated Oxindoles and Indolo[2,1-a]isoquinolin-6(5H)-ones

An efficient and environmentally friendly electrochemical synthesis of phosphorylated oxindoles and indolo[2,1-a]isoquinolin-6(5H)-ones mediated by readily available Cp2Fe has been developed, which illustrated a broad substrate scope and diverse functional group compatibility. This protocol featured an external oxidant-free process and was at room temperature, which was proposed to be driven by the anodic oxidation of Cp2Fe.