Radical relay cyclization/C-C bond formation of allyloxy-tethered aryl iodides with quinoxalin-2(1H)-ones via polysulfide anion photocatalysis.

A visible-light-induced radical relay cyclization/C-C bond formation of quinoxalin-2(1H)-ones with allyloxy-tethered aryl iodides using polysulfide anions as a photocatalyst is described. This protocol allows efficient access to a variety of complicated molecules bearing both quinoxalin-2(1H)-one and 2,3-dihydrobenzofuran motifs in high yields under mild reaction conditions with a broad range of substrates.

Visible-light-induced halocyclization of 2-alkynylthioanisoles with simple alkyl halides towards 3-halobenzo[b]thiophenes without an external photocatalyst.

A new strategy for the preparation of 3-halobenzo[b]thiophenes via a photo-driven halocyclization/demethylation of 2-alkynylthioanisoles with simple alkyl halides was developed. The reaction can proceed smoothly at room temperature under visible-light irradiation without any external photocatalyst, and the protocol has a range of advantages, including simplicity and mildness of the reaction conditions, good functional-group tolerance, and excellent yields of the products.

Photoinduced Radical Cyclization of 2-Alkynylthioanisoles with Disulfides without an External Photocatalyst.

An efficient strategy for the synthesis of 3-arylthiobenzo[b]thiophenes via a photodriven radical cyclization of 2-alkynylthioanisoles with disulfide was developed. The reaction proceeded smoothly under visible-light irradiation without any external photocatalyst and generated the desired products in high yields with good functional group tolerance.

Electrophilic Halospirocyclization of N-Benzylacrylamides to Access 4-Halomethyl-2-azaspiro[4.5]decanes.

An electrophilic spirocyclization of N-benzylacrylamides with N-halosuccinimides (NXS) as the halogenating reagents has been developed. This reaction is carried out at room temperature under simple conditions without relying on metal reagents, photochemistry, or electrochemistry, providing a fast and efficient route to synthesize a wide variety of 4-halomethyl-2-azaspiro[4.5]decanes with satisfactory yields. The approach is further highlighted through gram-scale synthesis and diverse transformations of the spiro products.

Metal-Free Synthesis of 2H-Indazole Skeletons by Photochemistry or Thermochemistry.

A simple and tuned synthesis of a 2H-indazole skeleton under metal-free conditions was developed. Under visible-light irradiation at room temperature, 2-((aryl/alkyl/H)ethynyl))aryltriazenes reacted with arylsulfinic acids to afford 3-functionalized 2H-indazoles without extra photocatalyst via an electron donor-acceptor complex. In the presence of arylsulfinic acid, 2-(ethynyl)aryltriazenes underwent an intramolecular oxidation/cyclization to provide 2H-indazole-3-carbaldehydes at 50 °C in air.

Microwave-promoted radical addition/cyclization of biaryl vinyl ketones with diacyl peroxides in water under metal-free conditions.

This communication reports an efficient microwave-promoted radical addition/cyclization reaction of biaryl vinyl ketones with diacyl peroxides in water under metal-free conditions. A series of 10-methyl-10-benzyl(alkyl)phenanthren-9(10H)-ones were obtained in high yields with good functional group tolerance.

Electrochemical monofluoroalkylation cyclization of N-arylacrylamides to construct monofluorinated 2-oxindoles.

An electrochemical monofluoroalkylation cyclization of N-arylacrylamides to synthesize monofluorinated 2-oxindoles has been developed, which employs common dimethyl 2-fluoromalonate as a monofluoroalkyl radical precursor and obviates the use of prefunctionalized monofluoroalkylation reagents and sacrificial oxidants. A variety of monofluorinated nitrogen-containing heterocyclic compounds were efficiently obtained with satisfactory yields from readily available materials.

Synthesis of Fully Substituted 5-(o-Hydroxybenzoyl)imidazoles via Iodine-Promoted Domino Reaction of Aurones with Amidines.

An iodine-promoted domino reaction of aurones with amidines has been successfully explored. The reaction proceeds in a consecutive manner containing Michael addition, iodination, cyclization from intramolecular nucleophilic substitution, and dehydrogenative aromatization from spiro ring opening. Following this novel strategy, a variety of 1,2,4-trisubstituted 5-(o-hydroxybenzoyl)imidazoles were efficiently synthesized in moderate to good yields from readily available starting materials. A plausible mechanism has been proposed.

Synthesis of polychloromethylated and halogenated spiro[5,5]trienones via dearomative spirocyclization of biaryl ynones.

We disclosed a selective polychloromethylation and halogenation reaction of alkynes via a radical addition/spirocyclization cascade sequence, in which polyhaloalkanes were used as the precursor for polyhalomethyl and halogen radicals. Using this strategy, a series of valuable halogen-, CHCl2- or CCl3-containing spiro[5,5]trienones were synthesized in good yields with good functional group tolerance in one pot under simple and mild conditions. It is noted that an unprecedented halogenation instead of dibromomethylation was achieved when CH2Br2 was used in this work.

Electrochemical Dearomatizing Spirocyclization of Alkynes with Dimethyl 2-Benzylmalonates to Spiro[4.5]deca-trienones.

An electrochemical dearomatizing spirocyclization of alkynes with dimethyl 2-benzylmalonates for the preparation of spiro[4.5]deca-trienones has been developed. This approach adopts ferrocene (Cp2Fe) as an electrocatalyst to produce carbon-centered radical intermediates from C-H-based malonates, which obviates the forthputting of noble-metal reagents, sacrificial chemical oxidants and 2-bromomalonates. A wide variety of spiro compounds are efficiently prepared with satisfactory results under mild conditions.

Microwave-accelerated and benzoyl peroxide (BPO)-initiated cyclization of 1,5-enynes having cyano groups with cyclic alkanes under metal-free conditions.

A novel and efficient method for preparing exocyclic indan derivatives, with this method involving benzoyl peroxide (BPO)-initiated cyclization of 1,5-enynes having cyano groups with simple cyclic alkanes under microwave irradiation, has been developed. The presented approach showed advantages of simple conditions, an environmentally friendly protocol, good functional-group tolerance, and high yields of products.

Electrochemical Regioselective Cross-Dehydrogenative Coupling of Indoles with Xanthenes.

An electrochemical cross-dehydrogenative coupling of indoles with xanthenes has been established at room temperature. This coupling reaction could proceed in the absence of any catalyst or external oxidant, and generate the indole derivatives in moderate yields. Mechanistic experiments support that a radical pathway maybe involved in this reaction system.

Merging cobalt and photoredox catalysis for the C8-H alkoxylation of 1-naphthylamine derivatives with alcohols.

A combined cobalt and photoredox catalysis system to realize the C8-H alkoxylation of 1-naphthylamine derivatives with alcohols was developed. Using commercially available alkyl alcohols as raw materials and Co(OAc)2 and rose bengal as catalysts, 1-naphthylamine derivatives reacted with alcohols to generate the corresponding C8-H alkoxylation products in good yields.

Direct Synthesis of Sulfinylated Benzofulvenes via BF3·Et2O-Promoted Cascade Reactions of Arylsulfinic Acids with 1,3-Enynes.

A novel and efficient method for the selective synthesis of sulfinylated benzofulvenes has been developed through the BF3·Et2O-promoted electrophilic addition/cyclization of 1,3-enynes. This metal-free cascade reaction employs readily accessible arylsulfinic acids as sulfinyl cation sources at room temperature and provides a wide range of functionalized benzofulvenes in good to excellent yields under mild conditions.

Synthesis of Spirolactones via a BF3·Et2O-Promoted Cascade Annulation of α-Keto Acids and 1,3-Enynes.

A novel and effective method for the synthesis of spirolactones from readily available α-keto acids and 1,3-enynes is developed via a BF3·Et2O-promoted cascade annulation. This sequential process is conducted at room temperature, and it provides the functionalized spirolactones in good to excellent yield under metal-free conditions.

Site-Selective Electrochemical C-H Cyanation of Indoles.

An electrochemical approach for the site-selective C-H cyanation of indoles employing readily available TMSCN as cyano source has been developed. The electrosynthesis relies on the tris(4-bromophenyl)amine as a redox catalyst, which achieves better yield and regioselectivity. A variety of C2- and C3-cyanated indoles were obtained in satisfactory yields. The reactions are conducted in a simple undivided cell at room temperature and obviate the need for transition-metal reagent and chemical oxidant.

Metal-free dearomative [5+2]/[2+2] cycloaddition of 1H-indoles with ortho-(trimethylsilyl)aryl triflates.

Herein, we report a mild dearomative [5+2]/[2+2] cycloaddition of 1H-indoles with ortho-(trimethylsilyl)aryl triflates. The unique [5+2] cycloaddition enables the synthesis of a series of dibenzo[b,e]azepine derivatives in moderate to good yields. Increasing the steric hindrance at the C2-position of 1H-indoles leads to the [2+2] cycloaddition. Mechanistic investigations support that the reaction of 1H-indoles with arynes undergoes a [2+2] cycloaddition step, followed by a ring expansion to the [5+2] cycloaddition product.

Facile synthesis of carbamoylated benzimidazo[2,1-a]isoquinolin-6(5H)-ones via radical cascade cyclization under metal-free conditions.

A highly efficient synthesis of carbamoylated benzimidazo[2,1-a]isoquinolin-6(5H)-ones using 2-arylbenzoimidazoles and oxamic acids was developed. This strategy tolerated various substrates as the starting materials to generate the corresponding products in good yields under metal-free conditions.

Hydrogen-Bond-Assisted Sequential Reaction of Silyl Glyoxylates: Stereoselective Synthesis of Silyl Enol Ethers.

A novel hydrogen-bond-assisted sequential reaction of silyl glyoxylates is described. This method provides an efficient strategy for the synthesis of silyl enol ethers with high selectivity. In these transformations, hydrogen bonds from 2-nitroethanol and its derivatives are critical to the stereochemical outcome. Both E- and Z-isomers are achieved via Henry reaction/Brook rearrangement/elimination and Henry reaction/Brook rearrangement/retro-Henry reaction/elimination processes, respectively (up to 99:1 Z-selectivity, and 9.2:1 E-selectivity).

Visible-Light-Induced Decarboxylative Cyclization/Hydrogenation Cascade Reaction to Access Phenanthridin-6-yl(aryl)methanol by an Electron Donor-Acceptor Complex.

A novel and efficient visible-light-induced decarboxylative cyclization/hydrogenation cascade reaction of α-oxocarboxylic acids and 2-isocyanobiaryls has been developed. Without the need of any external photosensitizer, oxidant, and reductant, this method offers a mild and green approach for the synthesis of diverse alcohols in moderate to good yields. A mechanism indicated that an electron donor-acceptor complex-driven decarboxylation, radical addition/cyclization, and in situ photochemical reduction of ketones to alcohols could be involved in the reaction.