Electrochemical Selenylative Carbannulation of Biaryl Ynones to Seleno-Dibenzocycloheptenones/Spiro[5.5]Trienones

Carbonylative cyclization of biaryl enones with aldehydes and oxamic acids

An oxidative radical-promoted carbonylative cyclization strategy for the synthesis of phenanthren-9-(10H)-one frameworks from biaryl enones using aldehydes as the carbonyl radical sources is disclosed. The reaction proceeds through a sequential addition of a carbonyl radical to the olefin followed by cyclization with an aryl ring. The method is further extended to carbamoyl radicals generated from oxamic acids to access the corresponding phenanthrenones with amide functionalities.

BBr3-mediated dearomative spirocyclization of biaryl ynones: facile access to spiro[5.5]dienones

This report covers boron tribromide (BBr3) mediated dearomative spirocyclization of biaryl ynones. The direct synthesis of spiro[5.5]dienones with a tri-substituted double bond is described for the first time in this paper. The scope of the reaction is broad and the spirocyclic products were obtained in moderate to good yields.

Electrochemical Arene Radical Cation Promoted Spirocyclization of Biaryl Ynones: Access to Alkoxylated Spiro[5,5]trienones

Herein, a novel electrochemical arene radical cation promoted dearomative spirocyclization of biaryl ynones with alcohols is described, providing a conceptually novel transformation mode for producing diverse alkoxylated spiro[5,5]trienones. The catalyst- and chemical-oxidant-free spirocyclization protocol features broad substrate scope and high functional group tolerance. Mechanistic studies reveal that the generation of arene radical cation via anodic single-electron oxidation is crucial, with sequential 6-endo-dig cyclization, dissociation of hemiketal, anodic oxidation, and nucleophilic attack of alcohols.

Seleno/Thio-functionalized ipso-Annulation of N-Propiolyl-2-arylbenzimidazole to Construct Azaspiro[5,5]undecatrienones

Till date, the ipso-cyclization of propiolamides is limited to provide azaspiro[4,5]decatrienones. Herein, we present the first example of ipso-carbocyclization, leading to azaspiro[5,5]-undecatrienones from N-propiolyl-2-arylbenzimidazoles, involving both the radical-based and electrophilic reactions. This report establishes an access to a wide range of chalcogenated (SCN/SCF3/SePh) benzimidazo-fused azaspiro[5,5]undecatrienones in good yields.

ipso-Cyclization of unactivated biaryl ynones leading to thio-functionalized spirocyclic enones

Ceric ammonium nitrate (CAN)-promoted oxidative ipso-cyclization of unactivated biaryl ynones with S-centered radicals (SCN/SCF3) to access spiro[5,5]trienones has been established. This approach displayed excellent regioselectivity towards spirocyclization and tolerated a variety of functional groups. Dearomatization of hitherto unknown aryl/heteroaryl groups is also disclosed. DMSO is employed as a low-toxicity, inexpensive solvent as well as a source of oxygen.

Visible Light Promoted Brominative Dearomatization of Biaryl Ynones to Spirocycles

Bromine induced spiro cyclization of biaryl ynones facilitated the synthesis of spiro[5,5]trienones suitable for extended functionality at the C(3') position. Herein, a step-economic photo-oxidative brominative carbannulation of biaryl ynones employing ammonium bromide and riboflavin tetraacetate (RFTA) has been developed. The reactivity between distal phenyl C-H activated ortho-annulation and dearomative ipso-annulation is well exemplified. The eminent features of the methodology include metal-free, external additive free, low-loading photocatalyst (0.1 mol %), and use of a simple precursor.

Photo- or Electrochemical Cyclization of Dienes with Diselenides to Access Seleno-Benzo[b]azepines

A cascade selenylation/cyclization of dienes with diselenides has been realized under visible-light irradiation or electrolysis conditions. Employing O₂ or electricity as a "green" oxidant, this protocol provides a green and efficient method for an array of biologically important seleno-benzo[b]azepine derivatives in moderate to good yields. The direct sunlight irradiation and gram-scale reaction render the approach practical and attractive.

CAN-Promoted Thiolative ipso-Annulation of Unactivated N-Benzyl Acrylamides: Access to SCN/SCF3/SO2Ar Containing Azaspirocycles

A variety of acrylamides holding an unactivated N-benzyl group underwent dearomative ipso-cyclization induced by sulfur-centered radicals (SCN/ SCF₃/ SO₂Ar) in the presence of ceric ammonium nitrate (CAN) as the oxidant to furnish azaspirocycles in good yields. This is the first report on ipso-dearomatization of N-benzyl acrylamides that proceeds without a substituent at the para-position of the aromatic ring. The developed conditions are also found to be suitable for substrates holding substituents such as F, NO₂, OMe, OH, and OAc at the para-position. The reaction features water as the source of oxygen, is compatible with a variety of functional groups, and proceeds in a short time.

Nitro-Spirocyclization of Biaryl Ynones with tert-Butyl Nitrite: Access to NO2-Substituted Spiro[5,5]trienones

A metal/peroxide-free involved simple cascade 6-exo-trig spirocyclization of tert-butyl nitrite with biaryl ynones has been finished, which resulted in various NO₂-modified spiro[5,5]trienones with good regioselectivity/yields. A variety of scaled-up experiments, reduction/epoxidation operations, and mechanistic studies were performed to verify the merits and spirocyclization process of this radical system. Finally, the structure of the spirocycles was confirmed by single-crystal X-ray diffraction.

Radical selenylative cyclization of trifluoromethyl propargyl imines for the synthesis of trifluoromethyl- and seleno-azaspiro[4,5]-tetraenones and quinolines

A radical selenylative cyclization of trifluoromethyl propargyl imines with diselenides for the regiodivergent construction of diversely functionalized azaspiro[4,5]-tetraenones and quinolines has been developed, which enables dual incorporation of CF₃ and Se groups into heterocycles in a one-pot reaction. When using Oxone as a green oxidant, the reaction proceeds through oxidative dearomative ipso-annulation or intramolecular ortho-annulation exhibiting good regioselectivity. The synthetic utility of this method is demonstrated by a scale-up reaction and further modification of the obtained products.

Recent advances in electrooxidative radical transformations of alkynes

During the past few years, electrochemical oxidative reactions through radical intermediates have emerged as an environmentally-benign, powerful platform for the facile formation of C–E (E = C, N, S, Se, O and Hal) bonds through single-electron-transfer (SET) processes at the electrodes. Functionalized unsaturated molecules and unusual structural motifs can, for instance, be directly constructed under exceedingly mild reaction conditions through initial radical attack onto alkynes. This minireview highlights the recent advances in electrooxidation in radical reactions until June 2022, with a particular focus on radical additions onto alkynes.

Access to Diverse Seleno-spirocyclohexadienones via Ag(II)-Catalyzed Selenylative ipso-Annulation with Se and Boronic Acids

An efficient and straightforward synthesis of diversified seleno-azaspiro-2,5-cyclohexadienones from N-(4-methoxy aryl)propiolamides using elemental selenium and boronic acids has been demonstrated. The reaction proceeds through silver-catalyzed oxidative dearomatization in the presence of potassium persulfate (K₂S₂O₈) as the oxidant. Further, this approach was extended to N-(4-methoxy aryl)propiolates and biaryl ynones to access the corresponding selenylated oxospiro-2,5-cyclohexadienones and spiro[5,5]trienones, respectively. The present three-component method offers the diverse substitutions on selenium involving two C-Se and one C-C bond formations.

Synthesis of Spiro[5.5]trienones- and Spiro[4.5]trienones-Fused Selenocyanates via Electrophilic Selenocyanogen Cyclization and Dearomative Spirocyclization

A practical strategy for the synthesis of spiro[5.5]trienones-fused selenocyanates and spiro[4.5]trienones-fused selenocyanates through electrophilic selenocyanogen cyclization and dearomative spirocyclization is reported. This approach was conducted under mild conditions with broad substrate scope and good functional group tolerance. The utility of this procedure is exhibited in the late-stage functionalization of nature product and drug molecules.

Copper(II)-catalyzed oxidative ipso-annulation of N-arylpropiolamides and biaryl ynones with 1,3-diketones: construction of diketoalkyl spiro-trienones

An unprecedented copper-catalyzed ipso-annulation reaction of N-(p-methoxyaryl)propiolamides with 1,3-diketones has been developed, which enables the assembly of diketoalkylated spiro[4.5]trienones involving oxidative dearomatization in the presence of ammonium persulfate [(NH₄)₂S₂O₈] as the oxidant. This protocol was extended to biaryl ynones, efficiently affording the diketoalkylated spiro[5.5]trienones in good yields. The significance of the diketoalkyl functionality has been illustrated by further transformation into 3-pyrazoyl spiro-trienone, a structurally unique motif.

FeCl3-mediated selenylative benzannulation of aryl alkynones to 3-selenyl β-naphthols

An efficient selenylative cyclization of aryl-alkynones with diselenides in the presence of iron(III)chloride at room temperature to prepare 3-seleno-2-naphthols in good yields has been described. Furthermore, the resulting products were transformed into selenyl-naphthofuran and selenyl-1,2-naphthoquinone derivatives.

K2S2O8/I2-Promoted Electrophilic Selenylative Cyclization To Access Seleno-Benzo[b]azepines

A novel and simple organoselenium-involved 7-membered cyclization to access diverse seleno-benzo[b]azepines has been developed. This protocol involves an electrophilic cyclization process and is accomplished under mild conditions. Discussion of the mechanism rationalizes the regioselectivity observed in transformation. The studies of further transformation of seleno-benzo[b]azepines and large-scale experiment reveal the promising utility of this methodology.

Synthesis of Seleno-Dibenzocycloheptenones/Spiro[5.5]Trienones by Radical Cyclization of Biaryl Ynones

We report herein an alternative method for the synthesis of seleno-dibenzocycloheptenones and seleno-spiro[5.5]trienones through the radical cyclization of biaryl ynones in the presence of diorganyl diselenides, using Oxone as a green oxidizing agent. The reactions were conducted using acetonitrile as the solvent in a sealed tube at 100 °C. The protocol is operationally simple and scalable, exhibits high regioselectivity, and allows the synthesis of 24 dibenzocycloheptenones/spiro[5.5]trienones in yields of up to 99%, 17 of which are unpublished compounds. Additionally, synthetic transformations of the prepared compounds, such as oxidation and reduction reactions, are demonstrated.

Regio- and stereoselective electrochemical selenoalkylation of alkynes with 1,3-dicarbonyl compounds and diselenides

A regio- and stereoselective electrochemical approach for the selenoalkylation of alkynes with 1,3-dicarbonyl compounds and diselenides has been developed.

Rapid synthesis of spirodienones via electrochemical dearomative spirocyclization in flow

An electrochemical dearomative spirocyclization in flow has been developed, featuring the use of electrons as the clean oxidant in a minimum amount of electrolytes to afford diverse spirodienones in a short reaction time.

Selective polychloromethylation and halogenation of alkynes with polyhaloalkanes

We disclosed a selective polychloromethylation and halogenation reaction of alkynes via a radical addition/spirocyclization cascade sequence, in which applying polyhaloalkanes as the precursor of polyhalomethyl and halogen radical. Across this...

Radical spirocyclization of biaryl ynones for the construction of NO2-containing spiro[5.5]trienones

An efficient 6-exo-trig radical cascade reaction of biaryl ynones with NaNO2 was developed to afford nitro-functionalized spiro[5.5]trienones with yields of up to 88%.

Visible Light-Promoted Selenylative Spirocyclization of Biaryl Ynones toward the Formation of Selenated Spiro[5.5]trienones

A visible-light induced dearomative cascade cyclization of biaryl ynones with diselenides under photocatalyst and external additive-free conditions has been explored, giving a series of selenated spiro[5.5]trienones in moderate to good...