Iron-Catalyzed Dearomatization of Biaryl Ynones with Aldehydes via Double C-H Functionalization in Eco-Benign Solvents: Highly Atom-Economical Synthesis of Acylated Spiro[5.5]trienones

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.

Regioselective synthesis of N-containing polycyclic compounds via radical annulation cyclization of 1,7-dienes with aldehydes

A convenient method for oxidant-promoted radical cascade acylation or decarbonylative alkylation of 1,7-dienes with aldehydes has been established. This method allows for the rapid construction of N-containing polycyclic skeletons in a highly regio- and stereoselective manner. This transformation provides a simple and efficient method for the preparation of a range of tetrahydro-6H-indeno[2,1-c]quinolinone derivatives by sequential formation of three new carbon-carbon bonds. Additionally, this radical cascade cyclization can selectively convert aldehydes into aroyl/primary aliphatic acyl radicals and secondary or tertiary alkyl radicals.

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.

Recent advances in radical thiocyanation cyclization or spirocyclization reactions

Organic thiocyanates are valuable biological moities and drug-building blocks. They can also transform effectively into thioethers, thiols, alkynyl thioethers, and thiocarbamates in synthetic chemistry. With respect to the merits of thiocyanates, many chemists and our research team have developed diverse strategies to access SCN-revised heterocycles/spirocycles via an effective radical cyclization process. Hence, this review article first describes the importance/application of thiocyanates. Subsequently, it summarizes the reaction conditions, substrate scopes, and plausible mechanism, respectively, of the excellent work stated above.

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.

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.

Dearomatization of Biaryls through Polarity Mismatched Radical Spirocyclization

Dearomatization reactions involving radical cyclizations can facilitate the synthesis of complex polycyclic systems that find applications in medicinal chemistry and natural product synthesis. Here we employ redox-neutral photocatalysis to affect a radical spirocyclization that transforms biaryls into spirocyclic cyclohexadienones under mild reaction conditions. In a departure from previously reported methods, our work demonstrates the polarity mismatched addition of a nucleophilic radical to an electron rich arene, and allows the regioselective synthesis of 2,4- or 2,5-cyclohexadienones with broad functional group tolerance. By transforming biaryls into spirocycles, our methodology accesses underexplored three-dimensional chemical space, and provides an efficient means of creating quaternary spirocenters that we apply to the first synthesis of the cytotoxic plant metabolite denobilone A.

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.

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.

Trifluoromethylthiolative spirocyclization of biaryl ynones without leaving groups on the para-position of dearomatized aryl rings

A direct and efficient strategy for the oxidative spirocyclization of biaryl ynones has been developed, where nonsubstituted groups were on the para-position of the dearomatized aryl rings.

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...

Tandem vinyl radical Minisci-type annulation on pyridines: one-pot expeditious access to azaindenones

A new regiospecific alkylative/alkenylative cascade annulation of pyridines has been achieved whilst the corresponding classic Minisci alkylative annulation failed. This protocol provides a novel and expeditious access to azaindenones and related compounds via cross-dehydrogenative coupling with the long-standing problem of C2/C4 regioselectivity of pyridines being well addressed.