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

A Domino Dearomative ipso-Annulation/Desymmetrization Approach: Stereoselective Access to Tricyclic Alkaloid Skeletons

Herein, we reveal an unprecedented domino annulation of N-benzyl-acrylamides with 1,3-dicarbonyls for the assembly of fused tricyclic alkaloid frameworks incorporating a spirocycle via an alkylation/dearomative ipso-annulation/Michael addition (desymmetrization) sequence. This conversion involves three carbon-carbon bond formations, generating four chiral carbons, including three quaternary carbon centers, in a single diastereomer in one pot under identical reaction conditions. The synthetic potential of this atom-economic method is illustrated by modifications of the functional groups present in the products obtained.

Synthesis of Indenones via Persulfate Promoted Radical Alkylation/Cyclization of Biaryl Ynones with 1,4-Dihydropyridines

The oxidative radical cascade cyclization of alkynes has emerged as a versatile strategy for the efficient construction of diverse structural units and complex molecules in organic chemistry. This work reports an alkyl radical initiated 5-exo-trig cyclization of biaryl ynones with 1,4-dihydropyridines to selectively synthesize indenones.

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.

Radical-mediated sulfonylative/thiolative cyclization of biaryl enones to phenanthrone derivatives

An approach for the assembly of phenanthrone derivatives bearing all carbon quaternary centres has been developed through visible light-promoted tandem sulfonylation/intramolecular-arylation of biaryl enones with sulfonyl chlorides. A series of sulfonylated 10,10-dialkylphenanthrones were obtained in good yields. In addition, the approach has been extended to thiotrifluoromethyl (SCF3) and thiocyanato (SCN) radicals to obtain the corresponding phenanthrones under oxidative conditions. The synthetic utility was also illustrated by the scalability and further transformations of the product.

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.

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.

Synthesis of sulfur-containing benzo[b]pyrrolo[2,1-c][1,4]oxazine-3,9-diones: blue light promoted radical cyclization process

The selective and controllable construction of spio-tricyclic skeletons through visible light promoted radical cyclization still remains challenging. Herein, a general and convenient protocol for the blue light-promoted radical-mediated cascade spiro-cyclization/Michael addition of N-arylpropiolamides with thiophenols under metal-free conditions was developed. In this protocol, commercially available hydrochloric acid was employed as the cheap promoter and air as the sustainable oxidant. In addition, many functional groups tolerate the reaction conditions and produce a series of sulfur-containing benzo[b]pyrrolo[2,1-c][1,4]oxazine-3,9-diones.