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

Photoinduced Ag-Mediated Azaspirocyclic Approach Involves Cyclization and Dearomatization

A visible-light-promoted protocol for azaspirocyclic synthesis from N-benzylacrylamides and alkyl chlorooxoacetates has been established. This cascade reaction proceeds through sequential free radical addition, cyclization, and dearomatization, enabling the convenient construction of key azaspirocyclic derivatives and the introduction of valuable ester groups in a single step. In addition, this transformation demonstrates broad substrate compatibility and high tolerance toward different functional groups, showcasing remarkable efficiency in functional group insertion and bond formation.

Ag-Catalyzed Domino Decarboxylative Alkylation/Dearomative Annulation: Entry to Fused-Pyrido[4,3-b]Indolones

Here we report the development of unprecedented silver-catalyzed intramolecular annulations of N-acrolyl-2-(3-indolyl) benzimidazoles with alkyl carboxylic acids to construct complex fused-pentacyclic alkaloid scaffolds. Divergent reactivities are noticed with altered groups at C2-indole of the substrate. The reaction proceeds through decarboxylative alkylation, followed by dearomative annulation in a domino manner with excellent diastereoselectivity. Owing to the reactivity of the tert-OH group, these aza-enriched scaffolds can be further functionalized.

Acid-Mediated Intramolecular Cyclizations of (N-Aryl)-acetylenic Sulfonamides: Synthesis of Fused and Spirocyclic Sultams

Herein, we report acid-mediated divergent annulations of (N-aryl)-alkynyl sulfonamides. The substituent at the para position of the N-aryl group determines two diverse reaction paths, leading to the selective assembly of benzo-fused sultams and spirocyclic sultams. This strategy provides a series of benzo/spiro-sultams with wide functional group compatibility and good to excellent yields under mild reaction conditions. Additionally, scale-up reaction and further transformations of the products were also carried out to demonstrate the utility of the protocol.

Electrochemical selenylative ipso-annulation of N-benzylacrylamides to construct seleno-azaspiro[4.5]decadienones

Herein, we present the electrochemical synthesis of selenylated azaspiro[4.5]decadienones through domino selenylation/ipso-annulation of N-benzylacrylamides with diselenides. The method showed a wide substrate scope under mild and external oxidant-free reaction conditions, involving the construction of C-Se and C-C bonds. Gram-scale synthesis and further functional group conversion of the product are also demonstrated.

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.

Dearomative ipso-Cyclization to Spiropseudoindoxyls: An Extendable Approach To Access Indolo[3,2-c]quinolinones and Isocryptolepine

A metal-free oxidative intramolecular dearomative spirocyclization of indole-3-formyl-2-carboxamides has been developed for the first time, affording spiropseudoindoxyls in good yields. This domino process proceeds through sequential oxidation, decarboxylation and ipso-arylation. The unique feature of this approach includes the compatibility of N-protected-indole-2-carboxamides. Further, a hitherto unknown rearrangement of spiropseudoindoxyls to indoloquinolones has been achieved. The synthetic utility of this strategy has also been showcased by the construction of a natural alkaloid, isocryptolepine.

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.

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.

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.