Photo-mediated synthesis of halogenated spiro[4,5]trienones of N-aryl alkynamides with PhI(OCOCF3)2 and KBr/KCl

Oxidative Cascade Iodocyclization of 1,n-Dienes: Synthesis of Iodinated Benzo[b]azepine and Benzo[b]azocine Derivatives

An oxidative cascade iodocyclization of 1,7- or 1,8-dienes has been realized under mild conditions. By employing I2 as an iodine source, this protocol provides a concise and efficient approach to a great deal of biologically significant iodinated benzo[b]azepine and benzo[b]azocine derivatives in moderate to good yields. The gram-scale synthesis and further transformation of products render the approach practical and attractive. Radical trapping and deuterium-labeling experiments help to understand the mechanism.

Electrochemical Oxidative Dearomatization Strategy for Accessing Spiro[4.5]dienones and Derivatives

Electrochemical dearomatization has been recognized as an attractive tool for the rapid construction of structurally diverse molecules. The designed methodology encompasses an eco-friendly and efficient electrochemical approach to synthesizing spiro[4.5]dienones under mild reaction conditions. Furthermore, detailed mechanistic studies strongly bolster our hypothesis and emphasize the role of HFIP in the mechanism. The protocol is scalable and showcases a broad substrate scope with tolerance toward numerous functional groups. Henceforth, this strategy can be deployed as an alternative and sustainable tool for accessing spiro[4.5]dienones.

Unified Approach to Diverse Heterocyclic Synthesis: Organo-Photocatalyzed Carboacylation of Alkenes and Alkynes from Feedstock Aldehydes and Alcohols

We report an organo-photocatalyzed carboacylation reaction that offers a springboard to create chemical complexity in a diversity-driven approach. The modular one-pot method uses feedstock aldehydes and alcohols as acyl surrogates and commercially available Eosin Y as the photoredox catalyst, making it simple and affordable to introduce structural diversity. Several biologically relevant skeletons have been easily synthesized under mild conditions in the presence of visible light irradiation by fostering a radical acylation/cyclization cascade. The proposed reaction mechanism was further illuminated by a number of spectroscopic studies. Furthermore, we applied this protocol for the late-stage functionalization of pharmaceuticals and blockbuster drugs.

Metal-Free Oxidative Dearomatization-Alkoxylation/Acyloxylation of Indoles: Synthesis of 2-Monosubstituted Indolin-3-ones

A metal-free route for the preparation of 2-monosubstituted indolin-3-ones, including 2-alkoxyindolin-3-ones and 2-acyloxyindolin-3-ones from commercially available indoles, has been developed employing (bis(trifluoroacetoxy)iodo)benzene (PIFA) as an oxidant. The present protocol features mild reaction conditions, good tolerance with diverse functional groups, and a wide substrate scope, affording the desired products in good yields. This transformation is easy to scale up, and the desired products can be further modified. Most importantly, this method is suitable for the late-stage modification of bioactive molecules. Mechanism studies show that this transformation involves metal-free radical dearomatization and oxygenation. Furthermore, this method also provides a practical and efficient way to prepare indolin-3-ones from commercially available reagents in one step.

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.

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.

Synthesis of 3-Haloindoles via Cascade Oxidative Cyclization/Halogenation of 2-Alkenylanilines Mediated by PIDA and LiBr/KI

The treatment of 2-alkenylanilines with phenyliodine(III) diacetate (PIDA) and LiBr or KI in HFIP was found to afford the corresponding 3-haloindoles via cascade oxidative cyclization/halogenation encompassing oxidative C-N/C-X (X = Br, I) bond formations. A plausible mechanism involving the in situ formation of the reactive AcO-X (X = Br, I) from the reaction of PIDA and LiBr/KI was postulated.

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.

Photomediated Spirocyclization of N-Benzyl Propiolamide with N-Iodosuccinimide for Access to Azaspiro[4.5]deca-6,9-diene-3,8-dione

A metal- and oxidant-free route for affording azaspiro[4.5]deca-6,9-diene-3,8-dione via photomediated iodinated spirocyclization of N-(4-methoxybenzyl) propiolamide has been developed. The reaction underwent a radical addition/ipso-cyclization/dearomatization process at room temperature and successfully constructed C-C and C-I bonds. This green and convenient approach could be generally expanded to produce a range of iodinated spirocyclization products in moderate to good yields.

Alkylation/Ipso-cyclization of Active Alkynes Leading to 3-Alkylated Aza- and Oxa-spiro[4,5]-trienones

A method for the preparation of 3-alkylated spiro[4.5]trienones via alkylation/ipso-cyclization of activated alkynes with 4-alkyl-DHPs under transition-metal-free conditions is proposed. This alkylation successively undergoes the generation of alkyl radicals, addition of alkyl radicals to the alkynes, and intramolecular ipso-cyclization. The mechanism studies suggest that the alkylation/ipso-cyclization involves a radical process. This ipso-cyclization procedure shows a series of advantages, such as accessibility, mild conditions, high efficiency, greater safety, and an environmentally friendly method.

Synthesis of acyloxy-2H-azirine and sulfonyloxy-2H-azirine derivatives via a one-pot reaction of β-enamino esters, PIDA and carboxylic acid or sulfonic acid

PIDA mediated oxidative acyloxylation/azirination and sulfonyloxylation/azirination of β-enamino esters were investigated. A series of functionalized acyloxy-2H-azirine and sulfonyloxy-2H-azirine derivatives was synthesized in moderate to good yields. This represents the first oxidative sulfonyloxylation/azirination of β-enamino esters with PIDA and sulfonic acid for access to sulfonyloxy-2H-azirine. Hypervalent iodine reagents enable cascade C-O/C-N bond formation. Furthermore, a possible reaction pathway was proposed based on the experimental results.

Visible-Light-Induced Tandem Difluoroalkylated Spirocyclization of N-Arylpropiolamides: Access to C3-Difluoroacetylated Spiro[4,5]trienones

A visible-light-catalyzed difluoroacetylated spirocyclization of N-arylpropiolamides with ethyl bromodifluoroacetate as a CF2CO2Et radical precursor is described. This approach allows the formation of two carbon-carbon bonds and one carbon-oxygen bond in...

Transition-metal catalyzed oxidative spirocyclization of N-aryl alkynamides with methylarenes under microwave irradiation

A practical synthetic route to construct a variety of 3-benzyl spiro[4,5]trienones was developed via transition-metal Cu/Ag-catalyzed oxidative ipso-annulation of activated alkynes with unactivated toluenes using TBPB as an oxidant under microwave irradiation. This method allows the formation of two carbon-carbon bonds and one carbon-oxygen bond in a single reaction through a sequence of C-H oxidative coupling, ipso-carbocyclization and dearomatization. The advantages of this protocol are its operational simplicity and broad substrate scope, and the ability to afford the desired products in moderate to good yields.

Chalcogenative spirocyclization of N-aryl propiolamides with diselenides/disulfides promoted by Selectfluor

A practical and efficient synthetic route to construct a variety of 3-arylselenenyl/3-arylthio spiro[4.5]trienones was developed using Selectfluor reagent as a mild oxidant. This reaction proceeds via a sequence of electrophilic cation addition, spirocyclization and dearomatization, then offers an approach to introduce Se/S-centered cation into the C–C triple bonds. The utility of this protocol were justified by the excellent compatibility of a wide range of functional groups, good yields and scalability under mild reaction conditions.

Strategies and methodologies for the construction of spiro-γ-lactams: an update

This review gives an insight into the most recent synthetic methodologies towards spiro-γ-lactams, a class of compounds that are present in a wide range of synthetic bioactive and naturally occurring molecules.

Visible-light-induced metal-free cascade cyclization of N-arylpropiolamides to 3-phosphorylated, trifluoromethylated and thiocyanated azaspiro[4.5]trienones

Photocatalytic strategies for the preparation of 3-functionalized azaspiro[4.5]trienones via a radical-initiated cascade annulation reaction was developed.