Radical bicyclization of 1,6-enynes with sulfonyl hydrazides by the use of TBAI/TBHP in the aqueous phase

A novel 5-exo-dig/6-endo-trig bicyclization of 1,6-enynes with sulfonyl hydrazides in the aqueous phase using the cheap and available tetrabutylammonium iodide (TBAI)-tert-butyl hydroperoxide (TBHP) combined system is reported. The resulting reaction of diverse nitrogen- and oxygen-polyheterocycles displays high chemical selectivity, high step-economy, and a moderate substrate scope. Moreover, iodosulfonylation can be realized by modulating the structure of the 1,6-enynes.

Copper- and Visible-Light-Catalyzed Cascade Radical Cyclization of N-Propargylindoles with Cyclic Ethers

An efficient visible-light-assisted, copper-catalyzed tandem radical cyclization of N-propargylindoles with cyclic ethers is established. A series of 2-oxoalkyl-9H-pyrrolo[1,2-a]indol-9-ones with potential biological activities were synthesized in moderate yields by using a dual catalytic system with copper acetate as a transition metal catalyst and eosin Y as a visible light catalyst. The investigation of reaction mechanism shows that it goes through a cascade oxoalkyl radical addition, cyclization, and oxidation process.

Iodo-sulphonylation of 1,6-enynones: a metal-free strategy to synthesize N-substituted succinimides

An iodine-mediated radical cyclization of 1,6-enynones with sulphonyl hydrazides using tert-butyl hydroperoxide (TBHP) as the oxidant has been developed for the synthesis of iodo-sulphonylated-succinimide derivatives. The notable advantages of the developed method are metal-free conditions, broad functional group tolerance, column chromatography-free purification, high stereoselectivity (E isomer), shorter reaction times, and the cascade construction of three new bonds (C-S, C-I, and C-C). The synthetic application of the iodo-functionality has been extended to the Heck coupling reaction with acrylonitrile and to the Suzuki coupling reaction with benzene boronic acid.

Metal-free sulfonylation of arenes with N-fluorobenzenesulfonimide via cleavage of S-N bonds: expeditious synthesis of diarylsulfones

A novel metal-free sulfonylation of arenes with N-fluorobenzenesulfonimide (NFSI) toward the synthesis of diarylsulfones has been developed. The reaction represents a rare example of sulfonylation reaction using NFSI as an efficient sulfonyl donor and the first example of acid-mediated sulfonylation of unactivated arenes with NFSI via selective cleavage of S-N bonds. This protocol provides a concise approach for the construction of pharmaceutically and biologically important diarylsulfones. Applications in the functionalization of natural products (e.g., β-estradiol) and in the synthesis of a key intermediate to an inhibitor of farnesyl-protein transferase, as well as in the gram-scale synthesis of the EPAC2 antagonist, are demonstrated.

Visible-Light-Induced Transition-Metal-Free Nitrogen-Centered Radical Strategy for the Synthesis of 2-Acylated 9H-Pyrrolo[1,2-a]indoles

A convenient and efficient visible-light-induced tandem acylation/cyclization of N-propargylindoles with aryl- or alkyl-substituted acyl oxime esters for the synthesis of 2-acyl-substituted 9H-pyrrolo[1,2-a]indoles under transition-metal-free conditions, which proceeds via nitrogen-centered radical-mediated cleavage of the C-C σ-bond in acyl oxime esters, is established. The aryl or alkyl acyl radicals, which come from acyl oxime esters, attack the C-C triple bonds in N-propargylindoles and then go through intramolecular cyclization/isomerization.

Recent advances in the synthesis of pyrrolo[1,2-a]indoles and their derivatives

The pyrrolo[1,2-a]indole unit is a privileged heterocycle found in numerous natural products and has been shown to exhibit diverse pharmacological properties. Thus, recent years have witnessed immense interest from the synthesis community on the synthesis of this scaffold. In light of the ever-increasing demand for pyrrolo[1,2-a]indoles in drug discovery, this review provides an overview of recent synthesis methods for the preparation of pyrrolo[1,2-a]indoles and their derivatives. The mechanistic pathway and stereo-electronic factors affecting the yield and selectivity of the product are briefly explained. Furthermore, we have attempted to demonstrate the utility of the developed methods in the synthesis of bioactive molecules and natural products, wherever offered.

Sulfonyl radical triggered selective iodosulfonylation and bicyclization of 1,6-dienes

A novel sulfonyl radical triggered selective iodosulfonylation and bicyclization of 1,6-dienes has been described for the first time. High selectivity and efficiency, mild reaction conditions, excellent functional group compatibility, and broad substrate scope are the attractive features of this synthetic protocol, which provides a unique platform for precise radical cyclization.

Palladium-Catalyzed Cascade Difluoroalkylation and Phosphinoylation of 2-Vinyloxy Arylalkynes: Selective Synthesis of Difluoroalkyl-Containing Tetrasubstituted Alkenylphosphine Oxides

A Pd-catalyzed difluoroalkylation/cyclization/phosphinoylation of 2-vinyloxy arylalkynes with ethyl difluoroiodoacetate and diarylphosphine oxides has been successfully developed. This reaction allows the formation of C_sp3-CF₂, C_sp3-C_sp2, and C_sp2-P(O) bonds in one step, providing a straightforward route to difluoroalkyl-containing tetrasubstituted alkenylphosphine oxides with complete stereoselectivities under mild conditions.

NaI/KI/NH4I and TBHP as powerful oxidation systems: use in the formation of various chemical bonds

In modern organic synthesis, the execution of reactions in the absence of expensive transition metals has received significant attention from the view-point of green chemistry and sustainable development. As a consequence, the combination of MI-TBHP as an oxidation system (M = Na, K, NH4) has opened a new avenue with significant impact for the succinct synthesis of complex heterocycle molecules via the construction of various chemical bonds [C-X (X = C, N, S, O), N-X (X = N, P) and S-N]. This comprehensive review article delineates the progress of recent developments in this emerging area, with an in-depth discussion on the substrate scope, limitations and proper mechanistic underpinnings. We hope this review will highlight the great potential of this MI-TBHP as a powerful oxidation system and inspire researchers to conduct further endeavors in this domain.

Recent advances in cascade radical cyclization of radical acceptors for the synthesis of carbo- and heterocycles

This review is devoted to highlighting main achievements in the development of cascade radical cyclization of radical acceptors for the synthesis of carbo- and heterocycles.

Cascade trifluoromethylthiolation and cyclization of N-[(3-aryl)propioloyl]indoles

A cascade oxidative trifluoromethylthiolation and cyclization of N-[(3-aryl)propioloyl]indoles with AgSCF₃ is described. This protocol allows for the synthesis of novel bis(trifluoromethylthiolated) or trifluoromethylthiolated pyrrolo[1,2-a]indol-3-ones in moderate to good yields. Mechanistic investigations indicated that radical processes were probably involved in these transformations.

An update on the use of sulfinate derivatives as versatile coupling partners in organic chemistry

The use of sulfinic acids and their salts continues to be extensively developed in organic chemistry. This is attributable to their dual capacity for acting as nucleophilic or electrophilic reagents, as well as their ease of preparation and stability on storage. This report highlights the research accomplished since 2015 on this topic, updating a previous review published by our team in 2014.

Copper-Catalyzed Phosphonylation/Trifluoromethylation of N-p-NO2-Benzoylacrylamides Coupled with Dearomatization and Denitration

A novel and efficient copper-tert-butyl hydroperoxide mediated intramolecular spirocyclization of N-p-NO₂-benzoylacrylamides through a cascade radical addition-ipso-cyclization-dearomatization-denitration process has been developed, affording a convenient and powerful tool for the preparation of valuable phosphonated or trifluoromethylated azaspiro[4.5]decadientriones under mild conditions in good yields.

Regiospecific Cleavage of S-N Bonds in Sulfonyl Azides: Sulfonyl Donors

Sulfonyl azides have been widely used as sulfonamido, diazo, and azido donors, as well as all-nitrogen 1,3-dipoles donors in synthetic chemistry. Here, the sulfonyl azides were used as efficient sulfonyl donors, which is very unusual. Trifluoromethanesulfonic acid-induced formation of the sulfonyl cation reactive species from sulfonyl azides was developed and used for the first time to couple various inactivated arenes to prepare sulfones at ambient temperature.

Metal-free oxysulfonylation and aminosulfonylation of alkenyl oximes: synthesis of sulfonylated isoxazolines and cyclic nitrones

Intramolecular oxysulfonylation of alkenyl oximes was reported. Using iodine as the catalyst, TBHP as the oxidant, and sulfonyl hydrazides as the sulfonyl radical source, a variety of sulfonylated isoxazolines were obtained in moderate to excellent yields. Cyclic nitrones could also be readily obtained under the same conditions.

A simple approach to indeno-coumarins via visible-light-induced cyclization of aryl alkynoates with diethyl bromomalonate

Visible-light-induced triple-domino cyclization between aryl alkynoates and diethyl bromomalonate was developed for the synthesis of indeno-coumarins.

Visible-light-induced cascade sulfonylation/cyclization of N-propargylindoles with aryldiazonium tetrafluoroborates via the insertion of sulfur dioxide

A simple and efficient visible-light-catalyzed cascade sulfonylation/cyclization of N-propargylindoles with K₂S₂O₅ and aryldiazonium tetrafluoroborates for the construction of 2-sulfonyl-substituted 9H-pyrrolo[1,2-a]indoles is developed.

Photoredox-catalyzed cascade annulation of N-propargylindoles with sulfonyl chlorides: access to 2-sulfonated 9H-pyrrolo[1,2-a]indoles

A photoredox-catalyzed cascade radical reaction of N-propargylindoles and sulfonyl chlorides to 2-sulfonated 9H-pyrrolo[1,2-a]indoles under external oxidant-free conditions was developed.

Copper-catalyzed radical 1,2-cyclization of indoles with arylsulfonyl hydrazides: access to 2-thiolated 3H-pyrrolo[1,2-a]indoles

A copper-catalyzed cascade radical 1,2-cyclization of indoles with arylsulfonyl hydrazides was developed, affording a series of 2-thiolated 3H-pyrrolo[1,2-a]indoles in moderate to excellent yields.