Synthesis of 3-selanylbenzo[b]furans promoted by SelectFluor®

Visible-light induced selenocyclization of 2-ethynylanilines under ambient conditions: simple FeBr3 as a dual-functional catalyst

We report herein a visible-light induced, Fe-catalyzed selenocyclization of 2-ethynylanilines with diselenides under ambient conditions, employing ethyl acetate as a benign solvent with no stoichiometric additive required. The simple iron salt FeBr3 serves as both a photo-induced LMCT (Ligand-to-Metal Charge Transfer) catalyst and a Lewis acid catalyst to promote the desired transformation in a sustainable manner, enabling the facile synthesis of diverse 3-selenylindoles with extended substitution patterns. Moreover, gram-scale reactions and late-stage functionalization of bioactive molecules further highlight the synthetic practicality of this method.

C-H Bond Functionalization of N-Heteroarenes Mediated by Selectfluor

Herein, recent developments for Selectfluor-mediated C-H functionalization of N-heteroarenes are described. This type of C-H bond activation is an attractive and competitive alternative to traditional methodologies, allowing the functionalization of a variety of chemical functions. In addition, Selectfluor is a more sustainable and economically accessible oxidant compared with expensive/toxic metals or hazardous peroxides. For a practical understanding, the current review classified systematically the reported strategies in four subsections as follows: (1) carbon-carbon formation, (2) carbon-nitrogen bond formation, (3) carbon-chalcogen bond, and (4) carbon-halogen bond formation. Mechanistic aspects and reaction conditions are fully discussed to provide an understanding of the aspects that govern C-H functionalization in N-heteroarenes mediated by Selectfluor.

Regioselective intramolecular cyclization of o-alkynyl arylamines with the in situ formation of ArXCl to construct poly-functionalized 3-selenylindoles

In this article, a practical and metal-free method for the synthesis of poly-functionalized 3-selenyl/sulfenyl/telluriumindoles from o-alkynyl arylamines has been achieved. In this protocol, the in situ formation of selenenyl chloride, sulfenyl chloride or tellurenyl chloride is considered as the key intermediate and the 3-selenyl/sulfenyl/telluriumindoles can be obtained in good to excellent yields. Furthermore, the product 2-phenyl-3-(phenylselanyl)-1-tosyl-1H-indole can be selectively oxidized to compounds 2-phenyl-3-(phenylseleninyl)-1-tosyl-1H-indole and 2-phenyl-3-(phenylselenonyl)-1-tosyl-1H-indole in good yields.

Direct Electrooxidative Selenylation/Cyclization of Alkynes: Access to Functionalized Benzo[b]furans

A mild, practical, metal and oxidant-free methodology for the synthesis of various C-3 selenylated benzo[b]furan derivatives was developed through the intramolecular cyclization of alkynes promoted with diselenides via electrooxidation. A wide range of selenium-substituted benzo[b]furan derivatives were obtained in good to excellent yields with high regioselectivity under constant current in an undivided cell equipped with carbon and platinum plates as the anode and cathode, respectively. Moreover, the convergent approach exhibited good functional group tolerance and could be easily scaled up with good efficiency, providing rapid access to a diverse range of selenylated benzo[b]furans derivatives from simple, readily available starting materials.

Versatile Electrochemical Synthesis of Selenylbenzo[b]Furan Derivatives Through the Cyclization of 2-Alkynylphenols

We report an electrochemical oxidative intramolecular cyclization reaction between 2-alkynylphenol derivatives and different diselenides species to generate a wide variety of substituted-benzo[b]furans. Driven by the galvanostatic electrolysis assembled in an undivided cell, it provided efficient transformation into oxidant-, base-, and metal-free conditions in an open system at room temperature. With satisfactory functional group compatibility, the products were obtained in good to excellent 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.

Meyer-Schuster-Type Rearrangement of Propargylic Alcohols into α-Selenoenals and -enones with Diselenides

We describe a mild and broadly applicable protocol for the preparation of a diverse array of multisubstituted α-selenoenals and -enones from readily accessible propargylic alcohols and diselenides. The transformation proceeds via the Selectfluor-promoted selenirenium pathway, which enables selenenylation/rearrangement of a variety of propargylic alcohols. Gram-scale experiments showed the potential of this synergistic protocol for practical application.

Synthetic strategies for aryl/heterocyclic selenides and tellurides under transition-metal-catalyst free conditions

Aryl and heteroaryl selenides and tellurides are found to have broad applications in the diverse fields such as medicine, biology, materials science, pharmaceutical etc. and thus their synthesis remains a challenging field for synthetic chemists in last decade. Although a large no of methodologies have been developed based on metal catalyzed C-Se/Te coupling, a large number of researches has been focused on developing metal catalyst free protocols due to their sustainability in recent times. This review covers all the recent developments in last decade on their synthesis under metal catalyst free conditions by using different sustainable techniques e.g. greener reagents and solvents, ball milling, visible light photocatalysis, microwave, ultrasound etc.

Transition Metal-Free Synthesis of Carbo- and Heterocycles via Reaction of Alkynes with Organylchalcogenides

This manuscript intends to overview the most recent advances in the synthesis of carbo- and heterocycles through reactions of alkynes with organyl chalcogenides (S, Se, Te) under metal-free conditions. Firstly, the use of electrophilic chalcogenyl halides as a selective reagent for alkyne carbon-carbon triple bond activation will be presented. After that, radical cyclization protocols employing electrochemical oxidative conditions, light-induced photoredox catalysis, or mild oxidants with direct chalcogenyl group installation will be discussed accompanied by the proposed mechanisms.

Site-specific C–H chalcogenation of quinoxalin-2(1H)-ones enabled by Selectfluor reagent

A site-specific C6–H chalcogenation of quinoxalin-2(1H)-ones with various diselenides and dithiols is presented by employing Selectfluor reagent as an oxidant.