Synthesis of heterocycles via electrophilic cyclization of alkynes containing heteroatom

Photocatalytic Markovnikov-type addition and cyclization of terminal alkynes leading to 4-sulfonyl quinoline-2(1H)-ones

A new and expedient photocatalytic protocol for the construction of quinolin-2(1H)-ones via Markovnikov-type sulfonylation/6-endo-trig cyclization/selective C(O)-CF₃ bond cleavage starting from N-alkyl-N-(2-ethynylphenyl)-2,2,2-trifluoroacetamides and sulfinic acids has been developed. It is as an unprecedented protocol for the preparation of 4-sulfonylquinoline-2(1H)-ones with high efficiency, mild reaction conditions, acceptable yields and a wide range of substrates.

Palladium-Catalyzed Cascade 5-endo-dig Cyclization of Ynamides to Form 4-Alkynyloxazolones

The selective synthesis of 4-alkynyloxazolones and their further applications as substrates to electrophile-promoted nucleophilic cyclization have been developed. The reaction of ynamides with terminal alkynes proceeded smoothly to give 4-alkynyloxazolones in the presence of a catalytic amount of palladium(II) acetate. The products were obtained with the sequential formation of new C-C and C-O bonds via a cascade procedure. The first step involved a carbon-oxygen bond formation, via a 5-endo-dig closure, which was confirmed by X-ray analyses of the crystalline sample. Subsequently, the reaction of 4-alkynyloxazolones with an electrophilic selenium source gave 3-phenylselanyl benzofuran derivatives via an electrophile-promoted nucleophilic cyclization.

Selenium atoms induce organic doped systems to produce pure phosphorescence emission

A host-guest system is constructed using a guest containing two selenium atoms. The selenium atoms can increase the spin-orbit coupling constant and the conjugation degree, thereby increasing the emission wavelength, and making the materials show only phosphorescence emission.

Ag2O-mediated Tandem Reaction between Terminal Alkyne and o-Iodibenzoic Acid: Construction of 3-Ethylideneisobenzofuran-1(3H)-ones

Taking aryl propargyl ether and o-iodibenzoic acid as substrates, a series of aryl cyclolactones bearing an exocyclized C=C bond were constructed with moderate to good yields. Diverse substituent groups could be tolerant in the reaction, which indicated excellent compatibility of the reaction. In this tandem reaction, Ag2O was employed as the media and Et3N was screened as the base to facilitate the reaction. A concise mechanism was proposed on the basis of the expansion of the substrates and theoretical analysis. Sonogashira type coupling coupled with intramolecular nucleophilic addition in one pot to construct the product, 3-ethylideneisobenzofuran-1(3H)-one.

Excited-State Copper Catalysis for the Synthesis of Heterocycles

Heterocycles are one of the largest groups of organic moieties with significant medicinal, chemical, and industrial applications. Herein, we report the discovery and development of visible-light-induced, synergistic excited-state copper catalysis using a combination of Cu(IPr)I as a catalyst and rac-BINAP as a ligand, which produces more than 10 distinct classes of heterocycles. The reaction tolerates a broad array of functional groups and complex molecular scaffolds, including derivatives of peptides, natural products, and marketed drugs. Preliminary mechanistic investigation suggests in situ generations of [Cu(BINAP)₂ ]⁺ and [Cu(IPr)₂ ]⁺ catalysts that work cooperatively under visible-light irradiation to facilitate catalytic carbo-aroylation of unactivated alkenes, affording a wide range of useful heterocycles.

Synthesis of unprotected glyco-alkynones via molybdenum-catalyzed carbonylative Sonogashira cross-coupling reaction

Herein we report a novel Mo-catalyzed carbonylative Sonogashira cross-coupling between 2-iodoglycals and terminal alkynes. The reaction displays major improvements compared to a related Pd-catalyzed procedure previously published by our group, such as utilizing unprotected sugar derivatives as starting materials and tolerance to substrates bearing chelating groups. In this work we also demonstrate the utility of the glyco-alkynone products as platform for further functionalization by synthesizing glyco-flavones via Au-catalyzed 6-endo-dig cyclization.

Synthesis and antimicrobial activity of functional derivatives of thiazolo[2,3-c][1,2,4]triazoles

Background:

Condensed triazoles are a well-known class of heterocyclic compounds due to a wide range of biological activity. The study is dedicated to the evaluation of the antimicrobial potential of new functional derivatives of thiazolo[2,3-c][1,2,4]triazoles.

Methods:

Effective, easy-to-implement and low-cost routes to the production of title compounds via electrophilic intramolecular heterocyclization are reported. Bactericidal and fungicidal activities against Gram-positive and Gram-negative bacteria, and fungus were studied. The influence of functional groups on the biological activity of tested thiazolo[2,3-c][1,2,4]triazoles is discussed.

Results:

Microbiological evaluation shows that 6-[(trichlorotellanyl)methyl]-[1,3]thiazolo[2,3-c][1,2,4]triazol-3-amine hydrogen chloride 2a and 3-(2-hydroxyphenyl)-6-[(trichloro-λ4-tellanyl)methyl]-5,6-dihydro-[1,3]thiazolo[2,3-c][1,2,4]triazole 2g have a high bactericidal activity and Cu (I) salts of 3-(2-hydroxyphenyl)-6-iodomethyl/6-methylidene-5,6-dihydro-[1,3]thiazolo-[2,3-c][1,2,4]triazoles 5a,c have a high fungicidal activity.

Conclusion:

it must be concluded that these products or their derivatives may be of practical benefit as bactericidal and fungicidal agents.

PhSe(O)OH/Al(NO3)3-Catalyzed selectivity controllable oxidation of sulphide owing to the synergistic effect of Se, Al3+ and nitrate

Catalyzed by PhSe(O)OH/Al(NO3)3, selective oxidation of sulphides to produce sulfoxides or sulphones could be achieved under mild conditions. The synergistic effect of Se, Al3+ and nitrate is the key factor for the reaction.

Selectfluor-mediated construction of 3-arylselenenyl and 3,4-bisarylselenenyl spiro[4.5]trienones via cascade annulation of N-phenylpropiolamides with diselenides

A cascade annulation of N-phenylpropiolamides with diselenides leading to the construction of 3-arylselenenyl spiro[4.5]trienones was realized under mild conditions with Selectfluor as the sole oxidant.

Rongalite in PEG-400 as a general and reusable system for the synthesis of 2,5-disubstituted chalcogenophenes

Herein we report the use of rongalite in PEG-400 as a general, efficient, and environmentally benign reductive system for the synthesis of a wide range of 2,5-disubstituted chalcogenophenes from elemental sulfur, selenium and tellurium.

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...

Synthesis and Evaluation of 3-Halobenzo[b]thiophenes as Potential Antibacterial and Antifungal Agents

The global health concern of antimicrobial resistance has harnessed research interest to find new classes of antibiotics to combat disease-causing pathogens. In our studies, 3-halobenzo[b]thiophene derivatives were synthesized and tested for their antimicrobial activities using the broth microdilution susceptibility method. The 3-halo substituted benzo[b]thiophenes were synthesized starting from 2-alkynyl thioanisoles using a convenient electrophilic cyclization methodology that utilizes sodium halides as the source of electrophilic halogens when reacted along with copper(II) sulfate. This environmentally benign methodology is facile, uses ethanol as the solvent, and results in 3-halo substituted benzo[b]thiophene structures in very high yields. The cyclohexanol-substituted 3-chloro and 3-bromobenzo[b]thiophenes resulted in a low MIC of 16 µg/mL against Gram-positive bacteria and yeast. Additionally, in silico absorption, distribution, metabolism, and excretion (ADME) properties of the compounds were determined. The compounds with the lowest MIC values showed excellent drug-like properties with no violations to Lipinski, Veber, and Muegge filters. The time-kill curve was obtained for cyclohexanol-substituted 3-chlorobenzo[b]thiophenes against Staphylococcus aureus, which showed fast bactericidal activity at MIC.

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.

Repurposing π Electrophilic Cyclization/Dealkylation for Group Transfer

A metal-free regio- and stereocontrolled group-transfer route toward the synthesis of trisubstituted alkenes is described. In this route, an electrophilic heterocyclization is followed by ring-opening group transfer. Specifically, a thioboration reaction transforms readily available alkynyl sulfide precursors into alkenyl boronates and alkenyl sulfides with defined regio- and stereochemistry in one synthetic step using commercially available B-chlorocatecholborane (ClBcat). Mechanistic studies identified the likely pathway as proceeding through zwitterionic rather than haloborated intermediates. The regio- and stereochemistry set in the initial cyclization step is preserved in the final acyclic alkene product, producing alkenes with up to four modifiable substituents with predictable regio- and stereochemistry. Downstream functionalization reactions showcase the versatility of the substitutions of the resulting alkenes. The mechanistic concept maps onto future reaction designs, given the abundance of known electrophiles and nucleophiles for electrophilic heterocyclization/dealkylation sequences.

Sc(OTf)3-Catalyzed Iodocyclization/Ritter-Type Amidation of N-Alkoxypropiolamides: A Synthetic Strategy for Isoxazol-3(2H)-ones

A Sc(OTf)₃-catalyzed iodocyclization/Ritter-type amidation of N-alkoxypropiolamides for the synthesis of 4-iodoisoxazol-3(2H)-ones bearing an amide group has been developed. This domino protocol allows the construction of a valuable heterocycle, isoxazol-3(2H)-one, as well as the introduction of two functional groups. The reaction has a broad substrate scope and can be carried out on a large scale. Control experiments suggest that Sc(OTf)₃ acts as a dual activator for both the iodocyclization and amidation steps. In addition, the N-alkoxy group in the substrate suppresses some of the side reactions.

Visible-Light-Catalyzed N-Radical-Enabled Cyclization of Alkenes for the Synthesis of Five-Membered N-Heterocycles

Five-membered N-heterocycles play an important role in organic synthesis and material chemistry, as they are widespread through pharmaceutical molecules and natural products. Chemists have developed many synthetic strategies for constructing five-membered N-heterocycles from N-centered radicals, but the availability of mild and green methods for these transformations is still limited. The cyclization of visible-light-generated N-centered radicals with alkenes has emerged as a powerful tool to enable these chemical transformations in recent years. Through chosen representative examples, the significant developments in this promising field were outlined, including the selection of catalysts, substrate scope, mechanistic understanding (especially density functional theory calculations), and applications. The contents of this Minireview are categorized by intramolecular cyclization and intermolecular N-centered radical addition/cyclization reactions.

Recent advances in directed sp2 C-H functionalization towards the synthesis of N-heterocycles and O-heterocycles

Heterocyclic compounds are widely present in the core structures of several natural products, pharmaceuticals and agrochemicals, and thus great efforts have been devoted to their synthesis in a mild and simpler way. In the past decade, remarkable progress has been made in the field of heterocycle synthesis by employing C-H functionalization as an emerging synthetic strategy. As a complement to previous protocols, transition metal catalyzed C-H functionalization of arenes using various directing groups has recently emerged as a powerful tool to create different classes of heterocycles. This review is mainly focussed on the recent key progress made in the field of the synthesis of N,O-heterocycles from olefins and allenes by using nitrogen based and oxidizing directing groups.

Oxymetalation or oxidative cyclization? mechanism of Pd-catalyzed annulation of enynones

Enynones are powerful synthons for constructing furan derivatives in the presence of transition metal catalysts. Unlike the conventional intramolecular nucleophilic attack with the activation of coinage metals, we propose that enynones undergo an oxidative cyclization process with a Pd(0) species. The full catalytic cycle involves oxidative cyclization, isocyanide insertion, and reductive elimination, which was supported by DFT calculations. Geometric and electronic analyses confirmed the oxidative cyclization process, which proceeds via a Pd(ii) intermediate.

Chemoselective Ullmann Reaction of α-Trisubstituted Thioamides: Synthesis of Novel 2-Iminobenzothiolanes

New classes of unexplored benzo[b]thiolanes are synthesized from trisubstituted thioamides through copper-catalyzed intramolecular S-arylation of thioamides for the first time. This method provides good to excellent yields with fully controlled chemoselectivity. Unusually, iminobenzo[b]thiolanes are very stable under mild acidic conditions. A plausible mechanism is proposed for the chemoselective S-arylation process.

Difunctionalization of Alkynones by Base-Mediated Reaction with α,α-Dithioketones

A novel 1,2-difunctionalization of alkynones via an umpolung strategy for the synthesis of tetrasubstituted olefins has been developed. This procedure is realized by a formal C-C σ-bond cleavage reaction of cyclic α,α-dithioketones and subsequent deprotection. Notable features of this approach include excellent yields, mild reaction conditions, a broad substrate scope, and operational simplicity.

The Use of Electrophilic Cyclization for the Preparation of Condensed Heterocycles

Condensed heterocycles are well-known for their excellent biological effects and they are undeniably important compounds in organic chemistry. Electrophilic cyclization reactions are widely used for the synthesis of mono-heterocyclic compounds. This review highlights the utility of electrophilic cyclization reactions as an effective generic tool for the synthesis of various condensed heterocycles containing functional groups that are able to undergo further chemical transformations, such as nucleophilic substitution, elimination, re-cyclization, cleavage, etc. This review describes the reactions of unsaturated derivatives of different heterocycles with various electrophilic agents (halogens, arylsulfanyl chlorides, mineral acids) resulting in annulation of an additional partially saturated heterocycle. The electrophilic reaction conditions, plausible mechanisms and the use of such transformations in organic synthesis are also discussed. The review mainly focuses on research published since 2002 in order to establish the current state of the art in this area.

1 Introduction

2 Electrophilic Cyclization Pathways Involving a Nitrogen Nucleo­philic Center

3 Electrophilic Cyclization Pathways Involving a Chalcogen Nucleophilic Center

3.1 Sulfur Centers

3.2 Oxygen Centers

3.3 Selenium Centers

4 Strategies and Mechanisms

5 Conclusion

Visible-Light-Induced Formation of Thiavinyl 1,3-Dipoles: A Metal-Free [3+2] Oxidative Cyclization with Alkynes as Easy Access to Thiophenes

A visible-light-induced [3+2] oxidative cyclization of various alkynes with easily available ketene dithioacetals as the previously unknown thiavinyl 1,3-dipoles in the presence of an acridine photosensitizer is reported. A series of multisubstituted thiophenes were achieved regioselectively in ≤98% yields under very mild metal-free conditions without other additives. This reaction could tolerate a wide range of substrates and achieve good efficiency in large-scale syntheses. The reaction mechanism and their applications are described in detail to reveal the reactivity of the new 1,3-dipoles and the selectivity of the reactions.

Base mediated synthesis of functionalized 2-(alkynyl)arylnitriles and their molecular docking study with aromatase receptor

A simple, efficient, and transition metal-free approach to synthesize functionalized 2-(alkynyl)benzonitriles has been developed using suitably functionalized 2H-pyran-2-ones and 4-phenyl/trimethylsilanyl-but-3-yn-2-ones as precursors. The reaction proceeds in the presence of a base at room temperature to yield internal as well as terminal alkynes. The structure of the synthesized compound was confirmed by single-crystal X-ray analysis. The molecular docking study was performed to evaluate the binding mode of action of newly synthesized alkyne derivatives with known human breast cancer target receptor aromatase (PDB ID: 3EQM).

Diorganyl Dichalcogenides and Copper/Iron Salts: Versatile Cyclization System To Achieve Carbo- and Heterocycles from Alkynes

Organochalcogen-containing cyclic molecules have shown several promising pharmacological properties. Consequently, different strategies have been developed for their synthesis in the past few years. Particularly due to the low cost and environmental aspects, copper- and iron-promoted cyclization reactions of alkynyl substrates have been broadly and efficiently applied for this purpose. This short review presents an overview of the most recent advances in the synthesis of organochalcogen-containing carbo- and heterocycles by reacting diorganyl disulfides, diselenides, and ditellurides with alkyne derivatives in the presence of copper and iron salts to promote cyclization reactions.

1 Introduction

2 Synthesis of Carbo- and Heterocycles via Reactions of Alkynes with Diorganyl Dichalcogenides and Copper Salts

3 Synthesis of Carbo- and Heterocycles via Reactions of Alkynes with Diorganyl Dichalcogenides and Iron Salts

4 Conclusions

Development of a Flexible and Robust Synthesis of Tetrahydrofuro[3,4-b]furan Nucleoside Analogues

In the context of a PRMT5 inhibitor program, we describe our efforts to develop a flexible and robust strategy to access tetrahydrofuro[3,4-b]furan nucleoside analogues. Ultimately, it was found that a Wolfe type carboetherification from an alkenol derived from d-glucofuranose diacetonide was capable of furnishing the B-ring and installing the desired heteroaryl group in a single step. Using this approach, key intermediate 1.3-A was delivered on a gram scale in a 62% yield and 9.1:1 dr in favor of the desired S-isomer. After deprotection of 1.3-A, a late-stage glycosylation was performed under Mitsunobu conditions to install the pyrrolopyrimidine base. This provided serviceable yields of nucleoside analogues in the range of 31-48% yield. Compound 1.1-C was profiled in biochemical and cellular assays and was demonstrated to be a potent and cellularly active PRMT5 inhibitor, with a PRMT5-MEP50 biochemical IC₅₀ of 0.8 nM, a MCF-7 target engagement EC₅₀ of 3 nM, and a Z138 cell proliferation EC₅₀ of 15 nM. This work sets the stage for the development of new inhibitors of PRMT5 and novel nucleoside chemical matter for alternate drug discovery programs.