Copper-catalyzed chalcogenation of imidazoheterocycles with sulfur/selenium powder and coumarinyl triflates

Copper-Catalyzed Tandem Cyclization/Chalcogenation with Elemental S8/Se: Concise Synthesis of 3-(β-Hydroxychalcogen)benzofurans

A novel copper-catalyzed cyclization/chalcogenation of o-alkynylphenols with epoxides and elemental S8/Se was developed for the synthesis of a 3-chalcogen-benzofuran architecture in a domino process with no intermediate isolation or purification. Various sensitive functional groups were compatible at room temperature and furnished chalcogenation derivatives in moderate to good yields.

Ketosulfonylmethylenation and sulfonylethyleneation of imidazoheterocycles with dimethylformamide as a methylene source

A hitherto unreported ketosulfonylmethylenation occurring at the C-3 position of imidazoheterocycles, with dimethylformamide as the methylene source was described. Using CoCl2·6H2O or Fe(acac)3 as efficient and inexpensive catalysts, some important biologically active methylenated compounds were prepared, with high efficacy, favorable functional group compatibilities, and a broad substrate scope.

Organoselenium Compounds: Chemistry and Applications in Organic Synthesis

Selenium, originally described as a toxin, turns out to be a crucial trace element for life that appears as selenocysteine and its dimer, selenocystine. From the point of view of drug developments, selenium-containing drugs are isosteres of sulfur and oxygen with the advantage that the presence of the selenium atom confers antioxidant properties and high lipophilicity, which would increase cell membrane permeation leading to better oral bioavailability. In this article, we have focused on the relevant features of the selenium atom, above all, the corresponding synthetic approaches to access a variety of organoselenium molecules along with the proposed reaction mechanisms. The preparation and biological properties of selenosugars, including selenoglycosides, selenonucleosides, selenopeptides, and other selenium-containing compounds will be treated. We have attempted to condense the most important aspects and interesting examples of the chemistry of selenium into a single article.

Selective oxidative β-C-H bond sulfenylation of tetrahydroisoquinolines with elemental sulfur

In this article, a convenient and efficient KIO₃-promoted oxidative sulfenylation at the β-position of tetrahydroisoquinolines and subsequent aromatization in the presence of elemental S₈ is presented. The reaction proceeds with moderate to good yields via a double C-S formation process. A wide range of structurally diverse 4-sulfenylisoquinolines/3-sulfenylpiperidine were synthesized with excellent functional group tolerance and high efficiency.

Access to Sulfur-Containing Bisheterocycles through Base-Promoted Consecutive Tandem Cyclization/Sulfenylation with Elemental Sulfur

A convenient and efficient tandem cyclization/sulfenylation of o-alkynyl-phenols/-anilines/enaminones for the synthesis of diverse sulfur-containing bisheterocycles has been developed using stable, odorless, and easy-to-handle elemental S₈ as a building block under green chemistry conditions. Notably, a one-step simple base-mediated organic transformation affords a benzofuran (indole or chromone) ring and two C-S bonds. Attractive features of this methodology include the absence of a metal catalyst, mild conditions, good functional group tolerance, and valuable product structures.

Synthesis of novel alkynyl imidazopyridinyl selenides: copper-catalyzed tandem selenation of selenium with 2-arylimidazo[1,2-a]pyridines and terminal alkynes

Alkynyl selenides have attracted considerable research interest recently, owing to their applications in the biological and pharmaceutical fields. The Cu-catalyzed tandem reaction for the synthesis of novel alkynyl imidazopyridinyl selenides is presented. A one-pot synthesis route afforded alkynyl imidazopyridinyl selenides in moderate to good yields. This was achieved by a two-step reaction between terminal alkynes and diimidazopyridinyl diselenides, generated from imidazo[1,2-a]pyridines and Se powder, using 10 mol % of CuI and 1,10-phenanthroline as the catalytic system under aerobic conditions. The C(sp²)–Se and C(sp)–Se bond-formation reaction can be performed in one-pot by using inexpensive and easy to handle Se powder as the Se source. The reaction proceeded with terminal alkynes having various substitutions, such as aryl, vinyl, and alkyl groups. The obtained alkynyl imidazopyridinyl selenide was found to undergo nucleophilic substitution reaction on Se atom using organolithium reagents and 1,3-dipolar azide–alkyne cycloaddition based on the alkyne moiety.

Mild and Expeditious Synthesis of Sulfenyl Enaminones of l-α-Amino Esters and Aryl/Alkyl Amines through NCS-Mediated Sulfenylation

Sulfenylation or selenylation of enaminones of l-α-amino esters requires mild reaction conditions due to the presence of a racemization-prone chiral center and reactive side chains. An N-chlorosuccinimide (NCS)-mediated methodology has been developed for rapid sulfenylation of enaminones of l-α-amino esters and aryl/alkyl amines at room temperature in open air under metal-free conditions. Enaminones of l-α-amino esters bearing aliphatic, aromatic, and heterocyclic side chains react efficiently with diverse aryl/alkyl/heteroaryl thiols (R1SH) in the presence of NCS to afford a library of biologically important sulfenyl enaminones in good-to-excellent yields (71-90%). Under similar reaction conditions, the enaminones also react with benzeneselenol to produce selenyl enaminones in good yield (73-83%). The NCS-mediated pathway generates sulfenyl chloride (R1SCl) as an intermediate which leads to rapid sulfenylation of enaminones through cross-dehydrogenative coupling (CDC) under mild reaction conditions.

Synthetic developments on the preparation of sulfides from thiol-free reagents

This critical review covers the main thiolating reagents with respect to their characteristics and reactivities. In fact, they are complementary to each other and bring different thiolation strategies, avoiding the hazardous thiol derivatives.

Catalyst and additive-free oxidative dual C-H sulfenylation of imidazoheterocycles with elemental sulfur using DMSO as a solvent and an oxidant

Dual C-H sulfenylation was used to obtain 3-vulcanized imidazoheterocycles using odorless elemental sulfur under catalyst- and additive-free conditions. C-H activation of both imidazoheterocycles and arylamines/arenols/indoles was realized by a practical protocol in which DMSO served as both a solvent and an internal oxidant.

Efficient synthesis of 4-sulfanylcoumarins from 3-bromo-coumarins via a highly selective DABCO-mediated one-pot thia-Michael addition/elimination process

A facile and efficient protocol for the highly selective direct sulfanylation of 3-bromocoumarins under DABCO promotion, was developed. The transformation took place with aromatic and aliphatic thiols as well as with α,ω-dithiols, affording the expected products in very good to excellent yields. Simple and convenient ways to access 4-((ω-mercaptoalkyl) thio)coumarins and the dimeric 4,4′-(alkane-1,4-diylbis(sulfanediyl))bis(coumarins) were also devised with the use of α,ω-alkanedithiols in different ratios with regards to the starting 3-bromocoumarin. The transformation seems to proceed through the DABCO-mediated thia-Michael stereoselective addition of the thiolate anion to the α,β-unsaturated carbonyl system of the coumarin, followed by a DABCO-assisted stereoselective dehydrobromination of the resulting α-bromo carbonyl intermediate.

A facile, simple and metal-free protocol for the 4-sulfanylation of 3-bromocoumarins was developed. It involves a thia-Michael addition and a dehydrobromination under DABCO assistance.

Photoinduced synthesis of 2-sulfonylacetonitriles with the insertion of sulfur dioxide under ultraviolet irradiation

Metal-free insertion of sulfur dioxide with aryl iodides and 3-azido-2-methylbut-3-en-2-ol under ultraviolet irradiation at room temperature is achieved, giving rise to 2-(arylsulfonyl)acetonitriles in moderate to good yields. Alkyl iodide is also workable under these conditions. This transformation proceeds smoothly under mild conditions with a broad substrate scope. Various functional groups are compatible including amino, ester, halo, and trifluoromethyl groups. No metal catalyst or additive is needed during the reaction process. Mechanistic studies show that under ultraviolet irradiation, an aryl radical is generated in situ from aryl iodide, which undergoes subsequent sulfonylation via the insertion of sulfur dioxide leading to arylsulfonyl radical intermediates. Then the arylsulfonyl radical reacts with 3-azido-2-methylbut-3-en-2-ol giving rise to the corresponding 2-(arylsulfonyl)acetonitrile.

Catalyst-free direct cross-dehydrogenative coupling of imidazoheterocycles with glyoxal hydrates: an efficient approach to 1,2-diketones

An efficient and convenient methodology for catalyst-free cross-dehydrogenative coupling of imidazoheterocycles with glyoxal hydrates in good yields was developed. This methodology exhibits a broad substrate scope and excellent functional group tolerance and offers a straightforward means to produce different heterocycles such as imidazoheterocyclic quinoxaline, imidazoheterocyclic hydantoin and imidazoheterocyclic α-keto ketamine under relatively mild conditions. Biological evaluation showed that the most potent compound 3m possesses significant in vitro antiproliferative activities against human-derived lung cancer cell lines with an IC50 value of 14.8 μM.

A Three-Component Strategy for Benzoselenophene Synthesis under Metal-Free Conditions Using Selenium Powder

An efficient three-component benzoselenophenes formation has been developed from substituted indoles, acetophenones, and selenium powder under metal-free conditions. 2-Aryl indoles played an important role to promote benzoselenophene formation from acetophenone derivatives and selenium powder. One C-C and two C-Se bonds were selectively formed to provide 40 new benzoselenophenes in good yields.

Metal-free difunctionalization of alkynes leading to alkenyl dithiocyanates and alkenyl diselenocyanates at room temperature

A simple and practical method for the synthesis of alkenyl dithiocyanates and alkenyl diselenocyanates has been developed via stereoselective difunctionalization of alkynes with NaSCN or KSeCN at room temperature. Through this methodology, a series of alkenyl dithiocyanates and alkenyl diselenocyanates could be efficiently and conveniently obtained in moderate to good yields under mild and metal-free conditions by the simple use of oxone and PhI(OAc)2 as the oxidants.

Oxidative dual C–H selenation of imidazoheterocycles with ethers or alkanes using selenium powder via a radical pathway

A DCP-mediated oxidative dual C–H selenation radical reaction of imidazoheterocycles with ethers or alkanes using selenium powder was developed.

Photoredox-catalyzed hydrosulfonylation reaction of electron-deficient alkenes with substituted Hantzsch esters and sulfur dioxide

A sulfonylation reaction of 4-substituted Hantzsch esters, DABCO·(SO₂)₂, and electron-deficient alkenes at room temperature in the presence of photoredox catalysis under visible light irradiation is described.

Copper-catalyzed C–H/N–H cross-coupling reactions for the synthesis of 3-heteroaryl quinoxalin-2(1H)-ones

An effective copper-catalyzed C–H/N–H cross-coupling of quinoxalin-2(1H)-ones with diverse unprotected 2-quinoxalinones and 2-quinolinones was developed.

Oxidative oxy-cyclization of 2-alkynylbenzamide enabled by TBAB/Oxone: switchable synthesis of isocoumarin-1-imines and isobenzofuran-1-imine

A TBAB-controlled switchable synthesis of isocoumarin-1-imine and isobenzofuran-1-imine from 2-alkynylbenzamide in water is described in this paper.

An unexpected reaction of aryldiazonium tetrafluoroborates, sodium metabisulfite, and thiourea under photoinduced conditions

A photoinduced synthesis of S-aryl thiosulfonates through a three-component reaction of aryldiazonium tetrafluoroborates, sodium metabisulfite, and thiourea is achieved. In this transformation, a radical coupling pathway is proposed.

Using SeO2 as a selenium source to make RSe-substituted aniline and imidazo[1,2-a]pyridine derivatives

A mild and practical method is developed for the synthesis of ArSe-substituted aniline and imidazo[1,2-a]pyridine derivatives using SeO₂ as a selenium agent.

Synthesis of β-hydroxysulfones through a copper(ii)-catalyzed multicomponent reaction with the insertion of sulfur dioxide

A copper(ii)-catalyzed aerobic oxidative reaction of arylhydrazines, DABCO·(SO₂)₂ and alkenes is reported. Diverse β-hydroxysulfones are generated in moderate to good yields through the hydroxysulfonylation of alkenes with the insertion of sulfur dioxide under mild conditions. In some cases, β-ketosulfones are produced.

Metal-catalyzed radical-type transformation of unactivated alkyl halides with C–C bond formation under photoinduced conditions

Recent advances in the metal-catalyzed radical-type transformation of unactivated alkyl halides with C–C bond formation under photoinduced conditions are summarized. Usually, a broad reaction scope is observed including tertiary, secondary, and primary alkyl halides, with good functional group compatibility.

Photoredox-catalyzed sulfonylation of alkenylcyclobutanols with the insertion of sulfur dioxide through semipinacol rearrangement

A photoredox-catalyzed sulfonylation of alkenylcyclobutanols with the insertion of sulfur dioxide through semipinacol rearrangement under visible light irradiation is developed.

Copper-catalyzed direct C–H arylselenation of 4-nitro-pyrazoles and other heterocycles with selenium powder and aryl iodides. Access to unsymmetrical heteroaryl selenides

A one-pot, Cu-catalyzed direct C–H arylselenation protocol using elemental Se and aryl iodides was developed for nitro-substituted, N-alkylated pyrazoles, imidazoles and other heterocycles including 4H-chromen-4-one. This general and concise method allows one to obtain a large number of unsymmetrical heteroaryl selenides bearing a variety of substituents. The presence of the nitro group was confirmed to be essential for the C–H activation and can also be used for further functionalisation and manipulation. Several examples of heteroannulated benzoselenazines were also synthesized using the developed synthetic protocol.

In this work, we elaborated a general and straightforward method which permits the rapid assembly of unsymmetrical heteroaryl-aryl selenides containing 4-nitropyrazole, 4-nitroimidazole and a few other heterocyclic scaffolds.

T3P® mediated domino C(sp2)–H sulfenylation/annulation of enaminones and methylsulfinyls for the synthesis of chromone thioether derivatives

Regio-selective preparation of 3-sulfenylated chromone using T3P® has been described for the first time.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Molecular iodine-mediated synthesis of thiocarbamates from thiols, isocyanides and water under metal-free conditions

A simple and practical molecular iodine-mediated method for the efficient construction of thiocarbamates from isocyanides, thiols and water under metal-free and mild conditions has been developed. A variety of thiocarbamates were easily synthesized through this methodology, which has the advantages of simple operation, eco-friendly conditions, good functional group tolerance, and readily accessible raw materials.

Palladium-catalyzed oxidative C–H/C–H cross-coupling of imidazopyridines with azoles

A palladium-catalyzed oxidative C–H/C–H cross-coupling of imidazopyridines with azoles using air as the oxidant has been developed.

Copper-catalyzed C–N bond formation with imidazo[1,2-a]pyridines

An efficient Cu-catalyzed C–N bond formation with imidazo[1,2-a]pyridines on the C-3 position via a radical pathway is reported.