Iodine-Mediated Difunctionalization of Imidazopyridines with Sodium Sulfinates: Synthesis of Sulfones and Sulfides

Metal-Free Regioselective Alkylation of Imidazo[1,2-a]pyridines with N-Hydroxyphthalimide Esters under Organic Photoredox Catalysis

A visible-light-induced direct C–H alkylation of imidazo[1,2-a]pyridines has been developed. It proceeds at room temperature by employing inexpensive Eosin Y as a photocatalyst and alkyl N-hydroxyphthalimide (NHP) esters as alkylation reagents. A variety of NHP esters derived from aliphatic carboxylic acids (primary, secondary, and tertiary) were tolerated in this protocol, giving the corresponding C-5-alkylated products in moderate to excellent yields. Mechanistic studies indicate that a radical decarboxylative coupling pathway was involved in this process.

Visible light-induced photocatalytic C–H ethoxycarbonylmethylation of imidazoheterocycles with ethyl diazoacetate

A visible-light-promoted regioselective ethoxycarbonylmethylation of imidazoheterocycles has been developed using an α-diazoester via a radical pathway.

Peroxide-mediated site-specific C–H methylation of imidazo[1,2-a]pyridines and quinoxalin-2(1H)-ones under metal-free conditions

An effective approach to realize the direct methylation of imidazo[1,2-a]pyridines and quinoxalin-2(1H)-ones with peroxides under metal-free conditions is described.

Synthesis of naphtho[1′,2′:4,5]imidazo[1,2-a]pyridines via Rh(iii)-catalyzed C–H functionalization of 2-arylimidazo[1,2-a]pyridines with cyclic 2-diazo-1,3-diketones featuring with a ring opening and reannulation

An unprecedented synthesis of functionalized naphtho[1′,2′:4,5]imidazo[1,2-a]pyridines via rhodium-catalyzed cascade reactions of 2-arylimidazo[1,2-a]pyridine-3-carbaldehydes with cyclic α-diazo-1,3-diketones is presented.

Solvent-free and room temperature microwave-assisted direct C7 allylation of indolines via sequential C–H and C–C activation

A Ru or Rh-catalyzed efficient and atom-economic C7 allylation of indolines with vinylcyclopropanes was developed via sequential C–H and C–C activation. A wide range of substrates were well tolerated to afford the corresponding allylated indolines in high yields and E/Z selectivities under microwave irradiation. The obtained allylated indolines could further undergo transformations to afford various value-added chemicals. Importantly, this reaction proceeded at room temperature under solvent-free conditions.

A Ru or Rh-catalyzed direct C7 allylation of indolines with vinylcyclopropanes via sequential C–H/C–C activation under microwave irradiation has been disclosed.

Oxidative sulfonamidomethylation of imidazopyridines utilizing methanol as the main C1 source

An efficient one pot, three component synthesis of C3 sulfonamidomethylated imidazopyridines has been disclosed under metal-free conditions, which utilized the commercially available and renewable reagent methanol as the main methylene source. A wide range of substituted imidazopyridines and sulfamides/amines were well tolerated to afford the corresponding products in up to 92% yield. In the isotopic labelling experiment, it was found that a minor part of the methylene also originated from DTBP. Moreover, the radical scavenger reactions were conducted, which suggested that a free-radical mechanism was probably not involved. The current methodology featured several advantages, including broad substrate scope, good functional group tolerance and high reaction efficiency.

Copper-Catalyzed Electrophilic Cyclization of N-Propargylamines with Sodium Sulfinate for the Synthesis of 3-Sulfonated Quinolines

A convenient and effective protocol for the synthesis of 3-sulfonated quinolines via copper-catalyzed electrophilic cyclization of N-propargylamines has been developed, in which cheap and stable sodium sulfinates were utilized as green sulfonylation reagents. This cascade transformation involves radical addition, cyclization and dehydrogenative aromatization processes in a one-pot reaction under mild conditions.

Iodine mediated oxidative cross coupling of 2-aminopyridine and aromatic terminal alkyne: a practical route to imidazo[1,2-a]pyridine derivatives

A novel, transition-metal free route leading to imidazo[1,2-a]pyridine derivatives via iodine mediated oxidative coupling between 2-aminopyridine and aromatic terminal alkyne has been demonstrated. This newly developed method discloses an operationally simple way for the construction of imidazoheterocycles. Commercially available antiulcer drug zolimidine may readily be synthesized employing this method.

One-Pot NBS-Promoted Synthesis of Imidazoles and Thiazoles from Ethylarenes in Water

A facile and eco-friendly method has been developed for the synthesis of imidazoles and thiazoles from ethylarenes in water. The reaction proceeds via in situ formation of α-bromoketone using NBS as a bromine source as well as an oxidant, followed by trapping with suitable nucleophiles to provide the corresponding products in good yields under metal-free conditions.

Iodine-promoted radical alkyl sulfuration of imidazopyridines with dialkyl azo compounds and elemental sulfur

Dialkyl azo compounds were found to be effective alkyl radical sources for direct alkyl sulfuration with imidazopyridines using elemental sulfur under metal-free conditions. Iodine, an inexpensive and mild reagent, could promote alkyl sulfuration. A variety of quaternary cyanoalkyl radicals were successfully coupled with elemental sulfur. A subsequent C-H sulfuration of imidazopyridines afforded a diverse array of imidazopyridine derivatives bearing cyanoalkylthio groups. The cyano group could be modified and further underwent condensation with 2-aminothiazole to afford an interesting heterocyclic amide. Control experiments showed that iodine could greatly suppress the self-coupling of cyanoalkyl radicals, thus making the sulfuration proceed smoothly.

Metal-Free Catalytic Synthesis of Thiocarbamates Using Sodium Sulfinates as the Sulfur Source

A novel molecular iodine-catalyzed protocol for the construction of thiocarbamates from readily available sodium sulfinates, isocyanides, and water has been described. The present methodology offers a facile and practical route to a variety of thiocarbamates in moderate to good yields with favorable functional group tolerance by use odorless sodium sulfinates as the sulfur source. The mechanistic studies suggest the present transformation involves a radical process.

Transition-Metal-Free Regioselective One-Pot Synthesis of Aryl Sulfones from Sodium Sulfinates via Quinone Imine Ketal

A novel, efficient, and regioselective transition-metal-free one-pot synthesis of aryl sulfones via the reactive quinone imine ketal intermediate is demonstrated using easily accessible bench-stable sulfinate salts. A broad range of functionality on p-anisidine substrates as well as sulfinate salts was tolerated under mild reaction conditions to provide the corresponding aryl sulfones in good to excellent yields.

Metal-free cascade rearrangement/radical addition/oxidative C–H annulation of propargyl alcohols with sodium sulfinates: access to 2-sulfenylindenones

A facile protocol for the construction of 2-sulfenylindenones via one-pot cascade rearrangement/radical addition/oxidative C–H cyclization of propargyl alcohols with sodium sulfinates has been developed.

Catalyst free, C-3 functionalization of imidazo[1,2-a]pyridines to rapidly access new chemical space for drug discovery efforts

Multicomponent reactions (MCRs) are robust tools for the rapid synthesis of complex, small molecule libraries for use in drug discovery and development. By utilizing MCR chemistry, we developed a protocol to functionalize the C-3 position of imidazo[1,2-a]pyridine through a three component, decarboxylation reaction involving imidazo[1,2-a]pyridine, glyoxalic acid, and boronic acid.

K₂S₂O₈-Promoted Aryl Thioamides Synthesis from Aryl Aldehydes Using Thiourea as the Sulfur Source

Thiourea as a sulfur atom transfer reagent was applied for the synthesis of aryl thioamides through a three-component coupling reaction with aryl aldehydes and N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAC). The reaction could tolerate various functional groups and gave moderate to good yields of desired products under the transition-metal-free condition.

Rapid transformation of sulfinate salts into sulfonates promoted by a hypervalent iodine(III) reagent

An alternative method for forming sulfonates through hypervalent iodine(III) reagent-mediated oxidation of sodium sulfinates has been developed. This transformation involves trapping reactive sulfonium species using alcohols. With additional optimization of the reaction conditions, the method appears extendable to other nucleophiles such as electron-rich aromatic systems or cyclic ethers through a ring opening pathway.

One-Pot Multicomponent Mechanosynthesis of Polysubstituted trans-2,3-Dihydropyrroles and Pyrroles from Amines, Alkyne Esters, and Chalcones

An efficient and practical one-pot multicomponent reaction of amines with alkyne esters and chalcones promoted by I₂/PhI(OAc)₂ has been developed under solvent-free ball-milling conditions to afford a variety of polysubstituted trans-2,3-dihydropyrroles in moderate to good yields. The present method features a short reaction time, mild reaction conditions, broad substrate scope, and feasibility of large-scale synthesis. Intriguingly, this protocol can also furnish the corresponding synthetically more attractive pyrroles with the addition of an oxidant in a one-pot way.

Regioselective synthesis of unsymmetrical biheteroaryls via copper(ii)-catalyzed cascade annulation

A facile and efficient copper-catalyzed cascade annulation of an imidazoheterocycle with salicylaldehyde, piperidine, and terminal alkyne was developed to afford unsymmetrical biheteroaryl derivatives in high yields.

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.

Exogenous-oxidant-free electrochemical oxidative C–H sulfonylation of arenes/heteroarenes with hydrogen evolution

This work describes an exogenous-oxidant-free radical C–H sulfonylation using an electrochemical oxidative protocol.