Reactivity of p-Toluenesulfonylmethyl Isocyanide: Iron-Involved C–H Tosylmethylation of Imidazopyridines in Nontoxic Media

Cu(II)-Mediated Sulfonylation of (Hetero)arenes with TosMIC Using Monodentate Directing Groups

Monodentate chelation-assisted direct ortho-C-H sulfonylation of (hetero)arenes using TosMIC as the novel sulfonylating reagent has been developed. A broad range of substrates, including indolines, indoles, 2-phenylpyridines, and others were well tolerated to afford the corresponding products in moderate to good yields. Mechanistic studies revealed that the sulfonyl radical might be involved. Inspired by the above discovery, preliminary para-C-H sulfonylation of naphthalene substrate was also successfully realized. The current protocol featured with cheap metal catalysis, good functional group compatibility, and operational convenience.

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.

Synthesis and site selective C-H functionalization of imidazo-[1,2-a]pyridines

Imidazo[1,2-a]pyridine has attracted much interest in drug development because of its potent medicinal properties, therefore the discovery of novel methods for its synthesis and functionalization continues to be an exciting area of research. Although transition metal catalysis has fuelled the most significant developments, extremely beneficial metal-free approaches have also been identified. Even though pertinent reviews focused on imidazo[1,2-a]pyridine synthesis, properties (physicochemical and medicinal), and functionalization at the C3 position have been published, none of these reviews has focused on the outcomes obtained in the field of global ring functionalization. We wish here to describe a brief synthesis and an overview of all the functionalization reactions at each carbon atom, viz, C2, C3, C5, C6, C7 and C8 of this scaffold, divided into sections based on site-selectivity and the type of functionalization methods used.

Regioselective C3-H Alkylation of Imidazopyridines with Donor-Acceptor Cyclopropanes

Alkylated imidazopyridines are crucial structures for medicinal chemistry. Here, an efficient method for the C3-H alkylation of imidazopyridines was devised. Under Lewis acid-catalyzed conditions, reactions of imidazopyridines with different donor-acceptor cyclopropanes were carried out. Finally, 1,3-bisfunctionalizaton of donor-acceptor cyclopropanes was performed. In addition, synthesized C3-alkylated imidazopyridines are amenable for diverse synthetic applications.

Transition Metal Catalyst-Free C-3 Sulfonylmethylation of Imidazo[1,2-a]pyridines with Glyoxylic Acid and Sodium Sulfinates in Water

Herein, we describe an efficient and benign protocol for direct C-3 sulfonylmethylation of imidazo[1,2-a]pyridines with glyoxylic acid and sodium sulfinates. Various sulfonylmethylated imidazo[1,2-a]pyridines were synthesized in water under transition metal catalyst-free conditions. This multicomponent reaction featured available substrates, good functional group tolerance, moderate to excellent yields, and mild reaction conditions.

A new method for C(sp2)-H sulfonylmethylation with glyoxylic acid and sodium sulfinates

We herein describe a C4 sulfonylmethylation of pyrazol-5-amines with glyoxylic acid and sodium sulfinates. The reaction only needed to add water as the solvent, and it featured mild reaction condition,...

Fe(III)-Catalyzed N-Amidomethylation of Secondary and Primary Anilines with TosMIC

A Fe(III)-catalyzed N-amidomethylation of secondary and primary anilines with p-toluenesulfonylmethyl isocyanide (TosMIC) in water is described. TosMIC plays dual roles as the source of methylene as well as an amidating reagent to form α-amino amides in this multicomponent reaction. The combination of TosMIC and other isocyanides was also investigated to give the desired products in acceptable yields. The current protocol features use of iron catalyst and nontoxic media, broad substrate scope, mild conditions, and operational simplicity.

Methylene-Tethered Arylsulfonation and Benzotriazolation of Aryl/Heteroaryl C-H Bonds with DMSO as a One-Carbon Surrogate

The Selectfluor-mediated approach toward the synthesis of methylene-tethered arylsulfonation and benzotriazolation of imidazopyridines has been described. The reaction involves imidazopyridine, aryl sulfinate, or benzotriazole and dimethyl sulfoxide (DMSO) in the presence of Selectfluor, where DMSO acts as a one-carbon synthon. The protocol has been extended to the methylene-tethered arylsulfonation and benzotriazolation of β-naphthols. The mechanistic insights show that the intermediate 3-((methylthio)methyl)-2-phenylimidazo[1,2-a]pyridine is generated from imidazopyridine, DMSO, and Selectfluor. The nucleophilic displacement by the aryl sulfinate salt or benzotriazole on the intermediate afforded the product.

Rongalite as C1 Synthon and Sulfone Source: A Practical Sulfonylmethylation Based on the Separate-Embedding Strategy

Rongalite has been used in several challenging synthetic transformations with operationally simple and effective protocols. However, the employment of multiple characteristics of rongalite in synthetic chemistry is comparatively little known. Herein we report a separate-embedding type sulfonylmethylation of sulfoxonium ylides in which rongalite concurrently acted as a sulfone source, C1 synthon, radical initiator, and potential reducing reagent for the first time. Notably, this facile and easy-handling reaction does not require a catalyst or prefunctionalized sulfonylmethylation reagents.

Regioselective N-F and α C(sp3)-H Arylation of Aliphatic N-Fluorosulfonamides with Imidazopyridines

A regioselective arylation of aliphatic N-fluorosulfonamides with imidazopyridines enabled by breaking of N-F and α C(sp³)-H bond to form C-N and C-C bonds was described. With CuCl as the catalyst, a radical mechanism was proposed to produce N-arylated aliphatic sulfonamides via a N radical intermediate. Importantly, under acidic conditions, an in situ generated imine was the possible intermediate, which was trapped by imidazopyridines to form α C(sp³)-H arylated aliphatic sulfonamides. The current protocol featured a broad substrate scope, tunable reaction conditions, operational convenience, and good regioselectivity.

Iron-Mediated Selective Sulfonylmethylation of Aniline Derivatives with p-Toluenesulfonylmethyl Isocyanide (TosMIC)

An iron-mediated highly selective C-H sulfonylmethylation of aniline derivatives with p-toluenesulfonylmethyl isocyanide in a mixture solvent of H₂O and PEG₄₀₀ under an Ar atmosphere has been realized. This transformation proceeds with operational convenience, use of earth-abundant metal catalyst and nontoxic media, broad substrate scope, and good functional group tolerance. The current methodology could be applied to the regioselective C-H sulfonylmethylation of indolines, tetrahydroquinolines, and tertiary anilines.

Manganese-catalyzed dehydrogenative Csp3-Csp2 coupling of imidazo[1,2-a]pyridines with methyl ketones

A Mn(ii)-catalyzed efficient C-H alkylation of imidazoheterocycles with methyl ketones has been developed via dehydrogenative C(sp3)-C(sp2) coupling which can serve as a novel approach toward hydrocarboxylated imidazolopyridines. The merit of this strategy is illustrated by excellent functional group tolerance and the use of cheap and readily available starting materials.

Crystal structure of 2-(3-methoxyphenyl)-3-((phenylsulfonyl)methyl)imidazo[1,2-a]pyridine, C21H18N2O3S

C21H18N2O3S, monoclinic, P21/n (no. 14), a = 12.1263(2) Å, b = 11.6913(3) Å, c = 12.7643(3) Å, β = 92.340(2)°, V = 1808.11(7) Å3, Z = 4, R gt(F) = 0.0433, wR ref(F 2) = 0.1310, T = 293(2) K.

Oxidant-directed chemoselective sulfonylation and sulfonyloximation of alkenes via cleaving the C–S bond in TosMIC

Oxidant-directed chemoselective sulfonylation and sulfonyloximation reactions for the divergent synthesis of valuable vinyl sulfones and α-sulfonylethanone oximes are developed.

Copper-mediated direct sulfonylation of C(sp2)–H bonds employing TosMIC as a sulfonyl source

Cu-Mediated sulfonylation of C(sp²)–H bonds with p-tosylmethyl isocyanide (TosMIC) as a sulfonyl source was developed utilizing a removable N,O-directing group.

γ-Carboline Synthesis by Heterocyclization of TosMIC Derivatives

A new method for the synthesis of γ-carbolines by a heterocyclization that involves α-indol-2-ylmethyl TosMIC derivatives and different electrophiles has been developed. This methodology has been successfully applied to the synthesis of several highly substituted γ-carbolines.

Cobalt-catalyzed cross-dehydrogenative coupling of imidazo[1,2-a]pyridines with isochroman using molecular oxygen as the oxidant

A cobalt-catalyzed cross-dehydrogenative coupling of 2-arylimidazo[1,2-a]pyridines with isochroman is developed using molecular oxygen as the oxidant.

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.

Rhodium-Catalyzed Direct Bis-cyanation of Arylimidazo[1,2-α]pyridine via Double C-H Activation

An efficient Cp*Rh(III)-catalyzed selective bis-cyanation of arylimidazo[1,2-α]pyridines with N-cyano-N-phenyl-p-methylbenzenesulfonamide via N-directed ortho double C-H activation has been developed. The reaction proceeds with broad functional group tolerance to furnish various cyanated imidazopyridines in high yields. The current methodology exhibits unique characteristics, including high bis-cyanation selectivity, operational convenience, and gram-scale production.

Visible-light mediated regioselective (phenylsulfonyl)difluoromethylation of fused imidazoles with iododifluoromethyl phenyl sulfone

A visible-light catalyzed direct and regioselective (phenylsulfonyl)difluoromethylation of imidazo[1,2-

Visible light-induced C3-sulfonamidation of imidazopyridines with sulfamides

A visible light-induced regioselective sulfonamidation of imidazo[1,2-a]pyridines was developed using sulfamides as the nitrogen sources and aqueous NaClO solution as the oxidant under mild conditions.