DMSO as a Dual Carbon Synthon and Water as Oxygen Donor for the Construction of 1,3,5-Oxadiazines from Amidines

Utilization of DMSO as a solvent-cum-reactant: synthesis of fused 2-aryl-4-methylquinolines

Herein, we disclose the synthesis of a variety of disubstituted fused quinoline, such as 4-methyl-2-arylbenzo[h]quinolines (3a-j), 1-methyl-3-arylbenzo[f]quinolines (3k-r), 1-methyl-3-arylnaphtho[2,3-f]quinolines (3s-x), and 2-aryl-5,7-dimethoxy-4-methylquinolines (4a-c), derivatives from the reaction of an aryl aldehyde with 1-naphthylamine (1a), 2-naphthylamine (1b), 2-aminoanthracene (1c) and 3,5-dimethoxyaniline (1d), respectively, at 80 °C in the presence of 30 mol% (±)-10-camphorsulfonic acid ((±)-CSA) using DMSO as the solvent-cum-reactant. DMSO molecules regioselectively incorporate three carbon atoms into the target molecule in this distinct reaction. The other advantages of the present protocol are that it can be performed under mild reaction conditions and does not require metal catalysts, additional additives or oxidants.

DMSO promoted catalyst-free oxidative C-N/C-O couplings towards synthesis of imidazoles and oxazoles

Dimethyl sulfoxide (DMSO)-promoted catalyst-free oxidative C-N coupling and C-O coupling under oxidant-free conditions are outlined. This protocol is operationally simple and leads to various functionalized substituted imidazoles or oxazoles in good yields. To date, a very limited number of oxidation protocols have been established, where DMSO acts solely as a catalyst or an oxidant or both. In this report, DMSO is not only used as a C-N/C-O coupling agent but is also used as the oxidant required for these oxidative transformations. Hence, our demonstrated DMSO-promoted catalyst-free coupling transformation has the ability to lead to a new dimension in the field of oxidative coupling.

Cu(II)-Catalyzed [3 + 1 + 1 + 1] Cyclization of 1,3-Diketones and 2-Naphthols Using N,N-Dimethylethanolamine as a Dual Carbon Synthon for the Synthesis of 2H-Chromenes

Reactions with diverse C1 synthons to realize homologation were well explored. However, homologations occurring twice with one C1 synthon in a reaction were less reported. We disclose herein a Cu(II)-catalyzed novel and efficient synthesis of 2H-chromenes from 2-naphthols, 1,3-diketones, and N,N-dimethylethanolamine (DMEA) as a dual carbon synthon. Various 2H-chromenes with different functional groups are constructed in moderate to good yields. This is the first report that DMEA acts as a dual C1 synthon.

NH4OAc/DMSO-Promoted Benzylation of Pyrrolo[2,1-a]isoquinolines

Benzylation of pyrrolo[2,1-a]isoquinoline derivatives has been realized with various phenols by the use of ammonium acetate as a promoter (20 examples, up to 84% yield). DMSO served as the source of methylene and solvent. The employment of iron chloride as a catalyst can also afford the desired benzylated products in moderate to good yields (11 examples, up to a 74% yield).

Dimethyl Sulfoxide Provides Three Different Units in Synthesis of Chroman-4-ones Containing Sulfur and a Quaternary Carbon Center under HOAc Conditions

HOAc-promoted construction of chroman-4-ones with a sulfur atom and an α-carbonyl quaternary carbon center directly from ortho-hydroxyacetophenones and DMSO is described. In these unique reactions, DMSO is activated by HOAc and provides three different units (CH2, CH2OH, and CH2SMe) in the target molecules. This reaction displays good substrate scope and reaction yields with a series of substitutes. The mechanism showed that the three units were formed in sequential order.

Copper-catalyzed intermolecular formal (5 + 1) annulation of 1,5-diynes with 1,2,5-oxadiazoles

One-carbon homologation reactions based on one-carbon insertion into the N-O bond of heterocycles have received tremendous interest over the past decades. However, these protocols have to rely on the use of hazardous and not easily accessible diazo compounds as precursors, and examples of the relevant asymmetric catalysis have not been reported. Here we show that a copper-catalyzed intermolecular formal (5 + 1) annulation of 1,5-diynes with 1,2,5-oxadiazoles involving one-carbon insertion into the heterocyclic N-O bond via non-diazo approach. This method enables practical and atom-economic synthesis of valuable pyrrole-substituted oxadiazines in generally moderate to good yields under mild reaction conditions. In addition, the possibility of such an asymmetric formal (5 + 1) annulation also emerges.

Halogen cation-promoted and solvent-regulated electrophilic cyclization for the regioselective synthesis of 3-haloquinolines and 3-halospirocyclohexadienones

A novel approach for the production of halogen cations through the reaction of halogens with silver ions is described in this paper. On this basis, the regioselective synthesis of 3-haloquinolines and 3-halospirocyclohexadienones is realized through solvent regulation. The gram-scale reaction and the compatibility of complex substrates demonstrate the synthetic potential of this protocol, which will be an appealing strategy in organic synthesis.

Selectfluor-Promoted Reactions of Aryl Methyl Ketones with Dimethyl Sulfoxide to Give 2,5-Diacylthiophenes and β-Acyl Allylic Methylsulfones

In this paper, a convenient synthesis of 2,5-diacylthiophenes and β-acyl allylic methylsulfones from aryl methyl ketones with dimethyl sulfoxide (DMSO) through Selectfluor-promoted cascade cyclization and cross-coupling reactions by simple solvent modification is described. This method enables the formation of new C-C and C-S bonds via the selection of different solvent ratios, in which DMSO molecules as synthons can be selectively introduced into methyl ketones. The features of this transformation include readily available starting materials, excellent chemoselectivity, and good functional group tolerance.

Recent Advances in DMSO-Based Direct Synthesis of Heterocycles

Besides serving as a low-toxicity, inexpensive and easily accessible solvent, dimethyl sulfoxide (DMSO) has also been extensively used as a versatile reagent for the synthesis of functionalized molecules. Dimethyl sulfoxide can not only be utilized as a carbon source, a sulfur source and an oxygen source, but also be employed as a crucial oxidant enabling various transformations. The past decade has witnessed a large number of impressive achievements on the direct synthesis of heterocycles as well as modifications of heterocyclic compounds by applying DMSO as a reagent. This review summarized the DMSO-based direct heterocycle constructions from 2012 to 2022.

Application of N,N-Dimethylethanolamine as a One-Carbon Synthon for the Synthesis of Pyrrolo[1,2-a]quinoxalines, Quinazolin-4-ones, and Benzo[4,5]imidazoquinazolines via [5 + 1] Annulation

The synthesis of N-heterocycles composes a significant part of synthetic chemistry. In this report, a Cu(II)-catalyzed green and efficient synthesis of pyrrolo[1,2-a]quinoxaline, quinazolin-4-one, and benzo[4,5]imidazoquinazoline derivatives was developed, employing N,N-dimethylethanolamine (DMEA) as a C1 synthon. Green oxidant O₂ is critical in these transformations, facilitating the formation of a key intermediate─a reactive iminium ion. The method conducted under mild conditions is compatible with a diversity of functional groups, providing an appealing alternative to the previously developed protocols.

Modification of Pyrrolo[2,1-a]isoquinolines and Polysubstituted Pyrroles via Methylenation with Acetyl Chloride and Dimethylsulfoxide

A convenient synthesis of methylene-bridged pyrrolo[2,1-a]isoquinolines has been developed. Treatment of pyrroloisoquinolines with acetyl chloride and dimethylsulfoxide (DMSO) at ambient temperature afforded bispyrroloisoquinolylmethanes in 17-85% yields. This reaction system can also be expanded to the synthesis of bispyrrolylmethanes (34-94% yields). Easy chemical transformation of methylene-bridged pyrroloisoquinoline provided an unsymmetric acid and amide possessing a privileged framework.

Selectfluor-Mediated Synthesis of β-Acyl Allyl Sulfones/β-Acyl Allyl Benzotriazoles from Ketones/Acetylenes, Aryl Sulfinates/Benzotriazole, and DMSO as a Dual-Carbon Synthon

A Selectfluor-mediated approach for the synthesis of β-acyl allyl sulfones/β-acyl allyl benzotriazoles with excellent atom economy from readily available acetophenones/aryl acetylenes, aryl sulfinates/benzotriazoles, and dimethyl sulfoxide (DMSO) is described. In this protocol, DMSO acts as a dual-carbon synthon, resulting in a transition-metal-free construction of two C-C and one C-S or two C-C and one C-N bonds in one pot. This approach is extended to generate chemically diverse compounds. Additionally, β-acyl allyl sulfones/β-acyl allyl benzotriazoles were prepared from acetylenes instead of acetophenones.

DMSO as a Dual Carbon Synthon in One-pot Tandem Synthesis of N-alkylated Quinazolinones from Anthranilamides and Acetophenones

A new, efficient, metal-free, and DMSO intervened approach for the synthesis of N-alkylated quinazolinones from readily available 2-aminobenzamide and aryl methyl ketones in the presence of an oxidizing agent has...

Iron-catalyzed [3+2+1] annulation of 2-aminobenzimidazoles/3-aminopyrazoles and aromatic alkynes using N,N-dimethylaminoethanol as one carbon synthon for the synthesis of pyrimido[1,2-a]benzimidazoles and pyrimido[1,2-b]indazoles

A simple and efficient method for the synthesis of pyrimido[1,2-a]benzimidazoles and pyrimido[1,2-b]indazoles from 2-aminobenzimidazoles/3-aminoindazoles, alkynes and N,N-dimethylaminoethanol in a three-component [3+2+1] annulation catalyzed by FeCl3 has been established, where N,N-dimethylaminoethanol...

DMSO as a C1 Source for [2 + 2 + 1] Pyrazole Ring Construction via Metal-Free Annulation with Enaminones and Hydrazines

A cascade reaction between enaminones, hydrazines, and dimethyl sulfoxide (DMSO) for the synthesis of 1,4-disubstituted pyrazoles catalyzed by molecular iodine in the presence of Selectfluor has been realized. DMSO plays a dual role as the C₁ source and the reaction medium. In addition, the synthesis of 1,3,4-trisubstituted pyrazoles using aldehydes as alternative C₁ building blocks has also been achieved.