Trithiocarbonate Anion as a Sulfur Source for the Synthesis of 2,5-Disubstituted Thiophenes and 2-Substituted Benzo[b]thiophenes

Synthesis of Cyclic Trithiocarbonates from Carbon Disulfide and Propargyl Alcohols under Mild Conditions

A versatile method for the synthesis of cyclic trithiocarbonates has been successfully developed from readily synthesized propargyl alcohols and easily accessible carbon disulfide (CS2), where terminal and nonterminal propargyl alkynols are compatible with this methodology. The developed protocol features simple, mild, atom-economic, and transition-metal-free reaction conditions resulting in the corresponding cyclic trithiocarbonates in moderate to excellent yields.

Domino Reaction Protocol to Synthesize Benzothiophene-Derived Chemical Entities as Potential Therapeutic Agents

An efficient synthesis of 3-amino-2-formyl-functionalized benzothiophenes by a domino reaction protocol and their use to synthesize a library of novel scaffolds have been reported. Reactions of ketones and 1,3-diones with these amino aldehyde derivatives formed a series of benzothieno[3,2-b]pyridine and 3,4-dihydro-2H-benzothiopheno[3,2-b]quinolin-1-one, respectively. A plausible mechanism for the formation of fused pyridine derivatives by the Friedlander reaction has been elucidated by density functional theory (DFT) calculations. Furthermore, hydrazones were obtained by reacting the aldehyde functional group of benzothiophenes with different hydrazine derivatives. Preliminary screening of these compounds against several bacterial strains and cancer cell lines led to the discovery of several hit molecules. Hydrazone and benzothieno[3,2-b]pyridine derivatives are potent cytotoxic and antibacterial agents, respectively. One of the potent compounds effected ∼97% growth inhibition of the LOX IMVI cell line at 10 μM concentration.

Thiolation of Terminal Alkynes with Thiuram Disulfide Reagents Using Water as the Hydrogen Source: Stereoselective Synthesis of (Z)-Vinyl Sulfides

A stereoselective and environmentally friendly thiolation of terminal alkynes was reported. Thiuram disulfide reagents (tetramethylthiuram disulfide and tetraethylthiuram disulfide) that reacted with alkynes in dimethyl sulfoxide (DMSO)/H2O could give (Z)-vinyl sulfides in good yields (up to 88%). This protocol features broad substrate scope, good stereoselectivity, high atom economy, good yields, and is transition metal-free. Mechanistic studies revealed that water and DMSO served as hydrogen sources, which greatly highlighted the unique reactivity of this special reaction involving two H-atom donors.

CS2/KOH System-Promoted Stereoselective Synthesis of (E)-Alkenes from Diarylalkynes and a "Hidden" Zinin-Type Reduction of Nitroarenes into Arylamines

In this work, we present the CS2/KOH system as a practical and efficient reductive medium for obtaining (E)-alkenes from alkynes through a highly stereoselective semireduction reaction. This cost-effective system enabled successful semireduction reactions of diverse alkynes using water as a hydrogen source, yielding moderate to excellent yields. The versatility of this protocol is further demonstrated through the synthesis of relevant compounds such as pinosylvin and resveratrol precursors, along with the notable anticancer agent DMU-212. Furthermore, during the reaction scope investigation, we serendipitously disclosed that this reductive system was also able to promote a Zinin-type reaction to reduce nitroarenes into arylamines.

Nickel-Catalyzed Sodium Hypophosphite-Participated Direct Hydrophosphonylation of Alkyne toward H-Phosphinates

The traditional methods for the synthesis of phosphinate esters use phosphorus trichloride (PCl₃) as the phosphorous source, resulting in procedures that are often highly polluting and energy intensive. The search for an alternative approach that is both mild and environmentally friendly is a challenging, yet highly rewarding task in modern chemistry. Herein, we use an inorganic phosphorous-containing species, NaH₂PO₂, to serve as the source of phosphorous that participates directly in the nickel-catalyzed selective alkyne hydrophosphonylation reaction. The transformation was achieved in a multicomponent fashion and at room temperature, and most importantly, the H-phosphinate product generated is an advanced intermediate which can be readily converted into diverse phosphinate derivatives, including those bearing new P-C, P-S, P-N, P-Se, and P-O bonds, thus providing a complimentary method to classic phosphinate ester synthesis techniques.

Synthesis of Substituted Thiophenes through Dehydration and Heterocyclization of Alkynols

A protocol was described for obtaining a variety of substituted thiophenes with functional potential via metal-free dehydration and sulfur cyclization of alkynols with elemental sulfur (S₈) or EtOCS₂K in moderate-to-good yields. The method provides the base-free generation of a trisulfur radical anion (S₃^•-) and its addition to alkynes as an initiator. This research broadens the applications of S₃^•- in the synthesis of sulfur-containing heterocycles.

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.

Photocatalytic Activation of Elemental Sulfur Enables a Chemoselective Three-Component Thioesterification

A mild and chemoselective three-component thioesterification using olefins, α-ketoacids, and elemental sulfur has been developed. The photocatalytic activation of elemental sulfur, a cheap and abundant sulfur source, enables the rapid installation of a sulfur atom into molecules, reactions that ordinarily would require the use of reactive and malodorous sulfur-containing compounds such as thiols and thioacids. This novel reaction is characterized by high yields and a broad substrate scope, which enables the introduction of thioester moieties into complex molecules including a steroid, a peptide, and a nonprotected glycoside. Mechanistic studies indicated that the success of this transformation depends on the multiple roles played by the elemental sulfur, including those of a sulfurizing agent, a terminal oxidant, and a HAT mediator.

Evidence of a Photoinduced Electron-Transfer Mechanism in the Fluorescence Self-quenching of 2,5-Substituted Selenophenes Prepared through In Situ Reduction of Elemental Selenium in Superbasic Media

A series of new 2,5-disubstituted selenophene derivatives are described from elemental selenium and 1,3-diynes in superbasic media. The activation of elemental selenium in a KOH/DMSO system allows cyclization with conjugated diynes at room temperature. The cyclization reaction is extended to a broad range of functional groups, for which photophysics were experimentally and theoretically investigated. The selenophene derivatives present absorption maxima in the UV-A region and fluorescence emission in the violet-to-blue region. Fluorescence decay profiles were obtained showing a monoexponential decay with fast fluorescence lifetimes (∼0.118 ns), as predicted by the Strickler-Berg relations. In general, in both investigations, no dependence on the solvent polarity on the absorption and emission maxima location was observed. On the other hand, solvents and substituents are shown to play a role in the fluorescence quantum yield values. In addition, a fluorescence self-quenching behavior could be observed, related to a photoinduced electron-transfer mechanism. Theoretical calculations performed at the MP2/ADC(2)/cc-pVDZ level of theory were performed in order to investigate the photophysical features of this series of selenophene derivatives.