Transition-Metal-Free Sulfuration/Annulation of Alkenes: Economical Access to Thiophenes Enabled by the Cleavage of Multiple C-H Bonds

Nickel-Catalyzed Regioselective Ring-Opening Hydroarylation of Methylenecyclopropanes

The hydroarylation of methylenecyclopropanes (MCPs) is a challenging process due to the difficulty in controlling regioselectivity and the complex reaction patterns involved. Herein, we report a simple external ligand-free Ni-catalyzed ring-opening hydroarylation of MCPs with high efficiency and unprecedented regioselective arylation as well as broad functional group tolerance by using inexpensive aryl boronic acids as the arylation source. The synthetic utility has been demonstrated for the facile preparation of versatile highly valued products. Mechanistic studies suggest that Ni(II)-H, formed via the oxidative addition of Ni(0) to the proton in the system, might act as a key intermediate.

Expedient Synthesis of Substituted Thieno[3,2-b]thiophenes and Selenopheno[3,2-b]selenophenes Through Cascade Cyclization of Alkynyl Diol Derivatives

Thieno[3,2-b]thiophenes are used as key components in optoelectronic materials, porous hydrogen-storage hosts, organic solar cells, and polymer semiconductors. A step-efficient synthetic protocol was proposed herein for obtaining multisubstituted thieno[3,2-b]thiophene and selenopheno[3,2-b]selenophenes in moderate to good yields via the bisulfur/biselenium cyclization of alkynyl diols with I2/Na2S2O3 or selenium. Using this strategy, substitution patterns were obtained for backbone modification in functional materials.

Medicinal chemistry-based perspectives on thiophene and its derivatives: exploring structural insights to discover plausible druggable leads

Thiophene is a privileged pharmacophore in medicinal chemistry owing to its diversified biological attributes. The thiophene moiety has been ranked 4th in the US FDA drug approval of small drug molecules, with around 7 drug approvals over the last decade. The present review covers USFDA-approved drugs possessing a thiophene ring system. Our analysis reveals that 26 drugs possessing thiophene nuclei have been approved under different pharmacological classes. The review further covers reported thiophene and its substituted analogues with diverse biological activities, including anti-diabetic, anticancer, anti-inflammatory, anticonvulsant, and antioxidant activity. Besides, a section is dedicated to appreciating the implications of structural bioinformatics in drug discovery. Additionally, the manuscript delves into structure-activity relationship studies to explore the chemical groups responsible for eliciting potential therapeutic activities. The review may provide invaluable insights for researchers working with thiophene nuclei in developing novel analogues with greater efficacy and fewer side effects.

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.

One-pot synthesis of 11-sulfenyl dibenzodiazepines via tandem sulfenylation/cyclization of o-isocyanodiaryl amines and diaryl disulfides

A one-pot sulfenylation/cyclization of o-isocyanodiaryl amines has been described for the preparation of 11-sulfenyl dibenzodiazepines. This AgI-catalyzed reaction covers an unexplored tandem process to give seven-membered N-heterocycles. This transformation shows a broad range of substrate scope, simple operation, and moderate to good yields under aerobic conditions. Diphenyl diselenide can also be produced in an acceptable yield.

Nickel-catalyzed divergent Mizoroki-Heck reaction of 1,3-dienes

Developing efficient strategies to realize divergent arylation of dienes has been a long-standing synthetic challenge. Herein, a nickel catalyzed divergent Mizoroki-Heck reaction of 1,3-dienes has been demonstrated through the regulation of ligands and additives. In the presence of Mn/NEt₃, the Mizoroki-Heck reaction of dienes delivers linear products under Ni(dppe)Cl₂ catalysis in high regio- and stereoselectivities. With the help of catalytic amount of organoboron and NaF, the use of bulky ligand IPr diverts the selectivity from linear products to branched products. Highly aryl-substituted compounds can be transformed from dispersive Mizoroki-Heck products programmatically. Preliminary experimental studies are carried out to elucidate the role of additives.

Nickel-catalyzed arylative substitution of homoallylic alcohols

Direct coupling of unactivated alcohols remains a challenge in synthetic chemistry. Current approaches to cross-coupling of alcohol-derived electrophiles often involve activated alcohols such as tosylates or carbonates. We report the direct arylative substitution of homoallylic alcohols catalyzed by a nickel-bisphosphine complex as a facile method to generate allylic arenes. These reactions proceed via formation of an allylic alcohol intermediate. Subsequent allylic substitution with arylboroxine nucleophiles enables the formation of a variety of allylic arenes. The presence of p-methoxyphenylboronic acid is crucial to activate the allylic alcohol to achieve high product yields.

Metal-Free C-S Bond Formation in Elemental Sulfur and Cyclobutanol Derivatives: The Synthesis of Substituted Thiophenes

A general approach for the metal-free synthesis of thiophenes by tert-cyclobutanols and elemental sulfur has been developed. This protocol provides a strategy for constructing multisubstituted thiophene derivatives via C-S bond formation under air. This reaction shows good functionality tolerance under the reaction conditions, and the mechanism is validated by control experiments and density functional theory calculations.

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.

Cu-catalyzed [2 + 2 + 1] cascade annulation of vinyl iodonium salts with elemental sulfur/selenium for the modular synthesis of thiophenes and selenophenes

The Cu-catalyzed [2 + 2 + 1] regioselective synthesis of thiophenes/selenophenes was realized from aryl-vinyl iodonium salts and elemental sulfur/selenium.

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.

Double C-S bond formation via multiple Csp3-H bond cleavage: synthesis of 4-hydroxythiazoles from amides and elemental sulfur under metal-free conditions

A novel and efficient approach for the synthesis of 4-hydroxythiazoles from amides and elemental sulfur has been developed. In the presence of P₂O₅, DMSO and HMPA, this metal-free protocol proceeds smoothly and tolerates a spectrum of functional groups. Furthermore, this strategy involves the process of double Csp³-S bond formation through the cleavage of multiple Csp³-H bonds for the first time.

Recent strategies in the synthesis of thiophene derivatives: highlights from the 2012-2020 literature

Thiophene-based analogs have been fascinated by a growing number of scientists as a potential class of biologically active compounds. Furthermore, they play a vital role for medicinal chemists to improve advanced compounds with a variety of biological effects. The current review envisioned to highlight some recent and particularly remarkable examples of the synthesis of thiophene derivatives by heterocyclization of various substrates from 2012 on.

Diethylaminosulfur Trifluoride: A Novel, Low-Cost, Stable Double Thiolation Reagent for Imidazo[1,2-α]pyridines

We report a novel, inexpensive double thiolation reagent that sulfurizes a broad range of imidazo[1,2-α]pyridines under mild conditions. Importantly, diethylaminosulfur trifluoride, as a common nucleophilic fluorinating reagent, was utilized as a novel thiolation reagent.

Fe-S Catalyst Generated In Situ from Fe(III)- and S3•--Promoted Aerobic Oxidation of Terminal Alkenes

An iron-sulfur complex formed by the simple mixture of FeCl₃ with S₃^•- generated in situ from K₂S is developed and applied to selective aerobic oxidation of terminal alkenes. The reaction was carried out under an atmosphere of O₂ (balloon) and could proceed on a gram scale, expanding the application of S₃^•- in organic synthesis. This study also encourages us to explore the application of an Fe-S catalyst in organic reactions.

Trisulfur-Radical-Anion-Triggered C(sp2)-H Amination of Electron-Deficient Alkenes

A trisulfur-radical-anion (S₃̇^-)-triggered C(sp²)-H amination of α,β-unsaturated carbonyl derivatives with simple amines has been demonstrated. This protocol provides convenient access to a variety of synthetically valuable N-unprotected and secondary β-enaminones with absolute Z selectivity and tertiary β-enaminones with E selectivity. Mechanistic probe and electronic structure theory calculations suggest that S₃̇^- initiates the nucleophilic attacks via a thiirane intermediate.

Access to Substituted Thiophenes through Xanthate-Mediated Vinyl C(sp2)-Br Bond Cleavage and Heterocyclization of Bromoenynes

An environmentally sustainable strategy for the chemoselective heterocyclization of bromoenynes through a transition-metal-free sulfuration/cyclization process is reported. Using inexpensive and safe EtOCS₂K as a thiol surrogate and tetrabutylphosphonium bromide and H₂O as a mixed solvent, the reaction provided a range of substituted thiophenes in moderate to good yields. In addition, 2,3,4,5-tetrasubstituted thiophenes were able to be prepared under mild reaction conditions by electrophilic heterocyclization with NH₄I and EtOCS₂K in good yields.

Cascade cyclization versus chemoselective reduction: a solvent-controlled product divergence

A convenient controllable cascade cyclization and partial reduction of enones for the divergent construction of two types of valuable compounds including polysubstituted thiophenes and saturated ketones are developed.

Synthesis of tetrasubstituted thiophenes via a [3+2] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates and activated allenes

A [3+2] cascade cyclization reaction of pyridinium 1,4-zwitterionic thiolates and activated allenes was developed to access tetrasubstituted thiophenes.

Trisulfur radical anion-triggered stitching thienannulation: rapid access to largely π-extended thienoacenes

Largely π-extended rylene diimide-fused thienoacenes, a new family of fully fused electron donor-acceptor (D-A) molecules, have been readily synthesized by a novel trisulfur radical anion (S3˙-)-triggered stitching thienannulation strategy. The ladder-type fused thiophene cores are constructed in a stitching manner through multiple carbon-sulfur bond formation between acetylenic rylene dyes and S3˙-. A detailed mechanistic study of these stitching thienannulations unveiled the multiple reactivities of S3˙-. Physical properties of the newly formed D-A, A-D-A, and D-A-D type thienoacenes have also been investigated, which revealed their precisely controllable electronic properties.

Ring-opening/annulation reaction of cyclopropyl ethanols: concise access to thiophene aldehydes via C–S bond formation

The synthesis of thiophene aldehydes from easily available cyclopropyl ethanol derivatives and potassium sulfide has been developed.

A trisulfur radical anion (S3˙−) involved sulfur insertion reaction of 1,3-enynes: sulfide sources control chemoselective synthesis of 2,3,5-trisubstituted thiophenes and 3-thienyl disulfides

Cascade cyclization reactions of S₃˙⁻in situ generated from S₂⁻ with 1,3-enynes for the chemoselective synthesis of 2,3,5-trisubstituted thiophenes and 3-thienyl disulfides controlled by sulfide salts are developed.