Iodine-Catalyzed Intramolecular Oxidative Thiolation of Vinylic Carbon-Hydrogen BondsviaTandem Iodocyclization and Dehydroiodination: Construction of 2-Methylene-3-thiophenones

Scaffold-Hopping Strategies in Aurone Optimization: A Comprehensive Review of Synthetic Procedures and Biological Activities of Nitrogen and Sulfur Analogues

Aurones, particular polyphenolic compounds belonging to the class of minor flavonoids and overlooked for a long time, have gained significative attention in medicinal chemistry in recent years. Indeed, considering their unique and outstanding biological properties, they stand out as an intriguing reservoir of new potential lead compounds in the drug discovery context. Nevertheless, several physicochemical, pharmacokinetic, and pharmacodynamic (P3) issues hinder their progression in more advanced phases of the drug discovery pipeline, making lead optimization campaigns necessary. In this context, scaffold hopping has proven to be a valuable approach in the optimization of natural products. This review provides a comprehensive and updated picture of the scaffold-hopping approaches directed at the optimization of natural and synthetic aurones. In the literature analysis, a particular focus is given to nitrogen and sulfur analogues. For each class presented, general synthetic procedures are summarized, highlighting the key advantages and potential issues. Furthermore, the biological activities of the most representative scaffold-hopped compounds are presented, emphasizing the improvements achieved and the potential for further optimization compared to the aurone class.

Electro-organic synthesis of isatins and hydrazones through C-N cross-coupling and C(sp2)-H/C(sp3)-H functionalization

An efficient and unique approach to synthesize isatin (indole-2,3-dione) from 2-aminoacetophenone under electrochemical conditions supported by I2-DMSO through C-N cross-coupling and C(sp2)-H/C(sp3)-H functionalization is presented. This synthetic method spans a wide range of substituted 2-aminoacetophenone substrates. The use of iodine as a promoter and shorter reaction times produced good to very good yields of isatin derivatives, which is a significant improvement over the reaction in a batch process. Further, hydrazones of isatin were synthesized by using hydrazine hydrate which produces electrochemically active molecules, namely isatin-hydrazones. The hydrazones of acetophenone were also obtained using the same reaction protocol. Additionally, the effect of increasing scan rate studied using cyclic voltammetry shows that the process followed a diffusion-controlled mechanism.

A concise synthesis of thioaurones via NBS-induced cyclization of MOM-protected 2'-mercaptochalcones

A mild and efficient approach for the synthesis of thioaurones via NBS-induced cyclization of methoxymethyl-protected mercapto-chalcones has been developed. This simple method is highly functional group tolerant and provides straightforward access to thioaurones in good to high yields.

Regio- and Chemoselective Access to Dihydrothiophenes and Thiophenes via Halogenation/Intramolecular C(sp2)-H Thienation of α-Allyl Dithioesters at Room Temperature

An operationally simple, practical, and efficient cascade approach employing α-allyl dithioesters and NBS/NIS has been achieved to access a series of dihydrothiophenes and thiophenes containing diverse functional groups of different electronic and steric natures in good to excellent yields at room temperature in open air. The reaction proceeds via the electrophilic addition of a halogen source (NBS/NIS) to an allylic double bond, followed by intramolecular regio- and chemoselective S-cyclization. This protocol avoids potential toxicity and tedious work-up conditions, and features easy synthesis from readily available starting materials under catalyst-free conditions. Furthermore, 4,5-dihydrothiophenes were aromatized to thiophenes by treatment with KOH in DMF at room temperature. A probable mechanism for the formation of dihydrothiophenes and thiophenes from α-allyl dithioesters has been suggested. Notably, a large-scale experiment and the transformations of products indicated the potential utility of this reaction compared to competing processes for the synthesis of 4,5-dihydrothiophenes and thiophenes.

Cu-Catalyzed and iodine mediated synthesis of thioaurones via in situ C-S bond generation using xanthate as a sulfur surrogate

An efficient method for synthesizing thioaurones has been developed using xanthate as an odorless sulfur surrogate. This reaction's key success lies in the use of iodine as a reagent, which promotes the α-iodination followed by cyclization of saturated ketones. This methodology has also been demonstrated with less reactive 2'-bromochalcones in good yield. Synthesis of the red isomer of indigo, i.e. a thia-analog of indirubin, was also achieved.

Et3N/DMSO-supported one-pot synthesis of highly fluorescent β-carboline-linked benzothiophenones via sulfur insertion and estimation of the photophysical properties

A robust transition-metal-free strategy is presented to access novel β-carboline-tethered benzothiophenone derivatives from 1(3)-formyl-β-carbolines using elemental sulfur activated by Et3N/DMSO. This expeditious catalyst-free reaction proceeds through the formation of β-carboline-based 2-nitrochalcones followed by an incorporation of sulfur to generate multifunctional β-carboline-linked benzothiophenones in good to excellent yields. The synthetic strategy could also be extended towards the synthesis of β-carboline-linked benzothiophenes. Moreover, the afforded products emerged as promising fluorophores and displayed excellent light-emitting properties with quantum yields (ΦF) up to 47%.

Solvent-free N-iodosuccinimide-promoted synthesis of spiroimidazolines from alkenes and amidines under ball-milling conditions

An environmentally benign and N-iodosuccinimide-promoted intermolecular cyclization between alkenes and amidines has been demonstrated under solvent-free ball-milling conditions, affording a variety of spiroimidazolines with remarkable functional group tolerance and good to excellent yields.

Tandem four-component reaction for efficient synthesis of dihydrothiophene with substituted amino acid ethyl esters

The one-pot four-component reaction of aromatic aldehydes, malononitrile, 1,3-thiazolidinedione and ethyl glycinate hydrochloride in ethanol in the presence of triethylamine afforded trans-dihydrothiophene ureidoformamide derivatives in moderate to good yields. The other α-amino acid ethyl esters resulted in the corresponding diastereoisomeric dihydrothiophene derivatives with various molecular ratios. The functionalized thiophene derivatives were also successfully prepared by sequential dehydrogenation reaction with DDQ.

The one-pot four-component reaction of aromatic aldehydes, malononitrile, 1,3-thiazolidinedione and ethyl glycinate hydrochloride in ethanol in the presence of triethylamine afforded trans-dihydrothiophene.

NaH promoted [4+3] annulation of crotonate-derived sulfur ylides with thioaurones: synthesis of 2,5-dihydrobenzo[4,5]thieno[3,2-b]oxepines

The [4+3] annulation reaction of crotonic acid derivative sulfur ylides with thioaurones has, for the first time, been reported using NaH as the base. A diverse array of 2,5-dihydrobenzo[4,5]thieno[3,2-b]oxepines is obtained in good to excellent yields. The proposed mechanism is investigated and supported by DFT calculations.

Iodine-catalyzed C–H/S–H oxidative coupling: from 1,3-diketones and thiophenols to β-dicarbonyl thioethers

A novel I₂-catalyzed Csp³-H/S–H oxidative coupling between alkyl 1,3-diketones and thiophenols to form β-carbonyl thioethers was demonstrated.

Silver-mediated oxidative vinylic C–H bond sulfenylation of enamides with disulfides

A silver-mediated oxidative vinylic C–H bond sulfenylation of enamides was developed. This method is compatible with diaryl and dialkyl disulfides to deliver the biologically precious chalcogenated olefins efficiently. A plausible non-chain radical mechanism was proposed for understanding this novel sulfenylation based on the mechanistic studies.