Synthesis of 1,3,4-Thiadiazoles and 1,4,2-Oxathiazoles from α-Enolic Dithioesters and Active 1,3-Dipoles

A decade update on the application of β-oxodithioesters in heterocyclic synthesis

The diverse synthesis of heterocyclic compounds has always been one of the popular subjects of organic chemistry. To this end, great efforts have been devoted to developing new reagents and establishing new strategies and methods concerning efficiency, selectivity and sustainability. β-Oxodithioesters and their enol tautomers (i.e., α-enolic dithioesters), as a class of simple and readily accessible sulfur-containing synthons, have been widely applied in the construction of various five- and six-membered heterocycles (e.g., thiophenes, thiopyrans, thiazoles, pyridines and quinolines) and other useful open-chain frameworks. Due to their unique chemical structures, β-oxodithioesters bear multiple reaction sites, which enable them to participate in two-component or multicomponent reactions to construct various heterocyclic compounds. In the past decade, the application of β-oxodithioesters in the synthesis of heterocycles has made remarkable progress. Herein, an update on the recent advances in the application of β-oxodithioesters in the synthesis of heterocycles during the period from 2013 to 2023/06 is provided. According to the different types of rings concerning heteroatoms in products, this review is divided into five sections under discussion including (i) synthesis of sulfur-containing heterocycles, (ii) synthesis of sulfur and nitrogen-containing heterocycles, (iii) synthesis of nitrogen-containing heterocycles, (iv) synthesis of nitrogen and oxygen-containing heterocycles, and (v) modification to other open-chain frameworks.

Radical-Cascade Avenue to Access 1,2-Dithioles Employing Dithioesters and Edman's Reagent

An operationally simple and efficient domino etiquette has been developed for the facile construction of 1,2-dithioles employing easily accessible dithioesters as a three-atom CCS synthon and aryl isothiocyanates as a two-atom CS unit in the absence of any catalyst and additive at room temperature under open air. The reaction proceeded efficiently affording the desired 1,2-dithioles in good yields having various functional groups of a diverse electronic and steric nature. This approach avoids possible toxicity and tiresome workup conditions and features easy to handle, cheap, and readily accessible reagents, O₂ as a green oxidant, and gram-scale ability. Notably, the final S-S bond formation and cascade ring construction follow a radical pathway, which has been recognized via a radical trapping experiment with BHT during the course of the reaction. Notably, the exocyclic C═N bond at position 3 of 1,2-dithiole possesses Z stereochemistry.

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.

Method for Preparing N-Tosylhydrazonyl Chlorides

A facile and efficient method for preparing N-tosylhydrazonyl chlorides was developed. The reaction was general for a variety of substrates and displayed wonderful compatibility to diverse substituents. A range of N-tosylhydrazonyl chlorides was prepared for the first time.

Synthesis of thiazolidin-4-ones from α-enolic dithioesters and α-halohydroxamates

A facile access to thiazolidin-4-ones from α-enolic dithioesters and α-halohydroxamates in situ derived active 1,3-dipolar aza-oxyallyl cations was achieved under mild conditions.