Synlett

Reactions of bis(cyclopentadienyl)titanacyclopentenes with BiI3 gave coupling products of one Cp ligand and the alkenyl carbons in moderate yields. An NMR study of the tetracyanoethylene (TCNE) adduct of the product showed that the coupled Cp ring and the alkenyl carbons were connected by one carbon–carbon double bond. This is in sharp contrast to coupling reactions of one Cp ligand with the diene moiety in bis(cyclopentadienyl)titanacyclopentadienes, where two carbon–carbon single bonds were formed between those two components to give dihydroindenes or spiro compounds.

This account describes the latest developments on 3d-metal-catalyzed single-electron-transfer (SET)-induced strategies that use carboxylic acids and their synthetic equivalents as substrates. In general, 3d-metal-promoted SET-mediated transformations of free carboxylic acids proceed readily via the formation of carboxylate radicals, whilst those of carboxylic acid equivalents, bearing an N-donor substituent, proceed via the formation of α-carbo radicals. The advantages of these strategies combine the low-cost of carboxylic acid starting materials and 3d metal catalysts with the possibility of realizing structurally diverse ranges of compounds in an atom- and step-economic manner. Developments primarily achieved by our group and a few by other researchers on this topic are discussed in this account.1 Introduction2 Mechanistic Considerations of 3d-Metal-Catalyzed SET-Mediated Transformations3 Developments Based on SET-Mediated Transformations of Carboxylic Acids4 Developments Based on SET-Mediated Transformations of Carboxylic Acid Equivalents5 Conclusion and Outlook

This report describes a Ru(II)-catalyzed C–H allylation of N,N-dialkylthiobenzamides with allyl methyl carbonate. The reaction is carried out using [RuCl2(p-cymene)]2 in the presence of Cu(OAc)2 and Ag2O. This method represents the first example of a Ru-catalyzed C–H allylation directed by a sulfur-containing group. As a further advantage, the method is performed in sustainable and ecofriendly MeCN as the solvent.

6-Hydroxy-8-chlorooctanoate ethyl ester, an intermediate of α-lipoic acid, was synthesized via a chemoenzymatic method. High-throughput screening revealed that keto reductase HGD-1 could effectively catalyze the preparation of 6-hydroxy-8-chlorooctanoate ethyl ester, achieving a substantial conversion rate. The reaction conditions were optimized subsequently, the parameters for the complexation reaction were established as follows: a weight of AlCl3 1.8 times that of the substrate; a reaction time of 4 h; a temperature range of 20–25 °C. The parameters for the enzyme-catalyzed reaction were as follows: a temperature range of 25–30 °C; a reaction time of 4 h; a solution pH of 6.5–7.5; a substrate concentration of 50 g/L; concentrations of keto reductase HGD-1, coenzyme glucose dehydrogenase, and nicotinamide adenine dinucleotide phosphate of 3 g/L, 4 g/L, and 0.05 g/L, respectively. Under these optimal conditions, the substrate conversion rate exceeded 95%, and 92% yield of 6-hydroxy-8-chlorooctanoate ethyl ester is obtained, suggesting a viable, eco-friendly method for synthesizing α-lipoic acid, and it provides a green process route for the industrial production of α-lipoic acid.

We synthesized diarylated 10-(1,3-dithiol-2-ylidene)anthracene-9-(10H)-one derivatives, which serve as important precursors of unsymmetrical arylated TTFAQs, via the palladium-catalyzed direct C–H arylation. Unsymmetrical diarylated TTFAQs were synthesized by the Horner–Wadsworth–Emmons reaction using diarylated 10-(1,3-dithiol-2-ylidene)anthracene-9-(10H)-one as the starting materials. Additionally, we have successfully synthesized unsymmetrical tetraarylated TTFAQs by a second palladium-catalyzed C–H arylation of diarylated TTFAQs.

Cyclobutane derivatives are important motifs in natural products and bioactive compounds. Owing to their inherent strain, the asymmetric synthesis of cyclobutanes remains a formidable challenge. With the development of various stereospecific transformations of alkylboronic esters, chiral cyclobutylboronates are expected to serve as promising synthetic intermediates for accessing chiral cyclobutane derivatives. However, obtaining highly enantioenriched cyclobutylboronates poses a daunting task in the field of organic synthesis. In this context, we highlight recent significant advances in the synthesis of chiral cyclobutylboronates.1 Introduction2 Enantioselective Borylation of Cyclobutenes3 Enantioselective Borylation of Cyclobutanes4 Other Methods5 Conclusions

This study introduces an efficient, environmentally friendly, and sustainable method for synthesizing N-acylhydrazone analogues by engaging isoniazid in a condensation reaction with variously substituted benzaldehydes. The deep-eutectic solvent (ZnCl2/urea) employed in this study acted not only as a solvent but also as a catalyst to facilitate the synthesis of the target compounds within two to six minutes without the requirement of any lengthy purification techniques. The synthetic protocol is operationally simple and offers other remarkable advantages such as a short reaction time, good to excellent yields, a scalable protocol, and a recyclable and reusable catalyst. Additionally, green metrics calculations suggest the present method to be environmentally benign. Finally, the frontier molecular orbitals and the global reactivity parameters of the synthesized compounds were predicted by using density functional theory calculations.

This study introduces an efficient, environmentally friendly, and sustainable method for synthesizing N-acylhydrazone analogues by engaging isoniazid in a condensation reaction with variously substituted benzaldehydes. The deep-eutectic solvent (ZnCl2/urea) employed in this study acted not only as a solvent but also as a catalyst to facilitate the synthesis of the target compounds within two to six minutes without the requirement of any lengthy purification techniques. The synthetic protocol is operationally simple and offers other remarkable advantages such as a short reaction time, good to excellent yields, a scalable protocol, and a recyclable and reusable catalyst. Additionally, green metrics calculations suggest the present method to be environmentally benign. Finally, the frontier molecular orbitals and the global reactivity parameters of the synthesized compounds were predicted by using density functional theory calculations.

Diaryl diselenides and diaryl ditellurides are commonly employed as selenyl or telluryl sources, and they have a wide range of applications in organic synthesis. Herein, various diaryl diselenides/ditellurides are furnished in moderate to excellent yields under metal-free conditions. This method features high efficiency, good functional group tolerance, straightforward operation, and easy scale-up (running in 4 mmol-scale for most cases). Mechanistic studies indicate that this reaction may proceed via a radical pathway. Significantly, the correct matching of Br– and dimethyl sulfoxide under an air atmosphere is critical to this transformation.

The present article provides a personalized account of our recent work on the synthesis of substituted and fused five-membered heterocycles using various organosulfur building blocks, derived primarily through base-mediated condensation of active methylene compounds with (het)aryl/alkyl dithioesters, which have not been previously explored. We initially describe the ring-opening transformations of 4-[(methylthio)-(het)aryl-methylene]-2-phenyl-5-oxazolones, leading to the synthesis of functionalized oxazoles, thiazoles, and bisoxazoles. We then go on to focus on the synthesis of substituted benzothiophenes, indoles, and benzofurans, as well as their hetero-fused analogs. These compounds are synthesized via transition-metal-catalyzed intramolecular C–heteroatom (C–S, C–N, C–O) bond formation (via cross-coupling or C–H bond functionalization) of various reactive organosulfur intermediates, derived from base-mediated condensation of 2-bromo(het)arylacetonitriles, acetates, or desoxybenzoins or the corresponding 2-unsubstituted precursors. Finally, we highlight the synthetic applications of a new class of previously unexplored organosulfur building blocks, namely, unsymmetrically substituted 1,3-bis(het)aryl-1,3-monothioketones, derived via base-mediated condensation of ketones with (het)aryl/alkyl dithioesters, for the regioselective synthesis of substituted pyrazoles, isoxazoles, thiophenes, imidazoles, and benzothiophenes.1 Introduction2 4-[(Methylthio)-het(aryl)-methylene]-2-phenyl/2-(2-thienyl)-5-oxazolones: Versatile Templates for the Synthesis of Oxazoles, Thiazoles, and Bisoxazoles3 Synthesis of Benzothiophenes, Indoles, and Benzofurans via Transition-Metal-Catalyzed Intramolecular C–Heteroatom Bond Formation4 1,3-Bis(het)arylmonothio-1,3-diketones and 1,3-Bis(Het)aryl-3-(methylthio)-2-propenones: Versatile Intermediates for the Regioselective Synthesis of Five-Membered Heterocycles5 Conclusion