Yb(OTf)3-Mediated Access to Furans from β-Ketothioamides via Eschenmoser Sulfide Contraction Reaction

PIDA-promoted metal-free [3 + 2] heteroannulation of β-ketothioamides with 4-hydroxy coumarins: chemo-/regioselective access to furo[3,2-c]chromen-4-ones at room temperature

Herein, we report a viable protocol to access furo[3,2-c]chromen-4-ones by engaging easily accessible 4-hydroxy coumarins as a three-atom CCO unit and thioamides as a C2 coupling partner, mediated by phenyliodine(III) diacetate (PIDA) at room temperature in a highly efficient and pot-/step-economical manner. This strategy not only avoids potential toxicity and tiresome workup conditions, but also features operational simplicity, a broad substrate scope, good functional group tolerance, high yields, easy scalability and exclusive selectivity. A mechanistic study has shown that this metal-free reaction is triggered by PIDA via activation of the β-carbon of 4-hydroxy coumarin, followed by a nucleophilic addition/intramolecular cyclization/dethiohydration cascade. High-resolution mass spectra (HRMS) study confirms the key intermediates involved during the course of the reaction, elucidating the reaction pathways, and demonstrates the excellent regio- and chemoselectivity of this approach.

Synthesis of pyrrole disulfides via umpolung of β-ketothioamides

A Na₂CO₃-promoted reaction of β-ketothioamides (KTAs) and cyanoacetates was developed for the synthesis of pyrrole disulfides using air as a green oxidant. This protocol features a broad substrate scope and mild reaction conditions. Preliminary mechanistic studies indicate that the reaction involves a tandem unusual umpolung of KTAs, N-cyclization, tautomerization and oxidative coupling process.

Metal-Free One-Pot Annulative Coupling of 2-Hydroxybenzaldehydes with β-Ketothioamides: Access to Diverse 2-Arylimino-2H-Chromenes

A concise and practical one-pot sustainable approach for expedient synthesis of 2-arylimino-2H-chromenes by two-component cascade [4 + 2] annulative coupling of easily available 2-hydroxybenzaldehydes with β-ketothioamides has been developed in good yields for the first time. Remarkably, metal- and additive-free conditions, use of simple K₂CO₃ as a mild base, open atmosphere, exclusive regioselectivity, step/atom economy, nonhazardous reagents, and easy purification are added characteristics to the strategy. This annulative protocol will not only provide an efficient method to access diverse chromene scaffolds, but also enrich the research domain of β-ketothioamides.

Phosphonium ylide catalysis: a divergent diastereoselective approach to synthesize cyclic ketene acetals [thia(zolidines/zinanes)] from β-ketothioamides and dihaloalkanes

Phosphonium ylides are being reported here as a catalyst for the formation of thiazolidines and 1,3-thiazinanes from β-ketothioamides with dihaloalkanesvia[3 + 2] and [3 + 3] annulations under metal-free conditions.

A facile method for the synthesis of fused perhydropyrano[2,3-b]pyrans promoted by Yb(OTf)3

A stereospecific three-component domino reaction between glycals, alkylidene malonate and aldehydes catalyzed by Yb(OTf)3 is described. Multi-substituted cis-fused perhydropyrano[2,3-b]pyran derivatives were obtained with high diastereoselectivity.

NaHS·nH2O-induced umpolung: the synthesis of 2-acyl-3-aminoindoles from aryl methyl ketones and 2-aminobenzonitriles

An efficient method for constructing 2-acyl-3-aminoindoles from methyl ketones and 2-aminobenzonitriles is described, in which NaHS·nH₂O is used as a novel umpolung reagent for the first time in organic synthesis.

Synthesis of disulfides tethered pyrroles from β-ketothioamides via a bicyclization/ring-opening/oxidative coupling reaction

A DABCO-promoted three-component reaction of β-ketothioamides, arylglyoxals and 2-cyanoacetate to construct disulfides tethered pyrroles has been developed.

Synthesis of N,N-disubstituted 2-aminothiophenes by the cyclization of gem-difluoroalkenes with β-keto thioamides

A novel and effective method for the construction of highly functionalized aminothiophenes via the cyclization of gem-difluoroalkenes with β-keto tertiary thioamides is described.

Direct Construction of 2-Aryliminochromenes from Arynes, N,S-Keteneacetals, and DMF

A concise and direct synthetic strategy for the construction of 2-aryliminochromene skeleton by cascade three-component coupling reaction of arynes, N,S-keteneacetals, and DMF in good yields has been disclosed. The process demonstrates the first example of aryne chemistry combined with N,S-keteneacetals. Using this strategy, an expeditious synthesis of biologically important arylimino-2H-chromene-3- carboxamides was achieved.

Acid-promoted rapid solvent-free access to substituted 1,4-dihydropyridines from β-ketothioamides

1,4-Dihydropyridines were synthesized via a tandem reaction of β-ketothioamides with aldehydes and β-enaminonitriles by AcOH as a promoter within 5 min.