Synthesis of 2-Aminofurans and 2-Aminothiophenes through Elemental Sulfur-Promoted Switchable Redox Condensation Reaction of Enaminones with Methylene Nitriles.

Herein, we report an elemental sulfur-promoted switchable redox condensation reaction that can selectively prepare 2-aminofurans and 2-aminothiophenes from the corresponding enaminones and methylene nitriles, respectively. Mechanistic studies demonstrated that the enaminones, as dual nucleophiles, reacted with nitrile acetate to produce 2-aminofurans via 3,5-annulation under promotion by elemental sulfur. These reactions used readily available starting materials, transition metal-free, eco-friendly procedures, gram-scale syntheses, and wide functional group tolerance. The methodology may be useful for the construction of 2-aminofuran and 2-aminothiophene derivatives with potential biological activity.

Methylene-Bridged Dimerization by Cu-Catalyzed Deconstructive C-C Cleavage of Oxacycloalkane.

Herein, we demonstrate the successful utilization of copper catalysis and oxygen oxidation for consecutive C(sp3)-C(sp3) bond cleavage in alkyl cyclic ethers. A key step involves a copper-oxygen autoxidation process, generating in situ alkoxy radicals and triggering sequential C-C bond cleavage. This ß-oxidative cleavage strategy enables the use of cyclic ethers as valuable C1 building blocks for the synthesis of bridged methylene dimers. This reaction holds promise for inspiring alternative methods targeting inert C(sp3)-C(sp3) bond cleavage.

Palladium-Catalyzed [2+3] Cycloaddition/Cross-Coupling Reaction: Z/E and Diastereoselective Synthesis of Dendralene-Functionalized Dihydrofurans.

Herein, we describe a Pd-catalyzed [2+3] cycloaddition/cross-coupling reaction of allenyl acetates for the Z/E selective and diastereoselective synthesis of dendralene-functionalized dihydrofurans. Remarkably, mechanistic studies show the formation of an epoxide from a carbonyl bond via cycloaddition, which is practically and mechanistically significant for the construction of other bioactive heterocyclic epoxides. This research also revealed the utility and potential of allenic esters as C2 synthons and 1,2-biselectrophiles in cycloaddition reactions.