Rearrangement of aryl- and benzylthiopyridinium imides with participation of a methyl substituent

Copper-Catalyzed Aerobic Oxidative [3+2] Annulation for the Synthesis of 5-Amino/Imino-Substituted 1,2,4-Thiadiazoles through C-N/N-S Bond Formation

A copper-catalyzed aerobic oxidative annulation reaction of 2-aminopyridine/amidine with isothiocyanate has been reported. This strategy involving C-N/N-S bond formations provides various 5-amino/imino-substituted 1,2,4-thiadiazole derivatives under a Cu/O₂ catalytic system. This method has demonstrated high reactivity, mild reaction conditions, and a broad substrate scope. Furthermore, the synthetic utilities of the approach are demonstrated by further modifications.

Transformation of Zwitterionic Pyridine Derivatives to a Spiro-Fused Ring System: Azoniabenzo[de]fluorine. Synthesis and Mechanistic Rationalization

Reaction of aryl- and benzylsulfanopyridinium amidates bearing a methyl group in position 6 with 2 equiv of diphenylketene afforded a spiro-fused ring system: azoniabenzo[de]fluorine. By use of an excess amount of ketene, a distinct reaction was observed via which a 1H-pyrrolo[3,2-b]pyridin-2(3H)-one derivative was furnished. The structure of the tetracyclic spiro-fused ring system was unambiguously confirmed by X-ray diffraction, and its formation was rationalized by DFT calculations.