Novel thermal rearrangement of fused diaryl-υ-triazolium salts to neutral indazole derivatives. Fused azolium salts. 16

摘要

Alkylation of 1,3-diaryl-υ-triazolo[1,5-a]benzimidaole (1) by trimethyloxonium salt afforded selectively the 4-methyl quaternary salt 2, whereas reaction with dimethyl sulfate at elevated temperature resulted in ring transformation, implying ring opening to a nitrenium cation and a subsequent electrophilic ring closure to give a benzimidazolylindazole product 5. Independent of the methylation, a similar easy thermal rearrangement was observed with alkylated 1,3-diaryl- υ-triazolo[1,5-a]benziidazolium (2→4) and the related benzothiazolium salt (7→8).