Nitrosylsulfuric acid as an oxidant in the synthesis of 3,5-diarylisoxazoles

R4NHal/NOHSO4: A Usable System for Halogenation of Isoxazoles, Pyrazoles, and Beyond

“…22−25 Recently, we have shown that nitrosylsulfuric acid can be successfully used in the synthesis of 3,5-diarylisoxazoles from the corresponding 1,2diarylcyclopropanes. 26,27 We envisioned the scenario depicted in Scheme 2 Indeed, the portion-wise addition of 1.5 followed by 1 equiv of nitrosylsulfuric acid in an hour or two to a solution of 1,2diarylcyclopropane in MeNO 2 resulted in the sequential formation of the corresponding 3,5-diaryl-4,5-dihydroisoxazole followed by 3,5-diarylisoxazole that can be monitored by TLC. Finally, the introduction of an additional portion of nitrosylsulfuric acid and tetramethylammonium halide into the resulting mixture afforded the targeted 4-haloisoxazole.…”

“…One of the routes for the construction of five-membered N , O -heterocyclic scaffolds, isoxazolines, or isoxazoles is nitrosation of cyclopropanes. − Recently, we have shown that nitrosylsulfuric acid can be successfully used in the synthesis of 3,5-diarylisoxazoles from the corresponding 1,2-diarylcyclopropanes. , We envisioned the scenario depicted in Scheme…”