Nitrosylsulfuric acid as a tandem reagent in the synthesis of 3,5-diarylisoxazoles from 1,2-diarylcyclopropanes

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

A new convenient and versatile halogenating system (R₄NHal/NOHSO₄), giving straightforward and general access to halogenated 3,5-diaryl- and alkylarylisoxazoles, pyrazoles and electron-rich benzenes from the corresponding scaffolds, is suggested. The method provides excellent regioselectivity, scalability to the gram scale, and a broad scope for both aromatics and halogens. A three-step, one-pot reaction protocol was developed, and a series of 3,5-diaryl-4-haloisoxazoles has been efficiently synthesized from 1,2-diarylcyclopropanes under suggested nitrosating-halogenating conditions.