Ring‐Opening Chlorination and Bromination of Pyrazolopyridines and Isoxazoles

We report the development of electrophilic ring-opening chlorination and bromination reactions of pyrazoloazines and isoxazoles using chlorinating and brominating agents. These transformations proceed via selective cleavage of heteroaromatic N─N or N─O bonds, delivering structurally diverse tertiary halogenated compounds. Furthermore, treatment of formylated pyrazolopyridines with two equivalents of chlorinating or brominating agents afforded dihalogenated products in good yields. This strategy represents a valuable platform for constructing halogenated scaffolds from simple heteroaromatic precursors and broadens the synthetic utility of skeletal transformations in the functionalization of heteroaromatics.