Access to Mono-, Di- and Tri-(Het)Arylated Pyrazolo[5,1-b]oxazoles Using Cyclization, C-H Activation and Suzuki-Miyaura Palladium-Catalyzed Reactions

A first access to mono-, di- and tri-(Het)arylated pyrazolo[5,1-b]oxazoles is reported. The series were generated from a library of 3-(Het)arylpyrazolo[5,1-b]oxazole platforms selectively functionalized through regioselective arylation procedures. The regioselective functionalization in C-2 and C-7 positions was investigated. Each Palladium-catalyzed cross-coupling condition was optimized and a representative library of the scope and limitations of the reactions was studied.