Rh(III)-catalyzed [4 + 1] annulation of 1-arylindazolones with alkynyl cyclobutanols: access to indazolo[1,2- a ]indazolones.

A convenient and efficient synthesis of structurally diverse indazolo[1,2- a ]indazolones via a Rh(III)-catalyzed [4 + 1] annulation of 1-arylindazolones with alkynyl cyclobutanols has been achieved by combining C-H and C-C bond cleavage. This cascade reaction features readily available starting materials, good functional group tolerance, broad substrate scope, and excellent atom-economy.