Pd/Cu cooperative catalysis: an efficient synthesis of (3-isoindazolyl)allenes via cross-coupling of 2-alkynyl azobenzenes and terminal alkynes.

An efficient synthesis of (3-isoindazolyl)allenes from 2-alkynyl azobenzenes and terminal alkynes via cooperative Pd(PPh3)2Cl2/CuI-catalyzed cross-coupling has been developed. By making use of this approach, (3-isoindazolyl)allenes with various substituents can be synthesized in good to excellent yields. A rapid synthesis of biologically active indazolo[2,3-a]quinoline was also achieved using this method as the key step.