Synthesis of pyrazolo[5,1-a]isoquinolines via C-H/N-H annulation of pyrazoles and alkynes with ruthenium(II) catalysts

Abstract

A series of pyrazolo[5,1-a]isoquinolines have been synthesized by ruthenium(II)-catalyzed annulation of pyrazole derivatives with alkynes in the presence of Cu(OAc)2‧H2O and AgSbF6 producing pyrazolo[5,1-a]isoquinolines. The reaction proceeded efficiently in water under nitrogen atmosphere leading to an excellent yield of the products. This annulation process can also be performed in alcohol at a lower temperature without Cu(OAc)2‧H2O and silver salt but in the presence of a carboxylate ligand under air. The compounds were characterized based on spectroscopic data and the crystal structure of one of the representative compound, pyrazolo[5,1-a]isoquinoline derivative has been determined by single-crystal X-ray crystallography.