Silver Triflate‐Palladium Chloride Cooperative Catalysis in a Tandem Reaction for the Synthesis of H‐Pyrazolo[5,1‐a]isoquinolines

Abstract

AbstractA tandem reaction of N′‐(2‐alkynylbenzylidene)hydrazone with alcohol in the presence of oxygen co‐catalyzed by silver triflate and palladium chloride under mild conditions is reported, providing H‐pyrazolo[5,1‐a]isoquinolines in good yields. During the transformation, isoquinolinium‐2‐yl amide was the key intermediate via a silver(I)‐catalyzed 6‐endo cyclization of N′‐(2‐alkynylbenzylidene)hydrazone. The presence of a palladium catalyst and molecular oxygen promoted the oxidation of the alcohol to the aldehyde or ketone. Subsequent nucleophilic attack of the in situ generated enolate to isoquinolinium‐2‐yl amide, intramolecular condensation, and aromatization afforded the H‐pyrazolo[5,1‐a]isoquinolines. The easily available starting materials, good substrate generality, mild reaction conditions, and experimental ease should make this method attractive for further library construction.magnified image