Multicomponent C─H Annulation of 1,3‐Diketones, Alkynes, and Hydrazine to Yield (Cationic) Pyrazolo[5,1‐ a ]isoquinolines

ABSTRACT

Transforming inorganic nitrogen source to complex organic compounds is a basic task in chemistry area. In this study, Rh(III)‐catalyzed multicomponent C─H activation and (4+2) annulation reactions of 1,3‐diketones, alkynes, and hydrazine hydrate have been disclosed, leading to neutral pyrazolo[5,1‐ a ]isoquinolines (PIQs, 3 ) and cationic PIQs ( 4 ) with good yields. The divergency is adjusted by the numbers of the C2‐substituents of 1,3‐diketones, enabling pyrazolo[5,1‐ a ]isoquinolin‐4‐ium cations ( 4 ) for the first time. Some key intermediates were successfully isolated and characterized by ESI‐MS to verify the mechanism. Furthermore, the photophysical properties of the resulting products have been characterized.