Catalytic System-Controlled [4 + 1] and [4 + 2] Annulation for the Construction of Pyrazolo[1,2-<i>a</i>]indazoles and Pyrazolo[1,2-<i>a</i>]cinnolines from Pyrazolidinones and Diazo Indandiones

Pyrazolo[1,2-<i>a</i>]indazoles and pyrazolo[1,2-<i>a</i>]cinnolines can be constructed selectively via catalytic system-controlled C(sp²)-H activation/[4 + 1] cyclization and C(sp²)-H activation/[4 + 2] cyclization reaction, utilizing pyrazolidinones and diazo indandiones. Employing two different Rh(III) catalysts, we successfully synthesized two distinct types of nitrogen-containing heterocyclic compounds, pyrazolo[1,2-<i>a</i>]indazoles and pyrazolo[1,2-<i>a</i>]cinnolines, respectively. Moreover, an inexpensive Ru(II) catalyst could also effectively generate pyrazolo[1,2-<i>a</i>]cinnolines with moderate to good yields. Overall, these methodologies offer advantages such as regioselectivity, broad substrate scope, operational simplicity, and product availability.