Selective Synthesis of Indazolo[2,3‐ a ]quinolines via Rh(III)‐Catalyzed Oxidant‐Free [4+2] or [5+1] Annulation of 2‐Aryl‐2 H ‐indazoles with α ‐Diazo Carbonyl Compounds

A selective synthesis of 5,6‐disubstituted and 5‐substituted indazolo[2,3‐ a ]quinolines through a Rh(III)‐catalyzed oxidant‐free annulation of 2‐aryl‐2 H ‐indazoles with α ‐diazo carbonyl compounds is reported. With 2‐aryl‐2 H ‐indazoles as the substrates, α‐diazo carbonyl compounds could act as a C2 synthon to afford 5,6‐disubstituted indazolo[2,3‐ a ]quinolines via a Rh(III)‐catalyzed [4+2] annulation. On the other hand, when 2‐aryl‐3‐formyl‐2 H ‐indazoles were used as the substrates, α‐diazo carbonyl compounds switched to act as a C1 synthon to undergo a more complicated [5+1] annulation process to furnish 5‐substituted indazolo[2,3‐ a ]quinolines.