Rhodium-catalyzed oxidative annulation of 1H-indazoles with alkynes for the synthesis of indazolo[3,2-a]isoquinolines via C–H bond functionalization†
A Rh(III)-catalyzed oxidative annulation of 1H-indazoles with internal alkynes via C–C and C–N coupling for the preparation of highly functionalized indazolo[3,2-a]isoquinolines is disclosed. This reaction features the use of easily accessible starting materials, is operationally simple, has a relatively wide substrate scope, and shows good functional group tolerance. Furthermore, some of the prepared compounds exhibit bright emission in both dilute solution and in the solid state, with a Stokes shift of up to 161 nm. The derivative 3ia, bearing the strong electron-withdrawing group –NO2, exhibits remarkable solvatochromic fluorescence.