Rhodium-catalysed regioselective [4 + 2]-type annulation of 1-H-indazoles with propargyl alcohols: direct access to 6-alkenylindazolo[3,2-a]isoquinolines

Abstract

An efficient method for the synthesis of 6-alkenylindazolo[3,2-a]isoquinolines via rhodium(III)-catalysed C–H bond activation/subsequent [4 + 2] cyclization starting from easily available 3-aryl-1-H-indazoles and propargyl alcohols has been developed. A series of 6-alkenylpolycyclic aza-aromatics were obtained in up to 86% yields with broad functional group tolerance and excellent regioselectivity. Furthermore, the title products exhibited robust DNA staining patterns in agarose gel electrophoresis and were able to label the yolk of zebrafish larvae. Coupled with the favourable fluorescence properties of the products, this strategy might provide a novel way to synthesize conjugated π-system polyheteroarenes with potential utility in various functional materials and fluorescence staining applications.