Rh(iii)-catalyzed synthesis of tetracyclic isoquinolinium salts via C-H activation and [4+2] annulation of 1-phenyl-3,4-dihydroisoquinolines and alkynes in ethanol.

An efficient and convenient method to construct tetracyclic isoquinolinium salts via [Cp*RhCl 2 ] 2 catalyzed C-H activation and [4 + 2] annulation reactions in ethanol is described. This reaction is very fast and highly efficient in the green solvent ethanol. The reaction works with a broad substrate scope affording the products in good to excellent yields in a short time. Moreover, a ratio of S/C up to 10 000 could be achieved with gram scale synthesis.