Rh(Ⅲ)-Catalyzed sequential ring-retentive/-opening [4+2]annulations of 2H-imidazoles towards full-color emissive imidazo[5,1-a]isoquinolinium salts and AIE-active non-symmetric 1,1-biisoquinolines

Rhodium-catalyzed C4aryl-H activation and ring-retentive annulation of 2H-imidazoles with internal alkynes to build imidazo[5,1-a]isoquinolinium salts with high yields and broad scope has been disclosed.These novel salts serve as new full-color emissive fluorophores(433-633 nm),just by simply modifying the substituents on C3 and C4 positions of isoquinoline ring.Furthermore,these salts can undergo ring-opening C5_(aryl)-H activation/annulation with a different alkyne to form non-symmetric and AIE-active1,1-biisoquinolines,where NH_(4)OAc plays an indispensable role that accounts for Hofmann elimination and imine formation,leading to an unprecedented imine dance:cyclic imine→N-alkenyl imine→NH imine.The15N labelling experiments indicate that the 2ndannulation includes two pathways:N-exchange(major)and N-retention(minor).