Synthesis of Imidazo‐Fuzed Pyrazino[2,1‐ <i>b</i> ]quinazolinones Through Gold(I)‐ and Base‐Promoted Intramolecular Hydroamination Cyclization

We describe a facile method to prepare a variety of imidazo‐fuzed pyrazino[2,1‐ b ]quinazolinone scaffolds in good to excellent yields through gold(I)‐catalyzed and base‐mediated intramolecular hydroamination reactions of N3‐alkynyl quinazolinone tethered imidazoles. It was found that 5‐methylene imidazo‐fuzed pyrazino[2,1‐ b ]quinazolinones were obtained under gold(I)‐catalyzed conditions, while base‐mediated conditions afforded 5‐alkyl imidazo‐fuzed pyrazino[2,1‐ b ]quinazolinones. The reaction could be easily prepared on a gram scales. More importantly, the prepared 5‐methylene imidazo‐fuzed pyrazino[2,1‐ b ]quinazolinones could be applied in the various metal ions recognition based on their fluorescence properties.