Transition metal- and oxidant-free [3 + 2] cycloaddition of N-amino(iso)quinolinium salts with vinyl acetate as an acetylene surrogate

A metal- and external oxidant-free [3 + 2] annulation of N-amino(iso)quinoline salts with vinyl acetate as the acetylene surrogate under simple and mild reaction conditions is described. A series of valuable pyrazolo(iso)quinoline scaffolds were synthesized through this process. Mechanistic investigations revealed that the reaction proceeds through a Mannich/cyclization/aromatization sequence. Furthermore, scale-up experiments and derivative syntheses of the product were conducted.