[3 + 2] Cycloaddition of N-Amino(iso)quinolinium Salts with Vinylsulfonium Salt: Synthesis of Pyrazolo[1,5-a]quinoline and Pyrazolo[5,1-a]isoquinoline Derivatives

In this study, we reported the utilization of vinylsulfonium salt as a highly efficient dipolarophile, leveraging the facile leaving ability of its sulfide moiety, to engage in a [3 + 2] cycloaddition with N-amino(iso)quinolinium salts. This approach facilitates the construction of various C₁/C₂-unsubstituted pyrazolo(iso)quinoline skeletons. The transformation is conducted under catalyst- and external oxidant-free conditions. Furthermore, the extended gram-scale reaction demonstrates the practical applicability of the developed protocol.