Light-Promoted C(sp³)–H Functionalization: Alkyl Amines as C2 Synthons in Formal [3+2] Cycloaddition with N-Imino(iso)quinolinium Ylides

The classical 1,3-dipolar cycloaddition reaction predominantly generates five-membered heterocycles through cycloaddition between 1,3-dipoles and unsaturated hydrocarbons, such as alkenes or alkynes. Herein, we report a light-mediated approach that employs saturated amines as alternatives to conventional unsaturated hydrocarbons, enabling their reaction with N-imino(iso)quinolinium ylides to achieve efficient synthesis of pyrazolo-fused (iso)quinoline core structures. This method demonstrates operational simplicity, mild reaction conditions, and excellent functional group compatibility. Mechanistic investigations reveal that the N-imino(iso)quinolinium ylides not only serve as substrates but also function as photosensitizers, facilitating the formation of critical pyrazolo-fused (iso)quinoline structural units through the single-electron oxidation of amines to generate enamine intermediates.