Photoredox-Induced Dearomatization of 2-Alkenyl Aromatic Carboxylic Acids with Terminal Alkynes

Dearomatization of the aromatic ring to form a three-dimensional (3D) skeleton can greatly improve its performance in drug design. Aromatic carboxylic acids are rich in structure, inexpensive, and easy to obtain, making them the most ideal aryl fragments. However, the direct dearomatization of aromatic carboxylic acids to construct 3D molecules is a highly desirable process that still needs to be explored. Herein, we report a photoredox-induced dearomatization of o-vinyl aromatic carboxylic acids with terminal alkynes to chemoselectively construct oxa-spiro polycycles. Control experiments and DFT calculations indicate that adding a base and increasing the reaction temperature facilitate the thermodynamically and kinetically favorable 6-endo radical cyclization to equilibrate 5-exo radical cyclization to initiate the subsequent radical addition into terminal alkynes, dearomatization, and reductive quenching.