Self-photocatalysis with multiple activities: divergent synthesis of benzo[b]fluorenones and benzo[b]fluorenols from enone-ynes†

Abstract

Herein, we report a self-photocatalysis-enabled divergent synthesis of benzo[b]fluorenones and benzo[b]fluorenols from enone-ynes in batch and flow under mild and metal-, photocatalyst- and redox-agent-free conditions. The photocatalytic system exhibits multiple activities, including energy, electron and hydrogen atom transfers as well as photocycloaddition. Under blue-light irradiation, benzo[b]fluorenones were synthesized through an oxidative mechanism involving superoxide radical and singlet oxygen as key hydrogen-atom transfer intermediates. Alternatively, benzo[b]fluorenols were obtained via a redox-neutral pathway under violet-light irradiation, utilizing quinuclidine as a hydrogen atom transfer catalyst. The scalability and flow adaptability as well as sunlight experiments highlight the practical potential.