Direct Photochemical Synthesis of Substituted Benzo[b]fluorenes

We report a new and straightforward route toward substituted benzo[b]fluorenes via the direct photochemical conversion of alkynylated chalcones. This transformation exploits a high-power light-emitting diode emitting ultraviolet A light to enable the rapid formation of the target products (tres = 5 min). A continuous flow approach thereby facilitates reproducibility and scalability, granting streamlined access to these important scaffolds and their derivatives. A mechanistic proposal based on a biradical species is presented and supported by deuteration studies.