Visible light-driven highly atom-economical divergent synthesis of substituted fluorenols and cyclopropylcarbaldehydes

Herein, we report a visible light-promoted intramolecular regiodivergent tandem radical reaction featuring cyclization/ring expansion followed by contraction to construct functionalized 9-fluorenol and naphthalene-fused cyclopropylcarbaldehyde derivatives. This method involves mild reaction conditions, a wide substrate scope (more than 34 examples), outstanding step efficiency with 100% atom economy, and excellent scalability. Moreover, it requires no external chemical oxidant. In the reaction, the alkyne moiety may act as a radical acceptor, reacting with the carbonyl group that has been activated through a combination of iridium photocatalysis and Lewis acid conditions under blue LED irradiation at room temperature. The generation of fluorenols and cyclopropyl-fused carbaldehydes directly from more stable and simpler conjugated enyne compounds has remained a challenge despite the highly desirable benefits of minimal prefunctionalization and increased operational safety. In the present study, the novelty of the designed protocol was demonstrated via the synthesis of chrysene analogs as well as other late-stage functionalizations. We report a visible light-promoted intramolecular radical cascade reaction to construct fluorenol and naphthalene-fused cyclopropyl carbaldehyde derivatives.

Automated summary

Here, we report a visible light-promoted intramolecular radical cascade reaction for the construction of fluorenol and naphthalene-fused cyclopropyl carbaldehyde derivatives. This method offers mild reaction conditions, a broad substrate scope, excellent step efficiency, and scalability, without the need for external chemical oxidants. The novelty of this protocol was demonstrated by synthesizing chrysene analogs and performing late-stage functionalizations.