Time-Dependent Divergent Synthesis via Photochemical Rearrangement

Divergent synthesis is a powerful and economical approach in synthetic chemistry and materials science. However, achieving precise control over divergent reactions using only reaction time as a variable is still rare. Herein, we show a time-dependent photochemical rearrangement driven by energy transfer catalysis under visible light. Remarkably, by simply adjusting the reaction time, we can selectively synthesize two distinct types of fluorinated strained rings using the same photocatalyst. Mechanistic experiments and computational studies reveal that this photochemical rearrangement follows a kinetically controlled pathway, involving a sequence of steps: diradical formation, 1,4-aryl migration, and 1,3-diradical formation. Interestingly, when the reaction time is extended, the newly formed difluoromethyl cyclopropanes can reversibly revert to the starting materials. This indicates that the final product is not simply kinetically or thermodynamically favored in the ground state potential energy surface. Instead, the excited state introduces additional complexity to the situation, as the starting materials are then fully converted into 1,1-difluorocyclopropanes through an excited-state thermodynamic control pathway-defined as the product distribution being governed by the relative thermodynamic stabilities of intermediates on the excited-state potential energy surface (PES), in contrast to conventional ground-state thermodynamic control, which relies on singlet ground-state PES stabilities under thermal conditions.