Photo‐Mediated Silacyclization by Wavelength‐Dependent Selective C─F or C─H Functionalization

Abstract Silacycles have gained significant attention within the synthetic community due to their pivotal roles in medicinal chemistry and materials science. Despite recent advancements, the defluorosilylation of aryl fluorides with hydrosilanes and the selective silylation of arenes without external oxidants remains challenging. Herein, we present a wavelength‐dependent photo‐mediated cascade silacyclization of allylbenzene derivatives with dihydrosilanes to efficiently construct six‐membered benzosilacycles. By employing a synergistic system of an organophotocatalyst and a thiol‐based hydrogen atom transfer catalyst, our approach exploits specific light‐emitting diode (LED) wavelengths (456 and 335 nm) to achieve selective C–F and C–H functionalization. This wavelength modulation enables the first successful defluorosilacyclization of ortho ‐fluoroallylbenzenes and facilitates an acceptorless dehydrosilacyclization, demonstrating precise site‐selective functionalization. Mechanistic investigations reveal a hydrogen atom transfer (HAT)‐facilitated intermolecular hydrosilylation followed by a wavelength‐dependent, chemoselective intramolecular silacyclization cascade. Additionally, an unprecedented light‐assisted hydrogen evolution process involving silane and thiol is uncovered within the cascade C–H silacyclization. This photo‐mediated strategy offers a sustainable and versatile platform for the synthesis of valuable silacycle compounds, exhibiting broad functional group tolerance and precise wavelength‐dependent chemoselectivity.