Visible light-driven dearomative meta-cycloadditions of 2-acetonaphthalenes via triplet energy transfer cascade.

Abstract

Dearomative cycloadditions (DACs) with ortho- and para-variants have been well documented under visible light-mediated triplet-triplet energy transfer (^VLEnT) catalysis. The prospective [3 + 2] or the meta-DACs propelled via ^VLEnT catalysis remains elusive. Classically, meta-DACs are known under harsher UV irradiations and are symmetry allowed in the excited singlet potential energy surface. Herein, we report formal meta-DACs of 2-acetonaphthalenes propagated via a two-step ^VLEnT cascade circumventing the attainment of energetically higher singlet excited states. The photosensitizer selectively promotes the [4 + 2] cycloaddition followed by a contra-thermodynamic di-π-methane type skeleton rearrangement cascade. The DFT studies in conjugation with electrochemical, photoluminescence, kinetic, quadratic dependency, and control experiments support the ^VLEnT cascade. The described protocol delivers highly sp³-rich polycyclic frameworks in high yields with wide functional group tolerance. The inclusion of bioactive molecules and the establishment of a wide array of post-synthetic derivatizations further underscores the adaptability of the methodology for generating complex three-dimensional molecules.