Energy Transfer-Enabled Photocycloaddition of Oxazino Pyridines with Vinyl Azides to Access Meta -Functionalized Pyridines

Temporary dearomatization strategies have attracted growing interest for their ability to streamline the diverse transformation of N-containing drug-like molecules. Among them, oxazino pyridines, readily prepared from pyridines, have been introduced as highly valuable intermediates for the structural modification of pyridines. However, the reaction modes of these nucleophilic dienamine-type intermediates have been largely restricted to reactions with electrophiles or transient electrophilic radicals. Herein, we report a visible-light-mediated intermolecular formal cycloaddition of oxazino pyridines with vinyl azides, which provides efficient access to meta -alkylated pyridines─key metyrapone analogues. From a mechanistic perspective, energy transfer enables the generation of excited triplet oxazino pyridines and establishes an unconventional pathway for the meta -functionalization of pyridine cores. Due to their high triplet energy, direct excitation of pyridines with established photosensitizers is not possible. The broad substrate scope, feasibility of one-pot operation, and potential for synthetic applications underscore the practical value of this methodology.