Photolytic Access to Oxaspirodecanes and Chromenes from Vinyldiazo Ester Cycloaddition with p-Quinones. A Vinylcarbene is not Involved

Synthetic methods that provide access to skeletally diverse heterocyclic motifs are poised to accelerate drug discovery and streamline synthesis of advanced intermediates and materials. However, the development of such synthetic methods necessitates leveraging previously unexplored mechanistic pathways. We report herein an efficient blue LED light-induced reaction of vinyldiazoacetates and quinones that produces spirocyclic dihydrofurans, featuring the synthetically challenging oxaspiro[4.5]decane core of numerous medicinal agents, agrochemicals, and natural products. In a departure from the well-established photochemical reactivity of diazo compounds, these reactions do not involve vinylcarbene intermediates formed by photolytic dinitrogen extrusion. Instead, they result from photoexcitation of the quinone to its triplet state with subsequent triplet energy transfer to the vinyldiazo ester. The subsequent addition of the vinylogous carbon of the triplet vinyldiazoacetate to the quinone oxygen affords the triplet diradical that collapses to the spirocyclic dihydrofuran upon the loss of dinitrogen. A strain release-driven and Brønsted acid-catalyzed rearrangement of the spirocyclic products unravels the fused bicyclic ring system of equally synthetically and medicinally valuable chromenes, enabling facile skeletal diversification of the important heterocyclic motifs.