Spirocyclic compounds are key scaffolds in many drugs and other bioactive molecules. While cyclopropanation of allenes is relatively straightforward, synthesis of spirocyclic compounds from these substrates is scarce. We report a photocatalytic, transition-metal-free cyclopropanation of allenoates with oxadiazolines as carbene precursors . Thioxanthone, serving as an energy transfer catalyst, enables mild reaction conditions and short reaction times.

Spirocyclic compounds are valuable scaffolds in medicinal chemistry and are important components of numerous drugs and other bioactive molecules. Although the cyclopropanation of allenes using typical methods is relatively straightforward, only limited approaches for the synthesis of spirocyclic compounds from allenoates have been reported. Herein, a photocatalytic, transition-metal-free cyclopropanation of these substrates using oxadiazolines as a source of nucleophilic carbenes is described. The application of thioxanthone as an energy transfer catalyst under violet light irradiation enables the formation of alkylidenecyclopropanes in synthetically useful yields.