Despite ubiquitous synthetic routes toward stabilized diazoalkanes, the chemistry of non-stabilized, explosive analogues remains underexplored. The Gryko group and prof. Chaładaj reported that 1,3,4-oxadiazolines can be activated by triplet energy transfer catalysis under visible-light irradiation giving access to these reactive intermediates. They react with electron-poor olefins, giving valuable spirocyclopropanes. Mechanistic investigations, both theoretical and experimental, uncover plausible pathways and highlight the importance of the triplet energy transfer steps.