Photogenerated donor–donor diazo compounds enable facile access to spirocyclopropanes

Prompted by the increasing interest in strained hydrocarbons as potential drug candidates, we developed a simple and efficient photochemical protocol for (spiro)cyclopropanes from bench stable tosylhydrazones and electron poor olefins. This two-step one-pot transformation proceeds by (3+2)-cycloaddition of in situ formed donor–donor diazo compounds, followed by nitrogen extrusion of the Δ¹-pyrazoline intermediates. Notably, kinetic analysis enabled the isolation of intermediary spiro-heterocycles.