Stereospecific photochemistry of Δ-1,2,3-triazolines in solution and in the solid state: scope and mechanistic studies.

The stereospecific photochemistry of ten N-aryl-substituted cis- or trans-Δ-1,2,3-triazolines to form the corresponding cis- or trans-aziridines was investigated both in solution and in the solid-state. We found that photochemical reactions in the solid state are more stereospecific than in solution for the 8 crystalline Δ-1,2,3-triazolines. Additionally, triplet sensitization for some triazolines results in triplet biradicals, which provide the more thermodynamically favored trans-aziridine regardless of the starting triazoline stereochemistry.