Stereospecific Synthesis of Substituted Aziridines by a Crystal-to-Crystal Photodenitrogenation of Δ2‑1,2,3-Triazolines

Crystalline cis- or trans-Δ2-1,2,3-triazolines prepared by highly stereospecific and regioselective hydrogen bonding-catalyzed dipolar cycloaddition of activated cis- or trans-alkenes with aryl azides undergo a highly stereospecific photodenitrogenation to form the corresponding cis- or trans- azidirines in high chemical yields. While examples involving disubstituted and trisubstituted triazolines highlight steric challenges encountered in the dipolar cycloaddition reaction, the stereochemical control exerted by the crystalline lattice is enhanced by bulky substituents in the triazoline precursors to generate aziridines photochemically.