Photoaddition of Aliphatic Ethers to 4-Methyl-1,2,4-triazoline-3,5-dione: Application to the Synthesis of Functionalized Crown Ethers and Mechanism

The photoaddition of 4-methyl-1,2,4-triazoline-3,5-dione (4-MTAD) with a wide variety of acyclic, cyclic and crown aliphatic ethers has been investigated. Monochromatic (λ = 514.5 nm) or polychromatic (λ ≥ 310 nm) irradiations give identical mono-urazolyl ethers as reaction products. Unsymmetrical acyclic ethers afford a mixture of the two α and α′ mono-urazolyl ethers. In the case of 12-crown-4, mono and di-substituted products are obtained. ESR experiments and quantum calculations at the AM1 and 6-31G* levels were performed and a possible reaction mechanism is proposed in which the most probable photochemical process is the H-abstraction leading to a urazolyl radical.