Photo addition of aliphatic ethers to 4-methyl-1,2,3-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 wi de variety of acyclic, cyclic and crown aliphatic ethers has been investiga ted. Monochromatic (lambda = 514.5 nm) or polychromatic (lambda greater tha n or equal to 310 nm) irradiations give identical mono-urazolyl ethers as r eaction products. Unsymmetrical acyclic ethers afford a mixture of the two alpha and alpha' mono-urazolyl ethers. In the case of 12-crown-4, mono and di-substituted products are obtained. ESR experiments and quantum calculati ons at the AM1 and 6-31G* levels were performed and a possible reaction mec hanism is proposed in which the most probable photochemical process is the H-abstraction leading to a urazolyl radical.