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

Abstract

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.

Direct synthetic routes to functionalised crown ethers

“…Risi et al studied the photochemical coupling reaction between cyclic ethers and 4-methyl-1,2,4-triazoline-3,5-dione (4-MTAD). 58 The interest in such a specific functionalisation originates from the wide application of triazolinedione compounds in the fields of polymer science and click chemistry. 59 Slow addition of 4-MTAD to an excess of CE 12-crown-4 (1), 2 or 3 under continuous laser irradiation at λ = 514.5 nm for several days, allowed for the formation of the corresponding α-urazolyl derivatives.…”

Shining Light on Poly(ethylene glycol): From Polymer Modification to 3D Laser Printing of Water Erasable Microstructures

“…Figure 1a) were also detected, suggesting that the photoaddition proceeds via a reductive pathway. [ 27 ] Full TAD conversion was also observed for equimolar solutions of BuTAD and ether in acetonitrile, albeit after slightly prolonged irradiation times (i.e., 2 h, cf. Figures S2 and S3, Supporting Information).…”

“…TADs namely exhibit good hydrogen abstraction reactivity in ether‐containing solvents upon exposure to light with the formation of a covalent addition product (see Figure 1a). [ 26 ] While initially reported in the 1970s as merely an undesired side reaction, Risi et al exploited this photoaddition for the modification of crown ethers under irradiation, [ 27 ] yet no useful transformations have been reported since. Intrigued by the originally observed side reaction, we initially sought to exploit the photoinduced TAD‐ether conjugation in a polymer context as a more straightforward synthesis route toward backbone‐functionalized polyethers (cf.…”

Reactivity of 4-R-1,2,4-triazoline-3,5-diones towards nitrone spin-traps: spectral study of the reaction with 5,5-dimethylpyrroline-N-oxide

“…The RTAD solutions in different solvents always contain traces of urazole (urazole impurities in catalytic concen-trations) or tetrazane which can decompose to give urazole and the corresponding RTAD. These urazole traces may add to DMPO to give the corresponding hydroxylamine, according to reaction (1).…”