Reactions of Azodiones with Electron-Rich Alkenes. 1,2,4-Triazoline-3,5-diones and Vinyl Ethers

Article abstract of DOI:10.1021/jo00154a014

4-Substituted-1,2,4-triazoline-3,5-diones (R-TAD) react with vinyl ethers to give mixtures of 1,2-diazetidines and polymers.The ratio of diazetidine to polymer is very dependent on the nature of the alkoxy substituent of the vinyl ether.For example, ethyl vinyl ether gives only polymer, but 2-chloroethyl vinyl ether gives only 1,2-diazetidine.The rate of reaction is very dependent on the vinyl ether structure, decreasing in the order CH3CH2OCH=CH2 > ClCH2CH2OCH=CH2 > C6H5OCH=CH2, but is not very sensitive to the nature of the 4-substituent in the triazolinedione.The involvement of a 1,4-dipole in 1,2-diazetidine formation was proven by trapping the intermediate in the reaction of 2-chloroethyl vinyl ether and C6H5-TAD with acetone.However, the rate of the reaction is insensitive to the polarity of the solvent.In order to reconcile these facts, the initial formation of a charge-transfer complex is postulated, which in turn collapses to a 1,4-dipole.