Exploring the Limits of Reactivity of N-Methyl-1,2,4-triazoline-3,5-dione (MeTAD) with Disubstituted Bicycloalkadienes in the Homo-Diels–Alder Reaction

Abstract

The [2+2+2] cycloaddition (homo-Diels–Alder reaction) of N-substituted 1,2,4-triazoline-3,5-diones (TADs) with bicycloalkadienes produces strained heterocyclic compounds. A reaction with the unsubstituted dienes occurs readily to produce only the expected homo-Diels–Alder adducts. However, previous work in the literature showed that the attachment of a single electron-withdrawing group to the diene system results in the formation of not only the expected homo-Diels–Alder adducts, but also interesting “insertion” products. To probe the limits of reactivity of these diene systems, we investigated the reaction of N-methyl-1,2,4-triazoline-3,5-dione (MeTAD) with bicycloalkadienes substituted with two electron-withdrawing groups, i.e., two carbomethoxy or two cyano groups. We hoped to learn whether the reaction still proceeded, and if so, whether the homo-Diels–Alder adducts and/or other types of products were formed. We found that a reaction between MeTAD and the dienes takes place upon substitution with two carbomethoxy groups, albeit at a considerably slower rate than other reactions. The only products observed were the homo-Diels–Alder adducts. However, attachment of two CN groups completely inhibited reactivity.