Further Insight into the Castagnoli–Cushman-type Synthesis of 1,4,6-Trisubstituted 1,6-Dihydropyridin-2-(3H)‑ones from 3‑Arylglutaconic Acid Anhydrides

The earlier reported three-component Castagnoli–Cushman-type synthesis of 1,4,6-trisubstituted 1,6-dihydropyridin-2-(3H)-ones from 3-arylglutaconic acids, primary amines, and aromatic aldehydes has been further investigated. It was shown to proceed via 3-arylglutaconic anhydrides, which, in turn, were found to give superior results in the two-component reactions with imines. The initial formation of the Castagnoli–Cushman carboxylic acids was shown to be the case, and their decarboxylation was found to follow a complex, “forked” pathway, which was confirmed by deuterium incorporation experiments.