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. The reaction was shown to proceed via 3-arylglutaconic anhydrides which, in turn, were found to give superior results in two-component reactions with imines in terms of yields and reagent scope. 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.