Mechanism of Annulation ([2 + 4] Cyclocondensation) of Cyclic Azomethines with β-Dicarbonyl and β,β'-Tricarbonyl Compounds and Their Enol Derivatives in Protogenic Media

摘要

The annulation of azomethines (Setoff's bases) with β-dicarbonyl and β,β'-tricarbonyl compounds (β-diCCs and β,β'-triCCs, respectively), described in the general form by the transformation I + II→ III (Scheme 1), is an effective regio- and stereospecific method of construction of molecular skeletons of azangular heterocy-cles—heterocyclic compounds with a nitrogen atom shared by fused rings [1-6]. Compounds containing similar fragments are widely encountered in natural objects, have valuable properties, and are used in human scientific and practical activity, in particular, in the search for and development of new pharmacological and biochemical agents for medicine, veterinary, and bioengineering, which explains the attention focused on the development of methods of their synthesis and on studying their properties [1-4]. The reaction of [2 + 4] cyclocondensation of 3,4-dihydroisoquino-lines with acetylacetone derivatives, benzoylacetone, 2-acetylcycloalkanones, 3-acetyl-4-piperidones, and 2-acetyldimedone [5] yields, in one step, the partially hydrogenated γ-pyndone ring of the molecular skeletons of azangular heterocycles III.