Mechanism for annelation ([2+4] cyclocondensation) of Schiff bases by β-dicarbonyl and β,β′-tricarbonyl compounds in amphiprotic media (review)

Abstract

The mechanism was established for annelation ([2+4] cyclocondensation) of Schiff bases or azomethines by β-dicarbonyl and β,β'-tricarbonyl compounds in amphiprotic media. The condensation was found to be a self-catalyzed pericyclic process achieved through six-membered transition states. The key reaction intermediates are dipoles of quaternized azomethine ions and enol-anions of the β-dicarbonyl and β,β'-tricarbonyl compounds, which display 1,4-dipolarophilicity.

Computational Study of the Ene/Rearrangement Reaction between (F3C)2B═NMe2, 1, and Acetonitrile: Reactant-Catalyzed Mechanism of the Ketenimine–Nitrile-Like Rearrangement

“…While reaction self-catalysis is well established in biochemical − and polymer/materials processes, − it is rather rarer in organic synthesis , and rarer still in inorganic/organometallic synthesis. , The reaction studied here represents an intriguing example of aminoborane self-catalysis providing a functional group rearrangement. We plan to examine other pericyclic reactions in this area to see if other unusual reactions can be explained by self-catalysis.…”