Fulgencio Tovar

Surpassing Torquoelectronic Effects in Conrotatory Ring Closures: Origins of Stereocontrol in Intramolecular Ketenimine–Imine [2+2] Cycloadditions

Unexpectedand almost perfect stereochemical control is obtained in the title reactions [Eq. (a)], although torquoelectronic theory predicts negligible stereoselection. According to ab initio and DFT calculations, this stereocontrol is determined by the geometry of the first transition state of the stepwise mechanism. In good agreement with the model proposed, the presence of an additional methylene group attached to the iminic nitrogen atom promotes a significant loss of stereocontrol.

Intramolecular [2 + 2] cycloaddition of ketenimines with imines. Synthesis and chemical behaviour of azeto[2,1-b]quinazolines

Abstract Azeto[2,1- b ]quinazolines 5 have been prepared by the novel intramolecular [2 + 2] cycloaddition reaction of ketenimines with imines. The applicability and limitations of the synthetic methodology, and explorations on the reactivity of compounds 5 are discussed.

Formal [4+2] intramolecular cycloaddition ketenimine-imine. Synthesis of benzimidazo[1,2-b]isoquinolines

Abstract Benzimidazo[1,2- b ]isoquinolines have been prepared by a formal [4+2] intramolecular cycloaddition of ketenimines with imines.

Periselective intramolecular [4+2] cycloadditions of ketenimines: synthesis of pyrido[1,2-a]benzimidazoles

Abstract A new synthesis of pyrido[1,2- a ]benzimidazole derivatives is described. Easily available N -(2-propenylideneaminophenyl)ketenimines underwent an intramolecular [4+2] cycloaddition reaction, in which the cumulated CC bond of the ketenimine fragment acts as the 2π-electron component and the α,β-unsaturated imine function as the 4π-electron component, yielding the titled compounds in a periselective manner.

Highly stereocontrolled [2+2] cycloaddition versus unprecedented imino-ene reactions of imino-ketenimines

Abstract N-[(2-Benzylideneamino)phenyl]-C-methylketenimines undergo intramolecular cyclization via two different reaction pathways, a [2+2] cycloaddition and a rare imino-ene reaction, to yield azeto[1,2-a]benzimidazoles and 2-(α-styryl)benzimidazoles, respectively. The results are interpreted in terms of a two-step mechanism involving two stereoisomeric conjugated betaines as intermediates.