Thermal biradical C-2 C-5 cyclizations of enyne-ketenimines ¹

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In 1989 Myers et. al. [1] published a C-1 C-6 6-ring cyclization of enyne-ketenimines. Seven years later Schmittel et. al. [2,3] discovered a C-2 C-6 5-ring cyclization. The two reactions are schown below:

After the experimental discovery quantum chemical screening calculation on a model system were successfully carried out [4,5,6,7] to predict the gain of synthesis with varying rests R. The theoretical results are schown below:

From the theoretical point of view the description of the transition states requires a multi-reference wavefunction due to the existence of the diradical structure of the molecule.

Footnotes

... enyne-ketenimines¹

In cooperation with M. Schmittel and P. J. Steffen and W. A. M. Angel and M. Strittmatter, University of Würzburg and B. Engels and C. Lennartz, University of Bonn