On the regioselectivity of the cyclization of enyne-ketenes: a computational investigation and comparison with the Myers-Saito and Schmittel reaction.

The Moore (C(2)-C(7)) cyclization and the alternative C(2)-C(6) cyclization of enyne-ketenes belong to the family of biradical cyclization reactions such as the Bergman reaction of ene-diynes, both the cyclizations of enyne-allenes and enyne-cumulenes. The latter garnered substantial interest due to their antitumor efficacy. The mechanisms of both cyclization modes of enyne-ketenes are still unclear, but as the enyne-ketenes can formally be regarded as heteroanalogues of enyne-allenes, both cyclizations are expected to react via biradical routes.

Which Structural Elements Are Relevant for the Efficacy of Neocarzinostatin?

While the general course of the mode of action of the antitumor agent neocarzinostatin (NCS) is clarified, it is still unclear which structural elements are relevant for the high efficacy of NCS. This question and the role of alternatively possible biradicals are addressed.