Two Novel Thermal Biradical Cyclizations in Theory and Experiment: New Synthetic Routes to 6H-Indolo[2,3-b]quinolines and 2-Aminoquinolines from Enyne-Carbodiimides

Michael Schmittel; Jens-Peter Steffen; Bernd Engels; Christian Lennartz; Michael Hanrath

doi:10.1002/(SICI)1521-3773(19980918)37:17<2371::AID-ANIE2371>3.0.CO;2-N

Two Novel Thermal Biradical Cyclizations in Theory and Experiment: New Synthetic Routes to 6H-Indolo[2,3-b]quinolines and 2-Aminoquinolines from Enyne-Carbodiimides

Angew Chem Int Ed Engl. 1998 Sep 18;37(17):2371-2373. doi: 10.1002/(SICI)1521-3773(19980918)37:17<2371::AID-ANIE2371>3.0.CO;2-N.

Authors

Michael Schmittel¹, Jens-Peter Steffen¹, Bernd Engels², Christian Lennartz², Michael Hanrath²

Affiliations

¹ Institut für Organische Chemie der Universität, Am Hubland, D-97074 Würzburg (Germany), Telefax: (+49) 931-888-4606.
² Institut für Physikalische und Theoretische Chemie der Universität, Wegelerstrasse 12, D-53115 Bonn (Germany), Telefax: (+49) 228-73-9066.

Abstract

The regioselectivity of the biradical cyclization of enyne-carbodiimides 1 can easily be controlled by variation of R¹ at the alkyne terminus. Attachment of a hydrogen atom (R¹ =H) leads to C² -C⁷ cyclization and formation of biradical 2, whereas C² -C⁶ cyclization to provide biradical 3 is observed with R¹ =Me₃ Si or Ph.

Keywords: Carbodiimides; Cycloaromatizations; Diradicals; Enynes; Quantum chemical calculations.