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

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.