Visible-Light Cascade Photooxygenation of Tetrahydrocarbazoles and Cyclohepta[b]indoles: Access to C,N-Diacyliminium Ions.

Tetrahydrocarbazoles and perhydrocyclohepta[b]indoles undergo a catalytic cascade singlet oxygenation in alkaline medium, which leads to chiral tricyclic perhydropyrido- and perhydroazepino[1,2-a]indoles in a single operation. These photooxygenation products are new synthetic equivalents of uncommon C,N-diacyliminium ions and can be functionalized with the aid of phosphoric acid organocatalysis.