Diels‐alder reactions of methyl‐ and π‐acceptor‐substituted 2‐vinylindoles with dimethyl acetylenedicarboxylate and tetracyanoethylene: Novel functionalized carbazoles

The Diels‐Alder reactions of the 2‐vinylindoles 1a‐1d , which are now readily accessible, with dimethyl acetylenedicarboxylate and tetracyanoethylene give rise to the novel 1,2‐dihydro‐ and 1,2,3,4‐tetrahydrocarbazoles 2, 4 , and 5 as well as the fully aromatized carbazoles 3 . With regard to the product spectrum, the mechanistic rationale comprises a Diels‐Alder step, formal 1,3‐hydrogen shift, ene reaction, and dehydrogenation. Conformational aspects of the 1,2‐dihydrocarbazoles 2b and 2c are also discussed.