Single and consecutive cyclization reactions of alkynyl carbene complexes and 8-azaheptafulvenes: direct access to polycyclic pyrrole and indole derivatives.
The reactivity of alkynyl and enynyl Fischer carbene complexes towards 8-azaheptafulvenes is examined. Alkynyl carbenes 1 a-f undergo regioselective [8+2] heterocyclization with 8-aryl-8-azaheptafulvenes 2 a, b providing cycloheptapyrroles 3 and 4 with metal carbene or ester functionality at C3. Moreover, consecutive cyclization reactions are involved when enynyl carbenes are used. Thus, the cyclopenta[b]pyrrole framework 7 is formed by the consecutive [8+2] cyclization and cyclopentannulation reactions. The initially formed cyclopentannulation adduct can be intercepted through a Diels-Alder reaction with classic dienophiles to afford increasing structural complexity (compounds 8 and 9). More importantly, the construction of the indole skeleton is accomplished with a high degree of substitution and functionalization (compounds 11-15) by a one-pot sequence that involves [8+2] cyclization, R--NC or CO insertion, and ring closure.
Barluenga
José
J
Instituto Universitario de Química Organometálica Enrique Moles Unidad Asociada al CSIC, Universidad de Oviedo, Julián Clavería 8, 33006 Oviedo, Spain. barluenga@uniovi.es
García-Rodríguez
Jaime
J
Suárez-Sobrino
Angel L
AL
Tomás
Miguel
M