Single and Consecutive Cyclization Reactions of Alkynyl Carbene Complexes and 8-Azaheptafulvenes: Direct Access to Polycyclic Pyrrole and Indole Derivatives

✍ Scribed by José Barluenga; Jaime García-Rodríguez; Ángel L. Suárez-Sobrino; Miguel Tomás

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 303 KB
• Volume: 15
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200901257

✦ Synopsis

Abstract

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.