A Unified Approach to the Isomeric α‑, β‑, γ‑, and δ‑Carbolines via their 6,7,8,9-Tetrahydro Counterparts

A cross-coupling/reductive cyclization protocol has been employed in a unified approach to all four carbolines. So, for example, the 2-nitropyridine 8, which is readily prepared through an efficient palladium-catalyzed Ullmann cross-coupling reaction, is reductively cyclized under conventional conditions to give 6,7,8,9-tetrahydro-α-carboline that is itself readily aromatized to give α-carboline (1).