Stereoselective Synthesis of Chiral Polycyclic Indolic Architectures through Pd 0 ‐Catalyzed Tandem Deprotection/Cyclization of Tetrahydro‐β‐carbolines on Allenes

Enantioenriched N ‐allyl tetrahydro‐β‐carbolines were prepared by chiral phosphoric acid‐catalyzed Pictet–Spengler reactions. The compounds undergo Pd 0 ‐catalyzed cyclizations through a tandem deprotection/cyclization process. The regioselectivity of the attack is controlled by the chain length and by the substitution pattern of the allene function. Products resulting from 5‐ exo ‐ or 6‐ exo ‐attack were obtained with diastereoisomeric ratio up to 95:5. Azepinopyrrido[3,4‐ b ]indoles were obtained by 7‐ endo ‐cyclizations.