Stereoselective Synthesis of Chiral Polycyclic Indolic Architectures through Pd0-Catalyzed Tandem Deprotection/Cyclization of Tetrahydro-β-carbolines on Allenes

Enantioenriched N-allyl tetrahydro--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.