Pd(0)-Catalyzed Tandem Deprotection/Cyclization of Tetrahydro-β-carbolines on Allenes: Application to the Synthesis of Indolo[2,3-a]quinolizidines

The pallado-catalyzed tandem deprotection/cyclization reaction of enantioenriched N-allyl tetrahydro-beta-carbolines on allenes is described. The first step generates in situ a deprotected tetrahydro-beta-carboline, which then undergoes a cyclization on the allene function via an intermediate pi-allyl Pd(II) derivative. This reaction results in the synthesis of various chiral indolic tetracycles (mainly indolo[2,3a]-quinolizidine derivatives) presenting a vinyl function.