Straightforward methodology for the enantioselective synthesis of benzo[a]- and indolo[2,3-a]quinolizidines.
Mercedes Amat, Maria M M Santos, Oriol Bassas, Núria Llor, Carmen Escolano, Arantxa Gómez-Esqué, Elies Molins, Steven M Allin, Vickie McKee, Joan Bosch
An enantioselective two-step route to substituted benzo[a]- and indolo[2,3-a]quinolizidines has been developed. It consists of (i) a stereoselective cyclocondensation of a racemic or prochiral delta-oxo(di)ester with either (S)-(3,4-dimethoxyphenyl)alaninol or (S)-tryptophanol in a process involving a dynamic kinetic resolution and/or the differentiation of enantiotopic or diastereotopic ester groups, and (ii) a subsequent stereocontrolled cyclization on the aromatic ring taking advantage of the masked N-acyl iminium ion present in the resulting oxazolopiperidone lactams.
