Enantioselective Cascade Sequence to Indoloquinolizidines and Its Application in the Synthesis of epi-Geissochizol

An organocatalyzed one-pot Michael addition and Pictet-Spengler sequence utilizing beta-keto amide and aliphatic alpha,beta-unsaturated aldehydes was developed, which provided access to highly substituted indolo[2,3-a]quinolizidines as a mixture of keto and enol tautomers. Such tautomeric pairs were transformed into stable compounds with an E-ethylidenyl group in telescoped steps. This method was successfully applied in the synthesis of epi-geissoschizol.