Intramolecular Mannich reaction in the asymmetric synthesis of polysubstituted piperidines: concise synthesis of the dendrobate alkaloid (+)-241D and its C-4 epimer.

[reaction: see text] The intramolecular Mannich reaction of delta-amino beta-keto esters with aldehydes and ketones is a new methodology for the synthesis of polysubstituted piperidines and is illustrated by the concise asymmetric synthesis of the dendrobate alkaloid (+)-241D and its C-4 epimer.