An unexpected reversal in the stereochemistry of transannular cyclizations. A stereoselective synthesis of (±)-epilupinine.

The transannular cyclizations of N-benzylhexahydroazec-5-en-2-one and N-benzylhexahydroazon-5-en-2-one using iodine or phenylselenenyl bromide affords substituted quinolizidines and indolizidines, respectively. In the case of the ten-membered ring lactams an unexpected reversal in stereochemistry was observed. These results were confirmed by elaboration of the iodo cycloadduct 4a into (±)-epilupinine.