Development of the intramolecular Prins cyclization/Schmidt reaction for the construction of the azaspiro[4,4]nonane: application to the formal synthesis of (±)-stemonamine.

A TiCl(4)-promoted tandem intramolecular Prins cyclization/Schmidt reaction has been designed and developed to be an efficient method for the construction of the azaspiro[4,4]nonane. The present tandem protocol has been employed to construct the tricyclic azaquaternary skeleton (ring A, B, and C) of stemonamine.