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 TiCl4-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.