Organometallic Enantiomeric Scaffolds in the Synthesis of Alkaloids: I. Homo-SN2´-like Reaction/Annulative Demetallation and the Application in the Synthesis of (+)-Isofebrifugine II. Uncatalyzed Electrophilic C-C Bond Forming Reactions of Pyranyl and Pyridinyl Molybdenum Complexes