η³-Pyranyl and η³-Pyridinyl Molybdenum π-Complexes as Chiral Scaffolds for the Enantioselective Construction of Substituted Oxa- and Aza[3.3.1]bicyclics:  First Enantio- and Regiocontrolled [5+3] Cycloaddition Reactions

The first Mo-mediated [5+3] cycloadditions are reported. 3-Substituted pyranyl and pyridinyl molybdenum π-complexes participate in enantiocontrolled [5+3] cycloadditions and provide a new and efficient synthetic approach to oxa- and aza[3.3.1]bicyclics of high enantiomeric purity. The reaction proceeds in good to excellent yields and with complete regio- and endo-selectivities; it diverts to a [2+3] cycloaddition pathway when 2-substituted heterocycle π-complexes are used. This methodology, coupled with a variety of general demetalation protocols, holds much promise in synthetic applications.