Reductive Fragmentation of Tetrazoles: Mechanistic Insights and Applications toward the Stereocontrolled Synthesis of 2,6-Polysubstituted Morpholines

A new methodology to synthesize 2,6-di-, and 2,2′,6-trisubstituted morpholines via the reduction of oxabicyclic tetrazoles under mild conditions is described. The reaction proved successful for a wide range of tetrazoles, including sterically encumbered ones harboring gem-substituents on tertiary carbon centers. The mechanism for the decades-old reduction of tetrazoles to secondary amines is elucidated.