Novel chiral bridged azepanes: stereoselective ring expansion of 2-azanorbornan-3-yl methanols

The reaction of 2-azanorbornan-3-yl methanols under Mitsunobu or mesylation conditions with various nucleophiles led to a series of chiral-bridged azepanes with configuration at C-4 dependent on the configuration of the starting alcohol. High yielding, stereoselective ring expansion to novel 2-azabicyclo[3.2.1]octane system occurred via aziridinium intermediates, which were specifically opened by nucleophilic attack at the more substituted carbon.