Endo-selectivity and kinetic control in alkali metal–NH3–NH4+ reductions of bicyclo[2.2.1]heptan-2-ones

Abstract

Reduction of five bicyclo[2.2.1]heptan-2-ones (6), (9), (12), (15), (18) and the parent bicyclo[2.2.1]hept-5-en-2-one (21) by alkali metals dissolving in NH₃ and a cosolvent saturated with NH₄Cl affords in every case predominantly (83–<99%) the corresponding endo-alcohol (7), (10), (13), (16), (19), and (22), and since two of these endo-alcohols are the thermodynamically more stable [(7), (19)] and two the less stable [(10), (13)] isomers, these reductions are probably all kinetically controlled; a correlation is made between this endo-selectivity and exo-hydrogen-exchange in the ketones (6), (9), (12), (15), and (21).