Enantiospecific synthesis of natural (-)-cocaine and unnatural (+)-cocaine from D- and L-glutamic acid

Natural (-)-cocaine and unnatural (+)-cocaine have been synthesized enantiospecifically from D- and L-glutamic acid, respectively. The axial-equatorial substitutents were introduced by a stereo- and regiospecific dipolar cycloaddition to the corresponding (LR,5S)- and (1S,5R)-N-BOC-nortropenes with (ethoxycarbonyl)formonitrile N-oxide. A sequence of subsequent stereochemically controlled transformations converted the fused isoxazoline to the requisite P-hydroxy ester. Synthesis of the key intermediate N-BOC-nortropenes involved construction of the 8-azabicyclo[3.2.1]octane framework by Dieckmann condensation of cis-5-substituted D-and L-proline esters. For comparison, (1R,SS)-N-BOC-nortropene also was derived by degradation from natural cocaine. The cis-5-substituted D-and L-proline esters were obtained by sulfide contraction and subsequent catalytic hydrogenation to induce stereospecifically the C-5 stereochemistry from D-and L-thiopyroglutamate, which in turn were prepared from D-and L-glutamic acids, respectively.