Synthesis of optically pure epibatidine analogs: (1R, 2R, 5S)-2β-(2-chloro-5-pyridinyl)-8-azabicyclo[3.2.1]octane and (1R, 2S, 5S)-2α-(2-chloro-5-pyridinyl)-8-azabicyclo[3.2.1]octane from (−)-cocaine