| 摘要 |
Processes and intermediates for preparing 2-substituted piperidines such as 2-substituted d-threo piperidines are provided. In preferred embodiments, the processes of the invention comprise the steps of reacting a 2-substituted pyridine with hydrogen in the presence of a catalyst in an alkanoic acid, and adding an alkyl alkanoate to the resulting mixture of threo and erythro 2-piperidine stereoisomers to precipitate alkanoate salts of the erythro stereoisomers preferentially with respect to alkanoate salts of the threo stereoisomers. The erythro salts thenare reacted with aqueous base to form the corresponding mixture of erythro amide free bases, which are reacted with a suitable organic acid resolving agent in an alkyl alcohol solvent to form acid salts of the l-erythro stereoisomers preferentially with respect to the d-erythro stereoisomers. The l-erythro acid salts are then reacted with aqueous base to form the l-erythro piperidine amide free base which, in turn, is epimerized to produce the desired d-threo product by treating it in an organic solvent with an alkali metal alkoxide.
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