| Abstract
| - Asymmetric syntheses of (2S,3S)-3-(tert-butoxycarbonyl)-2-piperidinecarboxylic acid (1b), (3R,4S)-4-(tert-butoxycarbonyl)-3-piperidinecarboxylic acid (2b), and their corresponding N-Boc and N-Cbzprotected analogues 8a,b and 17a,b are described. Enantiomerically pure 1b has been synthesizedin five steps starting from l-aspartic acid β-tert-butyl ester. Tribenzylation of the starting materialfollowed by alkylation with allyl iodide using KHMDS produces the key intermediate 5a in a 6:1diastereomeric excess. Upon hydroboration, the alcohol 6a is oxidized, and the resulting aldehyde7 is subjected to a ring closure via reductive amination, providing 1b in an overall yield of 38%.Optically pure 2b has been synthesized beginning with N-Cbz-β-alanine. The synthesis involvesthe induction of the first stereogenic center using Evans's chemistry and sequential LDA-promotedalkylations with tert-butyl bromoacetate and allyl iodide. Further elaboration by ozonolysis andreductive amination affords 2b in an overall yield of 28%.
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