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Asymmetric Synthesis of the Four Stereoisomers of 4-Hydroxypipecolic Acid
31 December 2000 (online)
The asymmetric synthesis of all four stereoisomers of 4-hydroxypipecolic acid (1) from the polyfunctionalized chiral building blocks δ-amino β-keto esters (S S, R)-(+)-5 or (R s, S)-(-)-5 is described. Key steps in the synthesis are the stereoselective reductions of b-phenylpiperidine-2,4-dione (6) and N-sulfinyl δ-amino β-keto esters 5 to cis-4-hydroxy 2-piperidinone 7 and syn-δ-amino β-hydroxy ester 9, respectively. The only protecting/deprotecting group chemistry required is related to the oxidation step.
stereoselective reductions - hydrides - cyclization - asymmetric synthesis - piperidines