Synthesis of 2S,5S-and 2R,5S-5-hydroxypipecolic acid via amide-methylenation of S-5-hydroxy-2-piperidone with dimethyltitanocene.-Science-Chemical Encyclopedia-lookchem

Synthesis of 2S,5S-and 2R,5S-5-hydroxypipecolic acid via amide-methylenation of S-5-hydroxy-2-piperidone with dimethyltitanocene.
Add time:07/22/2019 Source:sciencedirect.com

A route to 2S,5S-and 2R,5S-hydroxypipecolic acid is presented, starting with the enantiopure 5S-5-hydroxy-piperidone 7. The key step of this reaction sequence is the chemoselective methylenation of the amide carbonyl group of 8 with dimethyltitanocene 9 to 10. The transformation of the exocyclic enecarbamate double bond to the carboxylic acid group is best accomplished via hydroboration/oxidation to the alcohol 11a,b. Separation and oxidation of the diastereomers 11a,b, to 14a, and 14b, and hydrolysis furnishes the diastereomeric pipecolic acids 15a and 15b in enantiopure form.

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