Asymmetric Synthesis of the Four Stereoisomers of 4-Hydroxypipecolic Acid

All articles of this category 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