[reaction: see text] The intramolecular Mannich reaction of delta-amino beta-keto esters with aldehydes and ketones is a new methodology for the synthesis of polysubstituted piperidines and is illustrated by the concise asymmetric synthesis of the dendrobate alkaloid (+)-241D and its C-4 epimer.
[formula: see text] delta-Amino beta-keto esters 3 and 11 are designed polyfunctionalized chiral building blocks for alkaloid synthesis and are prepared in one step from the corresponding sulfinimine (N-sulfinyl imine). Concise highly enantioselective four-step syntheses of 2-phenylpiperidine (7) and SS20846A (14) from 3 and 11, respectively, are described.
The asymmetric synthesis of all four stereoisomers of 4-hydroxypipecolic acid (1) from the polyfunctionalized chiral building blocks d-amino b-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 d-amino b-keto esters 5 to cis 4-hydroxy 2-piperidinone 7 and syn-d-amino b-hydroxy ester 9, respectively. The only protecting/deprotecting group chemistry required is related to the oxidation step.
[reaction: see text]A highly stereoselective asymmetric synthesis of the quinolizidinealkaloid (-)-lasubine II from a delta-amino beta-hydroxy ketone, a new polyfunctionalized chiral building block, is described.
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