Enantioselective Synthesis of Piperidine, Indolizidine, and Quinolizidine Alkaloids from a Phenylglycinol-Derived δ-Lactam

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Abstract
Starting from a common lactam, (3R,8aS)-5-oxo-3-phenyl-2,3,6,7,8,8a-hexahydro-5H-oxazolo[3,2-a]pyridine (1), or its enantiomer, the enantioselective synthesis of 2-alkylpiperidines and cis- and trans-2,6-dialkylpiperidines is reported. The potential of this approach is illustrated by the synthesis of the piperidine alkaloids (R)-coniine, (2R,6S)-dihydropinidine, (2R,6R)-lupetidine, and (2R,6R)-solenopsin A, the indolizidine alkaloids (5R,8aR)-indolizidine 167B and (3R,5S,8aS)-monomorine I, and the nonnatural base (4R,9aS)-4-methylquinolizidine.