Short, Enantiospecific Syntheses of Indolizidines 209B and 209D, and Piclavine A from Diethyl‐ L ‐Glutamate

The 1 H ‐pyrrole derivative obtained from diethyl L ‐glutamate hydrochloride and tetrahydro‐2,5‐dimethoxyfuran was cyclized with BBr 3 to ethyl (5 S )‐5,6,7,8‐tetrahydro‐8‐oxoindolizine‐5‐carboxylate ( 18 ). Catalytic hydrogenation of 18 over Pd/C in AcOH gave ethyl (5 S ,8a R )‐octahydroindolizine‐5‐carboxylate ( 21 ), whereas hydrogenation over Rh/Al 2 O 3 in EtOH/AcOH 99:1 afforded mainly ethyl (5 S ,8 S ,8a S )‐octahydro‐8‐hydroxyindolizine‐5‐carboxylate ( 22 ). By functional‐group interconversions, 21 was transformed into piclavine A ( 1 ) and indolizidine 209D ( 2 ). Similarly, (5 R ,8 R ,8a S )‐octahydro‐5‐pentylindolizine‐8‐methanol ( 37 ), the final relay for indolizidine 209B ( 3 ), was obtained from 22 .