SHORT, ENANTIOSPECIFIC SYNTHESES OF INDOLIZIDINES 209B AND 209D, AND PICLAVINE-A FROM DIETHYL-L-GLUTAMATE

The 1H-pyrrole derivative obtained from diethyl L-glutamate hydrochlor ide and tetrahydro-2,5-dimethoxyfuran was cyclized with BBr3 to )-5,6, 7,8-tetrahydro-8-oxoindolizine-5-carboxylate (18). Catalytic hydrogena tion of 18 over Pd/C in AcOH gave ethyl (5S,8aR)-octahydroindolizine-5 -carboxylate (21), whereas hydrogenation over Rh/Al2O3 in EtOH/AcOH 99 :1 afforded mainly ethyl S,8aS)-octahydro-8-hydroxyindolizine-5-carbox ylate (22). By functional-group interconversions, 21 was transformed i nto piclavine A (1) and indolizidine 209D (2). Similarly, 5R,8R,8aS)-o ctahydro-5-pentylindolizine-8-methanol (37), the final relay for indol izidine 209B (3), was obtained from 22.