An enantiospecific entry to indolizidines by intramolecular acylation of N-pyrrole esters
作者:Charles W. Jefford、Steven R. Thornton、Krzysztof Sienkiewicz
DOI:10.1016/s0040-4039(00)76698-6
日期:1994.6
L-Glutamic diethyl ester hydrochloride was converted to its pyrrole derivative 22 by condensation with 2,5-dimethoxytetrahydrofuran in water. Cyclization of 22 with BBr3 afforded (5S)-5,6-dihydro-5-ethoxycarbonyl-8(7H)-indolizinone (23). Catalytic hydrogenation of 23 over Pd/C in acetic acid gave exclusively (5S,9R)-5-ethoxycarbonylindolizidine in an overall yield of 41%, whereas hydrogenation over Rh/Al2O3 in ethanol gave predominantly (5S,8S,9S)-5-ethoxycarbonyl-8-hydroxyindolizidine in 48.5% overall yield.