232. “An enantiospecific entry to indolizidines by intramolecular acylation of N-pyrrole esters”
     Jefford, C.W.; Thornton, S.R.; Sienkiewicz, K.
     Tetrahedron Lett. 1994, 35, 3905-3908.

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.

DOI : 10.1016/S0040-4039(00)76698-6 

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