Add time:07/26/2019         Source:sciencedirect.com

A synthetic route to obtain (R)-(−) (1), (S)-(+)-3-(1-pyrrolyl)propyl-N-(3,5-dinitrobenzoyl)-α-phenylglycinate (2) and derivatives is described. In a first step, pyrrole derivatives were prepared using the Clauson-Kaas method. The esterification, second step, was performed using basic conditions due to sensitivity of the pyrrole group toward acidic conditions. A tautomeric equilibrium involving the stereogenic center induces the product epimerization. The substitution of DMAP and Et3N by a highly hindered base, proton-sponge®, furnished the final products without racemization. The ee of 1, 2 and of the corresponding methyl esters (3 and 4) were determined by 1H NMR analysis in the presence of optically active Eu(tfc)3. Epimerization was not observed in the preparation of the carboxylate salts (5–8).

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