Synthesis of (R)-(−) and (S)-(+)-3-(1-pyrrolyl)propyl- N-(3,5-dinitrobenzoyl)-α-phenylglycinate and derivatives. A suitable chiral polymeric phase precursor

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 Et 3 N 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 1 H NMR analysis in the presence of optically active Eu(tfc) 3 . Epimerization was not observed in the preparation of the carboxylate salts ( 5 – 8 ).