A Convenient Synthesis of Enantiomeric Pairs of 2,5-Disubstituted Pyrrolidines of C2-Symmetry

By the use of (-)-1-phenylethylamine as a chiral auxiliary, three diastereomeric isomers of 2,5-bis(methoxycarbonyl)pyrrolidine derivatives are prepared from dimethyl rac-2,5-dibromoadipate and separated by crystallization and chromatographic fractionation involving stereoselective hydrolysis. The cis isomer is recovered and epimerized to the trans counterparts. Starting from each of the two trans isomers, optically active 2,5-disubstituted [2,5-bis(methoxymethyl) and 2,5-bis(methoxymethoxymethyl)] pyrrolidines of C 2-symmetry are synthesized by a short route.