The Synthesis of Dimethyldl-3-Ethyl-4-methyl-1,2-cyclopentanedicarboxylates

The four 3,4-cis-stereoisomers of dimethyl dl-3-ethyl-4-methyl-1,2-cyclopentanedicarboxylates (1a, 1b, 1c, and 1d) have been synthesized and their configurations established. A comparison of the spectral data and the GLC behaviors has shown that the corresponding ester, one of the key degradation products of ikarugamycin, has the r-1, t-2, c-3, c-4-configuration (1a). The r-1, t-2, c-3, t-4-stereoisomer (1f) has also been prepared.