Reductive dimerization of 2-substituted cyclopropane-1,1-dicarboxylates using samarium(II) diiodide

In the presence of samarium diiodide, 2-aryl and 2-heteroaryl cyclopropane- l,l-dicarboxylic esters were readily dimerized to give 3,4-disubstituted 1, 1,6,6-hexanetetracarboxylic esters as diastereomeric mixtures in moderate t o good yields. The diastereomeric mixtures were separated by preparative HP LC and stereo-chemistries of the isolated meso and racemic compounds were d etermined on the basis of HPLC analysis on chiral stationary phases. Betwee n the H-1-NMR spectra of the separated diastereomers, the characteristic di fferences in the chemical shifts of the C2-H (C5-H) signals were observed a nd explained based on the MOPAC calculation.