Reductive dimerization of alkylidenemalonates using samarium(II) diiodide and H-1-NMR behavior of the dimers, 2,3-diaryl-1,1,4,4-butanetetracarboxylates

Alkylidenemalonates were readily dimerized in the presence of SmI2 to give 2,3-disubstituted 1,1,4,4-butanetetracarboxylates as mixtures of meso and r acemic isomers in moderate to good yields. The structure of the less polar isomer of tetraethyl 2,3-diphenyl-1,1,4,4-butanetetracarboxylate was determ ined by X-ray crystallographic analysis to be the meso form. Characteristic H-1-NMR behavior of the meso and racemic isomers is also discussed.