Asymmetric reaction. XV. Structure and relative configuration of a reductive dimerization product of ethyl phenylglyoxylate,diethyl diphenyltartrate

The hydrogenation of ethyl phenylglyoxylate catalyzed by bis(dimethylglyoximato)cobalt(II)-quinine gave a novel reductive dimerization product, diethyl diphenyltartrate, with a slight optical activity. The crystals obtained from its benzene-hexane solution were investigated by X-ray diffraction method. The crystal is triclinic, space group p1, a = 10.078(3), b = 10.283(2), c = 9.781(3) Å, α = 109.80(2), β = 102.35(3), γ = 78.50(2)°, Z = 2, V = 922.7 ų, Dc = 1.29 g cm^?3,μ = 7.46 cm^?1 for Cu Kα. The structure was solved by the direct method, and refined by a block-diagonal least-squares procedure: R = 0.059 for 2568 reflections with | Fo | >3σ(| Fo | ). The relative configuration around the two chiral carbons indicated that the molecule is in the threo-form, and the Newman projection showed that the molecule has the staggered conformation. There were two relatively strong intramolecular hydrogen bonds between the two hydroxyl groups and the two carbonyl oxygen atoms of ethoxycarbonyl groups.