Two Diastereomers of Benzylidene-D-erythronolactone

The title compounds 2,3-O-(R)-benzylidene-D-erythronolactone (endo isomer) and 2,3-O-(S)-benzylidene-D-erythronolactone (exo isomer), C₁₁H₁₀O₄, which crystallize in the same space group with quite similar cell constants, are model compounds for the key intermediate in the synthesis of endo-brevicomine. The X-ray structure determination was performed in order to discover whether inherent molecular properties of these species might account for the observed endo selectivity but no such features could be found. To substantiate this conclusion from the energetic point of view, we performed non-empirical as well as semi-empirical quantum chemical calculations which revealed that both isomers are almost isoenergetic with a slight preference for the exo isomer. From our combined results we believe that the observed reactivity is most likely to be kinetically controlled.

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