Recently, Knight and Sibley (D. W. Knight and A. W. Sibley, J. Chem. Soc., Perkin Trans. 1, 1997, 2179-2187) reported that the displacement of N-benzyloxycarbonyl-O-p-toluenesulfonyl serine methyl ester (or methyl (S)-2-benzyloxycarbonylamino-3-methylsulfonyloxypropanoate) with freshly prepared sodium thiophenylate in DMF at about 0° C. afforded the desired N-benzyloxycarbonyl-S-phenyl-L-cysteine methyl ester (or methyl (R)-2-benzyloxycarbonylamino-3-phenylthiopropanoate) in 98% yield providing a reported optical rotation of [α]20D−17.2 (c, 1.8; MeOH). No enantiomeric ratio of the product was reported. Furthermore, the use of sodium phenolate, prepared from sodium hydride, thiophenol and DMF is not amenable to large scale manufacture.
