Phenyldiazoacetic acid

The enol form of mandelic acid (101) has been generated by flash photolysis of phenyldiazoacetic acid in aqueous solution.101 The enol forms by hydration of the intermediate carbene (102). The reaction of chloramine-T (TsNClNa O) with methyl p-tolyl sulfide to give the corresponding sulfimide (103) appears to proceed via a nitrene-transfer mechanism in the presence of copper(I) and a second nitrogen ligand (such as acetonitrile).102... 

Independently, Davies et al.l also reported the same approach as descrihed above hy Winkler et al. The Rh2(S-DOSP)4-catalyzed decomposition of methyl phenyldiazoacetate (40) in the presence of WBOC-piperidine (41, 4 equivalents) in 2,3-dlmethylbutane at room temperature, followed by treatment with tri-fluoroacetic acid, resulted in the formation of a mixture of threo- and e/yZftro-methylphenidate in 49% yield. However, the Zftreo-isomer was the minor diastereomer and was formed in only 54% ee. A major improvement in enantioselectivity and diastereo-selectivity was achieved hy carrying out the reaction with the Rh2(S-biDOSP)2 catalyst. The ratio of threo to erythro isomers was improved to 2.5 1 (75% yield), respectively. The (27 ,2 7 )-Z/ireo-isomer was formed in 86% ee and isolated in 52% yield. 

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