1999/08/04 by Zdenko Hameršak, Berislav Perić, Biserka Kojić‐Prodić +5
Chemistry · Biochemistry, Genetics and Molecular Biology · #Synthesis and Biological Evaluation #Chemical Synthesis and Analysis #Synthesis and Catalytic Reactions
paper · doi:10.1002/(sici)1522-2675(19990804)82:8<1289::aid-hlca1289>3.0.co;2-w
Acid-catalyzed methanolysis of N-hydroxy-α-oxobenzeneethanimidoyl chloride (1), a 2-(hydroxyimino)-1-phenylethan-1-one derivative obtained in one step from acetophenone, leads to a constant ratio of methyl α-oxobenzeneacetate (2) and methyl α-(hydroxyimino)benzeneacetate (3). 13C(α) Labelled [13C]-1 affords 13C(α) labelled [13C]-3, thus discarding the hypothesis of its formation via 1,2-arene migration. The reported sequence opens a novel approach to phenylglyoxylic and mandelic acid esters (=α-oxobenzeneacetic and α-hydroxybenzeneacetic acid esters), from acetophenone. The molecular structures of 1 and 3 were determined by X-ray structure analysis and compared with previously reported crystallographic data of α-oxo-oximes (=α-(hydroxyimino) ketones) 4 and 6 – 8. The unique stereoelectronic characteristics of the α-oxo-oxime moiety are discussed. All α-oxo-oximes share the following structural characteristics: (E)-configuration of the oxime C=N−OH bond (i.e. OH and C=O trans), the s-trans conformation of the oxo and imino moieties about the C(α)-C(=NOH) single bond, and intermolecular H-bonding. They differ from the isostructural β-diketone enols by the absence of resonance-assisted intramolecular H-bonding.