Preparation and mechanism of solvolysis of N-hydroxy-alpha-oxobenzeneethanimidoyl chloride, a 2-(hydroxyimino)-1-phenylethan-1-one derivative: Molecular structure of alpha-oxo-oximes (=alpha-(hydroxyimino) ketones)

Acid-catalyzed methanolysis of N-hydroxy-alpha-oxobenzeneethanimidoyl chlor ide (1), a. 2-(hydroxyimino)-1-phenylethan-1-one derivative obtained in one step from acetophenone, leads to a constant ratio of methyl alpha-oxobenze neacetate (2) and methyl alpha-(hydroxyimino)benzeneacetate (3). C-13(alpha ) Labelled [C-13]-1 affords C-13(alpha) labelled [C-13]-3, thus discarding the hypothesis of its formation via 1,2-arena migration. The reported seque nce opens a novel approach to phenylglyoxylic and mandelic acid esters ( al pha-oxobenzeneacetic and alpha-hydroxybenzeneacetic acid esters), from acet ophenone. The molecular structures of 1 and 3 were determined by X-ray stru cture analysis and compared with previously reported crystallographic data of alpha-oxo-oximes (= alpha-(hydroxyimino) ketones) 4 and 6-8. The unique stereoelectronic characteristics of the alpha-oxo-oxime moiety are discusse d. All alpha-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-tran s conformation of the oxo and imino moieties about the C(alpha)-C(=NOH) sin gle bond, and intermolecular H-bonding. They differ from the isostructural beta-diketone enols by the absence of resonance-assisted intermolecular H-b onding.