Stereochemistry of Products of Reactions between 3-diazo-naphthalene-1,2,4-trione and β-dicarbonyl Compounds. Structure of ethyl 2-[(3-hydroxy-1,4-dioxo-1,4-dihydro-naphthalen-2-yl)-hydrazono]-3-phenyl-3-oxo-propionate

Abstract

3-Hydroxy-2-[(R¹CO)(R²CO)]C=NNH-1,4-naphthoquinones, obtained from reactions of 3-diazonaphthalene-1,2,4-trione with β-diketones, R¹C(O)CH₂COR², have been previously found to have high antibacterial activity. However, confirmation of the stereochemistry about the C=N bond could not be achieved by spectroscopic means for products having different R¹ and R² groups, thereby limiting the utility of the reaction. Full characterisation of the product isolated from reaction of 3-diazonaphthalene-1,2,4-trione with PhC(O)CH₂CO₂Et is now reported, from a single crystal X-ray structure determination: the product, 3-hydroxy-2-[(PhCO)(EtCO₂)]C=NNH-1,4-naphthoquinone has a (Z)-stereochemistry. The Z-isomer is obtained rather than the E form due to the preferred formation of the stronger intramolecular N–H—O hydrogen-bond with the ester carbonyl oxygen rather than a weaker one with the ketone oxygen. Weaker C–H—O hydrogen bonds link the molecules into columns. It is suggested that similar Z geometries will arise from other RC(O)CH₂CO₂Rⁱ reactants.