Crystal structure of (2Z,4E)-3-hydroxy-5-phenyl-penta-2,4-dienonic acid methyl ester, (C6H5)(CH)2COH(CH)CO2CH3

Abstract

Source of materialThe title compound was found as asideproductinthe formation of the respective saturated derivative 3-oxo-5-phenyl-pentanoic acid methyl ester according to [1]. After purification via column chromatography as mall amounto fc olorlessn eedles was obtained from am ixture of both compounds after several weeks (m.p. 72°C). Analytical data are in accordance with the previously published data [2]. Experimental detailsHydrogen atoms were located from Fourier difference maps, and refined with isotropic displacement parameters based on the bondedatoms. Discussion 1,3-Dicarbonyl compounds are of substantial interest as dielectrophilic sources in the synthesis of various heterocyclic compounds [3,4]. The preparation of the title compoundispossible in different ways.Methyl cinnamate was convertedwith methyl acetate in an ester condensation to yieldthe desiredcompound [5]. Furthermore it can be obtaineda sb y-product in lipase-catalysed reactions of b-hydroxy-b-arylpropionates [6] or through conversion of 3-oxo-5-phenyl-pent-4-enoic acidm ethyl ester with oxalate [7]. Otherwise,inthe multi-stepsynthesis of the natural product ABT-418 [8] the titlecompound was synthesized as an important intermediate. The double bond in the title molecule adopts a trans configuration with at orsion angle of almost1 80°(178.09(1)°). The aromatic system, the double bonds and the carbonyl group at C11 form a conjugated p-system. Due to the conjugation with the carbonyl groups the double bond is activated, hence substrate addition follows in aregioselective manner. The lengthofthe bond C9=C10 (1.336(3) Å)isinthe range of typical C=Cdouble bonds. Otherwise, the C9-O3 distance (1.342(2) Å)corresponds to aC-O single bond. An intramolecular hydrogen bond is found between the OH group at C9 and the adjacent carboxyl group. In solution this compound shows keto-enol tautorism(20:80 ratio ratified by NMR measurement [2]).The refinementofthe occupation of the H3B siteshows, thatthe enolic form is preferred in the crystalline solid state.