3-(4-Methoxyphenyl)pent-2-ene-1,5-dioic acid

In the title compound, C12H12O5, molecules are linked into antiparallel hydrogen-bonded sheets through inversion dimers generated via two O—H⋯O hydrogen bonds. Using the R 2 2(8) motif as a building block, hydrogen-bonded chains of a C 2 2(8) superstructure are then generated.

In the title compound, C 12 H 12 O 5 , molecules are linked into antiparallel hydrogen-bonded sheets through inversion dimers generated via two O-HÁ Á ÁO hydrogen bonds. Using the R 2 2 (8) motif as a building block, hydrogen-bonded chains of a C 2 2 (8) superstructure are then generated.
It is a precursor for many heterocyclic ring structures due to its inherent ability to form cyclic anhydrides. A number of heterocycles like pyridine-2,6-diones can be obtained from this dicarboxylic acid (Pednekar et al., 2004). Introduction of double bond at the α,β-position of the glutaric acid, leads to the formation of a glutaconic acid. As a consequence of this, there is a noticeable change in its reactivity. The reactivity of methylene group at γ-position is primarily responsible for the electrophilic substitutions taking places at the γ-position of 3-(4-Methoxyphenyl) -2-pentene-1,5-dioic acid.
The title compound, (I) crystallizes in the monoclinic crystal system in the centrosymmetric space group P2 1 /c with Z = 4. Fig. 1 shows the asymmetric unit and the atom-numbering scheme. Selected bond lengths and torsion angles are given in Table 1. In the asymmetric unit, compound (I) adopts the E conformation, with the =CH-COOH group in the plane of the methoxy phenyl ring (C6-C3-C2-C1 dihedral angle is 174.73°) while the -CH 2 -COOH group lies nearly perpendicular to the phenyl ring (C6-C3-C4-C5 dihedral angle is 89.25 °). Within the aryl rings, the C-C bonds are in the range of 1.374 (3) to 1.395 (3) Å, which is in accordance with those found in similar structures. The C-C single bonds (1.462 (3)  The molecular assembly is stabilized by extensive intermolecular O-H···O hydrogen bonding, besides intramolecular C-H···O stabilizing weak interactions (Fig. 2). O1 at (x,y,z) acts as a hydrogen-bond donor to O2 at (3 -x,2 -y,-z) to form an inversion dimer centered at (1/2,0,0) and characterized by the usual R 2 2 (8) motif (Bernstein et al., 1995). The inversion dimer acts as a building block and leads to propagation of hydrogen bonded chains to generate a C 2 2 (8) superstructure.
Similarly, O3 (x,y,z) acts as a hydrogen-bond donor to O4 at (2 -x,1 -y,-z) to form an inversion dimer centered at (1,1/2,0), also characterized by the R 2 2 (8) motif. Furthermore, the combination of two inversion dimers nearly perpendicular to one another leads to the formation of an intermolecular hydrogen-bonded staircase with neighboring inversion dimers generated via O1-H1···O2 strong hydrogen bonds being connected by O3-H3···O4 interactions. The overall supramolecular packing shows a layered arrangement, with alternate layers mutually parallel.

Experimental
To synthesize compound (I), citric acid [0.13 mol] was warmed in conc. H 2 SO 4 (98%) with constant stirring till foam disappeared to obtain acetone dicarboxylic acid. By immersing the reaction flask in an ice bath; temperature was dropped down to 0°C. Anisole [0.113 mol] was then added slowly with vigorous stirring, over a period of one hour. During the addition, temperature was maintained at 0°C. Stirring was continued for a period of 6 hrs, while maintaining the temperature between 0°C to 5°C. The reaction mixture was then poured over crushed ice with stirring. The solid obtained was then supplementary materials sup-2 filtered and washed with water and colorless single crystals grown from hot water (yield 12%, m.p. 445-447 K). 1 H NMR (DMSO):δ 12.284 (s, 2H), 7.489 (d, 2H), 6.951 (d, 2H), 6.173 (s, 1H), 4.103 (s, 2H), 3.768 (s, 3H).