N-{2-[N-(4-Methylphenyl)oxamoyl]phenyl}propanamide

The title compound, C18H18N2O3, is the product of the heterocyclic ring cleavage at position 2 of 1-propionylisatin. Two centrosymmetric cyclic motifs, viz. R 2 2(14) and R 2 2(18), are formed by N—H⋯O hydrogen bonds with the propanamide and aminophenyl units, respectively, as the N—H donors. These motifs combine into two C 2 2(8) chain motifs parallel to the b axis. The chain structure is stabilized by C—H⋯π interactions between the benzene rings, where C—H is from the phenyl ring of the cleaved part of 1-propionylisatin.

The title compound, C 18 H 18 N 2 O 3 , is the product of the heterocyclic ring cleavage at position 2 of 1-propionylisatin. Two centrosymmetric cyclic motifs, viz. R 2 2 (14) and R 2 2 (18), are formed by N-HÁ Á ÁO hydrogen bonds with the propanamide and aminophenyl units, respectively, as the N-H donors. These motifs combine into two C 2 2 (8) chain motifs parallel to the b axis. The chain structure is stabilized by C-HÁ Á Á interactions between the benzene rings, where C-H is from the phenyl ring of the cleaved part of 1-propionylisatin.

Experimental
Cg1 is the centroid of C1-C6 benzene ring. MA gratefully acknowledges the Higher Education Commission (HEC), Islamabad, Pakistan, for providing him with a Scholarship under the Indigenous PhD Program and also for partial funding of this research work.

Comment
We recently have reported the synthesis and crystal structures of certain isatin derivatives (Pervez et al., 2009(Pervez et al., , 2010a(Pervez et al., , 2010b. The title compound (I), (Fig. 1) is the side product obtained in low yield due to the heterocyclic ring cleavage at position-2 of 1-propionylisatin when reacted with p-toluidine.
In the crystal structure of (I), the tolylamino group A (C1-C7/N1) and B(C9-C15/N2) of the cleaved part of 1-propionylisatin are planar with r. m. s. deviation of 0.0364 and 0.0456 Å, respectively. The dihedral angle between A/B is 80.25 (5) °. There exist an S(5) ring motif (Bernstein et al., 1995) due to N-H···O interactions (Table 1). In the central part short intramolecular C═O···C═O contact replaces a hydrogen-bond plausible S(6). The central part of (I) has twisting flexibility to set the orientation of substituated phenyl rings. The intermolecular interactions of N-H···O and C-H···O types complete R 2 2 (12) and R 2 2 (18) ring motifs setting the two molecules in dimeric way. These dimers are interlinked through N-H···O interactions with R 2 2 (14) ring motif (Table 1, Fig. 2). The polymeric chain extends along the crystallographic b axis. The C-H···π interaction (Table 1) also play role in stabilizing the molecules.

Experimental
To a refluxing solution of 1-propionylisatin (1.02 g, 5 mmol) in ethanol (15 ml) containing 2-3 drops of concentrated sulfuric acid was added the solution of p-toluidine (0.54 g, 5 mmol) made in ethanol (5 ml). The reaction mixture was then refluxed for 2 h, after which it was left at room temperature overnight. The reddish yellow solid formed was collected by suction filtration, washing of which with ethanol to get rid of the soluble impurities, however, gave a dirty white solid.
Recrystallization of the same from ethanol furnished the title heterocyclic ring cleavage product (I) in pure form (0.33 g, 21%) m.p. 423 K. The single crystals of (I) for x-ray analysis were grown in ethyl acetate-petroleum ether (1:4) by diffusion method at room temperature.