2-Methoxy-3-[(3,4,5-trimethoxyanilino)methylidene]-3,4-dihydro-2H-1-benzopyran-4-one

The title molecule, C20H21NO6, adopts a keto–amine tautomeric form. An intramolecular N—H⋯O hydrogen bond, classified as a resonanse-assisted hydrogen bond, influences the molecular conformation; the two benzene rings form a dihedral angle of 24.6 (1)°. In the crystal structure, weak intermolecular C—H⋯O hydrogen bonds link molecules into chains propagating along [001].

The title molecule, C 20 H 21 NO 6 , adopts a keto-amine tautomeric form. An intramolecular N-HÁ Á ÁO hydrogen bond, classified as a resonanse-assisted hydrogen bond, influences the molecular conformation; the two benzene rings form a dihedral angle of 24.6 (1) . In the crystal structure, weak intermolecular C-HÁ Á ÁO hydrogen bonds link molecules into chains propagating along [001]. Experimental Crystal data C 20 H 21 NO 6 M r = 371.38

Comment
The present paper is a continuation of X-ray studies of a group of chromone derivatives (Małecka & Budzisz, 2006, Małecka, 2007. Due to their biological activity (Khan et al., 2009) and the presence of intramolecular N-H···O hydrogen bond which could be classified as resonanse assisted hydrogen bond (RAHB) (Gilli et al., 1994).
The more detailed insight into the molecular structure of the title compound shows that N-H···O hydrogen bond (Table   1) may be classified as resonance assisted hydrogen bond (RAHB). Such interactions RAHB have been investigated for homonuclear O-H···O interactions and for heteronuclear N-H···O RAHBs (Bertolasi et al., 1998).
Considering O4═C4-C3═C31-N1-H1 fragment it is not observed the equalization of C4-C3 and C3═C31 in comparison to previuos examined structures However, it was found the elongation and shortening of C4═O4 and C3-N1 bonds, respectively. The π-electron delocalization effect is not so evident as in earlier investigated structures. It is associated with lack of the planarity and non-aromatic character of main part of molecule.
The packing of the molecules in the crystal lattice is stabilized via C-H···O hydrogen bonds (Table 1). Atom C14 is involved in a weak C-H···O intermolecular interaction with atom O4 related by symmetry x, 1/2 -y, -1/2 + z what results in forming chains C(11) along c axis. Experimental 4-Oxo-4H-1-benzopyran-3-carboxaldehyde (0.348 g, 0.002 mol) was dissolved in hot toluene (20 ml) together with a small amount of p-toluenesulphonic acid as a catalyst. Resulting solution was kept under reflux while the solution of 3,4,5-trimethoxyaniline (0.366 g, 0.002 mol) in toluene (20 ml) was slowly added. When the addition was finished, the solution was kept under reflux for following 3 h. Then it was left in room temperature for 24 h. Approximately half of the solvent was removed under reduced pressure and resulting solution was left in the refrigerator for 48 h. Obtained precipitate was filtered off, added to 30 ml of methanol and refluxed for 30 minutes. The hot solution was filtered off to remove insolubilities. Then it was left in room temperature for 2 h. Approximately half of the solvent was removed under reduced pressure. Next the solution was left in the refrigerator for 4 days. Resulting precipitate was filtered off, washed with small amount of methanol and diethyl ether and dried under reduced pressure.
supplementary materials sup-2 Refinement All H-atoms were positioned geometrically and refined with a riding model; for methyl H atoms U iso were constrained to be 1.5 times U eq of the carrier atom and C-H=0.98 Å; for others H atoms U iso were constrained to be 1.2 times U eq of the carrier atom and C-H=0.95 Å, 0.88 Å, for aromatic, amine groups, respectively. The incomplete data sets was collected due to poor quality, weakly diffracted crystal. Fig. 1. Molecular structure of the title compound, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. The N1-H1···O4 hydrogen bond classified as resonance assisted hydrogen bond (RAHB) is shown as dashed line. as those based on F, and R-factors based on ALL data will be even larger.