(E)-3-(1-Naphthylamino)methylene-(+)-camphor

In the crystal structure of the title ketoamine {systematic name: (E)-1,7,7-trimethyl-3-[(1-naphthylamino)methylidene]bicyclo[2.2.1]heptan-2-one}, C21H23NO, there are two independent molecules in the asymmetric unit. Both molecules have an E configuration about the alkene function. The main conformational difference between the molecules is in the orientation of the plane of the naphthyl rings with respect to the camphor fragment. The torsion angle about the enamine C—N bond is 21.3 (7)° for molecule A, but −24.4 (8)° for molecule B. Intermolecular N—H⋯O hydrogen bonds between the amino and ketone groups of adjacent independent molecules sustain the crystal, and the resulting extended chains, containing an alternating sequence of the two independent molecules, run parallel to the [001] direction and can be described by a graph-set motif of C 2 2(12).

In the crystal structure of the title ketoamine {systematic name: (E)-1,7,7-trimethyl-3-[(1-naphthylamino)methylidene]bicyclo[2.2.1]heptan-2-one}, C 21 H 23 NO, there are two independent molecules in the asymmetric unit. Both molecules have an E configuration about the alkene function. The main conformational difference between the molecules is in the orientation of the plane of the naphthyl rings with respect to the camphor fragment. The torsion angle about the enamine C-N bond is 21.3 (7) for molecule A, but À24.4 (8) for molecule B. Intermolecular N-HÁ Á ÁO hydrogen bonds between the amino and ketone groups of adjacent independent molecules sustain the crystal, and the resulting extended chains, containing an alternating sequence of the two independent molecules, run parallel to the [001] direction and can be described by a graph-set motif of C 2 2 (12).   Table 1 Hydrogen-bond geometry (Å , ). Comment β-Ketoamines are the neutral protic form of β-aminoketonate bidentate anionic ligands that have been used in the coordination chemistry of transition and main group metals (Lesikar et al., 2008;Sedai et al., 2008). The electronic and steric dissymmetry of these ligands is easily modified in order to tune the reactivity of the metal centre. β-Aminoketonate complexes have been used effectively in stoichiometric (Hsu, Chang et al., 2004;Hsu, Li et al., 2007) and catalytic processes, such as Suzuki cross-coupling (Lai et al., 2005), polymerization (Wang et al., 2006) and copolymerization (Pan et al., 2008) reactions. Interestingly, there are only a few reports on chiral camphor-derived β-aminoketonate ligands (Everett & Powers, 1970;Casella et al., 1979). Generally, β-ketoamines have Z conformations that are stabilized by intramolecular hydrogen bonding (Zharkova et al., 2009). The structure of the title compound was determined in order to confirm the anticipated E conformation about the alkene bond for the major product of the synthesis.

Related literature
There are two molecules (A and B) of the title compound in the asymmetric unit (Fig. 1). The slightly twisted conformations of the (1-naphthylamino)methylene fragments are similar to that in the structure of 2,2-dimethyl-5-(1-naph- The preference for the E conformation during the synthesis of the title compound may be attributed to the large size of the naphthyl group, whose steric pressure overcomes the competing intramolecular N-H···O hydrogen bonding, which is facilitated in the Z conformer. The observed intermolecular N-H···O hydrogen bonds between the amino and keto groups of adjacent independent molecules, which link the molecules into extended chains running parallel to [001] (Fig. 2), are an additional stabilizing factor of the E conformation. They can be described by a graph-set motif of C 2 2 (12) [Bernstein et al., 1995].
While the chirality of the (+)-camphor fragment means that both symmetry-independent molecules are of the same enantiomer, it is interesting to note that there is significant pseudo-inversion symmetry in the structure, with 82% of the atoms in one molecule matching closely with those of the inverted structure of the other molecule; the r.m.s. fit of 21 atoms from each molecule is 1.14 Å. Slight in-plane disorder of the naphthyl groups leads to enlarged displacement ellipsoids for some of the atoms of these groups with the direction of elongation being in the naphthyl plane.

Experimental
The title compound was prepared by refluxing 1-naphthylamine (6.77 g, 37.6 mmol) with (+)-hydroxymethylenecamphor (Lintvedt & Fatta, 1968) (5.92 g, 41.3 mmol) in dry ethanol (200 ml) and formic acid (2.5 ml) for 48 h. After removing the solvent under reduced pressure, the resulting yellow solid was dried in vacuo for 4 h. The crude product contained both conformers, which after washing with hexane and HV drying afforded 6.53 g (57%) of the pure (E)-conformer [the (Z)-conformer being more soluble in alkanes]. Yellow single crystals suitable for an X-ray analysis were grown from a

Refinement
In the final cycles of refinement, in the absence of significant anomalous scattering effects, 2643 Friedel pairs were merged and Δf " set to zero. The enantiomer used in the refinement model was chosen to match the known configuration of the (+)-camphor fragment. The amine H atoms were located in a difference Fourier map and their positions were refined freely with U iso (H) = 1.2U eq (N). The C-bound H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms: C-H = 0.95, 0.98, 1.00 Å, for CH, CH 3 and CH 2 H-atoms, respectively, with U iso (H) = k × U eq (C), where k = 1.5 for CH 3 H-atoms and k = 1.2 for all other H-atoms.   Table 1 for details]. Hydrogen atoms not involved in hydrogen bonding have been omitted for clarity.