Crystal structure of 5,5-dimethyl-3-(naphthalen-1- ylamino)cyclohex-2-enone, C18H19NO

Abstract

Source of materialAm ixture of the 5,5-dimethylcyclohexane-1,3-dione (2.86 g, 20.mmol), naphthalen-1-amine (2.75 g, 19.6 mmol) and sulfamic acid (0.2 g, 0.2 mmol) in methanol (5 mL) was stirred under reflux for 2hours. After completion of the reaction, it was evaporated to dryness, followed by chromatography to the pure enaminone 4.25.g(82 %). Experimnetal detailsHatoms bonded to Natoms were located in adifference Fourier map and refined isotropically without restraints. Hatoms bonded to Catoms were positioned geometrically and allowed to ride on their parent atoms with d(C-H) =0 .93 Å and U iso (H) =1 .2 U eq (C). The ketone-enaminone structure is manifested by the C13-O1 and C11-C12 bond lengths of 1.2480 Å and 1.3656 Å,respectively. The fragment (N1−C11−C12−C13−O1) is nearly planar (the maximum deviation being −0.009(2) Å for C11). The shortening of N1-C11 and C12-C13 bond length and coplanarity of the fragment indicates the significant conjugation. The other bond lengths and angles are quite typical, thus they don't call for further discussion. In the title compound, cyclohexanone ring adopts ah alf-chair conformation with the maximum deviation being 0.304(2) Å for C15. The naphthyl and cyclohexenone moieties are not coplanar. The dihedral angle between the leastsquares planes is 77.72(8)°,which is slightly larger than its relative structures because of the more bulky naphthyl group, but much bigger than its acyclic b-enaminone [4,5]. Unlike the acyclic b-enaminones [4,5], the formation of the intramolecular hydrogen bond is forbidden [6] because of the torsional strain in the cyclic compounds. Thus, the secondary amine can only give rise to intermolecular H-bonds with oxygen atom of carbonyl group. One-dimensional helical infinite chain via intramolecular Hbond is observed in the crystal. It is worthy of note, that the Hbond is nearly linear (N1−H1···O1 =174°).