3-Methyl-1,2,3,4,5,6,1′,2′,3′,4′-deca­hydro­spiro­[benz[f]isoquinoline-1,2′-naphthalen]-1′-one

The title compound, C(23)H(23)NO, is the product of a tandem transformation of the double Mannich base bis­(1-oxo-1,2,3,4-tertrahydro-2-naphtho­ylmeth­yl)amine hydro­chloride in HBr solution upon heating. The tetra­hydro­pyridine ring has a non-symmetrical half-chair conformation, whereas the cyclo­hexa­diene and cyclo­hexene rings adopt non-symmetrical half-boat conformations. The dihedral angle between the planes of the terminal benzene rings is 62.85 (6)°. The N atom has a trigonal–pyramidal geometry [sum of the bond angles = 332.4 (3)°]. In the crystal, mol­ecules form [001] chains via weak non-classical C—H⋯N hydrogen bonds. The chains are stacked along the b axis.