Ethyl (1R,1'S,2'S,7a'R)-2-oxo-1'-[(3aR,5R,5aS,8aS,8bR)-2,2,7,7-tetra-methyl-tetra-hydro-3aH-bis-[1,3]dioxolo[4,5-b:4',5'-d]pyran-5-yl]-1',2',5',6',7',7a'-hexa-hydro-2H-spiro-[acenaphthyl-ene-1,3'-pyrrolizine]-2'-carboxyl-ate.

In the title compound, C(32)H(37)NO(8), the central pyran ring adopts a twist-boat conformation and the 1,3-dioxoane rings adopt envelope conformations. The acenaphthyl-enone unit and two C atoms of a pyrrolidine ring are disordered over two sets of sites [occupancy ratio 0.669 (7):0.331 (7)]. The major fraction of the disordered pyrrolidine ring exhibits an envelope conformation while the minor component is essentially planar [maximum deviation = 0.037 (12) Å]. The other pyrrolidine ring also adopts an envelope conformation. The dihedral angle between the mean planes of the two wings of the pyrrolidine ring is 30.6 (2)°. Both the major and minor components of the acenaphthyl-enone unit are essentially planar, the maximum deviations being 0.025 (10) and 0.047 (19) Å, respectively; the dihedral angle between the mean planes of the two components is 1.72 (3)°. The crystal packing features C-H⋯O inter-actions.