Ethyl 1′-methyl-2-oxo-4′-[(3aR,5R,5aS,8aS,8bR)-2,2,7,7-tetramethyltetrahydro-3aH-bis[1,3]dioxolo[4,5-b:4′,5′-d]pyran-5-yl]-2H-spiro[acenaphthylene-1,2′-pyrrolidine]-3′-carboxylate