Fig. 4. The Michael addition of 6 to crotonaldehyde (7) or trans-β-nitrostyrene (8) using rotaxanes 1, 1-H⁺·CF₃CO₂ ^– or thread 2-H⁺·CF₃CO₂ ^– as catalysts. Conditions: 5 mol% catalyst, 10 mol% NaOAc, 0.5 M 6 (1 equiv.), 7 (2 equiv), 8 (1 equiv.), RT, 18 h (1-H⁺·CF₃CO₂ ^–) or 72 h (1 or 2-H⁺·CF₃CO₂ ^–). ¹H NMR spectra (600 MHz, CDCl₃, 293 K): (a) trans-β-nitrostyrene (8); (b) crotonaldehyde (7); (c) reaction mixture of 6, 7 and 8 after 72 h in the presence of 1; (d) reaction mixture of 6, 7 and 8 after 18 h in the presence of 1-H⁺·CF₃CO₂ ^–; (e) reaction mixture of 6, 7 and 8 after 72 h in the presence of 2-H⁺·CF₃CO₂ ^–; (f) 10; (g) 9.