fig2

Figure 2. Synthesis routes of “impossible” [2]rotaxanes 5, 10, and [3]rotaxane 13 with all-benzene scaffolds. Reagents and conditions: (i) Pd(OAc)₂, dppf, K₂CO₃, toluene/H₂O, 80 °C; (ii) LiAlH₄, 1,4-dioxane, 120 °C; (iii) t-Bu-ONO, THF, 0 °C, then 50% aq. H₃PO₂, 60 °C; (iv) Pd G4-SPhos, B₂pin₂, KOAc, 1,4-dioxane, 90 °C; (v) Pd(OAc)₂, dppf, K₂CO₃, toluene/H₂O, 50 °C; (vi) sodium naphthalenide, THF, -78 °C, then quenched with I₂; (vii) LiAlH₄, 1,4-dioxane, 120 °C; (viii) t-Bu-ONO, THF, 0 °C, then 50% aq. H₃PO₂, 25 °C; (ix) Pd(OAc)₂, dppf, K₂CO₃, toluene/H₂O, 80 °C; (x) Pd(OAc)₂, dppf, K₂CO₃, toluene/H₂O, 80 °C; (xi) LiAlH₄, 1,4-dioxane, 120 °C; (xii) t-Bu-ONO, THF, 0 °C, then 50% aq. H₃PO₂, 60 °C.