Figure 3.

(a) Synthesis of benzo-1,1′-bipyreno-26-crown-8 macrocycle (8). Reagents and conditions: (i) MeI, K₂CO₃, acetone, 0 °C to reflux, 18 h, 83%; (ii) (1) ^tBuLi, Pd(dba)₂, XPhos, toluene, rt, 20 h, 79%; (2) BF₃·SMe₂, CH₂Cl₂, rt, 6 h, 26%; (iii) LiBr, acetone, reflux, O/N, 92%; (iv) ^tBuOK, KPF₆, ⁿBu₄NI, 0.6 mM, dioxane, rt to reflux, 24 h, 34%. (b) Front (left) and side (right) views of the stick representation of the X-ray diffraction structure of 8⊂K⁺. The coordination bonds between K and the crown ether O atoms are shown with dashed lines. Hydrogen atoms and the PF₆ counterion have been omitted for clarity. Color coding: C, gray; O, red; K, purple.