The formation of 5 was confirmed by a prominent peak at 1375 m/z in the ESI(þ) mass spectrum, corresponding to the doubly charged supramolecular ion. The head-to-head stereosequence of the two calix-wheels in 4 was retained after thestoppering reaction as evidenced by the 1H NMR spectrum of 5 in CDCl3 (Figure S18), which showed a typical signature at highfield values (from 1.0 to 1.2 ppm) and no resonances in the 46 ppm region, similarly to that of (H,H)-4.