Serendipitous one-pot formation of an unusual calix[5]arene-bis-crown-3 receptor

Alkylation of p-tert-butylcalix[5]arene 1c with an excess of 2-(2-chloroethoxy)ethyl tosylate 2 and anhydrous K2CO3, has led to the serendipitous regioselective formation of cone-in (1,2–3,5)-calix[5]arene bis-crown-3 derivative 4 possessing a reactive 2-(2-chloroethoxy)ethoxy pendant functionality at the lower rim. The structure and conformation of 4 have firmly been assigned by a combination of NMR analysis and HF/6-31G∗ ab initio calculations, as well as by an independent stepwise synthesis. A preliminary ESI-MS screening of the binding properties of 4 toward alkali metal ions has shown a clear preference for the larger cations.