Selective bridging of p-tert-butylcalix[6]arene with polyethylene glycol ditosylates

A convenient method for preparing various p-tert-butylcalix[6]crowns and re lated compounds has been developed. By refluxing p-tert-butylcalix[6]arene with ethylene glycol ditosylate or polyethylene glycol ditosylates using K2 CO3 as a base in acetonitrile, 1,2-ethylenecalix[6]arene, 1,3- and 1,4-cali x[6]crown-3, 1,3- and 1,4-calix[6]crown-4, 1,4-calix[6]benzocrown-4, 1,2- a nd 1,3-calix[6]crown-5 were obtained selectively. A rather flattened (o, o, o, o, o, o) conformation, adopted by the constrained 1,4-calix[6]crown-3 a t ambient temperature, was observed for the first time. (C) 1999 Elsevier S cience Ltd. All rights reserved.