Doubly Bridged Calix[8]crowns

Biscrowned calix[8]arenes were obtained by alkylation of p-tert-butylcalix[8]arene or calix- [8]monocrowns with triethylene glycol ditosylate, in the presence of various bases. Of the 22 possible isomers, 1,4:2,5-, 1,3:2,5-, 1,4:2,3-, 1,4:5,8-, and 1,2:3,4-calix[8]biscrown-4 (3–7) were isolated in 7–30% yields. The presence of two crown bridges in 1,3:2,5- and 1,4:2,5- biscrown-4 (4, 5) leads to a significant rigidness of the calix[8]arene macrocycle and implies inherent chirality. The increased preorganization of calix[8]biscrowns, with respect to monocrowns, leads to significant complexing abilities for alkali cations with a marked preference for Cs+ over Na+.