Synthesis of C-alkylcalix[4]arenes .5. Design, synthesis, computational studies, and homodimerization of polymethylene-bridged resorc[4]arenes

Treatment of tetraaIcohol 1 with glutaroyl (2a, n = 3), adipoyl (2b, n = 4), and pimeloyl (2c, n = 5) dichlorides in the presence of Et(3)N gave the corresponding double-spanned calix[4]resorcarenes 3a-c, in which the insertion of two polymethylene bridges led to the formation of a cavity-shaped architecture resembling a basket. NMR, X-ray, and molecular dynamic-studies showed that one of the two equivalent flattened-cones, which constituted the original cone conformation of 1, had been frozen in the basket derivative. In the solid state the calixarene 3b exists as a supramolecular dimer, in which one of the handles is inserted in the concave cavity of an adjacent molecule. A molecular modeling study revealed that the minimum absolute free energy was associated to the unsymmetrical type of dimer named AB-AC.