Synthesis of Oxacalix[4]arene and the Study of Its Dynamic Behavior

High Resolution Image Download MS PowerPoint Slide The preparation of a new member of the mixed-bridged calixarenes, monooxacalix[4]arene, is described. The key step is the synthesis of an oxygen-bridged bisphenol, which was obtained by an Ullmann-type cross-coupling reaction using 2,2,6,6-tetramethylheptane-3,5-dione/CuI as a catalytic system in a microwave reactor. Final fragment condensation under high-dilution conditions allowed the isolation of oxacalix[4]arene in 36% yield. The dynamic behavior of the new macrocycle was studied using VT NMR experiments, and the energy barriers of the basic dynamic processes ( cone – cone interconversion and flip – flop motion of hydrogen bonds at the lower rim) were determined. Preliminary attempts to immobilize the macrocycle in a specific conformation revealed a surprising effect of the oxygen bridge on the conformational outcome of the alkylation reactions ( cone vs partial cone ).