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Solid-phase Synthesis of [4.4] Spirocyclic Oximes
Published on: February 6, 2019
Synthesis of Oxacalix[4]arene and the Study of Its Dynamic Behavior
Michal Churý1, Karla Hovorková1, Radek Staník1
1Department of Organic Chemistry, University of Chemistry and Technology Prague (UCTP), Technická 5, 166 28 Prague 6, Czech Republic.
Abstract:
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).
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