Supramolecular Assistance for the Selective Demethylation of Calixarene-Based Receptors

Abstract

The selective demethylation of methoxy groups of several multifunctionalized 1,3,5-trimethoxycalix[6]arene-based receptors has been achieved. It is shown in this study that the best reagent is trimethylsilyl iodide (TMSI) and that the conformation adopted by the calixarene core is crucial for both the selectivity and the efficiency of the process. A key feature appears to be the "in" or "out" orientation of the methoxy substituents relative to the macrocyclic cavity. If projected inward, the reaction is slow and not selective. If projected outward, the reaction is fast and selective. A strategy that consists of exploiting the host-guest properties of the receptors to change their conformation and to permit their selective demethylation has been developed. Four cases of such a supramolecular assistance are reported, demonstrating the efficiency of the strategy. Such an allosteric control is highly reminiscent of biological processes allowing selective transformation of multifunctional molecules.

Cooperative Binding of Metal Cations to a Spiropyran‐Conjugated Calix[4]arene

“…Calixarenes, a notable class of molecules in supramolecular chemistry, have been used as hosts for ions, neutral molecules, bioactive molecules, and macromolecules. 1,2,3‐triazole can be appended to calixarenes via copper(I)‐catalyzed azide‐alkyne cycloaddition (CuAAC) to form a binding pocket from the phenolic oxygens of calixarenes and nitrogen atom(s) from 1,2,3‐triazole for a metal ion sensor.…”

Calix[6]arene Functionalized at Four Bridges: Conformation and Intramolecular Guest Exchange

“…This protection was deemed necessary to avoid the formation of highly reactive quinone methide intermediates in the C–Br bond cleavage step. However, in general the robust protection imparted by methyl ether functionalities is a double edge sword since their full cleavage in the deprotection step may require strenuous reaction conditions 7. On these grounds we reasoned that it would be useful if calixarene derivatives possessing both bromomethine bridges and phenolic OH groups protected by the relatively more labile tert ‐butoxycarbonyl (Boc) groups were synthetically available.…”

Efficient synthesis of 4-substituted-ortho-phthalaldehyde analogues: toward the emergence of new building blocks

“…Accordingly, hydrogen bromide was employed as a deprotection agent, as previously used by Borisenko et al [23], to finally achieve the desired product 6 but in a very poor yield (5%). A second deprotection agent was tested, trimethylsilyl iodide, as it was recently published by Danjou et al [24] as a removal agent of methoxy groups on calixarenes architectures. Although we succeeded with the removal of methoxy groups, both aldehydes were reduced.…”