Efficient Synthesis of Calix[6]tmpa: A New Calix[6]azacryptand with Unique Conformational and Host–Guest Properties

Abstract

A new C(3v)-symmetrical calix[6]azacryptand, that is, calix[6]tmpa (11), was synthesized by efficient [1+1] macrocyclization reactions. Remarkably, both linear and convergent synthetic strategies that were applied lead to equally good overall yields. Calix[6]tmpa behaves as a single proton sponge and appeared reluctant to undergo polyprotonation, unlike classical tris(2-pyridylmethyl)amine (tmpa) derivatives. It also acts as a good host for ammonium ions. Interestingly, it strongly binds a sodium ion and a neutral guest molecule, such as a urea, an amide, or an alcohol, in a cooperative way. A (1)H NMR study indicated that the ligand, as well as its complexes, adopt a major flattened cone conformation that is the opposite of that observed with the previously reported calix[6]cryptands. Characterization of the monoprotonated derivative 11H(+) by X-ray diffraction also revealed the presence of a 1,3-alternate conformation, which is the first example of its kind in the calix[6]arene family. This conformer is probably also present in solution as a minor species. The important covalent constraint induced by the polyaromatic tmpa cap on the calixarene skeleton, and conversely from the calix core onto the tmpa moiety, is the likely basis for the unique conformational and chemical properties of this host.

Functional Polypyridine Co Complex as an Efficient Catalyst for Photo‐Induced Water Oxidation

“…[7] Subsequently, methyl 6-(hydroxymethyl) picolinate was bromized by PBr 3 in CHCl 3 and resulted in the smooth conversion to the methyl 6-(bromomethyl)picolinate. [7] Subsequently, methyl 6-(hydroxymethyl) picolinate was bromized by PBr 3 in CHCl 3 and resulted in the smooth conversion to the methyl 6-(bromomethyl)picolinate.…”

Supramolecular Modeling of Mono-copper Enzyme Active Sites with Calix[6]arene-based Funnel Complexes

“…Three different capped calix [6]arenes (calix [6]tren, 12 calix[6]PN 3 13 and calix [6]tmpa 14 ) were synthesized ( Figure 5), the key step consisting in a [1 + 1] macrocyclization reaction between two tripodal partners.…”

Induced‐Fit Encapsulation by a 1,3,5‐Alternate Calix[6]arene

“…[8] However, seven other conformations, which differ in the syn or anti orientations of the aromatic units with respect to one another, are theoretically possible. [9] While the partial cone, [10] 1,2-alternate, [11] 1,3-alternate, [12] 1,4-alternate, [13] and 1,2,3-alternate [14] conformations are known, the 1,2,4-alternate and 1,3,5-alternate conformations have not been reported to date. The 1,3,5-alternate conformation is particularly attractive since it should display a highly symmetrical closed cavity and could constitute a useful platform for the introduction of two divergent functional domains in a spatially controlled manner.…”