Campestarenes: novel shape-persistent Schiff basemacrocycles with 5-fold symmetry

Abstract

A simple 1-step procedure yields a family of easily modifiable, stable, conjugated Schiff base macrocycles with 5-fold symmetry mediated by 3-center hydrogen bonding.

The Rich Tautomeric Behavior of Campestarenes

“…ROESY and variable-concentration 1 HNMR spectroscopy demonstrated that these signals correspond to two species in equilibrium, and av ariable-temperature 1 HNMR studyo f campestarene 1c in [D 6 ]DMSO between 25 and 101 8Cp roved the presence of am onomer/dimer equilibrium. [52] Attempts to make campestarenes with less bulky substituents were wrought with difficulties in purification and characterization- the macrocyclesa ppeared to stack into large aggregates that were difficulttob reak up.…”

“…In 2011, we reported anew family of Schiff-base macrocycles with five-fold symmetry (Figure 2), named campestarenes, availablet hrough ao ne-pot reduction-condensation procedure. [52] By performing the cyclization both in the presence of excess alkali metal cations and in the absence of alkali metal cations,w ed emonstratedt hat the cyclization is not templated by sodium cations.M oreover,i tw as not possible to isolate the macrocycle when the hydroxyl group wasp rotected with am ethyl group, indicating that the hydroxyl group is necessary to obtain the macrocycle. The fact that the five-fold symmetry product is preferentially formedo ver the anticipated sixfold symmetry product, together with the very downfield signal for the protoni nside the macrocycle (H a is observed around1 7ppm in the 1 HNMR spectrum), suggests av ery strong hydrogen bond in the molecule.…”

One‐Pot Multimolecular Macrocyclization for the Expedient Synthesis of Macrocyclic Aromatic Pentamers by a Chain Growth Mechanism

“…other foldamer systems except for pentameric Schiffs base macrocycle recently reported. [11] Theoretical treatments of circularly folded macrocycles containing from 4 to 7 residues provide the additional energetic details that help clarify the preferred formation of five-residue macrocycles over the other alternative sizes. By using DFT, macrocyclic foldamers of varying sizes in Figure 3 were optimized at the B3LYP/6-31G* level, followed by a single-point energy calculation at the B3LYP/6-311 + G** level in the gas phase, CH 2 Cl 2 , and CH 3 CN (Table 3).…”

Different Types of Nickel, Cobalt, and Manganese Complexes originating from 2‐Imidazolecarboxaldiimine of Triethylenetetraamine

“…[1][2][3][4][5][6][7][8][9] Spin crossover [10][11][12][13][14][15][16] shown by some of complexes of these ligands and also their synthetic utilities in the synthesis of hetero and homochiral supramolecular complexes [17][18][19][20][21][22] have provided impetus to understand coordination behavior of such flexible polydentate ligands. Imidazole bearing Schiff base complexes find applications in catalysis [23][24][25][26] and polydentate macrocycle like scaffolds derived from Schiff bases leave scope to develop complexes [27][28] of general interest. On the other hand, some Schiff bases are hydrolytically unstable; [29] hence, the stability of such metal complexes and their differentiating reactivity to correlate the signal transduction process makes them promising class of ligands.…”