Campestarenes: new building blocks with 5-fold symmetry

Abstract

Campestarene is a planar, shape-persistent macrocycle with 5-fold symmetry. A range of derivatives bearing peripheral functional groups suitable for generating supramolecular interactions has been designed and synthesised for potential applications in creating 2D quasicrystal molecular assemblies. The new campestarene derivatives bear ester, carboxylic acid, methoxy, bromo, 4-pyridyl, 4-cyanophenyl and 4-phenyl carboxylic acid groups, including further derivatives of the latter two bearing alkyl chains on the phenyl groups to improve solubility. The campestarene derivatives were prepared by reductive condensation of phenol precursors bearing nitro and formyl groups using Na2S2O4. The target functional groups were installed either by pre-cyclisation derivatisation or by synthesis of methoxy-substituted campestarene and subsequent derivatisation. The cyclisation reaction is tolerant of the functional groups introduced. The ten new campestarene derivatives were characterised by NMR spectroscopy and MALDI-TOF MS, although the poor solubility of some examples precluded their detailed characterisation.

Imine or Enamine? Insights and Predictive Guidelines from the Electronic Effect of Substituents in H-Bonded Salicylimines

“…Application to imine/enamine cavitands serves to illustrate the scope further. Thus, campestarenes, a family of stable, novel shape-persistent conjugated Schiff base macrocycles with 5-fold symmetry mediated by 3-center hydrogen bonding ( 109 , R = alkyl), can be obtained from aminosalicylaldehydes ( 108 ). These compounds, like the macrocycle with 3-fold symmetry 110 , , have an imine structure, as the starting salicylaldehydes, such as 108 (R = t Bu) and 90 , have negative values of σ ef .…”

“…It is known that many tautomerizations are strongly solvent-dependent. As an illustrative example, the keto-enamine form of macrocycle 109 is favored in polar solvents, whereas nonpolar solvents do favor the imine tautomer …”

Macrocyclic pentamers functionalised around their periphery as potential building blocks

“…We recently published the peripheral elaboration of campestarenes containing peripheral pyridine and carboxylic acid functions designed for this purpose. 23 In this paper we focus on the ve-fold symmetric macrocyclic aromatic pentamers ( Fig. 1a) and approaches to a macrocycle bearing peripheral hydroxyl groups (R ¼ OH) which could potentially be used to explore further functionalisation for use as a pentagonal building block.…”