Horning-crown Macrocycles

A major advantage of the macrocyclic dienones obtained from building blocks described herein is the extensive potential for facile transformations that can 

The present discussion is limited to isoaromatization. About 60 years ago. Horning reported that 2,6-dibenzylphenol could be obtained by thermolysis of (2 , 6 )-dibenzylidenecyclohexanone in the presence of a Pd catalyst. He coined the word isoaromatization to describe the process. Since then, others have attempted the same conversion, with variable degrees of success, under homogeneous catalysisand with acid in the absence of metal. 

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Isoaromatization of dienone macrocycles afforded Horning-crown macro-cycles - flexible macrocycles bearing structural elements reminiscent of those found in both calixarenes and crown ethers. In some cases the Horning-crown macrocycles exhibited solvent-dependent and switchable conformations. For macrocycles with the same short linker, self-complementarity was observed, and dimers tended to crystallize as solvates or inclusion compounds. This tendency was suppressed with longer linkers and in some Horning-crowns derived from trapezoidal macrocycles. These properties suggest potential applications in analysis, separation and detection (Figure 6.8). ... 

Figure 6.8 (a) Trapezoidal Horning-crown macrocycles with flexible tethers such as 28... 

The cascade reaction for the preparation of anilines is particularly well suited to the synthesis of potential ligands, as is illustrated by the scorpion ligand A,A-4-tris(pyridin-2-ylmethyl)aniline (37), which forms a range of Cu complexes with widely varying solid-state structures.Clearly, from the metal coordination geometries illustrated in Figure 6.9, Horning-crown macrocycles may fulfill similar roles. 

Figure 6.11 Horning-crown macrocycle (derived from isoaromatization of 25) inclusion complexes with oc-methylphenethylamine and propylenedia-mine contain ball-like structures (left) and sheath/core structures (right), respectively.

Figure 6.1 Representative structures of products accessible using the strategies outlined below include bis-arylidinealkenones (3), 2,6-dibenzylphenols (4), dienone (5 and 7) and Horning-crown (6 and 8) macrocycles, rods (9) and flexible phenol/formaldehyde oligomers (10).

HORN-BORNIG PLOT HORSERADISH PEROXIDASE HOST-GUEST INTERACTIONS HOST MOLECULE CROWN ETHERS MACROCYCLES INCLUSION COMPLEXES HOCKEL MOLECULAR-ORBITAL CALCULATIONS... 

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