Ordered Arrays of Polyphenols by Tandem Reactions

Dave Reingold, Juniata College, Pennsylvania

We propose a new method of making polycyclic phenols, all based on simple condensation chemistry, that could lead to Kekulenes, polyacenes, and cyclacenes. Such condensed aromatic compounds are related to larger structures. Polyacenes and Kekulenes are subsets of graphite, as shown.   According to Mallory, polyacenes with large numbers of benzene rings might be useful as electrical conductors or nonlinear optical materials.¹ Cyclacenes are polyacenes that are formed into belts, and are found in fullerenes.

Our plan is to create these types of structures using variations on simple condensation chemistry.  For the synthesis of Kekulene-related compounds, for example, the key reaction is the following Michael-Claisen condensation:

Allowing this to occur on a protected cyclohexadiene would quickly assemble five six-membered rings, with six ketones after hydrolysis.

 

This is nearly half of the Kekulene skeleton.  The other half can be introduced by using a ketodiester instead of a ketomonoester as the second starting material:

It is reasonable to anticipate that dehydrogenation with a reagent such as DDQ will lead from polyketone to polyphenol.  This is a hydroxylated version of Kekulene.² There is a hole in the middle of this polyphenol that might be able to hold various metal ions, like the crown ethers, especially if there is enough flexibility to allow the OH groups to jut alternately up and down; and hydroxy groups decorating the outside that should make the molecule soluble in water, or alternatively be good sites for attaching long chains that could help solubilize it in non-aqueous solvents.

By adjusting starting materials appropriately, one could make similar arrays of polyphenols, this time linear.  Possible topologies include the following:

Either of these, during synthesis, could curl back on itself to form eventually a cyclacene, the elusive “aromatic belt” that is so attractive a target that is was the logo for a recent conference on Novel Aromatic Compounds.  Cyclacenes have been sought, so far without success, by Stoddart, Schluter, and Cory, among others.³

References  (1)  Mallory, F. B.; Butler, K. E.; Evans, A. C.; Brondyke, E. J.; Mallory, C. W.; Yang, C.; Ellenstein, A. J. Am. Chem. Soc. 1997, 119, 2119.  (2)  Staab, H.; Diederich, F. Chem. Ber. 1983, 116, 3487.  (3)  For a review, see Cory, R. M.; McPhail, C. L.  Adv. Theor. Int. Mol. 1998, 4, 53.

Dr. David Reingold
Juniata College
Huntingdon, PA 16652
Phone: 814-641-3565


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