Chemical modifications of furan-based calixarenes by Diels-Alder reactions

The simple chemical modification by Diels- Alder reactions of the cyclic he xamer of furan and acetone, utilising two readily accessible dienophiles, b enzyne and dimethylacetylenedicarboxylate (DMAD), is described. The studies have explored the ease with which different furan units within the macrocy cle can be converted into either naphthalenes, o-phthalic ester residues or 3,4-furandicarboxylate units. The cycloaddition products are shown to diff er as a function of stoichiometry. regiochemistry and stereochemistry. The problems encountered in the attempts to aromatise the benzyne adducts to th eir corresponding naphthafurophanes hamper the exploitation of these compou nds as acenophtine precursors. Similarly, the DMAD adducts are not suitable precursors for derivatives containing phthalic acid units. On the other ha nd, they readily provide access to furnaophanes containing carboxyl substit uents. The X-ray crystal structures of a variety of kev derivatives have be en determined and their conformations analysed and compared.