Modifications to the methylene bridge lead to a variety of new calixarenes. The 2-oxo-p-tert-butyltetramethoxycalix[4]arene (1) is converted to an oxime derivative (2) upon treatment with NH2OH in pyridine. The oxime undergoes rearrangement to a cis amide (3) upon treatment with iodine and PPh3 (10 mol%) in dry acetonitrile. Exposure to temperatures above 200 °C result in conversion of cis-amide 3 to its trans isomer (4). Demethylation of cis-amide 3 is accomplished with BBr3 in CH2Cl2, yielding the tetraphenol species 5. Calixarene 5 is judged by 1H and 13C NMR spectroscopy to adopt a cone conformation. The substitution of a single amide for a methylene group leads to a substantially more rigid molecule compared to unmodified calixarene 6.

Selective synthesis of cis and trans isomers of calix[4]arenes with an amide incorporated in the macrocycle skeleton

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