Barium(II) complexes of calixcrowns derived from p-tert-butylcalix[5]arene as potential transacylation catalysts. Regio- and stereo-selective monoacylation of the calixcrown
- 1 January 1998
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 2,p. 419-424
- https://doi.org/10.1039/a703966b
Abstract
Several crown ethers derived from tert-butylcalix[5]arene have been studied in the form of their barium(II) salts as turnover catalysts in the methanolysis of p-nitrophenyl acetate in MeCN–MeOH (9∶1, v/v) using UV spectroscopy and HPLC. The liberation of p-nitrophenol can be interpreted for 1,3-crown ether derivatives by a double displacement mechanism, although their catalytic activity is lower than for the corresponding tert-butylcalix[4]arene derivative. Regioselective O-acylation of ring 2 has been proved for crown-5 and crown-6 by 1H NMR of the isolated intermediate. Whilst this monoacetyl derivative of crown-6 assumes the expected cone conformation, it is formed exclusively as the partial cone conformer from the crown-5. This observation enables the regio- and stereo-selective monoacylation of the 1,3-crown-5 derivative also on a preparative scale by reaction with p-nitrophenyl esters in the presence of one molar equivalent of Ba2+ ions.Keywords
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