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■ Preparation of Crown Ethers with Isoxazolyl-Lariats: Homologation of Isoxazole Aldehydes, and a Critical Comparison of Lariat Functional Moieties for Lanthanide Extraction

Xiong Bing Xia, Mark S. Munsey, Hongshan Du, Chien M. Wai, and Nicholas R. Natale*

*Department of Chemistry, University of Idaho, 301 Renfrew Hall, Moscow, ID 83844-2343, U.S.A.

Abstract

A critical comparison of several lariat ether functional moieties is presented. The synthesis of two isoxazolyl-lariat ethers is described. The lariat ether (2, n=1) undergoes β-fragmentation on electron transfer reductive ring-opening with samarium diiodide. The isoxazole moiety was then homologated to overcome this problem, and isoxazole lariat ether (2, n=3) was obtained. The isoxazole (2, n=3) and β-diketone (3, n=3) crowns were evaluated in lanthanide shift studies and liquid-liquid extraction studies. Finally, lateral metalation and electrophilic quenching with carbon dioxide produced the carboxylic acid (12) which proved to be an efficient ligand for the liquid-liquid extraction of lanthanides.