Synthesis of highly lipophilic crown ether carboxylic acids

Sonochemical reformatsky reactions of α‐bromoesters with sym‐(keto)dibenzo‐16‐crown‐5

“…sym-(Keto)dibenzo-16-crown-5 (1) was prepared by a reported method [10]. Tetrahydrofuran was distilled from sodium-benzophenone ketyl radical.…”

Sterically congested, geminal aryl-substituted, proton-ionizable sym-dibenzo-16-crown-5 lariat ethers: synthesis and alkali metal cation extraction

“…6 The dibenzo-16-crown-5 ring system provides a convenient scaffold for investigating the influence of structural variation within lariat ethers upon their selectivity and efficiency in metal ion complexation processes due to its synthetic accessibility with pendant groups attached to the central carbon of the three-carbon bridge. [7][8] In earlier studies, we found that the introduction of a lipophilic decyl group geminal to the functional side arm in symdibenzo-16-crown-5 oxyacetic acid ( Figure 1) increased the Na + selectivity by preorganization of the binding site in which the alkyl group oriented the oxyacetic acid side arm over the polyether cavity. Various alkyl groups have been attached geminal to the proton-ionizable side arm in symdibenzo-16-crown-5 ethers to form effective and selective extractants for alkali metal cations.…”

Synthesis of lariat ether carboxylic acids based on dibenzo‐16‐crown‐5

“…Lariat ether carboxylic acids 9-11 (Table 1) with lipophilic groups at both the geminal position and on the side arm were prepared by reaction of the appropriate lariat ether alcohol and sodium or potassium hydride in tetrahydrofuran and the appropriate 2-bromocarboxylic acid as shown in Scheme 2. The sym-(R)(hydroxy)dibenzo-16-crown-5 precursors were prepared by reaction of [9] and the appropriate Grignard reagent [9,19,21,27]. In addition to reducing ligand loss from the organic phase during extraction of metal ions from aqueous solutions, the geminal substituent preorganizes the metal ion binding site by orienting the carboxylic acid group over the crown ether cavity [36].…”

“…Previously we have described the preparation of several dibenzo-16-crown-5 carboxylic acids [7,9,11,13,14,19,26,[32][33][34]. However, these compounds provide only limited structural variation.…”