Abstract
Various boronic acid appended calixarene assemblies were constructed on the macrocyclic lower rim. Treatment of the appropriate calix[4]arene with controlled amounts of base and 2bromomethylphenylethylene boronate affords the monoboronic acid triphenol or the distally separated diboronic acid of choice. Upper rim p-allyl calix[4]arene phenyl boronic acids were prepared. These ligands were designed to allow further study of guest complexation in nonaqueous, aqueous and on solid substrates.
Highlights
There is considerable evidence of the interest in the Lewis acid binding properties of organoboron compounds for organic synthesis and molecular recognition.1 Trigonal sp2 hybridized boronic acids RB(OH)2 bind hydrophilic diols, either by the reversible formation of a neutral trigonal boronate ester, or through a mechanism which is considered to be more favourable involving an ion-paired sp3 hybridized tetrahedral anion
Complex formation between boronic acids and polyols2 forms the basis of chromatographic separations and solid phase extraction chemistries; for example, Hagemeier et al have utilized silica-bonded m-aminophenylboronic acid for the chromatographic analysis and elution of cis-diols containing ribonucleosides and ribonucleic acids in clinical samples
There is a wealth of literature in chemical journals and in specialised books concerning the synthesis and properties of calixarenes
Summary
There is considerable evidence of the interest in the Lewis acid binding properties of organoboron compounds for organic synthesis and molecular recognition.1 Trigonal sp2 hybridized boronic acids RB(OH)2 bind hydrophilic diols, either by the reversible formation of a neutral trigonal boronate ester, or through a mechanism which is considered to be more favourable involving an ion-paired sp3 hybridized tetrahedral anion. A mixture of p-tert-butylcalix[4]arene 7 (2.50 g, 3.86 mmol), 2-bromo-methylphenylethyleneboronate 6 (1.23 g, 5.10 mmol) and potassium carbonate (0.32 g, 2.31 mmol) in dry acetonitrile (100 mL) were heated under reflux in dry N2 conditions for 40 hrs.
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