Preorganized ligand arrays based on spirotetrahydrofuranyl motifs. Synthesis of the stereoisomeric 1,8,14-trioxatrispiro[4.1.4.1.4. 1]octadecanes and the contrasting conformational features and ionic binding capacities of these belted ionophores.
The cis,trans trispiro ether 4 is accessible from several synthetic directions as a consequence of a crossover in reaction selectivity when proceeding from nucleophilic attack on the cis dispiro ketone to oxygenation of the alpha,beta-unsaturated ester 17. Its cis,cis isomer 3 was obtained in 17 steps and 14.6% overall yield from 3, 5-dimethoxybenzoic acid by making use of the alicyclic side chain in N as a "conformational lock". Although 4 shows no measurable tendency to complex with alkali metal ions, 3 binds strongly to Li(+) and Na(+) ions, as well as to CH(3)NH(3)(+). Whereas the 3eq conformation is populated in the solid state and in solution, complex formation occurs readily. (13)C NMR studies have defined slow exchange limits as the 2:1 sandwich complex with lithium ion is initially formed and transformed progressively into a 1:1 species upon the addition of more LiClO(4). Only the 2:1 complex with sodium ion is formed during comparable titration with NaClO(4). Association constants, molecular mechanics calculations, and X-ray crystallographic studies provide insight into the binding capacity of this belted tridentate ionophore.
Paquette
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Evans Chemical Laboratories, The Ohio State University, Columbus, Ohio 43210, USA. paquette1@osu.edu
Tae
J
J
Hickey
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Trego
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Rogers
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RD
D018360:Crystallography, X-Ray; D005663:Furans / Q000737:chemistry*; D007476:Ionophores / Q000138:chemical synthesis* / Q000737:chemistry; D008024:Ligands; D008672:Metals, Alkali / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013141:Spiro Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D005663:Furans; D007476:Ionophores; D008024:Ligands; D008672:Metals, Alkali; D013141:Spiro Compounds