Hyun-Soon Chong

Synthesis and Alkali Metal Picrate Extraction Capabilities of Novel, Cage-Functionalized, Pyridine Containing Crown Ethers and Cryptands

Abstract The syntheses of novel cage-functionalized crown ethers,11–13, that contain one or more pyridyl units are reported. The results of alkali metal picrate extraction experiments performed by using11 and12 are compared with those obtained by using the corresponding model (non-cage) crown ethers. Cage-functionalized crown ether11 displays greater avidity toward Li+ picratevis-a`-vis the corresponding model system,2, whereas12 displays considerably lower avidity than its corresponding model system,3, toward extraction of alkali metal picrates from aqueous solution into CHCl3. In addition, a highly preorganized, cage-annulated cryptand,16, was prepared; this unusual host molecule was found to be both highly avid highly selective toward extraction of Li+ and Na+ picrates. Download : Download full-size image

Evaluation of alkali metal binding selectivities of caged aza-crown ether ligands by microelectrospray ionization/quadrupole ion trap mass spectrometry

Microelectrospray ionization mass spectrometry (MESI-MS) is used to evaluate alkali metal binding selectivities of a variety of macrocyclic compounds. Well-studied crown ethers are used to validate the MESI-MS method. A quantitative correlation between MESI mass spectral ion intensities and solution equilibrium distributions of complexes is obtained for the mixtures containing a single host and different alkali metal guest ions. The MESI-MS method is successfully applied for the determination of the alkali metal binding selectivities of a series of cage-functionalized aza-crown ethers and relevant model compounds in methanol and chloroform solutions. The binding selectivities parallel previous results obtained using conventional spectrophotometric extraction methods. Structural differences in the host compounds, such as the presence of a cage functionality, binding cavity size, and overall flexibility, cause significant changes in the binding selectivities.

Synthesis of a novel cage-functionalized chiral binaphthol host: a potential new agent for enantioselective recognition of chiral ammonium salts

Abstract Optically active, cage-functionalized crown ether ( R )- 3 which contains a 1,1′-bi-2-naphthol moiety has been prepared. Subsequently, the ability of ( R )- 3 to selectively recognize the enantiomers of guest ammonium salts, i.e., 4 and 5 in transport experiments was studied. Host ( R )- 3 displays significantly enhanced enantiomeric selectivity toward complex formation with 4 vis-a-vis complex formation with 5 . The relative energetics of various relevant host–guest complexes have been investigated computationally.

SYNTHESIS AND ALKALI METAL PICRATE EXTRACTION CAPABILITIES OF NOVEL, CAGE-FUNCTIONALIZED DIAZA(17-CROWN-5) ETHERS

Abstract The syntheses of novel cage-annulated diaza (17-crown-5) lariat crown ethers, i.e.,10–16 are reported. A series of alkali metal picrate extraction experiments have been performed by using this new class of synthetic ionophores in order to evaluate the effects of cage-annulation and the influence ofN-pivotside-arms upon complexation properties. The results thereby obtained indicate that complexation of these lariat crown ethers with alkali metal cations is influenced by both of these structural features. In particular, the cage-annulated diaza crown ether11 displays much greater avidity toward all alkali metal cations studied than does the corresponding model system (1). It was observed that ligands11 and13 display bimodal behavior toward extraction of alkali metal picrates, whereas ligands15 and16 behave as relatively non-selective alkali metal picrate extractants. A cage-annulated cryptand,19, was prepared, and its alkali metal picrate extraction profile was obtained. Highly preorganized cryptand19 displays particularly high avidity toward complexation of K+ and Rb+ picrates in solution. The syntheses and alkali metal picrate extraction profiles of several new crown ethers (11, 13, 15, and16) and a novel, cage-functionalized cryptand (19) are described. Download : Download full-size image

Synthesis and Alkali Metal Picrate Extraction Studies of p-tert-Butylcalix[4]arene Crown Ethers Bridged at the Lower Rim with Pyridyl Units

Abstract The syntheses of pyridyl containing calix[4]arene receptors (4, 5, and 11) that adopt the cone conformation are reported. The complexation properties of these host molecules were estimated via the results of alkali metal picrate extraction experiments. A singly-bridged bis-calix[4]arene, i.e. 4 does not appear to be an efficient alkali metal picrate extractant. A doubly-bridged bis-calix[4]arene, i.e. 5, displays elevated extraction avidity toward Rb+ and Cs+ picrates when compared with that of 4. A pyridyl containing calix[4]arene-crown-5, i.e. 11, shows improved avidity and selectivity toward extraction of K+ and Rb+ picrates vis-a-vis the corresponding behavior of 4 and 5.

Synthesis and alkali metal picrate extraction studies of lower rim functionalized p-tert-butylcalix[4]arene crown ethers

The syntheses of four new calix[4]arene receptors, i.e. 4 – 7 , each of which contains an oxahexacyclic cage moiety, are reported. The structures of two of these receptors, i.e. 4 and 7 , have been established via single crystal X-ray structural analysis. The complexation properties of 4 – 7 were determined via a series of alkali metal picrate extraction experiments. Two of the cage-functionalized calix[4]arene-crown-5 hosts, i.e. 4 and 5 , display somewhat greater extraction avidity toward Na + picrate vis-a-vis the remaining alkali metal picrates. By way of contrast, host systems 6 and 7 function effectively as a moderately selective K + extractants and display significantly increased extraction avidity toward K + picrate vis-a-vis 4 and 5 .

Acid and base promoted rearrangements of Hexacyclo[11.2.1.02,12.05,10.05.15.010,14]hexadeca-6,8-diene-4,11-dione

Abstract Hexacyclo[11.2.1.02,12.05,10.05,15.010,14]hexadeca-6,8-diene-4,11-dione (3) was synthesized via ring-expansion of hexacyclo[10.2.1.02,11.04,9.04,14.09,13]pentadeca-5,7-diene-3,10-dione (1). Reaction of a toluene solution of 3 with a catalytic amount of HCl resulted in extensive skeletal rearrangement, thereby affording 6,7-benzotetracyclo[7.3.0.04,12.05,10]dodecane-2,6-dione (4). Subsequent reaction of 4 with 3,6-diphenyl-1,2,4,5-tetrazine (5) afforded a novel molecular cleft, 6. Compound 3 reacted smoothly with ethanolic KOH at ambient temperature (in 3 h) or at reflux (in 0.5 h) to afford a rearranged product, 7. The structures of 3, 4, 5, and 7 were established unequivocally via application of single crystal X-ray crystallographic methods.

π-Facial selectivities and proximal/distal regioselectivities in Diels–Alder reactions of unsymmetrical, cage-annulated 1,3-cyclohexadienes

Abstract Diels–Alder cycloaddition of hexacyclo[7.5.1.01,6.06,13.08,12.010,14]pentadeca-2,4-diene-7,15-dione (1) to ethyl propiolate proceeds with π-facial selectivity to afford two cycloadducts, 4b and 5b (product ratio: 4b/5b=80:20). Thermal [4+2] cycloaddition of hexacyclo[7.5.2.01,6.06,13.08,12.010,14]hexadeca-2,4-diene-7,16-dione (2) to ethyl propiolate affords two isomeric cycloadducts, i.e. 6c and 6d (product ratio: 6c/6d=40:60). Cycloadducts 6c and 6d are formed with a high degree of endo π-facial selectivity but with only modest proximal/distal regioselectivity. The corresponding [4+2] cycloaddition of 2 (diene) to dimethyl acetylenedicarboxylate (dienophile) produced a single cycloadduct, 7b. These observations have been further examined by employing Hartree–Fock relative energies of transition states presumably formed enroute to the various products. Interestingly, filled orbital electrostatic repulsion between the incoming dienophile and the CO groups in the diene substrate does not appear to be a significant factor that might influence π-facial selection in this [4+2] cycloaddition. Finally, thermal [4+2] cycloaddition of cyclopentadiene (diene) to dienophile 3 proceeded with a high degree of π-facial selectivity to afford a single cycloadduct, 9b.

One-Pot Synthesis of Cage-Functionalized, Ketal-Containing Crown Ethers

Acid-catalyzed reaction of pentacyclo[5.4.0.02,6.03,10.05.9]undecane-8,11-dione (1) with penta(ethylene glycol) produced two cage-functionalized, ketal-containing crown ethers, i.e., 2 and 3, in low yield. The structure of 2 was established unequivocally by direct methods. Alkali metal picrate extraction data obtained for 2 and for a structurally related model compound, i.e., 18-crown-6,indicate that 2 is an inefficient alkali metal picrate extracting agent.