Crown Conformation Research Articles

Se22-, Se52-, and Se72- Ligands in [NEt4]2[As2Se6], [enH][AsSe6]·2.2.2-cryptand, [NEt4][AsSe8], and [(en)2In(SeAs(Se)Se2)]·en

The extraction in ethylenediamine (en) of “AsSe4”, “TlAsSe4”, and “InAsSe4”, followed by reaction with cation sources or 2.2.2-cryptand, has led to the isolation of [NEt4]2[As2Se6] (1), [enH][AsSe6]·2.2.2-cryptand (2), [NEt4][AsSe8] (3), and [(en)2In(SeAs(Se)Se2)]·en (4). These compounds contain AsSe+ units coordinated to Se22-, Se52-, and Se72- ligands in 1 and 4, 2, and 3, respectively. The [As2Se6]2- anion features two AsSe+ units joined by Se22- ligands; the resultant As2Se4 ring exhibits a chair conformation. The [AsSe6]- anion features an AsSe+ unit coordinated in a bidentate fashion by a Se52- ligand to create an AsSe5 ring with a chair conformation. The [AsSe8]- anion contains an AsSe+ unit coordinated by a bidentate Se72- ligand; the resultant AsSe7 ring has a crown conformation. [(en)2In(SeAs(Se)Se2)] features an octahedral In atom bridged by one Se2- and one Se22- ligand to an AsSe+ unit; two bidentate en ligands complete the coordination about the In center.

Monolayers of Calix[4]resorcinarenes with Azobenzene Residues Exhibiting Efficient Photoisomerizability

Abstract Azobenzenes tethered from the lower rim of crown conformer of O-octacarboxymethoxylated calix[4]resorcinarenes display efficient E-to-Z photoisomerizability in densely packed monolayers on a water surface, in LB films and in surface-adsorbed monolayers, respectively.

Macrocyclic amphiphiles. Part 2.†—Multi-point adsorptivity of the crown conformer of calix[4]resorcinarenes and their derivatives on surfaces of amorphous polar substrates

The adsorption behavior of the crown conformer of calix[4]resorcinarenes (CRAs), cyclic tetramers of resorcinol and aliphatic aldehydes, and theirO-carboxymethoxylated and O-hydroxyethyloxylated derivatives on a quartz surface was investigated. The adsorption of the macrocyclic amphiphiles from solutions of less polar solvents such as toluene at concentrations of >10–3 mol dm–3 obeyed the Langmuir equation to give monomolecular layers. The absorption equilibrium constant for CRA was two orders of magnitude greater than that of the corresponding resorcinol. Such efficient adsorptivity of the macrocyclic compounds arises from their characteristic structures which possess eight hydrogen-donating polar residues on the same rim of the cylindrical molecular skeleton. CRA molecules are also adsorbed on the surface of a poly(vinyl alcohol) thin film, suggesting that these cyclic tetramers provide a general procedure to give monomolecular layers deposited on polar surfaces of amorphous solids.

Synthesis and fluorescence behavior of calix[4]resorcinarenes possessing pyrenyl group(s)

A mixture of octa-o-acetylated calix[4]resorcinarenes (CRAs) with varying numbers of 2-(pyren-1-yl)ethyl residues is synthesized by acid-catalyzed condensation of resorcinol with 3-(pyren-1-yl) propanal, followed by acetylation. The product is separated using reversed phase silica gel column HPLC. NMR spectra of the isolated octa-o-acetylated CRAs substituted with different numbers of pyrenyl groups revealed that all the cyclic tetramers are of the crown conformation. The product distribution is almost in accordance with theoretical values, assuming that the reaction rates of the two aldehydes are the same. 1H NMR chemical shifts of the pyrenyl groups are shifted to an upper field with increasing number of pyrenyl groups because of the ring current effect. Measurements of steady state spectra and decay time of pyrene fluorescence of the CRAs revealed that they form two types of excimer and that strain in the excimer does not depend on the number of pyrenylethyl groups.

5,8-Bis(4-methoxy-2,3,6-trimethylbenzenesulfonyl)-1,4-dioxa-5,8-diazocane

The molecular shape of the title compound, C24H34N2O8S2, in the crystalline state is characterized by internal twofold symmetry, with the eight-membered ring adopting a crown conformation.

Novel 1,2-bridged calix[4]crowns in the 1,2-alternate conformation

Treatment of 1,2-di[(2-pyridylmethyl)oxy]calix[4]arenes 1 (R = t-Bu, H) with tri- to pentaethylene glycol ditosylates in anhydrous toluene in the presence of t-BuOK affords a mixture of 1,2-alternate and cone (1,2)-calix[4]crown conformers 2 and 3 in a 55–70% overall yield. The conformational features of 2 have been deduced by NMR, and further confirmed by single-crystal X-ray analysis on crown-5 derivative 2e.

Facile and Rational Route for High-Yield Synthesis of Titanasiloxanes from Aminosilanetriols

Reactions of aminosilanetriols RN(SiMe3)(Si(OH)3) (R = 2,6-Me2C6H3 (1a), 2,6-i-Pr2C6H3 (1b), 2,4,6-Me3C6H2 (1c)) with titanium orthoesters Ti(OR‘)4 (R‘ = Et, i-Pr) in hexane at room temperature afford new cubic titanasiloxanes [RN(SiMe3)SiO3Ti(OR‘)]4 (2a−f) in nearly quantitative yield. These compounds have been characterized by mass, IR, and multinuclear NMR spectroscopy. The X-ray crystal structure of [(2,6-i-Pr2C6H3)N(SiMe3)SiO3Ti(OEt)]4 (2c) is described. The molecular structure of 2c reveals a Si4Ti4O12 cubic core. The six Si−O−Ti puckered eight-membered rings in the cubic framework adopt a crown conformation with the two Si and two Ti atoms describing a plane and the four oxygen atoms in an almost parallel plane.

X-ray crystal structure and1H-NMR chiral shift reagent study of a crown trimer

3,4,5-Trimethoxybenzyl alcohol was cyclooligomerized with a bentonite clay used as a catalyst. Results of the crystal structure analysis of the racemic (±) nonamethoxy[1,1,1]orthocyclophane trimer, C30H36O9, are described. The structure was determined by X-ray diffraction at 293 K and shown to belong to the triclinic space group P\(\bar 1\). The compound possesses a distorted crown conformation with unusual C−H...O intermolecular interactions, and with a crystal packing not observed before in other related derivatives. The racemic mixture was also discriminated in its two enantiomeric isomers, using proton NMR and Eu(III) as a chiral shift reagent.

New chiral heterocycles: 5-[(r)-(+)-1′-methylbenzyyl-1,3,5-dithiazine and 3-7-di-[(R)-(+)-1′-methylbenzyu-3-7-diaza-1,5-dithiacyclooctane. Conformational studies and their reactions with borane.

We report herein the syntheses of a new 5-[(R)-(+)-1′-methylbenzyl]-1,3,5-di- thiazine 1, the 5-isopropyl-1,3,5-dithiazine 2 and the 3,7-di-[(R)-(+)-1′-methylbenzyl]- 3,7-dlaza-1,5-dithiacyclooctane 3, two of them ( 1 and 3) are new sulfur and nitrogen heterocycles bearing a chiral N-substituent. Compounds 1 and 2 were found in conformational equilibrium when observed at rt at 1H-270 MHz or 13C-67.8 MHz, when cooling a preferred chair conformation was observed with the N-substituent in the axial position. Heterocycle 3 was in an anchored crown conformation at rt. A conformational study of ring inversions for 1 and 3 was performed and their thermodynamic data were obtained, AG = 48.1 ± 0.8 for 1 and ΔG = 64.8± 1.2 kJ/mol for 3. The reactivity of 1-3 with BH 1-3THF was investigated, the N- or S-BH 3 adducts were not stable, the reactions afforded cleanly the N-borane-N-dimethyl-N-alkylamine adducts. The reaction of 3 with BD 3 gave the N-BD 3 adduct of [CH 2D] 2N-CH[CH 3]C 6H 5. An X-ray diffraction study of 3 confirmed its crown conformation with the N-substituents in pseudo-axial position.

Structure of the stacked cyclic oligoamides: 1,6-diaza-2,7-cyclodecadione and 1,5,9-triaza-2,6,10-cyclododecatrione. A ring model of the α-helix

The structure of two cyclic amides, comprised of methylene and peptide groups, is described. The cyclic amides form parallel columns of stacked hydrogen-bonded rings. The cyclic dimer of butyramide (1,6-diaza-2,7-cyclodecadione) (I), C 8 H 14 N 2 O 2 , forms monoclinic crystals, space group P2 1 /n, a=4.874 (2), b=11.714 (4), c=8.088 (2) A, β=107.3 (3) o , R=0.125 for 536 observed reflections, I>3σ(I), Z=2, D x =1.28 g cm -3 , λ(Cu, Kα)=1.5418 A, μ=7.26 cm -1 , T=298 K. The ten-membered ring skeleton adopts a centrosymmetric crown conformation which is rarely found in other ten-atom ringse, but has been described for its isomer 1,5-diaza-6,10-cyclododecadione

The structure of a potassium-copper complex with six-membered macrocyclic ethylsiloxanolate ligands

The structure of K2{[EtSiO2]6K2Cu4[O2SiEt]6} · 4n-BuOH, a novel mixed sandwich-like complex of K+ and Cu2+ with two 6-membered macrocyclic ethylsiloxanolate ligands, was established by means of X-ray study. The ligands have an all-cis configuration and a crown conformation. Four Cu2+ and two K+ ions form a planar hexagon sandwiched between antiparallel coaxial macrocyclic ligands. The K+ ions occupy two opposite apices of the hexagon. The Cu2+ ions have square-planar coordination with four siloxanolate OM atoms, while the K+ ions, are coordinated with two O atoms of the solvating butanol molecules, in addition to four OM atoms. The electric neutrality of the whole complex is due to the two outer-sphere K+ counter-ions, each located over one of the two siloxanolate macrocycles, i.e., over the «decks» of the sandwich and coordinated with endocyclic siloxane OSi atoms, as in crown-ether complexes.

2-(1-Aza-4,7,10-trioxacyclododecyl)ethyl]dimethylammonium iodide. An intramolecular trifurcated hydrogen bond

C12Hz7N20~-.I-, Mr = 374.3, monoclinic, P2~/e, a = 23.925 (3), b = 7.7933 (8), c = 19.182(3)A,/3= 113.113(I0) °, V= 3289.5(8)A 3, Z = 8, Dx = 1-511 g cm -3, a(Mo Ka) = 0.71073 ~, p, = 19.3 cm-1, F(000) = 1520, T = 296 K, R = 0-045 for 3684 observations having I> lo-(/) (of 5785 unique data). There are two independent formula units in the asymmetric unit. The two macrocyclic cations have nearly identical conformations, with the 12-membered ring in the crown conformation, having all four donor atoms on the same side of the ring. The side arm, which contains the quaternary ammonium, is folded over the ring, with the H atom pointing towards the ring. The two independent cations exhibit a mean difference in 15 torsion angles describing their conformations of only 1.5 °, with a maximum individual difference of 4.7(11) ° . The N--H hydrogen atom is involved in a trifurcated intramolecular hydrogen bond with the ring N and two O atoms of the ring. The N...acceptor distance range is 2.828 (8)-3.158 (8)A,, and the H..-acceptor distance range is 2-25 (10)-2.40 (10) A.

An Unusual sandwich-type nickel oxide-siloxanolate complex {[PhSiO]} 6 (μ 4-O) 2 (μ 3-O) 4[Ni 8(μ 3-0) 2](μ 3-O) 4(μ 4-O) 2 [PhSiO] 6}·14n-BuOH·10H 2O·2Me 2CO. Synthesis and crystal structure

An X-ray crystal study of the nickel oxide-siloxanolate complex {[PhSiO] 6(μ 4-O) 2(μ 3-O) 4[Ni 8(μ 3O) 2] (μ 3-O) 4(μ 4-O) 2[PhSiO] 6}·14n-BuOH·10H 2O·2MeCO (I or Ia without noncoordinating solvate molecules) having a cage structure has been carried out. The complex studied was prepared by the interaction of NiCl 2 with the product of the reaction of phenylsilsesquioxane (PhSiO 1.5) n with NaOH. The polynuclear cage-like centrosymmetric molecule Ia has a sandwich-type structure. The inner two-dimensional nickel oxide fragment Ni 8o 2(μ-O) 12 2 = Ni 8O 8 is structurally identical to a fragment of the NiO crystal layer which is one Ni atom thick and parallel to the (111) plane. All Ni atoms have oxygen atoms in an octahedral coordination (oxide, silanolate, molecules of water, butanol and acetone). The O atoms of the nickel oxide layer have both trigonal pyramidal (μ 3-O) and distorted tetrahedral (μ 4-O) coordination. The nickel oxide layer is bonded by NiOSi bridges through silanolate O atoms with two outer 12-membered hexasiloxane (SiO) 6 cycles (sandwich “caps”) with an almost ideal crown conformation. Some of the butanol and H 2O crystallosolvate molecules do not coordinate the Ni atoms being included in the cavities between Ia molecules. The NiO bond lenghts are 2.006–2.159 Å, while the average SiO(Si) and SiO(Ni) bond lengths are 1.637 and 1.618 Å, respectively.

Synthesis of the lichen metabolite (+)-bourgeanic acid and conformational analysis of its dilactone

An enantiospecific synthesis of the depside (+)-bourgeanic acid via (-)-hemibourgeanic acid defines the latter as (2S,3S,4R,6R)-3-hydroxy-2,4,6-trimethyloctanoic acid and the former as its self-esterification product. Conformational analysis of the dilactone derived from bourgeanic acid shows that the eight-membered ring adopts a crown conformation with C 2 symmetry and all substituents in equatorial orientation

Crystal and molecular structure of cyclotriveratrylene

Slow evaporation of a solution made from rigorously dried toluene and cyclotriveratrylene (CTV) has led to crystals of the guest-free CTV. These belong to the monoclinic space groupP21/n witha=12.582(3),b=9.575(5),c=19.738(5) A,β=95.15(2)°;D c =1.26 g cm−3 forZ=4. Refinement based on 1708 observed reflections led toR=0.045. The nine-membered ring of the CTV has the expected crown conformation.

Raman spectra and conformations of dibenzo- and dicyclohexano-18-crown-6

Conformations of dibenzo-18-crown-6 (DBC), dicyclohexano-18-crown-6 (DCC) and their alkali cation complexes in the solid state and in solution have been investigated by Raman spectroscopy. The Raman spectra were analysed by using the relationships between Raman frequencies and conformations previously found for unsubstituted crown ethers. DBC takes a conformation, ( tCttGttG′t) 2, with gauche ( G) or gauche' ( G′) 2CH 2 bonds, trans ( t) CO bonds and cis ( C) OCCO linkages at the benzene rings, when it complexes with a cation in the solid state and in solution. Uncomplexed DBC adopts another conformation in the solid state, which contains both the trans and gauche conformations about the CH 2CH 2 and CO bonds. In solution, uncomplexed DBC exists as a mixture of conformers including the two conformers described above. Vibrational couplings between the oxyethylene and cyclohexane rings are strong in DCC and its strength depends on the crown conformation. The cation-bound crown rings of DCC isomers A and B in solution predominantly take the same conformation, ( tG′ ttGt) 3, found for the crystalline isomer B-NaBr complex. A metastable conformer containing trans CH 2CH 2 bonding is found for the Na + complexes of both isomers in solution. Uncomplexed DCC adopts different crown ring conformations in isomers A and B in the solid state and diverse conformational states in solution.

Nuclear magnetic resonance elucidation of ring-inversion processes in macrocyclic octaols

The conformational behaviour of the three macrocyclic octaols (4)–(6), obtained by acid-catalysed condensation of resorcinol with heptanal, is elucidated for the first time. Two of them, namely the diamond (5a) and the chair (6a) stereoisomers, undergo a ring-inversion conformational process in acetone to give the corresponding crown conformers (5b) and (6b). In DMSO or on addition of acetic acid to an acetone solution of diamond octaol (5), conformer (5a) is favoured. The presence of such equilibria and solvent effects are interpreted as an interplay between the tendency of the phenolic OH groups to form intramolecular hydrogen bonds and the alky chains to assume the endo position, avoiding steric repulsions and allowing self-aggregation.

Conformational dependence of 17O chemical shifts in 1,3‐dioxa‐2‐silacyclooctanes: Anomeric effect

Abstract17O NMR spectra of 1,3‐dioxa‐2‐silacyclooctanes have been studied. The 17O NMR signal of derivatives existing in the crown conformation is shifted downfield by 7–10 ppm relative to derivatives existing predominantly in conformations belonging to the boat–chair family. This shift is assumed to be due to the anomeric effect in 1,3‐dioxa‐2‐silacyclooctanes.

F-Element/crown ether complexes. Crown conformations in hydrogen-bonded complexes of hydrated actinide salts

<i>f</i>-Element/crown ether complexes. Crown conformations in hydrogen-bonded complexes of hydrated actinide salts

Sesquiterpene lactones from Gutenbergia cordifolia

Gutenbergia cordifolia afforded an eudesmanolide, gutenbergin, and a germacranolide, idomain. The structures of the new sesquiterpene lactones were established by spectral methods, mainly 1H NMR.X-ray analysis of idomain showed that this germacranolide has the common chair-like crown conformation ([ 15D 5,1D 14]conformation) of trans ,trans- germacra-1(10), 4-dien- trans-6,12-olides.