The addition of the potassium salt of (R)-4-phenyl-2-oxazolidinone to dialkyl alkylidenemalonates under various conditions is reported. Very good diastereoselectivities (> 90% de) were obtained in several cases. Conversion of one of the adducts to the beta-amino acid (S)-beta-leucine was achieved in two straightforward steps.

As a heterofunctional pro-ligand with both hard and soft coordination sites, trans-3-(3-pyridyl)acrylic acid (LH) is of potential interest for the design of heterometallic complexes of f- and d-block cations, as previously shown in the case of lanthanides. The reaction of LH with uranyl nitrate in water/acetonitrile at 180 degrees C yields the complex [(UO2)(3)(L)(HL)(O)(OH)(3)]center dot 2.5H(2)O center dot CH3CN (2), which is different from the previously reported complex [UO2(L)(OH)] (1). Complex 2 crystallizes as a ribbon-like 1D coordination polymer with a skeleton bridged by oxido and hydroxido ligands, in which the uranyl cation is bound to the bridging bidentate carboxylato groups, and the pyridyl groups (one of them protonated) are directed sideways. In the presence of copper nitrate, the reaction affords the heterometallic complex [(UO2)(2)Cu(L)(3)(O)(H2O)](NO3) (3), in which the harder uranium atom is bound to two 3-oxido anions and to chelating and bridging carboxylato groups to generate a tetranuclear secondary building unit, whereas the softer copper cations are bound to three pyridyl groups and only one carboxylato donor. The copper atoms are further involved in cation-cation interactions with uranyl oxido groups, and the Cu-O(oxido) bond lengths of 2.162(13) and 2.248(16) angstrom are among the shortest measured to date. 3 crystallizes as a 3D assembly, which displays narrow channels, and it illustrates the ability of copper cations, in combination with a ditopic ligand, to assemble discrete uranyl-containing units into a framework structure. The emission spectra of complexes 1 and 2 in the solid state display the usual vibronic progression of the uranyl ion in the range 450-650 nm, and the width of the bands indicates that they may be the superposition of slightly different series, due to the inequivalent uranyl centres in the lattices.

A series of pulvinones were prepared in three steps from a common precursor, methyl 3-phenylglycidate. This compound was readily converted to several diesters containing an ether function. Then, treatment of these compounds with lithium hexamethyldisilazide afforded the corresponding pulvinones, via tandem Dieckmann condensation–alkoxide β-elimination. The use of a 2,2,2-trifluoroethyl ether instead of a methyl ether facilitated the β-elimination and led to better yields of product.

AbstractReaction of acyloxyesters containing a trifluoroethoxy group (I) and (III) with LiHMDS proceeds via tandem Dieckmann condensation—alkoxide β‐elimination to give pulvinones (II) and (IV), respectively.

A new fluorogenic calix[4]tetraaza-crown-6 (4) bearing two pyrene amide groups has been prepared. It was shown to be selective for Mg2+. When Mg2+ is bound to 4, the pyrene monomer emission increased while the excimer emission declined in a ratiometric manner. It is shown by 1H NMR that this ratiometric change is due to the conformational changes of the pyrenes during the chelation of Mg2+ by the amide functions to form a 1:1 complex.

Reaction Of UCl4 with Li(C5Me4-2-C5H4N) (LiCp*Py) gave (CP*PY)(2)UCl2 (1), which was subsequently transformed into (CP*PY)(2)UX2 [X = Me (2), BH4 (3)]. Treatment of 3 with HNEt3BPh4 afforded the cationic derivative f(CP*PY)(2)U(BH4)][BPh4]. The ansa-metallocene C2H4(eta(5) -C5Me3-2-C5H4N)(2)UCl2 (5) was unexpectedly obtained in one reaction of 2 and CUCl2. The crystal structures of 1 and 5 have been determined.

[GRAPHICS]A novel calix[4]arene-based chemosensor I based on Hg2+-induced fluorescence resonance energy transfer (FRET) was synthesized, and its sensing behavior toward metal ions was investigated by UV/vis and fluorescence spectroscopies. Addition of Hg2+ to a CH3CN solution of I gave a significantly enhanced fluorescence at similar to 575 nm via energy transfer (FRET-ON) from the pyrenyl excimer to a ring-opened rhodamine moiety. In contrast, addition of Al3+ induced a distinct increase of pyrenyl excimer emission (similar to 475 nm), while no obvious FRET-ON phenomenon was observed. Different binding behaviors of 1 toward Hg2+ and Al3+ were also proposed for the interesting observation.

Both the consequences of 1,3-cyclization of calix[4]arenes by diamide formation, and the effect of 2- and 2,4-alkoxycarbonylmethylation of two 1,3-bridged calix[4]azacrowns on their metal ion-binding capacities have been studied by synthesis of the derivatives in their cone conformation and measurement of the stability constants for their complexation in a range of alkaline earth and transition metal cations. In these two cases, the conformation of the ligand in the solid state has been defined in detail by a crystal structure determination. In the first case, a tubular architecture performing methanol channels is displayed, however, in the second case a zigzag architecture generated by a chloroform network connecting calixarene molecules is present. Speciation in solution appears to be limited to the formation of 1:2 and/or 1: 1 and/or 2:1 (M-L) complexes, depending on the system, with values of the stability constants determined by absorption spectroscopy in acetonitrile, lying in the ranges log beta(12) ca. 10, log beta(11) ca. 2-5, and log beta(21) ca. 7-9. There is evidence for selectivity toward Cu(II) and for some unexpected anion effects. None of these ligands appear to be an efficient extractant for the metals as their picrate. (c) 2006 Elsevier Ltd. All rights reserved.

This led us toinvestigate the oxidation of thiacalix[4]biscrown-5. Wereport herein the synthetic method and the physical proper-ties and crystal structure of the resulting molecules. In a first step, para-tert-butylphenol was cyclized withsulfur to give para-tert-butylthiacalix[4]arene (1) as shownin Scheme 1. Dealkylation using AlCl

The first crystal structures of complexes of tetrahydroxy-[3.1.3.1]metacyclophanes, also termed homocalix[4]-arenes, are reported. In the two uranyl ion complexes obtained, with different para-substituents, the complex core is analogous to that in tetrahomodioxacalix[4]arene complexes, with the cation in a tetra-phenoxide, distorted square-planar environment. The packing in one of these complexes comprises two different arrangements, one of them being a columnar stacking of complex molecules with sandwiched triethylammonium counter-ions hydrogen bonded to one complex and held by cation-pi and CH-pi interactions within the cavity of the other neighbouring one.

A systematic study of extraction properties and complexation behaviour of the calix[4](aza)crown 1 towards alkaline earth (Mg 2+ , Ca 2+ ,Sr 2+ , Ba 2+ ) and transition metal (Co 2+ , Ni 2+ , Cu 2+ ,Zn 2+ ) cations is presented. The binding behaviour of 1 was also investigated by 1 H-NMR and the crystal structure of the 1:1 complex with Mg 2+ isdescribed.

The synthesis of nitro derivatives of 1,3-calix[4]arene bis-crown-6 is reported. The X-ray structure of one of them is given. The complexation of cesium cation is presented and shows the role of the nitro groups for the complexation to occur.

Crystal structure determinations for the hexarubidium and octacesium derivatives of calix[6]arene hexasulfonic acid, as well as of a new solvate of the pentasodium derivative of calix[4]arene tetrasulfonic acid, and comparison with structural data from the literature for alkali metal complexes of sulfonated calixarenes, have provided further evidence for the importance of interactions with aromatic pi-electrons for the heavier alkali metal cations. There is evidence as well that this interaction can be enhanced by extended ionization of the sulfonated calixarene.

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The reaction of p-tert -butyl calix[4]arene 1 withα,α'-dibromo-o-xylene in basic conditions leads totwo new compounds. One of them is a bis-calix[4]arene, whose crystal structure has been determined.

The use of [2.2.2] cryptand as a deprotonating agent during the synthesis of the mononuclear, monoanionic, uranyl ion complexes of p-R-hexahomotrioxacalix [3] arenes ( R = tert-butyl, phenyl) results in the formation of supramolecular assemblies, which have been characterized by their crystal structures and H-1 NMR spectra in solution. In the 1 : 1 complex cryptand assembly, the endo monoprotonated cryptand has its ammonium end embedded in the complex cavity, whereas, in the 2 : 1 complexes, the endo diprotonated cryptand is encapsulated in a sandwich mode by two complexes with convergent concave surfaces. The latter complexes are the first examples of the use of [2.2.2] cryptand as a connector to build calixarene supramolecular systems. The importance of cation-pi interactions in this assembling process is discussed.

The synthesis of calix[4](aza)crowns capped by one ‘tren’ or doubly capped by two azacrowns is described. The crystal structure of the tripodal ‘tren’ is given. Complexing properties towards Co2+, Ni2+, Zn2+ and Cu2+ are described. Conclusions are drawn on the role of functional groups and molecular topology in the complexation behavior of calix[4](aza)crowns.