Search

Abstract: We investigate a biomimetic model of a TyrZ/His190 pair, a hydrogen‐bonded phenol/imidazole covalently attached to a porphyrin sensitizer. Laser flash photolysis in the presence of an external electron acceptor reveals the need for water molecules to unlock the light‐induced oxidation of the phenol through an intramolecular pathway. Kinetics monitoring encompasses two fast phases with distinct spectral properties. The first phase is related to a one‐electron transfer from the phenol to the porphyrin radical cation coupled with a domino two‐proton transfer leading to the ejection of a proton from the imidazole–phenol pair. The second phase concerns conveying the released proton to the porphyrin N4 coordinating cavity. Our study provides an unprecedented example of a light‐induced electron‐transfer process in a TyrZ/His190 model of photosystem II, evidencing the movement of both the phenol and imidazole protons along an isoenergetic pathway. [ABSTRACT FROM AUTHOR]

Abstract: We describe a photochemical reaction using two starting materials, a cyclopent‐2‐enone and an alkene, which are transformed in a controlled manner via the initial [2+2]‐photocycloaddition adducts into cyclobutene aldehydes (conveniently trapped as stable acetals) or unprecedented angular tricyclic 4:4:4 oxetane‐containing skeletons. These compounds are formed through tandem or triple cascade photochemical reaction processes, respectively. Small libraries of each compound class were prepared, thus suggesting that this photochemistry approach opens new opportunities for synthesis design and for widening molecular diversity. [ABSTRACT FROM AUTHOR]

A new and flexible approach toward the synthesis of 6,12-guaianolide anticancer drugs such as trilobolides or thapsigargin has been developed that could be applied to the preparation of analogues with a modified ring system. The synthesis starts from commercial 2-methylcyclopentane-1,3-dione, only relying on diastereoselective reactions for the construction of the stereogenic centers at C1, C3, C6, and C10 and features a high-yielding ring-closing enyne metathesis (RCEYM) step for the formation of the [5,7] bicyclic core. [ABSTRACT FROM AUTHOR]

Abstract: Transformations of alkene and alkyne substrates relevant to π‐Lewis acid catalysis have been performed using low‐valent Ga(I) species for the first time. [Ga(I)(PhF)2]+[Al(ORF)4]− and gallium dichloride (i. e. [Ga(I)]+[GaCl4]−) proved to be efficient catalysts for cycloisomerizations, Friedel‐Crafts reactions, transfer hydrogenations, and reductive hydroarylations. Their activity is compared to more common Ga(III) complexes. This study shows that even the readily available and yet overlooked gallium dichloride salt can be a more active π‐Lewis acid catalyst than gallium trichloride or other Ga(III) species. [ABSTRACT FROM AUTHOR]

The preparation of a tetranuclear NiII complex, constructed of two binuclear species each containing a macrocyclic cryptand‐like ligand and bridged by a nitrate anion, is reported. The metal ions within the binuclear species are hexacoordinate with different distorted environments. One nickel site, Ni1, has as a compressed octahedral geometry, whereas the other nickel site, Ni2, has a geometry closer to a square pyramid due to the presence of a long metal–ligand bond length. A study of the magnetic properties showed that the intradimer exchange coupling is larger than the interdimer coupling due to differences in the metal–ligand intra‐ and interdimer bond lengths, as confirmed by broken‐symmetry DFT calculations. Wave‐function‐based calculations allowed analysis of both the nature and the magnitude of the magnetic anisotropy of the two Ni sites. The Ni1 and Ni2 sites have, respectively, easy and hard axes of magnetization that are almost orthogonal. Magnetostructural correlations showed that the hard axis of magnetization of Ni2 is due to its geometry, which is closer to square‐pyramidal despite the hexacoordination. On the other hand, the easy axis of magnetization of the Ni1 site is a result of the compressed octahedral geometry. [ABSTRACT FROM AUTHOR]

We describe here an efficient synthesis of both diastereomers of cyclic β,γ-diamino acids starting from L-glutamic acid, based on the Blaise reaction. We show that by changing the protecting group, we can access either the five-memberedring lactam, which can be used as a β-amino acid, or the sixmembered-ring lactam, as a γ-amino acid. We also discovered an interesting kinetic resolution during the synthesis that allowed easier separation of diastereomers. The products can be easily used in peptide synthesis, and a tetramer with alternating trans cyclic γ-amino acid and AIB (2-aminoisobutyric acid) residues was synthesized. [ABSTRACT FROM AUTHOR]

We report that triflic acid, a strong Brønsted acid, is a very powerful alternative to FeCl3 to mediate the hydroarylation of N−Ac indoles, which delivers regioselectively 3-arylindolines, 3,3-spiroindolines or 2-arylindolines. Mechanistic explorations point towards the existence of a highly electrophilic intermediate by simultaneous activation of the acetyl and of the C2=C3 bond by protons. [ABSTRACT FROM AUTHOR]

Abstract: [Rh2(Esp)2] (Esp=α,α,α′,α′‐tetramethyl‐1,3‐benzenedipropionate) is a well‐established catalyst for intra‐ and intermolecular C(sp)3−H bond amination. We have prepared and isolated complex I, [Rh2(Esp)2(NHTces)2]2−, where the catalyst bears sulfonamidate ligands (−NHTces=−NHSO3CH2CCl3) as nitrogen sources in the coordination sphere of the rhodium centre. The possibility for light activation instead of chemical activation of the [Rh2(Esp)2] catalyst and complex I is demonstrated using [Ru(bpy)3]2+ as the photosensitizer. The oxidation of the two dinuclear Rh complexes occurs through two distinct pathways. On one hand, [Rh2(Esp)2] is oxidized in a bimolecular reaction with the RuIII species formed after excitation of the photosensitizer in the presence of an electron acceptor. In contrast, the lower oxidation potential of complex I allows for its oxidation to occur directly from the excited state of the photosensitizer, helped by ion‐pair formation between the negatively charged complex I with [Ru(bpy)3]2+. The charge‐separated state of the oxidized complex I/reduced photosensitizer had a lifetime of 50 μs. [ABSTRACT FROM AUTHOR]

In this paper, we describe the synthesis, characterization, and stability studies of new FeII complexes prepared with the ligand N,N'-dimethyl-N,N'-bis(4-nitropyridin-2-ylmethyl)ethane-1,2-diamine (L4²NO2). The properties of these complexes were probed by magnetic, spectroscopic, and electrochemical techniques and compared with those of the parent complexes prepared with the unsubstituted ligand N,N'-dimethyl-N,N'-bis(pyridin-2-ylmethyl)ethane-1,2-diamine (BPMEN or L4²). The para functionalization of the pyridine moieties with π-accepting nitro groups increases the ligand-field strength and the Lewis acidity of the metal center without altering the stability of the complex. [ABSTRACT FROM AUTHOR]

Herein, we report a mechanistic exploration of the unusual FeCl3-mediated hydroarylation of N-Ac indoles. Electron density topology analysis of a crystal, in situ IR monitoring, Hammett and Taft studies as well as DFT computations allowed us to determine that activation of acetyl with FeCl3 and of the C2=C3 bond with a proton is involved. [ABSTRACT FROM AUTHOR]

To access the benzofuro[3,2-b]indoline scaffold of the natural product phalarine, we planned an NIS-mediated oxidative coupling of an N-acetyltryptamine derivative and a phenol. To control the regioselectivity of benzofuroindoline formation, the phenol was appended, before the cyclisation, at the 2-position of the indole ring through an optimised gram-scale C-H arylation. The indole nucleus was indeed oxidised at its 3- position, however, the cyclisation did not occur through the phenol but through the acetamide and a 4',5'-dihydrospiro- [indole-3,6'-[1,3]oxazine] was obtained instead of the benzofuro- [3,2-b]indoline scaffold of the natural product. [ABSTRACT FROM AUTHOR]

A series of three short oligomers (di-, tri-, and tetramers) of cis-2-(aminomethyl)cyclobutane carboxylic acid, a γ-amino acid featuring a cyclobutane ring constraint, were prepared, and their conformational behavior was examined spectroscopically and by molecular modeling. In dilute solutions, these peptides showed a number of low-energy conformers, including ribbonlike structures pleated around a rarely observed series of intramolecular seven-membered hydrogen bonds. In more concentrated solutions, these interactions defer to an organized supramolecular assembly, leading to thermoreversible organogel formation notably for the tripeptide, which produced fibrillar xerogels. In the solid state, the dipeptide adopted a fully extended conformation featuring a one-dimensional network of intermolecularly H-bonded molecules stacked in an antiparallel sheet alignment. This work provides unique insight into the interplay between inter- and intramolecular H-bonded conformer topologies for the same peptide template. [ABSTRACT FROM AUTHOR]

Because of the emergence of new viruses, the need for new antiviral broad-spectrum compounds remains important. In this context, herein the synthesis of C-nucleosides, structurally close to ribavirin, a nucleoside presenting various biological activities and used until now particularly for its broad-spectrum antiviral properties, is reported. The compounds were designed in order to increase their stability and the number of hydrogen bond donor or acceptor in comparison to ribavirin, and to investigate the role of the carboxamide group on the biological activity. The efficient synthesis of 11 C-nucleosides is based on an indium-mediated alkynylglycosylation as the key step, followed by the construction of the triazole heterocycle. Amidation was performed with primary and secondary amines in yields up to 85%. An analogue nucleoside with a triazole without carboxamide group was also prepared in order to compare its activity. Finally, the carboxamide group was moved to the N-1 triazole position to mimic ribavirin. [ABSTRACT FROM AUTHOR]

One of the fundamental and intriguing aspects of life is the homochirality of the essential molecules. In this field, the absolute asymmetric synthesis of α-amino acids is a major challenge. Herein, we report access, by chemical means, to tertiary α-amino acid derivatives in up to 96 % ee without using any chiral reagent. In our strategy, the dynamic axial chirality of tertiary aromatic amides is frozen in a crystal and is responsible for the stereoselectivity of the subsequent steps. Furthermore, we could control the configuration of the final product by manually sorting and selecting the initial crystals. Based on vibrational circular dichroism studies, we could rationalize the observed stereoselectivity. [ABSTRACT FROM AUTHOR]

We have synthesized and fully characterized a photochromic zinc complex with a terphenylthiazole-based ligand with a salen-like cavity. The solution stability of the complex was found to be greatly dependent on the state of the photochromic ligand and an interesting photo-triggered release and uptake of zinc ions was found as well as monitored by its fluorescence. The contrasting stability difference of the zinc complex between its two isomeric states was rationalized by DFT calculations. [ABSTRACT FROM AUTHOR]

The magnetic properties of the pentacoordinate [MII(Me4cyclam)N3]+ (Me4cyclam=tetramethylcyclam; N3=azido; M=Ni, Co) complexes were investigated. Magnetization and EPR studies indicate that they have an easy plane of magnetization with axial anisotropy parameters D close to 22 and greater than 30 cm−1 for the Ni and Co complexes, respectively. Ab initio calculations reproduced the experimental values of the zero-field splitting parameters and allowed the orientation of the anisotropy tensor axes with respect to the molecular frame to be determined. For M=Ni, the principal anisotropy axis lies along the Ni−Nazido direction perpendicular to the Ni(Me4cyclam) mean plane, whereas for M=Co it lies in the Co(Me4cyclam) mean plane and thus perpendicular to the Co−Nazido direction. These orientations match one of the possible solutions experimentally provided by single-crystal cantilever torque magnetometry. To rationalize the geometry and its impact on the orientation of the anisotropy tensor axis, calculations were carried out on model complexes [NiII(NCH)5]2+ and [CoII(NCH)5]2+ by varying the geometry between square pyramidal and trigonal bipyramidal. The geometry of the complexes was found to be the result of a compromise between the electronic configuration of the metal ion and the structure-orienting effect of the Me4cyclam macrocycle. Moreover, the orientation of the anisotropy axes is mainly dependent on the geometry of the complexes. [ABSTRACT FROM AUTHOR]

Abstract: Two new head-to-head cyclobutane photodimers have been obtained in single stereoisomeric form by irradiation of 5-phenyl- and 6-phenyluracils in acetone solution. While the latter substrate gives a cis–anti–cis adduct, the former provides, for the first time in a solution phase reaction, a cis–syn–cis photodimer as the only product. [Copyright &y& Elsevier]

By using complementary experimental techniques and first-principles theoretical calculations, magnetic anisotropy in a series of five hexacoordinated nickel(II) complexes possessing a symmetry close to C2 v, has been investigated. Four complexes have the general formula [Ni(bpy)X2] n+ (bpy=2,2′-bipyridine; X2=bpy ( 1), (NCS−)2 ( 2), C2O42− ( 3), NO3− ( 4)). In the fifth complex, [Ni(HIM2-py)2(NO3)]+ ( 5; HIM2-py=2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1 H-imidazolyl-1-hydroxy), which was reported previously, the two bpy bidentate ligands were replaced by HIM2-py. Analysis of the high-field, high-frequency electronic paramagnetic resonance (HF-HFEPR) spectra and magnetization data leads to the determination of the spin Hamiltonian parameters. The D parameter, corresponding to the axial magnetic anisotropy, was negative (Ising type) for the five compounds and ranged from −1 to −10 cm−1. First-principles SO-CASPT2 calculations have been performed to estimate these parameters and rationalize the experimental values. From calculations, the easy axis of magnetization is in two different directions for complexes 2 and 3, on one hand, and 4 and 5, on the other hand. A new method is proposed to calculate the g tensor for systems with S=1. The spin Hamiltonian parameters ( D (axial), E (rhombic), and gi) are rationalized in terms of ordering of the 3 d orbitals. According to this orbital model, it can be shown that 1) the large magnetic anisotropy of 4 and 5 arises from splitting of the eg-like orbitals and is due to the difference in the σ-donor strength of NO3− and bpy or HIM2-py, whereas the difference in anisotropy between the two compounds is due to splitting of the t2g-like orbitals; and 2) the anisotropy of complexes 1- 3 arises from the small splitting of the t2g-like orbitals. The direction of the anisotropy axis can be rationalized by the proposed orbital model. [ABSTRACT FROM AUTHOR]

A method to extend the scope of the aza-Piancatelli reaction between 2-furylcarbinols and anilines is depicted. We found that 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) is the solvent of choice for this transformation, as it outcompetes the usual solvents in terms of rate and yield. Side reactions and other issues raised by the title reaction are prevented, thereby providing an avenue to complex molecules that were previously inaccessible. Lewis acidity studies and computations were carried out to unveil the role of HFIP. Based on these results, we propose that HFIP is, in fact, acting as a Lewis acid and that its acidity can be enhanced when combined with a calcium(II) salt. [ABSTRACT FROM AUTHOR]

A short synthesis of all four stereoisomers of 3-amino-2-oxetanecarboxylic acid (oxetin) is described. The oxetane core is built using a Paternò-Büchi photochemical [2 + 2] cycloaddition; from the key intermediates, complementary resolution protocols provide access to enantiomerically pure oxetin and epi-oxetin on gram-scale. [ABSTRACT FROM AUTHOR]

Copper (II) complexes synthesized from the products of condensation of S-methyl- and S-benzyldithiocarbazate with 2,5-hexanedione (SMHDH2 and SBHDH2 respectively) have been characterized using various physicochemical (elemental analysis, molar conductivity, magnetic susceptibility) and spectroscopic (infrared, electronic) methods. The structures of SMHDH2, its copper (II) complex, CuSMHD, and the related CuSBHD complex as well as a pyrrole byproduct, SBPY, have been determined by single crystal X-ray diffraction. In order to provide more insight into the behaviour of the complexes in solution, electron paramagnetic resonance (EPR) and electrochemical experiments were performed. Antibacterial activity and cytotoxicity were evaluated. The compounds, dissolved in 0.5% and 5% DMSO, showed a wide range of antibacterial activity against 10 strains of Gram-positive and Gram-negative bacteria. Investigations of the effects of efflux pumps and membrane penetration on antibacterial activity are reported herein. Antiproliferation activity was observed to be enhanced by complexation with copper. Preliminary screening showed Cu complexes are strongly active against human breast adenocarcinoma cancer cell lines MDA-MB-231 and MCF-7. [ABSTRACT FROM AUTHOR]

We synthesized in a few steps both diastereomers of orthogonally protected β,γ-diamino acids starting from l-phenylalanine or l-tryptophan. These final compounds are interesting building blocks for peptide synthesis and foldamer chemistry. The key step is a Blaise reaction performed under ultrasound conditions. [ABSTRACT FROM AUTHOR]

With the rising interest in asymmetric catalysis promoted by earth-abundant elements, a chiral ligand will undoubtedly be the most valuable unit of the catalyst. The first proof of concept of the use of a multitask chiral ligand in an asymmetric assisted tandem catalysis protocol that successively combines metallo- and organocatalytic processes is reported herein. In this protocol, the chiral ligand of the newly designed rare-earth catalyst of the first reaction is converted into a novel chiral organocatalyst for the second transformation by the simple addition of HCl. The observation of some enantioinduction in the tandem sequence-alkyne hydroamination followed by enantioselective Friedel-Crafts alkylation-confirms the relay of the chiral N, N, N′, N′-tetradentate ligand and the importance of its pyridylmethylamine scaffold. [ABSTRACT FROM AUTHOR]

We report the FeCl3-mediated direct addition of electron-rich arenes to the C2-position of electrophilic N-Ac indoles under mild conditions (room temperature, air). No functional group is required on the arene nucleophile: one of its C–H bonds is added to the C2=C3 double bond of the indole nucleus in a Friedel–Crafts-type reaction. This dearomatisation process delivered a broad range of C2-arylated indolines. [ABSTRACT FROM AUTHOR]

Short segments of zigzag single-walled carbon nanotubes (SWCNTs) were obtained from a calixarene scaffold by using a completely new, simple and expedited strategy that allowed fine-tuning of their diameters. This new approach also allows for functionalised short segments of zigzag SWCNTs to be obtained; a prerequisite towards their lengthening. These new SWCNT short segments/calixarene composites show interesting behaviour in solution. DFT analysis of these new compounds also suggests interesting photophysical behaviour. Along with the synthesis of various SWCNTs segments, this approach also constitutes a powerful tool for the construction of new, radially oriented π systems. [ABSTRACT FROM AUTHOR]

This paper demonstrates the engineering and tuning of Ising-type magnetic anisotropy in trigonal bipyramidal Co(ii) complexes. Here, we predict that employing a ligand that forces a trigonal bipyramidal arrangement and has weak equatorial σ-donating atoms, increases (in absolute value) the negative zero field splitting parameter D. With these considerations in mind, we used a sulfur containing ligand (NS3iPr), which imposes a trigonal bipyramidal geometry to the central Co(ii) ion with long equatorial Co–S bonds. The resulting complex exhibits a larger anisotropy barrier and a longer relaxation time in comparison to the complex prepared with a nitrogen containing ligand (Me6tren). [ABSTRACT FROM AUTHOR]

Cyclic homologated amino acids are important building blocks for the construction of helical foldamers. N-aminoazetidine-2-carboxylic acid (AAzC), an aza analogue of trans-2-aminocyclobutanecarboxylic acid ( tACBC), displays a strong hydrazino turn conformational feature, which is proposed to act as an 8-helix primer. tACBC oligomers bearing a single N-terminal AAzC residue were studied to evaluate the ability of AAzC to induce and support an 8-helix along the oligopeptide length. While tACBC homooligomers assume a dominant 12-helix conformation, the aza-primed oligomers preferentially adopt a stabilized 8-helix conformation for an oligomer length up to 6 residues. The (formal) single-atom exchange at the N terminus of a tACBC oligomer thus contributes to the sustainability of the 8-helix, which resists the switch to a 12-helix. This effect illustrates atomic-level programmable design for fine tuning of peptide foldamer architectures. [ABSTRACT FROM AUTHOR]

The idea of a possible control of metal ion properties by constraining the coordination sphere geometry was introduced by Vallee and Williams with the concept of entasis, which is frequently postulated to be at stake in metallobiomolecules. However, the interactions controlling the geometry at metal centers remain often elusive. In this study, the coordination properties toward copper ions--CuII or CuI--of a geometrically constrained glycoligand centered on a sugar scaffold were compared with those of an analogous ligand built on an unconstrained alkyl chain. The sugar-centered ligand was shown to be more preorganized for CuII coordination than its open-chain analogue, with an unusual additional stabilization of the CuI redox state. This preference for CuI was suggested to arise from geometric constraints favoring an optimized folding of the glycoligand minimizing steric repulsions. In other words, the CuI d10 species is stabilized by valence shell electron pair repulsion (VSEPR). This idea was rationalized by a theoretical noncovalent interactions (NCI) analysis. The cumulative effects of weak forces were shown to create an efficient buckle as in a hook-and-loop fastener, and fine structural features within the glycoligand reduce repulsive interactions for the CuI state. This study emphasizes that monosaccharide platforms are appropriate ligand backbones for a delicate geometric control at the metal center, with a network of weak interactions within the ligand. This structuration availing in glycoligands makes them attractive for metallic entasis. [ABSTRACT FROM AUTHOR]

An anthracene group was linked to the N-heterocyclic carbene moiety of a M71-SIPr-type Ru complex. The tagged complex thus obtained was immobilized by charge-transfer interactions to a 2,4,7-trinitrofluoren-9-one-grafted passivated silica. The immobilized complex proved to be an efficient olefin metathesis catalyst and was reused five times in a multisubstrate olefin metathesis procedure. [ABSTRACT FROM AUTHOR]

A terthiazole-based molecular switch associating 6p electrocyclization, excited state intramolecular proton transfer (ESIPT), and strong metal binding capability was prepared. The photochemical and photophysical properties of this molecule and of the corresponding nickel and copper complexes were thoroughly investigated by steady-state and ultrafast absorption spectroscopy and rationalized by DFT/TDDFT calculations. The switch behaves as a biphotochrome with time-dependent photochemical outcome and displays efficient ESIPT-based fluorescence photoswitching. Both photochemical reactions are suppressed by nickel or copper metalation, and the main factors contributing to the quenching of the electrocyclization are discussed. [ABSTRACT FROM AUTHOR]

The first cluster containing acc was prepared via supramolecular self-assembly. This Cu(II) cluster traps Na+, as shown in the solid state by the crystal structure and in solution by ESI-MS. Further characterisations revealed a ferromagnetic intracluster exchange and an irreversible reduction with a rapid intracluster electron transfer. [ABSTRACT FROM AUTHOR]

Azide-tagged CuI-NHC reacts in an 'auto-click' process to furnish complexes functionalized by 1,2,3-triazoles bearing diverse substituents. The resulting CuI complexes are amenable to further transmetallation to AuI. The whole strategy proceeds with mild conditions and constitutes an efficient entry to functionalised metal-NHCs with biorelevant moieties. [ABSTRACT FROM AUTHOR]

A catalytic enantioselective synthesis of α-arylaminocyclobutanones from racemic α-hydroxycyclobutanone and a selection of N-alkylanilines has been established, via a tandem condensation/keto-enol tautomerization process reminiscent of the Amadori and Heyns rearrangements. [ABSTRACT FROM AUTHOR]

The conformational equilibrium and thermodynamic parameters of cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene ( 1a) and its trans derivative 1c are presented. Irradiation of both compounds was carried out by using 365 nm light, which affects the cis/ trans isomerisation process, whereas irradiation with 405 nm light preferentially promotes the formation of the cyclised product. Prolonged irradiation of 1a at 365 nm leads to the formation of a new derivative showing photochromic properties. Evidence for the formation of the novel derivative is presented, and details of its photochromic properties were investigated; a tentative mechanism has also been proposed. [ABSTRACT FROM AUTHOR]

Four model compounds and four dipeptides containing N-aminoazetidinecarboxylic acid (AAzC) and a particular stereoisomer of 2-aminocyclobutanecarboxylic acid (ACBC) were studied to establish their solution state conformational preferences, particularly regarding the ability of AAzC to induce a three-center hydrogen-bonded folding feature known as a "hydrazino turn". On the basis of IR and NMR experiments, supported by molecular modeling, the AAzC residue adopted a trans configuration amenable to the formation of a cyclic eight-membered hydrogen bond conformation in solution, in all cases studied. The implication of the heterocyclic nitrogen atom of AAzC in the trans-like structure was demonstrated via a refined ¹H--15N HMBC experiment giving exploitable data at natural 15N isotopic abundance, providing unprecedented evidence for the solution state hydrazino turn conformation. The predominance of this secondary structural feature depended on the configuration of the neighboring ACBC residue in the dipeptides: while the trans-ACBC derivatives prefer the hydrazino turn, the cis-ACBC derivatives may also populate low-energy 10-membered hydrogen-bonded ring structures. X-ray diffraction analysis of three compounds confirmed the presence of a solid state hydrazino turn in two cases, with geometries similar to those deduced from the solution state studies, but in the third compound, no intramolecular hydrogen-bonding feature was in evidence. [ABSTRACT FROM AUTHOR]

Abstract: All four stereoisomers of 2-(aminomethyl)cyclobutane-1-carboxylic acid have been prepared starting from a single chirally derivatized unsaturated γ-lactam. A photochemical [2+2] cycloaddition reaction of this compound with ethylene was employed to create the four-membered ring exclusively with a cis ring configuration. The two diastereoisomers were separated conveniently by chromatography then the chiral appendage replaced by the more convenient Boc protecting group. Base-mediated lactam hydrolysis provided each of the cis target structures as single enantiomers. An efficient, tandem epimerization/hydrolysis protocol was applied to a carboxamide derivative of each cis compound, to furnish the corresponding trans compounds as single isomers, for the first time. [Copyright &y& Elsevier]

Abstract: Centimetre-size single crystals of LiCoO2 were successfully grown using a floating-zone method associated with an image furnace. A high-pressure oxygen atmosphere and a relatively small growth speed were found necessary to prevent the formation of impurity phases in the grown crystal. A single crystal with a reduced amount of lithium was obtained by means of the chemical de-lithiation process using as grown LiCoO2 single crystal as the starting material. Growth conditions together with magnetic and structural properties of these crystals are discussed here. [Copyright &y& Elsevier]

[Display omitted] • Photochemical access to a functionalized bicyclo[3.2.0]heptane skeleton. • Preparation of a constrained analogue of glutamic acid. • Use of an oxazolidinone for chiral resolution of an amino acid. • High stereoselectivity in a Bucherer-Bergs reaction. A concise method is reported for the synthesis of 2-aminobicyclo[3.2.0]heptane-2,7-dicarboxylic acid, a close analogue of the glutamate receptor ligand LY354740, in both enantiomeric forms. The strategy features the creation of the core structure at the start of the synthesis via a photochemical [2 + 2] cycloaddition reaction, an efficient resolution procedure using a chiral oxazolidinone, and requires only minimal purification of the synthetic intermediates. The title compounds showed little or no affinity for the mGlu2 and mGlu3 receptors. [ABSTRACT FROM AUTHOR]