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Through a combination of X-ray and neutron total scattering and Empirical Potential Structure Refinement (EPSR) we explore the prenucleation structures of saturated aqueous magnesium sulfate. The atomistic model we present reveals a system characterised by isolated octahedral aquo magnesium species Mg(H2O)6, magnesium sulfate pairs (Mg(H2O)5SO4) and extended clusters built from corner-sharing MgO6 and SO4 polyhedra. Many of these features are directly observed in the crystal structures of the known solid form hydrates, including isolated polyhedra, corner sharing chains and rings, and it is only for the extended 3D polyhedral networks of the lower hydrates (mono- & di-) that no proto structures are observed in 2M solution. Looking at the average first solvation shell of the sulfate anion we see a complex and flexible environment that commonly includes water molecules brought into proximity by a coordinated hydrated magnesium. What emerges is a high probability that 10 water molecules will be observed in a combined tetrahedral/octahedral arrangement with a further 7 taking up more dispersed positions giving an average coordination of 17. The tendency for ions to aggregate into clusters allows areas of bulk water to exist that exhibit subtle differences in structure to that of pure water.

p class="Abstract"span lang="EN-GB"Herein, we present a highly diastereoselective method to furnish acyclic 3-amino-1,5-diol derivatives using a tandem double-aldol-Tishchenko protocol (italicdr/italicup togt;99:1) using a butanone derived sulfinylimine. In most cases only 1 diastereomer predominates, from a possible 16. The reaction is also regioselective. In addition, the highly challenging cyclobutanone and 3-pentanone derivatives are also amenable to a double-aldol-Tishchenko reaction, although theitalicdr/italicvalues are modest. Despite that, clean single diastereoisomers can be isolated, which should prove very useful in medicinal chemistry and other areas. Detailed DFT calculations support the observed stereoselectivities in all cases, providing a rationale for the excellentitalicdr/italicvalues in the butanone series and the moderate values for the 3-pentanone class.o:p/o:p/span/p.

An open-cage fullerene incorporating phosphorous ylid and carbonyl group moieties on the rim of the orifice can be filled with gases (H2 , He, Ne) in the solid state, and the cage opening then contracted in situ by raising the temperature to complete an intramolecular Wittig reaction, trapping the atom or molecule inside. Known transformations complete conversion of the product fullerene to C60 containing the endohedral species. As well as providing an improved synthesis of large quantities of 4 He@C60 , H2 @C60 , and D2 @C60 , the method allows the efficient incorporation of expensive gases such as HD and 3 He, to prepare HD@C60 and 3 He@C60 . The method also enables the first synthesis of Ne@C60 by molecular surgery, and its characterization by crystallography and 13 C NMR spectroscopy.

This work is aimed at providing a systematic and comprehensive analysis of the anomeric effect exerted by the isothiocyanato (NCS) group taking the xylopyranose ring as a scaffold because enhanced effects have been detected in that ring-bearing halogen and pseudohalogen substituents. To this end, both α- and β-anomers of tri-O-acetoxypyranosyl-D-xylose have been prepared and thoroughly characterized. The axial preference of the isothiocyanato group reflects a dominant anomeric effect, whose origin could be determined through DFT calculations with identification of the stereoelectronic interactions as revealed by Natural Bond Orbital (NBO) analysis. In this way, this study expands the repertoire of groups biasing the conformation and reactivity of monosaccharides and related heterocycles.

A dichotomy between the additions of organolithiums and lithium amides to cyclobutenediones is described wherein the former give carbonyl addition products while the latter induce ring opening by enone cleavage via O- to C-lithium transfer.This distinct mode of ring scission gives access to 2-oxobut-3-enamides and tetrasubstituted furans.

The discovery of novel catalytic materials is predicated on understanding contemporary synthetic processes. With this fundamental knowledge in place it becomes possible to modify the final material with subtle changes to the synthesis process. In this vein, hierarchical materials, formed by the addition of a mesoporogen within the hydrothermal synthesis, have attracted a significant amount of attention due to their catalytic benefits over analogous microporous species. In this work we monitor the hydrothermal synthesis in situ of a hierarchical and a microporous aluminophosphate, for the first time, combining total scattering and pairwise distribution function data. In doing so we observe the local formation of the species, and the longer range crystallisation processes concurrently.

AZD9898 has previously been used as a candidate for a potentially active pharmaceutical ingredient. AZD9898 form A hydrate was discovered during development and this form undergoes dehydration upon heating to give anhydrous form B. Further heating results in a solid–solid phase transition to a new anhydrous phase, form C. This study reports the crystal structures of form A, B, and C obtained by heating the single crystal of form A in situ on the diffractometer which establish the dehydration and solid–solid phase transition mechanisms. The dehydration from form A hydrate to form B anhydrous is an isostructural process while the solid–solid phase transition from form B to form C requires major structural changes. The relevant thermal profiles and vapour sorption behaviour of these forms are also reported in this study.

Luminescent lanthanide metal-organic frameworks (Ln-MOFs) have been shown to exhibit relevant optical properties of interest for practical applications, though their implementation still remains a challenge. To be suitable for practical applications, Ln-MOFs must be not only water stable but also printable, easy to prepare, and produced in high yields. Herein, we design and synthesize a series of

Ninhydrin bis-acetals give access to 8-ring lactones, benzocyclo-butenes and spirocyclic orthoanhydrides through photoextrusion and tandem photoextrusion reactions. Syntheses of fimbricalyxlactone B, isoshihunine and numerous biologically-relevant heterocycles show the value of the methods, while TA-spectroscopy and TD-DFT studies provide mechanistic insights on their wavelength dependence.

Luminescent lanthanide metal-organic frameworks (Ln-MOFs) have been shown to exhibit relevant optical properties of interest for practical applications, though their implementation still remains a challenge. To be suitable for practical applications, Ln-MOFs must be not only water stable but also printable, easy to prepare, and produced in high yields. Herein, we design and synthesize a series of m CB-Eu y Tb 1-y (y = 0-1) MOFs using a highly hydrophobic ligand mCBL1: 1,7-di(4-carboxyphenyl)-1,7-dicarba-closo-dodecaborane. The new materials are stable in water and at high temperature. Tunable emission from green to red, energy transfer (ET) from Tb3+ to Eu3+, and time-dependent emission of the series of mixed-metal m CB-Eu y Tb 1-y MOFs are reported. An outstanding increase in the quantum yield (QY) of 239% of mCB-Eu (20.5%) in the mixed mCB-Eu0.1Tb0.9 (69.2%) is achieved, along with an increased and tunable lifetime luminescence (from about 0.5 to 10 000 μs), all of these promoted by a highly effective ET process. The observed time-dependent emission (and color), in addition to the high QY, provides a simple method for designing high-security anticounterfeiting materials. We report a convenient method to prepare mixed-metal Eu/Tb coordination polymers (CPs) that are printable from water inks for potential applications, among which anticounterfeiting and bar-coding have been selected as a proof-of-concept., This work was financially supported by the MINECO (PID2019-106832RB-I00), MICINN through the Severo Ochoa Program for Centers of Excellence for the FUNFUTURE (CEX2019-000917-S, MDM-2017-0767, and SEV-2017-0706 projects), grant RTI2018-098027-B-C21 funded by MCIN/AEI/10.13039/501100011033 and by ERDF A way of making Europe and the Generalitat de Catalunya (2017/SGR/1720 and SGR2017-1289). Z.L. is enrolled in the UAB Ph.D. program and acknowledges the China Scholarship Council (CSC) for his Ph.D. grant (201808310071)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

The reaction of 2,6-diformyl-4-methylphenyl disulfide with [Ni(tn)3]Cl2 (tn = 1,3-diaminopropane), in methanol and in the presence of NaBPh4 resulted in the isolation of [Ni2(L1)](DMF)2(BPh4)2 (I), (L1 = 15,95-dimethyl-3,7,11,15-tetraaza-1,9(1,3)-dibenzenacyclohexadecaphane-2,7,10,15-tetraene-12,92-bis(thiolate). This reaction represents a 2-electron solvent assisted reduction of the disulfide bond to form two thiolate ligands where methanol is converted to formaldehyde and the two nickel centres remained in the + 2 oxidation state. The crystal structure of I showed the two nickel(II) atoms are bridged by two thiolates in a binuclear Ni2S2 core inside of a macrocyclic framework. The IR spectrum showed a band at 1625 cm−1, assigned to the imine ν(C [dbnd]N) stretch of the macrocyclic ligand, and bands at 734, 706 cm−1, are assigned to the tetraphenylborate counter ions. This is the first example of solvent assisted S–S bond cleavage being used to prepare a dicompartmental macrocyclic complex.

The stereoselective formation of 5 contiguous chiral centers in a single pot reaction is demonstrated using an aldol, aldol-Tishchenko reaction of N-tert-butyl sulfinimines. One diastereoisomer (from 32 possibilities) predominates, and a series of cyclic and acyclic 3-amino-1,5-diol derivatives are synthesized in good yields (up to 80%) and excellent diastereoselectivities (up to >98:2 dr). Investigations support two reversible aldol steps, and multiple intermediates which are funnelled through a remarkably selective, irreversible, Tishchenko reduction, in a Curtin-Hammett phenomenon. DFT calculations using a disolvated (THF) model reveal the factors controlling stereoselectivity in the final irreversible Tishchenko step.

The cubane ring has received intense attention as a 3D benzene isostere and scaffold. Mono- and 1,4-disubstituted cubanes are well-described. Here we report a practical procedure for a direct radical-mediated chlorocarbonylation process initially reported by Bashir-Hashemi, to access a range of 2-substituted 1,4-cubanedicarboxylic ester derivatives. A subsequent regioselective ester hydrolysis to give fully differentiated 1,2,4-trisubstituted cubanes is demonstrated.

Protein-carbohydrate interactions are implicated in many biochemical/biological processes that are fundamental to life and to human health. Fluorinated carbohydrate analogues play an important role in the study of these interactions and find application as probes in chemical biology and as drugs/diagnostics in medicine. The availability and/or efficient synthesis of a wide variety of fluorinated carbohydrates is thus of great interest. Here, we report a detailed study on the synthesis of monosaccharides in which the hydroxy groups at their 4- and 6-positions are replaced by all possible mono- and difluorinated motifs. Minimization of protecting group use was a key aim. It was found that introducing electronegative substituents, either as protecting groups or as deoxygenation intermediates, was generally beneficial for increasing deoxyfluorination yields. A detailed structural study of this set of analogues demonstrated that dideoxygenation/fluorination at the 4,6-positions caused very little distortion both in the solid state and in aqueous solution. Unexpected trends in α/β anomeric ratios were identified. Increasing fluorine content always increased the α/β ratio, with very little difference between regio- or stereoisomers, except when 4,6-difluorinated.

The highly strained cubane system is of great interest as a scaffold and rigid linker in both pharmaceutical and materials chemistry. The first electrochemical functionalisation of cubane by oxidative decarboxylative ether formation (Hofer–Moest reaction) was demonstrated. The mild conditions are compatible with the presence of other oxidisable functional groups, and the use of flow electrochemical conditions allows straightforward upscaling., Just go with the flow: Oxidative anodic decarboxylation of cubane carboxylic acids leading to cubyl ethers is described. This first direct electrochemical functionalisation at the cubane system is chemoselective and scalable, with yields of up to 60 % (see scheme).

In line with the postulated intermediacy of aminoxazoles derived from small sugars toward the direct assembly of nucleoside precursors, we show here a potential prebiotic scenario where aminoxazolines might have also played further roles as complexing and/or sequestering agents of other primeval blocks, namely amino acids. To this end, a bis-aminoxazoline derivative, generated from dihydroxyacetone and cyanamide, gives rise to stable co-crystal forms with dicarboxylic amino acids (Asp and Glu), while ionic interactions owing to proton transfer are inferred from spectroscopic data in aqueous solution. The structure of a 1:2 aminoxazoline: aspartic acid complex, discussed in detail, was elucidated by X-ray diffractometry. Optimized geometries of such ionic structures with bulk aqueous solvation were assessed by DFT calculations, which disclose preferential arrangements that validate the experimental data. Peripherally, we were able to detect in a few cases amino acid dimerization (i.e. dipeptide formation) after prolonged incubation with the bis-aminoxazole derivative. A mechanistic simulation aided by computation provides some predictive conclusions for future explorations and catalytic design.

3-nitro-2H-chromenes and derivatives are compounds with diverse biological activity, among them, new 2-glyco-3-nitro-2H-chromenes have been prepared by one-pot oxa-Michael-Henry-dehydration reactions between carbohydrate-derived nitroalkenes and several salicylaldehydes, using a minimal amount of solvent and DBU as catalyst. The antiproliferative activity of these new compounds has been evaluated against a panel of six human solid tumor cell lines, and compared to pharmacological reference compounds, finding that their activities are in the low micromolar range and that some of them are more effective than the standards.

The endohedral fullerene CH4@C60, in which each C60 fullerene cage encapsulates a single methane molecule, has been synthesised for the first time. CH4 is the largest molecule, with the greatest number of atoms, to have been encapsulated in C60 to date. The key orifice contraction step, a photochemical desulfinylation of an open fullerene, was successfully completed, even though it is significantly inhibited by the presence of the endohedral molecule. The 13C NMR resonance for the cage nuclei in CH4@C60 is deshielded by Dd = +0.52 ppm relative to C60. The crystal structure of the nickel(II) octaethylporphyrin / benzene solvate shows no significant distortion of the carbon cage, relative to the C60 analogue, and shows the methane hydrogens as a shell of electron density around the central carbon, indicative of the quantum nature of the methane, existing in a set of quantised rotational-translational states at 100 K. The 1H and 13C spin-lattice relaxation times (T1) for endohedral methane havebeen measured. The 1H T1 values are similar to those observed in the gas phase, also indicating that methane is freely rotating inside the C60 cage. The 1H relaxation rate constant T1 -1 increases with increasing temperature and suggests a significant spin-rotation contribution to the relaxation. The successful synthesis of CH4@C60 opens a route to endofullerenes incorporating larger guest molecules than those encapsulated previously.

The chrysophaentins are a newly discovered natural product family displaying promising anti-infective activity. Herein we describe an approach to chrysophaentin F that uses an array of metal catalysed coupling reactions (Cu, Ni, Pd, W, Mo) to form key bonds.

This work was financially supported by MICINN (PID2019-106832RB-I00, PGC2018-093863-B-C21), MICINN through the Severo Ochoa Program for Centers of Excellence for the FUNFUTURE (CEX2019-000917-S and MDM-2017-0767 projects) and the Generalitat de Catalunya (2017/SGR/1720 and SGR2017-1289). D. Ch.-L. acknowledges funding by project no. PGC2018-102047-B-I00 (MCIU/AEI/FEDER, UE). J. Soldevila-Sanmartin is enrolled in the UAB PhD program and acknowledges the PIF pre-doctoral Fellowship from the UAB for his pre-doctoral grant (no. 19032/2). E. R. acknowledges computer resources, technical expertise and assistance provided by the CSUC. We thank Prof. D. Ruiz and Dr C. Roscini for the quantum yield measurements. The present publication is dedicated to Prof. Elena Shubina on the occasion of her 70th birthday., Incorporation of one or two o-carborane moieties at the backbone of the pyrazole ring was achieved by lithiation and nucleophilic addition onto the corresponding 3,5-dimethyl-1-(2-toluene-p-sulfonyloxyethyl)pyrazole. Two monosubstituted carboranyl pyrazoles (L2 and L3) and one disubstituted carboranyl pyrazole (L4) were synthesized and fully characterized. All new compounds, and the corresponding monosubstituted phenylderivative (L1) behave as N-type ligands upon coordination with CuI to afford different polynuclear Cu(I) compounds 1-4. Compounds 1-4 were fully characterized and their molecular structures were determined by X-ray diffraction. It is noteworthy that whereas the pyrazolylphenyl ligand L1, without o-carborane, provides a 1D coordination polymer (1), ligands containing carborane, L2-L3, affords 0D coordination compounds 2 and 3, and disubstituted carboranyl pyrazole ligand L4 gives rise to a 3D coordination polymer. The photoluminescence behaviour of compounds 1-4 has been investigated in the solid state and by TDDFT calculations for molecular compounds 2 and 3. Complex 2 exhibits blue emission with a maximum at 483 nm and a high fluorescence quantum yield of 66.5%. According to TDDFT calculations the emission occurs from LUMO to HOMO-1 and HOMO-2 and deexcitation could be described as cluster-centred excited state of d-s transition in origin. This result contradicts previous studies of scarce tri-coordinated rhombohedral Cu(I) clusters, where it was assumed the origin of their emissions is (X + M)LCT in nature by analogy with tetra-coordinated rhombohedral Cu(I) clusters. Complex 3 exhibits very weak emission (Phi(F) of 5%) in the green region with a maximum at 517 nm, which according to TDDFT is through a (CC)-C-3 state. Calculations also show that, upon excitation, 3 suffers a notable distortion resulting in the total cleavage of the Cu4I4 framework. This cleavage could be the cause of the relatively large Stokes shift observed for 3. To the best of our knowledge, this is the first time that such behaviour is observed for this type of octahedral compounds. Additionally, the 1D polymer 1 exhibits weak fluorescence emission in the orange range with a maximum at 609 nm and a remarkable Stokes shift, whereas the 3D polymer 4 exhibits a similar emission to compound 2, with a moderate quantum yield (FF of 13.7%)., Spanish Government European Commission PID2019-106832RB-I00 PGC2018-093863-B-C21, MICINN through the Severo Ochoa Program for Centers of Excellence for the FUNFUTURE CEX2019-000917-S MDM-2017-0767, Generalitat de Catalunya 2017/SGR/1720 SGR2017-1289, MCIU/AEI/FEDER, UE PGC2018-102047-B-I00, UAB 19032/2

Protein-carbohydrate interactions are implicated in many biochemical/biological processes that are fundamental to life and to human health. Fluorinated carbohydrate analogues play an important role in the study of these interactions and find application as probes in chemical biology and as drugs/diagnostics in medicine. The availability and/or efficient synthesis of a wide variety of fluorinated carbohydrates is thus of great interest. Here, we report a detailed study on the synthesis of monosaccharides in which the hydroxy groups at their 4- and 6-positions are replaced by all possible mono- and difluorinated motifs. Minimization of protecting group use was a key aim. It was found that introducing electronegative substituents, either as protecting groups or as deoxygenation intermediates, was generally beneficial for increasing deoxyfluorination yields. A detailed structural study of this set of analogues demonstrated that dideoxygenation/fluorination at the 4,6-positions caused very little distortion both in the solid state and in aqueous solution. Unexpected trends in α/β anomeric ratios were identified. Increasing fluorine content always increased the α/β ratio, with very little difference between regio- or stereoisomers, except when 4,6-difluorinated.

A new route to azocines and benzoazocines from furopyridinones is described through a photochemically induced [1,3]-sigmatropic rearrangement. The method gives access to these 8-membered nitrogen heterocycles from dimethyl squarate in four stages and with excellent atom economy by sequencing thermal and photochemical ring expansion steps under continuous flow.

The analysis and interpretation of the pair distribution function (PDF), as derived from total scattering measurements, is still seen by many as a technique confined to central synchrotron and neutron facilities. This situation has begun to change with a rising visibility of total scattering experiments reported in mainstream scientific journals and the modification of an increasing number of laboratory diffractometers. However, the rigor required during data reduction and the complexities of data interpretation mean the technique is still very far from being routine. Herein, we report the first application of a large area curved image plate system based on a Rigaku SPIDER (R-AXIS RAPID II) equipped with an Ag tube for collecting data amenable to high quality PDF refinement/modeling of crystalline, amorphous, and liquid samples. The advantages of such a system are the large Q range available without scanning (routinely in excess of 20 Å−1) and the inherent properties of an image plate detector (single photon sensitivity, large dynamic range [1.05 × 106], and effectively zero noise). Data are collected and structural models refined for a number of standard materials including NIST 640f silicon for which a Rwp ≤ 0.12 value was obtained with data collected in 60 min (excluding background measurements). These and other data are discussed and compared to similar examples in the literature.

Density functional theory computations have elucidated the mechanism and origins of stereoselectivity in McGlacken's aldol-Tishchenko reaction for the diastereoselective synthesis of 1,3-amino alcohols using Ellman's t-butylsulfinimines as chiral auxiliaries. Variations of stereochemical outcome are dependent on the nature of the ketone starting materials used, and the aspects leading to these differences have been rationalized. The intramolecular hydride transfer step is the rate- and stereochemistry-determining step, and all prior steps are reversible.

Polymorphatin A was reported as a constituent of Marchantia polymorpha in 2007 following much speculation as to its likely existence as a natural product. Interest was rekindled when a claimed total synthesis revealed inconsistencies in spectral data between the synthetic sample and those reported for the natural product. Herein we describe a total synthesis of polymorphatin A, supported by an X-ray crystal structure of its trimethyl ether, that adds further intrigue as our synthetic sample displays physical and spectral characteristics that differ from data provided in the aforementioned reports.

Oxidations with molecular oxygen are ubiquitous processes in biological systems where cofactor-dependent enzymes activate either oxygen or hydrogen peroxide to induce multichannel pathways. In stark contrast, such slow atmospheric oxidations are seldom harnessed in chemical synthesis and analysis. The present study unveils an unusual aerobic oxidation of a mesoionic dipole leading easily to a more functionalized skeleton. Although the synthetic scope has not been explored, two key considerations emerge from this transformation, as it proceeds with complete diastereoselection and could be successfully extrapolated to structurally related mesoionic chirons without racemization. How this oxidation actually occurs proved to be puzzling from the onset and only high-level computation reveals a cascade transformation, whose results reconcile theory and experiment. Hopefully, the mechanistic insights should help us to understand better the autoxidative reactions of organic molecules.

The first synthesis of 3-deoxy-3-fluoro-l-fucose is presented, which employs a d- to l-sugar translation strategy, and involves an enzymatic oxidation of 3-deoxy-3-fluoro-l-fucitol. Enzymatic activation (FKP) and glycosylation using an α-1,2 and an α-1,3 fucosyltransferase to obtain two fluorinated trisaccharides demonstrates its potential as a novel versatile chemical probe in glycobiology.

Biofuels are considered sustainable and renewable alternatives to conventional fossil fuels. Biobutanol has recently emerged as an attractive option compared to bioethanol and biodiesel, but a significant challenge in its production lies in the separation stage. The current industrial process for the production of biobutanol includes the ABE (acetone-butanol-ethanol) fermentation process from biomass; the resulting fermentation broth has a butanol concentration of no more than 2 wt% (the rest is essentially water). Therefore, the development of a cost-effective process for separation of butanol from dilute aqueous solutions is highly desirable. The use of porous materials for the adsorptive separation of ABE mixtures is considered a highly promising route, as these materials can potentially have high affinities for alcohols and low affinities for water. To date, zeolites have been tested toward this separation, but their hydrophilic nature makes them highly incompetent for this application. The use of metal-organic frameworks (MOFs) is an apparent solution; however, their low hydrolytic stabilities hinder their implementation in this application. So far, a few nanoporous zeolitic imidazolate frameworks (ZIFs) have shown excellent potential for butanol separation due to their good hydrolytic and thermal stabilities. Herein, we present a novel, porous, and hydrophobic MOF based on copper ions and carborane-carboxylate ligands

Herein, we report a one-pot process that marries mechanistically distinct, traditional cross-coupling reactions with C–H functionalization using the same precatalyst. The reactions proceed in yields of up to 95%, in air, and require no extraneous ligand. The reactions are thought to be facilitated by harnessing the substrate quinoline as an N-ligand, and evidence of the palladium–quinoline interaction is provided by 1H-15N HMBC NMR spectroscopy and X-ray crystallographic structures. Application of the methodology is demonstrated by the quick formation of fluorescent, π-extended frameworks.

N,N′-Diphenyl-3,7-diazacyclooctane and structurally related N,N′-diphenylbispidine derivatives react with silver(I) ions in a high-yielding C–C coupling reaction to produce dication–diradical species, with the silver ions serving a double function both as template and as an oxidant. The resulting bis(benzidino)phane derivatives are persistent organic radicals, stable for several months in solution as well as in the solid state, at room temperature and above, as well as being exposed to the atmosphere. The molecular structure features a double-decker cyclophane motif, stabilized by intramolecular π-dimerization of two delocalized benzidinium radical segments. Intermolecular π-dimers are formed in the solid state. Graphical abstract Electronic supplementary material The online version of this article (10.1007/s00706-018-2298-4) contains supplementary material, which is available to authorized users.

A one-pot procedure for preparing a series of chiral imines by direct condensation of D-glucamine with 2-hydroxyacetophenones is described. Under conventional acetylation an unexpected mixture of two different peracetylated molecules is obtained, one with an open enamine structure, and the other incorporating an N-acetyl-1,3-oxazolidine into the acyclic skeleton. Surprisingly, both molecules coexist within the crystal's unit cell, as inferred from single-crystal X-ray analysis of a 5-bromo-substituted aryl derivative. Moreover, the 1,3-oxazolidine ring exists as rotational conformers (E,Z) owing to the restricted rotation around the N-acetyl bond. The equilibrium involving imine and enamine structures has been assessed in detail, providing in addition linear free-energy relationships between the tautomerization constants (KT) and the electronic effect of the substituents.

This paper describes a mechanistic study, with the interplay of experiment and theory, on the cycloadditions of a bicyclic mesoionic 1,3-dipole versus a series of representative symmetrical (1-phenyl-1H-pyrrole-2,5-dione and dimethyl maleate) and asymmetrical [(E)-(2-nitrovinyl)benzene, acrylonitrile, and but-3-en-2-one] olefinic dipolarophiles. These results allow a comparative analysis with monocyclic dipoles and open further avenues to structurally diversified heteroatom-rich rings. The unichiral version of the bicyclic dipole leads to adducts containing up to five chiral centers, whose formation proceeds with high levels of facial stereoinduction in reactions involving bulky dipolarophiles. The second and largest part of this study provides a theoretical interrogation on the pericyclic mechanism with DFT-methods [M06-2X/6-311++G(d,p)]. In order to get further mechanistic insights, we have also explored charge transfers between reaction partners using NBO analysis, which satisfactorily justifies the stereochemical outcome.

The Lucite Alpha process is the predominant technology for the preparation of acrylics. This two-stage process involves the palladium-catalysed formation of methyl propanoate from ethene, CO, and methanol, followed by the oxidative formylation of methyl propanoate into methyl methacrylate. A range of bis-1,2-disubstituted aminomethylferrocenes has been prepared and characterised. These complexes serve as precursors to a variety of bulky ferrocenylmethyldiphosphanes that, in turn, function as ligands in the palladium-catalysed process. We describe the crystal structures of five ligand precursors and provide a rationale for their design. In situ catalyst testing on palladium complexes derived from ferrocenylphosphanes demonstrates that these are highly selective (&gt, 99.5%) catalysts for the formation of methyl propanoate from ethene, CO, and methanol and have turnover numbers exceeding 50,000. This article credits those researchers who worked on this project in the early days, who received little or no credit for their achievements and endeavours.

An asymmetric synthesis of α-spiro-δ-lactam via organocascade reaction from easily accessible starting materials is reported. The catalytic sequence undergoes enantioselective Michael addition of β-ketoamide to α,β-unsaturated aldehyde catalysed by a secondary amine catalyst, followed by hemiaminal annulation. Optically enantiopure compounds with two contiguous stereogenic centres are obtained in good yields and excellent selectivities (up to >20:1 dr and up to >99% ee).

We report a combined experimental and computational study on the cycloadditions of bicyclic 1,3-thiazolium-4-olates, derived from thiazolidin-2-thiones, with asymmetrically-substituted acetylenes. These results provide further mechanistic insights into the above dipolar cycloadditions and enable an unequivocal characterization by NMR spectroscopy of regiochemical patterns as previous derivatives had substituents at both C-2 (in the dipole) and C-6 (in products). Accordingly, new dihydrothiazolopyrid-2-ones have been obtained from a thioisomunchnone lacking substitution at C-2. With the aim of assessing the steric hindrance as well as the facial stereoselection induced by a bulky group on the Si face (relative to C-7a) of the mesoionic heterocycle, a chiral thioisomunchnone has also been obtained along with the resulting optically active thiazolopyridones. A computational study of these particular cycloadditions, largely based on an NBO analysis, allowed us to evaluate the influence of substituents on intermolecular steric repulsions, charge transfers, as well as solvent effects.

The white complexes, [TaOCl3(OPPh3)2], [TaOCl3(L-L)] (L-L = 1,10-phenanthroline, 2,2′-bipyridyl, Ph2P(O)CH2P(O)Ph2, Ph2P(O)CH2CH2P(O)Ph2 and o-C6H4(P(O)Ph2)2), have been prepared from TaCl5, O(SiMe3)2 and the ligands in anhydrous CH2Cl2 solution. The corresponding yellow [TaSCl3(OPPh3)2] and [TaSCl3(L-L)] were made similarly using S(SiMe3)2. The complexes have been characterised by microanalysis, IR and NMR (1H, 31P{1H}) spectroscopy. X-ray crystal structures have been obtained for [TaOCl3(1,10-phen)], [TaSCl3(1,10-phen)], [TaOCl3{o-C6H4(P(O)Ph2)2}], [TaSCl3(OPPh3)2], [TaSCl3{Ph2P(O)CH2CH2P(O)Ph2}] and [TaSCl3(MeCN)2], which all contain mer-chlorines and with the neutral ligands trans to O/Cl or S/Cl. The structure of the Ta(V) dimer [Cl2S(1,10-phen)Ta(µ-O)Ta(1,10-phen)SCl2], formed by trace hydrolysis, is also reported. Comparisons between the complexes of TaOCl3 and TaSCl3 and their niobium analogues are discussed.

Fluorinated carbohydrates have been employed as probes for fundamental studies of protein–carbohydrate interactions, but also in the development of mechanism-based enzyme inhibitors. There is a continuing demand for novel fluorinated carbohydrate probes. Whereas most examples so far involved monodeoxyfluorinated sugars, multiply deoxyfluorinated sugars have gained much interest. Here we report the synthesis and characterisation of novel vicinal dideoxy-difluorinated D-galactoses with fluorination at the 3,4-positions, and at the 2,3-positions, the latter in both the pyranose and furanose forms. This includes a successful pyranose-into-furanose isomerisation protocol.

International audience; Fluorinated proline derivatives have found diverse applications in areas ranging from medicinal chemistry over structural biochemistry to organocatalysis. Depending on the stereochemistry of monofluorination at the proline 3- or 4-position, different effects on the conformational properties of proline (ring pucker, cis/ trans isomerization) are introduced. With fluorination at both 3- and 4-positions, matching or mismatching effects can occur depending on the relative stereochemistry. Here we report, in full, the syntheses and conformational properties of three out of the four possible 3,4-difluoro-l-proline diastereoisomers. The yet unreported conformational properties are described for (3 S,4 S)- and (3 R,4 R)-difluoro-l-proline, which are shown to bias ring pucker and cis/ trans ratios on the same order of magnitude as their respective monofluorinated progenitors, although with significantly faster amide cis/ trans isomerization rates. The reported analogues thus expand the scope of available fluorinated proline analogues as tools to tailor proline's distinct conformational and dynamical properties, allowing for the interrogation of its role in, for instance, protein stability or folding.

There is an increasing interest in investigating how polyfluorination of carbohydrates modifies their physical and biological properties. An example that has caught much attention is 2,3,4-trideoxy-2,3,4-trifluoroglucose. Four syntheses of this compound have been reported, which are either low yielding or long (13 or more steps). We report a 6-step synthesis of 2,3,4-trideoxy-2,3,4-trifluoroglucose starting from levoglucosan. The solution-phase structure of an intermediate, 1,6-anhydro-2,4-dideoxy-2,4-difluoroallose, features a rare example of a bifurcated F center dot center dot center dot H(O)center dot center dot center dot F hydrogen bond and is compared to its crystal structure.

The palladium(II) chlorostibine complex [PdCl2(SbMe2Cl)2]2 has a dimeric structure in the solid state, stabilized by hyper-coordination at the Lewis amphoteric Sb centers. Reaction with 8 equiv of MeLi forms [Pd4(μ3-SbMe3)4(SbMe3)4], whose structure comprises a tetrahedral Pd(0) core with four terminal SbMe3 ligands and four μ3-SbMe3 ligands, one capping each triangular Pd3 face. Density functional theory calculations, supported by energy decomposition analysis and the natural orbitals for chemical valence scheme, highlight significant donor and acceptor orbital contributions to the bonding between both the terminal and the bridging SbMe3 ligands and the Pd4 core.