A concise three-component synthesis of α-amino esters derived from phenylglycine and phenylalanine

α-Amino esters have been synthesized using a straightforward three-component reaction among preformed or in situ-generated aromatic or benzylic organozinc reagents, primary or secondary amines and ethyl glyoxylate. The procedure, which is characterized by its simplicity, allows the concise synthesis of phenylglycine and phenylalanine derivatives.     

Synthetic Studies on 2H-Thiopyran Compounds: A Reinvestigation of the Reaction Between Benzaldehydes and Sodium Sulfide

An investigation regarding the synthesis of 2H-thiopyran compounds from substituted benzaldehydes with sodium sulfide (Na₂S·10H₂O) in aqueous ethanol was carried out. The structural elucidation of the products was performed by spectroscopic methods and in one example as X-ray crystallographic analysis. A plausible mechanistic pathway is also proposed that is entirely different from an earlier report.     

Structure revision of plakotenin based on computational investigation of transition states and spectroscopic properties

We show that the previously [Tetrahedron Lett.1992, 33, 2579] proposed structure of natural plakotenin must be revised. Recently, the total synthesis of plakotenin was achieved via an intramolecular Diels-Alder reaction from a (E,E,Z,E)-tetraene as linear precursor. Using density functional theory, the computation of the four possible transition states for this reaction shows that the previously proposed structure could only have been formed via an energetically high-lying transition state, which is very unlikely. Instead, we suggest that the structure of plakotenin corresponds to the product formed via the lowest transition state. A comparison of experimental and theoretical optical rotation, circular dichroism, and two-dimensional nuclear Overhauser enhancement spectra conclusively proves that the structure of plakotenin is the one that is suggested by the transition state computations. Moreover, the simulation of the nuclear Overhauser enhancement spectra suggests that it is most likely that the misassignment of the (1)H chemical shifts of two methyl groups has led to the wrong structure prediction in the 1992 work. The previously proposed structure of iso-plakotenin remains unaffected by our structure revision, but the structures of homo- and nor-plakotenin must also be revised. The present work shows how the total synthesis of a natural product, together with the theoretical determination of the barrier heights of the reactions involved, can be of great help to assign its structure. It appears that intramolecular Diels-Alder reactions can be modeled accurately by today's first-principles methods of quantum chemistry.     

Enhancement of poly(vinyl ester) solubility in supercritical CO2 by partial fluorination: the key role of polymer-polymer interactions

An enhancement of poly(vinyl ester) solubility in supercritical carbon dioxide (sc-CO(2)) can be achieved by decreasing the strength of the polymer-polymer interactions. To demonstrate this, a library of statistical copolymers of vinyl acetate and vinyl trifluoroacetate was synthesized by RAFT/MADIX polymerization with varying compositions at a given number-average molecular weight. These copolymers exhibited unprecedentedly low cloud-point pressures in sc-CO(2) at 40 °C compared with previously reported poly(vinyl esters). Surface tension measurements combined with a computational approach evidenced the prominent role played by polymer-polymer interactions.     

Electronic excitation energy transfer between nucleobases of natural DNA

Transfer of the electronic excitation energy in calf thymus DNA is studied by time-resolved fluorescence spectroscopy. The fluorescence anisotropy, after an initial decay starting on the femtosecond time scale, dwindles down to ca. 0.1. The in-plane depolarized fluorescence decays are described by a stretched exponential law. Our observations are consistent with one-dimensional transfer mediated by charge-transfer excited states.     

Händigkeit – leben in einer chiralen Welt

We may “live in a material world” as claimed by Madonna but we definitely evolve in a chiral one. As we are born into a chiral environment, where a lot of objects are not identical with their mirror images, we most naturally and often unconsciously adapt to it. It is only when one exchanges for example the corkscrewer by its left‐handed counterpart that we actually notice that something is not as usual. We will – supported by six practical experiments – explain to you and guide you through the fascinating world of chirality.     

The cis-bis(decanoate)tin phthalocyanine/DPPC film at the air/water interface

Films made of cis-bis-decanoate-tin(IV) phthalocyanine (PcSn10) and racemic dipalmitoylphosphatidylcholine (DPPC) are studied with compression isotherms and Brewster angle microscopy (BAM) at the air/water interface. Films enriched in PcSn10 present phase separation elliptical-shaped domains. These domains present optical anisotropy and molecular order. They are enriched in PcSn10, and the film outside these domains is enriched in DPPC, as shown in by high-angle annular dark-field transmission electron microscopy on Langmuir-Blodgett (LB) transferred films. Film collapse area and atomic force microscopy images of LB transferred films on mica indicate that the films are actually multilayers. A computational survey was performed to determine how the PcSn10 molecules prefer to self-assemble, in films basically made of PcSn10. The relative energetic stability for several dimeric assemblies was obtained, and a crystal model of the film was developed through packing and repeating the PcSn10 molecules, along the crystallographic directions of the unit cell. Our results contribute to understanding the strong interaction between PcSn10 and DPPC at the air/water interface, where even small quantities of DPPC (~1-2%) can modify the film in an important way.     

Deprotonative metalation of aromatic compounds using mixed lithium–iron combinations

The deprotonation of 2-methoxypyridine was attempted using putative (TMP)₃FeLi prepared from different iron sources. Using iodine to intercept the metalated 2-methoxypyridine, the best result was obtained from FeBr₂ (1 equiv) using THF at room temperature; nevertheless, in addition to the expected iodide, the corresponding 2,2′-dimer was obtained (86% total yield). The origin of the competitive formation of the 2,2′-dimer was not identified but mechanisms were suggested to explain its formation. It was observed that the nature of the electrophile employed to trap the 3-metalated 2-methoxypyridine has a strong impact on this dimer formation, the latter being favored using iodine (35% yield), but also benzophenone (28%), benzoyl chloride (22%), methyl iodide (27%), allyl bromide (15%), benzyl bromide (41%), and tetramethylthiuram disulphide (36%); for this reason, the yields of the expected derivatives were only 51, 15, 62, 0, <5, 18, and 0%, respectively. In contrast, using aldehydes readily led to the expected pyridine alcohols without dimerization (59% yield using 3,4,5-trimethoxybenzaldehyde and 66% yield using pivalaldehyde). 2,6-Dimethoxypyridine (in 68% yield), anisole (47%), 2,4-dimethoxypyrimidine (50% at C5 and 3% at C6), 2-fluoropyridine (64%), and thiophene (49%) were similarly converted into the corresponding alcohols after subsequent trapping with pivalaldehyde. Using iodine to trap the 2-metalated anisole did not lead to dimer formation, and 2-iodoanisole was isolated in 71% yield.