Gram scale synthesis of the C(1)–C(9) fragment of amphidinolide C

An allylic cis-epoxide prepared by Sharpless asymmetric epoxidation was transformed in nine steps and 41% overall yield to the cyclization precursor 4 via a key one carbon homologation. Cobalt-catalyzed aerobic oxidative cyclization of 4 gave the trans-THF in 94% yield at gram scale. Subsequent manipulations, including a Still–Gennari olefination, Sharpless asymmetric dihydroxylation, Corey–Fuchs alkynylation, and Kazmaier hydrostannylation provided the fully functionalized C(1)–C(9) fragment 2 suitable for cross-coupling. The sequence is readily scalable and provides gram quantities of 2.     

Studies towards the synthesis of superstolide A. Synthesis and stereochemical assignment of the C(21)C(26) fragment of superstolide A

An asymmetric synthesis of the C(21)C(26) fragment of superstolide A is described. A fragment, corresponding to a reductive ozonolysis product of superstolide, was also prepared. Comparison of spectroscopic and optical properties of the corresponding fragment obtained by degradation of natural superstolide A allowed the confirmation of the stereochemistry of the natural product.     

Total synthesis of the ionophore antibiotic X-206. Studies relevant to the stereoselective synthesis of the C(17)–C(26) synthon.

A stereoselective synthesis of the keto-aidehyde 4, which embodies the structural features of the C(17)–C(26) section of the polyether X-206, is described.     

Studies on the syntheses of the aplysiatoxins: Synthesis of a selectively-protected form of the C27 – C30 (dihydroxybutanoate) moiety of oscillatoxin A

A protected form of (R)-3,4-dihydroxybutanoic acid bearing a benzyl protecting group at the C₄ hydroxyl and a dimethylthexylsilyl protecting group at the C₃ hydroxyl was synthesized via a selective Ag(l)-mediated monobenzylation of (R)-methyl 3,4-dihydroxybutanoate. An alternative synthetic route from a chiral allylic ether was successful but problematic. The acid could be cleanly coupled to a model for the C₃ – C₁₁ moiety of the aplysiatoxins.     

Synthesis and biological activity of chromones annelated at the C(7)–C(8) bond with heterocycles (review)

Published data on the synthesis of chromones annelated at the C(7)–C(8) bond with nitrogen-, oxygen-, and sulfur-containing heterocycles of various sizes, including those with two and three heteroatoms, are discussed. Data on the biological activity of chromone derivatives isolated from natural sources and obtained synthetically are presented.     

Synthesis of a C(9)—C(13) fragment of acutiphycin from levoglucosan

Alkylation of (1R,2R,5R)-2-benzenesulfonyl-6,8-dioxa-bicyclo[3.2.1]octan-3-one, which is accessible from levoglucosan, afforded (1R,2R,5R)-2-benzenesylfonyl-2,4,4-trimethyl-6,8-dioxabicyclo[3.2.1]octan-3-one. This was further converted into (1S,2R,3S,5R)-2,4,4-trimethyl-6,8-dioxabicyclo[3.2.1]octan-3-ol representing the C9—C13 fragment of acutiphycin molecule.     

Unconventional Pathway in the Gas-Phase Synthesis of 9H-Fluorene (C13H10) via the Radical–Radical Reaction of Benzyl (C7H7) with Phenyl (C6H5)

The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five-membered ring—9H-fluorene (C₁₃H₁₀)—is produced isomer-specifically in the gas phase by reacting benzyl (C₇H₇⋅) with phenyl (C₆H₅⋅) radicals in a pyrolytic reactor coupled with single photon ionization mass spectrometry. The unconventional mechanism of reaction is supported by theoretical calculations, which first produces diphenylmethane and unexpected 1-(6-methylenecyclohexa-2,4-dienyl)benzene intermediates (C₁₃H₁₂) accessed via addition of the phenyl radical to the ortho position of the benzyl radical. These findings offer convincing evidence for molecular mass growth processes defying conventional wisdom that radical-radical reactions are initiated through recombination at their radical centers. The structure of 9H-fluorene acts as a molecular building block for complex curved nanostructures like fullerenes and nanobowls providing fundamental insights into the hydrocarbon evolution in high temperature settings.     

Stereoselective synthesis of the middle (C10–C17) and right (C18–C30) segments and their coupling to complete a formal synthesis of the polyether antibiotic salinomycin

The middle (C10–C17) and right (C18–C30) segments of the polyether antibiotic salinomycin were stereoselectively synthesized from D-glucose, D-mannitol and ethyl L-lactate. Coupling of the two segments followed by construction of the bisketal ring system gave the C10–C30 segment, which was already converted to salinomycin by Kishi.     

CN and CC Bond Formations in the Thermal Reactions of "Bare" Ni(NH(2) )(+) with C(2) H(4) : Mechanistic Insight on the Metal-Mediated Hydroamination of an Unactivated Olefin

Strike! While pure ammonia is out of luck, Ni(NH(2) )(+) gets one strike after another at the "ethylene bowling championship". In fact, Ni(NH(2) )(+) is so effective that no pin, not even at the neighboring lane, is safe from it.     

On the Reaction Mechanism of the Rhodium‐Catalyzed Arylation of Fullerene (C60) with Organoboron Compounds in the Presence of Water

Density functional theory (DFT) calculations were carried out to study the reaction mechanism of the Suzuki–Miyaura rhodium‐catalyzed hydroarylation of fullerene (C₆₀) by phenylboronic acid in the presence of water. As found experimentally, our results confirm that addition of the phenyl group and the hydrogen atom in C₆₀ occurs at the [6,6] bond. The rate‐determining step corresponds to the simultaneous transfer of a hydrogen atom from a water molecule to C₆₀ and the recovery of the active species. The use of 2‐phenyl‐1,3,2‐dioxaborinane and the 4,4,5,5‐tetramethyl‐2‐phenyl‐1,3,2,‐dioxaborolane instead of phenylboronic acid as organoborate agents does not lead to great modifications of the energy profile. The possible higher steric hindrance of 4,4,5,5‐tetramethyl‐2‐phenyl‐1,3,2,‐dioxaborolane should not inhibit its use in the hydroarylation of C₆₀. Overall, we show how organoboron species arylate C₆₀ in rhodium‐based catalysis assisted by water as a source of protons.     

Synthesis of Pyrazoles by the Condensation of C(α)- and Trianions with Esters

In addition to our previous papers^2,3 on the preparation of pyrazoles from the C(α), N-dianions of phenylhydrazones and C(α), N, N-trianions of hydrazones, we wish to report preliminary results on (I) the preparation and condensation of methylhydrazone dianions with methyl benzoate followed by acid cyclization, (II) the condensation of the dianions of phenylhydrazone with methylformate, and the preparation and condensation of the trianions of cyclopentanone (III) and α - tetralone (IV) hydrazones.     

An alternate route to the C(7)C(13)subunit of erythronolide B via A hydropyran template

Conversion of (R)-3-benzyloxy-2-methylpropionaldehyde (4) to the erythronolide B C(7)C(13) subunit 13 in 15% overall yield is described. Chelation-controlled carbonyl additions and a dioxanone-to-dihydropyran Claisen rearrangement are key steps.     

Enantioselective Catalytic Crotylboration Based Syntheses of the C(7)–C(18(20)) Fragments of Polyketides Isolated from Streptomyces gramineus

A general modular enantioselective synthetic approach to the C(7)–C(18) and the C(7)–C(20) fragment belonging to E-492, actinofuranone A, and JBIR-108 was developed. The crucial synthetic step relies on highly enantioselective crotylboration of aldehydes catalyzed by a chiral TRIP PA giving rise to highly enantioenriched terminal alkenes (86 and 88 % ee on the preparative scale). The alkenes were subsequently converted into the title products. Further important synthetic steps included Ru-catalyzed alkene cross-metathesis and Suzuki coupling reactions. The approach consists of five synthetic steps starting from easily available aldehydes and other reaction partners.     

Reinvestigate the C2Π-X2Π(0,0) Band of AgO

The \begin{document}$ C^2\Pi $\end{document}-\begin{document}$ X^2\Pi $\end{document}(0, 0) band of AgO has been reinvestigated by laser induced fluorescence spectroscopy with a spectral resolution of \begin{document}$ \sim $\end{document}0.02 cm\begin{document}$ ^{-1} $\end{document}. The AgO molecules are produced by discharging a gas mixture of O\begin{document}$ _2 $\end{document}/Ar with silver needle electrodes in a supersonic jet expansion. By employing a home-made narrowband single longitude mode optical parametric oscillator (SLM-OPO) as the laser source, high-resolution spectra of the \begin{document}$ C^2\Pi $\end{document}-\begin{document}$ X^2\Pi $\end{document}(0, 0) band have been recorded for both \begin{document}$ ^{107} $\end{document}Ag\begin{document}$ ^{16} $\end{document}O and \begin{document}$ ^{109} $\end{document}Ag\begin{document}$ ^{16} $\end{document}O isotopologues. The spectroscopic constants of the \begin{document}$ C^2\Pi $\end{document} state are consequently determined, with the \begin{document}$ ^{109} $\end{document}Ag\begin{document}$ ^{16} $\end{document}O one being reported for the first time. The nature of the spin-orbit coupling effect in the \begin{document}$ C^2\Pi $\end{document} state is proposed to be due to state mixing with the nearby repulsive \begin{document}$ ^{4}\Sigma^{-} $\end{document} and \begin{document}$ ^{4}\Pi $\end{document} states.     

Formation of the triosmium μ-carbyne complex in the reaction of with dimethylphenylphosphine. X-ray structure of HOs3(CO)10{μ-CC(Ph)CC(Ph)Re(CO)4PMe2Ph}

The μ-acyl complex B″O

(I) reacts with PMe₂Ph to yield the allenyl-substituted μ-carbyne complex HOs₃(CO)₁₀{μ-CC(Ph)CC(Ph)Re(CO)₄PMe₂Ph} (II). Complex II has been characterized by an X-ray structural study.     

Study of the behavior of chromium(III) in potassium nitrate solutions at 25°C

Solubility in the KNO₃-Cr(NO₃)₃-H₂O system at 25°C was studied by an isothermal method. The existence of solid phases of potassium nitrate and chromium(III) nitrate nonahydrate was confirmed by constructing a phase diagram, chemical analysis, and IR spectroscopy. Crystallization of potassium nitrate from aqueous solutions was studied. Potassium nitrate does not interact with chromium(III) nitrate within the range of micro and macro concentrations. The capture of chromium(III) by KNO₃ crystals is due to adsorption and occlusion of a mother solution.     

Total synthesis of (±)-cylindricine C

A concise synthesis of (±)-cylindricine C and its C(13)-epimer is described. Starting from 1-octyne, cylindricine C and 13-epi-cylindricine C were prepared in 11% and 15% yields, respectively. The synthesis involves the preparation of the central tricyclic moiety via a radical α-iodoketone carboazidation/bis-reductive amination sequence. Inversion of the stereochemistry at C(13) and C(5) was efficiently achieved on late stage intermediates.     

Temperature dependence of the derived properties of mixtures containing chlorobenzene and aliphatic linear alkanes (C6–C12)

This article reports experimental densities, refractive indices and speeds of sound of the binary mixtures chlorobenzene?+?(n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane or n-dodecane) and speeds of sound of the ternary mixtures chlorobenzene?+?n-hexane?+?(n-undecane or n-dodecane) at 298.15?K and atmospheric pressure, over the whole concentration range. The corresponding derived properties were computed from the experimental data. The results were fitted by means of the Redlich–Kister equation for binary mixtures and the Nagata equation for ternary mixtures. A set of estimation methods were applied, and an interpretation in terms of structure and length of molecular chain of the n-alkane molecules was made.     

Simulation of the random scission of C–C bonds in the initial stage of the thermal degradation of polyethylene

We performed molecular dynamics simulations to analyze the initial stage of the thermal degradation of polyethylene, which is dominated by the random scission reaction. The simulations were initiated from structures that were taken from previously equilibrated snapshots of the amorphous polymer and of a free-standing thin film. Isolated chains were also used for comparison. Our systems were coupled to a thermal heat bath, and the effect of different coupling constants was studied. Rate of random scission increases as the strength of the temperature coupling increases. Rates of reaction are almost similar in thin films and the bulk, whereas the rates are much faster in isolated chains. Expansion of the free-standing thin film accompanies degradation, producing fragments of various sizes. Chains of higher molecular weights than the initial chains can be produced due to recombination of fragments during the expansion of thin films. The polydispersity index of the resulting fragments is higher in thin films compared to the bulk. The bonds at the low density portion of the thin films have a higher probability of being broken.