A window of opportunity : A general copper‐catalyzed C? H bond‐activation path allows arylation of heterocycles with a wide range of aryl bromides (see scheme). The reaction shows excellent regioselectivity and exhibits good functional group tolerance. The 8‐aryl xanthines exhibit fluorescence in a variety of solvents and show promise as reagents for biological imaging.
A series of N‐sulfinyl dienophiles 1c‐i has been screened in asymmetric hetero‐Diels‐Alder reactions using chiral bis(oxazoline)copper(II) and ‐zinc(II) triflates. The survey pointed out N‐sulfine 1c (R ? P(?O)(OPh)2) as the most promising N‐sulfine regarding yield and stereoselectivity (up to 97% ee). The relative configurations, and in one case the absolute configuration, of the HDA adducts were established by X‐ray analysis. 相似文献
Intelligent design : The total synthesis of the cytotoxic (?)‐FR182877 relies on 1) tandem Diels–Alder reactions to close rings A–D (see scheme), 2) a palladium‐mediated 7‐exo‐trig reaction, and 3) an iridium‐mediated isomerization followed by epimerization and stereoselective reduction.
Throw your hat in the ring : A highly diastereoselective synthesis of the ABC rings of (?)‐norzoanthamine has been achieved starting from the (?)‐Hajos–Parrish ketone (see scheme). Three asymmetric quaternary carbon centers on the C ring were constructed by a 1,4‐addition, and an intramolecular Diels–Alder reaction provided a trans‐decalin scaffold on the AB rings.
Inorganic enzyme? Ceria nanoparticles exhibit unique oxidase‐like activity at acidic pH values. These redox catalysts can be used in immunoassays (ELISA) when modified with targeting ligands (see picture; light blue and yellow structures are nanoparticles with attached ligands). This modification allows both for binding and for detection by the catalytic oxidation of sensitive colorimetric dyes (e.g. TMB).
A question of coordination mode : Two new borane compounds are prepared. They act as bifunctional ligands as illustrated by their reaction with ruthenium polyhydrides which leads to the formation of two complexes (see scheme) displaying either a δ‐agostic interaction of a η2‐B? H bond involving a trivalent boron atom or a dihydroborate ligation.
Electron by electron : β‐Diketiminato nickel(I) complex fragments are capable of activating N2 through coordination. The resulting complex can be reduced in two single‐electron steps, which further activates the N? N bond. The picture shows the structure of the singly reduced complex with μ‐η1:η1‐bound N2.
Mark us bent! The synthesis, structure, and single‐ and two‐photon spectroscopic properties of a series of pyrimidine‐based (bent‐shaped) molecules are reported. These allow structure‐property relationships and guidelines for both the development and application of TPA compounds to be derived.
Back to the grindstone : Certain crystalline complexes of gold, platinum, and vanadium undergo dramatic changes in their luminescence or their color upon grinding. The picture shows the transformation of colorless crystals of [(F5C6Au)2(μ‐1,4‐CN2C6H4)] powder from a blue‐emitting form (λmax=415 nm) to a yellow/green‐emitting form (λmax=533 nm) on grinding with a pestle. The process is reversible.
Playing the sax : The enantioselective total syntheses of (?)‐ and (+)‐decarbamoyloxysaxitoxin (doSTX) and (+)‐saxitoxin (STX) are reported. A new methodology was developed for the synthesis of STXs, featuring discriminative reduction of the nitro group and N? O bond in nitroisoxazolidine.
Taking shortcuts : A remarkably short and high‐yielding asymmetric total synthesis of (?)‐oseltamivir takes advantage of organocatalysis and single‐pot domino operations. The target, known as the drug Tamiflu, is prepared efficiently in a short time, and also its derivatives can be synthesized effectively.
Discriminating elimination : A new method for the synthesis of methyl‐branched trisubstituted Z olefins, a structural motif in many polyketides with anticancer activity, relies on an ?OH‐induced decarboxylative Grob‐type fragmentation (see scheme; Ms=mesyl). The starting materials are β‐mesyloxy lactones with a quaternary α center, which are prepared by aldol reactions in a diastereo‐ and enantioselective manner.
Preferred protonation : Does electrospray ionization mass spectrometry produce gas‐phase or liquid‐phase structures? The preferred protonation site in p‐aminobenzoic acid depends upon the medium, and the structure of its conjugate acid varies with the solvent used during spraying.
Y not? A unique, three‐coordinate Y‐shaped bis(silyl)platinum(II) complex was isolated and characterized (see structure; C light gray, N blue, Si pink, Pt dark gray). DFT studies on a model system shed light on the nature of this unusual coordination mode for platinum(II).
Oxidizing gold? A gold(I)/gold(III) catalytic cycle is essential for the first oxidative cross‐coupling reaction in gold catalysis. By using Selectfluor for gold(I) oxidation, this chemistry reveals the synthetic potential of incorporating gold(I)/gold(III) catalytic cycles into contemporary gold chemistry and promises a new area of gold research by merging powerful gold catalysis and oxidative metal‐catalyzed cross‐coupling reactions.
The structural features of polycyclic polyether natural products can, in some cases, be traced to their biosynthetic origin. However in case that are less well understood, only biosynthetic pathways that feature dramatic, yet speculative, epoxide‐opening cascades are proposed. We summarize how such epoxide‐opening cascade reactions have been used in the synthesis of polycyclic polyethers (see scheme) and related natural products.
Bulking up: The thermal barrier to rearrangement of a vic‐disulfoxide is significantly increased through steric buttressing about the (O)S? S(O) bond. Whereas the title compounds represent the most thermally stable vic‐disulfoxides known to date, they also undergo a novel photomediated epimerization at room temperature (see scheme).
Ring leader : PtCl2 catalyzes intramolecular cyclization of o‐isopropyl or o‐benzyl aryl alkynes to give substituted indene derivatives with good yields and high selectivity. This reaction appears to proceed through an sp3 C? H activation and 1,4‐hydrogen migration pathway (see scheme).
