7,7-Dimethyl-4a-(3-methyl-2-buten­yl)-2-oxo-4a,5,6,7-tetra­hydro-2H-chromen-4-yl benzoate

An intra­molecular Claisen-like cyclization of ethyl 2-acet­oxy-4,4-dimethyl-1-(3-methyl­but-2-en­yl)cyclo­hex-2-enecarboxylate followed by dialkyl­ation yielded the bicyclic title compound, C23H26O4. In both of the fused six-membered rings exist fragments of four atoms which are planar, whereas the remaining two atoms deviate by up to 0.682 (3) Å on one side of the plane of the ring containing an O atom and by up to 0.415 (3) Å on opposite sides of the other ring. The dihedral anglebetween the planar fragments of the six-membered rings is 41.76 (10)

Iron-Catalyzed Cycloisomerization and C−C Bond Activation to Access Non-canonical Tricyclic Cyclobutanes: In memory of Professor Klaus Hafner

Cycloisomerizations are powerful skeletal rearrangements that allow the construction of complex molecular architectures in an atom-economic way. We present here an unusual type of cyclopropyl enyne cycloisomerization that couples the process of a cycloisomerization with the activation of a C−C bond in cyclopropanes. A set of substituted non-canonical tricyclic cyclobutanes were synthesized under mild conditions using [(Ph₃P)₂Fe(CO)(NO)]BF₄ as catalyst in good to excellent yields with high levels of stereocontrol

identification of a reversible EC-mechanism

Bu4N[Fe(CO)3(NO)] displays unique catalytic properties in electron-transfer catalysis such as in allylic substitutions, hydrosilylation, transesterifications, or carbene transfer chemistry. Herein we present a detailed spectroelectrochemical investigation of this complex that unravels an interesting electrochemical–chemical transformation in which two parts of [Fe(CO)3(NO)]− are oxidized and undergo a disproportionation in the presence of CO to [Fe(CO)5] and [Fe(CO)2(NO)2]. Upon re-reduction the former two complexes regenerate [Fe(CO)3(NO)]− to about 85

Chemoenzymatic Synthesis of Triazololactams Structurally Related to Pancratistatin

Four tricyclic lactams that structurally resemble alkaloids with the pancratistatin skeleton were synthetized from bromobenzene by a chemoenzymatic strategy. The sequence involved enzymatic dihydroxylation, efficient stereodirected oxidation of double bonds, inter- or intramolecular Huisgen cycloaddition, and a solvent-free cyclization. The complex structures were obtained in high chemical and optical purity and may be good candidates for biological testing.Fil: de la Sovera, Victoria. Universidad de la República. Facultad de Química. Departamento de Química Orgánica; UruguayFil: Suescun, Leopoldo. Universidad de la República. Laboratorio de Cristalografía, Estado Sólido y Materiales; UruguayFil: Bellomo Peraza, Ana Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias ; ArgentinaFil: González, David. Universidad de la República. Facultad de Química. Departamento de Química Orgánica; Urugua

Mechanistic insights into selective oxidation of polyaromatic compounds using RICO chemistry

Ruthenium‐ion‐catalyzed oxidation (RICO) of polyaromatic hydrocarbons (PAHs) has been studied in detail using experimental and computational approaches to explore the reaction mechanism. DFT calculations show that regioselectivity in these reactions can be understood in terms of the preservation of aromaticity in the initial formation of a [3+2] metallocycle intermediate at the most‐isolated double bond. We identify two competing pathways: C−C bond cleavage leading to a dialdehyde and C‐H activation followed by H migration to the RuOx complex to give diketones. Experimentally, the oxidation of pyrene and phenanthrene has been carried out in monophasic and biphasic solvent systems. Our results show that diketones are the major product for both phenanthrene and pyrene substrates. These diketone products are shown to be stable under our reaction conditions so that higher oxidation products (acids and their derivatives) are assigned to the competing pathway through the dialdehyde. Experiments using 18O‐labelled water do show incorporation of oxygen from the solvents into products, but this may take place during the formation of the reactive RuO4 species rather than directly during PAH oxidation. When the oxidation of pyrene is carried out using D2O, a kinetic isotope effect (KIE) is observed implying that water is involved in the rate‐determining step leading to the diketone products

Oxidative Cleavage of Alkene C=C Bonds Using a Manganese Catalyzed Oxidation with H2O2 Combined with Periodate Oxidation

A one-pot multi-step method for the oxidative cleavage of alkenes to aldehydes/ketones under ambient conditions is described as an alternative to ozonolysis. The first step is a highly efficient manganese catalyzed epoxidation/cis-dihydroxylation of alkenes. This step is followed by an Fe(III) assisted ring opening of the epoxide (where necessary) to a 1,2-diol. Carbon-carbon bond cleavage is achieved by treatment of the diol with sodium periodate. The conditions used in each step are not only compatible with the subsequent step(s), but also provide for increased conversion compared to the equivalent reactions carried out on the isolated intermediate compounds. The described procedure allows for carbon-carbon bond cleavage in the presence of other alkenes, oxidation sensitive moieties and other functional groups; the mild conditions (r.t.) used in all three steps make this a viable general alternative to ozonolysis and especially for use under flow or continuous batch conditions

The Polycyclic Polyprenylated Acylphloroglucinol Antibiotic PPAP 23 Targets the Membrane and Iron Metabolism in Staphylococcus aureus

Recently, a series of endo-type B polycyclic polyprenylated acylphloroglucinols (PPAP) derivatives with high antimicrobial activities were chemically synthesized. One of the derivatives, PPAP 23, which showed high antimicrobial activity and low cytotoxicity, was chosen for further investigation of its bactericidal profiles and mode of action. PPAP 23 showed a better efficacy in killing methicillin resistant Staphylococcus aureus (MRSA) and decreasing the metabolic activity of 5-day-old biofilm cells than vancomycin. Moreover, S. aureus did not appear to develop resistance against PPAP 23. The antimicrobial mechanism of PPAP 23 was investigated by RNA-seq combined with phenotypic and biochemical approaches. RNA-seq suggested that PPAP 23 signaled iron overload to the bacterial cells because genes involved in iron transport were downregulated and iron storage gene was upregulated by PPAP 23. PPAP 23 affected the membrane integrity but did not induce pore formation; it inhibited bacterial respiration. PPAP 23 preferentially inhibited Fe–S cluster enzymes; it has a mild iron chelating activity and supplementation of exogenous iron attenuated its antimicrobial activity. PPAP 23 was more effective in inhibiting the growth of S. aureus under iron-restricted condition. The crystal structure of a benzylated analog of PPAP 23 showed a highly defined octahedral coordination of three PPAP ligands around a Fe (3+) core. This suggests that PPAPs are generally capable of iron chelation and are able to form defined stable complexes. PPAP 23 was found to induce reactive oxygen species (ROS) and oxidative stress. Fluorescence microscopic analysis showed that PPAP 23 caused an enlargement of the bacterial cells, perturbed the membrane, and dislocated the nucleoid. Taken together, we postulate that PPAP 23 interacts with the cytoplasmic membrane with its hydrophobic pocket and interferes with the iron metabolism to exert its antimicrobial activity in Staphylococcus aureus

Magnetite and Metal-Impregnated Magnetite Catalysts in Organic Synthesis: A Very Old Concept with New Promising Perspectives

Magnetite is a well-known material, with the impregnation of transition metals onto its surface being a very old protocol for preparing catalysts. However, only recently, the combination of both, magnetite and impregnation protocols, have been recognized as a powerful methodology to prepare catalysts. The impregnation protocol, of nearly all transition metals in the magnetite surface, has rendered the first generation of catalysts. These simple catalysts have been used in a very broad range of organic transformations. Thus, simple imine derivative formation or unknown reactions such as the direct cross β-alkylation of primary alcohols, through dehydrogenation, oxidation, addition, hydrogen autotransfer, and multicomponent reactions has been accomplished using these catalysts. In most cases, these catalysts could be just isolated by magnetic decantation and reused several times without a detrimental effect on the initial results. In some cases, the study of the surface of the catalyst by means of several surface characterization techniques has permitted to determine the real species involved in the process and their structural changes within the reaction cycles. Furthermore, the post-modification of the catalysts by reduction or oxidation of the immobilized metal, or by the addition of ligands, has enlarged the applicability of this type of catalysts.This work was supported by the current Spanish Ministerio de Economía y Competitividad (CTQ2011-24151) and by the University of Alicante