5 research outputs found

    Ruthenium-Catalyzed Self-Coupling of Primary and Secondary Alcohols with the Liberation of Dihydrogen

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    The dehydrogenative self-condensation of primary and secondary alcohols has been studied in the presence of RuCl<sub>2</sub>(I<i>i</i>Pr)­(<i>p</i>-cymene). The conversion of primary alcohols into esters has been further optimized by using magnesium nitride as an additive, which allows the reaction to take place at a temperature and catalyst loading lower than those described previously. Secondary alcohols were dimerized into racemic ketones by a dehydrogenative Guerbet reaction with potassium hydroxide as the additive. The transformation gave good yields of the ketone dimers with a range of alkan-2-ols, whereas more substituted secondary alcohols were unreactive. The reaction proceeds by dehydrogenation to the ketone, followed by an aldol reaction and hydrogenation of the resulting enone

    Synthetic Applications and Mechanistic Studies of the Hydroxide-Mediated Cleavage of Carbon–Carbon Bonds in Ketones

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    The hydroxide-mediated cleavage of ketones into alkanes and carboxylic acids has been reinvestigated and the substrate scope extended to benzyl carbonyl compounds. The transformation is performed with a 0.05 M ketone solution in refluxing xylene in the presence of 10 equiv of potassium hydroxide. The reaction constitutes a straightforward protocol for the synthesis of certain phenyl-substituted carboxylic acids from 2-phenylcycloalkanones. The mechanism was investigated by kinetic experiments which indicated a first order reaction in hydroxide and a full negative charge in the rate-determining step. The studies were complemented by a theoretical investigation where two possible pathways were characterized by DFT/M06-2X. The calculations showed that the scission takes place by nucleophilic attack of hydroxide on the ketone followed by fragmentation of the resulting oxyanion into the carboxylic acid and a benzyl anion

    Dehydrogenative Synthesis of Carboxylic Acids from Primary Alcohols and Hydroxide Catalyzed by a Ruthenium N‑Heterocyclic Carbene Complex

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    Primary alcohols have been reacted with hydroxide and the ruthenium complex [RuCl<sub>2</sub>(I<i>i</i>Pr)­(<i>p</i>-cymene)] to afford carboxylic acids and dihydrogen. The dehydrogenative reaction is performed in toluene, which allows for a simple isolation of the products by precipitation and extraction. The transformation can be applied to a range of benzylic and saturated aliphatic alcohols containing halide and (thio)­ether substituents, while olefins and ester groups are not compatible with the reaction conditions. Benzylic alcohols undergo faster conversion than other substrates, and a competing Cannizzaro reaction is most likely involved in this case. The kinetic isotope effect was determined to be 0.67 using 1-butanol as the substrate. A plausible catalytic cycle was characterized by DFT/B3LYP-D3 and involved coordination of the alcohol to the metal, β-hydride elimination, hydroxide attack on the coordinated aldehyde, and a second β-hydride elimination to furnish the carboxylate

    Palladium-Catalyzed Carbonylative Couplings of Vinylogous Enolates: Application to Statin Structures

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    The first Pd-catalyzed carbonylative couplings of aryl and vinyl halides with vinylogous enolates are reported generating products derived from C–C bond formation exclusively at the γ-position. Good results were obtained with a dienolate derivative of acetoacetate (1,3-dioxin-4-one). These transformations occurred at room temperature and importantly with only stoichiometric carbon monoxide in a two-chamber reactor. The methodology was applied to the synthesis of two members of the statin family generating the <i>cis</i>-3,5-diol acid motif by a γ-selective carbonylation followed by a <i>cis</i>-stereoselective reduction of the 3,5-dicarbonyl acid intermediates

    Efficient Fluoride-Catalyzed Conversion of CO<sub>2</sub> to CO at Room Temperature

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    A protocol for the efficient and selective reduction of carbon dioxide to carbon monoxide has been developed. Remarkably, this oxygen abstraction step can be performed with only the presence of catalytic cesium fluoride and a stoichiometric amount of a disilane in DMSO at room temperature. Rapid reduction of CO<sub>2</sub> to CO could be achieved in only 2 h, which was observed by pressure measurements. To quantify the amount of CO produced, the reduction was coupled to an aminocarbonylation reaction using the two-chamber system, COware. The reduction was not limited to a specific disilane, since (Ph<sub>2</sub>MeSi)<sub>2</sub> as well as (PhMe<sub>2</sub>Si)<sub>2</sub> and (Me<sub>3</sub>Si)<sub>3</sub>SiH exhibited similar reactivity. Moreover, at a slightly elevated temperature, other fluoride salts were able to efficiently catalyze the CO<sub>2</sub> to CO reduction. Employing a nonhygroscopic fluoride source, KHF<sub>2</sub>, omitted the need for an inert atmosphere. Substituting the disilane with silylborane, (pinacolato)­BSiMe<sub>2</sub>Ph, maintained the high activity of the system, whereas the structurally related bis­(pinacolato)­diboron could not be activated with this fluoride methodology. Furthermore, this chemistry could be adapted to <sup>13</sup>C-isotope labeling of six pharmaceutically relevant compounds starting from Ba<sup>13</sup>CO<sub>3</sub> in a newly developed three-chamber system