18 research outputs found

    Synthesis of Functionalized Cyclohexenone Core of Welwitindolinones via Rhodium-Catalyzed [5 + 1] Cycloaddition

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    The cyclohexenone core of welwitindolinones was synthesized by a Rh(I)-catalyzed [5 + 1]-cycloaddition of an allenylcyclopropane with CO. A pentasubstituted cyclopropane was prepared successfully by a Rh(II)-catalyzed intramolecular cyclopropanation of alkenes with chlorodiazoacetates

    Stereoselective Total Synthesis of Hainanolidol and Harringtonolide via Oxidopyrylium-Based [5 + 2] Cycloaddition

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    The tetracyclic carbon skeleton of hainanolidol and harringtonolide was efficiently constructed by an intramolecular oxidopyrylium-based [5 + 2] cycloaddition. An anionic ring-opening strategy was developed for the cleavage of the ether bridge in 8-oxabicyclo[3.2.1]颅octenes derived from the [5 + 2] cycloaddition. Conversion of cycloheptadiene to tropone was realized by a sequential [4 + 2] cycloaddition, Kornblum鈥揇eLaMare rearrangement, and double elimination. The biomimetic synthesis of harringtonolide from hainanolidol was also confirmed

    Rhodium-Catalyzed Tandem Annulation and (5 + 1) Cycloaddition: 3鈥慔ydroxy-1,4-enyne as the 5鈥慍arbon Component

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    A Rh-catalyzed tandem annulation and (5 + 1) cycloaddition was realized. 3-Hydroxy-1,4-enyne served as the new 5-carbon component for the (5 + 1) cycloaddition. Substituted carbazoles, dibenzofurans, and tricyclic compounds containing a cyclohexadienone moiety could be prepared efficiently. The identification of a byproduct suggests that metal carbene and ketene intermediates may be involved in the (5 + 1) cycloaddition

    Harnessing the Reactivity of Iridium Hydrides by Air: Iridium-Catalyzed Oxidation of Aldehydes to Acids in Water

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    An iridium-catalyzed oxidation of aldehydes to acids was realized by using air as the oxidant and water as the solvent in the presence of base. Interestingly, the same type of catalysts were also used for the reduction of aldehydes under acidic conditions. A common iridium hydride intermediate is proposed for both redox reactions. The oxidation has a number of advantages such as high yields, great functionality tolerance, and easy purification without chromatography

    Rhodium-Catalyzed Carbonylation of 3-Acyloxy-1,4-enynes for the Synthesis of Cyclopentenones

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    Functionalized cyclopentenones were synthesized by a Rh-catalyzed carbonylation of 3-acyloxy-1,4-enynes, derived from alkynes and 伪,尾-unsaturated aldehydes. The reaction involved a Saucy鈥揗arbet 1,3-acyloxy migration of propargyl esters and a [4 + 1] cycloaddition of the resulting acyloxy substituted vinylallene with CO

    Syntheses, structures, and properties of two 2-D Cd(II) complexes based on 2-(1<i>H</i>-imidazol-1-methyl)-1<i>H</i>-benzimidazole and polycarboxylate ligands

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    <div><p>Two 2-D Cd(II) complexes, {[Cd(imb)(bdc)(H<sub>2</sub>O)]路CH<sub>3</sub>OH}<sub><i>n</i></sub> (<b>1</b>) and {[Cd(imb)(Hbtc)(CH<sub>3</sub>OH)]路2H<sub>2</sub>O路CH<sub>3</sub>OH}<sub><i>n</i></sub> (<b>2</b>), have been synthesized by reactions of CdCl<sub>2</sub>路2.5H<sub>2</sub>O with 2-(1<i>H</i>-imidazol-1-methyl)-1<i>H</i>-benzimidazole (imb) and 1,3-benzenedicarboxylic acid (H<sub>2</sub>bdc) or 1,3,5-benzenetricarboxylic acid (H<sub>3</sub>btc). Single-crystal X-ray diffraction shows that <b>1</b> possesses an infinite 2-D layered structure in which all the carboxylates chelate Cd(II) and imb bridge Cd(II) ions. Complex <b>2</b> also features an infinite 2-D layered structure and imb ligands also bridge Cd(II) ions, but two carboxylates of each 1,3,5-benzenetricarboxylate coordinate to Cd(II) in monodentate or chelating mode, leaving the third one, which is not deprotonated, uncoordinated. IR spectra, fluorescent properties, and thermogravimetric analyses of both complexes have been investigated.</p></div

    Rh-Catalyzed (5+2) Cycloadditions of 3鈥慉cyloxy-1,4-enynes and Alkynes: Computational Study of Mechanism, Reactivity, and Regioselectivity

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    The mechanism of Rh-catalyzed (5+2) cycloadditions of 3-acyloxy-1,4-enyne (ACE) and alkynes is investigated using density functional theory calculations. The catalytic cycle involves 1,2-acyloxy migration, alkyne insertion, and reductive elimination to form the cycloheptatriene product. In contrast to the (5+2) cycloadditions with vinylcyclopropanes (VCPs), in which alkyne inserts into a rhodium鈥揳llyl bond, alkyne insertion into a Rh鈥揅颅(sp<sup>2</sup>) bond is preferred. The 1,2-acyloxy migration is found to be the rate-determining step of the catalytic cycle. The electron-rich <i>p</i>-dimethylaminobenzoate substrate promotes 1,2-acyloxy migration and significantly increases the reactivity. In the regioselectivity-determining alkyne insertion step, the alkyne substituent prefers to be distal to the forming C鈥揅 bond and thus distal to the OAc group in the product

    Chiral Catalyst-Directed Dynamic Kinetic Diastereoselective Acylation of Lactols for <i>De Novo</i> Synthesis of Carbohydrate

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    The control of the stereochemistry at the anomeric position is still one of the major challenges of synthetic carbohydrate chemistry. We have developed a new strategy consisting of a chiral catalyst-directed acylation followed by a palladium-catalyzed glycosidation to achieve high 伪- and 尾-stereoselectivity on the anomeric position. The former process involves a dynamic kinetic diastereoselective acylation of lactols derived from Achmatowicz rearrangement, while the latter is a stereospecific palladium-catalyzed allylic alkylation

    Rhodium-Catalyzed Carbonylation of Cyclopropyl Substituted Propargyl Esters: A Tandem 1,3-Acyloxy Migration [5 + 1] Cycloaddition

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    We have developed two different types of tandem reactions for the synthesis of highly functionalized cyclohexenones from cyclopropyl substituted propargyl esters. Both reactions were initiated by rhodium-catalyzed Saucy鈥揗arbet 1,3-acyloxy migration. The resulting cyclopropyl substituted allenes derived from acyloxy migration then underwent [5 + 1] cycloaddition with CO. The acyloxy group not only eased the access to allene intermediates but also provided a handle for further selective functionalizations

    Rhodium-Catalyzed Chemo- and Regioselective Cross-Dimerization of Two Terminal Alkynes

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    Cross-dimerization of terminal arylacetylenes and terminal propargylic alcohols/amides has been achieved in the presence of a rhodium catalyst. This method features high chemo- and regioselectivities rendering convenient and atom economical access to functionalized enynes
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