- Photocatalytic degradation of water taste and odour compounds in the presence of polyoxometalates and TiO2: Intermediates and degradation pathways
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Geosmin (GSM) and 2-methylisoborneol (MIB) are produced by several species of cyanobacteria and actinomycetes. These compounds can taint water and fish causing undesirable taste and odours. Studies have shown that GSM/MIB are resistant in standard water treatments. Polyoxometalates (POM) are efficient photocatalysts in the degradation and mineralization of a great variety of organic pollutants, presenting similar behaviour with the widely published titanium dioxide (TiO2). Photocatalytic degradation of GSM and MIB under UV-A light in the presence of a characteristic POM photocatalyst, SiW 12O404-, in aqueous solution has been studied and compared with the photodegradation by TiO2 suspensions. GSM and MIB are effectively degraded in the presence of both photocatalysts. Addition of OH radical scavengers (KBr and tertiary butyl alcohol, TBA) retards the photodegradation rates of both compounds, suggesting that photodegradation mechanism takes place via OH radicals. Intermediates identified using GC-MS in the case of GSM and MIB, are mainly identical in the presence of both photocatalysts, also suggesting a common reaction mechanism. Possible photocatalytic degradation pathway for both GSM and MIB is proposed.
- Fotiou, Theodora,Triantis, Theodoros M.,Kaloudis, Triantafyllos,Papaconstantinou, Elias,Hiskia, Anastasia
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- Palladium(0)-catalyzed reaction of cyclopropylidenecycloalkanes with carbon dioxide
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Cyclopropylidenecycloalkanes, which are highly strained methylenecyclopropane (MCPs) containing a cycloalkane moiety, react with carbon dioxide smoothly to give the corresponding five-membered lactone derivatives in moderate to good yields through a cyclo
- Chen, Kai,Jiang, Min,Zhang, Zhen,Wei, Yin,Shi, Min
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p. 7189 - 7193
(2012/01/19)
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- Enantioselective decarboxylative alkylation reactions: Catalyst development, substrate scope, and mechanistic studies
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α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center. Sly as a PHOX: The development of an enantioselective decarboxylative palladium-catalyzed allylic alkylation reaction, utilizing phosphinooxazoline ligands, is described. The catalyst is applied to a range of allyl enol carbonate, silyl enol ether, and allyl β-ketoester substrates to provide alkylated ketone products in excellent yield and good ee (see scheme). The utility of these products is demonstrated by their use in several asymmetric syntheses. Mechanistic studies are reported suggesting an unusual inner-sphere mechanism. Copyright
- Behenna, Douglas C.,Mohr, Justin T.,Sherden, Nathaniel H.,Marinescu, Smaranda C.,Harned, Andrew M.,Tani, Kousuke,Seto, Masaki,Ma, Sandy,Novak, Zoltan,Krout, Michael R.,McFadden, Ryan M.,Roizen, Jennifer L.,Enquist Jr., John A.,White, David E.,Levine, Samantha R.,Petrova, Krastina V.,Iwashita, Akihiko,Virgil, Scott C.,Stoltz, Brian M.
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p. 14199 - 14223
(2012/02/01)
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- Enantioselective alkylations of tributyltin enolates catalyzed by Cr(salen)CI: Access to enantiomerically enriched all-carbon quaternary centers
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The catalytic asymmetric α-alkylation of tributyltin enolates with a range of primary alkyl halides is catalyzed by a chiral Cr(salen) complex. The reaction constitutes the first transition-metal-catalyzed system for α-alkylation of carbonyl substrates wi
- Doyle, Abigail G.,Jacobsen, Eric N.
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- The enantioselective Tsuji allylation
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The first catalytic enantioselective examples of the Tsuji allylation using enol carbonates and enol silanes are described. The products possess a quaternary stereogenic center and are useful building blocks for synthetic chemistry. Copyright
- Behenna, Douglas C.,Stoltz, Brian M.
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p. 15044 - 15045
(2007/10/03)
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- Synthesis of Enantiomerically Pure Hydrinden-2-ones and Benzinden-2-ones via Asymmetric Alkylations of Chiral Bicyclic Lactams
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A route to the titled compounds in >99percent ee was achieved from sequential diastereoselective alkylations of chiral, nonracemic bicyclic lactams 6 and 15.An intramolecular addition of the organolithium species derived from 17a-c and 28a-d gave, after hydrolysis, diketones 25a-c and 30a-d, which were cyclized to the titled compounds 4a-c and 31a-d.As an example of the versatility of this method, the ABC ring system of the triterpene stelliferin A, isolated from marine organisms, was prepared in high enantiomeric excess.
- Snyder, Lawrence,Meyers, A. I.
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p. 7507 - 7515
(2007/10/02)
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- 3-Chloro-2-(trimethylsiloxy)-1-propene as an Electrophilic Acetonyl Equivalent. A Novel Regioselective Synthesis of 1,4-Dicarbonyl Compounds
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α-Metalated imines, hydrazones, and activated methylene compounds are acetonylated with 3-chloro-2-(trimethylsiloxy)-1-propene in high yield.Highly regioselective acetonylation at either the tertiary or secondary α-carbon of 2-methylcyclohexanone can be carried out by selecting the reaction conditions.
- Hosomi, Akira,Shirahata, Akihiko,Araki, Yoshitaka,Sakurai, Hideki
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p. 4631 - 4633
(2007/10/02)
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- Enolstannanes as electrofugal groups in allylic alkylation
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Enolstannanes serve as nucleophiles towards allylic acetates under the influence of palladium(O) catalyst.
- Trost, Barry M.,Keinan, Ehud
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p. 2591 - 2594
(2007/10/02)
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