- Cascade Coupling of Ene-Reductases and ω-Transaminases for the Stereoselective Synthesis of Diastereomerically Enriched Amines
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One-pot sequential and cascade processes performed by employing ene-reductases (ERs) together with ω-transaminases (ω-TAs) for the obtainment of diastereomerically enriched (R)- and (S)-amine derivatives containing an additional stereocenter were investigated. By using either α- or β-substituted unsaturated ketones as substrates and by coupling purified ERs belonging to the Old Yellow Enzyme (OYE) family with a panel of commercially available ω-TAs, the desired products were obtained in up to >99% conversion and >99%de. The sequential reactions were performed in a one-pot fashion with no need to adapt the reaction conditions to the reductive amination step or to purify the reaction intermediate. Moreover, high chemoselectivity of the tested ω-TAs for the saturated ketones was shown in the cascade reactions.
- Monti, Daniela,Forchin, Maria Chiara,Crotti, Michele,Parmeggiani, Fabio,Gatti, Francesco G.,Brenna, Elisabetta,Riva, Sergio
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- A method to prepare optically active acyclic α-benzyl ketones by thermodynamically controlled deracemization
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Thermodynamically controlled deracemization of some acyclic ketones bearing a chiral center at the position α to the carbonyl group was satisfactorily achieved. Acyclic ketones with high optical purities could be isolated after treatment of the racemic ketones with base in aqueous MeOH in the presence of (-)-(2R,3R)-trans-2,3-bis(hydroxydiphenylmethyl)-1,4-dioxaspiro[5. 4]decane (1a). The efficiency of the deracemization was appreciably influenced by the ratio of H2O/MeOH used as solvent. Racemic ketones bearing a chiral center at the position α to the carbonyl group were converted into optically active ketones in the presence of TADDOL-type host molecule 1a in H2O/MeOH in suspension in basic media. Copyright
- Kaku, Hiroto,Imai, Takahiro,Kondo, Risa,Mamba, Shiho,Watanabe, Yu,Inai, Makoto,Nishii, Takeshi,Horikawa, Mitsuyo,Tsunoda, Tetsuto
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- Multi-enzyme cascade synthesis of the most odorous stereoisomers of the commercial odorant Muguesia
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The most odorous stereoisomers of the chiral commercial fragrance Muguesia are prepared by a very effective linear biocatalysed cascade reaction, in which a suitable unsaturated ketone is submitted to the sequential action of two enzymes, an ene-reductase and an alcohol dehydrogenase, which are added together to the same reaction vessel with the cofactor regeneration system. Two stereogenic centres in 1,2 relative position are thus created under high stereochemical control by a two-step one-pot enzymatic procedure.
- Brenna, Elisabetta,Crotti, Michele,Gatti, Francesco G.,Monti, Daniela,Parmeggiani, Fabio,Pugliese, Andrea,Santangelo, Sara
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- Highly Enantioselective Iridium-Catalyzed Hydrogenation of Conjugated Trisubstituted Enones
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Asymmetric hydrogenation of conjugated enones is one of the most efficient and straightforward methods to prepare optically active ketones. In this study, chiral bidentate Ir-N,P complexes were utilized to access these scaffolds for ketones bearing the stereogenic center at both the α- and β-positions. Excellent enantiomeric excesses, of up to 99%, were obtained, accompanied with good to high isolated yields. Challenging dialkyl substituted substrates, which are difficult to hydrogenate with satisfactory chiral induction, were hydrogenated in a highly enantioselective fashion.
- Peters, Bram B. C.,Jongcharoenkamol, Jira,Krajangsri, Suppachai,Andersson, Pher G.
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p. 242 - 246
(2021/01/13)
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- Indene Derived Phosphorus-Thioether Ligands for the Ir-Catalyzed Asymmetric Hydrogenation of Olefins with Diverse Substitution Patterns and Different Functional Groups
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A family of phosphite/phosphinite-thioether ligands have been tested in the Ir-catalyzed asymmetric hydrogenation of a range of olefins (50 substrates in total). The presented ligands are synthesized in three steps from cheap indene and they are air-stable solids. Their modular architecture has been crucial to maximize the catalytic performance for each type of substrate. Improving most Ir-catalysts reported so far, this ligand family presents a broader substrate scope, covering different substitution patterns with different functional groups, ranging from unfunctionalized olefins, through olefins with poorly coordinative groups, to olefins with coordinative functional groups. α,β-Unsaturated acyclic and cyclic esters, ketones and amides werehydrogenated in enantioselectivities ranging from 83 to 99% ee. Enantioselectivities ranging from 91 to 98% ee were also achieved for challenging substrates such as unfunctionalized 1,1′-disubstituted olefins, functionalized tri- and 1,1′-disubstituted vinyl phosphonates, and β-cyclic enamides. The catalytic performance of the Ir-ligand assemblies was maintained when the environmentally benign 1,2-propylene carbonate was used as solvent. (Figure presented.).
- Margalef, Jèssica,Biosca, Maria,de la Cruz-Sánchez, Pol,Caldentey, Xisco,Rodríguez-Escrich, Carles,Pàmies, Oscar,Pericàs, Miquel A.,Diéguez, Montserrat
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supporting information
p. 4561 - 4574
(2021/04/05)
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- Capturing the Monomeric (L)CuH in NHC-Capped Cyclodextrin: Cavity-Controlled Chemoselective Hydrosilylation of α,β-Unsaturated Ketones
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The encapsulation of copper inside a cyclodextrin capped with an N-heterocyclic carbene (ICyD) allowed both to catch the elusive monomeric (L)CuH and a cavity-controlled chemoselective copper-catalyzed hydrosilylation of α,β-unsaturated ketones. Remarkably, (α-ICyD)CuCl promoted the 1,2-addition exclusively, while (β-ICyD)CuCl produced the fully reduced product. The chemoselectivity is controlled by the size of the cavity and weak interactions between the substrate and internal C?H bonds of the cyclodextrin.
- Bistri-Aslanoff, Olivia,Derat, Etienne,Leloux, Sébastien,Leyssens, Tom,Ménand, Micka?l,Meijide Suárez, Jorge,Riant, Olivier,Roland, Sylvain,Sollogoub, Matthieu,Xu, Guangcan,Zhang, Pinglu,Zhang, Yongmin
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p. 7591 - 7597
(2020/03/23)
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- Silicon Carbide Supported Palladium-Iridium Bimetallic Catalysts for Efficient Selective Hydrogenation of Cinnamaldehyde
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Selective hydrogenation of α,β-unsaturated carbonyls into saturated carbonyls is important to obtain remunerative products. However, it is still a challenge to achieve high activity and selectivity under mild conditions. Herein, Pd, Ir and bimetallic Pd-Ir nanoparticles were uniformly deposited with high dispersity on the surface of SiC by a facile impregnation method, respectively. The as-prepared Pd/SiC catalysts efficiently hydrogenate cinnamaldehyde to hydrocinnamaldehyde at room temperature and atmospheric pressure, and the activity of Pd/SiC is observed further enhanced by adding Ir component (conversion of 100%). In addition, the dependence of Pd-Ir catalyst activity on Pd/Ir molar ratio confirms a synergistic effect between Ir and Pd, which originates from the electron transfer between Pd and Ir.
- Guo, Xiang-Yun,Jin, Guoqiang,Li, Penghui,Tong, Xili,Wang, Yingyong,Wang, Yunwei
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- Giving a Second Chance to Ir/Sulfoximine-Based Catalysts for the Asymmetric Hydrogenation of Olefins Containing Poorly Coordinative Groups
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This work identifies a family of Ir/phosphite-sulfoximine catalysts that has been successfully used in the asymmetric hydrogenation of olefins with poorly coordinative or noncoordinative groups. In comparison with analogue Ir/phosphine-sulfoximine catalysts previously reported, the presence of a phosphite group extended the range of olefins than can be efficiently hydrogenated. High enantioselectivities, comparable to the best ones reported, have been achieved for a wide range of olefins containing relevant poorly coordinative groups such as α,β-unsaturated enones, esters, lactones, and lactams as well as alkenylboronic esters.
- Biosca, Maria,Pàmies, Oscar,Diéguez, Montserrat
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p. 8259 - 8266
(2019/06/17)
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- Phosphite-thioether/selenoether Ligands from Carbohydrates: An Easily Accessible Ligand Library for the Asymmetric Hydrogenation of Functionalized and Unfunctionalized Olefins
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A large family of phosphite-thioether/selenoether ligands has been easily prepared from accessible L-(+)-tartaric acid and D-(+)-mannitol and applied in the M-catalyzed (M=Ir, Rh) asymmetric hydrogenation of a broad number of substrates (46 in total). Its highly modular architecture has been crucial to maximize the catalytic performance. Improving most of the reported approaches, this ligand family presents a broad substrate scope. By selecting the ligand parameters high enantioselectivities (ee's up to 99 %) have therefore been achieved in a broad range of both, functionalized and unfunctionalized substrates. Interestingly, both enantiomers of the hydrogenation products can be usually achieved by changing the ligand parameters.
- Margalef, Jèssica,Borràs, Carlota,Alegre, Sabina,Alberico, Elisabetta,Pàmies, Oscar,Diéguez, Montserrat
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p. 2142 - 2168
(2019/04/13)
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- Ir/Thioether-Carbene, -Phosphinite, and -Phosphite Complexes for Asymmetric Hydrogenation. A Case for Comparison
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We studied for the first time the potential of novel and simple Ir/thioether-NHC complexes in the asymmetric hydrogenation of unfunctionalized olefins and cyclic β-enamides. For comparison, we prepared and applied the analogues thioether-phosphinite/phosphite complexes. We found that the efficiency of the new Ir/thioether-NHC catalyst precursors varies with the type of olefin. Thus, while the Ir/thioether-NHC catalyst precursors provided lower catalytic performance than their related Ir/thioether-P complexes in the hydrogenation of olefins lacking a coordinating group, the catalysts had similar good performance for the reduction of functionalized olefins (e.g., tri- and disubstituted enol phosphonate derivatives). Catalytic results together with the studies of the reactivity toward H2 indicated that the thioether-carbene design favors the formation of inactive trinuclear species, which are responsible for the low activities obtained with these carbene-type catalysts. Nevertheless, this catalyst deactivation can be avoided by using functionalized olefins such as enol phosphonates. We also report the discovery of simple-to-synthesize Ir/thioether-P catalysts containing a simple backbone that gave high enantioselectivities for some trisubstituted olefins, some challenging 1,1′-disubstituted olefins, and cyclic β-enamides.
- Cruz-Sánchez, Pol De La,Faiges, Jorge,Mazloomi, Zahra,Borràs, Carlota,Biosca, Maria,Pàmies, Oscar,Diéguez, Montserrat
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p. 4193 - 4205
(2019/10/16)
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- Proline-promoted dehydroxylation of α-ketols
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A new single-step proline-potassium acetate promoted reductive dehydroxylation of α-ketols is reported. We introduce the unexplored reactivity of proline and, for the first time, reveal its ability to function as a reducing agent. The developed metal-free and open-flask operation generally results in good yields. Our protocol allows the challenging selective dehydroxylation of hydroxyketones without affecting other functional groups.
- Mostinski, Yelena,Lankri, David,Konovalov, Yana,Nataf, Riva,Tsvelikhovsky, Dmitry
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p. 9345 - 9350
(2019/10/22)
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- Mild Chemoenzymatic Oxidation of Allylic sec-Alcohols. Application to Biocatalytic Stereoselective Redox Isomerizations
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The design of catalytic oxidative methodologies in aqueous medium under mild reaction conditions and using molecular oxygen as final electron acceptor represents a suitable alternative to the traditional oxidative transformations. These methods are especially relevant if other functionalities that can be oxidized are present within the same molecule, as in the case of allylic alcohols. Herein we apply a simple chemoenzymatic system composed of the laccase from Trametes versicolor and 2,2,6,6-tetramethylpiperidinyloxy radical (TEMPO) to oxidize a series of racemic allylic sec-alcohols into the corresponding α,β-unsaturated ketones. Afterward, these compounds react with different commercially available ene-reductases to afford the corresponding saturated ketones. Remarkably, in the case of trisubstituted alkenes, the bioreduction reaction occurred with high stereoselectivity. Overall, a bienzymatic one-pot two-step sequential strategy has been described with respect to the synthesis of saturated ketones starting from racemic allylic alcohols, thus resembling the metal-catalyzed redox isomerizations of these derivatives that have been previously reported in the literature.
- Martínez-Montero, Lía,Gotor, Vicente,Gotor-Fernández, Vicente,Lavandera, Iván
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p. 2413 - 2419
(2018/03/13)
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- Syndiotactic Poly(aminostyrene)-Supported Palladium Catalyst for Ketone Methylation with Methanol
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Palladium nanoparticles immobilized on an amino-functionalized syndiotactic polystyrene (sPS-N) served as a novel recyclable catalyst for the dimethylation and cross methyl alkylation of a wide range of ketones with methanol as the methylation agent. This heterogeneous catalyst (Pd@sPS-N) was highly robust and showed excellent thermal stability and chemical resistance. It not only showed remarkably high activity, but it could also be easily recovered by filtration without loss of activity.
- Jiang, Lei,Guo, Fang,Shi, Zhenghai,Li, Yang,Hou, Zhaomin
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p. 3827 - 3832
(2017/09/25)
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- Extractive biocatalysis in the asymmetric reduction of α-alkyl, β-aryl enones by Baker's yeast
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We prepared various chiral α-alkyl, β-aryl ketones with good to excellent enantiomeric excess through the Baker's yeast asymmetric double-bond reduction of the corresponding α,β-unsaturated substrates adsorbed onto the resin Amberlite XAD-7. This methodology was compatible with substrates bearing both electron-donating and withdrawing groups attached to the aromatic ring. Elongation of the α-alkyl substituent of the starting material strongly affected the reactivity and enantioselectivity of the reaction.
- Silva, Rafaela M.,Okano, Laura T.,Rodrigues, J. Augusto R.,Clososki, Giuliano C.
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p. 939 - 944
(2017/07/11)
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- Alternatives to Phosphinooxazoline (t-BuPHOX) Ligands in the Metal-Catalyzed Hydrogenation of Minimally Functionalized Olefins and Cyclic β-Enamides
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This study presents a new series of readily accessible iridium- and rhodium-phosphite/oxazoline catalytic systems that can efficiently hydrogenate, for the first time, both minimally functionalized olefins and functionalized olefins (62 examples in total) in high enantioselectivities (ees up to >99%) and conversions. The phosphite-oxazoline ligands, which are readily available in only two synthetic steps, are derived from previous privileged 4-alkyl-2-[2-(diphenylphosphino)phenyl]-2-oxazoline (PHOX) ligands by replacing the phosphine moiety by a biaryl phosphite group and/or the introduction of a methylene spacer between the oxazoline and the phenyl ring. The modular design of the ligands has given us the opportunity not only to overcome the limitations of the iridium-PHOX catalytic systems in the hydrogenation of minimally functionalized Z-olefins and 1,1-disubstituted olefins, but also to expand their use to unfunctionalized olefins containing other challenging scaffolds (e.g., exocyclic benzofused and triaryl-substituted olefins) and also to olefins with poorly coordinative groups (e.g., α,β-unsaturated lactams, lactones, alkenylboronic esters, etc.) with enantioselectivities typically >95% ee. Moreover, both enantiomers of the hydrogenation product could be obtained by simply changing the configuration of the biaryl phosphite moiety. Remarkably, the new catalytic systems also provided excellent enantioselectivities (up to 99% ee) in the asymmetric hydrogenation of another challenging class of olefins – the functionalized cyclic β-enamides. Again, both enantiomers of the reduced amides could be obtained by changing the metal from Ir to Rh. We also demonstrated that environmentally friendly propylene carbonate can be used with no loss of enantioselectivity. Another advantage of the new ligands over the PHOX ligands is that the best ligands are derived from the affordable (S)-phenylglycinol rather than from the expensive (S)-tert-leucinol. (Figure presented.).
- Biosca, Maria,Magre, Marc,Coll, Mercè,Pàmies, Oscar,Diéguez, Montserrat
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supporting information
p. 2801 - 2814
(2017/08/23)
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- Mononuclear Ruthenium and Osmium Complexes with a Bicyclic Guanidinate Ligand: Synthesis and Catalytic Behavior in Olefin Isomerization Processes
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The preparation of the first mononuclear RuII, RuIV, and OsII complexes containing the anion of the bicyclic guanidine 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (Hhpp) as a chelating ligand, namely [RuX{κ2-(N,N′)-hpp}(η6-arene)] [arene = p-cymene, X = Cl (2a), Br (2b), I (2c); arene = C6Me6, X = Cl (7)], [RuCl{κ2-(N,N′)-hpp}(η3:η3-C10H16)] (9; C10H16 = 2,7-dimethylocta-2,6-diene-1,8-diyl), and [OsCl{κ2-(N,N′)-hpp}(η6-p-cymene)] (11), is described. Compounds 2a–c, 7, 9, and 11 have been fully characterized by elemental analysis, HRMS, IR and NMR spectroscopy. In addition, the structure of 2a has been unequivocally confirmed by single-crystal X-ray diffraction methods. The catalytic behavior of these metal guanidinate complexes in the base-free redox isomerization of allylic alcohols is explored, with the ruthenium(IV) derivative 9 showing the best performance (TOF up to 5940 h–1). All of the synthesized complexes have also proven to be active in the isomerization of the allylbenzene estragole into the industrially relevant 1-propenylbenzene anethole, with a trans selectivity of up to 95 %.
- Gámez-Rivera, Sebastián A.,Francos, Javier,Borge, Javier,Cadierno, Victorio
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p. 4138 - 4146
(2017/09/28)
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- Regioselective 1,2-Diol Rearrangement by Controlling the Loading of BF3·Et2O and Its Application to the Synthesis of Related Nor-Sesquiterene- and Sesquiterene-Type Marine Natural Products
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The regiocontrolled rearrangement of 1,2-diols has been achieved by controlling the loading of BF3·Et2O. Its applicability is showcased by the divergent synthesis of austrodoral, austrodoric acid, and 8-epi-11-nordriman-9-one, as well as a formal synthesis of siphonodictyal B and liphagal. A new light is shed on piancol-type rearrangements that will be useful in diversity-oriented synthesis of related natural products.
- Wang, Jun-Li,Li, Hui-Jing,Wang, Hong-Shuang,Wu, Yan-Chao
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p. 3811 - 3814
(2017/07/26)
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- Bioreduction of α-Acetoxymethyl Enones: Proposal for an SN2′ Mechanism Catalyzed by Enereductase
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(Z)-3-Acetoxymethyl-4-R-3-buten-2-ones (R=aryl, alkyl) and (Z)-3-methyl-4-R-3-buten-2-ones (R=aryl) were synthesized and submitted to reduction by the yeast Saccharomyces cerevisiae producing the (R)- and (S)-4-R-3-methybutan-2-ones, respectively. This stereochemistry control strategy was applied in the syntheses of (R)- and (S)-Tropional with moderate to high enantiomeric excesses. Other (Z)-3-acyloxymethyl-4-phenyl-3-buten-2-ones showed similar behavior to the (Z)-3-acetoxymethyl counterpart, and the acylated Morita–Baylis–Hillman adduct 1-acetoxy-2-methylene-1-phenylbutan-3-one produced a mixture of products, with and without the acetoxy group, via three different reaction pathways. In addition to experiments employing whole cells, those in which isolated enereductases were used suggested that the main pathway through which the loss of the acetoxy group occurs during the biocatalytic cascade is an SN2′-type reaction, rather than formal hydrogen addition followed by acetic acid elimination. Finally, related ethyl enones were reduced enantioselectively by the yeast Candida albicans, producing both (R)- and (S)-reduction products, depending on the presence of the acetoxy group in the starting material. (Figure presented.).
- Paula, Bruno R. S.,Zampieri, Davila,Rodrigues, J. Augusto R.,Moran, Paulo J. S.
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p. 3555 - 3571
(2016/11/25)
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- Chiral ferrocene-based P,S ligands for Ir-catalyzed hydrogenation of minimally functionalized olefins. Scope and limitations
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A family of 12 modular ferrocenyl planar chiral phosphine-thioethers (P,S) has been studied in the asymmetric hydrogenation of minimally functionalized alkenes. These ligands differ by the substituent on sulfur or by the linker between the ferrocene moiety and the sulfur atom (no linker, methylene or methyl substituted methylene linker bearing an additional element of chirality). The cationic iridium(cod) complexes of the different P,S ligands have been efficiently synthesized. For the majority of the ligands, coordination yielded only a single diastereoisomer with full control of the absolute configuration on sulfur. The different iridium complexes have been used in the hydrogenation of various di, tri, and tetrasubstituted minimally functionalized olefins. Conversions and enantioselectivities are highly dependent on the ligand and substrate structure. Full conversions and low-to-excellent enantioselectivities could be obtained (maximum ee from 14 to 94% for 1,1-disubsituted alkenes, from 17 to 99% for trisubstituted olefins, and 34% for the tetrasubstituted alkene).
- Biosca, Maria,Coll, Mercè,Lagarde, Florian,Brémond, Emma,Routaboul, Lucie,Manoury, Eric,Pàmies, Oscar,Poli, Rinaldo,Diéguez, Montserrat
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p. 2623 - 2631
(2015/03/30)
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- Iridium-Catalyzed Asymmetric Hydrogenation with Simple Cyclohexane-Based P/S Ligands: In Situ HP-NMR and DFT Calculations for the Characterization of Reaction Intermediates
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We report a reduced but structurally valuable phosphite/phosphinite-thioether ligand library for the Ir-hydrogenation of 40 minimally functionalized alkenes, including relevant examples with poorly coordinative groups. We found that enantiomeric excesses are mainly dependent on the substrate structure and on some ligand parameters (i.e., the type of thioether/phosphorus moieties and the configuration of the phosphite group), whereas the substituents of the biaryl phosphite moiety had little impact. By tuning the ligand parameters we were able to find highly selective catalysts for a range of substrates (ees up to 99%). These phosphite/phosphinite-thioether ligands have a simple backbone and thus yield simple NMR spectra that reduce signal overlap and facilitate the identification of relevant intermediates. Therefore, by combining HP-NMR spectroscopy and theoretical studies, we were also able to identify the catalytically competent Ir-dihydride alkene species, which made it possible to explain the enantioselectivity obtained.
- Borràs, Carlota,Biosca, Maria,Pàmies, Oscar,Diéguez, Montserrat
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supporting information
p. 5321 - 5334
(2015/11/18)
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- Extending the substrate scope of bicyclic p-oxazoline/thiazole ligands for ir-catalyzed hydrogenation of unfunctionalized olefins by introducing a biaryl phosphoroamidite group
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This study identifies a series of Ir-bicyclic phosphoroamidite-oxazoline/thiazole catalytic systems that can hydrogenate a wide range of minimally functionalized olefins (including E- and Z-tri- and disubstituted substrates, vinylsilanes, enol phosphinates, tri- and disubstituted alkenylboronic esters, and ?±,?2-unsaturated enones) in high enantioselectivities (ee values up to 99%) and conversions. The design of the new phosphoroamidite-oxazoline/thiazole ligands derives from a previous successful generation of bicyclic N-phosphane-oxazoline/thiazole ligands, by replacing the N-phosphane group with a p-acceptor biaryl phosphoroamidite moiety. A small but structurally important family of Ir-phosphoroamidite-oxazoline/thiazole precatalysts has thus been synthesized by changing the nature of the Ndonor group (either oxazoline or thiazole) and the configuration at the biaryl phosphoroamidite moiety. The substitution of the N-phosphane by a phosphoroamidite group in the bicyclic N-phosphane-oxazoline/thiazole ligands extended the range of olefins that can be successfully hydrogenated.
- Biosca, Maria,Paptchikhine, Alexander,P??mies, Oscar,Andersson, Pher G.,Di??guez, Montserrat
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supporting information
p. 3455 - 3464
(2015/03/04)
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- A theoretically-guided optimization of a new family of modular P,S-ligands for iridium-catalyzed hydrogenation of minimally functionalized olefins
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A library of modular iridium complexes derived from thioether-phosphite/phosphinite ligands has been evaluated in the asymmetric iridium-catalyzed hydrogenation of minimally functionalized olefins. The modular ligand design has been shown to be crucial in finding highly selective catalysts for each substrate. A DFT study of the transition state responsible for the enantiocontrol in the Ir-catalyzed hydrogenation is also described and used for further optimization of the crucial stereodefining moieties. Excellent enantioselectivities (enantiomeric excess (ee) values up to 99%) have been obtained for a range of substrates, including E- and Z-trisubstituted and disubstituted olefins, α,β-unsaturated enones, tri- and disubstituted alkenylboronic esters, and olefins with trifluoromethyl substituents.
- Margalef, Jèssica,Caldentey, Xisco,Karlsson, Erik A.,Coll, Mercè,Mazuela, Javier,Pàmies, Oscar,Diéguez, Montserrat,Pericàs, Miquel A.
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supporting information
p. 12201 - 12214
(2015/03/31)
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- DMF as carbon source: Rh-catalyzed α-methylation of ketones
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An unprecedented Rh-catalyzed direct methylation of ketones with N,N-dimethylformamide (DMF) is disclosed. The reaction shows a broad substrate scope, tolerating both aryl and alkyl ketones with various substituents. Mechanistic studies suggest that DMF delivers a methylene fragment followed by a hydride in the methylation process.
- Li, Yang,Xue, Dong,Lu, Wei,Wang, Chao,Liu, Zhao-Tie,Xiao, Jianliang
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supporting information
p. 66 - 69
(2014/01/23)
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- Substrate scope and synthetic applications of the enantioselective reduction of α-alkyl-β-arylenones mediated by Old Yellow Enzymes
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The ene-reductases mediated bioreduction of a selection of open-chain α-alkyl-β-aryl enones afforded the corresponding saturated α-chiral ketones in high yield and optical purity in several cases. The stereo-electronic requirements of the reaction have been investigated, considering the nature and location of substituents on the aromatic ring as well as the steric hindrance at the α-position and adjacent to the carbonyl functionality. The general considerations drawn allow us to guide the design of α,β-unsaturated ketones to be employed as substrates of ene-reductases in future preparative applications. An interesting case of orthogonality between enzyme-based and substrate-based stereocontrol within the highly homologous ene-reductases from Saccharomyces species (OYE1-3) has been reported and rationalized with the help of computational docking studies. Furthermore, to demonstrate the synthetic versatility of the reaction, the key chiral precursors of biologically active compounds such as (2′R)- stenusines and (S)-iopanoic acid were obtained. The very robust protocol allowed us to run the reactions on preparative scale in quantitative yields, with a simple work-up and no chromatographic purification steps. The Royal Society of Chemistry 2013.
- Brenna, Elisabetta,Cosi, Sara Lucia,Ferrandi, Erica Elisa,Gatti, Francesco G.,Monti, Daniela,Parmeggiani, Fabio,Sacchetti, Alessandro
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p. 2988 - 2996
(2013/07/25)
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- Enantiodivergence in the reduction of α-methyl and α-halomethyl enones by microorganisms
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Enones (Z)-3-methyl-(Z)-3-chloromethyl- and (Z)-3-bromomethyl-4-R-3-buten- 2-one (R = n-pentyl, phenyl, 2′- and 4′-chlorophenyl, 3′- and 4′-nitrophenyl, 4′-methoxyphenyl) were synthesized and subjected to reduction by the microorganisms Saccharomyces cerevisiae andGeotrichum candidum. Whereas the bioreduction of 3-methy-4-R-3-buten-2-ones afforded the corresponding (S)-4-R-3-methybutan-2-ones, the bioreduction of 3-chloromethyl- and 3-bromomethyl-4-R-3-buten-2-ones afforded the corresponding (R)-4-R-3-methybutan-2-ones.
- De Paula, Bruno R.S.,Zampieri, Davila S.,Rodrigues, J. Augusto R.,Moran, Paulo J.S.
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p. 973 - 981
(2013/09/23)
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- Expanded scope of the asymmetric hydrogenation of minimally functionalized olefins catalyzed by iridium complexes with phosphite-thiazoline ligands
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We have replaced the oxazoline group with a thiazoline moiety in one of the most successful of the phosphite-oxazoline ligand families for the Ir-catalyzed hydrogenation of minimally functionalized olefins. A small but structurally important library of Ir phosphite-thiazoline precatalysts (Ir-L1-L2a-e) has been developed by changing the substituents/configurations at the biaryl phosphite group. We found that the replacement of the oxazoline with a thiazoline moiety in the ligand design is beneficial in terms of substrate scope.
- Mazuela, Javier,Pamies, Oscar,Dieguez, Montserrat
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p. 2410 - 2417
(2013/08/23)
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- A phosphite-pyridine/iridium complex library as highly selective catalysts for the hydrogenation of minimally functionalized olefins
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A modular library of readily available phosphite-pyridine ligands has been successfully applied for the first time in the iridium-catalyzed asymmetric hydrogenation of a broad range of minimally functionalized olefins. The modular ligand design has been shown to be crucial in finding highly selective catalytic systems for each substrate. Excellent enantioselectivities (ees up to 99%) have therefore been obtained in a wide range of E- and Z-trisubstituted alkenes, including more demanding triaryl-substituted olefins and dihydronaphthalenes. This good performance extends to the very challenging class of terminal disubstituted olefins, and to olefins containing neighbouring polar groups (ees up to 99%). Both enantiomers of the reduction product can be obtained in excellent enantioselectivities by simply changing the configuration of the carbon next to the phosphite moiety. The hydrogenations were also performed using propylene carbonate as solvent, which allowed the iridium catalyst to be reused and maintained the excellent Copyright
- Mazuela, Javier,Pamies, Oscar,Dieguez, Montserrat
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p. 2569 - 2583
(2013/10/21)
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- Cobalt-salen complex-catalyzed oxidative generation of alkyl radicals from aldehydes for the preparation of hydroperoxides
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Catalytic generation of alkyl radicals from aldehydes via oxidative deformylation was realized using a cobalt-salen complex with H2O 2. The deformylation was thought to proceed through homolytic cleavage of peroxohemiacetal intermediates to provide even primary alkyl radicals under mild conditions. Variously substituted and functionalized hydroperoxides were obtained from corresponding aldehydes in good yield.
- Watanabe, Eiichi,Kaiho, Atsushi,Kusama, Hiroyuki,Iwasawa, Nobuharu
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supporting information
p. 11744 - 11747
(2013/09/02)
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- Stereospecific intramolecular C-H amination of 1-aza-2-azoniaallene salts
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We report that 1-aza-2-azoniaallene salts, generated from α-chloroazo compounds by treatment with halophilic Lewis acids, participate in intramolecular C-H amination reactions to provide pyrazoline products in good to excellent yield. This intramolecular amination occurs readily at both benzylic and tertiary aliphatic positions and proceeds at an enantioenriched chiral center without loss of enantiomeric excess. A competition reaction shows that insertion occurs more readily at an electron-rich benzylic position than an electron-deficient one. These observations are consistent with the 1-aza-2-azoniaallene intermediate reacting as a nitrenium-like ion by a concerted insertion mechanism.
- Bercovici, Daniel A.,Brewer, Matthias
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supporting information; body text
p. 9890 - 9893
(2012/08/08)
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- Development of catalysts for the stereoselective hydrogenation of α,β-unsaturated ketones
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Iridium phosphinitoxazoline complexes were found to be new efficient catalysts for the asymmetric hydrogenation of arylated α,β- unsaturated ketones. Linear as well as cyclic substrates are hydrogenated with similar success, giving selectivities of up to 99.7% ee.
- Maurer, Frauke,Huch, Volker,Ullrich, Angelika,Kazmaier, Uli
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experimental part
p. 5139 - 5143
(2012/07/03)
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- Organozinc-promoted ring opening of cyclopropanols
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Regioselective ring opening of cyclopropanols by the use of organozinc reagents or ZnI2 is presented. Mechanistic studies are discussed with respect to the possible involvement of zinc ketone homoenolates. ARKAT-USA, Inc.
- Das, Pragna Pratic,Parida, Bibhuti Bhusan,Cha, Jin Kun
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- Regioselective asymmetric α,α-bisalkylation of ketones via complex-induced Syn -deprotonation of chiral N -amino cyclic carbamate hydrazones
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The first general method for the asymmetric α,α-bisalkylation of ketones having both α- and α′-protons is described. Both excellent regio- and stereoselectivity result. The transformation is enabled by complex-induced syn-deprotonation (CIS-D), which completely reverses the inherent preference of lithium diisopropylamide (LDA) to remove the less sterically hindered of two similarly acidic protons. CIS-D also overrides the normal tendency of LDA to remove the more strongly acidic proton in a substrate having protons differing significantly in their acidity. The regiochemical outcome is, thus, the opposite of that normally obtained for kinetic LDA-mediated deprotonation of ketones and (S)-1-amino-2- methoxymethylpyrrolidine/(R)-1-amino-2-methoxymethylpyrrolidine (SAMP/RAMP)hydrazones. Conveniently, this strategy allows access to either ketone enantiomer using a single enantiomer of the auxiliary. The utility of this method is demonstrated by a concise and highly efficient formal synthesis of both (R)- and (S)-stigmolone.
- Wengryniuk, Sarah E.,Lim, Daniel,Coltart, Don M.
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supporting information; experimental part
p. 8714 - 8720
(2011/07/30)
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- Pyranoside phosphite-oxazoline ligands for the highly versatile and enantioselective Ir-catalyzed hydrogenation of minimally functionalized olefins. A combined theoretical and experimental study
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A modular set of phosphite-oxazoline (P,N) ligands has been applied to the title reaction. Excellent ligands have been identified for a range of substrates, including previously challenging terminally disubstituted olefins, where we now have reached enantioselectivities of 99% for a range of substrates. The selectivity is best for minimally functionalized substrates with at least a moderate size difference between geminal groups. A DFT study has allowed identification of the preferred pathway. Computational prediction of enantioselectivities gave very good accuracy.
- Mazuela, Javier,Norrby, Per-Ola,Andersson, Pher G.,Pamies, Oscar,Dieguez, Montserrat
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supporting information; experimental part
p. 13634 - 13645
(2011/10/10)
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- Novel reactivity of N-bridged diiron phthalocyanine in the activation of C-H bonds: Hydroacylation of olefins as an example of the efficient formation of C-C bonds
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Bridge over troubled iron: An N-bridged diiron tetra-tert- butylphthalocyanine complex, usually employed for oxidation reactions, also catalyzes the addition of acetaldehyde to olefins (see scheme) to provide methylketones with a high selectivity (up to 92%) and high turnover numbers (3600-5700). Copyright
- Alvarez, Leonardo X.,Kudrik, Evgeny V.,Sorokin, Alexander B.
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supporting information; experimental part
p. 9298 - 9301
(2011/10/09)
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- Ionic liquids for enhancing the enantioselectivity of isolated BVMO-catalysed oxidations
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The present study describes the first-time usage of an isolated thermostable Baeyer-Villiger monooxygenase (phenylacetone monooxygenase, PAMO) in the presence of ionic liquids. The stability, activity and selectivity of PAMO as an oxidative enzyme in the presence of different ionic liquids were studied. This revealed that the addition of some specific ionic liquids, such Ammoeng 102 and [bmim]MeSO4, can significantly enhance the E-value in the oxidation of racemic benzylketones. Moreover, the use of ionic liquids increases the optimal substrate concentration for performing Baeyer-Villiger oxidation, thereby extending the biocatalytic repertoire of PAMO for synthetic applications.
- Rodriguez, Cristina,De Gonzalo, Gonzalo,Fraaije, Marco W.,Gotor, Vicente
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supporting information; experimental part
p. 2255 - 2260
(2011/02/24)
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- Chemoselective conjugate reduction of α,β-unsaturated ketones catalyzed by rhodium amido complexes in aqueous media
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Although a notable feature of Noyori's Ru-TsDPEN complex is that the transfer hydrogenation reaction is highly chemoselective for the C-O functional group and tolerant of alkenes, our early report indicated that the chemoselectivity could be switched from C-O to C-C bonds in the transfer hydrogenation of activated α,β-unsaturated ketones. Now we have found that a variety of α,β-unsaturated ketones, even without other electron-withdrawing functional groups, could be reduced on the alkenic double bonds with high selectivities employing amido-rhodium hydride complex in aqueous media, and up to 100% chemoselectivity has been achieved. It is notable that the chemoselectivity was improved significantly on going from organic solvent to water. Moreover, a 1,4-addition mechanism has been proposed on the basis of the corresponding experimental details and computational analysis.
- Li, Xuefeng,Li, Liangchun,Tang, Yuanfu,Zhong, Ling,Cun, Linfeng,Zhu, Jin,Liao, Jian,Deng, Jingen
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supporting information; experimental part
p. 2981 - 2988
(2010/07/05)
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- Synthesis of α-methyl ketones by a selective, iridium-catalyzed cyclopropanol ring-opening reaction
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A mild method for synthesizing α-methyl ketones from substituted cyclopropanols is reported. This process, catalyzed by [CpIrCl2] 2, cleaves cyclopropanol rings regioselectively and more efficiently than the other conditions examined. While tertiary cyclopropanols afford α-methyl ketones, secondary cyclopropanols and cyclopropyl silyl ethers are less reactive and yield other isomerization products.
- Ziegler, Daniel T.,Steffens, Andrew M.,Funk, Timothy W.
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supporting information; experimental part
p. 6726 - 6729
(2011/02/25)
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- CuH-catalyzed enantioselective 1,2-reductions of α,β-unsaturated ketones
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The first study on a general technology for arriving at valued nonracemic allylic alcohols using asymmetric ligand-accelerated catalysis by copper hydride is described.
- Moser, Ralph,Boskovia, Zarko V.,Crowe, Christopher S.,Lipshutz, Bruce H.
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supporting information; experimental part
p. 7852 - 7853
(2010/08/04)
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- Baeyer-Villiger monooxygenase-catalyzed kinetic resolution of racemic α-alkyl benzyl ketones: enzymatic synthesis of α-alkyl benzylketones and α-alkyl benzylesters
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The application of three BVMOs for the enantioselective oxidation of 3-phenylbutan-2-ones with different substituents in the aromatic moiety is described. By choosing the appropriate biocatalyst and substrate combination, chiral ketones and esters can be obtained with excellent enantiopurities. This methodology could also be applied to the resolution of racemic α-alkyl benzylketones with longer alkyl chains as well as with two substituted α-substituted benzylacetones. A kinetic analysis revealed that the BVMOs studied effectively convert all tested compounds showing that the enzymes are tolerant towards the substrate structure while being highly enantioselective. These properties render BVMOs as valuable biocatalysts for the preparation of compounds with high interest in organic synthesis.
- Rodriguez, Cristina,Gonzalo, Gonzalo de,Torres Pazmino, Daniel E.,Fraaije, Marco W.,Gotor, Vicente
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experimental part
p. 1168 - 1173
(2009/10/02)
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- Ruthenium-catalyzed redox isomerization/transfer hydrogenation in organic and aqueous media: A one-pot tandem process for the reduction of allylic alcohols
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The hexamethylbenzene-ruthenium(ii) dimer [{RuCl(μ-Cl) (η6-C6Me6)}2] 1 and the mononuclear bis(allyl)-ruthenium(iv) complex [RuCl2(η 3:η2:η3-C12H 18)]2, associated with base and a hydrogen donor, were found to be active catalysts for the selective reduction of the CC bond of allylic alcohols both in organic and aqueous media. The process, which proceeds in a one-pot manner, involves a sequence of two independent reactions: (i) the initial redox-isomerization of the allylic alcohol, and (ii) subsequent transfer hydrogenation of the resulting carbonyl compound. The highly efficient transformation reported herein represents, not only an illustrative example of auto-tandem catalysis, but also an appealing alternative to the classical transition-metal catalyzed CC hydrogenations of allylic alcohols. The process has been successfully applied to aromatic as well as aliphatic substrates affording the corresponding saturated alcohols in 45-100% yields after 1.5-24 h. The best performances were reached using (i) 1-5 mol% of 1 or 2, 2-10 mol% of Cs2CO3, and propan-2-ol or (ii) 1-5 mol% of 1 or 2, 10-15 equivalents of NaO2CH, and water. The catalytic efficiency is strongly related to the structure of the allylic alcohol employed. Thus, in propan-2-ol, the reaction rate essentially depends on the steric requirement around the CC bond, therefore decreasing with the increasing number of substituents. On other hand, in water the transformation is favoured for primary allylic alcohols vs. secondary ones.
- Cadierno, Victorio,Crochet, Pascale,Francos, Javier,Garcia-Garrido, Sergio E.,Gimeno, Jose,Nebra, Noel
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scheme or table
p. 1992 - 2000
(2010/06/19)
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- The chiral auxiliary N-1-(1′-Naphthyl)ethyl-O-tert- butylhydroxylamine: A chiral weinreb amide equivalent
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The chiral auxiliary N-1-(1′-naphthyl)ethyl-O-terf- butylhydroxylamine is readily prepared from N-hydroxyphthalimide in four steps, with resolution giving access to both enantiomers in >98% ee, on a multigram (>25 g) scale. Conversion to a range of N-acyl derivatives, followed by highly diastereoselective alkylation (≥94% de) gives the corresponding chiral, 2-substituted derivatives as single diastereoisomers (>98% de) after chromatography. Reductive cleavage with LiAlH4 allows direct access to chiral aldehydes, and treatment with MeLi gives chiral methyl ketones in excellent enantiopurity (≥94% ee). The auxiliary can be recovered in >98% ee and recycled.
- Chernega, Alexander N.,Davies, Stephen G.,Goodwin, Christopher J.,Hepworth, David,Kurosawa, Wataru,Roberts, Paul M.,Thomson, James E.
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supporting information; experimental part
p. 3254 - 3257
(2009/12/05)
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- Synthesis of enol lactones via Cu(I)-catalyzed intramolecular O-vinylation of carboxylic acids
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With the catalysis of Cul/trans-W,W-dimethylcyclohexane-1,2-diamine, a number of carboxylic acids underwent efficient intramolecular O-vinylation with vinyl bromides leading to the synthesis of the corresponding five- and six-membered enol lactones. The same catalytic system also led to the efficient cycloisomerization of alkynoic acids.
- Sun, Changhul,Fang, Yewen,Li, Shuang,Zhang, Yue,Zhao, Qlwu,Zhu, Shana,Li, Chaozhong
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scheme or table
p. 4084 - 4087
(2009/12/06)
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- Highly enantioselective synthesis of optically active ketones by iridium-catalyzed asymmetric hydrogenation
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(Chemical Equation Presented) Close to perfect enantioselectivity (up to 99% ee, see scheme) is found for the formation of α-substituted ketones by the asymmetric hydrogenation of enones with an iridium-phosphinooxazoline catalyst. In an operationally simple process, both linear and cyclic substrates react well and afford the desired products in high yields. A wide variety of substituents are tolerated, thus making the method synthetically appealing.
- Lu, Sheng-Mei,Bolm, Carsten
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supporting information; experimental part
p. 8920 - 8923
(2009/05/30)
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- Transposition of allylic alcohols into carbonyl compounds catalyzed by rhodium-phosphinine complexes
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The isomerization of a variety of allylic alcohols with formation of the corresponding saturated carbonyl compounds is readily accomplished by a new catalyst system comprising rhodium and a trisubstituted phosphinine (phosphabenzene derivative), especially when the Rh complex is activated by hydrogen prior to the transposition reaction. Georg Thieme Verlag Stuttgart.
- Reetz, Manfred T.,Guo, Hongchao
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p. 2127 - 2129
(2008/02/08)
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- Pyrrole and pyrazole DAAO inhibitors
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Methods for increasing D-Serine concentration and reducing concentration of the toxic products of D-Serine oxidation, for enhancing learning, memory and/or cognition, or for treating schizophrenia, Alzheimer's disease, ataxia or neuropathic pain, or preventing loss in neuronal function characteristic of neurodegenerative diseases involve administering to a subject in need of treatment a therapeutically effective amount of a compound of formula I, or a pharmaceutically acceptable salt or solvate thereof: wherein R1 and R2 are independently selected from hydrogen, halo, nitro, alkyl, acyl, alkylaryl, and XYR5; or R1 and R2, taken together, form a 5, 6, 7 or 8-membered substituted or unsubstituted carbocyclic or heterocyclic group; X and Y are independently selected from O, S, NH, and (CR6R7)n; R3 is hydrogen, alkyl or M+; M is aluminum, calcium, lithium, magnesium, potassium, sodium, zinc ion or a mixture thereof; Z is N or CR4; R4 is from selected from hydrogen, halo, nitro, alkyl, alkylaryl, and XYR5; R5 is selected from aryl, substituted aryl, heteroaryl and substituted heteroaryl; R6 and R7 are independently selected from hydrogen and alkyl; n is an integer from 1 to 6; at least one of R1, R2 and R4 is other than hydrogen; and at least one of X and Y is (CR6R7)n. D-serine or cycloserine may be coadministered along with the compound of formula I.
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Page/Page column 27-28
(2008/06/13)
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- The Heck-type arylation of allylic alcohols with arenediazonium salts
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The Heck coupling of ArN2BF4 with secondary allylic alcohols, carried out in methanol using Pd(dba)2 as catalyst without extra ligands and base, leads to the corresponding β-arylated carbonyl compounds. Such conditions afford arylated acetals from primary allylic alcohols.
- Masllorens, Judit,Bouquillon, Sandrine,Roglans, Anna,Hénin, Fran?oise,Muzart, Jacques
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p. 3822 - 3826
(2007/10/03)
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- Direct conversion of N-methoxy-N-methylamides (Weinreb amides) to ketones via a nonclassical Wittig reaction
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(Chemical Equation Presented) N-Methoxy-N-methylamides (Weinreb amides) are converted efficiently into ketones by reaction with alkylidenetriphenylphosphoranes and in situ hydrolysis of the product.
- Murphy, John A.,Commeureuc, Aurelien G. J.,Snaddon, Thomas N.,McGuire, Thomas M.,Khan, Tanweer A.,Hisler, Kevin,Dewis, Mark L.,Carling, Robert
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p. 1427 - 1429
(2007/10/03)
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- Chirality and fragrance chemistry: Stereoisomers of the commercial chiral odorants muguesia and pamplefleur
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(Chemical Equation Presented) The work describes the enzyme-mediated preparation and the odor evaluation of the single stereoisomers of the commercial odorants Muguesia and Pamplefleur. The synthetic approach to Muguesia stereoisomers helped to clear the assignment of the relative configuration of intermediate diols 5. The odor response of Pamplefleur isomers was found to be rather unusual. No stereoisomer prevailed, but each one played a definite role in establishing the odor sensation of the final blend.
- Abate, Agnese,Brenna, Elisabetta,Fuganti, Claudio,Gatti, Francesco G.,Giovenzana, Tommaso,Malpezzi, Luciana,Serra, Stefano
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p. 1281 - 1290
(2007/10/03)
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- Application of A Recyclable Pseudoephedrine Resin in Asymmetric Alkylations on Solid Phase
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A pseudoephedrine resin has been successfully employed in asymmetric alkylations on solid phase. Immobilized pseudoephedrine amides are conveniently prepared by the one-step attachment of pseudoephedrine to Merrifield resin through the hydroxyl group and subsequent acylation on nitrogen. Deprotonation and alkylation of the resin-bound amides proceeds smoothly. Ketones and alcohols are cleaved from the resin in high enantiomeric excess and moderate to good overall yield. The parallel, asymmetric solid-phase synthesis of a small library of chiral ketones and alcohols has been carried out to illustrate the utility of the approach. Finally, the pseudoephedrine resin can be conveniently recycled and utilized with no significant loss in the yield or enantiomeric excess of the products.
- Hutchison, Panee C.,Heightman, Tom D.,Procter, David J.
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p. 790 - 801
(2007/10/03)
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- Rhodium-catalyzed conjugate addition of aryl- and alkenyl-stannanes to α,β-unsaturated carbonyl compounds
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The addition of aryl- or alkenyl-trimethylstannanes to α,β-unsaturated carbonyl compounds in the presence of a catalytic amount of a cationic rhodium complex ([Rh(cod)(MeCN)2]BF4) and water to afford the conjugate addition products in good yields was examined. It was observed that addition of water was necessary for the reaction to proceed smoothly. The aryl- or alkenyl-rhodium complex, which is generated by the transmetalation from the organotin compound, is considered to be the active catalytic species.
- Oi, Shuichi,Moro, Mitsutoshi,Ito, Hisanori,Honma, Yoshio,Miyano, Sotaro,Inoue, Yoshio
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