- Shedding light on the use of Cu(ii)-salen complexes in the A3 coupling reaction
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One Cu(ii) complex, {Cu(ii)L} (1S), has been synthesised, in two high yielding steps under ambient conditions, and characterised by single-crystal X-Ray diffraction (SXRD), IR, UV-Vis, circular dichroism (CD), elemental analysis, thermogravimetric analysis (TGA) and electron spray ionization mass spectroscopy (ESI-MS). This air-stable compound enables the generation, at room temperature and in open-air, of twenty propargylamines, nine new, from secondary amines, aliphatic aldehydes and alkynes with a broad scope with yields up to 99%. Catalyst loadings can be as low as 1 mol%, while the recovered material retains its structural integrity and can be used up to 5 times without loss of its activity. Control experiments, SXRD, cyclic voltammetry and theoretical studies shed light on the mechanism revealing that the key to success is the use of phenoxido salen based ligands. These ligands orchestrate topological control permitting alkyne binding with concomitant activation of the C-H bond and simultaneously acting as a template temporarily accommodating the abstracted acetylenic proton, and continuously generating, via in situ formed radicals and a Single Electron Transfer (SET) mechanism, a transient Cu(i) active site to facilitate this transformation. The scope and limitations of this protocol are discussed and presented.
- Sampani, Stavroula I.,Zdorichenko, Victor,Danopoulou, Marianna,Leech, Matthew C.,Lam, Kevin,Abdul-Sada, Alaa,Cox, Brian,Tizzard, Graham J.,Coles, Simon J.,Tsipis, Athanassios,Kostakis, George E.
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supporting information
p. 289 - 299
(2020/01/21)
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- Salen manganese (III) complexes as catalysts for R-(+)-limonene oxidation
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The epoxidation of R-(+)-limonene using in situ generated dimethyldioxirane (DMD) as the oxidizing agent and four Jacobsen-type catalysts ((R,R)-Jacobsen, (S,S)-Jacobsen, racemic Jacobsen and achiral Jacobsen) was examined. The effect of the amount of KHSO5 and acetone in the catalyzed and un-catalyzed reaction was also assessed. The main reaction products were diepoxide and endocyclic monoepoxide. In the absence of catalyst, the amount of KHSO5 did not significantly influence conversion and selectivity. The catalyst can be segregated to a different phase and separated from the reaction media when the amount of KHSO5 is above the stoichiometric ratio, R-(+)-limonene/KHSO5 = 0.5 mmol/mmol, and acetone/mmol R-(+)-limonene = 2 mL/mmol. However, when the amount of KHSO5 is below the stoichiometric ratio (R-(+)-limonene/KHSO5 = 1.5 mmol/mmol) the catalyst is difficult to separate. Under the reaction conditions of this study, when the catalyst is segregated, no effect of the catalyst chiral center, (R,R)-Jacobsen or (S,S)-Jacobsen, was found on conversion and selectivity. Additionally, the (R,R)-Jacobsen's catalyst proved to be very stable to oxidative degradation.
- Cubillos, Jairo,Vásquez, Santiago,Montes de Correa, Consuelo
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experimental part
p. 57 - 65
(2010/10/02)
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- Catalytic asymmetric synthesis of O-acetylcyanohydrins from potassium cyanide, acetic anhydride, and aldehydes, promoted by chiral salen complexes of titanium(IV) and vanadium(V)
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The utility of the chiral [Ti(μ-O)(salen)]2 complexes (R)- and (S)-1 (H2salen was prepared from (R,R)- or (S,S)-cyclohexane-1,2-diamine and 3.5-di(tert-butyl)-2-hydroxybenzaldehyde) as catalysts for the asymmetric addition of KCN and Ac2O to aldehydes to produce O-acetylcyanohydrins was investigated. It was shown that the complexes were active at a substrate/catalyst ratio of 100:1 and produced the O-protected cyanohydrins with ee in the range of 60-92% at -40°. Other complexes, [Ti2(AcO)2(μ-O)(salen)2] ((R)-4) and [Ti(CF3COO)2(salen)] ((R)-5), were prepared from (R)-1 by treatment with different amounts of Ac2O and (CF3CO)2O, and their catalytic activities were tested under the same conditions. The efficiency of (R)-4 was found to be even greater than that of (R)-1, whereas (R)-5 was inactive. The synthesis of the corresponding salen complexes of VIV and VV,[V(O)(salen)] ((R)-2) and [V(O)(salen)(H2O)][S(O)3OEt] ((R)-3), was elaborated. and their X-ray crystal structures were determined. The efficiency of (R)-3 was sufficient to produce O-acetyl derivatives of aromatic cyanohydrins with ee in the range of 80-91% at -40°.
- Belokon, Yuri N.,Carta, Paola,Gutnov, Andrey V.,Maleev, Viktor,Moskalenko, Margarita A.,Yashkina, Lidia V.,Ikonnikov, Nicolai S.,Voskoboev, Nikolai V.,Khrustalev, Viktor N.,North, Michael
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p. 3301 - 3312
(2007/10/03)
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