- A Bimetallic Aluminium(Salphen) Complex for the Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide
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A bimetallic aluminium(salphen) complex is reported as a sustainable, efficient and inexpensive catalyst for the synthesis of cyclic carbonates from epoxides and carbon dioxide. In the presence of this complex and tetrabutylammonium bromide, terminal and internal epoxides reacted at 50 °C and 10 bar carbon dioxide pressure to afford their corresponding cyclic carbonates in yields of 50–94 % and 30–71 % for terminal and internal cyclic carbonates, respectively. Mechanistic studies using deuterated epoxides and an analogous monometallic aluminium(salphen) chloride complex support a mechanism for catalysis by the bimetallic complex, which involves intramolecular cooperative catalysis between the two aluminium centres.
- Wu, Xiao,North, Michael
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- Stereochemical divergence in the formation of organic carbonates derived from internal epoxides
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Catalysis of the challenging cycloaddition of carbon dioxide to internal epoxides has been studied using iron (III) amine triphenolate complexes and particular focus has been given to the stereochemical regulation of this process. When pure cis- or trans-2,3-epoxybutane is used as substrate, the stereochemistry of the product can be controlled yielding selectively cis- or trans-cyclic carbonates for both epoxidic substrates. This stereochemical divergence relates to two accessible catalytic pathways leading to either the cis or trans product via two distinct ring-closure steps. The involved mechanism and stereocontrol is a function of the catalyst/co-catalyst loading, and is further influenced by the medium, temperature and catalyst/co-catalyst structure. Other trans-internal epoxides could also be successfully converted into the pure trans-cyclic carbonate products without any loss of stereochemical information.
- Whiteoak, Christopher J.,Martin, Eddy,Escudero-Adan, Eduardo,Kleij, Arjan W.
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p. 2233 - 2239
(2013/10/01)
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- Reaction of 1,2-cyclic sulfites with some soft nucleophiles. Formation of enantiomerically pure γ-lactones
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The reaction between 1,2-cyclic sulfites and soft carbon centered nucleophiles has been investigated. For monosubstituted cyclic sulfites, the main products were γ-lactones or acetoxy esters. For 1,2-disubstituted cyclic sulfites, cyclopropanes, carbonate and dioxolanes were the main products. A mechanistic rationale for the product formation is presented. Acta Chemica Scandinavica 1998.
- Nymann, Kirsten,Svendsen, John S.
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p. 338 - 349
(2007/10/03)
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- A practical route to enantiopure 1,2-aminoalcohols
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A series of enantiopure aminoalcohols were synthesized from the corresponding diols by activation of the diols as cyclic carbonates, azide opening of the carbonates, and hydrogenation of the resulting azidoalcohols. Factors affecting the azide opening of the carbonates, a simple workup procedure, and a large scale synthesis of (1R,2S)-(-)-2-amino-1,2-diphenylethanol are described.
- Chang, Han-Ting,Sharpless, K. Barry
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p. 3219 - 3222
(2007/10/03)
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