41049-51-8Relevant articles and documents
A broadly applicable and practical oligomeric (salen)Co catalyst for enantioselective epoxide ring-opening reactions
White, David E.,Tadross, Pamela M.,Lu, Zhe,Jacobsen, Eric N.
supporting information, p. 4165 - 4180 (2014/06/09)
The (salen)Co catalyst (4a) can be prepared as a mixture of cyclic oligomers in a short, chromatography-free synthesis from inexpensive, commercially available precursors. This catalyst displays remarkable enhancements in reactivity and enantioselectivity relative to monomeric and other multimeric (salen)Co catalysts in a wide variety of enantioselective epoxide ring-opening reactions. The application of catalyst 4a is illustrated in the kinetic resolution of terminal epoxides by nucleophilic ring-opening with water, phenols, and primary alcohols; the desymmetrization of meso epoxides by addition of water and carbamates; and the desymmetrization of oxetanes by intramolecular ring opening with alcohols and phenols. The favorable solubility properties of complex 4a under the catalytic conditions facilitated mechanistic studies, allowing elucidation of the basis for the beneficial effect of oligomerization. Finally, a catalyst selection guide is provided to delineate the specific advantages of oligomeric catalyst 4a relative to (salen)Co monomer 1 for each reaction class.
Radical and non-radical mechanisms for alkane oxidations by hydrogen peroxide-trifluoroacetic acid
Camaioni,Bays,Shaw,Linehan,Birnbaum
, p. 789 - 795 (2007/10/03)
The oxidation of cyclohexane by the H2O2-trifluoroacetic acid system is revisited. Consistent with a previous report (Deno, N.; Messer, L. A. Chem. Comm. 1976, 1051), cyclohexanol forms initially but then esterifies to cyclohexyl trifluoroacetate. Small amounts of trans-1,2-cyclohexadiyl bis-(trifluoroacetate) also form. Although these products form irrespective of the presence or absence of O2, dual mechanisms are shown to operate. In the absence of O2, the dominant mechanism is a radical chain reaction that is propagated by CF3· abstracting H from C6H12 and SH2 displacement of C6H11· on CF3CO2OH. The intermediacy of C6H11· and CF3· is inferred from production of CHF3 and CO2 along with cyclohexyl trifluoroacetate, or CDF3 when cyclohexane-d12 is used. In the presence of O2, fluoroform and CO2 are suppressed, the reaction rate slows, and the rate law approaches second order (first order in peracid and in C6H12). Trapping of cyclohexyl radicals by quinoxaline is inefficient except at elevated (～75°C) temperatures. Fluoroform and CO2, telltale evidence for the chain pathway, were not produced when quinoxaline was present in room temperature reactions. These observations suggest that a parallel, nonfree radical, oxenoid insertion mechanism dominates when O2 is present. A pathway is discussed in which a biradicaloid-zwiterionic transition state is attained by hydrogen transfer from alkane to peroxide oxygen with synchronous O-O bond scission.
Oxidation of Alkenes by Iodine Tris(trifluoroacetate). On the cis-Effect of the Trifluoroacetate Group in Oxidations
Buddrus, Joachim,Plettenberg, Horst
, p. 1494 - 1506 (2007/10/02)
Iodine tris(trifluoroacetate) oxidizes alkenes to α-glycol bis(trifluoroacetates) (eq. (1) and tab. 1).By-products are acylals emerging out of a 1,2-shift (eq. (3)). 1,2-Disubstituted alkenes are mainly transformed into cis-glycol derivatives and tri- and tetrasubstituted alkenes to cis/trans mixtures.The oxidations proceed via 2-acyloxy-1,3-dioxolanes, formerly postulated by Winstein et al. as intermediates in similar oxidations, but only now isolated (comp. 3) and examined by NMR and rearranged to the corresponding α-glycols (3 -> 5).A similar reaction course isproposed for certain other alkene oxidations known from literature, in which a trifluoroacetate group is involved and which proceed under cis-addition (table 3).
