99799-04-9Relevant articles and documents
Catalytic asymmetric formation of δ-Lactones from Unsaturated acyl halides
Tiseni, Paolo S.,Peters, Rene
supporting information; experimental part, p. 2503 - 2517 (2010/09/03)
Previously unexplored enantiopure zwitterionic ammonium dienolates have been utilized in this work as reactive intermediates that act as diene components in hetero-Diels-Alder reactions (HDAs) with aldehydes to produce optically active δ-lactones, subunits of numerous bioactive products. The dienolates were generated in situ from E/Z mixtures of a,b- unsaturated acid chlorides by use of a nucleophilic quinidine derivative and Sn (OTf)2 as co-catalyst. The latter component was not directly involved in the cycloaddition step with aldehydes and simply facilitated the formation of the reactive dienolate species. The scope of the cycloaddition was considerably improved by use of a complex formed from Er- (OTf)3 and a simple commercially available norephedrine-derived ligand that tolerated a broad range of aromatic and heteroaromatic aldehydes for a cooperative bifunctional Lewis-acid-/ Lewis-base-catalyzed reaction, providing a,b-unsaturated d-lactones with excellent enantioselectivities. Mechanistic studies confirmed the formation of the dienolate intermediates for both catalytic systems. The active ErIII complex is most likely a monomeric species. Interestingly, all lanthanides can catalyze the title reaction, but the efficiency in terms of yield and enantioselectivity depends directly on the radius of the Ln III ion. Similarly, use of the pseudolanthanides ScIII and YIII also resulted in product formation, whereas the larger La III and other transition metal salts, as well as main group metal salts, proved to be inefficient. In addition, various synthetic transformations of 6- CCl3- or 4-silyl-substituted α,β-unsaturated d-lactones, giving access to a number of valuable δ-lactone building blocks, were investigated.
Direct observation of dienols produced by photochemical enolisation of α,β-unsaturated ketones: rates and activation parameters for dienol reketonisation via a 1,5-hydrogen shift
Duhaime, Randy M.,Weedon, Alan C.
, p. 1867 - 1872 (2007/10/02)
The production of stable solutions of Z-dienols by ultraviolet light irradiation of α,β-unsaturated ketones at low temperatures (ca. -76 deg C) in d4-methanol is reported.The rates of reketonisation of the dienols via a 1,5-sigmatropic hydrogen shift were determined at various temperatures between -43 deg C and +2 deg C by monitoring the proton nmr spectra of the dienols.From the data the activation parameters for the reaction were calculated.For the dienol Z-2-hydroxy-4-methyl-2,4-pentadiene, 2, derived from photoenolisation of 4-methyl-3-penten-2-one, 1, the activation energy from the Arrhenius plot is 62 +/- 4 kJ/mol, and the activation entropy and enthalpy from the Eyring plot are -87 +/- 15 J/mol K and 60 +/- 4 kJ/mol, respectively.For the dienol Z-4-tert-butyl-2-hydroxy-2,4-pentadiene, 4, obtained from photoenolisation of 4,5,5-trimethyl-3-hexen-2-one, 3, the activation energy, entropy, and enthalpy were found to be 47 +/- 5 kJ/mol, -135 +/- 19 J/mol K, and 45 +/- 5 kJ/mol, respectively.
