17492-61-4Relevant articles and documents
Ab initio analysis on metal ion catalysis in the enolization reactions of some acetylheterocycles: Kinetics of the enolization reactions of 3-acetyl-5-methylisoxazole, 5-acetyl-3-methylisoxazole and 3(5)-acetylpyrazole
Fontana, Antonella,De Maria, Paolo,Pierini, Marco,Siani, Gabriella,Cerritelli, Simona,Macaluso, Gabriella
, p. 247 - 257 (2002)
Kinetic data on the enolization reaction of 3-acetyl-5-methylisoxazole, 5-acetyl-3-methylisoxazole, 3(5)-acetylpyrazole and some previously studied acetylheterocycles have been the object of a comprehensive ab initio analysis. Enolization rate constants were measured spectrophotometrically by the halogen trapping technique at 25 °C and ionic strength of 0.3 mol dm-3 in water, in acetate buffers, in dilute hydrochloric acid, in dilute sodium hydroxide and in the presence of some metal ion salts. In the spontaneous (water) and base (acetate) catalysed reactions the ketones investigated are generally more reactive than acetophenone, according to the electron-withdrawing effect of the heterocyclic ring compared with the benzene ring. In particular, acetylisoxazoles, 3(5)-acetylpyrazole and acetylthiazoles are more reactive than acetylfurans, 2-acetylpyrrole and acetylthiophenes respectively, and this can be attributed to the additional effect of the second heteroatom in the heterocyclic moiety. On the other hand, the compounds investigated are generally less reactive than acetophenone in the H3O+ -catalysed reaction. Ab initio calculations on the relative stability of the protonated and unprotonated forms of the substrates investigated have been compared with the kinetic results obtained in acid solutions. As far as the metal ion catalysis is concerned, an approach in terms of ΔΔE can give an estimate of the combined contributions of charge densities and frontier orbitals to the interaction of the substrate with the metal ion catalyst. A comparison of experimental metal activating factor values and ab initio calculations outlines the importance of charge density on the carbonyl oxygen atom of acetylheterocycles with one heteroatom. An analogous comparison for acetylheterocycles with two heteroatoms suggests the formation of a chelate complex or transition state, in which the metal ion coordinates both the carbonyl oxygen and the aza nitrogen, whenever these two atoms are suitably placed within the molecular structure of the acetylheterocycle. Copyright
Synthesis of Isoxazolines and Isoxazoles via Generation of Nitrile Oxides from O-Stannyl Aldoximes
Moriya, Osamu,Takenaka, Hideo,Urata, Yoshikiyo,Endo, Takeshi
, p. 1671 - 1672 (2007/10/02)
The reactions of O-tributylstannyl aldoximes and active halogen compounds such as tert-butyl hypochlorite or N-bromosuccinimide, whereby nitrile oxides are generated effectively, are applied to the preparations of isoxazolines and isoxazoles via d
Silyl Nitronates in Organic Synthesis. Routes to Heterocycles and Cyclopentanoids. Synthesis of Allethrolone and Calythrone. Acylation and Cyanohydroxylation of Double Bonds. An Exploratory Study
Andersen, Soeren H.,Das, Nalin B.,Joergensen, Ruth D.,Kjeldsen, Gunhild,Knudsen, Jes S.,et al.
, p. 1 - 14 (2007/10/02)
Silyl nitronates are versatile reagents for the preparation of heterocycles by dipolar addition to double bonds.The intermediate isoxazolidines can be transformed to 2-isoxazolines, isoxazoles, furans, dihydrofuranones, pyrazoles, pyridazines and pyridazones.Reduction of 2-isoxazolines with Ti3+ leads to hydroxylated 1,4-diketones, which subsequently can be cyclized to cyclopentenones.Routes to calythrone, rethrolones, prostanoids and a number of naturally occurring dihydrofuranones are devised, as well as synthetic procedures for acylation, preparation of endiones, hydroxyacylation, cyanation and hydroxycyanation of double bonds.
