Xi:Irritant;19894-99-6Relevant articles and documents
Opening of epoxide rings catalyzed by niobium pentachloride
Constantino, Mauricio Gomes,Lacerda Jr., Valdemar,Invernize, Paulo Roberto,Filho, Luiz Carlos Da Silva,Da Silva, Gil Valdo Jose
, p. 3529 - 3539 (2008/03/13)
The behavior of several epoxides when treated with NbCl5 was studied. In general, the studied epoxides reacted rapidly with NbCl5, giving, in most cases, more than one product (chlorohydrins, products containing solvent residues, as well as rearrangement products). A detailed study was performed to verify the effects of the temperature (rt, 0°C, or -78°C) and of the NbCl5 molar concentration on the composition of the products, yield, and time required for the reactions. Copyright Taylor & Francis Group, LLC.
Diastereoselective epoxidation of olefins by organo sulfonic peracids, II
Kluge,Schulz,Liebsch
, p. 2957 - 2976 (2007/10/03)
We have investigated the behaviour of sulfonic peracids 2 in situ generated towards olefins 7a, 7b, 9, 11, 14, 16, 18, allylic acid and homoallylic alcohols 20, 22, 24, 26, 28, 30, 33 and α,β-unsaturated ketones 35, 37, 39. Generally, the epoxidation proceeds in a peracid-like manner with greater diastereoselectivity than those by common oxidants. In particular, the epoxidation of Δ4 3-ketosteroids 39a-i led to 4α,5α-epoxides 40a-i with remarkable high de-values. Enhanced α-selectivity was also found in the epoxidation of cholesterol 28b. Due to the mild reaction conditions, even acid sensitive epoxides 8a, 8b, 10, 12, 13, 15, 17, 19 were obtained in good yields.
Stereocontrolled Regiospecificity of the Water Loss from trans-Sobrerol Radical Cation upon Electron Ionization
Selva, Antonio,Ferrario, Francesco,Ventura, Paolo,Pellegata, Renato
, p. 523 - 529 (2007/10/02)
Water loss from trans-sobrerol upon electron impact ionization selectively involves the tertiary OH group, predominantly occuring by a stereocontrolled H-transfer from C(5) position in a rate-determining step process, as proved by 18O and deuterium labelling.Monomethyl ethers behave accordingly.Ionic structures of the water-loss product or products are investigated by metastable ion and collision activation mass-analysed ion kinetic energy spectroscopy, using model ions generated from some substrates, which are chemically related to trans-sobrerol in condensed phase, i.e. α-pinane epoxide, cis-sobrerol and pinol.A substantial conversion of cis-sobrerol molecular ions to ionized pinol by loss of water has been demonstrated.
