96784-47-3Relevant articles and documents
Substituent effects on the photogeneration and selectivity of triaryl vinyl cations
Van Dorp, Jan Willem J.,Lodder, Gerrit
, p. 5416 - 5428 (2008/12/21)
(Chemical Equation Presented) The photochemical reactions of a series of triaryl vinyl halides IX in acetic acid and in acetonitrile have been studied using product analysis as a function of the time of irradiation. The quantum efficiencies of formation of the products derived from the photogenerated vinyl cations 1+ depend on the α-aryl substituent, the β-aryl substituent, the leaving group X (= bromide or chloride), and the temperature at which the irradiations are carried out. Hammett correlation or noncorrelation of the α-aryl substituent effects with (excited-state) substituent constants indicates that the ions 1+ are formed directly from the excited states of 1X by heterolytic cleavage of the carbon-halogen bond. Homolytic cleavage, yielding radicals 1?, is a parallel process: the partitioning into ion and radical occurs in the excited state. This conclusion is corroborated by the leaving group effect and the temperature effect. By performing the photochemical reactions of IX in the presence of HOAc and/or NaOAc as well as the labeled common halide ion 82Br - or 36Cl-, the relative reactivities of the cations 1+ toward these nucleophiles were determined. The selectivities follow the Reactivity-Selectivity Principle. The temperature effect data show that the reactions of the cations with the anionic nucleophiles are (de)solvation controlled and their reactions with the neutral nucleophile activation controlled.
Photoreactivity of Some α-Arylvinyl Bromides in Acetic Acid. Selectivity toward Bromide versus Acetate Ions as a Mechanistic Probe
Van Ginkel, Frits I. M.,Cornelisse, Jan,Lodder, Gerrit
, p. 4261 - 4272 (2007/10/02)
The photochemical reactions of four α-anisyl-β,β-diarylvinyl bromides (1a-1d), three α-phenyl-β,β-diarylvinyl bromides (1e-1g), and 9-(α-bromo-p-methoxybenzylidene)anthrone (2) in acetic acid in the presence of sodium acetate and tetraethylammonium bromide (labeled with 82Br) have been studied quantitatively. Bromide exchange, acetate formation, E/Z isomerization, an anisyl 1,2-shift, stilbene-type cyclization to phenanthrenes, reductive debromination, and oxidation are observed as primary pathways. For all compounds 1, nucleophilic substitution, accompanied by E/Z isomerization in both starting material and product with 1b,c and 1f,g and an anisyl 1,2-shift in 1e but not in 1f,g, is quite efficient and by far the most important process. (Quantum yields range from 0.1 to 0.3 as compared to 0.01-0.02 for cyclization and 0.001-0.01 for reduction). The α-anisylvinyl bromide 2 is virtually inert for photosubstitution. The selectivity constants toward bromide and acetate ions, corrected for their temperature dependence, the amounts of E/Z isomerized starting material and product, the occurrence or nonoccurrence of an anisyl 1,2-shift, and the nature of the capturing nucleophile in the acetolysis are all in quantitative agreement with the corresponding data for the thermal reactions of 1 in the same medium. The results strongly support a mechanism for the nucleophilic vinylic photosubstitution reactions that involves the generation of a product-forming intermediate, which is exactly the same as the intermediate formed in the thermal reaction, a "cold" (thermally relaxed) linear free vinyl cation.
Reaction of Olefins with Malonamide in the Presence of Manganese(III) Acetate. Formation of α,β-Unsaturated γ-Lactones and γ-Lactams
Nishino, Hiroshi
, p. 217 - 222 (2007/10/02)
The reaction of olefins with malonamide in the presence of manganese(III) acetate gave 2-buten-4-olides and/or 1H-pyrrol-2(5H)-ones in one-step, short reaction time and moderate yields.The product distribution can be accounted for in terms of the stabilization of the intermediate carbocation in the oxidation process.The synthetic application and limitation, and the oxidation mechanism for the formations of α,β-unsaturated γ-lactones and γ-lactams are discussed.
The Facile Synthesis of Dihydrofurans by the Oxidation of Olefins with Tris(2,4-pentanedionato)manganese(III)
Nishino, Hiroshi
, p. 1922 - 1927 (2007/10/02)
Eleven olefins were oxidized with tris(2,4-pentanedionato)manganese(III) at the reflux temperature to give the corresponding 3-acetyl-2-methyl-4,5-dihydrofurans in good yields.The oxidation of 9-benzylidene-9,10-dihydroanthracene under the same reaction conditions did not produce the corresponding dihydrofuran, but 9--9,10-dihydroxyanthracene.When 1,1-diphenylethene was oxidized at room temperature, 3-acetyl-2-hydroperoxy-2-methyl-5,5-diphenyltetrahydrofuran was obtained in a high yield.The effects of the solvent and the additives on the yield of dihydrofuran, the comparable reactivities of other (2,4-pentanedionato)metal complexes, such as Co(III), Cr(III), Fe(III), and Cu(II), and the reaction mechanism are discussed.
