28358-60-3Relevant articles and documents
Effect of immobilization on catalytic characteristics of saturated Pd-N-heterocyclic carbenes in Mizoroki-Heck reactions
Aksin, ?zge,Türkmen, Hayati,Artok, Levent,?etinkaya, Bekir,Ni, Chaoying,Büyükgüng?r, Orhan,?zkal, Erhan
, p. 3027 - 3036 (2007/10/03)
A saturated Pd-N-heterocyclic complex was immobilized on an amorphous silica. The complex itself is of very high thermal stability. However, TEM observations, hot filtration, reusability, and poisoning tests all revealed that the complex acted only as a precatalyst to highly active Pd species in Mizoroki-Heck reactions when immobilized. The complex appears more stable when used under homogeneous reaction conditions. The immobilized complex afforded high turnover numbers, 104-105. The higher turnover frequencies were realized at the lower Pd concentrations, which is a characteristic property of ligand-free Pd catalyzed reactions.
Substituent-Dependent Electron-Transfer Induced Photooxygenation of 1,1-Diarylethylenes
Gollnick, Klaus,Schnatterer, Albert,Utschick, Gerald
, p. 6049 - 6056 (2007/10/02)
Rates and products of 9,10-dicyanoanthracene-sensitized photooxygenations of 1,1-diarylethylenes (1a-r) in acetonitrile were studied.If at least one of the aryl groups carries an electron-donating substituent at the para (or ortho) position (1a-l), 3,3,6,6-tetraaryl-1,2-dioxanes (2a-l) are generated in high yields (85-100percent).Benzophenones (3) are the only other observable products. 1,1-Diphenylethylene (1n) and its m-methoxy (1m), p-chloro (1o,p), and p-nitro (1q,r) derivatives, however, yield mainly benzophenones (3m-r) (>50percent) (the p-nitro compounds only in the presence of biphenyl). 1,2-Dioxanes (2m-p), cyclobutanes (4n-p), and α-tetralones (5m-o) are obtained as side products.Dioxanes, benzophenones, and α-tetralones are products of electron-transfer induced oxygenations involving triplet ground-state molecular oxygen, 3O2.Singlet molecular oxygen, O2(1Δg), contributes to the benzophenone formation from strongly electron-donor substituted diarylethylenes.An exception is the most powerful electron-donor substituted diarylethylene 1a, with which O2(1Δg) undergoes an electron-transfer reaction affording dioxane 2a.Dioxane formation proceeds via free-radical cations 1.+, which enter into a chain reaction with 1, 3O2, and another molecule of 1 to yield dioxane 2 and a new radical cation 1.+ that maintains the chain reaction.The efficiency of this chain process, however, is found to be several orders of magnitude smaller than expected.To explain this result, a 1,6-biradical .1-1-O2. is proposed to be generated in this chain reaction as the product-determining intermediate that predominantly fragments into 3O2 and two molecules of 1.Cyclization to dioxane 2 and transformation to benzophenone 3 occur at presumably less than 0.1percent from this biradical.The pathways leading to cyclobutanes (4) and α-tetralones (5) are also discussed.
Herbicidal 12-substituted 12H-dibenzo(D,G)(1,3)dioxocin-6-carboxylic acids
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, (2008/06/13)
Dibenzo[d,g][1,3]dioxocin-6-carboxylic acids substituted by methyl or ethyl or a moiety --CH2 CH2 -- at the 12-position and optionally substituted at other positions, such as methyl 4'-chlorospiro(cyclopropane-1,12'(12'H)-dibenzo[d,g][1,3]dioxocin)-6'-carboxylic acid, and their agriculturally acceptable esters, amides, and salts are useful for the control of undesirable vegetation. The 1,1-diarylcyclopropane intermediates required for the spirocyclopropane compounds can be prepared from appropriately substituted 1,1-diarylethene procursors by reaction with phenylthiomethyl lithium reagent.
