- Electrochemical generation and catalytic use of selenium electrophiles
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The generation and use of selenium electrophiles in catalytic, electrochemically driven selenenylation-elimination sequences is described. Georg Thieme Verlag Stuttgart.
- Niyomura, Osamu,Cox, Matthew,Wirth, Thomas
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p. 251 - 254
(2007/10/03)
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- Product studies and laser flash photolysis on alkyl radicals containing two different β-leaving groups are consonant with the formation of an olefin cation radical
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1-Bromo-2-methoxy-1-phenylpropan-2-yl (3) and 2-methoxy-1-phenyl-1-diphenylphosphatopropan-2-yl (4) were generated under continual photolysis from the respective PTOC precursors in a mixture of acetonitrile and methanol. The radicals undergo heterolytic fragmentation of the substituent in the β-position to generate the olefin cation radical (5). Z-2-Methoxy-1-phenylpropene (15) is the major product formed in the presence of 1,4-cyclohexadiene, and is believed to result from hydrogen atom transfer to the oxygen of the olefin cation radical, followed by deprotonation. Laser flash photolysis experiments indicate that reaction between 5 and 1,4-cyclohexadiene occurs with a rate constant of ~6 × 105 M-1 s-1. 2,2-Dimethoxy-1-phenylpropane (18) is observed as a minor product. Laser flash photolysis experiments place an upper limit on methanol trapping of 5 at k 3 M-1 s-1 and do not provide any evidence for the formation of reactive intermediates other than 5. The use of two PTOC precursors containing different leaving groups to generate a common olefin cation radical enables one to utilize product analysis to probe for the intermediacy of other reactive intermediates. The ratio of 15:18 is dependent upon hydrogen atom donor concentration, but is independent of the PTOC precursor. These observations are consistent with the proposal that both products result from trapping of 5 that is formed via heterolysis of 3 and 4.
- Bales,Horner,Huang,Newcomb,Crich,Greenberg
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p. 3623 - 3629
(2007/10/03)
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- ELECTROOXIDATION OF ALKEN-1-YLARENES IN AQUEOUS ALCOHOL SOLUTIONS
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In the initial stages of the electrooxidation of alken-1-ylarenes-propenyl-benzene (Ia) and 4-propenylanisole (Ib) - in aqueous alcohol solutions, 1,2-dialkoxypropyl- (II), 1-hydroxy-2-alkoxypropyl- (VII), and 1,2-dihydroxy-propyl arenes (VIII) are formed.Subsequent rupture of the C-C benzyl bond converts the ethers (II) into benzaldehyde acetals (III) and benzaldehydes (IV), and compounds (VII) and (VIII) into (IV).Benzaldehydes (IV) are also formed from (II) by hydrolysis of the acetals (III) - partly for (IIIa) and completely for (IIIb).Electrolysis of (Ia and Ib) in aqueeous alcohol solution leads mainly to their conversion into benzaldehydes (IV).
- Ogibin, Yu. N.,Ilovaiskii, A. I.,Nikishin, G. I.
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p. 2065 - 2070
(2007/10/02)
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- ELECTROCHEMICAL CLEAVAGE OF THE DOUBLE BOND OF 1-ALKENYLARENES
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A study has been made of the electrochemical cleavage of the double bond of propenylbenzene (Ia) and p-propenylanisole (Ib), which takes place upon anodic oxidation of (Ia, b) in alcoholic solutions of sodium trifluoroacetate and other electrolytes and which leads to conversion of (Ia, b) to benzaldehyde dialkylacetals.Conditions are found that provide for highly selective (>80percent) conversion of (Ib) and p-propenyltoluene to p-methyl- and p-methoxybenzaldehyde dimethylacetals.
- Ogibin, Yu. N.,Sokolov, A. B.,Ilovaiskii, A. I.,Elison, M. N.,Nikishin, G. I.
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p. 561 - 566
(2007/10/02)
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- ELECTROOXIDATIVE REARRANGEMENT OF CONJUGATED ARYLOLEFINS TO ARYLACETALDEHYDE DIMETHYL ACETALS
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Electrochemical oxidation of conjugated arylolefins 1 in trimethyl orthoformate containing iodine gave arylacetaldehyde dimethyl acetals 2 in high yields.
- Shono, Tatsuya,Matsumura, Yoshihiro,Katoh, Susumu,Ikeda, Kaoru,Fujita, Tetsuhiro,Kamada, Tohru
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p. 5309 - 5312
(2007/10/02)
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- METHOXYCHLORINATION AND DIMETHOXYLATION OF ALKENES. THE REACTIONS OF SUBSTITUTED STYRENES WITH PHENYLSELENENYL CHLORIDE IN METHANOL
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The addition of PhSeCl to α- and β-substituted styrenes in methanol is regio- and stereospecific and affords the products of methoxyselenenylation.These compounds further react with PhSeCl to give the deselenenylation products.In the case of α-substituted styrenes, 1-methoxy, 2-chloroalkanes are produced, whereas with β-substituted styrenes the major reaction products are the 1,2-dimethoxyalkanes and the 2,2-dimethoxyalkanes in which phenyl migration has occured.It is shown that these reactions proceed through the intermediate formation of the alkyl phenylselenium dichlorides, PhCR(OMe)CHR1SeCl2Ph, which evolve with different mechanisms depending on the structure of the starting alkenes.
- Tiecco, Marcello,Testaferri, Lorenzo,Tingoli, Marco,Chianelli, Donatella,Bartoli, Donatella
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p. 2261 - 2272
(2007/10/02)
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- Metalation of Alkynes. Part 2. Behaviour of Alkynes with Mercury(II)Acetate in Methanol: a Systematic Reinvestigation
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The reaction of a series of alkynes with mercury(II)acetate, both in equimolar and catalytic amounts, were investigated in methanol.Hex-1-yne, oct-1-yne, oct-4-yne, 1,4-diacetoxybut-2-yne, methyl oct-2-ynoate, methyl 3-phenylpropynoate, oct-2-ynoic acid, phenylpropynoic acid, oct-1-yn-3-ol, 1-ethynylcyclohexanol, 1-ethynylcyclohexamine, phenylethyne, diphenylethyne, and ethynylferrocene were the examined substrates.The non-mercuriated products from the reaction were the corresponding vinyl ether, dialkoxyalkane, and ketone, isolated under preparative conditions.The presence of 0.1percent toluene-p-sulphonic acid increased the reactivity.The reactions of oct-1-yne and oct-4-yne were studied in detail by following with time the formation of the products under a variety of conditions, and a mechanistic scheme was drawn.For comparison, styrene, trans-oct-4-ene, and trans-β-methylstyrene were treated with 5 molpercent mercury(II) acetate.The reaction of alkenes was found to be non-catalytic.
- Bassetti, Mauro,Floris, Barbara
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p. 227 - 234
(2007/10/02)
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- Photochemical Electron-transfer Reaction between Aromatic Olefins and Metal Ions. Dependence of the Reaction Course on the Structure of the Olefins
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To investigate the photochemical electron transfer from aromatic olefins to copper(II) or iron(III) ions, a series of substituted styrenes (1) was irradiated in the presence of copper(II) or iron(II) salts in methanol, which gave dimethoxylated monomers (2) and one or more of three types of dimethoxylated dimers .The formation of these products are reasonably attributed to the participation of hte cation radicals of the olefins generated by electron transfer from excited olefins to the methal ions.Substituents on the substrates are found to govern the reaction products.
- Kojima, Masanobu,Sakuragi, Hirochika,Tokumaru, Katsumi
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p. 521 - 524
(2007/10/02)
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