- A facile synthesis of secondary α-alkoxy or α-acetoxy aromatic ketones
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The treatment of HNIB with aromatic ketones and subsequent solvolysis using alcohol or acetic acid in one-pot system makes it possible to give corresponding secondary α-alkoxy or α-acetoxy ketones in high yields.
- Lee, Jong Chan,Hong, Taiyoung
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p. 4085 - 4090
(2007/10/03)
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- Side-chain fragmentation of arylalkanol radical cations. Carbon-carbon and carbon-hydrogen bond cleavage and the role of α- and β-OH groups
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A product analysis and kinetic study of the one-electron oxidation of a number of 1-arylpropanols, 1,2-diarylethanols, and some of their methyl ethers by potassium 12-tungstocobaltate(III) (abbreviated as Co(III)W) in aqueous acetic acid was carried out and complemented by pulse radiolysis experiments. The oxidations occur via radical cations which undergo side-chain fragmentation involving the C(α)-H and/or C(α)-C(β) bond. With 1-(4-methoxyphenyl)-2-methoxypropane (1), only deprotonation of the radical cation is observed. In contrast, removing the ring methoxy group leads to exclusive C-C bond cleavage in the radical cation. Replacing the side-chain β-OMe by β-OH, the radical cation undergoes both C-C and C-H bond cleavage, with both pathways being base catalyzed. C-C bond breaking in the radical cation is also enhanced by an α-OH group, as shown by 1-(4-methoxyphenyl)-2,2-dimethyl-1-propanol (7), where this pathway, which is also base catalyzed, is the only one observed. Interestingly, α- and β-OH groups exhibit a very similar efficiency in assisting the C-C bond cleavage route in the radical cations, as is evident from the kinetic and products study of the oxidation of 1-phenyl-2-(4-methoxyphenyl)ethanol (5) and 1-(4-methoxyphenyl)-2-phenylethanol (6) by Co(III)W, and from pulse radiolysis experiments on 5 and 6. C-C bond cleavage is the main reaction for both radical cations which exhibit a very similar rate of fragmentation (k = 2.0 and 3.2 x 104 s-1, respectively). In both fragmentation reactions a small solvent isotope effect, k(H2O)/k(D2O) (1.4 for 5.+ and 1.2 for 6.+) and negative activation entropies are observed. These data suggest that a key role in the assistance by α- or β-OH groups to C-C bond cleavage is played by hydrogen bonding or specific solvation of these groups. The kinetic study of the oxidations promoted by Co(III)W has also shown that when only one group, OH or OMe, is present in the side chain (either on C(α) or C(β)), the fragmentation step or both the electron transfer and fragmentation steps contribute to the overall oxidation rate. However, with an OH group on both carbons of the scissile bond, as in 1-(4-methoxyphenyl)-1,2-propanediol (9), the rate of C-C bond cleavage is so fast that the electron transfer step becomes rate determining.
- Baciocchi, Enrico,Bietti, Massimo,Putignani, Lorenza,Steenken, Steen
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p. 5952 - 5960
(2007/10/03)
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- Photochemistry of substituted propiophenones: An interesting α-and aryl substituents effect on their photobehaviour
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Photochemistry of different α-substituted and phenyl-substituted propiophenones in methanol is investigated with a view to delineate the substituent effect with a special reference tu their rearrangement to α-arylpropanoic acids, an important class of nonsteroidal antiinflammatory agents. The results thus obtained bringsforth an important element of their reactivityprofile i.e. the α-chloro-substituent in combination with nuclear alkyl substituents (para>meta) favours 1,2-arylmigration leading to the synthetically useful reaction for α-arylpro panoic acids.
- Sonawane, Harikisan R.,Bellur, Nanjundiah S.,Nazeruddin
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p. 11281 - 11294
(2007/10/02)
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- Photochemical Rearrangement of α-Chloro-Propiophenones to α-Arylpropanoic Acids: Studies on Chirality Transfer and Synthesis of (S)-(+)-Ibuprofen and (S)-(+)-Ketoprofen
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A new single-step efficient photochemical approach for α-arylpropanoic acids (4) from α-chloro-propiophenones (5) is described.It involves carbonyl triplet excited state directed 1,2-aryl migration of the aryl group which has been found to be highly dependent upon the nature of the aryl substituent.The mode of the rearrangement is probed by the study of the photobehaviour of a set of optically active α-chloro-propiophenones.The results suggest that the nature of the carbonyl triplets (n, ?*/ ?, ?*) plays an important role in the chirality transfer.This method finds application in the synthesis of optically active ibuprofen (4e) and ketoprofen (26), though in moderate optical yields.
- Sonawane, Harikisan,Bellur, Nanjundiah S.,Kulkarni, Dilip G.,Ayyangar, Nagaraj R.
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p. 1243 - 1260
(2007/10/02)
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- SILVER ASSISTED REARRANGEMENT OF PRIMARY AND SECONDARY α-BROMO-ALKYLARYLKETONES
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The silver assisted rearrangement of primary and secondary α-bromo-alkylarylketones is reported for the first time.The influence of the acidity on the reaction selectivity is discussed.
- Giordano, Claudio,Castaldi, Graziano,Casagrande, Francesco,Abis, Luigi
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p. 1385 - 1386
(2007/10/02)
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