- Organic Electrochemistry: Expanding the Scope of Paired Reactions
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Paired electrochemical reactions allow the optimization of both atom and energy economy of oxidation and reduction reactions. While many paired electrochemical reactions take advantage of perfectly matched reactions at the anode and cathode, this matching of substrates is not necessary. In constant current electrolysis, the potential at both electrodes adjusts to the substrates in solution. In principle, any oxidation reaction can be paired with any reduction reaction. Various oxidation reactions conducted on the anodic side of the electrolysis were paired with the generation and use of hydrogen gas at the cathode, showing the generality of the anodic process in a paired electrolysis and how the auxiliary reaction required for the oxidation could be used to generate a substrate for a non-electrolysis reaction. This is combined with variations on the cathodic side of the electrolysis to complete the picture and illustrate how oxidation and reduction reactions can be combined.
- Moeller, Kevin D.,Wu, Tiandi
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supporting information
p. 12883 - 12890
(2021/05/07)
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- Rhodium-Catalyzed Room Temperature C-C Activation of Cyclopropanol for One-Step Access to Diverse 1,6-Diketones
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A rhodium-catalyzed room temperature C-C activation of cyclopropanol has been demonstrated for the single-step synthesis of a range of electronically and sterically distinct 1,6-diketones. This reaction proceeds efficiently in shorter reaction time following a highly atom-economical pathway. To illustrate the synthetic potential of 1,6-diketones, aldol and macrocyclization reactions have been successfully demonstrated. Preliminary mechanistic studies revealed the involvement of nonradical pathways.
- Ghosh, Asit,Pati, Bedadyuti Vedvyas,Ravikumar, P. C.
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supporting information
(2020/04/02)
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- Catalytic Cyclopropanol Ring Opening for Divergent Syntheses of γ-Butyrolactones and δ-Ketoesters Containing All-Carbon Quaternary Centers
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Catalytic ring opening cross coupling reactions of strained cyclopropanols have been useful for the syntheses of various β-substituted carbonyl products. Among these ring opening cross coupling reactions, the formation of α,β-unsaturated enone byproducts often competes with the desired cross coupling processes and has been a challenging synthetic problem to be addressed. Herein, we describe our efforts in developing divergent syntheses of a wide range of γ-butyrolactones and δ-ketoesters containing all-carbon quaternary centers via copper-catalyzed cyclopropanol ring opening cross couplings with 2-bromo-2,2-dialkyl esters. Our mechanistic studies reveal that unlike the previously reported cases, the formation of α,β-unsaturated enone intermediates is actually essential for the γ-butyrolactone synthesis and also contributes to the formation of the δ-ketoester product. The γ-butyrolactone synthesis is proposed to go through an intermolecular radical conjugate addition to the in situ generated α,β-unsaturated enone followed by an intramolecular radical cyclization to the ester carbonyl double bond. The reactions are effective to build all-carbon quaternary centers and have broad substrate scope.
- Ye, Zhishi,Cai, Xinpei,Li, Jiawei,Dai, Mingji
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p. 5907 - 5914
(2018/05/24)
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- One-electron oxidation of 2-(4-methoxyphenyl)-2-methylpropanoic and 1-(4-methoxyphenyl)cyclopropanecarboxylic acids in aqueous solution. The involvement of radical cations and the influence of structural effects and pH on the side-chain fragmentation reactivity
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(Chemical Equation Presented) A product and time-resolved kinetic study on the one-electron oxidation of 2-(4-methoxyphenyl)-2-methylpropanoic acid (2), 1-(4-methoxyphenyl)cyclopropanecarboxylic acid (3), and of the corresponding methyl esters (substrates 4 and 5, respectively) has been carried out in aqueous solution. With 2, no direct evidence for the formation of an intermediate radical cation 2?+ but only of the decarboxylated 4-methoxycumyl radical has been obtained, indicating either that 2?+ is not formed or that its decarboxylation is too fast to allow detection under the experimental conditions employed (k > 1 × 107 s -1). With 3, oxidation leads to the formation of the corresponding radical cation 3?+ or radical zwitterion -3 ?+ depending on pH. At pH 1.0 and 6.7, 3?+ and -3?+ have been observed to undergo decarboxylation as the exclusive side-chain fragmentation pathway with rate constants k = 4.6 × 103 and 2.3 × 104 s-1, respectively. With methyl esters 4 and 5, direct evidence for the formation of the corresponding radical cations 4?+ and 5?+ has been obtained. Both radical cations have been observed to display a very low reactivity and an upper limit for their decay rate constants has been determined as k 3 s-1. Comparison between the one-electron oxidation reactions of 2 and 3 shows that the replacement of the C(CH3)2 moiety with a cyclopropyl group determines a decrease in decarboxylation rate constant of more than 3 orders of magnitude. This large difference in reactivity has been qualitatively explained in terms of three main contributions: substrate oxidation potential, stability of the carbon-centered radical formed after decarboxylation, and stereoelectronic effects. In basic solution, -3?+ and 5 ?+ have been observed to react with -OH in a process that is assigned to the -OH-induced ring-opening of the cyclopropane ring, and the corresponding second-order rate constants (k-OH) have been obtained. With -3?+, competition between decarboxylation and -OH-induced cyclopropane ring-opening is observed at pH ≥ 10, with the latter process that becomes the major fragmentation pathway around pH 12.
- Bietti, Massimo,Capone, Alberto
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p. 618 - 629
(2008/09/18)
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- Reactions of 1,2-diketones with vinyllithium: Addition reactions and dianionic oxy Cope rearrangements of cyclic and acyclic substrates
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Dianionic oxy Cope rearrangements have been shown to take place at low temperature upon syn double addition of alkenyllithium derivatives to cyclobutanedione compounds such as benzocyclobutenedione chromium complex 1 or squaric acid esters. In order to obtain some insight into the more general applicability of this type of reaction sequence beyond these special cases, a number of 1,2-diketones were treated with vinyllithium. The diketones tested include benzil derivatives, aliphatic acyclic 1,2-diketones, ortho-quinones, and cyclic aliphatic 1,2-diketones. With benzil and heterobenzil derivatives, the desired double addition/dianionic oxy Cope rearrangement was found to take place at low temperature, leading to 1,6-diketones and their intramolecular aldol adducts in up to 80% overall yield. With acyclic aliphatic 1,2-diketones as substrates, this reaction sequence was also found, albeit with somewhat lower yields and requiring higher temperatures than in the benzil cases. A brief investigation of the intramolecular aldol adduct/1,6-hexanedione equilibrium indicated that the preferential formation of intramolecular aldol adducts at lower temperatures and at shorter reaction times appears to be the result of kinetic reaction control, whereas the preference for 1,6-diketones at higher temperatures is caused by thermodynamic reaction control, ortho-Quinones reacted with vinyllithium only by addition; no dianionic oxy Cope rearrangement was observed. This was also the case for most aliphatic cyclic diketones; however, in the case of 1,2-indanedione, rearrangement products were obtained in moderate yield at elevated reaction temperatures.
- Clausen, Christian,Wartchow, Rudolf,Butenschoen, Holger
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- Novel synthetic inhibitors of selectin-mediated cell adhesion: Synthesis of 1,6-bis[3-(3-carboxymethylphenyl)-4-(2-α-D-mannopyranosyloxy)phenyl] hexane (TBC1269)
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Reports of a high-affinity ligand for E-selectin, sialyl di-Lewis(x) (sLe(x)Le(x), 1), motivated us to incorporate modifications to previously reported biphenyl-based inhibitors that would provide additional interactions with the protein. These compounds were assayed for the ability to inhibit the binding of sialyl Lewis(x) (sLe(x), 2) bearing HL-60 cells to E-, P-, and L- selectin fusion proteins. We report that dimeric or trimeric compounds containing multiple components of simple nonoligosaccharide selectin antagonists inhibit sLe(x)-dependent binding with significantly enhanced potency over the monomeric compound. The enhanced potency is consistent with additional binding interactions within a single selectin lectin domain; however, multivalent interaction with multiple lectin domains as a possible alternative cannot be ruled out. Compound 15e (TBC1269) showed optimal in vitro activity from this class of antagonists and is currently under development for use in the treatment of asthma.
- Kogan, Timothy P.,Dupré, Brian,Bui, Huong,McAbee, Kathy L.,Kassir, Jamal M.,Scott, Ian L.,Hu, Xin,Vanderslice, Peter,Beck, Pamela J.,Dixon, Richard A. F.
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p. 1099 - 1111
(2007/10/03)
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- Photoinduced Electron Transfer (PET) cyclization and photooxygenation of 2,6-diaryl-1,6-heptadienes and 2,7-diaryl-1,7-octadienes
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The 2,6-diaryl-substituted 1,6-heptadienes 3a-c and the 2,7-diaryl-substituted 1,7-octadienes 4a-b were cleanly converted into the corresponding anellated cyclobutanes 5 and 6, resp., when irradiated under photoelectron-transfer conditions (9,10-dicyanoanthracene in acetonitrile). Only for 4c did the rearranged compound 7c become the dominant photoproduct. Oxygen trapping experiments with formation of endoperoxides 8, 9 were successful in the case of the electron-rich substrates 3b, c and 4c. VCH Verlagsgesellschaft mbH, 1996.
- Griesbeck, Axel G.,Sadlek, Oliver,Polborn, Kurt
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p. 545 - 549
(2007/10/03)
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- Photochemistry of nonconjugated diketones: internal self-quenching and energy transfer
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The triplet state behavior of nine α,ο-dibenzoylalkanes indicates the occurrence of a rapid quenching interaction between the two carbonyl groups.This quenching is fastest (k=3E7 s-1) in dibenzoylbutane, is slightly slower (ca.E7 s-1) in dibenzoylethane, dibenzoylpentane, and 2,2-dibenzoylpropane, but is absent in 1,3-dibenzoylpropane.It also occurs in several "mixed" 1,4-diaroylbutanes incorporating p-ethylbenzoyl or p-methoxybenzoyl chromophores.This internal self-quenching is interpreted as the intramolecular counterpart of the well-know bimolecular self-quenching of aryl ketones, although no exact mechanism can be proposed.Such internal quenching does not occur as rapidly, if at all, in three "turned around" diketones: δ-(p-acetylphenyl)valerophenone, δ-(p-acetylphenoxy)valerophenone, and γ-(p-acetylphenoxy)butyrophenone.This fact, together with the varying rates of internal self-quenching in the dibenzoylalkanes, indicates the necessity for a very specific and close orientation of the two carbonyl groups for self-quenching.In the mixed diketones containing a p-alkylbenzoyl group, triplet excitation appears to be fully equilibrated between the two chromophores.However, in those containing a p-methoxybenzoyl group, excitation does not fully equilibrate before triplet decay, as evidenced by different quenching efficiencies for products from the two carbonyls.Analysis indicates intramolecular energy transfer rate constants -1.These are sufficiently lower than in other bichromophoric systems to suggest relatively slow energy hopping in the polymers of phenyl vinyl ketone.Key words: nonconjugated diketones, dibenzoylalkanes, sefl-quenching, energy transfer, triplet ketones.
- Wagner, Peter J.,Frerking, Harlan W. Jr.
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p. 2047 - 2061
(2007/10/03)
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- Bisbenzoxazines and pharmaceutical use
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Compounds of the formula: STR1 wherein, R is H, alkyl, cycloalkyl, aryl, or heteroaryl; R1 is H, alkyl, cycloalkyl, aryl, heteroaryl, substituted heteroaryl, aralkyl, substituted aryl, halo, OR2, SR2, NR2, CF3, NO2, CN, COOR2, CHO, SO3 H or SO2 NH2, wherein R2 is H, methyl, ethyl or propyl; Y is STR2 Z is O, S, NH or CH2 ; X is --CH2 --, STR3 or --(CH2)n CHOH(CH2)n --; wherein R2 is H, methyl, ethyl or propyl; n is 1-10, and pharmaceutically acceptable salts thereof have antiallergy and antiinflammatory activity.
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- Synthesis and structure activity relationships of fibrinolytic 1,ω diphenyl 1,ω alkanediamines
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The promising results obtained in animal clot lysis experiments with the fibrinolytic bis(tetrahydroiso quinolines) VI prompted the preparation of a related series of 1,ω diphenyl 1,ω alkanediamines V. As measured in the standard rat screen (ip) the compo
- Fliedner Jr,Myers,Schor,Pachter
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p. 749 - 754
(2007/10/06)
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