- Modification of face selectivity by inclusion in cyclodextrins
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The photocycloadditions of 5-X-adamantan-2-ones (5-X-AD, where X = F, Cl, Br, OH, Ph, and t-Bu) with fumaronitrile have been studied in acetonitrile and in aqueous solutions. When X is Cl, Br, Ph, or t-Bu, irradiation of an aqueous solution containing β-cyclodextrin (β-CD) leads to a dramatic reversal in face selectivity compared to that found in acetonitrile and water; however, there is no significant change in product ratio compared to that found in aqueous solution in the presence of α- and γ-CD. The effect observed with β-CD is interpreted with the assumption that the carbonyl π face syn to the bulky 5-substituent is partially blocked by the torus of the host due to complexation of the AD and CD. 1H NMR and concentration dependence studies provide support for this interpretation. Similar reversals of face selectivity upon complexation with β-CD are observed in the thermal reduction of these ketones by sodium borohydride. It is also noted that a much enhanced syn hydride delivery occurs in water as compared to organic solvents and that this enhancement vanishes upon cooling.
- Chung, Wen-Sheng,Turro, Nicholas J.,Silver, Jack,Le Noble, William J.
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- Open-Shell Fluorination of Alkyl Bromides: Unexpected Selectivity in a Silyl Radical-Mediated Chain Process
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We disclose a novel radical strategy for the fluorination of alkyl bromides via the merger of silyl radical-mediated halogen-atom abstraction and benzophenone photosensitization. Selectivity for halogen-atom abstraction from alkyl bromides is observed in the presence of an electrophilic fluorinating reagent containing a weak N-F bond despite the predicted favorability for Si-F bond formation. To probe this surprising selectivity, preliminary mechanistic and computational studies were conducted, revealing that a radical chain mechanism is operative in which kinetic selectivity for Si-Br abstraction dominates due to a combination of polar effects and halogen-atom polarizability in the transition state. This transition-metal-free fluorination protocol tolerates a broad range of functional groups, including alcohols, ketones, and aldehydes, which demonstrates the complementary nature of this strategy to existing fluorination technologies. This system has been extended to the generation of gem-difluorinated motifs which are commonly found in medicinal agents and agrochemicals.
- Lovett, Gabrielle H.,Chen, Shuming,Xue, Xiao-Song,Houk,MacMillan, David W. C.
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p. 20031 - 20036
(2019/12/27)
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- C-HALOGEN BOND FORMATION
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Methods of halogenating a carbon containing compound having an sp3 C-H bond are provided. Methods of fluorinating a carbon containing compound comprising halogenation with Cl or Br followed by nucleophilic substitution with F are provided. Methods of direct oxidative C-H fluorination of a carbon containing compound having an sp3 C-H bond are provided. The halogenated products of the methods are provided.
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Paragraph 0196-0197
(2013/03/26)
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- Structure-activity relationship of an ozonide carboxylic acid (oz78) against fasciola hepatica
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In this paper, we describe the SAR of ozonide carboxylic acid OZ78 (1) as the first part of our search for a trematocidal synthetic peroxide drug development candidate. We found that relatively small structural changes to 1 resulted most commonly in loss of activity against Fasciola hepatica in vivo. A spiroadamantane substructure and acidic functional group (or ester prodrug) were required for activity. Of 26 new compounds administered at single 100 mg/kg oral doses to F. hepatica infected rats, 8 had statistically significant worm burden reductions, 7 were partially curative, and 1 (acylsulfonamide 6) was completely curative and comparable to 1 in flukicidal efficacy. This study also showed that the activity of 1 is peroxide-bond-dependent, suggesting that its flukicidal efficacy depends upon hemoglobin digestion in F. hepatica.
- Zhao, Qingjie,Vargas, Mireille,Dong, Yuxiang,Zhou, Lin,Wang, Xiaofang,Sriraghavan, Kamaraj,Keiser, Jennifer,Vennerstrom, Jonathan L.
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experimental part
p. 4223 - 4233
(2010/09/04)
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- 2 H-azirines from a concerted addition of alkylcarbenes to nitrile groups
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Photolysis of aziadamantanes in the presence of fumaronitrile (FN) unexpectedly afforded conjugated 2H-azirines resulting from addition of the carbene to the CN triple bond. This represents the first example of a direct azirine formation starting from an alkylcarbene for which a concerted pathway is postulated. The novel outcome of the reaction is favored by the prior formation of a carbene-alkene complex, a type of adduct that only recently has been described.
- Knoll, Wolfgang,Mieusset, Jean-Luc,Arion, Vladimir B.,Brecker, Lothar,Brinker, Udo H.
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supporting information; experimental part
p. 2366 - 2369
(2010/07/13)
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- Transmission of Polar Substituent Effects in the Adamantane Ring System As Monitored by 19F NMR: Hyperconjugation as a Stereoinductive Factor
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A limited series of (E)- and (Z)-5-substituted adamant-2-yl fluorides 8 and 9, respectively, has been synthesized and characterized, and 19F chemical shifts have been measured in several solvents.A wide range of 19F substituent chemical shifts (SCS, ppm)
- Adcock, William,Trout, Neil A.
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p. 3229 - 3238
(2007/10/02)
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- Fluorination of Adamantane Derivatives with Oxygen Difluoride
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Fluorination of adamantane and adamantane derivatives 1 with OF2 in the absence of an HF-trap gives fluoroadamantanes 2 and adamantanols 3 in varying amounts.Increasing yields of 2 are obtained in the presence of Na2CO3 as an HF-trap.In addition, the fluorooxahomoadamantanes 4b and e are formed in this reaction.The fluorination of adamantanone (5) with OF2 leads to analogous products.
- Bolte, Gerd,Haas, Alois
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p. 1982 - 1986
(2007/10/02)
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- ELECTROPHILIC ATTACK OF ELEMENTAL FLUORINE ON ORGANIC HALOGENS. SYNTHESIS OF FLUOROADAMANTANES
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Elemental fluorine acts on bromo- and iodoadamantanes in an electrophilic mode to produce the corresponding fluoroadamantanes.The course of the reaction was investigated in several solvents.It was found that the best yields of the fluoroadamantanes were obtained when Freon (CFCl3) or Freon-chloroform was used.Using methylene chloride as a solvent with iodoadamantanes-but not with the bromo derivatives-resulted in considerable amounts of the corresponding chloro compounds.
- Rozen, Shlomo,Brand, Michael
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p. 733 - 736
(2007/10/02)
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