- NaI/PPh3-Mediated Photochemical Reduction and Amination of Nitroarenes
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A mild transition-metal- and photosensitizer-free photoredox system based on the combination of NaI and PPh3 was found to enable highly selective reduction of nitroarenes. This protocol tolerates a broad range of reducible functional groups such as halogen (Cl, Br, and even I), aldehyde, ketone, carboxyl, and cyano. Moreover, the photoredox catalysis with NaI and stoichiometric PPh3 provides also an alternative entry to Cadogan-type reductive amination when o-nitrobiarenes were used.
- Qu, Zhonghua,Chen, Xing,Zhong, Shuai,Deng, Guo-Jun,Huang, Huawen
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supporting information
p. 5349 - 5353
(2021/07/21)
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- Nucleophilic aromatic substitution of unactivated fluoroarenes enabled by organic photoredox catalysis
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Nucleophilic aromatic substitution (SNAr) is a classical reaction with well-known reactivity toward electron-poor fluoroarenes. However, electron-neutral and electron-rich fluoro(hetero)arenes are considerably underrepresented. Herein, we present a method for the nucleophilic defluorination of unactivated fluoroarenes enabled by cation radical-accelerated nucleophilic aromatic substitution. The use of organic photoredox catalysis renders this method operationally simple under mild conditions and is amenable to various nucleophile classes, including azoles, amines, and carboxylic acids. Select fluorinated heterocycles can be functionalized using this method. In addition, the late-stage functionalization of pharmaceuticals is also presented. Computational studies demonstrate that the site selectivity of the reaction is dictated by arene electronics.
- Nicewicz, David A.,Pistritto, Vincent A.,Schutzbach-Horton, Megan E.
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supporting information
p. 17187 - 17194
(2020/11/02)
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- Discovery and characterization of an acridine radical photoreductant
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Photoinduced electron transfer (PET) is a phenomenon whereby the absorption of light by a chemical species provides an energetic driving force for an electron-transfer reaction1–4. This mechanism is relevant in many areas of chemistry, including the study of natural and artificial photosynthesis, photovoltaics and photosensitive materials. In recent years, research in the area of photoredox catalysis has enabled the use of PET for the catalytic generation of both neutral and charged organic free-radical species. These technologies have enabled previously inaccessible chemical transformations and have been widely used in both academic and industrial settings. Such reactions are often catalysed by visible-light-absorbing organic molecules or transition-metal complexes of ruthenium, iridium, chromium or copper5,6. Although various closed-shell organic molecules have been shown to behave as competent electron-transfer catalysts in photoredox reactions, there are only limited reports of PET reactions involving neutral organic radicals as excited-state donors or acceptors. This is unsurprising because the lifetimes of doublet excited states of neutral organic radicals are typically several orders of magnitude shorter than the singlet lifetimes of known transition-metal photoredox catalysts7–11. Here we document the discovery, characterization and reactivity of a neutral acridine radical with a maximum excited-state oxidation potential of ?3.36 volts versus a saturated calomel electrode, which is similarly reducing to elemental lithium, making this radical one of the most potent chemical reductants reported12. Spectroscopic, computational and chemical studies indicate that the formation of a twisted intramolecular charge-transfer species enables the population of higher-energy doublet excited states, leading to the observed potent photoreducing behaviour. We demonstrate that this catalytically generated PET catalyst facilitates several chemical reactions that typically require alkali metal reductants and can be used in other organic transformations that require dissolving metal reductants.
- MacKenzie, Ian A.,Wang, Leifeng,Onuska, Nicholas P. R.,Williams, Olivia F.,Begam, Khadiza,Moran, Andrew M.,Dunietz, Barry D.,Nicewicz, David A.
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- Direct synthesis of anilines and nitrosobenzenes from phenols
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A one-pot synthesis of anilines and nitrosobenzenes from phenols has been developed using an ipso-oxidative aromatic substitution (iSOAr) process. The products are obtained in good yields under mild and metal-free conditions. The leaving group effect on reactions that proceed through mixed quionone monoketals has also been investigated and a predictive model has been established.
- St Amant,Frazier,Newmeyer,Fruehauf,Read De Alaniz
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p. 5520 - 5524
(2016/07/06)
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- Site-selective arene C-H amination via photoredox catalysis
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Over the past several decades, organometallic cross-coupling chemistry has developed into one of the most reliable approaches to assemble complex aromatic compounds from preoxidized starting materials. More recently, transition metal-catalyzed carbon-hydrogen activation has circumvented the need for preoxidized starting materials, but this approach is limited by a lack of practical amination protocols. Here, we present a blueprint for aromatic carbon-hydrogen functionalization via photoredox catalysis and describe the utility of this strategy for arene amination. An organic photoredox-based catalyst system, consisting of an acridinium photooxidant and a nitroxyl radical, promotes site-selective amination of a variety of simple and complex aromatics with heteroaromatic azoles of interest in pharmaceutical research. We also describe the atom-economical use of ammonia to form anilines, without the need for prefunctionalization of the aromatic component.
- Romero, Nathan A.,Margrey, Kaila A.,Tay, Nicholas E.,Nicewicz, David A.
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p. 1326 - 1330
(2015/10/12)
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- Pd/C-mediated depropargylation of propargyl ethers/amines in water
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Propargyl ethers and amines are effectively depropargylated to the parent alcohols or amines via a C-O/C-N bond cleavage catalyzed by 10% Pd/C in water. This simple, facile, and inexpensive methodology could be utilized for the selective removal of propargyl groups from a variety of aryl ethers and amines.
- Rambabu,Bhavani,Swamy, Nalivela Kumara,Basaveswara Rao,Pal, Manojit
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p. 1169 - 1173
(2013/04/10)
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- A new class of heterogeneous platinum catalysts for the chemoselective hydrogenation of nitroarenes
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A new series of nanostructured platinum catalysts able to catalyze the selective reduction of nitroarenes has been developed. The materials, made of organosilica physically doped with nanostructured platinum(0), are stable and efficient. Reactions in general proceed with high yield and often go to completion, while the catalysts can be reused in further reaction runs. This establishes a new class of relevant solid catalysts for synthetic organic chemistry named SiliaCat Platinum-Hydrogel.
- Pandarus, Valerica,Ciriminna, Rosaria,Beland, Francois,Pagliaro, Mario
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scheme or table
p. 1306 - 1316
(2011/06/25)
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- 4′-Alkoxyl substitution enhancing the anti-mitotic effect of 5-(3′,4′,5′-substituted)anilino-4-hydroxy-8-nitroquinazolines as a novel class of anti-microtubule agents
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Mitosis inhibitors are powerful anticancer drugs. Based on a novel anti-microtubule agent of 5-(4′-methoxy)anilino-4-hydroxy-8-nitroquinazoline, a series of 5-(3′,4′,5′-substituted)anilino-4-hydroxy-8- nitroquinazolines were designed and synthesized to investigate the effect of the substitution on the inhibitory activity against mitotic progression of tumor cells. The large alkoxyl substitution on the 4′-position of 5-anilino ring is beneficial for the potency. The 5-(3′,4′,5′-trimethoxy)anilino-8-nitroquinazoline (1h) displays an overwhelming activity in arresting the cells at the G2/M phase, providing a promising new template for further development of potent microtubule-targeted anti-mitotic drugs.
- Jin, Yi,Zhou, Zu-Yu,Tian, Wei,Yu, Qiang,Long, Ya-Qiu
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p. 5864 - 5869
(2007/10/03)
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- Analogues of camptothecin, their use as medicaments and the pharmaceutical compositions containing them
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A compound of the formula wherein the substituents are defined as in the specification which compounds are useful in the treatment of cancer.
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- New analogues of camptothecin, their use as medicaments and the pharmaceutical compositions containing them
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A compound of the formula wherein the substituents are defined as in the specification which compounds are useful in the treatment of cancer.
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- Phenylureas. Part 1. Mechanism of the basic hydrolysis of phenylureas
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The mechanism of the hydrolytic decomposition of phenylureas in basic media in the pH range 12 to 14 is investigated. In this pH range a levelling of the rate-pH curve is observed as well as a change of the substituent influence on the hydrolysis rate. These experimental findings suggest the formation of an unreactive side product of the phenylurea in a parasitic side equilibrium at sufficiently high pH. The urea dissociates at the aryl-NH group to give its conjugate base. For the hydrolytic decomposition of phenylureas an addition-elimination mechanism is proposed as has been established for the alkaline hydrolysis of carboxylic acid esters and amides.
- Laudien,Mitzner
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p. 2226 - 2229
(2007/10/03)
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- Phenylureas. Part 2. Mechanism of the acid hydrolysis of phenylureas
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The mechanism of the hydrolytic decomposition of phenylureas in acid media is investigated. It includes, in part, knowledge already present in the literature. Over the investigated pH range the occurrence of a rate maximum in the pH curves due to the strongly reduced water activity at higher acid strengths is observed. An addition-elimination mechanism with rate-determining attack of water at the N-protonated substrate is proposed. The reversion of the substituent influence on the reaction rate with increasing acidity of the reaction medium points to a change of the hydrolytic decomposition mechanism in strongly acidic media.
- Laudien, Robert,Mitzner, Rolf
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p. 2230 - 2232
(2007/10/03)
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- Camptothecin analogues, preparation methods therefor, use thereof as drugs, and pharmaceutical compositions containing said analogues
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A camptothecin analog characterized in that the hydroxy lactone of the camptothecin is a β-hydroxy lactone or the corresponding β-hydroxyacid, resulting from the opening of said lactone, or a derivative of said β-hydroxyacid, or a Pharmaceutically acceptable salt thereof, is disclosed. In particular, compounds of formulae (I) and (II) are disclosed. Methods for preparing the compounds of formulae (I) and (II), pharmaceutical compositions containing said containing said compounds, and their use, particularly as topoisomerase inhibitors and antitumoral drugs, are also disclosed.
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- 2,5-dimethylpyrrole protection facilitates copper(I)-mediated methoxylations of aryl iodides in the presence of anilines
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Converting iodoanilines to the corresponding 2,5-dimethylpyrroles was found to facilitate CuCI-mediated methoxide substitution. Examples with ortho-, meta-, or para-relationships between the iodide and aniline are presented. Several other aniline blocking groups were investigated and found not to be successful in this sequence.
- Ragan, John A.,Makowski, Teresa W.,Castaldi, Michael J.,Hill, Paul D.
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p. 1599 - 1603
(2007/10/03)
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- Polyaza Heterocycles. Part 2. Nucleophilic Substitution of Halogens in Halogenoquinoxalinocinnolines
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10-Chloroquinoxalinocinnoline readily undergoes methoxydechlorination when treated with sodium methoxide.The 1-, 2-, 3-, 4- and 9-chloro isomers are unreactive towards this reagent, but the 9,10-dichloro derivative undergoes substitution of both chlorines (the 10-position being much the more reactive).The 9- and 10-bromo analogues are both unreactive towards sodium methoxide, but the 9- and 10-fluoro analogues are both highly reactive, to the extent that it has not been possible even to isolate the 10-fluoro compound.Routes to 9- and 10-piperidinoquinoxalinocinnolines are described.
- Ahmad, Arshad,Dunbar, Linda J.,Green, Iain G.,Harvey, Ian W.,Shepherd, Thomas,et al.
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p. 2751 - 2758
(2007/10/02)
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- β-alkylmelatonins as ovulation inhibitors
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β-Alkylmelatonins are useful as ovulation inhibitors.
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- Azo reactive dyestuffs having an aryl-triazinyl-aryl diazo component
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Optionally metallized azo dyestuffs which in the form of the free acid correspond to the formula STR1 wherein K is the radical of a benzene, naphthalene, pyrazolone, pyridone, pyrimidone, acetoacetic acid arylide or aminopyrazole coupling component; A is a non-ionic substituent; X is STR2 wherein W is a direct bond or a bridge member to a C atom of the benzene or naphthalene nucleus or the coupling component K; R is hydrogen or C1 -C4 -alkyl; B is a direct bond or a bridge member, especially -CO- or -SO2 -, to a C atom of Q; Q is a reactive radical; m is 0, 1 or 2; n is 0, 1 or 2; p is 0 or 1; q is 0, 1 or 2; and r is 0 or 1; and their use for the dyeing and printing of natural and regenerated cellulose fibre materials such as cotton and rayon, as well as natural and synthetic polyamide fibre materials, for example those of wool, silk, poly-ε-caprolactam or polycondensate of hexamethylene-diamine and adipic acid. The dyeings obtained, espeically those on cotton and rayon, are distinguished by good fastness properties, especially fastness to wet processing and to light.
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- The Kinetics of the Reactions of Picryl Chloride with Some Substituted Anilines. Part 6. 4-Substituted and 3,4-Disubstituted Anilines
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Arrhenius parameters have been measured for the reactions of picryl chloride with the following substituted anilines in acetonitrile: 4-X- (X = F, Cl, Br, I, Me, or OMe); 3,4-X2- (X = Cl, Br, Me, or OMe); 4-X-3-nitro- (X = F, Cl, or Me); 3-X-4-methoxy- (X = F, Cl, Br, or I); 3-fluoro-4-nitro-; and 3,4,5-trimethoxy-aniline.In the 3,4-disubstituted series the effect of two methyl groups on the free energy of activation is strictly additive, but for the rest the measured rate constants are greater than those calculated on the assumption of additivity.The results are rationalized in terms of the positions of the transition state on the reaction co-ordinate.
- Emokpae, Thomas A.,Eguavoen, Osa,Khalil-Ur-Rahman,Hirst, Jack
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p. 832 - 834
(2007/10/02)
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