- Rearomatization of trifluoromethyl sulfonyl dihydropyridines: Thermolysis vs photolysis
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In this article, we describe the static gas-phase pyrolysis, microwave-induced pyrolysis, and photolysis reactions of trifluoromethyl sulfonyl dihydropyridines. The goal of this work was to find a methodology that allows obtaining of substituted pyridines-which are known to be difficult to synthesize-to be reused in a new substitution reaction. We demonstrated that it is possible to achieve the rearomatization process by the elimination of the trifluoromethyl sulfonyl moiety through the 3 processes, with the static pyrolysis being the best method to obtain the substituted pyridines. In addition, we propose the 1,4-elimination (CF3SO2 + H) as the first step, since it is the less energetic process, as has also been corroborated by calculations. A competitive reaction (CO2 extrusion) also occurs, yielding undesired products. Copyright
- Firpo, Guadalupe,Cooke, María V.,Peláez, Walter J.,Chans, Guillermo M.,Argüello, Gustavo A.,Gómez, Elizabeth,Alvarez-Toledano, Cecilio
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- Visible-Light-Mediated C-H Alkylation of Pyridine Derivatives
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We report herein a visible-light-mediated C-H alkylation of pyridine derivatives that proceeds by simple combination of a large variety of N-alkoxypyridinium ions with alkanes in the presence of 2 mol % of fac-Ir(ppy)3 under blue illumination. The mild reaction conditions together with the high group functional tolerance make of this process a useful synthetic platform for the construction of structurally strained heterocycles. Detailed mechanistic investigations, including density functional theory calculations and quantum yield measurement, allowed us to understand factors controlling the reactivity and the selectivity of the reaction.
- Rammal, Fatima,Gao, Di,Boujnah, Sondes,Gaumont, Annie-Claude,Hussein, Aqeel A.,Lakhdar, Sami
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p. 7671 - 7675
(2020/10/09)
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- Dearomative Photocatalytic Construction of Bridged 1,3-Diazepanes
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The construction of diverse sp3-rich skeletal ring systems is of importance to drug discovery programmes and natural product synthesis. Herein, we report the photocatalytic construction of 2,7-diazabicyclo[3.2.1]octanes (bridged 1,3-diazepanes) via a reductive diversion of the Minisci reaction. The fused tricyclic product is proposed to form via radical addition to the C4 position of 4-substituted quinoline substrates, with subsequent Hantzsch ester-promoted reduction to a dihydropyridine intermediate which undergoes in situ two-electron ring closure to form the bridged diazepane architecture. A wide scope of N-arylimine and quinoline derivatives was demonstrated and good efficiency was observed in the construction of sterically congested all-carbon quaternary centers. Computational and experimental mechanistic studies provided insights into the reaction mechanism and observed regioselectivity/diastereoselectivity.
- Dixon, Darren J.,Duarte, Fernanda,Leitch, Jamie A.,Rogova, Tatiana
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supporting information
p. 4121 - 4130
(2020/02/05)
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- Organocatalyzed, Visible-Light Photoredox-Mediated, One-Pot Minisci Reaction Using Carboxylic Acids via N-(Acyloxy)phthalimides
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An improved, one-pot Minisci reaction has been developed using visible light, an organic photocatalyst, and carboxylic acids as radical precursors via the intermediacy of in situ-generated N-(acyloxy)phthalimides. The conditions employed are mild, demonstrate a high degree of functional group tolerance, and do not require a large excess of the carboxylic acid reactant. As a result, this reaction can be applied to drug-like scaffolds and molecules with sensitive functional groups, enabling late-stage functionalization, which is of high interest to medicinal chemistry.
- Sherwood, Trevor C.,Li, Ning,Yazdani, Aliza N.,Dhar, T. G. Murali
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p. 3000 - 3012
(2018/03/09)
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- Visible-Light-Initiated Manganese Catalysis for C?H Alkylation of Heteroarenes: Applications and Mechanistic Studies
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A visible-light-driven Minisci protocol that employs an inexpensive earth-abundant metal catalyst, decacarbonyldimanganese Mn2(CO)10, to generate alkyl radicals from alkyl iodides has been developed. This Minisci protocol is compatible with a wide array of sensitive functional groups, including oxetanes, sugar moieties, azetidines, tert-butyl carbamates (Boc-group), cyclobutanes, and spirocycles. The robustness of this protocol is demonstrated on the late-stage functionalization of complex nitrogen-containing drugs. Photophysical and DFT studies indicate a light-initiated chain reaction mechanism propagated by .Mn(CO)5. The rate-limiting step is the iodine abstraction from an alkyl iodide by .Mn(CO)5.
- Nuhant, Philippe,Oderinde, Martins S.,Genovino, Julien,Juneau, Antoine,Gagné, Yohann,Allais, Christophe,Chinigo, Gary M.,Choi, Chulho,Sach, Neal W.,Bernier, Louise,Fobian, Yvette M.,Bundesmann, Mark W.,Khunte, Bhagyashree,Frenette, Mathieu,Fadeyi, Olugbeminiyi O.
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supporting information
p. 15309 - 15313
(2017/11/01)
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- Synthesis and utility of dihydropyridine boronic esters
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When activated by an acylating agent, pyridine boronic esters react with organometallic reagents to form a dihydropyridine boronic ester. This intermediate allows access to a number of valuable substituted pyridine, dihydropyridine, and piperidine products.
- Panda, Santanu,Coffin, Aaron,Nguyen, Q. Nhu,Tantillo, Dean J.,Ready, Joseph M.
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supporting information
p. 2205 - 2209
(2016/02/18)
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- Efficient synthesis of substituted quinolines through intramolecular addition of aryl anion to carbonyl carbon
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Substituted quinolines were synthesized in three steps from the Boc amides of substituted 2-iodoanilines and alkyl vinyl ketones. This method consists of (1) N-Michael addition of the Boc amide of 2-iodoaniline to alkyl vinyl ketone in the presence of Cs2CO3 in MeCN; (2) I-Mg exchange of the adduct with 3.5 equiv of i-PrMgCl·LiCl, and (3) acid-catalyzed reaction (excess AcCl in EtOH) of the resulting alcohol. Six examples are given with good yields.
- Kobayashi, Yuichi,Igarashi, Junji,Feng, Chao,Toshifumi,Tojo
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p. 3742 - 3745
(2012/09/25)
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- Mechanism of the Gif-Barton type alkane functionalization by halide and pseudohalide ions.
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The functionalization of alkanes by halide ions under the conditions of a Gif system can be explained by free-radical redox processes.The evidence is provided by trapping the intermediate alkyl radical by protonated heteroaromatic bases.
- Minisci, Francesco,Fontana, Francesca
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p. 1427 - 1430
(2007/10/02)
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- Polar Effects in Free-Radical Reactions. Homolytic Heteroaromatic Substitutions by Alkyl Bromides
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Alkyl bromides have been utilized for the first time as radical sources for heteroaromatic substitution.A variety of procedures was revealed to be successful for bromine abstraction: Bu3SnH with AIBN, (Me3Si)3SiH with AIBN, Ph2SiH2, or Et3SiH associated with peroxides (H2O2, t-BuOOH, (t-BuO)2, (t-BuOOCO)2, (PhCOO)2).The importance of the polar effects is discussed.
- Minisci, Francesco,Fontana, Francesca,Pianese, Guiseppe,Yan, Yong Ming
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p. 4207 - 4211
(2007/10/02)
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- A novel radical reaction of alkyl xantates useful for the selective substitution of heteroaromatic bases
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Cyclohexyl radical is generated from cyclohexyldithiocarbonate and benzoyl peroxide. The radical source is used for the alkylation of heteroaromatic bases.
- Coppa, Fausta,Fontaria, Francesca,Minisci, Francesco,Pianese, Giuseppe,Tortoreto, Paola,Zhao, Lihua
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p. 687 - 690
(2007/10/02)
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- A NEW PHOTOCHEMICAL METHOD OF HOMOLYTIC ALKYLATION OF HETEROAROMATIC BASES BY ALKYL IODIDES AND IODOSOBENZENE DIACETATE
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Photolysis of iodobenzene diacetate in the presence of alkyl iodides, protonated heteroaromatic bases and benzoic acid resulted in the selective alkylation of the α and γ positions on lepidine and quinoline.
- Fontana, Francesca,Minisci, Francesco,Barbosa, Maria Claudia Nogueira,Vismara, Elena
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p. 167 - 168
(2007/10/02)
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- Homolytic alkylation of heteroaromatic bases : The problem of monoalkylation
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The silver-catalyzed decarboxylation of carboxylic acids by persulphate leads to alkyl radicals, which have been utilized for the selective alkylation of heteroaromatic bases. The method is particularly efficient in a water-chlorobenzene two-phase system for two reasons : it considerably increases the selectivity in monoalkylation when more positions of high nucleophilic reactivity (i.e. α and γ) are available in the heterocyclic ring (i.e. quinoline , 4-cyano- and 4-ethylpyridine, pyrazine , quinoxaline etc.) and it determines a much higher efficiency for the radical sources when the silver salt catalysis is deactivated by complexation of the salt with the heterocyclic compound . The high selectivity in monoalkylation has been obtained by the combination of polar effects and the increased lipophilicity of the alkylated product, which makes its extraction from the aqueous solution by the organic solvent easier.
- Fontana,Minisci,Barbosa, M. C. Nogueira,Vismara
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p. 2525 - 2538
(2007/10/02)
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- A NEW GENERAL METHOD OF HOMOLYTIC ALKYLATION OF PROTONATED HETEROAROMATIC BASES BY CARBOXYLIC ACIDS AND IODOSOBENZENE DIACETATE.
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A new general, simple and mild procedure is reported in this communication, based on the photochemically induced decarboxylation of carboxylic acids by iodosobenzene diacetate to obtain the substitution of bases by nucleophilic alkyl radicals.
- Minisci, Francesco,Vismara, Elena,Fontana, Francesca,Barbosa, Maria Claudia Nogueira
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p. 4569 - 4572
(2007/10/02)
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- Polar Effects in Free-Radical Reactions. Rate Constants in Phenylation and New Methods of Selective Alkylation of Heteroaromatic Bases
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The rate constants for the addition of the phenyl radical to protonated and unprotonated 4-substituted pyridines have been determined by competition with chlorine abstraction from CCl4.The constants range from 2 * 105 to 6 * 106 M-1 s-1 depending on the substituent and on the degree of protonation.The phenyl radical shows a clear-cut nucleophilic character.On the basis of these rate constants, the use of phenyl radical from diazonium salt or benzoyl peroxide to generate alkyl radicals by iodine or hydrogen abstraction has been developed as a general procedure for the alkylation of heteroaromatic bases.This reaction is characterized by high yields and selectivities.
- Minisci, Francesco,Vismara, Elena,Fontana, Francesca,Morini, Giampiero,Serravalle, Marco,Giordano, Claudio
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p. 4411 - 4416
(2007/10/02)
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