How transient photoconductivity reveals significant features of the reduction of ground-state aromatic ketones by amino-alkyl radicals through a thermal electron-transfer process

The rate constants kred of the thermal electron-transfer reaction between several aminoalkyl radicals and two ground-state aromatic ketones, benzophenone (BP) and thioxanthone (TX), were measured by nanosecond transient photoconductivity in acetonitrile. The kred values were strongly at variance from those expected from the free energy change Gred of the reaction within the framework of the Marcus' theory of electron transfer. Moreover, addition of small amounts of water in acetonitrile strongly enhanced kred and the ion quantum yield. These results were rationalized by invoking a 1 : 1 complex formation between amino-alkyl radicals and water, and semi-empirical AM1 calculations were used to sustain this explanation.     

Synthesis and some reactions of sterically hindered 3-imidazoline 3-oxides

Sterically hindered 3-imidazoline 3-oxides were obtained by condensation of -amino oximes with ketones. It is shown that the reaction of these compounds with electrophilic agents takes place at both the nitrone grouping and the amino group. The oxidation of the products makes it possible to obtain stable nitroxyl radicals.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 103–109, January, 1979.     

NHC and visible light-mediated photoredox co-catalyzed 1,4-sulfonylacylation of 1,3-enynes for tetrasubstituted allenyl ketones

The modulation of selectivity of highly reactive carbon radical cross-coupling for the construction of C–C bonds represents a challenging task in organic chemistry. N-Heterocyclic carbene (NHC) catalyzed radical transformations have opened a new avenue for acyl radical cross-coupling chemistry. With this method, highly selective cross-coupling of an acyl radical with an alkyl radical for efficient construction of C–C bonds was successfully realized. However, the cross-coupling reaction of acyl radicals with vinyl radicals has been much less investigated. We herein describe NHC and visible light-mediated photoredox co-catalyzed radical 1,4-sulfonylacylation of 1,3-enynes, providing structurally diversified valuable tetrasubstituted allenyl ketones. Mechanistic studies indicated that ketyl radicals are formed from aroyl fluorides via the oxidative quenching of the photocatalyst excited state, allenyl radicals are generated from chemo-specific sulfonyl radical addition to the 1,3-enynes, and finally, the key allenyl and ketyl radical cross-coupling provides tetrasubstituted allenyl ketones.

Unprecedented NHC and photocatalysis co-catalyzed radical 1,4-sulfonylacylation of 1,3-enynes has been realized, providing structurally diversified tetrasubstituted allenyl ketones via allenyl and ketyl radical cross-coupling.     

Interception of Cobalt‐Based Carbene Radicals with α‐Aminoalkyl Radicals: A Tandem Reaction for the Construction of β‐Ester‐γ‐amino Ketones

The interception of cobalt‐based carbene radicals with α‐aminoalkyl radicals was combined with the Kornblum–DeLaMare reaction and provides β‐ester‐γ‐amino ketones, which are otherwise difficult to obtain in high chemoselectivity. Mechanistically, this transformation is an interplay of cobalt‐based carbene radicals, organoradicals, and ionic intermediates and involves the construction of two C? C bonds and one C?O bond in a one‐pot process. The reaction also features a wide substrate scope and is highly efficient and insensitive to moisture and air.     

Cobalt-electrocatalytic C–H hydroxyalkylation of N-heteroarenes with trifluoromethyl ketones

Trifluoromethyl carbinols and N-heteroarenes are both prevalent in bioactive molecules. However, access to high-value pharmacophores combining these two functional groups still remains a challenge. Herein, we report an electro-chemical redox-neutral coupling for the synthesis of N-heteroaryl trifluoromethyl carbinols from readily available N-heteroarenes and trifluoromethyl ketones. The reaction starts with reversing the polarity of ketones to nucleophilic ketyl radicals through an electrocatalytic proton-coupled electron transfer (PCET), followed by radical addition to heteroarenes and rearomatization to afford tertiary alcohol products. Importantly, the merging of paired electrolysis and cobalt catalysis is crucial to this regioselective C–H hydroxyalkylation of heteroarenes, and thus avoids several known competing pathways including the spin-center shift (SCS) process. Collectively, this protocol provides straightforward access to heteroaryl trifluoromethyl carbinols, featuring ideal atom economy, excellent regioselectivity, and paired redox-neutral electrolysis.

By merging paired electrolysis and cobalt catalysis, we have developed an electrochemical redox-neutral coupling for the synthesis of N-heteroaryl trifluoromethyl carbinols from readily available N-heteroarenes and trifluoromethyl ketones.     

Merging the Norrish type I reaction and transition metal catalysis: photo- and Rh-promoted borylation of C–C σ-bonds of aryl ketones

Synthesis of arylboronates via borylation of C–C σ-bonds of aryl ketones was achieved by the combined use of photoenergy and a Rh catalyst. The cooperative system enables α-cleavage of photoexcited ketones to generate aroyl radicals via the Norrish type I reaction, which are successively decarbonylated and borylated with the rhodium catalyst. This work establishes a new catalytic cycle merging the Norrish type I reaction and Rh catalysis and demonstrates the new synthetic utility of aryl ketones as aryl sources for intermolecular arylation reactions.

Synthesis of arylboronates via borylation of C–C σ-bonds of aryl ketones was achieved by the combined use of photoenergy and a Rh catalyst.     

Aryl aminoalkyl sulfones

Two methods are proposed for the preparation of aryl aminoalkyl sulfones substituted in the aromatic ring: a method based on the oxidation of aryl aminoalkyl sulfides by hydrogen peroxide or of their bases in the presence of HClO₄ and a method based on the oxidation of aryl -chloroalkyl sulfides to chlorosulfones by hydrogen peroxide followed by their condensation with amines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2580–2585, November, 1989.     

Composition of Reductive Cleavage Products of Cyclopenta[d]isoxazolines

The composition of the reductive cleavage products of cyclopenta[d]isoxazolines in acid medium depends on the acid, Raney nickel, and solvent used. Depending on the reaction conditions, we obtained -hydroxy ketones, ,-unsaturated ketones, or 2-acylcyclopentanes as the major products.     

类Mannich反应合成2,5-二苯基-3,3-二取代-2,3-二氢-1,4,2-氧氮磷杂环戊烯-2-氧化物

本文报道了以苯甲酰胺,醛(或酮)苯基二氯化膦为原料进行的Mannich反应,其产物经部分水解合成了α-(N-苯甲酰氨基)二取代甲基苯基膦酸(Ⅰ),此化合物脱水关环得2,5-二苯基-3,3-二取代-2,3-二氢-1,4,2-氧氮磷杂环戊烯-2-氧化物(Ⅱ).经¹HNMR及元素分析证明了Ⅰ和Ⅱ的结构,并对反应机理进行了探讨。     

Enantioselective synthesis of α-amino ketones through palladium-catalyzed asymmetric arylation of α-keto imines

Chiral α-amino ketones are common structural motifs in natural products and pharmaceuticals, as well as important synthons in organic synthesis. Thus, establishing efficient methods for preparing compounds with these privileged scaffolds is an important endeavor in synthetic chemistry. Herein we disclose a new catalytic asymmetric approach for the synthesis of chiral α-amino ketones through a chiral palladium-catalyzed arylation reaction of in situ generated challenging α-keto imines from previously unreported C-acyl N-sulfonyl-N,O-aminals, with arylboronic acids. The current reaction offers a straightforward approach to the asymmetric synthesis of acyclic α-amino ketones in a practical and highly stereocontrolled manner. Meanwhile, the multiple roles of the chiral Pd(ii) complex catalyst in the reaction were also reported.

Chiral α-amino ketones are common structural motifs in natural products and pharmaceuticals, as well as important synthons in organic synthesis.     

Mechanism for the inhibition of the autooxidation of cyclohexanone by alkylammonium salts

Conclusions Tetraalkylammonium salts may efficiently hinder the oxidation of ketones by catalyzing the decomposition of -ketohydroperoxides, mainly through a pathway not involving the formation of free radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2100–2102, September, 1987.     

Synthesis of 1,3-diaryl-4,7-phenanthrolines

A number of new 1,3-diaryl-4,7-phenanthrolines were synthesized by heterocyclization of arylidene-6-quinolylamines with acetophenones in the presence of an acidic catalyst. Intermediate amino ketones and side products, viz., N-(R¹-benzyl)-6-quinolylamines and ,-unsaturated ketones, were isolated. The IR, UV, PMR, and mass spectra of the synthesized compounds are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1398–1401, October, 1985.     

Electronic spectra of α, Β-unsaturated diketone derivatives of thiophene

The electronic absorption spectra of ,-unsaturated diketone derivatives of thiophene of the p-dichalcone type have been studied. As a rule, these compounds have deeper colors than the monoketone thiophene analogs of the chalcones corresponding to them. Electron-donating substituents in the aromatic nucleus of 2,5-dicinnamoylthiophene and also the replacement of the phenyl radicals in them by heterocyclic radicals cause a bathochromic shift of the long-wave absorption maximum (frequency) which correlates satisfactorily with Hammett's constants. Some ketones with strong electron-donating groupings fluoresce under UV irradiation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 6, pp. 744–749, June, 1970.     

On the electrochemical behaviour of pyruvic and lactic acids at a platinized platinum electrode in acid medium

The electrochemical oxidation of pyruvic and lactic acids at a platinized platinum electrode has been studied in acidic (M H₂SO₄) medium. The oxidation process takes place at potentials more positive than 900–1000 mV (on RHE scale). The final products are acetic acid and CO₂. Unambiguous polarization measurements could be carried out only in the case of preoxidized surfaces. For the interpretation of the phenomena observed, a mechanism involving reactions of organic species with electrochemically formed OH radicals is proposed.Studying the reduction of pyruvic acid, it has been stated that, similar to the behaviour of simple aliphatic ketones, the conversion of the

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group into -CH₂- occurs to a significant extent.     

Hydrogen peroxide formation in the oxidation of carbonyl-containing compounds at β-CH bonds

The concepts of the selective inhibition of reactions with the participation of HO ₂^· radicals by nitrobenzene in accordance with a cyclic mechanism were supported using cyclohexanol oxidation as an example. It was demonstrated that the nitroxyl radical generated from nitrobenzene selectively reacts with HO₂ ^· to form hydrogen peroxide and nitrobenzene. A decrease in the rates of oxidation of esters, carboxylic acids, and ketones with specially chosen structures in the presence of nitrobenzene, as well as the detection of H₂O₂ and corresponding ,-unsaturated compounds among the reaction products, indicated that the degradation of -peroxyl radicals of the above compounds occurred under conditions of the liquid-phase oxidation of organic substances that result in the formation of the HO₂^· radical and an unsaturated compound.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 814–820.Original Russian Text Copyright © 2004 by Nepomnyashchikh, Nosacheva, Perkel.     

Synthesis of 2‐phenylquinolin‐4‐amines substituted with diverse amino and aminoalkyl groups

Facile synthetic approaches to 2‐phenylquinolin‐4‐amines containing an aminoalkyl group at N⁴ of the quinolin‐4‐amine and amino or aminoalkyl groups at the phenyl moiety are presented.     

Catalyst-controlled selective borocarbonylation of benzylidenecyclopropanes: regiodivergent synthesis of γ-vinylboryl ketones and β-cyclopropylboryl ketones

Regioselective catalytic multi-functionalization reactions enable the rapid synthesis of complexed products from the same precursors. In this communication, we present a method for the regiodivergent borocarbonylation of benzylidenecyclopropanes with aryl iodides. Various γ-vinylboryl ketones and β-cyclopropylboryl ketones were produced in moderate to good yields with excellent regioselectivity from the same substrates. The choice of the catalyst is key for the regioselectivity control: γ-vinylboryl ketones were produced selectively with IPrCuCl and Pd(dppp)Cl₂ as the catalytic system, while the corresponding β-cyclopropylboryl ketones were obtained in high regioselectivity with Cu(dppp)Cl, [Pd(η³-cinnamyl)Cl]₂ and xantphos as the catalytic system. Moreover, γ-vinylboryl ketones and β-cyclopropylboryl ketones were successfully transformed into several other value-added products.

A novel procedure for regiodivergent borocarbonylation of benzylidenecyclopropanes has been developed. A variety of valuable γ-vinylboryl ketones and β-cyclopropylboryl ketones can be obtained selectively in excellent yields.     

Vapor-Phase Conversion of Esters into Ketones in the Presence of an Sn-, Ce-, and Rh-Containing Oxide Catalyst

The catalytic conversion of acyclic and cyclic esters into ketones was studied. Based on an analysis of data on the yields of the products of ester conversion, the conclusion was drawn that ketones result from a reaction between two ester molecules with the intermediate formation of a -ketoester. This reaction is accompanied by the partial thermal decomposition of esters to aldehydes (reverse Tishchenko reaction) with the subsequent condensation.     

Photochemistry of purine systems,part III Photoreactions of theophylline with alcohols in the presence of aliphatic ketones

Photochemical reactions of theophylline with primary and secondary alcohols in the presence of aliphatic ketones result in substitution of an -hydroxyalkyl group for the hydrogen atom at C-8 position. The results indicate that both the -hydroxyalkyl radicals derived by H-abstraction from alcohol and the ketyl radicals generated by photoreduction of ketone are involved in the reactions.Photochemische Reaktionen von Theophyllin mit primären und sekundären Alkoholen in Gegenwart von aliphatischen Ketonen liefern C-8-Substitutionsprodukte. Die Ergebnisse sprechen dafür, daß an den Reaktionen sowohl die durch H-Abstraktion aus Alkoholen gebildeten -Hydroxyalkylradikale als auch die durch Photoreduktion von Ketonen entstandenen Ketylradikale beteiligt sind.

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Photochemie des Purinsystems, 3. Mitt.: Photochemische Reaktionen von Theophyllin mit Alkoholen in Gegenwart von aliphatischen Ketonen

     

Polarity‐Reversed Allylations of Aldehydes,Ketones, and Imines Enabled by Hantzsch Ester in Photoredox Catalysis

The polarity reversal (umpolung) reaction is an invaluable tool for reversing the chemical reactivity of carbonyl and iminyl groups, which subsequent cross‐coupling reactions to form C−C bonds offers a unique perspective in synthetic planning and implementation. Reported herein is the first visible‐light‐induced polarity‐reversed allylation and intermolecular Michael addition reaction of aldehydes, ketones, and imines. This chemoselective reaction has broad substrate scope and the engagement of alkyl imines is reported for the first time. The mechanistic investigations indicate the formation of ketyl (or α‐aminoalkyl) radicals from single‐electron reduction, where the Hantzsch ester is crucial as the electron/proton donor and the activator.