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Relevant academic research and scientific papers

Acyl radicals from α-keto acids using a carbonyl photocatalyst: Photoredox-catalyzed synthesis of ketones

Acyl radicals have been generated from α-keto acids using inexpensive and commercially available 2-chloro-thioxanthen-9-one as the photoredox catalyst under visible light illumination. These reactive species added to olefins or coupled with aryl halides via a bipyridylstabilized Ni(II) catalyst, enabling easy access to a diverse range of ketones. This reliable, atom-economical, and eco-friendly protocol is compatible with a wide range of functional groups.

A novel approach for the synthesis of β-keto esters: One-pot reaction of carboxylic acids with chlorosulfonyl isocyanate

β-Keto esters were synthesized by direct carboxylation of various 4- and 5-oxo-carboxylic acid derivatives in the presence of chlorosulfonyl isocyanate in excellent yield under mild conditions. Additionally, optimization conditions were examined for synthesis β-keto esters. Finally, it has been found that trifluoroacetic acid is efficient in DCM under optimized conditions. This efficient one-pot novel method is very usefull, fair price and easy to handle of β-keto esters.

A Sequential Umpolung/Enzymatic Dynamic Kinetic Resolution Strategy for the Synthesis of γ-Lactones

Combining biological and small-molecule catalysts under a chemoenzymatic manifold presents a series of significant advantages to the synthetic community. We report herein the successful development of a two-step/single flask synthesis of γ-lactones through the merger of Umpolung catalysis with a ketoreductase-catalyzed dynamic kinetic resolution, reduction, and cyclization. This combined approach delivers highly enantio- and diastereoenriched heterocycles and demonstrates the feasibility of integrating NHC catalysis with enzymatic processes.

Hydrogen Atom Transfer Reactions via Photoredox Catalyzed Chlorine Atom Generation

The selective functionalization of chemically inert C?H bonds remains to be fully realized in achieving organic transformations that are redox-neutral, waste-limiting, and atom-economical. The catalytic generation of chlorine atoms from chloride ions is one of the most challenging redox processes, where the requirement of harsh and oxidizing reaction conditions renders it seldom utilized in synthetic applications. We report the mild, controlled, and catalytic generation of chlorine atoms as a new opportunity for access to a wide variety of hydrogen atom transfer (HAT) reactions owing to the high stability of HCl. The discovery of the photoredox mediated generation of chlorine atoms with Ir-based polypyridyl complex, [Ir(dF(CF3)ppy)2(dtbbpy)]Cl, under blue LED irradiation is reported.

Direct Aldehyde Csp2?H Functionalization through Visible-Light-Mediated Photoredox Catalysis

The development of methods for carbon–carbon bond formation under benign conditions is an ongoing challenge for synthetic chemists. In recent years there has been considerable interest in using selective C?H activation as a direct route for generating rea

A Direct, Versatile, and Chemoselective Synthesis of Vinylogous Bis- and Monourethanes/amides and β-Keto Esters by Aza-Knoevenagel-Type Reactions of Tertiary Amides with Enolates

Full details of our investigations into aza-Knoevenagel-type reactions with common tertiary amides as the electrophilic partner are reported. The method is based on the addition of stabilized carbanionic nucleophiles to the amides, which are activated in situ with triflic anhydride (Tf2O). The reaction proceeds under mild conditions and tolerates several sensitive functional groups including enamide and tert-butyldimethylsilyloxy (TBSO) groups. Significantly, with amides bearing more reactive ester, cyano, and aldehyde groups, the reaction occurs chemoselectively at the least reactive amide group. Such “umpolung” of the chemoselectivity in C=C bond formation is challenging, rare, and of synthetic value. Vinylogous bis-urethanes (aza-Knoevenagel-type condensation products), vinylogous urethanes, and vinylogous amides can be synthesized by employing enolates/carbanions generated from methyl ketones, malonic acid monoester, 2-phenylacetate, or (benzylsulfonyl)benzene. Moreover, when higher homologues of acetate were used, β-keto esters were obtained directly from amides. The method has been applied to the one-step syntheses of several known key intermediates in the total syntheses of alkaloids and 4-quinolone antibiotics. An efficient and mild intramolecular Friedel–Crafts-type cyclization of an anilinyl ester has also been achieved with Tf2O as an effective promoter. This amide-based method is a direct and umpoled alternative to the versatile but stepwise one based on thionation and the Eschenmoser sulfide contraction.

Thiazolium-catalyzed additions of acylsilanes: A general strategy for acyl anion addition reactions

A strategy utilizing N-heterocyclic carbenes (NHCs) derived from thiazolium salts has been developed for the generation of carbonyl anions from acylsilanes. Synthetically useful 1,4-diketones and N-phosphinoyl-α- aminoketones have been prepared in good to excellent yields via NHC-catalyzed additions of acylsilanes to the corresponding α,β-unsaturated systems and N-phosphinoylimines. These organocatalytic reactions are air- and water-tolerant methods to execute robust carbonyl anion addition reactions. Additionally, polysubstituted aromatic furans and pyrroles have been efficiently synthesized in a one-pot process using this carbonyl anion methodology. The addition of alcohols to the reaction renders the process catalytic in thiazolium salt. In an effort to synthesize a potential intermediate along the proposed reaction pathway, silylated thiazolium carbinols have been identified to provide good yields of carbonyl anion addition products when subjected to the standard reaction conditions in the presence of suitable electrophiles.

The Thiazolium-Catalyzed Sila-Stetter Reaction: Conjugate Addition of Acylsilanes to Unsaturated Esters and Ketones

A new acyl anion addition reaction between acylsilanes and α,β-unsaturated conjugate acceptors promoted by a nucleophilic organic catalyst has been disclosed. The 1,4-dicarbonyl products produced in this reaction are highly useful synthons. Neutral carbenes (or zwitterions) generated in situ from commercial thiazolium salts are used as effective catalysts for the reaction which is in contrast to established anionic catalysts typically employed to promote the required Brook rearrangement (1,2-silyl shift from carbon to oxygen) involved in the reported reaction. This process successfully utilizes acylsilanes as tunable acyl anion progenitors and is tolerant of a wide range of structural diversity on the acylsilane or the conjugate acceptor. Copyright

Alkoxycarbonylcarbene Transfer to Acyclic Tertiary Enaminones

Copper-catalyzed alkoxycarbonylcarbene transfer from methyl or tert-butyl diazoacetate to acyclic enaminoesters 6a,b and enaminocarboxanilide 13 yields vicinal push-pull-substituted cyclopropanes 7a,b, 8, and 14. In contact with dry silica gel, the latter compounds undergo facile ring-opening leading to enaminoesters 9,10, and 15. Treatment with aqueous acid transforms 9 and 10 into 2-acylsuccinates 11 and 12, and 15 into pyrrolinone 16. Methoxycarbonylcarbene transfer to enaminoketones 1a-c does not yield isolable cyclopropanes, but after hydrolytic work-up α-acyl-γ-ketoesters 2a-c are obtained.

Photochimie en solution. XXIV. Mecanisme de l'addition des aldehydes aux double liaisons ethyleniques activees par des groupements attracteurs d'electrons

The mechanism of the photochemical addition of aliphatic aldehydes to electron-deficient olefins has been rationalized.No addition to α,β-unsaturated ketones was observed when the latter were excited.The reaction can be explained by a first self-quenching step of the aliphatic aldehyde involving its lowest triplet state, which is reached with a moderate quantum yield (0.5).The radical R-C.=O produced in the self quenching process adds to the olefin at the more positively-charged carbon atom.The reaction ends by a hydrogen atom exchange between the radical produced by this addition and the radical R-C.HOH.The quantum yield of the product formation is much higher with benzaldehyde owing to the almost unity value of the intersystem crossing, but it competes with the formation of benzile.