Metal-free visible-light synthesis of quaternary α-perfluoroalkyl aldehydes via an enamine intermediate

Radical-Mediated α-tert-Alkylation of Aldehydes by Consecutive 1,4- and 1,3-(Benzo)thiazolyl Migrations

The direct alkylation of the α-position of aldehydes is an effective method for accessing a wide range of structurally diverse aldehydes, yet tert-alkylation has proven to be a challenging task. In this study, we present a novel radical-mediated tert-alkylation approach targeting the α-position of aldehydes, enabling the synthesis of complex aliphatic aldehydes. The transformation is initiated by the interaction between an in situ generated enamine intermediate and α-bromo sulfone, forming an electron donor-acceptor (EDA) complex, followed by consecutive 1,4- and 1,3-functional group migrations. This protocol operates under metal-free and mild photochemical conditions, delivering a broad scope of products and providing new mechanistic insights into radical rearrangement reactions.

Visible-Light Promoted Radical Fluoroalkylation of O- and N-Substituted Alkenes

Interaction of enol ethers enol acetates, enamides and enamines with fluorinated reagents may be considered as a reliable method for the synthesis of organofluorine compounds. While classic nucleophile/electrophile substitution or addition mechanisms cannot be realized for coupling of these components, their intrinsic reactivities are revealed with the aid of photoredox catalysis. A combination of these electron donating and accepting components provides a perfect balance needed for individual redox steps, which in some cases may proceed even without a photocatalyst. The same electronic factors also support the key C,C-bond forming event involving addition of fluorinated radical at the electron rich double bond.

The Revival of Enantioselective Perfluoroalkylation - Update of New Synthetic Approaches from 2015-2022

Over the last years, methods devoted to the synthesis of asymmetric molecules bearing a perfluoroalkylated chain have been limited in number. Among them, only a few can be used on a large variety of scaffolds. This microreview aims at summarizing these recent advances in enantioselective perfluoroalkylation (-CF3 , -CF2 H, -Cn F2n+1 ) and highlights the need for new enantioselective methods to easily synthesize chiral fluorinated molecules which would be useful for the pharmaceutical and agrochemical industries. Some perspectives are also mentioned.

Catalytic Asymmetric α-Functionalization of α-Branched Aldehydes

Aldehydes constitute a main class of organic compounds widely applied in synthesis. As such, catalyst-controlled enantioselective α-functionalization of aldehydes has attracted great interest over the years. In this context, α-branched aldehydes are especially challenging substrates because of reactivity and selectivity issues. Firstly, the transient trisubstituted enamines and enolates resulting upon treatment with an aminocatalyst or a base, respectively, would exhibit attenuated reactivity; secondly, mixtures of E- and Z-configured enamines/enolates may be formed; and third, effective face-discrimination on such trisubstituted sp2 carbon intermediates by the incoming electrophilic reagent is not trivial. Despite these issues, in the last 15 years, several catalytic approaches for the α-functionalization of prostereogenic α-branched aldehydes that proceed in useful yields and diastereo- and enantioselectivity have been uncovered. Developments include both organocatalytic and metal-catalyzed approaches as well as dual catalysis strategies for forging new carbon–carbon and carbon–heteroatom (C-O, N, S, F, Cl, Br, …) bond formation at Cα of the starting aldehyde. In this review, some key early contributions to the field are presented, but focus is on the most recent methods, mainly covering the literature from year 2014 onward.

Amine-catalyzed Synthesis of Fluorine-containing Polymers through Halogen Bonding

Fluorine-containing polymers are one of the most useful materials among various polymers. In this study, we have developed synthesis methods for fluorine-containing polymers through sequential and chain polymerization based on the generation of perfluoroalkyl radicals by photoirradiation halogen bonding of perfluoroalkyl iodide and amines. In sequential polymerization, fluoroalkyl-alkyl-alternating polymers were synthesized by the polyaddition of diene and diiodoperfluoroalkane. In chain polymerization, polymers with perfluoroalkyl terminals were synthesized by polymerization of general-purpose monomers, with perfluoroalkyl iodide as the initiating species. Block polymers were also synthesized by successive chain polymerization to the polyaddition product.

Metal-free visible-light-induced hydroxy-perfluoroalkylation of conjugated olefins using enamine catalyst

We developed a simple and sustainable method for the hydroxy-perfluoroalkylation of electron-deficient conjugated olefins and styrenes. In this protcol, in situ generated enamine forms electron-donor-accepter (EDA) complexes with perfluoroalkyl iodide, and reaction proceed with visible-light irradiation. Tertiary amine also interacts with perfluoroalkyl iodide via halogen-bonding, promoting the perfluoroalkyl radical generation. This reaction does not require any transition-metal or photoredox catalyst, and gaseous oxygen is used as the green hydroxy source. Moreover, various commercially available substrates and perfluoroalkyl iodides were tolerated, affording the desired hydroxy-perfluoroalkylated products in good to moderate yields (>50 examples, up to 90%).

Visible light-assisted organocatalytic α-acyloxylation of ketones using carboxylic acids and N-halosuccinimides

The α-acyloxylcarbonyl motif can be found in many important pharmaceuticals and biologically active natural products and their derivatives. In this manuscript, the direct synthesis of α-acyloxylketones from ketones and readily available carboxylic acids was realized using a photo-assisted halogen bond-mediated organocatalytic α-acyloxylation reaction. The desired α-acyloxylation products were obtained in good to high yields.

Nickel-Catalyzed Cross-Coupling of Acyl Chloride with Racemic α-Trifluoromethyl Bromide to Access Chiral α-Trifluoromethyl Ketones

The nickel-catalyzed reductive cross-coupling reaction of acyl chloride with racemic secondary α-trifluoromethyl bromide has been developed. By this chemistry, a series of structurally interesting chiral α-CF₃ carbonyl compounds could be accessed with great enantioselectivity and good functional group tolerance. The study of late-stage transformation indicated that this chemistry could be used as the robust method to prepare products that contain a bioactive motif. Furthermore, the importance of the α-trifluoromethyl group to this reaction has been illustrated by control experiments.

Photoinitiated stereoselective direct C(sp2)–H perfluoroalkylation and difluoroacetylation of enamides

Photoinitiated regio- and stereoselective C(sp²)–H perfluoroalkylation and difluoroacetylation of enamides are developed, furnishing biologically and physiologically privileged fluoro-containing enamide scaffolds.

Visible-light mediated carbonyl trifluoromethylative amination as a practical method for the synthesis of β-trifluoromethyl tertiary alkylamines

We report the development of an operationally straigtforward, visible-light-mediated multicomponent strategy for the construction of β-trifluoromethylated tertiary alkylamines from feedstock aldehydes, secondary amines and a convenient source of trifluoromethyl iodide. The new process does not require a photocatalyst, is metal-free, displays a broad functional group tolerance and offers rapid, one-pot access to trifluoromethylated drug-like compounds that will be of interest in medicinal chemistry.

An operationally straightforward, visible-light-mediated multicomponent strategy for the construction of β-trifluoromethylated tertiary alkylamines from aldehydes, secondary amines and a convenient source of trifluoromethyl iodide is reported.

Aldehyde catalysis - from simple aldehydes to artificial enzymes

Chemists have been learning and mimicking enzymatic catalysis in various aspects of organic synthesis. One of the major goals is to develop versatile catalysts that inherit the high catalytic efficiency of enzymatic processes, while being effective for a broad scope of substrates. In this field, the study of aldehyde catalysts has achieved significant progress. This review summarizes the application of aldehydes as sustainable and effective catalysts in different reactions. The fields, in which the aldehydes successfully mimic enzymatic systems, include light energy absorption/transfer, intramolecularity introduction through tether formation, metal binding for activation/orientation and substrate activation via aldimine formation. Enantioselective aldehyde catalysis has been achieved with the development of chiral aldehyde catalysts. Direct simplification of aldehyde-dependent enzymes has also been investigated for the synthesis of noncanonical chiral amino acids. Further development in aldehyde catalysis is expected, which might also promote exploration in fields related to prebiotic chemistry, early enzyme evolution, etc.