Efficient Decarboxylative/Defluorinative Alkylation for the Synthesis of gem ‐Difluoroalkenes through an S N 2 ’‐Type Route

Transition-Metal-Free Late-Stage Decarboxylative gem-Difluoroallylation of Primary Alkyl Acids

A transition-metal-free late-stage decarboxylative gem-difluoroallylation of carboxylic acids with α-trifluoromethyl alkenes has been described by the use of organo-photoredox catalysis. Both primary alkyl and heteroaryl acids were readily incorporated. This approach merits feedstock materials, mild reaction conditions, and wide functionality tolerance. The synthetic utility of this approach has been highlighted by the late-stage functionalization of a variety of acid-containing natural products and drug molecules.

Visible-Light-Promoted Iron(II)/Lewis Base Catalysis for the Alkylation of Morita-Baylis-Hillman Acetates Using Carboxylic Acids

A novel photoinduced Fe(OTf)2/2,4,6-collidine-catalyzed alkylation of Morita-Baylis-Hillman (MBH) acetates using carboxylic acids in a regio- and stereoselective manner is reported. This method demonstrates a broad scope, encompassing various carboxylic acids and MBH acetates, including drugs and bioactive molecules, to synthesize densely functionalized cinnamates and acrylates. The reactions are performed in the green solvent dimethyl carbonate under oxidant-free conditions. Based on control experiments, a plausible mechanism involving an Fe(II)-Fe(III)-Fe(II) cycle is proposed.

Photocatalytic Defluorinative α-Aminoalkylation of Allylic Difluorides

A photocatalytic process was devised to synthesize monofluoroalkenes via defluorinative functionalization of allylic difluorides. N-Alkylanilines are used as precursors to α-aminoalkyl radicals, which undergo regioselective addition to allylic difluorides, and subsequent SET and fluoride elimination produce monofluoroalkenes. C-C bond formation on the aniline is site-selective for the least substituted carbon α to nitrogen.

Photocatalytic Synthesis of γ,γ-Difluoroallylic Ketones and δ,δ-Difluoroallylic Ketones via a Desulfurative/Defluorinative Alkylation Process

The gem-difluoroalkene moiety is frequently found in medicinal chemistry. From α-keton sulfides and thioic acids, we were able to develop a universal approach for the synthesis of γ,γ-difluoroallylic ketones and δ,δ-difluoroallylic ketones via a desulfurative/defluorinative alkylation process. We expect that this mild and efficient method will be complementary to other known strategies.

Organo-photoredox catalyzed gem-difluoroallylation of ketone-derived dihydroquinazolinones via C(sp3)-C bond and C(sp3)-F bond cleavage

An organo-photoredox catalyzed gem-difluoroallylation of both acyclic and cyclic ketone derivatives with α-trifluoromethyl alkenes has been demonstrated, thus giving access to a diverse set of gem-difluoroalkenes in moderate to high yields. Pro-aromatic dihydroquinazolinones can be either pre-formed or in situ generated for ketone activation. This reaction is characterized by readily available starting materials, mild reaction conditions, and broad substrate scope. The feasibility of this reaction has been highlighted by the late-stage modification of several natural products and drug-like molecules as well as the in vitro antifungal activity.

Synthesis of gem-Difluorohomoallyl Amines via a Transition-Metal-Free Defluorinative Alkylation of Benzyl Amines with Trifluoromethyl Alkenes

A mild and transition-metal-free defluorinative alkylation of benzyl amines with trifluoromethyl alkenes is reported. The features of this protocol are easy-to-obtain starting materials, a wide range of substrates, and functional group tolerance as well as high atom economy, thus offering a strategy to access a variety of gem-difluorohomoallyl amines, which are extensively distributed in pharmaceuticals and bioactive agents, with excellent chemoselectivity. The primary products can be further transformed to a diversity of 2-fluorinated pyrroline compounds.

Transition metal-free decarboxylative olefination of carboxylic acid salts

The cost-effective and efficient synthesis of alkenes is highly significant due to their extensive applications in both synthetic and polymer industries. A transition metal-free approach has been devised for the chemoselective olefination of carboxylic acid salts. This modular approach provides direct access to valuable electron-deficient styrenes in moderate to good yields. Detailed mechanistic studies suggest anionic decarboxylation is followed by halogen ion transfer. This halogen transfer leads to an umpolung of reactant electronics, allowing for a rate-limiting rebound elimination.

Selective and controllable amination and defluoroamidation of α-trifluoromethylstyrene

We present a blueprint for the amination and defluoroamidation of α-trifluoromethylstyrene. This practical protocol presents a general method for the diversity-oriented synthesis of vicinal trifluoromethyl amines and gem-difluoro alkenes from α-trifluoromethylstyrene maintaining excellent chemoselectivity. The synthetic strategy features outstanding atom economy and wide functional group tolerance under mild reaction conditions.

Base-Mediated α-gem-Difluoroalkenylations of Aldehydes and Ketones

Herein, we present a base-mediated nucleophilic substitution reaction of α-trifluoromethylstyrenes with simple silyl enol ethers, enabling the efficient synthesis of carbonyl-substituted gem-difluoroalkenes. The merit of this protocol is exhibited by its mild reaction conditions, broad substrate scope, and scalable preparation. Notably, this method demonstrates its applicability for late-stage functionalization of structurally complex molecules. Moreover, we illustrate that the resulting products can serve as valuable precursors for the synthesis of diverse medicinally relevant compounds.

Deaminative defluoroalkylation of α-trifluoromethylalkenes enabled by photoredox catalysis

Herein, we disclose a new photoredox-catalysed strategy to access gem-difluoroallylarenes from α-trifluoromethylalkenes with sterically hindered primary amines via C-N and C-F bond activation. This deaminative and defluorinative allylation is generally compatible with diverse functional groups and sterically hindered α-3° and 2° primary amines.

Visible-light-initiated external photocatalyst-free synthesis of α,α-difluoro-β-ketoamides from 4-aminocoumarins

A concise and efficient ring-opening difluorination strategy was developed for the synthesis of highly functionalized hydroxy-containing α,α-difluoro-β-ketoamides from the one-pot multicomponent reaction of 4-aminocoumarins, NFSI, and water in dimethyl carbonate (DMC) as a green solvent. The reactions were smoothly achieved under visible light irradiation in air at room temperature without the addition of any other external photocatalysts. With this protocol, various α,α-difluoro-β-ketoamides were successfully synthesized under mild conditions (25 examples, 73-91% yields). This transition-metal-free synthetic procedure shows good functional group compatibility and attractive practical potential for large-scale synthesis.

Alkylboronic acids as alkylating agents: photoredox-catalyzed alkylation reactions assisted by K3PO4

Despite the ubiquity of alkylboronic acids in organic synthesis, their utility as alkyl radical precursors in visible-light-induced photocatalytic reactions is limited by their high oxidation potentials. In this study, we demonstrated that an inorganophosphorus compound can modulate the oxidation potentials of alkylboronic acids so that they can act as alkyl radical precursors. We propose a mechanism based on the results of fluorescence quenching experiments, electrochemical experiments, ¹¹B and ³¹P NMR spectroscopy, and other techniques. In addition, we describe a simple and reliable alkylation method that has good functional group tolerance and can be used for direct C-B chlorination, cyanation, vinylation, alkynylation, and allylation, as well as late-stage functionalization of derivatized drug molecules. Notably, alkylboronic acids can be selectively activated in the presence of a boronic pinacol ester.

Oxalates as Activating Groups for Tertiary Alcohols in Photoredox-Catalyzed gem-Difluoroallylation To Construct All-Carbon Quaternary Centers

Construction of challenging and important all-carbon quaternary centers has received growing attention. Herein, with oxalates as activating groups for tertiary alcohols, we report photoredox-catalyzed gem-difluoroallylation to construct all-carbon quaternary centers enabled by efficient tertiary radical addition to α-trifluoromethyl alkenes. This transformation shows good functional group tolerance for both α-trifluoromethyl alkenes and oxalates. Moreover, this strategy is also successfully applied to the synthesis of monofluoralkenes from the corresponding electron-rich gem-difluoroalkenes and cesium tertiary alkyl oxalates under modified conditions.

Photoredox-Catalyzed Allylic Defluorinative Alkoxycarbonylation of Trifluoromethyl Alkenes through Intermolecular Alkoxycarbonyl Radical Addition

The gem-difluoroalkene moiety is an ideal carbonyl bioisostere in medicinal chemistry, but efficient synthesis of β-gem-difluoroalkene esters remains challenging so far. Herein, we disclose a photoredox-catalyzed allylic defluorinative alkoxycarbonylation of trifluoromethyl alkenes enabled by intermolecular alkoxycarbonyl radical addition. A wide variety of alcohol oxalate derivatives were amenable, affording various β-gem-difluoroalkene esters with excellent functional group tolerance. Notably, the potential synthetic value of this method is highlighted by successful late-stage modification for bioactive molecules.

Iron-catalysed reductive coupling for the synthesis of polyfluorinated compounds

Iron-catalysed reductive cross-coupling of difluorobromo acetic acid derivatives with trifluoromethyl olefins to afford polyfluorinated molecules, containing a difluorenyl and difluoroalkyl group, with a broad substrate scope.