Electrochemical Oxidative Aryl(alkyl)trifluoromethylation of Allyl Alcohols via 1,2-Migration

Enantioselective acyl-trifluoromethylation of olefins by bulky thiazolium carbene catalysis

Enantioenriched α-chiral β-fluorinated ketones are valuable structural motifs with application in several fields. The recently emerged concept of NHC-catalyzed radical acyl-trifluoromethylation of olefins offers a rapid route to construct racemic β-fluorinated ketones in a single step. Due to the lack of competent chiral NHC catalysts constructing these molecules in an enantioselective manner remains an unmet challenge. Herein, we report a family of chiral thiazolium carbenes having bulky chiral flanking groups and offering three distinct positions with broad steric and electronic tunability. The catalysts display so far unmatched enantioselectivities for acyl-trifluoromethylations of simple unactivated olefins with a wide variety of aldehydes and Togni's reagent. The method provides a variety of enantioenriched β-trifluoromethylated α-chiral ketones in high yields and excellent enantioselectivities up to 98:2 er. A potential applicability of this methodology is demonstrated through enantio- and diastereoselective late-stage functionalizations of pharmaceutical compounds.

Navigating electrochemical oxidative functionalization of olefins: selected mechanistic and synthetic examples

The functionalization of olefins to form added-value compounds is a cornerstone of modern organic chemistry, promoting the synthesis of complex molecules from simple feedstock materials. In parallel, electrochemistry has emerged as a powerful and sustainable technique for enabling challenging transformations under mild conditions by generating reactive intermediates in a controlled manner. This review highlights recent advances in oxidative electrochemical methods for olefin functionalization, showcasing key developments that underscore the versatility of this approach. Using selected representative examples, we explore diverse mechanistic pathways, bond-forming strategies, and the integration of electrochemical techniques with catalytic systems. By providing a concise overview of this rapidly evolving field, we aim to inspire further innovation in electrochemical methodologies to expand the frontiers of olefin chemistry.

Radical Brook rearrangement: past, present, and future

The Brook rearrangement has emerged as one of the most pivotal transformations in organic chemistry, with broad applications spanning organic synthesis, drug design, and materials science. Since its discovery in the 1950s, the anion-mediated Brook rearrangement has been extensively studied, laying the groundwork for the development of numerous innovative reactions. In contrast, the radical Brook rearrangement has garnered comparatively less attention, primarily due to the challenges associated with the controlled generation of alkoxyl radicals under mild conditions. However, recent advancements in visible-light catalysis and transition-metal catalysis have positioned the radical Brook rearrangement as a promising alternative synthetic strategy in organic synthesis. Despite these developments, significant limitations and challenges remain, warranting further investigation. This review provides an overview of the radical Brook rearrangement, tracing its development from past to present, and offers perspectives on future directions in the field to inspire the creation of novel synthetic tools based on this transformation.

Decennary Update on Oxidative-Rearrangement Involving 1,2-Aryl C-C Migration Around Alkenes: Synthetic and Mechanistic Insights

In recent years, numerous methodologies on oxidative rearrangements of alkenes have been investigated, that produce multipurpose synthons and heterocyclic scaffolds of potential applications. The present review focused on recently established methodologies for oxidative transformation via 1,2-aryl migration in alkenes (2013-2023). Special emphasis has been placed on mechanistic pathways to understand the reactivity pattern of different substrates, challenges to enhance selectivity, the key role of different reagents, and effect of different substituents, and how they affect the rearrangement process. Moreover, synthetic limitations and future direction also have been discussed. We believe, this review offers new synthetic and mechanistic insight to develop elegant precursors and approaches to explore the utilization of alkene-based compounds for natural product synthesis and functional materials.

PhI(OAc)2-Promoted 1,2-Transfer Reaction between 1,1-Disubstituted Allylic Alcohols and Thiophenols

The PhI(OAc)2-promoted 1,2-transfer reaction between allylic alcohols and thiophenols, conducted in an argon atmosphere, has proven to be effective in producing β-carbonyl sulfides from 1,1-disubstituted allylic alcohols in high yields. This method offers a fast and efficient way to synthesize β-carbonyl sulfides, which are valuable intermediates in organic synthesis. This discussion focuses on the effects of the oxidizer, temperature, and solvent on the reaction. A proposed tentative mechanism for this reaction is also discussed.

Rhodium(III)-Catalyzed Oxidative 1,3-Aryl Migration of α-Aryl Allylic Alcohols

A Rh(III)-catalyzed oxidative 1,3-aryl migration of α-arylallylic alcohols via Csp2-Csp3 σ bond activation has been developed. This method provides an efficient strategy to allow for allylic alcohol-based skeleton rearrangement, in which various secondary and tertiary α-arylallylic alcohols are rapidly converted to β-aryl-α, β-unsaturated ketones and aldehydes.

gem-Bromonitroalkane Involved Radical 1,2-Aryl Migration of α,α-Diaryl Allyl Alcohol TMS Ether via Visible-Light Photoredox Catalysis

A mild and efficient coupling method concerning the reactions of gem-bromonitroalkanes with α,α-diaryl allyl alcohol trimethylsilyl ethers was reported. A cascade consisting of visible-light-induced generation of an α-nitroalkyl radical and a subsequent neophyl-type rearrangement was key to realize the coupling reactions. Structurally diverse α-aryl-γ-nitro ketones, especially those bearing a nitrocyclobutyl structure, were prepared in moderate to high yields, which could be converted into spirocyclic nitrones and imines.

Electrochemical trifluoromethylation of 2-isocyanobiaryls using CF3SO2Na: synthesis of 6-(trifluoromethyl)phenanthridines

An efficient trifluoromethylation of 2-isocyanobiaryls was developed through the constant current electrolysis, employing sodium trifluoromethanesulfinate (CF₃SO₂Na) as the trifluoromethyl source. The method enabled the syntheses of a series of 6-(trifluoromethyl)phenanthridine derivatives in moderate to high yields under metal- and oxidant-free conditions. A gram-scale synthesis highlights the synthetic versatility of the reported protocol.

Electrochemical monofluoroalkylation cyclization of N-arylacrylamides to construct monofluorinated 2-oxindoles

An electrochemical monofluoroalkylation cyclization of N-arylacrylamides to synthesize monofluorinated 2-oxindoles has been developed, which employs common dimethyl 2-fluoromalonate as a monofluoroalkyl radical precursor and obviates the use of prefunctionalized monofluoroalkylation reagents and sacrificial oxidants. A variety of monofluorinated nitrogen-containing heterocyclic compounds were efficiently obtained with satisfactory yields from readily available materials.

Triarylamines as catalytic donors in light-mediated electron donor–acceptor complexes

EDA complexes with catalytic triarylamines allow C–H perfluoroalkylation of arenes and heteroarenes under visible light irradiation in pH- and redox-neutral conditions. A detailed photophysical characterization of the EDA complex is provided.

Photocatalytic difluoromethylarylation of unactivated alkenes via a (hetero)aryl neophyl-like radical migration

Photoredox-catalyzed addition of the difluoromethylradical to unactivated alkenes has been found to trigger neophyl-like aryl and heteroaryl migrations which allowed the construction of a diverse series of difluoromethyl ketones. The reaction featured mild reaction conditions and broad substrate scope.

Electrochemical alkene azidocyanation via 1,4-nitrile migration

An electrochemical method for the azidocyanation of alkenes via 1,4-nitrile migration has been developed. This organic oxidant free method is applicable across various alkene containing cyanohydrins, and provides access to a broad range of synthetically useful 1,2-azidonitriles (28 examples). This methodology was extended to an electrochemical alkene sulfonylcyanation procedure, as well as to access a trifunctionalized hexanenitrile from a malononitrile starting material. The orthogonal derivatization of the products was also demonstrated through chemoselective transformations.

Recent progress in aryltrifluoromethylation reactions of carbon-carbon multiple bonds

Due to the increasing relevance of fluorine-containing organic molecules in drug design, the synthesis of organofluorine compounds has gained high significance in synthetic organic chemistry. Trifluoromethylative difunctionalizations of carbon-carbon multiple bonds, with the simultaneous incorporation of a CF 3 group and another functional element, have considerable potential. Because of the high importance of carbon-carbon bond-forming reactions in organic synthesis, carbotrifluoromethylations and, in particular, aryltrifluoromethylations or heteroaryltrifluoromethylations are considered to be increasing fields of synthetic organic chemistry. The aim of the current review is to summarize recent developments of aryltrifluoromethylation or heteroaryltrifluoromethylation reactions.

Organophotoredox-catalyzed semipinacol rearrangement via radical-polar crossover

Over the past century, significant progress in semipinacol rearrangement involving 1,2-migration of α-hydroxy carbocations has been made in the areas of catalysis and total synthesis of natural products. To access the α-hydroxy carbocation intermediate, conventional acid-mediated or electrochemical approaches have been employed. However, the photochemical semipinacol rearrangement has been underdeveloped. Herein, we report the organophotoredox-catalyzed semipinacol rearrangement via radical-polar crossover (RPC). A phenothiazine-based organophotoredox catalyst facilitates the generation of an α-hydroxy non-benzylic alkyl radical followed by oxidation to the corresponding carbocation, which can be exploited to undergo the semipinacol rearrangement. As a result, the photochemical approach enables decarboxylative semipinacol rearrangement of β-hydroxycarboxylic acid derivatives and alkylative semipinacol type rearrangement of allyl alcohols with carbon electrophiles, producing α-quaternary or α-tertiary carbonyls bearing sp3-rich scaffolds.

Progress in the Electrochemical Reactions of Sulfonyl Compounds

Electrosynthesis has recently attracted more and more attention due to its great potential to replace chemical oxidants or reductants in molecule-electrode electron transfer. Sulfonyl compounds such as sulfonyl hydrazides, sulfinic acids (and their salts), sulfonyl halides have been discovered as practical precursors of several radicals. As electrochemical redox reactions can provide green and efficient pathways for the activation of sulfonyl compounds, studies for electrosynthesis have rapidly increased. Several types of radicals can be generated from anodic oxidation or cathodic reduction of sulfonyl compounds and can initiate fluoroalkylation, benzenesulfonylation, cyclization or rearrangement. In this Review, we summarize the electrosynthesis developments involving sulfonyl compounds mainly in the last decade.

Photons or Electrons? A Critical Comparison of Electrochemistry and Photoredox Catalysis for Organic Synthesis

Redox processes are at the heart of synthetic methods that rely on either electrochemistry or photoredox catalysis, but how do electrochemistry and photoredox catalysis compare? Both approaches provide access to high energy intermediates (e.g., radicals) that enable bond formations not constrained by the rules of ionic or 2 electron (e) mechanisms. Instead, they enable 1e mechanisms capable of bypassing electronic or steric limitations and protecting group requirements, thus enabling synthetic chemists to disconnect molecules in new and different ways. However, while providing access to similar intermediates, electrochemistry and photoredox catalysis differ in several physical chemistry principles. Understanding those differences can be key to designing new transformations and forging new bond disconnections. This review aims to highlight these differences and similarities between electrochemistry and photoredox catalysis by comparing their underlying physical chemistry principles and describing their impact on electrochemical and photochemical methods.

Halogen bond promoted aryl migration of allylic alcohols under visible light irradiation

A simple and catalyst-free radical addition/1,2-aryl migration cascade process of ally alcohol driven by halogen bond was developed under visible light irradiation, featuring mild conditions, practical procedures, and broad substrate scope.

Oxidative thiocyanation of allylic alcohols: an easy access to allylic thiocyanates with K2S2O8 and NH4SCN

A practical method for the synthesis of allylic thioacyanates from allylic alcohols was disclosed employing K2S2O8 as the oxidant and NH4SCN as the thiocyanate source.

Electrochemical-Promoted Nickel-Catalyzed Oxidative Fluoroalkylation of Aryl Iodides

This work describes a general strategy for metal-catalyzed cross-coupling of fluoroalkyl radicals with aryl halides under electrochemical conditions. The contradiction between anodic oxidation of fluoroalkyl sulfinates and cathodic reduction of low-valent nickel catalysts can be well addressed by paired electrolysis, allowing for direct introduction of fluorinated functionalities into aromatic systems.

Radical-mediated rearrangements: past, present, and future

Rearrangement reactions, one of the most significant transformations in organic chemistry, play an irreplaceable role in improving synthetic efficiency and molecular complexity. Concomitant cleavage and reconstruction of chemical bonds can display the great artistry and the glamour of synthetic chemistry. Over the past century, ionic rearrangement reactions, in particular those involving cationic pathways, have represented most of the research. Alongside the renaissance of radical chemistry, radical-mediated rearrangements have recently seen a rapid increase of attention from the chemical community. Many new radical rearrangements that extensively reveal the migratory behaviour of functional groups have been unveiled in the last decade. This Review provides a comprehensive perspective on the area from the past to present achievements, and brings up the prospects that may inspire colleagues to develop more useful synthetic tools based on radical rearrangements.

Electrochemical trifluoromethylation/cyclization for the synthesis of isoquinoline-1,3-diones and oxindoles

Herein, we describe a protocol for electrochemical cathode reduction to generate trifluoromethyl radicals. The trifluoromethylation reagent (IMDN-SO₂CF₃) used in this strategy is inexpensive and easy to obtain, and the reaction can be conducted efficiently without the addition of additional redox reagents. Using this strategy, we achieved electrochemical trifluoromethylation/cyclization for the synthesis of isoquinoline-1,3-diones and oxindoles. This protocol has good functional group tolerance and a broad substrate scope.

Electrochemical Installation of CFH2 -, CF2 H-, CF3 -, and Perfluoroalkyl Groups into Small Organic Molecules

Electrosynthesis can be considered a powerful and sustainable methodology for the synthesis of small organic molecules. Due to its intrinsic ability to generate highly reactive species under mild conditions by anodic oxidation or cathodic reduction, electrosynthesis is particularly interesting for otherwise challenging transformations. One such challenge is the installation of fluorinated alkyl groups, which has gained significant attention in medicinal chemistry and material science due to their unique physicochemical features. Unsurprisingly, several electrochemical fluoroalkylation methods have been established. In this review, we survey recent developments and established methods in the field of electrochemical mono-, di-, and trifluoromethylation, and perfluoroalkylation of small organic molecules.

Divergent, Strain-Release Reactions of Azabicyclo[1.1.0]butyl Carbinols: Semipinacol or Spiroepoxy Azetidine Formation

The azetidine moiety is a privileged motif in medicinal chemistry and new methods that access them efficiently are highly sought after. Towards this goal, we have found that azabicyclo[1.1.0]butyl carbinols, readily obtained from the highly strained azabicyclo[1.1.0]butane (ABB), can undergo divergent strain-release reactions upon N-activation. Treatment with trifluoroacetic anhydride or triflic anhydride triggered a semipinacol rearrangement to give keto 1,3,3-substituted azetidines. More than 20 examples were explored, enabling us to evaluate selectivity and the migratory aptitude of different groups. Alternatively, treatment of the same alcohols with benzyl chloroformate in the presence of NaI led to iodohydrin intermediates which gave spiroepoxy azetidines upon treatment with base. The electronic nature of the activating agent dictates which pathway operates.

Electrochemical rearrangement protocols towards the construction of diverse molecular frameworks

Rearrangement reactions constitute a critical facet of synthetic organic chemistry and demonstrate an attractive way to take advantage of existing structures to access various important molecular frameworks. Electroorganic chemistry has emerged as an environmentally benign approach to carry out organic transformations by directly employing an electric current and avoids the use of stoichiometric chemical oxidants. The last few years have witnessed a resurgence of electroorganic chemistry that has promoted a renaissance of interest in the development of novel redox electroorganic transformations. This review manifests the evolution of electrosynthesis in the area of rearrangement chemistry and covers the achievements in the field of migration, ring expansion, and rearrangements along with the mechanisms involved.

Ligand Promoted Olefination of Anilides for Indirectly Introducing Fluorinated Functional Groups via Palladium Catalyst

We report a palladium-catalyzed, ligand promoted, C-H fluorine-containing olefination of anilides with 4-bromo-3,3,4,4-tetrafluorobutene as the fluorinated reagent, which has a potential transformation into other compounds due to its -CF₂CF₂Br functional group. -CF₂CF₂H was obtained by using the mild reducing agent sodium borohydride. Bioactive compounds such as aminoglutethimide derivative and propham were well-tolerated in this reaction, both of which highlight the synthetic importance of this method.

Radical Addition Enables 1,2-Aryl Migration from a Vinyl-Substituted All-Carbon Quaternary Center

An efficient method for photocatalytic perfluoroalkylation of vinyl-substituted all-carbon quaternary centers involving 1,2-aryl migration has been developed. The rearrangement reactions use fac-Ir(ppy)₃ , visible light and commercially available fluoroalkyl halides and can generate valuable multisubstituted perfluoroalkylated compounds in a single step that would be challenging to prepare by other methods. Mechanistically, the photoinduced alkyl radical addition to an alkene leads to the migration of a vicinal aryl substituent from its adjacent all-carbon quaternary center with the concomitant generation of a C-radical bearing two electron-withdrawing groups that is further reduced by a hydrogen donor to complete the domino sequence.

Recent advances in electrochemically driven radical fluorination and fluoroalkylation

Electrochemical fluorination (ECF) refers to the introduction of fluorine-containing moieties into organic molecules under electrochemical conditions.

Electrochemical tandem trifluoromethylation of allylamines/formal (3 + 2)-cycloaddition for the rapid access to CF3-containing imidazolines and oxazolidines

A straightforward and environmentally friendly synthesis of CF₃-containing imidazolines and oxazolidines has been developed through an electrochemical three-component reaction among allylamines, the Langlois reagent, and nitrile or carbonyl compounds.

Recent advances in multi-component reactions and their mechanistic insights: a triennium review

This review summarizes the recent developments in MCRs, incorporating different strategies along with their mechanistic aspects.

K2S2O8 promoted dehydrative cross-coupling between α,α-disubstituted allylic alcohols and thiophenols/thiols

K₂S₂O₈ promoted dehydrative cross-coupling between α,α-disubstituted allylic alcohols and thiophenols/thiols is demonstrated for the first time, leading to a wide range of allyl sulfides in good to high yields.

An Indirect Strategy for Trifluoromethylation via an Iridium Catalyst: Approach to Generate Isocoumarin Skeletons in Bioactive Molecules

3-Bromo-1,1,1-trifluoroacetone was first disclosed as an effective indirect trifluoromethylation reagent to construct the important 3-trifluoromethyl isocoumarin skeleton. The reaction proceeds through a ligand-promoted, iridium-catalyzed ortho-selective C-H alkylation of benzoic acid and an intermolecular cyclization reaction promoted by silver acetate. A wide range of 3-trifluoromethyl isocoumarins can be easily obtained in moderate to good yields. Importantly, the isocoumarin skeleton can be easily formed in bioactive compounds, highlighting the importance of this reaction.