Amino- and azidotrifluoromethylation of alkenes

Two-step synthesis of vicinal trifluoromethyl primary amines from α-(trifluoromethyl)styrenes and phthalimide

A novel two-step synthesis of β-trifluoromethyl primary amines from readily available α-(trifluoromethyl)styrenes and phthalimide is developed. The first step involves a hydroamination between α-(trifluoromethyl)styrenes and phthalimide (PhthNH) with the assistance of a base. Next, the hydrazinolysis of the resulting N-(β-trifluoromethyl-β-arylethyl)phthalimides with hydrazine hydrate affords the desired N-(β-trifluoromethyl-β-arylethyl)amines.

Understanding and Controlling Fluorinated Diacyl Peroxides and Fluoroalkyl Radicals in Alkene Fluoroalkylations

The demand for practical methods for the synthesis of novel fluoroalkyl molecules is increasing owing to their diverse applications. Our group has achieved efficient difunctionalizing fluoroalkylations of alkenes using fluorinated carboxylic anhydrides as user-friendly fluoroalkyl sources. Fluorinated diacyl peroxide, prepared in situ from carboxylic anhydrides, enables the development of novel reactions when used as a radical fluoroalkylating reagent. In this account, we aim to provide an in-depth understanding of the structure, bonding, and reactivity of fluorinated diacyl peroxides and radicals as well as their control in fluoroalkylation reactions. In the first part of this account, the physical properties and reactivity of diacyl peroxides and fluoroalkyl radicals are described. In the subsequent part, we categorize the reactions into copper-catalyzed and metal-free methods utilizing the oxidizing properties of fluorinated diacyl peroxides. We also outline examples and mechanisms.

Radical 1,2,3-tricarbofunctionalization of α-vinyl-β-ketoesters enabled by a carbon shift from an all-carbon quaternary center

Herein, we report an intermolecular, radical 1,2,3-tricarbofunctionalization of α-vinyl-β-ketoesters to achieve the goal of building molecular complexity via the one-pot multifunctionalization of alkenes. This reaction allows the expansion of the carbon ring by a carbon shift from an all-carbon quaternary center, and enables further C–C bond formation on the tertiary carbon intermediate with the aim of reconstructing a new all-carbon quaternary center. The good functional group compatibility ensures diverse synthetic transformations of this method. Experimental and theoretical studies reveal that the excellent diastereoselectivity should be attributed to the hydrogen bonding between the substrates and solvent.

Herein, we report an intermolecular, radical 1,2,3-tricarbofunctionalization of α-vinyl-β-ketoesters to achieve the goal of building molecular complexity via the one-pot multifunctionalization of alkenes.

Radical hydrotrifluoromethylation of ynamides: a route toward β-CF3 enamides

We report here a radical hydrotrifluoromethylation of ynamides to provide an alternative route toward β-CF3 enamides.

Copper-Catalyzed 1,2-Trifluoromethylation Carbonylation of Unactivated Alkenes: Efficient Access to β-Trifluoromethylated Aliphatic Carboxylic Acid Derivatives

A novel copper-catalyzed carbonylative trifluoromethylation of unactivated alkenes has been developed. A broad range of β-trifluoromethylated carboxylic acid derivatives were prepared in moderate to excellent yields from simple alkenes with excellent regioselectivity. It is noteworthy that ethylene gas, as the simplest olefin, can also be applied directly to obtain β-trifluoromethylated amides and ester. This transformation presents the first example on carbonylative trifluoromethylation of alkenes.

ZnI2-Catalyzed Aminotrifluoromethylation Cyclization of Alkenes Using PhICF3Cl

We report here an alternatively catalytic aminotrifluoromethylation of alkenes using PhICF₃Cl as a bifunctional reagent along with ZnI₂ as a dual catalyst. A combined catalytic strategy was established for the intramolecular aminotrifluoromethylation of 4-pentenamines. As a result, a set of 2-trifluoroethyl-pyrrolidines was obtained in a high selectivity. Mechanism studies revealed that the reaction included an iodine anion-catalyzed radical chlorotrifluoromethylation of alkenes and a sequential Lewis acid-promoted aminocyclization of the resulting chlorotrifluoromethylated intermediates.

Visible light photoredox alkylazidation of alkenes with sodium azide and heteroarenium salts: entry to azido-containing 1,4-dihydropyridines

A three-component alkene alkylazidation using sodium azide as the azido resource and heteroarenium salts as functionalized alkyl reagents for producing highly valuable 2-azido-1-(1,4-dihydropyridin-4-yl)-ethanes is described. This reaction allows the incorporation of both an azido group and a 1,4-dihydropyridin-4-yl group across C[double bond, length as m-dash]C bonds to construct two new bonds in a single reaction step, and represents a practical and mechanistically distinct alternative that harnesses an electrophilic heteroarenium ion to accomplish the alkene difunctionalization reaction.

Fluorofunctionalizations of C-C Multiple Bonds and C-H Bonds

In spite of only a few naturally occurring products having one or more fluorine atoms, organofluorine compounds have been widely utilized in pharmaceutical, agrochemical, and functional material science fields due to the characteristic properties of the fluorine atom. Therefore, the development of new methods for the introduction of fluorine-containing functional groups has been a long-standing research topic. This article discusses our contributions to this area. The first topic is on the trifluoromethylations of C-C multiple bonds using Togni reagent based on our working hypothesis that hypervalent iodine could be activated by coordination of the carbonyl moiety to the Lewis acid catalyst. The second topic relates to asymmetric fluorofunctionalization of alkenes. A newly designed phase-transfer catalyst consisting of a carboxylate anion functioning as a phase-transfer agent and a primary hydroxyl group as a site that captures the anionic substrate was revealed to be an effective catalyst for asymmetric fluorolactonization. Inspired by the mechanistic studies of fluorolactonization, we produced a linked binaphthyl dicarboxylate catalyst, which catalyzes the 6-endo-fluorocyclization and the deprotonative fluorination of allylic amides in a highly enantioselective manner. The third topic is on C-H fluorofunctionalizations using either catalysis or photoactivation. Benzylic trifluoromethylation, which is still a rare reaction, using Togni reagent and aromatic C-H trifluoromethylation using Umemoto reagent under simple photoirradiation conditions were achieved. In addition, the Csp³-H fluorination of alkyl phthalimide derivatives is demonstrated.

Radical Pentafluoroethylation of Unactivated Alkenes Using CuCF2CF3

We have found that the CuCF₂CF₃ complex generated from low-cost pentafluoroethane is a convenient and practical source for the CF₂CF₃ radical under aerobic conditions at room temperature. Using this system, readily available unactivated alkenes can be pentafluoroethylated to provide novel allylic CF₂CF₃ compounds with excellent E-selectivity and functional group tolerability. Mechanistic studies including TEMPO-CF₂CF₃ trapping and radical clock experiments provided strong evidence for radical pathways, offering a new opportunity for copper-mediated radical perfluoroalkylation.

Copper-Catalyzed Asymmetric Radical 1,2-Carboalkynylation of Alkenes with Alkyl Halides and Terminal Alkynes

A copper-catalyzed intermolecular three-component asymmetric radical 1,2-carboalkynylation of alkenes has been developed, providing straightforward access to diverse chiral alkynes from readily available alkyl halides and terminal alkynes. The utilization of a cinchona alkaloid-derived multidentate N,N,P-ligand is crucial for the efficient radical generation from mildly oxidative precursors by copper and the effective inhibition of the undesired Glaser coupling side reaction. The substrate scope is broad, covering (hetero)aryl-, alkynyl-, and aminocarbonyl-substituted alkenes, (hetero)aryl and alkyl as well as silyl alkynes, and tertiary to primary alkyl radical precursors with excellent functional group compatibility. Facile transformations of the obtained chiral alkynes have also been demonstrated, highlighting the excellent complementarity of this protocol to direct 1,2-dicarbofunctionalization reactions with C(sp²/sp³)-based reagents.

Iron-Catalyzed Alkylazidation of 1,1-Disubstituted Alkenes with Diacylperoxides and TMSN3

An iron-catalyzed radical alkylazidation of electron-deficient alkenes is reported. Alkyl diacyl peroxides work as the alkyl source, and trimethylsilyl azide acts as the azido reservoir. This method features mild reaction conditions, wide substrate scope, and good functional group tolerance, providing a range of α-azido esters, an α-azido ketone, and an α-azido cyanide in high yields. These azides can be easily transferred into many kinds of amino acid derivatives.

Copper(I)-Catalyzed Asymmetric Reactions Involving Radicals

Asymmetric functionalization of alkyl radicals represents a robust yet underdeveloped method for efficient construction and decoration of carbon skeletons in chiral organic molecules. In this field, we have been inspired by the excellent redox, alkyl radical trapping, and Lewis acidic properties of copper to develop several catalytic modes for asymmetric reactions involving alkyl radicals. At the beginning, we discovered tandem radical hydrotrifluoromethylation of unactivated alkenes and enantioselective alkoxylation of remote C(sp³)-H bonds by copper/chiral phosphate relay catalysis. This success has stimulated us to develop an asymmetric three-component 1,2-dicarbofunctionalization of 1,1-diarylalkenes using a similar strategy via radical intermediates. Meanwhile, we also discovered a copper/chiral secondary amine cooperative catalyst for asymmetric radical intramolecular cyclopropanation of alkenes using α-aldehyde methylene groups as C1 sources. The trapping of alkyl radical intermediates by Cu^II species during the reaction was essential for the chemoselectivity toward cyclopropanation. Encouraged by the efficient enantiocontrol with chiral phosphate and the effective trapping of alkyl radicals with Cu^II species, we then sought to develop copper/chiral phosphate as a single-electron-transfer catalyst for asymmetric reactions involving alkyl radicals. Subsequently, we successfully achieved a series of highly enantioselective 1,2-aminofluoroalkylation, -aminoarylation, -diamination, -aminosilylation, and -oxytrifluoromethylation of unactivated alkenes. The key for high enantioinduction was believed to be the effective trapping of alkyl radicals by Cu^II/chiral phosphate complexes. Besides, an achiral pyridine ligand was found to be indispensable for achieving high enantioselectivity, presumably via stabilization of Cu^III species in the 1,2-alkoxytrifluoromethylation reaction. This discovery reminded us of tuning the redox properties and chemoreactivity of copper centers with an ancillary ligand. As a result, we subsequently identified cinchona alkaloid-derived sulfonamides as novel neutral-anionic hybrid ligands for simultaneous chemo- and enantiocontrol. We thus accomplished highly enantioselective 1,2-iminoxytrifluoromethylation of unactivated alkenes under the catalysis of copper/cinchona alkaloid-derived sulfonamide ligand, affording trifluoromethylated isoxazolines in high enantiomeric excess. Our copper-catalyzed asymmetric reactions with alkyl radicals provide expedient access to a diverse range of valuable chiral molecules with broad application potential in areas of organic synthesis, medicine, agrochemical, and material sciences.

Zinc-catalyzed asymmetric nitrooxylation of β-keto esters/amides with a benziodoxole-derived nitrooxy transfer reagent

Zinc-catalyzed asymmetric nitrooxylation to afford a series of α-nitrooxy β-keto esters/amides in high yields and with low to moderate enantioselectivities has been disclosed.

Recent Advances in First-Row Transition Metal/Chiral Phosphoric Acid Combined Catalysis

Since the pioneering independent reports of Akiyama and Terada, the use of chiral phosphoric acids (CPAs) and derivatives as a versatile tool for asymmetric synthesis with good reactivity, regioselectivity, diastereoselectivity and enantioselectivity has emerged, forming an important part of the implementation of asymmetric counteranion-directed catalysis reported to date. In these achievements, the combination of metals with CPAs has enabled various catalytic modes beyond the scope of typical acid catalysis, such as relay catalysis, ion-pairing catalysis, and binary acid catalysis. The first-row transition metals (Sc-Zn) are considered to be sustainable transition metals and have received a great deal of attention. These naturally abundant metals display excellent Lewis acidity and function as powerful redox catalysts in synthesis involving both one and two-electron transfers. Hence, in this chapter, we summarize recent advances in the development of asymmetric reactions using a combination of first-row transition metals and CPAs. Furthermore, we provide a detailed discussion of the mechanisms involved in order to understand the interaction of the metal/phosphate and the origins of the asymmetric control of the transformations.

[3 + 2] Cycloaddition and Cascade Radical Reactions for the Synthesis of Trifluoromethylated Tetrahydrobenzodiazepin-3-ones

A reaction sequence involving three-component [3 + 2] cycloaddition of azomethine ylides followed by CuI-catalyzed cascade trifluoromethyl radical addition and cyclization is developed for diastereoselective synthesis of fused-tetrahydrobenzodiazepin-3-ones.

Aryltrifluoromethylative cyclization of unactivated alkenes by the use of PhICF3Cl under catalyst-free conditions

A concise and catalyst-free aryltrifluoromethylative cyclization of unactivated alkenes has been developed herein. The use of PhICF3Cl as a powerful trifluoromethylating agent allows easy transformations. A set of trifluoroethylated carbocycles and aza-hereocycles were efficiently synthesized in good yield and selectivity. A broad substrate scope, mild reaction conditions, and easy operation would make this method well-suited for applications.

Catalyst-free and selective trifluoromethylative cyclization of acryloanilides using PhICF3Cl

Trifluoromethylative cyclization and biscyclization reactions of acryloanilides efficiently occurred under catalyst-free conditions.

Intermolecular, redox-neutral azidoarylation of alkenes via photoredox catalysis

An intermolecular, redox-neutral azidoarylation of alkenes with pyridines and TMSN₃ has been reported via visible light-induced photoredox catalysis.

Metal-free alkene oxy- and amino-perfluoroalkylations via carbocation formation by using perfluoro acid anhydrides: unique reactivity between styrenes and perfluoro diacyl peroxides

A practical metal-free perfluoroalkylation using acid anhydrides with unique reaction mode via carbocation has been developed.

We present a strategy for metal-free, alkene difunctionalization-type, oxy- and amino-perfluoroalkylations, using perfluoro acid anhydrides as practical and user-friendly perfluoroalkyl sources. This method provides efficient access to oxy-perfluoroalkylation products via carbocation formation due to the unique reactivity between styrenes and bis(perfluoroacyl) peroxides generated in situ from perfluoro acid anhydrides. This reaction is also applicable to metal-free intramolecular amino-perfluoroalkylation of styrenes bearing a pendant amino group. Synthetic utility of the oxy-trifluoromethylation products was confirmed by demonstrating derivatization via hydrolysis, elimination, and acid-catalyzed substitution with carbon nucleophiles. The mechanism of the carbocation formation was investigated experimentally and theoretically.

Hydrofunctionalization of alkenols triggered by the addition of diverse radicals to unactivated alkenes and subsequent remote hydrogen atom translocation

Concomitant anti-Markovnikov hydrofunctionalization of alkenes and oxidation of remote alcohols are achieved through intramolecular 1,5(6)-hydrogen atom transfer.