Transition-Metal-Free Trifluoromethylation of Aldehyde Derivatives with Sodium Trifluoromethanesulfinate

Photocatalytic synthesis of polyfluoroalkylated dihydropyrazoles and tetrahydropyridazines

A photocatalytic trifluoromethylation/cyclization reaction of N-allyl and N-homoallyl aldehyde hydrazones with trifluoromethyl thianthrenium triflate was developed for the synthesis of trifluoromethylated dihydropyrazoles and tetrahydropyridazines. Besides, PhI(O2CCHF2)2 was employed to realize the construction of difluoromethylated dihydropyrazoles and tetrahydropyridazines. These protocols exhibit a broad substrate scope and good functional group tolerance.

Organocatalytic Oxidative C-H Amination of Aldehyde Hydrazones with Azoles at Ambient Temperature

An efficient, metal-free, and direct oxidative amination of aldehyde-derived hydrazones with azoles has been developed using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone as an organocatalyst at ambient temperature. This protocol provides a wide range of aminated hydrazone derivatives in a step and atom economical fashion. The reaction possibly follows a radical mechanism.

Electrochemical Trifluoromethylation of Glycals

Carbohydrates play essential roles in various physiological and pathological processes. Trifluoromethylated compounds have wide applications in the field of medicinal chemistry. Herein, we report a practical and efficient trifluoromethylation of glycals by an electrochemical approach using CF₃SO₂Na as the trifluoromethyl source and MnBr₂ as the redox mediator. A variety of trifluoromethylated glycals bearing different protective groups are obtained in 60-90% yields with high regioselectivity. The successful capture of a CF₃ radical indicates that a radical mechanism is involved in this reaction.

1,2-Addition to trifluoromethylated β-enamino diketones: regioselective synthesis of trifluoromethyl-containing azomethine pyrazoles and isoxazoles

Trifluoromethylated β-enamino diketones undergo type 1,2-addition leading to regioselective synthesis of trifluoromethylated azoles containing an azomethine group.

Denitrogenative Hydrotrifluoromethylation of Benzaldehyde Hydrazones: Synthesis of (2,2,2-Trifluoroethyl)arenes

Reacting hydrazones of arylaldehydes with Togni's CF₃ -benziodoxolone reagent, in the presence of potassium hydroxide and cesium fluoride, induces a denitrogenative hydrotrifluoromethylation event to produce (2,2,2-trifluoroethyl)arenes. This novel reaction was tolerant to many electronically-diverse functional groups and substitution patterns, as well as naphthyl- and heteroaryl-derived substrates. Advantages of this process include the easy access to hydrazone precursors on a large scale, speed and operational simplicity, and being transition metal-free.

Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts

Organosulfur compounds have long played a vital role in organic chemistry and in the development of novel chemical structures and architectures. Prominent among these organosulfur compounds are those involving a sulfur(IV) center, which have been the subject of countless investigations over more than a hundred years. In addition to a long list of textbook sulfur-based reactions, there has been a sustained interest in the chemistry of organosulfur(IV) compounds in recent years. Of particular interest within organosulfur chemistry is the ease with which the synthetic chemist can effect a wide range of transformations through either bond formation or bond cleavage at sulfur. This review aims to cover the developments of the past decade in the chemistry of organic sulfur(IV) molecules and provide insight into both the wide range of reactions which critically rely on this versatile element and the diverse scaffolds that can thereby be synthesized.

Copper(i) reagent-promoted hydroxytrifluoromethylation of enamides: flexible synthesis of substituted-3-hydroxy-2-aryl-3-(2,2,2-trifluoro-1-arylethyl)isoindolin-1-one

A novel CuBr-catalyzed hydroxytrifluoromethylation reaction was investigated. Substituted 3-benzylidene-2-arylisoindolin-1-ones was reacted with sodium trifluoromethanesulfinate to afford substituted-3-hydroxy-2-aryl-3-(2,2,2-trifluoro-1-arylethyl)isoindolin-1-one. The reaction proceeded at 25 °C in air atmosphere in the absence of base and ligands. Our results indicate that trifluoromethyl free radical tends to attack a double bond rather than aryl in this reaction.

Exploration of C-H Transformations of Aldehyde Hydrazones: Radical Strategies and Beyond

The chemistry of hydrazones has gained great momentum due to their involvement throughout the evolution of organic synthesis. Herein, we discuss the tremendous developments in both the methodology and application of hydrazones. Hydrazones can be recognized not only as synthetic equivalents to aldehydes and ketones but also as versatile synthetic building blocks. Consequently, they can participate in a range of practical synthetic transformations. Furthermore, hydrazone derivatives display a broad array of biological activities and have been widely applied as pharmaceuticals. Owing to the weak directing group effect of simple aldehydes and ketones in C-H bond functionalizations, the C-H bond functionalizations of hydrazones that have been developed in the past five years represent a significant step forward. These novel transformations open a new door to a broader library of functionalized and complex small molecules. Moreover, a wide range of biologically important N-heterocycles (dihydropyrazoles, pyrazoles, indazoles, cinnolines, etc.) can be efficiently synthesized in an atom- and step-economical manner through single, double, or triple C-H bond functionalizations of hydrazones. Both radical C-H functionalizations and transition-metal-catalyzed directing-group strategies have enhanced the synthetic utility of hydrazones in the chemical community because these strategies solve the long-standing challenge of C-H functionalizations adjacent to aldehydes and ketones. We began this study based on our ongoing interest in visible-light photoredox catalysis. Visible-light photoredox catalysis has become a powerful tool in contemporary synthetic chemistry due to its remarkable advantages in sustainability and use of radical chemistry. By exploiting a photoredox-catalyzed aminyl radical polar crossover (ARPC) strategy, we successfully achieved visible-light-induced C(sp²)-H difluoroalkylation, trifluoromethylation, and perfluoroalkylation of aldehyde-derived hydrazones. This intriguing result was later applied in the C(sp²)-H amination of hydrazones and a cascade cyclization reaction for the synthesis of polycyclic compounds. Encouraged by this redox-neutral C-H functionalization of aldehyde hydrazones, we extended the oxidative C-H/P-H cross-coupling method, which represents a novel and efficient method for the synthesis of α-iminophosphine oxides. Furthermore, an elegant [3 + 2] cycloaddition of azides and aldehyde hydrazones for the synthesis of functionalized tetrazoles was advantageously developed during our investigation of the oxidative C(sp²)-H azidation of aldehyde hydrazones with TMSN₃. The sequential C(sp²)-H/C(sp³)-H bond functionalization of aldehyde-derived hydrazones with simple 2,2-dibromo-1,3-dicarbonyls was achieved by employing relay photoredox catalysis, and it provides a novel method of accessing bioactive fused dihydropyrazole derivatives. The notable feature of this approach was further reflected in the formal [4 + 1] annulation of aldehyde-derived N-tetrahydroisoquinoline hydrazones with 2-bromo-1,3-dicarbonyls. To complement these radical C-H functionalization strategies, we recently applied a directing-group strategy in the Rh-catalyzed C(aldehyde)-H functionalization of aldehyde-derived hydrazones for the synthesis of distinctive and bioactive 1H-indazole scaffolds. In summary, this Account presents recent contributions to the exploration, development, mechanistic insights, and synthetic applications of C-H bond functionalizations of aldehyde hydrazones.

C(sp2)–H functionalization of aldehyde-derived hydrazones via a radical process

This review is focused on the recent advances in the C(sp²)–H functionalization of aldehyde-derived hydrazones via a radical process. Diverse substituted hydrazones including N-heterocycles are afforded under mild conditions with excellent selectivities. In general, an aminyl radical as the key intermediate is involved during the reaction process.