A novel dual visible-light-photoredox- and titanocene-catalyzed protocol for the highly regioselective access to α-vinyl, β-hydroxy esters is reported. Thanks to a comprehensive investigation on the reaction conditions, the disclosure of an original protocol based on the Barbier-type properties of titanocene complexes in low oxidation state is achieved. The reaction showed very good compatibility with several functional groups and a detailed photophysical studies highlighted the role played by each component of the reaction.

Abstract

For the first time, a dual photoredox- and titanocene-catalyzed methodology for the regioselective access to α-vinyl-β-hydroxy esters towards aldehyde allylation with 4-bromobut-2-enoate is reported. The protocol is based on the Barbier-type properties of the inexpensive and available Cp₂TiCl₂ in catalytic amount (5 mol%). The developed mild reaction conditions gave access to a library of differently functionalized α-vinyl-β-hydroxy esters in moderate diastereoselectivity, employing the commercially available ethyl 4-bromobut-2-enoate and both aromatic and aliphatic aldehydes. The reaction was realized under visible light irradiation, in the presence of an organophotocatalyst (3DPAFIPN, 2 mol%) combined with Hantzsch's ester as the sacrificial reductant. In contrast to other Barbier-type reactions employing ethyl 4-bromobut-2-enoate, the photoredox system ensures a better regioselectivity. Moreover, the use of preformed organometallic nucleophilic species (e. g., dienolborinates), and the need of metal reductants or stoichiometric amount of transition metals in low oxidation state for Barbier-type reactions, is avoided. To support the experimental evidence, a detailed photophysical study shed light on the mechanism of the reaction.

This review provides an overview of recent advances in direct C−H trifluoromethylselenolation and fluoroalkylselenolation from development to the application of corresponding reagents.

Abstract

Due to their high lipophilicity and strong electron-withdrawing property, more and more attention has been paid to introducing trifluoromethylseleno and fluoroalkylseleno moieties into organic molecules. In this short review, we categorize the synthesis of compounds that combine selenium and fluorinated moieties into two main types: trifluoromethylselenolation (CF₃Se) and fluoroalkylselenolation (R_fSe, except CF₃Se). This review aims to provide a summary of the recent advances in direct C−H trifluoromethylselenolation and fluoroalkylselenolation from the synthesis of trifluoromethylselenolation and fluoroalkylselenolation reagents to their application. Based on the method of how the R_fSe group was introduced, the main content is divided into three parts: transition-metal-free reactions, transition-metal-mediated/catalyzed reactions and photo-catalyzed reactions. The general substrate scope, mechanism and limitations would also be discussed so that we hope the review will serve as an inspiration for further research in this appealing research field.

The Front Cover celebrates the combination of photoredox catalysis with titanium catalysis and all the exciting and stimulating transformations that can be achieved without the use of metal reductants. In the present report, the combination of an organophotocatalyst with a catalytic amount of titanocene dichloride gave access to a library of differently functionalized α-vinyl-β-hydroxy esters through an α-selective vinylogous Reformatsky approach emploiyng the Hantzsch’ ester as stoichiometric organic reductant. More information can be found in the Research Article by P. G. Cozzi, F. Calogero et al.

The synthesis of phenanthridinones and carbazoles by intramolecular photo- and Base-promoted Homolityc Aromatic Substitution photo-BHAS) reaction from N-(2-halobenzyl)-N-methylanilines or N-substituted-N-phenyl anilines is presented. The synthetic protocol uses only KO ^t Bu and DMSO to generate aryl radicals under visible-light irradiation. An exciplex complex between the substrates and the dimsyl anion could be involved in the initiation step.

Abstract

A visible-light-driven approach towards phenanthridin-6(5H)-one and carbazole rings synthesis under transition-metal-free conditions is here reported. Phenanthridinones and carbazoles are synthesized through an intramolecular arylation of the corresponding N-(2-halobenzyl)-N-methylanilines or N-substituted-N-phenyl anilines using KO ^t Bu as base in dimethyl sulfoxide (DMSO) at room temperature (rt), employing blue light emitting diodes (LEDs) as the light source. The reaction proceeds through photo- and base-promoted homolytic aromatic substitution via photoinduced electron transfer mechanism and it exhibits good tolerance to different functional groups, resulting in good to very good yields (up to 86 %).

The ring-opening of cyclic sulfamidates and sulfates with α-fluorocarbanion generated from fluorobis(phenylsulfonyl)methane (FBSM) and subsequent reductive desulfonylation have been developed. This fluoromethylation approach allows access to γ- and δ-fluoroamines as well as γ- and δ-fluoroalcohols in high yields. The monofluoromethylation of cyclic sulfamidates with α-fluorocarbanion of ethyl 2-fluoroacetoacetate was also described.

Abstract

A regioselective fluoromethylation by ring-opening of cyclic sulfamidates and sulfates with α-fluorocarbanions and subsequent reductive desulfonylation is developed. Fluorobis(phenylsulfonyl)methane (FBSM) was explored as fluoromethide equivalent and the reaction was extended to the α-fluorocarbanion of ethyl 2-fluoroacetoacetate. This approach allows access to γ- and δ-fluoroamines as well as γ- and δ-fluoroalcohols in high yields.

A facile and efficient method to synthesize thioethers from readily available sulfonyl chlorides and benzylic trimethylammonium salts via C−N cleavage of benzyl ammonium salts has been developed. This methodology features mild reaction conditions and good substrate compatibility.

Abstract

A facile and efficient method to synthesize thioethers from sulfonyl chlorides and benzylic trimethylammonium salts is presented. This protocol provides a simple and direct approach to realize the reductive coupling reaction of readily available sulfonyl chlorides with benzyl ammonium salts in the presence of triphenylphosphine along with base via C−N cleavage of benzyl ammonium salts. This reaction features mild conditions and good substrate compatibility to afford thioethers in moderate to good yields.

Abstract: Trifluoromethylation-based difunctionalization of alkenes provides a step-economical route to CF3-containing polyfunctionalized organics. New and scalable process is highly desired in this field. Here, we report a simple and environmentally benign method for olefinic thiocyanotrifluoromethylation. By the use of PhICF3Cl as unique CF3 agent and NaSCN as the SCN source, the difunctionalization of alkenes selectively occurs on water at ambient condition. Mechanism studies suggest a radical process in which SCN anion is proposed to act as not only reductive initiator but also S-nucleophile. All tested reactions are compatible with mono-, di-, tri-, and tetra-substituted alkenes and with high functional group tolerance. This method is also suitable for the selenocyanotrifluoromethylation of alkenes. Therefore, a sustainable platform has been established to synthesize valuable β-trifluoromethylated thio(seleno)cyanates in green way. Keywords: Alkenes; Difunctionalization; Radical addition; Thiocyanotrifluoromethylation; On water

Lithium trialkylzincate-mediated I/Zn exchange reaction has been revisited computationally through a micro-solvation approach. A never yet investigated iodoaryl derivative bearing a potential bulky para-directing group, namely 4-iodobenzyl mesylate, was considered as a substrate. THF as typical solvent and Et3ZnLi have also been considered for the first time in such a reaction. Three mechanistic pathways have been calculated, including (1) a literature-inspired pathway with full preservation of the synergic character of the reagent as well as a complementary mesylate group-directed pathway, (2) a THF-solvated open complex-promoted pathway and (3) an anionic pathway. While the anionic pathway appeared to be unlikely, pathway involving a THF-solvated open zincate complex turned out to be the most energetically favoured. Equivalent thermodynamic profiles were found for both complementary pathways with preservation of the synergic character of the reagent, albeit a slight preference could be attributed to that occurring with initial chelation of Li to the mesylate group (OMs) through micro-solvation approach. The I/Zn exchange was shown to proceed through a lithium-assisted aryl shuttle-like process. The iodoaryl substrate is first converted into ArLi intermediate which in turns reacts with the remaining diorganozinc reagent.

Indirect electrolysis method using appropriate mediators enables numerous chemical reactions. This review describes the general principles of mediators, with a particular focus on non-transition metal mediators, and introduces recent representative examples of bond formation reactions by indirect electrolysis.

This review summarizes the recent advancements in synthetic applications involving aryl radicals, utilizing aryl sulfonium salts as precursors. This topic, while challenging, holds paramount significance for drug design and the agrochemical industry. The mechanisms underlying these transformations are also discussed.

Abstract

The utilization of aryl radicals as open-shelled intermediates has become an essential tool for both conventional and state-of-the-art synthetic chemistry. However, the current methods for generating aryl radicals are still inefficient, greatly impeding their practical applications. Encouragingly, sulfonium salts have emerged as appealing sources of aryl radicals for a wide range of transformations aimed at creating novel chemical bonds driven by their distinctive structural attributes and chemical tendencies. This review primarily focuses on the specific reaction mechanisms underlying the cleavage of C−S bonds in sulfonium salts, leading to the generation of corresponding aryl radicals within diverse reaction conditions.