Intermolecular C-O Bond Formation with Alkoxyl Radicals: Photoredox-Catalyzed α-Alkoxylation of Carbonyl Compounds

Harnessing Bromo/Acyloxy Transposition (BrAcT) and Excited-State Copper Catalysis for Styrene Difunctionalization

1,2-Difunctionalization of styrenes, adding two distinct functional groups across the C═C double bond, has emerged as a powerful tool for enhancing molecular complexity. Herein, we report the development of a regioconvergent β-acyloxylation-α-ketonylation of styrenes through bromo/acyloxy transposition (BrAcT) and excited-state copper catalysis. This approach is amenable to gram-scale synthesis and tolerates a wide range of functional groups and complex molecular frameworks, including derivatives of natural products and marketed drugs. Our experimental and computational studies suggest a unique mechanism featuring a dynamic, ionic BrAcT process and excited-state copper-catalyzed redox reactions. We anticipate that this BrAcT process could serve as a broadly applicable and versatile strategy for β-acyloxylation-α-functionalization of styrenes, creating valuable intermediates for preparing new pharmaceuticals, agrochemicals, and functional materials.

Electrochemical Synthesis of α-Thiocyanated/Methoxylated Ketones Using Enol Acetates

We have developed the synthesis of α-substituted ketone compounds with enol acetates in an electrochemical way. By using cheap NH4SCN and MeOH as the radical sources, a series of valuable α-thiocyanates/methoxy ketones were synthesized under mild electrolysis conditions in acceptable yields with diverse functional group compatibility. Additionally, the scale-up experiment and synthetic transformations reveal potential applications in organic synthesis.

Expanding the chemical space of enol silyl ethers: catalytic dicarbofunctionalization enabled by iron catalysis

Enol silyl ethers are versatile, robust, and readily accessible substrates widely used in chemical synthesis. However, the conventional reactivity of these motifs has been limited to classical two electron (2-e) enolate-type chemistry with electrophilic partners or as radical acceptors in one electron (1-e) reactivity leading, in both cases, to exclusive α-monofunctionalization of carbonyls. Herein we describe a mild, fast, and operationally simple one-step protocol that combines readily available fluoroalkyl halides, silyl enol ethers, and, for the first time, hetero(aryl) Grignard reagents to promote selective dicarbofunctionalization of enol silyl ethers. From a broader perspective, this work expands the synthetic utility of enol silyl ethers and establishes bisphosphine-iron catalysis as enabling technology capable of orchestrating selective C-C bond formations with short-lived α-silyloxy radicals with practical implications towards sustainable chemical synthesis.

Electrochemical Radical Reactions of Enol Acetates and Free Alcohols Directly Access to α-Alkoxylated Carbonyl Compounds

The efficient intermolecular alkoxylation reactions of various enol acetates and different alcohols are developed in the electrochemical process for the first time. Enol acetates derived from either aromatic, alkyl, or alicyclic ketones, and abundant free alcohols directly used in this synthetic strategy, make this transformation very valuable in synthesis and application in the future.

Visible light/copper catalysis enabled alkylation of silyl enol ethers with arylsulfonium salts

An efficient protocol has been developed herein for the site-selective alkylation of silyl enol ethers with arylsulfonium salts giving access to valuable aryl alkyl thioethers under visible light conditions. Enabled by copper (I) photocatalysis, the C-S bond of arylsulfonium salts can be selectively cleaved to deliver C-centered radicals under mild conditions. This developed method provides a straightforward approach to utilize arylsulfonium salts as sulfur sources for the synthesis of aryl alkyl thioethers.

Highly selective γ-alkoxylation, γ-amination and γ-alkylation of unbiased enals by means of photoredox catalysis

We report herein a general and highly selective γ-functionalization protocol under visible light irradiation. This mild radical approach enables the expansion of the scope of application to unbiased enals and the introduction of a wide variety of alkoxy, amino and alkyl functionalities in the γ position with complete regioselectivity.

Visible-Light Photoredox-Catalyzed C(sp2)-H Difluoromethoxylation of (Hetero)arenes Utilizing a Shelf-Stable Pyridinium Reagent

Difluoromethoxyarene moieties have been demonstrated to impart desirable physio-chemical properties to organic molecules. Presented herein is a shelf-stable radical difluoromethoxylating reagent that enables facile and direct C(sp²)-H difluoromethoxylation of (hetero)arenes under blue light photoredox catalysis. 4-Cyano-1-(difluoromethoxy)pyridin-1-ium trifluoromethanesulfonate is prepared in one simple step from the parent pyridine N-oxide. The current protocol tolerates a variety of synthetically and pharmacologically relevant functional groups. Applicability toward the late-stage functionalization of APIs and druglike molecules is also demonstrated.

Branching out: redox strategies towards the synthesis of acyclic α-tertiary ethers

Acyclic α-tertiary ethers represent a highly prevalent functionality, common to high-value bioactive molecules, such as pharmaceuticals and natural products, and feature as crucial synthetic handles in their construction. As such their synthesis has become an ever-more important goal in synthetic chemistry as the drawbacks of traditional strong base- and acid-mediated etherifications have become more limiting. In recent years, the generation of highly reactive intermediates via redox approaches has facilitated the synthesis of highly sterically-encumbered ethers and accordingly these strategies have been widely applied in α-tertiary ether synthesis. This review summarises and appraises the state-of-the-art in the application of redox strategies enabling acyclic α-tertiary ether synthesis.

Recent advances in difunctionalization of alkenes using pyridinium salts as radical precursors

In this review, we summarise the recent applications of pyridinium salts in the radical-mediated difunctionalization of alkenes. Pyridinium salts are a privileged class of compounds that show great utility in natural products and synthetic chemistry. Various organic transformations of pyridinium salts, especially in radical chemistry, have been developed in recent years. We prepared this review based on the two distinguished properties of pyridinium salts in radical transformation: (1) pyridinium salts can easily undergo single electron reduction to deliver X radicals. (2) Pyridinium salts are highly electrophilic so that alkyl radical intermediates can easily add to the pyridine core. Based on the role of pyridinium salts in difunctionalization of alkenes, the main body of this review is divided into three parts: (1) using pyridinium salts as X transfer reagents. (2) Using pyridinium salts as novel pyridine transfer reagents. (3) Using pyridinium salts as bifunctional reagents (X and pyridine). The C2 and C4 selectivity during pyridylation is discussed in detail. We hope that this review will provide a comprehensive overview of this topic and promote the wider development and application of pyridinium salts.