Visible light-promoted metal-free C-H activation: diarylketone-catalyzed selective benzylic mono- and difluorination

Triethylborane-initiated radical chain fluorination: a synthetic method derived from mechanistic insight

We offer a mild, metal-free sp(3) C-H fluorination alternative using Selectfluor and a substoichiometric amount of triethylborane--an established radical initiator in the presence of O2. This radical-chain-based synthetic method is particularly noteworthy as an offspring of the insight gained from a mechanistic study of copper-promoted aliphatic fluorination, constructively turning O2 from an enemy to an ally. Furthermore, BEt3/O2 is a preferred initiator in industrial processes, as it is economical, is low in toxicity, and lends way to easier workup.

A continuous-flow protocol for light-induced benzylic fluorinations

A continuous-flow protocol for the light-induced fluorination of benzylic compounds is presented. The procedure uses Selectfluor as the fluorine source and xanthone as an inexpensive and commercially available photoorganocatalyst. The flow photoreactor is based on transparent fluorinated ethylene propylene tubing and a household compact fluorescent lamp. The combination of xanthone with black-light irradiation results in very efficient fluorination. Good to excellent isolated yields were obtained for a variety of substrates bearing different functional groups applying residence times below 30 min.

Direct, catalytic monofluorination of sp³ C-H bonds: a radical-based mechanism with ionic selectivity

Recently, our group unveiled a system in which an unusual interplay between copper(I) and Selectfluor effects mild, catalytic sp(3) C-H fluorination. Herein, we report a detailed reaction mechanism based on exhaustive EPR, (19)F NMR, UV-vis, electrochemical, kinetic, synthetic, and computational studies that, to our surprise, was revealed to be a radical chain mechanism in which copper acts as an initiator. Furthermore, we offer an explanation for the notable but curious preference for monofluorination by ascribing an ionic character to the transition state.

Late stage benzylic C-H fluorination with [¹⁸F]fluoride for PET imaging

We describe the first late-stage (18)F labeling chemistry for aliphatic C-H bonds with no-carrier-added [(18)F]fluoride. The method uses Mn(salen)OTs as an F-transfer catalyst and enables the facile labeling of a variety of bioactive molecules and building blocks with radiochemical yields (RCY) ranging from 20% to 72% within 10 min without the need for preactivation of the labeling precursor. Notably, the catalyst itself can directly elute [(18)F]fluoride from an ion exchange cartridge with over 90% efficiency. Using this feature, the conventional and laborious dry-down step prior to reaction is circumvented, greatly simplifying the mechanics of this protocol and shortening the time for automated synthesis. Eight drug molecules, including COX, ACE, MAO, and PDE inhibitors, have been successfully [(18)F]-labeled in this way.

A simple method for the electrophilic cyanation of secondary amines

Bleach oxidizes trimethylsilyl cyanide to generate an electrophilic cyanating reagent that readily reacts with an amine nucleophile. This oxidative N-cyanation reaction allows for the preparation of disubstituted cyanamides from amines without using highly toxic cyanogen halides.

Vanadium-Catalyzed C(sp3)-H Fluorination Reactions

Vanadium(III) oxide catalyzes the direct fluorination of C(sp³)-H groups with Selectfluor. This reaction is operationally simple. The catalyst and the reaction byproduct can be removed easily by filtration. Using this method, a fluorine atom can be introduced to the tertiary position of 1,4-cineole and L-menthone selectively.

Selective fluorination of alkyl C–H bonds via photocatalysis

We report the generation of cationic N-radicals from Selectfluor® via energy transfer with anthraquinone as a photocatalyst for the fluorination of unactivated C–H bonds.

Formal fluorine atom transfer radical addition: silver-catalyzed carbofluorination of unactivated alkenes with ketones in aqueous solution

Using a combination of ketones and Selectfluor to mimic α-fluoroketones, formal fluorine-atom-transfer radical addition (F-ATRA) reactions were successfully developed in high efficiency.

Recent advances in C–H fluorination

Highlighted in this article are recent advances in C(sp²)–H and C(sp³)–H fluorination reactions.

Catalytic fluorination of unactivated C(sp3)–H bonds

This Highlight discusses the most recent advances in catalytic fluorination of benzylic, allylic, and aliphatic unactivated C(sp³)–H bonds.

Synthesis of cross-linked polymers via multi-component Passerini reaction and their application as efficient photocatalysts

Cross-linked polymers containing Ru complexes synthesized via multi-component Passerini reaction were shown to be highly effective and recyclable heterogeneous photocatalysts.