Site-Selective Photobromination of O-Acetylated Carbohydrates in Benzotrifluoride

Ferrier photobromination enables direct synthetic access to valuable 5-C-bromosugars but has limitations that restrict its broader use. The reaction is typically conducted in CCl4 heated at reflux with irradiation by broad spectrum, energy-inefficient heat lamps. Herein, we demonstrate that the reaction proceeds rapidly and efficiently with PhCF3 as a safe and environmentally benign alternative to CCl4 at mild temperatures (≤40 °C) inside a compact photoreactor fitted with purple light-emitting diodes (LEDs).

Indium chloride catalysed benzyl bromination using continuous flow technology

This report describes the development of a water-tolerant green catalyst for benzyl bromination. The catalyst, indium chloride, exhibits high catalytic activity with a variety of toluene derivatives in continuous flow. Good yields (59-77%) were obtained in all the cases. Improved selectivity was observed under flow conditions, when compared to batch operation.

Technological Innovations in Photochemistry for Organic Synthesis: Flow Chemistry, High-Throughput Experimentation, Scale-up, and Photoelectrochemistry

Photoinduced chemical transformations have received in recent years a tremendous amount of attention, providing a plethora of opportunities to synthetic organic chemists. However, performing a photochemical transformation can be quite a challenge because of various issues related to the delivery of photons. These challenges have barred the widespread adoption of photochemical steps in the chemical industry. However, in the past decade, several technological innovations have led to more reproducible, selective, and scalable photoinduced reactions. Herein, we provide a comprehensive overview of these exciting technological advances, including flow chemistry, high-throughput experimentation, reactor design and scale-up, and the combination of photo- and electro-chemistry.

Photons or Electrons? A Critical Comparison of Electrochemistry and Photoredox Catalysis for Organic Synthesis

Redox processes are at the heart of synthetic methods that rely on either electrochemistry or photoredox catalysis, but how do electrochemistry and photoredox catalysis compare? Both approaches provide access to high energy intermediates (e.g., radicals) that enable bond formations not constrained by the rules of ionic or 2 electron (e) mechanisms. Instead, they enable 1e mechanisms capable of bypassing electronic or steric limitations and protecting group requirements, thus enabling synthetic chemists to disconnect molecules in new and different ways. However, while providing access to similar intermediates, electrochemistry and photoredox catalysis differ in several physical chemistry principles. Understanding those differences can be key to designing new transformations and forging new bond disconnections. This review aims to highlight these differences and similarities between electrochemistry and photoredox catalysis by comparing their underlying physical chemistry principles and describing their impact on electrochemical and photochemical methods.

Visible light-induced mono-bromination of arenes with BrCCl3

A highly efficient and regioselective bromination of electron-rich arenes and heteroarenes using commercially available BrCCl3 as a "Br" source has been developed. The reaction was performed in air under mild conditions with photocatalyst Ru(bpy)3Cl2·6H2O, avoiding the usage of strong acids and strong oxidants. Mono-brominated products were obtained with medium to excellent yields (up to 94%). This strategy has shown good compatibility and high para-selectivity, which will facilitate the complicated synthesis.

C-H functionalization reactions enabled by hydrogen atom transfer to carbon-centered radicals

Selective functionalization of ubiquitous unactivated C-H bonds is a continuous quest for synthetic organic chemists. In addition to transition metal catalysis, which typically operates under a two-electron manifold, a recent renaissance in the radical approach relying on the hydrogen atom transfer (HAT) process has led to tremendous growth in the area. Despite several challenges, protocols proceeding via HAT are highly sought after as they allow for relatively easy activation of inert C-H bonds under mild conditions leading to a broader scope and higher functional group tolerance and sometimes complementary reactivity over methods relying on traditional transition metal catalysis. A number of methods operating via heteroatom-based HAT have been extensively reported over the past few years, while methods employing more challenging carbon analogues have been less explored. Recent developments of mild methodologies for generation of various carbon-centered radical species enabled their utilization in the HAT process, which, in turn, led to the development of remote C(sp3)-H functionalization reactions of alcohols, amines, amides and related compounds. This review covers mostly recent advances in C-H functionalization reactions involving the HAT step to carbon-centered radicals.

Tracking down the brominated single electron oxidants in recent organic red-ox transformations: photolysis and photocatalysis

A wide range of organic and inorganic brominated compounds including molecular bromine have been extensively used as oxidants in many organic photo-redox transformations in recent years, an area of ever growing interest because of greener and milder approaches. The oxidation power of these compounds is utilized through both mechanistic pathways (by hydrogen atom transfer or HAT in the absence of a photocatalyst and a combination of single electron transfer or SET and/or HAT in the presence of a photocatalyst). Not only as terminal oxidants for regeneration of photocatalysts, but brominated reactants have also contributed to the oxidation of the reaction intermediate(s) to carry on the radical chain process in several reactions. Here in this review mainly the non-brominative oxidative product formations are discussed, carried out since the last two decades, skipping the instances where they acted as terminal oxidants only to regenerate photocatalysts. The reactions are used to generate natural products, pharmaceuticals and beyond.