Chloride based ionic liquids as promoting agents for Meerwein reaction in solventless conditions

Visible-Light-Induced Meerwein Fluoroarylation of Styrenes

An unprecedented approach for assembling a broad range of 1,2-diarylethane derivatives with fluorine-containing fully substituted carbon centers was developed. The protocol features straightforward operation, proceeds under metal-free condition, and accommodates a large variety of synthetically useful functionalities. The critical aspect to the success of this novel transformation lies in using aryldiazonium salts as both aryl radical progenitor and also as single electron acceptor which elegantly enables a radical-polar crossover manifold.

Visible-Light Photocatalysis: Does It Make a Difference in Organic Synthesis?

Visible-light photocatalysis has evolved over the last decade into a widely used method in organic synthesis. Photocatalytic variants have been reported for many important transformations, such as cross-coupling reactions, α-amino functionalizations, cycloadditions, ATRA reactions, or fluorinations. To help chemists select photocatalytic methods for their synthesis, we compare in this Review classical and photocatalytic procedures for selected classes of reactions and highlight their advantages and limitations. In many cases, the photocatalytic reactions proceed under milder reaction conditions, typically at room temperature, and stoichiometric reagents are replaced by simple oxidants or reductants, such as air, oxygen, or amines. Does visible-light photocatalysis make a difference in organic synthesis? The prospect of shuttling electrons back and forth to substrates and intermediates or to selectively transfer energy through a visible-light-absorbing photocatalyst holds the promise to improve current procedures in radical chemistry and to open up new avenues by accessing reactive species hitherto unknown, especially by merging photocatalysis with organo- or metal catalysis.

Thermally Induced Carbohydroxylation of Styrenes with Aryldiazonium Salts

The radical carbohydroxylation of styrenes with aryldiazonium salts has been achieved under mild thermal conditions. A broad range of aryldiazonium salts was tolerated, and the reaction principle based on a radical-polar crossover mechanism could be extended to carboetherification as well as to a two-step, metal-free variant of the Meerwein arylation leading to stilbenes.

The Cu(I) catalyzed Meerwein reaction in aqueous solutions proceeds via a radical mechanism. The effect of several ligands

The effect of the ligands 2,5,8,11-tetramethyl-2,5,8,11-tetraaza-dodecane and fumarate on the mechanism and kinetics of the Cu(I) catalyzed Meerwein reaction was studied. The results point out that initially the Cu(I) ion binds to the aromatic ring with the diazo substituent. This reaction is followed by a redox process involving N2 loss and the formation of an aryl radical, R˙. The following kinetics depends on the nature of the ligand, its effect on the redox potential and the steric hindrance it induces on the central copper ion. Clearly the ligand 2,5,8,11-tetramethyl-2,5,8,11-tetraaza-dodecane does not form an optimal catalyst with Cu(I) while it does for the Ullmann reaction.

A Practical Synthesis of α-Aryl Methyl Ketones via a Transition-Metal-Free Meerwein Arylation

We report herein a simple, scalable, transition-metal-free approach to the synthesis of alpha-aryl methyl ketones from diazonium tetrafluoroborate salts under mild conditions. This methodology uses easily accessible and nontoxic starting material and was applied to the multi-kilogram-scale preparation of 1-(3-bromo-4-methylphenyl)propan-2-one.