Transition-Metal-Free Catalytic Carboalkoxylation of Styrenes at Room Temperature

Abstract

Herein, we describe the first transition-metal-free catalytic carboalkoxylation of styrenes with aryl diazonium salts by Meerwein addition in the presence of a phenalenyl ligand at room temperature without requiring any light stimulation. This three-component reaction allows facile difunctionalization of styrene derivatives with various alcohols (such as 1, 2, and 3°) as the source of alkoxy group during this transformation. The key intermediates and the transition states involved in this reaction path were unraveled by a series of control experiments coupled with density functional theory calculations. The full mechanistic investigation provides an understanding of the selectivity toward carboalkoxylation (Meerwein arylation addition elimination) in the presence of various alcohols over the simple arylation to multiple bond (Meerwein arylation–elimination) reaction.

Visible Light Promoted, Catalyst‐Free Radical Carbohydroxylation and Carboetherification under Mild Biomimetic Conditions

“…[19] In addition, the chain propagation is likelyt ob ei mproved by af aster or even at once addition of the diazonium salt to the reactionm ixture, given that the homocoupling of radical 2 to diazonium ion 1 [20] to give 7 remains slower than the desired addition of aryl radical 2 to styrene 3. [21] Ther esultso fs elected preliminary experiments are summarized in Ta ble 1.…”

Recent Development of Aryl Diazonium Chemistry for the Derivatization of Aromatic Compounds

“…An electron-rich complex-induced carboalkoxylation of styrenes 20 with aryl diazonium salts was realized at room temperature (Scheme ). This Meerwein addition proceeded in the presence of a phenalenyl catalyst 28 (PLY) at room temperature, allowing the difunctionalization of styrene using alcohol as the alkoxy donor. On the basis of the experimental results and detailed DFT calculations, the authors proposed a mechanism in which a [PLY-K] complex serves as an electron carrier to catalyze the decomposition of the diazonium salt and the formation of the product.…”

Revisiting aromatic diazotization and aryl diazonium salts in continuous flow: highlighted research during 2001–2021

“…The above cases of single-step continuous flow synthesis of azo compounds from aryl diazonium salts highlight the advantages of continuous flow, i.e., mass transfer enhancement, equipment flexibility and process stability which fully illustrate the great potential for the application of aryl diazonium salts in continuous flow. Since the relatively safer and more stable borate ion often used in batch is not necessarily the most effective counter-ion, [88][89][90][91] more kinds of aryl diazonium salt counter ions with dangerous properties can be prepared in situ and consumed rapidly in continuous flow. In 2003, de Mello et al first developed a simple reaction system consisting of three pumps, two chip reactors, and a microscope for monitoring the production of azo compounds; this system included diazotization and coupling reactions.…”