Single electron transfer-induced Grignard cross-coupling involving ion radicals as exclusive intermediates

Abstract

The mechanism of the previously developed cross-coupling reaction of aryl Grignard reagents with aryl halides was explored in more detail. Single electron transfer from an aryl Grignard reagent to an aryl halide initiates a radical chain by giving an anion radical of the aryl halide. The following propagation cycle consists entirely of anion radical intermediates.

Transition‐Metal‐Free Reaction of Aryltrimethylammonium Iodides with Arylzinc Reagents

“…It seems that this transformation is a free radical process. Formation of homo‐coupling products of arylzinc reagents also supported a free radical process . We also attempted to further prove the process using the method reported by Hayashi et al .…”

“…Formation of homo‐coupling products of arylzinc reagents also supported a free radical process . We also attempted to further prove the process using the method reported by Hayashi et al . However, we found that a fast reaction occurred between 4,4′‐di‐ tert ‐butylbiphenylide (LDBB) and NMP at room temperature.…”

“…These experimental facts further supported a free radical process. Based on our experimental results and the related studies reported in literature, a SET mechanism is proposed (Scheme ). Thus, reaction of ArNMe 3 + I − with Ar 1 ZnCl forms [ArNMe 3 + I ‐ ] ⋅− via SET .…”

Formal Nucleophilic Boryl Substitution of Organic Halides with Silylborane/Alkoxy Base System

“…In this proposed mechanism, potassium methoxide first coordinates the boron atom of the silylborane 1 to give the silylborane/alkoxy base complex A, whose existence was suggested by the 11 B NMR experiment [25]. On the basis of the studies on the reactions of silyllithium species and organohalides reported by Strohmann and co-workers [55,56], the aryl anion species seems to be produced subsequently through the formation of the ate complex B, which is generated via nucleophilic attack of the silyl group to the Br atom of the aryl bromide [57][58][59][60][61]. Next, the aryl anion attacks the boron electrophile preferentially rather than silyl bromide to give the corresponding aryl pinacol borate, followed by the reaction of methoxide with the in situ generated silyl bromide.…”

Photocontrolled Synthesis of n‐Type Conjugated Polymers

“…We initially sought to develop polymerization conditions for CPs based on catalyst‐free conditions for coupling aryl Grignards and aryl halides reported by Hayashi and co‐workers in 2012 (Figure a) . These reactions are proposed to proceed through a thermally initiated S RN 1 pathway via an aryl halide radical anion . Shortly thereafter, Studer and co‐workers used similar conditions to polymerize phenylene and naphthalene monomers (Figure b) .…”