Mechanochemical Radical Boronation of Aryl Diazonium Salts Promoted by Sodium Chloride

Abstract

Arylboronates are helpful building blocks in organic synthesis. Here, we present an efficient mechanochemical synthesis of arylboronates from arene diazonium salts. Importantly, this transformation was significantly enhanced by sodium chloride, which probably promotes the decomposition of diazonium salts via anion exchange. Chloride anions also participate in the formation of strongly reducing ClÀ B anion radical intermediate that promotes radical chain reaction. The reaction proceeds more efficiently with a small amount of polar solvent as a liquid-assisted grinding additive. Quantum chemical calculations support the mechanistic proposal.

Mechanochemical Synthesis of Aryl Fluorides by Using Ball Milling and a Piezoelectric Material as the Redox Catalyst

“…NaCl was used instead of tet ‐BaTiO 3 under standard conditions (Supporting Information, Scheme S5). Despite the low yield observed under these conditions, this result also suggests that the fluorination reaction likely proceeds via an aryl radical pathway [13] …”

“…Despite the low yield observed under these conditions, this result also suggests that the fluorination reaction likely proceeds via an aryl radical pathway. [13] Based on the results above, a plausible reaction mechanism can be proposed (Figure 3c). Temporarily highly polarized tet-BaTiO In summary, we have successfully developed a mechanochemical fluorination of aryldiazonium salts catalyzed by the piezoelectric material tet-BaTiO 3 .…”

Solvent-Free Mechanoradical-Mediated Minisci-Type C–H Alkylation of N-Heteroarenes

“…Given the widespread applications in both radical chemistry and mechanochemistry, we strive to develop processes merging these two areas together, more specifically, to investigate how a radical is generated in the solid state and if new types of bond-formation/-breaking reactions and/or reaction mechanisms (distinct from solution-phase reactions) can be discovered. Despite the long history of mechanoradicals, implementing this force-directed concept in organic synthesis, especially in C–H activation and C–C bond-formation reactions, is relatively unexplored. , Recently, Ito and Bolm elegantly demonstrated the generation of aryl radicals by incorporation of redox-active piezoelectric materials in ball-milling reactions (Scheme b_i). We hypothesized that in situ generated mechanoradicals can be used to trigger a series of single-electron transfer (SET) and hydrogen-atom transfer (HAT) processes, en route to subsequent coupling reactions (Scheme b_ii).…”