Observations on transition metal free biaryl coupling: potassium tert-butoxide alone promotes the reaction without diamine or phenanthroline catalysts

Abstract

Biaryl coupling (often labelled 'C-H activation') of aromatic systems can be achieved by potassium tert-butoxide alone in the absence of any amine or bipyridine catalyst (1,10-phenanthroline or N,N'-dimethylethylenediamine being the most common), previously reported to be essential. Various mechanistic studies and observations are presented which suggest that when 1,10-phenanthroline is employed as the catalyst, the alkoxide is destroyed almost immediately.

Double Deprotonation of Pyridinols Generates Potent Organic Electron‐Donor Initiators for Haloarene–Arene Coupling

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Themechanism for these reactions features base-promoted homolytic aromatic substitution (BHAS;Scheme 1). [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Themechanism for these reactions features base-promoted homolytic aromatic substitution (BHAS;Scheme 1).…”

Base‐Promoted Aerobic Oxidation/Homolytic Aromatic Substitution Cascade toward the Synthesis of Phenanthridines

“…[19] Another butoxide base showed substantial conversion, however weak base like K 3 PO 4 was not suitable, which signified that stronger base was necessary for the effective deprotonation of alcohol in the dehydrogenative process. In view of the functional group tolerability, ligand-free approach at further higher temperature was Scheme 1.…”

Dual Roles for Potassium Hydride in Haloarene Reduction: CSNAr and Single Electron Transfer Reduction via Organic Electron Donors Formed in Benzene

“…18,19 Our recent study critically examined the evidence presented for KOtBu as a single electron donor to haloarenes in a number of different reports and found that, in each case, organic additives initiate the BHAS reaction by forming organic electron donors in situ, 20 for example, electron donor 9 from phenanthroline 6 (Scheme 2A). 18 While organic additives are not absolutely required for most substrates in this transformation, 9,10,15 they significantly enhance the yield of the coupled products, simultaneously allowing reactions to be conducted at lower temperatures and for a shorter duration. 18,21−23 In the absence of suitable organic additives, 15 BHAS reactions can be initiated by arynes (benzynes), formed by base-induced elimination of HX from substrate haloarenes ArX such as 1 (see later, Scheme 4).…”

“…18 While organic additives are not absolutely required for most substrates in this transformation, 9,10,15 they significantly enhance the yield of the coupled products, simultaneously allowing reactions to be conducted at lower temperatures and for a shorter duration. 18,21−23 In the absence of suitable organic additives, 15 BHAS reactions can be initiated by arynes (benzynes), formed by base-induced elimination of HX from substrate haloarenes ArX such as 1 (see later, Scheme 4).…”