A Practical Transition Metal‐Free Aryl‐Aryl Coupling Method: Arynes as Key Intermediates

Abstract

Upon treatment of various aryllithium intermediates with 1,2-dibromobenzene or 1-bromo-2-iodobenzene, dissymmetrical ortho,ortho'-di-, triand even tetrasubstituted bromo-or iodobiaryls become readily available. The crucial steps in all these reactions were the nucleophilic addition of the organolithium precursor to a transient aryne species released from it by b-elimination of a lithium halide and, stabilization of the resulting 2-biaryllithium intermediate by in situ transfer of bromine or iodine from the starting material. This straightforward transition metal-free access to biaryls allows the preparation of highly valuable halobiaryls on a gram scale in excellent yields. These precursors can be subsequently functionalized by highly regioselective halogen/metal permutations into a vast variety of target molecules. This was demonstrated in the synthesis of several mono-and diphosphine ligands.

Catalytic Palladium Phosphination: Modular Synthesis of C1‐Symmetric Biaryl‐Based Diphosphines

“…[16] It allows the preparation of ortho,ortho'-dibromobiphenyl precursors, which can then be submitted to double phosphination reactions for which two strategies were investigated: The classical phosphination pathway, which relies on lithiation, and a new double palladium-catalyzed phosphination reaction. Synthesis of the precursors: Substituted C 1 -symmetric biaryl scaffolds were obtained by transition-metal-free "aryne" coupling in excellent yields either directly (2 d-k) or by the functionalization of 2,2',6-tribromobiphenyl (3; Scheme 4).…”

Conversion of 2‐Iodobiaryls into 2,2′‐Diiodobiaryls via Oxidation‐Iodination Sequences: A Versatile Route to Ladder‐Type Heterofluorenes

“…Alternatively,b iaryls bearing appropriate ortho-substituents (Si, P, S) may undergo an intramolecular heteroatom-aryl bond formation, thus affording dibenzosiloles, [14] dibenzophospholes, [15] or dibenzothiophenes (route C, Scheme 1a). [17] Routes Ba nd Ca re suitable for the synthesis of specific heterofluorenes with various substituents,but are not apriori divergent with respect to the heteroatom. [17] Routes Ba nd Ca re suitable for the synthesis of specific heterofluorenes with various substituents,but are not apriori divergent with respect to the heteroatom.…”

Efficient and Complementary Methods Offering Access to Synthetically Valuable 1,2‐Dibromobenzenes

“…[2] Arynes react with a large number of N-, S-, and O-nucleophiles [3] and, as recently shown, with P-nucleophiles [4] as well as with carbanions [5] in addition reactions. With alkenes they undergo Diels-Alder-type cycloaddition reactions, [6] [2+2] cycloadditions, [7] and 1,3-dipolar cycloadditions.…”