ジアリールヨードニウム塩を用いる求核剤のアリール化反応

—リガンドによる反応性と選択性の制御—

抄録

Diaryliodonium(III) salts (Ar¹Ar²I⁺X⁻) are hypervalent iodine(III) compounds that function as useful arylation agents forming aryl-carbon and aryl-heteroatom bonds with or without transition metal catalysts. The iodine(III) center of diaryliodonium salts has electrophilic properties, which induces the arylation reactions of nucleophiles. For the cases with Ar¹≠Ar² in diaryliodonium salts, the chemoselectivity of aryl-group transfers depends on the nature of the aryl ligands, including electronic and steric effects. This article describes ligand control strategy leading to unified aryl selectivity and enhanced reactivity for the arylation of various nucleophiles.

Diaryliodonium(III) salts bearing trimethoxyphenyl (TMP) or mesityl (Mes) groups underwent the selective arylations, wherein TMP and Mes groups serve as “dummy ligand” to form aryl-carbon or aryl-heteroatom bonds with the other aryl groups. TMP-iodonium salts were employed for various types of arylation via single electron transfer process, metal-free ligand coupling, and metal-catalyzed coupling to afford the corresponding arylation products with unified selectivity. Furthermore, we found that TMP-iodonium acetates (Ar(TMP)I⁺AcO⁻) exhibit extremely high reactivities for metal-free arylation of phenols and hydroxylamines, wherein the interaction between the ortho-methoxy groups of TMP and the iodine(III) center presumably enhances the basicity of the acetate anion to cooperatively activate the nucleophiles. These effective metal-free arylations would provide practical methods for the synthesis of organic functional aromatic molecules.