Transition Metal-Free N-Arylation of Amino Acid Esters with Diaryliodonium Salts.

A transition metal-free approach for the N-arylation of amino acid derivatives has been developed. Key to this method is the use of unsymmetric diaryliodonium salts with anisyl ligands, which proved important to obtain high chemoselectivity and yields. The scope includes the transfer of both electron deficient, electron rich and sterically hindered aryl groups with a variety of different functional groups. Furthermore, a cyclic diaryliodonium salt was successfully employed in the arylation. The N-arylated products were obtained with retained enantiomeric excess.

Metal-free formal synthesis of phenoxazine.

A transition metal-free formal synthesis of phenoxazine is presented. The key step of the sequence is a high-yielding O-arylation of a phenol with an unsymmetrical diaryliodonium salt to provide an ortho-disubstituted diaryl ether. This species was cyclized to acetylphenoxazine in moderate yield. The overall yield in the three-step sequence is 72% based on recovered diaryl ether. An interesting, unusually stable iodine(III) intermediate in the O-arylation was observed by NMR and could be converted to the product upon longer reaction time.

Transition metal-free, chemoselective arylation of thioamides yielding aryl thioimidates or N-aryl thioamides.

Reactions of secondary thioamides with diaryliodonium salts under basic, transition metal-free conditions resulted in chemoselective S-arylation to provide aryl thioimidates in good to excellent yields. Equimolar amounts of thioamide, base and diaryliodonium salt were sufficient to obtain a diverse selection of products within short reaction times. Reactions with thiolactams delivered N-arylated thioamides in good yield at room temperature.

Regiospecific N-Arylation of Aliphatic Amines under Mild and Metal-Free Reaction Conditions.

A transition metal-free N-arylation of primary and secondary amines with diaryliodonium salts is presented. Both acyclic and cyclic amines are well tolerated, providing a large set of N-alkyl anilines. The methodology is unprecedented among metal-free methods in terms of amine scope, the ability to transfer both electron-withdrawing and electron-donating aryl groups, and efficient use of resources, as excess substrate or reagents are not required.