Synthesis of quaternary aryl phosphonium salts: photoredox-mediated phosphine arylation

We report a synthesis method for the construction of quaternary aryl phoshonium salts at ambient temperature. The regiospecific reaction invovles the coupling of phosphines with aryl radicals derived from diaryliodonium salts under photoredox conditions

The Discovery and Development of Metal-Free Arylation Reactions with Unsymmetrical Diaryliodonium Salts

Functionalizing arenes and heteroarenes has been an active area of research since the 19th century, due to the presence of these molecular structures in many industrially important sectors. A tremendous amount of research has been published in achieving these chemical transformations using stoichiometric reagents and transition metal-catalyzed reactions. However, challenges still remain. An alternative and comparable methodology to metal-catalyzed reactions to overcome the drawbacks will advance this particular area of research is desirable. Hypervalent iodine compounds offer a promising approach to metal-free arylation reactions. These mild, air and moisture stable compounds have showed significant success as non-toxic and metal-free reagents for the arylation reactions. In particular, unsymmetrical diaryliodonium salts offer functionalization of complex arene structure in an efficient and sustainable pathway. A base-mediated coupling reaction for the metal-free synthesis of alkyl-aryl ethers by using unsymmetrical diaryliodonium salts and aliphatic alcohols is described. This method shows broad substrate scope with respect to both of the coupling partners to produce industrially useful alkyl-aryl ethers in moderate to excellent yields. The reaction is operationally simple, proceeds at mild temperature, and is atom-economical. Sustainability and synthetic utility of this reaction is demonstrated by the use of unsymmetrical aryl(mesityl)iodonium salts as the arylating agents. A limitation of poor reactivity of electron rich unsymmetrical diaryliodonium salts was overcome by designing 2nd generation conditions and using trimethoxy benzene (TMP) as the auxiliary group. Additionally discovery and development of an efficient method to access highly functionalized arynes from unsymmetrical aryl(mesityl)iodonium tosylate salts is presented. The aryne intermediates are generated by ortho C-H deprotonation of aryl(mesityl)iodonium salt with an amide base and subsequently trapped in a cycloaddition reaction with furan in moderate to good yields. Selective iodonium moiety elimination is discussed and the effect of auxiliary and temperature to reduce the regioisomeric ratio is demonstrated. Finally, additional coupling partner including benzyl azide and aliphatic amines are presented to show further utility of this methodology. Also, mechanistic investigations leading to the moderate reactivity of some electron rich unsymmetrical diaryliodonium salts is discussed

Base Mediated Synthesis of Alkyl-aryl Ethers from the Reaction of Aliphatic Alcohols and Unsymmetric Diaryliodonium Salts

The base mediated coupling of aliphatic alcohol pronucleophiles with unsymmetric diaryliodonium salt electrophiles is described. This metal-free reaction is operationally simple, proceeds at mild temperature, and displays broad substrate scope to generate industrially important alkyl-aryl ethers in moderate to excellent yield. The synthetic utility of these reactions is demonstrated, and aspects of sustainability are highlighted by the use of unsymmetric aryl­(mesityl)­iodonium arylating reagents

Unsymmetrical Aryl(2,4,6-trimethoxyphenyl) Iodonium Salts: One-Pot Synthesis, Scope, Stability, and Synthetic Studies

Diaryliodonium salts have recently attracted significant attention as metal-free-arylation reagents in organic synthesis, and efficient access to these salts is critical for advancement of their use in reaction discovery and development. The trimethoxybenzene-derived auxiliary is a promising component of unsymmetrical variants, yet access remains limited. Here, a one-pot synthesis of aryl(2,4,6-trimethoxyphenyl)iodonium salts from aryl iodides, m-CPBA, p-toluenesulfonic acid, and trimethoxybenzene is described. Optimization of the reaction conditions for this one-pot synthesis was enabled by the method of multivariate analysis. The reaction is fast (h), provides a high yield of product (\u3e85% average), and has broad substrate scope (\u3e25 examples) including elaborate aryl iodides. The utility of these reagents is demonstrated in moderate to high yielding arylation reactions with C-, N-, O-, and S-nucleophiles including the synthesis of a liquid crystal molecule

A Selective C-H Deprotonation Strategy to Access Functionalized Arynes by Using Hypervalent Iodine

Described here is an efficient method to accesshighly functionalizedarynes from unsymmetrical aryl-(mesityl)iodonium tosylate salts.The iodonium salts areprepared in asingle pot from either commercially availablearyl iodides or arylboronic acids.The aryne intermediates aregenerated by ortho-C¢Hdeprotonation of aryl-(mesityl)iodonium salt with acommercially available amidebase and trapped in acycloaddition reaction with furan inmoderate to good yields.Coupling partners for the aryneintermediates beyond furan are also described, includingbenzyl azide and alicyclic amine nucleophiles.The regio-and chemoselectivity of this reaction is discussed and evidencefor the spectator aryl ligand of the iodonium salt as acriticalcontrol element in selectivity is presented

A Selective C−H Deprotonation Strategy to Access Functionalized Arynes by Using Hypervalent Iodine

Described here is an efficient method to accesshighly functionalizedarynes from unsymmetrical aryl-(mesityl)iodonium tosylate salts.The iodonium salts areprepared in asingle pot from either commercially availablearyl iodides or arylboronic acids.The aryne intermediates aregenerated by ortho-C¢Hdeprotonation of aryl-(mesityl)iodonium salt with acommercially available amidebase and trapped in acycloaddition reaction with furan inmoderate to good yields.Coupling partners for the aryneintermediates beyond furan are also described, includingbenzyl azide and alicyclic amine nucleophiles.The regio-and chemoselectivity of this reaction is discussed and evidencefor the spectator aryl ligand of the iodonium salt as acriticalcontrol element in selectivity is presented