Remote Substituents as Potential Control Elements for the Solid-State Structures of Hypervalent Iodine(III) Compounds

Recent Progress in Cyclic Aryliodonium Chemistry: Syntheses and Applications

Hypervalent aryliodoumiums are intensively investigated as arylating agents. They are excellent surrogates to aryl halides, and moreover they exhibit better reactivity, which allows the corresponding arylation reactions to be performed under mild conditions. In the past decades, acyclic aryliodoniums are widely explored as arylation agents. However, the unmet need for acyclic aryliodoniums is the improvement of their notoriously low reaction economy because the coproduced aryl iodides during the arylation are often wasted. Cyclic aryliodoniums have their intrinsic advantage in terms of reaction economy, and they have started to receive considerable attention due to their valuable synthetic applications to initiate cascade reactions, which can enable the construction of complex structures, including polycycles with potential pharmaceutical and functional properties. Here, we are summarizing the recent advances made in the research field of cyclic aryliodoniums, including the nascent design of aryliodonium species and their synthetic applications. First, the general preparation of typical diphenyl iodoniums is described, followed by the construction of heterocyclic iodoniums and monoaryl iodoniums. Then, the initiated arylations coupled with subsequent domino reactions are summarized to construct polycycles. Meanwhile, the advances in cyclic aryliodoniums for building biaryls including axial atropisomers are discussed in a systematic manner. Finally, a very recent advance of cyclic aryliodoniums employed as halogen-bonding organocatalysts is described.

Sterically crowded 1,4-diiodobenzene as a precursor to difunctional hypervalent iodine compounds

A bulky 1,4-di-iodobenzene having four adjacent para-^tBu-C₆H₄ group (Ar') substituents (1) was used to prepare the di-hypervalent iodine compound 1,4-[I(OAc)₂]₂-2,3,5,6-Ar'₄-C₆ (2). Despite the steric encumbrance of the iodine center by the flanking aryl substituents, compound 2 undergoes ready cyclization under mild conditions (excess CF₃COOH at 55 °C, 30 min) to afford a dicyclic di-iodonium di-triflate salt 3. The single crystal structures of compounds 2 and 3 were examined and compared to the formerly characterized precursor 1. The para-tert-butyl groups on these compounds also render the compounds more soluble than multifunctional hypervalent iodine (HVI) compounds. HVI compounds having multiple iodine(III) centers are increasingly of interest for applications as recyclable reagents, materials precursors, and as Lewis acids.