Diaryliodoniums as Hybrid Hydrogen- and Halogen-Bond-Donating Organocatalysts for the Groebke–Blackburn–Bienaymé Reaction

Abstract

Dibenziodolium and diphenyliodonium triflates display high catalytic activity for the multicomponent reaction that leads to a series of imidazopyridines. Density functional theory (DFT) calculations indicate that both the salts can play the role of hybrid hydrogen- and halogen-bond-donating organocatalysts, which electrophilically activate the carbonyl and imine groups during the reaction process. The ortho-H atoms in the vicinal position to the I atom play a dual role: forming additional noncovalent bonds with the ligated substrate and increasing the maximum electrostatic potential on the σ-hole at the iodine atom owing to the effects of polarization. Dibenziodolium triflate exhibits higher catalytic activity, and the results obtained from 1H nuclear magnetic resonance (NMR) titrations, in conjunction with those from DFT calculations, indicate that this could be explained in terms of the additional energy required for the rotation of the phenyl ring in the diphenyliodonium cation during ligation of the substrate.

Orbital analysis of bonding in diarylhalonium salts and relevance to periodic trends in structure and reactivity

“…The Lewis acidity of diarylhalonium salts is an emerging property of particular relevance to catalysis. 1 b , d ,25 Pioneering studies by Ochiai and more recent developments by Legault have established an empirical relative Lewis acidity scale. 26 Additionally, Legault and Huber have conducted theoretical studies to glean insight into the fundamental basis for the strength of halogen bond donors.…”

Halonium, chalconium, and pnictonium salts as noncovalent organocatalysts: a computational study on relative catalytic activity

“…2). Since it has been shown theoretically and experimentally that cyclic dibenzohalolium cations (7-9) exhibit a higher Lewis acidity and catalytic activity than their acyclic analogues, namely diarylhalonium cations Ar 2 X + , 51,54,71 in this study we focused on the cyclic derivatives 1-9. Cations 1-3 represent pnictonium(V) derivatives, whereas species 4-6 are the representative examples of sulfonium, selenonium, and telluronium cations, respectively.…”

“…In the case of the nucleophilic addition of ammonia to the carbonyl group (TS2), the total electronic energy of activation is reduced for 1-9 from −11 kJ mol Although the experimental data on the relative catalytic activity between the ChB-and XB-donating organocatalysts are scarce, the computational results obtained by Method 2 seem to be more coherent with our recent works on the experimental determination of the catalytic activity of onium salts. 68,71 Thus, it has been found for the Groebke-Blackburn-Bienaymé multicomponent reaction including the electrophilic activation of the carbonyl group that the iodonium salt 9 OTf exhibits significantly higher catalytic activity than the selenonium salt 5 OTf , which, in turn, provides a slightly higher catalytic effect than the sulfonium salt 4 OTf . 55,68,71 In addition, Yoshida and his co-workers have shown that iodonium salts exhibit a significantly higher catalytic effect than bromonium and chloronium salts 55 (see Fig.…”

“…68,71 Thus, it has been found for the Groebke-Blackburn-Bienaymé multicomponent reaction including the electrophilic activation of the carbonyl group that the iodonium salt 9 OTf exhibits significantly higher catalytic activity than the selenonium salt 5 OTf , which, in turn, provides a slightly higher catalytic effect than the sulfonium salt 4 OTf . 55,68,71 In addition, Yoshida and his co-workers have shown that iodonium salts exhibit a significantly higher catalytic effect than bromonium and chloronium salts 55 (see Fig. 4, energy diagram for Method 2).…”

Ionic Liquids as Organocatalysts for Nucleophilic Fluorination: Concepts and Perspectives

“…This class of nucleophilic fluorination has been under intensive study since the development of diaryliodonium salts as very useful substrates by Pike and coworkers [ 52 ] in 1998. The efficacy of solvent/promoter ILs for fluorination of diaryliodonium salts [ 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 ], however, has not been systematically tested so far. There seems to be a great possibility that ILs could make a profound difference in the efficiency of this class of reaction, because the hypervalent I + in the substrates may directly interact with the IL anion by the strong Coulombic force.…”