DFT mechanistic investigation into phenol dearomatization mediated by an iodine(<scp>iii</scp>) reagent

Ganji, Babak; Ariafard, Alireza

doi:10.1039/c9ob00028c

Cited by 42 publications

(36 citation statements)

References 51 publications

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“…According to thec alculations by Ariafard, this pathway is the most energetically favorable option in the PIDA-promoted addition of methanolt op-cresol, requiring to cross av iable % 24 kcal mol À1 barrier. [9] The incorporation of an iodine atom into the phenol ring, observed in some reactions with PIDA, also indirectly lends support to this mechanistic possibility. [10] Interestingly,n one of the mechanisms presented in Scheme 2c an fully account for all the observed characteristics of the reaction.…”

Section: Introductionmentioning

confidence: 85%

“…In particular, the substantial rate enhancement with the increaseo fw ater content speaks strongly against the dissociative mechanism (Scheme 2, pathway 2), in which H 2 Oi se ngaged only after the rate-determining dissociation of intermediate A.T his is furtherr einforced by the large negative entropyo f activation,u nlikely for ad issociative process.T he measured experimental free energy barrier (22-23 kcal mol À1 )i sa lso considerably lower than that determined computationally for pathway 2( > 28 kcal mol À1 ), [7] but in agreement to those computed for pathways 1a nd 3( 21-24 kcal mol À1 ). [6,9] However,t he computational studies on the associativem echanisms have shown that in both the transition states of type TS1 and TS3 (Scheme 2, pathways 1a nd 3) for the barriers to be feasible, the attack of nucleophile must proceed with as imultaneous deprotonation by an acetate anion (not shown in the scheme). [6,9] This is, however,inconsistent with the lack of asolvent kinetic isotope effect upon the exchange of H 2 Of or D 2 O. Overall,t he data allows with high confidence to discard the pathways shown in Scheme 2a st he correct reactionm echanisms.…”

Section: Kineticsmentioning

confidence: 99%

“…[6,9] However,t he computational studies on the associativem echanisms have shown that in both the transition states of type TS1 and TS3 (Scheme 2, pathways 1a nd 3) for the barriers to be feasible, the attack of nucleophile must proceed with as imultaneous deprotonation by an acetate anion (not shown in the scheme). [6,9] This is, however,inconsistent with the lack of asolvent kinetic isotope effect upon the exchange of H 2 Of or D 2 O. Overall,t he data allows with high confidence to discard the pathways shown in Scheme 2a st he correct reactionm echanisms.…”

Section: Kineticsmentioning

confidence: 99%

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Mechanism of Iodine(III)‐Promoted Oxidative Dearomatizing Hydroxylation of Phenols: Evidence for a Radical‐Chain Pathway

Kraszewski

Tomczyk

Drabińska

et al. 2020

Chemistry A European J

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The oxidative dearomatization of phenols with the addition of nucleophiles to the aromatic ring induced by hypervalent iodine(III) reagents and catalysts has emerged as a highly useful synthetic approach. However, experimental mechanistic studies of this important process have been extremely scarce. In this report, we describe systematic investigations of the dearomatizing hydroxylation of phenols using an array of experimental techniques. Kinetics, EPR spectroscopy, and reactions with radical probes demonstrate that the transformation proceeds by a radical‐chain mechanism, with a phenoxyl radical being the key chain‐carrying intermediate. Moreover, UV and NMR spectroscopy, high‐resolution mass spectrometry, and cyclic voltammetry show that before reacting with the phenoxyl radical, the water molecule becomes activated by the interaction with the iodine(III) center, causing the Umpolung of this formally nucleophilic substrate. The radical‐chain mechanism allows the rationalization of all existing observations regarding the iodine(III)‐promoted oxidative dearomatization of phenols.

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Section: Introductionmentioning

confidence: 85%

Section: Kineticsmentioning

confidence: 99%

Section: Kineticsmentioning

confidence: 99%

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Mechanism of Iodine(III)‐Promoted Oxidative Dearomatizing Hydroxylation of Phenols: Evidence for a Radical‐Chain Pathway

Kraszewski

Tomczyk

Drabińska

et al. 2020

Chemistry A European J

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“…The possibility of ligand exchange between HFIP and PIDA has been excluded and any altered reactivity to the oxidants is ruled out as the HFIP is a low nucleophilic solvent. [43][44][45][46][47] All of the above-mentioned study concerns the first step of the reaction, the SEO step, and seems to us in need for further understandings despite the subsequent steps that lead to the all trans cyclobutane ring are not considered, at least to the best of our knowledge, by other workers under these conditions. 26,[48][49][50] An important question that should be raised is the number of electrons to be transferred to the iodine reagent to initiate the reaction.…”

Section: Introductionmentioning

confidence: 99%

Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization Initiation Proceeds with Two-Electron Reductive Cleavage

Hussein

Ma²,

Al-Yasari³

2020

Preprint

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<a>A mechanistic insight into </a>the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The initialization involving direct bimolecular one-electron transfer is found to be highly unfavored, especially for the PIDA system. At this point, we suggest that the reaction is initiated with an overall two-electron reductive cleavage of two I─O bond cleavages, affording I(III) (iodinane) and I(I) (iodobenzene) product with DMP and PIDA as oxidant, respectively. The resulting acetate groups are stabilized by the solvent HFIP through strong hydrogen bonding interaction, which promotes the electron transfer process. The nature of the electron transfer is studied in detail and found that the overall two-electron transfer occurs within tri-molecular complex organized by π-stacking interactions and as a stepwise and concerted mechanism for I(III) and I(V) oxidants, respectively. The reaction rate is determined by the initialization step: for I(III), the initiation is thermodynamically endergonic, whereas the endergonicity for I(V) is modest. Upon initialization, the reaction proceeds through a stepwise [2+2] pathway, involving a radical-cationic π-π stacked intermediate, either hetero- or homodimerized. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is dynamically competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations.

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“…The possibility of ligand exchange between HFIP and PIDA has been excluded and any altered reactivity to the oxidants is ruled out as the HFIP is a low nucleophilic solvent. [43][44][45][46][47] All of the above-mentioned study concerns the first step of the reaction, the SEO step, and seems to us in need for further understandings, however, the subsequent steps that lead to the all trans cyclobutane ring are not considered, at least to the best of our knowledge, by other workers under these conditions. 26,[48][49][50] At this point, the reaction mechanism and reactivity of HVIR-mediate dimerization exclusively appears incomplete and warrants further attentions ( Figure 2).…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Insights on Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization

Hussein¹,

Al-Yasari²,

Ma³

2020

Preprint

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A mechanistic insight into the hetero- and homodimerizations (HETD and HOMD) of styrenes promoted by hypervalent iodine reagents (HVIRs; DMP and PIDA) and facilitated by HFIP to yield all trans cyclobutanes is reported using density functional theory (DFT) calculations. The HFIP molecules lower the energy of the single electron oxidation (SEO) or initiation as a result of strong hydrogen bonding interactions that substantially stabilize the frontier orbitals before and after electron addition. The HETD or HOMD is a radically-characterized π-π stacked head-to-head stepwise [2+2] cycloaddition initiated via SEO by DMP or PIDA, respectively. DFT results supported by quasiclassical molecular dynamics simulations show that HOMD is a competing pathway to HETD although the latter is relatively faster, in accordance with experimental observations. The initiation is a rate-determining step as a thermodynamically endergonic and propagation is accomplished by radically-cationic hetero- and homodimerized intermediate as propagation is faster than single electron reduction (SER) or termination by radically-anionic HVIRs. Initiation by DMP found to be faster and less endergonic than by PIDA due to (1) the energy gap of electron transfer in a SEO step by I(V) is lower than I(III) and (2) the SOMO energy of the radical anion I(V) is lower than I(III). Furthermore, the presence of p-methoxy group is essential to underpin the SEO by which the more thermodynamically favorable SEO leads to a successful cycloaddition as the thermodynamic term represents a major contribution in the initiative barrier.

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DFT mechanistic investigation into phenol dearomatization mediated by an iodine(iii) reagent

Abstract: The key intermediate for the oxidative dearomatization of phenols by phenyliodine(iii) diacetate (PIDA) was found to be a dearomatized phenolate species.

Cited by 42 publications

References 51 publications

Mechanism of Iodine(III)‐Promoted Oxidative Dearomatizing Hydroxylation of Phenols: Evidence for a Radical‐Chain Pathway

Mechanism of Iodine(III)‐Promoted Oxidative Dearomatizing Hydroxylation of Phenols: Evidence for a Radical‐Chain Pathway

Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization Initiation Proceeds with Two-Electron Reductive Cleavage

Mechanistic Insights on Hypervalent Iodine-Mediated Styrene Hetero- and Homodimerization

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