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Metathetical Redox Reaction of (Diacetoxyiodo)Arenes and Iodoarenes

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Metathetical Redox Reaction of (Diacetoxyiodo)Arenes and Iodoarenes Article Metathetical Redox Reaction of (Diacetoxyiodo)arenes and Iodoarenes Antoine Jobin-Des Lauriers and Claude Y. Legault * Received: 25 November 2015 ; Accepted: 15 December 2015 ; Published: 17 December 2015 Academic Editors: Wesley Moran and Arantxa Rodríguez Centre in Green Chemistry and Catalysis, Department of Chemistry, University of Sherbrooke, 2500 boul. de l’Université, Sherbrooke, QC J1K 2R1, Canada; [email protected] * Correspondence: [email protected]; Tel./Fax: +1-819-821-8017 Abstract: The oxidation of iodoarenes is central to the field of hypervalent iodine chemistry. It was found that the metathetical redox reaction between (diacetoxyiodo)arenes and iodoarenes is possible in the presence of a catalytic amount of Lewis acid. This discovery opens a new strategy to access (diacetoxyiodo)arenes. A computational study is provided to rationalize the results observed. Keywords: hypervalent iodine; (diacetoxyiodo)arenes; metathesis 1. Introduction In the recent years, the development of hypervalent iodine-mediated synthetic transformations has been receiving growing attention [1–5]. This is not surprising considering the importance of improving oxidative reactions and reducing their environmental impact. Hypervalent iodine reagents are a great alternative to toxic heavy metals often used to effect similar transformations [6–10]. Among the plethora of iodine(III) compounds [11], it is undeniable that the (diacetoxyiodo)arenes remain the most common and used ones [12]. They are usually stable solids and can serve as precursors to numerous other iodanes, such as other (diacyloxyiodo)arenes and [hydroxy(tosyloxy) iodo]arenes [13,14]. Access to (diacetoxyiodo)arenes is, of course, usually accomplished by the oxidation of the corresponding iodoarene substrate. The traditional method involves peracetic acid oxidation in acetic acid [15]. One unexploited strategy to access these specific reagents is the metathetical redox reaction between (diacetoxyiodo)arenes and related iodoarenes (Scheme1a). While it is widely accepted that the ligands on iodane species are typically easily exchanged, the interconversion of oxidation states between λ3-iodane and iodoarenes is much rarer. The first example of such a metathetical redox reaction was reported by Koser et al., using [hydroxy(tosyloxy)-iodo] benzene (HTIB) as the oxidant, enabling transfer to a variety of iodoarenes (Scheme1b) [16]. Two applications of this initial method were subsequently reported, including one example using [bis(trifluoroacetoxy)iodo]benzene (BTI) [17,18]. More recently, Ciufolini et al. have reported the iodonium salt metathesis reaction with iodoarenes (Scheme1c) [19]. To the best of our knowledge, the metathetical redox reaction between (diacetoxyiodo)arenes and iodoarenes has never been reported. Expanding the scope of iodane metathesis to these commonly used reagents would be of great interest as an alternative synthetic method. Herein we report a protocol to achieve such a metathesis of (diacetoxyiodo)benzene and iodoarenes. We also provide a computational study to determine the origin of the observed reactivity. Molecules 2015, 20, 22635–22644; doi:10.3390/molecules201219874 www.mdpi.com/journal/molecules Molecules 2015, 20, 22635–22644 Molecules 2015, 20, page–page Molecules 2015, 20, page–page Molecules 2015, 20, page–page SchemeScheme 1. Concept 1. Concept and and examples examples of of metathetical metathetical re redoxdox reactions reactions of ofiodanes iodanes and and iodoarenes. iodoarenes. Scheme 1. Concept and examples of metathetical redox reactions of iodanes and iodoarenes. 2. Results and Discussion 2. Results and Discussion 2. ResultsTheScheme reactivity and Discussion 1. Concept of HTIB and and examples (diacetoxyiodo)ben of metathetical rezenedox (DIB)reactions toward of iodanes iodo andarenes iodoarenes. was evaluated, The reactivity of HTIB and (diacetoxyiodo)benzene (DIB) toward iodoarenes was evaluated, usingThe conditions reactivity analogous of HTIB toand Koser’s (diacetoxyiodo)ben successful iodanezene metathesis(DIB) toward with iodo HTIBarenes [16]. was We evaluated,submitted using2. conditionsResults and analogous Discussion to Koser’s successful iodane metathesis with HTIB [16]. We submitted usingp-methyliodobenzene conditions analogous and p-bromoiodobenzene to Koser’s successful to iodane metathesismetathesis withwith HTIB HTIB (Scheme [16]. We 2a) submitted and DIB p-methyliodobenzenepat-methyliodobenzene roomThe temperaturereactivity andof (SchemeandHTIBp-bromoiodobenzene p-bromoiodobenzene and 2b). (diacetoxyiodo)ben In accordance to wiiodane iodanethzene the metathesis (DIB)metathesisresults toward reported with with iodo HTIB by HTIBarenes Koser,(Scheme (Scheme was equilibrium 2a) evaluated, and2a) andDIB is DIB at roomusingatachieved room temperature conditions temperature for the reactionanalogous (Scheme (Scheme with2 tob). 2b).HTIBKoser’s In Inaccordance within accordance successful 96 h. withInwiiodane thcontrast, the metathesis results results no metathesis reported reported with HTIB bywas by Koser, [16].observed Koser, Weequilibrium equilibriumsubmitted after 72 ish is achievedpachievedwith-methyliodobenzene forDIB. thefor the reaction reaction and with withp-bromoiodobenzene HTIB HTIB within within 9696 h. h.to Iniodane contrast, contrast, metathesis no no metathesis metathesis with HTIB was was(Scheme observed observed 2a) after and after 72DIB h 72 h withatwith DIB. room DIB. temperature (Scheme 2b). In accordance with the results reported by Koser, equilibrium is achieved for the reaction with HTIB within 96 h. In contrast, no metathesis was observed after 72 h with DIB. Scheme 2. Evaluation of the reactivity of DIB toward the metathetical redox process. Scheme 2. Evaluation of the reactivity of DIB toward the metathetical redox process. TheseScheme results 2. demonstrateEvaluation of the the very reactivity different of DIB reac towardtivity profiles the metathetical of DIB and redox HTIB. process. The origin of this reactivityThese resultsScheme dichotomy demonstrate 2. Evaluation was investigated. theof the very reactivity different In aof re DIB centreac toward tivitycomputational theprofiles metathetical of study, DIB redox and we haveHTIB.process. suggested The origin that of Thesethisreaction reactivity results with HTIBdichotomy demonstrate would was involve, theinvestigated. very at room different In temp a reerature,cent reactivity computational iodonium profiles intermediates, study, of DIB we and have through HTIB. suggested The a ligand originthat of this reactivityreactiondissociationThese with dichotomyresults mechanism HTIB demonstrate would was [20]. involve, investigated.Due the to veryat theroom different large temp In differ aerature, reac recentencetivity iodoniumin computational profiles effective intermediates,of electronegativity DIB and study, HTIB. through we The between have origina ligand suggested the of that reactionthisdissociationhydroxy reactivity and with mechanismtosyloxy dichotomy HTIB groups would [20]. was on Dueinvestigated. involve, HTIB, to the ionization large at In room a differre incent solution temperature,ence computational in iseffective achievable iodonium study,electronegativity at room we intermediates,have temperature suggested between [21,22] that throughthe In contrast, (diacetoxyiodo)arenes have identical ligands involved in the three-center four-electron a ligandreactionhydroxy dissociation withand tosyloxy HTIB mechanismwould groups involve, on HTIB, [20 at]. room ionization Due temp to in theerature, solution large iodonium is difference achievable intermediates, inat room effective temperature through electronegativity a ligand[21,22] dissociationbonding, and mechanism thus dissociation [20]. Due is expectedto the large to bediffer difficultence in [23]. effective We have electronegativity evaluated the betweenenergetic the of betweenIn contrast, the hydroxy (diacetoxyiodo)arenes and tosyloxy have groups identical on HTIB, ligands ionization involved in the solution three-center is achievable four-electron at room hydroxydissociation and for tosyloxy HTIB, groupsDIB, and on diphenyliodoniumHTIB, ionization in saltsolution 4 (see is the achievable computational at room details temperature in Section [21,22] 4), temperaturebonding, [21and,22 thus]. dissociation In contrast, is (diacetoxyiodo)arenesexpected to be difficult [23]. have We identical have evaluated ligands the involvedenergetic of in the Indissociationthe contrast, results are (diacetoxyiodo)arenesfor illustrated HTIB, DIB, in and Scheme diphenyliodonium have 3. identical ligands salt 4 (see involved the computational in the three-center details four-electronin Section 4), three-center four-electron bonding, and thus dissociation is expected to be difficult [23]. We have bonding,the results and are thusillustrated dissociation in Scheme is expected 3. to be difficult [23]. We have evaluated the energetic of evaluateddissociation the energeticfor HTIB, DIB, of dissociationand diphenyliodonium for HTIB, salt DIB, 4 (see and the computational diphenyliodonium details in salt Section4 (see 4), the computationalthe results are details illustrated in Section in Scheme4), the 3. results are illustrated in Scheme3. Scheme 3. Energetics of ligand dissociation on DIB, 4, and HTIB (energies reported in kcal/mol). Scheme 3. Energetics of ligand dissociation on DIB,2 4, and HTIB (energies reported in kcal/mol). 2 SchemeScheme 3. Energetics 3. Energetics of ligandof
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