Mechanistic Study on Aryl-Exchange Reaction of Diaryl-λ3-iodane with Aryl Iodide

Article abstract of DOI:10.1021/acs.joc.7b02701

Because of its hyper-leaving ability, as well as its strong oxidizing ability, diaryl(triflato)-λ³-iodane transfers one of the aryl groups to iodoarenes simply upon gentle heating (>85 °C) in nonpolar solvents. We have performed an in-depth mechanistic study of this unusual aryl transfer reaction. A combination of experimental (product analysis, kinetic study, and substituent effects) and density functional theoretical approaches revealed that the reaction proceeds through a concerted bimolecular transition state, in which ipso-carbon binds loosely to both iodine centers. We also evaluated electronic effects on the thermodynamic stability of diaryl-λ³-iodanes.

Full text of DOI:10.1021/acs.joc.7b02701

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Article
Mechanistic Study on Aryl Exchange
Reaction of Diaryl-#3-iodane with Aryl Iodide
Yui Masumoto, Kazunori Miyamoto, Takuto Iuchi, Masahito Ochiai,
Keiichi Hirano, Tatsuo Saito, Chao WANG, and Masanobu Uchiyama
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b02701 • Publication Date (Web): 28 Nov 2017
Downloaded from http://pubs.acs.org on December 1, 2017
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Mechanistic Study on Aryl Exchange Reaction of
Diaryl-λ3-iodane with Aryl Iodide
Yui Masumoto,†,‡ Kazunori Miyamoto,*,† Takuto Iuchi,§ Masahito Ochiai,§ Keiichi Hirano,† Tatsuo
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Saito,† Chao Wang,† and Masanobu Uchiyama*, †,‡
†Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7ꢀ3ꢀ1 Hongo Bunkyoꢀku,
Tokyo 113ꢀ0033 (Japan)
‡Elements Chemistry Laboratory, RIKEN, and Advanced Elements Chemistry Research Team, RIKEN
Center for Sustainable Resource Science (CSRS), Wakoꢀshi, Saitama 351ꢀ0198 (Japan)
§Graduate School of Pharmaceutical Sciences, Tokushima University, 1ꢀ78 Shomachi, Tokushima
770ꢀ8505 (Japan)
Email: kmiya@mol.f.uꢀtokyo.ac.jp
uchiyama@mol.f.uꢀtokyo.ac.jp
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required
according to the journal that you are submitting your paper to)
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ABSTRACT: Because of its hyperꢀleaving ability, as well as its strong oxidizing ability,
diaryl(triflato)ꢀλ3ꢀiodane transfers one of the aryl groups to iodoarenes simply upon gentle heating (>85
°C) in nonꢀpolar solvents. We have performed an inꢀdepth mechanistic study of this unusual aryl
transfer reaction. A combination of experimental (product analysis, kinetic study, and substituent
effects) and density functional theoretical approaches revealed that the reaction proceeds through a
concerted bimolecular transition state, in which ipsoꢀcarbon binds loosely to both iodine centers. We
also evaluated electronic effects on the thermodynamic stability of diarylꢀλ3ꢀiodanes.
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INTRODUCTION
Since their discovery in 1894, diarylꢀλ3ꢀiodanes (Ar2IX) 1 have found many applications,1 not only
in chemistry, but also in pharmaceutical and materials science, serving as uniquely reactive precursors in
organic synthesis, imaging reagents for positronꢀemission tomography (PET),1f–1h tools for optical
engineering,1e and so on. They are excellent arylating agents toward various nucleophiles, such as
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enolates, cyanides, amides, nitrites, azides, phosphines, stibanes, alkoxides, thiolates, sulfides, selenides,
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and all kinds of halides (F–, Cl–, Br–, I–, and At–) under mild reaction conditions.1,2
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In 2014, a unique aryl transfer reaction of diarylꢀλ3ꢀiodane Ar2IX (X = OTf, FBF3) 1 to
iodoarene 2 was independently and simultaneously reported by Ciufolini and us (Scheme 1).3
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Scheme 1. Aryl exchange reaction of diarylꢀλ3ꢀiodane with aryl iodide.
The reaction procedure is simple (heating at over 85 °C in nonꢀpolar solvents), in sharp contrast to
traditional procedures, in which strong oxidants (AcOOH, mꢀCPBA, oxone, etc.) and strong
Brønsted/Lewis acids (TfOH, TMSOTf, BF3ꢀEt2O, etc.) are indispensable.1 Therefore, the present
reaction is attractive as a synthetic tool for multiꢀfunctionalized diarylꢀλ3ꢀiodanes (Ar2IX) 1,4 and it
provides a practical option for lateꢀstage arylation. For example, diarylꢀλ3ꢀiodane 1xy serves as a
precursor of PET imaging agent [18F]FDA (Scheme 2).1g However, the synthesis of 1xy requires two
steps (path A: introduction of trimethylstannyl group (step 1), followed by ligand exchange reaction
with diacetoxyꢀλ3ꢀiodane (step 2)), since the enhanced nucleophilicity of arylstannane suppresses
undesirable oxidative degradation of the aromatic ring and/or functional groups. In contrast, the present
direct aryl transfer (path B) would provide a straightforward alternative approach.
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reported process (path A)
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step 1
OBoc
OBoc
OBoc
OBoc
(Me3Sn)2
Me3Sn
I
Pd(PPh3)4
dioxane
reflux
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NHBoc
CO2Et
NHBoc
CO2Et
50%
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step 2
~60%
ArI(OAc)2 CHCl3/CH3CN
TsOH
50 ºC
then TfOK
direct aryl transfer
(path B)
OH
OH
OBoc
Ar
"18F–"
Ar2IOTf / ꢀ
18F
I
OBoc
OTf
NH2
CO2Et
[18F]FDA
NHBoc
CO2Et
1xy
Scheme 2. Synthesis of PET diagnostic agent [18F]FDA: reported route (path A) and proposed
alternative pathway (path B) using aryl transfer reaction.
Despite the potential synthetic usefulness of the new reaction, its mechanistic features (origin of the
reactivity and selectivity of the aryl transfer) remain largely unexplored. Diaryꢀλ3ꢀiodane 1 could
undergo aryl transfer via various possible intermediates/mechanisms, such as (1) ligand coupling
(SNAr),5 (2) phenyl cation (SN1), (3) benzyne,6 or (4) single electron transfer (SET).7 We report herein a
combined experimental and computational mechanistic study, which reveals that the aryl transfer
reaction proceeds via a concerted nucleophilic aromatic substitution (CSNAr) pathway,8 involving a
unique “inverse electron demand” transition state, where the migrating aryl group takes a positive
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charge owing to the hyperꢀnucleofugality of λ3ꢀiodanyl groups (106 times greater than triflate9) and
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coordinative stabilization of the weakly nucleophilic ligand.
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RESULTS AND DISCUSSION
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(1) Ligand coupling: In this pathway, 1) ligand exchange of X in 1 with nucleophile occurs first, and
then 2) the nucleophile bound on the apical site of the iodine(III) center attacks the ipsoꢀcarbon of the
equatorial aryl group (Scheme 3a).5,10 However, although iodoarene can exhibit nucleophilicity,11 it
showed very low/negligible nucleophilicity toward diarylꢀλ3ꢀiodanes (see Figure S1), and hence it
would be difficult for the initial ligand exchange to proceed in this system. In addition, the experimental
observation that the more electronꢀrich aromatic ring is transferred preferentially is inconsistent with the
conventional ligand coupling mechanism, where the nucleophile favors the electronꢀdeficient aromatic
ring.5a,5b
(2) The phenyl cation (SN1) mechanism is also ruled out because no formation of aryl cationꢀderived
byꢀproducts (aryl triflate, fluoroarene, etc.) was observed.12 Thermal decomposition of diazonium salt 3
in the presence of excess iodoarene resulted in formation of the BalzꢀSchiemann product (fluorobenzene,
56%), and only 2% of diarylꢀλ3ꢀiodane 1aa-FBF3 was obtained (Scheme 3b).13
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Scheme 3. a) Ligand coupling mechanism. b) Thermal decomposition of diazonium salt 3 in the
presence of iodoarene 2.
(3) Benzyne pathway: To examine this mechanism, we prepared 1aa-d5 having one
deuteriumꢀlabeled phenyl ring (Scheme 4a). Exposure of 1aa-d5 to excess pꢀiodotoluene 2b (20 equiv.)
in 1,2ꢀdichloroethane at 85 °C for 2.5 h gave equimolar amounts of phenyl(pꢀtolyl)ꢀλ3ꢀiodane (1ab) and
its deuterated analogue (1ab-d5) with recovery of starting 1aa-d5. This result clearly demonstrates the
absence of D/H scrambling and a secondary kinetic isotope effect, ruling out benzyne formation.
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(4) SET mechanism: Careful H NMR/GCꢀMS analysis of the present reaction in the presence of
9,10ꢀdihydroanthracene clarified the absence of anthracene and benzene during the course of reaction,
suggesting that the mechanism does not involve the SET pathway (Scheme 4b). A radical clock
experiment using diarylꢀλ3ꢀiodane with an oꢀallyloxy group 1ac provided further evidence that the
reaction mechanism does not involve any radical intermediate (Scheme 4c, Table S1).14–16
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We next investigated the reaction order in order to obtain a clue as to the reaction mechanism. The
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rate of the aryl transfer reaction of 1aa was measured by means of H NMR measurement at 85 °C in
1,2ꢀdichloroethane with various concentrations of 2b. The observed reaction rates proved proportional
to the concentration of 2b and the slope of the plot afforded a secondꢀorder rate constant k2 of 7.8 x 10ꢀ1
Mꢀ1sꢀ1 (r = 1.0), which strongly suggests that reagents 1 and 2 are both involved in the transition state
(Scheme 4d, Table S2).
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Scheme 4. Mechanistic study of the aryl exchange reaction. a) Deuterium labeling experiment. b)
Radical scavenger addition experiment. c) Radical clock experiment. d) Kinetic study of aryl exchange
reaction.
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With these experimental findings in hand, we performed a density functional theory (DFT) study to
examine in detail the reaction pathways and the origin of the ligand transfer selectivity of the present
aryl transfer reaction, as well as to clarify the structural and electronic features of the transition state.
The results of several examinations using diphenyl(tetrafluoroborato)ꢀλ3ꢀiodane 1aaꢀFBF3 and 2a as
model substrates indicated that the reaction pathway of the aryl transfer reaction shown in Figure 1a is
the most probable.17 Firstly, reactants weakly coordinate through FBF3 (1aa)•••I–Ph (2a) interaction to
give the precursor for the aryl transfer (CP1) with 7.4 kcal/mol endothermicity; the hypervalent Tꢀshape
structure of 1aa is maintained. To reach the transition state of aryl transfer (TS), the orientation of the
equatorial phenyl ring of 1aa changes so that the ipsoꢀcarbon (1aa) on the migrating aryl group can
interact with I–Ph (2a) with an activation energy of 26.4 kcal/mol. This transfer of the Ph group from
1aa to 2a takes place as a single event, as indicated by the smooth charge changes during the reaction.
The positive charge of the I(III) atom in 1aa decreases monotonously from RT to PD, whereas the
positive charge of I(I) in 2a increases monotonously toward PD (Figure 1b). This is a signature of the
involvement of a redox process in this reaction, and the exchange of the electrons occurs exclusively
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between trivalent I(III) and monovalent I(I). Note that in the TS both iodine atoms show the same total
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charge (i.e., divalent I(II)) and FBF3 ligand coordinate through weak hypervalent F•••I–Ph bonds
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(Figure 1c). Readily exchangeable oxidation states of iodine atoms18 and stabilization by coordination of
anionic ligand would be the origin of the driving force of this aryl transfer reaction with a concerted
transition state. Positive charge development at ipsoꢀcarbon of the migrating phenyl group as well as the
large C6–C1–C2 angle of 129°19 suggest that the reaction mechanism involves a CSNArꢀtype transition
state with some SN1Ar character (Figure 1c).7,19a,20
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Figure 1. a) Energy profile in the reaction of 1aaꢀFBF3 and 2b (M06ꢀ2X/LanL2DZ for I and 6ꢀ31G*
for the other atoms). b) Natural charge analysis (M06ꢀ2X/6ꢀ311+G* for I and 6ꢀ31+G* for the other
atoms).21 c) Detailed structure of the TS (M06ꢀ2X/LanL2DZ for I and 6ꢀ31G* for the other atoms).
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Given that the reaction proceeds via a concerted mechanism, the whole process is reversible. This
means the reaction should give thermodynamically controlled products. Because of the lack of a suitable
method, it is difficult to evaluate the aromatic ring substituent effect on the thermodynamic stability of
λ3ꢀiodanes. However, we succeeded in evaluating electronic substituent effects on the thermodynamic
stability of bis(triflyl)aryliodonium ylides (Tf2C––I+Ar) by utilizing Rh2(OAc)4ꢀmediated ylide transfer
reaction, in which an electronꢀdonating group effectively stabilizes aryliodonium ylide with a Hammett
ρ constant of –2.5.22 The present aryl transfer reaction could analogously be used to estimate the relative
stability of diarylꢀλ3ꢀiodanes 1.
To elucidate the thermodynamic stability of diarylꢀλ3ꢀiodanes, we analyzed the ratio of 1aa:1ax:1xx
formed in competitive reactions (Scheme 5). Exposure of aryl(phenyl)ꢀλ3ꢀiodane (1ax) to a 1:1 mixture
of 2a and 2x (100ꢀfold excess) in refluxing 1,2ꢀdichloroethane resulted in the formation of 1aa:1ax:1xx
in various ratios, which can be taken as an indicator of relative thermodynamic stability (Table S3). A
Hammett plot showed an excellent correlation of log([1ax]/[1aa]) with substituent constants σp and gave
a ρ value of –2.9 (r = 0.98) (Figure 2), which is comparable to the value (–2.5) observed in competitive
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transylidation of bis(triflyl)iodonium ylides.22 These results clearly indicate that the thermodynamic
stability of diarylꢀλ3ꢀiodanes 1 is mostly determined by the electronic nature of aryl pꢀsubstituents: an
electronꢀdonating group effectively stabilizes diarylꢀλ3ꢀiodane. DFT calculation for isodesmic reaction
(1aa + 2x –> 1ax + 2a) also provided an estimate of the substituent effect on the thermodynamic
stability of diarylꢀλ3ꢀiodanes 1 (Table S4).
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Scheme 5. Competitive experiment.
OMe
y = –2.9 x + 0.19
1
0
Me
r = 0.98
H
Cl
–1
–2
CF3
–0.4
–0.2
0
0.2
0.4
0.6
σp
Figure 2. Hammett plot of log ([1ax]/[1aa]) vs σp constants.
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In conclusion, we have clarified the mechanism of the unique aryl transfer reaction of
diarylꢀλ3ꢀiodanes to iodoarenes, in which the chemoꢀ/regioꢀselectivity is quite different from those of
other common aromatic substitution reactions. The results of isotope labeling, radical trapping/clock
experiments, and kinetic study are all consistent with a concerted bimolecular transition state with a
migrating aryl group possessing aryl cationic character. Theoretical study shows a continuous change of
oxidation states on the iodine(III/I) centers, and coordination of anionic ligand facilitates the whole
process. Furthermore, the relative thermodynamic stability of diarylꢀλ3ꢀiodanes was evaluated by
making use of this transformation. The insights presented here will be helpful to develop practical
syntheses of highly functionalized diarylꢀλ3ꢀiodanes, and work along this line is in progress in our
laboratory.17 Furthermore, the unique mechanism of this aryl transfer reaction is expected to open up
new chemistry of diarylꢀλ3ꢀiodanes with weakly nucleophilic reactants.2g
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EXPERIMENTAL SECTION
General Information.
NMR spectra were obtained on either a 300, 400, or 500 MHz spectrometer. Unless otherwise noted,
samples were recorded in CDCl3, dimethyl sulfoxideꢀd6 (DMSOꢀd6), acetoneꢀd6, or pyridineꢀd5 at room
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temperature. Chemical shifts are expressed in δ (ppm) values. H NMR spectra were referenced to
tetramethylsilane (0 ppm), CHCl3 (7.26 ppm), DMSO (2.50 ppm) or acetoneꢀd5 (2.05 ppm) as an
internal standard. The following abbreviations are used: s = singlet, d = doublet, dd = double of doublets,
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ddt = doublet of doublet of triplets, t = triplet. Low mass spectra (MS) were measured on TOFꢀMS with
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an ESI probe.
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Unless otherwise noted, materials were purchased from commercial suppliers and were used after
appropriate purification (distillation or recrystallization).
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Substrates.
General Procedure A: Synthesis of diarylꢀλ3ꢀiodanes from iodosylbenzenes and arenes according to
the reported procedure.23
2,3,4,5,6ꢀPentadeuteriophenyl(phenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1aa-d5): To a stirred
suspension of iodosylbenzene (55.0 mg, 0.25 mmol) in CH2Cl2 (1.5 mL) was added dropwise TfOH
(26.5 ꢁL, 0.30 mmol) at 0 °C under argon and the mixture was stirred at 0 °C for 2 h. Then, benzeneꢀd6
(99.5%D) (53.1 ꢁL, 0.60 mmol) was added dropwise to the mixture at 0 °C and stirred at 26 °C for 64 h.
Volatiles were removed under the reduced pressure and the residue was washed with hexane and Et2O
several times at 0 °C, giving 1aa-d5 (60 mg, 55%) as a white solid. Mp 174−175 °C (recrystallized from
CH2Cl2ꢀEt2O). 1H NMR (400 MHz, acetoneꢀd6): δ = 8.36 (d, J = 8.0 Hz, 2H), 7.71 (t, J = 7.4 Hz, 1H),
7.62 (dd, J = 8.0 Hz, 7.4 Hz, 2H). Analytical data were in agreement with the previous report.24
Diphenyl(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1aa): By using the general procedure A, the title
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compound was obtained as a white solid in 54% yield. Mp 177−178 °C (recrystallized from
CH2Cl2ꢀEt2O) (literature, 176−177 °C23). 1H NMR (400 MHz, acetoneꢀd6): δ = 8.36 (d, J = 8.0 Hz, 4H),
7.77 (t, J = 7.5 Hz, 2H), 7.62 (dd, J = 8.0 Hz, 7.5 Hz, 4H). Analytical data were in agreement with the
previous report.24
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General Procedure B: Synthesis of diarylꢀλ3ꢀiodane from oxidation of iodoarene by mꢀCPBA
according to the reported procedure.24
(4ꢀMethylphenyl)(phenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1ab): mꢀChloroperbenzoic acid
(mꢀCPBA) (77% purity, 247 mg, 1.1 mmol) was dried under vacuum for 15 min at room temperature
prior to use. To a stirred solution of mꢀCPBA in CH2Cl2 (4.0 mL), iodobenzene (111 ꢁL, 1.0 mmol) and
toluene (159 ꢁL, 1.5 mmol) was added dropwise TfOH (177 ꢁL, 2.0 mmol) at –78 °C under argon. The
mixture was stirred for 10 min at 0 °C and volatiles were removed under the reduced pressure. The
residue was washed with hexane and Et2O several times by decantation at 0 °C to give a white powder,
which was recrystallized from CH2Cl2ꢀEt2O in the freezer to give 1ab (174 mg, 40%) as colorless
prisms. Mp 119−120 °C (literature, 120−121 °C24). 1H NMR (400 MHz, CDCl3): δ = 7.97 (d, J = 8.0 Hz,
2H), 7.88 (d, J = 8.4 Hz, 2H), 7.59 (t, J = 7.3 Hz, 1H), 7.44 (dd, J = 8.0, 7.3 Hz, 2H), 7.25 (d, J = 8.4 Hz,
2H), 2.40 (s, 3H). Analytical data were in agreement with the previous report.24
Bis(4ꢀmethylphenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1bb): By using the general procedure B, the
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title compound was obtained as colorless crystals in 40% yield. Mp 132–135 °C (recrystallized from
CH2Cl2ꢀEt2O) (literature, 145−148 °C25). 1H NMR (500 MHz, DMSOꢀd6): δ = 8.08 (d, J = 8.3 Hz, 4H),
7.32 (d, J = 8.3 Hz, 4H), 2.33 (s, 6H). Analytical data were in agreement with the previous report.24
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General Procedure C: Synthesis of diarylꢀλ3ꢀiodane from (diacetoxy)iodoarene with arylboronic acid
according to the reported procedure.26
(4ꢀChlorophenyl)(phenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1ae): To a stirred mixture of
pꢀchrolophenylboronic acid (156 mg, 1.0 mmol) and BF3･Et2O (127 µL, 1.0 mmol) in CH2Cl2 (10.0
mL) was added dropwise a solution of (diacetoxyiodo)benzene (319 mg, 1.0 mmol) in CH2Cl2 (10.0
mL) at 0 °C under argon and the mixture was stirred for 3 h at 0 °C. After the addition of a saturated
aqueous sodium tetrafluoroborate solution, the reaction mixture was extracted with CH2Cl2. The organic
layer was filtered to remove residual water and evaporated. The solid residue was washed with hexane
several times by decantation, and then the resultant powder was recrystallized from CH2Cl2ꢀhexane to
give 1ae (312 mg, 78%) as a white solid. In order to exchange ligand (FBF3 to OTf), to a suspension of
1ae (105 mg, 0.26 mmol) in CH2Cl2 (1.1 mL) was added dropwise TMSOTf (142 ꢁL, 0.79 mmol) at
0 °C under argon and the mixture was stirred at 0 °C for 15 min. After the mixture was evaporated and
dried under vacuum, the mixture was washed with hexane by decantation. The solid was recrystallized
from CH2Cl2ꢀEt2O to give 1ae as colorless prisms. Mp 119−121 °C (literature, 108−110 °C27). 1H NMR
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(400 MHz, acetoneꢀd6): δ = 8.38 (d, J = 8.0 Hz, 2H), 8.38 (d, J = 8.8 Hz, 2H), 7.79 (t, J = 7.5 Hz, 1H),
7.66 (d, J = 8.8 Hz, 2H), 7.64 (dd, J = 8.0, 7.5 Hz, 2H). Analytical data were in agreement with the
previous report.24
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(4ꢀMethoxylphenyl)(phenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1ad): By using the general
procedure C, the title compound was obtained as a white solid in 63% yield. Mp 111–113 °C (literature,
109−111 °C23). 1H NMR (500 MHz, DMSOꢀd6): δ = 8.19 (d, J = 7.5 Hz, 2H), 8.17 (d, J = 8.8 Hz, 2H),
7.65 (t, J = 7.5 Hz, 1H), 7.52 (dd, J = 7.5, 7.5 Hz, 2H), 7.08 (d, J = 8.8 Hz, 2H), 3.79 (s, 6H). Analytical
data were in agreement with the previous report.24
Phenyl[4ꢀ(trifluoromethyl)phenyl](trifluoromethanesulfonato)ꢀλ3ꢀiodane (1af): By using the general
procedure C, a the title compound was obtained as a white solid in 65% yield. Mp 119–120 °C
(recrystallized from CH2Cl2ꢀEt2O) (literature, 120−122 °C28). 1H NMR (500 MHz, CDCl3): δ = 8.38 (d,
J = 8.0 Hz, 2H), 8.24 (d, J = 8.4 Hz, 2H), 7.86 (t, J = 8.4 Hz, 1H), 7.75 (t, J = 7.5 Hz, 1H), 7.59 (dd, J =
8.0, 7.5 Hz, 2H), MS (ESI (+)) m/z calcd for C13H9F3I+ [(MꢀOTf)+] 349, found 349.28
[2ꢀ(2ꢀPropenyloxy)(phenyl)](tetrafluoroborato)ꢀλ3ꢀiodane (1ac): By using the reported procedure,14
a
the title compound was obtained as colorless crystals in 70% yield. Mp 179–181.5 °C (recrystallized
from CH2Cl2ꢀEt2O) (literature, 182−183 °C14c). 1H NMR (400 MHz, acetoneꢀd6) δ = 8.30 (d, J = 8.2 Hz,
1H), 8.24 (br d, J = 8.4 Hz, 2H), 7.80–7.77 (m, 4H), 7.63–7.53 (m, 2H), 7.37 (d, J = 8.4 Hz, 1H), 7.20–
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7.14 (m 1H), 6.10 (ddt, J = 17.2, 10.8, 5.6 Hz, 1H), 5.45 (dd, J = 17.2, 1.6 Hz, 1H), 5.35 (dd, J = 10.8,
1.2 Hz, 1H), 4.86 (ddd, J = 5.6, 1.6, 1.2 Hz, 2H). Analytical data were in agreement with the previous
report.14c
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General Procedure for Verification Experiment to Exclude Benzyne/Radical Mechanism.
A
Typical Example (For Scheme 4aꢀc; Table S1, entry 2): To
a
suspension of
diphenyl(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1aa) (21.5 mg, 0.050 mmol) was added a solution of
pꢀiodotoluene (218 mg, 1.0 mmol) and galvinoxyl (21.1 mg, 0.050 mmol) in 1,2ꢀdichloroethane (1.0
mL) at room temperature under argon and the mixture was stirred at 85 °C for 24 h. The mixture was
evaporated under reduced pressure to give a solid residue, which was washed with hexane several times
by decantation at 0 °C to give a solid as a mixture of diphenyl(trifluoromethanesulfonato)ꢀλ3ꢀiodane
1
(1aa) (63%, determined by H NMR), (4ꢀmethylphenyl)(phenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane
1
(1ab) (22%, determined by H NMR) and bis(4ꢀmethylphenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane
(1bb) (14%, determined by 1H NMR).
General Procedure for Kinetic Measurement.
A
Typical Example (For Scheme 4d; Table S1, entry 2): To
a
suspension of
diphenyl(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1aa) (21.5 mg, 0.050 mmol) in 1,2ꢀdichloroethane (1.0
mL) was added pꢀiodotoluene (109 mg, 0.50 mmol) and nꢀC22H46 (3.1 mg, 0.010 mmol) as an internal
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standard at room temperature under argon, and the mixture was stirred at 85 °C. At regular time
intervals, a portion (100 ꢁL) of reaction mixture was syringed out and dried under reduced pressure to
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give
a
mixture
of
diphenyl(trifluoromethanesulfonato)ꢀλ3ꢀiodane
(1aa),
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(4ꢀmethylphenyl)(phenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane
(1ab)
and
bis(4ꢀmethylphenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1bb). The product ratio among 1aa, 1ab
and 1bb was determined by 1H NMR.
General Procedure for Competitive Aryl Exchange.
A
Typical Example (For Scheme 5; Table S3, entry 5): To
a
mixture of
(4ꢀmethylphenyl)(phenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1ab) (20.0 mg, 0.045 mmol) and
pꢀiodotoluene (981 mg, 4.5 mmol) was added iodobenzene (915 mg, 4.5 mmol) at room temperature
under argon and the mixture was stirred at 85 °C for 24 h. The mixture was added excess hexane and
resulting precipitate was washed with hexane several times by decantation at 0 °C to give a mixture of
diphenyl(trifluoromethanesulfonato)ꢀλ3ꢀiodane
(1aa)
(8%,
determined
by
1H
NMR),
(4ꢀmethylphenyl)(phenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1ab) (23%, determined by H NMR),
1
and bis(4ꢀmethylphenyl)(trifluoromethanesulfonato)ꢀλ3ꢀiodane (1bb) (34%, determined by 1H NMR).
Computational Details.
All DFT calculations were performed with Gaussian 09 program (Revision D.01).29 Structure
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optimizations were carried out at the M06ꢀ2X level30 in the gas phase using the LANL2DZ basis set31
for I and Br, and the 6ꢀ31G* basis set32 for H, B, C, O and F. The vibrational frequencies were computed
at the same level to check whether each optimized structure is an energy minimum (no imaginary
frequency) or a transition state (one imaginary frequency) and to evaluate its zeroꢀpoint vibrational
energy (ZPVE) and thermal corrections at 298 K. Intrinsic reaction coordinates (IRC) were calculated to
confirm the connection between the transition states and the correct reactants/products. NBO (Natural
Bond Orbital) calculation were performed with NBO3.1 program33 at the M06ꢀ2X level using the basis
set (7433111/743111/7411/2 + 1s1p1d1f)34 for I and the 6ꢀ31+G* basis set32,35 for H, B, C, O, S and F.
The basis set (7433111/743111/7411/2 + 1s1p1d1f) was used as the substitute for 6ꢀ311+G* basis set36
to calculate using all electron basis set with diffusion function for I. Structure optimizations for the
analysis of substituent effect on thermodynamic stability were carried out at the M06ꢀ2X level in the gas
phase using the basis set (7433111/743111/7411/2 + 1s1p1d1f) for I, and the 6ꢀ311+G* basis set for H,
B, C, O, F and Cl. The optimized structures were confirmed by the frequency analysis with the same
computation method.
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Supporting Information
Results of NMR experiments to examine the interaction between diarylꢀλ3ꢀiodanes and iodobenzene
(Figure S1), verification experiments to exclude benzyne/radical mechanism (Table S1), kinetic
measurements (Table S2), competitive aryl transfer reaction to iodobenzenes (Table S3), energy profile
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of the reaction of 1aa–OTf and 2b (Figure S2), a detailed method and results for calculation of
substituent effects on thermodynamic stability (Table S4), and cartesian coordinates and energies for
reaction pathway. This material is available free of charge via Internet at http://pubs.acs.org.
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ACKNOWLEDGMENTS
This work was supported by grants from JSPS KAKENHI (S) (17H06173), KAKENHI (B)
(17H03017), NAGASE Science & Technology Development Foundation, Sumitomo Foundation, and
RIKEN Junior Research Associate Program.
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A. Tetrahedron 2017, in press, https://doi.org/10.1016/j.tet.2017.10.065.
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references 2f and 2j.
(8) Concerted SNAr reactions on arenes that have no electronꢀwithdrawing group have been reported
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Neumann, C. N.; Hooker, J. M.; Ritter, T. Nature 2016, 534, 369. (b) Tang, P.; Wang, W.; Ritter, T.
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(10) (a) MartínꢀSantamaría, S.; Carroll, M. A.; Carroll, C. M.; Carter, C. D.; Pike, V. W.; Rzepa, H. S.;
Widdowson, D. A. Chem. Commun. 2000, 649. (b) Carroll, M. A.; MartínꢀSantamaría, S.; Pike, V.
W.; Rzepa, H. S.; Widdowson, D. A. J. Chem. Soc. Perkin Trans. 2 1999, 2707.
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(11) Iodoarene serves as nucleophilic catalyst in some cases: (a) Albert B. J.; Yamanoto, H. Angew.
Chem. Int. Ed. 2010, 49, 2747. (b) Brady, P. B.; Albert, B. J.; Akakura, M.; Yamamoto, H. Chem.
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Ochiai, M.; Miyamoto, K. Eur. J. Org. Chem. 2008, 4229. (d) Dohi T.; Kita, Y. Chem. Commun.
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Chem. Asian J. 2014, 9, 950.
(12) Kirmse, W. Angew. Chem. Int. Ed. Engl. 1976, 15, 251.
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J. Org. Chem. 1978, 43, 463.
(14) (a) Ochiai, M.; Tsuchimoto, Y.; Hayashi, T. Tetrahedron Lett. 2003, 44, 5381. (b) Chen, D.ꢀW.;
Ochiai, M. J. Org. Chem. 1999, 64, 6804. (c) Ochiai, M.; Kitagawa, Y.; Toyonari, M. ARKIVOC
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2003, 6, 43.
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(15) Cr(II)ꢀmediated arylation of aldehyde with 1 was shown to involve an aryl radical intermediate,
which was confirmed by using 1ac. See also references 14b and 14c.
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(16) No formation of dihydrobenzofuran derivatives 6 and 7 was observed.
(17) A similar pathway with ꢂG‡ of 28.3 kcal/mol was obtained when Ph2IOTf was used as a model
substrate, but a higherꢀlevel calculation of the activation barrier may be necessary. See Figure S2.
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Scholten, T.; Schroer, T.; Welting, D. Z. Anorg. Allg. Chem. 1998, 624, 1669.
(19) For an SN1Ar type transition state, the corresponding angle was estimated to be around 140–149°.
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