Pseudocyclic Arylbenziodoxaboroles: Efficient Benzyne Precursors Triggered by Water at Room Temperature

Article abstract of DOI:10.1002/chem.201704393

New organohypervalent iodine compounds, arylbenziodoxaborole triflates, were prepared from 1-acetoxybenziodoxaboroles and arenes by treatment with trifluoromethanesulfonic acid under mild conditions. Single crystal X-ray crystallography of these compounds revealed a pseudocyclic structure with a short intramolecular interaction of 2.698 to 2.717 ? between oxygen and iodine in the benziodoxaborole ring. These new pseudocyclic aryliodonium salts readily generate aryne intermediates upon treatment with water at room temperature. The generated aryne intermediates react with various substrates to give the corresponding aryne adducts in moderate to good yields. Furthermore, the new benzyne precursors can also work as arylating reagents towards aromatic rings. The aryne intermediates generated from arylbenziodoxaborole triflates selectively react with tert-butyl phenol forming products of ortho arylation in moderate yields.

Full text of DOI:10.1002/chem.201704393

A Journal of
Accepted Article
Title: Pseudocyclic Arylbenziodoxaboroles: Efficient Benzyne
Precursors Triggered by Water at Room Temperature
Authors: Viktor Zhdankin, Akira Yoshimura, Jonathan Fuchs, Kyle
Middleton, Andrey Maskaev, Gregory Rohde, Akio Saito,
Pavel Postnikov, Mekhman Yusubov, and Victor Nemykin
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To be cited as: Chem. Eur. J. 10.1002/chem.201704393
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Supported by

10.1002/chem.201704393
Chemistry - A European Journal
COMMUNICATION
Pseudocyclic Arylbenziodoxaboroles: Efficient Benzyne
Precursors Triggered by Water at Room Temperature
Akira Yoshimura,*[a,b] Jonathan M. Fuchs,[b] Kyle R. Middleton,[b] Andrey V. Maskaev,[b] Gregory T.
Rohde,[c] Akio Saito,[d] Pavel S. Postnikov,[a] Mekhman S. Yusubov,[a] Victor N. Nemykin,[e] and Viktor V.
Zhdankin*[a,b]
Dedication ((optional))
Abstract:
New
organohypervalent
triflates, were
iodine
compounds,
from 1-
hypernucleofuge and has the leaving group ability about a
million times greater than that of triflate).[4] The known
hypervalent iodine based benzyne precursors are represented
by structures 1-3 shown in Scheme 1a.[5]
arylbenziodoxaborole
prepared
acetoxybenziodoxaboroles and arenes by treatment with
trifluoromethansulfonic acid under mild conditions. Single crystal X-
ray crystallography of these compounds revealed a pseudocyclic
structure with a short intramolecular interaction of 2.698 to 2.717 Å
between oxygen and iodine in the benziodoxaborole ring. These new
(1a) Known iodonium benzyne precursors:
(1b) This work:
hypenucleofugic ArI
pseudocyclic
aryliodonium
salts
readily
generate
aryne
–OTf
X–
Ar I+
Ph I+
Ph
I
O
Ar
I+
TMS
–OTf
intermediates upon treatment with water at room temperature. The
generated aryne intermediates react with various substrates to give
the corresponding aryne adducts in moderate to good yields.
Furthermore, the new benzyne precursors can also work as arylating
reagents towards aromatic ring. The aryne intermediates generated
from arylbenziodoxaborole triflates selectively react with tert-butyl
phenol forming products of ortho arylation in moderate yields.
H2O
O
OH
rt
B
H
3
2
benzyne
O
1
OH
H
oxophilic –B(OH)2
conditions for benzyne generation:
benzyne is generated by treatment
with H2O at room temperature
1: 130-160 oC
3: powerful
bases
2: Bu4NF, CH2Cl2
Scheme 1. Hypervalent iodine-based benzyne precursors.
Benzyne and related aryne species are common reactive
intermediates
involved
in
many
important
chemical
transformations.[1] Numerous reactions employing benzyne
intermediates have been developed and utilized in organic
synthesis. Benzyne species are highly unstable intermediates
that can be generated in situ from various precursors. Classical
benzyne precursors[1,2] are represented by the benzene
derivatives with good leaving groups such as aryl halides,[2a-c]
arene-diazonium-2-carboxylates,[2d-f] 1,2,3-benzothiadiazole 1,1-
dioxides,[2g] 1-aminobenzotriazole,[2h,2i] and ortho-silylaryl triflates
(Kobayashi’s reagent).[2j] These common benzyne precursors
are usually activated by either a metal or a strong base and
often require high temperature for benzyne generation.
The classical benzyne precursor, phenylbenziodoxole 1, can
generate benzyne via decarboxylation at high temperatures
o
(130-160 C).[5a-c] More recently, Kitamura and co-workers have
prepared a very effective noncyclic benzyne precursor, phenyl[2-
(trimethylsilyl)phenyl]iodonium triflate (Kitamura’s reagent) 2 by
a ligand exchange reaction of 1,2-bis(trimethylsiyl)benzene with
(diacetoxyiodo)benzene
in
the
presence
of
trifluoromethanesulfonic acid (TfOH). Kitamura’s iodine(III)
reagents generate the corresponding benzyne intermediates in
situ upon treatment with tetrabutylammonium fluoride (TBAF) as
the desilylating base.[5d-f] Recently, the Stuart’s group reported
effective trapping of benzyne generated from diaryliodonium
precursors 3 by reaction with strong base.[5i,j] Following this
study, Wang and co-workers have also reported benzyne
reactions of diaryliodonium triflates under strongly basic
conditions.[5k] It should be emphasized that harsh or strongly
basic conditions are required for the efficient generation of
benzyne intermediates from all known benzyne precursors.
Development of new benzyne precursors that can be activated
in neutral solution at room temperature is an important and
challenging goal.
Organohypervalent iodine compounds, known as versatile
reagents for organic synthesis,[3] can also be used as efficient
benzyne precursors because of the exceptionally high leaving
group ability of the iodobenzene group (the PhI group is called
[a]
[b]
Prof. Dr. A. Yoshimura, Prof. Dr. M. S. Yusubov, Dr. P. S. Postnikov
The Tomsk Polytechnic University 634050 Tomsk (Russia)
E-mail: ayoshimu@d.umn.edu
J. M. Fuchs, K. R. Middleton, A. V. Maskaev, Prof. Dr. V. V.
Zhdankin
Department of Chemistry and Biochemistry
University of Minnesota Duluth, MN 55812 (USA)
E-mail: vzhdanki@d.umn.edu
Dr. G. T. Rohde
Marshall School, Duluth, Minnesota 55811, (USA)
Prof. Dr. A. Saito
Division of Applied Chemistry, Institute of Engineering
Tokyo University of Agriculture and Technology
2-24-16 Naka-cho, Koganei, Tokyo 184-8588 (Japan)
Prof. Dr. V. N. Nemykin
Department of Chemistry
University of Manitoba, Winnipeg, MB R3T 2N2, (Canada)
Herein, we present the first preparation, structural
investigation,
and
reactivity
of
pseudocyclic
[c]
[d]
arylbenziodoxaborole triflates, which can readily generate aryne
intermediates by treatment with water at room temperature
(Scheme 1b). These reagents combine in one molecule the
exceptionally nucleofugic iodonium leaving group and the
B(OH)2 substituent as an efficient oxophilic activating group.
According to X-ray diffraction data, these compounds have a
pseudocyclic structure due to the presence of additional
intramolecular non-covalent coordination at the iodine center. In
[e]
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/chem.201704393
Chemistry - A European Journal
COMMUNICATION
comparison with common hypervalent iodine reagents,
pseudocyclic hypervalent iodine compounds have higher
thermal stability, better solubility, and improved reactivity.[6]
not afford the corresponding arylbenziodoxaborole sulfonate
salts. In the reaction of p-TsOH, we isolated only the
corresponding 1-tosyloxy-fluoro-benziodoxaborole in good yield.
The structure of this product was established by single crystal X-
ray crystallography (see Supporting Information).
Our approach to the synthesis of pseudocyclic
arylbenziodoxaborole triflates is based on the ligand exchange
reaction between the corresponding hypervalent iodine
heterocycles (1-acetoxybenziodoxaboroles) and arenes in the
presence of strong acid.[7] In the initial experiment, the reaction
of 1-acetoxy-4-fluorobenziodoxaborole 4a[8] (1 equiv) with
mesitylene in the presence of triflic acid (2 equiv) under mild
conditions
afforded
the
corresponding
1-
mesitylbenziodoxaborole triflate 5a in 95% yield (Scheme 2).
Decreasing the amount of TfOH to 1.2 or 1.5 equiv resulted in a
lower yield of product 5a. Other arylbenziodoxaborole triflates
5a-d
were
prepared
in
good
yields
from
1-
5b
5c
acetoxybenziodoxaboroles 4 and different arenes under similar
conditions (Scheme 2). Two of the products, 1-phenyl-4-
Figure 1. X-ray crystal structure of compounds 5b and 5c.
fluorobenziodoxaborole
triflate
5b
and
1-p-tolyl-4-
fluorobenziodoxaborole triflate 5c were characterized by single
crystal X-ray crystallography (Figure 1). X-ray analysis of 5b
confirmed the pseudocyclic benziodoxaborole structure with the
intramolecular interaction between the iodine and oxygen I-O(1)
= 2.698 Å. This bond length is similar to other previously
reported pseudocyclic diaryliodonium salts.[6,9] An additional
interaction between a triflate oxygen and the iodine center
results in the overall pseudo square planar geometry. Crystal
structure of 5c is similar to the structure 5b (Figure 1).
We
expected
that
the
new
pseudocyclic
arylbenziodoxaborole triflates 5 could serve as viable benzyne
precursors analogous to Kitamura’s reagent 2, since the ortho –
B(OH)2 group has similar to –SiMe3 affinity towards hard bases.
Previously, Kitamura and co-workers used fluoride anion as a
trigger for benzyne generation from reagent 2.[5d] In the initial
study, we investigated benzyne trapping reactions between
anthracene and reagents
5 as the benzyne precursor in
dichloromethane solution in the presence of fluoride anion as
activator (Table 1). The reaction of anthracene 6 (1 equiv) with
arylbenziodoxaborole triflate 5a (1.5 equiv) and potassium
fluoride (2 equiv) produced the expected fluorotriptycene 7a in
70% yield along with mesityl iodide as the side product (entry 1).
Ar
I+
OAc
1) TfOH (2.0 equiv), CH2Cl2, 0 °C, 2 h
2) ArH (excess), rt, overnight
–OTf
OH
I
O
B
B
OH
OH
X
X
4
5
Reducing the amount of 5a or using 5b instead of 5a under
the same conditions led to lower yields of 7a (entries 2 and 3).
Interestingly, when the reaction was performed in the absence of
potassium fluoride and without aqueous work-up, the triptycene
7 was not formed (entry 5). However, the same reaction in the
absence of potassium fluoride followed by quenching the
reaction mixture with H2O produced triptycene 7 in moderate
yield (entry 4). These results implied that the addition of water to
the reaction mixture was essential for the formation of product 7
even in the absence of fluoride anion.
50-95%
X = F; 4a or H; 4b
Me
Me
Me
Me
–OTf
–OTf
OH
–OTf
OH
I+
I+
I+
OH
B
B
B
OH
OH
OH
F
F
F
5ca, 81%
5b, 80%
5a, 95%
Me
Motivated by these results, we then attempted to optimize
reaction conditions using water as the only activator. Out of
several solvents tested, dichloromethane was found to be the
best solvent in this reaction system (entries 6-11). Increasing the
water/solvent ratio lowered the product yields (entries 12 and
13). The reactions using (2-fluoro-6-iodophenyl)boronic acid or
1-acetoxy-4-fluorobenziodoxaborole 4a as potential benzyne
precursor did not produce any product 7 (entries 14 and 15).
Using arylbenziodoxaborole triflates 5b or 5d as benzyne
precursors gave product 7 in similar yields (entries 16 and 17).
The water-triggering conditions were also effective in the
reaction of anthracene with benziodoxaborole triflate 5e,
producing triptycene 7b in 79% yield (entry 18).
Me
Me
Me
Me
–OTf
I+
I+
–OTf
OH
OH
B
B
OH
OH
5e, 50%
5d, 87%
a
Scheme 2. Preparation of arylbenziodoxaborole triflates 5. Small amount of
the isomeric 1-o-tolyl-4-fluorobenziodoxaborole triflate was detected.
Reactions of benziodoxaborole 4a with arenes in the
presence of other sulfonic acids such as p-toluenesulfonic acid
(p-TsOH) and methanesulfonic acid (MsOH) instead of TfOH did
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10.1002/chem.201704393
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COMMUNICATION
iodophenyl)boronic acid.
To the best of our knowledge, we have found the first
example of a water-triggered benzyne generating reaction using
pseudocyclic aryliodonium salts bearing the –B(OH)2 substituent
as an efficient oxophilic activating group. It should be noted that
previously the –B(OH)2 substituent has been explored as an
activating group using 2-borylphenyl triflates as benzyne
precursors.[10] However, benzyne generation from 2-borylphenyl
triflates required strong bases (t-BuLi, s-BuLi, or t-BuOK at 100
oC) or CsF at 120 oC.[10] Replacement of the triflate leaving
group with the hypernucleofugic aryliodonium group in a 2-
borylphenyl benzyne precursor has a dramatic effect on the
reactivity, which makes possible the water-triggered benzyne
generation.
X
X
Me
7a, X = F, 79%
7b, X = H, 79%
Me
Me
9a, X = F, 87%
9b, X = H, 96%
Me
6
8
Mes
–OTf
O
I+
10b
Table 1. Optimization of aryne generation using anthracene 6 as a trap.[a]
O
rt, 3 h
CH2Cl2-H2O (9:1)
OH
B
OH
X
X
X
Ph
O
X
Ar
I+
11a, X = F, 87%
11b, X = H, 79%
X = F; 5a or X= H; 5e
Aryne
intermediate
–OTf
OH
solvent
rt, 3 h
+
Tol
N3
Ph
12
B
Ph
N3
16
14
OH
X
Ph
O
Tol
Bn
5
(1.5 equiv)
7
(X = F; 7a, X =H; 7b)
6
(1 equiv)
N
N
N
N
N
N
X
Ph
X
X
17a, X = F, 75%
17b, X = H, 66%
15a, X = F, 78%
15b, X = H, 57%
13a, X = F, 82%
13b, X = H, 77%
7, Yield (%)[b]
Solvent
(ratio)
Reagent
(equiv)
KF
(equiv)
Entry
Scheme 3. Aryne-trapping reactions using 5a or 5e as reagents.a Reaction
conditions: 5a or 5e (1.5 equiv) and the aryne trapping reagent (1 equiv) were
stirred in dichloromethane-water (9:1) mixture at room temperature for 3 hours.
b Excess of furan 10 (5 equiv) was used.
1
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
5a (1.5)
5a (1.2)
5b (1.5)
5a (1.5)
5a (1.5)
5a (1.5)
5a (1.5)
5a(1.5)
2
7a, 70
7a, 60
7a, 66
7a, 64
7a, 0
2
2
3
2
4[c]
5[d]
6
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
Next we investigated several common benzyne-trapping
reactions with various substrates using reagents 5a or 5e as
benzyne precursors in aqueous solvent system under optimized
reaction conditions (Scheme 3). Reactions with 9,10-
dimethylanthracene 8 under optimized conditions gave the
CH2Cl2-H2O (9:1)
(CH2Cl)2-H2O (9:1)
CHCl3-H2O (9:1)
MeCN-H2O (9:1)
AcOEt-H2O (9:1)
Heptane-H2O (9:1)
CH2Cl2-H2O (7:3)
CH2Cl2-H2O (1:1)
CH2Cl2-H2O (9:1)
CH2Cl2-H2O (9:1)
CH2Cl2-H2O (9:1)
CH2Cl2-H2O (9:1)
CH2Cl2-H2O (9:1)
7a, 77(79)
7a, 74
7a, 50
7a, 20
7a, 50
7a, 44
7a, 73
7a, 67
7a, 0
7
corresponding dimethyl triptycenes
9 in good yields. The
structure of 9a was established by a single crystal X-ray analysis
(see Supporting Information). The reaction of furan 10 with 5a
under these conditions afforded adduct 11a in a low yield, which
was improved to 87% by using excess of furan (5 equiv). The
reaction of reagent 5e with furan (5 equiv) furnished product 11b
in 79% yield. In the reaction of 1,3-diphenylisobenzofuran 12
using 5a or 5e under optimized conditions, the corresponding
products 13 were obtained in high yields. As expected, the
cycloaddition reaction of azides 14 or 16 using 5a or 5e under
similar conditions gave the corresponding triazoles 15 or 17 in
moderate to good yields. Reactions of azides with reagent 5a
were highly regioselective forming exclusively products 15a and
17a. These highly regioselective reactions are in agreement with
Garg and Houk’s experimental results and computational studies
of the benzyl azide cycloaddition with 3-fluorobenzyne.[11] In
general, compared to the previously reported aryne-generating
reactions using hypervalent iodine precursors,[5] our procedure is
much milder and gives comparable or higher yields of the aryne
adducts.
8
9
5a (1.5)
5a (1.5)
5a (1.5)
5a (1.5)
5a (1.5)
ArI (1.5)[e]
4a (1.5)
5b (1.5)
5d (1.5)
5e (1.5)
10
11
12
13
14
15
16
17
18
7a, 0
7a, 79
7a, 76
7b, (79)
[a] Reaction conditions: iodine(III) reagent 5 (1.5 equiv) and anthracene 6 (1
equiv) stirred in a solvent with an additive at room temperature for 3 hours. [b]
Yields of product 7 determined from 1H NMR spectra of reaction mixtures are
shown (numbers in parentheses show isolated yield of 7). [c] Water was added
at the end of reaction. [d] No water added for quenching. [e] ArI = (2-fluoro-6-
Pseudocyclic arylbenziodoxaborole triflates 5 belong to the
general class of diaryliodonium salts and are expected to react
as aryl transfer reagents.[12] Previously, Olofsson and co-workers
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10.1002/chem.201704393
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COMMUNICATION
The organic layer was dried over anhydrous Na2SO4 and concentrated
under reduced pressure. Purification by preparative TLC (hexane-ethyl
acetate = 9 : 1) afforded the analytically pure 7.
have reported that diaryliodonium salts are efficient aryl transfer
reagents towards phenolate anions producing diaryl ethers
under basic conditions.[13] Likewise, Larock and co-workers have
reported that the reaction of phenols with arynes also affords
diaryl ethers via addition of the phenolic oxygen to the
electrophilic aryne.[14] Based on these literature data, we
expected that the reaction of arylbenziodoxaborole triflates 5
with phenol will also produce phenolic ethers. To our surprise,
the reaction of reagent 5a with tert-butylphenol 18 under our
standard conditions gave the di-arylated phenol 19b as a major
product and a small amount of unreacted starting phenol. No
diaryl ether was detected in the reaction mixture. Increasing the
amount of reagent 5a until full consumption of tert-butylphenol
18 resulted in the formation of a mixture of mono-ortho-arylated
phenol 19a in 65% yield and di-ortho-arylated phenol 19b in
30% yield (Scheme 4). The analogous reaction of reagent 5e
produced the mono- and di-ortho-arylated phenols 20 in 40%
Acknowledgements
This work was supported by research grants from the National
Science Foundation (CHE-1262479), the Russian Science
Foundation (RSF-16-13-10081), and Tomsk Polytechnic
University (VIU-316/2017). A.S. is also thankful to JSPS Grants-
in-Aid for Scientific Research (C) (Grant No 15K07852).
Keywords: arynes • benzyne • hypervalent iodine • iodine •
iodonium
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and
13%
yields.
These
results
indicate
that
arylbenziodoxaborole triflates 5 can also react as aryl transfer
reagents yielding products of C-arylation of phenols with high
chemoselectivity. Previously, highly selective ortho-arylation
reactions of phenols with arynes were reported the groups of
Daugulis[15] and Hoye.[16]
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OH
OH
OH
5a (2.5 equiv)
F
F
F
+
CH2Cl2-H2O (9:1)
rt, 3 h
tBu
tBu
tBu
18
19a (65%)
19b (30%)
OH
OH
5e (2.5 equiv)
18
+
[3]
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Structure and Synthetic Application of Polyvalent Iodine Compounds,
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CH2Cl2-H2O (9:1)
rt, 3 h
tBu
tBu
20b (13%)
20a (40%)
Scheme 4. Reaction of tert-butyl phenol with 5a or 5e.
In conclusion, we have reported the preparation and X-ray
structures of novel pseudocyclic arylbenziodoxaborole triflates.
These pseudocyclic aryliodonium salts readily generate aryne
intermediates upon treatment with water at room temperature.
The generated aryne intermediates react with various substrates
to give the corresponding aryne adducts in moderate to good
yields. Furthermore, the new benzyne precursors can also work
as chemoselective arylating reagents towards aromatic ring of
tert-butyl phenol.
[4]
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Experimental Section
Anthracene
6 (18 mg, 0.10 mmol) was added to a solution of
arylbenziodoxaborole triflate 5a or 5e (0.15 mmol) in methylene chloride
(1.8 mL) and water (0.2 mL). The reaction mixture was stirred at room
temperature for 3 hours. After completion of reaction, saturated NaHCO3
(5 mL) was added and the mixture was extracted with dichloromethane.
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Chemistry - A European Journal
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
OAc
OH
Ar
I
Preparation and X-ray
structures of novel
pseudocyclic
arylbenziodoxaborole
Akira Yoshimura,* Jonathan M.
Fuchs, Kyle R. Middleton,
Andrey V. Maskaev, Gregory T.
Rohde, Akio Saito, Pavel S.
Postnikov, Mekhman S.
O
B
OH
X
tBu
O
X = H, F
OH
X
triflates are reported.
TfOH,
ArH
O
These compounds readily
generate aryne
intermediates upon
treatment with water at
room temperature.
Yusubov, Victor N. Nemykin,
and Viktor V. Zhdankin*
tBu
Ar
Ar
I+
–OTf
N
Water Trigger
N
Ar
N3
OH
N
CH2Cl2-H2O (9:1)
B
Page No. – Page No.
X
Ar = Ph, Tol
OH
X
X
Pseudocyclic
Aryne
Arylbenziodoxaboroles:
Efficient Benzyne Precursors
Triggered by Water at Room
Temperature
X
R
O4A#
O5#
O3#
R
C7#
O1#
I1#
C1#
R
R
R = H, Me
This article is protected by copyright. All rights reserved.