Simple and Efficient Generation of Aryl Radicals from Aryl Triflates: Synthesis of Aryl Boronates and Aryl Iodides at Room Temperature

Article abstract of DOI:10.1021/jacs.7b03538

Despite the wide use of aryl radicals in organic synthesis, current methods to prepare them from aryl halides, carboxylic acids, boronic acids, and diazonium salts suffer from limitations. Aryl triflates, easily obtained from phenols, are promising aryl radical progenitors but remain elusive in this regard. Inspired by the single electron transfer process for aryl halides to access aryl radicals, we developed a simple and efficient protocol to convert aryl triflates to aryl radicals. Our success lies in exploiting sodium iodide as the soft electron donor assisted by light. This strategy enables the scalable synthesis of two types of important organic molecules, i.e., aryl boronates and aryl iodides, in good to high yields, with broad functional group compatibility in a transition-metal-free manner at room temperature. This protocol is anticipated to find potential applications in other aryl-radical-involved reactions by using aryl triflates as aryl radical precursors.

Full text of DOI:10.1021/jacs.7b03538

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Article
Simple and efficient generation of aryl radicals from aryl triflates:
synthesis of aryl boronates and aryl iodides at room temperature
Wenbo Liu, Xiaobo Yang, Yang Gao, and Chao-Jun Li
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 04 Jun 2017
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Simple and efficient generation of aryl radicals from aryl triflates:
synthesis of aryl boronates and aryl iodides at room temperature
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†
, §
†, ‡, §
†
, †
Wenbo Liu , Xiaobo Yang
, Yang Gao and Chao-Jun Li*
†
Department of Chemistry and FQRNT Centre for Green Chemistry and Catalysis, McGill University, 801 Sher-
brooke St. W., Montreal, Quebec H3A 0B8, Canada;
‡
Institute of Catalysis for Energy and Environment, College of Chemistry & Chemical Engineering, Shenyang Nor-
mal University, Shenyang, Liaoning, 110034, P. R. China.
ABSTRACT: Despite the wide use of aryl radicals in organic synthesis, current methods to prepare them from aryl halides,
carboxylic acids, boronic acids and diazonium salts suffer from limitations. Aryl triflates, easily obtained from phenols,
are promising aryl radical progenitors but remain elusive in this regard. Inspired by single electron transfer process for
aryl halides to access aryl radicals, we developed a simple and efficient protocol to convert aryl triflates to aryl radicals.
Our success lies in exploiting sodium iodide as the soft electron donor assisted by light. This strategy enables the scalable
synthesis of two types of important organic molecules i.e. aryl boronates and aryl iodides in good to high yields, with
broad functional group compatibility in a transition metal-free manner at room temperature. This protocol is anticipated
to find potential applications in other aryl radical-involved reactions by using aryl triflates as aryl radical precursor.
the best of our knowledge, despite these benefits, aryl
1
. Introduction
triflates and other phenol derivatives have never been
3
7-38
Aryl radicals are versatile synthetic intermediates in
organic chemistry. In addition, they also play inter-
esting roles in biology, such as in the DNA cleavage
process. However, due to their high reactivity, aryl
radicals can only be accessed from limited functional
groups, including aryl halides,
employed to prepare aryl radicals.
To fill this gap,
1
-9
herein we described a simple and efficient approach to
access aryl radicals from aryl triflates under mild con-
ditions in absence of transition metal-catalyst at room
temperature (Scheme 1b). Moreover, to illustrate its
synthetic utility, we have demonstrated that this ap-
proach allows the efficient and scalable synthesis of
two types of organic compounds i.e. aryl boronates and
aryl iodides, which represent the two reactants among
one of the most important cross-coupling reactions i.e.
Suzuki coupling in modern chemical science.
1
0
1
1-12
aryl carboxylic
1
3-16
17-21
22-23
acids,
aryl boronic acids,
aryl diazonium salts
Although these meth-
3
, 24-25
as well as their variations.
ods have found broad applications, they still suffer
from at least one of the following limitations: 1) toxic
or expensive reagents, such as tin or silicon reagents,
are used for aryl halides; 2) stoichiometric amounts of
harsh oxidants or reductants, such as K S O or
2. Results and discussion
2
2
8
Mn(OAc) are used for aryl carboxylic acids or boronic
3
,
2.1. Research design. In 2008, the Itami group re-
ported a transition-metal-free approach to synthesize
biaryls from aryl halides and electron-deficient nitro-
acids, and SmI2 for aryl halides or aryl diazonium salts;
) transition metals, such as silver salt, are used for aryl
3
3
9
boronic acids and aryl carboxylic acids; 4) energy in-
tensive reagents aryl diazonium salts are used directly
gen heterocycles promoted by t-BuOK. Following this
4
0
41
42
43-
seminal work, Hayashi , Shi , Lei and many others
5
2
(
Scheme 1a). Therefore, developing an approach to
further extended the scope of electron-deficient
generate aryl radicals, which can exploit more sustain-
able precursor without harsh oxidants or reductants
and in a transition metal-free manner would be highly
desirable.
arenes to regular arenes by adding catalytic amounts of
nitrogen bases or other promoters in presence of t-
BuOK or t-BuONa. This type of reaction, via aryl radi-
cal addition onto the arenes, is called the “homolytic
5
3-54
aromatic substitution”.
Recently, Murphy group,
Aryl triflates are common reactants in coupling reac-
Lei group and Jiao group have conducted mechanistic
investigations on how aryl radicals were generated in
tions, such as the Suzuki and the Stille couplings
26-29
among many others.
Aryl triflates are synthesized
5
5-62
these reactions.
Their studies suggest a single-
from phenols, which can be obtained from abundant
3
0-
electron-transfer process (SET) from the initiators to
aryl halides. Following SET, the aryl halide radical ani-
ons tend to fragment to produce aryl radicals and
and renewable biomass, for instance lignin and coal.
3
1
In this context, aryl triflates as well as other phenol
3
2-36
derivatives
able chemical synthesis than other aryl compounds. To
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Scheme 1. a): Known methods to generate aryl radi-
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cals. b): This work.
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example, Murphy and co-workers have shown that aryl
triflates are reduced to phenols in high yields via S-O
cleavage with super electron donors as the
69
reductants. Yus and co-workers have also shown that
even in presence of stoichiometric amount of NiCl2,
the major products of aryl triflates under Birch reduc-
71
tion conditions are phenols as well. Jutand and co-
halide anions. Usually, these t-BuOK-involved reac-
tions require high temperature to induce the SET. In
addition to the thermal-driven approaches, photo-
induced aryl radical formation methods were also re-
ported at room temperature, known as photo induced
workers disclosed that aryl triflates can be mainly re-
duced to phenols under electro-chemical conditions
even in presence of palladium catalyst together with C-
O bond cleavage products. It is noteworthy that tran-
sition metal catalysts including Pd and Ni can insert
into the C-O bonds in triflates, which would facilitate
the reduction of aryl triflates to arenes. Despite the
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2
63-67
electron transfer (PET).
Inspired by these prece-
dents (Scheme 2a), we hypothesized that an analogous
SET could also occur from an appropriate electron do-
nor to aryl triflates to induce the fragmentation and
subsequently generate aryl radicals.
71-
metal catalysts’ assistance, under reduced conditions,
72
the S-O cleavage still outweighs the C-O cleavage.
Thus, it can be predicted that S-O cleavage in aryl tri-
flates to generate phenols under reduced conditions
represent a considerable competing reaction with the
desired C-O cleavage. Therefore, identifying an appro-
priate electron donor without reacting in an undesira-
ble way would be crucial for aryl triflates to undergo
SET to generate aryl radicals. Considering the unique
properties of iodide ion i.e. high reducing ability and
weak nucleophilicity to aryl triflates, we hypothesized
that simple sodium iodide
electron donor in this regard (Scheme 2c). With all the-
se considerations in mind, we both evaluated the
thermal and photo conditions by mixing sodium iodide
and aryl triflates in presence of radical trappers.
Although this hypothesis is conceptually simple, two
major challenges remain to overcome in order to real-
ize this SET strategy from aryl halides to aryl triflates.
First, above-mentioned methods suitable for aryl hal-
ides require t-BuOK(or t-BuONa) and electron-rich
additives (usually strong nucleophiles after deprotona-
5
7
tion by t-BuOK) , which are incompatible with aryl
triflates. These strong nucleophiles would react with
aryl triflates to generate phenol salts through addition-
73-74
would be an applicable
68
elimination mechanism (Scheme 2b, path 1). Second,
even when SET occurs, the sulfur atom in aryl triflates
as the most electron-deficient site instead of the arene
ring would accept the electron and aryl triflates would
be eventually reduced to phenol salts instead of the
69-70
2.2. Evaluation of thermal vs photo conditions
and evidences of the generation of aryl radical.
Aryl radicals have been thoroughly investigated in the
context of arylation of arenes such as the Gomberg-
Bachmann reaction. Trapped by arenes can be consid-
ered as the evidence of aryl radicals’ presence. Initial-
desired aryl radicals
(Scheme 2b, path 2). For
Scheme 2: a): Well studied process to convert aryl hal-
ides into aryl radical via SET. b): Challenges for aryl
triflates to undergo SET. c): Design strategy for aryl
triflates as the radical precursor.
4
53
ly, the thermal conditions were examined for SET from
sodium iodide (NaI) to p-tolyl trifluoromethanesul-
fonate with benzene as the aryl radical trapper. How-
o
ever, even at 120 C, the desired compound could not
be detected (Scheme 3a). Fortunately, under photo-
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irradiation, the desired biaryl compound could be ob-
served (Scheme 3b). To obtain further evidence to cor-
roborate the presence of aryl radical, another experi-
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a
b
ment to trap the aryl radical by Bu SnH was conducted
200
150
3
0 NaI
(
Scheme 3c). It has been measured that hydrogen ab-
0.2
0.4
µM NaI
µM NaI
µM NaI
µM NaI
µM NaI
0
.6
straction rate from Bu SnH by aryl radical is close to
3
0.8
1.0
75
1
00
50
0
diffusion limit.
As expected, by using 4-
acetamidophenyl trifluoromethanesulfonate as the
substrate, the desired reducing product can be ob-
tained. In addition, it has been documented that aryl
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440 460 480 500 520 540 560 580 600 620
Wavelength (nm)
radical can abstract chlorine from CCl to produce aryl
4
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6
chloride. To further confirm the generation of aryl
radical, CCl was added as a co-solvent besides CH CN.
Figure 1: a: Fluorescence of 4-methylphenyltriflate
with various concentration of NaI. The excitation
wavelength was selected at 260 nm and the concentra-
tion of 4-methylphenyltriflate is 1 µM. b: The EPR sig-
nal of adduct of aryl radical with spin trap (3,3,5,5-
tetramethyl-1-pyrroline N-oxide) in presence of NaI.
4
3
As depicted in Scheme 3d, aryl chloride was obtained
from aryl triflate. Control experiments without NaI of
b, c, d in Scheme 3 failed to produce any desired com-
pounds, which indicate the crucial role of NaI in these
reactions. These trapping experiments clearly suggest
the generation of aryl radical from aryl triflate under
photo irradiation by using NaI as the electron donor.
Moreover, as a direct evidence of SET, the Stern-
Volmer analysis were conducted. p-methyl aryl triflate
has a strong absorption at 254 nm and the emission
maxima is located at 520 nm. The fluorescence of aryl
triflate can be gradually quenched by adding NaI (Fig.
2
.3. Synthesis of aryl boronates. Recently, aryl bo-
ronic compounds have become very powerful due to
the development of the Suzuki coupling among others
such as the Petasis reaction and the Chan-Lam cou-
26, 77
pling.
Classical approaches to synthesize them are
by converting aryl halides into aryl metal reagents,
which can subsequently react with boronic electro-
philes. However, this approach needs stoichiometric
amounts of metallic reagents, which are not conven-
ient to handle. In addition, numerous catalytic meth-
ods have also been reported, among which is the well-
1
a). These experiments suggest that under photo-
irradiation, SET from NaI to aryl triflate occurs to gen-
erate aryl radical. Finally, the EPR signal of aryl radical
with the spin trap (3,3,5,5-tetramethyl-1-pyrroline N-
oxide) can be detected under photo conditions but not
under thermal conditions in presence of NaI (Fig. 1b).
After successfully verifying the generation of the aryl
radicals from aryl triflates under such mild conditions,
we then decided to exploit the synthetic potentials of
this interesting chemistry. By using this method, we
wish to report two important applications via aryl radi-
cals as intermediates: synthesis of aryl boronates and
aryl iodides as described below.
78-79
known Miyaura borylation catalyzed by Pd.
One
drawback of this method is the undesired Suzuki cou-
pling between products and the aryl halides in situ. To
avoid such by-products and the metal catalysts, various
80-
transition-metal-free protocols have been developed.
87
However, these protocols require diazonium inter-
mediates and other sensitive reagents. Earlier in 2016,
three groups independently reported mild and simple
photo-promoted protocols to convert aryl halides into
aryl boronic species.
veloped an elegant protocol to transform aryl halides
8
8-90
More recently, Jiao et al. de-
Scheme 3: Comparison of thermal and photo condi-
9
1
tions to promote SET and aryl radical trapping experi-
into aryl boronic esters using pyridine as the catalyst.
a
ments
Jiao’s mechanistic studies supports a radical-radical
coupling process via an aryl radical intermediate. By
taking advantage of our method to generate aryl radi-
cal, we postulated that aryl triflates can be directly
transformed into aryl boronates without any transition
metals following a mechanistic hypothesis as shown in
Scheme 4.
benzene and CH
3
CN
(
1 mL+ 1 mL)
OTf
OTf
+
+
NaI
NaI
(a)
(b)
1
20 oC, 6 h
No product
benzene and CH
3
CN
(
1 mL+ 1 mL)
3 oC, hv, 6 h
2
Scheme 4: Proposed strategy to synthesize aryl boro-
nates via aryl triflates as radical precursors with iodide
as the electron donor
O
O
Bu
3
SnH
HN
OTf
OTf
+
+
NaI
NaI
(c)
(d)
2
3 oC, hv, 6 h
CH CN
HN
H
3
O
O
CCl
23 oC, hv, 6 h
4
HN
HN
Cl
CH CN
3
a
The products were confirmed by GC/MS analysis.
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Table 1: Evaluation of various conditions for aryl borylation
a, b
entry
1
solvent
additives
yield (%)
CH
CH
CH
CH
CH
CH
CH
CH
CH
3
CN
3
CN
3
CN
3
CN
3
CN
3
CN
3
CN
3
CN
3
CN
NaI (0.5 eq.)
49
a
Reaction conditions: aryl trilfate (0.1 mmol), NaI (0.05
mmol), B (pin) (0.2 mmol), TMDAM (0.1 mmol), CH CN (1
2
3
4
5
6
7
8
9
NaI (0.5 eq.)/TMDAM (0.5 eq.)
NaI (0.5 eq.)/TMDAM (1 eq.)
NaI (0.5 eq.)/DIPEA (1 eq.)
NaI (0.5 eq.)/Py (1 eq.)
58
2
2
3
o
mL), at room temperature (ca 25 C) under Ar atmosphere.
72 (iso.)
b
Isolated yields.
69
21
43
5
fortunately beneficial. TMDAM (0.5 equiv) can in-
crease the isolated yield to 58% (entry 2, Table 1) and
TMDAM (1 equiv) can increase the isolated yield to
72% (entry 3, Table 1). DIPEA shows a similar impact as
TMDAM (69%) (entry 4, Table 1) but different from
Jiao’s work44, whereas pyridine and DBU would de-
crease the yields to 21% and 43% respectively (entries 5
and 6, Table 1). As a control experiment, TMDAM
alone can only produce a yield of 5% (entry 7, Table 1),
suggesting the importance of iodide to this reaction
system. Further control experiments show that either
less or more NaI in this system would result in harmful
effect (41% and 40%) (entries 8 and 9, Table 1). Brief
investigation of solvent effect demonstrates that
MeOH and acetone are not as efficient as acetonitrile
NaI (0.5 eq.)/DBU (1 eq.)
TMDAM (1 eq.)
NaI (0.2 eq.)/TMDAM (1 eq.)
NaI (1 eq.)/TMDAM (1 eq.)
NaI (0.5 eq.)/TMDAM (1 eq.)
NaI (0.5 eq.)/TMDAM (1 eq.)
NaI (0.5 eq.)/TMDAM (1 eq.)
41
40
17
25
10
MeOH
11
Acetone
c
12
3
CH CN
38
a
Reaction conditions: 4-methoxyphenyltriflate (0.1 mmol),
NaI (0.05 mmol), B (pin) (0.2 mmol), solvent (1 mL), at room
(
entries 10 and 11, Table 1). Finally, when the reaction
2
2
was performed in air instead of argon, the yield
dropped to 38% (entry 12, Table 1), which also suggests
a radical mechanism. With the optimized conditions
established, the scope of this borylation was subse-
quently explored (Scheme 5). Various substituted bo-
ronic esters, including non-substituted (2a), alkyl (2b,
b
temperature (ca. 25°C) under Ar atmosphere. Isolated yields.
In air. TMDAM: N, N, N’, N’-tetramethyldiaminomethane;
c
DIPEA: N, N-diisopropylethylamine; Py: pyridine; DBU: 1,8-
diazabicyclo (5.4.0) undec-7-ene.
To begin the study, 4-methoxyphenyltriflate was
selected as the model substrate. To our delight, under
photo-irradiation, when NaI was added, the desired
boronates can be isolated at 49% yield (entry 1, Table
1). In order to generate the ate-complex to facilitate
SET, various base additives were evaluated, which are
2d, 2e), methoxy (2c), nitrile (2f), ester (2g), -CF (2h),
3
-Ph (2i), and -Bn (2j) substituted, could be obtained in
good yields by using this protocol. It is noticeable that
a di-boronic ester can also be produced under our
conditions in synthetically useful yield (2k). Further-
more, vinyl boronic ester can be obtained smoothly
from vinyl triflate as well (2l). This broad functional
group compatibility would likely find applications in
multi-step synthesis. Besides aryl triflate, aryl mesylate
Scheme 5: Scope of the borylation reaction
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can also serve as the reactants albeit with a lower yield
2a). To the best of our knowledge, this approach repre-
sents the first method to prepare aryl boronates from
phenol derivatives without involving transition metal
catalysts.
would also be a significant obstacle to ensure a satis-
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(
factory yield. Finally, aryl triflates would tend to un-
dergo S-O homolytic cleavage, which would also com-
pete with the desired reaction.
Despite these challenges, to start the study, we se-
lected 2-acetamidophenyltriflate as the model sub-
2.4. Synthesis of aryl iodides. Aryl halides are
strate considering its less volatility, using CH CN as
3
basic building blocks in organic synthesis. Many well-
known reactions, which are performed on daily basis in
every synthetic laboratory all around the world, such
as the Suzuki coupling, the Heck coupling and the
Buchwald-Hartwig aminations etc., all require aryl hal-
ides. Among them, aryl iodides display the highest re-
activity and can be operated at mild temperature with-
the solvent and NaI as the iodide source with 0.1
equivalent of I within 24 hrs under argon. To our de-
2
0
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light, the desired aryl iodide could be detected in 50%
yield (entry 1, Table 2). Encouraged by this result, vari-
ous base additives were examined. It was found that
TMDAM, DIPEA, KF, NaF and CsF all resulted in infe-
rior results (entries 2-6, Table 2). However, when LiF
was used, the yield increased to 57% with aryl triflate
not completely consumed (entry 7, Table 2). Fortu-
nately, after the reaction time was prolonged to 48 hrs,
aryl triflate reacted completely and the desired product
could be isolated in 85% yield (entry 8, Table 2). Based
on this condition, control experiments were further
performed. Entry 9 demonstrated that water (10%) as
the co-solvent poses deleterious effect on this reaction.
Similarly, 50% acetone in this reaction system also de-
creased the yield to 46% (entry 10, Table 2). Control
experiment in the darkness could not afford any prod-
uct (entry 11, Table 2). In addition, when the reaction
was conducted in air instead of argon, the yield
dropped to 50% (entry 12, Table 2). The control exper-
26, 77, 92
out special ligands and additives.
Unfortunately,
aryl iodides are expensive and less accessible due to
the challenge to synthesize them. Therefore, novel
methods that can produce aryl iodides from abundant
precursors at room temperature with broad functional
group compatibility would be highly useful. Consider-
ing the remarkable advantages of aryl triflates toward
sustainable chemical synthesis, simple and efficient
protocols that can transform aryl triflates into aryl io-
dides would be desirable. To achieve this goal, harsh
9
3-94
79, 95
conditions
or multi-step synthesis
were usually
required. However, a few relatively general metal-
catalyzed methods have recently been disclosed. In
2009, the Hayashi group reported a protocol convert-
ing vinyl triflates into vinyl halides catalyzed by Ru in
96
iment without adding I produces a yield of 67% (entry
2
presence of Grignard additive. Although one aryl tri-
13, Table 2). Finally, when 2 equivalents of NaI instead
of 4 equivalents was employed in this reaction, the
yield dropped to 54% (entry 14, Table 2).
flate example was shown, it was only limited to the
special 2-naphthyl triflate and the protocol is not ap-
plicable to regular aryl triflates. In 2012, the same
group reported an updated protocol by using another
Ru catalyst as well as increasing the temperature,
which could convert regular aryl triflates into aryl hal-
Scheme 6: a): Proposed strategy to synthesize aryl io-
dides from aryl triflates; b): Potential challenges for
this strategy to synthesize aryl iodides.
9
7
ides. In addition to Hayashi’s Ru protocols, in 2010,
the Buchwald group developed a Pd-catalyzed ap-
proach that can transform aryl (vinyl) triflates into aryl
(
vinyl) bromides and chlorides, which was later im-
9
8-99
proved to a more friendly version in 2011;
however,
aryl iodides cannot be synthesized by the palladium
system due to their higher reactivity than that of aryl
triflates. It has been well recognized that the rate con-
stant for aryl radical abstracting iodine atom from oth-
er iodine source is close to diffusion rate limit, which
would be synthetically appropriate to generate aryl
iodides. Therefore, we hypothesized that through our
method, aryl triflates may be transformed into aryl
iodides in presence of elemental I or other iodine
2
sources (Scheme 6a). However, despite this promising
hypothesis, some potential challenges can be foreseen
(
Scheme 6b). First, aryl iodides are more photo-
reactive than aryl triflates. To synthesize more reactive
molecules from less reactive reactants would cause a
dilemma. Second, the hydrogen abstraction for phenyl
radical from solvent to produce the reducing product
With the optimized conditions identified (Table 3,
entry 8), we then turned our attention to the substrate
scope investigation. Various aryl triflates with different
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Journal of the American Chemical Society
Page 6 of 8
b
1
substituents can be converted into the desired aryl io-
dides (Scheme 7). Firstly, the substrates with para sub-
stituents were examined. Diverse aryl triflates with
electron-withdrawing and electron-donating groups
can undergo the reaction smoothly, with the corre-
sponding iodides isolated in modest to good yields
lent). Yields were determined by H-NMR, with 1,3,5-
c
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
trimethoxybenzene as the internal standard. In the
darkness. Under air atmosphere. Isolated yield. Only
2 equivalents of NaI used instead of 4 equivalents.
d
e
f
Scheme 7: Scope of the substrates for the iodination.
(
49-61%) (3a-3g). However, when the para substituent
is acyl group, the yield dropped to 20% (3h). Subse-
quently, substrates with substituents at other positions
were tested. 3-Fluoro phenyl iodide (3i) and 3-
trifluoromethylphenyl iodide (3j) can both be obtained
in good yields. In addition, different aryl triflates with
phenyl substituents can also be converted into aryl
iodides smoothly (3k-3m). Interestingly, when the aryl
triflate bears an iodo substituent, the di-iodo arene
compound could be synthesized (3n), which suggests
the mildness of our protocol since, in previous transi-
tion-metal-catalyzed protocols, the iodo substituent
can not be tolerated. In addition, various aniline de-
rived iodides are also accessible by this method (3o-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
s). Some heterocycles are also compatible with our
conditions, with 4-iodoindole (3t) and 4-iodocarbozole
3u) being produced in good
(
Table 2: Evaluation of different conditions for aryl io-
dination
b
entry
1
solvent
additives
time
24h
yield (%)
50
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
3
3
3
3
3
3
CN
CN
CN
CN
CN
CN
CN
CN
CN/H
I
I
I
I
I
I
I
I
I
I
I
I
2
2
2
2
2
2
/none
/TMDAM
/DIPEA
/KF
2
3
24h
24h
24h
24h
24h
24h
48h
48h
48h
48h
48h
48h
48h
19
23
39
41
43
57
4
5
6
7
8
9
a
Reaction conditions: 1 (0.1 mmol), NaI (0.4 mmol), LiF
/NaF
/CsF
(0.1 mmol), I (0.01 mmol), CH CN (1 mL), at rt (ca 25
2
3
o
b
C) under Ar atmosphere, reaction time: 48 hrs Yields
1
were
determined
by
H-NMR,
with
1,3,5-
c
3
3
2
/LiF
trimethoxybenzene as the internal standard. Reaction
time: 72 hrs.
e
2
/LiF
85 (iso.)
yields. Besides the phenyl triflates, naphthyl triflate
also undergoes the transformation well (3v). Due to
the importance of Suzuki coupling, the boron substit-
uent was also examined and 4-iodo phenyl boronic
ester (3w) could be isolated in 79% yield. The unique
structure feature of this compound (3w) may find
broad applications in polymer chemistry, considering
the complementary reactive sites in the compound.
More importantly, the successful synthesis of this
compound further illustrates the power of our proto-
col. In order to further evaluate the synthetic utility of
our protocol, some complicated substrates were sub-
jected to the standard conditions. It was found that
tyrosine-derived triflate could deliver the iodide, on
3
3
3
3
3
3
2
O
2
2
2
2
/LiF
Trace
46
0
10
CN/acetone
/LiF
c
1
1
1
CN
CN
CN
CN
/LiF
d
2
/LiF
50
13
LiF
/LiF
67
f
1
4
I
2
54
a
Reaction conditions: 2-acetamidophenyl trifluoro-
methanesulfonate (0.1 mmol), NaI (0.4 mmol), I (0.1
mmol), solvent (1 mL), at rt (ca 25°C) under Ar atmos-
phere and base additives are all 0.1 mmol (1 equiva-
2
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Journal of the American Chemical Society
gram scale, in 81% and 71% yields, respectively. Sterol-
based aryl triflate could also be converted into the io-
ACKNOWLEDGMENT
1
We are grateful to the Canada Research Chair Foundation (to
C.-J. Li), the CFI, FQRNT Center for Green Chemistry and
Catalysis, NSERC, and McGill University for support of our
research. We also thank Dr. Rajesh Malakalapalli (McGill
University) for the fluorescence measurement assistance.
Wenbo Liu is grateful to McGill Chemistry department for
fellowship support and Dr. Xiaobo Yang is grateful for the
support from China Scholarship Council (CSC).
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
dide with good yield (3y). This broad functional group
compatibility and the scalability would find applica-
tions in complex natural product synthesis. In addition
to aryl triflates, vinyl triflates could also be converted
to the corresponding vinyl iodides in moderate to good
’
yields (3z, 3a). To obtain more insight on this reaction,
reactivity comparison of aryl triflates with other phe-
nol derivatives were conducted, which suggested that
aryl triflates display the highest reactivity (3a in
Scheme 7) even though some other phenol derivatives
are also reactive (Scheme 8).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
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The authors declare no competing financial interest.
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