O-arylation of carboxylic acids using (phenyl)[2-(trimethylsilyl)phenyl] iodonium triflate as a precursor of arynes

Article abstract of DOI:10.1080/00397910701397417

Using (phenyl)[2-(trimethylsilyl)phenyl]iodonium triflate as a precursor of arynes, Larock's method for O-arylation of carboxylic acids and arynes was developed. A variety of acids including simple aliphatic carboxylic acids, aromatic carboxylic acids, allenoic acids, and p-toluenesulfonic acid under mild reaction conditions could generate the aryl esters. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701397417

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O‐Arylation of Carboxylic Acids using (Phenyl)
[2‐(trimethylsilyl)phenyl]iodonium Triflate as
a Precursor of Arynes
Jian Xue a & Xian Huang a b
a Department of Chemistry , Zhejiang University (Campus Xixi) , Hangzhou,
China
b State Key Laboratory of Organometallic Chemistry , Shanghai Institute of
Organic Chemistry, Chinese Academy of Sciences , Shanghai, China
Published online: 03 Jul 2007.
To cite this article: Jian Xue & Xian Huang (2007) O‐Arylation of Carboxylic Acids using (Phenyl)
[2‐(trimethylsilyl)phenyl]iodonium Triflate as a Precursor of Arynes, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:13, 2179-2185, DOI:
10.1080/00397910701397417
To link to this article: http://dx.doi.org/10.1080/00397910701397417
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Synthetic Communicationsw, 37: 2179–2185, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701397417
O-Arylation of Carboxylic Acids using
(Phenyl)[2-(trimethylsilyl)phenyl]iodonium
Triflate as a Precursor of Arynes
Jian Xue
Department of Chemistry, Zhejiang University (Campus Xixi),
Hangzhou, China
Xian Huang
Department of Chemistry, Zhejiang University (Campus Xixi),
Hangzhou, China and State Key Laboratory of Organometallic
Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy
of Sciences, Shanghai, China
Abstract: Using (phenyl)[2-(trimethylsilyl)phenyl]iodonium triflate as a precursor of
arynes, Larock’s method for O-arylation of carboxylic acids and arynes was
developed. A variety of acids including simple aliphatic carboxylic acids, aromatic car-
boxylic acids, allenoic acids, and p-toluenesulfonic acid under mild reaction conditions
could generate the aryl esters.
Keywords: aryl esters, arynes, carboxylic acids, O-arylation
Arynes as useful reactive intermediates have received considerable attention
in synthetic applications.[1] Before Himeshima et al. first reported that 2-(tri-
methylsilyl)phenyl triflate 1 can generate arynes under mild conditions,[2] the
general method for its generation was deprotonation from aromatic halogen
compounds with a strong base, which is unfavorable to some substrates con-
taining base-sensitive functional groups. Recently, using 1 as a precursor,
reactions (especially a variety of nucleophile addition to arynes) have been
Received January 6, 2007
Address correspondence to Xian Huang, Department of Chemistry, Zhejiang Uni-
versity (Campus Xixi), Hangzhou 310028, China. E-mail: huangx@mail.hz.zj.cn
2179

2180
J. Xue and X. Huang
studied for synthesizing polysubstituted arenes, which otherwise are difficult
to prepare. Element– elements-bonds, such as H-X (X ¼ N,O,S)[3] N-Si,[4]
C-C,[5] C-N,[6] C-P,[7] S-N,[6b] and S-Sn[8] inserts to arynes and Pd-
catalyzed insert of arynes into Si-Si,[9] Sn-Sn,[10] and C-Sn,[11] have been
reported.
Very recently Liu and Larock reported that through the reactions between
arynes generated by 1 and aromatic carboxylic acids, the corresponding aryl
ester was obtained, which is impossible to prepare by the direct esterification
of phenols with carboxylic acids, but they failed to get aryl esters from the
simple aliphatic carboxylic acids.[3b]
Recently (phenyl)[2-(trimethylsilyl)phenyl]iodonium triflate[12] 2 has
been reported to be a new and efficient precursor that can generate arynes
under mild and neutral conditions. Precursor 2 has higher efficiency.
Kitamura et al. used 2 to react with furan to give adduct in a quantitative
yield, whereas the reaction of aryne precursor 1 with furan under the same
conditions led to a lower yield of adduct and required a longer reaction
time.[12d] During our research on methodology of arynes, we thought that
the precursor 2 reacted with simple aliphatic carboxylic acids to afford aryl
esters (Scheme 1).
Initially we examined the reaction of HOAc (3a) with 1 equiv of 2 in
the presence of 1 equiv of potassium fluoride (KF) and 1 equiv of 18-
crown-6 in 10 ml CH2Cl2 at room temperature (Table 1, entry 1). As
expected, the desired ester 4a was obtained in 71% after 5 h. With this
encouraging result, a systematic study was undertaken for the O-arylative
process. The results are summarized in Table 1. Using 1.5 equiv of KF
and 1.5 equiv of 18-crown-6, this reaction proceeded efficiently to give
4a in 76% yield for 3.5 h (Table 1, entry 2), and the yield of 4a
remained similar when increasing the amount of KF and 18-crown-6 to 2
equiv (Table 1, entry 3). By increasing the amount of 2 to 1.2 equiv, the
yield of 4a could be improved to 84% (Table 1, entry 4) and increasing
the amount of 2 up to 1.4 equiv failed to increase the yield of 4a
(Table 1, entry 5). Therefore, the reaction conditions chosen to undergo
this reaction were CH2Cl2 with 1.2 equiv of 2, acids, 1.8 equiv of KF,
and 1.8 equiv of 18-crown-6 in CH2Cl2 for 3.5 h at room temperature.
Scheme 1.

O-Arylation of Carboxylic Acids
2181
Table 1. Esterification of HOAc with arynesa
18-Crown-6
(mmol)
Entry
2 (mmol)
KF (mmol)
Time (h)
Yield (%)
1
2
3
4
5
0.5
0.5
0.5
0.6
0.7
0.5
0.75
1
0.5
0.75
1
5
71
76
75
84
82
3.5
3
0.9
1.05
0.9
1.05
3.5
3.5
a3a (0.5 mmol) was reacted with 2 in the presence of KF and 18-crown-6 in 10 ml of
CH2Cl2 at rt.
Under the optimal reaction conditions, a variety of simple aliphatic car-
boxylic acids were investigated to get the corresponding esters in good
yields. As shown in Table 2, the existence of a halogen group and double
bond can be tolerated under certain conditions (entries 4 and 5). Allene is
also compatible in our reaction conditions, and the yield is good (entry 6).
We also used these conditions to prepare aryl esters from aromatic car-
boxylic acids, and the yields were higher than Larock’s method[3a] (entries
7–9). When p-toluenesulfonic acid was used, we also got the corresponding
product in excellent yield (entry 10).
In summary, we have developed Larock’s method for O-arylation of a
variety of carboxylic acids and arynes using 2 as a precursor. Our method is
more applicable than Larock’s method. Further studies, including the
methods of aryne generation, the reaction mechanism, and synthetic appli-
cation of arynes, are in progress.
EXPERIMENTAL
General
1
All H NMR spectra were measured in CDCl3 and recorded on a Bruker
Avance-400 (400-MHz) spectrometer with TMS as the internal standard.
13C NMR spectra were measured in CDCl3 and recorded on a Bruker
Avance-400 (100-MHz) spectrometer with TMS as the internal standard.
Chemical shifts are expressed in parts per million (ppm), and J values are
given in Hertz. IR spectra were run on a Bruker vector 22 spectrometer.
Electron impact mass spectrometry (EIMS) were determined with a
HP5989B mass spectrometer.

2182
J. Xue and X. Huang
Table 2. Preparation of aryl ester from arynes and carboxylic acidsa
Yieldb
(%)
Entry
1
Acid
Product
4a 84
4b 80
4c 68
4d 73
2
3
4
5
6
4e 85
4f 83
7c
8c
4g 87
4h 81
4i 97
4j 91
9c
10c
aReaction conditions: The reaction was carried out in CH2Cl2 (10 ml) at rt
using 0.6 mmol of aryne precursor 2, 0.5 mmol acids, 0.9 mmol 18-crown-6, and
0.9 mmol KF.
bIsolated yield based on starting acids.
cThe reaction time is 40 min.
General Procedure for the Synthesis of 4a–4j
To a CH2Cl2 solution (5 ml) of aryne precursor 2 (0.6 mmol), an acid
(0.75 mmol), and 18-crown-6 (0.75 mmol), KF (0.75 mmol) was added, and

O-Arylation of Carboxylic Acids
2183
the resulting mixture was stirred at room temperature for 4 h. After completion
of the reaction, the mixture was then diluted with EtOAc (15 ml) and washed
with water and brine. The organic layer was dried over MgSO4. Removal of
the solvent in vacuum and purification of the residue by silica-gel chromato-
graphy with n-hexane–EtOAc (10:1) as eluent gave the product.
Data
4a: oil.[13] 1H NMR (400 MHz, CDCl3) 7.38–7.34 (m, 2H), 7.23–7.19
(m, 1H), 7.08–7.06 (d, 2H), 2.94 (s, 3H); MS (EI): m/z (%) ¼136 (Mþ,
6.88), 43 (100), 77 (14.66).
4b: oil.[14] 1H NMR (400 MHz, CDCl3) 7.43–7.39 (m, 2H), 7.27–7.26
(m, 1H), 7.14–7.12 (d, 2H), 2.65–2.59 (m, 2H), 1.32–1.29 (m, 3H); MS
(EI): m/z (%) ¼ 148 (Mþ, 31.04), 57 (100), 77 (11.00).
4c: oil.[15] 1H NMR (400 MHz, CDCl3) 7.38–7.34 (m, 2H), 7.22–7.18
(m, 1H), 7.08–7.06 (d, 2H), 2.56–2.52 (m, 2H), 1.77–1.73 (m, 2H), 1.41–
1.36 (m, 4H), 0.94–0.91 (m, 3H); MS (EI): m/z (%) ¼ 184 (Mþ, 4.86), 94
(100), 77 (12.97).
4d: oil. 1H NMR (400 MHz, CDCl3) 7.41–7.37 (m, 2H), 7.26–7.24 (m, 1H),
7.13–7.10 (d, 2H), 4.60–4.56 (m, 1H), 1.94–1.92 (d, 3H); MS (EI): m/z
(%) ¼ 228 (Mþ, 4.86), 94 (100), 77 (10.40).
4e: oil. 1H NMR (400 MHz, CDCl3) 7.41–7.37 (m, 2H), 7.26–7.24 (m, 1H),
7.14–7.11 (d, 2H), 6.62–6.58 (d, 1H), 6.35–6.31 (m, 1H), 6.02–5.99 (d, 1H);
MS (EI): m/z (%) ¼ 148 (Mþ, 12.55), 55 (100), 77 (19.14).
4f: oil. IR (KBr): 3070, 2985, 1965, 1728, 1294, 1240 cm21 1H NMR
.
(400 MHz, CDCl3): 7.39–7.35 (m, 2H), 7.23–7.22 (d, 1H), 7.11–7.09
(m, 2H), 5.94–5.83 (m, 1H), 5.27–5.09 (m, 2H), 5.19–5.09 (m, 2H), 3.09–
3.08 (m, 2H). 13C NMR (400 MHz, CDCl3): 214.6, 165.5, 150.9, 134.4,
129.3, 125.7, 121.5, 116.7, 98.5, 79.8, 32.6. MS (EI): m/z (%) ¼ 200
(Mþ, 7.79), 201 (27.94), 107 (100), 77 (87.50), 65 (24.70). Anal. calcd. for
C13H12O2: C, 77.98; H, 6.04. Found: C, 77.76; H, 6.13.
4g: oil. 1H NMR (400 MHz, CDCl3) 7.90–7.84 (m, 4H), 7.44–7.40 (m, 2H),
7.28–7.26 (m, 1H), 7.20–7.08 (m, 2H); MS (EI): m/z (%) ¼ 324 (Mþ, 5.99),
231 (100), 76 (66.38).
4h: white solid: mp 127–1298C (lit.[3b] mp 127–1288). 1H NMR (400 MHz,
CDCl3) 7.41–7.37 (m, 2H), 7.26–7.24 (m, 1H), 7.13–7.10 (d, 2H), 4.60–4.56

2184
J. Xue and X. Huang
(m, 1H), 1.94–1.92 (d, 3H); MS (EI): m/z (%) ¼ 228 (Mþ, 4.86), 94 (100), 77
(10.40).
1
4i: white solid: mp 67–69.8C (lit.[3b,16] mp 67–698C). H NMR (400 MHz,
CDCl3) 8.15–8.13 (m, 2H), 7.40–7.38 (m, 2H), 7.24–7.18 (m, 3H),
6.97–6.95 (m, 2H), 3.85 (s, 3H); MS (EI): m/z (%) ¼ 228 (Mþ, 1.86), 135
(100), 107 (19.12), 77 (29.49).
1
4j: white solid: mp 95–978C (lit.[17] mp 94–958C). H NMR (400 MHz,
CDCl3) 7.71–7.69 (d, 2H), 7.31–7.25 (m, 5H), 6.99–6.97 (m, 2H), 2.44
(s, 3H).
ACKNOWLEDGMENT
This work was supported by the National Natural Science Foundation of
China (20332060, 20472072).
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