A DDQ-promoted metal-free cross-coupling of 1,3-diarylpropynes with hydroxyl via Sp3 C-H bond activation to form C-O bond

Article abstract of DOI:10.1016/j.tet.2011.05.030

A metal-free coupling reaction between 1,3-diarylpropynes and alcohols/phenols/acids via propargylic sp³ C-H bonds activation and C-O bond formation reaction promoted by DDQ was realized. The reaction afforded series of propargyl ethers, propargyl esters and propargyl ketals.

Full text of DOI:10.1016/j.tet.2011.05.030

Tetrahedron 67 (2011) 4793e4799
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Tetrahedron
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A DDQ-promoted metal-free cross-coupling of 1,3-diarylpropynes with hydroxyl
via Sp3 CeH bond activation to form CeO bond
*
Hanjie Mo, Weiliang Bao
Department of Chemistry, Zhejiang University, Xixi Campus, Hangzhou 310028, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
A metal-free coupling reaction between 1,3-diarylpropynes and alcohols/phenols/acids via propargylic
sp3 CeH bonds activation and CeO bond formation reaction promoted by DDQ was realized. The reaction
afforded series of propargyl ethers, propargyl esters and propargyl ketals.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 3 March 2011
Received in revised form 27 April 2011
Accepted 9 May 2011
Available online 13 May 2011
Keywords:
CeH bonds activation
CeO bond formation
Metal-free
Cross-coupling
1. Introduction
workers used phenylethynyl bromide and ketones as the substrates
with KHMDS/NaOtBu as the strong base to synthesize the propargyl
The formation of carboneheteroatom bonds from a common
intermediate is of great significance to the drug discovery and pro-
duction process.1 In particular, the construction of an ether linkage
adjacent to a sterically hindered carbon centre is important for the
synthesis of many biologically active compounds.2 The conventional
method for ether synthesis is the direct SN2-type O-alkylation
(Williamson ether synthesis). However, this protocol is sometimes
synthetically impractical owing tothe strong basicity of the alkoxide
anion, which may be incompatible with other functional groups
presented in the system.3 Therefore some modified methods were
developed,4e6 for example, transition metal-catalyzed cross-cou-
pling of aryl halides with phenols or alcohols.4b,c,e,f,l However,
transition metal-based protocols, although successful, usually have
some inherent limitations, such as moisture sensitivity, costly metal
catalysts and environmental toxicity.4c With the prevalence of ‘atom
economy’7 and ‘green chemistry’,8 the cross-coupling reaction for
constructing CeO bonds without any metal catalysts via CeH
functionalization has attracted great interest.
ethers,10b but the substrates were costly and not easy to obtain with
their limitations in structure. So it is meaningful and worthy of di-
rectly using propargylic sp3 CeH bonds and hydroxyl without any
metal catalyst to form propargyl ethers/esters.
For the construction of CeO bonds, our group reported a metal-
free coupling reaction to form CeO bonds between
1,3-diarylpropenes and alcohols promoted by DDQ, which afforded
a new path to synthesize various types of CeO bonds.11 Recently,
both 1,3-diarylpropynes and 1,3-diarylpropenes were reported to
react with 1,3-dicarbonyl compounds to form CeC bonds by our
group.12 By comparing these, it suggested that the coupling reaction
of 1,3-diarylpropenes was faster and more simple, and the desired
product of 1,3-diarylpropenes was more stable and the yield was
higher than the desired substituted product of 1,3-diarylpropynes.
Thus the formation of CeO bonds between 1,3-diarylpropynes and
hydroxyl directlystill remains a challenge. Hereinwe report a metal-
free oxidative coupling reaction promoted by DDQ between 1,3-
diarylpropynes and alcohols/phenols/acids to form a series of
propargyl ethers, esters and ketals.
Propargyl ethers/esters are useful structural motifs that can serve
as substrates or intermediates in countless transformations,9 espe-
cially in the synthesis of allenes. In the past few years, only few
methods were reported to prepare propargyl ethers/esters.10 How-
ever, using transition metal catalysts, such as Au or Ru compounds is
costly and environmental harmful.10a,c Recently, Gevorgyan and co-
2. Discussion
To begin our study, 1-phenyl-3-(40-methoxyl)phenylpropyne
and ethanol were chosen as the standard substrates to search for
suitable reaction conditions. When 1-phenyl-3-(40-methoxyl)
phenylpropyne and ethanol were mixed in 1 mL CH2Cl2 with
a stoichiometric amount of DDQ, 0.1 equiv of CuBr as the catalyst,
* Corresponding author. Tel./fax: þ86 571 8827 3814; e-mail address: wlbao@
css.zju.edu.cn (W. Bao).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.05.030

4794
H. Mo, W. Bao / Tetrahedron 67 (2011) 4793e4799
the desired product was isolated in 61% yield (Table 1, entry 1).
Then the same reaction was taken without any metal catalyst.
Surprisingly, the yield of the desired product was improved to 73%
(Table 1, entry 2). The reactions of 1,3-diarylpropynes and alcohols
finished in 2 h, which is longer than the reactions of 1,3-
diarylpropenes and alcohols.11 By decreasing the amount of DDQ
to 0.5 equiv, the product was obtained in 42% yield (Table 1, entry
3). Only 29% yield of the product was isolated when 1.5 equiv of
DDQ was used (Table 1, entry 4). Further, different temperatures
were screened, which suggested that the reaction performed best
under 0 ꢀC (Table 1, entries 2, 5 and 6). A number of solvents were
screened and the desired product was obtained in moderate yield
in DCE, toluene, CHCl3, DMF, THF and benzene. However, consid-
erable amounts of undesired products were formed in CH3NO2,
cyclohexane and 1,4-dioxane (Table 1, entries7e16).
disfavourable (2j). This means that the 1,3-diarylpropynes were
oxidized to cations as intermediates.
When ethane-1,2-diol and 2,2-dimethylpropane-1,3-diol
were used as the substrate, 3a and 3b were isolated in high
yields (Scheme 1). Thus a series of propargyl ketals can be easily
obtained. Unfortunately, when we use pyrocatechol as the sub-
strate, trace of the desired product was obtained. Then we used
1a as the substrate to react with methanol, only less than 20%
yield of desired unsymmetric ketal product was obtained.
To expand the scope of the reaction, the reaction of 1,3-
diarylpropynes with several acids were also tested. Firstly, we
chose 1-phenyl-3-(40-methoxyl)phenylpropyne and acetic acid as
the standard substrates. For the poor nucleophilicity of the acetic
acid, the yield of the desired product was not satisfactory under the
reaction condition of alcohols (Table 4, entry 2). Thus different re-
Table 1
Screening of reaction conditionsa
O
DDQ
+
OH
Solvent
OMe
OMe
1a
Entry
Metal
Oxidant/equiv
Solvent
Temp (ꢀC)
Yieldb (%)
1
2
3
4
5
6
7
8
CuBr (0.1 equiv)
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
DDQ/1.0
DDQ/1.0
DDQ/0.5
DDQ/1.5
DDQ/1.0
DDQ/1.0
DDQ/1.0
DDQ/1.0
DDQ/1.0
DDQ/1.0
DDQ/1.0
DDQ/1.0
DDQ/1.0
DDQ/1.0
DDQ/1.0
DDQ/1.0
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
DCE
Toluene
CHCl3
CH3CN
CH3NO2
DMF
0
0
0
0
rt
50
0
0
0
0
0
0
0
0
0
0
61
73
43
29
47
20
63
50
58
55
47
65
61
30
49
59
9
10
11
12
13
14
15
16
THF
Cyclohexane
1,4-Dioxane
Benzene
a
1-Phenyl-3-(40-methoxyl)phenylpropyne (0.25 mmol), 0.27 mmol of ethanol, 1 mL of solvent, 2 h.
Isolated yield.
b
With the optimized reaction conditions established, we further
action temperatures were screened, and a moderate yield of de-
sired product (4a) was isolated when the reaction was taken under
the room temperature (Table 4, entry 2). But the yield of the desired
product decreased to 17% when the reaction was taken under 50 ꢀC
(Table 4, entry 3). When we decreased the reaction time, the yield
of the product increased slowly, and 30 min would be the most
suitable reaction time (Table 4, entries 2, 4, 5 and 6).
With the suitable reaction condition established, a series of
propargyl esters were obtained in Table 5. Both aromatic and ali-
phatic acids can react with 1,3-diarylpropynes. But the yields of es-
ters were lower than ethers, maybe the stability of esters were lower
than ethers. The yields of aromatic esters were lower than the cor-
responding aliphatic esters (4aec). The electron-donating groups on
1,3-diarylpropynes werealsobeneficialtotheformationofesters(4a,
b). Thus most types of propargyl CeO bonds have been formed.
According to literature11,12a and based on our experiments,
a possible mechanism was proposed in Scheme 2. The formation of
product may have two pathways, hydride transferred directly from
propargylic position and/or hydrogen abstraction after an electron
was transferred from the propargylic triple bond to DDQ. However,
sole products 1l, m and n were obtained, respectively. The in-
coming nucleophile attacks mainly at the original benzylic cation
position. This means the mechanism of hydride abstraction may be
more possible.
explored the generality and efficiency of the DDQ-mediated oxi-
dative cross-coupling reaction between various 1,3-diarylpropyne
compounds with different alcohols, and a series of products were
obtained in Table 2. Alcohols with electron-withdrawing groups
reacted well with the 1,3-diarylpropynes under the standard con-
dition (1c, g and h). However, a moderate yield was achieved when
alcohols with electron-donating groups were used (1b, f and i). The
steric effect caused the lower yield of the product (1f). Various 1,3-
diarylpropyne compounds were also examined. High yields of the
coupling products were obtained when there were electron-do-
nating group on the aromatic ring (1j, l and m), while moderate
yields were given if electron-withdrawing group existed (1n).
After screening the alcohols, phenols were used as the sub-
strates to react with 1,3-diarylpropynes. For the stronger acidity of
phenols, the cross-coupling reaction finished in 30 min, and a series
of propargyl phenyl ethers were obtained in Table 3. The sub-
stituent effects were the same as the alcohols. Phenols with
electron-withdrawing groups reacted well with the 1,3-
diarylpropynes under the standard reaction condition (2b and e),
and a moderate yield was achieved when phenols with electron-
donating groups were used (2c, d and g). For 1,3-diarylpropynes,
electron-donating substituents were favourable to obtain high
yields (2a, i, k and l), but electron-withdrawing groups were

H. Mo, W. Bao / Tetrahedron 67 (2011) 4793e4799
4795
Table 2
Formation of propargyl ethers between 1,3-diarylpropynes and alcoholsa,b
a
1,3-Diarylpropynes (0.25 mmol), 0.27 mmol of alcohols, 0.25 mmol of DDQ, 1 mL of CH2Cl2, 0 ꢀC, 2 h.
Isolated yield.
b
Table 3
Formation of propargyl ethers between 1,3-diarylpropynes and phenolsa,b
a
1,3-Diarylpropynes (0.25 mmol), 0.27 mmol of phenols, 0.25 mmol of DDQ, 1 mL of CH2Cl2, 0 ꢀC, 30 min.
Isolated yield.
b
3. Conclusion
4. Experimental section
4.1. General procedure for products 1
To mL round-bottom flask with
In summary, we have developed an efficient cross-coupling re-
action between 1,3-diarylpropynes and alcohols/phenols/acids to
form CeO bonds via sp3 CeH bond activation promoted by DDQ.
This provides a wide scope of propargyl ethers/esters and propargyl
ketals in scientific research.
a
5
a
mixture of 1,3-
diarylpropynes (0.25 mmol) and alcohol (0.3 mmol) in CH2Cl2
(1 mL), DDQ (0.27 mmol) was added at 0 ꢀC. The resulting mixture

4796
H. Mo, W. Bao / Tetrahedron 67 (2011) 4793e4799
was stirred for 1 h. Purification was done by column chromatog-
O
O
DDQ (2.0eq)
CH2Cl2, 0oC
OH
80%
OMe
raphy on silica gel (petroleum ether/ethyl acetate¼20/1), and the
+
HO
HO
OMe
fraction with an Rf¼0.6 was collected to give the desired product.
3a
4.1.1. 1-(1-Ethoxy-3-phenylprop-2-ynyl)-4-methoxybenzene
(1a). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d¼7.53e7.46 (m,
O
O
DDQ (2.0eq)
CH2Cl2, 0oC
83%
OMe
4H), 7.33e7.30 (m, 3H), 6.94e6.91 (m, 2H), 5.35 (s, 1H), 3.82 (s, 3H),
3.80e3.59 (m, 2H), 1.28 (t, J¼7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3):
+
OH
OMe
3b
d
¼15.2, 55.3,63.7, 71.4, 87.0, 87.5,113.8,122.7,128.2,128.3,128.8,131.2,
Scheme 1.
131.7, 159.6. IR (neat): 3058, 2926, 2857, 2221, 1609, 1512, 1465, 1249,
1170, 1077, 1036, 921, 828, 753, 690 cmꢁ1. MS (70 eV, EI) m/z¼266.
Table 4
Screening of cross-coupling reaction conditions between 1,3-diarylpropynes and acidsa
O
O
O
DDQ
+
OH
CH2Cl2
OMe
OMe
4a
Entry
Temp (ꢀC)
Time (min)
Yieldb (%)
1
2
3
4
5
6
0
120
120
120
60
30
10
29
36
17
45
61
57
rt
50
rt
rt
rt
a
1-Phenyl-3-(40-methoxyl)phenylpropyne (0.25 mmol), 0.27 mmol of acetic acid, 1 mL of CH2Cl2.
Isolated yield.
b
Table 5
4.1.2. 1-(1-(Hexyloxy)-3-phenylprop-2-ynyl)-4-methoxybenzene
(1b). Light yellow oil. 1H NMR (400 MHz, CDCl3):
Formation of propargyl esters between 1,3-diarylpropynes and acidsa,b
d¼7.52e7.46 (m,
4H), 7.33e7.30 (m, 3H), 6.92 (d, J¼8.4 Hz, 2H), 5.34 (s, 1H), 3.82 (s,
3H), 3.73e3.51 (m, 2H),1.66e1.60 (m, 2H),1.40e1.26 (m, 6H), 0.88 (t,
J¼6.8 Hz, 3H). 13C NMR (100 MHz, CDCl3):
¼13.9, 22.5, 25.8, 29.6,
d
31.5, 55.2, 68.2, 71.4, 87.0, 87.5, 113.7, 122.7, 128.1, 128.3, 128.7, 131.2,
131.7,159.5. IR (neat): 3056, 2927, 2856, 2223,1610,1511, 1461, 1247,
1173, 1076, 1034, 916, 827, 755, 691 cmꢁ1. MS (70 eV, EI) m/z¼322.
HRMS (EI): m/z calcd for C22H26O2 (Mþ): 322.1933. Found, 322.1931.
½ꢂ
4.1.3. 1-(1-(Benzyloxy)-3-phenylprop-2-ynyl)-4-methoxybenzene
(1c). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.51e7.21 (m,
12H), 6.90 (d, J¼8.4 Hz, 2H), 5.38 (s, 1H), 4.75e4.66 (m, 2H), 3.79 (s,
3H). 13C NMR (100 MHz, CDCl3):
d¼55.2, 69.8, 70.5, 87.0, 87.6, 113.8,
122.6,127.6,128.1,128.2,128.3,128.4,128.9,130.8,131.7,137.8,159.7.
IR (neat): 3056, 2926, 2859, 2227, 1609, 1511, 1491, 1457, 1302, 1248,
1173, 1031, 917, 830, 753, 693 cmꢁ1. MS (70 eV, EI) m/z¼328. HRMS
(EI): m/z calcd for C23H20O2 (Mþ): 328.1463. Found, 328.1465.
a
1,3-Diarylpropynes (0.25 mmol), 0.27 mmol of acids, 0.25 mmol of DDQ, 1.5 mL
of CH2Cl2, room temperature, 30 min.
b
4.1.4. 1-Methoxy-4-(1-phenethoxy-3-phenylprop-2-ynyl)benzene
Isolated yield.
(1d). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.45e7.42 (m,
4H), 7.29e7.17 (m, 8H), 6.87 (d, J¼8.8 Hz, 2H), 5.34 (s, 1H),
3.93e3.71 (m, 2H), 3.78 (s, 3H), 2.94 (t, J¼7.2 Hz, 2H). 13C NMR
OH
O
O
H
Cl
Cl
CN
CN
H
(100 MHz, CDCl3):
d
¼36.2, 55.2, 68.9, 71.6, 87.1, 87.3, 113.7, 122.6,
Cl
Cl
CN
CN
126.1, 128.17, 128.2, 128.4, 128.8, 128.9, 130.9, 131.7, 138.8, 159.6. IR
(neat): 3061, 3028, 2923, 2855, 2221, 1608, 1510, 1457, 1247, 1173,
1070, 1032, 828, 753, 693 cmꢁ1. MS (70 eV, EI) m/z¼342. HRMS (EI):
m/z calcd for C24H22O2 (Mþ): 342.1620. Found, 342.1624.
+
R1
R1
R2
O
R2
OH
O
Cl
Cl
CN
CN
+
OH
4.1.5. 1-Methoxy-4-(3-phenyl-1-(3-phenylpropoxy)prop-2-ynyl)ben-
R1
zene (1e). Light yellow oil. 1H NMR (400 MHz, CDCl3):
(m, 12H), 6.91e6.88 (m, 2H), 5.31 (s, 1H), 3.79 (s, 3H), 3.75e3.50 (m,
2H), 2.71 (t, J¼7.6 Hz, 2H), 1.98e1.90 (m, 2H). 13C NMR (100 MHz,
d
¼7.51e7.13
OH
R2
1
Scheme 2. A possible mechanism.

H. Mo, W. Bao / Tetrahedron 67 (2011) 4793e4799
4797
CDCl3):
d
¼31.2, 32.3, 55.2, 67.2, 71.6, 87.1, 87.4, 113.8, 122.6, 125.6,
(100 MHz, CDCl3):
d
¼15.1, 15.2, 28.7, 63.8, 71.8, 86.5, 87.4, 119.7,
128.17, 128.2, 128.3, 128.5, 128.8, 131.1, 131.7, 141.9, 159.6. IR (neat):
3056, 3028, 2924, 2855, 2223, 1609, 1510, 1453, 1247, 1173, 1070,
1033, 915, 828, 753, 693 cmꢁ1. MS (70 eV, EI) m/z¼356. HRMS (EI):
m/z calcd for C25H24O2 (Mþ): 356.1776. Found, 356.1777.
127.4, 127.7, 128.2, 128.4, 131.7, 139.0, 144.8. IR (neat): 3030, 2968,
2928, 2870, 2223, 1510, 1452, 1308, 1162, 1070, 1021, 972, 918, 885,
751, 697 cmꢁ1. MS (70 eV, EI) m/z¼264. HRMS (EI): m/z calcd for
C19H20O (Mþ): 264.1514. Found, 264.1517.
4.1.6. 1-Methoxy-4-(1-(1-methylcyclohexyloxy)-3-phenylprop-2-
4.1.13. 1-(3-Ethoxy-3-phenylprop-1-ynyl)-4-methoxybenzene
ynyl)benzene (1f). Light yellow oil. 1H NMR (400 MHz, CDCl3):
(1m). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.61e7.34 (m,
d
¼7.52e7.29 (m, 7H), 6.90 (d, J¼9.2 Hz, 2H), 5.44 (s,1H), 3.87 (s, 3H),
2.01e1.97 (m, 2H), 1.78e1.75 (m, 2H), 1.58e1.22 (m, 9H). 13C NMR
(100 MHz, CDCl3):
7H), 6.85 (d, J¼8.8 Hz, 2H), 5.39 (s, 1H), 3.82 (s, 3H), 3.82e3.59 (m,
2H), 1.30 (t, J¼6.8 Hz, 3H). 13C NMR (100 MHz, CDCl3):
¼15.1, 55.2,
d
d
¼24.1, 24.2, 24.3, 25.7, 31.8, 32.9, 55.2, 68.5, 75.5,
63.7, 71.9, 85.8, 87.1, 113.8, 114.7, 127.4, 128.1, 128.4, 133.2, 139.1,
159.6. IR (neat): 3061, 2972, 2925, 2222, 1747, 1605, 1508, 1453,
1289, 1173, 1070, 1030, 885, 831, 753, 698 cmꢁ1. MS (70 eV, EI) m/
z¼266. HRMS (EI): m/z calcd for C18H18O2 (Mþ): 266.1307. Found,
266.1309.
86.2, 88.3,113.7,122.8,128.1,128.2,128.6,131.7,131.9,159.4. IR (neat):
3056, 3000, 2929, 2855, 2225, 1610, 1510, 1448, 1246, 1173, 1065,
1032, 946, 825, 755, 691 cmꢁ1. MS (70 eV, EI) m/z¼334. HRMS (EI):
m/z calcd for C23H26O2 (Mþ): 334.1933. Found, 334.1930.
4.1.7. 1-(1-(Allyloxy)-3-phenylprop-2-ynyl)-4-methoxybenzene
4.1.14. 1-Chloro-4-(1-ethoxy-3-phenylprop-2-ynyl)benzene1
(1g). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.53e7.30 (m,
(1n). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.54e7.31 (m,
7H), 6.92 (d, J¼8.8 Hz, 2H), 6.04e5.94 (m, 1H), 5.40 (s, 1H),
9H), 5.36 (s, 1H), 3.85e3.57 (m, 2H), 1.28 (t, J¼7.2 Hz, 3H). 13C NMR
5.38e5.21 (m, 2H), 4.26e4.13 (m, 2H), 3.82 (s, 3H). 13C NMR
(100 MHz, CDCl3):
d
¼15.1, 63.9, 71.1, 86.6, 87.5, 122.3, 128.2, 128.5,
(100 MHz, CDCl3):
d
¼55.2, 68.9, 70.6, 87.1, 87.3, 113.8, 117.6, 122.6,
128.55, 128.7, 131.7, 134.0, 137.5. IR (neat): 3060, 2975, 2870, 2221,
128.2, 128.4, 128.8, 130.9, 131.7, 134.3, 159.6. IR (neat): 3056, 2925,
2853, 2226, 1610, 1511, 1460, 1302, 1247, 1173, 1034, 924, 827, 756,
691 cmꢁ1. MS (70 eV, EI) m/z¼278. HRMS (EI): m/z calcd for
C19H18O2 (Mþ): 278.1307. Found, 278.1301.
1596, 1488, 1444, 1290, 1169, 1081, 1014, 915, 890, 754, 690 cmꢁ1
.
MS (70 eV, EI) m/z¼270.
4.2. General procedure for products 2
4.1.8. 1-Methoxy-4-(3-phenyl-1-(prop-2-ynyloxy)prop-2-ynyl)ben-
To a 5 mL round-bottom flask with a mixture of 1,3-
zene (1h). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.53e7.24
diarylpropynes (0.25 mmol) and phenol (0.3 mmol) in CH2Cl2
(1 mL), DDQ (0.27 mmol) was added at 0 ꢀC. The resulting mixture
was stirred for 0.5 h. Purification was done by column chromatog-
raphy on silica gel (petroleum ether/ethyl acetate¼20/1), and the
fraction with an Rf¼0.5 was collected to give the desired product.
(m, 7H), 6.93e6.89 (m, 2H), 5.59 (s, 1H), 4.44e4.24 (m, 2H), 3.81 (s,
3H), 2.48 (t, J¼2.8 Hz, 1H). 13C NMR (100 MHz, CDCl3):
¼55.16,
d
55.23, 70.1, 74.8, 79.4, 86.1, 87.8, 113.9, 122.3, 128.2, 128.5, 129.1,
130.0, 131.7, 159.8. IR (neat): 3290, 3056, 2926, 2856, 2225, 1610,
1511, 1443, 1302, 1248, 1174, 1055, 1031, 927, 827, 756, 689 cmꢁ1. MS
(70 eV, EI) m/z¼276. HRMS (EI): m/z calcd for C19H16O2 (Mþ):
276.1150. Found, 276.1146.
4.2.1. 1-Methoxy-4-(1-phenoxy-3-phenylprop-2-ynyl)benzene
(2a). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.60 (d,
J¼8.8Hz, 2H), 7.45e6.94 (m, 12H), 6.00 (s, 1H), 3.83 (s, 3H). 13C NMR
4.1.9. 2-((1-(4-Methoxyphenyl)-3-phenylprop-2-ynyloxy)methyl)fu-
(100 MHz, CDCl3):
d
¼55.6, 70.7, 86.9, 88.5, 114.3, 116.7, 121.8, 122.6,
ran (1i). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.52e7.25
128.5, 128.9, 129.2, 129.6, 130.5, 132.0, 157.9, 160.2. IR (neat): 3056,
3004, 2930, 2834, 2225, 1591, 1489, 1460, 1303, 1249, 1219, 1173,
1110, 1074, 1031, 962, 870, 752, 689 cmꢁ1. MS (70 eV, EI) m/z¼314.
HRMS (EI): m/z calcd for C22H18O2 (Mþ): 314.1307. Found, 314.1301.
(m, 8H), 6.91 (d, J¼8.8 Hz, 2H), 6.39e6.35 (m, 2H), 5.41 (s, 1H), 4.67
(d, J¼4.8 Hz, 2H), 3.82 (s, 3H). 13C NMR (100 MHz, CDCl3):
¼55.3,
d
61.7, 70.4, 86.7, 87.7, 109.8, 110.3, 113.8, 122.6, 128.2, 128.5, 129.0,
130.5, 131.8, 142.9, 151.4, 159.7. IR (neat): 3059, 2931, 2858, 2226,
1641, 1463, 1248, 1176, 1075, 1031, 922, 831, 751, 689 cmꢁ1. MS
(70 eV, EI) m/z¼318. HRMS (EI): m/z calcd for C21H18O3 (Mþ):
318.1256. Found, 318.1253.
4.2.2. 1-Chloro-4-(1-(4-methoxyphenyl)-3-phenylprop-2-ynyloxy)
benzene (2b). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d¼7.56
(d, J¼8.4 Hz, 2H), 7.43e7.23 (m, 7H), 7.05 (d, J¼9.2 Hz, 2H), 6.94 (d,
J¼8.8 Hz, 2H), 5.93 (s, 1H), 3.82 (s, 3H). 13C NMR (100 MHz, CDCl3):
4.1.10. 1-(1-Ethoxy-3-phenylprop-2-ynyl)-4-methylbenzene1
d
¼55.3, 70.8, 86.0, 88.5, 114.0, 117.8, 122.0, 126.5, 128.2, 128.7, 128.9,
(1j). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.50e7.19 (m,
9H), 5.36 (s, 1H), 3.83e3.58 (m, 2H), 2.37 (s, 3H), 1.29 (t, J¼7.6 Hz,
3H). 13C NMR (100 MHz, CDCl3):
129.2, 129.7, 131.7, 156.0, 160.0. IR (neat): 3060, 3028, 2925, 2857,
2227, 1610, 1511, 1486, 1302, 1249, 1224, 1173, 1091, 1032, 960, 872,
755, 690 cmꢁ1. MS (70 eV, EI) m/z¼349. HRMS (EI): m/z calcd for
C22H17ClO2 (Mþ): 348.0917. Found, 348.0912.
d
¼15.1, 21.1, 63.7, 71.7, 87.0, 87.4,
122.7, 127.4, 128.1, 128.3, 129.1, 131.7, 136.0, 138.0. IR (neat): 3056,
2923, 2863, 2222, 1718, 1599, 1512, 1489, 1444, 1305, 1176, 1073,
1023, 889, 812, 754, 691 cmꢁ1. MS (70 eV, EI) m/z¼250.
4.2.3. 1-Methoxy-4-(3-phenyl-1-(p-tolyloxy)prop-2-ynyl)benzene
(2c). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d¼7.58 (d,
4.1.11. (3-Ethoxyprop-1-yne-1,3-diyl)dibenzene1 (1k). Light yellow
J¼8.8 Hz, 2H), 7.44e7.27 (m, 5H), 7.09 (d, J¼8.4 Hz, 2H), 7.02 (d,
J¼8.8 Hz, 2H), 6.93 (d, J¼8.8 Hz, 2H), 5.94 (s, 1H), 3.81 (s, 3H), 2.29
oil. 1H NMR (400 MHz, CDCl3):
d
¼7.60e7.30 (m, 10H), 5.39 (s, 1H),
3.85e3.59 (m, 2H), 1.31e1.26 (t, J¼7.6 Hz, 3H). 13C NMR (100 MHz,
(s, 3H). 13C NMR (100 MHz, CDCl3):
d
¼20.5, 55.2, 70.6, 86.7, 88.0,
CDCl3):
d¼15.1, 63.8, 71.8, 87.17, 87.19, 122.6, 127.4, 128.1, 128.2,
113.9,116.3,122.3,128.1,128.5,128.8, 129.7,130.3,130.8,131.7,155.4,
159.8. IR (neat): 3061, 3033, 3000, 2923, 2856, 2224, 1610, 1508,
1460,1303,1248,1219,1173,1110,1032, 964, 873, 755, 690 cmꢁ1. MS
(70 eV, EI) m/z¼328. HRMS (EI): m/z calcd for C23H20O2 (Mþ):
328.1463. Found, 328.1459.
128.3, 128.4, 131.7, 138.9. IR (neat): 3059, 2974, 2926, 2223, 1599,
1489, 1449, 1309, 1160, 1070, 1027, 917, 885, 755, 692 cmꢁ1. MS
(70 eV, EI) m/z¼236.
4.1.12. 1-(3-Ethoxy-3-phenylprop-1-ynyl)-4-ethylbenzene (1l). Light
yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.65e7.36 (m, 7H), 7.18 (d,
4.2.4. 1-Methoxy-4-(1-(4-methoxyphenoxy)-3-phenylprop-2-ynyl)
J¼8.4 Hz, 2H), 5.43 (s, 1H), 3.88e3.63 (m, 2H), 2.68 (q, J1¼7.6 Hz,
benzene (2d). Light yellow oil. 1H NMR (400 MHz, CDCl3):
J2¼15.2 Hz, 2H), 1.32 (t, J¼6.8 Hz, 3H), 1.27 (t, J¼7.6 Hz, 3H). 13C NMR
d
¼7.59e6.82 (m, 13H), 5.89 (s, 1H), 3.83 (s, 3H), 3.77 (s, 3H). 13C

4798
H. Mo, W. Bao / Tetrahedron 67 (2011) 4793e4799
NMR (100 MHz, CDCl3):
d
¼55.2, 55.6, 71.7, 86.7, 88.1, 113.9, 114.4,
138.2, 157.6, 159.9. IR (neat): 3056, 2922, 2856, 2224, 1724, 1601,
1491, 1455, 1290, 1221, 1172, 1107, 1076, 1030, 963, 863, 751,
693 cmꢁ1. MS (70 eV, EI) m/z¼314. HRMS (EI): m/z calcd for
C22H18O2 (Mþ): 314.1307. Found, 314.1309.
118.1, 128.1, 128.3, 128.5, 128.9, 130.3, 131.7, 151.5, 154.5, 159.8. IR
(neat): 3058, 2929, 2835, 2223, 1609, 1505, 1461, 1302, 1247, 1210,
1174, 1107, 1032, 964, 873, 755, 691 cmꢁ1. MS (70 eV, EI) m/z¼344.
HRMS (EI): m/z calcd for C23H20O3 (Mþ): 344.1412. Found, 344.1417.
4.2.12. 1-Ethyl-4-(3-phenoxy-3-phenylprop-1-ynyl)benzene
4.2.5. 1-Bromo-4-(1-(4-methoxyphenyl)-3-phenylprop-2-ynyloxy)
(2l). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.74e7.02 (m,
14H), 6.08 (s, 1H), 2.63 (q, J1¼8 Hz, J2¼11.2 Hz, 2H), 1.25 (q, J¼7.6 Hz,
3H). 13C NMR (100 MHz, CDCl3):
benzene (2e). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.59e6.94 (m, 13H), 5.95 (s, 1H), 3.83 (s, 3H). 13C NMR (100 MHz,
d
¼15.3, 28.8, 70.8, 85.7, 88.6, 116.3,
CDCl3):
d
¼55.3, 70.7, 85.9, 88.6, 113.8, 114.0, 118.2, 122.0, 128.2,
119.4, 121.6, 127.4, 127.8, 128.6, 129.4, 131.8, 138.1, 145.2, 157.6. IR
(neat): 3056, 3030, 2964, 2926, 2862, 2225, 1593, 1492, 1453, 1306,
1221, 1174, 1076, 1026, 965, 863, 750, 693 cmꢁ1. MS (70 eV, EI) m/
z¼312. HRMS (EI): m/z calcd for C23H20O (Mþ): 312.1514. Found,
312.1517.
128.7, 128.9, 129.6, 131.7, 132.1, 159.8. IR (neat): 3056, 2926, 2856,
2223, 1610, 1511, 1484, 1303, 1250, 1223, 1173, 1109, 1071, 1032, 960,
872, 755, 690 cmꢁ1. MS (70 eV, EI) m/z¼393. HRMS (EI): m/z calcd
for C22H17BrO2 (Mþ): 392.0412. Found, 392.0405.
4.2.6. 1-Chloro-3-(1-(4-methoxyphenyl)-3-phenylprop-2-ynyloxy)-
4.3. General procedure for products 3
2-methylbenzene (2f). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.58 (d, J¼8.4 Hz, 12H), 7.43e6.94 (m, 9H), 5.94 (s, 1H), 3.84 (s,
To a 5 mL round-bottom flask with a mixture of 1,3-
3H), 2.31 (s, 3H). 13C NMR (100 MHz, CDCl3):
d
¼13.1, 55.2, 71.3, 86.3,
diarylpropynes (0.25 mmol) and diol (0.3 mmol) in CH2Cl2
(1 mL), DDQ (0.55 mmol) was added at 0 ꢀC. The resulting mixture
was stirred for 1 h. Purification was done by column chromatog-
raphy on silica gel (petroleum ether/ethyl acetate¼10/1), and the
fraction with an Rf¼0.6 was collected to give the desired product.
88.2, 112.8, 113.9, 122.1, 122.4, 126.4, 128.2, 128.6, 128.7, 129.6, 130.1,
131.6, 135.1, 156.5, 159.9. IR (neat): 3062, 2928, 2827, 2228, 1610,
1462, 1249, 1172, 1070, 1031, 962, 855, 751, 689 cmꢁ1. MS (70 eV, EI)
m/z¼363. HRMS (EI): m/z calcd for C23H19ClO2 (Mþ): 362.1074.
Found, 362.1072.
4.3.1. 2-(4-Methoxyphenyl)-2-(phenylethynyl)-1,3-dioxolane
4.2.7. 2,4-Di-tert-butyl-1-(1-(4-methoxyphenyl)-3-phenylprop-2-
(3a). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.72 (d,
ynyloxy)benzene (2g). Light yellow oil. 1H NMR (400 MHz, CDCl3):
J¼8.8 Hz, 2H), 7.52e7.32 (m, 5H), 6.94 (d, J¼8.8 Hz, 2H), 4.35e4.31
d
¼7.49e6.82 (m, 12H), 5.67 (s, 1H), 3.82 (s, 3H), 1.42 (s, 9H), 1.31 (s,
(m, 2H), 4.22e4.18 (m, 2H), 3.84 (s, 3H). 13C NMR (100 MHz, CDCl3):
9H). 13C NMR (100 MHz, CDCl3):
d
¼29.8, 31.6, 34.3, 35.0, 39.5, 55.2,
d
¼55.3, 65.1, 85.6, 86.4, 113.5, 113.9, 121.9, 127.5, 128.2, 128.8, 131.9,
86.1, 88.7, 113.8, 114.1, 123.2, 124.4, 126.5, 128.3, 128.7, 129.7, 131.5,
131.7, 136.8, 142.3, 150.5, 158.7. IR (neat): 2955, 2924, 2857, 2221,
1608,1461,1298,1248,1176,1115,1035, 882, 824, 755, 690 cmꢁ1. MS
(70 eV, EI) m/z¼426. HRMS (EI): m/z calcd for C30H34O2 (Mþ):
426.2559. Found, 426.2561.
132.9, 160.3. IR (neat): 3060, 2923, 2856, 2198, 1632, 1595, 1510,
1489, 1462, 1287, 1251, 1165, 1077, 1027, 967, 830, 756, 689 cmꢁ1. MS
(70 eV, EI) m/z¼280. HRMS (EI): m/z calcd for C18H16O3 (Mþ):
280.1099. Found, 280.1097.
4.3.2. 2-(4-Methoxyphenyl)-5,5-dimethyl-2-(phenylethynyl)-1,3-
4.2.8. (3-Phenoxyprop-1-yne-1,3-diyl)dibenzene2 (2h). Light yellow
dioxane (3b). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.80 (d,
oil. 1H NMR (400 MHz, CDCl3):
d
¼7.72 (d, J¼7.6 Hz, 2H), 7.49e7.04
J¼8.8 Hz, 2H), 7.58e7.37 (m, 5H), 6.95 (d, J¼8.8 Hz, 2H), 4.25 (d,
(m, 13H), 6.08 (s, 1H). 13C NMR (100 MHz, CDCl3):
d
¼70.7, 86.3, 88.4,
J¼10.8 Hz, 2H), 3.85 (s, 3H), 3.66 (d, J¼10.8 Hz, 2H), 1.33 (s, 3H), 0.88
116.3, 121.6, 122.2, 127.4, 128.2, 128.66, 128.7, 129.4, 131.8, 138.0,
157.6. IR (neat): 3060, 3033, 2922, 2856, 2225, 1592, 1489, 1450,
1306, 1220, 1173, 1075, 1030, 965, 863, 751, 689 cmꢁ1. MS (70 eV, EI)
m/z¼284.
(s, 3H). 13C NMR (100 MHz, CDCl3):
d
¼22.0, 23.2, 29.9, 55.3, 73.4,
84.7, 88.3, 96.0, 113.5, 122.0, 127.2, 128.4, 128.9, 131.9, 133.6, 160.1. IR
(neat): 3058, 2954, 2864, 2221, 1612, 1513, 1489, 1464, 1279, 1208,
1172, 1087, 1036, 982, 831, 756, 690 cmꢁ1. MS (70 eV, EI) m/z¼322.
HRMS (EI): m/z calcd for C21H22O3 (Mþ): 322.1569. Found, 322.1571.
4.2.9. 1-Methyl-4-(1-phenoxy-3-phenylprop-2-ynyl)benzene
(2i). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.61 (d,
4.4. General procedure for products 4
J¼8.0 Hz, 2H), 7.49e7.02 (m, 12H), 6.06 (s, 1H), 2.42 (s, 3H). 13C NMR
(100 MHz, CDCl3):
d
¼21.2, 70.6, 86.6, 88.2, 116.3, 121.6, 122.3, 127.4,
To a 5 mL round-bottom flask with a mixture of 1,3-
128.2, 128.6, 129.4, 131.8, 135.1, 138.6, 157.6. IR (neat): 3061, 2921,
2853, 2224, 1592, 1489, 1445, 1304, 1220, 1176, 1074, 1030, 964, 872,
751, 689 cmꢁ1. MS (70 eV, EI) m/z¼298. HRMS (EI): m/z calcd for
C22H18O (Mþ): 298.1358. Found, 298.1359.
diarylpropynes (0.25 mmol) and acid (0.3 mmol) in CH2Cl2
(1 mL), DDQ (0.27 mmol) was added at room temperature. The
resulting mixture was stirred for 30 min. Purification was done by
column chromatography on silica gel (petroleum ether/ethyl
acetate¼10/1), and the fraction with an Rf¼0.5 was collected to give
the desired product.
4.2.10. 1-Chloro-4-(1-phenoxy-3-phenylprop-2-ynyl)benzene
(2j). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.64 (d,
J¼8.8 Hz, 2H) 7.47e7.02 (m, 12H), 6.04 (s, 1H). 13C NMR (100 MHz,
4.4.1. 1-(4-Methoxyphenyl)-3-phenylprop-2-ynyl acetate (4a). Light
CDCl3):
d
¼70.0, 85.9, 88.6, 116.3, 121.8, 122.0, 128.3, 128.4, 128.7,
yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.56 (d, J¼6.8 Hz, 2H),
7.51e7.32 (m, 5H), 6.94 (d, J¼6.8 Hz, 2H), 6.68 (s, 1H), 3.84 (s, 3H),
2.13 (s, 3H). 13C NMR (100 MHz, CDCl3):
128.8, 129.4, 131.8, 134.6, 136.6, 157.3. IR (neat): 3059, 2919, 2227,
1593, 1489, 1406, 1305, 1220, 1173, 1089, 1014, 966, 871, 751,
688 cmꢁ1. MS (70 eV, EI) m/z¼319. HRMS (EI): m/z calcd for
C21H15ClO (Mþ): 318.0811. Found, 318.0807.
d
¼21.2, 55.3, 65.8, 85.8,
86.8, 114.0, 122.2, 128.3, 128.7, 129.38, 129.4, 131.9, 160.1, 169.9. IR
(neat): 3056, 2956, 2925, 2862, 2222, 1738, 1492, 1453, 1306, 1219,
1176, 1077, 963, 875, 755, 690 cmꢁ1. MS (70 eV, EI) m/z¼280.
4.2.11. 1-Methoxy-4-(3-phenoxy-3-phenylprop-1-ynyl)benzene
(2k). Light yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼7.70 (d,
J¼7.6 Hz, 2H), 7.47e7.00 (m, 10H), 6.84 (d, J¼8.8 Hz, 2H), 6.06 (s,
1H), 3.81 (s, 3H). 13C NMR (100 MHz, CDCl3):
¼55.2, 70.8, 85.0,
88.4, 113.8, 116.3, 121.5, 127.4, 128.3, 128.6, 128.62, 129.3, 133.3,
4.4.2. 3-Phenyl-1-p-tolylprop-2-ynyl acetate (4b). Light yellow oil.
1H NMR (400 MHz, CDCl3):
d
¼7.53e7.23 (m, 9H), 6.70 (s, 1H), 2.40
(s, 3H), 2.14 (s, 3H). 13C NMR (100 MHz, CDCl3):
¼21.1, 21.2, 66.0,
85.8, 86.8, 122.2, 127.8, 128.2, 128.7, 129.3, 131.9, 134.3, 138.9, 169.8.
d
d

H. Mo, W. Bao / Tetrahedron 67 (2011) 4793e4799
4799
3. Lam, F. K.; Au-Yeung, TT.-L.; Kwong, F. Y.; Zhou, Z.; Wong, K. Y.; Chan, A. S. C.
Angew. Chem. 2008, 120, 1300e1303; Angew. Chem., Int. Ed. 2008, 47, 1280e1283.
4. For transition metal-catalyzed ether formation, see (a) Kayaki, Y.; Koda, T.;
Ikariya, T. J. Org. Chem. 2004, 69, 2595e2597; (b) Gao, G.-Y. V.; Ruppel, J.; Fields,
K. B.; Xu, X.; Chen, Y.; Zhang, X. P. J. Org. Chem. 2008, 73, 4855e4858; (c) Niu, J.
J.; Zhou, H.; Li, Zh. G.; Xu, J. W.; Hu, Sh. J. J. Org. Chem. 2008, 73, 7814e7817; (d)
Chen, G. Sh.; Chan, A. S. C.; Kwong, F. Y. Tetrahedron Lett. 2007, 48, 473e476; (e)
Kuwabe, S.; Torraca, K. E.; Buchwald, S. L. J. Am. Chem. Soc. 2001, 123,
12202e12206; (f) Vorogushin, A. V.; Huang, X. H.; Buchwald, S. L. J. Am. Chem.
Soc. 2005, 127, 8146e8149; (g) Shelby, Q.; Kataoka, N.; Mann, G.; Hartwig, J. J.
Am. Chem. Soc. 2000, 122, 10718e10719; (h) Lim, C.; Kang, J.-E.; Lee, J.-E.; Shin, S.
Org. Lett. 2007, 9, 3539e3542; (i) Sherry, B. D.; Radosevich, A. T.; Toste, F. D. J.
Am. Chem. Soc. 2003, 125, 6076e6077; (j) Liu, Y.; Hua, R. M.; Sun, H.-B.; Qiu, X.
Q. Organometallics 2005, 24, 2819e2821; (k) Sawyer, J. S. Tetrahedron 2000, 56,
5045e5065; (l) Palucki, M.; Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1996,
118, 10333e10334.
5. For metal-free ether formation, see (a) Patra, A.; Roy, A. K.; Joshi, B. S.; Roy, R.;
Batra, S.; Bhaduri, A. P. Tetrahedron 2003, 59, 663e670; (b) Protti, S.; Fagnoni,
M.; Albini, A. J. Am. Chem. Soc. 2006, 128, 10670e10671.
6. For transition metal-catalyzed direct CeH functionalization to form CeO bonds,
see (a) Lee, J. M.; Park, E. J.; Cho, S. H.; Chang, S. J. Am. Chem. Soc. 2008, 130,
7824e7825; (b) Canty, A. J.; Denney, M. C.; Koten, G.; Skelton, B. W.; White, A.
H. Organometallics 2004, 23, 5432e5439; (c) Lee, J. M.; Chang, S. Tetrahedron
Lett. 2006, 47, 1375e1379.
IR (neat): 3058, 2952, 2926, 2227, 1735, 1491, 1309, 1223, 1174, 1075,
962, 871, 753, 691 cmꢁ1. MS (70 eV, EI) m/z¼264.
4.4.3. 1-(4-Methoxyphenyl)-3-phenylprop-2-ynyl benzoate (4c). Light
yellow oil. 1H NMR (400 MHz, CDCl3):
d
¼8.11 (d, J¼6.0 Hz, 2H),
7.67e7.27 (m, 10H), 6.97 (d, J¼6.8 Hz, 2H), 6.93 (s, 1H), 3.84 (s, 3H).
13C NMR (100 MHz, CDCl3):
d¼55.3, 66.4, 85.9, 87.2, 114.0, 122.2,
128.2, 128.3, 128.7, 128.8, 129.4, 129.5, 129.9, 131.9, 133.1, 160.1, 165.5.
IR (neat): 3062, 2957, 2929, 2226, 1738, 1310, 1222, 1176, 1076, 961,
875, 755, 693 cmꢁ1. MS (70 eV, EI) m/z¼342. HRMS (EI): m/z calcd for
C23H18O3 (Mþ): 342.1256. Found, 342.1252.
4.4.4. 3-Phenyl-1-p-tolylprop-2-ynyl benzoate (4d). Light yellow
oil. 1H NMR (400 MHz, CDCl3):
d
¼8.16e7.27 (m, 14H), 6.98 (s, 1H),
2.41 (s, 3H). 13C NMR (100 MHz, CDCl3):
d
¼21.2, 66.5, 85.8, 87.1,
122.2, 127.8, 128.2, 128.3, 128.7, 129.3, 129.9, 131.9, 133.1, 134.4,
138.8, 165.4. IR (neat): 3061, 2956, 2928, 2221, 1732, 1309, 1227,
1169, 1071, 961, 872, 752, 691 cmꢁ1. MS (70 eV, EI) m/z¼326. HRMS
(EI): m/z calcd for C23H18O2 (Mþ): 326.1307. Found, 326.1303.
7. (a) Trost, B. M. Acc. Chem. Res. 2002, 35, 695e705; (b) Trost, B. M. Angew. Chem.
1995, 107, 285e307; Angew. Chem., Int. Ed. Engl. 1995, 34, 259e281; (c) Trost, B.
M. Science 1991, 254, 1471e1477.
Acknowledgements
8. Winterton, N. Green Chem. 2001, 3, G73.
9. (a) Pu, X.; Qi, X.; Ready, M. J. J. Am. Chem. Soc. 2009, 131, 10364e10365; (b)
ꢀ
Barluenga, J.; Riesgo, L.; Vicente, R.; Lopez, A. L.; Tomas, M. J. Am. Chem. Soc.
This work was financially supported by the Natural Science
Foundation of China (No. 21072168).
2008, 130, 13528e13529; (c) Bolte, B.; Odabachian, Y.; Gagosz, F. J. Am. Chem.
Soc. 2010, 132, 7294e7296; (d) Facoetti, D.; Abbiati, G.; Rossi, E. Eur. J. Org.
Chem. 2009, 2872e2882; (e) Shu, X.-Z.; Zhao, S.-C.; Ji, K.-G.; Zheng, Z.-J.; Liu,
X.-Y.; Liang, Y.-M. Eur. J. Org. Chem. 2009, 117e122; (f) Barluenga, J.; Trincado,
Supplementary data
ꢀ
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References and notes
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