NHC-Pd(II)-Im (NHC=N-heterocyclic carbene, Im=1-methylimidazole) complex catalyzed coupling reaction of arylboronic acids with carboxylic acid anhydrides in water

Article abstract of DOI:10.1016/j.tet.2012.05.016

A well-defined N-heterocyclic carbene (NHC)-palladium chloride-imidazole complex exhibited high catalytic activity in the coupling reaction of arylboronic acids with carboxylic acid anhydrides in pure water under mild conditions. Under the optimal conditions, all reactions gave the desired coupling products in moderate to high yields.

Full text of DOI:10.1016/j.tet.2012.05.016

Tetrahedron 68 (2012) 5806e5809
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
NHCePd(II)eIm (NHC¼N-heterocyclic carbene, Im¼1-methylimidazole) complex
catalyzed coupling reaction of arylboronic acids with carboxylic acid anhydrides
in water
*
Xiao-Fang Lin, Yao Li, Shuang-Yan Li, Zheng-Kang Xiao, Jian-Mei Lu
College of Chemistry and Materials Engineering, Wenzhou University, Chashan University Town, Wenzhou, Zhejiang Province 325035, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A well-defined N-heterocyclic carbene (NHC)epalladium chlorideeimidazole complex exhibited high
catalytic activity in the coupling reaction of arylboronic acids with carboxylic acid anhydrides in pure
water under mild conditions. Under the optimal conditions, all reactions gave the desired coupling
products in moderate to high yields.
Received 22 February 2012
Received in revised form 13 April 2012
Accepted 4 May 2012
Available online 14 May 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
N-Heterocyclic carbene
Palladium complex
Coupling reaction
Water
Synthetic method
1. Introduction
NHCepalladium chloride-1-methylimidazole [NHCePd(II)eIm]
complex 1 derived from IPr$HCl [1,3-bis(2,6-diisopropylphenyl)e
Diaryl ketones are fundamental intermediates in the synthesis of
natural products and biologically active small molecules.1 Classical
route to synthesize diaryl ketones is the FriedeleCrafts acylation of
aromatic compounds in the presence of excess amounts of Lewis
acid.2 During the past years, transition metal-catalyzed reactions
had provided many opportunities for the synthesis of these com-
pounds.3 For instance, the palladium-catalyzed acylation of carbon
nucleophiles, such as arylboronic acids with carboxylic acid de-
rivatives is one of the most efficient reactions.4 However, the above
mentioned methods are usually carried out in organic solvents in
the presence of phosphine-based ligands. Comparing to toxic, vol-
atile and flammable organic solvents, water, is nontoxic, non-
flammable, and environmentally benign and had attracted much
attention in synthetic organic chemistry.5 In addition, comparing to
air- and thermal-sensitive phosphine ligands, N-heterocyclic car-
benes (NHCs), usually with higher air- and thermal-stability, have
become a big challenger to phosphine ligands in the metal-
catalyzed carbonecarbon and carboneheteroatom bond forma-
tion reactions.6 However, to the best of our knowledge, applications
of NHCemetal complexes in pure water were rarely reported to
imidazolium chloride], PdCl2 and 1-methylimidazole (Fig. 1), and
found it to be an efficient catalyst in the formation of carbon-
ecarbon and carbonenitrogen bonds.8 For example, it was reported
that complex 1 exhibited high catalytic activity in the Suzu-
kieMiyaura coupling of aryl chlorides performed in pure water
under mild conditions.8c These results prompted us to find out more
applications of this complex in organic synthesis performed in
water. In continuing research, we found that complex 1 was also an
efficient catalyst for the coupling reaction of arylboronic acids with
carboxylic acid anhydrides in pure water. Herein, we report these
results in detail.
Pri
Pri
Pri
Pri
Pri
1'
Pri
Pri
Cl
Cl
Pd
Cl
Cl
Pd
Cl
N
N
N
N
N
N
N
date.7 Recently, we have synthesized
a
well-defined
Pri
1
* Corresponding author. Tel./fax: þ86 577 86689300; e-mail address: ljm@
wzu.edu.cn (J.-M. Lu).
Fig. 1. NHCePd(II)eIm complex 1 and PEPPSI 10.
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.05.016

X.-F. Lin et al. / Tetrahedron 68 (2012) 5806e5809
5807
Table 2
2. Results and discussion
NHCePd(II)eIm complex 1-catalyzed reactions of arylboronic acids 2 and benzoic
anhydride 3a in H2O
Initial studies were carried out using phenylboronic acid 2a
(0.75 mmol) and benzoic anhydride 3a (1.5 mmol) as the sub-
strates, NHCePd(II)eIm complex 1 (1.0 mol %) as the catalyst, H2O
(2.0 mL) as the solvent at room temperature to find out the best
base. As can be seen from Table 1, the best similar results can be
achieved when K2CO3, Na2CO3, Cs2CO3, and NaHCO3 were used as
the base, respectively, (Table 1, entries 1, 2, 4, and 7). For other
bases, such as Li2CO3, NaOH, and KHCO3, all reactions proceeded
smoothly to give product 4a in lower yields within 12 h (Table 1,
entries 3, 5, and 6). A similar complex, such as PEPPSI 109 (Fig.1) was
also tested in this reaction, and inferior result was obtained (Table 1,
entry 8). Owing to the lower molecular mass and lower cost,
NaHCO3 was chosen as the best base. So the optimal reaction
conditions were established as using NHCePd(II)eIm complex 1
(1.0 mol %) as the catalyst, NaHCO3 as the base in water at room
temperature.
B(OH)2
O
O
O
complex 1
(1.0 mol%)
O
+
NaHCO3,
H2O, 12 h
4
R1
3a
R1
2
Entrya
2 (R1)
Temp (ꢀC)
Yield (%)b
1
2
3
4
5
6
7
8
2b (4-F)
rt
rt
4b, 98
4c, 99
4d, 88
4e, 52
4f, 80
4g, 70
4h, 85
4i, 92
2c (3,5-Me2)
2d (4-MeO)
2e (4-Cl)
2f (2-Me)
2g (3-NO2)
2h (4-Me)
2i (3-Me)
50
rt
50
70
50
rt
B(OH)2
B(OH)2
9
50
50
4j, 94
2j
Table 1
Optimization for the NHCePd(II)eIm complex 1-catalyzed reaction of phenyl-
boronic acid 2a and benzoic anhydride 3a in H2O
2k
10
4k, 43
O
O
B(OH)2
O
S
complex 1
a
All reactions were carried out using 2 (0.75 mmol), 3a (2.0 equiv), 1 (1.0 mol %),
O
(1.0 mol%)
+
NaHCO3 (2.4 mmol) in H2O (2.0 mL) at the listed temperature for 12 h.
b
base, H2O,
rt, 12 h
Isolated yields.
3a
4a
2a
Entrya
Base
Yield (%)b
contrary, substituents on the carboxylic acid anhydrides 3 affected
the reactions in some extent. For example, although the reaction
was retarded when substrate 3c having electron-rich para-MeO on
the phenyl ring was used, good yield can also be obtained when the
reaction time was prolonged to 24 h (Table 3, entry 5). Substrate 3f
having electron-poor para-Cl group on the phenyl ring was not
suitable and no desired product was observed (Table 3, entry 12).
Substrate 3d having an ortho-EtO group on the phenyl ring only
gave product 4n in 58% yield presumably due to its steric hindrance
(Table 3, entry 6). Heteroarylboronic acid, such as 2-thienylboronic
acid 2k was also tested and only 43% yield of product 4k was
obtained (Table 1, entry 10).
1
2
3
4
5
6
7
8c
K2CO3
Na2CO3
Li2CO3
Cs2CO3
NaOH
KHCO3
NaHCO3
NaHCO3
97
92
53
97
44
62
99
60
a
All reactions were carried out using 2a (0.75 mmol), 3a (2.0 equiv), 1 (1.0 mol %),
base (2.4 mmol) in H2O (2.0 mL) at rt for 12 h.
b
Isolated yields.
PEPPSI 10 as the catalyst.
c
With the optimal reaction conditions in hand, we then first in-
vestigated the reactions of various arylboronic acids 2 with benzoic
anhydride 3a to test the generality. As can be seen from Table 2, all
reactions took place smoothly to give the corresponding coupling
products 4 in moderate to high yields under suitable temperature.
Substituents on the arylboronic acids 2 have some effect on these
reactions. For instance, for 4-fluorophenylboronic acid 2b, 3,5-
dimethylphenylboronic acid 2c and 3-methylphenylboronic acid
2i, the corresponding ketones 4b, 4c, and 4i were formed in high
yields at room temperature (Table 2, entries 1, 2, and 8). For 4-
methoxyphenylboronic acid 2d, 2-methylphenylboronic acid 2f,
4-methylphenylboronic acid 2h and 1-naphthylboronic acid 2j, the
ketone products 4d, 4f, 4h, and 4j were obtained in good yields at
50 ꢀC (Table 2, entries 3, 5, 7, and 9). Only moderate yields of
products 4e and 4g were obtained when moderately electron-poor
4-chlorophenylboronic acid 2e and strongly electron-poor 3-
nitrophenylboronic acid 2g were used as the substrates (Table 2,
entries 4 and 6).
Table 3
NHCePd(II)eIm complex 1-catalyzed reactions of arylboronic acids 2 and carboxylic
acid anhydrides 3 in H2O
O
B(OH)2
O
O
complex 1
(1.0 mol%)
O
+
Na2CO3
H2O, 50 oC
R2
R2
R2
4
R1
R1
2
3
Entrya
2 (R1)
3 (R2)
Yield (%)b
1
2
3
2a (H)
2b (4-F)
2d (4-MeO)
2h (4-Me)
2h
2h
2a
2h
3b (4-Me)
4h, 91
4l, 80
4m, 91
4n, 82
4m, 86
4o, 58
4i, 89
4p, 83
4q, 89
4r, 93
4s, 86
d
3b
3b
3b
4
5c
6
3c (4-MeO)
3d (2-EtO)
3e (3-Me)
3e
3e
3e
7
8
9
10
11
12
2d
The reactions between various arylboronic acids 2 and carboxylic
acid anhydrides 3 were also investigated under the similar reaction
conditions. It is worthy of note here that Na2CO3 was found to be the
most suitable base in these cases. Most reactions took place
smoothly to give the corresponding diaryl ketones 4 in good to high
yields at 50 ꢀC within 12 h (Table 3). Substituents on the arylboronic
acids 2 almost have no obvious effect on the reactions. On the
2i (3-Me)
2j (2-Me)
2d
3e
3f (4-Cl)
a
Otherwize specified, all reactions were carried out using 2 (0.75 mmol), 3
(2.0 equiv), 1 (1.0 mol %), Na2CO3 (2.4 mmol) in H2O (2.0 mL) at 50 ꢀC for 12 h.
b
Isolated yields.
The reaction time was 24 h.
c

5808
X.-F. Lin et al. / Tetrahedron 68 (2012) 5806e5809
3. Conclusion
4H, Ar). 13C NMR (125 MHz, CDCl3)
135.9, 137.3, 138.9, 195.5.
d 128.4, 128.6, 129.9, 131.5, 132.6,
In conclusion, the well-defined NHCePd(II)eIm complex 1 de-
rived from commercially available IPr.HCl, PdCl2, and 1-methyl-
imidazole showed efficient catalytic activity in the coupling
reactions of arylboronic acids with carboxylic acid anhydrides in
pure water under mild conditions. Under the optimal reaction
conditions, all reactions took place smoothly to give the desired
diaryl ketones in moderate to high yields. It is worth noting here
that the results reported in this paper is the application of
NHCemetal complexes in pure water, which are not developed very
popularly to date and will open new opportunities for NHCemetal
complexes in organic synthesis.
4.2.6. Compound 4f.10 A white solid. 1H NMR (500 MHz, CDCl3,
TMS)
d 2.24 (s, 3H, Me), 7.22e7.29 (m, 3H, Ar), 7.30e7.46 (m, 3H,
Ar), 7.57 (t, J¼7.0 Hz, 1H, Ar), 7.80 (d, 2H, J¼7.0 Hz, Ar). 13C NMR
(125 MHz, CDCl3)
d 19.9, 125.1, 128.40, 128.45, 130.1, 130.2, 130.9,
133.1, 136.7, 137.7, 138.6, 198.6.
4.2.7. Compound 4g.12 A lightyellowsolid.1H NMR(500 MHz, CDCl3,
TMS)
d
7.54 (t, J¼7.5 Hz, 2H, Ar), 7.67 (t, J¼7.5 Hz, 1H, Ar), 7.71 (t,
J¼8.0 Hz, 1H, Ar), 7.81 (d, J¼8.0 Hz, 2H, Ar), 8.15 (d, J¼7.5 Hz, 2H, Ar),
8.45 (d, J¼8.0 Hz, 1H, Ar), 8.63 (s, 1H, Ar). 13C NMR (125 MHz, CDCl3)
d
124.7,126.7,128.7,129.6,130.0,133.4,135.4,136.2,139.1,148.1,194.2.
4.2.8. Compound 4h.10 A white solid. 1H NMR (500 MHz, CDCl3,
TMS)
2.45 (s, 3H, Me), 7.29 (d, J¼8.5 Hz, 2H, Ar), 7.48 (t, J¼7.5 Hz,
4. Experimental section
4.1. General remarks
d
2H, Ar), 7.58 (t, J¼7.5 Hz, 1H, Ar), 7.73 (d, J¼8.5 Hz, 2H, Ar), 7.79 (d,
J¼7.5 Hz, 2H, Ar). 13C NMR (125 MHz, CDCl3)
d 21.7, 128.2, 129.0,
129.9, 130.3, 130.6, 132.2, 134.9, 138.0, 143.2, 196.5.
1H and 13C NMR spectra were recorded on a Bruker Avance-
300 or 500 MHz spectrometer for solution in CDCl3 with
tetramethylsilane (TMS) as an internal standard; J-values are in
Hertz. Commercially obtained reagents were used without
further purification. Flash column chromatography was carried
out using Huanghai 300e400 mesh silica gel at increased
pressure.
4.2.9. Compound 4i.10 A white solid.1H NMR (500 MHz, CDCl3, TMS)
d
7.23e7.30 (m, 2H, Ar), 7.37 (t, J¼7.5 Hz, 2H, Ar), 7.46e7.53 (m, 3H,
Ar), 7.70 (d, J¼7.5 Hz, 2H, Ar). 13C NMR (125 MHz, CDCl3)
d 21.3, 127.3,
128.0, 128.2, 129.9, 130.4, 132.2, 133.1, 137.6, 137.7, 138.1, 196.8.
4.2.10. Compound 4j.10 A white solid. 1H NMR (500 MHz, CDCl3,
4.2. Experimental procedures
TMS)
(125 MHz, CDCl3)
d
7.26e7.60 (m, 7H, Ar), 7.87e8.00 (m, 5H, Ar). 13C NMR
d
124.3, 125.7, 126.4, 127.2, 127.8, 128.36, 128.40,
Under N2 atmosphere, NaHCO3 (2.4 mmol), benzoic anhydride
3a (1.5 mmol), phenylboronic acid 2a (0.75 mmol), and H2O were
successively added into a Schlenk reaction tube. The mixture was
stirred at room temperature for about 10 min. Then NHCePd(II)e
Im complex 1 (1.0 mol %) was added. The mixture was stirred at
room temperature for 12 h and then was diluted with CH2Cl2,
washed with saturated brine, dried over anhydrous Na2SO4. The
dried organic phase was then filtered, concentrated under reduced
pressure and purified by flash column chromatography on silica gel
to give the pure product 4a.
130.4, 131.0, 131.2, 133.2, 133.7, 136.3, 138.3, 198.0.
4.2.11. Compound 4k.3a A white solid. 1H NMR (500 MHz, CDCl3,
TMS)
d
7.17 (dd, J¼6.5, 8.0 Hz, 1H, Ar), 7.47e7.53 (m, 2H, Ar),
7.57e7.63 (m, 1H, Ar), 7.65 (dd, J¼1.5, 6.5 Hz, 1H, Ar), 7.73 (dd, J¼1.5,
8.0 Hz, 1H, Ar), 7.85e7.88 (m, 2H, Ar). 13C NMR (125 MHz, CDCl3)
d
127.9, 128.4, 129.1, 132.2, 134.2, 134.8, 138.2, 143.6, 188.2.
4.2.12. Compound 4k.10 A white solid. 1H NMR (300 MHz, CDCl3,
TMS)
d
2.45 (s, 3H, Me), 7.16 (t, J¼8.4 Hz, 2H, Ar), 7.26e7.31 (m, 2H,
Ar), 7.69 (d, J¼8.4 Hz, 2H, Ar), 7.83 (dd, J¼9.0, 5.4 Hz, 2H, Ar). 13C
4.2.1. Compound 4a.10 A white solid. 1H NMR (500 MHz, CDCl3,
NMR (125 MHz, CDCl3)
132.5 (d, JCeF¼9.0 Hz), 134.1 (d, JCeF¼3.0 Hz), 134.7, 143.3, 165.2 (d,
JCeF¼252.1 Hz), 195.0.
d
21.6, 115.3 (d, JCeF¼21.6 Hz), 129.0, 130.1,
TMS)
d
7.47e7.57 (m, 4H, Ar), 7.58e7.61 (m, 2H, Ar), 7.80e7.82
(m, 4H, Ar). 13C NMR (125 MHz, CDCl3)
137.6, 196.7.
d 128.2, 130.0, 132.4,
4.2.13. Compound 4l.9 A white solid. 1H NMR (300 MHz, CDCl3,
4.2.2. Compound 4b.10 A white solid. 1H NMR (500 MHz, CDCl3,
TMS)
7.03 (t, J¼8.5 Hz, 2H, Ar), 7.36 (t, J¼7.5 Hz, 2H, Ar), 7.46 (t,
J¼7.5 Hz, 1H, Ar), 7.65 (d, J¼7.5 Hz, 2H, Ar), 7.72 (dd, J¼8.5, 5.5 Hz,
2H, Ar). 13C NMR (125 MHz, CDCl3)
TMS)
7.28 (d, J¼8.1 Hz, 2H, Ar), 7.68 (d, J¼8.1 Hz, 2H, Ar), 7.82 (d, J¼9.0 Hz,
2H, Ar). 13C NMR (125 MHz, CDCl3)
21.6, 55.5, 113.5, 128.9, 130.0,
132.4, 135.5, 142.6, 144.4, 163.0, 195.4.
d
2.44 (s, 3H, Me), 3.89 (s, 3H, OMe), 6.94 (d, J¼9.0 Hz, 2H, Ar),
d
d
d
116.7 (d, JCeF¼22.3 Hz), 119.4
(d, JCeF¼21.2 Hz), 125.8 (d, JCeF¼2.9 Hz), 128.4, 129.9 (d,
JCeF¼9.0 Hz), 132.7, 137.0, 139.7 (d, JCeF¼6.3 Hz), 162.5 (d,
JCeF¼246.6 Hz), 195.3.
4.2.14. Compound 4m.10 A white solid. 1H NMR (300 MHz, CDCl3,
TMS)
2.44 (s, 6H, Me), 7.27 (d, J¼8.1 Hz, 4H, Ar), 7.70 (d, J¼8.1 Hz, 4H,
Ar). 13C NMR (125 MHz, CDCl3)
21.6, 128.9, 130.2, 135.2, 142.9, 196.2.
d
d
4.2.3. Compound 4c.11 A white solid. 1H NMR (500 MHz, CDCl3,
TMS)
d
2.23 (s, 6H, Me), 7.08 (s, 1H, Ar), 7.25e7.49 (m, 5H, Ar), 7.67
4.2.15. Compound 4n. A colorless liquid. 1H NMR (300 MHz, CDCl3,
TMS)
1.11 (t, J¼7.2 Hz, 3H, Me), 2.41 (s, 3H, Me), 3.97 (q, J¼7.2 Hz,
(s, 2H, Ar). 13C NMR (125 MHz, CDCl3)
132.2, 134.1, 137.7, 137.9, 197.2.
d
21.2, 127.8, 128.2, 130.0,
d
2H), 6.94e7.04 (m, 2H, Ar), 7.22 (d, J¼7.5 Hz, 2H, Ar), 7.35e7.46 (m,
2H, Ar), 7.70 (d, J¼7.5 Hz, 2H, Ar). 13C NMR (125 MHz, CDCl3)
d 14.3,
4.2.4. Compound 4d.10 A white solid. 1H NMR (500 MHz, CDCl3,
TMS)
3.75 (s, 3H, OMe), 6.84 (d, J¼9.0 Hz, 2H, Ar), 7.35 (t, J¼7.5 Hz,
21.7, 64.0, 112.5, 120.4, 128.8, 129.5, 129.8, 131.6, 135.6, 143.5, 156.6,
d
196.4. IR (neat) n 1659, 1597, 1447, 1131, 1298, 1239, 1150, 1117, 1041,
2H, Ar), 7.44 (t, J¼7.5 Hz, 1H, Ar), 7.64 (d, J¼7.5 Hz, 2H, Ar), 7.72 (d,
931, 916, 835, 752, 731, 682 cmꢁ1. MS (ESI, m/z): 241 [MþH]þ;
HRMS (ESI): Calcd for C16H17O2 [MþH]þ: 241.1223; Found:
241.1237.
J¼9.0 Hz, 2H, Ar). 13C NMR (125 MHz, CDCl3)
d 55.4, 113.5, 128.1,
129.6, 130.0, 131.8, 132.4, 138.2, 163.1, 195.4.
4.2.5. Compound 4e.10 A white solid. 1H NMR (500 MHz, CDCl3,
TMS) 7.46e7.51 (m, 4H, Ar), 7.59e7.62 (m, 1H, Ar), 7.45e7.78 (m,
4.2.16. Compound 4o.10 A white solid. 1H NMR (300 MHz, CDCl3,
TMS) d 2.42 (s, 3H, Me), 2.44 (s, 3H, Me), 7.26e7.37 (m, 4H, Ar),
d

X.-F. Lin et al. / Tetrahedron 68 (2012) 5806e5809
5809
7.55e7.61 (m, 2H, Ar), 7.72 (d, J¼8.1 Hz, 2H, Ar). 13C NMR (125 MHz,
3. For some recent selected examples, please see: (a) Li, H.-L.; Yang, M.; Qi, Y.-X.;
Xue, J.-J. Eur. J. Org. Chem. 2011, 2662e2667; (b) Rao, H.-H.; Yang, L.; Shuai, Q.;
Li, C.-J. Adv. Synth. Catal. 2011, 353, 1701e1706; (c) Liu, J.; Zhou, X.-Y.; Rao, H.-H.;
Xiao, F.-H.; Li, C.-J.; Deng, G.-J. Chem.dEur. J. 2011, 17, 7996e7999; (d) Li, M.-Z.;
Wang, C.; Ge, H.-B. Org. Lett. 2011, 13, 2062e2064; (e) Kobayashi, K.; Nishimura,
Y.; Gao, F.-X.; Gotoh, K.; Nishihara, Y.; Takagi, K. J. Org. Chem. 2011, 76,
1949e1952; (f) Yang, L.; Zeng, T.-Q.; Shuai, Q.; Guo, X.-Y.; Li, C.-J. Chem. Com-
mun. 2011, 2161e2163; (g) Khedkar, M. V.; Tambade, P. J.; Qureshi, Z. S.;
Bhanage, B. M. Eur. J. Org. Chem. 2011, 6981e6986; (h) Jafarpour, F.; Rashidi-
Ranjbar, P.; Kashini, A. O. Eur. J. Org. Chem. 2011, 2128e2132.
CDCl3)
d 21.2, 21.5, 127.1, 127.9, 128.8, 130.17, 130.24, 132.8, 135.0,
137.91, 137.95, 143.0, 196.6.
4.2.17. Compound 4p.10 A white solid. 1H NMR (300 MHz, CDCl3,
TMS)
7.32e7.37 (m, 2H, Ar), 7.52e7.58 (m, 2H, Ar), 7.83 (d, J¼9.0 Hz, 2H,
Ar). 13C NMR (125 MHz, CDCl3)
21.4, 55.5, 113.5, 127.0, 128.0, 130.2,
d
2.42 (s, 3H, Me), 3.89 (s, 3H, OMe), 6.97 (d, J¼9.0 Hz, 2H, Ar),
d
4. For some selected examples, please see: (a) Gooßen, L. J.; Ghosh, K. Angew.
Chem., Int. Ed. 2001, 40, 3458e3460; (b) Gooßen, L. J.; Ghosh, K. Eur. J. Org.
Chem. 2002, 3254e3267; (c) Xin, B.-W.; Zhang, Y.-H.; Cheng, K. J. Org. Chem.
130.3, 132.5, 132.6, 138.0, 138.3, 163.2, 195.8.
4.2.18. Compound 4q.3e A white solid. 1H NMR (300 MHz, CDCl3,
ꢀ
ꢀ
ꢀ
2006, 71, 5725e5731; (d) Polackova, V.; Toma, S.; Augustíinova, I. Tetrahedron
2006, 62, 11675e11678; (e) Xin, B.-W.; Zhang, Y.-H.; Cheng, K. Synthesis 2007,
1970e1978; (f) Kakina, R.; Narahashi, H.; Shimizu, I.; Yamamoto, A. Bull.
Chem. Soc. Jpn. 2002, 75, 1333e1345; (g) Kwon, Y. B.; Choi, B. R.; Lee, S. H.;
Seo, J.-S.; Yoon, C. M. Bull. Korean Chem. Soc. 2010, 31, 2672e2674; (h)
Kakino, R.; Yasumi, S.; Shimizu, I.; Yamamoto, A. Bull. Chem. Soc. Jpn. 2002,
75, 137e148.
TMS) d C
2.42(s, 6H, Me), 7.33e7.41(m, 4H, Ar),7.55e7.62(m, 4H, Ar).13
NMR (125 MHz, CDCl3)
197.2.
d 21.3, 127.3, 128.0, 130.4, 133.1, 137.7, 138.1,
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€
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€
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137.7, 138.3, 138.8, 198.8.
Acknowledgements
Financial support from the National Natural Science Foundation
of China (No. 21002072) and the Opening Foundation of Zhejiang
Provincial Top Key Discipline (No. 1000612001) is greatly ac-
knowledged. Y.L. and S.-Y.L. thank Science and Technology De-
partment of Zhejiang Province (Xinmiao Programme) for financial
support (Nos. 2011R424016 and 2010R424016).
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Supplementary data
ꢀ
7. (a) Churruca, F.; SanMartin, R.; Ines, B.; Tellitu, I.; Domínguez, E. Adv. Synth.
ꢀ
Catal. 2006, 348, 1836e1840; (b) Ines, B.; SanMartin, R.; Moure, M. M.;
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2012.05.016. These data in-
clude MOL files and InChiKeys of the most important compounds
described in this article.
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