Highly efficient copper-catalyzed amidation of aldehydes by C-H activation

Article abstract of DOI:10.1002/chem.200801620

We have developed a highly efficient method for the copper-catalyzed amidation of aldehydes in the presence of N-bromosuccinimide (NBS). This method is simple, economical, and has practical advantages for synthesis of imides.

Full text of DOI:10.1002/chem.200801620

DOI: 10.1002/chem.200801620
À
Highly Efficient Copper-Catalyzed Amidation of Aldehydes by C H
Activation
Long Wang,[a] Hua Fu,*[a] Yuyang Jiang,[a, b] and Yufen Zhao[a]
Abstract: We have developed a highly efficient method for the copper-catalyzed
amidation of aldehydes in the presence of N-bromosuccinimide (NBS). This
method is simple, economical, and has practical advantages for synthesis of imides.
Keywords: aldehydes · amide bond
À
formation
·
C H activation
·
copper · homogeneous catalysis
Introduction
there are limitations, such as the lability of the activated
acid derivatives and tedious procedures.[2]
Construction of amide bonds is of great interest in organic,
biological, medicinal, and materials chemistry because the
amide functional group is ubiquitous in natural products,
pharmaceuticals, and polymers.[1] Traditional methods for
the synthesis of amides are highly concentrated on the cou-
pling of activated carboxylic acid derivatives and amines.
Although these methods have been shown to be exception-
ally efficient for the synthesis of small peptides (Scheme 1a),
In view of the shortcomings above, alternative amide
bond formation strategies have been actively pursued. The
À
direct reactions of the acyl C H bond in aldehydes with
amines has attracted attention (Scheme 1b).[3–8] For example,
the radical-mediated oxidative amidation with radical initia-
tors,[3] the amidation by means of Cannizzaro reactions with
lithium diisopropylamide (LDA)[4] or lanthanide reagents,[5]
and the N-heterocyclic carbene (NHC)-catalyzed amida-
tion[6] were reported. Most catalytic amidation processes
have utilized transition-metal complexes[7] (such as cop-
per,[7a] rhodium,[7b] ruthenium,[7c] and palladium[7d]) in the
presence of an oxidant. In addition, metal-free oxidative
amidation of aldehydes has also been reported.[8] Very re-
cently, Milstein and co-workers developed a direct, endo-
thermic ruthenium-catalyzed amidation from alcohols and
amines with the liberation of H2 via aldehyde intermedi-
ates.[9] The previous methods for the amidation of aldehydes
used amines (strong nucleophilic reagents) as the partners;
however, coupling of various amides, such as sulfonamides
and carboxamides (weak nucleophilic reagents), with alde-
hydes is still limited. The direct functionalization of carbon–
hydrogen bonds has recently received increasing atten-
tion,[10] and great progress on the intramolecular and inter-
Scheme 1. a) The coupling of activated carboxylic acid derivatives and
À
amines to form amides; b) the direct reactions of the acyl C H bond in
aldehydes with amines to form amides.
[a] L. Wang, Prof. Dr. H. Fu, Prof. Dr. Y. Jiang, Prof. Dr. Y. Zhao
Key Laboratory of Bioorganic Phosphorus Chemistry
and Chemical Biology (Ministry of Education)
Department of Chemistry, Tsinghua University
Beijing 100084 (China)
À
molecular amidation of C H bonds has been achieved in
the past two decades.[11–14] Recently, rhodium and rutheni-
um-catalyzed sulfamidation of aldehydes has been devel-
oped via metal–nitrene intermediates.[15]
Fax : (+86)10-6278-1695
E-mail: fuhua@mail.tsinghua.edu.cn
To the best of our knowledge, amidation of aldehydes to
form imides by using free amides as the partners has not
been reported, although the imide motif often appears as a
key component in a variety of reactions[16] and in certain
natural products, such as fumaramidmycin,[17] coniothyrio-
mycin,[18] and SB-253514.[19] Very recently, we have devel-
[b] Prof. Dr. Y. Jiang
Key Laboratory of Chemical Biology (Guangdong Province)
Graduate School of Shenzhen, Tsinghua University
Shenzhen 518057 (China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200801620.
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Chem. Eur. J. 2008, 14, 10722 – 10726

FULL PAPER
oped the iron or copper catalyst/N-halosuccinimide (NXS)-
electron-withdrawing groups showed higher activity. Nitro-
gen-containing heterocyclic compound, 2-pyridinecarboxal-
dehyde, also provided the target products in good yields
(Table 2, entries 14 and 15). Couplings of secondary amides
with aldehydes gave good results (Table 2, entries 16–18).
We attempted copper-catalyzed intramolecular cyclization
of 4 containing an aldehyde and a secondary amide group
under our standard conditions and the cyclic compound 3s
was obtained in 85% yield (Table 2, entry 19). To the best
of my knowledge, there are no examples for couplings of
secondary amides with aldehydes. Remarkable functional-
group tolerability was observed with coupling occurring in
the presence of nitro, carbon–halogen bonds on aryl ring,
and nitrogen-containing heterocycles.
mediated direct functionalization of carbon–hydrogen bonds
[20]
À
À
to form C N and C C bonds. Herein, we report a novel,
simple, and highly efficient copper-catalyzed coupling of al-
dehydes with free amides in the presence of N-bromosucci-
nimide (NBS) to give imides (Scheme 2).
À
Scheme 2. Our strategy: direct reactions of the acyl C H bond in alde-
hydes with amides to form imides.
Results and Discussion
Conclusion
To achieve the amidation of 4-nitrobenzaldehyde, we exam-
ined a variety of conditions including N-halosuccimides,
copper salts, and solvents at 708C under a nitrogen atmos-
phere (Table 1). Several solvents were tested by using
We have developed a highly efficient copper-catalyzed ami-
dation of aldehydes in the presence of NBS, the correspond-
ing target products were obtained in good to excellent
yields, and an array of functional groups are tolerated under
the mild conditions with respect to both amides and alde-
hydes. The protocol uses inexpensive and low loading CuBr
as the catalyst. No additional ligand and additive were re-
quired, so the method is simple, economical, and has practi-
cal advantages for synthesis of imides. Further investigations
in this direction are in progress.
Table 1. Copper-catalyzed coupling of 4-nitrobenzaldehyde with butyra-
mide in the presence of N-halosuccinimide: Optimization of conditions.[a]
Entry
Cat.
NXS
Solvent
Yield [%][b]
1
2
3
4
5
6
7
8
CuBr
CuBr
CuBr
CuBr
CuI
NBS
NBS
NBS
NBS
NBS
NBS
NBS
NCS
THF
CH3COOCH3
CH3CN
CH3CN/CCl4
CH3CN/CCl4
CH3CN/CCl4
CH3CN/CCl4
CH3CN/CCl4
trace
25
69
87
72
68
70
trace
Experimental Section
[c]
[c]
[c]
[c]
[c]
General methods: All reactions were carried out under a nitrogen atmos-
phere. Unless stated otherwise, all reagents were purchased commercially
without further purification. All reagents were weighed and handled in
air at room temperature. 1H and 13C NMR spectra were recorded by
using tetramethylsilane (TMS) in CDCl3 (1H NMR: TMS at d=
0.00 ppm, CHCl3 at d=7.24 ppm; 13C NMR: CDCl3 at d=77.0 ppm) or
[D6]DMSO as the internal standard (1H NMR: TMS at d=0.00 ppm,
DMSO at d=2.50 ppm; 13C NMR: DMSO at d=40.0 ppm).
CuCl2
Cu
N
CuBr
[a] Reaction conditions: nitrogen atmosphere, 4-nitrobenzaldehyde
(1 mmol), butyramide (1.2 mmol), catalyst (0.05 mmol), N-halosuccini-
mide (1.5 mmol), solvent (3 mL). [b] Yield of isolated product.
[c] CH3CN/CCl4 (v/v 1:5).
General procedure for the synthesis of compounds 3a–s: A round-bot-
tomed flask (10 mL) was charged with a magnetic stirrer, and CH3CN/
CCl4 (volume ratio 1:5, 3 mL), aldehyde (1) (1 mmol), amide (2)
(1.2 mmol), and CuBr (0.05 mmol, 7 mg) were added to the flask at room
temperature under a nitrogen atmosphere (for Table 2, entries 14 and 15,
1.5 mmol of MgO was used to neutralize HBr freed from the reaction).
After stirring for 15 min, NBS (1.5 mmol, 267 mg) was added to the solu-
tion. The mixture was stirred for a time and at a temperature as shown in
Tables 1 and 2. The resulting solution was cooled to room temperature
and filtered. The solid was washed with ethyl acetate (2ꢁ5 mL) and the
combined filtrate was concentrated by a rotary evaporator. The residue
was purified by column chromatography on silica gel by using petroleum
ether/ethyl acetate as eluent to give the desired product.
4-Nitrodibenzamide (3a):[21] Eluent: petroleum ether/ethyl acetate 1:1;
white solid; yield: 242.8 mg, 90%; m.p. 167–1698C; 1H NMR
([D6]DMSO, 300 MHz): d=11.63 (s, 1H), 8.33 (d, 3J=8.6 Hz, 2H), 8.10
(d, 3J=8.6 Hz, 2H), 7.95 (d, 3J=7.6 Hz, 2H), 7.66 (t, 3J=7.8 Hz, 1H),
7.54 ppm (t, 3J=8.0 Hz, 2H); 13C NMR ([D6]DMSO, 75 MHz): d=167.9,
167.6, 150.0, 140.4, 133.8, 133.5, 130.4, 129.3, 129.0, 123.9 ppm; ESI-MS:
m/z: 292.9 [M+Na]+.
5 mol% CuBr as the catalyst and NBS as the oxidant
(Table 1, entries 1–4), and the mixed solvent, CH3CN/CCl4
(volume ratio 1:5), proved to be the best medium for this re-
action (Table 1, entry 4). We attempted to use various
copper salts, including CuBr, CuI, CuCl2, and CuACTHNURGTNEUNG(OAc)2
(Table 1, entries 4–7), and CuBr showed the highest catalytic
activity. Only a trace amount of imide 3c was observed
when N-chlorosuccinimide (NCS) replaced NBS as the oxi-
dant (Table 1, entry 8). After the optimization process, cou-
plings of various aldehydes and amides were carried out
under our standard conditions: 5 mol% CuBr as the cata-
lyst, 1.5 equivalents of NBS as the oxidant (relative to alde-
hydes), and CH3CN/CCl4 (volume ratio 1:5) as the solvent.
As shown in Table 2, all the substrates examined provided
good to excellent yields. Aromatic aldehydes containing
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H. Fu et al.
Table 2. (Continued)
Entry Aldehyde
Table 2. Copper-catalyzed amidation of aldehydes in the presence of
NBS.[a]
Amide
T [8C]/t [h] Product [Yield][b]
16
17
18
1a
1d
1e
90/15
90/15
75/28
Entry Aldehyde
1
Amide
T [8C]/t [h] Product [Yield][b]
2 f
2 f
90/15
2
3
1a
1a
90/15
90/15
19
75/12
[a] Reaction conditions: nitrogen atmosphere, aldehyde (1 mmol), amide
(1.2 mmol), CuBr (0.05 mmol), NBS (1.5 mmol), CH3CN (0.5 mL), CCl4
(2.5 mL). [b] Yield of isolated product. [c] 1.5 mmol of MgO was used to
neutralize HBr freed from the reaction.
4
5
1a
1a
90/15
90/15
N-Acetyl-4-nitrobenzamide (3b):[21] Eluent: petroleum ether/ethyl ace-
tate 1:1; white solid; yield: 193.2 mg, 93%; m.p. 236–2388C; 1H NMR
([D6]DMSO, 300 MHz): d=11.3 (s, 1H), 8.33 (d, 3J=8.9 Hz, 2H), 8.11
(d, 3J=8.9 Hz, 2H), 2.35 ppm (s, 3H); 13C NMR ([D6]DMSO, 75 MHz):
d=172.5, 165.9, 150.2, 139.6, 130.4, 124.0, 26.0 ppm; ESI-MS: m/z: 230.7
[M+Na]+.
6
7
2c
2c
90/15
75/28
N-Butyryl-4-nitrobenzamide (3c): Eluent: petroleum ether/ethyl acetate
3:1; white solid; yield: 226.6 mg, 96%; m.p. 142–1448C; 1H NMR
(CDCl3, 300 MHz): d=9.63 (s, 1H), 8.35 (d, 3J=8.6 Hz, 2H), 8.14 (d,
3J=8.6 Hz, 2H), 3.00 (t, 3J=7.2 Hz, 2H), 1.76 (m, 2H), 1.04 ppm (t, 3J=
7.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz): d=177.1, 164.3, 150.5, 138.3,
129.3, 124.1, 39.7, 17.5, 13.8 ppm; ESI-MS: m/z: 258.7 [M+Na]+.
Ethyl N-(4-nitrobenzoyl)carbamate (3d):[22] Eluent: petroleum ether/
ethyl acetate 3:1; white solid; yield: 204.6 mg, 86%; m.p. 123–1268C;
1H NMR (CDCl3, 300 MHz): d=8.61 (s, 1H), 8.33 (d, 3J=8.6 Hz, 2H),
8.04 (d, 3J=8.6 Hz, 2H), 4.30 (q, 3J=7.2 Hz, 2H), 1.33 ppm (t, 3J=
7.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz): d=164.2, 151.2, 150.3, 138.6,
129.2, 124.0, 63.0, 14.3 ppm; ESI-MS: m/z: 260.8 [M+Na]+.
8
2a
90/15
9
1d
1d
2c
2b
2a
90/15
90/15
75/28
N-(4-Nitrobenzoyl)stearamide (3e): Eluent: petroleum ether/ethyl ace-
tate 5:1; white solid; yield: 345.5 mg, 80%; m.p. 88–908C; 1H NMR
(CDCl3, 300 MHz): d=9.24 (s, 1H), 8.35 (d, 3J=8.9 Hz, 2H), 8.07 (d,
3J=8.9 Hz, 2H), 2.99 (t, 3J=7.56 Hz, 2H), 1.70 (m, 2H), 1.32 (s, 28H),
0.88 ppm (t, 3J=6.6 Hz, 3H); 13C NMR (CDCl3, 75 MHz): d=176.7,
164.1, 150.5, 138.4, 129.2, 124.1, 37.8, 32.0, 29.8, 29.7, 29.6, 29.5, 29.2, 24.1,
22.8, 14.2 ppm; ESI-MS: m/z: 455.4 [M+Na]+.
10
11
N-Butyryl-2-nitrobenzamide (3 f): Eluent: petroleum ether/ethyl acetate
3:1; white solid; yield: 203.0 mg, 86%; m.p. 108–1108C; 1H NMR
(CDCl3, 300 MHz): d=9.26 (s, 1H), 8.20 (d, 3J=8.3 Hz, 1H), 7.74 (m,
1H), 7.62 (m, 1H), 7.44 (m, 1H), 2.56 (t, 3J=7.5 Hz, 2H), 1.64 (m, 2H),
0.95 ppm (t, 3J=7.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz): d=173.4,
167.9, 145.4, 134.4, 132.6, 130.7, 127.8, 124.4, 39.0, 17.7, 13.6 ppm; ESI-
MS: m/z: 258.7 [M+Na]+.
12
13
1e
1e
2b
2c
75/28
75/28
N-Butyryl-2-bromobenzamide (3g): Eluent: petroleum ether/ethyl ace-
tate 3:1; white solid; yield: 198.9 mg, 74%; m.p. 98–1028C; 1H NMR
(CDCl3, 300 MHz): d=8.58 (s, 1H), 7.60 (m, 1H), 7.50 (m, 1H), 7.38 (m,
2H), 1.91 (t, J=7.2 Hz, 2H), 1.73 (m, 2H), 1.02 ppm (t, J=7.2 Hz, 3H);
13C NMR (CDCl3, 75 MHz): d=174.9, 166.4, 136.6, 133.8, 132.4, 129.3,
127.8, 119.2, 39.6, 17.3, 13.8 ppm; ESI-MS: m/z: 292.0, 293.9 [M+Na]+.
14[c]
2b
2c
RT/15
RT/15
3
3
15[c]
1 f
N-(4-Chlorobenzoyl)benzamide (3h):[21] Eluent: petroleum ether/ethyl
1
acetate 3:1; white solid; yield: 165.6 mg, 64%; m.p. 132–1348C; H NMR
(CDCl3, 300 MHz): d=9.36 (s, 1H), 7.85 (d, 3J=7.6 Hz, 2H), 7.79 (d,
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Chem. Eur. J. 2008, 14, 10722 – 10726

Copper-Catalyzed Amidation of Aldehydes
FULL PAPER
3J=8.6 Hz, 1H), 7.55 (t, 3H), 7.44 ppm (m, 4H); 13C NMR (CDCl3,
75 MHz): d=166.9, 166.5, 139.5, 133.3, 133.2, 131.8, 129.8, 129.1,
128.2 ppm; ESI-MS: m/z: 281.9 [M+Na]+.
Acknowledgements
This work was supported by the National Natural Science Foundation of
China (Grant No. 20672065), Chinese 863 Project (Grant No.
2007 AA02Z160), Programs for New Century Excellent Talents in Uni-
versity (NCET-05–0062), Changjiang Scholars and innovative Research
Team in University (PCSIRT) (No. IRT0404) in China, and the Key Sub-
ject Foundation from the Beijing Department of Education
(XK100030514).
4-Chloro-N-(1-oxobutyl)benzamide (3i): Eluent: petroleum ether/ethyl
1
acetate 5:1; white solid; yield: 206.8 mg, 92%; m.p. 151–1538C; H NMR
(CDCl3, 300 MHz): d=9.41 (s, 1H), 7.90 (d, 3J=8.6 Hz, 2H), 7.47 (d,
3J=8.6 Hz, 2H), 2.99 (t, 3J=7.2 Hz, 2H), 1.74 (m, 2H), 1.03 ppm (t, 3J=
7.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz): d=177.2, 164.9, 139.7, 131.2,
129.5, 129.3, 39.7, 37.6, 13.8 ppm; ESI-MS: m/z: 247.7 [M+Na]+.
N-Acetyl-4-chlorobenzamide (3j):[23] Eluent: petroleum ether/ethylace-
tate 3:1; white solid; yield: 143.6 mg, 73%; m.p. 145–1468C; 1H NMR
(CDCl3, 300 MHz): d=9.31 (s, 1H), 7.87 (d, 3J=8.6 Hz, 2H), 7.48 (d,
3J=8.3 Hz, 2H), 2.61 ppm (s, 3H); 13C NMR (CDCl3, 75 MHz): d=174.2,
165.0, 139.9, 131.1, 129.4, 129.3, 25.8 ppm; ESI-MS: m/z: 219.7 [M+Na]+.
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N-Benzoylbenzamide (3k):[21] Eluent: petroleum ether/ethylacetate 3:1;
white solid; yield: 137.1 mg, 61%; m.p. 149–1508C; 1H NMR (CDCl3,
300 MHz): d=9.12 (s, 1H), 7.86 (d, 3J=7.6 Hz, 4H), 7.59 (t, 3J=7.2 Hz,
3
2H), 7.49 ppm (t, J=7.2 Hz, 4H); 13C NMR (CDCl3, 75 MHz): d=166.7,
133.2, 128.9, 128.1 ppm; ESI-MS: m/z: 247.7 [M+Na]+.
N-Acetylbenzamide (3l):[21] Eluent: petroleum ether/ethylacetate 3:1;
white solid; yield: 107.3 mg, 66%; m.p. 97–998C; 1H NMR (CDCl3,
300 MHz): d=9.10 (s, 1H), 7.88 (d, 3J=8.3 Hz, 2H), 7.59 (t, 3J=6.9 Hz,
3
1H), 7.49 ppm (t, J=7.6 Hz, 2H); 13C NMR (CDCl3, 75 MHz): d=173.9,
165.9, 133.3, 132.8, 129.0, 127.9, 25.7 ppm; ESI-MS: m/z: 185.2 [M+Na]+.
N-Butyrylbenamide (3m):[16a] Eluent: petroleum ether/ethylacetate 5:1;
white solid; yield: 145.0 mg, 76%; m.p. 104–1068C; 1H NMR (CDCl3,
300 MHz): d=9.24 (s, 1H), 7.92 (d, 3J=7.2 Hz, 2H), 7.58 (t, 3J=7.2 Hz,
1H), 7.49 (t, 3J=7.9 Hz, 2H), 2.99 (t, 3J=7.2 Hz, 2H), 1.76 (m, 2H),
1.02 ppm (t, 3J=7.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz): d=176.8,
165.9, 133.2, 132.9, 129.0, 127.9, 39.6, 17.6, 13.8 ppm; ESI-MS: m/z: 213.4
[M+Na]+.
N-Acetyl-2-pyridinecarboxamide (3n): Eluent: petroleum ether/ethylace-
tate 3:1; white solid; yield: 119.6 mg, 73%; m.p. 73–758C; 1H NMR
(CDCl3, 300 MHz): d=10.48 (s, 1H), 8.63 (d, 3J=4.8 Hz, 1H), 8.26 (d,
3J=7.9 Hz, 1H), 7.94 (m, 1H), 7.56 (m, 1H), 2.62 ppm (s, 3H); 13C NMR
(CDCl3, 75 MHz): d=172.1, 163.0, 148.5, 148.2, 137.9, 127.7, 123.2,
25.5 ppm; ESI-MS: m/z: 186.2 [M+Na]+.
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N-Butyryl-2-pyridinecarboxamide (3o): Eluent: petroleum ether/ethyla-
cetate 3:1; white solid; yield: 155.5 mg, 81%; m.p. 42–438C; 1H NMR
(CDCl3, 300 MHz): d=10.47 (s, 1H), 8.62 (d, 1H, 3J=4.5 Hz), 8.26 (d,
3J=7.9 Hz, 1H), 7.94 (t, 3J=7.2 Hz, 1H), 7.55 (m, 1H), 2.96 (t, 3J=
7.2 Hz, 2H), 1.76 (m, 2H), 1.04 ppm (t, 3J=7.2 Hz, 3H); 13C NMR
(CDCl3, 75 MHz): d=174.8, 162.6, 148.4, 148.3, 138.1, 127.7, 123.3, 39.6,
17.7, 13.8 ppm; ESI-MS: m/z: 214.4 [M+Na]+.
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598–600.
N-(4-Nitrobenzoyl)caprolactam (3p): Eluent: petroleum ether/ethyl ace-
tate 3:1; white solid; yield: 225.2 mg, 86%; m.p. 100–1028C; 1H NMR
3
3
(CDCl3, 300 MHz): d=8.24 (d, J=8.9 Hz, 2H), 7.60 (d, J=8.8 Hz, 2H),
4.03 (s, 2H), 2.71 (m, 2H), 1.86 ppm (s, 6H); 13C NMR (CDCl3, 75 MHz):
d=177.7, 171.9, 148.8, 143.0, 128.0, 123.6, 44.9, 38.8, 29.5, 29.2, 23.8 ppm;
ESI-MS: m/z: 285.0 [M+Na]+.
N-(4-Chlorobenzoyl)caprolactam (3q): Eluent: petroleum ether/ethyl
acetate 5:1; liquid; yield: 160.5 mg, 64%; colorless oil; 1H NMR (CDCl3,
300 MHz): d=7.47 (d, 3J=8.6 Hz, 2H), 7.35 (d, 3J=8.6 Hz, 2H), 3.96 (t,
2H), 2.69 (t, 2H), 1.83 ppm (m, 6H); 13C NMR (CDCl3, 75 MHz): d=
177.7, 173.2, 137.6, 135.1, 129.3, 128.5, 45.3, 38.9, 29.6, 29.3, 23.8 ppm;
ESI-MS: m/z: 273.8 [M+Na]+.
N-Benzoyl caprolactam (3r):[24] Eluent: petroleum ether/ethylacetate 8:1;
liquid; yield: 151.6 mg, 70%; 1H NMR (CDCl3, 300 MHz): d=7.54 (d,
3J=6.8 Hz, 2H), 7.46 (m, 1H), 7.38 (m, 2H), 3.97 (s, 2H), 2.69 (m, 2H),
1.84 ppm (s, 6H); 13C NMR (CDCl3, 75 MHz): d=177.7, 174.3, 136.7,
131.4, 128.2, 127.8, 45.3, 39.0, 29.7, 29.3, 23.8 ppm; ESI-MS: m/z: 239.8
[M+Na]+.
N-Methylphthalimide (3s):[25] Eluent: petroleum ether/ethylacetate 3:1;
white solid; yield: 136.9 mg, 85%; m.p. 130–1328C; 1H NMR (CDCl3,
300 MHz): d=7.84 (m, 2H), 7.72 (m, 2H), 3.18 ppm (s, 3H); 13C NMR
(CDCl3, 75 MHz): d=168.5, 133.9, 132.3, 123.2, 24.0 ppm; ESI-MS: m/z:
200.4 [M+K]+.
À
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Received: August 6, 2008
Published online: October 15, 2008
10726
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Chem. Eur. J. 2008, 14, 10722 – 10726