Bismuth trichloride-catalyzed C-alkylation of pyrroles with electron-deficient olefins

Article abstract of DOI:10.1080/00397910500522074

The BiCl₃-catalyzed reaction of pyrroles with electron-deficient olefins generated the corresponding Michael adducts in high yields. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910500522074

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Bismuth Trichloride–Catalyzed C‐Alkylation of
Pyrroles with Electron‐Deficient Olefins
Zhuang‐Ping Zhan a , Jing‐Liang Yu a & Wen‐Zhen Yang a
a Department of Chemistry and the Key Laboratory for Chemical Biology of
Fujian Province , College of Chemistry and Chemical Engineering, Xiamen
University , Xiamen, China
Published online: 16 Aug 2006.
To cite this article: Zhuang‐Ping Zhan , Jing‐Liang Yu & Wen‐Zhen Yang (2006) Bismuth Trichloride–Catalyzed
C‐Alkylation of Pyrroles with Electron‐Deficient Olefins, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 36:10, 1373-1382
To link to this article: http://dx.doi.org/10.1080/00397910500522074
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Synthetic Communicationsw, 36: 1373–1382, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500522074
Bismuth Trichloride–Catalyzed
C-Alkylation of Pyrroles with
Electron-Deficient Olefins
Zhuang-Ping Zhan, Jing-Liang Yu, and Wen-Zhen Yang
Department of Chemistry and the Key Laboratory for Chemical Biology
of Fujian Province, College of Chemistry and Chemical Engineering,
Xiamen University, Xiamen, China
Abstract: The BiCl3-catalyzed reaction of pyrroles with electron-deficient olefins
generated the corresponding Michael adducts in high yields.
Keywords: Bismuth trichloride, electron-deficient olefins, Michael addition, pyrroles
Pyrroles and their derivatives are extremely important as valuable building
blocks for the synthesis of biologically active compounds and natural
products,[1] and their synthesis and reactions have been a focus of considerable
attention in synthetic organic chemistry as well as in medical chemistry for
more than a century. Because the 2-position of pyrrole is the preferred site
for electrophilic substitution, 2-alkyl or 2-acyl pyrroles are versatile inter-
mediates for the synthesis of a wide range of pyrrole derivatives. Several
indirect routes leading to C-alkyl pyrroles have been established: (1)
Wolff–Kishner reduction of 2-formyl or 2-acetyl pyrroles;[2] (2) the isomer-
ization of N-alkyl pyrroles by thermal rearrangement at high temperature,
resulting in the 2- and 3-alkyl pyrroles;[3] and (3) preparation of 2- and
3-alkyl pyrroles using pyrrolyl magnesium halides.[4] However, these
Received in Japan September 6, 2005
Address correspondence to Zhuang-Ping Zhan, Department of Chemistry and the
Key Laboratory for Chemical Biology of Fujian Province, College of Chemistry and
Chemical Engineering, Xiamen University, Xiamen 361005, China. Fax: þ86-592-
2185780; E-mail: zpzhan@xmu.edu.cn
1373

1374
Z.-P. Zhan, J.-L. Yu, and W.-Z. Yang
indirect methods share the drawbacks of multistep synthetic reactions, and
they tend to polymerize under most reaction conditions. The direct C-alky-
lation of pyrroles by the Friedel–Crafts approach has been considered imprac-
tical because the acidic catalysts (Brønsted or Lewis) employed can induce
polymerization and polyalkylation[5] that result in low yields of products.
Lately, it has been reported that using InCl3,[6] Cu(II)-bis(oxazoline),[7] and
benzyl imidazolidinone–HX salts[8] as catalysts, monoalkylation of pyrrole
with a,b-unsaturated compounds can be achieved. Though several such
catalysts are available for preparation of C-alkyl pyrroles, there is also a
need for cheaper and more efficient Lewis acid catalysts for this class of
reactions. To our knowledge, C-alkylation of pyrroles with a,b-unsaturated
compounds catalyzed by bismuth(III) compounds has not been reported.
Recently, bismuth(III) compounds have received attention in organic
synthesis because of their low toxicity, low cost, and relative insensitivity
to air and to small amounts of moisture. Bismuth has an electron configuration
of [Xe]4f145d106s26p3. Because of the weak shielding of the 4f electrons
(Lanthanide contraction), bismuth(III) compounds exhibit Lewis acidity,
and they have been used in many chemical transformations.[9] Bismuth tri-
chloride is particularly attractive for us because it is commercially
available, inexpensive, and stabile. Herein, we describe the remarkable
catalytic activity of bismuth trichloride in the Michael addition of pyrroles
with electron-deficient olefins (Scheme 1).
Our first aim was to test the catalytic activity of BiCl3 in Michael addition
of pyrroles with electron-deficient olefins, so we carried out the reaction of
pyrrole with methyl vinyl ketone in the presence of 10 mol% BiCl3 using
dichloromethane as the reaction medium. We were delighted to discover
that the reaction proceeded rapidly with high regioselectivity within 1 h to
afford the corresponding 2-alkyl pyrrole in 85% yield. 2,5-Dialkylated
pyrrole as the side product was obtained in 10% yield (Table 1, entry 1).
The reaction was clean, and there was no formation of other side products
such as dimers or trimers that are normally observed under the influence of
strong acids. Phenyl vinyl ketone also reacted well to give corresponding
2-alkyl pyrrole in 78% yield (entry 2).
However, when the more hindered chalcone was treated with pyrrole
under the same condition, the reaction proceeded rather slowly, and after
12 h some of the starting materials still remained unconsumed. The yields
of corresponding alkylated pyrroles were fairly low: monoalkylpyrrole as
the major product in 41% yield and dialkylpyrrole as the minor product in
Scheme 1.

Table 1. BiCl3 (10% mol) mediated Michael addition of pyrroles with electron-deficient olefins
Reaction
medium
Time
(h)
Isolated
yield (%)
Entry
1
Nucleophile
Electrophile
Product
85 (10)a
83b
CH2Cl2
CH2Cl2
CH3CN
CH2Cl2
1
1
78 (12)a
74b
2
3
4
0.4
12c
41(32)a
41 (16)a
32 (51)a
5
6
CH3CN
CH3CN
1
1
80
75b
(continued)

Table 1. Continued
Reaction
medium
Time
(h)
Isolated
yield (%)
Entry
7
Nucleophile
Electrophile
Product
86
88b
CH2Cl2
CH2Cl2
1
2
8
83
9
CH3CN
CH3CN
20
4
88
91
10

80
80b
11
CH2Cl2
1
76
74b
12
13
14
CH2Cl2
CH2Cl2
CH2Cl2
1
4
4
83
85
aIsolated yields of corresponding 2,5-dialkylpyrroles.
bIn the presence of 5% mol BiCl3.
cSome of chalcone remained unconsumed.

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Z.-P. Zhan, J.-L. Yu, and W.-Z. Yang
16% yield (entry 4). As a solution, acetonitrile was utilized instead of
dichloromethane as the reaction medium. The reaction proceeded rapidly,
and the reaction time was sharply shortened to 1 h. This led to an interesting
result: monoalkylpyrrole as the minor product in 32% yield and dialkylpyrrole
as the major product in 51% yield (entry 5). By comparison of entry 4 and
entry 5, we might make a conclusion that BiCl3 in CH3CN increased
catalytic activity but decreased regioselectivity more than in CH2Cl2. The
reaction difference between entries 2 and 3 added further support to this
conclusion.
Various a,b-unsaturated ketones also reacted well with 2-alkylpyrroles
and gave the corresponding 2,5-dialkylated products in good to excellent
yields. In some cases acetonitrile was needed as the reaction medium to
enhance catalytic activity of BiCl3. In contrast with reactions of free
pyrrole, reactions of 2-alkylpyrroles with a,b-unsaturated ketones afforded
C-alkylation products in higher yields (entry 6, 80% versus entry 5, 32%;
entry 7, 86% versus entry 2, 78%). 2-Benzylidenemalononitrile and diethyl
2-benzylidenemalonate failed to react with free pyrrole catalyzed by BiCl3
in CH3CN; while using 2-alkylpyrrole instead of free pyrrole as the nucleo-
phile, this Michael reaction proceeded smoothly and corresponding C-alkyl-
pyrroles products were obtained in excellent yields (entries 9, 10). The
result indicated that 2-alkylpyrroles have much more reactivity than free
pyrrole in the presence of a catalytic amount of BiCl3 in acetonitrile. Further-
more, N-benzylpyrrole also reacted smoothly with electron-deficient olefins
with high regioselectivity and afforded corresponding 2-alkylpyrroles in
good yields (entries 11, 12), and the addition of pyrrole to b-nitrostyrene
also generated the corresponding 2-alkylated pyrroles in high yields (entries
13, 14). In some cases, the reactions employing 5% mol BiCl3 as the
catalyst were as good as that catalyzed by 10% mol BiCl3 (entries 1, 2, 6, 7,
11, 12).
In conclusion, we have developed a new, efficient, bismuth trichloride–
mediated procedure for the synthesis of C-alkylated pyrroles. Mild reaction
conditions, good yields, high regioselectivity, and operational simplicity are
some of the relevant advantages that make it a useful and attractive process
for the synthesis of alkylated pyrroles derivatives.
EXPERIMENTAL
Infrared spectra were measured with a Nicolet Avatar 360 FT-IR spec-
1
trometer. H NMR and 13C NMR spectra were recorded in CDCl3 on a
Varian unity þ500 spectrometer with tetramethylsilane (TMS) as an
internal standard. Chemical shifts are expressed in d (ppm) units downfield
from TMS. Mass spectra were recorded by Bruker Dalton Esquire 3000
plus and Finnigan Mat-LCQ (ESI direct injection). Elemental analysis was
performed using a Vario RL analyzer.

C-Alkylation of Pyrroles
1379
General Experimental Procedures
(a) 2-Alkylpyrroles (a–c, i–l): To a stirred solution of vinyl ketone (3 mmol)
or b-nitrostyrene and bismuth trichloride (10 mol%, 95 mg) in CH2Cl2 (6 mL)
or CH3CN, pyrrole (6 mmol) or N-benzylpyrrole was added at 08C and stirred
at ambient temperature for an appropriate time (Table 1). After complete con-
version, as indicated by TLC, the reaction mixture was diluted with water
(6 mL) and extracted with dichloromethane (3 ꢀ 15 mL). The combined
organic layers were dried over anhydrous Na2SO4, concentrated in vacuo,
and purified by column chromatography on silica gel to afford the pure
product.
(b) 2,5-Dialkylpyrroles (d–h): To a stirred solution of vinyl ketone
(3.6 mmol) or 2-benzylidenemalononitrile or diethyl 2-benzylidenemalonate
and bismuth trichloride (10 mol%, 95 mg) in CH2Cl2 (6 mL) or CH3CN,
2-alkylpyrrole (3 mmol) was added at 08C and stirred at ambient temperature
for an appropriate time (Table 1). After complete conversion, as indicated by
TLC, the reaction mixture was diluted with water (6 mL) and extracted with
dichloromethane (3 ꢀ 15 mL). The combined organic layers were dried
over anhydrous Na2SO4, concentrated in vacuo, and purified by column
chromatography on silica gel to afford the pure product.
Data
The 1H NMR, 13C NMR, MS and IR spectra data and CHN analysis results of
all the compounds are given here.
4-(1H-Pyrrol-2-yl)-butan-2-one (a). IR (film): ymax ¼ 3377, 3097,
1711 cm21 1H NMR (500 MHz, CDCl3): d 8.54 (br s, 1H), 6.68–6.64
;
(m, 1H), 6.12–6.08 (m, 1H), 5.92–5.88 (m, 1H), 2.87 (t, J ¼ 6.5 Hz, 2H),
2.81 (t, J ¼ 6.5 Hz, 2H), 2.17 (s, 3H); 13C NMR (125 MHz, CDCl3): d
209.6, 131.4, 116.6, 107.7, 105.1, 44.0, 30.0, 21.2; MS (ESI): (m/z)
[M þ H]þ 138. Anal. calcd. for C8H11NO: C, 70.04; H, 8.08; N, 10.21.
Found: C, 70.03; H, 8.12; N, 10.07.
1-Phenyl-3-(1H-pyrrol-2-yl)-propan-1-one (b). IR (film): ymax ¼ 3363,
1
3094, 1678, 1595, 1574, 1472, 1450 cm21; H NMR (500 MHz, CDCl3): d
8.55 (br s, 1H), 7.95–7.35 (m, 5H), 6.63–6.59 (m, 1H), 6.05–6.01 (m, 1H),
5.90–5.86 (m, 1H), 3.28 (t, J ¼ 6.5 Hz, 2H), 3.00 (t, J ¼ 6.5 Hz, 2H); 13C
NMR (125 MHz, CDCl3): d 200.6, 136.7, 133.3, 131.7, 128.6, 128.0, 116.7,
107.8, 105.4, 39.4, 21.5; MS (ESI): (m/z) [M þ H]þ 200. Anal. calcd. for
C13H13NO: C, 78.36; H, 6.58; N, 7.03. Found: C, 78.12; H, 6.42; N, 7.38.
1,3-Diphenyl-3-(1H-pyrrol-2-yl)-propan-1-one (c). IR (film): ymax ¼ 3386,
1
3062, 1681, 1599, 1578, 1493, 1450 cm21; H NMR (500 MHz, CDCl3): d

1380
Z.-P. Zhan, J.-L. Yu, and W.-Z. Yang
8.24 (br s, 1H), 7.93–7.15 (m, 10H), 6.62–6.58 (m, 1H), 6.05–6.01 (m, 1H),
5.81–5.77 (m, 1H), 4.73 (t, J ¼ 7.5 Hz, 1H), 3.76 (dd, J ¼ 17.5 and 8.0 Hz,
1H), 3.54 (dd, J ¼ 17.5 and 5.5 Hz, 1H); 13C NMR (125 MHz, CDCl3): d
199.0, 142.9, 136.9, 134.6, 133.3, 128.7, 128.6, 128.2, 128.1, 126.8, 117.1,
107.8, 105.4, 45.3, 39.3; MS (ESI): (m/z) [M þ H]þ 276. Anal. calcd. for
C19H17NO: C, 82.88; H, 6.22; N, 5.09. Found: C, 82.90; H, 6.37; N, 5.55.
3-[5-(3-Oxo-3-phenyl-propyl)-1H-pyrrol-2-yl]-1,3-diphenyl-propan-1-one
(d). IR (film): ymax ¼ 3370, 3070, 1681, 1678, 1595, 1577, 1498, 1450 cm21
;
1H NMR (500 MHz, CDCl3): d 8.38 (br s, 1H), 7.98–7.26 (m, 15H), 5.78
(d, J ¼ 2.5 Hz, 1H), 5.70 (d, J ¼ 2.5 Hz, 1H), 4.73 (t, J ¼ 7.5 Hz, 1H), 3.76
(dd, J ¼ 17.5 and 7.5 Hz, 1H), 3.55 (dd, J ¼ 17.5 and 6.0 Hz, 1H), 3.24
(t, J ¼ 6.5 Hz, 2H), 2.94 (t, J ¼ 6.5 Hz, 2H); 13C NMR (125 MHz, CDCl3):
d 200.1, 198.8, 143.0, 136.9, 136.8, 133.3, 133.1, 131.0, 128.6, 128.5, 128.1,
128.0, 126.7, 105.0, 104.8, 45.2, 39.4, 39.1, 21.8; MS (ESI): (m/z)
[M þ H]þ 408. Anal. calcd. for C28H25NO2: C, 82.53; H, 6.18; N, 3.44.
Found: C, 82.47; H, 6.40; N, 3.34.
4-[5-(3-Oxo-3-phenyl-propyl)-1H-pyrrol-2-yl]-butan-2-one (e). IR (film):
1
ymax ¼ 3363, 3067, 1697, 1673, 1599, 1582, 1483, 1449 cm21; H NMR
(500 MHz, CDCl3): d 8.56 (br s, 1H), 8.04–7.30 (m, 5H), 5.79
(d, J ¼ 2.5 Hz, 1H), 5.74 (d, J ¼ 2.5 Hz, 1H), 3.31 (t, J ¼ 6.5 Hz, 2H), 3.00
(t, J ¼ 6.5 Hz, 2H), 2.80 (t, J ¼ 6.5 Hz, 2H), 2.78 (t, J ¼ 6.5 Hz, 2H), 2.15
(s, 3H); 13C NMR (125 MHz, CDCl3): d 209.1, 200.2, 136.8, 133.2, 130.6,
130.4, 128.6, 128.0, 104.9, 104.8, 44.0, 39.2, 30.0, 21.7, 21.5; MS (ESI):
(m/z) [M þ H]þ 270. Anal. calcd. for C17H19NO2: C, 75.81; H, 7.11; N,
5.20. Found: C, 75.60; H, 7.37; N, 5.41.
3-[5-(3-Oxo-3-phenyl-propyl)-1H-pyrrol-2-yl]-cyclohexan-one (f). IR (film):
ymax ¼ 3374, 3061, 1705, 1678, 1595, 1580, 1448 cm21; 1H NMR (500 MHz,
CDCl3): d 8.52 (br s, 1H), 8.10–7.40 (m, 5H), 5.83 (d, J ¼ 2.5 Hz, 1H), 5.79
(d, J ¼ 2.5 Hz, 1H), 3.33 (t, J ¼ 6.0 Hz, 2H), 3.06 (m, 1H), 3.01 (t, J ¼ 6.0 Hz,
2H), 2.71-1.72 (m, 8H); 13C NMR (125 MHz, CDCl3): d 210.9, 200.9, 136.6,
133.7, 133.4, 130.9, 128.6, 128.0, 105.2, 103.4, 47.5, 41.2, 39.4, 37.4, 31.6,
24.8, 21.5; MS (ESI): (m/z) [M þ H]þ 296. Anal. calcd. for C19H21NO2: C,
77.26; H, 7.17; N, 4.74. Found: C, 77.36; H, 7.22; N, 4.58.
2-((5-(3-Oxo-3-phenylpropyl)-1H-pyrrol-2-yl)(phenyl) methyl) malononi-
trile (g). IR (film): ymax ¼ 3374, 3062, 2254, 1681, 1598, 1577, 1497,
1449 cm21 1H NMR (500 MHz, CDCl3): d 8.43 (br s, 1H), 7.95–7.31
;
(m, 10H), 6.17 (d, J ¼ 2.5 Hz, 1H), 5.91 (d, J ¼ 2.5 Hz, 1H), 4.56
(d, J ¼ 7.0 Hz, 1H), 4.28 (d, J ¼ 7.0 Hz, 1H), 3.28 (t, J ¼ 6.5 Hz, 2H), 2.95
(t, J ¼ 6.5 Hz, 2H); 13C NMR (125 MHz, CDCl3): d 200.6, 136.6, 135.9,
133.4, 133.1, 129.3, 129.0, 128.6, 128.2, 128.0, 125.3, 112.0, 111.7, 107.4,
106.2, 45.8, 39.0, 29.5, 21.4; MS (ESI): (m/z) [M þ H]þ 354. Anal. calcd.

C-Alkylation of Pyrroles
1381
for C23H19N3O: C, 78.16; H, 5.42; N, 11.89. Found: C, 78.36; H, 5.78; N,
11.79.
Diethyl 2-((5-(3-oxo-3-phenylpropyl)-1H-pyrrol-2-yl)(phenyl) methyl)
malonate (h). IR (film): ymax ¼ 3385, 3059, 1750, 1730, 1682, 1597, 1580,
1
1497, 1449 cm21; H NMR (500 MHz, CDCl3): d 8.50 (br s, 1H), 7.95–
7.15 (m, 10H), 5.78 (d, J ¼ 2.5 Hz, 1H), 5.76 (d, J ¼ 2.5 Hz, 1H), 4.72
(d, J ¼ 11.0 Hz, 1H), 4.13 (q, J ¼ 7.0 Hz, 2H), 4.10 (d, J ¼ 11.0 Hz, 1H),
3.91 (q, J ¼ 7.0 Hz, 2H), 3.24 (t, J ¼ 6.5 Hz, 2H), 2.93 (t, J ¼ 6.5 Hz, 2H),
1.15 (t, J ¼ 7.0 Hz, 3H), 0.94 (t, J ¼ 7.0 Hz, 3H); 13C NMR (125 MHz,
CDCl3): d 200.0, 168.5, 167.5, 139.8, 136.7, 133.1, 131.3, 130.2, 128.5,
128.4, 128.3, 128.0, 127.0, 105.9, 105.1, 61.7, 61.3, 58.0, 44.4, 39.0, 21.8,
13.9, 13.6; MS (ESI): (m/z) [M þ H]þ 448. Anal. calcd. for C27H29NO5: C,
72.46; H, 6.53; N, 3.13. Found: C, 72.55; H, 6.69; N, 3.40.
4-(1-Benzyl-1H-pyrrol-2-yl) butan-2-one (i). IR (film): ymax ¼ 3062, 1714,
1
1604, 1496, 1485, 1453 cm21; H NMR (500 MHz, CDCl3): d 7.34–6.95
(m, 5H), 6.65–6.61 (m, 1H), 6.14–6.10 (m, 1H), 5.93–5.89 (m, 1H), 5.04
(s, 2H), 2.72 (t, J ¼ 7.5 Hz, 2H), 2.65 (t, J ¼ 7.5 Hz, 2H), 2.07 (s, 3H); 13C
NMR (125 MHz, CDCl3): d 207.6, 138.2, 131.7, 128.6, 127.3, 126.3, 121.3,
107.1, 105.8, 50.2, 42.4, 29.8, 20.0; MS (ESI): (m/z) [M þ H]þ 228. Anal.
calcd. for C15H17NO: C, 79.26; H, 7.54; N, 6.16. Found: C, 79.35; H, 7.81;
N, 6.47.
3-(1-Benzyl-1H-pyrrol-2-yl)-1-phenylpropan-1-one (j). IR (film): ymax
¼
3051, 1677, 1594, 1578, 1495, 1449 cm21; H NMR (500 MHz, CDCl3): d
7.90–6.95 (m, 10H), 6.68–6.64 (m, 1H), 6.16–6.14 (m, 1H), 6.02–5.98
(m, 1H), 5.09 (s, 2H), 3.18 (t, J ¼ 7.5 Hz, 2H), 2.91 (t, J ¼ 7.5 Hz, 2H); 13C
NMR (125 MHz, CDCl3): d 199.0, 138.3, 136.7, 133.0, 132.0, 128.7, 128.5,
127.9, 127.4, 126.3, 121.4, 107.2, 106.1, 50.3, 37.8, 20.5; MS (ESI): (m/z)
[M þ H]þ 290. Anal. calcd. for C20H19NO: C, 83.01; H, 6.62; N, 4.84.
Found: C, 83.29; H, 6.87; N, 4.65.
1
2-(2-Nitro-1-phenyl-ethyl)-1H-pyrrole (k) IR (film): ymax ¼ 3427, 3029,
1
1600, 1550, 1493, 1454, 1377 cm21; H NMR (500 MHz, CDCl3): d 7.84
(br s, 1H), 7.38–7.21 (m, 5H), 6.71–6.66 (m, 1H), 6.20–6.15 (m, 1H),
6.11–6.06 (m, 1H), 4.98 (dd, J ¼ 12.5 and 7.5 Hz, 1H), 4.90 (t, J ¼ 7.5 Hz,
1H), 4.81 (dd, J ¼ 12.5 and 7.5 Hz, 1H); 13C NMR (125 MHz, CDCl3): d
137.9, 129.2, 128.9, 128.1, 127.9, 118.2, 108.6, 105.7, 79.2, 42.9; MS
(ESI): (m/z) [M þ H]þ 217. Anal. calcd. for C12H12N2O2: C, 66.65; H,
5.59; N, 12.96. Found: C, 66.66; H, 5.25; N, 12.80.
2-[1-(4-Methoxy-phenyl)-2-nitro-ethyl]-1H-pyrrole (l). IR (film): ymax
3424, 3030, 1610, 1548, 1509, 1463, 1376 cm21 1H NMR (500 MHz,
CDCl3): d 7.82 (br s, 1H), 7.17–6.86 (m, 4H), 6.71–6.67 (m, 1H),
¼
;

1382
Z.-P. Zhan, J.-L. Yu, and W.-Z. Yang
6.19–6.15 (m, 1H), 6.09–6.05 (m, 1H), 4.97 (dd, J ¼ 12.5 and 7.5 Hz, 1H),
4.86 (t, J ¼ 7.5 Hz, 1H), 4.77 (dd, J ¼ 12.5 and 7.5 Hz, 1H), 3.80 (s, 3H);
13C NMR (125 MHz, CDCl3): d 159.5, 130.0, 129.3, 129.0, 118.0, 114.7,
108.8, 105.7, 79.5, 55.3, 42.3; MS (ESI): (m/z) [M þ H]þ 247. Anal. calcd.
for C13H14N2O3: C, 63.40; H, 5.73; N, 11.38. Found: C, 63.01; H, 5.57; N,
11.39.
ACKNOWLEDGMENT
The project was supported by the Natural Science Foundation of Fujian
Province of China (No. C0510002).
REFERENCES
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Pergamon: Oxford, 1984; Vol. 4, pp. 313–376; (b) Saxton, J. E. Recent progress in
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