Selective substitution reactions of methoxycarbonylamino-1-(1- benzotriazolyl)alkanes with active methylene compounds

Article abstract of DOI:10.1002/jhet.612

Benzotriazole adducts methoxycarbonylamino-1-(1-benzotriazolyl)alkanes 1 were derived from the condensation of an aldehyde, benzotriazole, and methylcarbamate. The leaving tendency of methoxycarbonylamino group (MeOCONH) and benzotriazole group (Bt) was i

Full text of DOI:10.1002/jhet.612

434
Selective Substitution Reactions of Methoxycarbonylamino-1-
(1-benzotriazolyl)alkanes with Active Methylene Compounds
Vol 48
Liejin Zhou,a,b Xin Lv,a,b Hui Mao,a,b and Xiaoxia Wanga,b
*
aZhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Zhejiang Normal University,
Jinhua 321004, People’s Republic of China
bCollege of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004,
People’s Republic of China
*E-mail: wangxiaoxia@zjnu.cn
Received March 15, 2010
DOI 10.1002/jhet.612
Published online 21 January 2011 in Wiley Online Library (wileyonlinelibrary.com).
Benzotriazole adducts methoxycarbonylamino-1-(1-benzotriazolyl)alkanes 1 were derived from the
condensation of an aldehyde, benzotriazole, and methylcarbamate. The leaving tendency of methoxycar-
bonylamino group (MeOCONH) and benzotriazole group (Bt) was investigated by treatment of the
adducts with active methylene compounds under either Lewis acid-catalyzed or basic conditions. In the
presence of SmI3, MeOCONH take priority over Bt in the leaving process, whereas in the presence of
MeONa, the Bt was substituted in preference. Thus, the tunable substitution of the two leaving groups
could be used for different synthetic purposes.
J. Heterocyclic Chem., 48, 434 (2011).
INTRODUCTION
bonanion from organozinc reagents [4c]. Interestingly,
the acyloxy (AOCOR) in the same substrates could be
selectively removed via SmI2-mediated reduction [4d].
Nevertheless, examples concerning such conditions-de-
pendent selectivity are limited and more examples for
the selective scission of either Bt or the other concurrent
leaving group are required so as to make it more appli-
cable in organic synthesis.
Benzotriazole is a useful synthetic auxiliary due to
the readily introduction and good leaving ability of the
benzotriazolyl (Bt). A large number of benzotriazole
derivatives have been reported as key intermediates for
the synthesis of various compounds [1].
Benzotriazole derivatives of type BtACAOR was
reported to be ionized [2] either by BtAC bond scission
to form alkyleneonium cations CþAOR and Btꢀ or by
CAO bond scission to give ROꢀ anion and a benzotria-
zole stabilized carbocation Bt¼¼Cþ, depending on the
substituents in the molecules. Recently, the selective sub-
stitution of Bt or amido group in N-(a-benzotriazolyl-
alkyl)amides (BtACANHCOR type) were achieved by
using different Lewis acid catalysts. Promoted by AlCl3
[3a] or SmI3 [3b], the Bt could be substituted selectively
by active methylene compounds. However, in the pres-
ence of Dy(OTf)3, selective substitution of the amido
group (ANHCOR) in the same substrates was found
[3c]. The Bt in 1-(benzotriazole-1-yl)alkyl ester [4a]
(BtACAOCOR type) could be selectively substituted by
C-nucleophiles such as cyanide anion [4b] and the car-
RESULTS AND DISCUSSION
As a part of our continuing work in benzotriazole
chemistry, we wish to report the selective substitution
reactions of methoxycarbonylamino-1-(1-benzotriazolyl)
alkanes 1 with active methylene compounds.
The substrates methoxycarbonylamino-1-(1-benzotri-
azoly)alkanes 1 could be facilely prepared by the con-
densation of an aldehyde, benzotriazole, and methylcar-
bamate (Table 1). They were obtained in moderate to
good yields (Table 1, entries 1–8).
With compounds 1 in hand, we then tried to investigate
the substitution reaction with active methylene compounds.
C
V
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Selective Substitution Reactions of Methoxycarbonylamino-1-(1-benzotriazolyl)
alkanes with Active Methylene Compounds
435
Table 1
Synthesis of Methoxycarbonylamino-1-(1-benzotriazoly)alkanes 1.a
Entry
1
Ar
Compounds 1
Time (h)
24
Yields (%)b
1a
83
2
3
4
5
1b
1c
1d
1e
24
24
24
24
56
61
60
58
6
7
8
1f
1g
1h
24
24
24
72
68
70
a Reaction conditions: aldehyde (10 mmol), benzotriazole (10 mmol), methyl methyl-carbamate (10 mmol), toluene (30 mL), p-TsOH (0.1 mmol), reflux.
b Isolated yield.
Methyl N-(1-benzotriazol-1-phenylmethyl)carbamate 1a
and ethyl acetoacetate were initially used as the model
substrates. The first attempt was performed in THF with
SmI3 (20 mol %) as the catalyst under reflux (Table 2,
entry 1). Interestingly, in contrast with the previous
results [3b], the major product now obtained was b,b-
dicarbonyl derivatives 2a (35% yield), where the methox-
ycarbonylamino (ANHCOOMe) was replaced and the Bt
was reserved. We then tested other Lewis acid catalysts
such as AlCl3, and metal triflates (Table 2, entries 2–4).
Table 2
Substitution of 1a with ethyl acetoacetate under different conditions.a
Entry
Catalyst (equiv.)
Solvent
Temperature (ꢁC)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
SmI3 (0.2)
THF
THF
Reflux
Reflux
1
12
12
12
1
35
19
AlCl3 (1.0)
Zn(OTf)2 (0.2)
Cu(OTf)2 (0.2)
SmI3 (0.2)
SmI3 (0.2)
SmI3 (0.2)
THF
THF
Reflux
Reflux
Trace
Trace
37
40
48
CH3CN
Toluene
Dioxane
CH2Cl2
CH2Cl2
Reflux
70
4
Reflux
Reflux
Room temperature
2
1
SmI3 (0.2)
SmI3 (0.2)
67
36
5
a Reaction conditions: acetoacetate (1.1 mmol), 1 (1 mmol), solvent (10 mL).
b Isolated yield.
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L. Zhou, X. Lv, H. Mao, and X. Wang
Vol 48
Table 3
SmI3-catalyzed nucleophilic substitution reaction of methoxycarbonyl-amino-1-(1-benzotriazoly)alkanes 1 with 1,3-dicarboyl compounds.a
Entry
Ar in 1
R1
R2
Time (h)
1
Products
Yields (%)b
67
1
2
3
4
5
6
7
Me-
EtO-
2a
Me-
Me-
EtO-
Me-
Me-
Me-
MeO-
Me-
10
24
10
8
2b
2c
2d
2e
2f
70
40
58
63
54
59
EtO-
MeO-
EtO-
EtO-
4
10
2g
8
9
Me-
Me-
EtO-
MeO-
MeO-
EtO-
10
10
10
2h
2i
60
65
53
10
2j
c
11
12
Me-
Me-
EtO-
Me-
10
10
–
–
–
c
–
a Reaction conditions: 1 (1 mmol), active methylene compounds (1 mmol), SmI3 (0.2 mmol), solvent (10 mL), reflux.
b Isolated yield.
c Complete decomposition of compound 1.
However, these acid catalysts did not give encouraging
results and serious decomposition of substrate 1 to the
original aldehyde, benzotriazole, and methyl carbamate
was observed. Fortunately, screening of the solvents
(Table 2, entries 5–8) and examination of the temperature
(Table 2, entries 8–9) showed that refluxing in CH2Cl2
with 20 mol % of SmI3 could afford 2a in improved
yield (67% yield) (Table 2, entry 8).
time and gave a lower yield (Table 3, entry 3). Compounds
1 bearing electron-donating groups (such as methyl and
methoxy) on the phenyl ring could afford the desired prod-
ucts 2 in moderate yields (Table 3, entries 1–10). How-
ever, electron-withdrawing groups (such as bromo and
nitro groups) led to the rapid decomposition of com-
pounds 1, and the desired products 2 could not be
obtained in these cases (Table 3, entry 11 and entry 12).
Because Bt is also a good leaving group, it could
be anticipated that the Bt might be substituted under
suitable conditions. Recent studies showed that the Bt
in benzyloxycarbonylamino-1-(1-benzotriazoly)alkanes
could be smoothly substituted by tert-butyl acetates using
lithium diisopropyl amine (LDA) as a base [5]. The
above results inspired us to envision a selective substitu-
tion of Bt in 1 by the active methylene compounds via
forming an enolate under proper basic conditions. We
After the reaction conditions were optimized, various
methoxycarbonylamino-1-(1-benzotri-azoly)alkanes 1 and
active methylene compounds were used as the substrates to
examine the scope and limitations. The results were sum-
marized in Table 3. We were pleased to find a variety of
active methylene compounds could smoothly react with 1
(Table 3, entries 1–10). Both b-keto esters and malonates
were good C-nucleophiles for the reaction, whereas the
substitutions with a b-diketone required longer reaction
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Table 4
MeONa-promoted nucleophilic substitution of methyl (1H-benzotriazolylaryl)methylcarbamate with 1,3-dicarboyl compounds.a
Entry
1
Ar
R1
R2
Time (min)
45
Product 3
Yields (%)b
Me-
EtO-
3a
77
83
86
72
64
65
2
3
4
5
6
Me-
Me-
Me-
Me-
EtO-
EtO-
EtO-
EtO-
EtO-
EtO-
60
35
3b
3c
3d
3e
3f
40
120
210
a Reaction conditions: 1 (1 mmol), active methylene compounds (1 mmol), CH3ONa (1 mmol), solvent (10 mL), room temperature.
b Isolated yields.
found that this substitution could proceed successfully in
the presence of MeONa. Generally, moderate to good yield
of the expected b-amino acid derivatives 3 could be
obtained within 3.5 h despite the electronic effect (Table 4).
Very recently, the reaction between N-(a-amidoalkyl)-
benzotriazoles and 1,3-diketones-dervied potassium enolates
was used for the preparation of the b-amido b-diketones by
the loss of Bt [6]. Combination with Katritzky’s research
[5a] and ours, it could be concluded that Bt is a better
leaving group than either amido or alkoxycarbonylamino
because the enolates consistently substitute the Bt in the
three types of substrates. In the base conditions, the above
reactions proceeded more probably via SN2 mechanism.
However, in the presence of SmI3, the benzotriazole
derivatives should ionize either to the benzotriazole anion
and cation 4 [5b] or to the alkoxycarbonylamino anion
and cation 5 [2] depending upon the substrate structures
(Scheme 1). In contrast with the BtACANHCOR stucutre
[3b], which tended to ionize to cation 4 in the presence of
SmI3, good chelation may exist for the BtACANHCOOMe
moeity because samarium salt was reported to coordinate
well with both OA and NA donors [7]. Hence, the leaving
ability of ANHCOOMe was effectively enhanced until an
alternative ionization mode to form cation 5 predominated.
Attack of cation 5 with active methylene compounds
afforded product 2.
NHCOOMe could be selectively substituted by the
active methylenyl group, and the benzotriazole deriva-
tives could be obtained in moderate to good yields;
whereas using MeONa as the base, the Bt was substi-
tuted preferentially and the b-amino acid derivatives
were prepared under mild conditions. The tunable leav-
ing tendency of the two leaving groups may be useful
for other synthetic purposes.
EXPERIMENTAL
Methylene chloride was distilled from calcium hydride im-
1
mediately before use. Melting points are uncorrected. H-NMR
Scheme 1. Proposed mechanism for the selective substitution of
ANHCOOMe with SmI3 as a catalyst.
In summary, selective substitution of either NHCOOMe
or Bt in N-(a-benzotriazol-1-ylalkyl) methylcarbamates
was achieved by performing the reaction under different
conditions. With SmI3 as the Lewis acid catalyst,
Journal of Heterocyclic Chemistry
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L. Zhou, X. Lv, H. Mao, and X. Wang
Vol 48
(400 MHz) spectra were recorded on a Bruker AV400 NMR
instrument as CDCl3 solutions using tetramethyl silane (TMS)
as internal standard. Chemical shifts (r) are reported in parts per
million (ppm) and coupling constants J are given in hertz. IR
spectra were recorded in film or using KBr disks with a Nicolet
Nexus 670 FTIR spectrometer. Mass spectra were recorded on a
HP 5989B MS spectrometer (70 eV). Elemental analyses were
performed on a Vario-ELIII instrument. Compounds 1 were pre-
pared using the method analogous to that for the preparation of
benzyloxycarbonylamino-1-(1-benzotriazolyl)alkanes [8].
Methyl (1H-benzo[d][1,2,3]triazol-1-yl)(m-tolyl)-methylcar-
bamate (1d). White solid, mp 168–170ꢁC. IR (KBr): 3337,
3131, 1702, 1530, 1400, 1234 cmꢀ1 1H-NMR (400 MHz,
.
CDCl3): d ¼ 8.09 (d, J ¼ 8.0 Hz, 1H), 7.63–7.60 (m, 2H),
7.47–7.36 (m, 2H), 7.26–7.06 (m, 4H), 6.42 (s, 1H), 3.70 (s,
3H), 2.30 (s, 3H). 13C-NMR (100 MHz, CDCl3): d ¼ 155.8,
145.9, 139.1, 130.1, 129.0, 127.9, 126.9, 126.7, 124.3, 123.3,
120.1, 118.5, 109.8, 66.9, 52.9, 21.4. Anal. Calcd. for
C16H16N4O2: C, 64.85; H, 5.44; N, 18.91. Found: C, 65.05; H,
5.42; N, 18.87. See Table 1, entry 4.
General procedure for the preparation of b,b-dicarbonyl
benzotriazole derivatives 2. An oven-dried 50 mL flask was
charged with samarium powder (0.03 g, 0.2 mmol), anhydrous
THF (10 mL), and I2 (0.076 g, 0.3 mmol). The mixture was
stirred at room temperature for 1 h and concentrated in vacuo.
Then anhydrous CH2Cl2 (10 mL), 1,3-dicarbonyl compounds
(1 mmol) and N-(1-benzotriazol-1-ylalky1)carbamate deriva-
tives 1 (1 mmol) were added. The mixture was stirred under
reflux until the disappearance of 1 was observed [reaction
monitored by thin-layer chromatography (TLC)]. The reaction
was quenched with aq. HCl (0.1M, 3 mL) and extracted with
diethyl ether (3ꢂ 10 mL). The combined organic extracts were
washed with saturated Na2S2O3 (5 mL), then with brine, and
were dried over anhydrous Na2SO4. Removal of the solvent
under reduced pressure afforded the crude product, which was
purified by preparative TLC on silica gel using ethyl acetate/
petroleum ether (1/4, v/v) as eluent to give the corresponding
benzotriazole derivatives 2.
General procedure for the preparation of 3. A mixture of
1 (1 mmol), active methylene compounds (1 mmol), and
CH3ONa (1 mmol) in THF (5 mL) was stirred until the disap-
pearance of 1 (monitored by TLC). Then the reaction was
quenched with H2O and extracted with ethyl acetate (3ꢂ 10
mL). The combined organic extracts were washed with satu-
rated Na2CO3, then with brine, and were dried over anhydrous
Na2SO4, then filtrated and concentrated under reduced pres-
sure. The residue was purified by preparative TLC on silica
gel to give product 3.
Methyl (1H-benzo[d][1,2,3]triazol-1-yl)(o-tolyl-methylcarba-
mate (1e). White solid, mp 153–156ꢁC. IR (KBr): 3290, 3133,
1
1718, 1531, 1400, 1246 cmꢀ1. H-NMR (400 MHz, CDCl3): d
¼ 8.07 (d, J ¼ 8.0 Hz, 1H), 7.74 (d, J ¼ 9.6 Hz, 1H), 7.50–
7.27 (m, 3H), 7.26–7.14 (m, 4H), 6.39 (s, 1H), 3.70 (s, 3H),
2.37 (s, 3H). 13C-NMR (100 MHz, CDCl3): d ¼ 155.9, 146.0,
135.8, 134.1, 132.4, 131.2, 129.5, 127.8, 126.7, 125.8, 124.3,
120.1, 109.8, 65.2, 53.0, 19.2. Anal. Calcd. for C16H16N4O2:
C, 64.85; H, 5.44; N, 18.91. Found: C, 64.98; H, 5.43; N,
18.96. See Table 1, entry 5.
Methyl (1H-benzo[d][1,2,3]triazol-1-yl)(4-chloro-phenyl)-
methylcarbamate (1f). White solid, mp 154–156ꢁC. IR (KBr):
1
3295, 3023, 1718, 1549, 1400, 1250 cmꢀ1. H-NMR (400 MHz,
CDCl3): d ¼ 7.90–7.87 (m, 2H), 7.65 (s, 1H), 7.43–7.41 (m, 2H),
7.31 (d, J ¼ 8.4 Hz, 2H), 7.18 (d, J ¼ 8.4 Hz, 2H), 6.40 (s, 1H),
3.74 (s, 3H). 13C-NMR (100 MHz, CDCl3): d ¼ 156.3, 145.5,
134.8, 132.4, 128.3, 127.8, 127.1, 124.5, 123.7, 118.6, 109.2,
73.0, 53.2. Anal. Calcd. for C15H13ClN4O2: C, 56.88; H, 4.14; N,
17.69. Found: C, 57.06; H, 4.13; N, 17.73. See Table 1, entry 6.
Methyl (1H-benzo[d][1,2,3]triazol-1-yl)(4-bromo-phenyl)-
methylcarbamate (1g). White solid, mp 158–160ꢁC. IR (KBr):
3272, 3019, 1720, 1535, 1400, 1241 cmꢀ1 1H-NMR (400
.
MHz, CDCl3): d ¼ 7.89–7.87 (m, 2H), 7.65 (s, 1H), 7.47 (d, J
¼ 8.4Hz, 2H), 7.42–7.40 (m, 2H), 7.12 (d, J ¼ 8.4 Hz, 2H),
6,45 (s,1H), 3.74 (s, 3H). 13C-NMR (100 MHz, CDCl3): d ¼
156.2, 144.3, 135.4, 132.2, 128.1, 127.8, 127.0, 124.5, 123.7,
118.5, 109.5, 73.6, 53.1. Anal. Calcd. for C15H13BrN4O2: C,
49.88; H, 3.63; N, 15.51. Found: C, 49.73; H, 3.64; N, 15.55.
See Table 1, entry 7.
Methyl (1H-benzo[d][1,2,3]triazol-1-yl)(phenyl) methylcar-
bamate (1a). White solid, mp 120–122ꢁC (123–124ꢁC) [8].
See Table 1, entry 1.
Methyl (1H-benzo[d][1,2,3]triazol-1-yl)(4-nitro-phenyl)me-
thylcarbamate (1h). White solid, mp 147–150ꢁC. IR (KBr):
3278, 3043, 1717, 1545, 1400, 1239 cmꢀ1 1H-NMR (400
.
Methyl (1H-benzo[d][1,2,3]triazol-1-yl)(4-methoxy-phenyl)-
methylcarbamate (1b). White solid, mp 156–158ꢁC. IR (KBr):
MHz, CDCl3): d ¼ 8.21 (d, J ¼ 8.8 Hz, 2H), 8.11 (d, J ¼ 8.4
Hz, 1H), 7.77 (d, J ¼ 9.6 Hz, 1H), 7.66–7.42 (m, 5H), 6.61
(d, J ¼ 9.6 Hz, 1H), 3.73 (s, 3H). 13C-NMR (100 MHz,
CDCl3): d ¼ 156.2, 147.6, 137.5, 134.1, 130.9, 128.5, 127.7,
124.8, 124.2, 120.3, 109.4, 66.1, 53.3. Anal. Calcd. for
C15H13N5O4: C, 55.05; H, 4.00; N, 21.40. Found: C, 55.21; H,
4.01; N, 21.34. See Table 1, entry 8.
3414, 3193, 1715, 1546, 1400, 1252 cmꢀ1 1H-NMR (400
.
MHz, CDCl3): d ¼ 8.07 (d, J ¼ 8.4 Hz, 1H), 7.63–7.57 (m,
2H), 7.45–7.37 (m, 2H), 7.19 (d, J ¼ 8.4 Hz, 2H), 6.84 (d, J ¼
6.8 Hz, 2H), 6.50 (s, 1H), 3.77(s, 3H), 3.68 (s, 3H). 13C-NMR
(100 MHz, CDCl3): d ¼ 160.2, 156.0, 145.9, 132.5, 128.0,
127.8, 127.7, 124.3, 120.1, 114.4, 109.8, 67.1, 55.4., 52.9. Anal.
Calcd. for C16H16N4O3: C, 61.53; H, 5.16; N, 17.94. Found: C,
61.62; H, 5.15; N, 17.90. See Table 1, entry 2.
Ethyl 2-((1H-benzo[d][1,2,3]triazol-1-yl)(phenyl)-methyl)-3-
oxobutanoate (2a). White solid, mp 137–139ꢁC. IR (KBr):
Methyl (1H-benzo[d][1,2,3]triazol-1-yl)(p-tolyl)-methylcar-
bamate (1c). White solid, mp 154–157ꢁC. IR (KBr): 3413,
3414, 1743, 1717, 1618, 1400 cmꢀ1 1H-NMR (400 MHz,
.
CDCl3): d ¼ 7.98 (d, J ¼ 8.4 Hz, 1H), 7.48–7.45 (m, 3H),
7.42–7.40 (m, 1H), 7.30–7.28 (m, 4H), 6.43 (d, J ¼ 11.2 Hz,
1H), 5.45 (d, J ¼ 11.2 Hz, 1H), 4.06–4.03 (m, 2H), 2.40 (s,
3H), 1.07 (t, J ¼ 7.2 Hz, 3H). 13C-NMR (100 MHz, CDCl3):
d ¼ 199.2, 165.5, 146.1, 135.9, 132.9, 129.1, 129.0, 128.9,
127.9, 127.6, 124.3, 119.8, 109.9, 64.1, 62.1, 61.0, 30.3, 13.8.
Anal. Calcd. for C19H19N3O3: C, 67.64; H, 5.68; N, 12.46.
Found: C, 67.78; H, 5.66; N, 12.43. MS (ES): m/z 337.9, ([M
þ Na]þ) (ES): ([M þ Na]þ): 359.8. See Table 3, entry 1.
3212, 1732, 1532, 1400, 1241 cmꢀ1 1H-NMR (400 MHz,
.
CDCl3): d ¼ 8.08 (d, J ¼ 8.0 Hz, 1H), 7.61 (d, J ¼ 9.6 Hz,
1H), 7.58–7.36 (m, 4H), 7.15 (m, 4H), 6.35 (s, 1H), 3.71 (s,
3H), 2.32 (s, 3H). 13C-NMR (100 MHz, CDCl3): d ¼ 155.1,
146.0, 139.4, 129.8, 127.8, 126.7, 126.2, 124.3, 120.1, 118.5,
109.8, 67.3, 52.5, 21.1. Anal. Calcd. for C16H16N4O2: C,
64.85; H, 5.44; N, 18.91. Found: C, 64.62; H, 5.45; N, 18.94.
See Table 1, entry 3.
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7.09 (d, J ¼ 7.6 Hz, 2H), 6.40 (d, J ¼ 11.2 Hz, 1H), 5.43 (d, J ¼
11.2 Hz, 1H), 4.08–4.04 (m, 2 H), 2.40 (s, 3H), 2.27 (s, 3H), 1.10
(d, J ¼ 11.2 Hz, 3H). 13C-NMR (100 MHz, CDCl3): d ¼ 199.4,
165.5, 138.9, 133.0, 129.5, 127.7, 127.6, 124.2, 119.8, 110.0, 64.1,
62.1, 60.8, 30.4, 21.1, 13.8. Anal. Calcd. for C20H21N3O3: C,
68.36; H, 6.02; N, 11.96. Found: C, 68.54; H, 6.04; N, 12.01. MS
(ES): m/z 353, ([M þ Na]þ) (ESI): 389.9. See Table 3, entry 6.
Methyl 2-((1H-benzo[d][1,2,3]triazol-1-yl)(phenyl)-methyl)-
3-oxobutanoate (2b). White solid, mp 103–106ꢁC. IR (KBr):
3129, 1745, 1720, 1617, 1401 cmꢀ1. Major: 1H-NMR (400
MHz, CDCl3): d ¼ 7.98 (d, J ¼ 8.4 Hz, 1H), 7.49–7.27 (m,
8H), 6.44 (d, J ¼ 11.2 Hz, 1H), 5.46 (d, J ¼ 11.2 Hz, 1H),
3.60 (s, 3H), 2.41 (s, 3H). 13C-NMR (100 MHz, CDCl3): d ¼
199.2, 165.9, 146.5, 136.0, 129.1, 129.0, 127.8, 127.7, 124.3,
119.9, 109.9, 63.9, 61.0, 53.0, 30.4.
Ethyl 2-((1H-benzo[d][1,2,3]triazol-1-yl)(m-tolyl)-methyl)-3-
1
Minor: H-NMR (400 MHz, CDCl3): d ¼ 7.98 (d, J ¼ 8.4
oxobutanoate (2g). Colorless oil. IR (KBr): 3435, 1745, 1721,
1
1608 cmꢀ1. Major: H-NMR (400 MHz, CDCl3): d ¼ 7.98 (d,
Hz, 1H), 7.49–7.27 (m, 8H), 6.41 (d, J ¼ 11.2 Hz, 1H), 5.46
(d, J ¼ 11.2 Hz, 1H), 3.60 (s, 3H), 2.12 (s, 3H). 13C-NMR
(100 MHz, CDCl3): d ¼ 199.2, 166.4, 146.5, 135.7, 129.1,
129.0, 127.7, 127.6, 124.2, 119.8, 109.9, 109.7, 63.4, 61.2, 53.0,
31.9. Anal. Calcd. for C18H17N3O3: C, 66.86; H, 5.30; N, 13.00.
Found: C, 66.65; H, 5.31; N, 13.03. MS (ES): m/z 323.7, ([M þ
Na]þ) (ES): ([M þ Na]þ): 345.7. See Table 3, entry 2.
J ¼ 8.4 Hz, 1H), 7.55–7.41 (m, 2H), 7.31–7.06 (m, 5H), 6.37
(d, J ¼ 11.2 Hz, 1H), 5.44 (d, J ¼ 11.2 Hz, 1H), 4.07–4.00
(m, 2H), 2.40 (s, 3H), 2.28 (s, 3H), 1.08 (t, J ¼ 7.2 Hz, 3H).
13C-NMR (100 MHz, CDCl3): d ¼ 199.3, 165.5, 146.1, 138.7,
135.8, 132.9, 129.9, 128.7, 128.3, 127.6, 125.0, 124.2, 119.8,
109.9, 64.1, 62.1, 61.1, 30.3, 21.4, 13.8.
1
3-((1H-Benzo[d][1,2,3]triazol-1-yl)(phenyl)methyl)-pentane-
Minor: H-NMR (400 MHz, CDCl3): d ¼ 7.98 (d, J ¼ 8.4
2,4-dione (2c). White solid, mp 146–148ꢁC. IR (KBr): 3131,
Hz, 1H), 7.55–7.41 (m, 2H), 7.31–7.06 (m, 5H), 6.35 (d, J ¼
11.2 Hz, 1H), 5.44 (d, J ¼ 11.2 Hz, 1H), 4.07–4.00 (m, 2H),
2.28 (s, 3H), 2.15 (s, 3H), 1.03 (t, J ¼ 6.8 Hz, 3H). 13C-NMR
(100 MHz, CDCl3): d ¼ 200.2, 165.8, 145.9, 138.9, 135.7,
129.8, 128.9, 128.3, 127.6, 125.0, 124.2, 119.8, 109.7, 63.8, 62.1,
60.9, 31.8, 21.3, 13.7. Anal. Calcd. for C20H21N3O3: C, 68.36;
H, 6.02; N, 11.96. Found: C, 68.45; H, 6.01; N, 11.98. MS (ES):
m/z 351.9, ([M þ Na]þ) (ESI): 373.8. See Table 3, entry 7.
1
1743, 1721, 1696, 1406 cmꢀ1. H-NMR (400 MHz, CDCl3): d
¼ 7.83–7.81 (m, 2 H), 7.50–7.47 (m, 2H), 7.36–7.30 (m, 5H),
6.72 (d, J ¼ 11.6 Hz, 1H), 5.53 (d, J ¼ 11.6 Hz, 1H), 2.23 (s,
3H), 2.09 (s, 3H). 13C-NMR (100 MHz, CDCl3): d ¼ 199.6,
199.4, 144.3, 135.8, 129.3, 129.1, 127.7, 126.6, 118.2, 109.6,
72.9, 68.6, 30.8, 29.4. Anal. Calcd. for C18H17N3O2: C, 70.34;
H, 5.58; N, 13.67. Found: C, 70.46; H, 5.56; N, 13.65. MS
(ES): m/z 307, ([M þ Na]þ). (ES): ([M þ Na]þ): 329.7. See
Table 3, entry 3.
Methyl 2-((1H-benzo[d][1,2,3]triazol-1-yl)(m-tolyl)-methyl)-
3-oxobutanoate (2h). White solid, mp 122–125ꢁC. IR (KBr):
3130, 1748, 1717, 1400 cmꢀ1. Major: 1H-NMR (400 MHz,
CDCl3): d ¼ 8.02–8.00 (m, 1H), 7.55–7.39 (m, 2H), 7.32–7.16
(m, 5H), 7.07 (d, J ¼ 8.0 Hz, 1H), 6.43–6.36 (m, 1H), 5.45 (d,
J ¼ 11.2 Hz, 1H), 3.62 (s, 3H), 2.41 (s, 3H), 2.28 (s, 3H).
13C-NMR (100 MHz, CDCl3): d ¼ 200.2, 166.0, 146.1, 138.8,
135.9, 129.9, 128.7, 128.1, 127.6, 124.9, 124.3, 119.8, 110.0,
63.9, 61.0, 53.0, 30.5, 21.4.
Minor: 1H-NMR (400 MHz, CDCl3): d ¼ 8.00–8.02 (m,
1H), 7.55–7.39 (m, 2H), 7.32–7.16 (m, 5H), 7.07 (d, J ¼ 8.0
Hz, 1H), 6.43–6.36 (m, 1H), 5.45 (d, J ¼ 11.2 Hz, 1H), 3.59
(s, 3H), 2.28 (s, 3H), 2.12 (s, 3H). 13C-NMR (100 MHz,
CDCl3): d ¼ 199.3, 166.5, 146.1, 139.0, 135.6, 130.0, 129.0,
128.3, 128.1, 127.6, 124.9, 124.2, 119.8, 109.8, 63.4, 61.2,
52.9, 31.9, 21.4. Anal. Calcd. for C19H19N3O3: C, 67.64; H,
5.68; N, 12.46. Found: C, 67.80; H, 5.67; N, 12.44. MS (ES):
m/z 337.9, ([M þ Na]þ) (ESI): 359.7. See Table 3, entry 8.
Diethyl 2-((1H-benzo[d][1,2,3]triazol-1-yl)(phenyl)-methyl)-
malonate (2d). White solid, mp 105–108ꢁC. IR (KBr): 3132,
1745, 1721, 1400 cmꢀ1
.
1H-NMR (400 MHz, CDCl3): d ¼
8.01 (d, J ¼ 8.4 Hz, 1H), 7.56–7.50 (m, 3H), 7.45–7.43 (m,
1H), 7.34–7.30 (m, 4H), 6.39 (d, J ¼ 11.6 Hz, 1H), 5.17 (d, J
¼ 11.6 Hz, 1H), 4.09–4.00 (m, 4H), 1.07 (t, J ¼ 7.2 Hz, 3H),
1.01 (t, J ¼ 7.2 Hz, 3H). 13C-NMR (100 MHz, CDCl3): d ¼
166.3, 166.2, 146.1, 135.4, 133.0, 129.2, 128.9, 128.0, 127.6,
124.2, 120.0, 109.7, 62.2, 62.1, 61.6, 57.2, 13.8, 13.7. Anal.
Calcd. for C20H21N3O4: C, 65.38; H, 5.76; N, 11.44. Found:
C, 65.61; H, 5.66; N, 11.45. MS (ESI): m/z 367.8, ([M þ
Na]þ) (ESI): 389.9. See Table 3, entry 4.
Methyl 2-((1H-benzo[d][1,2,3]triazol-1-yl)(4-meth-oxyphe-
nyl)methyl)-3-oxobutanoate (2e). White solid, mp 102–104ꢁC.
IR (KBr): 3135, 1744, 1719, 1401 cmꢀ1. Major: 1H-NMR
(400 MHz, CDCl3): d ¼ 7.99 (d, J ¼ 8.4 Hz, 1H), 7.46–7.26
(m, 5H), 6.80 (d, J ¼ 8.4 Hz, 1H), 6.39 (d, J ¼ 11.2 Hz, 1H),
5.42 (d, J ¼ 11.2 Hz, 1H), 3.73 (s, 3H), 3.62 (s, 3H), 2.40 (s,
3H). 13C-NMR (100 MHz, CDCl3): d ¼ 199.4, 166.0, 159.9,
146.1, 132.8, 129.0, 127.9, 127.6, 124.3, 119.8, 114.2, 110.0,
64.0, 62.1, 55.2, 53.1, 30.5.
Methyl 2-((1H-benzo[d][1,2,3]triazol-1-yl)(o-tolyl)-methyl)-
3-oxobutanoate (2i). White solid, mp 98–101ꢁC. IR (KBr):
3434, 1745, 1720, 1450 cmꢀ1. Major: 1H-NMR (400 MHz,
CDCl3): d ¼ 7.97 (d, J ¼ 8.8 Hz, 1H), 7.53–7.30 (m, 4H),
7.18–7.15 (m, 3H), 6.75 (d, J ¼ 11.2 Hz, 1H), 5.51 (d, J ¼
11.2 Hz, 1H), 3.56 (s, 3H), 2.64 (s, 3H), 2.38 (s, 3H). 13C-
NMR (100 MHz, CDCl3): d ¼ 199.3, 166.0, 146.0, 136.2,
133.9, 132.8, 131.0, 129.0, 127.9, 127.6, 126.9, 124.2, 119.9,
109.8, 63.9, 56.5, 52.9, 30.4, 19.7.
1
Minor: H-NMR (400 MHz, CDCl3): d ¼ 7.99 (d, J ¼ 8.4
Hz, 1H), 7.46–7.26 (m, 5H), 6.80 (d, J ¼ 8.4 Hz, 1H), 6.34
(d, J ¼ 11.2 Hz, 1H), 5.42 (d, J ¼ 11.2 Hz, 1H), 3.73 (s, 3H),
3.59 (s, 3H), 2.13 (s, 3H). 13C-NMR (100 MHz, CDCl3): d ¼
200.4, 166.5, 159.9, 145.9, 132.8, 129.1, 127.9, 127.6, 124.2,
119.8, 114.4, 109.8, 63.4, 60.7, 55.3, 53.0, 30.5. Anal. Calcd.
for C19H19N3O4: C, 64.58; H, 5.42; N, 11.89. Found: C,
64.88; H, 5.44; N, 11.87. MS (ES): m/z 352.9, ([M þ Na]þ)
(ES): 386.9. See Table 3, entry 5.
1
Minor: H-NMR (400 MHz, CDCl3): d ¼ 7.98 (d, J ¼ 8.8
Hz, 1H), 7.53–7.30 (m, 4H), 7.18–7.15 (m, 3H), 6.70 (d, J ¼
11.2 Hz, 1H), 5.50 (d, J ¼ 11.2 Hz, 1H), 3.58 (s, 3H), 2.63 (s,
3H), 2.10 (s, 3H). 13C-NMR (100 MHz, CDCl3): d ¼ 200.1,
166.7, 146.0, 136.2, 134.0, 132.7, 131.2, 129.0, 127.9, 127.6,
127.0, 124.2, 119.9, 109.6, 63.2, 56.5, 53.0, 32.0, 19.8. Anal.
Calcd. for C19H19N3O3: C, 67.64; H, 5.68; N, 12.46. Found:
C, 67.53; H, 5.69; N, 12.45. MS (ES): m/z 337.8, ([M þ
Na]þ) (ES): 359.8. See Table 3, entry 9.
Ethyl 2-((1H-benzo[d][1,2,3]triazol-1-yl)(p-tolyl)-methyl)-3-
oxobutanoate (2f). White solid, mp 124–127ꢁC. IR (KBr): 3130,
1
1743, 1717, 1400 cmꢀ1. H-NMR (400 MHz, CDCl3): d ¼ 7.98
(d, J ¼ 8.0 Hz, 1H), 7.50 (d, J ¼ 8.0 Hz, 1H), 7.42–7.27 (m, 4H),
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

440
L. Zhou, X. Lv, H. Mao, and X. Wang
Vol 48
Minor: 1H-NMR (400 MHz, CDCl3): d ¼ 7.17–7.04 (m,
4H), 6.40 (s, 1H), 5.54 (s, 1H), 4.09–4.01 (m, 3H), 3.60 (s,
3H), 2.30 (s, 3H), 2.29 (s, 3H), 1.15–1.09 (m, 3H). 13C-NMR
(100 MHz, CDCl3): d ¼ 201.2, 168.3, 156.3, 139.4, 138.3,
128.5, 127.3, 123.5, 123.2, 64.2, 61.5, 53.3, 52.2, 30.4, 21.4,
13.9. Anal. Calcd. for C16H20O5: C, 65.74; H, 6.90; Found: C,
65.85; H, 6.91. See Table 4, entry 4.
Diethyl 2-((1H-benzo[d][1,2,3]triazol-1-yl)(o-tolyl)-methyl)-
malonate (2j). Colorless oil. IR (KBr): 3440, 1748, 1716, 1400
cmꢀ1. 1H-NMR (400 MHz, CDCl3): d ¼ 8.01 (d, J ¼ 8.4 Hz, 1H),
7.69 (d, J ¼ 8.0 Hz, 1H), 7.53–7.31 (m, 3H), 7.17–7.02 (m, 3H),
6.73 (d, J ¼ 10.0 Hz, 1H), 5.19 (d, J ¼ 10.0 Hz, 1H), 4.14–3.69
(m, 4H), 2.49 (s, 3H), 1.04–0.97 (m, 6H). 13C-NMR (100 MHz,
CDCl3): d ¼ 166.6, 166.1, 145.8, 136.2, 133.6, 133.0, 130.9,
129.0, 128.3, 127.6, 126.8, 124.1, 119.9, 109.7, 62.2, 62.0, 57.2,
57.1, 19.8, 13.9, 13.6. Anal. Calcd. for C21H23N3O4: C, 66.13; H,
6.08; N, 11.02; Found: C, 66.40; H, 6.06; N, 11.00. MS (ES): m/z
381.8, ([M þ Na]þ) (ESI): 404.0. See Table 3, entry 10.
Ethyl 2-((methoxycarbonyl)(4-nitrophenyl)methyl)-3-oxobu-
tanoate (3e). IR (KBr): 3349, 1732, 1715, 1698 cmꢀ1. Major:
1H-NMR (400 MHz, CDCl3): d ¼ 8.17–8.13 (m, 2H), 7.51–7.48
(m, 2H), 6.33 (d, J ¼ 0.8 Hz, 1H), 5.50 (m, 1H), 4.14–4.01 (m,
3H), 3.63 (s, 3H), 2.32 (s, 3H), 1.17 (t, J ¼ 7.2 Hz, 3H).
13C-NMR (100 MHz, CDCl3): d ¼ 200.3, 167.8, 166.5, 156.4,
147.4, 147.0, 127.7, 123.9, 63.4, 62.4, 53.8, 52.9, 30.7, 13.9.
Minor: 1H-NMR (400 MHz, CDCl3): d ¼ 8.17–8.13 (m,
2H), 7.51–7.48 (m, 2H), 6.50 (m, 1H), 5.60 (m, 1H), 4.14–
4.01 (m, 3H), 3.61 (s, 3H), 2.17 (s, 3H), 1.10 (t, J ¼ 7.2 Hz,
3H). 13C-NMR (100 MHz, CDCl3): d ¼ 202.5, 167.8, 166.5,
156.4, 147.3, 146.8, 127.4, 123.8, 63.4, 62.3, 53.8, 52.6, 29.0,
13.9. Anal. Calcd. for C15H17NO7: C, 55.73; H, 5.30; N, 4.33;
Found: C, 55.82; H, 5.29; N, 4.34. See Table 4, entry 5.
Ethyl 2-((4-bromophenyl)(methoxycarbonyl)methyl)-3-oxo-
butanoate (3a). IR (KBr): 3306, 1749, 1716, 1694 cmꢀ1
;
Major: 1H-NMR (400 MHz, CDCl3): d ¼ 7.45–7.42 (m, 2H),
7.19–7.16 (m, 2H), 6.15 (m, 1H), 5.40 (m, 1H), 4.17–4.04 (m,
2H), 4.00 (m, 1H), 3.63 (s, 3H), 2.16 (s, 3H), 1.20–1.13 (m,
3H). 13C-NMR (100 MHz, CDCl3): d ¼ 200.9, 167.8, 156.5,
138.7, 131.8, 128.0, 121.8, 63.9, 62.0, 53.9, 52.5, 29.0, 13.9.
Minor: 1H-NMR (400 MHz, CDCl3): d ¼ 7.45–7.42 (m,
2H), 7.19–7.16 (m, 2H), 6.40 (m, 1H), 5.52 (m, 1H), 4.17–
4.04 (m, 2H), 3.93 (m, 1H), 3.62 (s, 3H), 2.30 (s, 3H), 1.20–
1.13 (m, 3H). 13C-NMR (100 MHz, CDCl3): d ¼ 200.2, 166.5,
156.5, 138.7, 131.8, 128.4, 121.8, 62.8, 61.8, 53.9, 52.4, 29.0,
13.9. Anal. Calcd. for C15H17BrO5: C, 50.44; H, 4.80; Found:
C, 50.61; H, 4.79. See Table 4, entry 1.
Diethyl 2-((methoxycarbonyl)(4-nitrophenyl)-methyl)-malo-
nate (3f). IR (KBr): 3358, 1715, 1710, 1700 cmꢀ1 1H-NMR
.
(400 MHz, CDCl3): d ¼ 8.16 (d, J ¼ 8.8 Hz, 2H), 7.50 (d, J ¼
8.4 Hz, 2H), 6.5 (m, 1H), 5.6 (m, 1H), 4.21–4.03 (m, 4H), 3.90
(m, 1H), 3.64 (s, 3H), 1.22 (t, J ¼ 7.2 Hz, 3H), 1.13 (t, J ¼ 7.2
Hz, 3H). 13C-NMR (100 MHz, CDCl3): d ¼ 167.5, 166.4,
156.6, 147.5, 146.7, 127.5, 123.8, 62.3, 62.0, 56.2, 53.6, 52.5,
13.9, 13.8. Anal. Calcd. for C16H19NO8: C, 54.39; H, 5.42; N,
3.96; Found: C, 54.29; H, 5.43; N, 3.95. See Table 4, entry 6.
Ethyl 2-((methoxycarbonyl)(4-methoxyphenyl)-methyl)-3-
oxobutanoate (3b). IR (KBr): 3316, 1744, 1713, 1697 cmꢀ1
.
Major: 1H-NMR (400 MHz, CDCl3): d ¼ 7.26–7.20 (m, 2H),
6.85–6.82 (m, 2H), 6.10 (d, J ¼ 0.8 Hz, 1H), 5.38 (m, 1H),
4.13–4.06 (m, 2H), 4.00 (d, J ¼ 0.8 Hz, 1H), 3.77 (s, 3 H),
3.65 (s, 3H), 2.30 (s, 3H), 1.19–1.14 (m, 3H). 13C-NMR (100
MHz, CDCl3): d ¼ 200.9, 167.5, 159.0, 156.5, 131.6, 127.4,
114.0, 63.4, 61.8, 55.2, 53.9, 52.4, 28.8, 13.9.
Acknowledgments. We are grateful to the National Natural Sci-
ence Foundation of China (No. 20802070) for financial support.
Minor: 1H-NMR (400 MHz, CDCl3): d ¼ 7.26–7.20 (m, 2
H), 6.85–6.82 (m, 2H), 6.30 (m, 1H), 5.50 (s, 1H), 4.13–4.06
(m, 2H), 3.90 (m, 1H), 3.78 (s, 3H), 3.63 (s, 3H), 2.17 (s, 3H),
1.19–1.14 (m, 3H). 13C-NMR (100 MHz, CDCl3): d ¼ 200.9,
169.0, 159.0, 156.5, 131.5, 127.4, 114.0, 64.3, 61.6, 55.2, 53.9,
52.4, 28.8, 13.9. Anal. Calcd. for C16H20O6: C, 62.33; H, 6.54;
Found: C, 62.25; H, 6.55. See Table 4, entry 2.
REFERENCES AND NOTES
[1] For reviews, see: (a) Katritzky, A. R.; Lan, X.; Yang, J. Z.;
Denisko, O. V. Chem Rev 1998, 98, 409; (b) Katritzky, A. R.; Suzuki,
K.; Wang, Z. Synlett 2005, 1656; (c) Katritzky, A. R.; Manju, K.;
Singh, S. K.; Meher, N. K. Tetrahedron 2005, 61, 2555; (d) Katritzky,
A. R.; Angrish, P.; Todadze, E. Synlett 2009, 2392; (e) Katritzky, A.
R.; Rachwal, S. Chem Rev 2010, 110, 1564.
Ethyl 2-((methoxycarbonyl)(o-tolyl)methyl)-3-oxobutanoate
1
(3c). IR (KBr): 3334, 1740, 1717, 1692 cmꢀ1. Major: H-NMR
(400 MHz, CDCl3): d 7.23–7.12 (m, 4H), 6.06 (d, J ¼ 9.2, 1H),
5.68 (m, 1H), 4.12–4.04 (m, 2H), 3.97 (d, J ¼ 7.6 Hz, 1H), 3.57
(s, 3H), 2.47 (s, 3H), 2.18 (s, 3H), 1.13 (t, J ¼ 7.2 Hz, 3H). 13C-
NMR (100 MHz, CDCl3): d ¼ 200.8, 167.1, 156.2, 137.8, 134.8,
130.8, 127.8, 126.4, 125.6, 62.8, 61.7, 52.3, 50.7, 29.0, 19.3, 13.8.
[2] Katritzky, A. R.; Rachwal, S.; Rachwal, B. J Org Chem
1989, 54, 6022.
[3] (a) Katritzky, A. R.; Pernak, J.; Fan, W. Q.; Saczewski, F. J
Org Chem 1991, 56, 4439; (b) Wang, X.; Mao, H.; Yu, Y.; Zhu, X.;
Zhu, C. Synth Commun 2007, 37, 3751; (c) Li, W. X.; Ye, Y.; Zhang,
J.; Fan, R. H. Tetrahedron Lett 2009, 50, 5536.
1
Minor: H-NMR (400 MHz, CDCl3): d ¼ 7.24–7.13 (m, 4H),
[4] (a) Katritzky, A. R.; Pastor, A.; Voronkov, M. V. J Hetero-
cycl Chem 1999, 36, 777; (b) Katritzky, A. R.; Abdel-Fattah, A. A.
A.; Idzik, K. R.; El-Gendy, B. E.-D. M.; Soloducho, J. Tetrahedron
2007, 63, 6477; (c) Katritzky, A. R.; Rachwal, S.; Rachwal, B. Synthe-
sis 1991, 69; (d) Wang, X. X.; Mao, H.; Xie, G. Q.; Du, J. X. Synth
Commun 2008, 38, 2908.
6.49 (m, 1H), 5.68 (m, 1H), 4.12–4.04 (m, 2H), 3.84 (d, J ¼
5.2 Hz, 1H), 3.60 (s, 3H), 2.49 (s, 3H), 2.26 (s, 3H), 1.08 (t, J
¼ 7.2 Hz, 3H). 13C-NMR (100 MHz, CDCl3): d ¼ 168.5,
167.1, 156.2, 137.7, 134.8, 130.8, 127.8, 126.4, 126.0, 62.9,
61.6, 52.3, 50.1, 30.2, 19.2, 13.9. Anal. Calcd. for C16H20O5: C,
65.74; H, 6.90; Found: C, 65.90; H, 6.88. See Table 4, entry 3.
[5] (a) Katritzky, A. R.; Kirichenko, K.; Elsayed, A. M.; Ji, Y.;
Fang, Y. J Org Chem 2002, 67, 4957; (b) Katritzky, A. R.; Yao, G.;
Lan, X.; Zhao X. J Org Chem 1993, 58, 2086.
Ethyl 2-((methoxycarbonyl)(m-tolyl)methyl)-3-oxobutanoate
(3d). IR (KBr): 3339, 1745, 1716, 1701 cmꢀ1. Major: 1H-
NMR (400 MHz, CDCl3): d ¼ 7.17–7.04 (m, 4H), 6.18 (s,
1H), 5.40 (s, 1H), 4.09–4.01 (m, 3H), 3.62 (s, 3H), 2.30 (s,
3H), 2.15 (s, 3H), 1.15–1.09 (m, 3H). 13C-NMR (100 MHz,
CDCl3): d ¼ 203.1, 167.2, 156.3, 139.3, 138.3, 128.6, 127.0,
123.5, 123.2, 63.4, 61.8, 54.4, 52.3, 29.0, 21.4, 13.9.
¨
[6] C¸elik, I.; Kanıꢀskan, N.; Kokten, ꢀS. Tetrahedron 2009, 65, 328.
[7] Evans, W. J.; Gummersheimer, T. S.; Ziller, J. W. J Am
Chem Soc 1995, 117, 8999.
[8] Katritzky, A. R.; Xie, L.; Fan, W. J Org Chem 1993, 58,
4376.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet