Regioselective synthesis of 2,4-(dioxobutyl)dihydroquinolines and-pyridines by chloroformiae-mediated reaction of 1,3-bis(silyl enol ethers) with quinolines and pyridines

Article abstract of DOI:10.3987/COM-09-S(S)12

2,4-(Dioxobutyl)dihydroquinolines and-pyridines were prepared by chloroformiate-mediated reaction of 1,3-bis(silyl enol ethers) with quinolines and pyridines.

Full text of DOI:10.3987/COM-09-S(S)12

HETEROCYCLES, Vol. 80, No. 1, 2010
289
HETEROCYCLES, Vol. 80, No. 1, 2010, pp. 289 - 302. © The Japan Institute of Heterocyclic Chemistry
Received, 21st February, 2009, Accepted, 31st March, 2009, Published online, 1st April, 2009
DOI: 10.3987/COM-09-S(S)12
REGIOSELECTIVE SYNTHESIS OF 2,4-(DIOXOBUTYL)DIHYDRO-
QUINOLINES AND –PYRIDINES BY CHLOROFORMIATE-MEDIATED
REACTION OF 1,3-BIS(SILYL ENOL ETHERS) WITH QUINOLINES
AND PYRIDINES
Uwe Albrecht,a Anja Preuss,a Andreas Schmidt,a Christine Fischer,a, b and
Peter Langer* a, b
a
Institute of Chemistry, University of Rostock, Albert-Einstein-Str. 3a, 18059
Rostock, Germany, Fax: +381 4986412, E-mail: peter.langer@uni-rostock.de
b
Leibniz-Institute of Catalysis e. V. at the University of Rostock,
Albert-Einstein-Str. 29a, 18059 Rostock, Germany
Abstract – 2,4-(Dioxobutyl)dihydroquinolines and –pyridines were prepared by
chloroformiate-mediated reaction of 1,3-bis(silyl enol ethers) with quinolines and
pyridines.
INTRODUCTION
Quinoline, isoquinoline, and pyridine and their derivatives are of considerable pharmacological relevance
and are present in various antibiotics1, 2, 3 and natural products.4, 5 Quinolinium- and isoquinolinium salts,
generated by alkylation or acylation of quinoline and isoquinoline, represent important synthetic building
blocks for the synthesis of such compounds.6 Quinolines have been functionalized by the Reissert
The classic variant relies on the reaction of KCN in the presence of acylating agents. In a more recent
variant TMSCN in the presence of a fluoride source is employed.3, 7, 8 The addition of Grignard reagents
quinoline was reported to give 1,2-dihydroquinolines.9 The ethyl chloroformiate mediated reaction of a
quinoline with (trimethylsilylethinyl)magnesium chloride was used for the synthesis of
endiyne-antibiotics.9 Addition reactions of zink-,10 tin-11,12 and titanium-organometallic reagents13 to

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HETEROCYCLES, Vol. 80, No. 1, 2010
quinoline derivatives have been reported. Palladino et al. reported the benzoyl chloride mediated addition
of ethyl acetoacetate to quinoline to give 2,3-dihydroquinolines.14 The reaction of 4-silyloxyquinolinium
triflates with enamines afforded 2-substituted 4-silyloxy-1,2-dihydroquinolines.15 The reaction of
quinolinium salts with allylsilanes in the presence of AgOTf16 and ethyl trimethylsilylacetate17, 18 afforded
regioisomeric mixtures of 2- and 4-substituted dihydroquinolines. Reddy et al. reported the synthesis of
benzazepines by reaction of quinolinium- and isoquinolinium salts with diazoesters.19 Two-step
cyclocondensations of 1,1-bis(trimethylsilyloxy)ketene acetals with quinoline and isoquinoline have been
reported by Rudler20 and ourselves.21 Tropane derivatives were prepared by cyclization of 1,3-bis(silyl
ethers)22 with bis(iminium) salts of 2,5-dimethoxypyrrolidines.23 Recently, the cyclocondensation of
1,3-bis(silyl enol ethers) with isoquinolines,24 quinoxalines25 and quinazolines was reported.26 Herein, we
report a facile synthesis of 2,4-(dioxobutyl)dihydroquinolines and –pyridines by what are, to the best of
knowledge, the first condensation reactions of 1,3-bis(silyl enol ethers) with quinolines and pyridines.
RESULTS AND DISCUSSION
1,3-Bis(silyl enol ethers) 2 are available from the corresponding 1,3-dicarbonyl compounds in one or two
steps.27 The reaction of quinoline (1) with 1,3-bis(silyl enol ether) 2a, in the presence of methyl
chlorformate (3a), afforded 2,3-dihydroquinoline 4a (Scheme 1). The best yields were obtained when an
excess of 2a and of 3a was employed. The reactions were carried out at 0 °C. The yields dropped when
the reactions were carried out at 78 °C or at 20 °C. Notably, the yield dramatically decreased when
benzyl rather than methyl chloroformiate was used (vide infra). A complex mixture was formed when 1.2
equiv.of benzenesulfonyl chloride or 4-nitrobenzoyl chloride were employed. The formation of 4a can be
explained by formation of quinolinium salt A, regioselective attack of the terminal carbon atom of 2a
onto carbon atom C-2 of the quinolinium salt to give intermediate B, and subsequent hydrolysis.
1,3-Bis(silyl enol ethers) 2a-e were prepared from methyl, ethyl, isopropyl, methoxyethyl and isobutyl
acetoacetate, respectively (Scheme 2, Table 1).27 The reaction of 2a-d with quinoline, in the presence of
methyl chloroformiate (3a), afforded 1,2-dihydroquinolines 4a-d in moderate to good yields. The reaction
of 2a and 2b with 1, in the presence of benzyl chloroformiate (3b) rather than methyl chloroformiate (3a),
afforded 2,3-dihydroquinolines 4e and 4f, however, in only low yield. The benzyl chloroformiate
mediated reaction of quinoline with 2d and 2e afforded 1,2-dihydroquinolines 4g and 4h in moderate
yields. The reaction of 1,3-bis(silyl enol ethers) 2f and 2g, prepared from acetylacetone and
benzoylacetone, afforded 2,3-dihydroquinolines 4i and 4j in good yields, respectively.

HETEROCYCLES, Vol. 80, No. 1, 2010
291
O
Cl
OMe
N
O
O
1
3a
N
OEt
Me3SiO
+
OSiMe3
OEt
i
O
OMe
4a
2a
+ H2O
_ (Me3Si)2O
3a
OSiMe3
+
N
2a
_ Me3SiCl
N
Cl-
CO2OEt
MeO
O
MeO
O
B
A
Scheme 1. Mechanism of the formation of 4a, i: CH2Cl2, 0  20 °C, 16 h
The benzyl chloroformiate mediated reaction of 1,3-bis(silyl enol ethers) 2h and 2i, prepared from ethyl
3-oxohexanoate and ethyl 4-ethoxyacetoacetate, afforded 1,2-dihydroquinolines 4k and 4l, respectively.
Reactions of substituted quinoline derivatives have not been studied. All reactions proceeded with
excellent regioselectivity. The isolated products were regioisomerically pure (>98:2). The formation of
the other regioisomers, formed by attack of the diene to carbon C-4 of the quinoline, was not observed.
O
O
O
Cl
OR3
3a,b
N
1
N
R2
Me3SiO
R1
OSiMe3
R2
R1
+
R3O
O
i
4a-l
2a-i
Scheme 2. Synthesis of dihydroquinolines 4a-l; i: CH2Cl2, 0 → 20 °C, 16 h

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HETEROCYCLES, Vol. 80, No. 1, 2010
Table 1. Products and yields
a
R1
R2
R3
%
2
3
4
H
H
OEt
OMe
Me
Me
Me
Me
Bn
Bn
Bn
Bn
Me
Me
Bn
Bn
50
54
90
36
14
24
39
47
83
68
28
46
a
b
c
d
a
b
d
e
f
a
a
a
a
b
b
b
b
a
a
b
b
a
b
c
d
e
f
H
OiPr
H
O(CH2)2OMe
OEt
H
H
OMe
H
O(CH2)2OMe
OiBu
g
h
i
H
H
Me
H
Ph
g
h
i
j
Et
OEt
OEt
k
l
OEt
a Yields of isolated products
The methyl chloroformiate mediated reaction of pyridine (5) with 1,3-bis(silyl enol ether) 2a, carried out
following the procedure as developed for the analogous reactions of quinoline, afforded the unstable
1,4-dihydropyridine 6a in low yield (Scheme 3, Table 2). The formation of 6a can be explained by
formation of pyridinium salt C, regioselective attack of the terminal carbon atom of 2a onto carbon atom
C-4 of the pyridinium salt to give intermediate D, and subsequent hydrolysis. It is noteworthy that the
same regioselectivity was previously observed for the ethyl chloroformiate mediated reaction of pyridine
with simple silyl enol ethers.28 The reaction of 5 with 1,3-bis(silyl enol ethers) 2b and 2c, in the presence
of 3a, afforded 1,4-dihydropyridines 6b and 6c, again, in low yields. In contrast to the corresponding
reactions of quinoline, where the use of benzyl rather than methyl chloroformiate resulted in a decrease in
yield, a considerably higher yield was obtained in the reaction of 1,3-bis(silyl enol ethers) 2a and 2b with
pyridine when benzyl chloroformiate was employed (products 6d and 6e). The reaction of pyridine with
1,3-bis(silyl enol ether) 2f afforded 1,4-dihydropyridine 6f. The best yield was obtained when methyl
chloroformiate was used as the activating agent. The employment of 4-picoline or 2,6-lutidine proved to
be unsuccessful. All reactions proceeded with excellent regioselectivity. The isolated products were
regioisomerically pure (>98:2). The formation of the other regioisomers, formed by attack of the diene to
carbon C-2 of the pyridine, was not observed.

HETEROCYCLES, Vol. 80, No. 1, 2010
293
O
O
O
R1
Cl
OR2
3a,b
Me3SiO
OSiMe3
R1
+
N
N
i
O
OR2
2a-c,f
5
6a-f
+ H2O
_ (Me3Si)2O
3a,b
Me3SiO
R2O
O
O
2a-c,f
R1
+
N
N
R2O
O
C
D
Scheme 3. Synthesis of 1,4-dihydropyridines 6a-f, i: CH2Cl2, 0 → 20 °C, 16 h
Table 2. Products and yields
a
R1
R2
%
6
OEt
OMe
Me
Me
Me
Bn
Bn
Me
22
21
20
66
63
35
a
b
c
d
e
f
O(CH2)2OMe
OEt
OMe
Me
a Yields of isolated products
The different regioselectivities observed for the reactions of 1,3-bis(silyl enol ethers) 2 with quinoline and
pyridine might be explained by the assumption that the attack of the diene onto carbon atom C-4 is more
sterically hinderd than the attack to C-2. The fused benzene moiety might have a stronger steric influence
than the carbamate moiety. In the case of pyridine, there is no steric hindrance associated with the attack
of the diene to carbon atom C-4. On the other hand, the attack of the diene to carbon C-2 is hindered by
the steric influence of the carbamate group. In addition, electronic reasons might play a role.

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HETEROCYCLES, Vol. 80, No. 1, 2010
It is worth to be noted that, for pyridine, benzyl chloroformiate gave much better results than methyl
chloroformiate. The opposite is true for quinoline. This might be explained by solubility reasons. In
addition, the attack of the diene to carbon atom C-2 of the quinoline is more sterically hindered by the
benzyl- than by the methyl-substituted carbamate moiety. This steric hindrance plays not a role in case of
pyridine as the attack of the diene occurs at carbon C-4 of the pyridine moiety.
In conclusion, we reported the synthesis of 2,4-(dioxobutyl)dihydroquinolines and –pyridines by
chloroformiate-mediated reaction of 1,3-bis(silyl enol ethers) with quinolines and pyridines.
EXPERIMENTAL
General. All solvents were dried by standard methods and all reactions were carried out under an inert
1
13
atmosphere. For H and C NMR, the deuterated solvents indicated were used. Mass spectrometric data
(MS) were obtained by electron ionization (70 eV), chemical ionization (CI, H2O) or electrospray
ionization (ESI). For preparative scale chromatography, silica gel (60-200 mesh) was used. Melting
points are uncorrected.
General procedure for the reaction of 1,3-bis(silyl enol ethers) with quinoline and pyridine. To a
CH2Cl2 solution of quinoline or pyridine and of the 1,3-bis(silyl enol ether) was added the cloroformate at
0 °C. The solution was allowed to warm to 20 °C during 16 h and an aqueous solution of NH4Cl (20 mL,
1 M) was added. The organic and the aqueous layer were separated and the latter was extracted with
CH2Cl2 (2 x 20 mL). The combined organic layers were dried (Na2SO4), filtered and the filtrate was
concentrated in vacuo. The residue was purified by chromatography (silica gel, hexane/EtOAc = 5:1).
Due to the hindered rotation of the carbon-nitrogen bond of the carbamate group, a doubling of some
signals was observed in 1H and 13C NMR.
Ethyl 4-(1-N-methoxycarboyl-2-dihydroquinolyl)-3-oxobutanoate (4a). Starting with 1 (0.194 g,
1.5 mmol), 3a (0.161 g, 1.7 mmol) and 2a (0.822 g, 3.0 mmol), 4a was isolated as a yellow oil (0.237 g,
1
3
3
3
50%). H NMR (CDCl3, 300 MHz): δ = 1.22 (t, J = 7.0 Hz, 3 H, CH3), 2.70 (ddd, J = 18.0 Hz, J =
3
3
3
8.0 Hz, J = 6.0 Hz, 2 H, CH2), 3.41 (d, J = 8.0 Hz, 1 H, CH CH2), 3.70 (s, 3 H, CH3), 4.16 (q, J =
7.0 Hz, 2 H, CH2), 5.49 (ddd, 3J = 6.0 Hz, 1 H, CH), 6.14 (dd, 3Jcis = 10.0 Hz, 3J = 6.0 Hz, 1 H, CH), 6.49
(d, 3Jcis = 10.0 Hz, 1 H, CH), 7.08-7.10 (m, 2 H, CH), 7.21 -7.25 (m, 1 H, CH), 7.55 (d, 3J = 8.0 Hz, 1 H,
13
CH). C NMR (75 MHz, CDCl3): δ = 14.1 (CH3), 46.6 (CH2), 48.8 (CH), 49.5 (CH2), 53.2 (CH3), 61.4
(CH2), 124.6, 124.6, 125.5, 126.4, 126.8, 127.8 (CH), 128.4, 133.9, 154.5, 166.8, 200.0 (C). MS (EI,
70 eV): m/z = 316 (M+, 84), 214 (16), 183 (57), 169 (51), 116 (100). Anal. Calcd for C17H19NO5: C,

HETEROCYCLES, Vol. 80, No. 1, 2010
295
64.34; H, 6.03; N, 4.41. Found: C, 64.07; H, 5.64; N, 3.93.
Methyl 4-(1-N-methoxycarboyl-2-dihydroquinolyl)-3-oxobutanoate (4b). Starting with 1 (2.0 mmol,
1.0 equiv.), CH2Cl2 (20 mL) 2b (4.0 mmol, 2.0 equiv.) and 3a (0.23 g, 2.4 mmol, 1.2 equiv.), 4b was
isolated by chromatography (silica gel, hexane/EtOAc = 7:1) as a yellow oil (0.33 g, 54%). 1H-NMR (300
MHz, CDCl3):  = 2.62 - 2.80 (m, 2 H, CH2), 3.37 - 3.50 (m, 2 H, CH2, keto), 3.71, 3.73 (2 x s, 3 H, CH3,
keto, enol) 3.78, 3.80 (2 x s, 3 H, CH3, keto, enol), 4.89 (s, 1 H, CH, enol), 5.49 (dt, 3J = 6.0 Hz, 1 H, CH),
6.14 (dd, 3J = 6.0 Hz, 3Jcis = 9.0 Hz, 1 H, CH), 6.49 (d, 3Jcis = 9.0 Hz, 1 H, CH), 7.08 - 7.11 (m, 2 H, CH),
13
7.21 - 7.24 (m, 1 H, CH), 7.55 (br d, 3J = 8.0 Hz, 1 H, CH), 11.97 (s, 1 H, OH, enol). C-NMR (CDCl3,
75 MHz):  = 46.4 (CH2), 48.7 (CH3), 49.1 (CH2), 52.3 (CH3), 53.1 (CH), 124.5, 125.5, 125.6, 126.3
(CH), 126.7 (C), 127.7, 128.2 (CH), 133.8, 154.4, 167.1, 199.8 (C). UV-Vis (, log ): 231.49 (4.6).
~
IR (KBr): = 3033 (w), 3003 (w), 2956 (m), 1748 (s), 1714 (s), 1658 (m), 1604 (w), 1572 (w), 1528 (w),

1490 (s), 1440 (s). MS (EI, 70 eV): m/z (%) = 303 (M+, 1), 244 (6), 188 (100), 144 (48), 129 (12). Anal.
Calcd for C16H17NO5: C, 63.36; H, 5.65; N, 4.62. Found: C, 63.30; H, 6.08; N, 4.79.
Isopropyl 4-(1-N-methoxycarboyl-2-dihydroquinolyl)-3-oxobutanoate (4c). Starting with 1 (0.129 g,
1.0 mmol), 3a (0.104 g, 1.1 mmol) and 2c, 4c was isolated as a yellow oil (0.283 g, 90%, keto/enol = 5:1).
3
3
1H NMR (CDCl3, 300 MHz):  = 1.22 (d, J = 7.0 Hz, 6H, CH3), 2.62, 2.67, (d, J = 6.0 Hz, 1H, CH2,
keto, enol), 2.73, 2.79 (d, 3J = 8.0 Hz, 1H, CH2, keto, enol), 3.30, 3.35 (s, 1H, CH2, keto, enol), 3.38, 3.44
(s, 1H, CH2, keto, enol), 3.78 (s, 3H, CH3), 5.02 (sep., 3J = 7.0 Hz, 1H, CH), 5.49 (ddd, 3J = 6.0 Hz, 3J =
3
3
3
3
6.0 Hz, J = 8.0 Hz, 1H, CH), 6.15 (dd, J = 10.0 Hz, J = 6.0 Hz, 1H, CH), 6.48 (d, J = 10.0 Hz, 1H,
13
CH), 7.07 – 7.10 (m, 2H, CH), 7.20 – 7.26 (m, 1H, CH), 7.54 – 7. 56 (m, 1H, CH). C NMR (75 MHz,
CDCl3): δ = 22.0 (CH3), 46.9 (CH2), 49.2 (CH), 50.2 (CH2), 53.6, 69.5, 125.0, 125.9, 126.1, 126.8 (CH),
~
127.2 (C), 128.2, 128.8 (CH), 134.0, 154.6, 166.3, 200.1 (C). IR (KBr): = 3443 (w), 3037 (w), 2983

(m), 2958 (m), 2856 (w), 1710 (s), 1645 (m), 1611 (w), 1577 (w), 1490 (s), 1442 (s) cm-1. UV-Vis
(MeCN): λmax (lg ε) = 234.92 (4.43) nm. MS (EI, 70 eV): m/z = 331 (M+, 1), 272 (8), 188 (100), 144 (69),
129 (14). Anal. Calcd for C18H21NO5: C, 65.24; H, 6.39; N, 4.23. Found: C, 64.87; H, 6.74; N, 3.99.
Methoxyethyl 4-(1-N-methoxycarboyl-2-dihydroquinolyl)-3-oxobutanoate (4d). Starting with 1
(0.39 g, 3.0 mmol, 1.0 equiv.), 2c (1.83 g 6.0 mmol, 2.0 equiv.), 3a (0.34 g, 3.6 mmol, 1.2 equiv.) and
CH2Cl2 (20 mL), 4d was isolated by chromatography (silica gel, hexane/EtOAc = 3:1  2:1) as a yellow
oil (0.37 g, 36%). 1H-NMR (300 MHz, CDCl3):  = 2.63 – 2.81 (m, 2 H, CH2), 3.26 – 3.62 (m, 7 H, CH2,
CH2, CH3), 3.78, 3.79 (2 x s, 3 H, CH3), 4.25 – 4.29 (m, 2 H, CH2), 4.95 (s, 1 H, CH, enol), 5.49 (dt, 3J =

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HETEROCYCLES, Vol. 80, No. 1, 2010
7.0 Hz, 1 H, CH), 6.14 (dd, 3J = 6.0 Hz, 3Jcis = 9.0 Hz, 1 H, CH), 6.49 (d, 3Jcis = 9.0 Hz, 1 H, CH), 7.07 –
7.10 (m, 2 H, CH), 7.21 – 7.26 (m, 1 H, CH), 7.55 (m, 1 H, CH), 11.95 (s, 1 H, OH). 13C-NMR (75 MHz,
CDCl3):  = 46.5 (CH2), 48.8 (CH3), 49.3 (CH2), 50.2 (CH3), 53.2 (CH), 64.2 (CH2), 70.1 (CH2), 124.6,
125.7, 126.3, 126.4 (CH), 126.9 (C), 127.8, 128.3 (CH), 133.9, 154.4, 166.8, 199.8 (C). UV-Vis (,
~
log ): 231.40 (4.5). IR (KBr): = 2955 (w), 2931 (w), 2894 (w), 1744 (s), 1656 (w), 1489 (m), 1441 (s).

MS (EI, 70 eV): m/z (%) = 347 (M+, 1), 188 (100), 144 (51), 129 (22), 60 (16). Anal. Calcd for
C18H21NO6: C, 62.24; H, 6.09; N, 4.03. Found: C, 61.98; H, 6.14; N 4.19.
Ethyl 4-(1-N-benzyloxycarboyl-2-dihydroquinolyl)-3-oxobutanoate (4e). Starting with 1 (0.26 g,
2.0 mmol, 1.0 equiv.), 2a (1.098 g, 4.0 mmol, 2.0 equiv.), 3b (0.41 g, 2.4 mmol, 1.2 equiv.), and CH2Cl2
(20 mL), 4e was isolated by chromatography (silica gel, hexane/EtOAc = 7:1) as a yellow oil (0.109 g,
14%). 1H-NMR (300 MHz, CDCl3):  = 1.20 - 1.31 (t, 3J = 7.0 Hz, 3 H, CH3), 2.68 - 2.75 (m, 2 H, CH2),
3.03 - 3.39 (m, 2 H, CH2, keto), 4.11 - 4.18 (q, 3J = 7.0 Hz, 2 H, CH2), 4.86 (s, 1 H, CH, enol), 5.17 - 5.32
(m, 2 H, CH2), 5.51 (dt, 3J = 6.0 Hz, 1 H, CH), 6.13 (dd, 3J = 6.0 Hz, 3Jcis = 9.0 Hz, 1 H, CH), 7.08 - 7.10
(m, 2 H, CH2), 7.20 - 7.23 (m, 1 H, CH), 7.31 - 7.38 (m, 5 H, CH), 7.56 (m, 1 H, CH), 12.04 (s, 1 H, OH).
13C-NMR (75 MHz, CDCl3):  = 46.4 (CH2), 48.8 (CH3), 49.4 (CH2), 50.3 (CH), 61.3 (CH2), 67.9 (CH2),
124.6, 125.5, 126.4, 126.7 (CH), 127.7 (C), 127.9, 128.0, 128.0, 128.1, 128.3, 128.5 (CH), 133.8, 153.7,
~
166.7, 199.9 (C). IR (KBr): = 2983 (w), 1743 (s), 1652 (m), 1606 (w), 1491 (m), 1455 (m). UV-Vis (,

log ): 203.87 (4.6), 232.11 (4.5). MS (EI, 70 eV) m/z (%) = 393 (M+, 1), 264 (14), 220 (18), 129 (6), 91
(100). Anal. Calcd for C23H23NO5: C, 70.22; H, 5.89; N 3.56. Found: C, 70.10; H, 6.16; N, 3.51.
Methyl 4-(1-N-benzyloxycarboyl-2-dihydroquinolyl)-3-oxobutanoate (4f). Starting with 1 (0.26 g,
2.0 mmol, 1.0 equiv.), 2b (1.04 g, 4.0 mmol, 2.0 equiv.), 3b (0.82 g, 50% solution in toluene, 2.4 mmol,
1.2 equiv.), and 20 mL of CH2Cl2, 4f was isolated by chromatography (silica gel, hexane/EtOAc = 7:1) as
1
a yellow oil (0.18 g, 24%). H-NMR (300 MHz, CDCl3):  = 2.68 - 2.74 (m, 2 H, CH2), 3.33 - 3.41 (m,
2 H, CH2, keto), 3.69, 3.72 (2 x s, 3 H, CH3, keto, enol), 4.88 (s, 1 H, CH, enol), 5.17 - 5.32 (m, 2 H,
3
3
3
3
CH2), 5.54 (dt, J = 6.0 Hz, 1 H, CH), 6.13 (dd, J = 6.0 Hz, Jcis = 9.0 Hz, 1 H, CH), 6.49 (d, Jcis
=
9.0 Hz, 1 H, CH) 7.08 - 7.10 (m, 2 H, CH), 7.19 - 7.24 (m, 1 H, CH), 7.32 - 7.37 (m, 5 H, CH), 7.55 (m,
1 H, CH), 11.97 (s, 1 H, OH). 13C-NMR (75 MHz, CDCl3):  = 46.5 (CH2), 48.9 (CH3), 49.2 (CH2), 52.4
(CH), 68.0 (CH2), 124.7, 125.6, 125.8, 126.4 (CH), 126.8 (C), 127.8, 127.9, 128.1, 128.1, 128.2, 128.6
~
(CH), 133.9, 153.9, 167.2, 199.8 (C). IR (KBr): = 1747 (m), 1711 (s), 1657 (w), 1634 (w), 1491 (m),

1452 (m), 1441 (m). UV-Vis (, log ): 206.69 (4.2), 235.66 (4.5). MS (EI, 70 eV): m/z (%) = 379 (M+, 3),
264 (59), 220 (67), 142 (36), 91 (100). Anal. Calcd for C22H21NO5: C, 69.65; H, 5.58; N, 3.69. Found: C,

HETEROCYCLES, Vol. 80, No. 1, 2010
297
69.31; H, 5.81; N, 3.64.
Methoxyethyl 4-(1-N-benzyloxycarboyl-2-dihydroquinolyl)-3-oxobutanoate (4g). Starting with 1
(0.26 g, 2.0 mmol, 1.0 equiv.), 2d (1.22 g, 4.0 mmol, 2.0 equiv.), 3b (0.41 g, 2.4 mmol, 1.2 equiv.), and
20 mL of CH2Cl2, 4g was isolated by chromatography (silica gel, hexane/EtOAc = 4:1) as a yellow oil
1
(0.327 g, 39%). H-NMR (300 MHz, CDCl3)  = 2.69 - 2.75 (m, 2 H, CH2), 3.18 - 3.62 (m, 7 H, CH2,
CH2, CH3), 4.23 - 4.32 (m, 2 H, CH2), 4.94 (s, 1 H, CH, enol), 5.16 - 5.32 (m, 2 H, CH2, keto, enol), 5.51
3
3
3
3
3
(dt, J = 6.0 Hz, 1 H, CH), 6.14 (dd, J = 6.0 Hz, Jcis = 9.0 Hz, 1 H, CH), 6.48 (d, J = 6.0 Hz, Jcis
=
9.0 Hz, 1 H, CH), 7.08 - 7.10 (m, 2 H, CH), 7.20 - 7.22 (m, 1 H, CH), 7.31 - 7.36 (m, 5 H, CH), 7.55 (m,
1 H, CH), 11.91 (s, 1 H, OH). 13C-NMR (50 MHz, CDCl3):  = 45.5 (CH2), 47.9 (CH3), 48.3 (CH2), 57.9
(CH3), 63.2 (CH), 66.3 (CH2), 66.8 (CH2), 69.1 (CH2), 123.6, 124.5, 125.4, 125.4 (CH), 126.6 (C), 126.9,
127.0, 127.2, 127.2, 127.6 (CH), 135.5, 152.5, 166.7, 199.8 (C). UV-Vis (, log ): 232.18 (4.5).
~
IR (KBr) = 3064 (w), 3038 (w), 2981 (m), 2956 (w), 2932 (w), 2892 (m), 1654 (m), 1606 (m) 1572

(w), 1491 (s), 1454 (s). MS (EI, 70 eV) : m/z (%) = 425 (M+, 1), 264 (10), 220 (17), 129 (10), 91 (100),
45 (10). Anal. Calcd for C24H25NO6: C, 68.07; H, 5.95; N, 3.31. Found: C, 67.86; H, 6.00; N, 3.38.
Isobutoxy 4-(1-N-benzyloxycarboyl-2-dihydroquinolyl)-3-oxobutanoate (4h). Starting with 1 (0.26 g,
2.0 mmol, 1.0 equiv.), 2e (1.21 g, 4.0 mmol, 2.0 equiv.), 3b (0.41 g, 2.4 mmol, 1.2 equiv.), and 20 mL of
CH2Cl2, 4h was isolated by chromatography (silica gel, hexane/EtOAc = 7:1) as a yellow oil (0.399 g,
47%). 1H-NMR (300 MHz, CDCl3)  = 0.91 (d, 3J = 7.0 Hz, 6 H, CH3), 1.87 (tqq, 3J = 8.0 Hz, 1 H, CH),
3
2.61 - 2.80 (m, 2 H, CH2), 3.32 - 3.45 (m, 2 H, CH2, keto), 3.86 (d, J = 7.0 Hz, 2 H, CH2), 4.89 (s, 1 H,
CH, enol), 5.16 - 5.31 (m, 2 H, CH2), 5.53 (dt, 3J = 7.0 Hz, 1 H, CH), 6.14 (dd, 3J = 6.0 Hz, 3Jcis = 9.0 Hz,
3
1 H, CH), 6.49 (d, Jcis = 9.0 Hz, 1 H, CH), 7.07 - 7.09 (m, 2 H, CH), 7.18 - 7.24 (m, 1 H, CH), 7.31 -
7.32 (m, 5 H, CH), 7.55 (m, 1 H, CH), 12.03 (s, 1 H, OH). 13C-NMR (50 MHz, CDCl3):  = 46.7 (CH2),
49.0 (CH3), 49.5 (CH2), 50.5 (CH3), 68.0 (CH), 124.5, 125.6, 125.8, 126.4 (CH), 126.5 (C), 127.7, 127.9,
128.1, 128.1, 128.2, 128.4 (CH), 133.8, 153.7, 166.7, 199.9 (C). UV-Vis (, log ): 325.69 (4.5).
+
~
IR (KBr): = 2963 (m), 1741 (s), 1652 (w), 1491 (m), 1457 (w). MS (EI, 70 eV): m/z (%) = 423 (M , 1),

264 (16), 220 (28), 212 (10), 91 (100). Anal. Calcd for C25H27NO5: C, 71.24; H, 6.46; N, 3.32. Found: C,
71.09; H, 7.07; N, 3.46.
1-(1-N-Methoxycarboyl-2-dihydroquinolyl)-2,4-dioxopentane (4i). Starting with 1 (0.194 g, 1.5 mmol),
3a (0.161 g, 1.7 mmol) and 2f (0.732 g, 3.0 mmol), 4i was isolated as a yellow oil (0.356 g, 83%,
1
3
keto/enol = 2:1). H NMR (CDCl3, 300 MHz): δ = 1.95 (s, 3 H, CH3), 2.28, 2.31 (d, J = 7.0 Hz, 2 H,

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HETEROCYCLES, Vol. 80, No. 1, 2010
CH2), 3.70 (s, 3 H, CH3), 5.32 (s, 1 H, CH), 5.34 (dt, 3J = 7.0 Hz, 1 H, CH), 6.00 (dd, 3J = 7.0 Hz, 3Jcis =
10.0 Hz, 1 H, CH), 6.44 (d, 3Jcis = 10.0 Hz, 1 H, CH), 7.01 – 7.03 (m, 2 H, CH), 7.15 – 7.19 (m, 1 H, CH),
7.45 – 7.53 (m, 1 H, CH), 15.25 (br, 1 H, OH). 13C NMR (75 MHz, CDCl3): δ = 25.1 (CH3), 41.5 (CH2),
50.1 (CH), 53.1 (CH3), 57.8 (CH2, keto), 100.9 (CH, enol), 124.5, 124.6, 125.6, 126.4 (CH), 126.9 (C),
~
127.8, 128.2 (CH), 134.0 (C), 154.5, 189.2, 191.9 (CO). IR (KBr): = 3409 (w), 3068 (w), 3037 (w),

2975 (m), 2931 (w), 2862 (w), 1711 (s), 1623 (s), 1532 (m), 1490 (s), 1441 (s) cm-1. UV-Vis (MeCN):
λmax (lg ε) = 230.71 (4.33) nm. MS (EI, 70 eV): m/z = 287 (M+, 2), 228 (4), 188 (100), 144 (69), 129 (20).
Anal. Calcd for C16H17NO5: C, 66.89; H, 5.96; N, 4.88. Found: C, 67.09; H, 6.23; N, 5.25.
4-(1-N-Methoxycarboyl-2-dihydroquinolyl)-1,3-dioxo-1-phenylbutane (4j): Starting with 1 (0.194 g,
1.5 mmol), 3a (0.161 g, 1.7 mmol) and 2g (0.918 g, 3.0 mmol), 4j was isolated as a yellow oil (0.354 g,
1
3
68%, keto/enol > 98:2). H NMR (CDCl3, 300 MHz): δ = 3.02 (dt, J = 7.0 Hz, 2 H, CH2), 4.25 (s, 1 H,
CH3), 6.03 (dt, 3J = 7.0 Hz, 1 H, CH), 6.58 (s, 1 H, CH), 6.61 (dd, 3J = 7.0 Hz, 3Jcis = 10.0 Hz, 1 H, CH),
3
7.03 (d, Jcis = 10.0 Hz, 1 H, CH), 7.60 – 7.62 (m, 2 H, CH), 7.72 – 7.77 (m, 1 H, CH), 7.90 – 8.14 (m,
4 H, CH), 8.33 – 8 35 (m, 2 H, CH), 16.53 (br. s, 1 H, OH). 13C NMR (CDCl3, 75 MHz): δ = 42.26 (CH2),
50.15 (CH), 53.07 (CH3), 97.03 (CH), 121.34, 124.50 (CH), 125.07 (C), 125.64, 126.40, 127.02, 127.79,
~
128.53, 128.59, 132.42 (CH), 134.00, 134.74, 154.48, 183.88, 191.74 (C). IR (KBr): = 3067 (w), 2955

(s), 2926 (s), 2857 (m), 1728 (s), 1668 (m), 1603 (s), 1573 (s), 1489 (s), 1443 (s) cm-1. UV-Vis (MeCN):
λmax (lg ε) = 205.84 (4.06), 232.02 (4.07) nm. MS (EI, 70 eV): m/z = 349 (M+,2), 290 (7), 210 (6), 188
(100), 144 (77). HRMS (EI, 70 eV): Calcd for C21H19NO4: m/z = 188.0837; found: 188.0837 ± 2 ppm
[M+].
Ethyl 4-(1-N-benzyloxycarboyl-2-dihydroquinolyl)-4-ethyl-3-oxobutanoate (4k). Starting with 1
(0.26 g, 2.0 mmol, 1.0 equiv.), 2h (1.21 g, 4.0 mmol, 2.0 Äquiv.), 3b (0.41 g, 2.4 mmol, 1.2 equiv.), and
20 mL of CH2Cl2, 4k was isolated by chromatography (silica gel, hexane/EtOAc = 10:1) as a yellow oil
1
(0.237 g, 28%, mixture of diastereomers). H-NMR (300 MHz, CDCl3)  = 0.79 – 0.89 (m, 3 H, CH3),
1.25 – 1.39 (m, 2 H, CH2), 3.34, 3.35 (2 x s, 3 H, CH3), 4.15 – 4.26 (m, 2 H, CH2), 4.90 (s, 1 H, CH, enol),
5.34 – 5.49 (m, 2 H, CH2), 6.10 – 6.12 (m, 1 H, CH), 6.57 – 6.64 (m, 1 H, CH), 7.09 – 7.18 (m, 1 H, CH),
7.27 – 7.31 (m, 1 H, CH), 7.38 – 7.52 (m, 5 H, CH), 8.01 – 8.11 (m, 1 H, CH), 12.25 (s, 1 H, OH).
13C-NMR (75 MHz, CDCl3)  = 12.0 (CH3), 22.7 (CH2), 40.1 (CH3), 51.4 (CH2), 60.1 (CH), 68.1 (CH2),
121.7, 124.9, 126.1, 126.9 (CH), 127.6 (C), 128.0, 128.1, 128.3, 128.4, 128.4, 128.5, 128.5, 128.9 (CH),
~
135.5, 152.0, 166.5, 205.3 (C). IR (KBr): = 3067 (w), 3035 (w), 2968 (m), 2936 (m), 2878 (w), 1712

(s), 1652 (s), 1489 (s), 1457 (s). MS (EI, 70 eV): m/z (%) = 285 (24). UV (, log ): 205.99 (4.3), 235.92

HETEROCYCLES, Vol. 80, No. 1, 2010
299
(4.2). Anal. Calcd for C25H27NO5: C, 71.24; H, 6.46; N, 3.32. Found: C, 71.14; H, 6.01; N, 3.09.
Ethyl 4-(1-N-benzyloxycarboyl-2-dihydroquinolyl)-4-ethyoxy-3-oxobutanoate (4l). Starting with 1
(0.26 g, 2.0 mmol, 1.0 equiv.), 2i (1.27 g, 4.0 mmol, 2.0 equiv.), 3b (0.41 g, 2.4 mmol, 1.2 equiv.), and
20 mL of CH2Cl2, 4l was isolated (silica gel, hexane/EtOAc = 10:1) as a yellow oil (0.400 g, 46%,
mixture of diastereomers). 1H-NMR (300 MHz, CDCl3):  = 0.95 – 1.05 (t, 3J = 7.0 Hz, 3 H, CH3), 1.23 –
1.35 (m, 2 H, CH2), 3.29 – 3.62 (m, 5 H, CH2, CH3), 4.14 – 4.19 (m, 2 H, CH2), 4.70 (s, 1 H, CH, enol),
5.28 – 5.38 (m, 2 H, CH2), 5.96 (q, 1 H, CH), 6.58 – 6.61 (m, 1 H, CH), 7.07 – 7.09 (m, 1 H, CH), 7.10 –
7.17 (m, 1 H, CH), 7.27 – 7.39 (m, 5 H, CH), 8.01 – 8.05 (m, 1 H, CH), 12.55 (s, 1 H, OH).
13C-NMR (75 MHz, CDCl3):  = 13.9, 14.0, 14.7, 14.8 (CH3), 41.4, 41.5 (CH), 45.5, 45.7 (CH2), 46.4,
46.7 (CH2), 53.3 (CH), 61.1, 61.1 (CH2), 67.6, 67.7 (CH2), 84.9 (CH), 89.3 (CH), 97.6 (CH), 106.9 (CH),
122.8, 124.2, 124.6, 126.1, 126.5, 127.7, 127.8, 127.9, 128.0, 128.6, 128.9, 129.1 (CH), 135.7, 152.1,
~
166.9, 173.8, 203.5 (C). UV-Vis (, log ): 204.32 (4.4), 236.88 (4.3). IR (KBr): = 3066 (w), 3035 (w),

2979 (m), 2936 (m), 2899 (w), 2877 (w), 1655 (s), 1499 (s), 1454 (m). MS (EI, 70 eV): m/z (%) = 438
(M+, 4), 262 (14), 220 (19), 91 (100), 29 (13). Anal. Calcd for C25H27NO6: C, 68.64; H, 6.22; N, 3.20.
Found: C, 68.64; H, 6.22; N, 3.20.
Ethyl 4-(1-(N-methoxycarbonyl–4-dihydropyridyl)-3-oxobutanoate (6a). Starting with 5 (0.16 g,
2.0 mmol, 1.0 equiv.), 2a (1.09 g, 4.0 mmol, 2.0 equiv.), 3a (0.23 g, 2.4 mmol, 1.2 equiv.), and 20 mL of
CH2Cl2, 6a was isolated by chromatography (silica gel, hexane/EtOAc = 7:1) as a red oil (0.115 g, 22%).
1H-NMR (300 MHz, CDCl3)  = 1.33 (t, J = 7.0 Hz, 3 H, CH3), 2.66 (d, 3J = 7.0 Hz, 2 H, CH2), 3.42 -
3
3.52 (m, 3J = 8.0 Hz, 2 H, CH2, keto), 3.77, 3.79 ( 2 x s, 3 H, CH3), 4.16 - 4.23 (q, 3J = 7.0 Hz, 2 H, CH2),
4.84 - 4.87 (m, 1 H, CH), 5.03 (s, 1 H, CH, enol), 6.71 - 6.84 (m, 2 H, CH), 7.15 - 7.17 (m, 1 H, CH),
8.57 - 8.59 (m, 1 H, CH), 12.01 (s, 1 H, OH). Due to the instability of the compound, a 13C-NMR
~
spectrum could not be obtained. UV-Vis (, log ): 228.96 (4.1). IR (KBr): = 2984 (w), 2960 (w),

1722 (s), 1696 (s), 1654 (m), 1636 (m), 1445 (s). MS (EI, 70 eV): m/z (%) = 267 (M+, 7), 221 (31), 138
(93), 94 (40), 93 (100). Anal. Calcd for C13H17NO5: C, 58.42; H, 6.41; N, 5.24. Found: C, 58.77; H, 6.39;
N, 5.36.
Methyl 4-(1-(N-methoxycarbonyl–4-dihydropyridyl)-3-oxobutanoate (6b). Starting with 5 (0.16 g,
2.0 mmol, 1.0 equiv.), CH2Cl2 (20 mL), 2b (4.0 mmol, 2.0 equiv.) and 3a (0.23 g, 2.4 mmol, 1.2 equiv.),
6b was isolated by chromatography (silica gel, hexane/EtOAc = 7:1  5:1) as a red oil (0.107 g, 21%).
1H-NMR (300 MHz, CDCl3):  = 2.65 (d, 3J = 7.0 Hz, 2 H, CH2), 3.38 - 3.52 (m, 2 H, CH2, keto), 3.73,

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HETEROCYCLES, Vol. 80, No. 1, 2010
3.74 (2 x s, 3 H, CH3, keto, enol), 3.80, 3.83 (2 x s, 3 H, CH3), 4.84 - 4.87 (m, 1 H, CH), 4.99 (s, 1 H, CH,
enol), 6.72 - 6.83 (m, 2 H, CH), 7.15 - 7.17 (m, 1 H, CH), 8.57 - 8.59 (m, 1 H, CH), 12.02 (s, 1 H, OH).
13
Due to the instability of the compound, a C-NMR spectrum could not be obtained. UV-Vis (, log ):
~
229.41 (4.1). IR (KBr): = 2957 (w), 1695 (s), 1660 (w), 1634 (m), 1444 (s). MS (EI, 70 eV): m/z (%) =

253 (M+, 17), 252 (100), 178 (39), 150 (90), 101 (66). Anal. Calcd for C12H15NO5: C, 56.91; H, 5.97; N,
5.53. Found: C, 56.54; H, 5.34; N, 5.53.
Methoxyethyl 4-(1-(N-methoxycarbonyl–4-dihydropyridyl)-3-oxobutanoate (6c). Starting with 5
(0.316 g, 4.0 mmol), 3a (0.568 g, 6.0 mmol), and 2d (2.430 g, 8.0 mmol), 6c was isolated as a yellow oil
1
(0.241 g, 20%, keto/enol = 5:1). H NMR (CDCl3, 300 MHz): δ = 2.50 (d, 3J = 7.0 Hz, 1 H, CH), 3.16 –
3.19 (m, 3 H, CH, CH2, keto, enol), 3.30 (s, 3 H, CH3, enol), 3.32 (s, 3 H, CH3, keto), 3.30-3.43 (m, 2 H,
CH2, keto, enol), 3.58 (s, 3 H, CH3, enol), 3.60 (s, 3 H, CH3, keto), 4.07 – 4.10 (m, 2 H, CH2, keto, enol),
4.58-4.75 (m, 2 H, CH, keto), 4.86 (s, 1 H, CH, enol), 4.89 – 5.19 (m, 1 H, CH, enol), 5.39 – 5.81 (m, 1 H,
CH, enol), 6.39 – 6.69 (m, 1 H, CH, keto), 11.81 (s, 1 H, OH, enol). 13C NMR (75 MHz, CDCl3): δ = 29.6,
30.2 (CH, keto, enol), 49.2, 49.5 (CH2, keto, enol), 51.2 (CH2, keto), 53.0, 53.1, 58.4, 58.5 (CH3, keto,
enol), 63.8, 63.9, 69.9, 70.0 (CH2, keto, enol), 89.3 (CH, enol), 108.2, 108.7, 122.4, 122.6 (CH, keto,
enol), 151.98, 150.99, 166.3, 166.5, 171.6, 200.2 (C, keto, enol).
Ethyl 4-(1-(N-benzyloxycarbonyl–4-dihydropyridyl)-3-oxobutanoate (6d). Starting with 5 (0.16 g,
2.0 mmol, 1.0 equiv.), 2a (1.09 g, 4.0 mmol, 2.0 equiv.), 3b (0.41 g, 2.4 mmol, 1.2 equiv.), and 20 mL of
CH2Cl2, 6d was isolated by chromatography (silica gel, hexane/EtOAc = 10:1) as a red oil (0.453 g, 66%).
1H-NMR (300 MHz, CDCl3)  = 1.28 (t, 3J = 7.0 Hz, 3 H, CH3), 2.65 (d, 3J = 7.0 Hz, 2 H, CH2), 3.41 (s,
3
1 H, CH), 3.47 (q, J = 9.0 Hz, 2 H, CH2), 4.16 - 4.23 (m, 2 H, CH2,), 4.83 - 4.90 (m, 1 H, CH), 5.19 -
5.27 (m, 2 H, CH2), 5.29 (s, 1 H, CH, enol), 5.90 - 5.96 (m, 1 H, CH), 6.76 - 6.86 (m, 2 H, CH), 7.30 -
7.38 (m, 5 H, CH). 13C-NMR (50 MHz, CDCl3):  = 28.3 (CH), 49.9 (CH2), 51.7 (CH2), 61.5 (CH2), 68.2
~
(CH2), 124.8, 126.8 (CH), 127.4 (C), 127.9, 128.0, 128.1 (CH), 135.5, 166.8, 200.7 (C). IR (KBr)
=

3466 (w), 3442 (w), 3065 (w), 3035 (w), 2983 (m), 2938 (w), 2905 (w), 1650 (m), 1638 (m), 1583 (w),
1498 (w), 1451 (m). MS (EI, 70 eV): m/z = 343 (M+, 2), 170 (14), 93 (24), 92 (16), 91 (100). Anal. Calcd
for C19H21NO5: C, 66.46; H, 6.16; N, 4.08. Found: C, 65.40; H, 5.93; N, 3.98.
Methyl 4-(1-(N-benzyloxycarbonyl–4-dihydropyridyl)-3-oxobutanoate (6e). Starting with 5 (0.16 g,
2.0 mmol, 1.0 equiv.), 2b (1.04 g, 4.0 mmol, 2.0 equiv.) and 3b (0.41 g, 2.4 mmol, 1.2 equiv.), and 20 mL
of CH2Cl2, 6e was isolated by chromatography (silica gel, hexane/EtOAc = 7:1) as a red oil (0.414 g,

HETEROCYCLES, Vol. 80, No. 1, 2010
301
1
3
63%). H-NMR (300 MHz, CDCl3):  = 2.64 (d, J = 7 Hz, 2 H, CH2), 3.42 - 3.52 (m, 2 H, CH2, keto),
3.72, 3.73 (2 x s, 3 H, CH3, keto, enol), 4.82 - 4.92 (m, 1 H, CH), 5.19 - 5.26 (m, 2 H, CH2), 5.29 (s, 1 H,
CH, enol), 5.90 - 5.95 (m, 1 H, CH), 6.68 - 6.86 (m, 2 H, CH), 7.30 - 7.41 (m, 5 H, CH), 12.01 (s, 1 H,
OH). 13C-NMR (75 MHz, CDCl3):  = 28.2 (CH), 49.2 (CH2), 51.5 (CH2), 52.3 (CH3), 68.1 (CH2), 124.9,
126.9 (CH), 127.5 (C), 128.1, 128.2, 128.6 (CH), 135.5, 167.3, 200.7 (C). UV-Vis (, log ): 207.79 (4.0).
+
~
IR (KBr): = 1746 (m), 1715 (s), 1651 (w), 1635 (w). MS (EI, 70 eV): m/z (%) = 329 (M , 1), 214 (6),

170 (16), 92 (17), 91 (100). Anal. Calcd for C18H19NO5: C, 65.64; H, 5.81; N, 4.25. Found: C, 63.88; H,
5.24; N, 4.00.
1-(1-N-Methoxycarboyl-4-dihydropyridyl)-2,4-dioxopentane (6f). Starting with 5 (0.119 g, 1.5 mmol),
3a (0.213 g, 2.3 mmol), and 2f (0.732 g, 3.0 mmol), 6f was isolated as a yellow oil (0.126 g, 35%,
1
3
keto/enol = 3:1). H NMR (CDCl3, 300 MHz): δ = 2.07 (s, 3 H, CH3), 2.36 (d, J = 7.0 Hz, 2 H, CH2),
3.43 (m, 1 H, CH), 3.57 (s, 2 H, CH2, keto), 3.77 (s, 3 H, CH3), 4.82 - 4.91 (m, 2 H, CH), 5.48 (s, 1 H, CH,
13
enol), 6.68 – 6.85 (m, 2 H, CH), 15.43 (br, 1 H, OH). C NMR (75 MHz, CDCl3): δ = 25.0 (CH3), 30.1
(CH), 47.2 (CH2), 52.3 (CH2, keto), 53.3 (CH3), 100.9 (CH, enol), 108.5, 108.9, 123.2, 123.2 (CH, keto,
~
enol), 151.7, 190.5, 191.7 (C). IR (KBr): = 3437 (w), 2958 (m), 2923 (w), 1725 (s), 1697 (s), 1630 (s),

1610 (s), 1444 (s), 1417 (m) cm-1. UV-Vis (MeCN): λmax (lg ε) = 228.52 (4.03) nm. MS (EI, 70 eV): m/z
= 237 (M+, 10), 138 (100), 94 (62), 84 (32), 60 (14). Anal. Calcd for C12H15NO4: C, 60.75; H, 6.37; N,
5.90. Found: C, 61.09; H, 6.71; N, 5.52.
ACKNOWLEDGEMENTS
Financial support from the State of Mecklenburg-Vorpommern (scholarship for A. S.) is gratefully
acknowledged.
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