A convenient synthesis of 4-hydroxy-2-oxo-1,2-dihydro-1,8-naphthyridine-3- Carboxamide derivatives

Article abstract of DOI:10.1055/s-0028-1083307

A simple method for synthesizing 1-aryl-4-hydroxy-N,N-dimethyl-2-oxo-1,2- dihydro-1,8-naphthyridine-3-carboxam- ides has been developed. Thus, 3-(2-chloropyridin-3-yl)-.N, N-dimethyl-3-oxopropanamide, easily prepared by treating ethyl 2- chloropyridine-3-

Full text of DOI:10.1055/s-0028-1083307

PAPER
375
A Convenient Synthesis of 4-Hydroxy-2-oxo-1,2-dihydro-1,8-naphthyridine-3-
carboxamide Derivatives
S
ynthesis of 1,8-N
a
aphthyridin
z
e
D
erivativ
u
es hiro Kobayashi,* Daisuke Iitsuka, Shuhei Fukamachi, Hisatoshi Konishi
Division of Applied Chemistry, Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University,
4-101 Koyama-minami, Tottori 680-8552, Japan
Fax +81(857)315263; E-mail: kkoba@chem.tottori-u.ac.jp
Received 25 August 2008; revised 30 September 2008
The starting material, 3-(2-chloropyridin-3-yl)-N,N-di-
Abstract: A simple method for synthesizing 1-aryl-4-hydroxy-
methyl-3-oxopropanamide (1) was prepared by the reaction
of 2-chloropyridine-3-carboxylate with lithium enolate of
N,N-dimethylacetamide in 76% yield. We first conducted
N,N-dimethyl-2-oxo-1,2-dihydro-1,8-naphthyridine-3-carboxam-
ides has been developed. Thus, 3-(2-chloropyridin-3-yl)-N,N-di-
methyl-3-oxopropanamide, easily prepared by treating ethyl 2-
chloropyridine-3-carboxylate with lithium enolate of N,N-dimeth- the reaction of compound 1 with phenyl isocyanate in
ylacetamide, smoothly reacts with a range of aryl isocyanates in the
DMF in the presence of two molar amounts of sodium hy-
presence of two molar amounts of sodium hydride to provide the de-
sired products in moderate yields.
dride at 0 °C. These conditions are the same as those used
previously in the preparation of (Z)-3-amino-2-(chloro-6-
methylpyridin-3-yl)propenamide derivatives.3 TLC mon-
Key words: carbanions, fused-ring system, isocyanates, naphthy-
ridines, tandem reaction
itoring of the progress of the reaction revealed that it was
complete within 30 minutes. Unfortunately, however,
aqueous extractive work up gave only a trace amount of
3-Substituted 4-hydroxy-1,8-naphthyridin-2(1H)-one de-
rivatives are an important class of molecules in medicinal
chemistry.1 Among them, 4-hydroxy-2-oxo-1,2-dihydro-
1,8-naphthyridine-3-carboxamides have been reported to
exhibit useful biological activities.2 3-Substituted 4-hy-
droxy-1,8-naphthyridin-2(1H)-one derivatives have been
prepared by the reactions of 2-methyl-4H-pyrido[2,3-
d][3,1]oxazin-4-one with active methylene compounds.1
However, no general procedures are available to prepare
4-hydroxy-2-oxo-1,2-dihydro-1,8-naphthyridine-3-car-
boxamides directly from readily available compounds,
though 3-carboxylate derivatives have been converted
into the corresponding 3-carboxamide derivatives.2 On
the other hand, we previously reported a method to pre-
the desired product 2a. All other efforts to isolate 2a in
satisfactory yields were unsuccessful. Then, we conduct-
ed the reaction in THF as shown in Table 1. It also pro-
ceeded smoothly and was complete in one hour.
Successive addition of chloroform and saturated aqueous
ammonium chloride to the reaction mixture allowed 2a to
precipitate (see experimental section). Collection and sub-
sequent recrystallization of this precipitate gave pure 2a in
satisfactory yield. The reactions of 1 with other aryl iso-
cyanates were carried out in a manner similar to that de-
scribed above and the resulting 1-aryl-4-hydroxy-N,N-
dimethyl-2-oxo-1,2-dihydro-1,8-naphthyridine-3-carbox-
amides 2b–j were isolated in a similar way. Yields of the
desired products are summarized in Table 1. The modest
yields are ascribed to loss of the products during the work-
up and purification procedures, as TLC analyses did not
indicate formation of any distinct by-products. It should
be noted that the reactions using aliphatic isocyanates,
such as n-butyl isocyanate and tert-butyl isocyanate, did
not give the corresponding desired products, and the start-
ing keto amide 1 was recovered almost quantitatively in
each case. Unfortunately, we have no explanation of the
reason for this result.
pare
(Z)-2-(2-oxo-2,3-dihydropyrido[2,3-d]pyrimidin-
4(1H)-ylidene)acetamide derivatives, which was based on
the reaction of (Z)-3-amino-2-(chloro-6-methylpyridin-3-
yl)propenamide derivatives with aryl isocyanates in the
presence of sodium hydride.3 In continuation of this study,
we became interested in examining the reaction of 3-(2-
chloropyridin-3-yl)-3-oxopropanamides with isocyan-
ates. We envisaged that if the addition of the enolate an-
ions of 3-(2-chloropyridin-3-yl)-3-oxopropanamides to
isocyanates would occur at the carbon, the reaction should
lead to construction of 4-hydroxy-2-oxo-1,2-dihydro-1,8-
naphthyridine-3-carboxamides. In this report, we wish to
report the results of our study, which provide a facile
method for the synthesis of 1-aryl-4-hydroxy-N,N-di-
methyl-2-oxo-1,2-dihydro-1,8-naphthyridine-3-carbox-
amides 2 from 3-(2-chloropyridin-3-yl)-N,N-dimethyl-3-
oxopropanamide (1) and aryl isocyanates.
When an equimolar amount of sodium hydride was used,
considerable amounts of the starting material was recov-
ered and rather decreased yields of the desired products
were obtained. The necessity of two molar amounts of so-
dium hydride may be explained as shown in Scheme 1.
Thus, addition of sodium enolate of the keto amide 1, gen-
erated by deprotonation of the active methylene with the
first equivalent of sodium hydride, to an isocyanate gen-
erates the amide anion intermediate 3. Presumably, proton
transfer converts this intermediate into the much more sta-
ble enolate intermediate 4, whose NH hydrogen is depro-
tonated by the second equivalent of sodium hydride to
SYNTHESIS 2009, No. 3, pp 0375–0378
x
x
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x
x
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0
0
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Advanced online publication: 09.01.2009
DOI: 10.1055/s-0028-1083307; Art ID: F18508SS
© Georg Thieme Verlag Stuttgart · New York

376
K. Kobayashi et al.
PAPER
corded on a Shimadzu FTIR-8300 spectrophotometer. The 1H NMR
spectra were recorded in CDCl3 or DMSO-d6 using TMS as an in-
ternal reference on a JEOL ECP500 FT NMR spectrometer operat-
ing at 500 MHz. The 13C NMR spectra were recorded in DMSO-d6
using TMS as an internal reference on a JEOL ECP500 FT NMR
spectrometer operating at 125 MHz. Low-resolution MS spectra
were measured with a JEOL JMS AX505 HA spectrometer. TLC
was carried out on a Merck Kieselgel 60 PF254. Column chromatog-
raphy was performed using Merck Kieselgel 60 (0.063–0.200 mm).
All of the organic solvents used in this study were dried over appro-
priate drying agents and distilled prior to use. Ethyl 2-chloropyri-
dine-3-carboxylate was prepared according to the reported
procedure.4 All other chemicals used in this study were commer-
cially available.
Table 1 Products and Yields of the Reaction of Keto Amide 1 with
Aryl Isocyanates
O
OH
NaH (2 equiv)
ArNCO
CONMe2
CONMe2
O
THF, 0 °C
N
Cl
N
N
Ar
1
2
Product
2a
Ar
Ph
Yield (%)
58
33
40
51
55
57
52
52
59
54
2b
2c
2-MeC6H4
3-MeC6H4
3-ClC6H4
3-(2-Chloropyridin-3-yl)-N,N-dimethyl-3-oxopropanamide (1)
To a stirred solution of LDA (5.4 mmol; prepared by the standard
method) in THF (7 mL) at –78 °C was added DMA (0.24 g, 2.7
mmol) dropwise. After 15 min, a solution of ethyl 2-chloropyridine-
3-carboxylate (0.50 g, 2.7 mmol) in THF (2 mL) was added, and
stirring was continued for an additional 15 min at the same temper-
ature. H2O (10 mL) was added and the mixture was neutralized by
adding 10% aq HCl. The organic materials were extracted with
Et2O (3 × 10 mL), and the combined extracts were washed with
brine (10 mL) and dried (Na2SO4). After evaporation of the solvent,
the residue was purified by chromatography on silica gel (THF–
hexane, 1:2) to give 1 as a white solid; yield: 0.46 g (76%); mp 51–
52 °C (hexane–Et2O); exists as a tautomeric mixture with the corre-
sponding enol amide (ca. 2:8 in CDCl3).
2d
2e
4-ClC6H4
2f
3-Cl-4-MeC6H3
2,4-Cl2C6H3
4-BrC6H4
2g
2h
2i
3-MeOC6H4
1-naphthyl
2j
IR (KBr): 3495, 1643, 1601 cm–1.
1H NMR (CDCl3): d = 2.97 (s, 1.2 H), 3.07 (s, 4.8 H), 4.16 (s, 0.4
H), 5.88 (s, 0.8 H), 7.32 (dd, J = 7.3, 4.6 Hz, 0.8 H), 7.36 (dd,
J = 7.8, 4.6 Hz, 0.2 H), 7.99 (dd, J = 7.3, 2.3 Hz, 0.8 H), 8.05 (dd,
J = 7.8, 1.8 Hz, 0.2 H), 8.42 (dd, J = 4.6, 2.3 Hz, 0.8 H), 8.49 (dd,
J = 4.6, 1.8 Hz, 0.2 H), 11.14 (br s, 0.8 H).
generate the dianion intermediate 5. This undergoes in-
tramolecular substitution to afford, after aqueous workup,
the product 2.
O
O–
Anal. Calcd for C10H11ClN2O2: C, 52.99; H, 4.89; N, 12.36. Found:
C, 52.87; H, 5.00; N, 12.24.
CONMe2
O
CONMe2
O
NaH
1
ArNCO
N
Cl
N
Cl
4-Hydroxy-N,N-dimethyl-2-oxo-1-phenyl-1,2-dihydro-1,8-
naphthyridine-3-carboxamide (2a); Typical Procedure
To a stirred suspension of NaH (60% in oil; 54 mg, 1.4 mmol) in
THF (3 mL) at 0 °C was added dropwise a solution of 1 (0.15 g, 0.68
mmol) in THF (2 mL). After 15 min, PhNCO (81 mg, 0.68 mmol)
was added, and stirring was continued for an additional 1 h before
the successive addition of CHCl3 (7 mL) and sat. aq NH4Cl (5 mL).
The resulting precipitate was collected by suction and recrystallized
from Et2O–EtOH to give 2a as a white solid; yield: 0.12 g (58%);
mp 197–203 °C (dec.).
N
NH
Ar
Ar
3
4
O–
Cl
CONMe2
O
H3O+
NaH
2
– Cl–
N
N–
Ar
IR (KBr): 3398, 1620 cm–1.
5
1H NMR (DMSO-d6): d = 2.59 (br s, 3 H), 2.91 (br s, 3 H), 6.86 (t,
J = 7.8 Hz, 1 H), 7.21 (t, J = 7.8 Hz, 2 H), 7.25 (dd, J = 6.9, 5.0 Hz,
1 H), 7.51 (d, J = 6.9 Hz, 1 H), 7.57 (d, J = 7.8 Hz, 2 H), 8.20 (d,
J = 5.0 Hz, 1 H), 12.75 (br s, 1 H).
Scheme 1
In summary, we have developed a simple and efficient
method for the direct preparation of 4-hydroxy-2-oxo-1,2-
MS (EI, 70 eV): m/z (%) = 309 (25, [M+]), 265 (38), 217 (100).
Anal. Calcd for C17H15N3O3: C, 66.01; H, 4.89; N, 13.58. Found: C,
65.86; H, 5.01; N, 13.36.
dihydro-1,8-naphthyridine-3-carboxamide
derivatives
based on the reaction of the readily available starting ma-
terial, 3-(2-chloropyridin-3-yl)-N,N-dimethyl-3-oxopro-
panamide, with various aryl isocyanates. The present
method should be of use in synthesizing this class of het-
erocycles because of the ease of operations.
4-Hydroxy-N,N-dimethyl-1-(2-methylphenyl)-2-oxo-1,2-dihy-
dro-1,8-naphthyridine-3-carboxamide (2b)
White solid; mp 160–164 °C (Et2O–EtOH).
IR (KBr): 3227, 1615 cm–1.
1H NMR (DMSO-d6): d = 2.26 (s, 3 H), 2.60 (br s, 3 H), 2.96 (br s,
3 H), 6.77 (t, J = 7.3 Hz, 1 H), 7.04 (dd, J = 7.8, 7.3 Hz, 1 H), 7.10
(d, J = 7.3 Hz, 1 H), 7.24 (dd, J = 7.3, 4.9 Hz, 1 H), 7.52 (d, J = 7.3
All melting points were obtained on a Laboratory Devices MEL-
TEMP II melting apparatus and are uncorrected. IR spectra were re-
Synthesis 2009, No. 3, 375–378 © Thieme Stuttgart · New York

PAPER
Synthesis of 1,8-Naphthyridine Derivatives
377
Hz, 1 H), 8.17 (dd, J = 4.9, 1.8 Hz, 1 H), 8.45 (d, J = 7.8 Hz, 1 H),
12.54 (s, 1 H).
MS (EI, 70 eV): m/z (%) = 323 (36, [M+]), 217 (54), 191 (100).
1H NMR (DMSO-d6): d = 2.59 (s, 3 H), 2.93 (s, 3 H), 7.22–7.25 (m,
2 H), 7.48 (d, J = 2.4 Hz, 1 H), 7.51 (d, J = 7.3 Hz, 1 H), 8.17 (dd,
J = 4.3, 1.8 Hz, 1 H), 8.71 (d, J = 9.2 Hz, 1 H), 13.12 (s, 1 H).
MS (EI, 70 eV): m/z (%) = 377 (40, [M+]), 333 (100).
Anal. Calcd for C18H17N3O3: C, 66.86; H, 5.30; N, 13.00. Found: C,
66.80; H, 5.19; N, 12.99.
Anal. Calcd for C17H13Cl2N3O3: C, 53.99; H, 3.46; N, 11.11. Found:
C, 53.92; H, 3.32; N, 11.08.
4-Hydroxy-N,N-dimethyl-1-(3-methylphenyl)-2-oxo-1,2-dihy-
dro-1,8-naphthyridine-3-carboxamide (2c)
White solid; mp 145–148 °C (Et2O–EtOH).
1-(4-Bromophenyl)-4-hydroxy-N,N-dimethyl-2-oxo-1,2-dihy-
dro-1,8-naphthyridine-3-carboxamide (2h)
White solid; mp 214–217 °C (dec.) (Et2O–EtOH).
IR (KBr): 3415, 1611 cm–1.
1H NMR (DMSO-d6): d = 2.49 (s, 3 H), 2.84 (s, 3 H), 7.15 (dd,
J = 7.3, 4.9 Hz, 1 H), 7.25 (d, J = 8.5 Hz, 2 H), 7.41 (dd, J = 7.3, 1.8
Hz, 1 H), 7.44 (d, J = 8.5 Hz, 2 H), 8.08 (dd, J = 4.9, 1.8 Hz, 1 H),
12.83 (s, 1 H).
IR (KBr): 3194, 1612 cm–1.
1H NMR (DMSO-d6): d = 2.23 (s, 3 H), 2.57 (s, 3 H), 2.92 (s, 3 H),
6.65 (d, J = 7.3 Hz, 1 H), 7.06 (t, J = 7.3 Hz, 1 H), 7.22 (dd, J = 7.6,
4.6 Hz, 1 H), 7.31 (d, J = 7.6 Hz, 1 H), 7.41 (s, 1 H), 7.49 (d, J = 7.3
Hz, 1 H), 8.16 (dd, J = 4.6, 1.5 Hz, 1 H), 12.69 (s, 1 H).
MS (CI): m/z (%) = 324 (100, [M + 1]+).
MS (EI, 70 eV): m/z (%) = 387 (10, [M+]), 217 (100).
Anal. Calcd for C18H17N3O3: C, 66.86; H, 5.30; N, 13.00. Found: C,
66.82; H, 5.51; N, 12.96.
Anal. Calcd for C17H14BrN3O3: C, 52.60; H, 3.63; N, 10.82. Found:
C, 52.49; H, 3.62; N, 11.81.
1-(3-Chlorophenyl)-4-hydroxy-N,N-dimethyl-2-oxo-1,2-dihy-
dro-1,8-naphthyridine-3-carboxamide (2d)
White solid; mp 140–142 °C (Et2O–EtOH).
4-Hydroxy-1-(3-methoxyphenyl)-N,N-dimethyl-2-oxo-1,2-dihy-
dro-1,8-naphthyridine-3-carboxamide (2i)
White solid; mp 199–202 °C (dec.) (Et2O–EtOH).
IR (KBr): 3413, 1614 cm–1.
1H NMR (DMSO-d6): d = 2.64 (br s, 3 H), 2.94 (br s, 3 H), 3.71 (s,
3 H), 6.42 (d, J = 7.9 Hz, 1 H), 6.95 (d, J = 7.9 Hz, 1 H), 7.08 (t,
J = 7.9 Hz, 1 H), 7.23 (dd, J = 6.9, 3.8 Hz, 1 H), 7.40 (s, 1 H), 7.50
(d, J = 6.9 Hz, 1 H), 8.17 (d, J = 3.8 Hz, 1 H), 12.79 (s, 1 H).
IR (KBr): 3421, 1616 cm–1.
1H NMR (DMSO-d6): d = 2.60 (s, 3 H), 2.95 (s, 3 H), 6.88 (d,
J = 7.9 Hz, 1 H), 7.17–7.27 (m, 3 H), 7.51 (d, J = 7.3 Hz, 1 H), 8.02
(s, 1 H), 8.19 (dd, J = 4.9, 1.4 Hz, 1 H), 13.00 (s, 1 H).
MS (EI, 70 eV): m/z (%) = 343 (19, [M+]), 299 (20), 217 (100).
Anal. Calcd for C17H14ClN3O3: C, 59.40; H, 4.10; N, 12.22. Found:
C, 59.20; H, 4.18; N, 12.09.
MS (EI, 70 eV): m/z (%) = 339 (13, [M+]), 217 (48), 191 (100).
Anal. Calcd for C18H17N3O4: C, 63.71; H, 5.05; N, 12.38. Found: C,
63.69; H, 5.35; N, 12.38.
1-(4-Chlorophenyl)-4-hydroxy-N,N-dimethyl-2-oxo-1,2-dihy-
dro-1,8-naphthyridine-3-carboxamide (2e)
White solid; mp 213–215 °C (dec.) (Et2O–EtOH).
IR (KBr): 3371, 1620 cm–1.
1H NMR (DMSO-d6): d = 2.58 (br s, 3 H), 2.92 (br s, 3 H), 7.21–
7.26 (m, 3 H), 7.51 (d, J = 7.3 Hz, 1 H), 7.60 (d, J = 8.6 Hz, 2 H),
8.19 (d, J = 5.5 Hz, 1 H), 12.93 (br s, 1 H).
4-Hydroxy-N,N-dimethyl-1-(naphthalen-1-yl)-2-oxo-1,2-dihy-
dro-1,8-naphthyridine-3-carboxamide (2j)
White solid; mp 212–215 °C (dec.) (Et2O–EtOH).
IR (KBr): 3253, 1614 cm–1.
1H NMR (DMSO-d6): d = 2.62 (s, 3 H), 2.98 (s, 3 H), 7.26 (dd,
J = 7.3, 4.9 Hz, 1 H), 7.37 (t, J = 7.9 Hz, 1 H), 7.42 (d, J = 7.9 Hz,
1 H), 7.48–7.52 (m, 2 H), 7.57 (d, J = 7.3 Hz, 1 H), 7.85 (d, J = 7.9
Hz, 1 H), 8.20 (dd, J = 4.9, 1.8 Hz, 1 H), 8.37 (d, J = 8.7 Hz, 1 H),
8.61 (d, J = 8.2 Hz, 1 H), 13.63 (s, 1 H).
MS (EI, 70 eV): m/z (%) = 343 (9.8, [M+]), 217 (61), 191 (100).
Anal. Calcd for C17H14ClN3O3: C, 59.40; H, 4.10; N, 12.22. Found:
C, 59.28; H, 4.20; N, 12.07.
13C NMR (DMSO-d6): d = 34.31, 38.36, 101.72, 114.19, 120.15,
121.66, 121.96, 124.42, 125.21, 125.42 (2 C), 126.22, 128.26,
133.76, 137.07, 139.48, 147.05, 147.14, 166.21, 171.23, 174.97.
1-(3-Chloro-4-methylphenyl)-4-hydroxy-N,N-dimethyl-2-oxo-
1,2-dihydro-1,8-naphthyridine-3-carboxamide (2f)
White solid; mp 235–237 °C (dec.) (Et2O–EtOH).
IR (KBr): 3412, 1616 cm–1.
MS (EI, 70 eV): m/z (%) = 359 (45, [M+]), 314 (100).
Anal. Calcd for C21H17N3O3: C, 70.18; H, 4.77; N, 11.69. Found: C,
70.03; H, 4.80; N, 11.70.
1H NMR (DMSO-d6): d = 2.23 (s, 3 H), 2.49 (s, 3 H), 2.93 (s, 3 H),
7.09 (dd, J = 7.8, 1.8 Hz, 1 H), 7.15 (d, J = 7.8 Hz, 1 H), 7.23 (dd,
J = 7.3, 4.9 Hz, 1 H), 7.49 (d, J = 7.3 Hz, 1 H), 7.99 (d, J = 1.8 Hz,
1 H), 8.17 (dd, J = 4.9, 1.8 Hz, 1 H), 12.84 (s, 1 H).
13C NMR (DMSO-d6): d = 18.83, 34.29, 38.33, 100.84, 116.88,
118.28, 121.98, 126.52, 130.90, 132.93, 137.18, 139.44, 140.63,
146.96, 147.15, 166.02, 171.10, 175.06.
Acknowledgment
We are grateful to Mrs. Miyuki Tanmatsu of this university for de-
termining mass spectra and performing combustion analyses.
MS (EI, 70 eV): m/z (%) = 357 (40, [M+]), 312 (49), 217 (100).
References
Anal. Calcd for C18H16ClN3O3: C, 60.42; H, 4.51; N, 11.74. Found:
C, 60.24; H, 4.54; N, 11.58.
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hydro-1,8-naphthyridine-3-carboxamide (2g)
White solid; mp 170–171 °C (Et2O–EtOH).
IR (KBr): 3423, 1624 cm–1.
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K. Kobayashi et al.
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Synthesis 2009, No. 3, 375–378 © Thieme Stuttgart · New York