Synthesis of 4-aryl-1,7-naphthyridine-2(1H)-thiones by the electrocyclic reaction of 4-(1-arylalk-1-enyl)-3-isothiocyanatopyridines Generated in situ from the corresponding Isocyanides

Article abstract of DOI:10.1002/hlca.201100408

A convenient synthis for 4-substituted and 3,4-disubstituted 1,7-naphthyridine-2(1H)-thiones 7 has been developed. The method is based on the electrocyclic reaction of 4-(1-arylalk-1-enyl)-3-isothiocyanatopyridines 6, generated in situ by the treatment of the respective isocyanides 5 with S ₈ in the presence of a catalytic amount of selenium. The isocyanides 5 can be easily prepared from commercially available pyridin-3-amine by conventional organic reactions.

Full text of DOI:10.1002/hlca.201100408

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Helvetica Chimica Acta – Vol. 95 (2012)
Synthesis of 4-Aryl-1,7-naphthyridine-2(1H)-thiones by the Electrocyclic
Reaction of 4-(1-Arylalk-1-enyl)-3-isothiocyanatopyridines Generated in situ
from the Corresponding Isocyanides
by Kazuhiro Kobayashi*, Taketoshi Kozuki, and Teruhiko Suzuki
Division of Applied Chemistry, Department of Chemistry and Biotechnology, Graduate School of
Engineering, Tottori University, 4-101 Koyama-minami, Tottori 680-8552, Japan
(phone/fax þ 81(857)315263; e-mail: kkoba@chem.tottori-u.ac.jp)
A convenient synthis for 4-substituted and 3,4-disubstituted 1,7-naphthyridine-2(1H)-thiones 7 has
been developed. The method is based on the electrocyclic reaction of 4-(1-arylalk-1-enyl)-3-
isothiocyanatopyridines 6, generated in situ by the treatment of the respective isocyanides 5 with S8 in
the presence of a catalytic amount of selenium. The isocyanides 5 can be easily prepared from
commercially available pyridin-3-amine by conventional organic reactions.
Introduction. – We have previously reported the synthesis of 4-arylquinoline-
2(1H)-thiones by the electrocyclic reaction of 1-(1-arylalk-1-enyl)-2-isothiocyanato-
benzenes, generated in situ from the respective isocyanides [1]. Accordingly, we
became interested in investigating the possibility of preparing 1,7-naphthyridine-
2(1H)-thiones employing a similar sequence, and envisioned that 4-(1-arylalk-1-enyl)-
3-isocyanopyridines 5 could be prepared from commercially available pyridin-3-amine,
and they would give 4-aryl-1,7-naphthyridine-2(1H)-thiones 7 via the corresponding
isothiocyanates 6. A survey of the literature provided only one compound with the 1,7-
naphthyridine-2(1H)-thione skeleton [2]. Here, we report the results of our inves-
tigation, which led to the first practical synthesis of 1,7-naphthyridine-2(1H)-thiones.
This class of naphthyridines may be of biological interest, because some compounds
with the 1,7-naphthyridin-2(1H)-one skeleton display biological activities [3].
Results and Discussion. – Our synthetic route to 1,7-naphthyridine-2(1H)-thiones 7
starting from 4-aroylpyridine-3-amines 1 is outlined in the Scheme. The preparation of
4-(1-arylalk-1-enyl)-3-isocyanopyridines 5, precursors for the synthesis of 7, was
conducted in a four-step sequence from 1. These amines 1 could be easily prepared
from commercially available pyridin-3-amine according to the procedure described in
[4], and they were reacted with alkylmagnesium bromides to give the corresponding
amino alcohols 2. Use of SOCl2 as a dehydrating agent in THF in the presence of
pyridine afforded 3-amino-4-(1-arylalk-1-enyl)pyridines 3, which, by N-formylation
with HCO2H in the presence of Ac2O, gave N-[4-(1-arylalk-1-enyl)pyridin-3-yl]form-
amides 4. Subsequent dehydration of 4 with POCl3 in the presence of Et3N completed
the synthesis of 5. These conversions could be carried out generally with good yields as
compiled in Table 1.
ꢀ 2012 Verlag Helvetica Chimica Acta AG, Zꢁrich

Helvetica Chimica Acta – Vol. 95 (2012)
557
Scheme
Table 1. Preparation of 4-(1-Arylalk-1-enyl)-3-isocyanopyridines 5a)
Entry
1
Ar
R
2
Yield
3
Yield
4
Yield
5
Yield
1
2
3
4
5
6
7
8
1a Ph
1b m-Tolyl
1c p-Tolyl
H
H
H
H
H
H
2a
2b
2c
2d
2e
2f-i
97
98
99
92
81
99
79
3a
3b
3c
3d
3e
3f-i
3f-ii
67
64
64
58
63
68
84
4a
4b
4c
4d
4e
4f-i
4f-ii
94
79
84
74
79
89
87
5a
5b
5c
5d
5e
5f-i
5f-ii
94
83
86
91
85
87
62
1d 4-ClꢀC6H4
1e 4-MeOꢀC6H4
1f 3,4-(MeO)2ꢀC6H3
1f 3,4-(MeO)2ꢀC6H3 Me 2f-ii
1f 3,4-(MeO)2ꢀC6H3 Et
2f-iii 74
3f-iii 91
4f-iii 76
5f-iii 57
a) Yields of isolated products in [%].
The transformation of the obtained isocyano pyridines 5 into the desired 1,7-
naphthyridine-2(1H)-thiones 7 was then performed by treating them with S8 and a
catalytic amount of Se in refluxing THF in the presence of Et3N. These conditions are
the same as described earlier by Fujiwara et al. for the conversion of isocyanides to the
corresponding isothiocyanates [5]. First, conversion of 4-(1-arylalk-1-enyl)-3-isocya-
nopyridines 5a – 5f-i to 4-aryl-1,7-naphthyridine-2(1H)-thiones 7a – 7f-i, respectively,
via 6a – 6f-i, was carried out. The desired products were obtained in good yields as
collected in Table 2 (Entries 1 – 6). The reactions were monitored by TLC (SiO2) to
evaluate their progress, revealing that the conversion of isocyanides 5 to isothiocyanate
6 proceeded immediately in all cases, but the rate of the conversion of 6 to the
corresponding naphthyridin-2(1H)-thiones 7 were quite dependent on the substituents
of the aryl groups of 5 or 6 (cf. Table 2, Entries 1 – 6). The cyclization of the substrates
that carry one or two electron-donating MeO group(s) went to completion within 2.5 or
1 h, respectively, to give the corresponding products 7e or 7f-i (Entries 5 or 6, resp.).

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This may be attributed to the higher electron density of the ethenyl moieties. On the
other hand, the 4-ClꢀC6H4 substrate required 20 h for the completion of the reaction,
probably due to the lower electron density of the ethenyl moiety (Entry 4).
Table 2. Preparation of 1,7-Naphthyridine-2(1H)-thiones 7
Entry
5
Time [h]
7
Ar
R
Yielda)
1
2
3
4
5
6
7
8
5a
5b
5c
5d
15
7
8
20
2.5
1
18
20
7a
7b
7c
7d
Ph
m-Tolyl
p-Tolyl
4-ClꢀC6H4
H
H
H
H
H
H
Me
Et
81
82
80
87
96
82
99
99
5e
7e
4-MeOꢀC6H4
3,4-(MeO)2ꢀC6H3
3,4-(MeO)2ꢀC6H3
3,4-(MeO)2ꢀC6H3
5f-i
5f-ii
5f-iii
7f-i
7f-ii
7f-iii
a) Yields of isolated products in [%].
We next attempted to synthesize 3,4-disubstituted 1,7-naphthyridine-2(1H)-thiones
7f-ii or 7f-iii from the respective 4-(1-arylprop-1-enyl)- or 4-(1-arylbut-1-enyl)-3-
isocyanopyridines 5f-ii and 5f-iii. When the latter were treated with S8 in the presence
of Se under the same conditions as described for the preparation of 5a – 5f-i, the
isocyanides were also converted immediately to the corresponding isothiocyanates 6f-ii
and 6f-iii, but prolonged reaction times were required for the complete consumption of
the isothiocyanates. The sluggishness may be ascribed to the steric hindrance due to the
Me or Et substituents. Fortunately, however, the electrocyclic reaction proceeded
cleanly in each case and resulted in the formation of the desired products 7f-ii and 7f-iii
in almost quantitative yields (Table 2, Entries 7 and 8).
In conclusion, an efficient route for the preparation of 1,7-naphthyridine-2(1H)-
thiones 7 utilizing the electrocyclic reaction of the respective 4-(1-arylalk-1-enyl)-3-
isothiocyanatopyridines 6 has been developed, which starts from commercially
available pyridin-3-amine. This is the first practical method for preparing this type of
naphthyridine derivatives, and it is valuable for organic synthesis, because it consists of
simple procedures, and the starting materials are readily available.
Experimental Part
General. All org. solvents used in this study were dried over appropriate drying agents and distilled
prior to use. TLC: Merck silica gel 60 PF254. Column chromatography (CC): Wako Gel C-200E. M.p.:
Laboratory Devices MEL-TEMP II melting point apparatus; uncorrected. IR Spectra: Shimadzu FTIR-
1
8300 spectrophotometer. H- and 13C-NMR Spectra: with TMS as an internal reference with a JEOL
ECP500 FT NMR spectrometer, at 500 and 125 MHz, resp. LR-MS (EI, 70 eV): JEOL JMS AX505 HA
spectrometer.
2,2-Dimethyl-N-(pyridin-3-yl)propanamide was prepared according to the procedure described in
[6]. All of the other chemicals used in this study were commercially available.
(3-Aminopyridin-4-yl)arylmethanones 1. These compounds were prepared by the successive
treatment of 2,2-dimethyl-N-(pyridin-3-yl)propanamide with 2 equiv. of BuLi (Asia Lithium Corpo-
ration) and N-methoxy-N-methylbenzamides, followed by hydrolysis of the resulting N-(4-aroylpyridin-

Helvetica Chimica Acta – Vol. 95 (2012)
559
3-yl)-2,2-dimethylpropanamides with 10% HCl under the conditions reported in [4]. Compounds 1a [4],
1c [4], 1d [7], and 1e [4] are known compounds, and the data for new compounds follow.
2,2-Dimethyl-N-[4-(3-methylbenzoyl)pyridin-3-yl]propanamide. Yield 57%. White solid. M.p. 84 –
1
868 (hexane/Et2O). IR (KBr): 3327, 1661, 1603. H-NMR (CDCl3): 1.34 (s, 9 H); 2.44 (s, 3 H); 7.38 (d,
J ¼ 5.0, 1 H); 7.41 (dd, J ¼ 7.8, 7.3, 1 H); 7.47 (d, J ¼ 7.3, 1 H); 7.53 (d, J ¼ 7.8, 1 H); 7.58 (s, 1 H); 8.46 (d,
J ¼ 5.0, 1 H); 9.92 (s, 1 H); 10.41 (br. s, 1 H). Anal. calc. for C18H20N2O2 (296.36): C 72.95, H 6.80, N 9.45;
found: C 72.91, H 6.86, N 9.44.
(3-Aminopyridin-4-yl)(3-methylphenyl)methanone (1b). Yield 83%. Yellow solid. M.p. 105 – 1078
1
(hexane/CH2Cl2). IR (KBr): 3445, 3316, 1647, 1605. H-NMR (CDCl3): 2.43 (s, 3 H); 5.79 (br. s, 2 H);
7.24 (d, J ¼ 5.0, 1 H); 7.37 (dd, J ¼ 7.8, 7.3, 1 H); 7.40 (d, J ¼ 7.3, 1 H); 7.46 (d, J ¼ 7.8, 1 H); 7.50 (s, 1 H);
7.94 (d, J ¼ 5.0, 1 H); 8.28 (s, 1 H). Anal. calc. for C13H12N2O (212.25): C 73.56, H 5.70, N 13.20; found: C
73.36, H 5.78, N 13.02.
N-[4-(3,4-Dimethoxybenzoyl)pyridin-3-yl]-2,2-dimethylpropanamide. Yield 59%. White solid. M.p.
1
110 – 1128 (hexane/Et2O). IR (KBr) 3320, 1657. H-NMR (CDCl3): 1.33 (s, 9 H); 3.96 (s, 3 H); 3.99 (s,
3 H); 6.93 (d, J ¼ 8.2, 1 H); 7.34 (dd, J ¼ 8.2, 2.3, 1 H), 7.38 (d, J ¼ 5.0, 1 H); 7.42 (d, J ¼ 2.3, 1 H); 8.46 (d,
J ¼ 5.0, 1 H); 9.83 (s, 1 H); 10.07 (br. s, 1 H). Anal. calc. for C19H22N2O4 (342.39): C 66.65, H 6.48, N 8.18;
found: C 66.62, H 6.57, N 8.17.
(3-Aminopyridin-4-yl)(3,4-dimethoxylphenyl)methanone (1f). Yield 87%. Yellow solid. M.p. 107 –
1098 (hexane/CH2Cl2). IR (KBr): 3474, 3364, 1634, 1615. 1H-NMR (CDCl3): 3.94 (s, 3 H); 3.97 (s,
3 H); 5.48 (br. s, 2 H); 6.92 (d, J ¼ 8.2, 1 H); 7.26 (d, J ¼ 5.0, 1 H); 7.32 (dd, J ¼ 8.2, 1.8, 1 H); 7.37 (d, J ¼
1.8, 1 H); 7.98 (d, J ¼ 5.0, 1 H); 8.28 (s, 1 H). Anal. calc. for C14H14N2O3 (258.27): C 65.11, H 5.46, N 10.85;
found: C 65.00, H 5.53, N 10.82.
1-(3-Aminopyridin-4-yl)-1-arylethanols 2. These compounds were prepared by reacting 1
(3.0 mmol) with the respective alkylmagnesium bromide (12 mmol) in THF (15 ml) at 08 for 15 min.
1-(3-Aminopyridin-4-yl)-1-phenylethanol (2a). Pale-yellow solid. M.p. 184 – 1868 (hexane/THF). IR
(KBr) 3412, 3323, 3218, 1634. 1H-NMR (CDCl3): 1.90 (s, 3 H); 3.52 (br. s, 1 H); 3.86 (br. s, 2 H); 7.21 (d,
J ¼ 5.0, 1 H); 7.28 (tt, J ¼ 7.3, 1.8, 1 H); 7.34 (dd, J ¼ 7.8, 7.3, 2 H); 7.38 (dd, J ¼ 7.8, 1.8, 2 H); 7.98 (s, 1 H);
8.06 (d, J ¼ 5.0, 1 H). Anal. calc. for C13H14N2O (214.26): C 72.87, H 6.59, N 13.07; found: C 72.84, H 6.72,
N 12.94.
1-(3-Aminopyridin-4-yl)-1-(3-methylphenyl)ethanol (2b). Pale-yellow solid. M.p. 151 – 1538 (hex-
ane/CH2Cl2). IR (KBr): 3424, 3331, 3235, 1638, 1609. 1H-NMR (CDCl3): 1.88 (s, 3 H); 2.33 (s, 3 H); 3.58
(br. s, 1 H); 3.86 (br. s, 2 H); 7.09 (d, J ¼ 7.3, 1 H); 7.15 – 7.23 (m, 4 H); 7.96 (s, 1 H); 8.06 (d, J ¼ 4.6, 1 H).
Anal. calc. for C14H16N2O (228.29): C 73.66, H 7.06, N 12.27; found: C 73.59, H 7.18, N 12.08.
1-(3-Aminopyridin-4-yl)-1-(4-methylphenyl)ethanol (2c). Pale-yellow solid. M.p. 171 – 1738 (hexane/
THF). IR (KBr): 3410, 3337, 3220, 1627. 1H-NMR (CDCl3): 1.88 (s, 3 H); 2.33 (s, 3 H); 3.46 (br. s, 1 H);
3.89 (br. s, 2 H); 7.14 (d, J ¼ 8.2, 2 H); 7.19 (d, J ¼ 5.0, 1 H); 7.25 (d, J ¼ 8.2, 2 H); 7.95 (s, 1 H); 8.04 (d, J ¼
5.0, 1 H). Anal. calc. for C14H16N2O (228.29): C 73.66, H 7.06, N 12.27; found: C 73.37, H 7.13, N 12.27.
1-(3-Aminopyridin-4-yl)-1-(4-chlorophenyl)ethanol (2d). Pale-yellow solid. M.p. 164 – 1668 (hexane/
CH2Cl2). IR (KBr): 3472, 3374, 3088, 1603. 1H-NMR (CDCl3): 1.88 (s, 3 H); 3.74 (br., 1 H); 3.96 (br. s,
2 H); 7.17 (d, J ¼ 5.0, 1 H); 7.30 (s, 4 H); 7.95 (s, 1 H); 8.02 (d, J ¼ 5.0, 1 H). Anal. calc. for C13H13ClN2O
(248.71): C 62.78, H 5.27, N 11.26; found: C 62.59, H 5.40, N 11.19.
1-(3-Aminopyridin-4-yl)-1-(4-methoxyphenyl)ethanol (2e).White solid. M.p. 204 – 2068 (THF). IR
(KBr): 3414, 3325, 3240, 1627, 1610. 1H-NMR (CDCl3): 1.89 (s, 3 H); 3.30 (s, 1 H); 3.80 (s, 3 H); 3.88 (br.
s, 2 H); 6.86 (d, J ¼ 8.7, 2 H); 7.18 (d, J ¼ 5.0, 1 H); 7.29 (d, J ¼ 8.7, 2 H); 7.99 (s, 1 H); 8.06 (d, J ¼ 5.0, 1 H).
Anal. calc. for C14H16N2O2 (244.29): C 68.83, H 6.60, N 11.47; found: C 68.59, H 6.63, N 11.43.
1-(3-Aminopyridin-4-yl)-1-(3,4-dimethoxyphenyl)ethanol (2f-i). Yellow solid. M.p. 168 – 1708
1
(THF). IR (KBr): 3451, 3352, 3158, 1614. H-NMR (CDCl3): 1.89 (s, 3 H); 3.54 (br. s, 1 H); 3.84 (s,
3 H); 3.87 (s, 3 H); 3.88 (br. s, 2 H); 6.79 (d, J ¼ 8.7, 1 H); 6.82 (dd, J ¼ 8.7, 1.4, 1 H); 7.00 (d, J ¼ 1.4, 1 H);
7.19 (d, J ¼ 5.0, 1 H); 8.00 (s, 1 H); 8.07 (d, J ¼ 5.0, 1 H). Anal. calc. for C15H18N2O3 (274.32): C 65.63, H
6.61, N 10.21; found: C 65.41, H 6.61, N 10.10.
1-(3-Aminopyridin-4-yl)-1-(3,4-dimethoxyphenyl)propan-1-ol (2f-ii). Pale-yellow solid. M.p. 174 –
1
1768 (hexane/THF). IR (KBr): 3476, 3364, 3111, 1618. H-NMR (CDCl3): 0.91 (t, J ¼ 7.3, 3 H); 2.13 –
2.20 (m, 1 H); 2.29 – 2.36 (m, 1 H); 3.46 (br. s, 1 H); 3.82 (s, 3 H); 3.86 (s, 3 H); 3.93 (br. s, 2 H); 6.79

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(d, J ¼ 8.2, 1 H); 6.81 (dd, J ¼ 8.2, 1.4, 1 H); 6.93 (d, J ¼ 1.4, 1 H); 7.19 (d, J ¼ 5.0, 1 H); 7.95 (s, 1 H); 8.04
(d, J ¼ 5.0, 1 H). Anal. calc. for C16H20N2O3 (288.34): C 66.65, H 6.99, N 9.72; found: C 66.53, H 7.17, N
9.53.
1-(3-Aminopyridin-4-yl)-1-(3,4-dimethoxyphenyl)butan-1-ol (2f-iii). Pale-yellow solid. M.p. 178 –
1808 (hexane/CH2Cl2). IR (KBr): 3451, 3358, 3206, 1626. 1H-NMR (CDCl3): 0.93 (t, J ¼ 7.3, 3 H);
1.20 – 1.47 (m, 2 H); 2.06 – 2.13 (m, 1 H); 2.20 – 2.26 (m, 1 H); 3.63 (br. s, 1 H); 3.82 (s, 3 H); 3.86 (s, 3 H);
3.94 (br. s, 2 H); 6.78 – 6.81 (m, 2 H); 6.94 (d, J ¼ 1.4, 1 H); 7.20 (d, J ¼ 5.0, 1 H); 7.94 (s, 1 H); 8.02 (d, J ¼
5.0, 1 H). Anal. calc. for C17H22N2O3 (302.37): C 67.53, H 7.33, N 9.26; found: C 67.49, H 7.48, N 9.00.
4-(1-Arylethenyl)pyridin-3-amines 3. These compounds were prepared by treating 2 (2.0 mmol) with
SOCl2 (8.0 mmol) in THF (10 ml) in the presence of pyridine (Py) (30 mmol) at 08 for 30 min.
4-(1-Phenylethenyl)pyridin-3-amine (3a). Yellow oil. Rf (hexane/THF 1:1) 0.35. IR (neat): 3462,
3306, 1624. 1H-NMR (CDCl3): 3.57 (br. s, 2 H); 5.41 (d, J ¼ 0.9, 1 H); 5.86 (d, J ¼ 0.9, 1 H); 7.02 (d, J ¼
5.0, 1 H); 7.34 (dd, J ¼ 7.8, 7.3, 2 H); 7.38 (dd, J ¼ 7.8, 0.9, 2 H); 7.68 (td, J ¼ 7.3, 0.9, 1 H); 8.07 (d, J ¼ 5.0,
1 H); 8.08 (s, 1 H). Anal. calc. for C13H12N2 (196.25): C 79.56, H 6.16, N 14.27; found: C 79.43, H 6.34, N
14.08.
4-[1-(3-Methylphenyl)ethenyl]pyridin-3-amine (3b). Yellow oil. Rf (hexane/THF 1:1) 0.32. IR
(neat): 3460, 3323, 1616. 1H-NMR (CDCl3): 2.33 (s, 3 H); 2.57 (br. s, 2 H); 5.38 (s, 1 H); 5.83 (s, 1 H); 7.02
(d, J ¼ 4.6, 1 H); 7.12 – 7.15 (m, 3 H); 7.23 (t, J ¼ 7.8, 1 H); 8.04 (d, J ¼ 5.0, 1 H); 8.09 (s, 1 H). Anal. calc.
for C14H14N2 (210.27): C 79.97, H 6.71, N 13.32; found: C 79.96, H 6.76, N 13.20.
4-[1-(4-Methylphenyl)ethenyl]pyridin-3-amine (3c). Yellow oil. Rf (hexane/THF 1:1) 0.27. IR
(neat): 3460, 3316, 1614. 1H-NMR (CDCl3): 2.36 (s, 3 H); 3.56 (br. s, 2 H); 5.34 (s, 1 H); 5.81 (s, 1 H); 7.02
(d, J ¼ 5.0, 1 H); 7.15 (d, J ¼ 8.2, 2 H); 7.23 (d, J ¼ 8.2, 2 H); 8.04 (d, J ¼ 5.0, 1 H); 8.08 (s, 1 H). Anal. calc.
for C14H14N2 (210.27): C 79.97, H 6.71, N 13.32; found: C 79.95, H 6.88, N 13.13.
4-[1-(4-Chlorophenyl)ethenyl]pyridin-3-amine (3d). Yellow oil. Rf (hexane/THF 1:2) 0.41. IR
(neat): 3458, 3322, 3202, 1614. 1H-NMR (CDCl3): 3.57 (br. s, 2 H); 5.42 (s, 1 H); 5.85 (s, 1 H); 6.99 (d, J ¼
5.0, 1 H); 7.26 (d, J ¼ 8.7, 2 H); 7.31 (d, J ¼ 8.7, 2 H); 8.04 (d, J ¼ 5.0, 1 H); 8.11 (s, 1 H). Anal. calc. for
C13H11ClN2 (230.69): C 67.68, H 4.81, N 12.14; found: C 67.63, H 5.05, N 12.12.
4-[1-(4-Methoxyphenyl)ethenyl]pyridin-3-amine (3e). Yellow oil. Rf (hexane/THF 1:2) 0.30. IR
(neat): 3457, 3329, 1606. 1H-NMR (CDCl3): 3.58 (br. s, 2 H); 3.81 (s, 3 H); 5.28 (s, 1 H); 5.75 (d, J ¼ 0.9,
1 H); 6.87 (d, J ¼ 8.7, 2 H); 7.02 (d, J ¼ 5.0, 1 H); 7.27 (d, J ¼ 8.7, 2 H); 8.04 (d, J ¼ 5.0, 1 H); 8.09 (s, 1 H).
Anal. calc. for C14H14N2O (226.27): C 74.31, H 6.24, N 12.38; found: C 74.20, H 6.49, N 12.39.
4-[1-(3,4-Dimethoxyphenyl)ethenyl]pyridin-3-amine (3f-i). Yellow oil. Rf (hexane/THF 1:2) 0.29.
IR (neat): 3445, 3382, 1614. 1H-NMR (CDCl3): 3.59 (br. s, 2 H); 3.85 (s, 3 H); 3.89 (s, 3 H); 5.31 (s, 1 H);
5.75 (s, 1 H); 6.81 (d, J ¼ 8.2, 1 H); 6.84 (dd, J ¼ 8.2, 1.8, 1 H); 6.90 (d, J ¼ 1.8, 1 H); 7.03 (d, J ¼ 4.6, 1 H);
8.05 (d, J ¼ 4.6, 1 H); 8.09 (s, 1 H). Anal. calc. for C15H16N2O2 (256.30): C 70.29, H 6.29, N 10.93; found: C
70.21, H 6.45, N 10.89.
4-[(1E)-1-(3,4-Dimethoxyphenyl)prop-1-en-1-yl]pyridin-3-amine (3f-ii). Yellow oil. Rf (hexane/
THF 1:2) 0.49. IR (neat): 3460, 3367, 1618. 1H-NMR (CDCl3): 1.69 (d, J ¼ 6.9, 3 H); 3.61 (br. s, 2 H); 3.83
(s, 3 H); 3.86 (s, 3 H); 6.29 (q, J ¼ 6.9, 1 H); 6.70 (dd, J ¼ 8.2, 2.3, 1 H); 6.76 (d, J ¼ 8.2, 1 H); 6.85 (d, J ¼
2.3, 1 H); 6.92 (d, J ¼ 5.0, 1 H); 8.06 (d, J ¼ 5.0, 1 H); 8.16 (s, 1 H). Anal. calc. for C16H18N2O2 (270.33): C
71.09, H 6.71, N 10.36; found: C 71.08, H 6.79, N 10.28.
4-[(1E)-1-(3,4-Dimethoxyphenyl)but-1-en-1-yl]pyridin-3-amine (3f-iii). Pale-yellow oil. Rf (hexane/
1
THF 1:2) 0.50. IR (neat): 3460, 3368, 3203, 1622. H-NMR (CDCl3): 1.03 (t, J ¼ 7.3, 3 H); 2.02 (quint.,
J ¼ 7.3, 2 H); 3.60 (br. s, 2 H); 3.84 (s, 3 H); 3.86 (s, 3 H); 6.20 (t, J ¼ 7.3, 1 H); 6.71 (dd, J ¼ 8.2, 1.8, 1 H);
6.77 (d, J ¼ 8.2, 1 H); 6.85 (d, J ¼ 1.8, 1 H); 6.92 (d, J ¼ 4.6, 1 H); 8.05 (d, J ¼ 4.6, 1 H); 8.14 (s, 1 H). Anal.
calc. for C17H20N2O2 (284.35): C 71.81, H 7.09, N 9.85; found: C 71.54, H 7.23, N 9.55.
N-[4-(1-Arylethenyl)pyridin-3-yl]formamides 4. These compounds were prepared by treating 3
(1.8 mmol) with HCO2H (36 mmol) in the presence of Ac2O (9.0 mmol) at 08 for 30 min [7].
N-[4-(1-Phenylethenyl)pyridin-3-yl]formamide (4a). White solid. M.p. 118 – 1198 (hexane/AcOEt).
IR (KBr): 3183, 1695. 1H-NMR (CDCl3): 5.40, 5.42 (2s, 1 H); 5.95, 6.00 (2s, 1 H); 6.98 – 9.54 (m, 10 H).
Anal. calc. for C14H12N2O (224.26): C 74.98, H 5.39, N 12.49; found: C 74.90, H 5.40, N 12.48.
N-{4-[1-(3-Methylphenyl)ethenyl]pyridin-3-yl}formamide (4b). Pale-yellow solid. M.p. 112 – 1148
1
(hexane/Et2O). IR (KBr): 3231, 1695, 1668. H-NMR (CDCl3): 2.33 (s, 3 H); 5.37, 5.39 (2s, 1 H); 5.91,

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5.97 (2s, 1 H); 6.98 – 9.54 (m, 9 H). Anal. calc. for C15H14N2O (238.28): C 75.61, H 5.92, N 11.76; found: C
75.54, H 5.96, N 11.78.
N-{4-[1-(4-Methylphenyl)ethenyl]pyridin-3-yl}formamide (4c). Pale-yellow solid. M.p. 110 – 1118
1
(hexane/CH2Cl2). IR (KBr): 3180, 1691. H-NMR (CDCl3): 2.355, 2.362 (2s, 3 H); 5.33, 5.35 (2s, 1 H);
5.90, 5.95 (2s, 1 H); 7.00 – 9.55 (m, 9 H). Anal. calc. for C15H14N2O (238.28): C 75.61, H 5.92, N 11.76;
found: C 75.58, H 5.95, N 11.60.
N-{4-[1-(4-Chlorophenyl)ethenyl]pyridin-3-yl}formamide (4d). Pale-yellow solid. M.p. 116 – 1178
(hexane/Et2O). IR (KBr): 3175, 1692. 1H-NMR (CDCl3): 5.41, 5.43 (2s, 1 H); 5.95, 6.00 (2s, 1 H); 6.97 –
9.52 (m, 9 H). Anal. calc. for C14H11ClN2O (258.70): C 65.00, H 4.29, N 10.83; found: C 64.70, H 4.44, N
10.75.
N-{4-[1-(4-Methoxyphenyl)ethenyl]pyridin-3-yl}formamide (4e). Yellow oil. Rf (hexane/THF 1:2)
0.38. IR (neat): 3259, 1694, 1604. 1H-NMR (CDCl3): 3.82 (s, 3 H); 5.27, 5.28 (2s, 1 H); 5.83, 5.89 (2s, 1 H);
6.87 – 9.56 (m, 9 H). Anal. calc. for C15H14N2O2 (254.28): C 70.85, H 5.55, N 11.02; found: C 70.82, H 5.60,
N 10.91.
N-{4-[1-(3,4-Dimethoxyphenyl)ethenyl]pyridin-3-yl}formamide (4f-i). White solid. M.p. 161 – 1638
(hexane/CH2Cl2). IR (KBr): 3235, 1699. 1H-NMR (CDCl3): 3.85 (s, 3 H); 3.887, 3.893 (2s, 3 H); 5.30, 5.32
(2s, 1 H); 5.84, 5.90 (2s, 1 H); 6.64 – 9.55 (m, 8 H). Anal. calc. for C16H16N2O3 (284.31): C 67.59, H 5.67, N
9.85; found: C 67.53, H 5.71, N 9.60.
N-{4-[(1E)-1-(3,4-Dimethoxyphenyl)prop-1-en-1-yl]pyridin-3-yl}formamide (4f-ii). Colorless crys-
1
tals. M.p. 161 – 1638 (hexane/CH2Cl2). IR (KBr) 3345, 1694. H-NMR (CDCl3): 1.65, 1.66 (2d, J ¼ 6.9,
3 H); 3.83, 3.84 (2s, 3 H); 3.860, 3.864 (2s, 3 H); 6.37, 6.43 (2q, J ¼ 6.9, 1 H); 6.52 – 9.68 (m, 8 H). Anal.
calc. for C17H18N2O3 (298.34): C 68.44, H 6.08, N 9.39; found: C 68.39, H 6.06, N 9.34.
N-{4-[(1E)-1-(3,4-Dimethoxyphenyl)but-1-en-1-yl]pyridin-3-yl}formamide (4f-iii). White solid.
1
M.p. 155 – 1578 (hexane/CH2Cl2). IR (neat): 3345, 1697. H-NMR (CDCl3): 1.03 (t, J ¼ 7.3, 3 H); 1.93 –
1.99 (m, 2 H), 3.84, 3.85, 3.87 (3s, 6 H); 6.27, 6.34 (2t, J ¼ 7.8, 1 H); 6.52 – 9.66 (m, 8 H). Anal. calc. for
C18H20N2O3 (312.36): C 69.21, H 6.45, N 8.97; found: C 68.97, H 6.58, N 8.97.
4-(1-Arylethenyl)-3-isocyanopyridines 5. These compounds were prepared by treating 4 with POCl3/
Et3N in THF at 08 [8].
3-Isocyano-4-(1-phenylethenyl)pyridine (5a). Pale-yellow solid. M.p. 51 – 538 (hexane). IR (KBr):
2122, 1614. 1H-NMR (CDCl3): 5.52 (s, 1 H); 5.96 (s, 1 H); 7.23 – 7.25 (m, 2 H); 7.30 (d, J ¼ 5.0, 1 H); 7.35 –
7.37 (m, 3 H) 8.62 (d, J ¼ 5.0, 1 H); 8.69 (s, 1 H). Anal. calc. for C14H10N2 (206.24): C 81.53, H 4.89, N
13.58; found: C 81.26, H 4.98, N 13.30.
3-Isocyano-4-[1-(3-methylphenyl)ethenyl]pyridine (5b). Yellow oil. Rf (hexane/THF 3 :1) 0.49. IR
1
(neat): 2122. H-NMR (CDCl3): 2.34 (s, 3 H); 5.49 (s, 1 H); 5.94 (s, 1 H); 7.02 (d, J ¼ 7.3, 1 H); 7.04 (s,
1 H); 7.16 (d, J ¼ 7.3, 1 H); 7.24 (t, J ¼ 7.3, 1 H); 7.29 (d, J ¼ 5.0, 1 H); 8.61 (d, J ¼ 5.0, 1 H); 8.69 (s, 1 H).
Anal. calc. for C15H12N2 (220.27): C 81.79, H 5.49, N 12.72; found: C 81.73, H 5.40, N 12.60.
3-Isocyano-4-[1-(4-methylphenyl)ethenyl]pyridine (5c). Pale-yellow solid. M.p. 71 – 738 (hexane).
IR (KBr): 2122, 1609. 1H-NMR (CDCl3): 2.37 (s, 3 H); 5.45 (s, 1 H); 5.92 (s, 1 H); 7.12 (d, J ¼ 8.2, 2 H);
7.16 (d, J ¼ 8.2, 2 H); 7.29 (d, J ¼ 5.0, 1 H); 8.61 (d, J ¼ 5.0, 1 H); 8.68 (s, 1 H). Anal. calc. for C15H12N2
(220.27): C 81.79, H 5.49, N 12.72; found: C 81.70, H 5.49, N 12.49.
4-[1-(4-Chlorophenyl)ethenyl]-3-isocyanopyridine (5d). Pale-yellow solid. M.p. 43 – 448 (hexane).
IR (KBr): 2128, 1622. 1H-NMR (CDCl3): 5.54 (s, 1 H); 5.95 (s, 1 H); 7.17 (d, J ¼ 8.7, 2 H); 7.29 (d, J ¼ 5.0,
1 H); 7.33 (d, J ¼ 8.7, 2 H); 8.64 (d, J ¼ 5.0, 1 H); 8.70 (s, 1 H). Anal. calc. for C14H9ClN2 (240.69): C 69.86,
H 3.77, N 11.64; found: C 69.89, H 3.82, N 11.59.
3-Isocyano-4-[1-(4-methoxyphenyl)ethenyl]pyridine (5e). Pale-yellow solid. M.p. 61 – 628 (hexane/
Et2O). IR (KBr): 2124, 1604. 1H-NMR (CDCl3): 3.82 (s, 3 H); 5.39 (s, 1 H); 3.86 (s, 1 H); 6.87 (d, J ¼ 8.7,
2 H); 7.16 (d, J ¼ 8.7, 2 H); 7.30 (d, J ¼ 5.0, 1 H); 8.61 (d, J ¼ 5.0, 1 H); 8.68 (s, 1 H). Anal. calc. for
C15H12N2O (236.27): C 76.25, H 5.12, N 11.86; found: C 76.29, H 5.34, N 11.69.
4-[1-(3,4-Dimethoxyphenyl)ethenyl]-3-isocyanopyridine (5f-i). Pale-yellow solid. M.p. 97 – 1008
(hexane/Et2O). IR (KBr): 2126, 1614, 1603. 1H-NMR (CDCl3): 3.86 (s, 3 H); 3.89 (s, 3 H); 5.42 (s, 1 H);
5.87 (s, 1 H); 6.67 (dd, J ¼ 8.2, 2.3, 1 H); 6.81 (d, J ¼ 8.2, 1 H); 6.83 (d, J ¼ 2.3, 1 H); 7.30 (d, J ¼ 5.0, 1 H);
8.62 (d, J ¼ 5.0, 1 H); 8.69 (s, 1 H). Anal. calc. for C16H14N2O2 (266.29): C 72.16, H 5.30, N 10.52; found: C
72.10, H 5.59, N 10.80.

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4-[(1E)-1-(3,4-Dimethoxyphenyl)prop-1-en-1-yl]-3-isocyanopyridine (5f-ii). Pale-yellow solid. M.p.
1118 (dec.; hexane/CH2Cl2). IR (KBr): 2126, 1601. 1H-NMR (CDCl3): 1.70 (d, J ¼ 6.9, 3 H); 3.85 (s, 3 H);
3.86 (s, 3 H); 6.35 (q, J ¼ 6.9, 1 H); 6.53 (dd, J ¼ 8.2, 2.3, 1 H); 6.76 (d, J ¼ 8.2, 1 H); 6.78 (d, J ¼ 2.3, 1 H);
7.23 (d, J ¼ 5.5, 1 H); 8.64 (d, J ¼ 5.5, 1 H); 8.74 (s, 1 H). Anal. calc. for C17H16N2O2 (280.32): C 72.84, H
5.75, N 9.99; found: C 72.60, H 5.81, N 9.83.
4-[(1E)-1-(3,4-Dimethoxyphenyl)but-1-en-1-yl]-3-isocyanopyridine (5f-iii). Pale-yellow oil. Rf
(hexane/THF 2 :1) 0.66. IR (neat): 2124, 1601. 1H-NMR (CDCl3): 1.07 (t, J ¼ 7.3, 3 H); 1.98 (quint.,
J ¼ 7.3, 2 H); 3.857 (s, 3 H); 3.863 (s, 3 H); 6.24 (t, J ¼ 7.3, 1 H); 6.53 (dd, J ¼ 8.2, 1.8, 1 H); 6.76 (d, J ¼ 8.2,
1 H); 6.80 (d, J ¼ 1.8, 1 H); 7.24 (d, J ¼ 5.0, 1 H); 8.64 (d, J ¼ 5.0, 1 H); 8.73 (s, 1 H). Anal. calc. for
C18H18N2O2 (294.35): C 73.45, H 6.16, N 9.52; found: C 73.49, H 6.28, N 9.47.
4-Phenyl-1,7-naphthyridine-2(1H)-thione (7a; Representative Procedure). A soln. of 5 (0.21 g,
1.0 mmol), Et3N (0.24 g, 2.4 mmol) in THF (6 ml) containing S8 (39 mg, 1.2 mmol), and Se (3.9 mg,
0.050 mmol) was heated at reflux temp. for 15 h. After the mixture was cooled to r.t., it was concentrated
by evaporation of the solvent. The residual solid was recrystallized from hexane/CHCl3 to give 7a (0.19 g,
1
81%). Yellow solid. M.p. 217 – 2208. IR (KBr): 3183, 1614, 1121. H-NMR ((D6)DMSO): 7.31 (s, 1 H);
7.40 (d, J ¼ 5.5, 1 H); 7.52 – 7.57 (m, 5 H); 8.39 (d, J ¼ 5.5, 1 H); 8.98 (s, 1 H); 13.99 (br. s, 1 H). 13C-NMR
((D6)DMSO): 118.5; 125.4; 128.9; 129.0; 129.5; 134.5; 134.7; 135.0; 139.8; 143.4; 143.7; 181.5. MS: 238
(100, Mþ). Anal. calc. for C14H10N2S (238.31): C 70.56, H 4.23, N 11.76; found: C 70.51, H 4.23, N 11.89.
4-(3-Methylphenyl)-1,7-naphthyridine-2(1H)-thione (7b). Yellow solid. M.p. 232 – 2348 (hexane/
1
THF). IR (KBr): 3190, 1620, 1125. H-NMR ((D6)DMSO): 2.40 (s, 3 H); 7.31 (s, 1 H); 7.33 (d, J ¼ 7.9,
1 H); 7.36 (s, 1 H); 7.37 (d, J ¼ 7.3, 1 H); 7.44 (d, J ¼ 5.5, 1 H); 7.45 (dd, J ¼ 7.9, 7.3, 1 H); 8.40 (d, J ¼ 5.5,
1 H); 8.98 (s, 1 H); 13.97 (br. s, 1 H). 13C-NMR ((D6)DMSO): 20.9; 118.5; 125.4; 126.0; 128.8; 129.3;
130.1; 134.5; 134.7; 135.0; 138.4; 139.7; 143.4; 143.8; 181.5. MS: 252 (100, Mþ). Anal. calc. for C15H12N2S
(252.33): C 71.40, H 4.79, N 11.10; found: C 71.47, H 4.85, N 11.07.
4-(4-Methylphenyl)-1,7-naphthyridine-2(1H)-thione (7c). Yellow solid. M.p. 238 – 2418 (hexane/
CH2Cl2). IR (KBr): 3177, 1611, 1127. 1H-NMR ((D6)DMSO): 2.32 (s, 3 H); 7.30 (s, 1 H); 7.37 (d, J ¼ 8.0,
2 H); 7.43 – 7.45 (m, 3 H); 8.39 (d, J ¼ 5.5, 1 H); 8.98 (s, 1 H); 13.94 (s, 1 H). 13C-NMR ((D6)DMSO):
20.9; 118.5; 125.4; 128.8; 129.5; 131.6; 134.5; 135.0; 139.2; 139.8; 143.3; 143.7; 181.5. MS: 252 (100, Mþ).
Anal. calc. for C15H12N2S (252.33): C 71.40, H 4.79, N 11.10; found: C 71.36, H 4.91, N 11.04.
4-(4-Chlorophenyl)-1,7-naphthyridine-2(1H)-thione (7d). Yellow solid. M.p. 250 – 2528 (THF). IR
(KBr): 3194, 1616, 1128. 1H-NMR ((D6)DMSO): 7.34 (s, 1 H); 7.40 (d, J ¼ 5.5, 1 H); 7.58 (d, J ¼ 8.6, 2 H);
7.63 (d, J ¼ 8.6, 2 H); 8.40 (d, J ¼ 5.5, 1 H); 8.98 (s, 1 H); 14.02 (br. s, 1 H). 13C-NMR ((D6)DMSO):
118.4; 125.3; 129.0; 130.8; 133.3; 134.4; 134.9; 135.0; 139.8; 142.5; 143.4; 181.5. MS: 272 (100, Mþ). Anal.
calc. for C14H9ClN2S (272.75): C 61.65, H 3.33, N 10.27; found: C 61.59, H 3.48, N 10.08.
4-(4-Methoxyphenyl)-1,7-naphthyridine-2(1H)-thione (7e). Yellow solid. M.p. 238 – 2408 (hexane/
CH2Cl2). IR (KBr): 3177, 1609, 1127. 1H-NMR ((D6)DMSO): 3.83 (s, 3 H); 7.10 (d, J ¼ 9.2, 2 H); 7.28 (s,
1 H); 7.46 (d, J ¼ 5.5, 1 H); 7.48 (d, J ¼ 9.2, 2 H); 8.38 (d, J ¼ 5.5, 1 H); 8.97 (s, 1 H); 13.91 (br. s, 1 H).
13C-NMR ((D6)DMSO): 55.3; 114.5; 118.6; 125.5; 126.6; 130.4; 134.3; 135.1; 139.8; 143.3; 143.5; 160.3;
181.4. MS: 268 (100, Mþ). Anal. calc. for C15H12N2OS (268.33): C 67.14, H 4.51, N 10.44; found: C 66.87, H
4.56, N 10.46.
4-(3,4-Dimethoxyphenyl)-1,7-naphthyridine-2(1H)-thione (7f-i). Yellow solid. M.p. 267 – 2698
(Me2CO/MeOH). IR (KBr): 3192, 1618, 1601, 1129. 1H-NMR ((D6)DMSO): 3.81 (s, 3 H); 3.83 (s,
3 H); 7.09 (dd, J ¼ 8.6, 1.8, 1 H); 7.13 – 7.14 (m, 2 H); 7.35 (s, 1 H); 7.56 (d, J ¼ 5.5, 1 H); 8.41 (d, J ¼ 5.5,
1 H); 8.98 (s, 1 H); 13.93 (br. s, 1 H). 13C-NMR ((D6)DMSO): 55.6; 55.7; 111.9; 112.4; 118.8; 121.7; 125.6;
126.8; 134.3; 135.1; 139.7; 143.3; 143.7; 149.0; 149.9; 181.4. MS: 298 (100, Mþ). Anal. calc. for
C16H14N2O2S (298.36): C 64.41, H 4.73, N 9.39; found: C 64.25, H 4.77, N 9.26.
4-(3,4-Dimethoxyphenyl)-3-methyl-1,7-naphthyridine-2(1H)-thione (7f-ii). Pale-yellow solid. M.p.
252 – 2548 (THF). IR (KBr): 3178, 1611, 1130. 1H-NMR ((D6)DMSO): 2.20 (s, 3 H); 3.74 (s, 3 H); 3.83 (s,
3 H); 6.82 (dd, J ¼ 7.9, 1.2, 1 H); 6.91 (d, J ¼ 1.2, 1 H); 6.97 (dd, J ¼ 5.5, 1 H); 7.13 (dd, J ¼ 7.9, 1 H); 8.31
(d, J ¼ 5.5, 1 H); 8.98 (s, 1 H); 14.06 (br. s, 1 H). 13C-NMR ((D6)DMSO): 19.9; 55.5; 55.7; 112.0; 112.3;
119.0; 120.9; 127.1; 127.5; 133.2; 139.0; 139.2; 142.0; 143.0; 148.8; 149.0; 183.1. MS: 312 (100, Mþ). Anal.
calc. for C17H16N2O2S (312.39): C 65.36, H 5.16, N 8.97; found: C 65.06, H 5.34, N 8.84.

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4-(3,4-Dimethoxyphenyl)-3-ethyl-1,7-naphthyridine-2(1H)-thione (7f-iii). Yellow solid. M.p. 241 –
1
2438 (hexane/THF). IR (KBr): 3275, 1607, 1142. H-NMR ((D6)DMSO): 1.02 (t, J ¼ 7.3, 3 H); 2.68 –
2.80 (m, 2 H); 3.73 (s, 3 H); 3.83 (s, 3 H); 6.82 (dd, J ¼ 7.9, 1.8, 1 H); 6.86 (d, J ¼ 5.5, 1 H); 6.92 (d, J ¼
1.8, 1 H); 7.12 (d, J ¼ 7.9, 1 H); 8.28 (d, J ¼ 5.5, 1 H); 8.96 (s, 1 H); 14.01 (br. s, 1 H). 13C-NMR
((D6)DMSO): 12.9; 25.2; 55.5; 55.7; 111.9; 112.0; 119.1; 120.6; 127.2; 127.6; 133.2; 138.9; 142.0; 143.0;
144.4; 148.7; 148.9; 182.4. MS: 326 (100, Mþ). Anal. calc. for C18H18N2O2S (326.41): C 66.23, H 5.56, N
8.58; found: C 66.20, H 5.65, N 8.39.
We acknowledge Mrs. Miyuki Tanmatsu for her assistance in recording mass spectra and performing
combustion analyses.
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Received October 19, 2011