Synthesis of 2-arylfuro[3,2-c]pyridines and their derivatives

Article abstract of DOI:10.1135/cccc19961627

A series of 2-arylfuro[3,2-c]pyridines was synthesized. 3-(5-Aryl-2-furyl)propenoic acids 1a-1h were converted to the acid azides 2a-2h, which in turn were cyclized to give 2-arylfuro[3,2-c]pyridine-4(5H)-ones 4a-4h by heating in Dowtherm. The pyridones 4a-4f were aromatized with phosphorus oxychloride to the 2-aryl-4-chlorofuro[3,2-c]pyridines 5a-5f, which were reduced with zinc and acetic acid to the title compounds 6a-6f. Reacted with phosphorus(V) sulfide, the pyridones 4a-4f yielded the corresponding thiones 7a-7f.

Full text of DOI:10.1135/cccc19961627

Synthesis of 2-Arylfuro[3,2-c]pyridines
1627
SYNTHESIS OF 2-ARYLFURO[3,2-c]PYRIDINES AND THEIR DERIVATIVES
1
2
Alzbeta KRUTOSIKOVA and Robert SLEZIAK
Department of Organic Chemistry, Slovak Technical University, 812 37 Bratislava, Slovak Republic;
e-mail: 1 krutosik@chelin.chtf.stuba.sk, 2 sleziak@cvt.stuba.sk
Received March 28, 1996
Accepted July 6, 1996
A series of 2-arylfuro[3,2-c]pyridines was synthesized. 3-(5-Aryl-2-furyl)propenoic acids 1a–1h were
converted to the acid azides 2a–2h, which in turn were cyclized to give 2-arylfuro[3,2-c]pyridine-
4(5H)-ones 4a–4h by heating in Dowtherm. The pyridones 4a–4f were aromatized with phosphorus
oxychloride to the 2-aryl-4-chlorofuro[3,2-c]pyridines 5a–5f, which were reduced with zinc and
acetic acid to the title compounds 6a–6f. Reacted with phosphorus(V) sulfide, the pyridones 4a–4f
yielded the corresponding thiones 7a–7f.
Key words: Furopyridines; [1,5]-Prototropic rearrangement.
The fusion of a π-excessive furan ring to a π-deficient pyridine nucleus gives rise to six
isomeric furopyridines; the members of all types are known1. Approaches to the syn-
thesis of furo[3,2-c]pyridines are based either on furan ring formation starting from
substituted pyridines2–5 or on pyridine ring formation starting from suitable substituted
furans6–11
.
Previously we reported on the synthesis and reactions of 2-nitrophenylfuro[3,2-c]py-
ridine12, 2,3-dimethylfuro[3,2-c]-pyridine13, and pyrrolo[2′,3′:4,5]furo[3,2-c]pyridines14.
Reactions12,13,15–19, spectral20, and biological properties21 of the furo[3,2-c]pyridine
derivatives have been studied.
The present paper describes efficient syntheses of some representatives of the title
ring system (Scheme 1) developed in relation to our previous efforts aimed at the
preparation of fused O-, N-heterocycles. Condensation of 5-aryl-2-furancarbaldehydes
with malonic acid afforded 3-(5-aryl-2-furyl)propenoic acids 1a–1h. Since the formerly
described22 Perkin synthesis gave these compounds in low yields, we applied Doebner
reaction conditions in the synthesis resulting in very high yields of the products. The
acids 1a–1h were reacted with ethyl chloroformate and triethylamine in acetone to give
mixed acid anhydrides, which were converted to the acid azides 2a–2h with (E)-con-
figuration at the double bond (see values for J(A,B) in Table I). The azides 2a–2h were
heated in Dowtherm at 240 °C, which facilitated the Curtius rearrangement to the
corresponding non-isolated isocyanates 3a–3h. The isocyanates apparently undewent
isomerization from (E) to (Z) during the electrocyclic reaction leading to 4a–4h in the
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

1628
Krutosikova, Sleziak:
presence of tributylamine, which served to transfer a proton in the [1,5]-prototropic
rearrangement (Scheme 2).
The structures of the 2-arylfuro[3,2-c]pyridine-4(5H)-ones 4a–4h were confirmed by
spectroscopic data (Table II). Their IR spectra exhibit lactam ν(C=O) vibrations
4
5
3
CH CO H
CH CON
3
CH
N
C O
A
2
A
i, ii
iii
R
R
N
R
2 CH
CH
CH
B
B
O
1
O
O
1a-1h
2a-2h
3a-3h
Cl
4
3
X
1-7
5
-N
2
v
iv
vi
N
2
4-CH O
3
a
b
c
d
e
f
R
R
6
O
O
4-CH
3
H
O
1
7
5a-5f
NH
4-Br
4-Cl
R
6a-6f
O
S
3,4-Cl
2
4a-4h
NH
3-NO
2
g
h
R
4-NO
2
O
7a-7f
In formulae 1-7 R = X-substituted phenyl
i, (C H ) N, ClCO C H ; ii,NaN ; iii, (nC H ) N, dowtherm; iv, POCl ; v, Zn, CH CO H; vi, P S
2
5 3
2
2
5
3
4
9 3
3
3
2
4
10
SCHEME 1
TABLE I
1H NMR data (CDCl3) of compounds 2
Compound H-A(d)
H-B(d)
H-3(d)
H-4(d)
Arom.(m)
J(A,B)
J(3,4)
2aa
2ba
2c
6.30
6.34
6.35
6.36
6.65
6.37
6.40
6.42
7.47
7.29
7.38
7.35
7.48
7.48
7.46
7.48
6.76
6.77
6.77
6.76
6.62
6.69
6.63
6.65
6.91–7.72
7.18–7.77
7.42–7.94
7.53–7.81
7.29–7.71
7.49–7.76
7.60–8.54
7.89–8.32
15.3
15.4
15.4
15.3
15.7
15.3
15.4
15.3
3.5
3.5
3.5
3.5
–
2d
2e
6.76b
6.77b
2f
–
2g
2h
6.75
6.77
6.63
6.67
3.4
3.5
a
Other signals: 2a: 3.85 s, 3 H (CH3O); 2b: 2.38 s, 3 H (CH3).b s.
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

Synthesis of 2-Arylfuro[3,2-c]pyridines
1629
at 1 664–1 680 cm–1 and ν(NH) vibrations at 3 098–3 105 cm–1. The 2-arylfuro[3,2-c]-
pyridine-4(5H)-ones 4a–4f were transformed to 2-aryl-4-chlorofuro[3,2-c]pyridines
1
5a–5f by refluxing with phosphorus oxychloride. The H NMR spectra (Table II) of
compounds 5a–5f showed long-range coupling between H-3 and H-7, which is consist-
ent with the so-called “zig-zag” path hypothesis and has also been reported for
furo[3,2-c]pyridine2,7. Reduction of the compounds 5a–5f with zinc and acetic acid
afforded the 2-arylfuro[3,2-c]pyridines 6a–6f. The position of the pyridine ring protons
in the compounds 5a–5f and 6a–6f (Table II) was downfield shifted. As concerns the
effect of the 2-aryl group on the chemical shift on pyridine carbons (see compound 6a)
it is small as compared with the values of the parent furo[3,2-c]pyridine (ref.20), in
contrast to the effect on the furanoid carbons C-2 and C-3 which is high. This fact
indicates that the electronic effect of the pyridine ring in this fused system upon C-2
and C-3 is low.
Bu N
3
O
O
O
C
H
[1,5]shift
NH
N
N
R
R
R
O
O
O
SCHEME 2
Reaction of the selected pyridones 4a–4f with phosphorus(V) sulfide afforded the
corresponding thiones 7a–7f. The IR spectra of these compounds showed an absorption
band within the region of 3 170 to 3 110 cm–1 (ν(C–Harom)). The vibrational wavenum-
bers of the N–H and C=S bonds lay within the ranges of 3 210–3 250 cm–1 and
1
1 538–1 591 cm–1, respectively. H NMR spectral data of compounds 7 are sum-
marized in Table II. The thioamide group in compounds 7c and 7d in dimethyl sulfoxide
solutions showed a tendency to tautomerize into the thiol form, owing to which the
–SH group can be directly substituted by a hydrazino group. An example of this reac-
tion has been presented in ref.12.
Mass spectra of the final 2-arylfuro[3,2-c]pyridines 6a–6f displayed molecular peaks
(M+•) of 100% relative intensity (Table III).
EXPERIMENTAL
Melting points were determined on a Kofler stage and are uncorrected. 1H NMR spectra were re-
corded on a Tesla BS 587 (80 MHz) and 13C NMR spectra on a Varian VXR-300 (300 MHz) spec-
trometer in CDCl3 or (CD3)2SO with TMS and HMDS as internal standards. Chemical shifts are given
in ppm (δ-scale), coupling constants J in Hz. IR spectra were measured on an FTIR PU 9802/8
~
(Philips) spectrophotometer using the KBr technique (ν in cm–1), UV spectra of ethanolic solutions
(λ in nm, ε in m2 mol–1) were recorded on a Specord UV-VIS M-40 (Zeiss, Jena) instrument. Mass
spectra were taken on an MS 902-S instrument (AEI Manchester); direct inlet, ionizing electron energy
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

1630
Krutosikova, Sleziak:
J(3,7) J(6,7) Other signals
TABLE II
1H NMR data ((CD3)2SO) of compounds 4–7
H-3
(s)
H-4
(s)
N-H
(brs)
H-6
(d)
H-7
(d)
Arom.
(m)
Comp.
4a
4b
4c
4d
4e
4f
7.20
7.87
7.37
7.46
7.45
7.58
7.69
7.75
6.91b
7.02
7.08b
7.10
7.01b
7.11b
6.90
7.00
–
–
11.33
11.38
11.40
11.43
11.45
11.49
11.50
11.61
–
7.24
7.24
7.26
7.29
7.30
7.31
7.33
7.35
8.21
8.23
8.24
8.26
8.27
8.29
8.45
8.47
8.49
8.50
8.45
8.52
7.56
6.62
6.62
6.55
6.92–7.78
7.16–7.73
7.30–7.90
–
–
7.3 3.85 s, 3 H (CH3O)
7.1 2.4 s, 3 H (CH3)
–
–
7.1
7.2
7.3
7.1
7.3
7.3
–
–
–
–
–
–
–
6.64a 7.53–7.81
0.6
–
–
6.64
6.65
6.69
6.68
7.41–7.87
7.58–8.04
7.60–8.53
7.97–8.32
–
–
4g
4h
5a
5b
5c
5d
5e
5f
6ad
6b
6ce
6d
6e
6f
–
–
–
–
–
7.36a 6.93–7.85
c
0.9
–
5.7 3.87 s, 3 H (CH3O)
5.7 2.42 s, 3 H (CH3)
–
–
7.26–7.82
–
–
7.41a 7.42–7.94
0.9
–
5.7
5.7
5.7
5.7
–
–
–
–
–
–
7.41
7.54–7.81
–
–
7.41a 7.40–7.87
7.41a 7.48–7.97
0.8
0.7
–
–
8.87
8.90
–
7.42
6.93–8.42
7.23–7.81
7.93–7.93
7.54–7.81
7.38–7.85
7.51–7.94
7.18–7.87
6.49–7.21
5.7 3.86 s, 3 H (CH3O)
5.7 2.41 s, 3 H (CH3)
–
7.45
c
–
0.8
–
7.05b 8.91b
–
5.7
5.7
5.7
5.7
–
–
–
–
7.05
7.05
7.08
7.28
6.78
7.47b
7.54
7.51
7.69
8.92
8.92
8.93
–
–
7.44
c
–
–
–
7.46
7.14
6.54
–
7a
7b
7c
7d
7e
7f
13.17
12.60
13.21
13.23
13.21
13.25
–
7.1 3.27 s, 3 H (CH3O)
7.1 2.30 s, 3 H (CH3)
–
7.02
c
–
–
7.15a 7.35–7.94
0.6
–
7.0
6.9
6.5
7.1
–
–
–
–
c
c
–
7.11
7.12
7.13
7.51–7.88
7.40–8.05
7.62–8.15
–
–
–
7.57
–
a
b
c
dd. d. In the multiplet of aromatic protons. d 13C NMR spectrum (CDCl3): 160.60 (C-4′), 158.05
(C-7a), 157.09 (C-2), 144.05 (C-6), 143.48 (C-4), 126.86 (C-1′), 126.80 (C-2′), 122.26 (C-3a),
e
113.43 (C-3′), 106.77 (C-7), 97.35 (C-3), 55.41 (OCH3). J(4,7) = 0.8 Hz.
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

Synthesis of 2-Arylfuro[3,2-c]pyridines
1631
70 eV, trap current 100 µA, ion sorce temperature 160–220 °C. The starting 5-aryl-2-furancarbalde-
hydes were prepared following refs23,24
.
3-(5-Aryl-2-furyl)propenoic Acids 1a–1h. General Procedure
A mixture of 5-aryl-2-furancarbaldehyde (10 mmol), malonic acid (1.04 g, 10 mmol) and pyridine (5
ml) was heated on a steam bath for 8 h. The reaction mixture was poured on crushed ice acidified
with hydrochloric acid. The separated precipitate was filtered out. Characteristic data of the acids
1a–1e, 1g and 1h are consistent with ref.22.
3-[5-(3,4-Dichlorophenyl)-2-furyl]propenoic Acid (1f). 5-(3,4-Dichlorophenyl)-2-furancarbalde-
hyde afforded 95% of 1f, m.p. 125–128 °C (80% aqueous ethanol). For C13H8Cl2O3 (283.1) calcu-
lated: 55.15% C, 2.85% H, 25.05% Cl; found: 55.28% C, 2.88% H, 25.15% Cl. 1H NMR spectrum
((CD3)2SO): 12.24 brs, 1 H (CO2H); 7.56–8.15 m, 3 H (arom.); 7.37 d, 1 H J(AB) = 15.6 (H-B);
7.22 d, 1 H J(3,4) = 3.5 (H-3); 6.98 d, 1 H (H-4); 6.37 d, 1 H (H-A). IR spectrum: 1 664 (C=O).
3-(5-Aryl-2-furyl)propenoyl Azides 2a–2h. General Procedure
3-(5-Aryl-2-furyl)propenoic acid (8 mmol) dissolved in dry acetone (10 ml) was cooled to –10 °C,
and triethylamine (0.9 g, 9.3 mmol) and ethyl chloroformate (1.13 g, 10 mmol) in dry acetone (1 ml)
were added dropwise to the stirred system held at a temperature lower than 0 °C. The reaction mix-
ture was stirred for another 30 min at the same temperature, and a solution of sodium azide (0.8 g,
12 mmol) in water (5 ml) was added while keeping the temperature below 0 °C. The formed yellow
suspension was stirred for an additional hour and allowed to warm to room temperature. The mixture
TABLE III
Mass spectral data of compounds 6
Compound
m/z (relative abundance)
6a
6b
6c
6d
226 (18), 225 (M+•, 100), 210 (57), 182 (45), 127 (18), 126 (6.8), 112.5 (7.7),
101 (7.2), 77 (13.6), 75 (9.1), 63 (18.2), 62 (6.6)
209 (M+•, 100), 208 (25), 180 (12.5), 152 (12.5), 139 (12.2), 127 (8), 15 (8.5),
104.5 (7.5), 91.5 (9), 91 (9.2), 76 (9.7), 65 (10.2), 63 (12.5), 51 (8.5)
195 (M+•, 100), 166 (20), 140 (20), 139 (28), 114 (8.4), 97.5 (8), 77 (16), 63 (12),
51 (12)
275 (100), 273 (M+•, 100), 195 (11), 167, (11.7), 166 (5.2), 140 (17.2), 139 (37.9),
138 (10.2), 137.5 (10.2), 136 (10.3), 120 (11.7), 113 (16.2), 97 (6.2), 87 (9.7),
83 (6.6), 76 (15.9), 75 (20.7), 69.5 (20.7), 69 (7.6), 63 (27.6), 62 (10.2), 51 (8.6),
50 (17.2), 39 (8.4)
6e
6f
231 (36), 229 (M+•, 100), 195 (5.8), 173 (5.2), 166 (30), 140 (6.8), 139 (18),
14.5 (8), 113 (7), 111 (7.2), 75 (6), 63 (6), 62 (5.6), 50 (5.2), 39 (26)
267 (13.9), 265 (66.7), 263 (M+•, 100), 202 (7.2), 200 (27.8), 175 (9.6), 164 (5),
147 (9.6), 137 (5.3), 132.5 (5), 131.5 (7.8), 109 (6.1), 87 (9.6), 80 (6.9), 75 (6.4),
74 (8.3), 62 (7.8)
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

1632
Krutosikova, Sleziak:
TABLE IV
Yields and physical properties of compounds 2–5
Calculated/Found
% H
M.p., °C
(solvent)
Formula
(M.w.)
IR
ν(C=O)
Compound Yield, %
% C
% N
2a
2b
2c
2d
2e
2f
88
90
90
85
96
75
86
90
55
63
55
59
89
101–102 C14H11N3O3
(acetone) (269.3)
110–111 C14H11N3O2
(acetone) (253.3)
106–108 C13H9N3O2
(acetone) (239.1)
106–108 C13H8BrN3O2
62.45
62.33
4.12
3.92
15.61
15.21
66.40
66.32
4.38
4.22
16.59
16.12
65.25
64.95
3.79
3.60
17.57
16.98
49.08
48.62
2.53
2.43
13.21
12.93
(acetone)
(318.1)
105
C
13H8ClN3O2
(273.7)
57.05
56.94
2.95
3.27
15.35
14.91
(acetone)
78–80 C13H7Cl2N3O2
(acetone) (308.1)
118–120 C13H8N4O4
(acetone) (284.2)
126–127 C13H8N4O4
(acetone) (284.2)
240–242 C14H11NO3
(ethanol) (241.3)
272–274 C14H11NO2
50.68
50.38
2.29
2.28
13.64
13.58
2g
2h
4a
4b
4c
4d
4e
54.94
54.56
2.84
2.73
19.71
19.65
54.94
54.78
2.84
2.56
19.71
19.55
69.70
69.57
4.60
4.76
5.81
5.59
1 674
1 655
1 664
1 676
1 678
74.65
74.39
4.92
4.57
6.22
6.13
(DMF)
(225.3)
13H9NO2
(211.2)
258–259
(water)
C
73.92
73.57
4.29
4.39
6.63
6.57
318–320 C13H8BrNO2
(DMF) (290.11)
304–306 C13H8ClNO2
(DMF) (245.7)
53.82
53.70
2.78
2.63
4.83
4.81
63.56
63.39
3.28
3.25
5.70
5.64
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

Synthesis of 2-Arylfuro[3,2-c]pyridines
1633
TABLE IV
(Continued)
Calculated/Found
% H
M.p., °C
Compound Yield, %
(solvent)
Formula
(M.w.)
IR
ν(C=O)
% C
% N
4f
4g
4h
5a
5b
5c
5d
5e
5f
45
40
35
60
55
75
64
71
75
279–280 C13H7Cl2NO2
(ethanol) (280.1)
247–249 C13H8N2O4
(DMF) (352.2)
349–352 C13H8N2O4
(DMF) (352.2)
150–151 C14H10ClNO2
55.74
55.69
2.52
2.48
5.00
4.89
1 680
1 678
1 664
60.94
60.84
3.15
3.12
10.93
11.02
60.94
60.61
3.15
2.98
10.93
10.56
64.75
64.39
3.88
3.71
5.39
5.51
(i-hexane)
(259.7)
142–144
(ethanol)
C
14H10ClNO
(243.7)
69.00
68.75
4.14
4.31
5.75
5.90
96–98 C13H8ClNO
67.99
67.80
3.51
3.43
6.10
6.12
(ethanol)
(229.8)
203
C13H7BrClNO
(308.6)
50.60
50.34
2.29
2.21
4.54
4.56
(ethanol)
213
C13H7Cl2NO
(264.1)
59.12
58.94
2.67
2.52
5.30
5.28
(ethanol)
212–214 C13H6Cl3NO
(ethanol) (298.6)
52.30
52.28
2.03
2.00
4.69
4.65
was poured onto crushed ice and the yellow precipitate was filtered out and rinsed with water.
Yields, m.p. and elemental analyses are given in Table IV.
2-Arylfuro[3,2-c]pyridin-4(5H)-ones 4a–4h. General Procedure
A mixture of 3-(5-aryl-2-furyl)propenoyl azide (17 mmol), toluene (20 ml), Dowtherm (12 ml) and
tributylamine (3.69 ml, 22.5 mmol) was heated for 45 min at 180–200 °C, during which toluene was
allowed to distill off continuously. After cooling, diethyl ether was added, the precipitate formed was
filtered out and rinsed with diethyl ether. The characteristic data are given in Table IV.
2-Aryl-4-chlorofuro[3,2-c]pyridines 5a–5f. General Procedure
2-Arylfuro[3,2-c]pyridin-4(5H)-one (20 mmol) was refluxed in phosphorus oxychloride (10 ml) for 4 h.
POCl3 was distilled off at a reduced pressure, and ice was added to the residue. The mixture was then
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

1634
Krutosikova, Sleziak:
TABLE V
Yields and physical properties of compounds 6 and 7
Calculated/Found
Yield
%
M.p., °C
(solvent)
Formula
(M.w.)
IR
ν(C=S)
UV
λ(log ε)
Compound
% C
% H
% N
6a
6b
6c
6d
6e
6f
62
52
67
56
69
70
85
80
92
74
52
86
129–130 C14H11NO2
(i-hexane) (225.3)
74.65
74.36
4.92
4.85
6.22
6.08
306 (3.49)
206 (3.47)
–
–
–
115–116 C14H11NO
(i-hexane) (209.3)
80.36
80.43
5.30
5.30
6.69
6.67
302 (3.39)
204 (3.56)
115–116 C13H9NO
(ethanol (195.2)
79.98
79.84
4.65
4.62
7.17
7.11
296 (3.49)
201 (3.56)
167–168 C13H8BrNO
(ethanol) (274.1)
56.96
57.41
2.94
3.03
5.11
5.09
302 (3.61
203 (3.54)
113–114 C13H8ClNO
(ethanol (229.7)
67.99
67.94
3.51
3.65
6.10
5.90
301 (3.56)
202 (3.54)
–
–
153–158 C13H7Cl2NO
(ethanol) (264.1
257–259 C14H11NO2Sa
(ethanol) (257.3)
281–282 C14H11NOSa
(dioxane) (241.3)
244–246 C13H9NOSa
(ethanol) (227.3)
59.12
59.20
2.67
2.66
5.30
5.25
302 (3.52)
208 (3.45)
7a
7b
7c
7d
7e
7f
65.35
65.29
4.31
4.21
5.44
5.56
–
–
–
–
–
–
1 538
1 238
69.68
69.48
4.59
4.51
5.80
5.76
1 591
1 240
68.70
68.43
3.99
3.76
6.16
5.95
1 587
1 234
297–299 C13H8BrNOSa 51.00
(ethanol) (306.2) 50.74
257–258 C13H8ClNOSa 59.66
(ethanol) (261.7) 59.71
274–276 C13H7Cl2NOSa 52.72
(dioxane) (296.2) 52.34
2.63
2.62
4.57
4.38
1 587
1 238
3.08
2.83
5.35
5.24
1 570
1 240
2.38
2.32
4.73
4.48
1 570
1 240
a
% S; 7a calculated: 12.46, found: 12.34; 7b calculated: 13.29, found: 12.99; 7c calculated: 14.11,
found: 13.73; 7d calculated: 10.47, found: 10.28; 7e calculated: 12.25, found: 11.97; 7f calculated:
10.82, found: 10.61.
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

Synthesis of 2-Arylfuro[3,2-c]pyridines
1635
made basic with dilute aqueous ammonia. The precipitate obtained was filtered out, rinsed with
water, dried and crystallized. The characteristic data are given in Table IV.
2-Arylfuro[3,2-c]pyridines 6a–6f. General Procedure
A mixture of 2-aryl-4-chlorofuro[3,2-c]pyridine (5.5 mmol), Zn (pulverized, 2.2 g) and glacial acetic
acid (10 ml) was refluxed for 8 h. After cooling, the solid was removed by filtration and the filtrate
was evaporated to dryness at a reduced pressure. Dilute NaOH solution was added to the residue, and
the alkaline mixture was extracted with chloroform. The characteristic data are given in Table V.
2-Arylfuro[3,2-c]pyridin-4(5H)-thiones 7a–7f. General Procedure
A mixture of 2-arylfuro[3,2-c]pyridin-4(5H)-one 4a–4f (10 mmol) and phosphorus(V) sulfide (2.22 g,
5 mmol) was refluxed in pyridine (10 ml) for 4 h while stirred, and poured into hot water (30 ml).
The separated precipitate was filtered out, dried and crystallized. The characteristic data of com-
pounds 7 are given in Table V.
This study was supported by the Grant Agency of the Slovak Ministry of Education (Registr. No.
1/1417/94) and Istrochem, Bratislava. The authors are indebted to Mrs S. Markusova and Dr M. Hro-
bonova for measurement of IR and UV spectra as well as Dr M. Dandarova for measurement of the
NMR spectra and a stimulating discussion on their interpretation.
REFERENCES
1. Friedrichsen W. in: Comprehensive Heterocyclic Chemistry (C. V. Bird and G. W. H.
Cheeseman, Eds), Vol. 4, p. 973. Pergamon Press, Oxford 1984.
2. Lhommet G., Sliwa H., Maitte P.: Bull. Soc. Chim. Fr. 1972, 1442.
3. Bisagni E., Civier A., Marquet J.-P.: J. Heterocycl. Chem. 12, 461 (1975).
4. Abramovitch R. A., Deeb A., Kishore D., Mpango G. B. W.: Gazz. Chim. Ital. 118, 167 (1988).
5. Horlein G., Kubel B., Studeneer A., Salbeck A.: Justus Liebigs Ann. Chem. 1979, 371.
6. Eloy F., Deryckere A.: J. Heterocycl. Chem. 8, 57 (1971).
7. Bouzart J. D., Bisagni E.: Bull. Soc. Chim. Fr. 1971, 1727.
8. Molina P., Fresneda P. M., Hurtado F.: Synthesis 1987, 45.
9. Krutosikova A., Dandarova M., Chylova J., Vegh D.: Monatsh. Chem. 123, 807 (1992).
10. Krutosikova A., Dandarova M., Alfoldi J.: Chem. Papers 48, 268 (1994).
11. Krutosikova A., Dandarova M.: Heterocycles 37, 1695 (1994).
12. Korenova A., Krutosikova A., Kovac J., Celec S.: Collect. Czech. Chem. Commun. 52, 192
(1987).
13. Bobosik V., Krutosikova A., Jordis U.: Monatsh. Chem. 126, 747 (1995).
14. Benckova M., Krutosikova A.: Monatsh. Chem. 126, 753 (1995).
15. McFarland J. W., Essary W. A., Cilenti L., Cozart W., McFarland P. E.: J. Heterocycl. Chem. 12,
705 (1975).
16. Shiotani S., Morita H.: J. Heterocycl. Chem. 21, 725 (1984).
17. Morita H., Shiotani S.: J. Heterocycl. Chem. 24, 373 (1987).
18. Shiotani S., Morita H.: J. Heterocycl. Chem. 27, 637 (1990); 29, 413 (1992); 30, 1035 (1993).
19. Shiotani S., Tsukamoto Y.: J Heterocycl. Chem. 32, 1573 (1995).
20. Shiotani S., Morita H.: J. Heterocycl. Chem. 28, 1469 (1991).
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

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Krutosikova, Sleziak:
21. New J. S., Christopher W. L., Yevich J. P., Butler R., Schlemmer R. F., VanderMaelen C. P.,
Cipollina J. A.: J. Med. Chem. 32, 1147 (1989).
22. Krutosikova A., Sura J., Kovac J., Juhas S.: Collect. Czech. Chem. Commun. 40, 3362 (1975).
23. Davies C. S., Longheed G. S.: J. Heterocycl. Chem. 4, 153 (1957).
24. Frimm R., Kovac J., Krutosikova A.: Chem. Zvesti 27, 101 (1973).
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