A new synthesis of 4-alkyl/aryl-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-diones and molecular rearrangement of their 3-bromo derivatives to 2-alkyl/aryl-4-oxo-4,5-dihydrofuro[3,2-c]quinoline-3-carboxylic acids

Article abstract of DOI:10.3987/COM-02-9681

The treatment of 3-acyl-4-hydroxy-1H-quinolin-2-ones (1) with ethyl (triphenylphosphoranylidene)acetate leads to 5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-diones (2), which were brominated to 3-bromo derivatives (4). Alkaline hydrolysis of 4 gives 2-alkyl/aryl-4-oxo-4,5-dihydrofuro[3,2-c]quinoline-3-carboxylic acids (6), which were decarboxylated to 2-alkyl/aryl-5H-furo[3,2-c]quinolin-4-ones (8). The reaction of 3-acetyl-4-hydroxy-1-methyl-1H-quinolin-2-one (1a) with ethyl (triphenylphosphoranylidene)chloroacetate proceeds not only at the acetyl but also at the amide group to give a mixture of ethyl 3,5-dimethyl-4-oxo-4,5-dihydrofuro[3,2-c]quinoline-2-carboxylate (11a) and ethyl 4,6-dimethyl-2-oxo-5,6-dihydro-2H-pyrano[3,2-c]quinolin-5-ylidene- (chloro)acetate (12a). The reaction mechanism of the molecular rearrangement of 4 to 6 is discussed.

Full text of DOI:10.3987/COM-02-9681

HETEROCYCLES, Vol. 60, No. 4, 2003
799
HETEROCYCLES, Vol. 60, No. 4, 2003, pp. 799 - 815
Received, 2nd December, 2002, Accepted, 27th January, 2003, Published online, 4th February, 2003
A NEW SYNTHESIS OF 4-ALKYL/ARYL-5,6-DIHYDRO-2H-
PYRANO[3,2-c]QUINOLINE-2,5-DIONES AND MOLECULAR
REARRANGEMENT OF THEIR 3-BROMO DERIVATIVES TO 2-
ALKYL/ARYL-4-OXO-4,5-DIHYDROFURO[3,2-c]QUINOLINE-3-
CARBOXYLIC ACIDS
Antonín Klásek,a,* Kamil Kořistek,a Petr Sedmera,b and Petr Haladab
aDepartment of Chemistry and Environmental Technology, Faculty of
b
Technology, Tomas Bata University, 762 72 Zlín, Czech Republic and Institute
of Microbiology, Academy of Sciences of the Czech Republic, 142 20 Prague,
Czech Republic
_
Abstract The treatment of 3-acyl-4-hydroxy-1H-quinolin-2-ones (1) with ethyl
(triphenylphosphoranylidene)acetate leads to 5,6-dihydro-2H-pyrano[3,2-
c]quinoline-2,5-diones (2), which were brominated to 3-bromo derivatives (4).
Alkaline hydrolysis of
4
gives 2-alkyl/aryl-4-oxo-4,5-dihydrofuro[3,2-
c]quinoline-3-carboxylic acids (6), which were decarboxylated to 2-alkyl/aryl-5H-
furo[3,2-c]quinolin-4-ones (8). The reaction of 3-acetyl-4-hydroxy-1-methyl-1H-
quinolin-2-one (1a) with ethyl (triphenylphosphoranylidene)chloroacetate
proceeds not only at the acetyl but also at the amide group to give a mixture of
ethyl 3,5-dimethyl-4-oxo-4,5-dihydrofuro[3,2-c]quinoline-2-carboxylate (11a)
and ethyl 4,6-dimethyl-2-oxo-5,6-dihydro-2H-pyrano[3,2-c]quinolin-5-ylidene-
(chloro)acetate (12a). The reaction mechanism of the molecular rearrangement of
4 to 6 is discussed.
Various substituted 5H-furo[3,2-c]quinolin-4-ones are abundant in the plant kingdom.1 Compounds
unsubstituted in the furan ring were prepared from 3-formyl-4-hydroxy-1H-quinolin-2-ones through 5,6-
dihydro-2H-pyrano[3,2-c]quinoline-2,5-diones as the key intermediates.2 2-Methyl derivatives of 5H-
furo[3,2-c]quinolin-4-ones were prepared by condensation of diethyl 2-propynylmalonate with aniline,4
by cyclization and following dehydrogenation of 4-allyloxy-1H-quinolin-2-ones or 3-allyl-4-hydroxy-1H-
quinolin-2-ones, respectively,5 and by cyclization of 4-(2-propynyl)oxy-1H-quinolin-2-ones.6,7 2,3-
Disubstituted 5H-furo[3,2-c]quinolin-4-ones were prepared starting with substituted 2-

800
HETEROCYCLES, Vol. 60, No. 4, 2003
propynylbromides.7 Some 3-aryl-5H-furo[3,2-c]quinolin-2-ones were prepared by cyclization of 4-
aroylmethoxy-1H-quinolin-2-ones.8 Recently, the preparation was described of 3,5-dimethyl-5H-
furo[3,2]quinolin-4-one.9
4-Alkyl/Aryl-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-diones (2), arising from corresponding 4-
hydroxy-1H-quinolin-2-ones by the modified Pechmann reaction with β-enamino esters or β-keto
esters10,11 were expected to be suitable starting compounds for the synthesis of 3-alkyl/aryl-5H-furo[3,2-
c]quinolin-4-ones (7). However, the number of commercially available β-keto esters and, particularly, β-
enamino esters is limited. Therefore, we decided to prepare compounds (2) by the Wittig reaction of ethyl
(triphenylphosphoranylidene)acetate with 3-acyl-4-hydroxy-1H-quinolin-2-ones (1), which are accessible
by partial hydrolysis of 4-hydroxy-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-diones12 or by the Fries
rearrangement of 4-aroyloxy-1H-quinolin-2-ones.13
O
O
R
Br
R
O
O
O
N
OH
O
COOH
Br2
R
R
KOH
Ph3P=CHCOOC2H5
ethanol
N
O
N
O
O
N
O
CH3
CH3
CH3
CH3
6a-c
1a-d
2a-d
4a-c
Cu
KOH
NaOH
quinoline
ethanol
R
COOH
R
ethylene glycol
O
OH
O
O
N
R
R
O
N
O
N
O
N
O
CH3
CH3
CH3
CH3 7c
8a-c
3e,f
5a
a: R = CH3; b: R = n-C5H11; c: R = Ph; d: R = CH2Ph; e: R = H; f: R = (Ph)C=CH2
Scheme 1
Wittig reaction of 1 with ethyl (triphenylphosphoranylidene)acetate (Scheme 1) proceeds with high
stereoselectivity giving compounds (2) in good yields. Characteristic lactam (1644-1660 cm-1) and
lactone (1726-1737, 1747-1759 cm-1) absorptions in their IR spectra as well as 1H and 13C NMR spectra
(Tables I and II) were in agreement with the expected structures. These compounds are relatively stable to
alkaline hydrolysis. However, their treatment with sodium hydroxide in boiling ethylene glycol produced
complex mixture of products. With 2a, 4-hydroxy-1-methyl-1H-quinolin-2-one (3e) was isolated and
1
identified by comparison (IR, MS, H and 13C NMR – Table III) with the authentic compound. Its
formation can be explained by addition of water to the opened intermediate and subsequent
1
retroaldolization and decarboxylation. H NMR spectrum of compound C18H15NO2 obtained by
hydrolysis of 2c contained a phenolic OH, a N-methyl, four contiguous aromatic protons, signal of a
phenyl group, and an isolated exomethylene. The structure (3f) was deduced using HMBC data (Figure 1,
Table III).

HETEROCYCLES, Vol. 60, No. 4, 2003
801
Table I.
1H NMR Spectral Data (δ, ppm/Hz) of Compounds (2a-d) and (4a-c) (399.90 MHz, CDCl3,
30°C)
b
a
x
a
2bx
2c
2d
4aa
4bb
4ca
Proton/Ji,j
2a
H-3
6.166
1.3
7.381
8.6
6.195
6.231
5.891
1.3
7.278
7.6
J3,1
1.0
7.368
8.6
´
H-7
J7,8
J7,9
7.549
7.657
8.6
7.375
8.6
7.374
8.7
8.5
1.0
1.0
1.0
1.0
1.6
1.0
c
J7,10x
H-8
0.6x
7.687
7.2
0.5x
7.673
7.2
n.d.x
7.820
7.1
0.5x
7.699
7.2
n.d.x
7.730
7.2
n.d.
7.772
7.1
7.213
J8,9
7.7
J8,10
1.6
1.6
1.5
1.6
1.5
1.6
1.5
H-9
7.335
8.0
7.318
8.1
7.387
8.1
7.591
8.1
7.425
8.2
7.327
8.1
7.378
8.4
J9,10
H-10
N-Me
8.280
3.717
8.262
3.712
8.089
3.504
8.184
3.619
8.135
3.670
8.257
3.732
8.341
3.596
a
b
c
40°C; DMSO-d6; n.d. not determined. Additional signals: 2a – 2.728 (d, J3,Me = 1.3 Hz, 3H, 4-Me); 2b
– 3.127 (m, 2H, H-1 ), 1.639 (m, 2H, H-2 ), 1.443 (m, 2H, H-3 ), 1.368 (m, 2H, H-4 ), 0.917 (t, J = 7.1
Hz, 3H, H-5 ); 2c – 7.406 (m, 1H, H-4 ), 7.401 (m, 2H, H-3 and H-5 ), 7.336 (m, 2H, H-2 and H-6 ); 2d
– 7.249 (m, 2H, H-4 and H-6 ), 7.172 (m, 1H, H-5 ), 7.166 (m, 2H, H-3 and H-7 ), 4.494 (d, J = 13.0 Hz,
1H, H-1 d), 4.464 (d, J = 13.0 Hz, 1H, H-1 u); 4a – 2.982 (s, 3H, 4-Me); 4b – 3.437 (m, 2H, H-1 ), 1.614
(m, 2H, H-2 ), 1.522 (m, 2H, H-3 ), 1.417 (m, 2H, H-4 ), 0.942 (t, J = 7.2 Hz, 3H, H-5 ); 4c – 7.527 (m,
2H, H-3 and H-5 ), 7.499 (m, 1H, H-4 ), 7.143 (m, 2H, H-2 and H-6 ).
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
´
13
C Chemical Shifts (δ, ppm) of Compounds (2a-d) and (4a-c) (100.55 MHz, CDCl
3, 30°C)
Table II.
b
a
x
a
2ba
2c
2d
4ax
4bx
4cx
Carbon
2a
2
159.03
114.33
157.11
107.99
160.15
139.91
114.26
133.35
159.25
113.30
161.18
107.45
159.59
139.75
114.16
133.26
157.90
115.32
156.89
106.34
158.23
139.85
115.25
133.64
159.46
114.58
159.15
107.40
158.85
139.89
114.22
133.39
155.67
112.77
155.21
108.00
159.48
139.72
114.35
133.67
155.78
112.33
159.08
107.45
158.85
138.68
114.26
133.59
156.08
113.39
156.00
107.72
158.03
140.12
114.46
133.79
3
4
4a
5
6a
7
8

802
HETEROCYCLES, Vol. 60, No. 4, 2003
Table II – continued
9
122.81
124.63
113.50
158.99
29.58
122.70
124.53
113.40
159.22
29.66
122.70
123.47
112.59
158.61
29.46
122.80
124.61
113.43
159.13
26.69
123.07
124.52
112.85
156.95
29.93
122.94
124.42
112.79
157.36
30.02
123.01
124.45
112.86
157.37
29.91
10
10a
10b
N-Me
23.92
35.20
138.06
40.56
23.21
35.00
138.68
1
´
x
x
x
x
c
c
x
c
c
x
137.33x
27.82x
2
28.92
127.38
127.43
128.20
126.19
128.29
126.31
´
x
c
x
3
´
31.62
129.59
32.18
x
c
x
4
22.48
13.95
128.77
22.40
´
128.86
13.99
5
´
a
b
c
40°C; DMSO-d6; 2C
Table III.
1H and 13C NMR Spectral Data of Compounds (3e, 3f, 9b and 10b) (399.90 MHz and
100.55 MHz, DMSO-d6, 30°C)
1H NMR (δ, ppm/Hz)
13C NMR (δ, ppm)
3f 9b
162.56 161.56 162.66
Proton/Ji,j 3e
3f
9b
10b
Carbon 3e
10b
H-3
5.883 s
2
3
154.26
x
a
x
x
x
x
x
x
x
H-5
J5,6
7.889 8.017
8.003
8.0
99.97
111.78 105.87
122.74
113.97
158.19
8.0
1.6
8.0
1.6
3a
4
J5,7
1.5
161.07 156.71 157.22
116.09 115.97 116.18
123.13 123.72 123.17
H-6
J6,7
7.231 7.289
7.269
7.1
7.564 m
7.543 m
4a
5
7.1
1.0
7.1
1.0
J6,8
1.1
5a
6
137.287
115.36
128.87
121.97
H-7
J7,8
H-8
H-9
7.616 7.648
8.6 8.5
7.613
8.6
121.19 121.53 121.34
131.31 131.19 130.63
114.50 114.52 114.36
140.01 139.23 138.61
7
8
7.459 7.505
7.489
7.300 m
7.887 m
3.649
8a
9
N-Me
3.529 3.544
3.576
120.24
112.95
4-OH
11.318 10.134 10.350
3.707 s
9a
x
c
c
x
x
H-1
2.873 t
7.6
9b
151.72
29.11
´
N-CH3 28.47
29.08
29.16
J1 ,2
´ ´
x
c
c
x
x
x
x
H-2
1.676 m
1.327 m
1
´
140.03 38.47
26.50
´
7.360 mx
c
x
x
x
x
H-3´
2.489 t
2
139.59 207.44
27.55
´

HETEROCYCLES, Vol. 60, No. 4, 2003
803
Table III – continued
7.4
125.85 41.48
30.95
3
4
´
5
´
6
´
7
´
=CH2
J3 ,4
´
´ ´
7.291 mx
x
c
c
x
x
x
x
x
x
x
x
x
x
H-4
1.497 tt
1.318 m
128.27 23.00
21.87
13.90
´
x
x
x
x
J4 ,5
7.3
7.0
127.46 30.82
´ ´
7.251 mx
7.291 mx
x
x
c
d
x
H-5
1.265 m 0.871 t
128.27 21.95
´
c
x
H-6
1.240 m
125.8 5 13.82
´
x
x
x
J6 ,7
7.1
118.34
´ ´
x
x
d
H-7
7.360 m 0.858 t
´
b
6.075 d
C=CH2
5.261 d
a
b
c
d
J
5,8 = 0.5 Hz; Jgem = 1.2 Hz; 2H; 3H
COOH
CH3
CH3
H
H
H
OH
H
H
H
H
O
O
H
H
H
H
H
H
COOH
N
O
H
N
O
5a
N
O
H
H
CH3
3f
6a
CH3
CH3
H
H
H
H
OH
N
O
H
H
H
O
H
H
H
H
H
O
H
H
O
N
O
N
O
7c
8c
9b
CH3
H
CH3
H
CH3
Figure 1. Results of HMBC correlation of compounds (3f, 5a, 6a, 7c, 8c, and 9b)
Our strategy of preparing 3-alkyl/aryl-5H-furo[3,2-c]quinolin-4-ones (7) was based on the preassumption
that 3-bromo derivatives (4) can be converted to 5 (Scheme 1) by treatment with alkali, in analogy with
the described conversion of 3-bromo-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-diones unsubstituted in
position 4.2,3 This reaction is known as the Perkin rearrangement, common in the chemistry of coumarins;
its reaction mechanism was presented recently.14
The bromination of compounds (2) afforded mixtures containing besides the required 4 additional
compounds brominated at position 9. Because of poor solubility of these compounds, the separation was
1
13
difficult or even unsuccessful (with 4d). Their IR, H and C NMR spectra (Tables I and II) were very
similar to those of parent compounds.
Our attempts to perform the Perkin rearrangement of bromo derivatives (4) in ethanolic potassium
hydroxide produced complex mixtures. We believed that pure acids, isolated in moderate yields, had
structures (5a-c) (assuming the regular course of the Perkin rearrangement). However, the melting points

804
HETEROCYCLES, Vol. 60, No. 4, 2003
of their decarboxylation (quinoline/Cu dust) products, 117-119°C (a-series) and 213-215°C (c-series) did
not agree with those reported for 3-substituted furoquinolones (7a) (155-156°C, ref.9) and (7c) (105-106°C,
prepared to according ref.8). Furthermore, the mp of the former matched that given for 2-substituted
furoquinolone (8a) (118-119°C, ref.6; 118°C, ref.7). Also the comparison of NMR spectra of the c-series
decarboxylation product and 7c showed that both compounds were different (Tables IV and V). Large
1
values of J=180.8 Hz (8a) of the furan =CH and heteronuclear coupling of H-9 to a =C-O- type
quaternary carbon (8a-c) confirm the formation of a furan ring. However, chemical shifts of
corresponding carbons (Table V) are too low for furan α-carbons. HMBC results (Figure 1) showed that
the side chains are in all cases attached to a =C-O- carbon (i.e., indeed α-). Another evidence is the weak
coupling of the furan proton to C-4 (in turn unambiguously assigned using its coupling to the N-methyl),
which is observable in 2-substituted derivatives only. Thus, the decarboxylation products under
discussion have structures (8a, 8b, and 8c); the corresponding acids are 6a, 6b, and 6c.
Table IV.
1H NMR Spectral Data (δ, ppm/Hz) of Compounds (5a), (6a-c), (7c), and (8a-c) (399.90
MHz, CDCl3, 30°C)
b
a,b
a,b
b
x
x
x
x
Proton/Ji,j
5a
6a
6b
6c
7c
8a
8b
8c
2
7.716
3
6.644
7.415
8.5
6.661
7.423
8.6
7.275
7.443
8.6
6
7.553
8.5
7.874
8.5
7.870
8.6
7.838
8.6
7.438
8.6
J6,7
J6,8
J6,9
7
1.0
1.0
1.0
1.0
1.0
1.1
1.1
1.0
≠0
≠0
0.6
≠0
0.6
0.5
0.4
0.5
7.639
7.769
7.774
7.771
7.567
7.505
7.508
7.551
J7,8
J7,9
7.2
1.5
7.2
1.6
7.1
1.5
7.1
1.5
7.2
1.6
7.2
1.6
7.1
1.6
7.2
1.6
8
7.329
7.533
7.536
7.516
7.323
7.282
7.287
7.333
J8,9
9
7.8
7.871
7.8
8.067
7.9
8.100
7.9
8.180
7.9
8.041
7.8
7.943
7.9
7.963
7.8
8.080
N-Me
3.577
3.808
3.819
3.814
3.772
3.767
3.776
3.794
a
b
40°C; DMSO-d6. Additional signals: 5a – 2.579 (m, 3H, 3-Me); 6a – 2.794 (s, 3H, 3-Me); 6b – 3.239 (t,
J = 7.8 Hz, H-1 ), 1.761 (m, 2H, H-2 ), 1.349 (m, 2H, H-3 ), 1.340 (m, 2H, H-4 ), 0.877 (t, J = 7.1 Hz,
3H, H-5 ); 6c – 8.018 (m, 2H, H-2 and H-6 ), 7.562 (m, 1H, H-4 ), 7.554 (m, 2H, H-3 and H-5 ); 7c –
7.817 (m, 2H, H-2 and H-6 ), 7.457 (m, 2H, H-3 and H-5 ), 7.375 (m, 1H, H-4 ); 8a – 2.494 (d, J3,Me
1.1 Hz, 2-Me); 8b – 2.798 (dt, J = 1.0 and 7.5 Hz, 2H, H-1 ), 1.763 (m, 2H, H-2 ), 1.391 (m, 2H, H-3 ),
1.373 (m, 2H, H-4 ), 0.918 (t, J = 7.0 Hz, 3H, H-5 ); 8c – 7.836 (m, 2H, H-2 and H-6 ), 7.464 (m, 2H, H-
3 and H-5 ), 7.362 (m, 1H, H-4 ).
´
´
´
´
´
´
´
´
´
´
´
=
´
´
´
´
´
´
´
´
´
´
´
´
´
´

HETEROCYCLES, Vol. 60, No. 4, 2003
805
Table V.
13C NMR Chemical Shifts (δ, ppm) of Compounds (5a), (6a-c), (7c), and (8a-c)
(100.55 MHz, CDCl3, 30°C)
x
b
a,b
a,b
b
x
x
x
x
Carbon
5a
6a
6b
6c
7c
8a
8b
8c
2
141.16
128.80
114.64
158.49
138.92
115.80
131.08
122.54
121.17
112.34
154.64
28.77
163.71
110.90
111.10
160.37
137.05
116.88
130.99
124.25
120.95
111.81
153.38
30.22
166.87
110.99
110.75
160.36
136.94
116.80
130.89
124.13
120.88
111.75
153.34
30.16
157.62
112.37
113.23
159.71
137.54
116.65
131.17
123.86
121.34
111.66
153.79
30.11
140.75
126.77
112.99
159.33
138.28
114.83
129.67
121.27
122.16
112.83
156.28
29.29
154.58
104.04
116.47
159.35
137.72
114.92
128.84
122.12
120.77
113.20
154.13
29.36
159.07
103.26
116.31
159.49
137.74
114.92
128.82
120.83
122.10
113.29
154.02
29.37
155.88
102.88
117.21
159.33
138.18
115.07
129.39
122.34
121.12
113.09
154.47
29.45
3
3a
4
5a
6
7
8
9
9a
9b
N-Me
10.03
13.66
26.69
130.31
128.67
130.24
129.17
13.80
28.11
129.72
124.49
1
2
´
3
´
´
x
x
x
c
c
c
c
x
c
c
26.73
27.42
x
x
30.64
128.44
130.38
128.17
127.77
31.22
128.88
128.58
21.61
13.66
161.64
22.32
13.91
4
´
5
´
COOH
160.67
161.87
162.24
a
b
c
40°C; DMSO-d6; two carbons.
OH
O
O
KOH
ethanol
4b
6b
+
+
O
N
O
N
O
O
N
CH3
9b
CH3
CH3
10b
Scheme 2
Three compounds (6b, 9b, and 10b) were isolated from the alkaline hydrolysis of 4b (Scheme 2). The
structure of carboxylic acid (6b) is based on the examination of its decarboxylation product (8b) (see
above). IR spectrum of acidic compound C17H21NO3 excluded the presence of a carboxyl. According to
13
1
the C NMR spectrum (Table III) the molecule contained two =C-O- and one aliphatic C=O. The H
NMR spectrum (Table III) displayed singlets of a phenolic hydroxyl, N-methyl, and isolated methylene,
in addition to an ABCD spin system of four vicinal aromatic protons and a –(CH2)4CH3 moiety. HMBC

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HETEROCYCLES, Vol. 60, No. 4, 2003
experiment (Figure 1) leads to structure (9b). This structure was confirmed by intramolecular
condensation of 9b to 8b in conc. sulfuric acid. The intense ion with the highest mass in the MS spectrum
of the third component from the hydrolysis of 4b had m/z 269 and elemental composition C17H19NO2.
1
However, the observed H NMR spectrum (Table III) accounted for 18 protons only; an ABCD spin
system of four aromatic protons, a N-methyl, and n-pentyl. No evidence for an OH group was found
1
13
neither in IR nor in H NMR spectra. Seventeen signals observed in the C NMR spectrum (Table III)
represent two methyls, four aliphatic methylenes, four =CH, and seven sp2 hybridized carbons. Three of
these quaternary carbons are attached to oxygen. One (coupled to the N-methyl) is C-4; the second
(coupled to H-9) belongs to C-9b; the remaining one (coupled to the terminal CH2 of the side chain) is
therefore C-2. Thus a structure (10b) of symmetric 3-3´dimer analogous to 8b is proposed for this
compound. A weak molecular ion was indeed found at m/z 536. The ion m/z 269 might arise by
breakdown of the bond connecting both parts followed by hydrogen transfer.
It is evident from the foregoing that acids obtained by alkaline hydrolysis of bromo derivatives (4) have
not the expected structure (5), but isomeric structure (6). However, a detailed spectroscopic investigation
of crude mixture of acids obtained upon alkaline hydrolysis of 4a showed two components: a minor one,
5a and a major one 6a. These were differentiated using the HMBC coupling pattern of the CH3-C= group:
three crosspeaks (C-2, C-3, C-3b) for 5a and two (C-2, C-3) for 6a.
O-
R
O
R
Br
R
+
O-
O
O-
R
O-
COO-
Br
COO-
COO-
N
O
N
O
N
O
H+
N
O
CH3
C
CH3
CH3
CH3
A
D
E
6
HO-
HO-
COO-
OH
O
O- COO-
R
H+
R
R
4
5
O
O
OH
- CO2
N
N
O
N
O
9
F
CH3
CH3
B
CH3
Scheme 3
Our findings show that the hydrolysis of bromo derivatives (4) proceeds in analogy with the Perkin
rearrangement of 3-bromocoumarins to benzofuran-2-carboxylic acids in only a small extent to give 5a.
The formation of major product (6a) must proceed by some other molecular rearrangement. A proposed
reaction mechanism of the molecular rearrangement of 4 to acids (6) is given in Scheme 3. By the
opening of the pyrane ring of 4 in an alkaline medium, dianion (A) arises, the conversion of which can
proceeds in two independent ways. The first is represented by the regular Perkin rearrangement in which
anion (B) is formed and which, after acidification, yields the expected acid (5). The second and main way

HETEROCYCLES, Vol. 60, No. 4, 2003
807
passes through a conformer (C), the occurrence of which is more probable than A due to the longer
distance of two negatively charged functional groups. The following elimination of halogen atom at the
sp2 hybridized carbon atom is accompanied by a migration of the substituent in trans-position to the
departing halogen atom. This migratory group exhibits a partial carbanionic character due to its possible
tautomerism. This rearrangement, which is formally of the Wagner-Meerwein type, leads to the formation
of intermediate (D), which produces compound (E) and, consequently, product (6) after acidification. It is
probable that the conversion of C to E is concerted. This proposal also well explains the formation of side
product (9b) in the reaction of 4b. The addition of hydroxyl ion to intermediate (D) leads to the formation
of intermediate (F), which, according to its β-oxoacid character, smoothly decarboxylates with formation
of the anion of the isolated compound (9b). The origin of side product (10b) remains unanswered; it
probably arises through a dehydrogenative coupling of some reaction intermediate. However, 8b and 9b
cannot be precursors of 10b as their work-up in alkaline medium in the presence of air oxygen produced
no changes.
The observation of the new molecular rearrangement of 4 to 6 described above brings a doubt about the
correct structure of acid (5e), the preparation of which was described2 as the Perkin rearrangement of
bromo derivative (4e). The same is true of the structure of acid prepared3 from the N-unsubstituted
analogue of 4e. Unfortunately, the NMR spectra of both latter acids were not reported so that problem
remains unsolved.
O
COOC2H5
O
O
CH3
CH3
Ph3P=C(Cl)COOC2H5
1a
+
COOC2H5
N
O
N
CH3
11a
CH3 Cl
12a
Scheme 4
Owing to the unexpected molecular rearrangement of 3-bromo derivatives (4), our idea to prepare 7
starting from 2 failed. Therefore, we were looked for a new reaction path leading to compounds (5). We
have been studying the reaction of 3-acetyl-4-hydroxy-1H-quinolin-2-one (1a) with ethyl
(triphenylphosphoranylidene)chloroacetate15 (Scheme 4). In boiling xylene, the reaction gives a complex
mixture of compounds from which compound C16H15NO4 was isolated by repeated column
chromatography and identified as ethyl ester (11a) of 5a. The yield of the reaction is low, however,
according to our best knowledge, this is the first case of the successful reaction of a very stable
chlorinated ylide with ketones. The second reaction product C18H16NO4Cl contained an unsaturated
lactone moiety similar to 2a, an ethyl group and one additional sp2-type quaternary carbon. The
configuration of the new tetrasubstituted double bond in structure (12a) was not determined because of

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HETEROCYCLES, Vol. 60, No. 4, 2003
lack of protons in its vicinity. Its formation can be explained by the reaction of 1a with dechlorinated
Wittig reagent and the following reaction of so formed intermediate with chlorinated ylide at the lactam
group. The origin of dechlorinated Wittig reagent (ethyl (triphenylphosphoranylidene)acetate) in the
reaction mixture is so far not clear.
EXPERIMENTAL
Melting points were determined on a Kofler block or Gallencamp apparatus. IR (KBr) spectra were
recorded on a Mattson 3000 spectrophotometer. NMR spectra were recorded on a Varian INOVA-400
1
spectrometer (400 MHz for H, 100 MHz for 13C) in the respective solvents and temperatures stated.
Chemical shifts are given on the δ scale (ppm) and are referenced to internal TMS. All 2D experiments
(gCOSY, HMQC, HMBC) were performed using manufacturer´s software. The sequence for 1D-TOCSY
experiments16 was obtained through Varian User Library; sequence for gradient-selected HMBC17,18 was
provided by Varian Application Laboratory (Darmstadt, Germany). Proton spectra were assigned using
gCOSY. The NOE difference experiment (irradiation of N-methyl) was performed to find the peri-
disposed aromatic proton. The chemical shifts and coupling constants of some ABCD system proton
buried in the envelope were extracted from 1D-TOCSY spectra. Benzene ring protons were assigned
according to their characteristic multiplet pattern. Protonated carbons were assigned by HMQC; where
the direct observation of 13C NMR spectrum was not possible, HMQC readouts were used instead.
Quaternary carbons were assigned by HMBC or gHMQC, respectively. Positive ion electron impact mass
spectra were measured on a Finnigan MAT 95 spectrometer (70 eV, ion source temperature 250°C);
perfluorokerosene was used as a standard for the high-resolution measurement. Column chromatography
was carried out on silica gel (Merck, grade 60, 70-230 mesh) using a mixture of chloroform – ethanol
(19:1, S1) and benzene – ethyl acetate (9:1, S2) respectively, as eluent. The course of separation and also
the purity of isolated substances were monitored by TLC (elution systems benzene-ethyl acetate, 4:1, and
chloroform-ethanol, 9:1 and/or 19:1) on Silufol UV 254 foils (Kavalier, Votice). Elemental analyses (C,
H, N) were performed with an EA 1108 Elemental Analyzer (Fisons Instrument).
3-Acyl-4-hydroxy-1H-quinolin-2-ones (1) were prepared according to ref.19 (1a), ref.12 (1b and 1d), and
ref.13 (1c).
General Procedure for the Preparation of 4-Alkyl/Aryl-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-
diones (2a-d). A mixture of 1 (5 mmol) and ethyl (triphenylphosphoranylidene)acetate (1.92 g, 5.5
mmol) in xylene (20 mL) was refluxed for 4 h. After cooling, the precipitate was filtered off with suction
and recrystallized. From mother liquors, a further portion of 2 was obtained after concentration in vacuo.

HETEROCYCLES, Vol. 60, No. 4, 2003
809
4,6-Dimethyl-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-dione (2a): Colorless crystals, yield 70%,
mp 279-282°C (DMF) (lit.,10 mp 283-284°C), IR (cm-1): 3087, 2986, 2926, 1760, 1737, 1717, 1655,
1630, 1595, 1580, 1543, 1500, 1453, 1425, 1417, 1394, 1384, 1304, 1169, 1103, 1075, 1040, 917, 846,
768, 674, 644. EIMS, m/z (%): 241 (M+, 73), 213 (100), 198 (7), 184 (54), 170 (6), 156 (7), 132 (6), 115
(5), 104 (5), 77 (7), 63 (2), 51 (3). Anal. Calcd for C14H11NO3: C, 69.70; H, 4.60; N, 5.81. Found: C,
69.54; H, 4.76; N, 5.64.
6-Methyl-4-pentyl-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-dione (2b): Colorless crystals, yield
65%, mp 162-164°C (benzene), IR (cm-1): 3077, 2953, 2930, 2857, 1760, 1729, 1654, 1620, 1594, 1538,
1453, 1397, 1321, 1302, 1162, 1139, 1113, 1074, 1040, 990, 925, 882, 841, 758, 674, 633. EIMS, m/z
(%): 297 (M+, 46), 269 (49), 254 (58), 240 (42), 226 (92), 213 (100), 198 (9), 184 (24), 170 (6), 154 (11),
132 (7), 115 (7), 104 (9), 77 (13), 63 (2), 51 (3). Anal. Calcd for C18H19NO3: C, 72.71; H, 6.44; N, 4.71.
Found: C, 72.53; H, 6.57; N, 4.56.
6-Methyl-4-phenyl-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-dione (2c): Colorless crystals, yield
71%, mp 218-224°C (benzene-methanol), IR (cm-1): 3086, 3032, 2938, 2886, 1742, 1660, 1616, 1594,
1571, 1530, 1497, 1453, 1397, 1386, 1317, 1302, 1181, 1143, 1117, 1085, 1041, 984, 925, 896, 857, 849,
762, 699, 689, 597. EIMS, m/z (%): 303 (M+, 73), 302 (100), 275 (58), 274 (31), 246 (15), 232 (10), 218
(15), 204 (7), 104 (5), 77 (8), 63 (2), 51 (2). Anal. Calcd for C19H13NO3: C, 75.24; H, 4.32; N, 4.62.
Found: C, 74.96; H, 4.12; N, 4.43.
4-Benzyl-6-methyl-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-dione (2d): Colorless crystals, yield
64%, mp 199-202°C (benzene-ethanol), IR (cm-1): 3085, 3063, 3030, 2945, 2921, 2891, 1751, 1726, 1660,
1624, 1603, 1596, 1579, 1545, 1498, 1456, 1404, 1392, 1156, 1098, 1068, 986, 929, 910, 891, 843, 834,
763, 701, 680, 623, 550. EIMS, m/z (%): 317 (M+, 76), 289 (100), 274 (9), 260 (18), 134 (6), 115
(3), 104 (3), 77 (6), 65 (2), 51 (1). Anal. Calcd for C 20H15NO3: C, 75.70; H, 4.76; N, 4.41. Found: C,
75.92; H, 5.00; N, 4.64.
Alkaline Hydrolysis of 5,6-Dihydro-2H-pyrano[3,2-c]quinoline-2,5-diones (2a and 2c).
A mixture of 2 (0.7 mmol) and sodium hydroxide (0.14 g, 3.5 mmol) in water (0.21 mL) was diluted with
ethylene glycol (1.4 mL) and refluxed for 1 h. After cooling, water (6 mL) was added and the solution
was acidified with conc. hydrochloric acid. The separated precipitate was filtered off with suction and
crystallized. From 2a, compound (3e), identical in all respect with authentic specimen,10 was obtained in
59% yield (72 mg). From 2c, compound (3f) was obtained in 55% yield (107 mg).

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HETEROCYCLES, Vol. 60, No. 4, 2003
4-Hydroxy-3-(1-phenylethenyl)-1H-quinolin-2-one (3f): Colorless crystals, yield 55%, mp 246-252°C
(ethanol), IR (cm-1): 3096, 3077, 3041, 2949, 2896, 2817, 1728, 1610, 1574, 1508, 1492, 1418, 1402,
1339, 1329, 1196, 1187, 1161, 1101, 1071, 1043, 1027, 918, 866, 780, 758, 746, 714, 696, 632, 542.
EIMS, m/z (%): 277 (M+, 94), 276 (100), 262 (13), 248 (6), 234 (4), 200 (6), 115 (4), 104 (5), 77 (12), 63
(2), 51 (2). Anal. Calcd for C18H15NO2: C, 77.96; H, 5.45; N, 5.05. Found: C, 77.68; H, 5.22; N, 5.02.
General Procedure for the Preparation of 3-Bromo-6-methyl-5,6-dihydro-2H-pyrano[3,2-
c]quinoline-2,5-diones (4a-d). To the solution of appropriate pyranoquinolinedione (2) (10 mmol) in
chloroform (330 mL) bromine (2.4 g, 15 mmol) was added and the mixture was allowed to stand for 160
h (2a), 4h (2b), 18 h (2c), or 70 h (2d), respectively. The separated precipitate was filtered off with
suction and washed with chloroform. After concentration of mother liquor, the additional portion of
product was obtained. Crude products (4a) and (4c) exhibit only one spot on TLC in several solvent
systems. However, according to NMR spectrum, the crude 4b contain about 10% of 9-bromo derivative
and was purified by repeated crystallization. The crude product (4d) consists, according to NMR
spectrum, of the mixture of three compounds. All attempts on its purification by crystallization failed and
it was no used for further reaction.
3-Bromo-4,6-dimethyl-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-dione (4a): Yellow crystals, yield
82%, mp 323-327°C (chloroform), IR (cm-1): 3077, 2947, 1746, 1725, 1657, 1619, 1590, 1572, 1540, 1),
212 (10), 188 (9), 154 (9), 104 (3), 525, 1500, 1450, 1418, 1376, 1345, 1308, 1301, 1254, 1189, 1111,
1078, 1035, 955, 898, 873, 765, 694, 638, 526. EIMS, m/z (%): 319 (M+, 100), 291 (36), 262 (51), 240
(95), 212 (68), 184 (51), 169 (17), 154 (22), 140 (16), 128 (16), 115 (10), 104 (9), 77 (20), 63 (7), 51 (10).
Anal. Calcd for C14H10NO3Br: C, 52.52; H, 3.15; N, 4.38. Found: C, 52.79; H, 3.17; N, 4.17.
3-Bromo-6-methyl-4-pentyl-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-dione (4b): Yellow crystals,
yield 79%, mp 167-169°C (ethyl acetate), IR (cm-1): 2949, 2930, 2867, 1750, 1740, 1643, 1616, 1590,
1572, 1515, 1497, 1374, 1346, 1314, 1297, 1171, 1161, 1112, 1095, 1072, 1038, 950, 877, 789, 760, 696,
650, 525. EIMS, m/z (%): 375 (M+, 15), 332 (11), 319 (26), 296 (100), 268 (22), 252 (11), 240 (18), 226
(9), 212 (10), 188 (9), 154 (9), 104 (3), 77 (6), 63 (1), 51 (2). Anal. Calcd for C18H18NO3Br: C, 57.46; H,
4.82; N, 3.72. Found: C, 57.27; H, 4.67; N, 3.64.
3-Bromo-6-methyl-4-phenyl-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-dione (4c): Yellow crystals,
yield 77%, mp 281-284°C (benzene-methanol), IR (cm-1): 3078, 3058, 3024, 2948, 1745, 1699, 1656,
1618, 1591, 1572, 1515, 1450, 1418, 1376, 1352, 1315, 1296, 1254, 1189, 1122, 1078, 1035, 955, 936,

HETEROCYCLES, Vol. 60, No. 4, 2003
811
921, 879, 788, 775, 758, 689, 654, 602, 537. EIMS, m/z (%): 381 (M+, 100), 353 (36), 324 (10), 302 (39),
274 (13), 246 (87), 231 (6), 217 (31), 203 (14), 189 (14), 132 (6), 113 (9), 104 (8), 77 (14), 63 (6), 51 (4).
Anal. Calcd for C19H12NO3Br: C, 59.71; H, 3.16; N, 3.66. Found: C, 59.43; H, 3.01; N, 3.53.
Alkaline Hydrolysis of 4-Alkyl/Aryl-3-bromo-6-methyl-5,6-dihydro-2H-pyrano[3,2-c]quinoline-2,5-
diones (4a-c). Bromo derivative (4) (2.8 mmol) was added to the solution prepared by dissolving of
potassium hydroxide (0.79 g, 14 mmol) in water (1 mL) and dilution with ethanol (20 mL) and the
mixture was refluxed for 2 h. After evaporation to dryness, water (5 mL) and conc. hydrochloric acid (1
mL) were added. The deposited precipitate was filtered off with suction, washed with water and
recrystallized. In the case of 4a, 47 mg of an impure compound of mp 285-9°C was isolated from mother
liquors after separation of 6a. According to NMR spectrum, it is a mixture of compounds (5a) and (6a).
Attempts on the separation of pure compound (5a) by crystallization and column chromatography were
unsuccessful. From compound (4b), compound (6b) was obtained by crystallization with ethanol. Two
further compounds, (9b) and (10b), were isolated by column chromatography of mother liquors on silica
gel (solvent system S1).
2,5-Dimethyl-4-oxo-4,5-dihydrofuro[3,2-c]quinoline-3-carboxylic acid (6a): Colorless crystals, yield
28%, mp 268-269°C (ethanol), IR (cm-1): 3096, 2989, 2954, 2518, 1731, 1639, 1604, 1589, 1561, 1508,
1459, 1435, 1381, 1373, 1348, 1250, 1112, 1080, 1040, 963, 924, 869, 762, 698, 677, 670, 644. 515.
EIMS, m/z (%): 257 (M+, 93), 239 (100), 213 (78), 212 (60), 198 (15), 184 (26), 170 (16), 154 (11), 140
(7), 132 (17), 115 (11), 104 (11), 77 (14), 63 (4), 51 (5). Anal. Calcd for C14H11NO4: C, 65.37; H, 4.31;
N, 5.44. Found: C, 65.55; H, 4.08; N, 5.24.
5-Methyl-2-pentyl-4-oxo-4,5-dihydrofuro[3,2-c]quinoline-3-carboxylic acid (6b): Colorless crystals,
yield 26%, mp 187-188°C (benzene), IR (cm-1): 3439, 3194, 2950, 2929, 2859, 1731, 1640, 1607, 1587,
1554, 1503, 1467, 1434, 1410, 1357, 1248, 1112, 1056, 1043, 1017, 994, 964, 922, 791, 759, 658, 633,
554. EIMS m/z (%): 313 (M+, 45), 295 (67), 284 (19), 270 (27), 266 (34), 252 (100), 239 (17), 226 (11),
212 (48), 198 (6), 184 (7), 154 (6), 132 (13), 115 (5), 104 (5), 77 (7), 51 (1). HR EIMS Calcd for
C18H19NO4: 313.1314, Found: 313.1302.
5-Methyl-2-phenyl-4-oxo-4,5-dihydrofuro[3,2-c]quinoline-3-carboxylic acid (6c): Colorless crystals,
yield 34%, mp 271-280°C (benzene-ethanol), IR (cm-1): 3061, 3026, 2957, 2353, 1725, 1636, 1602, 1549,
1504, 1486, 1467, 1430, 1410, 1351, 1284, 1251, 1218, 1116, 1056, 1042, 990, 942, 891, 779, 760, 690,
657, 567. EIMS m/z (%): 319 (M+, 43), 275 (100), 246 (6), 232 (6), 132 (6), 105 (8), 77 (11), 63 (1), 51
(2). HR EIMS Calcd for C19H13NO4: 319.0845, Found: 319.0834.

812
HETEROCYCLES, Vol. 60, No. 4, 2003
1-Methyl-3(2-oxoheptyl)-4-hydroxy-1H-quinolin-2-one (9b): Colorless crystals, yield 15%, mp 124-
127°C (benzene), IR (cm-1): 3166, 2953, 2922, 2860, 1711, 1630, 1601, 1584, 1505, 1460, 1342, 1330,
1192, 1181, 1148, 1120, 1096, 1042, 754, 677. EIMS m/z (%): 287 (M+, 15), 244 (3), 230 (4), 216 (2),
202 (5), 189 (100), 188 (33), 175 (6), 160 (4), 146 (6), 134 (10), 104 (5), 77 (6), 55 (2), 51 (1). HR EIMS
Calcd for C17H21NO3: 287.1521, Found: 287.1513.
5,5´-Dimethyl-2,2´-dipentyl-4´,5´-dihydro-5H-[3,3´]bi[furo[3,2-c]quinolinyl]-4,4´-dione (10b).
Colorless crystals, yield 20%, mp 270-274°C (benzene-ethanol), IR (cm-1): 3399, 3106, 2965, 2950,
2930, 2870, 1659, 1601, 1579, 1557, 1503, 1468, 1450, 1393, 1347, 1229, 1108, 990, 816, 777, 746, 707,
658. EIMS m/z (%): 536 (M+, 0.1), 269 (48), 252 (7), 238 (2), 212 (100), 188 (3), 154 (3), 140 (2), 132
(5), 115 (3), 104 (2), 77 (4), 63 (1), 55 (2). HR EIMS Calcd for C 17H19NO2: 269.1416, Found: 269.1405.
Methyl-3-phenyl-5H-furo[3,2-c]quinolin-4-one (7c), yield 39%, mp 108-109°C (cyclohexane) was
prepared according to lit.,8 (mp 105-106°C). EIMS m/z (%): 275 (M+, 100), 274 (21), 246 (6), 232 (5),
217 (11), 189 (6), 77 (3), 63 (1), 51 (1).
General Procedure for the Preparation of 5-Methyl-5H-furo[3,2-c]-quinolin-4-ones (8). To the
solution of appropriate acid (6) (0.6 mmol) in quinoline (3 mL) copper dust (0.1 g) was added and the
mixture was heated under stirring for 30 min at 170-80°C and then 20 min at 180-200°C. After cooling,
copper was filtered off and the filtrate was diluted with benzene (70 mL). The solution was washed three
times with 5% hydrochloric acid (40 mL). Benzene layer was washed with water to the neutral reaction,
dried with sodium sulfate and evaporated to dryness. The dark residue was dissolved in ethanol, the
solution was filtered with charcoal, the filtrate was evaporated to dryness and the residue was crystallized.
2,5-Dimethyl-5H-furo[3,2-c]quinolin-4-one (8a): Colorless crystals, yield 47%, mp 117-119°C
(benzene-cyclohexane), (lit.,6 mp 118-119°C, lit.,7 mp 118°C), IR (cm-1): 2986, 2947, 2919, 2848, 1660,
1597, 1582, 1509, 1452, 1436, 1416, 1356, 1312, 1302, 1251, 1107, 1042, 971, 928, 828, 815, 756, 746,
643. EIMS, m/z (%): 213 (M+, 100), 212 (29), 198 (7), 184 (10), 170 (7), 156 (2), 142 (6), 115 (5), 104
(2), 77 (5), 63 (1), 51 (2). Anal. Calcd for C13H11NO2: C, 73.22; H, 5.20; N, 6.57. Found: C, 73.12; H,
5.34; N, 6.41.
5-Methyl-2-pentyl-5H-furo[3,2-c]quinolin-4-one (8b): Colorless crystals, yield 58%, mp 50-53°C
(benzene-hexane), IR (cm-1): 2966, 2924, 2853, 1665, 1588, 1576, 1516, 1505, 1418, 1459, 1435, 1365,
1311, 1296, 1234, 1110, 1100, 1038, 941, 862, 774, 746, 738, 726. EIMS, m/z (%): 269 (M+, 51), 212

HETEROCYCLES, Vol. 60, No. 4, 2003
813
(100), 184 (4), 175 (9), 154 (2), 132 (7), 115 (2), 104 (2), 77 (14), 63 (1), 51 (1). Anal. Calcd for
C17H19NO2: C, 75.81; H, 7.11; N, 5.20. Found: C, 75.58; H, 7.32; N, 5.17.
5-Methyl-2-phenyl-5H-furo[3,2-c]quinolin-4-one (8c): Colorless crystals, yield 43%, mp 213-215°C
(ethanol), IR (cm-1): 2984, 2942, 2884, 1650,1640sh, 1584, 1509, 1487, 1464, 1432, 1409, 1363, 1329,
1314, 1246, 1156, 1107, 1037, 1017, 967, 915, 868, 758, 688, 673, 658. EIMS, m/z (%): 275 (M+, 100),
246 (6), 232 (6), 217 (3), 170 (2), 115 (2), 105 (4), 77 (7), 63 (1), 51 (1). Anal. Calcd for C18H13NO2: C,
78.53; H, 4.76; N, 5.09. Found: C, 78.65; H, 4.93; N, 5.13.
Conversion of 1-Methyl-3(2-oxoheptyl)-4-hydroxy-1H-quinolin-2-one (9b) to 5-Methyl-2-pentyl-5H-
furo[3,2-c]quinolin-4-one (8b). Compound (9b) (29 mg, 0.1 mmol) was dissolved in conc. sulfuric acid
(0.5 mL) at rt. After 10 min, the reaction mixture was diluted with water (5 mL) and extracted three times
with chloroform (5 mL). Chloroform extract was dried with potassium carbonate and evaporated to
dryness. Compound (8b) (21 mg, 78%), identical in all respects with that isolated from decarboxylation
of 6b, was obtained by crystallization with benzene-hexane.
Reaction of 1a with Ethyl (Triphenylphosphoranylidene)chloroacetate. A mixture of 1a (1.09 g, 5
mmol) and ethyl (triphenylphosphoranylidene)chloroacetate15 (2.2 g, 5.75 mmol) in xylene (30 mL) was
refluxed for 2.5 h. After cooling, the solution was evaporated to dryness in vacuo and the dark residue of
resinous character was repeatedly extracted with boiling cyclohexane. The extract was concentrated in
vacuo and two pure compounds were isolated by column chromatography on silica gel using solvent
system S2.
Ethyl 3,5-Dimethyl-4-oxo-4,5-dihydrofuro[3,2-c]quinoline-2-carboxylate (11a): Pale yellow crystals,
yield 133 mg (19%), mp 182-189°C (benzene-cyclohexane). IR (cm-1): 3088, 2983, 2931, 2852, 1712,
1658, 1635, 1596, 1576, 1563, 1440, 1367, 1328, 1295, 1259, 1200, 1140, 1111, 1094, 1042, 984, 966,
861, 784, 769, 753, 673, 620, 543. 1H NMR (CDCl3, 30°C): 1.453 (t, J=7.1 Hz, 3H, CH3), 2.787 (s, 3H,
2-Me), 3.750 (s, 3H, N-Me), 4.453 (q, J=7.1 Hz, 2H, OCH2), 7.325 (ddd, J=7.9, 7.2, and 1.0 Hz, 1H, H-
8), 7.435 (ddd, J=8.7, 1.0, and 0.5 Hz, 1H, H-6), 7.607 (ddd, J=8.7, 7.2, and 1.6 Hz, 1H, H-7), 8.145
13
(ddd, J=7.9, 1.6, and 0.5 Hz, 1H, H-9). C NMR (CDCl3, 30°C): 10.38 (2-Me), 14.38 (CH3), 29.05 (N-
Me), 61.09 (OCH ), 112.51 (C-9a), 115.04 (C-6), 115.52 (C-3a), 122.37 (C-9), 122.46 (C-8), 130.60 (C-
2
3), 130.88 (C-7), 139.43 (C-5a), 141.05 (C-2), 155.84 (C-9b), 159.62 (C=O), 159.81 (C-4). EIMS, m/z
(%): 285 (M+, 100), 257 (21), 240 (11), 213 (41), 184 (29), 154 (7), 140 (3), 115 (2), 77 (2), 63 (1), 51
(1). HR EIMS Calcd for C16H15NO4: 285.1001, Found: 285.0992.

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HETEROCYCLES, Vol. 60, No. 4, 2003
Ethyl 4,6-Dimethyl-2-oxo-5,6-dihydro-2H-pyrano[3,2-c]quinolin-5-ylidene(chloro)acetate (12a):
Orange crystals, yield 62 mg (7%), mp 202-211°C (benzene-cyclohexane), IR (cm-1): 3084, 3040, 2977,
2920, 2869, 1688, 1649, 1629, 1600, 1587, 1561, 1545, 1504, 1455, 1424, 1391, 1382, 1365, 1318, 1295,
1
1218, 1184, 1170, 1123, 1060, 985, 866, 829, 784, 754, 677, 521. H NMR: (CDCl3), 30°C): 1.391 (t,
J=7.1 Hz, 3H, CH3), 2.590 (d, J=1.4 Hz, 3H, 4-Me), 3.663 (s, 3H, N-Me), 4.314 (q, J=7.1 Hz, 2H,
OCH2), 7.306 (ddd, J=8.4, 7.2, and 0.9 Hz, 1H, H-9), 7.316 (dd, J=8.6 and 0.9 Hz, 1H, H-7), 7.631 (ddd,
J=8.6, 7.2, and 1.6 Hz, 1H, H-8), 7.707 (q, J=1.4 Hz, 1H, H-3), 8.170 (dd, J=8.4 and 1.6 Hz, 1H, H-10).
13C NMR (CDCl3, 30°C): 14.36 (CH3), 23.00 (4-Me), 29.46 (N-Me), 61.26 (OCH2), 108.49 (C-4a),
113.47 (C-10a), 114.02 (C-7), 117.55 (C-3), 122.70 (C-9), 124.11 (C-10), 124.97 (=C-Cl), 132.75 (C-8),
139.64 (C-6a), 142.26 (C-4), 155.96 (C-10b), 156.63 (C-2), 159.88 (C-5), 163.92 (C=O). EIMS, m/z (%):
345 (M+, 100), 317 (12), 300 (11), 285 (8), 273 (68), 266 (85), 238 (23), 208 (7), 184 (7), 154 (2), 140
(2), 132 (4), 115 (2), 104 (3), 77 (6), 63 (1), 51 (2). HR EIMS Calcd for C18H16NO4Cl: 345.0768, Found:
345.0760.
ACKNOWLEDGEMENTS
This study was supported by the Ministry of Education, Youth and Sports of the Czech Republic (Grant
No. MSM 265200015). The authors thank Mrs. H. Geržová for technical help and Dr. V. Bekarek for
elemental analyses.
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