8
20
K. Rad-Moghadam and M. Mohseni
3
-Formyl-4-hydroxycoumarin (2)
3
A mixture of 6.2 mmol of 4-hydroxycoumarin, 7 cm of triethyl orthoformate, and 0.02 g of p-tolu-
3
enesulfonic acid monohydrate was placed in a 50cm beaker. The beaker was covered with a stemless
funnel and irradiated in the microwave oven for 1 min at 240W and then 1 min at 180 W. The resultant
residue was cooled to room temperature, the solvent was decanted, and the residue was dissolved in
3
1
5cm of 0.15 N Na CO solution. It was poured into a separatory funnel, acidified to pH¼ 4, and
2
3
3
extracted with 2ꢃ20cm of Et O. The crystals separated from evaporation of ethereal solution were
2
ꢄ
recrystalized from n-hexane to obtain 68% of 2 as yellow needles, mp 138–139 C (Ref. [7]
ꢄ
1
36–137 C).
General Procedure for the Preparation of Dialkyl 2H,5H-pyrano[3,2-c][1]benzopyran-
-one-2,3-dicarboxylates 4a–4c
5
To a magnetically stirred solution of 0.38g of 2 (2mmol) and 0.52 g of triphenylphosphine (2mmol) in
3
3
6
cm of CH Cl a solution of 2 mmol of dialkyl acetylenedicarboxylate in 4 cm of CH Cl was added
2 2 2 2
ꢄ
dropwise over 10min at ꢁ10 C. The reaction mixture was then allowed to warm up to room tem-
perature and stirred for 12 h. The solvent was removed under reduced pressure and the residue was
purified by column chromatography using n-hexane:ethyl acetate (3:1) as eluent. The products were
crystallised from the effluent solution and were recrystallised in n-hexane:ethyl acetate ¼ 4:1.
Dimethyl 2H,5H-pyrano[3,2-c][1]benzopyran-5-one-2,3-dicarboxylate (4a, C H O )
16 12 7
ꢄ
Yield 73%, colorless crystals, mp 196–197 C (n-hexane:ethyl acetate); IR (KBr): ꢀꢀ ¼ 3086, 2930 (C–
ꢁ
1
1
H), 1733 and 1718 (C¼O) cm ; H NMR (CDCl ): ꢁ ¼ 7.85 (s, 4-H), 7.84 (dd, J ¼ 7.9 and 1.3 Hz,
3
1
0-H), 7.63 (dt, J ¼ 1.3 and 7.9 Hz, 8-H), 7.39 (d, J ¼ 7.9Hz, 7-H), 7.38 (t, J ¼ 7.9 Hz, 9-H), 4.71 (s, 2-
13
H), 3.86 and 3.80 (2s, 2CH –O) ppm; C NMR (CDCl ): ꢁ ¼ 171.8, 165.4, 161.2 (3C¼O), 156.1,
3
3
1
53.0, 113.7, 109.8, 101.0 (5C), 149.5, 133.4, 125.0, 123.2, 117.3 (5CH), 53.5 and 36.5 (2CH ), 52.7
3
þ
þ
(
C-2) ppm; MS: m=z (%) ¼ 316 (M , 11), 257 (M ꢁ CO CH , 100), 227 (4), 214 (5).
2
3
Diethyl 2H,5H-pyrano[3,2-c][1]benzopyran-5-one-2,3-dicarboxylate (4b, C H O )
8 16 7
1
ꢄ
Yield 71%, colorless crystals, mp 177–178 C (n-hexane:ethyl acetate); IR (KBr): ꢀꢀ ¼ 3100, 2992 (C–
ꢁ
1
1
H), 1720 (br, C¼O) cm ; H NMR (CDCl ): ꢁ ¼ 7.83 (s, 4-H), 7.82 (dd, J ¼ 7.8 and 1.3 Hz, 10-H),
3
7
4
ꢁ
.62 (dt, J ¼ 1.3 and 7.8 Hz, 8-H), 7.37 (d, J ¼ 7.8 Hz, 7-H), 7.36 (t, J ¼ 7.8Hz, 9-H), 4.68 (s, 2-H),
13
.35–4.20 (m, 2CH –O), 1.35 (t, J ¼ 7.2 Hz, CH ), 1.31 (t, J ¼ 7.1 Hz, CH ) ppm; C NMR (CDCl ):
2
3
3
3
¼ 171.3, 165.0, 161.2 (3C¼O), 156.0, 153.0, 113.7, 110.1, 101.0 (5C), 149.2, 133.3, 124.9, 123.1,
17.2 (5CH), 62.4 (C-2), 61.7 and 36.7 (2CH –O), 14.6 and 14.4 (2CH ) ppm; MS: m=z (%) ¼ 345
1
2
3
þ
þ
(
M , 11), 271 (M ꢁ CO Et, 100), 243 (271ꢁ CH ¼CH , 50), 227 (5).
2
2
2
Di-tert-butyl 2H,5H-pyrano[3,2-c][1]benzopyran-5-one-2,3-dicarboxylate (4c, C H O )
22 24 7
ꢄ
Yield 66%, colorless crystals, mp 129–130 C (n-hexane:ethyl acetate); IR (KBr): ꢀꢀ ¼ 3097, 2994 (C–
ꢁ
1
1
H), 1720 (br, C¼O) cm ; H NMR (CDCl ): ꢁ ¼ 7.78 (d, J ¼ 7.9 Hz, 10-H), 7.71 (s, 4-H), 7.57 (t,
3
J ¼ 7.9 Hz, 8-H), 7.32 (d, J ¼ 7.9 Hz, 7-H), 7.31 (t, J ¼ 7.9 Hz, 9-H), 4.53 (s, 2-H), 1.54 (s, CMe ), 1.46
3
1
3
(
s, CMe ) ppm; C NMR (CDCl ): ꢁ ¼ 170.4, 164.1, 161.3 (3C¼O), 156.0, 153.0, 113.9, 111.6,
3
3
1
01.5, 82.7, 82.4 (7C), 148.5, 133.1, 124.8, 123.1, 117.2 (5CH), 37.8 (C-2), 28.5 (3CH ), 28.2 (3CH )
3 3
þ
þ
þ
ppm; MS: m=z (%) ¼ 401 (M , 2), 345 (M ꢁ C H , 10), 299 (M ꢁ CO CMe , 26), 289 (20), 243
4
8
2
3
(
299 ꢁ CH ¼CMe , 100), 149 (14).
2
2