C. E. Rodrigues-Santos, A. Echevarria / Tetrahedron Letters 48 (2007) 4505–4508
4507
Model MU31AO, a domestic oven). The reaction mixtures
were irradiated for 3 min for 2 (5a and d), 5 (5b–c) and 6
(5g–l) successive periods, with 2 min cooling intervals. The
time reaction was monitored by TLC (EtOAc–hexane,
7:3). After the irradiation, the reaction mixtures were
washed with water (40 mL), and the products were
extracted with CHCl3 (4 · 10 mL). This procedure does
not need subsequent purification. 7-Hydroxy-4-(4-meth-
oxyphenyl)-3,4-dihydrocoumarin (5a): orange solid; mp
152–153 ꢁC (lit.4 150 ꢁC); IR (KBr, cmÀ1): 1028; 1148;
presented a lower reactivity since it had taken 20 min to
all condensation reactions under microwave irradiation.
Thus, as indicated in Table 2, the yields achieved by
(CF3SO3)3Y catalyzed reactions and microwave irradia-
tion were good (65–80%), and performed in remarkable
time when compared to refluxing or to any different
reaction condition of the literature.9 The reactions were
regioselectives and all compounds were fully character-
ized by spectroscopic routine analysis as IR, 1H and
13C NMR and MS.
1
1243; 1450; 1618; 1735; 2838; 2926; 3003; 3335; H NMR
(DMSO-d6, 200 MHz): d 2.97 (m; 1H; J = 7.38 and
17.20 Hz); 3.04 (m; 1H; J = 6.90 and 16.70 Hz); 3.70 (s;
3H); 4.29 (t; 1H; J = 6.16 Hz); 6.52 (s; 1H); 6.54 (d; 1H;
J = 2.22 Hz); 6.81 (d; 1H; J = 8.1 Hz); 6.87 (d; 1H;
J = 8.36 Hz); 7.04 (d; 2H; J = 8.36 Hz); 13C NMR
(DMSO-d6, 50.3 MHz): d 36.95; 38.01; 55.05; 103.38;
111.72; 114.18; 116.60; 128.37; 128.39; 133.67; 151.99;
157.63; 158.56; 167.91; MS m/z (% rel.): 270 (M+Å, 100);
242 (25); 227 (40); 197 (47); 162 (15); 134 (15); 108 (97); 91
(5); 63 (8); 51 (7). 7-Hydroxy-4-(3-methoxyphenyl)-3,4-
dihydrocoumarin (5b): red oil; IR (KBr, cmÀ1): 1030;
1150; 1252; 1344; 1451; 1511; 1617; 1736; 2837; 2928; 3338;
In conclusion, we have described a new, fast, effortless
and efficient protocol for the preparation of 4-aryl-3,4-
dihydrocoumarins using (CF3SO3)3Y as catalyst under
microwave irradiation, in which the target compounds
were obtained in good yields and remarkable time
reactions.
Acknowledgements
1H NMR (DMSO-d6, 200 MHz):
d 2.99 (d; 2H;
J = 5.14 Hz); 4.27 (d; 2H; J = 5.14 Hz); 6.48 (ls; 2H);
6.85 (d; 2H; J = 6.85 Hz); 7.02 (d; 2H; J = 6.76 Hz); 9.74
(s; 1H); 13C NMR (DMSO-d6, 50.3 MHz): d 36.89; 37.92;
55.02; 103.30; 106.18; 111.64; 114.16; 116.55; 128.35;
133.65; 151.94; 157.55; 158.22; 167.83; MS m/z (% rel.):
270 (M+Å, 100); 242 (25); 227 (50); 197 (35); 184 (10); 77
(8); 63 (5); 51 (4); Calcd for C16H14O4: C, 71.09; H, 5.23.
Found: C, 71.11; H, 5.24. 7-Hydroxy-4-(2-methoxyphen-
yl)-3,4-dihydrocoumarin (5c): orange oil; IR (KBr,
cmÀ1): 1030; 1151; 1246; 1412; 1461; 1487; 1604; 1625;
1744; 2837; 2952; 3471; 1H NMR (DMSO-d6, 200 MHz): d
2.74 (d; 1H; J = 15.88 Hz); 3.05 (d; 1H; J = 15.52 Hz and
5.06); 4.44 (d; 1H; J = 6.5 Hz); 6.1 (d; 1H; J = 1.08 Hz);
6.4 (d; 1H; J = 1.08 Hz); 6.73 (d; 1H; J = 8.3 Hz); 6.78 (d;
1H; J = 6.48 Hz); 6.81 (d; 1H; J = 1.44 Hz); 6.92 (d; 1H;
J = 8.83 Hz); 7.15 (d; 1H; J = 7.22 Hz); 9.09 (s; 1H); 13C
NMR (DMSO-d6, 50.3 MHz): d 34.22; 35.13; 55.32;
103.27; 106.33; 111.91; 115.00; 120.64; 128.65; 129.35;
158.55; 157.67; 167.83; MS m/z (% rel.): 270 (M+Å, 100);
242 (15); 227 (15); 197 (65); 181 (7); 77 (15); 63 (7); 51 (12);
Calcd for C16H14O4: C, 71.09; H, 5.23. Found: C, 71.10;
H, 5.26. 7-hydroxy-4-(4-hydroxyphenyl)-3,4-dihydro-
coumarin (5d): yellow oil; IR (KBr, cmÀ1): 1036; 1347;
1457; 1512; 1606; 1742; 3378; 1H NMR (DMSO-d6,
200 MHz): d 2.86 (m; 1H; J = 5.24 and 15.74 Hz); 3.03
(m; 1H; J = 6.06 and 15.72 Hz); 4.20 (t; 1H; J = 6.08 Hz);
6.25 (d; 1H; J = 2.22 Hz); 6.53 (t; 2H; J = 2.28 and
8.28 Hz); 6.72 (d; 1H; J = 8.84 Hz); 6.84 (d; 1H;
J = 8.56 Hz); 6.95 (d; 2H; J = 8.56 Hz); 13C NMR
(DMSO-d6, 50.3 MHz): d 38.56; 40.29; 104.51; 107.67;
112.82; 116.55; 129.53; 130.90; 153.70; 157.64; 158.97;
170.31; MS m/z (% rel.): 256 (M+Å, 100); 228 (25); 197 (17);
163 (10); 91 (6); 77(10); 63 (8); 51 (5). 7-Hydroxy-4-(3-
hydroxy-4-methoxyphenyl)-3,4-dihydrocoumarin (5e): red
oil; IR (KBr, cmÀ1): 1026; 1269; 1368; 1452; 1512; 1622;
1743; 2845; 2972; 3381; 1H NMR (DMSO-d6, 200 MHz): d
2.97 (m; 1H; J = 4.52 and 13.56 Hz); 3.03 (m; 1H; J = 6.40
and 15.82 Hz); 4.16 (t; 1H; J = 6.04 Hz); 6.24 (d; 1H;
J = 1.88 Hz); 6.51 (d; 3H; J = 1.50 Hz); 6.83 (d; 2H;
J = 7.90 Hz); 13C NMR (DMSO-d6, 50.3 MHz): d 40.47;
40.81; 56.33; 103.43; 107.22; 112.44; 116.11; 129.45;
138.21; 146.98; 147.19; 156.56 (2 · C); 174.45; MS m/z
(% rel.): 286 (M+Å, 100); 253 (35); 243 (25); 227 (27); 176
(20); 124 (35); 91 (5); 77 (7); 63 (5); 51 (7); Calcd
for C16H14O5: C, 67.12; H, 4.94. Found: C, 67.09; H, 4.92.
The authors gratefully thank the Brazilian agencies
CNPq and CAPES for financial support and
fellowships.
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14. General procedure for 4-aryl-3,4-dihydrocoumarin (5a–l)
synthesis: the solutions of cinnamic acids (0.84 mmol),
phenols (0.84 mmol) and (CF3SO3)3Y (0.17 mmol) in
CH2Cl2 (3 mL) were dried, and the mixtures were later
put in the microwave oven (Consul Pratice-Brastemp S.A/