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N. Al-Maharik, N. P. Botting / Tetrahedron 59 (2003) 4177–4181
reduced pressure. The yellow solid was subjected to flash
chromatography on silica gel (CH2Cl2/MeOH 50:1) to
afford the title compound 1 as a white solid (0.135 g, 84%).
3.2. para-Claisen rearrangement of prenyl ether (7)
Reaction of 7 (0.15 g, 0.355 mmol) with Eu(fod)3 (0.038 g,
0.0356 mmol) for 36 h, as described above for the
preparation of compound 5 gave an intractable mixture of
the desired product 7,40-diacetoxy-5-hydroxy-8-C-prenyl-
flavone 8 and 7,40-diacetoxy-5-hydroxy-6-C-(1,1-dimethyl-
allyl)flavone 9 (0.123 g, 82% in 2:1 ratio) as light yellow
solid.
1
Mp 133–1348C (lit.8 mp 133–1358C); H 0N0 MR (acetone-
d6) d 1.66 (s, 3H, H-400), 1.81 (s, 3H, H-5 ), 3.45 (d, 2H,
J¼6.9 Hz, H-100), 5.23 (m, 1H, J¼1.5, 6.9 Hz, H-200), 6.37 (s,
1H, H-6), 6.90 (d, 2H, J¼9.0 Hz, H-30, 50), 70.47 (d, 2H,
J¼9.0 Hz, H-20, 60), 8.25 (s, 1H, H-2), 8.47 (4 -OH), 8.60
(7-OH), 12.97 (5-OH); 13C NMR (acetone-d6, 75 MHz) d
17.37 (C-500), 21.52 (C-100), 25.32 (C-400), 0 98.85 (C-6),
105.71 (C-4a), 106.66 (C-8), 115.41 (C-3 ,0 50), 122.54
(C-200), 122.66 (C-3), 123.16 (C-10), 130.61 (2 , 60), 131.54
(300), 153.82 (C-8a), 155.73 (C-2), 157.80 (C-40), 160.94
(C-5), 161.60 (C-7), 181.41 (C-4); EIMS m/z (%) 338
(Mþ, 96), 323 (100), 283 (32), 270 (48), 118 (9). Anal. calcd
for C20H18O5.H2O: C, 67.41; H, 5.66. Found: C, 67.40; H,
5.78.
3.2.1. Hydrolysis of the mixture containing 8 and 9 to 8-
prenylapigenin (6) and 6-(1,1-dimethylallyl)apigenin
(10). Treatment of the mixture of 8 and 9 (0.30 g,
7.11 mmol) with 10% aq. NaHCO3 in MeOH/THF
(5:5 ml), as described above for preparation of compound
1, gave after purification using flash chromatography
(CH2Cl2/MeOH 50:1) compounds 6 and 10. Compound 6
was obtained as a light yellow solid (0.057 g, 24%). Mp
173–1748C (decompose) (from CHCl3); nmax/cm21 (nujol)
3500–2800br (OH), 1652, 1609, 1557,001243, 1179, 832; 1H
NMR (acetone-d6) d 1.62 (s, 6H, H-4 , 500), 4.87 (dd, 1H,
J¼1.6, 10.6 Hz, H-3a00), 4.97 (dd, 1H, J¼00 1.6, 17.7 Hz,
H-3b00), 6.38 (dd, 1H, J¼10.6, 17.7 Hz, H-2 ), 6.54 (s, 1H,
H-8), 6.62 (s, 1H, H-3), 7.020 (d, 2H, J¼8.7 Hz, H-30, 50),
7.92 (d, 2H, J¼8.7 Hz, H-20, 6 ), 9.16 (40-OH), 9.22 (7-OH),
14.09 (5-OH); 13C NMR (acetone-d6, 75 MHz) d 28.81
(C-400, 500), 41.39 (C-100), 94.88 (C-8), 103.65 (C-3), 103.75
(4a),0 108.35 (C-6),0116.41 (C-300), 010 16.50 (C-30, 50), 122.89
(C-10), 128.84 (C-2 , 60), 150.36 (2 ), 156.23 (C-8a), 161.48
(C-4 ), 162.13 (C-7), 163.35 (C-2), 164.15 (C-5), 183.15
(C-4); EIMS m/z (%) 338 (Mþ, 47), 323 (100), 283 (15), 270
(12); HRMS (negative ion). Found 337.1073 C20H17O5
requires 337.1076. Compound 10 was obtained as yellow
3.1.5. 7,40-Diacetoxy-5-hydroxyflavone. Treatment of
apigenin (0.50 g, 1.85 mmol) with acetic anhydride
(0.35 ml, 3.70 mmol) gave, after recrystal0lisation from
ethanol/acetone, the title compound 7,4 -diacetoxy-5-
hydroxyflavone as a white solid (0.54 g, 82%). Mp 201–
1
2028C (lit.17 mp 203–2048C); H NMR (CDCl3) d 2.34 (s,
3H, CH3COO), 2.35 (s, 3H, CH3COO), 6.58 (d, 1H,
J¼2.1 Hz, H-6), 6.70 (s, 1H, H-3), 6.85 (0d, 1H, J¼2.1 Hz,
H-8), 7.28 (d,0 2H, J¼9.0 Hz, H-30, 5 ), 7.91 (d, 2H,
J¼9.0 Hz, H-2 , 60), 12.69 (s, 1H, 5-OH); 13C NMR
(CDCl3, 75 MHz) d 21.10 and 21.15 (2£CH3COO),
100.92 (C-80), 105.46 (C-6), 106.01 (C-3), 108.76 (C-4a),
122.40 (C-3 , 50), 127.69 (C-20, 60), 128.36 (C-10), 153.56
(C-40), 155.89 (C-7), 156.58 (C-8a), 161.81 (C-5), 163.71
(C-2), 168.22 (CH3COO), 168.73 (CH3COO), 182.61 (C-4);
EIMS m/z (%) 354 (Mþ, 44), 312 (20), 270 (100), 153
(10).
solid (0.149 g, 62%). Mp 177–1788C (from CHCl3); nmax
/
cm21 (nujol) 3500–2800br (OH), 1645, 1610, 1277, 1252,
1184, 830; 1H NMR (acetone-d6) d 1.66 (s, 3H, H-400), 1.82
(s, 3H, H-500), 3.5700(d, 2H, J¼6.9 Hz, H-100), 5.34 (m, 1H,
J¼1.5, 6.9 Hz, H-2 ), 6.34 (s, 1H, H-6), 6.63 (s, 1H, H-3),
7.05 (d, 2H, J¼9.0 Hz, H-30, 50), 7.96 (d, 2H, J¼9.0 Hz,
H-20, 60), 9.22 (1H, br s, 40-OH), 9.58 (1H, br s, 7-OH), 12.96
(5-OH); 13C NMR (acetone-d6, 75 MHz) d 18.22 (C-500),
22.47 (C-100), 25.94 (C-400), 99.38 (C-6), 104.01 (3), 105.47
(4a),00107.45 (C-8), 0116.95 (C-30, 50), 123.63 (C-10), 123.77
(C-2 ), 129.31 (C-20, 60), 132.11 (300), 156.07 (C-8a), 161.06
(C-5), 161.87 (C-4 ), 162.19 (C-7), 165.08 (C-2), 183.46
(C-4); EIMS m/z (%) 338 (Mþ, 27), 283 (8), 270 (25), 86
(100). Anal. calcd for C20H18O5.H2O: C, 67.41; H, 5.66.
Found: C, 67.44; H, 5.42.
3.1.6. 7,40-Diacetoxy-5-(3-methylbut-2-enyloxy)flavone
(7). Reaction of 7,40-diacetoxy-5-hydroxyflavone (0.37 g,
1.045 mmol) and 3-methyl-2-buten-1-ol (0.149 ml,
1.467 mmol) in the presence of diethyl azodicarboxylate
(0.273 ml, 1.568 mmol) and triphenylphosphine (0.33 g,
1.26 mmol) in dry THF (25 ml), as described for the
preparation of 4, afforded after purification using silica gel
(EtOAc/hexane 2:3) 7,40-diacetoxy-5-(3-methyl-but-2-enyl-
oxy)flavone 7 as a white solid (0.31 g, 70%). Mp 140–
1428C (from diethyl ether); nmax/cm21 (nujol) 1753, 1698,
1658, 1532, 1224, 1168, 1144, 1049, 1018; 1H NMR
(CDCl3) d 1.76 (s, 3H, H-400), 1.80 (s, 3H, H-500), 2.34 (s, 3H,
CH3COO), 2.35 (s, 3H, CH3COO), 4.80 (d, 2H, J¼6.6 Hz,
H-100), 5.69 (m, 1H, J¼1.5, 6.6 Hz, H-200), 6.69 (d, 1H,
J¼2.1 Hz, H-8), 6.76 (s, 1H, H-3), 7.06 (0d, 1H, J¼2.1 Hz,
H-6), 7.36 (d, 2H, J¼8.7 Hz, H-30, 5 ), 7.95 (d, 2H,
J¼8.7 Hz, H-20, 60); 13C NMR (CDCl3, 75 MHz) d 18.42
(C-400), 21.15 (CH3COO), 21.24 (CH3COO), 25.80 (C-500),
66.76 (C-100), 102.50 (C-8),00102.97 (C-6), 109.86 (C-3),
112.85 (C-4a), 118.90 (C-2 ), 122.22 (C-30, 50), 127.34
(C-20, 60), 128.86 (C-10), 138.13 (C-300), 152.96 (C-40),
154.38 (C-8a), 158.53 (C-7), 160.01 (C-2), 160.18 (C-5),
168.44 (CH3COO), 168.99 (CH3COO), 177.23 (C-4);
EIMS m/z (%) 422 (Mþ, 9), 354 (23), 312 (Mþ2OAc,
61), 270 (Mþ22OAc, 100), 153 (9), 118 (9). Anal. calcd
for C24H22O7: C, 68.24; H, 5.25. Found: C, 67.96; H,
5.37.
Acknowledgements
This work was funded by the Food Standards Agency (FSA)
under contracts T05001 and T05023.
References
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