6052
M. Barontini et al. / Tetrahedron 66 (2010) 6047e6053
substrate disappeared (24 h), the acetone was evaporated under
reduced pressure. The mixture was neutralised by 1 M HCl and the
product was extracted with ethyl acetate (3ꢂ10 mL). The organic
layers were washed with a saturated solution of NaCl and dried
over dry Na2SO4. The product was obtained pure in quantitative
yield.
H-7,8,30,40,50), 7.86e7.91 (2H, m, H-20,60). 13C NMR (50 MHz, CDCl3):
d
57.2, 61.9, 108.0, 113.4, 117.2, 119.1, 126.1, 129.0, 131.4, 133.8, 147.9,
150.0, 151.6, 161.6, 178.1. m/z: 282 (Mþ, 33), 267 (100), 239 (29), 165
(21), 133 (43), 102 (35), 77 (40). Anal. Calcd for C17H14O4 (282.29): C,
72.33; H, 5.00; O, 22.67. Found: C, 72.40; H, 5.08; O, 22.52.
4.4.2. 7,8-Dimethoxyflavone (18). Yellow solid (282 mg; yield:
>98%). Mp 145e147 ꢀC (lit.40 147e148 ꢀC). 1H NMR (200 MHz,
4.3.1. 5,6-Dimethoxyflavanone (15). Yellow solid (270 mg; yield:
95%). Mp 140e142 ꢀC (lit.37 142e144 ꢀC). 1H NMR (200 MHz, CDCl3)
CDCl3)
d
3.99 (s, 3H), 4.00 (s, 3H), 6.77 (s, 1H), 7.04 (d, 1H, J¼9.0 Hz),
d
2.81 (dd, 1H, J1¼16.7 and J2¼3.2 Hz), 3.02 (dd, 1H, J1¼16.7 and
7.51e7.54 (m, 3H), 7.93e7.98 (m, 3H). 13C NMR (50 MHz, CDCl3)
J2¼12.9 Hz), 3.79 (s, 3H), 3.88 (s, 3H), 5.36 (dd, 1H, J1¼3.2 and
J2¼12.9 Hz), 6.76 (d, 1H, J¼9.0 Hz), 7.10 (d, 1H, J¼9.0 Hz), 7.31e7.46
d 56.5, 61.6, 106.9, 109.9, 118.6, 121.0, 126.2, 129.1, 131.5, 131.9, 137.0,
150.6, 156.7, 163.0, 178.1. m/z 282 (Mþ, 100), 267 (33), 239 (17), 165
(53),137 (59), 109 (37), 66 (30). Anal. Calcd for C17H14O4 (282.29): C,
72.33; H, 5.00; O, 22.67. Found: C, 72.38; H, 5.08; O, 22.54.
(m, 5H). 13C NMR (50 MHz, CDCl3)
d 46.2, 57.2, 60.4, 79.0, 112.8,
116.0, 121.2, 126.1, 128.7, 128.8, 138.8, 147.7, 149.7, 156.1, 190.9. m/z
284 (Mþ, 36.5),180 (100), 165 (84),137 (39),109 (12). Anal. Calcd for
C17H16O4 (284.31): C, 71.82; H, 5.67; O, 22.51. Found: C, 71.90; H,
5.72; O, 22.38.
4.4.3. 5,7,30,40-Tetramethoxyflavone (20) (methylated luteolin). Yel-
low oil (281 mg; yield: 90%). Mp 190e194 ꢀC (lit.41 193 ꢀC). Spec-
troscopic data were according to the literature.41
4.3.2. 7,8-Dimethoxyflavanone (17). Yellow solid (284 mg; yield:
>98%). Mp 112e115 ꢀC (lit.38 114 ꢀC). Spectroscopic data were
according to the literature.38
4.4.4. 5,7,30-Trimethoxyflavone (23) (methylated apigenin). Yellow
solid (275 mg; yield: 88%). Mp 154e156 ꢀC (lit.41 157 ꢀC). Spectro-
scopic data were according to the literature.41
4.3.3. 5,7,30,40-Tetramethoxyflavanone (19) (methylated hesperetin).
Yellow oil (327 mg; yield: 95%). Spectroscopic data were according
to the literature.9a,b
4.4.5. 5-Methoxyflavone (25). White solid (252 mg; yield: >98%).
Mp 130e134 ꢀC (lit.42 131 ꢀC). Spectroscopic data were according to
the authentic commercial sample.
4.3.4. 5,7,30-Trimethoxyflavanone (22) (methylated naringenin).
Yellow oil (314 mg; yield: >98%). Spectroscopic data were accord-
ing to the literature.9a,b
4.4.6. 6-Methoxyflavone (27). White solid (202 mg; yield: 80%). Mp
164 ꢀC (lit.43 161e163 ꢀC). Spectroscopic data were according to the
authentic commercial sample.
4.4. General procedure for the dehydrogenation of
methylated flavanones
4.4.7. 7-Methoxyflavone (29). White solid (189 mg; yield: 75%). Mp
109e110 ꢀC (lit.44 110 ꢀC). Spectroscopic data were according to the
authentic commercial sample.
Dehydrogenation with homogeneous IBX. To a solution of sub-
strate (1.0 mmol) solubilised in DMSO (10 mL) was added IBX
(2.0 equiv), which was then stirred at 90 ꢀC for 24 h. At the end,
ethyl acetate was added to the mixture, then it was treated with
a solution of NaHCO3. The aqueous phase was extracted with ethyl
acetate. The organic phases were washed with a saturated solution
of NaCl and dried over Na2SO4. After evaporation of the solvent, the
corresponding flavones were isolated by chromatographic purifi-
cation on silica gel (230e400 mesh).
Acknowledgements
The authors are grateful to Dr. Gianfranco Provenzano for the
preparation of some samples. The University of Tuscia and Minis-
tero della Ricerca Scientifica e Tecnologica are acknowledged for
their financial support.
Dehydrogenation with homogeneous IBX and NMO. IBX
(1.2 mmol) and NMO (1.2 mmol) were added to DMSO (2.5 mL) and
stirred at room temperature until complete dissolution
(15e60 min). Then, the substrate was added (1.0 mmol), the mix-
ture was stirred and the reaction was monitored by TLC. The mix-
ture was diluted with a solution of NaHCO3 and extracted with
diethyl ether. The organic extracts were evaporated and dried over
Na2SO4. Finally, the organic phase was concentrated and the
product was purified by a chromatographic column of silica gel.
Dehydrogenation with polymer-supported IBX. The substrate
(1.0 mmol) was solubilised in DMSO (10 mL) at 90 ꢀC under mag-
netic stirring, then commercial polymer-supported IBX (3.0 mmol)
was added. When the substrate disappeared, the polymer was re-
covered by simple filtration. The products were extracted with
ethyl acetate. The organic phases were washed with a saturated
solution of NaCl and dried over Na2SO4. After evaporation of the
solvent, the corresponding flavones were isolated. Polymer-sup-
ported IBX was regenerated by treating the filtered resin with
a solution of tetrabutylammonium oxone and methanesulphonic
acid according to the procedure reported by us previously.17d,e
References and notes
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4.4.1. 5,6-Dimethoxyflavone (16). Yellow solid (268 mg; yield: 95%).
Mp 192e194 ꢀC (lit.39 196 ꢀC). 1H NMR (200 MHz, CDCl3):
d
3.92
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(3H, s, OCH3), 3.96 (3H, s, OCH3), 6.70 (1H, s, H-3), 7.46e7.54 (5H, m,