LETTER
Towards the Synthesis of Platachromone B
1119
thick-layer chromatography using dichloromethane as
2-styryl-9,10-dihydropyrano[2,3-f]chromen-4(8H)-ones.
Attempts to improve the yields and to obtain the natural
derivatives are under way.
eluent. After solvent evaporation and recrystallization of the
residue from EtOH, (E)-5-hydroxy-7-methoxy-6-(3-
methylbut-2-en-1-yl)-2-styryl-4H-chromen-4-ones 13a,b
were obtained.
(14) (E)-5-Hydroxy-7-methoxy-6-(3-methylbut-2-en-1-yl)-2-
styryl-4H-chromen-4-one (13b): Yield: 10%; yellow
powder; mp 160–161 °C. 1H NMR (300.13 MHz, CDCl3): δ
= 1.69 and 1.80 [s, 6 H, 6-CH2CH=C(CH3)2], 3.36 [d, J =
7.1 Hz, 2 H, 6-CH2CH=C(CH3)2], 3.94 (s, 3 H, 7-OCH3),
6.16 (s, 1 H, H-3), 5.22 [t, J = 7.1 Hz, 1 H, 6-
Acknowledgment
Thanks are due to the University of Aveiro, Fundação para a Ciên-
cia e a Tecnologia (FCT, Portugal), the European Union, QREN,
FEDER, COMPETE, for funding the Organic Chemistry Research
Unit (QOPNA) (project PEst-C/QUI/UI0062/2013) and the Portu-
guese National NMR Network (RNRMN). F.R.B. also thanks FCT
and QOPNA for a grant (SFRH/BI/33956/2009).
CH2CH=C(CH3)2], 6.49 (s, 1 H, H-8), 6.75 (d, J = 16.0 Hz,
1 H, H-α), 7.39–7.43 (m, 3 H, H-3′,4′,5′), 7.56–7.60 (m, 2 H,
H-2′,6′), 7.58 (d, J = 16.0 Hz, 1 H, H-β), 12.82 (s, 1 H, 5-
OH). 13C NMR (75.47 MHz, CDCl3): δ = 21.4 [6-
CH2CH=C(CH3)2], 17.8 and 25.8 [6-CH2CH=C(CH3)2],
55.9 (7-OCH3), 89.6 (C-8), 105.7 (C-4a), 109.1 (C-3), 112.9
(C-6), 119.9 (C-α), 121.9 [6-CH2CH=C(CH3)2], 127.7 (C-
2′,6′), 129.0 (C3′,5′), 129.9 (C-4′), 132.0 [6-
References and Notes
(1) (a) Gerwick, W. H.; Lopez, A.; Van Dyune, G. D.; Clardy,
J.; Ortiz, W.; Baez, A. Tetrahedron Lett. 1986, 27, 1979.
(b) Gerwick, W. H. J. Nat. Prod. 1989, 52, 252.
(2) Yoon, J. S.; Lee, M. K.; Sung, S. H.; Kim, Y. C. J. Nat. Prod.
2006, 69, 290.
(3) Yang, L.; Qiao, L.; Xie, D.; Yuan, Y.; Chen, N.; Dai, J.; Guo,
S. Phytochemistry 2012, 76, 92.
(4) Yang, C.-H.; Yang, Y.; Liu, J.-H. Phytochemistry 2013, 6,
387.
CH2CH=C(CH3)2], 134.9 (C-1′), 139.9 (C-β), 156.0 (C-8a),
158.4 (C-5), 161.8 (C-2), 163.3 (C-7), 182.5 (C-4). HRMS
+
(ESI+): m/z calcd for C23H23O4 : 363.1591; found: 363.1595.
(15) Demethylation of Methoxyprenyl-2-styrylchromones
11a–c; General Procedure: A solution of BBr3 in CH2Cl2
(1 M; 2.5 equiv for each methoxy group) was added to a
solution of the appropriate 2-styrylchromones 11a–c (0.25
mmol) in freshly distilled CH2Cl2 (20 mL) and the mixture
was cooled to –78 °C. The solution was then allowed to
warm to r.t. and stirred for 8 to 11 days. After the appropriate
period, H2O (40 mL) was added and the resulting solution
was stirred at r.t. The mixture was then extracted with
EtOAc (3 × 50 mL), and the combined organic layers were
dried over Na2SO4, filtered, and evaporated under reduced
pressure. The resulting residue was purified by column
chromatography using CH2Cl2 as eluent. After solvent
evaporation and recrystallization of the residue (EtOAc–
light petroleum), (E)-5-hydroxy-8,8-dimethyl-2-styryl-9,10-
dihydropyrano[2,3-f]chromen-4(8H)-ones 14a–c were
obtained.
(5) Gomes, A.; Freitas, M.; Fernandes, E.; Lima, J. L. F. C.
Mini-Rev. Med. Chem. 2010, 10, 1.
(6) (a) Jain, N.; Gambhir, G.; Krishnamurty, H. G. Indian J.
Chem., Sect. B: Org. Chem. Incl. Med. Chem. 2001, 40, 278.
(b) Pinto, D. C. G. A.; Silva, A. M. S.; Cavaleiro, J. A. S.
New J. Chem. 2000, 24, 85. (c) Santos, C. M. M.; Silva, A.
M. S.; Cavaleiro, J. A. S. Eur. J. Org. Chem. 2003, 4575.
(7) (a) Gester, S.; Metz, P.; Zierau, O.; Vollmer, G. Tetrahedron
2001, 57, 1015. (b) Yin, Y.; Chen, R.; Zhang, D.; Qiao, L.;
Li, J.; Wang, R.; Liu, X.; Yang, L.; Xie, D.; Zou, J.; Wang,
C.; Dai, J. J. Mol. Catal. B: Enzym. 2013, 89, 28.
(c) Kawamura, T.; Hayashi, M.; Mukai, R.; Terao, J.;
Nemoto, H. Synthesis 2014, 46, 170.
(8) Lee, Y. R.; Li, X.; Lee, S. W.; Yong, C. S.; Hwang, M.-R.;
Lyoo, W. S. Bull. Korean Chem. Soc. 2008, 29, 1205.
(9) Seixas, R. S. G. R.; Pinto, D. C. G. A.; Silva, A. M. S.;
Cavaleiro, J. A. S. Aust. J. Chem. 2008, 61, 718.
(10) Pinto, D. C. G. A.; Silva, A. M. S.; Almeida, L. M. P. M.;
Cavaleiro, J. A. S.; Lévai, A.; Patonay, T. J. Heterocycl.
Chem. 1998, 35, 217.
(16) (E)-5-Hydroxy-2-(4-hydroxystyryl)-8,8-dimethyl-9,10-
dihydropyrano[2,3-f]chromen-4(8H) -one (14b): Yield:
10%; yellow powder; mp 261–262 °C. 1H NMR
(300.13 MHz, acetone-d6): δ = 1.41 [s, 6 H, 8-(CH3)2], 1.96
(t, J = 6.8 Hz, 2 H, H-10), 2.98 (t, J = 6.8 Hz, 2 H, H-9), 6.13
(s, 1 H, H-3), 6.75 (s, 1 H, H-6), 6.95 (d, J = 8.8 Hz, 2 H, H-
3′,5′), 6.99 (d, J = 16.4 Hz, 1 H, H-α), 7.54 (d, J = 16.4 Hz,
1 H, H-β), 7.64 (d, J = 8.8 Hz, 2 H, H-2′,6′), 8.97 (s, 1 H, 4′-
OH), 12.75 (s, 1 H, 5-OH). 13C NMR (75.47 MHz, acetone-
d6): δ = 16.7 (C-9), 26.8 [8-(CH3)2], 32.2 (C-10), 76.8 (C-8),
100.2 (C-3), 100.9 (C-10a), 105.9 (C-4a), 108.4 (C-6), 116.8
(C-3′,5′), 117.7 (C-α), 127.7 (C-1′), 130.6 (C-2′,6′), 138.0
(C-β), 155.4 (C-10b), 160.3 (C-5), 160.6 (C-4′), 161.1 (C-2),
163.8 (C-7), 183.2 (C-4). HRMS (ESI+): m/z calcd for
(11) (E)-2-Styrylchromones 11d,e were prepared according to
the method described in references 6b and 6c.
(12) Selective 5-Demethylation of (E)-2-Styrylchromones
11d,e; General Procedure: AlCl3 (0.3334 g, 2.5 mmol) was
added to a solution of the appropriate 2-styrylchromone
11d,e (0.25 mmol) in MeCN (20 mL). The solution was
heated at reflux for approximately 24 hours. After this
period, ice and water were added and the resulting solid was
filtered. The crude product was purified by column
chromatography using CH2Cl2 as eluent. After solvent
evaporation and recrystallization from EtOH, (E)-5-
hydroxy-7-methoxy-2-styryl-4H-chromen-4-ones 12a,b
were obtained.
(13) Prenylation of (E)-5-Hydroxypolymethoxy-2-
styrylchromones 12a,b; General Procedure: Prenyl
bromide (0.234 mL, 2.04 mmol) was added to a solution of
(E)-5-hydroxypolymethoxy-2-styrylchromones 12a,b
(0.564 mmol) and K2CO3 (0.2340 g, 1.69 mmol) in acetone
(50 mL). The reaction mixture was heated at reflux, under
nitrogen, for 48 h. After this period, the solid K2CO3 was
removed by filtration and the acetone was evaporated under
reduced pressure. The resulting residue was purified by
+
C22H21O5 : 365.1383; found: 365.1381.
(17) 2′-Hydroxy-4′,6′-dimethoxy-3′-(3-methylbut-2-en-1-
yl)acetophenone (7a): Yield: 89%; white powder; mp 115–
116 °C. 1H NMR (300.13 MHz, acetone-d6): δ = 1.63 and
1.75 [s, 6 H, 3′-CH2CH=C(CH3)2], 2.59 (s, 3 H, H-2), 3.24
[d, J = 5.0 Hz, 2 H, 3′-CH2CH=C(CH3)2], 3.96 (s, 3 H, 4′-
OCH3), 3.99 (s, 3 H, 6′-OCH3), 5.17 [t, J = 5.0 Hz, 1 H, 3′-
CH2CH=C(CH3)2], 6.28 (s, 1 H, H-5′), 14.07 (s, 1 H, 2′-OH).
13C NMR (75.47 MHz, acetone-d6): δ = 21.8 [3′-
CH2CH=C(CH3)2], 17.7 and 25.8 [3′-CH2CH=C(CH3)2],
33.2 (C-2), 56.1 (4′,6′-OCH3), 87.5 (C-5′), 106.3 (C-1′),
109.6 (C-3′), 123.7 [3′-CH2CH=C(CH3)2], 131.0 [3′-
CH2CH=C(CH3)2], 163.0 (C-6′), 164.1 (C-2′), 164.4 (C-4′),
204.0 (C-1).
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 1116–1120