P. Pahari et al. / Tetrahedron 72 (2016) 3324e3334
3331
H), 7.02 (d, 1H, J¼9.0 Hz, C600-H), 6.71 (s, 1H, C30-H), 6.41 (s, 1H, C300-
H), 6.38 (d, 1H, J¼9.0 Hz, C500-H), 5.99 (s, 1H, C2-H), 5.96e5.82 (m,
1H, C2000-H), 5.08e4.98 (m, 2H, C3000-H2), 3.71 (s, 3H, OCH3), 3.69 (s,
3H, OCH3), 3.67 (s, 3H, OCH3), 3.66 (s, 3H, OCH3), 3.64 (s, 3H,
CO2CH3), 3.32 (d, 2H, J¼6.5 Hz, C1000-H); 13C NMR (CDCl3, 125 MHz)
(CH), 98.6 (CH), 33.9 (CH2); HRMS (EIþ) m/z 308.0681 ([M]þ
C18H12O5, requires 308.0685).
4.1.21. 9-Hydroxy-2-(3-methylbut-2-en-1-yl)-6H-benzofuro[3,2-c]
chromen-6-one (29). Grubb’s second-generation catalyst (3 mg,
0.0035 mmol) was added to a degassed solution of 25 (20 mg,
0.07 mmol) in CH2Cl2 (10 mL) and 2-methyl-2-butene (2 mL). The
solution was heated in a sealed tube at 100 ꢁC for 15 min by a mi-
crowave reactor (Biotage Initiator 2.0, standard configuration, tem-
perature control, external IR temperature sensor, fixed hold time).
CH2Cl2 was removed in vacuum, and the mixture was purified by
d
193.3 (C), 170.3 (C), 160.0 (C), 157.5 (C), 153.0 (C), 150.8 (C), 135.6
(CH), 135.3 (CH), 129.7 (CH), 123.7 (C), 115.9 (CH2), 115.1 (C), 113.3
(C), 111.5 (CH), 103.8 (CH), 98.0 (CH), 56.9 (CH3), 55.3 (CH3), 55.1
(CH3), 54.9 (CH3), 54.7 (CH3), 51.6 (CH), 34.0 (CH2); HRMS (EIþ) m/z
414.1677 ([M]þ C23H26O7, requires 414.1679).
4.1.17. 2-Allyl-9-hydroxy-6H-benzofuro[3,2-c]chromen-6-one
(25). This compound was prepared by the BBr3 mediated deme-
thylative cyclization of 21 as described for the synthesis of 14. Yield
72%; Rf 0.3 (1:1 ethyl acetate:hexane); mp 217e219 ꢁC; nmax (film)
cmꢂ1 1707, 1625, 1508, 1250, 1076; 1H NMR (DMSO-d6, 500 MHz)
reverse phase semipreparative HPLC (symmetry C18, 7 mm, solvent
gradient 9:1 CH3CN:H2O) to get compound 29 (17 mg, 77%) as
a white solid. Rf 0.4 (1:1 ethyl acetate:hexane); mp 110e112 ꢁC; nmax
1
(film) cmꢂ1 1735, 1629, 1508, 1443, 1375, 1093; H NMR (DMSO-d6,
500 MHz)
d
7.91 (d, 1H, J¼8.0 Hz, C7-H), 7.73 (s, 1H, C1-H), 7.40e7.32
d
10.29 (br s, 1H, OH), 7.65 (d, 1H, J¼8.0 Hz, C7-H), 7.61 (s, 1H, C1-H),
(m, 2H, C4-H & C3-H), 7.14 (s,1H, C10-H), 6.97 (d,1H, J¼8.0 Hz, C8-H),
7.39e7.34 (m, 2H, C4-H & C3-H), 7.11 (d, 1H, J¼2.0 Hz, C10-H), 6.92
(dd, 1H, J¼8.0, 2.0 Hz, C8-H), 6.00e5.92 (m, 1H, C20-H), 5.18e5.05
(m, 2H, C30-H2), 3.41 (d, 2H, J¼7.0 Hz, C10-H2); 13C NMR (DMSO-d6,
5.35 (t,1H, J¼6.0 Hz, C20-H), 3.44 (d, 2H, J¼6.0 Hz, C10-H2), 1.77 (s, 3H,
CH3), 1.75 (s, 3H, CH3); 13C NMR (DMSO-d6, 125 MHz)
d 159.7 (C),
158.8 (C), 156.9 (C),156.3 (C),151.8 (C),138.8 (C),133.9 (C),131.9 (CH),
129.6 (CH), 122.4 (CH), 122.2 (CH), 120.6 (C), 117.5 (CH), 114.4 (C),
112.8 (CH), 106.1 (C), 99.2 (CH), 33.9 (CH2), 26.0 (CH3), 18.1 (CH3);
HRMS (EIþ) m/z 320.1053 ([M]þ C20H16O4, requires 320.1049).
125 MHz)
d 158.5 (C), 157.9 (C), 157.7 (C), 156.6 (C), 151.3 (C), 137.2
(CH), 137.1 (C), 132.3 (CH), 121.4 (CH), 120.5 (CH), 117.3 (CH), 117.0
(CH2), 114.7 (C), 114.6 (C), 112.1 (CH), 105.5 (C), 98.9 (CH), 26.1 (CH2);
HRMS (EIþ) m/z 292.0733 ([M]þ C18H12O4, requires 292.0736).
4.1.22. 3-Hydroxy-2-(3-methylbut-2-en-1-yl)-6H-benzofuro[3,2-c]
chromen-6-one (30). This white solid compound was prepared by
the Grubb’s metathesis reaction of 26, following the same pro-
cedure as described for the synthesis of 29. Yield 72%; Rf 0.4 (1:1
ethyl acetate:hexane); mp 238e240 ꢁC; nmax (film) cmꢂ11719, 1635,
4.1.18. 2-Allyl-3-hydroxy-6H-benzofuro[3,2-c]chromen-6-one
(26). The BBr3 mediated demethylative cyclization of 22 to syn-
thesize this compound was similar to that described for the syn-
thesis of 14. Yield 75%; Rf 0.3 (1:1 ethyl acetate:hexane); mp
262e264 ꢁC; nmax (film) cmꢂ1 1697, 1625, 1597, 1419, 1257, 1141,
1418, 1260, 1141, 1007; 1H NMR (DMSO-d6, 500 MHz)
d 7.92 (d, 1H,
1012; 1H NMR (Acetone-d6, 500 MHz)
d
8.01e7.96 (m, 1H, C7-H),
J¼8.0 Hz, C7-H), 7.85 (d, 1H, J¼8.0 Hz, C10-H), 7.69 (s, 1H, C1-H),
7.52e7.44 (m, 2H, C8-H & C9-H), 6.95 (s, 1H, C4-H), 5.37 (t, 1H,
J¼6.0 Hz, C20-H), 3.33 (d, 2H, J¼6.0 Hz, C10-H2),1.75 (s, 3H, CH3),1.71
7.75 (s, 1H, C1-H), 7.74e7.72 (m, 1H, C10-H), 7.50e7.46 (m, 2H, C8-H
& C9-H), 7.00 (s, 1H, C4-H), 6.12e6.06 (m, 1H, C20-H), 5.25e5.10 (m,
2H, C30-H2), 3.52 (d, 2H, J¼7.0 Hz, C10-H2); 13C NMR (Acetone-d6,
(s, 3H, CH3); 13C NMR (DMSO-d6, 125 MHz)
d 160.7 (C), 159.8 (C),
125 MHz)
d
160.9 (C), 159.3 (C), 157.5 (C), 155.1 (C), 154.3 (C), 136.2
157.6 (C), 154.5 (C), 153.6 (C), 132.6 (C), 126.7 (C), 126.1 (CH), 125.2
(CH), 123.2 (C), 121.6 (CH), 121.5 (CH), 120.3 (CH), 112.0 (CH), 103.4
(C), 102.5 (CH), 101.6 (C), 27.5 (CH2), 25.6 (CH3), 17.7 (CH3); HRMS
(EIþ) m/z 320.1051 ([M]þ C20H16O4, requires 320.1048).
(CH), 125.1 (CH), 124.0 (C), 123.8 (C), 123.0 (C), 122.4 (CH), 120.7 (C),
115.8 (CH), 111.7 (CH2), 104.5 (C), 102.8 (CH), 33.1 (CH2); HRMS (EIþ)
m/z 292.0733 ([M]þ C18H12O4, requires 292.0735).
4.1.19. 2-Allyl-3,8-dihydroxy-6H-benzofuro[3,2-c]chromen-6-one
(27). This white solid compound was prepared by the BBr3 medi-
ated demethylative cyclization of 23 following a similar protocol for
the synthesis of 14. Yield 71%; Rf 0.3 (1:4:12 methanol:ethyl ace-
tate:hexane); mp 322e324 ꢁC; nmax (film) cmꢂ1 1724, 1636, 1599,
4.1.23. 3,8-Dihydroxy-2-(3-methylbut-2-en-1-yl)-6H-benzofuro[3,2-
c]chromen-6-one (31). The Grubb’s metathesis reaction for the
synthesis of this compound from 27 is similar to that described for
29. Yield 79%; Rf 0.5 (1:4:12 methanol:ethyl acetate:hexane);
mp>360 ꢁC, chars at 240 ꢁC; nmax (film) cmꢂ11718,1630,1426,1268,
1420, 1272, 1163, 1009; 1H NMR (DMSO-d6, 500 MHz)
d
10.74 (br s,
1163, 1005; 1H NMR (DMSO-d6, 500 MHz)
d 9.72 (br s, 1H, OH), 7.63
1H, OH), 9.60 (br s,1H, OH), 7.49 (d,1H, J¼9.0 Hz, C10-H), 7.46 (s,1H,
C1-H), 7.19 (d,1H, J¼3.0 Hz, C7-H), 6.83 (dd,1H, J¼9.0, 3.0 Hz, C9-H),
6.81 (s, 1H, C4-H), 6.05e5.95 (m, 1H, C20-H), 5.20e5.05 (m, 2H, C30-
H2), 3.30 (d, 2H, J¼6.5 Hz, C10-H2); 13C NMR (DMSO-d6, 125 MHz)
(s, 1H, C1-H), 7.61 (d, 1H, J¼9.0 Hz, C10-H), 7.24 (d, 1H, J¼2.5 Hz, C7-
H), 6.92 (s, 1H, C4-H), 6.88 (dd, 1H, J¼9.0, 2.5 Hz, C9-H), 5.34 (t, 1H,
J¼8.0 Hz, C20-H), 3.31 (d, 2H, J¼8.0 Hz, C10-H2),1.73 (s, 3H, CH3),1.70
(s, 3H, CH3); 13C NMR (DMSO-d6, 125 MHz)
d 161.1 (C), 159.8 (C),
d
160.8 (C), 159.3 (C), 157.5 (C), 155.1 (C), 153.4 (C), 148.4 (C), 136.1
157.8 (C), 155.3 (C), 153.5 (C), 148.5 (C), 132.7 (C), 126.7 (C), 124.2
(CH), 121.7 (CH), 121.3 (CH), 114.2 (C), 112.4 (CH), 105.2 (CH), 103.6
(C), 102.5 (C), 101.7 (CH), 27.6 (CH2), 25.7 (CH3), 17.7 (CH3); HRMS
(EIþ) m/z 336.0999 ([M]þ C20H16O5, requires 336.0997).
(CH), 125.0 (C), 124.0 (CH), 121.6 (CH), 116.5 (CH2), 114.1 (C), 112.2
(C), 105.2 (CH), 103.6 (C), 102.3 (CH), 101.7 (CH), 33.0 (CH2); HRMS
(EIþ) m/z 308.0691 ([M]þ C18H12O5, requires 308.0684).
4.1.20. 3-Allyl-2,9-dihydroxy-6H-benzofuro[3,2-c]chromen-6-one
(28). This white solid compound was prepared by the BBr3 medi-
ated demethylative cyclization of 24, similar to that described for
the preparation of 14. Yield 74%; Rf 0.3 (1:4:12 methanol:ethyl
acetate:hexane); mp 285e290 ꢁC; nmax (film) cmꢂ1 1686, 1555,
4.1.24. 2,9-Dihydroxy-3-(3-methylbut-2-en-1-yl)-6H-benzofuro[3,2-
c]chromen-6-one (32). This white solid compound was produced
by the Grubb’s metathesis reaction of 28, following the same pro-
cedure as described for the synthesis of 29. Yield 82%; Rf 0.5 (1:4:12
methanol:ethyl acetate:hexane); mp>360 ꢁC, chars at 230 ꢁC; nmax
(film) cmꢂ1 1685, 1629, 1560, 1438, 1383, 1251, 1097; 1H NMR
1415, 1245, 1101, 1025; 1H NMR (DMSO-d6, 500 MHz)
d 10.06 (br s,
1H, OH), 7.66 (d, 1H, J¼8.5 Hz, C7-H), 7.19 (s, 1H, C1-H), 7.15 (s, 1H,
C10-H), 7.14 (s, 1H, C4-H), 6.92 (d, 1H, J¼8.5 Hz, C8-H), 6.05e5.85
(m,1H, C20-H), 5.20e5.00 (m, 2H, C30-H2), 3.33 (d, 2H, J¼6.0 Hz, C10-
(DMSO-d6, 500 MHz)
d
10.20 (br s, 1H, OH), 7.72 (d, 1H, J¼8.0 Hz,
C7-H), 7.25 (s, 1H, C1-H), 7.24 (s, 1H, C10-H), 7.21 (s, 1H, C4-H), 6.97
(d, 1H, J¼8.0 Hz, C8-H), 5.32 (t, 1H, J¼7.5 Hz, C20-H), 3.33 (d, 2H,
J¼7.5 Hz, C10-H2), 1.72 (s, 3H, CH3), 1.70 (s, 3H, CH3); 13C NMR
H2); 13C NMR (DMSO-d6, 125 MHz)
d 158.3 (C), 157.5 (C), 157.4 (C),
156.2 (C), 152.0 (C), 146.1 (C), 135.8 (CH), 132.0 (C), 120.9 (CH), 117.7
(CH), 116.5 (CH2), 114.6 (C), 114.2 (CH), 110.4 (C), 104.7 (C), 104.4
(DMSO-d6, 125 MHz) d 159.0 (C), 158.1 (C), 157.9 (C), 156.7 (C), 152.6
(C), 146.7 (C), 134.1 (C), 133.4 (C), 121.7 (CH), 121.4 (CH), 117.8 (CH),