A. Sevestre et al. / Tetrahedron 62 (2006) 3969–3976
3975
21.8 (2C7), 25.9 (3C10), 27.0 (C15), 27.9 (C17), 62.0 (C5),
68.2 (C1), 71.6 (C4), 73. 8 (C3), 75.0 (C2), 109.3 (C6), 128.2,
130.0 (C12CC13), 132.8 (C14), 145.0 (C11), 170.0 (C16).
HRMS (ESIC) m/z: [MCHC]: calculated for C23H39O8SiS
503.2135, found 503.2141.
2H8), 0.92 (9H, s, 3H10), 1.39, 1.47 (6H, 2s, 2H7), 3.70 (2H,
m, H4CH5a), 3.85 (1H, dd, J5b–4Z5 Hz, J5b–5aZ12 Hz,
H5b), 4.12 (1H, dd, J1a–2Z6 Hz, J1a–1bZ10 Hz, H1a), 4.19
0
(1H, dd, J1b–2Z8 Hz, J1b–1aZ10 Hz, H1 ), 4.48 (1H, dd,
J3–2Z3 Hz, J3–4Z10 Hz, H3), 4.60 (1H, ddd, J2–3Z3 Hz,
0
0
J2–1aZ6 Hz, J2–1bZ8 Hz, H2), 6.25 (1H, d, J3 –4 Z9 Hz,
4.1.10. 4-O-Acetyl-2,3-O-isopropylidene-1-O-(20-oxo-
benzopyran-70-yl)-5-O-terbutyldimethylsilyl-D (16). The
tetrabutylammonium salt of umbelliferone was obtained by
mixing 616 mg (3.8 mmol, 1 equiv) of umbelliferone with
1.22 g (3.8 mmol, 1 equiv) of tetrabutylammonium bromide
in 10 mL of a NaOH solution (228 mg, 5.7 mmol,
1.5 equiv). After stirring for few minutes, the salt was
extracted with chloroform and the organic phase was dried
on MgSO4 and evaporated under vacuum. Thus 1.5 g of
crude salt was obtained and used without further purifi-
cation. The salt previously obtained was transferred to a
flask containing 200 mg of 15b (0.38 mmol, 1 equiv)
dissolved in 20 mL of anhydrous DMF. The mixture was
then stirred for 96 h at 50 8C under argon. The reaction was
monitored by TLC using cyclohexane/ethyl acetate 6:4 as
eluent. After disappearance of the starting compound,
50 mL of water was added followed by 50 mL of ethyl
acetate, and the aqueous phase was extracted twice with
2!50 mL of ethyl acetate. The organic phase was dried on
MgSO4 and evaporated under vacuum. The crude product
was purified by column chromatography on silica gel using
cyclohexane/ethyl acetate 6:4 as eluent. Compound 16 was
isolated in 60% yield as a white solid.
0
0
0
0
0
H3 ), 6.89 (1H, s, H8 ), 6.92 (1H, d, J6 –5 Z8 Hz, H6 ), 7.36
0
0
0
0
0
0
(1H, d, J5 –6 Z8 Hz, H5 ), 7.63 (1H, d, J4 –3 Z9 Hz, H4 ).
13C NMR (100 MHz, CDCl3) d: K5.2 (2C8), 18.5 (C9), 25.7
(2C7), 26.0 (3C10), 64.4 (C1), 68.1 (C5), 69.5 (C4), 76.1 (C2C
0
C3), 101.9 (C6 ), 109.6 (C6), 112.7 (C8 ), 112.8 (C9 ), 113.3
0
0
0
0
0
0
(C3 ), 128.8 (C5 ), 143.5 (C4 ), 155.8 (C10 ), 161.3 (C7 ), 162.2
0
C C
(C2 ). MS m/z 473 (MCNa ). HRMS m/z: [MCNa ]:
calculated for C23H34NaO7Si 473.1971, found 473.1965.
0
4.1.12.
2,3-O-Isopropylidene-4-oxo-5-O-terbutyl-
dimethylsilyl-70-(2,3,5-trihydroxy-4-oxo-pentyl)oxy-
coumarine (18). Four hundred and ten milligrams
(0.96 mmol, 1.4 equiv) of Dess–Martin reagent were
dissolved in 6 mL of anhydrous dichloromethane. 310 mg
(0.69 mmol, 1 equiv) of compound 17 dissolved in 4 mL of
anhydrous dichloromethane were then added and the
mixture was stirred for 5 h at room temperature. 30 mL of
diethyl ether were poured in followed by 12 mL of a 1.3 M
NaOH solution. The mixture was stirred for 10 min and the
organic layer was washed with 20 mL of water, dried on
MgSO4 and evaporated under reduced pressure to yield
230 mg (74%) of yellow oil, used in the next step without
further purification.
TLC: Rf (cyclohexane/AcOEt 6:4)Z0.42. Mp 95–96 8C. 1H
NMR (400 MHz, CDCl3) d: 0.03 (6H, s, 2H8), 0.87 (9H, s,
3H10), 1.39, 1.47 (6H, 2s, 2H7), 2.03 (3H, s, H12), 3.81
(1H, dd, J5a–4Z4 Hz, J5a–5bZ12 Hz, H5a), 3.92 (1H, dd,
TLC: Rf (cyclohexane/AcOEt 4:6)Z0.69. [a]2D4 K52.2
(c 1, CHCl3). H NMR (400 MHz, CDCl3) d: 0.06 (9H, s,
1
2H8), 0.88 (9H, s, 3H10), 1.40, 1.58 (6H, 2s, 2H7), 4.00 (1H,
0
0
dd, J1–2Z4 Hz, J1–1 Z10 Hz, H1), 4.15 (1H, dd, J1 –2
Z
0
0
J5b–4Z2 Hz, J5b–5aZ12 Hz, H5b), 4.09 (1H, dd, J1a–2
6 Hz, J1a–1bZ10 Hz, H1a), 4.15 (1H, dd, J1b–2Z5 Hz,
J1b–1aZ10 Hz, H1b), 4.48 (1H, dd, J3–2Z6 Hz, J3–4
8 Hz, H3), 4.56 (1H, m, H2), 5.02 (1H, ddd, J4–5bZ2 Hz,
Z
4 Hz, J1 –1Z10 Hz, H1 ), 4.52 (2H, 2s, J5a–5bZ19 Hz, 2H5),
4.77 (1H, ddd, J2–1Z4 Hz, J2–1 Z4 Hz, J2–3Z8 Hz, H2),
4.87 (1H, d, J3–2Z8 Hz, H3), 6.24 (1H, d, J3 –4 Z9 Hz, H3 ),
0
0
0
0
Z
0
0
0
0
6.77 (1H, s, H8 ), 6.79 (1H, d, J6 –5 Z8 Hz, H6 ), 7.33 (1H, d,
J4–5aZ4 Hz, J4–3Z8 Hz, H4), 6.24 (1H, d, J3 –4 Z10 Hz,
J5 –6 Z8 Hz, H5 ), 7.61 (1H, d, J4 –3 Z9 Hz, H4 ). 13C NMR
(100 MHz, CDCl3) d: K5.3 (2C8), 18.4 (C9), 24.9 (2C7),
26.0 (3C10), 66.5 (C1), 68.5 (C5), 76.0 (C2), 76.5 (C3), 102.2
0
0
0
0
0
0
0
0
0
0
0
0
0
H3 ), 6.78 (1H, s, H8 ), 6.82 (1H, d, J6 –5 Z9 Hz, H6 ), 7.36
0
0
0
0
0
0
(1H, d, J5 –6 Z9 Hz, H5 ), 7.62 (1H, d, J4 –3 Z10 Hz, H4 ).
13C NMR (100 MHz, CDCl3) d: K5.4 (2C8), 18.4 (C9), 21.3
(C12), 25.5 (2C7), 25.9 (3C10), 62.3 (C5), 67.3 (C1), 72.0
0
(C6 ), 110.5 (C6), 112.7 (C8 ), 113.2 (C9 ), 113.6 (C3 ), 128.9
0
0
0
0
0
0
0
0
(C5 ), 143.3 (C4 ), 154.8 (C10 ), 161.2 (C2 CC7 ), 206.5 (C4).
HRMS m/z [MCHC]: calculated for C23H33O7Si 449.1996,
found 449.2002.
0
(C2), 74.2 (C4), 75.4 (C3), 101.8 (C6 ), 109.2 (C6), 112.8
0
(C8 ), 113.0 (C9 ), 113.5 (C3 ), 129.0 (C5 ), 143.4 (C4 ), 155.9
0
0
0
0
C
0
0
0
(C10 ), 161.2 (C7 ), 161.8 (C2 ), 170.0 (C11). HRMS (ESI )
m/z: [MCHC]: calculated for C25H37O8Si 493.2258, found
493.2267.
4.1.13. 70-(2,3,5-Trihydroxy-4-oxo-pentyl)oxycoumarine
(3). Eighty six milligrams (0.19 mmol) of compound 18 and
48 mg (0.19 mmol, 1 equiv) of iodine were dissolved in
8 mL of methanol. The mixture was stirred and refluxed for
2 h. After disappearance of the starting compound
(dichloromethane/methanol 9:1), the reaction mixture was
cooled in an ice bath and 30 mg (1.9 mmol, 10 equiv) of
Na2SO3 was added under stirring. After evaporation of
methanol under vacuum and flash chromatography on silica
gel (dichloromethane/methanol 95:5), 32 mg of the final
compound 3 was obtained (56%) as a colourless oil.
4.1.11. 2,3-O-Isopropylidene-1-O-(20-oxo-benzopyran-
70-yl)-5-O-terbutyl-dimethylsilyl-D (17). To a solution of
191 mg (0.39 mmol) of compound 16 in 9 mL of methanol
were added 107 mg (0.77 mmol, 2 equiv) of potassium
carbonate. The mixture was stirred at room temperature for
4 h. After disappearance of the starting compound (cyclo-
hexane/ethyl acetate 4:6), a mixture of ethyl acetate and
water (v/v 1:1) was added and the solution was extracted.
The organic phase was dried under MgSO4 and evaporated
under vacuum to give 141 mg (90%) of compound 17 as a
colourless oil, used without further purification.
TLC: Rf (CH2Cl2/MeOH 9:1)Z0.62. [a]2D4 K16.4 (c 1,
MeOH). 1H NMR (400 MHz, CD3COCD3) d: 4.12 (1H, dd,
J1a–2Z6 Hz, J1a–1bZ10 Hz, H1a), 4.21 (2H, m, H1bCH2),
TLC: Rf (cyclohexane/AcOEt 4:6)Z0.65. [a]2D4 K22.75 (c
0.4, CHCl3). H NMR (400 MHz, CDCl3) d: 0.102 (6H, s,
4.35 (1H, d, J3–2Z5 Hz, H3), 4.52 (2H, 2 d, J5a–5bZ19 Hz,
1
0
0
0
0
2H5), 5.37 (1H, d, J3 –4 Z10 Hz, H3 ), 6.05 (1H, s, H8 ),