Racemic Modifications of Aiphanol and Three Congeners
249
3ꢀ,4ꢀ-Bis(tert-butyldimethylsiloxy)-3,5-
dihydroxystilbene (15)
the ensuing mixture heated at reflux for 6 h. The resulting mix-
ture was cooled, concentrated under reduced pressure, and the
residue dissolved in ethyl acetate (50 mL). The ensuing solution
was washed with brine (1 × 20 mL) and water (1 × 20 mL) then
the separated organic layer was dried (MgSO4), filtered, and the
filtrate concentrated under reduced pressure. The residue thus
obtained was subjected to column chromatography (silica, 1:1
v/v ethyl acetate/hexane elution) to afford, upon concentration
of the appropriate fractions (RF 0.5), the title compound 16[30,31]
(1.91 g, 90%) as a white, crystalline solid, mp 89–91◦C (lit.[31]
91–92◦C). νmax/cm−1 3408(br), 2948, 2842, 1702, 1632, 1514,
1456, 1339, 1285, 1216, 1112, 1041, 978, 828. δH (300 MHz,
CDCl3) 7.61 (1H, d, J 15.9), 6.77 (2H, s, ArH), 6.31 (1H, d, J
15.9), 5.76 (1H, br s, OH), 3.93 (6H, s), 3.80 (3H, s). δC (75 MHz,
CDCl3) 167.7, 147.3, 145.3, 137.3, 126.0, 115.7, 105.2, 56.6,
52.0. m/z (EI, 70 eV) 238 (M+•, 100%), 223 (5), 207 (30), 163
(21), 135 (16), 121 (14), 77 (12), 65 (16). Found: M+• 238.0838.
C12H14O5 requires 238.0841.
A magnetically stirred suspension of phosphonium salt 7
(401 mg, 0.9 mmol) in deoxygenated dry THF (10 mL) main-
tained at −78◦C (dry-ice/acetone bath) under an oxygen-free
nitrogen atmosphere was treated, dropwise over 10 min, with
BunLi (2.7 mL of a 1 M solution in hexane, 2.7 mmol). The
resulting red solution was warmed to 18◦C then stirred at this
temperature for 0.33 h. Next, a solution of aldehyde 8 (320 mg,
0.9 mmol) in deoxygenated and dry THF (5 mL) was added,
via cannula, to the by now deep-red reaction mixture. Stir-
ring was continued for a further 18 h at 18◦C then the reaction
mixture was quenched with cold HCl (5 mL of a 0.5 M aque-
ous solution), diluted with water (10 mL), and extracted with
ethyl acetate (3 × 30 mL). The combined ethyl acetate extracts
were washed with brine (1 × 30 mL) then dried (MgSO4), fil-
tered, and concentrated under reduced pressure.The residue thus
obtained was subjected to column chromatography (silica, 3:7
v/v ethyl acetate/hexane elution) to afford, upon concentration of
the appropriate fractions [RF 0.3(5)], the title compound 15[26]
(280 mg, 67%) as a brown gum. νmax/cm−1 3354(br), 2956,
2930, 2858, 1595, 1510, 1472, 1288, 1254, 1156, 909, 839,
782. δH (300 MHz, CDCl3) 6.96 (2H, m), 6.90 (1H, d, J 16.1),
6.80 (1H, d, J 7.1, ArH), 6.73 (1H, d, J 16.1), 6.54 (2H, d, J
2.2, ArH), 6.26 (1H, t, J 2.2, ArH), 1.01 (9H, s), 0.99 (9H, s),
0.23 (6H, s), 0.22 (6H, s) (signals due to hydroxy-group protons
not observed). δC (75 MHz, CDCl3) 157.0, 147.2, 147.1, 140.5,
130.9, 129.5, 126.3, 121.4, 120.4, 119.5, 106.2, 102.2, 26.4,
26.3, 18.9, 18.8, −3.6 (one signal obscured or overlapping). m/z
(EI, 70 eV) 472 (M+•, 47%), 415 (49), 301 (12), 115 (35), 73
(100). Found: M+• 472.2470. C26H40O4Si2 requires 472.2465.
Sinapic Alcohol (6)
A magnetically stirred solution of ester 16 (1.61 g, 6.8 mmol) in
freshly distilled toluene (50 mL) maintained at 0◦C (ice/water
bath) under an atmosphere of nitrogen was treated, dropwise
over 10 min, with DIBAL-H (24 mL of a 1 M solution in hexane,
2.4 mmol). After addition was complete, stirring was continued
for 1 h at 0◦C then the reaction mixture was slowly quenched
(CAUTION!) with ethanol (10 mL). The solvent was partially
removed under reduced pressure then water (20 mL) was added
to the residue, and the resulting gelatinous precipitate of alu-
minium salts was extracted with ethyl acetate (4 × 50 mL).
The combined ethyl acetate extracts were washed with brine
(1 × 50 mL) and water (1 × 50 mL) then dried (MgSO4), fil-
tered, and concentrated under reduced pressure. The resulting
oil was crystallized (DCM/hexane) to afford the title compound
6[27] (1.14 g, 80%) as a pale-yellow solid, mp 64–65◦C (lit.[27]
66.5–67.3◦C). νmax/cm−1 3485(br), 2938, 2840, 1606, 1516,
1455, 1424, 1333, 1216, 1115, 966, 846, 807, 730. δH (300 MHz,
CDCl3) 6.61 (2H, s, ArH), 6.47 (1H, dt, J 1.2 and 15.9), 6.23
(1H, dt, J 5.9 and 15.9), 5.41 (1H, br s, OH), 4.29 (2H, dd, J 1.2
and 5.9), 3.88 (6H, s) (signal due to one hydroxy-group proton
not observed). δC (75 MHz, CDCl3) 147.3, 134.9, 131.6, 128.4,
126.8, 103.5, 64.1, 56.6. m/z (EI, 70 eV) 210 (M+•, 100%), 167
(78), 154 (45), 149 (34), 121 (26), 107 (18), 91 (21), 77 (33).
Found: M+• 210.0891. C11H14O4 requires 210.0892.
(E)-3,3ꢀ,4,5ꢀ-Tetrahydroxystilbene (5)
Tetra-n-butylammonium fluoride (TBAF, 2.0 mL of a 1 M solu-
tion in THF, 2.0 mmol) was added to a magnetically stirred
solution of the bis-silylated stilbene 15 (230 mg, 0.5 mmol) in
dry THF (5 mL) maintained at 0◦C (ice/water bath) under an
atmosphere of nitrogen. After 5 min, and at which point TLC
analysis revealed no starting material remained, the reaction
mixture was quenched with ice/water (5 mL) then extracted
with ethyl acetate (3 × 20 mL). The combined organic extracts
were washed with brine (1 × 20 mL) then dried (MgSO4), fil-
tered, and concentrated under reduced pressure.The residue thus
obtained was subjected to column chromatography (silica, 3:2
v/v ethyl acetate/hexane elution) to afford, upon concentration
of the appropriate fractions (RF 0.3), the title compound 5[25,26]
(120 mg, 91%) as a light-brown solid, mp 232–234◦C (lit.[25]
229◦C). νmax/cm−1 3307(br), 2955, 2928, 2857, 1689, 1598,
1510, 1462, 1295, 1255, 1154, 782. δH (300 MHz, [D6]acetone)
8.15 (4H, br s, OH), 7.07 (1H, d, J 2.1, ArH), 6.95 (1H, d,
J 16.4), 6.90 (1H, dd, J 2.1 and 8.2, ArH), 6.82 (1H, d, J 16.4),
6.80 (1H, d, J 8.2, ArH), 6.52 (2H, d, J 2.2, ArH), 6.26 (1H, t,
J2.2,ArH). δC (75 MHz, [D6]acetone)158.8, 145.4(0), 145.3(6),
140.1, 130.0, 128.7, 126.2, 119.3, 115.5, 113.1, 105.0, 101.9.
m/z (EI, 70 eV) 244 (M+•, 100%), 227 (17), 197 (41), 178 (63).
Found: M+• 244.0735. C14H12O4 requires 244.0736.
5-[(1E)-2-[(2S,3S)-2,3-Dihydro-3-(4-hydroxy-3,5-
dimethoxyphenyl)-2-(hydroxymethyl)-1,4-
benzodioxin-6-yl]ethenyl]benzene-1,3-diol (1),
5-[(1E)-2-[(2R,3S)-2,3-Dihydro-3-(4-hydroxy-3,5-
dimethoxyphenyl)-2-(hydroxymethyl)-1,4-
benzodioxin-6-yl]ethenyl]benzene-1,3-diol (2),
5-[(1E)-2-[(2R,3R)-2,3-Dihydro-3-(4-hydroxy-3,5-
dimethoxyphenyl)-2-(hydroxymethyl)-1,4-
benzodioxin-7-yl]ethenyl]benzene-1,3-diol (3), and
5-[(1E)-2-[(2R,3S)-2,3-Dihydro-3-(4-hydroxy-3,5-
dimethoxyphenyl)-2-(hydroxymethyl)-1,4-
benzodioxin-7-yl]ethenyl]benzene-1,3-diol (4)
A magnetically stirred solution of stilbene 5 (94 mg, 0.38 mmol)
and alcohol 6 (81 mg, 0.38 mmol) in benzene/acetone (30 mL of
a 2:1 v/v mixture) was heated at 60◦C for 0.25 h then treated,
in one portion, with silver carbonate (107 mg, 0.38 mmol). The
resulting mixture was heated at 60◦C for 18 h then cooled and the
Methyl Sinapate (16)
A magnetically stirred solution of sinapic acid (9) (2.0 g,
9.3 mmol, ex. Aldrich Chemical Co.) in anhydrous methanol
(20 mL) was treated with H2SO4 (2 drops of 98% material) and