948
H. M. L. Da6ies, Q. Jin / Tetrahedron: Asymmetry 14 (2003) 941–949
combined organic extract was dried over MgSO4. The
crude product thus obtained was near pure and was
used directly in the next step without purification.
FTIR (film) 3374 (br), 2954, 2929, 2857, 1601, 1578,
1513, 1471, 1417, 1281, 1254, 1234, 1158, 1128, 1039,
2.58 (ddd, J=13.5, 11.6, 5.0 Hz, 1H), 2.51 (dtd, J=
13.5, 10.7, 6.4 Hz, 1H), 0.99 (s, 9H), 0.86 (s, 9H), 0.14
(s, 6H), 0.00 (s, 3H), −0.03 9s, 3H); 13C NMR (125
MHz, CDCl3) l 177.1, 151.3, 149.7, 144.1, 143.5, 135.9,
131.0, 127.8, 121.5, 121.0, 120.8, 112.5, 111.4, 71.9,
55.56, 55.40, 49.7, 47.4, 41.8, 29.2, 26.0, 25.7, 25.6, 18.4,
18.3, −4.70, −4.72, −4.73, −4.74; MS (FAB) m/z (rela-
tive intensity) 251.1 (54), 347.1 (21), 527.2 (M+−tBu,
100), 584.3 (M+, 11), 607.2 (M++Na, 58); HRMS (FAB)
m/z calcd for [C32H48NaO6Si2]+ (M++Na): 607.2882.
Found: 607.28830.
1
906, 840, 806, 782 cm−1; H NMR (500 MHz, CDCl3) l
6.83 (d, J=1.5 Hz, 1H), 6.80 (dd, J=8.0, 1.5 Hz, 1H),
6.76 (d, J=8.0 Hz, 1H), 6.66 (d, J=1.8 Hz, 1H), 6.63
(dd, J=7.9, 1.8 Hz, 1H), 6.34 (d, J=15.9 Hz, 1H), 5.93
(dd, J=15.9, 8.2 Hz, 1H), 3.81 (s, 3H), 3.74 (s, 3H),
3.66 (dd, J=10.7, 4.7 Hz, 1H), 3.54 (dd, J=10.7, 7.3
Hz, 1H), 2.75–2.60 (m, 2H), 0.99 (s, 9H), 0.98 (s, 9H),
0.15 (s, 6H), 0.13 (s, 6H); 13C NMR (75 MHz, CDCl3)
l 150.9, 150.5, 144.6, 143.2, 133.1, 132.0, 131.1, 128.7,
121.3, 120.8, 120.6, 119.0, 113.3, 109.7, 65.2, 55.4, 47.5,
37.6, 29.6, 25.7, 18.39, 18.35, −4.7. The crude was
dissolved in THF (4 mL), and TBAF (0.45 mL, 1 M in
THF) was added. The resulting mixture was stirred for
20 min at rt then quenched with aqueous NH4Cl. The
organic layer was separated and the aqueous layer was
extracted with ether. The combined organic extract was
dried over MgSO4. The crude product was purified by
flash chromatography on silica gel (1:2 pentane/ether)
to afford the product (+)-imperanene 19 (62 mg, 87%)
as a white solid: [h]D25 +115.2 (c 1.05, CHCl3); FTIR
(film) 3423 (br), 3013, 2935, 2848, 1600, 1514 1463,
TBAF (0.25 mL, 1 M in THF) was added to a stirred
solution of 23 (66 mg, 0.11 mmol) in THF (5 mL) at rt.
The resulting solution was stirred for 30 min at rt then
quenched with saturated aqueous NH4Cl. The mixture
was extracted with CH2Cl2, washed with brine and
dried over Na2SO4. The solvent was removed in vacuo
and the crude product was purified by flash chromatog-
raphy on silica gel (1:1–1:2 pentane/ether then 1:1
ether/CH2Cl2) to afford (−)-a-conidendrin 20 (32 mg,
78% yield) as a white solid: mp 255°C (lit14 mp 256°C);
Rf 0.65 (1:1 ether/CH2Cl2); [h]2D5 −50.4 (c 0.90, acetone);
1H NMR (500 MHz, CDCl3) l 6.87 (d, J=8.0 Hz, 1H),
6.64 (br s, 2H), 6.54 (s, 1H), 6.40 (s, 1H), 5.57 (s, 1H),
5.41 (s, 1H), 4.23 (dd, J=8.5, 6.1 Hz, 1H), 4.01 (pseudo
t, J=9.5 Hz, 1H), 3.89 (s, 3H), 3.85 (d, J=10.0 Hz,
1H), 3.82 (s, 3H), 3.21 (dd, J=15.6, 4.5 Hz, 1H), 2.98
(dd, J=15.6, 11.0 Hz, 1H), 2.62–2.50 (m, 2H); 13C
NMR (125 MHz, CDCl3, three drops of DMSO-d6 was
added to dissolve the sample) l 176.9, 147.2, 145.8,
145.0, 144.4, 133.7, 131.3, 125.6, 121.1, 115.4, 114.8,
111.4, 110.5, 71.7, 55.74, 55.70, 49.5, 47.2, 41.6, 29.0.
1
1450, 1429, 1370, 1271, 1236, 1154, 1033, 754 cm−1; H
NMR (500 MHz, CDCl3) l 6.84 (s, 3H), 6.82 (d, J=8.2
Hz, 1H), 6.70–6.66 (m, 2H), 6.35 (d, J=16.0 Hz, 1H),
5.92 (dd, J=16.0, 8.3 Hz, 1H), 5.64 (br s, 1H), 5.51 (br
s, 1H), 3.89 (s, 3H), 3.82 (s, 3H), 3.67 (dd, J=10.7, 4.9
Hz, 1H), 3.56 (dd, J=10.7, 7.2 Hz, 1H), 2.77–2.68 (m,
2H), 2.68–2.60 (m, 1H); 13C NMR (125 MHz, CDCl3)
l 146.6, 146.3, 145.2, 143.8, 132.1, 131.5, 129.7, 128.3,
121.8, 119.6, 114.4, 114.2, 111.7, 108.2, 65.2, 55.83,
55.81, 47.5, 37.6; HPLC analysis: 92% ee (Chiralcel
OD-H, 30.0% i-PrOH in hexane, 1.0 mL/min, u=254
nm, tR=13.8 min, minor; tR=16.6 min, major).
Acknowledgements
Financial support of this work by the National Science
Foundation (CHE 0092490) and the National Institutes
of Health (CA85641) is gratefully acknowledged.
4.16. (−)-a-Conidendrin, 2013
To a stirred suspension of paraformaldehyde (40 mg,
1.32 mmol) in a solution of (R)-21 (130 mg, 0.22 mmol)
in CH2Cl2 (5 mL) was added methylaluminum
sesquichloride (1.32 mL, 1 M in hexanes) at 0°C. The
resulting mixture was allowed to stir for 1 h then
quenched with water. The mixture was extracted with
ether, washed with brine then dried over Na2SO4. This
crude product was treated with TsOH·H2O (6 mg, 0.03
mmol) in CH2Cl2 for 1 h at rt. Water (5 mL) was added
and extracted with ether. The organic extract was
washed with brine then dried over Na2SO4. The solvent
was removed in vacuo and the crude product was
purified by flash chromatography on silica gel (10:1–5:1
pentane/ether) to afford product 23 (75 mg, 58% yield)
as a white solid: Rf 0.41 (1:1 pentane/ether); FTIR
(CDCl3) 2954, 2958, 2856, 1783, 1511, 1292, 1255, 902,
839 cm−1; 1H NMR (500 MHz, CDCl3) l 6.80 (d,
J=8.0 Hz, 1H), 6.64 (s, 1H), 6.60 (dd, J=8.0, 1.4 Hz,
1H), 6.52 (br s, 1H), 6.28 (s, 1H), 4.19 (dd, J=8.5, 6.4
Hz, 1H), 4.00 (dd, J=10.7, 8.5 Hz, 1H), 3.84 (d,
J=10.7 Hz, 1H), 3.79 (s, 3H), 3.71 (s, 3H), 3.20 (dd,
J=15.5, 5.0 Hz, 1H), 2.96 (dd, J=15.5, 11.6 Hz, 1H),
References
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