11642 J. Am. Chem. Soc., Vol. 120, No. 45, 1998
Saito et al.
The combined organic extracts were dried (Na2SO4) and concentrated
in vacuo. The residue was purified by PTLC (benzene/acetone ) 9/1
for separating epoxides 23 from N,N-dimethylphenylsulfinamide) to
give a mixture of epoxide 23 and epi-23 (110 mg), which was subjected
to HPLC analysis (Zorbax sil, 4.6 mm × 25 cm, hexane/THF ) 8/2,
flow rate 0.5 mL/s; 23, 34.3 min; epi-23, 51.4 min; 23:epi-23 ) 30:1).
The diastereomers were separated by PTLC (hexane/EtOAc ) 3/2) to
give epoxide 23 (105 mg, 84%) as a colorless oil and epi-23 (3.8 mg,
3%) as a pale yellow oil.
ether 26 (13.0 mg, 90%) as a pale yellow oil: 1H NMR (CDCl3) δ
0.39 (s, 3 H), 0.41 (s, 3 H), 1.07 (s, 9 H), 1.53 (s, 3 H), 1.55 (s, 3 H),
1.59-1.62 (m, 1 H), 1.66 (d, J ) 6.8 Hz, 3 H), 1.67 (s, 3 H), 2.21 (s,
3 H), 2.17-2.36 (m, 2 H), 3.78-3.83 (m, 1 H), 3.926 (s, 3 H) 3.931
(s, 3 H), 4.53 (q, J ) 6.8 Hz, 1 H), 4.79 (d, J ) 10.1 Hz, 1 H), 4.91
(d, J ) 10.1 Hz, 1 H), 5.11 (t, J ) 7.0 Hz, 1 H), 7.05 (s, 1 H), 7.32-
7.58 (m, 5 H); 13C NMR (CDCl3) δ -3.8, -3.7, 9.5, 14.2, 18.1, 18.6,
21.2, 25.9, 26.2, 32.0, 51.6, 60.5, 60.7, 75.9, 76.7, 90.1, 100.7, 110.0,
117.7, 121.1, 121.6, 127.8, 128.3, 128.7, 130.4, 134.5, 137.8, 142.5,
148.1, 149.0, 151.8, 156.4; IR (neat) 3550, 2940, 2850, 1620, 1600,
1570, 1450, 1390, 1330, 1270, 1100, 1050, 860 cm-1; [R]29D -12.7 (c
1.02, CHCl3); HRMS m/z 606.3369 (606.3377 calcd for C36H50O6Si,
M+).
23: 1H NMR (CDCl3) δ 1.48 (s, 3 H), 1.63 (d, 3 H, J ) 6.6 Hz),
2.28 (s, 3 H), 2.44 (dd, 1 H, J1 ) 2.7, J2 ) 4.9 Hz), 2.68 (dd, 1 H, J1
) 3.9, J2 ) 4.9 Hz), 3.02 (dd, 1 H, J1 ) 2.7, J2 ) 3.9 Hz), 3.40 (s, 3
H), 3.59-3.62 (m, 2 H), 3.86-3.89 (m, 2 H), 3.91 (s, 3 H), 3.93 (s, 3
H), 4.60 (q, 1 H, J ) 6.6 Hz), 4.79 (d, 1 H, J ) 10.1 Hz), 4.97 (d, 1
H, J ) 10.1 Hz), 5.41 (d, 1 H, J ) 6.4 Hz), 5.44 (d, 1 H, J ) 6.4 Hz),
7.22 (s, 1 H), 7.30-7.59 (m, 5 H); 13C NMR (CDCl3) δ 9.5, 14.1,
19.2, 44.0, 48.0, 54.4, 59.1, 60.4, 60.6, 68.1, 71.6, 76.5, 89.4, 93.0,
95.6, 110.4, 114.5, 121.6, 127.8, 128.2, 128.6, 130.7, 137.9, 143.1,
148.1, 149.2, 153.0, 156.1; IR (neat) 2930, 1630, 1580, 1460, 1380,
Synthesis of Quinone 27. A mixture of silyl ether 26 (30.1 mg,
49.6 µmol), cyclohexene (1.0 mL), and 10% Pd-C (30 mg) in EtOH
(2 mL) was refluxed for 1.5 h. After being cooled to room temperature,
the mixture was filtered through a Celite pad, which was washed with
EtOAc. The filtrate was concentrated in vacuo to give crude naphthol
(38 mg), which was dissolved in CH2Cl2 (1 mL). To the solution were
added t-BuOH (0.1 mL) and pH 7 phosphate buffer (0.1 mL), and the
mixture was cooled at 0 °C. DDQ (23 mg, 0.10 mmol) was added to
the mixture, which was stirred for 15 min. The reaction was quenched
by adding pH 7 phosphate buffer, and the products were extracted with
EtOAc (×5). The combined organic extracts were washed with brine,
dried (Na2SO4), and concentrated in vacuo. The residue was purified
by PTLC (hexane/EtOAc ) 75/25) to give quinone 27 (19.6 mg, 79%,
2 steps) as a bright yellow oil: 1H NMR (CDCl3) δ 0.38 (s, 3 H),
0.39 (s, 3 H), 1.03 (s, 9 H), 1.50 (s, 3 H), 1.53 (s, 3 H), 1.69 (s, 3 H),
1.75 (d, J ) 6.9 Hz, 3 H), 2.05 (s, 3 H), 2.08-2.15 (m, 1 H), 2.26-
2.37 (m, 1 H), 3.74-3.78 (m, 1 H), 4.02 (s, 3 H), 4.56 (q, J ) 6.9 Hz,
1 H), 5.04 (t, J ) 7.3 Hz, 1 H), 7.15 (s, 1 H); 13C NMR (CDCl3) δ
-3.8, -3.7, 9.3, 14.1, 18.1, 18.5, 20.4, 22.4, 25.9, 32.0, 50.7, 60.7,
75.1, 91.4, 109.7, 110.9, 120.5, 128.3, 133.4, 133.6, 136.1, 156.7, 157.0,
162.4, 180.7, 183.8; IR (neat) 3520, 2960, 2930, 2860, 1660, 1590,
1470, 1390, 1290, 1170, 1100, 1060, 870 cm-1; [R]26D -21.8 (c 1.21,
CHCl3); HRMS m/z 500.2589 (500.2594 calcd for C28H40O6Si, M+).
(-)-Furaquinocin D (1d). To a solution of quinone 27 (18.0 mg,
35.9 µmol) in THF (1.5 mL) was added a solution of TBAF (1.0 M in
THF, 0.05 mL, 50 µmol) at 0 °C. After the mixture was stirred for 20
min at 0 °C, the reaction was quenched by adding pH 7 phosphate
buffer, and the products were extracted with CHCl3 (×5). The
combined organic extracts were washed with brine, dried (Na2SO4),
and concentrated in vacuo. The residue was purified by PTLC (CHCl3/
MeOH ) 95/5) to give (-)-furaquinocin D (1d) (11.3 mg, 81%).
Reprecipitation from CHCl3 (+hexane) gave analytically pure 1d as
1320, 1110, 1050 cm-1; [R]21 +28.8 (c 1.15, CHCl3); HRMS m/z
D
524.2386 (524.2410 calcd for C30H36O8, M+).
epi-23: 1H NMR (CDCl3) δ 1.34 (s, 3 H), 1.64 (d, 3 H, J ) 6.6
Hz), 2.29 (s, 3 H), 2.69 (dd, 1 H, J1 ) 4.0, J2 ) 4.9 Hz), 2.80 (dd, 1
H, J1 ) 2.9, J2 ) 4.9 Hz), 3.09 (dd, 1 H, J1 ) 2.9, J2 ) 4.0 Hz), 3.41
(s, 3 H), 3.58-3.61 (m, 2 H), 3.83-3.86 (m, 2 H), 3.93 (s, 3 H), 3.94
(s, 3 H), 4.65 (q, 1 H, J ) 6.6 Hz), 4.86 (d, 1 H, J ) 10.3 Hz), 4.91
(d, 1 H, J ) 10.3 Hz), 5.39 (d, 1 H, J ) 6.5 Hz), 5.42 (d, 1 H, J ) 6.5
Hz), 7.23 (s, 1 H), 7.32-7.58 (m, 5 H); 13C NMR (CDCl3) δ 9.5, 14.7,
16.6, 43.5, 47.8, 52.7, 59.0, 60.4, 60.6, 67.9, 71.5, 76.5, 90.0, 92.9,
95.9, 110.4, 115.7, 121.7, 127.9, 128.3, 128.5, 130.3, 137.7, 143.1,
147.9, 149.2, 153.0, 155.4; IR (neat) 2920, 2850, 1630, 1450, 1380,
1100, 1050 cm-1; [R]24D -34.2 (c 1.15, CHCl3); HRMS m/z 524.2391
(524.2410 calcd for C30H36O8, M+).
Synthesis of Alcohol 25. To a solution of vinylstannane 24 (251
mg, 0.728 mmol) in THF (1 mL) was added n-BuLi (0.45 mL, 1.63 M
hexane solution, 0.73 mmol) at 0 °C, and the mixture was stirred for
10 min. The mixture was cooled to -78 °C, to which was added a
solution of epoxide 23 (74.6 mg, 0.142 mmol) in THF (2.5 mL)
followed by a freshly prepared solution of BF3‚OEt2 (0.20 mL, 0.70
M solution in THF, 0.14 mmol), and the mixture was stirred for 23 h
at -78 °C. The reaction was quenched by adding pH 7 phosphate
buffer, and the products were extracted with EtOAc. The combined
organic extracts were washed with brine, dried (Na2SO4), and concen-
trated in vacuo. The residue was purified by PTLC (hexane/EtOAc )
7/3) to give alcohol 25 (76.1 mg, 92%) as a pale yellow oil: 1H NMR
(CDCl3) δ 1.54 (s, 6 H), 1.67 (d, 3 H, J ) 6.8 Hz), 1.68 (s, 3 H), 1.73
(d, 1 H, J ) 5.3 Hz), 2.29 (s, 3 H), 2.24-2.30 (m, 2 H), 3.41 (s, 3 H),
3.60 (t, 2 H, J ) 4.6 Hz), 3.78-3.84 (m, 1 H), 3.87 (t, 2 H, J ) 4.6
Hz), 3.93 (s, 3 H), 3.95 (s, 3 H), 4.57 (q, 1 H, J ) 6.8 Hz), 4.78 (d, 1
H, J ) 10.0 Hz), 4.91 (d, 1 H, J ) 10.0 Hz), 5.15 (t, 1 H, J ) 6.7 Hz),
5.41 (d, 1 H, J ) 6.5 Hz), 5.47 (d, 1 H, J ) 6.5 Hz), 7.28 (s, 1 H),
7.31-7.59 (m, 5 H); 13C NMR (CDCl3) δ 9.5, 14.1, 18.0, 21.0, 25.8,
31.9, 51.9, 59.1, 60.4, 60.6, 68.0, 71.5, 75.7, 76.5, 90.3, 93.1, 95.9,
110.4, 115.8, 121.57, 121.65, 127.8, 128.2, 128.6, 130.5, 134.4, 137.7,
143.0, 148.0, 149.1, 153.1, 156.0; IR (neat) 2960, 2920, 2870, 2850,
1
bright yellow solids: mp 176-179 °C (lit.1c mp 177-179 °C); H
NMR (CDCl3) δ 1.32 (d, 3 H, J ) 6.4 Hz), 1.36 (s, 3 H), 1.73 (s, 3 H),
1.81 (s, 3 H), 2.05 (s, 3 H), 2.14-2.19 (m, 1 H), 2.52 (ddd, 1 H, J1 )
14.7, J2 ) J3 ) 9.9 Hz), 3.20-3.27 (broad, 1 H), 4.01 (s, 3 H), 4.03-
4.05 (m, 1 H), 4.67 (q, 1 H, J ) 6.4 Hz), 5.16-5.20 (m, 1 H), 7.17 (s,
1 H), 10.56 (s, 1 H); 13C NMR (CDCl3) δ 183.6, 180.7, 160.4, 158.4,
156.9, 139.2, 134.1, 133.7, 124.5, 118.4, 110.5, 109.2, 88.8, 73.0, 60.7,
52.1, 32.0, 26.1, 18.9, 18.3, 16.1, 9.33; IR (neat) 3500, 2930, 1660,
1630, 1575, 1400, 1380, 1300, 1275, 1160 cm-1; UV (νmax, MeOH)
270, 295, 405 nm; [R]24 -94 (c 0.75, CHCl3) (lit.1c [R]19 -95 (c
D
D
1460, 1440, 1380, 1200, 1130, 1120, 1080, 1020, 910, 870 cm-1; [R]25
0.53, CHCl3)); HRMS m/z 386.1737 (386.1728 calcd for C22H26O6,
M+). Anal. Calcd for C22H26O6: C, 68.38; H, 6.78. Found: C,
68.21; H, 7.08.
D
-10 (c 0.91, CHCl3); HRMS m/z 580.3016 (580.3036 calcd for
C34H44O8, M+).
Synthesis of Silyl Ether 26. A mixture of alcohol 25 (13.9 mg,
23.9 µmol) and p-TsOH‚H2O (0.9 mg, 5 µmol) in EtOH (2 mL) was
gently refluxed for 15 h. After the solution was cooled to 0 °C, the
reaction was quenched by adding saturated aqueous NaHCO3, and the
products were extracted with EtOAc. The combined organic extracts
were washed with brine, dried (Na2SO4), and concentrated in vacuo.
The crude material (16 mg) was dissolved in CH2Cl2 (1 mL), to which
was added 2,6-lutidine (26.1 mg, 0.24 mmol) and TBSOTf (38.1 mg,
0.14 mmol) at -78 °C. After the solution was stirred for 5 min, the
reaction was quenched by adding pH 7 phosphate buffer, and the
products were extracted with EtOAc. The combined organic extracts
were washed with brine, dried (Na2SO4), and concentrated in vacuo.
The residue was purified by PTLC (hexane/EtOAc ) 7/3) to give silyl
Total Synthesis of (-)-Furaquinocin A. (a) Synthesis of Alcohol
33a. To a solution of vinylstannane 30 (174 mg, 0.391 mmol) in THF
(1 mL) was added n-BuLi (0.24 mL, 1.64 M hexane solution, 0.39
mmol) at -78 °C, and the mixture was gradually warmed to -10 °C.
After the mixture was cooled to -78 °C, a solution of epoxide 23 (40.9
mg, 0.0781 mmol) in THF (2 mL) was added followed by a freshly
prepared solution of BF3‚OEt2 (0.20 mL, 1.86 M solution in THF, 0.37
mmol), and the temperature was gradually raised to -20 °C for 3 h.
The reaction was quenched by adding pH 7 phosphate buffer, and the
products were extracted with EtOAc (×3). The combined organic
extracts were washed with brine, dried (Na2SO4), and concentrated in
vacuo. The residue was purified by PTLC (hexane/EtOAc ) 6/4) to
give alcohol 33a (45.1 mg, 85%) as a colorless oil: 1H NMR (CDCl3)