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Y. Chen et al. / Tetrahedron: Asymmetry 9 (1998) 1923–1928
3.2. Dihydro-α-cyperol 6
Dry t-butanol (2.1 ml) was slowly added to a solution of LAH (398 mg, 10.5 mmol) in dry THF (42
ml) at 0°C. The solution of dihydro-α-cyperone 5 (450 mg, 2.05 mmol) in THF (21 ml) was added
with stirring and the mixture allowed to stand at 0°C for 30 min and then at room temperature for 18
h. The reaction mixture was poured into ice-cold 1 N HCL (60 ml) and extracted with petroleum ether.
The extracts were washed with sat. aq. NaHCO3 and brine. After drying over anhydrous MgSO4, the
solution was evaporated to dryness in vacuo. The crude products were purified by flash chromatography.
20
Compound 6 (420 mg, 92%) was obtained as white needles, m.p. 71–72°C. [α]D −5.7 (c, 2.96, CHCl3);
IR: 3342, 1644, 1451, 1377, 1025, 887 cm−1; 1H NMR (80 MHz): δ (ppm) 0.88 (s, 3H, 11-Me), 0.98 (d,
3H, J=5.5 Hz, 4-Me), 1.63 (brs, 3H, 12-Me), 3.14 (ddd, 1H, J=5.5, 9.5 and 9.6 Hz, 3-H), 4.71 (brs, 2H,
13-H); EIMS m/z (%): 222 (M+, 52), 204 (32), 189 (28), 175 (14), 161 (58), 122 (60), 41 (100).
3.3. 3α-Chloro-4β-H-eudesma-11,12-ene 7
To a magnetically stirred solution of NCS (239 mg, 1.80 mmol) in THF (2.2 ml), a solution of PPh3
(472 mg, 1.8 mmol) in THF (1 ml) was added dropwise. The solution was stirred at room temperature for
1 h. To this suspension, a solution of the alcohol 6 (350 mg, 1.58 mmol) in THF (3.5 ml) was added and
stirring was continued until most of the solid was dissolved (ca. 3 h). The reaction mixture was stripped
of solvent under reduced pressure and the residue was treated with water and ether. The organic layer was
washed with water, dried over anhydrous MgSO4, and evaporated. The crude products were purified by
26
flash chromatography. The compound 7 (334 mg, 88%) was obtained as a colourless oil. [α]D −68.8
(c, 3.9, CHCl3); IR: 1879, 1450, 886 cm−1; 1H NMR(400 MHz): δ (ppm) 0.85 (s, 3H, 10-Me), 0.94 (d,
3H, J=6.5 Hz, 4-Me), 1.73 (br s, 3H, 10-Me), 4.33 (br q, 1H, J=2.7 Hz, 3-H), 4.68 (br d, 1H, J=1.42
Hz, 13-H), 4.69 (br s, 1H, 13-H); EIMS m/z (%): 240 (M+, 64), 225 (15), 197 (89), 161 (44), 81 (100).
Found: C, 74.67%; H, 10.16%. Calcd for C15H25Cl: C, 74.81%; H, 10.46%.
3.4. (+)-α-Selinene 2
A suspension of compound 7 (42 mg, 0.18 mmol), LiBr (46 mg, 0.53 mmol) and Li2CO3 (52 mg,
0.7 mmol) in dry DMF (1.5 ml) was heated at 138–140°C for 5 h. After the solution was cooled, it was
diluted with ether and washed with water and brine. After drying over anhydrous MgSO4, the solution
was evaporated to dryness in vacuo. Purification by flash chromatography give pure 2 (31.6 mg, 86%).
[α]D8 +13.7 (c, 1.52, CHCl3, lit10 [α]D +15.7); IR: 2967, 2929, 2844, 1642, 1447, 1375, 1216, 887 cm−1
;
1H NMR (400 MHz): δ (ppm) 0.81 (s, 3H, 10-Me), 1.62 (brs, 3H, 11-Me) 1.77 (brs, 3H, 4-Me), 4.71 (s,
1H, 12-H), 4.74 (s, 1H, 12-H), 5.33 (brs, 1H, 3-H); EIMS m/z (%): 204 (M+, 69), 189 (100), 175 (31),
161 (41), 147 (36), 133 (63), 119 (40), 105 (66), 91 (85), 79 (67), 41 (82).
3.5. (−)-(11S)-3α-Chloro-13-hydroxy-α-eudesmol 8a
A 5 ml round-bottomed flask, equipped with a magnetic stirrer, was charged with 0.6 ml tert-butyl
alcohol, 0.6 ml of water, and 870 mg AD-mix-α. The mixture was stirred at room temperature until both
phases were clear, and then cooled at 0°C. Compound 7 (75 mg, 0.31 mmol) in 50% aqeous t-BuOH (1
ml) was added at once. The resulting mixture was stirred for 24 h at 0°C. Sodium sulfide (1.0 g) was added
to the mixture which was then warmed to room temperature and stirred for 1 h. The reaction mixture was
extracted several times with CH2Cl2. The extract was washed with 10% aqeous KOH, H2O and brine,