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Helvetica Chimica Acta – Vol. 89 (2006)
CHCl3). IR: 2969, 2871, 2840, 1715, 1446, 1382, 1264, 1188, 1128, 853, 724. 1H-NMR: 0.89 (s, 3 H); 1.10 (s,
3 H); 1.67 (s, 3 H); 1.73 (s, 3 H); 1.92–1.97 (m, 3 H); 2.63–2.66 (m, 1 H); 2.67–2.70 (m, 1 H); 2.83 (s, 1
H); 2.97 (d, J=6.8, 1 H); 5.24 (s, 1 H). 13C-NMR: 17.9 (q); 19.8 (q); 20.5 (q); 23.9 (q); 26.2 (t); 30.3 (t);
44.0 (t); 47.3 (s); 47.4 (d); 119.4 (d); 121.3 (s); 129.0 (s); 137.8 (s); 214.7 (s). EI-MS: 204 (61, M+C), 134
(100), 119 (65), 95 (69), 91 (47). HR-MS: 204.1510 (M+, C14H20O+C; calc. 204.1515).
(4aS,7R)-1,2,4a,5,7,8-Hexahydro-3,5,5,9-tetramethyl-7-(trimethylsilyl)-6H-benzocyclohepten-6-one
(18b). To a stirred soln. of 17 (0.60 g, 2.94 mmol) and BF3 ·OEt2 (0.4 ml, 3.16 mmol) in dry CH2Cl2 (15 ml)
was added 2M Me3SiCHN2 in toluene (1.6 ml, 3.2 mmol) at À408 under N2. After 2.5 h, H2O was added,
the org. soln. washed with brine, dried, and evaporated, and the residue subjected to CC (AcOEt/hexane
1:30): 18b (0.41 g, 48.1%) and 18a (0.11 g, 17.2%). 18b: [a]D =À97.4 (c=0.15, CHCl3). IR: 2963, 2908,
2727, 1695, 1464, 1447, 1378, 1247, 1096, 1051, 1031, 864, 838, 693, 615. 1H-NMR: 0.02 (s, 9 H); 0.84 (s, 3
H); 1.09 (s, 3 H); 1.56 (s, 3 H); 1.71 (s, 3 H); 1.78–1.91 (m, 3 H); 2.08 (dd, J=16.5, 10.8, 1 H), 2.50–2.67
(m, 2 H); 2.94 (t, J=9.9, 1 H); 3.58 (s, 1 H); 5.37 (s, 1 H). 13C-NMR: À2.6 (q); 17.7 (q); 20.9 (q); 23.1 (q);
24.0 (q); 27.0 (t); 30.1 (t); 35.0 (t); 35.1 (d); 44.0 (d); 55.2 (s); 118.7 (d); 126.8 (s); 132.0 (s); 136.5 (s); 218.1
(s). EI-MS: 290 (5, M+C), 185 (52), 170 (39), 143 (30), 73 (60), 43 (100), 41 (53), 32 (75). HR-MS: 290.2073
(M+, C18H30OSi+C; calc. 290.2067).
(4aS)-2,4a,5,6,7,8-Hexahydro-3,5,5,9-tetramethyl-6H-benzocyclohepten-6-one (18a). A mixture of
18b (0.25 g, 0.86 mmol) and 1M Bu4NF (1.7 ml, 1.7 mmol) in MeCN (10 ml) was stirred at r.t. for 3 h.
After evaporation, the residue was subjected to CC (AcOEt/hexane 1:30): 18a (0.11 g, 58.5%).
1
[a]D =À86.1 (c=0.10, CHCl3). IR: 2966, 2927, 2910, 2728, 1706, 1465, 1448, 1381, 1248, 1081, 851. H-
NMR: 0.88 (s, 3 H); 1.15 (s, 3 H); 1.63 (s, 3 H); 1.71 (s, 3 H); 1.84–2.00 (m, 3 H); 2.10–2.16 (m, 1 H);
2.22–2.30 (m, 1 H); 2.56–2.58 (m, 1 H); 2.64–2.68 (m, 1 H); 3.04–3.13 (m, 1 H); 3.33 (s, 1 H); 5.37 (s,
1 H). 13C-NMR: 18.8 (q); 20.2 (q); 23.9 (q); 24.2 (q); 26.1 (t); 30.1 (t); 30.8 (t); 36.2 (t); 43.8 (d); 53.6
(s); 118.6 (d); 127.4 (s); 132.7 (s); 136.6 (s); 215.5 (s). EI-MS: 218 (3, M+C), 119 (24), 105 (36), 91 (14),
55 (30), 43 (100), 41 (72), 39 (30), 32 (82). HR-MS: 218.1669 (M+, C15H22O+C; calc. 218.1671).
(4aS,6S,7R)-2,4a,5,6,7,8-Hexahydro-3,5,5,9-tetramethyl-7-(trimethylsilyl)-1H-benzocyclohepten-6-ol
(19). To a stirred soln. of 18b (0.16 g, 0.55 mmol) in EtOH (2 ml) was added NaBH4 (0.20 g, 5.28 mmol) in
portions during 5 min. After 36 h at r.t., the reaction was quenched with H2O and the mixture extracted
with Et2O. Drying, evaporation, and CC (AcOEt/hexane 1:30) gave 19 (0.14 g, 86.9%). [a]D =62.2
(c=0.15, CHCl3). IR: 3564, 2960, 2905, 1448, 1404, 1383, 1247, 1078, 1036, 995, 864, 834, 746. 1H-
NMR: 0.01 (s, 9 H); 0.89 (s, 3 H); 0.94 (s, 3 H); 1.41–1.44 (m, 1 H); 1.70 (s, 3 H); 1.72 (s, 3 H);
1.83–2.02 (m, 5 H); 2.61–2.78 (m, 2 H); 3.08 (s, 1 H); 3.47 (d, J=12.0, 1 H); 5.34 (s, 1 H). 13C-NMR:
–2.59 (q); 20.3 (q); 21.1 (q); 24.0 (q); 24.9 (d); 26.3 (t); 27.8 (q); 30.3 (t); 30.9 (t); 41.9 (s); 44.7 (d);
80.9 (d); 121.4 (d); 128.7 (s); 134.6 (s); 135.1 (s). EI-MS: 292 (2, M+C), 137 (67), 134 (38), 91 (43), 75
(38), 73 (100). HR-MS 292.2223 (M+, C18H32OSi+C; calc. 292.2224).
(4aR)-2,4a,5,8-Tetrahydro-3,5,5,9-tetramethyl-1H-benzocycloheptene (20). A 30% suspension of KH
in oil (100 mg, 0.87 mmol) was washed with hexane and suspended in THF (1 ml). A soln. of 19 (60 mg,
0.21 mmol) in THF (2 ml) was added. The resulting mixture was stirred for 24 h at r.t., quenched with sat.
NH4Cl soln., and poured into H2O overlaid with Et2O. The org. layer was washed with H2O (2×), dried,
and evaporated and the residue subjected to CC (hexane): 20 (30 mg, 72.3%). [a]D =+81.8 (c=0.10,
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CHCl3). IR: 3002, 2962, 2927, 2908, 2835, 1467, 1439, 1375, 1355, 1156, 980, 853, 744, 697. H-NMR:
0.82 (s, 3 H); 1.07 (s, 3 H); 1.72 (s, 3 H); 1.76 (s, 3 H); 1.95–2.00 (m, 3 H); 2.11 (q, J=9.0, 1 H);
2.63–2.68 (m, 1 H); 3.27–3.33 (m, 2 H); 5.15 (dd, J=11.4, 3.3, 1 H); 5.44–5.52 (m, 2 H). 13C-NMR:
20.1 (q); 24.1 (q); 24.3 (q); 26.0 (t); 29.1 (q); 30.2 (t); 33.2 (t); 38.4 (s); 45.4 (d); 121.5 (d); 123.2 (d);
131.7 (s); 131.8 (s); 136.1 (s); 142.1 (d). EI-MS: 202 (3, M+C), 104 (43), 103 (42), 91 (98), 77 (42), 44
(100). HR-MS: 202.1722 (M+, C15H2þ2C; calc. 202.1722).
(+)-b-Himachalene (=(4aR)-2,4a,5,6,7,8-Hexahydro-3,5,5,9-tetramethyl-1H-benzocycloheptene; 2)
from 18a. To a stirred soln. of 18a (100 mg, 0.46 mmol) in MeOH (1 ml) was added NaBH4 (50 mg,
1.32 mmol) at 08. After 1 h, H2O was added, the mixture extracted with Et2O, dried, and evaporated.The
obtained crude alcohol was directly mixed with DMAP (5 mg) in pyridine (1 ml) under N2, cooled to 08,
and treated with MsCl (0.1 ml, 1.29 mmol). On removal of the ice-bath, stirring was continued for 6 h.
Then the mixture was poured into ice-water and extracted with CH2Cl2 and the org. layer washed
twice with 10% HCl soln., sat. NaHCO3, and brine, dried, and evaporated: mesylate.