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HELVETICA CHIMICA ACTA – Vol. 88 (2005)
1 H); 7.57–7.60 (m, 1 H); 9.56 (t, J=2.4, 1 H). 13C-NMR: 21.22 (t); 32.79 (s); 37.75 (s); 42.10 (t); 43.00 (t); 52.14
(t); 55.17 (t); 66.40 (d); 76.44 (d); 106.79 (s); 111.76 (d); 118.28 (d); 120.30 (d); 121.51 (d); 128.29 (s); 133.07 (s);
137.61 (s); 202.61 (d). EI-MS: 310 (20, M+), 309 (30), 308 (16), 282 (72), 281 (100), 280 (52), 266 (20), 248 (14),
238 (63). HR-MS: 310.1676 (C19H22N2Oþ2 ; calc. 310.1683).
rac-(16a)-14,15-Dihydro-14-oxoeburnamenin-21-al (9). PDC (0.11 g, 0.29 mmol) was added to crude 8a/8b
(70 mg, 0.23 mmol) in anh. CH2Cl2 (5 ml), and the mixture was stirred at r.t. overnight. The oxidation product
was diluted with AcOEt (20 ml) and passed through Celite. The Celite pad was further rinsed, the combined fil-
trate evaporated, and the residue subjected to CC (AcOEt/hexane 1 :1): 9 (30 mg, 43%). Thick oil. Rf 0.50
(AcOEt/hexane 3 :1). IR: 1656, 1707 (C=O), 2943 (CH). 1H-NMR: 1.31 (ddt, J=13.4, 4.3, 1.5, 1 H); 1.59–
1.70 (m, 1 H); 1.79–1.93 (m, 3 H); 2.11 (td, J=13.5, 3.3, 1 H); 2.28 (dt, J=11.7, 3.6, 1 H); 2.44–2.53 (m, 2
H); 2.56–2.64 (m, 1 H); 2.74–2.86 (m, 1 H); 2.92 (td, J=14.1, 2.4, 1 H); 2.98–3.08 (m, 3 H); 7.20–7.28 (m, 2
H); 7.35–7.38 (m, 1 H); 8.26–8.29 (m, 1 H); 9.66 (t, J=2.1, 1 H). 13C-NMR: 21.08 (t); 21.43 (t); 32.92 (t);
39.12 (s); 43.16 (t); 44.62 (s); 51.86 (t); 55.00 (t); 65.07 (d); 113.72 (s); 116.27 (d); 118.27 (d); 124.04 (d);
124.45 (d); 129.62 (s); 131.92 (s); 134.96 (s); 166.52 (s); 200.99 (d). EI-MS: 308 (3.53, M+), 307 (14.73), 282
(10.45), 281 (56.79), 279 (100), 263 (15.54), 237 (22.77). HR-MS: 308.1529 (C19H20N2Oþ2 ; calc. 308.1526).
3-Epieburnamonine1) (=rac-(16a)-Eburnamenin-14(15H)-one1); 10). A mixture of 9 (30 mg, 0.098 mmol),
ethane-1,2-dithiol (0.03 ml, 0.35 mmol) and BF3·Et2O (0.02 ml, 0.16 mmol) in CH2Cl2 (5 ml) was stirred at 08 for
1 h, then at r.t. for 8 h. It was diluted with CH2Cl2 (15 ml), washed with 5% aq. NaHCO3 soln. and, brine, dried,
and evaporated. The residue was dissolved in EtOH (8 ml), treated with Raney-Ni (50% aq. slurry, ca. 0.5 ml)
and refluxed for 8 h. The cooled mixture was filtered through Celite, the latter washed with CH2Cl2 (15 ml), the
filtrate evaporated, and the residue subjected to CC (AcOEt/hexane 1:1): 10 (20 mg, 69%). White solid. Rf 0.40
(AcOEt/hexane 1:1 ). M.p. 135–1378 ([5]: 138–1398). IR: 1654, 1708 (C=O), 2854, 2926 (CH). 1H-NMR: 0.73–
0.87 (m, 4 H); 1.12–1.23 (m, 2 H); 1.57–1.63 (m, 2 H); 1.79–1.86 (m, 2 H); 2.29 (dt, J=14.4, 3.3, 1 H); 2.33 (dd,
J=16.8, 1.8, 1 H); 2.54 (dt, J=11.2, 4.2, 1 H); 2.58–2.68 (m, 1 H); 2.78 (d, J=17.1, 1 H); 2.78–2.92 (m, 1 H);
3.01–3.11 (m, 2 H); 7.22–7.30 (m, 2 H); 7.37–7.40 (m, 1 H); 8.29–8.32 (m, 1 H). 13C-NMR: 7.36 (q); 20.66
(t); 20.95 (t); 21.25 (t); 31.51 (t); 39.42 (s), 44.09 (t), 52.30 (t), 55.22 (t), 65.71 (d), 112.95 (s), 116.12 (d),
118.20 (d), 123.86 (d), 124.22 (d), 129.69 (s), 133.60 (s), 135.00 (s), 167.34 (s). EI-MS: 294 (64.6, M+), 293
(100), 265 (12.94), 237 (32.96). HR-MS: 294.1729 (C19H22N2O+; calc. 294.17336).
rac-(14b,16a)-14,15-Dihydroeburnamenine-14,21-diol1) (11a). To a soln. of 8a (0.12 g, 0.39 mmol) in EtOH
(5 ml) was added at r.t. NaBH4 (0.10 g, 2.64 mmol) in portions during 5 min. The resulting mixture was stirred for
1 h. Then H2O/CH2Cl2 1:5 (30 ml) was added, the org. layer washed with H2O and brine, dried, and evaporated,
and the residue subjected to CC (MeOH/CH2Cl2 5 :95): 11a (0.10 g, 82%). White solid. Rf 0.15 (MeOH/CH2Cl2
5 :95). M.p. 100–1028 ([3b]: 102–1038). IR: 2809, 2852, 2928 (CH), 3303 (OH). 1H-NMR: 0.96–1.04 (m, 1 H);
1.12–1.24 (m, 1 H); 1.41–1.60 (m, 3 H); 1.74 (d, J=13.5, 1 H); 1.85–2.04 (m, 1 H); 2.15–2.27 (m, 2 H); 2.44 (dt,
J=11.1, 4.2, 1 H); 2.63 (dd, J=14.4, 2.4, 1 H); 2.81 (s, 1 H); 2.81–3.00 (m, 3 H); 3.22–3.30 (m, 1 H); 3.52–3.60
(m, 1 H); 5.58 (dd, J=9.0, 5.7, 1 H); 7.08–7.15 (m, 2 H); 7.40–7.43 (m, 1 H); 7.55–7.58 (m, 1 H). 13C-NMR:
21.06 (t); 21.97 (t); 33.29 (t); 33.55 (t); 38.26 (s); 47.03 (t); 52.29 (t); 55.22 (t); 58.41 (t); 66.08 (d); 76.84(d);
106.31 (s); 111.54 (d); 118.30 (d); 120.23 (d); 121.40 (d); 128.32 (s); 133.05 (s); 137.59 (s). EI-MS: 312 (80,
M+), 311 (100), 310 (30), 294 (44), 293 (67), 267 (34), 249 (21), 237 (14). HR-MS: 312.1840 (C19 H24 N2 Oþ2 ;
calc. 312.1839).
rac-(14a,16a)-14,15-Dihydroeburnamenin-14,21-diol1) (11b). As described for 11a, with 13 (70 mg, 0.23
mmol), EtOH (5 ml), and NaBH4 (70 mg, 2.59 mmol): 11b (60 mg, 83%). White solid. Rf 0.33 (5% MeOH/
1
CH2Cl2). M.p. 168–1708 ([3b]: 172–1748). IR: 2803, 2852, 2935 (CH), 3292 (OH). H-NMR: 1.08–1.16 (m, 1
H); 1.44–1.58 (m, 2 H); 1.78–1.89 (m, 3 H); 2.07 (d, J=16.5, 1 H); 2.20 (dt, J=16.5, 3.3, 1 H); 2.35 (d, J=15,
1 H); 2.43 (dt, J=11.1, 4.5, 1 H); 2.67 (dd, J=15, 4.2, 1 H); 2.77 (s, 1 H); 2.86–2.92 (m, 1 H); 2.99–3.08 (m, 2
H); 3.60–3.70 (m, 2 H); 5.84 (d, J=5.1, 1 H); 7.05–7.15 (m, 2 H); 7.45 (dd, J=10.5, 7.5, 2 H). 13C-NMR:
21.10 (t); 29.84 (t); 32.25 (t); 33.96 (s); 41.59 (t); 53.30 (t); 55.76 (t); 58.43 (t); 67.74 (d); 74.61 (d); 105.10 (s);
111.10 (d); 118.04 (d); 119.56 (d); 120.80 (d); 128.16 (s); 131.25 (s); 135.73 (s). EI-MS: 312 (18, M+), 311
(33), 310 (22), 294 (29), 293 (100), 265 (8), 249 (7). HR-MS: 312.1836 (C19H24N2Oþ2 ; calc. 312.1839).
[(1RS,12bRS)-1-Ethyl-1,2,3,4,6,7,12,12b-octahydroindolo[2,3-a]quinolizine-1-ethanol (12). According to a
modified literature procedure [3b], a mixture 11a/11b (60 mg, 0.19 mmol), KOH (30 mg, 0.52 mmol), and hydra-
zine hydrate (0.32 ml, 6.6 mmol) in ethylene glycol (1.0 ml) was heated at 1308 for 2 h and then refluxed for 8 h.
After cooling to r.t., the mixture was diluted with H2O, and extracted with CH2Cl2, the org. soln. washed with
H2O and, brine, dried, and evaporated, and the residue subjected to CC (MeOH/CH2Cl2 5 :95) 12 (30 mg, 53%).
M.p. 168–1708 ([3b]: 173–1748). IR: 2758, 2808, 2852, 2929 (CH), 3317, 3480 (NH, OH). 1H-NMR: 1.08 (t,
J=7.5, 3 H); 1.29 (td, J=14.7, 3.3, 1 H); 1.55–1.82 (m, 6 H); 2.00–2.12 (m, 1 H); 2.41; (dt, J=12.0, 3.0, 1 H);