An Improved Stereocontrolled Route to cis-Erythrinanes
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(500 MHz): ꢂ ¼ 7.59–7.57 (m, N¼CH), 7.22 and 6.73 (2s, 2H), 5.93 and 5.92 (2d, each J ¼ 1.4 Hz,
OCH2O), 3.98–3.88 and 3.88–3.85 (2m, 3 þ 1H, OCH2CH2O), 3.53 (br t, J ¼ 7.4 Hz, N–CH2),
2.93 (dt, J ¼ 7.4=1.5 Hz, benzyl–CH2), 2.49 (dt, J ¼ 14.8=4.9 Hz, 1H, N¼C–CH2), 2.10–2.04 (ddd,
J ¼ 14.7=8.1=5.9 Hz, 1H, N¼C–CH2), 1.94–1.88 (m, CH), 1.90 (ddt, J ¼ 13.1=3.8=1.4Hz, 1H),
1.67–1.59 and 1.53–1.43 (2m, 3 þ 1H), 1.40–1.28 and 1.28–1.19 (2m, 2 þ 1H) ppm; 13C NMR
(100 MHz): ꢂ ¼ 166.10, 148.27, 146.98, 135.77, 118.51, 110.21, 110.17, 101.46, 87.94, 64.84, 64.51,
61.04, 42.42, 41.88, 35.64, 34.86, 29.89, 24.67, 23.83ppm.
[2-(1,4-Dioxaspiro[4.5]dec-6-yl)ethylidene][3-(2-iodo-4,5-dimethoxyphenyl)
propyl]amine (5e, C21H30INO4)
4 950 mg (5.16 mmol), 3e 1.66 g (5.16 mmol), toluene 60cm3; yield: 2.44g (97%); IR (film): ꢁꢀ¼ 1666
1
(N¼C) cmꢁ1; MS (CI): m=z (%) ¼ 488 (Mþꢄ þ 1, 100), 360 (32), 322 (20), 125 (20); H NMR
(400 MHz): ꢂ ¼ 7.71–7.68 (m, N¼CH), 7.20 and 6.74 (2s, 2 arom H), 3.96–3.88 (m, OCH2CH2O),
3.86 and 3.84 (2s, 2OCH3), 3.43 (t, J ¼ 6.8 Hz, N–CH2), 2.67–2.63 (m, benzyl–CH2), 2.54 (tt,
J ¼ 14.6=5.0 Hz, 1H, N¼C–CH2), 2.11 (ddd, J ¼ 14.6=8.2=5.7 Hz, 1H, N¼C–CH2), 2.00–1.93 (m,
CH), 1.92–1.83 and 1.83–1.58 (2m, 2 þ 4H), 1.55–1.43 and 1.43–1.19 (2m, 1 þ 3H) ppm; 13C NMR
(100 MHz): ꢂ ¼ 165.42, 149.34, 147.74, 137.22, 121.69, 112.18, 110.23, 87.95, 64.85, 64.54, 60.61,
56.16, 55.91, 42.47, 38.14, 35.69, 34.89, 31.58, 30.02, 24.75, 23.81 ppm.
General Procedure for the Synthesis of Secondary Amines 6
The crude imine 5 (see above) was dissolved in CH3OH and NaBH4 was added under ice cooling. After
refluxing the mixture for 2 h the solvent was removed in vacuo. The residue was diluted with 50cm3 of
H2O and extracted with 3 ꢃ 50 cm3 of Et2O. The combined organic extracts were dried (Na2SO4) and
evaporated in vacuo. The residue was purified by FC (eluents were the same as used for TLC).
[2-(2-Bromophenyl)ethyl][2-(1,4-dioxaspiro[4.5]dec-6-yl)ethyl]amine (6a, C18H26BrNO2)
5a 1.73 g (4.72 mmol), NaBH4 538 mg (14.2 mmol), CH3OH 70 cm3; yield: 1.14g (65%) colourless
oil; TLC (CH2Cl2:CH3OH:25% NH3 ¼ 100:5:0.5): Rf ¼ 0.28; IR (film): ꢁꢀ¼ 3321 (NH) cmꢁ1; MS
81
1
(CI): m=z (%) ¼ 370 (Mþꢄ þ 1, 100, Br), 368 (Mþꢄ þ 1, 100, 79Br), 198 (79), 138 (17); H NMR
(400 MHz): ꢂ ¼ 7.53 (br d, J ¼ 7.8 Hz, arom H), 7.26–7.22 (m, 2 arom H), 7.06 (ddd, J ¼
7.8=6.0=3.1 Hz, arom H), 3.98–3.89 (m, OCH2CH2O), 2.97–2.92 (m, benzyl–CH2), 2.90–2.85
(m, aryl–C–CH2N), 2.72 (ddd, J ¼ 11.3=9.9=5.3Hz, 1H, CH2N), 2.61 (ddd, J ¼ 11.3=9.4=6.4 Hz,
1H, CH2N), 1.83–1.73 and 1.66–1.57 (2m, each 3H), 1.55–1.40 and 1.40–1.17 (2m, 2 þ 4H) ppm;
13C NMR (100MHz): ꢂ ¼ 139.52, 132.84, 130.70, 127.76, 127.37, 124.58, 110.66, 64.72, 64.55, 49.48,
48.24, 42.65, 36.72, 34.57, 29.61, 28.98, 24.45, 23.77ppm.
[2-(1,4-Dioxaspiro[4.5]dec-6-yl)ethyl][2-(2-iodophenyl)ethyl]amine (6b, C18H26INO2)
5b 2.20 g (5.32 mmol), NaBH4 606 mg (16.0 mmol), CH3OH 70cm3; yield: 1.48 g (66%) colourless
oil; TLC (CH2Cl2:CH3OH:25% NH3 ¼ 100:4:0.5): Rf ¼ 0.41; IR (film): ꢁꢀ¼ 3321 (NH) cmꢁ1
;
1
MS (CI): m=z (%) ¼ 416 (Mþꢄ þ 1, 100), 288 (4), 198 (77); H NMR (500 MHz): ꢂ ¼ 7.81 (dd,
J ¼ 7.7=1.2 Hz, arom H), 7.27 (dt, J ¼ 7.6=1.2Hz, arom H), 7.23 (dd, J ¼ 7.6=1.9 Hz, arom H), 6.89
(dt, J ¼ 7.7=1.9Hz, arom H), 3.98–3.88 (m, OCH2CH2O), 2.94–2.89 and 2.87–2.83 (2m, benzyl–CH2
and aryl–C–CH2N), 2.72 (ddd, J ¼ 11.3=9.9=5.3 Hz, 1H, CH2N), 2.62 (ddd, J ¼ 11.3=9.4=6.4 Hz, 1H,
CH2N), 1.83–1.72 and 1.66–1.57 (2m, each 3H), 1.53–1.43 and 1.38–1.18 (2m, 1 þ 5H) ppm; 13C
NMR (100 MHz): ꢂ ¼ 142.80, 139.54, 129.77, 128.31, 127.95, 110.66, 100.67, 64.76, 64.60, 49.78,
48.30, 42.67, 41.26, 34.61, 29.62, 28.99, 24.48, 23.80ppm.