A. Rodrigues et al. / Tetrahedron 60 (2004) 8489–8496
8495
of the trans diastereomer (76%), mp 137.0–138.5 8C (from
diethyl ether/n-hexane). H NMR (CDCl3) (2 rotamers):
was submitted to column chromatography using diethyl
ether/n-hexane (1:2) as eluent to give compound 5
(106.8 mg, 91%), mp 119.5–121.0 8C (from diethyl ether/
1
1.34, 1.49, 1.57 (36H, 3s, CH3 Boc), 3.69, 3.78 (12H, 2s,
CH3 OMe), 4.89, 5.08 (2H, 2s, 2-H or 3-H), 6.15, 6.21 (2H,
2s, 2-H or 3-H), 7.48 (8H, broad s, ArH), 7.56, 7.78 (2H, 2s,
6-H); 13C NMR (CDCl3): 27.66, 28.00, 51.83, 52.87, 57.30,
57.60, 58.23, 59.77, 82.41, 84.29, 108,52, 122.44, 130.50,
132.04, 135.32, 150.67, 151.22, 164.26, 167.27. Anal. Calcd
for C24H31N2O8SBr (587.48): C 49.07; H 5.32; N 4.77; S
5.46; found C 49.40; H 5.52; N 4.81; S 5.40.
1
n-hexane). H NMR (CDCl3): 1.49, 1.53 (18H, 2s, CH3
Boc), 3.82, 3.88 (6H, 2s, CH3 OMe), 6.61 (1H, s, 3-H), 7.56
(1H, s, 6-H); 13C NMR (CDCl3): 27.70, 27.76, 52.24, 54.24,
68,71, 83.93, 85.91, 109.74, 122.00, 126.15, 148.79,
149.05, 163.20, 163.68; MS: m/z (%)Z470 (1) [MCC2],
468 (1.3) [MC], 368 (2) [MCKBoc], 268 (57) [MCK
2Boc], 233 (63) [MCK2Boc-Cl], 197 (100) [MCK2Boc-
2Cl]. HRMS found 468.1082, Calcd for C18H26N2O8Cl2
468.1066.
4.1.8. Synthesis of N,N-bis-(tert-butoxycarbonyl)-2,5-bis-
methoxycarbonyl-3-(benzylamino)-1,2,3,4-tetrahydro-
pyrazine (4d). The same procedure described for the
synthesis of compound 4a was applied substituting
benzylamine for 1,2,4-triazole. Removal of the solvent
afforded compound 4d as an enantiomeric mixture of the
trans diastereomer (82%), mp 106.5–107.5 8C (from diethyl
ether/n-hexane). 1H NMR (CDCl3) (2 rotamers): 1.42, 1.45,
1.52 (36H, 3s, CH3 Boc), 3.70 (6H, s, CH3 OMe), 3.80–3.92
(10H, m, CH3 OMeCCH2 Bn), 4.82, 4.97 (2H, 2s, 2-H or
3-H), 5.60, 5.65 (2H, 2s, 2-H or 3-H), 7.28–7.36 (10H, m,
ArH), 7.50, 7.71 (2H, 2s, 6-H); 13C NMR (CDCl3): 27.87,
27.97, 49.47, 51.77, 52.57, 59.27, 60.55, 62.41, 81.58,
84.02, 121.51, 127.25, 128.43, 128.56, 139.17, 150.69,
152.75, 164.99, 167.85, 168.07. Anal. Calcd for
C25H35N3O8 (505.56): C 59.39; H 6.98; N 8.31; found C
59.43; H 7.21; N 8.05.
4.1.11. Synthesis of N,N-bis-(tert-butoxycarbonyl)-2,5-
bis-methoxycarbonyl-1,2,3,4-tetrahydropyrazine (6).
The same procedure as described above was followed but
adding compound 2 (99.5 mg, 0.25 mmol) to the cathodic
1
compartment to give compound 6 (55.2 mg, 55.2%). H
NMR (CDCl3): 1.41, 1.52 (18H, 2s, CH3 Boc), 2.96–3.08
(1H, m, 3-H), 3.71, 3.78 (6H, s, 2CH3 OMe), 4.68–4.90 (2H,
m, 2-HC3-H), 7.53 (1H, s, 6-H); 13C NMR (CDCl3): 27.82,
27.88, 42.27, 51.75, 52.62, 54.70, 55.98, 81.69, 83.58,
83.90, 109.60, 123.01, 150.52, 150.64, 169.00, 169.35;
MS: m/z (%)Z400 (4) [MC], 200 (100) [MCK2Boc],
167 (11) [MCK2Boc-OMe], 141 (13) [MCK2Boc-
CO2Me]; HRMS found 400.1857, Calcd for C18H28N2O8
400.1846.
4.1.9. Synthesis of N,N-bis-(tert-butoxycarbonyl)-2,5-bis-
methoxycarbonyl-3-methoxy-1,2,3,4-tetrahydropyra-
zine (4e). The same procedure described for the synthesis of
compound 4a was applied substituting sodium methoxide
for 1,2,4-triazole. Removal of the solvent afforded com-
pound 4e as an enantiomeric mixture of the trans
Acknowledgements
ˆ
We wish to thank the Fundac¸a˜o para a Ciencia e a
Tecnologia for financial support (project no.
POCTI/1999/QUI/32689).
1
diastereomer (35%); oil; H NMR (CDCl3) (2 rotamers):
1.43, 1.47, 1.53 (36H, 3s, CH3 Boc), 3.40 (6H, s, CH3
COMe), 3.70, 3.79 (12H, 2s, CH3 COOMe), 4.89, 5.05 (2H,
2s, 2-H or 3-H), 5.79, 5.84 (2H, 2s, 2-H or 3-H), 7.51, 7.72
(2H, 2s, 6-H), 13C NMR (CDCl3): 27.85, 28.01, 51.77,
52.70, 55.26, 58.78, 60.18, 77.96, 82.02, 83.56, 83.91,
107.85, 122.47, 150.81, 167.37; MS: m/z (%)Z430 (8)
[MC], 230 (100) [MCK2Boc], 199 (21) [MCK2Boc-
OMe]; HRMS found 430.1947, Calcd for C19H30N2O9
430.1951.
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