N. W. Polaske et al. / Tetrahedron: Asymmetry 20 (2009) 2742–2750
2749
J = 2 Hz), 3.83 (1H, dd, J = 17 Hz and J = 2 Hz), 3.73 (3H, s), 2.96 (3H,
4.3.5. 3-Phenylsulfanyl-3-(tert-butoxycarbonyl)-1,4-dimethyl-
2,5-piperazinedione 16e
D = 27.1350 (c = 30 mg mLꢀ1, CH2Cl2, 35% ee).
IR (CH2Cl2) mmax (cmꢀ1) 1744, 1677, 1463, 1387, 1336, 1258,
1157, 1045.
s), 1.28 (3H, dt, J = 6 Hz and J = 1 Hz). 13C NMR (125 MHz, CDCl3):
d = 168.3, 163.1, 160.6, 64.01, 62.06, 53.51, 48.54, 33.65, 13.97.
HRMS-EI: m/z MÅ+ calcd for C9H14N2O4: 214.0954; found:
214.0955.
[a]
1H NMR (500 MHz, CDCl3) d 7.53–7.36 (5H, m), 3.41 (1H, d,
J = 18 Hz), 3.14 (3H, s), 2.75 (3H, s), 2.04 (1H, d, 18 Hz), 1.57 (9H, s).
13C NMR (125 MHz, CDCl3) d 163.49, 163.10, 161.03, 138.02,
130.92, 129.03, 128.75, 85.58, 81.74, 50.07, 33.47, 30.00, 27.70.
HRMS (EI) calcd for C17H22N2O4SNa+: 373.1192, found:
373.1189.
4.3. General procedure for asymmetric a-sulfenylation
To a flame dried flask purged with N2 and equipped with a stir
bar was added the b-amido ester, catalyst, and solvent. This solu-
tion was brought to the desired temperature, followed by addition
of the sulfenylating reagent. The mixture was stirred for the appro-
priate period of time. Then, the reaction was quenched with a sat-
urated solution of NH4Cl (same volume as solvent) and extracted
three times with CH2Cl2. The organic extracts were combined,
dried over MgSO4, filtered, and concentrated. The crude oils were
purified by column chromatography (silica-gel). Enantiomeric
excess (ee) was determined by 1H NMR spectroscopy using
Eu(hfc)3.
4.3.6. 3-Phenylsulfanyl-3-(ethoxycarbonyl)-1,4-diethyl-2,5-
piperazinedione 16f
[
a
]
D = ꢀ4.760 (c = 10 mg mLꢀ1, CH2Cl2, 10% ee).
IR (CH2Cl2) mmax (cmꢀ1) 1748, 1673, 1460, 1414, 1357, 1294,
1248, 1165, 1069, 1019.
1H NMR (500 MHz, CDCl3) d 7.51–7.33 (5H, m), 4.44–4.31 (2H,
m), 3.93–3.88 (1H, m), 3.44 (1H, d, J = 18 Hz), 3.33–3.22 (3H, m),
2.20 (1H, d, J = 18 Hz), 1.36 (3H, t, J = 7 Hz), 1.28 (3H, t, J = 7 Hz),
1.0 (3H, t, J = 7 Hz).
4.3.1. 3-Benzylsulfanyl-3-(methoxycarbonyl)-1,4-dimethylpiper-
azine-2,5-dione 10c
13C NMR (125 MHz, CDCl3) d 165.25, 163.44, 160.67, 138.22,
130.88, 129.15, 128.11, 81.30, 63.75, 47.72, 41.56, 41.34, 13.86,
12.72, 11.41.
[a] )
D = +15.4 (c 0.01, CH2Cl2, 40% ee). IR (CH2Cl2) mmax (cmꢀ1
1751, 1671, 1461, 1396, 1248, 1045. 1H NMR (500 MHz, CDCl3):
d = 7.34–7.26 (5H, m), 3.91–3.76 (4H, m), 3.88 (3H, s), 2.99 (3H,
s), 2.76 (3H, s). 13C NMR (125 MHz, CDCl3): d = 165.63, 163.1,
160.6, 135.5, 128.6, 128.5, 127.5, 54.22, 50.88, 34.63, 33.83,
30.58. HRMS-FAB: m/z [M+H]+ calcd for C15H18N2O4S: 323.1066;
found: 323.1062.
HRMS (EI) calcd for C17H22N2O4SNa+: 373.1192, found:
373.1204.
4.3.7. 3-Phenylsulfanyl-3-(ethoxycarbonyl)-1,4-dibenzyl-2,5-
piperazinedione 16g
[
a
]
D = ꢀ1.134 (c = 10 mg mLꢀ1, CH2Cl2, 5% ee).
IR (CH2Cl2) mmax (cmꢀ1) 1749, 1675, 1465, 1245, 1172, 1025.
1H NMR (500 MHz, CDCl3) d 7.40–7.09 (15H, m), 5.46 (1H, d,
J = 16 Hz), 4.58 (1H, d, J = 15 Hz), 4.46 (1H, d, J = 16 Hz), 4.13 (1H,
d, J = 15 Hz), 3.93–3.89 (1H, m), 3.52 (1H, d, J = 18 Hz), 3.17–3.13
(1H, m), 2.19 (1H, d, J = 18 Hz), 0.86 (3H, t, J = 7 Hz).
4.3.2. 3-Benzylsulfanyl-3-(ethoxycarbonyl)-1,4-dimethylpiper-
azine-2,5-dione 10d
[a] )
D = +22.1 (c 0.01, CH2Cl2, 62% ee). IR (CH2Cl2) mmax (cmꢀ1
1745, 1668, 1460, 1390, 1263, 1048. 1H NMR (500 MHz, CDCl3):
d = 7.37–7.26 (5H, m), 4.40–4.30 (2H, m), 3.91–3.77 (4H, m), 3.00
(3H, s), 2.76 (3H, s), 1.34 (3H, t, J = 7 Hz). 13C NMR (125 MHz,
CDCl3): d = 165.0, 163.2, 160.7, 135.6, 128.6, 128.5, 127.5, 76.79,
63.75, 50.89, 34.61, 33.79, 30.51, 13.93. HRMS-FAB: m/z [M+H]+
calcd for C16H20N2O4S: 337.1222; found: 337.1236.
13C NMR (125 MHz, CDCl3) d 164.56, 164.11, 161.41, 138.02,
135.79, 134.22, 130.85, 129.09, 129.01, 128.82, 128.63, 128.31,
128.17, 127.71, 127.56, 81.13, 63.18, 50.12, 47.69, 47.07, 13.20.
HRMS (EI) calcd for C27H26N2O4SNa+: 497.1505, found:
497.1501.
4.3.3. 3-Benzylsulfanyl-3-(tert-butoxycarbonyl)-1,4-dimethyl-
4.3.8. 3-Phenylsulfanyl-3-(tert-butoxycarbonyl)-1,4-dibenzyl-
piperazine-2,5-dione 10e
2,5-piperazinedione 16i
[a]
D = 30.1857 (c = 30 mg mL-1, CH2Cl2, 42% ee).
[a]D = +33.0 (c 0.01, CH2Cl2 75% ee).
IR (CH2Cl2) mmax (cmꢀ1) 1740, 1665, 1464, 1390, 1261, 1062.
1H NMR (500 MHz, CDCl3): d = 7.36–7.25 (5H, m), 3.88 (1H, d,
J = 17 Hz), 3.79 (2H, s), 3.77 (1H, d, J = 17 Hz), 3.01 (3H, s), 2.74
(3H, s), 1.53 (9H, s).
IR (CH2Cl2) mmax (cmꢀ1) 1746, 1680, 1462, 1402, 1238, 1038.
1H NMR (500 MHz, CDCl3) d 7.46–7.18 (15H, m), 5.3 (1H, d,
J = 16 Hz), 4.86 (1H, d, J = 14 Hz), 4.63 (1H, d, J = 16 Hz), 3.94
(J = 14 Hz), 3.56 (1H, d, J = 18 Hz), 2.17 (1H, d, J = 18 Hz).
13C NMR (125 MHz, CDCl3) d 164.26, 163.38, 161.77, 138.06,
135.38, 134.38, 130.79, 129.03, 128.77, 128.63, 128.20, 128.17,
128.01, 127.64, 127.21, 85.55, 82.49, 49.70, 47.96, 47.52, 26.99.
HRMS (EI) calcd for C29H31N2O4S [M+H]+: 503.1999, found:
503.2.
13C NMR (125 MHz, CDCl3): d = 163.7, 163.1, 161.0, 135.6, 128.4,
127.3, 85.15, 77.33, 50.81, 34.43, 33.65, 30.25, 27.54.
HRMS-FAB: m/z [M+H]+ calcd for C18H24N2O4S: 365.1536;
found: 365.1552.
4.3.4. 3-Benzylsulfanyl-3-(ethoxycarbonyl)-1-methylpiperazine-
2,5-dione 10h
4.3.9. 3-Benzylsulfanyl-3-(ethoxycarbonyl)-5-methoxy-1-methyl-
[
a]
D = 3.1 (c = 0.01, CH2Cl2 7% ee).
3,6-dihydro-1H-pyrazin-2-one 18
IR (acetone) mmax (cmꢀ1) 3219, 3107, 1746, 1680, 1403, 1239,
[a]D = 1.1 (c = 0.01, CH2Cl2 5% ee).
IR (CH2Cl2) mmax (cmꢀ1) 1744, 1672, 1385, 1252, 1031.
1H NMR (500 MHz, CDCl3): d = 7.35–7.21 (5H, m), 4.28–4.24
(2H, m), 4.06 (1H, d, J = 13 Hz), 3.98 (1H, d, J = 13 Hz), 3.90 (2H,
s), 3.76 (3H, s), 2.88 (3H, s), 1.30 (3H, t, J = 7 Hz).
1039.
1H NMR (600 MHz, CDCl3): d = 7.96 (1H, s), 7.33 (5H, m), 4.30–
3.96 (4H, m), 4.95 (1H, d, J = 18 Hz), 3.87 (1H, d, J = 18 Hz), 2.82
(3H, s), 1.31 (3H, t, J = 7 Hz).
13C NMR (150 MHz, CDCl3): d = 165.9, 165.6, 160.3, 135.6, 128.9,
128.4, 127.3, 68.54, 63.61, 51.53, 35.26, 34.24, 13.70.
HRMS-FAB: m/z [M+H]+ calcd for C15H19N2O4S: 323.1066;
found: 323.1078.
13C NMR (125 MHz, CDCl3): d = 167.7, 163.5, 160.9, 137.0, 129.0,
128.3, 127.0, 62.76, 53.97, 48.55, 35.17, 33.82, 13.94.
HRMS-FAB: m/z [M+H]+ calcd for C16H20N2O4S: 337.1222;
found: 337.1236.