950
F. Felluga et al. / Tetrahedron: Asymmetry 19 (2008) 945–955
4.2.4. Ethyl 5,5-dimethyl-2-hexenoate 5d. Compound 5d
was prepared from 3,3-dimethylbutanal 4d, and obtained
as a colourless oil, 85% yield, after distillation, bp 60 °C
(0.05 mmHg). IR (neat), 1721 (CO2Et), 1653 (C@C)
cmꢀ1. 1H NMR (400 MHz, CDCl3) d 6.96 (dt, Jtrans = 15.2,
104 °C (0.75 mmHg)]. IR (neat) 1731 (CO2Et), 1550, 1370
(NO2) cmꢀ1 1H NMR (400 MHz, CDCl3) d 4.49 (dd,
.
J1 = 13.1, J2 = 7.6 Hz, 1H, CH2NO2), 4.42 (dd, J1 = 13.1,
J2 = 5.9 Hz, 1H, CH2NO2), 4.14 (q, 2H, CH3CH2O); 2.67
(sept, J = 6.6 Hz, 1H, H-3), 2.41 (apparent d, 2H, H-2),
1.65 (sept, J = 7.0 Hz, CH(CH3)2), 1.24 (t + m, 5H,
CH3CH2O and H-4), 0.92, 0.90 (2d, J = 7.3 Hz, 6H,
(CH3)2CH). 13C NMR (100.1 MHz, CDCl3) d 171.4 (s),
78.7 (t, CH2NO2), 60.7 (t, CH2O), 40.5 (t), 36.0 (t), 32.1
(d, C-3), 25.0 (d, C-5), 22.5 (q), 22.2 (q), 14.1 (q). HRMS
(EI) calcd for C10H18O2 (MꢀHNO2)+Å 170.1384, found
170.1397. MS-EI 188 (Mꢀ29, 100%), 170 (MꢀHNO2)+Å,
82), 160 (42), 144 (78), 114 (70), 72 (90), 46 (58).
4
3J = 7.2 Hz, 1H, H-3), 5.77 (dt, Jtrans = 15.2, J = 1.3 Hz,
1H, H-2), 4.15 (q, 2H, CH3CH2O), 2.04 (dd, 3J = 7.2,
4J = 1.3 Hz, 2H, H-4), 1.24 (t, 3H, CH3CH2O), 0.92 (s,
9H, t-Bu). 13C NMR (100.1 MHz, CDCl3) d 166.5 (CO),
146.8 (C-3), 123.2 (d, C-2), 60.1 (t, CH2O), 46.6 (t, C-4),
29.3 (s, t-Bu), 14.2 (q, CH3CH2). ESI-MS 171.1 (M+H+),
193.0 (M+Na+). HRMS (EI) calcd for C10H18O2 (M+)
170.1307, found 170.1299. MS, m/z 170 (M+Å, 32%), 155
(24), 141 (76), 97 (100).
4.3.3. Ethyl ( )-3-nitromethyloctanoate 6c. Colourless oil,
69% yield, bp 110 °C (0.1 mmHg). IR (neat) 1733 (CO2Et),
4.2.5. Ethyl 4-phenyl-2-butenoate 5e. Compound 5e was
prepared from phenylethanal 4e, and obtained as a colour-
less oil, 78% yield, after distillation, bp 83 °C (0.1 mmHg).
IR (neat), 3062, 3028, 1603, 1496, 1453, 751, 699 (Ph), 1717
1
1552, 1378 (NO2) cmꢀ1. H NMR (400 MHz, CDCl3) d
4.49 (dd, J1 = 12.1, J2 = 6.2 Hz, 1H, CH2NO2), 4.42 (dd,
J1 = 12.1, J2 = 7.2 Hz, 1H, CH2NO2), 4.13 (q, 2H,
CH3CH2O), 2.60 (sept, J = 6.6 Hz, 1H, H-3), 2.41 (appar-
ent d, 2H, H-2), 1.34 (m, 2H), 1.33–1.24 (m + t, 9H,
CH2 + CH3CH2O), 0.85 (t, 3H, CH3CH2). 13C NMR
(100.1 MHz, CDCl3) d 171.5 (s), 78.5 (t, CH2NO2), 60.7
(t, CH2O), 35.8 (t, C-2), 34.2 (C-3, d), 31.5 (t), 31.3 (t),
26.0 (t), 22.4 (t), 14.1 (q), 13.9 (q). ESI-MS 208.0 (M+1).
HRMS (EI) calcd for C11H21O2 (MꢀNO2) 185.1542, found
185.1530. MS, m/z 231 (M+, 40%), 216 (12), 185 (MꢀNO2,
27), 169 (41), 139 (34), 111 (45), 71 (100).
1
(CO2Et), 1653 (C@C) cmꢀ1. H NMR (400 MHz, CDCl3)
d 7.31 (t, 2H, Ph), 7.24 (t, 1H, Ph), 7.17 (d, 2H, Ph), 7.10
3
(dt, Jtrans = 15.7, J = 7.0 Hz, 1H, H-3), 5.81 (dt, Jtrans
=
15.7, 4J = 1.5 Hz, 1H, H-2), 4.17 (q, 2H, CH3CH2O),
3
4
3.52 (dd, J3,4 = 7.0, J2,4 = 1.5 Hz, 2H, H-4), 1.27 (t, 3H,
CH3CH2O). 13C NMR (100.1 MHz, CDCl3) d 166.4 (s),
147.2 (d, C-3), 137.6 (s), 128.7, 128.6, 126.6 (d, Ph), 122.3
(d, C-2), 60.2 (t), 38.4 (t), 14.1 (q). ESI-MS 191.0 (MH+).
HRMS (EI) calcd for C12H14O2 (M+) 190.0994, found
190.0980. MS, m/z 190 (M+Å, 32%), 175 (24), 144 (56),
117 (86), 115 (100).
4.3.4. Ethyl ( )-5,5-dimethyl-3-nitromethylhexanoate (6d).
Colourless oil, 65% yield, after flash chromatography (elu-
ent: light petroleum/ethyl acetate 98:2). IR (neat) 1733
4.3. General procedure for the synthesis of racemic c-nitro
esters 6a–e20
(CO2Et), 1552, 1379 (NO2) cmꢀ1 1H NMR (400 MHz,
.
CDCl3) d 4.49 (dd, J1 = 12.4, J2 = 7.0 Hz, 1H, CH2NO2),
4.25 (dd, J1 = 12.4, J2 = 5.9 Hz, 1H, CH2NO2), 4.12 (q,
2H, CH3CH2O), 2.64 (sept, J = 6.0 Hz, 1H, H-3), 2.45
(apparent d, 2H, H-2), 1.29 (part AB of an ABX system,
JAB = 12.4, JAX = 5.1, JBX = 4.7 Hz, 2H, H-4), 1.25 (t,
3H, CH3CH2O), 0.92 (s, 9H, t-Bu). 13C NMR
(100.1 MHz, CDCl3) d 171.4 (s, CO2Et), 79.8 (t, CH2NO2),
60.7 (t, CH2O), 44.6 (t), 38.0 (t), 30.9 (s), 30.8 (d, C-3), 29.4
(q, t-Bu), 14.1 (q, CH3CH2). ESI-MS 254.0 (M+Na+).
HRMS (EI) calcd for C11H21NO4 (M+Å) 231.1471, found
231.1490. MS, m/z 231 (M+Å, 36%), 197 (82), 184
(MꢀHNO2, 71), 169 (100), 154 (65).
To a solution of the a,b-unsaturated ester (100 mmol) in
nitromethane (25 mL), DBU (100 mmol) was added drop-
wise and the solution was left stirring overnight at room
temperature. The nitromethane in excess was removed in
vacuo, after which the residue was dissolved in diethyl
ether and washed with 5% HCl; then the organic phase
was dried over Na2SO4 and evaporated to give a dark
brown oil which was purified by distillation or chromato-
graphed on SiO2 (eluent: light petroleum/ethyl acetate
99:1).
4.3.1. Ethyl ( )-3-nitromethylheptanoate 6a. Colourless
oil, 72% yield, bp 100 °C (0.2 mmHg) [lit.20 124–126 °C
(1.25 mmHg)]. IR (neat) 1732 (CO2Et), 1552, 1378 (NO2)
4.3.5. Ethyl ( )-3-nitromethyl-4-phenylbutanoate 6e. Col-
ourless oil, 70% yield, after distillation, bp 125 °C
(0.2 mmHg). IR (neat) 3064, 3029, 1603, 1496, 750, 702
1
cmꢀ1. H NMR (400 MHz, CDCl3) d 4.51 (dd, J1 = 11.9,
J2 = 6.2 Hz, 1H, CH2NO2), 4.43 (dd, J1 = 11.9, J2 =
5.9 Hz, 1H, CH2NO2), 4.14 (q, 2H, CH3CH2O), 2.62 (sept,
J = 6.6 Hz, 1 H, H-3), 2.43 (apparent d, 2H, H-2), 1.41 (m,
2H), 1.33 (m, 4H), 1.25 (t, 3H, CH3CH2O), 0.90 (t, 3H,
CH3CH2). 13C NMR (100.1 MHz, CDCl3) d 171.5 (s),
78.5 (t, CH2NO2), 60.6 (t, CH2O), 35.9 (t, C-2), 34.1 (d,
C-3), 31.0 (t), 28.4 (t), 22.4 (t), 14.1 (q), 13.7 (q). HRMS
(EI) calcd for C10H18O2 (MꢀHNO2) 170.1307, found
170.1312. ESI-MS 240.0 (M+Na+). MS, m/z 217 (M+Å,
12%), 170 (MꢀHNO2, 81), 169 (100), 155 (63).
(Ph), 1733 (CO2Et), 1552, 1379 (NO2) cmꢀ1 1H NMR
.
(400 MHz, CDCl3) d 7.32 (m, 2H, Ph), 7.25 (t, 1H, Ph),
7.19 (d, 2H, Ph), 4.47 (dd, J1 = 12.8, J2 = 6.6 Hz, 1H,
CH2NO2), 4.42 (dd, J1 = 12.8, J2 = 5.8, 1H, CH2NO2),
4.15 (q, CH3CH2O), 2.92 (sept, J = 6.6 Hz, 1H, H-3),
2.75 (apparent d, 2H, CH2Ph), 2.43 (part AB of an ABX
system, JAB = 16.8, JAX = 11.4, JBX = 7.0 Hz, 2H, H-2),
1.26 (t, 3H, CH3CH2O). 13C NMR (100.1 MHz, CDCl3),
d 171.4 (s, CO), 137.7 (s, Ph), 129.3, 128.8, 127.0 (d, Ph),
77.5 (t, CH2NO2), 60.9 (t, CH2O), 37.5 (t, C-2), 36.1 (d,
C-3), 35.4 (t, CH2Ph), 14.2 (q). HRMS (EI) calcd for
C13H17NO4 (M+Å) 251.1158, found 251.1140. ESI-MS
252.1 (MH+), 274.0 (M+Na+). MS, m/z 251 (M+Å, 12%),
4.3.2. Ethyl ( )-5-methyl-3-nitromethylhexanoate 6b. Col-
ourless oil, 75% yield, bp 110 °C (0.09 mmHg) [lit.20 103–