B. B. Snider, Q. Che / Tetrahedron 58 (2002) 7821–7827
7825
of acetic acid was stirred at 908C under nitrogen for 50 min.
Normal workup and flash chromatography on silica gel
(20:1 to 5:1 hexane/EtOAc) gave 12.9 mg (32%) of
recovered 9b, followed by 14.4 mg (39, 60% based on
recovered starting material) of (3a,3aa)-3a,4-dihydro-3-
ethyl-3H,6H-furo[3,4-c]isoxazol-6-one (10b) as a colorless
liquid: 1H NMR 4.74 (ddd, 1, J¼12.2, 6.7, 6.7 Hz), 4.71 (dd,
1, J¼9.1, 8.9 Hz), 4.29 (dd, 1, J¼8.9, 8.7 Hz), 3.94 (ddd, 1,
J¼12.2, 9.1, 8.7 Hz), 2.13–2.02 (m, 1), 1.98–1.87 (m, 1),
1.04 (t, 3, J¼7.3 Hz); 13C NMR 158.4, 157.1, 94.6, 69.9,
52.2, 25.7, 10.1; IR (neat) 2972, 1785, 1623, 1364, 1288,
1072.
Data for 19c. 1H NMR 4.84–4.76 (m, 1), 4.34 (q, 2,
J¼7.3 Hz), 3.25 (dd, 1, J¼17.7, 11.0 Hz), 2.84 (dd, 1,
J¼17.7, 8.5 Hz), 1.82–1.73 (m, 1), 1.64–1.56 (m, 1), 1.46–
1.26 (m, 7), 0.92 (br t, 3, J¼7.3 Hz); 13C NMR 160.9, 151.3,
84.2, 62.0, 38.3, 34.7, 27.2, 22.4, 14.1, 13.9; IR (neat) 1719,
1587, 1379, 1257, 1126; HRMS (DEI) calcd for
C10H18NOþ3 (MHþ) 200.1287, found 200.1284.
Data for 20c. 1H NMR 4.75–4.67 (m, 1), 4.33 (q, 2,
J¼7.2 Hz), 3.44 (dd, 1, J¼16.5, 9.1 Hz), 3.05 (dd, 1,
J¼16.5, 7.5 Hz), 1.90–1.80 (m, 1), 1.73–1.64 (m, 1), 1.50–
1.28 (m, 7), 0.92 (br t, 3, J¼7.3 Hz); 13C NMR 159.2, 108.5,
76.3, 61.7, 35.8, 34.4, 26.8, 22.3, 14.2, 13.8; IR (neat) 1734,
1616, 1382, 1244, 1027; HRMS (DEI) calcd for
C10H18NOþ4 (MHþ) 216.1236, found 216.1231.
3.1.7. Cyclization of ethyl nitroacetate with ethyl
acrylate (16a). Ethyl nitroacetate (12) (34.1 mg,
0.25 mmol) was added to a solution of Mn(OAc)3·2H2O
(135.4 mg, 0.50 mmol) and ethyl acrylate (16a) (50 mg,
0.50 mmol) in 10 mL of acetic acid at 258C under nitrogen.
The resulting mixture was stirred at 908C for 30 min at
which time the brown color of Mn(III) disappeared. The
reaction mixture was cooled, diluted with water (10 mL)
and extracted with CH2Cl2 (3£10 mL). The combined
organic extracts were washed successively with water and
saturated NaHCO3, dried over Na2SO4 and concentrated.
Flash chromatography on silica gel (10:1 hexane/EtOAc)
gave 17.1 mg (50%) of recovered 12 followed by 12.8 mg
(24, 47% based on recovered 12) of diethyl 4,5-dihydro-3,5-
isoxazoledicarboxylate (19a) as a colorless liquid: 1H NMR
5.19 (dd, 1, J¼11.6, 8.0 Hz), 4.37 (q, 2, J¼7.3 Hz), 4.27 (q,
2, J¼7.3 Hz), 3.53 (dd, 1, J¼18.3, 8.0 Hz), 3.48 (dd, 1,
J¼18.3, 11.6 Hz), 1.38 (t, 3, J¼7.3 Hz), 1.32 (t, 3,
J¼7.3 Hz); 13C NMR 168.9, 159.8, 151.0, 79.8, 62.4,
62.3, 37.5, 14.1 (2C); IR (neat) 2987, 1741, 1730, 1377,
1255, 1210. The spectral data are identical to those
previously reported.23,25
3.1.10. Preparation of ethyl 2-nitro-6-heptenoate (22a).
5-Iodo-1-pentene (21a) (196 mg, 1.0 mmol) was added to a
solution of ethyl nitroacetate (12) (133 mg, 1.0 mmol) in
2 mL of DMF containing tetraethylammonium chloride
(3.2 mg, 20 mmol) and anhydrous KHCO3 (100 mg,
1.0 mmol) at room temperature under nitrogen.36 The
reaction mixture was stirred at 708C for 20 h. DMF was
removed under vacuum, and the residue was diluted with
water and extracted with CH2Cl2 (4£5 mL). The combined
extracts were dried over MgSO4 and concentrated. Flash
chromatography on silica gel (40:1 to 10:1 hexane/Et2O)
gave 96 mg (48, 62% based on recovered starting material)
of 22a as a colorless liquid, followed by 31 mg (23%) of
recovered 12.
Data for 22a. 1H NMR 5.76 (ddt, 1, J¼17.1, 10.4, 6.7 Hz),
5.11 (dd, 1, J¼5.5, 9.8 Hz), 5.05 (dd, 1, J¼17.1, 1.2 Hz),
5.02 (dd, 1, J¼10.4, 1.2 Hz), 4.29 (q, 2, J¼7.0 Hz), 2.24–
2.34 (m, 1), 2.10–2.19 (m, 3), 1.53–1.46 (m, 2), 1.30 (t, 3,
J¼7.0 Hz); 13C NMR 164.5, 137.0, 115.9, 88.0, 63.0, 32.7,
29.6, 24.7, 13.9; IR (neat) 1749, 1558, 1372, 1186.
3.1.8. Cyclization of ethyl nitroacetate with styrene
(16b). A solution of ethyl nitroacetate (12) (34.1 mg,
0.25 mmol), styrene (16b) (26 mg, 0.25 mmol), and
Mn(OAc)3·2H2O (135.4 mg, 0.50 mmol) in 10 mL of acetic
acid was stirred at 908C under nitrogen for 1.5 h. Normal
workup and flash chromatography on silica gel (50:1 to10:1
hexane/EtOAc) gave 20.3 mg (60%) of recovered 12 and
1.8 mg (4, 10% based on recovered 12) of ethyl 4,5-dihydro-
5-phenyl-3-isoxazolecarboxylate 2-oxide (20b) as a color-
3.1.11. Preparation of ethyl 2-nitro-cis-6-nonenoate
(22b). Ethyl 2-nitro-cis-6-nonenoate (22b) was prepared
analogously to 22a from cis-7-iodo-3-heptene (21b)
(224 mg, 1.0 mmol), ethyl nitroacetate (12) (133 mg,
1.0 mmol) and KHCO3 (100 mg, 1.0 mmol) in 2 mL of
DMF in the presence of tetraethyl ammonium chloride
(3.2 mg, 20 mmol). Normal workup and flash chromato-
graphy on silica gel (50:1 to 10:1 hexane/EtOAc) gave
11 mg of recovered 21a, 86.7 mg (38, 53% based on
recovered 12) of 22b as a colorless liquid, followed by
38 mg (29%) of recovered 12:
1
less liquid: H NMR 7.48–7.41 (m, 5), 5.72 (dd, 1, J¼9.8,
8.0 Hz), 4.33 (q, 2, J¼7.3 Hz), 3.82 (dd, 1, J¼17.1, 9.8 Hz),
3.44 (dd, 1, J¼17.1, 8.0 Hz), 1.34 (t, 3, J¼7.3 Hz); IR (neat)
1733, 1690 (shoulder), 1620, 1557, 1370, 1242, 1021. The
spectral data are identical to those previously reported.30
Data for 22b. 1H NMR 5.47–5.40 (m, 1), 5.30–5.24 (m, 1),
5.09 (dd, 1, J¼5.5, 9.1 Hz), 4.29 (q, 2, J¼7.3 Hz), 2.33–
2.23 (m, 1), 2.19–1.98 (m, 5), 1.49–1.41 (m, 2), 1.31 (t, 3,
J¼7.3 Hz), 0.96 (t, 3, J¼7.3 Hz); 13C NMR 164.5, 133.2,
127.1, 88.1, 62.9, 29.7, 26.1, 25.5, 20.5, 14.2, 13.9; IR (neat)
3007, 1750, 1558, 1373.
3.1.9. Cyclization of ethyl nitroacetate with 1-hexene
(16c). A solution of ethyl nitroacetate (12) (34.1 mg,
0.25 mmol), 1-hexene (16c) (42.0 mg, 0.50 mmol), and
Mn(OAc)3·2H2O (134.1 mg, 0.50 mmol) in 4 mL of acetic
acid was stirred at 908C for 90 min in a sealed tube. Normal
workup and flash chromatography on silica gel (20:1
hexane/EtOAc) gave 10.0 mg (20, 25% based on recovered
starting material) of ethyl 5-butyl-4,5-dihydro-3-isoxazole-
carboxylate (19c) as a colorless liquid, followed by 7.2 mg
(21%) of recovered 12, and 27.4 mg (51, 65% based on
recovered starting material) of ethyl 5-butyl-4,5-dihydro-3-
isoxazolecarboxylate 2-oxide (20c) as a colorless liquid.
3.1.12. Oxidative cyclization of ethyl 2-nitro-6-hepteno-
ate (22a). Nitroheptenoate 22a (30 mg, 0.15 mmol) was
added to a solution of Mn(OAc)3·2H2O (81 mg, 0.30 mmol,
2 equiv.), Cu(OAc)2·H2O (30 mg, 0.15 mmol, 1 equiv.) and
NaOAc (24.6 mg, 0.30 mmol, 2 equiv.) in 2 mL of acetic
acid at 258C under nitrogen. The resulting mixture was