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78.4, 66.34, 56.4, 27.9 ppm; MS-ESI: m/z: calcd for [C22H22N2O5Na]+:
417.1421; found: 417.1419.
CDCl3): d=7.52–7.45 (m, 2H), 7.30–7.24 (m, 2H), 6.09 (s, 1H), 3.95
(s, 3H), 3.65 (s, 3H), 1.47 ppm (s, 9H); 13C NMR (75 MHz, CDCl3): d=
161.1, 157.9, 155.0, 150.0, 137.8, 131.9, 129.0, 122.8, 110.3, 84.6,
68.3, 53.6, 52.2, 28.0 ppm; MS-ESI: m/z calcd for [C18H20BrNO7Na]+:
464.0315; found: 464.0312.
2-tert-Butyl 4,5-dimethyl 3-(4-tert-butylphenyl)isoxazole-2,4,5-
tricarboxylate (3m): According to the general procedure, hydrox-
ylamine 1m (0.25 mmol, 72.8 mg, 1.00 equiv), dry CH2Cl2 (2 mL), 2a
(122 mL, 1.00 mmol, 4.00 equiv), and TEMPO (78.8 mg, 0.50 mmol,
2.00 equiv) were reacted. The crude product was purified by flash
column chromatography on silica gel eluting with pentane/AcOEt
[(%AcOEt): 1 (50), 5 (50), 10 (200), 25% (200 mL)] to give 3m as
pale-yellow viscous oil (0.16 mmol, 53.3 mg, 51%). 1H NMR
(300 MHz, CDCl3): d=7.40–7.29 (m, 4H), 6.12 (s, 1H), 3.95 (s, 3H),
3.66 (s, 3H), 1.46 (s, 9H), 1.30 ppm (s, 9H); 13C NMR (75 MHz,
CDCl3): d=161.4, 158.1, 155.5, 151.6, 149.8, 135.5, 126.9, 125.7,
125.5, 111.0, 84.2, 68.6, 53.5, 52.2, 34.6, 31.4, 31.3, 28.0 ppm; MS-
ESI: m/z: calcd for [C22H30NO7]+: 420.2018; found: 420.2017.
2-tert-Butyl 4,5-dimethyl 3-(4-chlorophenyl)isoxazole-2,4,5-tricar-
boxylate (3r): According to the general procedure, hydroxylamine
1r (0.25 mmol, 64.4 mg, 1.00 equiv), dry CH2Cl2 (2 mL), 2a (122 mL,
1.00 mmol, 4.00 equiv), and TEMPO (78.8 mg, 0.50 mmol,
2.00 equiv) were reacted. The crude product was purified by flash
column chromatography on silica gel eluting with pentane/AcOEt
[(%AcOEt): 1 (50), 5 (50), 10 (200), 15% (300 mL)] to give 3r as vis-
1
cous oil (0.16 mmol, 64.6 mg, 65%). H NMR (300 MHz, CDCl3): d=
7.33 (s, 4H), 6.10 (s, 1H), 3.95 (s, 3H), 3.65 (s, 3H), 1.47 ppm (s, 9H);
13C NMR (75 MHz, CDCl3): d=161.2, 157.9, 155.0, 150.0, 137.3,
134.6, 129.0, 128.7 110.4, 84.6, 68.3, 53.6, 52.2, 28.0 ppm; MS-ESI:
calcd for [C18H21ClNO7]+: 398.1001; found: 398.1000.
2-tert-Butyl 4,5-dimethyl 3-(4-methoxyphenyl)isoxazole-2,4,5-tri-
carboxylate (3n): According to the general procedure, hydroxyla-
mine 1n (0.25 mmol, 63.3 mg, 1.00 equiv), dry CH2Cl2 (2 mL), 2a
(122 mL, 1.00 mmol, 4.00 equiv), and TEMPO (78.8 mg, 0.50 mmol,
2.00 equiv) were reacted. The crude product was purified by flash
column chromatography on silica gel eluting with pentane/AcOEt
[(%AcOEt): 1 (50), 5 (50), 10 (200), 15 (300), 25% (200.00 mL)] to
give 3n as a viscous oil (0.21 mmol, 82.5 mg, 84%). 1H NMR
(300 MHz, CDCl3): d=7.33–7.26 (m, 2H), 6.91–6.83 (m, 2H), 6.08 (s,
1H), 3.94 (s, 3H), 3.79 (s, 3H), 3.64 (s, 3H), 1.46 ppm (s, 9H);
13C NMR (75 MHz, CDCl3): d=161.4, 159.9, 158.1, 155.2, 149.6,
130.8, 128.6, 114.1, 110.9, 84.2, 68.5, 55.3, 53.5, 52.1, 28.0 ppm; MS-
ESI: m/z calcd for [C19H23NO8Na]+: 416.1316; found: 416.1315.
2-tert-Butyl 4,5-dimethyl 3-(4-trifluoromethylphenyl)isoxazole-
2,4,5-tricarboxylate (3s): According to the general procedure, hy-
droxylamine 1s (0.25 mmol, 72.8 mg, 1.00 equiv), dry CH2Cl2 (2 mL),
2a (122 mL, 1.00 mmol, 4.00 equiv), and TEMPO (78.8 mg,
0.50 mmol, 2.00 equiv) were reacted. The crude product was puri-
fied by flash column chromatography on silica gel eluting with
pentane/AcOEt [(%AcOEt): 1 (50), 5 (50), 10 (200), 15% (300 mL)] to
give 3s as a viscous oil (0.16 mmol, 67.9 mg, 63%). 1H NMR
(300 MHz, CDCl3): d=7.62 (d, J=8.3 Hz, 2H), 7.52 (d, J=8.2 Hz,
2H), 6.18 (s, 1H), 3.95 (s, 3H), 3.65 (s, 3H), 1.47 ppm (s, 9H);
13C NMR (75 MHz, CDCl3): d=161.01, 157.78, 154.99, 150.28, 142.54
130.79 (q, J=32.5 Hz), 127.70 (q, J=266.8 Hz), 125.71 (q, J=
3.7 Hz), 122.10, 110.02, 84.72, 68.22, 53.56, 52.20, 27.97 ppm;
19F NMR (300 MHz, CDCl3): d=À62.67 ppm; MS-ESI: m/z calcd for
[C19H20F3NO7Na]+: 454.1084; found: 454.1073.
2-tert-Butyl 4,5-dimethyl 3-(3-methoxyphenyl)isoxazole-2,4,5-tri-
carboxylate (3o): According to the general procedure, hydroxyla-
mine 1o (0.25 mmol, 63.3 mg, 1.00 equiv), dry CH2Cl2 (2 mL), 2a
(122 mL, 1.00 mmol, 4.00 equiv), and TEMPO (78.8 mg, 0.50 mmol,
2.00 equiv) were reacted. The crude product was purified by flash
column chromatography on silica gel eluting with pentane/AcOEt
[(%AcOEt): 1 (50), 5 (50), 10 (200), 15% (300 mL)] to give 3o as
a pale-yellow viscous oil (0.18 mmol, 69.8 mg, 71%). 1H NMR
(300 MHz, CDCl3): d=7.26–7.20 (m, 1H), 7.02–6.70 (m, 3H), 6.06 (s,
1H), 3.91 (s, 3H), 3.76 (s, 3H), 3.61 (s, 3H), 1.43 ppm (s, 9H);
13C NMR (75 MHz, CDCl3): d=161.3, 159.9, 158.0, 155.2, 149.8,
140.1, 129.8, 119.5, 114.3, 112.8, 110.9, 84.3, 68.8, 55.3, 53.5, 52.2,
28.1 ppm; MS-ESI: calcd for [C19H23NO8Na]+: 416.1316; found:
416.1314.
2-tert-Butyl 4,5-dimethyl 3-vinylisoxazole-2,4,5-tricarboxylate
(3t): According to the general procedure, hydroxylamine 1t
(0.25 mmol, 43.3 mg, 1.00 equiv), dry CH2Cl2 (2 mL), 2a (122 mL,
1.00 mmol, 4.00 equiv), and TEMPO (78.8 mg, 0.50 mmol,
2.00 equiv) were reacted. The crude product was purified by flash
column chromatography on silica gel eluting with pentane/AcOEt
[(%AcOEt): 1 (100), 5 (100), 10% (300 mL)] to give 3t as a light
yellow oil (0.13 mmol, 39.1 mg, 50%). 1H NMR (300 MHz, CDCl3):
d=6.00–5.84 (m, 1H), 5.63 (d, J=6.1 Hz, 1H), 5.43 (d, J=17.0 Hz,
1H), 5.27 (d, J=10.2 Hz, 1H), 3.92 (s, 3H), 3.77 (s, 3H), 1.52 ppm (s,
9H); 13C NMR (100 MHz, CDCl3): d=161.5, 158.0, 155.7, 150.2,
133.8, 118.2, 109.8, 84.3, 67.31, 53.5, 52.2, 28.1 ppm; MS-ESI: m/z:
calcd for [C14H20NO7]+: 314.1234; found: 314.1234.
2-tert-Butyl 4,5-dimethyl 3-(2-methoxyphenyl)isoxazole-2,4,5-tri-
carboxylate (3p): According to the general procedure, hydroxyla-
mine 1p (0.25 mmol, 63.3 g, 1.00 equiv), dry CH2Cl2 (2 mL), 2a
(122 mL, 1.00 mmol, 4.00 equiv), and TEMPO (78.8 mg, 0.50 mmol,
2.00 equiv) were reacted. The crude product was purified by flash
column chromatography on silica eluting with pentane/AcOEt
[(%AcOEt): 1 (50), 5 (50), 15 (200), 20% (300 mL)] to give 3p as
light-yellow viscous oil (0.11 mmol, 42.4 mg, 43%). 1H NMR
(300 MHz, CDCl3): d=7.33–7.27 (m, 2H), 6.99–6.86 (m, 2H), 6.51 (s,
1H), 3.94 (s, 3H), 3.85 (s, 3H), 3.63 (s, 3H), 1.43 ppm (s, 9H);
13C NMR: 161.6, 158.4, 157.4, 155.4, 149.7, 130.1, 129.1, 126.5, 120.9,
111.2, 111.1, 83.9, 64.4, 55.8, 53.5, 52.1, 28.1 ppm; MS-ESI: m/z calcd
for [C19H23NO8Na]+: 416.1316; found: 416.1317.
2-tert-Butyl 4,5-dimethyl 3-cyclohexylsoxazole-2,4,5-tricarboxy-
late (3u): According to the general procedure, hydroxylamine 1u
(0.25 mmol, 50.8 mg, 1.00 equiv), dry CH2Cl2 (2 mL), 2a (122 mL,
1.00 mmol, 4.00 equiv), and TEMPO (78.8 mg, 0.50 mmol,
2.00 equiv) were reacted. The crude product was purified by flash
column chromatography on silica gel eluting with pentane/AcOEt
[(%AcOEt): 1 (100), 5 (50), 10% (300 mL)] to give 3u as a light-
yellow oil (0.19 mmol, 68.6 mg, 74%). 1H NMR (400 MHz, CDCl3):
d=5.07 (d, J=2.8 Hz, 1H), 3.89 (s, 3H), 3.76 (s, 3H), 1.68 (m, 5H),
1.50 (s, 9H), 1.20–0.84 ppm (m, 6H); 13C NMR (100 MHz, CDCl3): d=
162.1, 158.3, 157.2, 150.7, 109.3, 84.0, 70.7, 53.3, 52.2, 41.2, 30.0,
29.8, 28.1, 26.3, 26.2, 26.0, 25.8 ppm; MS-ESI: m/z: calcd for
[C18H28NO7]+: 370.1860; found: 370.1855.
2-tert-Butyl 4,5-dimethyl 3-(4-bromophenyl)isoxazole-2,4,5-tri-
carboxylate (3q): According to the general procedure, hydroxyla-
mine 1q (0.25 mmol, 75.5 mg, 1.00 equiv), dry CH2Cl2 (2 mL), 2a
(122 mL, 1.00 mmol, 4.00 equiv), and TEMPO (78.8 mg, 0.50 mmol,
2.00 equiv) were reacted. The crude product was purified by flash
column chromatography on silica gel eluting with pentane/AcOEt
[(%AcOEt): 1 (50), 5 (50), 10 (200), 15% (300 mL)] to give 3q as
light-yellow oil (0.16 mmol, 70.6 mg, 80%). 1H NMR (300 MHz,
2-tert-Butyl 4,5-dimethyl 3-ethylisoxazole-2,4,5-tricarboxylate
(3v): According to the general procedure, hydroxylamine 1v
(0.25 mmol, 43.8 mg, 1.00 equiv), dry CH2Cl2 (2 mL), 2a (122 mL,
1.00 mmol, 4.00 equiv), and TEMPO (78.8 mg, 0.50 mmol,
2.00 equiv) were reacted. The crude product was purified by flash
Chem. Eur. J. 2015, 21, 12053 – 12060
12059
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim