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14
General Procedure: To
the appropriate acetate (1.6 mmol) in THF:H2O (4 mL,
1:1, v/v) was added DABCO (1.6 mmol, 180 mg) and the reaction
was stirred at r.t. for 10 min. Thereafter NaN3 (2.4
mmol, 156 mg) was added under stirring. After 5 min the reaction
was extracted with ethyl acetate (2 × 20 mL), the organic
layers were combined, dried and evaporated to obtain a residue.
This residue was either triturated with hexanes in the case of solid
products or passed through a small band of silica gel using hexanes:ethyl acetate
(98:2, v/v) as eluent to obtain oils.
R = 3-NO2C6H4,
EWG = CO2Me. 1H
NMR (CDCl3, 200 MHz): δ = 3.92 (s,
3 H, CO2CH3), 4.16 (s, 2 H, CH2),
7.62 (t, 1 H, J = 8.0
Hz, Ar-H), 7.76 (d, 1 H, J = 7.7
Hz, Ar-H), 7.96 (s, 1 H, =CH), 8.23-8.30
(m, 2 H, Ar-H). 13C NMR (CDCl3, 75.4
MHz): δ = 46.5 (CH2), 52.6 (CH3),
124.0 (CH), 124.01 (CH), 129.3 (C), 129.8 (CH), 135.0 (CH), 135.5
(C), 141.2 (CH), 148.3 (C), 166.7 (C). Anal. Calcd for C11H10N4O4:
C, 50.38; H, 3.84; N, 21.36. Found: C, 50.61; H, 4.02; N, 21.08%.
R = 4-NO2C6H4,
EWG = CO2Et. 1H
NMR (CDCl3, 200 MHz): δ = 1.40 (t,
3 H, J = 7.2
Hz, CH3), 4.13 (s, 2 H, CH2), 4.37 (q, 2 H, J = 7.2 Hz,
CH2), 7.59 (d, 2 H, J = 8.8
Hz, Ar-H), 7.95 (s, 1 H, =CH), 8.28 (d, 2 H, J = 8.8 Hz,
Ar-H). Anal. Calcd for C12H12N4O4:
C, 52.17; H, 4.37; N, 20.28. Found: C, 52.00; H, 4.43; N, 19.94%.
R = 4-NO2C6H4,
EWG = CO2-n-Bu. 1H
NMR (CDCl3, 200 MHz): δ = 0.98 (t,
3 H, J = 7.3
Hz, CH3), 1.41-1.56 (m, 2 H, CH2),
1.68-1.82 (m, 2 H, CH2), 4.13 (s, 2 H, CH2),
4.31 (t, 2 H, J = 6.6
Hz, CH2), 7.59 (d, 2 H, J = 8.6
Hz, Ar-H), 7.94 (s, 1 H, =CH), 8.28 (d, 2 H, J = 8.6 Hz,
Ar-H). 13C NMR (CDCl3, 75.4
MHz): δ = 13.6 (CH3), 19.1 (CH2),
30.5 (CH2), 46.6 (CH2), 65.8 (CH2),
123.8 (2 × CH), 130.2 (2 × CH), 130.3 (C), 140.4
(C), 141.2 (CH), 147.9 (C), 166.2 (C). Anal. Calcd for C14H16N4O4:
C, 55.25; H, 5.30; N, 18.41. Found: C, 55.17; H, 5.25; N, 18.11%.
R = 4-CF3C6H4,
EWG = CO2-n-Bu. 1H
NMR (CDCl3, 200 MHz): δ = 0.98 (t,
3 H, J = 7.3
Hz, CH3), 1.41-1.52 (m, 2 H, CH2),
1.68-1.79 (m, 2 H, CH2), 4.13 (s, 2 H, CH2),
4.30 (t, 2 H, J = 6.6
Hz, CH2), 7.53 (d, 2 H, J = 8.2
Hz, Ar-H), 7.68 (d, 2 H, J = 8.2
Hz, Ar-H), 7.95 (s, 1 H, =CH). Anal. Calcd for C15H16F3N4O4:
C, 55.04; H, 4.92; N, 12.83. Found: C, 55.10; H, 5.03; N, 12.98%.
R = 3-(4-Methylphenyl)isoxazol-5-yl,
EWG = CO2Et. 1H NMR
(CDCl3, 200 MHz): δ = 1.39 (t, 3 H, J = 7.0 Hz,
CH3), 2.41 (s, 3 H, Ar-CH3), 4.36 (q, 2 H, J = 7.0 Hz,
CH2), 4.51 (s, 2 H, CH2), 6.84 (s, 1 H, =CH),
7.28 (d, 2 H, J = 8.0
Hz, Ar-H), 7.35 (s, 1 H, =CH), 7.71 (d, 2 H, J = 8.0 Hz,
Ar-H). 13C NMR (CDCl3, 75.4
MHz): δ = 14.1 (CH3), 21.3 (CH3), 46.7
(CH2), 62.0 (CH2), 106.6 (CH), 125.1 (C),
125.6 (CH), 126.6 (2 × CH), 129.6 (2 × CH), 130.4
(C), 140.6 (CH), 162.7 (C), 165.1 (C), 165.8 (C). Anal. Calcd for
C16H16N4O3: C, 61.52;
H, 5.16; N, 17.93. Found: C, 61.48; H, 5.33; N, 17.64%.
R = 3-(2-Chlorophenyl)isoxazol-5-yl,
EWG = CO2-t-Bu. 1H NMR
(CDCl3, 200 MHz): δ = 1.58 [s,
9 H, CO2(CH3)3], 4.46 (s,
2 H, CH2), 7.02 (s, 1 H, =CH), 7.37-7.41
(m, 3 H, Ar-H), 7.62 (s, 1 H, =CH), 7.69-7.78
(m, 1 H, Ar-H). Anal. Calcd for C17H17N4O3:
C, 56.59; H, 4.74; N, 15.52. Found: C, 56.42; H, 4.57; N, 15.88%.
15
General Procedure
for Reduction of Azide: To the appropriate solution of azide
derivative (1.01 mmol, Table
[1]
entry
4 or 12) in THF (5 mL) was added Ph3P (1.31 mmol, 345
mg) under stirring at r.t. After 1 h water (40 µL) was added
and the reaction was allowed to proceed for 16 h. Thereafter, on
completion, the reaction mixture was subjected to acid (5% HCl)
and base (5% NaOH) work up. The residue obtained after
washing(water), drying (Na2SO4) and evaporation
was passed through a small band of basic alumina using CHCl3:MeOH
(99.7:0.3, v/v) to obtain pure amine.
R = 3-NO2C6H4,
EWG = CO2-t-Bu
(amine from entry 4, Table
[1]
).
Yield: 75%.; Mp oil. IR (neat): 3340 (NH2),
1709 (CO2-t-Bu) cm-1. 1H
NMR (CDCl3, 200 MHz): δ = 1.57 [s, 9
H, CO2(CH3)3], 3.60 (s,
2 H, CH2), 7.45-7.71 (m, 3 H, 2 Ar-H and =CH),
8.17-8.33 (m, 2 H, Ar-H). 13C
NMR (CDCl3, 75.4 MHz): δ = 28.0 (3 × CH3),
38.5 (CH2), 81.5 (CH), 122.2 (CH), 124.0 (CH), 129.4
(C), 129.7 (CH), 131.9 (CH), 134.3 (CH), 136.3 (CH), 148.2 (C),
166.2 (C). Mass (FABMS+): 279 (M+ + 1).
Anal. Calcd for C14H18N2O4:
C, 60.42; H, 6.52; N, 10.07. Found: C, 60.22; H, 6.89; N, 9.91%.
R = 3-Phenylisoxazol-5-yl,
EWG = CO2Me (amine from entry
12, Table
[1]
). Yield:
67%. Mp 84-86 °C. IR(neat):
3428 (NH2), 1711 (CO2Me) cm-1. 1H
NMR (CDCl3, 200 MHz): δ = 3.88 (s,
3 H, CO2CH3), 3.96 (s, 2 H, CH2),
6.81 (s, 1 H, =CH), 7.47-7.49 (m, 3 H,
2 Ar-H and =CH), 7.80-7.85 (m, 2 H, Ar-H).
Mass (FABMS+): 259 (M+ + 1).
Anal. Calcd for C14H14N2O3:
C, 65.11; H, 5.46; N, 10.85. Found: C, 65.42; H, 5.59; N, 10.68%.
16a
Batra S.
Rastogi SK.
Kundu B.
Patra A.
Bhaduri AP.
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2000,
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16b
Batra S.
Srinivasan T.
Rastogi SK.
Kundu B.
Patra A.
Bhaduri AP.
Dixit M.
Bioorg.
Med. Chem. Lett.
2002,
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1905
17
Hamper BC.
Kolodziej SA.
Scates AM.
Smith RG.
Cortez E.
J. Org. Chem.
1998,
63:
708
18
General Procedure
for Solid Phase: To Wang acrylate resin (100 mg, 1.13 mmol/g,
Novabiochem) in 800 µL DMSO was added 3 equiv of DABCO
followed by 5 equiv of substituted 5-isoxazolecarboxaldehyde solution
in 300 µL of DMSO after 20 min. The resulting mixture was
shaken at 600 rpm for 8 h. Subsequently, the resin was washed with DMF
(4 mL × 6), MeOH (4 mL × 6) and DCM (4 mL × 3). To
this resin suspended in 700 µL of DCM was added 12 equiv
of DIEA. After 5 min a solution of 10 equiv of acetyl chloride in
800 µL was added dropwise through syringe and reaction
was shaken for 18 h. Thereafter the resin was washed thoroughly
as described above. To this was then added 1.5 mL of THF:H2O
(9:1, v/v) followed by 3 equiv of DABCO. After 20 min of
shaking, 10 equiv of sodium azide were added and the reaction was
continued for 1 h further. Then the resin was washed with THF (4
mL × 6), MeOH (4 mL × 6), DCM (4 mL × 3)
and Et2O (4 mL × 2). After drying the resin
was cleaved with TFA:DCM (50:50, v/v) for 1 h, filtered
and the filtrate was evaporated to obtain a residue which was lyophilized
using tert-butanol:H2O (4:1,
v/v). For the reduction to amine, the dried resin (50 mg)
was suspended in THF (700 µL) and to it 15 equiv of triphenyl phosphine
was added under shaking at r.t. After 2 h, 30 µL of water
was added and the shaking was continued for 24 h. The resin was
subsequently washed, dried and cleaved as described above.
Azide:
R = 3-(4-Methylphenyl)-isoxazol-5-yl.
Yield: 72%. Mp 162-164 °C. IR
(KBr): 2109 (N3), 1670 (CO2H) cm-1. 1H
NMR (CDCl3, 200 MHz): δ = 2.42 (s,
3 H, CH3), 4.54 (s, 2 H, CH2), 6.89 (s, 1
H, =CH), 7.28 (d, 2 H, J = 8.6
Hz, Ar-H), 7.70 (s, 1 H, =CH), 7.76 (d, 2 H, J = 8.6 Hz,
Ar-H). 13C NMR (CDCl3, 75.4
MHz): δ = 21.1 (CH3), 46.4 (CH2),
106.3 (CH), 125.3 (CH), 126.4 (2 × CH and C merged), 129.4
(2 × CH), 130.7 (C), 140.3 (CH), 162.4 (C), 165.2 (C),
167.6 (C). Mass (FABMS+): 285 (M+ + 1).
Anal. Calcd for C14H12N4O3:
C, 59.15; H, 4.25; N, 19.71. Found: C, 59.48; H, 4.39; N, 19.94%.