References and Notes
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Penke B.
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see the following and references therein:
3a
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Kiran MU.
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3b
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PhD Thesis
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7 See, for example: Elguero J.
Goya P.
Jagerovic N.
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8a
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imines, see: Jones
RCF.
Hollis SJ.
Iley JN.
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Ryu EJ.
Keum G.
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11 Cf. for α-amino-oximes:
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14
Typical Procedure
for NCS Chlorination and Method 1
(
S
)-3-(1-
tert
-Butoxycarbonylaminoethyl)-2-phenyl-4,5-dihydro-1
H
-pyrazole-5-carboxylic
Acid Ethyl Ester (7)
To (S)-[1-methyl-2-(phenylhydrazono)ethyl]carbamic
acid tert-butyl ester (5,
1.24 g, 4.72 mmol) in EtOAc (15 mL) at 60 ˚C was
added NCS (0.71 g, 5.35 mmol, 1.1 equiv) and the mixture stirred
for 1 h. Ethyl propenoate (0.918 g, 1.0 mL, 9.16 mmol, 1.9 equiv),
KHCO3 (2.41 g, 23.97 mmol, 5.1 equiv) and a few drops
of H2O were added and the mixture stirred at 70 ˚C
for 20 h. The mixture was then filtered and the filtrate concentrated
under reduced pressure to give a dark orange oil, purified by column
chromatography on silica gel eluting with light PE-EtOAc
(7:1, v/v) to yield the title compound 7 (0.72
g, 41%) in an inseparable 1:1 mixture of diastereomers,
as an orange solid; mp 93-95 ˚C. IR (CHCl3): νmax = 3354
(NH), 1599 (C=N), 1708 (C=O), 1168 (CO), 750 (PhCH)
cm-¹. ¹H NMR (400
MHz, CDCl3): δ = 1.16
(3 H, t, J = 7.2
Hz, CH2CH
3), 1.35
(3 H, d, J = 7.0 Hz,
CH
3CH), 1.38 [9 H,
s, C(CH
3)3],
2.99 (1 H, dd, J = 7.2, 17.6
Hz, 4-CHH), 3.24 (1 H, dd, J = 12.4,
17.6 Hz, 4-CHH), 4.14 (2 H, q, J = 7.2 Hz,
CH
2CH3), 4.43 (1
H, m, CH3CH), 4.54, 4,57 (each
0.5 H, dd, J = 7.2,
12.4 Hz, CHCO2Et, diastereomers
1 and 2), 5.00 (1 H, br s, NH), 6.78 (1 H, m, ArH), 6.93 (2 H, m,
ArH), 7.18 (2 H, m, ArH). ¹³C NMR (100
MHz, CDCl3): δ = 14.2,
21.1 (CH3) 28.2 [(CH3)3C], 40.15
(4-CH2), 46.1 (5-CH), 61.7 (OCH2), 113.0 (PhCH), 113.0,
119.7, 119.8, 129.0 (4 × CH), 129.1 (2 × C),
145.3 (CN), 171.2, 171.5 (2 × CO). MS
(EI): m/z = 362 [MH+], 171
(12), 154 (24), 147 (19), 123 (21), 111 (28), 109 (35), 95 (54),
81 (54), 69 (85), 57 (100), 55 (99). HRMS (EI): m/z calcd
for C19H27N3O4: 362.2074 [MH+];
found 362.2073 [MH+]. Anal.
Calcd (%) for C19H27N3O4:
C, 63.1; H, 7.5; N, 11.6. Found: C, 62.6; H, 7.2; N, 11.8.
15
Sharp JT. In
Synthetic Applications of 1,3-Dipolar Cycloaddition
Chemistry Toward Heterocycles and Natural Products
Padwa A.
Pearson WH.
John Wiley and Sons;
Hoboken:
2003.
p.473
16a
Molteni G.
Ponti A.
Orlandi M.
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16b
Broggini G.
Molteni G.
Orlandi M.
J.
Chem. Soc., Perkin Trans. 1
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17a For
a review of silver salts in pyrazole synthesis, see: Molteni G.
ARKIVOC
2007,
(ii):
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17b
De Benassuti L.
Garanti L.
Molteni G.
Tetrahedron
2004,
60:
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18
Zhang X.
Breslav M.
Grimm J.
Guan K.
Huang A.
Liu F.
Maryanoff CA.
Palmer D.
Patel M.
Qian Y.
Shaw C.
Sorgi K.
Stefanick S.
Xu D.
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19
Sakamoto T.
Kikugawa Y.
Chem. Pharm. Bull.
1988,
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800
20 Cf. ref. 16a for a discussion on the
reduced rate of nitrile imine cycloadditions with electron-rich
dipolarophiles and/or electron-poor dipoles.
21
Crystal Data for
7
C19H27N3O4, M = 361.44,
monoclinic, a = 5.14990
(10), b = 11.4316
(4), c = 16.8254
(6) Å, β = 96.320
(2), U = 984.52
(5) ų, T = 120
(2) K, space group P21, graphite monochromated
Mo Kα radiation, λ = 0.71073 Å, Z = 2, D
c
= 1.219
g cm-³, F(000) = 388,
colourless, dimensions 0.36 × 0.09 × 0.04 mm³, µ = 0.086
mm-¹, 3.02 < θ < 28.19˚, 11290
reflections measured, 2363 unique reflections, R
int = 0.0376.
The structure was solved by direct methods and refined on F
². Friedel pairs
were merged due to the lack of any significant anomalous scattering. wR2 = 0.0833
(all data, 244 parameters); R1 = 0.0351 [2223
data with F
²
> 2σ(F
²
)]. Crystallographic
data (excluding structure factors) for the structures in this paper
have been deposited with the Cambridge Crystallographic Data Centre
as supplementary publication no. 787832. Copies of the data can
be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [fax: +44 (1223)336033 or e-mail:
deposit@ccdc.cam.ac.uk).
For leading references, see:
22a
Huck BR.
Fisk JD.
Gellman SH.
Org. Lett.
2000,
2:
2607
22b
Fisk JD.
Powell DR.
Gellman SH.
J. Am. Chem. Soc.
2000,
122:
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