Synthesis of silylated β-enaminones and applications to the synthesis of silyl heterocycles

Article abstract of DOI:10.1016/S0040-4039(01)01966-9

Silyl β-enaminones have been synthesized by reductive cleavage of silylisoxazoles. These versatile synthons bearing the silyl group in different positions of the enamino ketonic system are of great interest in the construction of a variety of penta- and hexaheterocycles, which, in general, retain the silyl group attached at the ring or in a side chain.

Full text of DOI:10.1016/S0040-4039(01)01966-9

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 8981–8984
Synthesis of silylated b-enaminones and applications to the
synthesis of silyl heterocycles
Luis A. Calvo, Ana M. Gonza´lez-Nogal,* Alfonso Gonza´lez-Ortega and M. Carmen San˜udo
Departamento de Qu´ımica Orga´nica, Facultad de Ciencias, Universidad de Valladolid, Dr Mergelina s/n, 47011 Valladolid, Spain
Received 8 October 2001; accepted 19 October 2001
Abstract—Silyl b-enaminones have been synthesized by reductive cleavage of silylisoxazoles. These versatile synthons bearing the
silyl group in different positions of the enamino ketonic system are of great interest in the construction of a variety of penta- and
hexaheterocycles, which, in general, retain the silyl group attached at the ring or in a side chain. © 2001 Elsevier Science Ltd. All
rights reserved.
b-Enaminoketones are versatile synthetic intermediates
and have a large number of synthetic applications in
organic chemistry.1 They have, therefore, been the sub-
ject of attention by our research group, which has
prepared differently substituted b-enaminoketones by
catalytic hydrogenation of isoxazoles and studied their
application in the synthesis of several heterocycles.2
Likewise, reagents and methods based on organosilicon
chemistry are an area of increasing interest in organic
synthesis.3 In connection with our current study con-
cerning the preparation and synthetic utility of the
organosilanes,4 we decided to synthesize b-enaminones
containing silyl groups in different positions of the
enaminoketonic system5 with the aim of creating
through them a variety of penta- and hexaheterocyclic
compounds bearing versatile silicon functionality.
isoxazole with lithium dimethylphenylsilylcuprate.4e
The 5-silylisoxazole 2 was obtained from the corre-
sponding silylated acetylenic ketone by reaction with
hydroxylamine,7 the 4-silylmethylisoxazole 3 from the
respective 4-chloromethylisoxazole by reaction with
BuLi and trimethylchlorosilane and the 5-silyl-
methylisoxazoles 4a–d by hydrogen–lithium exchange
and quenching with the suitable chlorosilane.6
Although the SiꢀC bonds are stable toward catalytic
hydrogenation, when the 4-silylisoxazoles 1a–c reacted
with hydrogen in EtOH and in the presence of Raney
nickel,8 the desilylated b-enaminoenones 5a and 5b
were obtained. The reaction course was followed by
NMR spectroscopy and HPLC chromatography and at
no time was the desilylated isoxazole detected. This
probably indicates that the initial C-silylated b-enam-
inone undergoes silyl rearrangement to nitrogen,9 fol-
lowed by the facile cleavage of the NꢀSi bond (Scheme
1).
In this communication we describe the synthesis of
silylated b-enaminoketones by catalytic hydrogenation
of 4- and 5-silylisoxazoles, as well as those resulting
from the reductive cleavage of their 4- and 5-homo-
logues. Furthermore, we have used these synthons as
substrates in the synthesis of silylated pyrroles, pyra-
zoles, pyrimidines and pyridinones.
R23Si
Me
Me
H2 [Ni]
EtOH
NH2
N
R1
O
R1
[H]
O
5a-b
1a-c
The starting 4-trimethylsilylisoxazoles 1a,b were pre-
pared by reaction of the corresponding lithio derivative
with trimethylchlorosilane6 and the 4-dimethylphenylsi-
lyl isoxazole 1c by coupling of the appropriate 4-iodo
[H]
Me
NH2
Me
NH
Me
R23Si
R23Si
R1
H
NH
SiR2
R1
3
R1
O
O
O
Keywords: silicon 2-aminopyrimidines; silicon b-enaminones; silicon
pyrazoles; silicon 2-pyridones; silicon pyrroles.
* Corresponding author. Tel.: +34-983-423213; fax: +34-983-423013;
e-mail: agn@qo.uva.es
Scheme 1. (a) R1=Me, R2 =Me3; (b) R1=Ph, R2 =Me3;
3
3
(c): R1=Me, R2 =Me2Ph.
3
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01966-9

8982
L. A. Cal6o et al. / Tetrahedron Letters 42 (2001) 8981–8984
On the other hand, the catalytic hydrogenation of the
5-silylisoxazole 2 afforded the stable acylsilane deriva-
tive 6, able to react regioselectively with hydrazines
giving silylated pyrazoles.10 When phenylhydrazine or
semicarbazide was used as a nucleophile, we obtained
the corresponding 5-silylpyrazoles 7a and 7b, while the
reaction with methylhydrazine led to 3-silylpyrazole 8.
This latter result is very interesting because, as far as we
know, general procedures for synthesizing N-alkyl-3-
silylpyrazoles have not been previously described.
Moreover, we have prepared 4-formylpyrrole 9 from 6
by the modified Knorr synthesis using Weinreb a-
aminoamides (Scheme 2).11
generating, in mild conditions, enolate ions for aldol
reactions. Nitrogen bases like LDA usually attack the
a-hydrogen atom to give silicon-substituted enolates,
which can be alkylated and used in Peterson reac-
tions.15 Carbon nucleophiles and hydrides usually
Me
Me
N
Me3Si
O
N
2
Me3Si
N
R1
H2 [Ni]
EtOH
7a (85%)
7b (80%)
SiMe3
Me
4-Formylpyrrole 9 was presumably formed by [1,4]-
Brook rearrangement in the intermediate b-oxido
acylsilane 10 resulting from cyclization, with concomi-
tant elimination of R3SiOH (Scheme 3).
MeNHNH2
-NH3; -H2O
N
NH2
Me
N
Me3Si
O
Me
8 (60%)
6
This is a noteworthy result because 4-formylpyrroles
are impossible to prepare by this method in the absence
of the silicon group, since the necessary b-
aminoacrolein undergoes 1,2-addition in its reaction
with Weinreb a-aminoamides.
Me Me
O
H
N
Me
Me
H3N
Br
OMe
O
Me
N
H
9 (31%)
The silylated b-aminoenone 11, obtained by reductive
cleavage of 4-silylmethylisoxazole 3, is very stable
despite containing an allylsilane moiety and it was
shown to be reactive toward semicarbazide and mal-
ononitrile,10 giving the 4-silylmethylpyrazole 12 and the
5-silylmethyl-2-pyridone 13, respectively (Scheme 4).
Scheme 2. (a) R1=Ph; (b) R1=CONH2.
H
H2N
Me
Me
N
Me
-NH3
1. MeLi
2. H2O
+
6
Me
O
Me
O
N
O
N
OMe
SiMe3
OMe
Conversely, the stability of the silyl b-aminoenones
14a–d resulting from catalytic hydrogenolysis of 5-silyl-
methylisoxazoles 4a–d depends on the nature of the
silyl group. When this is trimethyl, the a%-silyl-b-enam-
inoketone 14a is unstable in the acidic reaction
medium. In its treatment with nucleophiles (hydrazine
hydrochloride derivatives, cyanamide and malononi-
trile) desilylated heterocycles were obtained. Neverthe-
less, b-enaminones bearing silyl groups of minor
nucleofugacity such as dimethylphenyl, diphenylmethyl
and tert-butyldiphenyl furnished pyrazoles10 15e–g,
pyrimidine 16, 2-pyridone 17, and pyrrole11 18, which
retain the silyl group (Scheme 5).
H
H
Me
N
Me
Me
N
O
Me
Me
H
EtOH
reflux
Me
O
H
O
O
10
SiMe3
Si
Me3
Me
O
H
N
H
N
Me
H
Me
Me
Me
Me
O
- Me3SiOH
OSiMe3
H
H
9
In conclusion, we have easily prepared b-enamino
acylsilanes, a-silylmethyl b-enaminones and a%-silyl b-
enaminones by reductive cleavage of 5-silyl-, 4-silyl-
methyl- and 5-silylmethylisoxazoles, respectively.
Moreover, we have demonstrated that they are interest-
ing synthons in the creation of pyrroles, pyrazoles,
pyrimidines and pyridinones bearing arylsilane, aryl-
methylsilane and a-silyl ketone moieties. The known
electrophilic ipso-substitution in heteroarylsilanes4e,12
may permit the introduction through the silyl group of
a variety of carbon or heteroatomic groups. Likewise,
arylmethylsilanes13 are synthetic equivalents of silicon-
stabilized carbanions with wide synthetic possibilities.
On the other hand, the synthetic utility of the a-silyl
ketone moiety is particularly noteworthy since it is
susceptible to nucleophilic attack at three sites. Halogen
and oxygen nucleophiles14 attack at the silicon atom
Scheme 3.
Me
Me
Me3Si
Me
[H]
Me3Si
NH2
N
O
Me
O
11
3
-NH3
-H2O
NH2NHCONH2
Me
Me
N
Me3Si
Me
CN
O
Me3Si
N
Me
13 (56%)
N
H
NH2
O
12 (78%)
Scheme 4.

L. A. Cal6o et al. / Tetrahedron Letters 42 (2001) 8981–8984
8983
Me
Yustos, P.; Garc´ıa, S.; Garc´ıa, E. J. Org. Chem. 1999, 64,
9493.
N
3. (a) Fleming, I. In Comprehensive Organic Chemistry;
Barton, D. H. R.; Ollis, W. D., Eds.; Pergamon Press:
Oxford, 1979; Vol. 3, p. 608; (b) Magnus, P.; Sarkar, T.;
Djuric, S. In Comprehensive Organometallic Chemistry;
Wilkinson, G. W.; Stone, F. G. A.; Abel, E. W., Eds.;
Pergamon Press: Oxford, 1982; Vol. 7, p. 515; (c) Colvin,
E. In Silicon in Organic Synthesis; Butterworths: London,
1981; (d) Weber, W. P. In Silicon Reagents for Organic
Synthesis; Springer-Verlag: Berlin, 1983; (e) Patai, S. In
The Chemistry of Organic Silicon Compounds; Rappo-
port, Z., Ed.; Wiley: Chichester, 1989.
O
4a-d
[H]
Me
SiR1
Me
Me
3
Me
H
N
N
i
Me
N
R2
R13Si
iv
NH2
O
SitBuPh2
15e-g (70-95%)
O
18 (35%)
SiR1
iii
3
Me
ii
Me
14a-d
(80-95%)
CN
N
4. (a) Cuadrado, P.; Gonza´lez-Nogal, A. M. Tetrahedron
Lett. 1997, 38, 8117; (b) Cuadrado, P.; Gonza´lez-Nogal,
A. M. Tetrahedron Lett. 1998, 39, 1449; (c) Cuadrado, P.;
Gonza´lez-Nogal, A. M. Tetrahedron Lett. 2000, 41, 1111;
(d) Cuadrado, P.; Gonza´lez-Nogal, A. M.; Sa´nchez, A. J.
Org. Chem. 2001, 66, 1961; (e) Calle, M.; Cuadrado, P.;
Gonza´lez-Nogal, A. M.; Valero, R. Synthesis 2001, 1949.
5. We have only found one paper by Dalpozzo et al.
concerning the synthesis of silyl enaminones. These
authors prepared a%- and g-silylenaminones by reaction
with chlorosilanes of a%- and g-dianions of b-enaminones:
Bartoli, G.; Bosco, M.; Dalpozzo, R.; De Nino, A.;
Iantorno, E.; Tagarelli, A.; Palmieri, G. Tetrahedron
1996, 52, 9179.
N
NH2
O
N
H
SitBuPh2
tBuPh2Si
17 (61%)
16 (56%)
a: R13 = Me3
e: R13 = Me2Ph; R2 = Ph
f: R13 = MePh2; R2 = Et
b: R13 = Me2Ph
c: R13 = MePh2
d: R13 = tBuPh2
g: R13 = tBuPh2; R2 = CONH2
Scheme 5. i=R2NHNH2; ii=NH2CN; iii=NCCH2CN; iv=
1. N-methoxy-N-methylalaninamide, 2. MeLi, 3. EtOH, D.
6. Nesi, R.; Ricci, A.; Taddei, M.; Tedeschi, P.; Seconi, G.
attack at the carbonyl group affording b-hydroxysi-
lanes,16 precursors of stereospecific Z- or E-olefins.
Furthermore, a-silyl ketones are also susceptible to
thermal isomerization17 to the versatile silyl enol ethers.
Finally, dimethylphenylsilyl derivatives have an addi-
tional advantage since this group can be converted into
a hydroxyl group.18
J. Organomet. Chem. 1980, 195, 275.
7. Birkofer, L.; Richtzenhain, K. Chem. Ber. 1979, 112,
2829.
8. Hydrogenolysis of silylated isoxazoles. General proce-
dure: A mixture of silylated isoxazol (20 mmol) and 1.0 g
of Raney nickel in 10 mL of dry ethanol was stirred
under 400 psi of hydrogen at rt for 24 h. Then, the
catalyst was removed by filtration and the solvent was
evaporated under reduced pressure. The concentrate was
chromatographed on silica gel using CH2Cl2/Et2O (20:1)
as eluent. The b-aminoenones 6, 11 and 14a–d were thus
prepared (80–95%). 3-Amino-1-trimethylsilylbut-2-en-1-
one (6). Yield 91%. Mp 84°C (from hexane). IR (KBr)
3255, 3097, 1618, 1522, 1385, 1269, 1246, 867, 840, 752,
The synthetic possibilities of these silylated units will
also be applied to the starting silyl b-enaminones and
we will use the combined versatility of b-enaminones
and silicon compounds in our future research.
679 cm−1 1H NMR (300 MHz, CDCl3) l 0.12 (s, 9H),
.
Acknowledgements
1.90 (s, 3H), 5.46 (s, 1H), 5.62 (br, 1H), 10.76 (br, 1H).
13C NMR (75.4 MHz, CDCl3) l 2.95, 22.00, 102.19,
159.78, 225.08. Anal. calcd for C7H15NOSi: C, 53.45; H,
9.61; N, 8.91. Found: C, 53.38; H, 9.73; N, 9.00. 4-
Amino-3-(trimethylsilylmethyl)pent-3-en-2-one (11). Yield
89%. Mp 58°C (from hexane). IR (KBr) 3338, 2953, 1602,
We thank the Ministerio de Ciencia y Tecnolog´ıa of
Spain for supporting this work (Grant BQU2000-0943).
1
1480, 1247, 851, 838 cm−1. H NMR (300 MHz, CDCl3)
l 0.02 (s, 9H), 1.63 (s, 2H), 1.90 (s, 3H), 2.11 (s, 3H). 13C
NMR (75.4 MHz, CDCl3) l −0.67, 17.20, 22.24, 28.77,
101.80, 156.96, 197.13. Anal. calcd for C9H19NOSi: C,
58.32; H, 10.33; N, 7.56. Found: C, 58.56; H, 10.31; N,
References
1. (a) Kuckla¨nder, U. In Enaminones as Synthones, Rappo-
port, Z., Ed. The chemistry of functional groups. John
Wiley and Sons: New York, 1994; Part 1, Chapter 10; (b)
Lue, P.; Greenhill, J. V. Adv. Heterocycl. Chem. 1997, 67,
207.
7.40.
(14c) Yield 90%. Mp 76°C (from hexane). IR (KBr) 3303,
3134, 1606, 1530, 1288, 1126, 1062, 777, 698 cm−1 1H
4-Amino-1-(methyl-diphenylsilyl)pent-3-en-2-one
.
2. (a) Alberola, A.; Gonza´lez-Ortega, A.; Sa´daba, M. L.;
San˜udo, M. C. J. Chem. Soc., Perkin Trans. 1 1998, 4061;
(b) Alberola, A.; Gonza´lez-Ortega, A.; Sa´daba, M. L.;
San˜udo, M. C. Tetrahedron 1999, 55, 6555; (c) Alberola,
A.; Alvaro, R.; Gonza´lez-Ortega, A.; Sa´daba, M. L.;
San˜udo, M. C. Tetrahedron 1999, 55, 13211; (d) Alberola,
A.; Calvo, L. A.; Gonza´lez-Ortega, A.; San˜udo, M. C.;
NMR (300 MHz, CDCl3) l 0.69 (s, 3H), 1.75 (s, 3H),
2.54 (s, 2H), 4.76 (s, 1H), 4.93 (br, 1H), 7.26–7.61 (m,
10H), 9.56 (br, 1H). 13C NMR (75.4 MHz, CDCl3) l
−4.04, 22.05, 34.29, 96.65, 127.68, 129.25, 134.49,
136.28, 159.51, 196.72. Anal. calcd for C18H21NOSi: C,
73.17; H, 7.16; N, 4.77. Found: C, 72.95; H, 7.22; N,
4.91.

8984
L. A. Cal6o et al. / Tetrahedron Letters 42 (2001) 8981–8984
9. An analogous tautomerism has previously been observed
Butyldiphenylsilyl)methyl)-3-methylpyrazole-1-carboxam-
ide. (15g) Yield 72%. Mp 108–110°C (from hexane). IR
in the conversion of C-silyl D1-pyrazolines to D2-pyrazoli-
nes by 1,3 silyl migration: Bassindale, A. R.; Brook, A.
G. Can. J. Chem. 1974, 52, 3474.
(KBr) 3401, 3236, 1698, 1395, 700, 488 cm−1 1H NMR
.
(300 MHz, CDCl3) l 1.11 (s, 9H), 2.04 (s, 3H), 3.36 (s,
2H), 5.21 (br, 1H), 5.50 (s, 1H), 6.81 (br, 1H), 7.30–7.55
(m, 10H). 13C NMR (75.4 MHz, CDCl3) l 11.07, 13.51,
18.43, 27.58, 109.03, 127.34, 129.13, 133.73, 136.04,
145.37, 150.09, 152.74. Anal. calcd for C22H27N3OSi:
C, 69.99; H, 7.21; N, 11.13. Found: C, 70.21; H, 7.32;
N, 10.89. 2-Amino-4-((tert-butyldiphenylsilyl)methyl)-6-
methylpyrimidine. (16). Yield 56%. Mp 82–83°C (from
10. General procedure for the preparation of silylated pyra-
zoles, 2-aminopyrimidines and 2-1H-pyridones. A mix-
ture of silylated b-aminoenone (2 mmol) and hydrazine
hydrochloride derivative, cyanamide or malononitrile (3
mmol) was refluxed in 8 mL of dry ethanol. At the end of
the reaction (monitored by TLC) the solvent was evapo-
rated under reduced pressure and the residue was
extracted with CH2Cl2/H2O. The organic layer was dried
and concentrated. The residue was recrystallized from
hexane/toluene (for pyridones) or chromatographed on
silica gel using as eluent CH2Cl2/Et2O (20:1–10:1) for
pyrazoles or CH2Cl2/Et2O (1:1) for 2-aminopyrimidines.
The compounds 7a,b, 8, 12, 13, 15e–g, 16 and 17 were
thus prepared. 3-Methyl-1-phenyl-5-trimethylsilylpyra-
zole (7a). Yield 85%. Bp 175–180°C/1.5 mmHg. IR (film)
1
hexane). IR (KBr) 2218, 1658, 858, 845 cm−1. H NMR
(300 MHz, CDCl3) l 1.01 (s, 9H), 1.99 (s, 3H), 2.70 (s,
2H), 4.78 (br, 2H), 5.69 (s, 1H), 7.27–7.61 (m, 10H). 13C
NMR (75.4 MHz, CDCl3) l 18.69, 23.48, 24.32, 27.74,
110.80, 127.39, 129.27, 133.61, 136.29, 162.26, 166.09,
169.94. Anal. calcd for C22H27N3Si: C, 73.08; H, 7.53; N,
11.62. Found: C, 73.21; H, 7.40; N, 11.58. 6-((tert-
Butyldiphenylsilyl)methyl)-3-cyano-4-methyl-2-pyridone
(17). Yield 61%. Mp 235°C (from hexane/toluene). IR
1600, 1501, 1252, 844, 762, 695 cm−1 1H NMR (300
.
MHz, CDCl3) l 0.10 (s, 9H), 2.34 (s, 3H), 6.33 (s, 1H),
7.33–7.41 (m, 5H). 13C NMR (75.4 MHz, CDCl3) l
−0.62, 12.84, 115.65, 125.74, 127.83, 128.53, 142.28,
144.26, 148.74. Anal. calcd for C13H18N2Si: C, 67.77; H,
7.88; N, 12.16. Found: C, 67.45; H, 8.00; N, 12.21.
1,5-Dimethyl-3-trimethylsilylpyrazole (8). Yield 60%, bp
1
(KBr) 2218, 1643, 1605, 701 cm−1. H NMR (300 MHz,
DMSO-d6) l 1.02 (s, 9H), 1.98 (s, 3H), 2.80 (s, 2H), 5.36
(s, 1H), 7.37–7.52 (m, 10H), 12.03 (s, 1H). Anal. calcd for
C24H26N2OSi: C, 74.57; H, 6.78; N, 7.25. Found: C,
74.78; H, 6.69; N, 7.13.
11. The experimental procedure is the same as that described
in Refs. 2b,c, except that the cyclization to pyrrol was
carried out at reflux in ethanol. 3-(2-(tert-Butyldi-
phenylsilyl)acetyl)-2,4,5-trimethylpyrrole (18). Yield 35%
oil, Rf=0.34 (CH2Cl2/Et2O, 20:1). IR (film) 3291, 1619,
95–98°C/0.5 mmHg, IR (film) 1247, 842, 757 cm−1 1H
.
NMR (300 MHz, CDCl3) l 0.26 (s, 9H), 2.25 (s, 3H),
3.80 (s, 3H), 6.13 (s, 1H). 13C NMR (75.4 MHz, CDCl3)
l 1.13, 10.86, 35.90, 111.60, 138.16, 151.36. Anal. calcd
for C8H16N2Si: C, 57.09; H, 9.58; N, 16.64. Found: C,
58.21; H, 9.60; N, 16.41. 3,5-Dimethyl-4-(trimethylsilyl-
methyl)pyrazole-1-carboxamide (12). Yield 78%. Mp 103–
104°C (from hexane). IR (KBr) 3431, 3332, 1731, 1700,
1426, 1108, 700 cm−1 1H NMR (300 MHz, CDCl3) l
.
1.11 (s, 9H), 1.94 (s, 3H), 1.98 (s, 3H), 2.08 (s, 3H), 3.06
(s, 2H), 7.23–7.65 (m, 10H), 7.40 (br, 1H). 13C NMR
(75.4 MHz, CDCl3) l 10.36, 11.54, 14.13, 18.69, 27.73,
30.46, 114.14, 121.66, 123.24, 127.12, 128.92, 131.06, 133
96, 136.11, 197.31.
1
1400, 863, 575 cm−1. H NMR (300 MHz, CDCl3) l 0.01
(s, 9H), 1.69 (s, 2H), 2.12 (s, 3H), 2.42 (s, 3H), 5.33 (br,
1H), 7.07 (br, 1H). 13C NMR (75.4 MHz, CDCl3) l
−1.32, 12.30, 12.47, 12.86, 118.60, 137.38, 149.69, 152.65.
Anal. calcd for C10H19N3OSi: C, 53.29; H, 8.50; N, 18.65.
Found: C, 53.57; H, 8.49; N, 18.40. 3-Cyano-4,6-
dimethyl-5-(trimethylsilylmethyl)-2-pyridone (13). Yield
56%. Mp 276–278°C (from hexane/toluene). IR (KBr)
12. See for example: (a) Birkofer, L.; Stuhl, O. Top. Curr.
Chem. 1980, 88, 62; (b) Pinkerton, F. H.; Thames, S. F.
J. Heterocycl. Chem. 1972, 9, 67; (c) Pratt, M. J. R.;
Pinkerton, F. H.; Thames, S. F. J. Organomet. Chem.
1972, 38, 29; (d) Fiorentino, M.; Testaferri, L.; Tiecco,
M.; Troisi, L. J. Chem. Soc., Chem. Commun. 1977, 317.
13. They are easily deprotonated by BuLi or LDA. See for
example: Konakahara, T.; Takagi, Y. Tetrahedron Lett.
1980, 21, 2073.
14. Birkofer, L.; Ritter, A. Angew. Chem., Int. Ed. 1965, 4,
417.
15. (a) Hudrlik, P. F.; Peterson, D.; Chou, D. Synth. Com-
mun. 1975, 5, 359; (b) Shimoji, K.; Taguchi, H.; Oshima,
K.; Yamamoto, H.; Nozaki, H. J. Am. Chem. Soc. 1974,
96, 1620.
1
2218, 1658, 858, 845 cm−1. H NMR (300 MHz, DMSO-
d6) l 0.01 (s, 9H), 1.90 (s, 2H), 2.20 (s, 3H), 2.28 (s, 3H),
10.80 (br, 1H). 13C NMR (75.4 MHz, DMSO-d6) l −0.64,
16.33, 18.13, 20.08, 100.18, 115.31, 116.76, 146.57, 158.45,
159.53. Anal. calcd for C12H18N2OSi: C, 61.50; H, 7.74;
N, 11.95. Found: C, 61.76; H, 7.65; N, 11.75. 1-Ethyl-
3 - methyl - 5 - ((methyldiphenylsilyl)methyl)pyrazole (15f).
Yield 93%. Bp 200–205°C/1 mmHg. IR (film) 1540, 1427,
1
1113, 808, 733, 700 cm−1. H NMR (300 MHz, CDCl3) l
0.62 (s, 3H), 1.22 (t, J=7.2 Hz, 3H), 2.20 (s, 3H), 2.52 (s,
2H), 3.71 (q, J=7.2 Hz, 2H), 5.56 (s, 1H), 7.36–7.52 (m,
10H, Ar). 13C NMR (75.4 MHz, CDCl3) l −4.48, 13.27,
13.50, 15.29, 42.90, 104.06, 127.92, 129.60, 134.39, 135.48,
138.71, 147.00. Anal. calcd for C20H24N2Si: C, 74.95; H,
7.55; N, 8.74. Found: C, 75.24; H, 7.50; N, 8.53. 5-(tert-
16. Hudrlik, P. F.; Peterson, D. J. Am. Chem. Soc. 1975, 97,
1464.
17. Brook, A. G. Acc. Chem. Res. 1974, 7, 77.
18. Fleming, I.; Henning, R.; Plant, H. J. Chem. Soc., Chem.
Commun. 1984, 29.