Regioselective synthesis of silylated pyrazolines and indazolines by reaction of pyrazolium and indazolium salts with silyllithium reagents

Article abstract of DOI:10.1002/ejoc.200500438

Pyrazolium salts react with dimethylphenylsilyl- and tert- butyldiphenylsilyllithium to give, in general, only one of the two possible 5-silyl-3-pyrazolines. On the other hand, indazolium and isoindazolium salts lead to 3-silylindazolines and occasionally

Full text of DOI:10.1002/ejoc.200500438

FULL PAPER
Regioselective Synthesis of Silylated Pyrazolines and Indazolines by Reaction
of Pyrazolium and Indazolium Salts with Silyllithium Reagents
Ana M. González-Nogal,*[a] Mariola Calle,[a] Luis A. Calvo,[a] Purificación Cuadrado,[a] and
Alfonso González-Ortega[a]
Keywords: Nitrogen heterocycles / Regioselectivity / Silylazolines
Pyrazolium salts react with dimethylphenylsilyl- and tert-bu-
tyldiphenylsilyllithium to give, in general, only one of the two
possible 5-silyl-3-pyrazolines. On the other hand, indazolium
and isoindazolium salts lead to 3-silylindazolines and occa-
sionally to compounds resulting from the opening or expan-
sion of the heterocyclic ring. All of these compounds are
interesting synthons in organic chemistry.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Introduction
Pyrazolium salts are not reactive toward organometallic
reagents[1] except when they bear a nitro group[2] at C-4.
Nevertheless, in a preliminary communication[3] we re-
ported the regioselective synthesis of 5-silylated 3-pyraz-
olines by reaction of 1,3,5-trisubstituted-2-methylpyraz-
olium iodides with dimethylphenylsilyl- and tert-butyldi-
phenylsilyllithium. We have extended this methodology to
functionalized pyrazolium, indazolium and isoindazolium
salts with the aim of knowing their scope and with the pur-
pose of synthesising new silylated pyrazolines and indazol-
ines. In this paper, we describe the full results obtained in
the addition of silyllithium reagents to pyrazolium or
benzopyrazolium salts with various substitution patterns.
Scheme 1.
lyllithium attacked the less hindered C-5 to give the 3-
pyrazoline 3a.
Results and Discussion
Moreover, when the substituents at C-3 and C-5 are dif-
ferent, the selective formation of either of the 3-pyrazolines
also depends on the nature of the 3- and 5-substituents.
Thus, the reaction of pyrazolium iodides 1c (R2 = Me, R3
= Ph) and 1d (R2 = Ph, R3 = Me) with dimethylphenylsi-
lyllithium afforded exclusively the 5-dimethylphenylsilyl-3-
pyrazolines 2d and 3b, respectively, in which the double
bond C=C is conjugated with the phenyl group. Although
in a preliminary communication[3] we described that the re-
action of 1c with dimethylphenylsilyllithium between –78
and 0 °C led to a mixture of the two possible 5-silyl-3-pyr-
azolines, we have now verified that the product to which we
had assigned the structure of the 3-pyrazoline regioisomer
of 2d, was a cleavage product whose ratio in the mixture
increased with the reaction time at 0 °C. If the reaction is
carried out at –78 °C, only the pyrazoline 2d is isolated.
On the other hand, we have been unable to repeat the
result described[3] in the reaction of 1c with tert-butyldi-
1,3,5-Trisubstituted-2-methylpyrazolium iodides 1a–f re-
act easily with dimethylphenylsilyl- and tert-butyldiphenyl-
silyllithium leading to 5-silyl-3-pyrazolines 2a–f or 3a–c re-
gioselectively, while 3- or 5-unsubstituted pyrazolium salts
1g and 1h were shown to be unreactive (Scheme 1). The
results obtained are collected in Table 1.
When R1 = Ph, the C-3 and C-5 positions of 2-methyl-
pyrazolium salts are different and the attack of the silyl
anion at C-3 or C-5 could lead to regioisomeric 5-silyl-3-
pyrazolines. The reaction of the 2-methylpyrazolium iodide
1b with dimethylphenylsilyllithium gave the 3-pyrazoline 2c
resulting from the attack of the silyl anion at the more elec-
tron-deficient C-3. However, the bulky tert-butyldiphenylsi-
[a] Departamento de Química Orgánica, Universidad de Vallado-
lid,
47011 Valladolid, Spain
E-mail: agn@qo.uva.es
Eur. J. Org. Chem. 2005, 4663–4669
DOI: 10.1002/ejoc.200500438
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4663

A. M. González-Nogal, M. Calle, L. A. Calvo, P. Cuadrado, A. González-Ortega
FULL PAPER
Table 1. Reactions of 2-methylpyrazolium iodides with silyllithium
reagents.[a]
Sub-
strate
R1
R2
R3
R3Si
Products and yields
(%)
1a
1a
1b
1b
1c
1c
1d
1d
1e
1e
1f
Me
Me
Ph
Ph
Ph
Ph
Me
Me
Me
Me
Ph
Ph
Ph
Ph
Ph
Ph
Me Me
Me Me
Me Me
Me Me
Me2Ph 2a (5%)[b]
tBuPh2 2b (25%)
Me2Ph 2c (82%)
tBuPh2 3a (57%)
Scheme 3.
Me
Me
Ph
Ph
Ph
Ph
Ph
Ph
H
Ph
Ph
Me
Me
Ph
Ph
Ph
Ph
Me
Me
H
Me2Ph 2d (91%)[c]
[d]
tBuPh2
–
We have also studied the behaviour of functionalized
Me2Ph 3b (89%)
pyrazolium salts toward these silyllithium reagents. Bulky
tert-butyldiphenylsilyllithium was shown to be unreactive
with all the pyrazolium salts tested (Scheme 4). The results
with dimethylphenylsilyllithium are summarised in Table 2.
tBuPh2 3c (73%)
Me2Ph 2e (84%)
[d]
tBuPh2
–
Me2Ph 2f (58%) + 4 (26%)[e]
[d]
1f
tBuPh2
Me2Ph
tBuPh2
Me2Ph
tBuPh2
–
–
–
–
–
[d]
[d]
[d]
[d]
1g
1g
1h
1h
H
Me
Me
H
[a] Reactions were carried out using a molar ratio of pyrazolium/
R3SiLi = 1:1 in THF as a solvent. [b] 5-Dimethylphenylsilyl-3-py-
1
razoline (2a) is very unstable and was only identified by H NMR
spectroscopy. [c] The reaction was carried out at –78 °C and hydro-
lysed with methanol at this temperature. [d] The starting product
was recovered. [e] Even at –78 °C, 2f is partially opened to 4.
phenylsilyllithium. In all conditions (–78 to 0 °C, 0 °C, 0
°C to room temp.) we have recovered 1c. The phenyl group
attached to the less-hindered C-5 increases the steric hin-
drance and probably prevents the approach of the bulky
tert-butyldiphenylsilyl group at C-3 and C-5. Furthermore,
the 1,2-dimethylpyrazolium iodide 1d, in which the C-3 and
C-5 positions are interchangeable, afforded the 5-tert-butyl-
diphenylsilyl-3-pyrazoline (3c) in its reaction with tert-bu-
tyldiphenylsilyllithium.
The 3,5-diphenylpyrazolium iodides 1e and 1f reacted
with dimethylphenylsilyllithium, but not with the bulkier
tert-butyldiphenylsilyl reagent, affording the 5-silyl-3-pyraz-
olines 2e and 2f. In the latter case, we also obtained the
N-silylated β-enamino imine 4. This product was probably
formed by the opening of the pyrazoline 2f with the con-
comitant 1,3-rearrangement of the silyl group from carbon
to nitrogen[4,5] (Scheme 2).
Scheme 4.
Although the electron-withdrawing groups increase the
electron deficiency of the pyrazolium salts, and conse-
quently their reactivity toward the nucleophilic silyllithium
reagent, the 4-nitro and 4-bromo derivatives 5a and 5b were
shown to be unreactive. Possibly, the large 4-nitro and 4-
bromo groups prevent coplanarity and hinder the addition
of the silyl group at C-3 or C-5. Meanwhile, the less bulky
4-ethoxycarbonyl group in the 1-methylpyrazolium salt 5d
increases the electronic deficiency of C-5 by conjugation
and favours the formation of pyrazoline 7b resulting from
the addition of the silyl group at that position. The presence
of the N-phenyl group in the pyrazolium salt 5c increases
the steric hindrance at C-5 and leads to a mixture of 3-
pyrazolines 6a and 7a resulting from the addition of the
silyl group at C-3 and at C-5, respectively.
On the other hand, a 3-ethoxycarbonyl group does not
sufficiently activate C-3 or C-5. Despite the fact that this
functional group enhances the electron deficiency of the 3-
position by an inductive effect, it also increases its steric
hindrance. The 3-(ethoxycarbonyl)pyrazolium salt 5f was
Scheme 2.
When C-3 or C-5 of the starting salts is unsubstituted, shown to be unreactive toward dimethylphenylsilyllithium.
the reaction with neither silyllithium reagent took place. Obviously, the presence at C-4 of an electron-donating
The pyrazolium iodides 1g and 1h were recovered even silyl group decreases the reactivity of the pyrazolium salts
using an excess of silyllithium (2 equiv.) at room tempera- 5g and 5h and increases the steric hindrance at C-3 and C-5,
ture for 24 h. Probably, the reagent behaves as a base, elimi- making the addition of the dimethylphenylsilyl anion more
nating the acidic H-3 or H-5 proton[6] to give the corre- difficult. Nevertheless, the 3,5-dimethyl-4-(dimethylphen-
sponding lithium derivative which regenerates the starting ylsilyl)pyrazolium salt 5g leads to an interesting 4,5-di-
product in the final hydrolysis (Scheme 3).
silylated 3-pyrazoline 6b, bearing an allyl- and a vinylsilane
4664
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2005, 4663–4669

Synthesis of Silylated Azolines from Azolium Salts
FULL PAPER
Table 2. Reactions of 4- or 5-functionalized pyrazolium salts with dimethylphenylsilyllithium.[a]
Substrate
R1
R2
R3
R4
R5
Products and yields (%)
[b]
5a
5b
5c
5d
5e
5f
Ph
Ph
Ph
Me
Ph
Ph
Ph
Ph
Ph
Ph
Et
Et
Et
Et
Et
Et
Et
Et
Me
Me
Me
Me
Me
Me
Me
CO2Et
Me
Ph
Me
Me
NO2
Br
CO2Et
CO2Et
H
Me
Me
Me
Me
CO2Et
Me
Me
Ph
Me2PhSi
tBuPh2Si
–
–
[b]
6a (33%) + 7a (49%)
7b (67%)
7c (84%)[c]
[b]
H
–
5g
5h
5i
Me2PhSi
Me2PhSi
H
6b (75%)
[b]
–
–
[d]
5j
H
6c (68%)
[a] Reactions were carried out using a molar ratio of pyrazolium/R3SiLi = 1:1 in THF as a solvent. [b] The starting product was recovered.
If the temperature or the time reaction was increased, the corresponding pyrazoles resulting from dequaternization were obtained. [c] The
5-silyl-3-pyrazoline 7c lost the silyl group and was isolated as ethyl 2-ethyl-3-methyl-1-phenyl-3-pyrazoline-5-carboxylate (7c; SiMe2Ph =
H). [d] Only unidentified decomposition products were detected.
moiety. The more hindered 3,5-diphenylpyrazolium salt 5h methyllithium at room temperature in order to obtain the
was recovered from its treatment with the dimethylphenylsi- 3-methylindazoline 9b.
lyllithium reagent. Although the 5-silylpyrazolium salts 5i
These 3-unsubstituted indazolium salts 8a and 8b were
and 5j were shown to be reactive toward the dimethylphen- shown to be very reactive toward dimethylphenyl- and tert-
ylsilyllithium reagent, only 3-tert-butyldiphenylsilyl-5-di- butyldiphenylsilyllithium to give exclusively the correspond-
methylphenylsilyl-3-pyrazoline (6c), resulting from the at- ing 3-silylindazolines 11a–c with good yields (Scheme 6).
tack of the silyl anion at C-3 of the 5-(tert-butyldiphenylsi-
lyl)pyrazolium salt 5j, was sufficiently stable to be isolated.
We were also interested to know the behaviour of benzo-
pyrazolium salts toward silyllithium reagents. Since we did
not find any references concerning the reactivity of these
substrates with organometallic compounds, we initially
studied the reaction of 1,2-dimethylindazolium methyl sul-
fate (8a) and 1-ethyl-2-phenylindazolium tetrafluoroborate
(8b) with methyllithium and methylmagnesium iodide
(Scheme 5).
The indazolium salt 8a reacted easily with both organo-
metallic reagents leading to 3-methylindazoline 9a, resulting
from the addition of the organometallic reagent at C-3.
When methyllithium was used as a nucleophile, the amino
ketone 10 formed by ring-cleavage, together with 9a, were
obtained. The isoindazolium salt 8b was shown to be less
reactive. It was necessary to carry out the reaction with Scheme 6.
Scheme 5.
Eur. J. Org. Chem. 2005, 4663–4669
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A. M. González-Nogal, M. Calle, L. A. Calvo, P. Cuadrado, A. González-Ortega
FULL PAPER
Scheme 7.
The indazolium salt 8a also reacted with dimethylphenylsi- termediate, which yields 13 in the final hydrolysis
lyllithium but the 1,2-dimethyl-3-dimethylphenylsilylind- (Scheme 9).
azoline product turned out to be very unstable and could
not be isolated.
The behaviour of the 3-substituted indazolium salts is
different and depends on the nature of the substituent
(Scheme 7). When 3-methylpyrazolium tetrafluoroborates
were treated with dimethylphenyl- or tert-butyldiphenylsi-
lyllithium at 0 °C for 8 h, the starting salt was recovered.
The silyllithium probably extracted a proton from the acidic
3-methyl group,[7] and the resulting lithium derivative be-
came the starting product in the final hydrolysis. On the
other hand, the 3-phenylpyrazolium salt 8c reacted with di-
methylphenylsilyllithium to give a mixture of the corre-
sponding 3-silylindazoline 11c and 2-methyl-1,4-diphenyl-
1,2-dihydroquinazoline (12). The latter, which is the major
Scheme 9.
product if a salt/silyllithium ratio = 1:2 is used, might be
formed by
(Scheme 8).
a heterocyclic opening/closing mechanism
Conclusions
We have developed a simple and suitable method to re-
gioselectively prepare 5-silylated 3-pyrazolines for the first
time, and with wide substitution patterns. Moreover, we
have studied the influence of the nature of the substituent
on the reactivity and regioselectivity of the reaction. These
5-silyl-3-pyrazolines are interesting compounds in organic
synthesis because their allylsilane moiety is easily substi-
tuted by electrophiles with double bond rearrangement to
give new 5-substituted 3-pyrazolines. We were able[3] to
prove the proto-, acetyl- and iododesilylation.
In addition, the application of this methodology to inda-
zolium salts has allowed us to synthesise 3-silylindazolines
and other interesting products obtained by the opening or
expansion of the heterocyclic ring.
Scheme 8.
Finally, the 3-(ethoxycarbonyl)indazolium tetrafluorobor-
ate 8d reacted with both silyllithium reagents, affording the
β-enamino amide 13 exclusively (Scheme 7). This result
could be explained by the initial reaction of the silyllithium
with the ester group leading to an acylsilane, which is at-
tacked by the fluoride ion with concomitant carbon mono-
Experimental Section
General: THF was distilled from sodium benzophenone ketyl in a
xide elimination and ring opening to give a ketenimine in- recycling still. All chromatographic and workup solvents were dis-
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Eur. J. Org. Chem. 2005, 4663–4669

Synthesis of Silylated Azolines from Azolium Salts
FULL PAPER
tilled prior to use. All reactions involving organometallic reagents
(s, 3 H), 0.99 (s, 3 H), 2.01 (s, 3 H), 2.43 (s, 3 H), 2.80 (s, 3 H),
4.06 (s, 1 H), 7.36–7.74 (m, 5 H) ppm.
1
were carried out under a nitrogen atmosphere. H and 13C NMR
spectra were recorded at 300 and 75 MHz, respectively, in CDCl3 as
an internal standard. Carbon multiplicities were assigned by DEPT
experiments. Reactions were monitored by TLC on pre-coated
plates of silica gel 60 (nano-SIL-20, Macherey–Nagel). Flash
chromatography was performed on silica gel 60 (230–400 mesh, M–
N). The 2-methylpyrazolium or indazolium iodides were prepared
by heating of corresponding pyrazoles or indazoles with methyl
iodide in a pressure tube, and 2-ethylpyrazolium tetrafluoroborates
were prepared by treatment of the respective pyrazoles and ind-
azoles with triethyloxonium fluoroborate in dry dichloromethane
at room temperature for several hours (12–20 h). All pyrazolium
and indazolium salts were recrystallized from acetone-ether.
5-tert-Butyldiphenylsilyl-1,2,3,5-tetramethyl-3-pyrazoline (2b): Yield
182 mg (25%). 1H NMR (300 MHz, CDCl3): δ = 0.85 (s, 3 H), 1.22
(s, 9 H), 1.97 (s, 3 H), 2.35 (s, 3 H), 2.78 (s, 3 H), 4.43 (s, 1 H),
7.46–7.78 (m, 10 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 18.96,
20.09, 27.47, 29.12, 31.82, 34.42, 51.08, 98.90, 127.50, 129.32,
133.71, 134.78, 147.06 ppm. IR (film): ν = 3020, 1598, 1509, 1100,
˜
810 cm–1. MS (EI, 70 eV): m/z (%) = 110 (M+ – tBuPh2SiMe,
100%), 95 (34), 82 (9). C23H32N2Si (364.23): calcd. C 75.77, H 8.85,
N 7.68; found C 75.70, H 8.91, N 7.73.
1,3,5-Trimethyl-5-dimethylphenylsilyl-2-phenyl-3-pyrazoline
(2c):
1
Yield 528 mg (82%). H NMR (300 MHz, CDCl3): δ = 0.46 (s, 3
H), 0.48 (s, 3 H), 1.30 (s, 3 H), 1.70 (s, 3 H), 2.36 (s, 3 H), 4.70 (s,
1 H), 7.25–7.70 (m, 10 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
–5.01, –4.82, 13.73, 17.59, 37.02, 59.74, 108.23, 126.14, 127.48,
128.67, 130.81, 132.97, 133.94, 137.33, 140.98, 146.76 ppm. IR
We prepared new 4-silyl- and 5-silylpyrazolium salts 5g–j by quat-
ernization of the corresponding 4-silyl- and 5-silylpyrazoles.[8] Their
spectroscopic data are given below.
2-Ethyl-3,5-dimethyl-4-dimethylphenylsilyl-1-phenylpyrazolium Tet-
rafluoroborate (5g): Yield 1.98 g (94%). M.p. 96–97 °C (recrystal-
lised from MeCOMe/Et2O). 1H NMR (300 MHz, CDCl3): δ = 0.61
(s, 6 H), 1.12 (t, J = 7.3 Hz, 3 H), 1.93 (s, 3 H), 2.32 (s, 3 H), 4.09
(q, J = 7.3 Hz, 2 H), 7.35–7.64 (m, 10 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = –1.34, 12.62, 13.15, 14.09, 42.83, 112.70, 128.36,
128.87, 129.92, 130.81, 131.17, 132.59, 133.92, 135.87, 151.62,
(film): ν = 3020, 1608, 1504, 1250, 1110, 820 cm–1. MS (EI, 70 eV):
˜
m/z (%) = 322 (M+, 1%), 200 (16), 135 (30), 120 (20), 77 (100).
C20H26N2Si (322.19): calcd. C 74.48, H 8.13, N 8.69; found C
74.57, H 8.03, N 8.59.
1,5-Dimethyl-5-dimethylphenylsilyl-2,3-diphenyl-3-pyrazoline (2d):
1
Yield 699 mg (91%). H NMR (300 MHz, CDCl3): δ = 0.21 (s, 3
H), 0.24 (s, 3 H), 1.26 (s, 3 H), 2.67 (s, 3 H), 5.47 (s, 1 H), 6.76–
7.60 (m, 15 H) ppm. 13C NMR (75 MHz, CDCl3): δ = –4.79, –4.57,
18.07, 40.73, 62.56, 115.23, 117.21, 119.45, 126.15, 127.35, 127.49,
127.96, 128.20, 132.74, 134.17, 137.28, 139.47, 141.63, 147.98 ppm.
151.83 ppm. IR (CH Cl ): ν = 1593, 1499, 1256, 1100 cm–1.
˜
2
2
2-Ethyl-4-dimethylphenylsilyl-1,3,5-triphenylpyrazolium Tetrafluo-
roborate (5h): Yield 2.45 g (90%). M.p. 144.3–145.6 °C (recrystal-
lised from MeCOMe/Et2O). 1H NMR (300 MHz, CDCl3): δ = 0.00
(s, 6 H), 0.99 (t, J = 7.2 Hz, 3 H), 4.16 (q, J = 7.2 Hz, 2 H), 7.15–
7.25 (m, 10 H), 7.44–7.70 (m, 10 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 3.11, 19.43, 49.16, 119.52, 132.46, 132.95, 133.43,
134.24, 135.17, 135.59, 136.31, 136.71, 137.43,138.75, 141.50,
IR (film): ν = 3020, 1608, 1504, 1250, 1120, 825 cm–1. MS (EI,
˜
70 eV): m/z (%) = 234 (M+ – SiMe3Ph, 100%), 218 (14), 77 (21).
C25H28N2Si (384.20): calcd. C 78.07, H 7.34, N 7.28; found C
78.15, H 7.26, N 7.37.
158.35, 159.20 ppm. IR (CH Cl ): ν = 1598, 1509, 1254, 1103 cm–1.
1,2-Dimethyl-5-dimethylphenylsilyl-3,5-diphenyl-3-pyrazoline (2e):
˜
2
2
1
Yield 645 mg (84%). H NMR (300 MHz, CDCl3): δ = 0.44 (s, 3
2,3-Dimethyl-5-dimethylphenylsilyl-1-phenylpyrazolium Iodide (5i):
Yield 1.97 g (91%). M.p. 155–157 °C (recrystallised from Me-
COMe/Et2O). 1H NMR (300 MHz, CDCl3): δ = 0.36 (s, 6 H), 2.64
(s, 3 H), 3.82 (s, 3 H), 6.62 (s, 1 H), 7.20–7.63 (m, 10 H) ppm. 13C
NMR (75 MHz, CDCl3): δ = –3.53, 13.33, 36.41, 116.30, 128.09,
129.28, 129.92, 130.26, 132.26, 132.36, 132.62, 133.66, 147.05,
H), 0.45 (s, 3 H), 2.43 (s, 3 H), 2.56 (s, 3 H), 5.55 (s, 1 H), 7.13–
7.62 (m, 15 H) ppm. 13C NMR (75 MHz, CDCl3): δ = –2.59, –2.15,
41.72, 43.16, 70.82, 107.86, 127.26, 127.63, 127.66, 128.26, 128.84,
129.00, 132.90, 133.02, 134.79, 137.91, 139.66, 141.63, 145.88,
150.03 ppm. IR (film): ν = 3020, 1608, 1504, 1250, 1100, 815 cm–1.
˜
MS (EI, 70 eV): m/z (%) = 234 (M+ – SiMe3Ph, 100%), 188 (10),
77 (18). C25H28N2Si (384.20): calcd. C 78.07, H 7.34, N 7.28; found
C 77.98, H 7.41, N 7.16.
150.95 ppm. IR (CH Cl ): ν = 3019, 1495, 1458, 1256, 1113 cm–1.
˜
2
2
5-tert-Butyldiphenylsilyl-2,3-dimethyl-1-phenylpyrazolium
Iodide
(5j): Yield 2.50 g (93%). M.p. 205–207 °C (recrystallized from Me-
COMe/Et2O). 1H NMR (300 MHz, CDCl3): δ = 1.09 (s, 9 H), 2.80
(s, 3 H), 3.79 (s, 3 H), 6.91–6.98 (m, 4 H), 7.09 (s, 1 H), 7.18–7.40
(m, 11 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 13.93, 18.63,
27.77, 36.99, 117.79, 128.19, 129.32, 129.62, 130.15, 131.57, 132.36,
1-Methyl-5-dimethylphenylsilyl-2,3,5-triphenyl-3-pyrazoline
(2f):
1
Yield 517 mg (58%). H NMR (300 MHz, CDCl3): δ = 0.38 (s, 3
H), 0.41 (s, 3 H), 2.78 (s, 3 H), 6.18 (s, 1 H), 6.96–7.69 (m, 20
H) ppm. 13C NMR (75 MHz, CDCl3): δ = 0.82, 43.30, 72.64,
111.18, 117.65, 119.69, 124.28, 125,62, 126.88, 127.01, 127.98,
128.19, 128.61, 129.19, 132.92, 133.77, 136.82, 138.87, 139.52,
135.75, 147.27, 147.63 ppm. IR (CHCl ): ν = 3019, 1590, 1493,
˜
3
1109 cm–1.
139,69, 143.06 ppm. IR (film): ν = 3020, 1600, 1504, 1250, 1100,
˜
General Procedure for the Reaction of Pyrazolium and Indazolium
Salts with Silyllithium Reagents: To a stirred solution of pyrazolium
or indazolium salt (2.0 mmol) in dry THF (20 mL) at –78 °C or
0 °C, under N2, was added a THF solution of dimethylphenylsilyl[9]
or tert-butyldiphenylsilyllithium[10] (2 mmol). The reaction mixture
(when cooled to –78 °C) was slowly allowed to warm to 0 °C and
was stirred at room temperature until TLC indicated that the reac-
tion was complete. The mixture was quenched with aqueous NH4Cl
and extracted with Et2O.The ethereal layer was dried with MgSO4
and the solvent was removed. The residue was purified by flash
chromatography (silica gel, hexanes/CH2Cl2 = 1:1) to give the fol-
lowing products:
810 cm–1. C30H30N2Si (446.22): calcd. C 80.67, H 6.77, N 6.27;
found C 80.54, H 6.82, N 6.19.
5-tert-Butyldiphenylsilyl-2,3,5-trimethyl-1-phenyl-3-pyrazoline (3a):
1
Yield 485 mg (57%). H NMR (300 MHz, CDCl3): δ = 1.21 (s, 9
H), 1.41 (s, 3 H), 2.26 (s, 3 H), 2.58 (s, 3 H), 3.90 (s, 1 H), 7.36–
7.77 (m, 15 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 18.90, 26.47,
28.68, 28.87, 35.23, 51.43, 108.78, 124.26, 126.68, 127.29, 129.04,
130.57, 133.64, 135.45, 146.58, 148.39 ppm. IR (film): ν = 3020,
˜
1600, 1500, 1100, 815 cm–1. MS (EI, 70 eV): m/z (%) = 172 (M+
–
tBuPh2SiMe, 100%), 157 (8), 95 (5), 77 (32). C29H34N2Si (426.25):
calcd. C 78.82, H 8.03, N 6.57; found C 78.95, H 7.97, N 6.70.
1,2,3,5-Tetramethyl-5-dimethylphenylsilyl-3-pyrazoline (2a): Yield
26 mg (5%). H NMR (300 MHz, CDCl3): δ = 0.53 (s, 3 H), 0.54 Yield 573 mg (89%). H NMR (300 MHz, CDCl3): δ = 0.42 (s, 3
1,2,5-Trimethyl-5-dimethylphenylsilyl-3-phenyl-3-pyrazoline
(3b):
1
1
Eur. J. Org. Chem. 2005, 4663–4669
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4667

A. M. González-Nogal, M. Calle, L. A. Calvo, P. Cuadrado, A. González-Ortega
137.99, 148.62 ppm. IR (film): ν = 1594, 1491, 1255, 1108 cm–1.
FULL PAPER
H), 0.44 (s, 3 H), 1.26 (s, 3 H), 2.44 (s, 3 H), 2.55 (s, 3 H), 4.92 (s,
1 H), 7.27–7.64 (m, 10 H) ppm. 13C NMR (75 MHz, CDCl3): δ = MS (EI, 70 eV): m/z (%) = 396 (M+ – SiMe3Ph, 23%), 339 (46),
–4.92, –3.96, 18.73, 38.06, 42.07, 61.96, 110.07, 126.61, 127.63, 262 (10), 239 (15), 135 (34), 77 (100). C35H42N2Si2 (546.29): calcd.
128.14, 128.34, 133.73, 134.52, 137.40, 138.77, 149.07 ppm. IR C 76.87, H 7.74, N 5.12; found C 76.71, H 7.67, N 5.25.
˜
(film): ν = 3040, 1605, 1500, 1250, 1110, 805 cm–1. MS (EI, 70 eV):
˜
Ethyl 2-Ethyl-3,5-dimethyl-5-dimethylphenylsilyl-1-phenyl-3-pyrazo-
line-4-carboxylate (7a): Yield 400 mg (49%). H NMR (300 MHz,
CDCl3): δ = 0.43 (s, 3 H), 0.48 (s, 3 H), 0.85 (t, J = 7.2 Hz, 3 H),
m/z (%) = 172 (M+ – SiMe3Ph, 100%), 157 (5), 77 (35), 56 (75).
1
C20H26N2Si (322.19): calcd. C 74.48, H 8.13, N 8.69; found C
74.64, H 8.05, N 8.80.
1.20 (t, J = 7.0 Hz, 3 H), 1.63 (s, 3 H), 2.22 (s, 3 H), 2.91 (m, 2 H),
5-tert-Butyldiphenylsilyl-1,2,5-trimethyl-3-phenyl-3-pyrazoline (3c):
Yield 622 mg (73%). H NMR (300 MHz, CDCl3): δ = 1.19 (s, 9
H), 1.33 (s, 3 H), 1.99 (s, 3 H), 2.51 (s, 3 H), 5.25 (s, 1 H), 7.29–
7.74 (m, 15 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 12.08, 18.84,
28.73, 35.75, 38.98, 57.11, 107.19, 127.50, 127.84, 128.88, 129.26,
4.00 (dq, J = 10.6, 7.0 Hz, 1 H), 4.14 (dq, J = 10.6, 7.0 Hz, 1 H),
7.06–7.65 (m, 10 H) ppm. 13C NMR (75 MHz, CDCl3): δ = –5.35,
–4.14, 12.12, 13.86, 14.04, 18.36, 44.05, 61.37, 65.02, 112.02,
115.44, 122.79, 126.96, 127.45, 128.48, 132.75, 137.59, 149.59,
1
157.01, 160.82 ppm. IR (film): ν = 1720, 1600, 1508, 1250, 1110,
˜
825 cm–1. MS (EI, 70 eV): m/z (%) = 408 (M+, 1%), 273 (20), 244
(54), 215 (30), 199 (100), 135 (51), 105 (18), 77 (91). C24H32N2O2Si
(408.22): calcd. C 70.55, H 7.89, N 6.86; found C 70.76, H 7.96, N
6.74.
129.82, 130.81, 136.14, 145.60, 147.85 ppm. IR (film): ν = 3020,
˜
1600, 1500, 1090, 800 cm–1. MS (EI, 70 eV): m/z (%) = 172 (M+
–
tBuPh2SiMe, 100%), 157 (10), 130 (40), 95 (5), 77 (50). C29H34N2Si
(426.25): calcd. C 78.82, H 8.03, N 6.57; found C 78.99, H 8.10, N
6.68.
Ethyl 2-Ethyl-1,3,5-trimethyl-5-dimethylphenylsilyl-3-pyrazoline-4-
carboxylate (7b): Yield 463 mg (67%). 1H NMR (300 MHz,
CDCl3): δ = 0.41 (s, 3 H), 0.43 (s, 3 H), 1.09 (t, J = 7.0 Hz, 3 H),
1.24 (t, J = 7.2 Hz, 3 H), 1.36 (s, 3 H), 2.10 (s, 3 H), 2.72 (s, 3 H),
2.95 (dq, J = 14.8, 7.0 Hz, 1 H), 3.15 (dq, J = 14.8, 7.0 Hz, 1 H),
4.06 (dq, J = 10.9, 7.2 Hz, 1 H), 4.18 (dq, J = 10.9, 7.2 Hz, 1 H),
7.30–7.60 (m, 5 H) ppm. 13C NMR (75 MHz, CDCl3): δ = –3.35,
–2.14, 11.45, 12.06, 14.12, 15.22, 42.36, 48.03, 58.67, 63.41, 104.53,
3-Phenyl-3-[(dimethylphenylsilyl)phenylamino]-2-propen-1-phenyl-
methylimine (4): Yield 232 mg (26%). 1H NMR (300 MHz, CDCl3):
δ = 0.33 (s, 6 H), 2.96 (s, 3 H), 5.03 (s, 1 H), 6.75 (dd, J = 1.2,
8.3 Hz, 2 H), 6.86 (tt, J = 1.2, 7.1 Hz, 1 H), 7.13 (dd, J = 7.2,
8.3 Hz, 2 H), 7.18–7.48 (m, 15 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = –4.00, 32.12, 97.54, 118.83, 121.71, 122.57, 125,12,
125.68, 127.60, 127.90, 128.14, 128.32, 128.75, 129.16, 133.71,
136.76, 138.77, 139.47, 150.16, 161.88, 166.55 ppm. IR (film): ν =
˜
127.45, 132.75, 134.07, 139.59, 155.21, 160.37 ppm. IR (film): ν =
˜
3020, 1600, 1504, 1250, 1100, 800 cm–1. C30H30N2Si (446.22): calcd.
C 80.67, H 6.77, N 6.27; found C 80.82, H 6.84, N 6.14.
1720, 1600, 1500, 1250, 1110 cm–1. MS (EI, 70 eV): m/z (%) = 346
(M+, 1%), 331 (15), 273 (10), 211 (24), 182 (30), 137 (100), 135
(46). C19H30N2O2Si (346.21): calcd. C 65.85, H 8.73, N 8.08; found
C 65.97, H 8.80, N 7.92.
Ethyl 1-Ethyl-3,5-dimethyl-5-dimethylphenylsilyl-2-phenyl-3-pyrazo-
1
line-4-carboxylate (6a): Yield 269 mg (33%). H NMR (300 MHz,
CDCl3): δ = 0.35 (s, 3 H), 0.38 (s, 3 H), 0.73 (t, J = 7.1 Hz, 3 H),
1.18 (s, 3 H), 1.20 (t, J = 7.0 Hz, 3 H), 2.20 (s, 3 H), 2.66 (dq, J =
14.1, 7.1 Hz, 1 H), 2.78 (dq, J = 14.1, 7.1 Hz, 1 H), 3.99 (dq, J =
10.8, 7.0 Hz, 1 H), 4.19 (dq, J = 10.8, 7.0 Hz, 1 H), 7.06–7.65 (m,
10 H) ppm. 13C NMR (75 MHz, CDCl3): δ = –4.40, –2.61, 11.99,
12.66, 14.21, 16.50, 42.33, 58.10, 61.37, 105.46, 118.32, 124.96,
127.45, 127.72, 128.98, 132.93, 139.91, 146.87, 153.85, 166.06 ppm.
Ethyl 2-Ethyl-3-methyl-1-phenyl-3-pyrazoline-5-carboxylate (7c):
Yield 437 mg (84%). H NMR (300 MHz, CDCl3): δ = 1.11 (t, J
1
= 7.0 Hz, 3 H), 1.36 (t, J = 7.1 Hz, 3 H), 1.89 (s, 3 H), 3.16 (q, J
= 7.0 Hz, 2 H), 4.31 (q, J = 7.1 Hz, 2 H), 4.74 (d, J = 2.4 Hz, 1
H), 4.84 (d, J = 2.4 Hz, 1 H), 6.97 (t, J = 7.4 Hz, 1 H), 7.10 (d, J
= 7.9 Hz, 2 H), 7.28 (dd, J = 7.4, 7.9 Hz, 2 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 10.08, 12.70, 14.28, 46.59, 61.15, 73.28,
98.88, 114.73, 120.33, 127.83, 145.14, 152.46, 172.22 ppm. IR
IR (film): ν = 1725, 1605, 1500, 1250, 1110, 820 cm–1. MS (EI,
˜
70 eV): m/z (%) = 408 (M+, 1%), 335 (5), 273 (20), 244 (54), 215
(30), 199 (100), 135 (51), 77 (91). C24H32N2O2Si (408.22): calcd. C
70.55, H 7.89, N 6.86; found C 70.69, H 7.80, N 6.98.
(film): ν = 1735, 1600, 1508, 825 cm–1. MS (EI, 70 eV): m/z (%) =
˜
260 (M+, 3%), 245 (42), 231 (4), 215 (30), 187 (51), 77 (100).
C15H20N2O2 (260.15): calcd. C 69.20, H 7.74, N 10.76; found C
69.08, H 7.67, N 10.92.
1-Ethyl-3,5-dimethyl-4,5-bis(dimethylphenylsilyl)-2-phenyl-3-pyrazo-
line (6b): Yield 705 mg (75%). 1H NMR (300 MHz, CDCl3): δ =
0.01 (s, 3 H), 0.13 (s, 3 H), 0.22 (s, 3 H), 0.33 (s, 3 H), 1.03 (t, J =
7,1 Hz, 3 H), 1.47 (s, 3 H), 1.96 (s, 3 H), 3.15 (dq, J = 7.1, 14.6 Hz,
1 H), 3.46 (dq, J = 7.1, 14.6 Hz, 1 H), 6.74 (t, J = 7.1 Hz, 1 H),
7.02 (d, J = 8.6 Hz, 2 H), 7.15 (dd, J = 7.1, 8.6 Hz, 2 H), 7.30–7.69
3-tert-Butyldiphenylsilyl-1,2-dimethylindazoline (11a): Yield 594 mg
1
(77%). H NMR (300 MHz, CDCl3): δ = 1.22 (s, 9 H), 2.40 (s, 3
H), 2.56 (s, 3 H), 4.38 (s, 1 H), 6.38 (d, J = 7.9 Hz, 1 H), 6.57 (m,
2 H), 6.95 (m, 1 H), 7.19–7.60 (m, 10 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 19.22, 28.62, 41.30, 48.08, 62.21, 110.19, 120.16,
122.72, 126.71, 127.22, 127.27, 127.62, 129.11, 130.69, 132.75,
(m, 10 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = –3.97,
–3.92, –3.82, –2.52, 14.11, 14.74, 15.03, 48.45, 61.92, 110.03,
112.89, 122.17, 127.46, 128.30, 128.81, 131.18, 132.34, 133.40,
134.95, 136.75, 136.87, 150.24 ppm. IR (film): ν = 1598, 1490,
˜
1106 cm–1. MS (EI, 70 eV): m/z (%) = 329 (M+ – Bu, 100%), 309
(15), 224 (22), 146 (31), 77 (40), 57 (53). C25H30N2Si (386.22):
calcd. C 77.67, H 7.82, N 7.25; found C 77.83, H 7.90, N 7.41.
133.48, 139.35, 139.74, 141.23, 151.55 ppm. IR (film): ν = 1608,
˜
1504, 1250, 1110 cm–1. MS (EI, 70 eV): m/z (%) = 306 (M+ – Si-
Me2EtPh, 61%), 291 (26), 229 (10), 135 (40), 77 (100). C29H39N2Si2
(470.26): calcd. C 73.98, H 8.14, N 5.95; found C 74.12, H 8.22, N
6.13.
1-Ethyl-3-dimethylphenylsilyl-2-phenylindazoline
(11b):
Yield
372 mg (52%). 1H NMR (300 MHz, CDCl3): δ = 0.45 (s, 3 H), 0.47
(s, 3 H), 1.24 (t, J = 7.2 Hz, 3 H), 2.85 (dq, J = 14.2, 7.2 Hz, 1 H),
3.12 (dq, J = 14.2, 7.2 Hz, 1 H), 4.61 (s, 1 H), 6.74 (d, J = 7.5 Hz,
3-tert-Butyldiphenylsilyl-1,5-dimethyl-5-dimethylphenylsilyl-2-
phenyl-3-pyrazoline (6c): Yield 742 mg (68%). 1H NMR (300 MHz,
CDCl3): δ = 0.36 (s, 3 H), 0.38 (s, 3 H), 1.05 (s, 9 H), 1.29 (s, 3 H), 1 H), 6.86 (m, 2 H), 7.10–7.64 (m, 11 H) ppm. 13C NMR (75 MHz,
2.59 (s, 3 H), 5.75 (s, 1 H), 6.65–6.76 (m, 5 H), 7.30–7.82 (m, 15
H) ppm. 13C NMR (75 MHz, CDCl3): δ = –4.14, –4.09, 19.07,
19.15, 28.31, 40.28, 63.08, 108.83, 120.93, 121.38, 127.31, 127.37,
127.63, 128.15, 128.96, 129.46, 132.98, 134.31, 134.38, 137.59,
CDCl3): δ = –3.97, 14.22, 45.03, 53.27, 112.37, 112.75, 116.25,
120.98, 123.87, 127.65, 128.37, 129.21, 132.45, 132.94, 133.80,
139.74, 149.64, 155.25 ppm. IR (film): ν = 3015, 1590, 1486, 1250,
˜
1100 cm–1. MS (EI, 70 eV): m/z (%) = 343 (M+ – Me, 16%), 281
4668
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 4663–4669

Synthesis of Silylated Azolines from Azolium Salts
FULL PAPER
(5), 223 (100), 194 (19), 135 (31), 77 (14). C23H26N2Si (358.19):
calcd. C 77.05, H 7.31, N 7.81; found C 76.91, H 7.26, N 7.98.
temperature and stirred at room temperature until TLC indicated
that the reaction was complete. The mixture was quenched with
aqueous NH4Cl and extracted with Et2O. The ethereal layer was
dried with MgSO4, the solvent was removed, and the residue was
purified by chromatography on silica gel, with dichloromethane/
hexanes (1:1) as eluent to give the following products:
3-tert-Butyldiphenylsilyl-1-ethyl-2-phenylindazoline (11c): Yield
684 mg (74%). 1H NMR (300 MHz, CDCl3): δ = 1.02 (t, J =
7.2 Hz, 3 H), 1.33 (s, 9 H), 2.25 (dq, J = 14.1, 7.2 Hz, 1 H), 2.51
(dq, J = 14.1, 7.2 Hz, 1 H), 5.28 (s, 1 H), 6.61 (m, 2 H), 6.94 (m,
2 H), 7.14–7.54 (m, 15 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
14.03, 19.01, 28.45, 50.93, 63.27, 111.95, 117.23, 121.02, 121.15,
122.22, 126.46, 127.17, 127.79, 128.69, 129.36, 132.45, 133.89,
1,2,3-Trimethylindazoline (9a): Yield 143 mg (59%) from meth-
yllithium and 201 mg (83%) from methylmagnesium iodide; 1H
NMR (300 MHz, CDCl3): δ = 1.32 (d, J = 7.0 Hz, 3 H), 2.47 (s, 3
H), 2.75 (s, 3 H), 3.72 (q, J = 7.0 Hz, 1 H), 6.35–7.14 (m, 4 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 19.05, 39.47, 43.40, 60.68, 111.24,
134.77, 135.66, 137.01, 137.08, 150.02, 157.18 ppm. IR (film): ν =
˜
3018, 1596, 1486, 1105 cm–1. MS (EI, 70 eV): m/z (%) = 405 (M+
–
119.46, 121.70, 126.71, 128.32, 145.63 ppm. IR (film): ν = 1598,
˜
Bu, 100%), 300 (18), 222 (11), 105 (15), 77 (20), 57 (54).
C31H34N2Si (462.25): calcd. C 80.47, H 7.41, N 6.05; found C
80.65, H 7.48, N 6.22.
1490, 720 cm–1. MS (EI, 70 eV): m/z (%) = 162 (M+, 1%), 146
(100), 103 (50), 91 (12), 77 (41). C10H14N2 (162.12): calcd. C 74.03,
H 8.70, N 17.27; found C 74.14, H 8.83, N 17.15.
2-Ethyl-3-dimethylphenylsilyl-1,3-diphenylindazoline (11d): Yield
382 mg (44%). 1H NMR (300 MHz, CDCl3): δ = 0.45 (s, 3 H), 0.47
(s, 3 H), 1.11 (t, J = 7.1 Hz, 3 H), 2.82 (dq, J = 14.2, 7.1 Hz, 1 H),
3.02 (dq, J = 14.2, 7.1 Hz, 1 H), 6.90 (t, J = 7.5 Hz, 1 H), 7.05 (m,
3 H), 7.18 (dd, J = 7.6, 8.0 Hz, 1 H), 7.21–7.58 (m, 14 H) ppm.
13C NMR (75 MHz, CDCl3): δ = –4.72, –4.05, 12.13, 52.19, 66.15,
112.05, 119.34, 121.60, 122.72, 124.11, 127.21, 127.45, 127.68,
127.90, 128.38, 128.90, 132.31, 132.75, 134.07, 139.59, 143.17,
1-Ethyl-3-methyl-2-phenylindazoline (9b): Yield 303 mg (85%). 1H
NMR (300 MHz, CDCl3): δ = 1.08 (t, J = 7.2 Hz, 3 H), 1.52 (d, J
= 7.1 Hz, 3 H), 3.23 (q, J = 7.2 Hz, 2 H), 4.55 (q, J = 7.1 Hz, 1
H), 6.30–7.20 (m, 9 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
12.05, 19.13, 48.77, 57.03, 111.47, 112.69, 118.25, 119.06, 124.62,
127.32, 128.44, 129.87, 139.49, 143.12 ppm. IR (film): ν = 3015,
˜
1600, 1493, 780, 752, 695 cm–1. MS (EI, 70 eV): m/z (%) = 238
(M+, 5%), 223 (21), 160 (100), 77 (54). C16H18N2 (238.15): calcd.
C 80.63, H 7.61, N 11.75; found C 80.74, H 7.73, N 11.91.
145.38, 147.55 ppm. IR (film): ν = 3015, 1605, 1500, 1246,
˜
1100 cm–1. C29H30N2Si (434.22): calcd. C 80.14, H 6.96, N 6.45;
found C 80.29, H 7.05, N 6.58.
o-(Methylamino)acetophenone (10): Yield 47 mg (21%). See ref.[11]
2-Methyl-1,4-diphenyl-1,2-dihydroquinazoline (12): Yield 226 mg
(38%). 1H NMR (300 MHz, CDCl3): δ = 1.47 (d, J = 6.3 Hz, 3 H), Acknowledgments
5.79 (q, J = 6.3 Hz, 1 H), 6.80 (t, J = 7.3 Hz, 1 H), 7.06 (d, J =
We thank the Spanish Ministerio de Ciencia y Tecnología for finan-
cial support (Grant BQU2000–0943).
8.1 Hz, 2 H), 7.14 (dd, J = 7.3, 8.1 Hz, 2 H), 7.27–7.64 (m, 9
H) ppm. 13C NMR (75 MHz, CDCl3): δ = 18.31, 71.91, 117.64,
118.77, 119.86, 122.65, 123.71, 128.08, 128.39, 128.58, 129.15,
129.35, 132.05, 138.02, 143.21, 144.70, 163.30 ppm. IR (film): ν =
˜
[1] J. Elguero, R. Jacquier, D. Tizané, Bull. Soc. Chim. France
1970, 1121 and 1129.
3018, 1664, 1607, 1494, 762, 690 cm–1. C21H18N2 (298.15): calcd. C
84.53, H 6.08, N 9.39; found C 84.71, H 6.01, N 9.22.
[2] P. Cuadrado, A. M. González-Nogal, S. Martínez, Tetrahedron
1997, 53, 8585.
N-Ethyl-2-(phenylamino)benzamide (13): Yield: 374 mg (78%) from
dimethylphenylsilyllithium and 163 mg (34%) from tert-butyldi-
[3] P. Cuadrado, A. M. González-Nogal, Tetrahedron Lett. 1998,
39, 1449.
phenylsilyllithium. M.p. 74–75 °C (recrystallised from cyclohex-
[4] A. R. Bassindale, A. G. Brook, Can. J. Chem. 1974, 52, 3474.
1
ane). H NMR (300 MHz, CDCl3): δ = 1.25 (t, J = 7.3 Hz, 3 H), [5] L. A. Calvo, A. M. González-Nogal, A. González-Ortega,
M. C. Sañudo, Tetrahedron Lett. 2001, 42, 8981.
[6] J. Elguero, in: Comprehensive Heterocyclic Chemistry, vol. 5
(Eds.: A. K. Katritzky, C. W. Rees), Pergamon, Oxford, 1984,
p. 245.
[7] N. F. Haley, J. Org. Chem. 1978, 43, 1233.
[8] M. Calle, P. Cuadrado, A. M. González-Nogal, R. Valero, Syn-
thesis 2001, 1949.
[9] I. Fleming, T. W. Newton, F. Roessler, J. Chem. Soc. Perkin
Trans. 1 1981, 2527.
[10] A. Barbero, P. Cuadrado, I. Fleming, A. M. González, F. J. Pu-
lido, A. Sánchez, J. Chem. Soc. Perkin Trans. 1 1995, 1525.
[11] F. Gao, K. F. Johnson, J. B. Schlenoff, J. Chem. Soc. Perkin
Trans. 2 1996, 271.
3.48 (dq, J = 5.4, 7.3 Hz, 2 H), 6.21 (s br, 1 H), 6.76 (t, J = 8.0 Hz,
1 H), 7.01 (dd, J = 7.1, 7.6 Hz, 1 H), 7.18–7.43 (m, 7 H), 9.32 (s.
1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 14.77, 34.68, 115.40,
117.91, 118.69, 120.47, 122.20, 127.42, 129.21, 131.95, 141.54,
145.15, 169.44 ppm. IR (film): ν = 3300 br, 3015, 1630, 1590, 1500,
˜
740, 690 cm–1. C15H16N2O (240.13): calcd. C 74.97, H 6.71, N
11.66; found C 75.11, H 6.68, N 11.53.
Reaction of Indazolium Salts with Organometallic Reagents. Typical
Procedure: To a stirred solution of indazolium salt 8a or isoindazol-
ium salt 8b (1.5 mmol) in dry Et2O (10 mL) at –20 °C or room
temperature, under N2, was added an ethereal solution of methyl-
magnesium iodide or methyllithium (1.5 mmol). The reaction mix-
ture (when cooled to –20 °C) was slowly allowed to warm to room
Received: June 16, 2005
Published Online: September 16, 2005
Eur. J. Org. Chem. 2005, 4663–4669
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4669