Reaction of 1-tert-butyl-3,4-diphenyl-1,2,4-triazol-5-ylidenes with a malonic ester

Article abstract of DOI:10.1039/b712885a

Four stable carbenes, 1-tert-butyl-3,4-diaryl-1,2,4-triazol-5-ylidenes 1a-d, including new fluorine-containing compounds 1c,d, react with a malonic ester to afford heterocyclic zwitterionic compounds 5a-d. The reactions with more acidic compounds (ethyl acetoacetate, malononitrile and 1,3-dimethylbarbituric acid) proceed with substrate deprotonation to form the respective azolium salts 6a-c. The X-ray crystal structure of 5a was also determined. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b712885a

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Reaction of 1-tert-butyl-3,4-diphenyl-1,2,4-triazol-5-ylidenes with
a malonic ester†
Nikolai I. Korotkikh,*a Alan H. Cowley,b Jennifer A. Moore,b Nataliya V. Glinyanaya,a Ilia S. Panov,a
Gennady F. Rayenko,a Tatyana M. Pekhterevaa and Oles P. Shvaikaa
Received 21st August 2007, Accepted 24th October 2007
First published as an Advance Article on the web 23rd November 2007
DOI: 10.1039/b712885a
Four stable carbenes, 1-tert-butyl-3,4-diaryl-1,2,4-triazol-5-ylidenes 1a–d, including new
fluorine-containing compounds 1c,d, react with a malonic ester to afford heterocyclic zwitterionic
compounds 5a–d. The reactions with more acidic compounds (ethyl acetoacetate, malononitrile and
1,3-dimethylbarbituric acid) proceed with substrate deprotonation to form the respective azolium salts
6a–c. The X-ray crystal structure of 5a was also determined.
Introduction
Results and discussion
The reactions of in situ-generated carbenes with C–H acidic
compounds are well known. For example, Pazdro and Polaczkova1
showed that dithiol-2-ylidene dimers will insert into the C–
H bonds of malononitrile, acetylacetone, ethyl acetoacetate
and cyclopentanone to afford the corresponding dihydrodithiol
derivatives. However, it is not clear whether such reactions
really proceed via the intermediacy of a free carbene. Similar
transformations with acetonitrile, dimethyl sulfone and acetylene
(pKa = 20–25) have been studied with stable carbenes2–5 and
resulted in the isolation of the respective C–H insertion products,
i.e. cyanomethylazolines.
The stable carbenes 1a–d, including the new stable fluorine-
containing carbenes 1c,d, were synthesized by the ring trans-
formations of 2-phenyl-1,3,4-oxadiazole 2a,b with anilines in
the presence of trifluoroacetic acid according to the literature
method,10 followed by quaternization of the resulting triazoles
3a–d with t-BuI to form the triazolium salts 4a–d (Scheme 1).
Deprotonation of the latter salts with potassium tert-butoxide in
tetrahydrofuran solution afforded the desired carbenes 1a–d. It is
noteworthy that the quaternization of triazoles 3a–d takes place
exclusively at the 1-position, hence only one isomer of salt 4a–d is
formed. The generation of tert-butyl iodide was carried out in situ
by treatment of tert-butyl chloride with sodium iodide in acetic
acid solution.
To the best of our knowledge,6 the reactions of isolable
carbenes with an ester functional group have not been stud-
ied thus far. However, it is known that in situ-generated 1,3-
=
diphenylcyclopropene-2-ylidene reacts with the C C bond of
dimethyl fumarate to form a spirocyclic adduct.7 Likewise, the
stable (phosphanyl)(silyl)carbenes react with the double bond of
dimethyl fumarate and other electron-poor alkenes to give the
corresponding trans-cyclopropanes.8 In the case of the reaction of
1,3,4-triphenyl-1,2,4-triazol-5-ylidene, the initially formed [2 + 1]
cycloaddition product undergoes ring opening and a 1,2-hydrogen
shift to afford methylenetriazoline derivatives.9
In the present contribution we describe (i) the synthesis of
new stable fluorine-containing carbenes of the 1,2,4-triazole
series, namely 1-tert-butyl-3-aryl-4-fluoroaryl-1,2,4-triazol-5-
ylidenes; (ii) the first Claisen reaction of stable carbenes with an
ester functional group of malonic esters to form new heterocyclic
zwitterionic compounds; and (iii) the deprotonations of 1,3-
dimethylbarbituric acid, malononitrile and ethyl acetoacetate by
the carbene.
Scheme 1 Reagents and conditions: (i) p-H2N-C6H4-R1 (− H2O); (ii) 1.
t-BuI; 2. NaClO4; (iii) t-BuOK (− t-BuOH).
A two-stage isolation of carbenes 1a–d by solvent evaporation
in the presence of an inorganic salt permitted complete decom-
position of the intermediate triazolium alkoxides. In the method
described earlier,5 the carbenes were isolated by filtration of the
inorganic salt, concentration of the filtrate and recrystallisation of
the crystalline residues in order to remove the remaining azolium
alkoxide impurities.
The reactions of carbenes 1a–d with diethyl malonate (pKa = 13)
were carried out in refluxing toluene for 2–4 h under conditions
such that evolved ethanol was removed by a controlled stream
of nitrogen. If this procedure is not followed, the reaction times
aThe L. M. Litvinenko Institute of Physical Organic and Coal Chemistry,
Ukrainian Academy of Sciences, 70, R. Luxemburg, Donetsk, 83114,
Ukraine. E-mail: nkorotkikh@ua.fm; Fax: +380 (62)3116830; Tel: +380
(62)3116835
bThe University of Texas at Austin, Department of Chemistry & Biochem-
istry, 1 University Station A5300, Austin, Texas, 78712-0165, USA. E-mail:
acowley@cm.utexas.edu; Fax: +1 (512) 471-6822; Tel: +1 (512) 471-7484
† Electronic supplementary information (ESI) available: Crystal structure
data for compound 5a. See DOI: 10.1039/b712885a
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increase to ∼40 h and the transformations are incomplete.
Following work-up of the reaction mixtures, the zwitterionic
compounds 5a–d were obtained in isolated yields of 51–81%. The
outcomes of the reactions can be rationalized on the basis of initial
nucleophilic attack of the carbene on the ester functional group
to form intermediate 5A (Scheme 2), followed by loss of EtOH
to produce the zwitterionic compounds 5a–d. It is noteworthy
that C–H insertion products are not observed in these processes.
Moreover, this new transformation can be considered to be a
carbene analogue of the Claisen reaction of esters.
1.16 and 3.91–3.96 ppm), and the CHC group of an aliphatic
fragment (d 4.78–4.84 ppm). The 13C NMR spectrum (see Fig. 1
for the atom numbering scheme) is distinguished by the presence
of resonances for the tert-butyl carbon atoms (d 28.6–28.8 and
65.8–66.1 ppm), the carbon atoms of the ethyl group (d 14.5–14.7
and 58.0–58.1 ppm) and benzene nuclei (d 115.8–134.0 ppm), the
triazole atoms C1 and C2 (d 149.0–150.5; 153.9–154.6 ppm), C21
of the aliphatic fragment (d 90.3–90.6 ppm), and two signals for
the carbonyl group (d 163.7–164.4 and 170.9–171.2 ppm). The
=
former signal was assigned to the C19 O group, and the latter to
=
the C21 O moiety. The IR spectrum of 5a shows the absence of
typical carbonyl stretching vibrations. The detection of a vibration
at 1653 cm−1 is consistent with the proposed delocalized structure
for 5a. The mass spectra of compounds 5a,c show molecular ions
[MH]+ corresponding to the monomers (m/z 392.5 for 5a; 410.0
for 5c). The molecular ions of compounds 5b–d undergo further
decomposition by elimination of isobutene and malonyl fragments
(see the Experimental section).
Scheme 2 Reagents and conditions: (i) CH2(COOEt)2, D; (ii) D (− EtOH).
The reaction of 1a with 1,3-dimethylbarbituric acid (pKa
=
4.68) results in protonation of the substrate and affords salt
6a. Compound 6a is a stable compound that does not undergo
further reaction. Less acidic malononitrile (pKa = 9) and ethyl
acetoacetate (pKa = 11) also undergo reaction with carbene 1b to
afford salts 6b and 6c, respectively. Compound 6b was isolated as
a toluene solvate. Carbon–hydrogen insertion was not observed in
any of these reactions.
Fig. 1 X-Ray crystal structure of zwitterionic compound 5a.†
Crystals of compound 5a suitable for X-ray diffraction study
were grown from diethyl ether solution. The X-ray data† confirm
the ionic character of the triazole ring. Significant structural
=
features are the somewhat elongated bonds of both C O groups
(123.6 and 126.6 pm), a shortened C19–C20 bond (137.3 pm) and,
to a lesser extent, a shortened C20–C21 aliphatic linkage (141.9
pm) (see Fig. 1 and Fig. 2). The C1–C19 bond distance of 152.6
pm corresponds to that of a typical C–C single bond, and the
Compounds 1 and 3–6 are colorless crystalline solids that
1
were characterized by elemental analysis, H, 13C NMR, IR and
=
C19 O1 carbonyl group is twisted with respect to the plane of
mass spectroscopy. The molecular structure of compound 5a was
the triazolium nucleus. The benzene rings attached to C2 and N3
established by single-crystal X-ray diffraction.
1
The H NMR spectra of salts 4c,d feature the signals for the
tert-butyl group (d 1.72–1.76 ppm), aromatic protons (d 7.3–
7.7 ppm) and the C5-H proton of the triazolium nucleus (d 10.65–
10.73 ppm). The 1H NMR spectra of carbenes 1c,d exhibit similar
signals for the tert-butyl (d 1.78–1.79 ppm) and aromatic protons (d
6.5–7.3 ppm). However, the chemical shift for the latter is notably
upfield relative to that of the salt. The 13C NMR spectra of 1c,d
exhibit resonances for the tert-butyl carbon atoms (d 30.2–30.4
and ipso-C 59.2–59.4 ppm), aromatic nuclei (d 115.0–164.0 ppm),
C3 (d 148.7–150.7 ppm) and the C5 atoms (d 206.6–208.6 ppm)
of the triazole nucleus. The 1H NMR spectra of zwitterionic
compounds 5a–d are characterized by the presence of resonances
for the tert-butyl protons (d 1.80–1.87 ppm), aromatic protons
(d 7.0–7.5 ppm), the ethyl group of an ester fragment (d 1.12–
Fig. 2 Selected bond lengths (pm) and angles (◦) for compound 5a.
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subtend dihedral angles of 26.9 and 71.1◦, respectively, in relation
to the plane of the triazolium ring. All the foregoing structural data
are consistent with the proposed zwitterionic structure for 5a.
The 1H NMR spectra of the triazolium salts 6a–c include signals
that can be assigned to the protons of both the cation and the
anion. Thus, the singlets at d 9.70–10.90 ppm can be assigned to
the C5-H proton of the cation, and the singlet at d 3.50–4.05 ppm
is attributable to the C2-H proton of the anion. Collectively, these
data confirm the ionic structure for 6a–c. The spectra for salts 6b,c
exhibit broad C5-H signals due to facile proton exchange.
H, 6.0; F, 6.3; N, 14.3. Calcd for C18H18FN3: C, 73.2; H, 6.1; F, 6.4;
N, 14.2%. dH (200 MHz, C6D6, Me4Si) 1.78 (9H, s, CH3C), 6.53
(2H, m, Ar), 7.02 (5H, m, Ar), 7.31 (2H, m, Ar). dC (50.3 MHz,
C6D6, Me4Si) 30.2 (CH3C), 59.2 (CH3C), 115.1, 115.6 (C3, ArN,
J 22.8 Hz), 125.2 (C1, Ar-C), 128.3, 128.5, 129.39, 129.51 (Ar),
135.5 (C1, ArN), 150.7 (C3), 159.1, 164.0 (C–F, J 246.9 Hz), 206.6
(C5).
1-tert-Butyl-3-o-chlorophenyl-4-p-fluorophenyl-1,2,4-triazol-5-
ylidene (1d). Yield 71%. Mp 103–105 ◦C (from toluene). Found:
C, 65.8; H, 5.2; Cl, 10.7; F, 5.8; N, 12.6. Calcd for C18H17ClFN3:
C, 65.6; H, 5.2; Cl, 10.8; F, 5.8; N, 12.7%. dH (200 MHz, C6D6,
Me4Si) 1.79 (9H, s, CH3C), 6.51 (2H, m, Ar), 6.72 (2H, m, Ar),
6.94 (1H, m, Ar), 7.13 (3H, m, Ar). dC (50.3 MHz, C6D6, Me4Si)
30.4 (CH3C), 59.4 (CH3C), 115.0, 115.5 (C3, ArN, J 22.8 Hz),
126.7, 126.8 (C2, ArN, J 8.3 Hz), 126.4, 129.7, 130.9, 131.9 (Ar),
128.0 (C1, Ar-C), 134.1 (C–Cl), 135.6, 135.7 (C1, ArN, J 3.0 Hz)
(Ar), 148.7 (C3), 159.0, 163.9 (C–F, J 246.5 Hz), 208.6 (C5).
Conclusion
In summary, we have demonstrated that the stable heteroaromatic
carbenes 1-tert-butyl-3,4-diaryl-1,2,4-triazol-5-ylidenes 1a–d react
with the ester functional group of diethyl malonate to produce
the heterocyclic zwitterionic derivatives 5a–d. These reactions
represent the first example of the carbene version of the Claisen
reaction of esters. No evidence was found for C–H insertion reac-
tions. It is known that less acidic C–H compounds either undergo
insertion reactions with stable carbenes (for example, acetonitrile,
ketones, sulfones, and acetylenes) or do not react (for example,
dimethyl sulfoxide, alkylarenes, and saturated hydrocarbons). The
reactions of 1a with the appreciably more acidic C–H compounds,
1,3-dimethylbarbituric acid, malononitrile and ethyl acetoacetate,
produce the salts 6a–c via the protonation of the carbene.
Procedure for the synthesis of 3a–d
These were obtained by the ring transformations of the respective
oxadiazoles ◦2a,b with anilines in the presence of trifluoroacetic
acid at 180 C according to the literature method.10,11 Isolation
of the new compounds 3c,d was carried out by washing the
unpurified products with diethyl ether and then, if necessary, by
recrystallization from the indicated solvent.
Experimental
3-Phenyl-4-p-fluorophenyl-1,2,4-triazole (3c). Yield 50%. Mp
137–139 ◦C (from DMF). Found: C, 70.5; H, 4.2; F, 8.0; N,
17.6. Calcd for C14H10FN3: C, 70.3; H, 4.2; F, 7.9; N, 17.6%. dH
(200 MHz, C6D6, Me4Si) 7.41 (9H, m, Ar), 8.89 (1H, s, CHN).
General methods
All experiments with the 1,2,4-triazol-5-ylidenes 1a–d were carried
out under an argon atmosphere. All solvents were dried by
standard methods prior to use. 1H and 13C NMR chemical shifts
are reported relative to tetramethylsilane (TMS, d = 0.00) as
internal standard. Mass spectra were taken on an Agilent 1100
Series chromatomass spectrometer (APCI, 3 kV, chromatography:
a column-Zorbax SB-C18, eluent acetonitrile–water 95 : 5 with
0.1% formic acid). IR spectra were measured as Nujol mulls,
and thin-layer chromatography was performed on silica gel with
chloroform or a 10 : 1 mixture of chloroform and methanol as
eluent, followed by development with iodine. Elemental analyses
were carried out at the Analytical Laboratory of the Litvinenko
Institute of Physical Organic and Coal Chemistry.
3-o-Chlorophenyl◦-4-p-fluorophenyl-1,2,4-triazole (3d). Yield
55%. Mp 128–130 C (from DMF). Found: C, 61.5; H, 3.2; Cl,
13.0; F, 6.8; N, 15.4. Calcd for C14H9ClFN3: C, 61.4; H, 3.3; Cl,
13.0; F, 6.9; N, 15.4%. dH (200 MHz, C6D6, Me4Si) 7.31 (4H, m),
7.51 (3H, m), 7.69 (1H, d, J 6.2 Hz) (Ar), 9.05 (1H, s, CHN).
General procedure for the preparation of
1-tert-butyl-3,4-diaryl-1,2,4-triazolium perchlorates (4a–d)
A mixture of sodium iodide (20.2 g, 0.135 mol), tert-butyl chloride
(15 mL, 0.135 mol) and the triazole 3a–d (0.05 mol) in acetic
acid (20 mL) was refluxed until the reaction was complete as
monitored by TLC (typically 20 h). The reaction mixture was
diluted with 0.5 L of water, heated until boiling, following which a
small amount of sodium sulfite along with 1 g of activated carbon
was added, and the mixture was filtered. A solution of sodium
perchlorate (8.58 g, 0.07 mol) in water (20 mL) was then added
and the resulting precipitate was filtered off and dried to give 67–
85% of salts 4a–d. The new compounds 4c,d are characterized as
indicated below.
General procedure for the synthesis of
1-tert-butyl-3,4-diphenyl-1,2,4-triazol-5-ylidenes 1a–d
Potassium tert-butoxide (280 mg, 2.55 mmol) was added to a
dispersion of salt 4a–d (2.65 mmol) in anhydrous tetrahydrofuran
(10 mL) and stirred at room temperature for 0.5 h. The solvent was
evaporated and the product was extracted with a further portion
of tetrahydrofuran (10 mL). The latter solution was re-evaporated
and the residue was stirred with petroleum ether (5 mL). The
resulting solid was filtered off and dried to afford carbenes 1a–d.
The new fluorine-containing carbenes 1c,d are characterized as
detailed below.
1-tert-Butyl-3-phenyl-4-p-fluorophenyl-1,2,4-triazolium perchlo-
rate (4c). Yield 85%. Mp 212–214 ◦C (from ethoxyethanol).
Found: C, 54.5; H, 5.0; Cl, 9.1; F 4.8; N, 10.5. Calcd for
C18H19ClFN3O4: C, 54.6; H, 4.8; Cl, 9.0; F, 4.8; N, 10.6%. dH
(200 MHz, DMSO-d6, Me4Si) 1.76 (9H, s, CH3C), 7.74 (9H, m,
Ar), 10.65 (1H, s, CHN).
1-tert-Butyl-3-phenyl-4-p-fluorophenyl-1,2,4-triazol-5-ylidene
(1c). Yield 79%. Mp 180–182 ◦C (from toluene). Found: C, 73.1;
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1-tert-Butyl-3-o-chlorophenyl-4-p-fluorophenyl-1,2,4-triazolium
perchlorate (4d). Yield 79%. Mp 179–181 ◦C (from
ethoxyethanol). Found: C, 50.5; H, 4.2; Cl, 16.5; F 4.5; N,
9.9. Calcd for C18H18Cl2FN3O4: C, 50.3; H, 4.2; Cl, 16.5; F, 4.4;
N, 9.8%. dH (200 MHz, DMSO-d6, Me4Si) 1.72 (9H, s, CH3C),
7.36–7.70 (8H, m, Ar), 10.73 (1H, s, CHN).
128.6, 128.7, 131.4 (Ar), 150.4 (C5), 154.6 (C3), 160.8, 165.8 (C–F,
+
=
=
J 252.4 Hz), 164.2 (C1 O), 171.2 (C3 O). m/z (APCI): (MH )
+
=
409.5, C23H26N3O3 requires 410.0;354.2 (M − Me2C CH2), 296.3
(M+ − COCH2COOEt), 240.2 (3c + H+ or M+ − COCH2COOEt −
=
Me2C CH2).
1-tert-Butyl-3-o-chlorophenyl-4-p-fluorophenyl-1,2,4-triazolium
5-(2-carbethoxyvinyl-1-oxide) (5d)
1-tert-Butyl-3,4-diphenyl-1,2,4-triazolium
5-(2-carbethoxyvinyl-1-oxide) (5a)
Obtained according to the method described above for compound
5a. Yield 75%. Mp 50–51 ◦C (precipitation from ether by
petroleum ether). Found: C 62.3, H 5.3, Cl 8.1, F 4.3, N 9.4.
Calcd for C23H23ClFN3O3: C 62.2, H 5.2, Cl 8.0, F 4.3; N 9.5%.
dH (200 MHz, CDCl3, Me4Si) 1.16 (3H, t, J 7.1 Hz, CH3CH2),
1.87 (9H, s, CH3C, t-Bu), 3.96 (2H, quart, J 7.1 Hz, CH3CH2),
4.84 (1H, s, C5-H–N), 7.00 (2H, dd, J 8.0 Hz, JF 9.1 Hz, C3-
H, ArN), 7.39 (m, 6H, Ar). dC (50.3 MHz, CDCl3, Me4Si) 14.5
(CH3CH2), 28.6 (CH3C, t-Bu), 58.0 (CH3CH2), 66.1 (CH3C, t-
Bu), 90.6 (C2–CO), 115.8, 116.2 (C3, ArN, J 23.3 Hz), 122.9
(C1, Ar-C), 127.1 (C1, ArN, J 12.6 Hz), 128.8 (C2, ArN, J
36.4 Hz), 126.9, 130.0, 132.3, 132.8 (Ar), 134.0 (C–C1), 149.0
Diethyl malonate (0.125 mL, 0.78 mmol) was added to a solution
of triazolylidene 1a (100 mg, 0.361 mmol) in anhydrous toluene
(2 mL) and the reaction mixture was refluxed for 4 h under
conditions such that the evolved ethanol was removed by a stream
of dry nitrogen gas. The toluene was evaporated and the solid
residue 5a (100 mg, 71%) was washed with petroleum ether, filtered
off and recrystallized from n-octane to afford 57.0 mg (40%) of the
pure product 5a. Mp 160–162 ◦C. Found: C 70.7, H 6.6, N 11.0.
Calcd for C23H25N3O3: C 70.6, H 6.4, N 10.7%. dH (200 MHz,
CDCl3, Me4Si) 1.14 (3H, t, J 7.1 Hz, CH3CH2C), 1.80 (s, 9H,
CH3C, t-Bu), 3.93 (2H, quart, J 7.1 Hz, CH3CH2C), 4.81 (1H, s,
C5-H–N), 7.42 (10H, m, Ar). dC (50.3 MHz, CDCl3, Me4Si) 14.7
(CH3CH2C), 28.8 (CH3C, t-Bu), 58.0 (CH3CH2C), 65.8 (CH3C,
t-Bu), 90.5 (C2–CO), 123.6 (C1, Ar-C), 127.2, 128.8 (enhanced
3
3
=
(C5), 153.9 (C3), 160.6, 165.6 (C–F, J 254.5 Hz), 163.7 (C1 O),
+
=
=
170.9 (C3 O). m/z (APCI): 388.1 (M − Me2C CH2), 330.2
(M+ − COCH2COOEt), 274.1 (3d or M+ − COCH2COOEt −
int.), 129.5, 130.8, 131.4 (Ar), 132.1 (C1, ArN), 150.5 (C5), 154.6
+
=
Me2C CH2), C23H23ClFN3O3 requires 443.9 (M ).
+
=
=
(C3), 164.4 (C1 O), 171.1 (C3 O). m/z (APCI): 392.5 (MH ),
C23H26N3O3 requires 392.5. CCDC reference number 607811. For
crystallographic data in CIF or other electronic format see DOI:
10.1039/b712885a
1-tert-Butyl-3,4-diphenyl-1,2,4-triazolium 1,3-dimethylbarbiturate
(6a)
A mixture of 1,3-dimethylbarbituric acid (110 mg, 0.721 mmol)
and triazolylidene 1 (200 mg, 0.72 mmol) in anhydrous toluene
(3 mL) was stirred for 1.5 h. The volume of the reaction mixture
was reduced by 50% and the resulting product was recrystallized
from a mixture of toluene and acetonitrile (10 : 1). The solid
product was filtered off and washed with petroleum ether to give
250 mg (75%) of salt 6a. Mp 172–174 ◦C (from 10 : 1 toluene–
acetonitrile). Found: C 66.7, H 6.5, N 16.2. Calcd for C24H27N5O3:
C 66.5, H 6.3, N 16.2%. dH (200 MHz, CD3CN, Me4Si) 1.77 (9H, s,
CH3C), 2.99 (6H, s, CH3N), 4.05 (4H, s, CHC), 7.48 (10H, m, Ar),
10.47 (1H, s, CHN).
1-tert-Butyl-3-phenyl-4-p-bromophenyl-1,2,4-triazolium
5-(2-carbethoxyvinyl-1-oxide) (5b)
Obtained according to the method described above for compound
5a. Yield 50%. Mp 54–56 ◦C (precipitation from ether by
petroleum ether). Found: C 58.8, H 5.0, Br 17.2; N 9.1. Calcd
for C23H24BrN3O3: C 58.7, H 5.1, Br 17.0; N 8.9%. dH (200 MHz,
CDCl3, Me4Si). 1.15 (3H, t, J 7.1 Hz, CH3CH2), 1.87 (9H, s,
CH3C, t-Bu), 3.94 (2H, quart, J 7.1 Hz, CH3CH2C), 4.82 (1H, s,
C5-H–N), 7.52 (9H, m, Ar). dC (50.3 MHz, CDCl3, Me4Si) 14.6
(CH3CH2), 28.7 (CH3C, t-Bu), 58.1 (CH3CH2), 65.9 (CH3C, t-
Bu), 90.6 (C2–CO), 123.2 (C1, Ar-C), 125.1 (C–Br), 131.5 (C1,
ArN), 127.7, 128.7, 130.9, 132.7, 133.0 (Ar), 150.3 (C5), 154.4
1-tert-Butyl-3,4-diphenyl-1,2,4-triazolium dicyanomethanide (6b)
+
=
=
(C3), 164.0 (C1 O), 171.1 (C3 O). m/z (APCI): 356.9 (M
−
Obtained by the same procedure as that described for salt 6a from
malononitrile (173 mg, 2.70 mmol) and triazolylidene 1a (500 mg,
1.80 mmol) in toluene (2 mL). Yield 384 mg (63%). Mp 147–
149 ◦C (from 1 : 1 toluene–acetonitrile). Found: C 73.7, H 6.3, N
20.3. Calcd for C21H21N5: C 73.4, H 6.2, N 20.4%. dH (200 MHz,
CD3CN, Me4Si) 1.76 (s, 9H, CH3C, t-Bu), 3.50 (s, 1H, CH), 7.4–7.6
(m, 10H, Ar), 9.70 (broad s, 1H, C5-H).
+
+
+
+
=
=
Me2C CH2 + H ), 299.9 (3b + H or M − Me2C CH2 + H −
COCH2COOEt). C23H24BrN3O3 requires 470.4.
1-tert-Butyl-3-phenyl-4-p-fluorophenyl-1,2,4-triazolium
5-(2-carbethoxyvinyl-1-oxide) (5c)
Obtained according to the method described above for compound
5a. Yield 73%. Mp 143–145 ◦C (from octane). Found: C 67.8, H
6.0, F 4.7; N 10.3. Calcd for C23H24FN3O3: C 67.5, H 5.9, F 4.6;
N 10.3%. dH (200 MHz, CDCl3, Me4Si) 1.12 (3H, t, J 7.1 Hz,
CH3CH2), 1.84 (9H, s, CH3C, t-Bu), 3.91 (quart, 2H, J 7.1 Hz,
1-tert-Butyl-3,4-diphenyl-1,2,4-triazolium ethyl acetoacetate (6c)
Obtained by the same procedure as that described for salt 6a
from ethyl acetoacetate (351 mg, 2.70 mmol) and triazolylidene 1a
(500 mg, 1.80 mmol) in toluene (2 mL). Yield 420 mg (67%). Mp
131–133 ◦C (from toluene). Found: C 70.7, H 7.1, N 10.2. Calcd
for C24H29N3O3: C 70.7, H 7.2, N 10.3%. dH (200 MHz, DMSO-
d6, Me4Si) 1.,02 (3H, s, CH3CH2), 1.76 (9H, s, CH3C, t-Bu), 1.89
3
CH3CH2C, Et), 4.78 (1H, s, C5-H–N), 7.11 (2H, dd, J 8.0 Hz,
3JF 9.1 Hz, C3-H, ArN), 7.38 (7H, m, Ar). dC (50.3 MHz, CDCl3,
Me4Si) 14.6 (CH3CH2, Et), 28.7 (CH3C, t-Bu), 58.0 (CH3CH2),
65.8 (CH3C, t-Bu), 90.3 (C5), 116.4, 116.8 (C3, ArN, J 18.0 Hz),
123.3 (C1, Ar-C), 127.5 (C1, ArN), 129.1 (C2, ArN, J 36.4 Hz),
198 | Org. Biomol. Chem., 2008, 6, 195–199
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(3H, s, CH3CO), 3.74 (2H, m, CH2CH3), 4.00 (1H, broad s, CH),
7.2–7.8 (10H, m, Ar), 10.90 (1H, broad s, C5-H).
4 A. J. Arduengo, III, J. C. Calabrese, F. Davidson, H. V. R. Dias, J. R.
Goerlich, R. Krafczyk, W. J. Marshall, M. Tamm and R. Schmutzler,
Helv. Chim. Acta, 1999, 82, 2348–2364.
5 N. I. Korotkikh, G. F. Rayenko, O. P. Shvaika, T. M. Pekhtereva, A. H.
Cowley, J. N. Jones and C. L. B. Macdonald, J. Org. Chem., 2003,
68(14), 5762–5766.
Acknowledgements
6 For reviews, see: (a) W. A. Herrmann and K. Kocher, Angew. Chem.,
Int. Ed. Engl., 1997, 36, 2162–2187; (b) D. Bourissou, O. Guerret, P.
Gabba¨ı and G. Bertrand, Chem. Rev., 2000, 100(1), 39–91; (c) Y. Cheng
and O. Meth-Cohn, Chem. Rev., 2004, 104, 2507–2530.
7 W. M. Jones, M. E. Stowe, S. E. E. Well and E. W. Lester, J. Am. Chem.
Soc., 1968, 90(7), 1849–1859.
8 (a) A. Igau, A. Baceiredo, G. Trinquier and G. Bertrand, Angew. Chem.,
Int. Ed. Engl., 1989, 28, 621–622; (b) S. Goumri-Magnet, T. Kato, H.
Gornitzka, A. Baceiredo and G. Bertrand, J. Am. Chem. Soc., 2000,
122, 4464–4470.
We thank the Ukrainian Academy of Sciences for financial support
and the Robert A. Welch Foundation (F-0003) for financial
support of the X-ray diffraction studies. We also express gratitude
to Dr A. A. Tolmachev (Enamine Ltd, Kiev) for the chromatomass
spectrometric data, Dr Chotiy (IPOCC, Donetsk) for recording
the IR spectra, and Dr M. Findlater for assistance with the X-ray
work.
9 D. Enders, K. Breuer, J. Runsink and J. H. Teles, Liebigs Ann. Chem.,
1996, 2019–2028.
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