Regioselectivity in the thermal rearrangement of unsymmetrical 4-methyl-4H-1,2,4-triazoles to 1-methyl-1H-1,2,4-triazoles

Article abstract of DOI:10.3390/61200969

The rearrangement of 4-methyl-3,5-diaryl-4H-1,2,4-triazoles to the corresponding 1-methyl-3,5-diaryl-1H-1,2,4-triazoles showed regioselectivity comparable to that observed for the alkylation of 3,5-diaryl-1H-1,2,4-triazoles. This lends support to a proposed mechanism for the rearrangement that involves consecutive nucleophilic displacements steps.

Full text of DOI:10.3390/61200969

Molecules 2001, 6, 969-978
molecules
ISSN 1420-3049
http://www.mdpi.org
Regioselectivity in the Thermal Rearrangement of
Unsymmetrical 4-Methyl-4H-1,2,4-triazoles to 1-Methyl-1H-
1,2,4-triazoles
Odd R. Gautun and Per H.J. Carlsen*
Department of Chemistry, Norwegian University of Science and Technology, N-7491 Trondheim,
Norway, Tel. +47 73 59 39 68, Fax +47 73 59 42 56.
* Author to whom correspondence should be addressed; e-mail: per.carlsen@chembio.ntnu.no
Received: 14 March 2000; in revised form 26 October 2001 / Accepted: 26 October 2001 / Published:
30 November 2001
Abstract: The rearrangement of 4-methyl-3,5-diaryl-4H-1,2,4-triazoles to the
corresponding 1-methyl-3,5-diaryl-1H-1,2,4-triazoles showed regioselectivity comparable
to that observed for the alkylation of 3,5-diaryl-1H-1,2,4-triazoles. This lends support to a
proposed mechanism for the rearrangement that involves consecutive nucleophilic
displacements steps.
Keywords: Thermolysis, 1,2,4-triazole, Rearrangement, Regioselective.
Introduction
Previous studies of the thermal rearrangement reactions of 4-alkyl substituted 4H-1,2,4-triazoles to
the corresponding 1-alkyl-1H-1,2,4-triazoles provided evidence supporting the existence of
intermolecular nucleophilic displacement reaction pathways, proceeding through the formation of
dialkyltriazolium triazolate ion-pair intermediates or neutral molecules in a chain reaction [1]. The
nucleophilic nature of these rearrangements therefore suggests that electronic effects may play a role in
their outcome. Alkylation of 3,5-disubstituted-1H-1,2,4-triazoles has also been reported to take place
exclusively at the ring 1-position [2]. On alkylation of unsymmetrical substituted triazoles Uda et al. [3]

Molecules 2000, 6
970
found that the 1-2 selectivity was affected by the nature of the substituents, and that alkylation takes place
preferentially at the nitrogen next to the ring-carbon with the most electron donating group [3]. The
selectivity was assumed to be a result of stereoelectronic control. The nucleophilic nature we have
proposed for the rearrangement of 4-alkyl-3,5-diphenyl-4H-1,2,4-triazoles to the corresponding 1-alkyl-
3,5-diphenyl-1H-1,2,4-triazoles should therefore also exhibit sensitivity to electronic effects. In this paper
we report a study of the regioselectivity for the rearrangement of a series of unsymmetrically substituted
triazoles.
Results and Discussion
A series of triazoles of the general structures 1 and 2 were required for this study. They were readily
prepared by a modification of a procedure using unsymmetric bis(α-alkylaminobenzylidene)-hydrazines,
5, which has been described earlier [4] and is outlined in Scheme 1. Compounds 5 were formed from the
corresponding N,N'-diarylhydrazides, 6, which in turn were obtained by reacting aroyl chlorides 7 with
monohydrazide 8. In the synthesis of compound 2 a 40% aqueous methylamine solution was used. For the
synthesis of triazole 1 saturated NH3 in 2-propanol was used, which was found to be superior to a
procedure described previously by Stollè et al. [5].
Scheme 1
O
O
O
H
N
PCl5
H2N
Et3N / THF
room temp.
Cl
N
H
N
H
+
o-dichloro-
benzene, 120 oC
O
X
X
6
7
8
Cl
N N
N
N
CH3NH2
reflux
N
X
Cl
CH3
X
5
X:
2
a: CH3O
b: CH3
c: Cl
N NH
NH3 in
2-propanol
d: CF3
N
X
1
The synthetic results are summarized in Table 1. The yields are those of the pure products obtained
after recrystallization or sublimation.

Molecules 2000, 6
Table 1. Synthesis of unsymmetrically substituted of 3,5-diaryl-1,2,4-triazoles
971
Substituent
Product 5
Product 1
Product 2
4-X
%
%
%
a: CH3O
b: CH3
c: Cl
49
28
57
75
53
74a
81
72
53
57
79
d: CF3
78
a Yield after sublimation
A series of neat unsymmetrical substituted 4-methyl-3,5-diaryl-4H-1,2,4-triazoles, 2, were next
o
thermolyzed at 330 C for 30 min to investigate the regioselectivity as a function of the electronic
conditions induced by the para-substituents in one of the phenyl rings. These results were also compared
with those obtained for the selectivity upon alkylation of the corresponding unsymmetrical 3,5-diaryl-1H-
1,2,4-triazoles, 1, with methyl iodide. The general reactions are shown in Scheme 2.
Scheme 2
N
N
N
330 oC
30 min
X
CH3
2
a
b
CH3
a
b
H3C
N N
N N
+
N
3
N
4
X
X
NH
N
X:
NaH / DMF
CH3I, rt.
N
a: CH3O
b: CH3
c: Cl
X
1
d: CF3
The thermolyses were carried out with samples of the appropriate triazoles in sealed glass tubes
under nitrogen at ca. 330 oC for 30 minutes. The unsymmetrically substituted triazoles rearrange, as
expected, to yield mixtures of the two possible regioisomers, i.e., the methyl group migrated to the a- and
b- ring positions respectively, as indicated in Scheme 2, thus forming compounds 3 and 4. The product
distributions are compiled in Table 2. The results of alkylation of triazole 1 with methyl iodide in DMF
using sodium hydride as base are also shown.

Molecules 2000, 6
972
Table 2. Distribution of regioisomers 3 and 4 on thermolysis of
triazoles 2 and alkylation of triazoles 1 with methyl iodide.
Thermolysis:
Product distibution
3 : 4
Alkylation:
Product distribution
3 : 4
Substituent
4-X
a: CH3O
b: CH3
c: Cl
51 : 49
52 : 48
42 : 58
42 : 58
54 : 46
54 : 46
40 : 60
36 : 64
d: CF3
The regioisomer ratios were determined by 400 MHz proton NMR spectroscopy of the crude reaction
mixtures by measuring the intensities of characteristic signals. The assignment of the regioisomers was
based on comparison of the NMR spectra to those of authentic samples of triazoles 3 [8], which were
prepared by independent syntheses. Triazoles 4 were not prepared independently. The experiments were
repeated and results were found to be reproducible within 1-2% of the values reported in the Table.
Authentic samples of the methyl substituted triazoles 3 were prepared using a modification of a
method developed by Huisgen and coworkers [6], by reacting 2-methyl-5-phenyl-1H-1,2,3,4-tetrazole
[7] with the appropriate 4-substituted benzonitriles, 4-X-Ph-CN, which in general gave better yields
than were reported before.
The results reported in Table 2 provide support for the proposed mechanism for the rearrangement
reactions. The data from the thermolysis series and the alkylation series, respectively, exhibited the
very same trend with respect to regioselectivity. This supports the feasibility of a nucleophilic type
mechanism in the rearrangements. The ratios were not identical. However, first of all, the reaction
conditions were very different, as were the systems that were reacted. At high temperatures, selectivity
will usually diminish. In the two systems, i.e., triazole 1 and 2, the electronic effects of the substituents
may also be transmitted to a different extent to the reaction sites. Thus, it was shown by X-ray
crystallography, that due to steric interactions with the methyl group, the phenyl ring in 2 are twisted
approx. 44 - 48 degrees out of the triazole ring plane, thereby diminishing the overlap of the π-electron
systems [8]. Triazole 1, on the other hand is nearly planar, with the phenyl ring only 8-9 degrees out of
plane [9]. Therefore, the trends are similar, but the transmission of electronic effects is diminished for
triazoles 2. Electron donating substituents in the aryl group resulted in an increased electron density
and therefore increased nucleophilicity at the a-position (Scheme 2). As a result of this, products 3
were slightly predominant for aryl groups para-substituted with methoxy- and methyl groups
respectively. The opposite effect, as expected, was clearly observed for the electron withdrawing
substituents (Cl-, CF3-).

Molecules 2000, 6
973
Conclusions
The rearrangement of 4-methyl-3,5-diaryl-4H-1,2,4-triazoles to the corresponding 1-methyl-3,5-
diaryl-1H-1,2,4-triazoles exhibited regioselectivity comparable to that for the alkylation of 3,5-diaryl-
1H-1,2,4-triazoles, providing further support to the previously proposed mechanism for the
rearrangement [19], which would involve consecutive nucleophilic displacements steps (Scheme 3).
Scheme 3
N N
CH3
Ph
N N
N
CH3
Ph
N N
N
Ar
Ph
N
N N
N
Ar
Ph
Ar
Re-
orientation
CH3
Ar
H3C
CH3
CH3
N N
N N
N
N N
Ion-pair
N N
N
Ar
Ph
N
Ar
Ph
Ar
Ph
Ar
Ph
N
CH3
CH3
Acknowledgements
The authors wish to thank The Norwegian Research Council, NFR, for financial support.
Experimental
General
1H- and 13C-NMR spectra were recorded on a JEOL JNM-EX400 FT NMR spectrometer, using
CDCl3 as the solvent (unless otherwise indicated) and tetramethylsilane (TMS) as the internal standard.
IR and GC-IR spectra were obtained on a Nicolet 20-SXC FT-IR (GC Carlo Erba 5160, 25 m, CP-Sil-5
CB). Mass spectra were recorded on a AEI MS-902 spectrometer at 70 eV (IP). GC measurements were
performed on a Varian 3700 capillary gas chromatograph.
Preparation of Substituted N,N'- Dibenzoylhydrazines (6a-d)
These compounds were prepared by reacting benzhydrazide 8 with the appropriate aroyl chlorides
7a-d in dry THF and triethylamine at reflux for 3 hr.
2-(4-Methoxybenzoyl)benzhydrazide (6a). Obtained in 74% yield with m.p. 190-91 oC (lit. [10] 186-87
oC). The IR spectrum was in agreement with literature values [11]. 1H-NMR (100 MHz, DMSO-d6): δ

Molecules 2000, 6
974
3.84 (s, 3H), 7.05 (d, 2H, J = 8.8 Hz), 7.50-7.65 (m, 3H), 7.92 (d, 4H, J = 8.3 Hz), 10.33 and 10.41
(2H, NH) ppm; MS [m/z (% rel. int.)]: 270 (6, M+), 252 (6), 135 (100).
o
2-(4-Methylbenzoyl)benzhydrazide (6b). Obtained in 76% yield with m.p. 226-27 C (lit.[12] 220-21
1
oC). H-NMR (100 MHz, DMSO-d6): δ 2.41 (s, 3H), 7.21-7.28 (m, 2H), 7.35-7.60 (m, 3H), 7.9 (m,
4H), 9.42 (2H, NH) ppm. IR (KBr): 3203, 3053, 3003, 1667, 1630, 1536, 1489, 1285, 877, 835, 704
cm-1. MS [m/z (% rel. int.)]: 254 (12, M+), 119 (100), 105 (29).
2-(4-Chlorobenzoyl)benzhydrazide (6c). Obtained in 71% yield with m.p. 230-230.5 oC (lit.[13] 232.5-
233.0 oC). The IR spectrum was in agreement with literature values [10]. 1H-NMR (100 MHz, DMSO-
d6): δ 7.58-7.65 (m, 5H), 7.88-8.00 (m, 4H), 10.50 and 10.58 (2H, NH) ppm. MS [m/z (% rel. int.)]:
276 (5), 275 (2), 274 (11, M+), 139 (43), 105 (100).
2-(4-Trifluoromethylbenzoyl)benzhydrazide (6d). Obtained in 76% yield with m.p. 205.0-206.5 oC. 1H-
NMR (100 MHz, DMSO-d6): δ 7.40-7.60 (m, 3H), 7.89-8.05 (m, 4H), 8.05-8.20 (m, 2H), 10.65 (2H,
NH) ppm. IR (KBr): 3251, 3085, 1676, 1631, 1582, 1521, 1486, 1331, 1287, 1173, 1121, 1070, 860,
772 cm-1. MS [m/z (% rel. int.)]: 308 (5, M+), 173 (10), 105 (100). Calculated for C15H11F3N2O2: M+
308.0773. Found: 308.0768.
General Procedure for the Synthesis of Substituted Di(α-chlorobenzylidene)hydrazines (5)
40 mmol of the appropriate dibenzoylhydrazine were added portionwise over 1.5 hr to a stirred
mixture of 80 mmol of PCl5 in 30 mL of 1,2-dichlorobenzene. Evaporation of the solvent gave the
desired product, which was recrystallized.
4-Methoxy-N-(chlorophenylmethylene)benzencarbohydrazonoyl chloride (5a). Obtained in 49% yield
with m.p. 118-20 oC. 1H-NMR (100 MHz): δ 3.88 (s, 3H), 6.96 (d, 2H, J = 8.8 Hz), 7.40-7.54 (m, 3H),
8.03-8.18 (m, 4H) ppm. IR (KBr): 1600, 1590, 1580, 1510, 1486, 1462, 1446, 1420, 1306, 1264, 1220,
1176, 1120, 1029, 1010, 1000, 920, 837, 792, 770 cm-1. MS [m/z (% rel. int.)]: 306 (73, M+).
Calculated for C15H12Cl2N2O: M+ 306.0327. Found: 306.0331
4-Methyl-N-(chlorophenylmethylene)benzencarbohydrazonoyl chloride (5b). Obtained in 28% yield
with m.p. 85-86 oC. 1H-NMR (100 MHz): δ 2.41 (s, 3H), 7.26 (d, 2H, J = 7.8 Hz), 7.40-7.54 (m, 3H),
7.98-8.17 (m, 4H) ppm. IR (KBr): 1601, 1575, 1563, 1504, 1488, 1445, 1227, 1212, 1177, 915, 822,
791, 764 cm-1. MS [m/z (% rel. int.)]: 290 (68, M+). Calculated for C15H12Cl2N2: M+ 290.0377. Found:
290.0379
4-Chloro-N-(chlorophenylmethylene)benzencarbohydrazonoyl chloride (5c). This compound,
o
1
previously reported by Cronin et al. [18], was obtained in 57% yield with m.p. 87-88 C. H-NMR

Molecules 2000, 6
975
(100 MHz): δ 7.39-7.54(m, 5H), 8.03-8.20 (m, 4H) ppm. IR (KBr): 1605, 1573, 1490, 1450, 1402,
1228, 1174, 1096, 1019, 929, 836, 766, 733 cm-1.
4-(Trifluoromethyl)-N-(chlorophenylmethylene)benzencarbohydrazonoyl chloride (5d). Obtained in
o
1
75% yield with m.p. 77-78 C. H-NMR (100 MHz): δ 7.37-7.58 (m, 3H), 7.73 (d, 2H, J = 8.3 Hz),
8.08-8.28 (m, 4H) ppm. IR (KBr): 1600, 1576, 1510, 1488, 1447, 1409, 1330, 1218, 1187, 1161, 1113,
1071, 1015, 922, 768 cm-1. MS [m/z (% rel. int.)]: 344 (40, M+). Calculated for C15H9Cl2N2F3: M+
344.0095. Found: 344.0092.
Synthesis of Unsymmetric 4-Methyl-3,5-diaryl-4H-1,2,4-triazoles (2)
These compounds were prepared from the corresponding di(α-chlorobenzylidene)hydrazines, 5, as
described previously in the literature [14] .
3-(4-Methoxyphenyl)-4-methyl-5-phenyl-4H-1,2,4-triazole (2a). The yield of the pure product was 72%
with m.p. 211-13 oC (recryst. from toluene). 1H-NMR (400 MHz): δ 3.69 (s, 3H), 3.88 (s, 3H), 7.05 (d,
13
2H, J = 8.8 Hz), 7.50-7.55 (m, 3H), 7.67 (d, 2H, J = 8.8 Hz), 7.70-7.75 (m, 2H) ppm. C-NMR (100
MHz): δ 33.2, 55.5, 114.3, 119.6, 127.4, 128.8, 129.4, 129.9, 130.3, 155.8, 160.9 ppm. IR (KBr): 3006,
2965, 2937, 1615, 1540, 1483, 1439, 1296, 1255, 1182, 1040, 1029, 834, 772, 741, 701 cm-1. MS [m/z
(% rel. int.)]: 266(18), 265 (100, M+), 264 (70), 148 (10), 134 (13), 118 (35). Calculated for
C16H15N3O: M+ 265.1215. Found: 265.1213. Analysis: Calc. for C16H15N3O: C, 72.43; H, 5.70; N,
15.84. Found: C, 72.59; H, 5.91; N, 15.78.
3-(4-Methylphenyl)-4-methyl-5-phenyl-4H-1,2,4-triazole (2b). The yield of the pure product was 53%
o
1
with m.p. 236.5-237.5 C (recryst. from ethanol). H-NMR (400 MHz): δ 2.44 (s, 3H), 3.70 (s, 3H),
13
7.35 (d, 2H, J = 8.5 Hz), 7.38-7.56 (m, 3H), 7.62 (d, 2H, J = 8.3 Hz), 7.72-7.74 (m, 2H) ppm. C-
NMR (100 MHz): δ 21.4, 33.2, 124.3, 127.3, 128.1, 128.9, 129.6, 130.0, 135.8, 140.2, 155.9 ppm; IR
(KBr): 3051, 3037, 3020, 1686, 1619, 1578, 1526, 1485, 1449, 1075, 832, 771, 736, 710, 700 cm-1.
MS [m/z (% rel. int.)]: 250 (17), 249 (100, M+), 248 (93), 132 (18), 118 (42). Calculated for C16H15N3:
M+ 249.1266. Found: 249.1268. Analysis: Calc. for C16H15N3: C, 77.08; H, 6.06; N, 16.85. Found: C,
77.25; H, 6.21; N, 17.01.
3-(4-Chlorophenyl)-4-methyl-5-phenyl-4H-1,2,4-triazole (2c). The yield of the pure product was 57%
with m.p. 276-77.5 oC (recryst. from toluene). 1H-NMR (400 MHz): δ 3.72 (s, 3H), 7.51-7.56 (m, 5H),
7.68-7.74 (m, 4H) ppm. 13C-NMR (100 MHz): δ 33.2, 125.7, 127.1, 128.9, 129.2, 130.1, 136.4, 154.9,
156.2 ppm. IR (KBr): 3067, 3051, 3025, 2970, 1605, 1480, 1456, 1437, 1402, 1098, 1074, 1014, 840,
827, 770 736, 717, 701 cm-1. MS [m/z (% rel. int.)]: 272 (5), 271 (32), 270 (42), 269 (100, M+), 268
(86), 267 (5), 152 (19), 118 (23). Calculated for C15H12ClN3: 269.0720. Found: 269.0717. Analysis:
Calc. for C15H12N3Cl: C, 66.79; H, 4.48; N, 15.58; Cl, 13.14. Found: C, 66.65; H, 4.28; N, 15.40.

Molecules 2000, 6
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3-(4-Trifluoromethylhenyl)-4-methyl-5-phenyl-4H-1,2,4-triazole (2d). The yield of the pure product
was 79% with m.p. 293-94 oC (recryst. from toluene). 1H-NMR (400 MHz): δ 3.75 (s, 3H), 7.52-7.58
(m, 3H), 7.72-7.76 (m, 2H), 7.80, 7.83, 7.89, 7.91 (4H, AA'BB') ppm. IR (KBr): 3074, 3055, 3027,
1481, 1408, 1334, 1319, 1170, 1157, 1116, 1089, 1073, 1061, 1022, 1014, 861, 842, 774, 732, 705
cm-1. MS [m/z (% rel. int.)]: 304 (16), 303 (94, M+), 302 (100), 186 (27), 145 (11), 118 (18), 104 (19).
Calculated for C16H12F3N2: 303.0983. Found: 303.0979. Analysis: Calc. for C16H12N3F3: C, 63.36; H,
3.99; N, 13.85; F, 18.79. Found: C, 63.48; H, 4.18; N, 13.67.
General Procedure for the Synthesis of 5-Aryl-3-phenyl-1H-1,2,4-triazoles (1a-d)
The appropriate substituted di(α-chlorobenzylidene)hydrazine, 5, (2 mmol) was dissolved in
2-propanol (100 mL) saturated with NH3, and the resulting mixture was stirred at room temperature
overnight and finally refluxed for 30 h. Evaporation of the solvent under reduced pressure gave the
crude product, which was further purified by crystallization or sublimation.
3-(4-Methoxyphenyl)-5-phenyl-1H-1,2,4-triazole (1a). Yield = 53% (after crystallization from toluene).
o
1
M.p. 169.5-72.0 C. H-NMR (100 MHz, DMSO-d6): δ 3.84 (s, 3H), 7.10 (d, 2H, J = 8.8 Hz), 7.49-
13
7.53 (m, 3H), 8.00-8.20 (m, 4H) ppm. C-NMR (25 MHz, DMSO-d6): δ 55.2, 114.2, 121.4, 125.9,
127.5, 128.7, 129.3, 129.7, 157.5, 160.3 ppm. IR (KBr): 3500-2500 (broad), 1614, 1508, 1471, 1441,
1408, 1394, 1310, 1304, 1290, 1278, 1260, 1180, 1142, 1034, 982, 836, 749, 722 cm-1. Analysis: Calc.
for C15H13N3O: C, 71.70; H, 5.21; N, 16.72; O, 6.37. Found: C, 71.88; H, 5.41; N, 16.67.
o
3-(4-Methylphenyl)-5-phenyl-1H-1,2,4-triazole (1b). Yield = 74% after sublimation. M.p. 178-80 C.
The spectroscopic properties were all in agreement with those reported in the literature [15].
3-(4-Chlorophenyl)-5-phenyl-1H-1,2,4-triazole (1c). Yield = 81% yield after crystallization from
toluene. M.p. 241-42 oC. The spectroscopic properties were all in agreement with those reported in the
literature [16].
3-(4-Trifluorophenyl)-5-phenyl-1H-1,2,4-triazole (1d). Yield = 74% yield after crystallization from
toluene. M.p. 224-26 oC. All the spectroscopic properties were in agreement with those reported in the
literature [17].
General Procedure for the Synthesis of 1-Methyl-3-aryl-5-phenyl-1H-1,2,4-triazoles (3a-d).
The method described by Huisgen et al. was applied [6]. Thus, a solution of 2-methyl-5-phenyl-
2H-1,2,3,4-tetrazole [7], (2.5 mmol) in the appropriate substituted benzonitrile, X-Ph-CN, (2 mL) was
refluxed for 3-5 h under nitrogen. The nitrile was then removed under reduced pressure by Kugelrohr
distillation, and the crude product was recrystallized.

Molecules 2000, 6
977
1-Methyl-5-(4-methoxyphenyl)-3-phenyl-1H-1,2,4-triazole (3a). Yield = 39% of a product of 98%
purity (GC) and with m.p. 82.5-85.5 oC. 1H-NMR (400 MHz): δ 3.88 (s, 3H), 4.00 (s, 3H), 7.04 (d, 2H,
J = 8.8 Hz), 7.37-7.46 (m, 3H), 7.68 (d, 2H, J = 8.8 Hz), 8.14 (d, 2H, J = 6.8 Hz) ppm. 13C-NMR (100
MHz, CDCl3): δ 36.9, 55.3, 114.4, 120.3, 126.2, 128.5, 129.0, 130.1, 131.1, 155.4, 160.9 ppm. IR
(KBr): 3040, 3023, 3009, 1611, 1545, 1486, 1473, 1444, 1396, 1355, 1298, 1256, 1186, 1172, 1131,
1033, 1023, 835, 790, 747, 724, 702 cm-1. MS [m/z (% rel. int.)]: 266 (19), 265 (100, M+), 264 (9), 132
(60), 131 (19), 105 (18), 104 (25). Calculated for C16H15N3O: 265.1215. Found: 265.1213. Analysis:
Calc. for C16H15N3O: C, 72.43; H, 5.70; N, 15.84. Found: C, 72.28; H, 5.77; N, 15.65.
1-Methyl-5-(4-methylphenyl)-3-phenyl-1H-1,2,4-triazole (3b). Yield = 55% of a product of 96% purity
o
1
(GC) and with m.p. 78-81 C. H-NMR (400 MHz): δ 2.44 (s, 3H), 4.01 (s, 3H), 7.32 (d, 2H, J = 7.3
Hz), 7.37-7.46 (m, 3H), 7.62 (d, 2H, J = 8.3), 8.14 (d, 2H, J = 7.3) ppm. 13C-NMR (100 MHz, DMSO-
d6): δ 21.4, 36.9, 125.1, 126.3, 128.5, 128.6, 129.0, 129.4, 131.1, 140.2, 155.7, 161.0 ppm. IR (KBr):
3072, 3024, 2946, 1610, 1482, 1472, 1447, 1353, 1138, 1070, 1014, 823, 749, 735, 713 cm-1. MS [m/z
(% rel. int.)]: 250(19), 249(100, M+), 248(8), 132(62), 131(16), 104(19). Calculated for C16H15N3:
249.1266. Found: 249.1268. Analysis: Calc. for C16H15N3: C, 77.08; H, 6.06; N, 16.85. Found: C,
77.20; H, 6.19; N, 16.78.
1-Methyl-5-(4-chlorophenyl)-3-phenyl-1H-1,2,4-triazole (3c). Yield = 83% of a product with >99 %
o
purity (GC) and m.p. 122.0-23.5 C. All spectroscopic properties were in agreement with those
reported in the literature [6].
1-Methyl-5-(4-trifluoromethylphenyl)-3-phenyl-1H-1,2,4-triazole (3d). Yield = 58% of a product of
o
o
1
99% purity (GC) and m.p. 131.5-33.5 C (lit.[17] 115-17 C). H-NMR (400 MHz): δ 4.05 (s, 3H),
13
7.26-7.45 (m, 3H), 7.79, 7.81, 7.88, 7.90 (4H, -AA'BB'), 8.14 (d, 2H, J = 7.6) ppm. C-NMR (100
MHz, CDCl3): δ 37.1, 123.7, (q, JCF = 270 Hz), 125.7, 125.9, 126.3, 128.6, 129.1, 129.3, 130.7, 131.5,
132.6, 154.2, 161.4 ppm. IR (KBr): 3074, 3058, 2955, 2927, 1623, 1472, 1447, 1437, 1331, 1314,
1165, 1122, 1078, 1057, 1023, 1014, 849, 789, 757, 748, 732, 704 cm-1. MS [m/z (% rel. int.)]: 304
(19), 303 (100, M+), 132 (69), 131 (23), 104 (28). Calculated for C16H12F3N3: 303.0983. Found:
303.0981; Analysis: Calc. for C16H12F3N3: C, 63.36; H, 3.99; N, 13.85; F, 18.79. Found: C, 63.61; H,
7.21; N, 13.51.
Thermolysis of 4-methyl-3-aryl-5-phenyl-4H-1,2,4-triazoles (1).
The triazole (30 mg) was placed under nitrogen in a sealed glass tube and then heated in an oven at
o
323-35 C for 30 min. The crude product contained the compounds 3 and 4. The compositions of the
reaction mixtures were determined by 400 MHz NMR spectroscopy by comparison with those of the
authentic samples. The regioisomers could not be separated by either GC or TLC.

Molecules 2000, 6
978
Methylation of 3-aryl-5-phenyl-1H-1,2,4-triazoles (1).
An appropriate 3-aryl-5-phenyl-1H-1,2,4-triazole, 1 (30 mmol), was dissolved in dry DMF (1 mL),
0.3 g NaH were added and the mixture was stirred under nitrogen for 1 h. Then CH3I (0.30 mmol) was
added and the reaction mixture stirred for 48 h. Water was added and the mixture extracted with
CH2Cl2, yielding the crude product which was analyzed by NMR as described above.
References
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Sample Availability: Available from the authors.
© 2001 by MDPI (http://www.mdpi.org). Reproduction is permitted for noncommercial purposes.