Triazoloazine-Diazomethylazine Valence Isomerization. [1,2,3]Triazolo[1,5-a]pyridines and 2-Diazomethylpyridines

Article abstract of DOI:10.1021/acs.joc.5b02639

2-Diazomethylpyridines 1D and 6D, the valence isomers of [1,2,3]triazolo[1,5-a]pyridines 1T and 6T, have been observed directly at ～2080 cm^-1 by a combination of mild flash vacuum pyrolysis (FVP) at 200-600°C with low temperature IR spectroscopy. Calculations confirm a ca. 17 kcal/mol barrier for the formation of 2-diazomethylpyridine 1D from [1,2,3]triazolo[1,5-a]pyridine 1T, the diazo compound lying ca. 5 kcal/mol above the triazole. In the higher temperature range (400-600°C) 2-diazomethylpyridine 1D eliminates N₂ with formation of 2-pyridylcarbene 2 and rearrangement to 1-cyanocyclopentadiene 4. 2-Diazomethylpyridine 1D undergoes 1,3-dipolar cycloaddition with tetracyanoethylene (TCNE) at 20-90°C to yield 3-(2-pyridyl)cyclopropanetetracarbonitrile 11 and 3-(tricyanovinyl)-[1,2,3]triazolo[1,5-a]pyridine 13T via unobserved pyrazolines 10 and 12. FVP of triazole 13T affords an IR absorption at 2080 cm^-1 ascribed to the corresponding diazo compound 13D.

Full text of DOI:10.1021/acs.joc.5b02639

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Article
Triazoloazine – Diazomethylazine Valence Isomerization.
[1,2,3]Triazolo[1,5-a]pyridines and 2-Diazomethylpyridines
Nigel Aylward, Hans-Wilhelm Winter, Ulrich Eckhardt, and Curt Wentrup
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.5b02639 • Publication Date (Web): 16 Dec 2015
Downloaded from http://pubs.acs.org on December 22, 2015
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Triazoloazine – Diazomethylazine Valence Isomerization.
[1,2,3]Triazolo[1,5-a]pyridines and 2-Diazomethylpyridines
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†
‡,§
‡
,†
Nigel Aylward, Hans-Wilhelm Winter, Ulrich Eckhardt and Curt Wentrup∗
†
School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld
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072, Australia. Email: wentrup@uq.edu.au
‡
Fachbereich Chemie der Philipps-Universität Marburg, D-35037 Marburg, Germany.
Present address: 57 Brewster Rd, RD1 Tuakau 2696, New Zealand.
§
H
N
N
N
N
T
N
N
1D
TCNE
1
CN
+
CN
CN
N
N
N
CN
N
NC CN
NC
11
13T
Abstract. 2-Diazomethylpyridines 1D and 6D, the valence isomers of [1,2,3]triazolo[1,5-
-1
a]pyridines 1T and 6T, have been observed directly at ~2080 cm by a combination of mild
o
flash vacuum pyrolysis (FVP) at 200-600 C with low temperature IR spectroscopy. Calculations
confirm a ca. 17 kcal/mol barrier for the formation of 2-diazomethylpyridine 1D from
[
1,2,3]triazolo[1,5-a]pyridine 1T, the diazo compound lying ca. 5 kcal/mol above the triazole. In
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the higher temperature range (400-600 C) 2-diazomethylpyridine 1D eliminates N with
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formation of 2-pyridylcarbene 2 and rearrangement to 1-cyanocyclopentadiene 4. 2-
Diazomethylpyridine 1D undergoes 1,3-dipolar cycloaddition with tetracyanoethylene (TCNE)
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at 20-90 C to yield 3-(2-pyridyl)cyclopropanetetracarbonitrile 11 and 3-(tricyanovinyl)-
[1,2,3]triazolo[1,5-a]pyridine 13T via unobserved pyrazolines 10 and 12. FVP of triazole 13T
-1
affords an IR absorption at 2080 cm ascribed to the corresponding diazo compound 13D.
Introduction
The tetrazole – azide valence tautomerization, e.g. in tetrazoloazines (Scheme 1) is well-
1
,2,3
known,
and it is usually possible to observe both the tetrazole and the azide valence isomer.
The tetrazoles are usually of lower enthalpy, but because the enthalpy differences are small,
positive entropies of azide formation make the azide forms accessible or even dominating, at
3
,4
mildly increased temperatures.
Scheme 1. Tetrazole – Azide Valence Isomerizationa
aIn this paper Z and E are used to denote s-Z and s-E conformers.
The corresponding triazoloazine – diazomethylazine valence tautomerization
(
Scheme 2) is much less well known. Calculations indicate an enthalpy difference of 6-10
kcal/mol between the triazole and the diazo compound, with the triazole at the lowest
enthalpy, and an activation barrier around 20 kcal/mol for the ring opening of the triazoles
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(
see details below). This makes it difficult to observe the diazo valence isomers directly
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in solution, and only a few cases, in the [1,2,3]triazolo[1,5-a]pyrimidine series (ꢀG =18±2
kcal/mol by H NMR spectroscopy), have been reported.7
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Scheme 2. Triazole – Diazomethane Valence Isomerization
However, once again, positive entropies make the ring-opened isomers relatively
more stable at elevated temperatures, and several α-diazomethylazines have in fact been
observed spectroscopically by low-temperature isolation of the products of flash vacuum
pyrolysis (FVP) of triazoles at temperatures below or near the temperatures needed for
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9
decomposition by N loss. Thus, 9-dizomethylphenanthridine and 2-diazomethylpyrazine
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were observed by IR spectroscopy, albeit as the minor constituents in the presence of
unchanged triazole. Photolysis may also generate diazo isomers from triazoles, but this of
course does not say anything about the thermochemistry, and the Z/E ratios obtained for
the diazo isomers on photolysis are not necessarily the thermodynamic ratios. Calculations
indicate that the Z-isomers of 2-azidoazines and 2-diazomethylazines are of lower energy
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than the E-isomers (Schemes 1 and 2). IR absorptions of photochemically generated 2-
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0
2-diazomethylpyrazine,9
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diazomethylpyridine,
2-diazomethylquinoline,
1-
diazomethylisoquinoline,11 2-diazomethylquinoxaline, and 4-diazomethylquinazoline13
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have been reported, but even under these conditions, it can sometimes be difficult to
observe appreciable amounts, and the triazoles may photolyze very sluggishly.8,11
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Results and Discussion
1. Direct observation of 2-Diazomethylpyridine
FVP was carried out in quartz tubes consisting of a sublimation zone and a pyrolysis zone,
each 10 cm x 0.8 cm I.D., housed in a vacuum chamber in an apparatus allowing the
deposition of thermolysis products at 77 K on a KBr target attached to a liquid nitrogen
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cryostat. The distance from the exit of the pyrolysis tube to the cold KBr target was 2.5
cm. Vacuum was maintained at ~10-4 hPa with a turbomolecular pump. Using this
apparatus, [1,2,3]triazolo[1,5-a]pyridine 1T (Scheme 3) did not undergo any reaction at
o
temperatures below 200 C. At higher temperatures 2-diazomethylpyridine 1D was formed,
-1
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with a maximal intensity of its 2080 cm absorption at 400 C (Figure 1a).
On subsequent warming of the cold pyrolyzate, the diazo absorption disappeared
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rapidily above -40 C (Figure 1b). The end spectrum was identical with that of the starting
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material 1T. The observation of a single, sharp absorption at 2080 cm suggests that the Z
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form, 1D-Z, is being observed because this is calculated to be of lower energy (cf. Figure 2),
although it is possible that the absorptions of the two isomers cannot be resolved in the 77
K IR spectrum. The same thermodynamic considerations do not apply under photolysis
conditions, where both 1D-Z and 1D-E may be formed, as indicated by a double absorption
at 2075 and 2095 cm-1 in the Ar-matrix IR spectrum. Similarly, in the case of 2-
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-1
diazomethylpyrazine, a double absorption at 2092 and 2076 cm was observed for the
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photochemically generated compound in Ar matrix, but we observe a single absorption at
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080 cm at 77 K under the FVP conditions described here.
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Scheme 3. [1,2,3]Triazolo[1,5-a]pyridine
Isomerization
–
2-Diazomethylpyridine Valence
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o
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Figure 1. (a) IR spectrum (-196 C) of the product of FVP of 1T at 400 C. The product
consists of a mixture of triazolopyridine 1T and 2-diazomethylpyridine 1D, with the diazo
-1
-1
peak (D) at 2080 cm . A very weak absorption at 2215 cm (C) is ascribed to
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cyanocyclopentadiene 4. Inset: peaks D and C resulting from FVP at 620 C. (b) Repetitive
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scanning of the 2080 cm peak during warm-up from -193 C towards room temperature.
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The heating rate is 10 C per minute.
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The intensity of the diazo absorption of 1D increased further at an FVP temperature
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of 500 C, but now cyanocyclopentadiene 4 (2215 cm ) was formed as well owing to the
elimination of N and rearrangement of the so-formed 2-pyridylcarbene 2 to phenylnitrene
and 4 (Scheme 4) as shown in Figures S1a-b (Supplementary Material). The mechanism
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of this reaction was described recently. At 620 C the diazo absorption of 1D at 2280 cm
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in Figure S1).
Scheme 4. Formation of 2-Pyridylcarbene 2, Phenylnitrene 3, and
Cyanocyclopentadiene 4a
aWiggly bonds denote undefined stereochemistry.
Diazo compound 1D is also formed on FVP of 2-(5-tetrazolyl)pyridine 5 (Scheme
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6
-1
5
). 1D either cyclizes to 1T or decomposes to 2, but the diazo absorption at 2080 cm can
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Scheme 5. Formation of 1D and 1T by FVP of Tetrazolylpyridine 5
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Similar pyrolyses of substituted [1,2,3]triazolo[1,5-a]pyridines 6T also resulted in
-1
the formation of absorptions at ~2080 cm ascribed to the diazo isomers 6D (Scheme 6),
although the absorptions were weak to very weak in all cases. The best result were
obtained for the 3-m-nitrophenyl, 3-p-nitrophenyl, 3-p-cyanophenyl and 3-p-
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methoxyphenyl derivatives 6Db-e in the 200-400 C range (see Figure S2, Supplementary
Material, for the m-nitrophenyl derivative 6Dc). At higher temperatures substituted
carbazoles 7 were formed due to the well-established carbene-nitrene rearrangement of
the phenyl(2-pyridyl)carbenes.17
Scheme 6. Substituted Triazolopyridines 6T Giving Rise to Weak Absorptions at
-
1
o a
~2080 cm Ascribed to the Diazo Valence Isomers 6D on FVP at 400 C
aa: R = H; b: R = p-MeO-C
; c: R = m-NO
; e: R = p-NC-C
H . At
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H
4
2
6
-C H
4 2 6
; d: R = p-O N-C H
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higher temperatures carbazoles 7 are formed via carbene-nitrene rarrangement.17
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. Thermochemistry
We calculated the relative enthalpies and free energies for 1T, 1DZ, and 1DE and the
transition states connecting them at the B3LYP/6-31G* level of theory (Table 1), which has
proved to be adequate for calculations on these and related systems.5,6 The free energies
are plotted in Figure 2.
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Figure 2. Free energy diagram (relative values of ꢀG in kcal/mol) for
triazolo/diazomethylpyridine 1T and 1D and their dissociation to 2-pyridylcarbene 2 and
N and the transition states connecting them at the B3LYP/6-31G* level. The corresponding
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values of ꢀH are 0, 17.5, 6.7, 16, 7.3, 48 and 47 kcal/mol.
The calculated entropy change ꢀS for the ring opening 1T ꢀ 1D-Z is 7.02 e.u. at this
level. Therefore, at room temperature (298 K) the TꢀS term contributes to a lowering of ꢀG
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corresponding equilibrium constant at room temperature, K298 is ~10 . If thermodynamic
equilibrium was attained – which is usually not guaranteed under FVP conditions – then
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the equilibrium constants calculated from the van’t Hoff equation at 400 and 500 C are
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K
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the diazo compound 1D at room temperature, but thanks to the strength of the diazo
absorption in the IR, it is very feasible at elevated temperatures as long as the diazo
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compound does not decompose. Since it does decompose to form 4 above 400 C, the
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optimal temperature for observing 1D is close to 400 C.
The thermal decomposition of 1T was also monitored in diphenyl ether, where it
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followed first order kinetics as measured by the volume of N
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evolution in the
o
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-6 -1
temperature range 180-220 C; e.g. at 180.5 C: k453.5 = 3.62 × 10 s . The Arrhenius
parameters were evaluated as log Aobs = 16; Ea(obs) = 43.5±1 kcal/mol, from which we obtain
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the experimental enthalpy of activation ꢀH* = 42±1 kcal/mol, ꢀS* = 12 cal·K mol and ꢀG*
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=
37±1 kcal/mol at 180 C. The consistency of the experimental with the calculated data
can be probed by considering the free energy of activation for 2-pyridylcarbene formation,
which will be dominated by the step 1D-E ꢀ 2 = 38 kcal/mol at 298 K according to Figure
o
2. At 453 K (180 C) this value becomes 36 kcal/mol in good agreement with the
experimental value of 37 ± 1 kcal/mol, seeing that the calculations (Figure 2) refer to the
gas phase, and the measurements to diphenyl ether solution.
5-(2-Pyridyl)tetrazole 5 also underwent first-order decomposition with N
2
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evolution in diphenyl ether solution at 180-220 C (log A = 15.2; Ea(obs) = 41.5±1 kcal/mol, or
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ꢀ
H* = 40.5±1 kcal/mol). This value is typical for tetrazoles, which are reported to
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other work,15 5 eliminates one molecule of N
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Figure 2.
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3. Reactions of the Diazo Valence Isomer in Solution
Although the diazo compound 1D is a reactive intermediate, which can only be observed
directly under special conditions due to its low equilibrium concentration, it should
nevertheless be generated rapidly in thermal equilibrium with 1T, and this allows its
trapping with dipolarophiles. We have reported the trapping with fumaronitrile, resulting
in the formation of the 1-pyrazoline 8.18 However, 1-pyrazolines formed from diazo
compound decompose very easily, often at room temperature, with the formation of
2
1
o
cyclopropanes. Therefore, under our reaction conditions (130-150 C in diphenyl ether) 8
undergoes fast elimination of N
2
to yield the cyclopropylpyridine 9 (Scheme 7).19
Scheme 7. Reaction of 1T/1D with Fumaronitrile (F)
The rate of N
2
evolution from 1T/1D in the presence of a large excess excess of
fumaronitrile (F) was measured previously and found to be ca. 100 times faster than the
o
-4 -1
value given above in the absence of fumaronitrile, e.g. at 150 C kobs = 3.61 x 10 s ; Ea(obs)
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~
17±2, or ꢀH* ~16±2 kcal/mol. Here, the steady-state approximation, assuming k
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is not
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rate determining, yielded kobs ~ k
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k
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[F]/(k-1+ k
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[F]) ([F] = 0.167 mol/L). Assuming the
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activation enthalpy for reaction of 1D with fumaronitrile is 8 kcal/mol and using ꢀH*obs
ꢀH* – ꢀH*-1 + ꢀH* with the calculated enthalpy values from Figure 2, we get ꢀH* = 17.5 –
0.8 + 8 = 15 kcal/mol in good agreement with the experimental value of 16 ± 2 kcal/mol.
If 1T
1D represents a fast pre-equilibrium, a better dipolarophile will result in a
larger k , faster displacement of the equilibrium, and faster consumption of 1T. From
=
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kinetic data for phenyl and diphenyldiazomethane21,22 we can estimate an enthalpy of
activation for cycloaddition of 1D to tetracyanoethylene (TCNE) as ~7.5 kcal/mol. In fact,
o
we have now determined that the reaction of 1T with TCNE proceeds at 50 C in toluene
solution to yield two products, 11 and 13T as well as a red, insoluble and unsublimable
o
solid. The reaction even took place slowly at 20 C in the course of 3 weeks with formation
of the same two products and the red polymer. The reaction is interpreted in terms of
initial formation of the 1-pyrazoline 10, which could not be isolated (Scheme 8). Even at
room temperature it decomposes with evolution of both N and HCN. The product 11, the
2
expected tetracyanocyclopropane derivative, precipitated together with the red solid and
was isolated by sublimation. The soluble compound 13T, which was the major product,
was isolated by chromatography. The amount of polymer increased as a function of
thermolysis time. Furthermore, separate thermolysis of the isolated compound 11 in
o
acetone solution at 50 C also afforded the red solid. Thus, the low isolated yield of 11
(
11%) is undoubtedly due to its instability under the reaction conditions.
The reactions are interpreted in Scheme 8 in terms of two competing reactions of
the 1-pyrazoline 10, (i) loss of N
2. The latter decomposes further by ring opening to the 2-diazomethylpyridine 13D,
which then ring closes to 13T. Compound 11 decomposes to the red solid, which features
2
to form 11, and (ii) loss of HCN to form the 3H-pyrazole
1
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nitrile absorptions at 2200 and 2230 cm ; NMR and mass spectra could not be obtained.
The red solid was not examined in detail because of its insolubility, but it is known that
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tetracyanocyclopropanes undergo both acid- and base-catalyzed ring opening, as well as
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nucleophile-induced ring opening and polymerization, and recent calculations indicate
that nucleophiles attack the “σ-hole” in the weakened bond between the two C(CN)
moieties.26
2
Scheme 8. Reaction of 1T/1D with Tetracyanoethylene
In contrast to 11, the major product 13T was stable under the thermolysis
o
conditions and remained stable after heating at 95 C in acetone solution in a closed system
for 8 days. However, since 13T is a [1,2,3]triazolo[1,5-a]pyridine, it should be capable of
ring-opening to diazo compound 13D. We subjected 13T to FVP under the conditions
o
described for 1T above. No change took place up to a temperature of 330 C, but after FVP
o
at 430 C, the low temperature IR spectrum featured a weak-to-medium absorption at 2080
-1
cm , which we ascribe to the 2-diazomethylpyridine 13D. This absorption disappeared on
o
warming of the pyrolyzate above -70 C, and the resulting IR spectrum was identical with
that of 13T (Scheme 9 and Figure S3).
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Scheme 9. 3-(Tricyanovinyl)-[1,2,3]triazolo[1,5a]pyridine –
(2-Pyridyl)(tricyanovinyl)diazomethane Valence Isomerization
10
11
12
13
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We examined the energetics of the interconversion of triazole 14T, diazo compound
1
4D, and 3H-pyrazole 14P (Scheme 10) at the B3LYP/6-31G* computational level.
Scheme 10. Vinyltriazole – Vinyldiazo – 3H-Pyrazole Interconversion
The results for 14T and 14D are very similar to those for 1T and 1D at this level: the
relative free energies
2, and 3 kcal/mol, respectively. For the tricyano-substituted compounds 14Tb, TS14Tb,
14Db, TS14Pb, and 14Pb (R = CN) the corresponding values of G are 0, 14, 10, 37, and 20
ꢀG for 14Ta, TS14Ta, 14Da, TS14Pa, and 14Pa (R = H) are 0, 17, 6,
3
ꢀ
kcal/mol. Thus, the CN groups make the triazole 14Tb (= 13T) ca. 20 kcal/mol more stable
than the pyrazole 14Pb (= 12) in agreement with the actual isolation of 13T. Activation
free energies for cyclization of other vinyldiazo compounds to pyrazoles are of the order of
2
7±2 kcal/mol.27
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Conclusion
The valence isomerization [1,2,3]triazolo[1,5-a]pyridine 1T – 2-diazomethylpyridine 2D is
endothermic by ~ 5 kcal/mol and has a free energy of activation of ~ 17 kcal/mol. This makes the
diazomethylpyridine isomers unobservable at ambient temperatures, but they become observable
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o
by low-temperature IR spectroscopy following FVP at ~400 C. At higher pyrolysis temperatures
the diazo compounds decompose by elimination of N , rearrangement of the 2-pyridylcarbene 2
2
so formed to phenylnitrene
pyridyl)diazomethanes 6D were observed analogously. 2-Diazomethylpyridine 2D is trapped in
,3-dipolar cycloaddition reactions in solution. The pyrazoline 10 so formed with
3
and ultimately cyanocyclopentadiene 4. Aryl(2-
1
tetracyanoethylene eliminates N to yield 3-(2-pyridyl)cyclopropanetetracarbonitrile 11 but also
2
undergoes elimination of HCN to afford 3-vinyl-[1,2,3]triazolo[1,5-a]pyridine-1’,2’,2’-
tricarbonitrile 13T.
Experimental Section
1
4
The apparatus and methods for flash vacuum pyrolysis (FVP) have been described. The
-4
apparatus illustrated in Figure 5 in ref. 14 was used. Vacuum was maintained at ~10 hPa
using a high performance turbomolecular pump. Starting materials were sublimed into the
o
pyrolysis tube at 40 C, and pyrolyses were carried out at the temperatures given in the
text. Pyrolysis products were isolated on KBr targets convectively cooled with liq. N for IR
2
1
13
spectroscopy. H and C NMR spectra were recorded at 100.0 and 25.1 MHz, respectively.
Mass spectra were recorded on a conventional sector instrument using electron ionization
at 70 eV.
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[
1,2,3]Triazolo[1,5-a]pyridine 1T
This compound was prepared from 5 as described previously and obtained as white crystals, mp
o
19 1
3
8-40 C. H NMR (DMSO-d ) 8.8 (d, J = 7 Hz, 1H), 7.9 (s, 1H), 7.7 (d, J = 9 Hz, 1H), 7.2 (dd,
6
10
11
12
13
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J = 9 and 6.5 Hz, 1H), 7.0 (dd, J = 6.5 and 7 Hz, 1H), see Figure S5. C NMR (DMSO-d ) 133.3
6
1
(C4), 125.6 (C8), 125.3 (C3), 117.9 (C5), 115.6 (C6, C7). For the decoupled and H-coupled
spectra and assignments, see Figures S6 and S7). IR (KBr) 1635 m, 1505 s, 1355 s, 1210 s, 1140
.
+
-1
s, 1010 s, 800 vs, 750 vs, 680 s cm . MS m/z (%), 119 ([M ], 62), 92 (9), 91 (100), 65 (14), 64
2
+
(
40), 63 (34), 52 (12), 51 (10), 50 (6), 45.5 ([M-N ] , 9), 44.5 (7).
2
2-Diazomethylpyridine 1D
o
-1
For FVP of 1T at 400 C and IR spectrum (77 K) of 2-diazomethylpyridine 1D (2080 cm ), see
o
Figure 1. For FVP of 1T at 330, 500 and 620 C showing IR absorptions (77 K) of 2-
-1
-1
diazomethylpyridine 1D (2080 cm ) and cyanocyclopentadiene 4 (2215 cm ), see Figure S1.
19
5
-(2-Pyridyl)tetrazole 5 was prepared as described previously. FVP of this compound at 400-
o
-1
5
00 C gave rise to an absorption at 2080 cm in the 77 K IR spectrum, which is ascribed to the
diazo compound 1D.
m-Nitrophenyl)(2-pyridyl)diazomethane 6Dc
m-Nitrophenyl)(2-pyridyl)diazomethane 6Dc is formed by slow sublimation of 3-(m-
o
nitrophenyl)-[1,2,3]triazolo[1,5-a]pyridine 6Tc and FVP of the vapor at 210 C. The IR spectrum
-1
of the neat pyrolyzate at 77 K features a diazo absorption at 2080 cm (see Figure S2). This
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o
absorption disappears on warming to -30 C (see Figure S2). FVP of 6cT/6Dc at 400 C results
1
7
in formation of the carbene and rearrangement to a mixture of 1- and 3-nitrocarbazoles 7.
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-(2-Pyridyl)cyclopropane-1,1,2,2-tetracarbonitrile 11.
A mixture of [1,2,3]triazolo[1,5-a]pyridine 1T (119 mg, 1 mmol) and 1280 mg (10 mmol) of
o
TCNE in 66 mL of toluene was heated with stirring at 50 C for 24 h. The resulting precipitate
was filtered, washed with toluene, and vacuum dried over CaCl to yield 58 mg of crude product,
2
o
o
1
which was sublimed at 130 C/3 hPa to yield 25 mg (11%) of 11, mp 160-161 C. H NMR
13
(
DMSO-d ) 8.63 (m 1H), 7.91 (m, 2H), 7.51 (m 1H), 5.28 (s, 1H), see Figure S9. C NMR
6
1
48.9, 146.3, 137.6, 126.5, 125.1, 111.3, 108.9, 41.1, 22.3, see Figures S10 and S11. IR (KBr)
-1
3070 m, 3060 s, 2260 s, 1600 s, 1580 s, 1480 s, 1405 s, 1140 m, 1000 s, 790 s, 750 s cm . MS
•
+
m/z (%) 220 (7), 219 (M , 50), 193 (45), 104 (17), 78 (100). Anal. Calcd for C N H : C, 65.76;
12
5
5
H, 2.30; N, 31.94. Found: C, 65.43; H, 2.25; N, 31.75.
3
-Vinyl-[1,2,3]triazolo[1,5-a]pyridine-1’, 2’,2’-tricarbonitrile 13T
The toluene was distilled in high vacuum from the filtrate from the above thermolysis
experiment, and the remaining substance was dissolved in ethyl acetate (5 mL per 100 mg) and
purified by preparative layer chromatography on silica gel 60, PF , eluting with ethyl acetate.
2
54
The main component with an RF value of 0.6 was isolated by extraction with acetone and
o
1
analyzed as 13T (1.23 g; 56%), mp 219-220 C. H NMR (DMSO-d ) 9.52 (d, 1H), 8.29 (d, 1H),
6
1
3
8
.08 (m, 1H), 7.63 (m, 1H), see Figure S14. C NMR (DMSO-d ) 134.4, 133.2, 128.6, 128.1,
6
•
+
127.9, 127.8, 119.0. 117.5, 113.2, 113.1, 112.1, see Figure S15. MS m/z (%) 221 (4), 220 (M ,
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8), 193 (12), 192 (100), 165 (21), 140 (62), 78 (100), see Figure S16. Anal. Calcd for C H N :
1
1
4
6
C, 60.01; H, 1.83; N, 38.16. Found: C, 59.79; H, 1.80; N, 37.91.
o
-1
FVP of this compound at 430 C gave rise to a weak absorption at 2080 cm ascribed to the
10
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-1
diazo compound 13D as well as cyano group absorptions at 2220-2260 cm (see Figure S3).
Computational Details
2
8
All calculations were performed using the Gaussian 03 suite of programs. Reported
energies (298.15 K) include zero-point vibrational energy corrections. Enthalpies,
entropies and free energies for all calculated compounds and imaginary frequencies for
transition state structures are reported in the Supporting Information.
ASSOCIATED CONTENT
Supporting Information
Partial IR spectra of 1T, 1D and 4, 3-(m-nitrophenyl)-[1,2,3]triazolo[1,5-a]pyridine 6Tc and
1
13
the corresponding diazo compound 6Dc, and 13D; IR, H and C NMR spectra of 1T, 11 and
3T, mass spectra of 11 and 13T, and computational data. The Supporting Information is
1
available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc….
AUTHOR INFORMATION
Corresponding Author
*E-mail: wentrup@uq.edu.au.
Notes
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The authors declare no competing financial interest
.
ACKNOWLEDGMENTS
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This work was supported by grants to CW by the Deutsche Forschungsgemeinschaft (We
774/4A), the Fonds der Chemischen Industrie (1328), the Australian National Computing
Infrastructure facility (MAS g01) and the Queensland Cyber Infrastructure Foundation
(QCIFg01).
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