Conversion of bicyclic C-azoaziridines to 2-substituted 2H-1,2,3-triazoles

Article abstract of DOI:10.1007/s10593-005-0319-9

In an acidified chloroform solution, bicyclic C-azo-N-(N-hetaryl)aziridines are converted to bicyclic 2H-1,2,3-triazoles. This transformation can occur on the surface of silica gel, and also during storage of these compounds at room temperature. 2005 Spri

Full text of DOI:10.1007/s10593-005-0319-9

Chemistry of Heterocyclic Compounds, Vol. 41, No. 10, 2005
CONVERSION OF BICYCLIC C-AZOAZIRIDINES
TO 2-SUBSTITUTED 2H-1,2,3-TRIAZOLES
1
1
2
S. M. Buchaka , M. A. Kuznetsov , and J. G. Schantl
In an acidified chloroform solution, bicyclic C-azo-N-(N-hetaryl)aziridines are converted to bicyclic 2H-
,2,3-triazoles. This transformation can occur on the surface of silica gel, and also during storage of
1
these compounds at room temperature.
Keywords: C-azoaziridines, 2H-1,2,3-triazoles.
Oxidative addition of N-aminophthalimide and 3-amino-2-methylquinazolin-4(3H)-one to a number of
-azocyclohexenes, 1-azocyclopentenes, and 3-azocyclohexen-2-ones leads to formation of two types of
1
compounds: C-azoaziridines 1, 2 and bicyclic 2H-1,2,3-triazoles 3 [1-4]. Since triazoles have not been obtained
previously in oxidative addition of N-amino heterocycles to olefins or to azo compounds, we might hypothesize
that triazole formation is connected with the characteristics of the conjugated azoalkene system. However, we
note that some azoaziridines 1, 2 decompose gradually in solutions and even in the crystalline state at room
temperature, yielding bicyclic triazoles 3 [4].
Azoaziridines with a 4-nitrophenyl substituent (1c, 2c, and 1g) have proven to be especially unstable: in
CDCl solution, they smoothly and practically quantitatively converted to a mixture of the bicyclic triazole 3c or
3
3
1
g and phthalimide or 2-methylquinazolin-4(3H)-one. The stability of these compounds increases in the order
g,c, 2c: according to NMR spectroscopy, the phthalimidoaziridine 1g decomposed completely even while
recording the carbon spectrum; the first signs of decomposition of phthalimidoaziridine 1c appeared 10 min after
preparation of the solution, and it decomposed completely after only 12 h. The appearance of decomposition
products of aziridine 2c was detected only a few hours after it was dissolved.
Conversion of azoaziridines 1, 2 to the bicyclic triazoles 3 is also possible on the surface of silica gel.
1
Thus in the H NMR spectrum of the untreated mixture of the products of reaction between 3-amino-2-
methylquinazolin-4(3H)-one and 1-nitro-4-(cyclopenten-1-ylazo)benzene, we saw the characteristic triplet from
the aziridine proton at 3.93 ppm; but after it was separated on a column with silica gel, we could obtain only the
corresponding bicyclic 2-(4-nitrophenyl)-2H-1,2,3-triazole (87%) and 2-methylquinazolin-4(3H)-one (82%) [4].
Finally, we note that in the reaction of 1-isopropylazocyclopentene with N-aminophthalimide and the reaction of
1
-phenylazocyclohexene with 3-amino-2-methylquinazolin-4(3H)-one, along with the major products (the
azoaziridines 1a and 2b), we isolated a small amount of the bicyclic triazoles 3a and 3b; and the only product
from reaction of both heterocycles with 4-(cyclohexen-1-ylazo)anisole proved to be 2-(4-methoxyphenyl)-
4
,5,6,7-tetrahydro-2H-benzo-1,2,3-triazole, since we obtained azoaziridines 1, 2 with the rest of the
azocyclohexene derivatives [4].
_
_________________________________________________________________________________________
1
St. Petersburg State University, St. Petersburg 198504, Russia; e-mail: mak@org.chem.lgu.spb.su.
2
Institute of Organic Chemistry, University of Innsbruck, Innsbruck A-6020, Austria; e-mail:
Joachim.Schantl@uibk.ac.at. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1573-1578,
October, 2005. Original article submitted August 16, 2004.
0
009-3122/05/4110-1321©2005 Springer Science+Business Media, Inc.
1321

R
N
R
N
HetN
N
R
NHet
N
N
N
N
N
N
+
H
SiO2
– HetNH
X
X
X
(
)n
( )n
( )n
R1
R1
R
1
R1
a–h, 2b–d
R1
R1
3a–d,f–h
1
1
a–h HetN = PiN; 2b–d HetN = MeQN;
O
N
N
O
PiN–
,
N
O
MeQN–
Me
1
1
1
–3 a n = 0, b–h n = 1; a R = i-Pr, R = H, X = CH ; b R = Ph, R = H, X = CH ;
2
2
1
1
c R = p-O NC H , R = H, X = CH ; d R = i-Pr, R = H, X = CH ;
2
6
4
2
2
OAc
R1
= H, X = CH ; f R = Ph, R
1
= H, X = C=O;
e R =
;
2
1
1
g R = p-O NC H , R = H, X = C=O; h R = Ph, R = Me, X = C=O
2
6
4
The facts listed above suggest that the primary products of oxidative addition of N-aminophthalimide
and 3-amino-2-methylquinazolin-4(3H)-one to conjugated azocycloalkenes in all cases are C-azoaziridines 1, 2,
which then can convert (rapidly or slowly) to the corresponding 2H-1,2,3-triazoles 3. In order to test the
generality of this assumption, we studied decomposition of the previously obtained [1-4] bicyclic
C-azoaziridines 1, 2 under various conditions. Since it was difficult to predict beforehand what would accelerate
decomposition of the azoaziridines, first we tested the effect of a protic acid and carried out decomposition of all
the C-azoaziridines 1,2 at room temperature (18-23°C) in a chloroform solution containing 1% CF COOH by
3
volume. The extent of conversion of the azoaziridines was monitored by TLC and NMR spectroscopy.
As in pure deuterated chloroform, the adducts 1c, 2c, and 1g with a 4-nitrophenyl substituent on the azo
group decomposed most rapidly in the presence of CF COOH; but the preparative yields of bicyclic triazoles
3
3
c,g proved to be appreciable lower. Phenyl azoaziridines 1b,f,h and 2b were converted smoothly and in good
yields to the bicyclic triazoles 3b,f,h, which shows they are less sensitive to a change in reaction conditions. But
the adducts 1a,d,e and 2d with an alkyl substituent on the azo group did not decompose to any appreciable
extent under these conditions. Raising the temperature of the reaction mixture to 50°C led to decomposition of
isopropyl azoaziridines 1d, 2d: transformation of the quinazoline derivative 2d to form triazole 3d occurred in
very high yield (90%), while transformation of its phthalimide analog 1d occurred in rather low yield (30%).
However, even in this case we did not observe formation of triazoles from alkyl azoaziridines 1a,e.
Since in chromatographic purification of azoaziridine 1a we nevertheless isolated a small amount of
triazole 3a, we hypothesized that silica gel, which is a Lewis acid, would be more effective and so we carried out
the decomposition of azoaziridines 1a,d,e on the surface of silica gel. For compound 1d, this allowed us to
double the yield of triazole 3d; in the case of 6-azabicyclohexane 1a, we were even able to detect a small amount
of triazole 3a, but the sterically overloaded azoaziridine 1e did not decompose even under these conditions.
1
322

We hypothesize that conversion of azoaziridines 1, 2 to 1,2,3-triazoles 3 occurs through a step involving
their rearrangement to form 1,2,3-triazolines, followed by aromatization as a result of loss of a phthalimide or
2
-methylquinazolin-4(3H)-one molecule. Transformation of azoaziridines to form 1,2,3-triazolines is similar to
the vinylcyclopropane–cyclopentene rearrangement, which is also well known for aziridine derivatives [5-7]. It
may occur both according to a concerted mechanism including a [1,3] sigmatropic shift and through biradical
formation. However, harsher conditions are typical for this process than the conditions under which we observed
conversion of azoaziridines to triazoles [5]. So we do not rule out the possibility that rearrangement to triazoline
occurs as a 6e-electrocyclic reaction with participation of the unshared pair of the aziridine nitrogen atom, the π-
electrons of the azo group, and the C–N σ-bond of the aziridine ring (we note that rearrangement of 1-amino-2-
vinylaziridines to 1-amino-3-pyrrolines also occurs at room temperature [7]). The presence of a protic acid or a
Lewis acid clearly affects the course of the reaction, but we cannot yet say anything specific about the
mechanism for their effect. The inability of azoaziridine 1e to be transformed to form the bicyclic 1,2,3-triazole
is probably explained by the fact that the nitrogen atom of the azo group bearing a bulky tertiary substituent
should experience more steric hindrance as it approaches the aziridine nitrogen atom.
Thus our experiments confirm that the C-azoaziridines 1,2 (obtained as a result of oxidative addition of
N-aminophthalimide and 3-amino-2-methylquinazolin-4(3H)-one to conjugated azocycloalkenes) can actually be
converted to bicyclic 1,2,3-triazoles 3, analogous to those isolated in reactions with some azocyclopentenes and
1
-(4-methoxyphenyl)azocyclohexene. This provides a basis for hypothesizing that oxidative addition of N-amino
heterocyclic compounds to the entire series of conjugated azocycloalkenes we studied in [1-4] initially occurs at
the carbon–carbon double bond to yield azoaziridines, and formation of bicyclic 1,2,3-triazoles is the result of
their secondary conversions in the reaction mixture and also during isolation and purification.
EXPERIMENTAL
1
13
The H and C NMR spectra were recorded on a Varian Gemini 2000 (200 MHz and 50 MHz
respectively) and a Bruker DPX-300 (300 MHz and 75 MHz respectively) in CDCl ; as the internal standard, we
3
used the signals from the residual protons (δ 7.25 ppm) and the carbon atom (δ 77.0 ppm) of the solvent. We
used the DEPT spectra to assign the signals for the carbon atoms. The mass spectra were obtained on Finnigan
MAT 95 and MX-1303 mass spectrometers. We used ionization by electron impact (ionizing electron energy 70
eV) and the FAB method (Cs source, 20 kV, 0.2 µA) in a matrix of 3-nitrobenzyl alcohol. Elemental analysis
was carried out on a Hewlett-Packard HP-185B automatic C,H,N analyzer. The melting points were measured on
a Boetius heating stage with a VEB Analytik PHMK 05 microscope within 0.2°C. The composition of the
reaction mixtures and the fractions obtained when the mixtures were separated and also the purity of the isolated
preparations were monitored by TLC on Macherey–Nagel Polygram Sil G/UV254 and Alugram Sil G/UV254
plates.
Decomposition of Azoaziridines 1, 2 (General Procedure). 1% by volume of CF COOH was added to
3
distilled chloroform that had been washed with concentrated H SO and dried with CaCl . Azoaziridine 1, 2
2
4
2
(
1 mmol) was dissolved in this mixture (10 ml) and held for several days at room temperature. The extent of
1
conversion was monitored by TLC and H NMR spectroscopy. At the end of the reaction, the solvent was driven
off under vacuum. The residue was separated by column chromatography on 40-63 µm silica gel using eluents of
different polarities.
Decomposition of 1-Phenylazo-7-phthalimido-7-azabicyclo[4.1.0]heptane (1b). From aziridine 1b
(
211 mg, 0.61 mmol), we obtained phthalimide (64 mg, 71%) and 2-phenyl-4,5,6,7-tetrahydro-2H-benzo-1,2,3-
1
triazole (3b) (97 mg, 80%), white needles; mp 94.7-95.2°C (95°C [8]; 92-94°C [9]), R 0.67 (ether). H NMR
f
spectrum, δ, ppm (J, Hz): 1.91 (4H, m, H-5,6); 2.82 (4H, m, H-4,7); 7.28 (1H, t, J = 7.5, C H , H-4); 7.46 (2H, t,
6
5
1
3
J = 7.5, C H , H-3,5); 7.99 (2H, d, J = 9, C H , H-2,6). C NMR spectrum, δ, ppm: 21.9 (C(5,6)); 23.1 (C(4,7));
6
5
6
5
1
323

1
18.2 (C
m/z (I, %): 200 (15), 199 [M] (81), 171 (6), 167 (1), 132 (4), 92 (10), 91 (100), 77 (15), 65 (5), 64(20), 63 (6),
1 (8), 41 (7), 39 (7), 27 (4). Found, %: C 72.36; H 6.53; N 20.76. C12 . Calculated, %: C 72.36; H 6.58;
N 21.11.
6 5 6 5 6 5 6 5
H , C(2,6)); 126.5 (C H , C(4)); 129.1 (C H , C(3,5)); 140.1 (C H , C(1)); 145.6 (C(3a,7a)). Mass spectrum,
+
5
13 3
H N
Decomposition of 1-(4-Nitrophenyl)azo-7-phthalimido-7-azabicyclo[4.1.0]heptane (1c). From
aziridine 1c (27 mg, 0.07 mmol), we obtained phthalimide (4 mg, 39%) and 2-(4-nitrophenyl)-4,5,6,7-
tetrahydro-2H-benzo-1,2,3-triazole (3c) (8.5 mg, 51%), yellow sawdust-like material; mp 219°C (208-210°C [9],
1
2
04-206°C [10]), R
f
0.37 (hexane–ether, 5:1). H NMR spectrum, δ, ppm (J, Hz): 1.90 (4H, m, H-5,6); 2.82 (4H,
1
3
m, H-4,7); 8.13 (2H, d, J = 9.2, Ar, H-2,6); 8.30 (2H, d, J = 9.4, Ar, H-3,5). C NMR spectrum, δ, ppm: 21.9
(C(5,6)); 22.8 (C(4,7)); 118.1 (Ar, C(2,6)); 125.2 (Ar, C(3,5)); 144.0 and 145.5 (Ar, C(1,4)); 147.8 (C(3a,7a)). Mass
+
spectrum, m/z (I, %): 245 (15), 244 [M ] (100), 243 (2), 228 (2), 216 (9), 214 (7), 198 (7), 170 (2), 157 (1), 149
(
(
3), 136 (16), 122 (5), 115 (4), 106 (9), 90 (36), 80 (16), 76 (10), 63 (30), 55 (8), 50 (8), 41 (10), 39 (24), 30
32), 27 (6).
Decomposition of 1-Isopropylazo-7-phthalimido-7-azabicyclo[4.1.0]heptane (1d). From aziridine 1d
(
1
339 mg, 1.09 mmol), we obtained phthalimide (119 mg, 75%) and 2-isopropyl-4,5,6,7-tetrahydro-2H-benzo-
1
,2,3-triazole (3d) (56 mg, 31%), greenish-yellow viscous liquid, R
f
0.43 (ether). H NMR spectrum, δ, ppm
(
J, Hz): 1.49 (6H, d, J = 6.6, 2CH
3
); 1.78 (4H, m, H-5,6); 2.64 (4H, m, H-4,7); 4.67 (1H, s, J = 6.7, CH).
C NMR spectrum, δ, ppm; 21.7 (C(5,6)); 22.4 (2CH ); 23.1 (C(4,7)); 56.4 (CH); 142.9 (C(3a,7a)). Mass spectrum,
m/z (I, %): 165 [M] (25), 164 (23), 151 (12), 150 (100), 123 (1), 122 (10), 110 (3), 109 (15), 104 (5), 95 (8), 94
1
3
3
+
(
(
9), 82 (4), 76 (5), 67 (23), 56 (5), 55 (10), 54 (12), 53 (10), 52 (8), 50 (3), 43 (25), 42 (50), 41 (43), 40 (10), 39
23).
Decomposition of 1-(1-Acetoxycyclohexyl)azo-7-phthalimido-7-azabicyclo[4.1.0]heptane (1e).
1
Analysis of samples of the reaction mixture by H NMR spectroscopy after 2 days and 5 days showed that no
decomposition of aziridine 1e (98 mg, 0.24 mmol) occurs. Raising the temperature of the reaction mixture up to
5
0°C (withdrawing samples after 2 h, 5 h, 24 h, 48 h) also did not cause decomposition of aziridine. Silica gel
(
5 ml) was added to the solution and the solvent was evaporated off under vacuum. The silica gel with the
supported azoaziridine was allowed to stand for 7 days at room temperature, and then was extracted several
times with ether. According to TLC data, the extract contains only azoaziridine 1e. The ether was evaporated
under vacuum; the azoaziridine (92 mg) was dissolved in acidified chloroform and heated at 50°C. The extent of
conversion was monitored by TLC. After 4 days, the intensity of the azoaziridine spot decreased, but signs of tar
formation in the reaction mixture appeared, markedly increasing within 24 hours. The solvent was driven off
under vacuum, the oily residue was separated on silica gel (10 g) using a 5:1 hexane–ether mixture as the eluent.
4
7 mg of azoaziridine 1e and 7 mg of phthalimide were isolated; checking by TLC the tarry residue moved from
the start as a blurred spot. We did not detect formation of bicyclic 1,2,3-triazole.
Decomposition of 6-Phenylazo-7-phthalimido-7-azabicyclo[4.1.0]heptan-2-one (1f). From aziridine
1
1
f (174 mg, 0.48 mmol), we obtained phthalimide (50 mg, 71%) and 2-phenyl-2,5,6,7-tetrahydro-4H-benzo-
,2,3-triazol-4-one (3f) (76 mg, 74%), white needles; mp 107-108°C, R 0.50 (methylene chloride). H NMR
f
1
spectrum, δ, ppm (J, Hz): 2.25 (2H, q, J = 6.4, H-6); 2.71 (2H, t, J = 6.2, H-7); 3.04 (2H, t, J = 6.2, H-5); 7.40
1
3
(
1H, t, J = 7.3, C
6
H
5
, H-4); 7.49 (2H, t, J = 7.7, C
6
H
5
, H-3,5); 8.14 (2H, d, J = 8.1, C
6 5
H , H-2,6). C NMR
spectrum, δ, ppm: 22.4 (C(6)); 23.8 (C(7)); 40.3 (C(5)); 120.4 (C
6
H
5
, C(2,6)); 129.4 (C
6
H
5
, C(4)); 130.0 (C
6
H
5
, C(3,5));
+
1
1
5
40.0 (C
6
H
5
, C(1)); 143.3 (C(7a)); 155.6 (C(3a)); 192.7 (C(4)). Mass spectrum, m/z (I, %): 214 (8), 213 [M] (48),
86 (2), 185 (12), 184 (2), 156 (0.5), 128 (2), 118 (5), 105 (16), 91 (33), 77 (100), 76 (8), 65 (6), 64 (14), 63 (6),
5 (7), 51 (25), 41 (11), 39 (11).
Decomposition of 6-(4-Nitrophenyl)azo-7-phthalimido-7-azabicyclo[4.1.0]heptan-2-one (1g). From
aziridine 1g (141 mg, 0.35 mmol), we obtained phthalimide (20 mg, 39%) and 2-(4-nitrophenyl)-2,5,6,7-
tetrahydro-4H-benzo-1,2,3-triazol-4-one (3g) (38 mg, 42%), orange platelets; mp 209°C, R 0.40 (methylene
chloride). H NMR spectrum, δ, ppm (J, Hz): 2.29 (2H, q, J = 6.3, H-6); 2.76 (2H, t, J = 6.7, H-7); 3.09 (2H, t,
f
1
1
3
J = 5.9, H-5); 8.36 (4H, m, C
6 4
H ). C NMR spectrum, δ, ppm: 22.4 (C(6)); 23.7 (C(7)); 40.5 (C(5)); 120.8 (Ar,
1
324

C
(2,6)); 125.9 (Ar, C(3,5)); 143.9 and 144.5 (Ar, C(1,4)); 148.0 (C(7a)); 156.5 (C(3a)); 192.4 (C(4)). Mass spectrum,
+
m/z (I, %): 259 (16), 258 [M] (100), 243 (2), 230 (20), 212 (2), 183 (2), 150 (14), 136 (3), 123 (5), 122 (65),
1
3
06 (3), 96 (5), 93 (6), 92 (12), 90 (7), 76 (18), 75 (17), 68 (6), 64 (8), 63 (12), 55 (21), 50 (10), 41 (12), 39 (12),
0 (8).
Decomposition of 4,4-Dimethyl-6-phenylazo-7-phthalimido-7-azabicyclo[4.1.0]heptan-2-one (1h).
From aziridine 1h (276 mg, 0.71 mmol), we obtained phthalimide (66 mg, 64%) and 6,6-dimethyl-2-phenyl-
,5,6,7-tetrahydro-4H-benzo-1,2,3-triazol-4-one (3h) (107 mg, 63%), white platelets; mp 113.5°C (116-118°C
2
1
[11]). H NMR spectrum, δ, ppm (J, Hz): 1.16 (6H, s, 2CH ); 2.57 (2H, m, H-7); 2.90 (2H, m, H-5); 7.39 (1H, t,
3
13
J = 7.2, C H , H-4); 7.49 (2H, t, J = 7.7, C H , H-3,5); 8.14 (2H, d, J = 8.2, C H , H-2,6). C NMR spectrum,
6
5
6
5
6
5
δ, ppm: 29.1 (2CH ); 36.2 (C ); 54.2 (C ); 120.3 (C H , C );129.4 (C H , C ); 130.0 (C H , C(3,5)); 140.1
3
(6,7)
(5)
6
5
(2,6)
6
5
(4)
6
5
(
C H , C ); 142.6 (C(7a)); 154.6 (C(3a)); 192.2 (C ). Found, %: C 69.72; H 6.13; N 17.61. C H N O.
6 5 (1) (4) 14 15 3
Calculated, %: C 69.69; H 6.26; N 17.41.
Decomposition of 2-Methyl-3-(1-phenylazo-7-azabicyclo[4.1.0]hept-7-yl)quinazolin-4(3H)-one (2b).
From aziridine 2b (177 mg, 0.49 mmol), we obtained quinazolinone (57 mg, 72%) and 2-phenyl-4,5,6,7-
tetrahydro-2H-benzo-1,2,3-triazole (3b) (83 mg, 85%); mp 93.5°C.
Decomposition of 2-Methyl-3-(1-(4-nitrophenyl)azo-7-azabicyclo[4.1.0]hept-7-yl)quinazolin-4(3H)-
one (2c). From aziridine 2c (78 mg, 0.19 mmol), we obtained quinazolinone (18 mg, 58%) and
2
-(4-nitrophenyl)-4,5,6,7-tetrahydro-2H-benzo-1,2,3-triazole (3c) (22 mg, 47%).
Decomposition of 3-(1-Isopropylazo-7-azabicyclo[4.1.0]hept-7-yl)-2-methylquinazolin-4(3H)-one
(
2d). From aziridine 2d (363 mg, 1.12 mmol), we obtained quinazolinone (103 mg, 58%) and 2-isopropyl-
4
,5,6,7-tetrahydro-2H-benzo-1,2,3-triazole (3d) (168 mg, 91%).
Decomposition of 1-Isopropylazo-6-phthalimido-6-azabicyclo[3.1.0]hexane (1a) on Silica Gel. A
solution of aziridine 1a (78 mg, 0.26 mmol) in ether was mixed with silica gel (1 g) and then the solvent was
evaporated off under vacuum. The silica gel with the applied aziridine was allowed to stand for 24 hours at room
temperature. The mixture of reaction products was extracted several times with ether. Then the solvent was
driven off under vacuum and the oily residue was separated on a column with silica gel (5 g) using a 7:1
petroleum ether–ether mixture as the eluent, gradually increasing the fraction of the latter up to 5:1. Liquid
1
2
-isopropyl-2,4,5,6-tetrahydrocyclopenta-1,2,3-triazole (3a) (7 mg, 18%) was isolated. H NMR spectrum,
δ, ppm (J, Hz): 1.53 (6H, d, J = 6.7, 2CH ); 2.48 (2H, q, J = 7.1, H-5); 2.73 (4H, t, J = 7.3, H-4,6); 4.72 (1H,
3
septuplet, J = 6.7, CH).
Decomposition of 1-Isopropylazo-7-phthalimido-7-azabicyclo[4.1.0.]heptane (1d) on Silica Gel. A
solution of aziridine 1d (312 mg, 1 mmol) in ether was mixed with silica gel (2 g) and then the solvent was
evaporated under vacuum. The reaction mixture was held for 4 days at room temperature. The mixture of
reaction products was extracted several times with ether and the solvent was driven off under vacuum. The oily
residue was dissolved in a minimal amount of ether and the precipitate formed was filtered out (phthalimide,
7
9 mg). The residue was separated on a column with silica gel (10 g), using a 5:1 hexane–ether mixture as the
eluent. We obtained 20 mg (total yield, 99 mg (67%)) of phthalimide and compound 3d (153 mg, 93%).
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