One-pot regioselective vinylation of tetrazoles: preparation of 5-substituted 2-vinyl-2H-tetrazoles

Article abstract of DOI:10.1016/j.tetlet.2010.01.021

The one-pot regioselective preparation of 5-aryl/alkyl-2-vinyl-2H-tetrazoles from 5-substituted tetrazoles via a very simple procedure using 1,2-dibromoethane and triethylamine without the need of any catalyst is described. The mechanism of this reaction is also discussed.

Full text of DOI:10.1016/j.tetlet.2010.01.021

Tetrahedron Letters 51 (2010) 1411–1414
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One-pot regioselective vinylation of tetrazoles: preparation of 5-substituted
2-vinyl-2H-tetrazoles
*
ˇ
Jaroslav Roh , Katerina Vávrová, Alexandr Hrabálek
Charles University in Prague, Faculty of Pharmacy, Department of Inorganic and Organic Chemistry, Heyrovského 1203, 50005 Hradec Králové, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
The one-pot regioselective preparation of 5-aryl/alkyl-2-vinyl-2H-tetrazoles from 5-substituted tetra-
zoles via a very simple procedure using 1,2-dibromoethane and triethylamine without the need of any
catalyst is described. The mechanism of this reaction is also discussed.
Received 1 October 2009
Revised 2 December 2009
Accepted 8 January 2010
Available online 13 January 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Nitrogen heterocycles
Regioselectivity
Vinylation
Tetrazole
The preparation of tetrazoles and their derivatives has been the
subject of intense investigation in recent years, especially due to
the use of 5-substituted-1H-tetrazoles as an isosteric replacement
for the carboxylic acid moiety in pharmaceutical chemistry.1 The
most significant representatives of biologically active compounds
containing the tetrazole ring are the antihypertensive angiotensin
II receptor antagonists named sartanes.1 Moreover, tetrazoles have
found widespread use as ligands in coordination chemistry, as
components of explosives and in the photographic industry.2 The
synthesis of 5-substituted tetrazoles via cycloaddition of an azide
anion to the corresponding nitrile is well described in the litera-
ture. All the synthetic approaches fall within three main catego-
ries: those that use tin, aluminium or silicon-containing
compounds as donors of azide anions,3 those that use Lewis acids,4
and finally those that proceed in acidic media or are acid-
catalyzed.5,6
The simplest preparation of 1,5- and 2,5-disubstituted tetra-
zoles is based on alkylation or arylation of 5-substituted tetrazoles.
The main disadvantage of this method is the lack of regioselectiv-
ity. The product obtained is usually a mixture of both isomers in an
approximately 1:1 ratio and these isomers are extremely difficult
to separate. Attempts to influence the regioselectivity by modifica-
tion of the reaction conditions have mostly failed.7 The synthesis of
1,5-disubstituted tetrazoles by different methods, starting mainly
from the corresponding amides, is well described.8 However, there
are only a few methods for the selective synthesis of 2,5-disubsti-
tuted tetrazoles from 5-substituted tetrazoles, such as the palla-
dium- and copper-catalyzed arylation with diaryliodonium salts.9
The majority of these methods take advantage of a bulky substitu-
ent, with preferential reaction at position 2 of the tetrazole (re-
viewed in Koldobskii et al.10).
Although several methods for the preparation of 5-substituted
2-vinyl-2H-tetrazoles have been published, all have substantial
disadvantages. The first method is direct vinylation of tetrazole
using vinyl acetate in the presence of mercuric acetate. The major
drawback lies in the toxicity of the mercuric substances along with
relatively low yields.11 Another possibility is the dehydration of
5-aryl-2-(2-hydroxyethyl)-2H-tetrazoles or dehydrohalogenation
of 5-aryl-2-(2-chloroethyl)-2H-tetrazoles. However, the prepara-
tion of these intermediates leads to both 1,5- and 2,5-isomers in
various ratios, which must be separated chromatographically.12
Although a mild copper-catalyzed vinylation of various azoles
has been described, it was unsuccessful in the case of tetrazoles.13
An unexpected formation of vinyltetrazoles was observed during
the preparation of tetrazole macrocycles. However, this reaction
was not regioselective and the obtained yields of both 1- and 2-vi-
nyl derivatives were low (10%), even after long reaction times (24–
120 h).14
We have developed a new, one-pot, regioselective method for the
preparation of 2-vinyltetrazoles. We found that the reaction of 5-
phenyl-1H-tetrazole (1a) with 1,2-dibromoethane and triethyl-
amine in a 1:1:2 molar ratio in acetonitrile led to the preferential for-
mation of 5-phenyl-2-vinyl-2H-tetrazole (2a) (Scheme 1). Tetrazole
1,1-, 1,2- and 2,2-dimers, that is, 1,1-bis(5-phenyl-1H-tetrazol-1-
yl)ethane (3a), 1-[2-(5-phenyl-2H-tetrazol-2-yl)ethyl]-5-phenyl-
1H-tetrazole (3b), and 2,2-bis(5-phenyl-2H-tetrazol-2-yl)ethane
(3c), were formed as side products (Fig. 1). Increasing the amount
* Corresponding author. Tel.: +420 495067339; fax: +420 495067166.
E-mail address: jaroslav.roh@faf.cuni.cz (J. Roh).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.01.021

1412
J. Roh et al. / Tetrahedron Letters 51 (2010) 1411–1414
moethane to form (2-bromoethyl)triethylammonium bromide,
which reacted with tetrazole 1a producing triethyl-2-(5-phenyl-
2H- tetrazol-2-yl)ethylammonium bromide. Substitution at posi-
tion 2 of the tetrazole ring is probably directed by the steric require-
ments of (2-bromoethyl)triethylammonium bromide. Under the
reaction conditions, triethyl-2-(5-phenyl-2H-tetrazol-2-yl)ethy-
lammonium bromide underwent spontaneous elimination to pro-
duce vinyl derivative 2a.
Scheme 1.
In order to confirm the proposed reaction mechanism, we at-
tempted to prepare the putative intermediate (2-bromoethyl)tri-
ethylammonium bromide by reaction of 1,2-dibromoethane with
triethylamine according to the procedure described previously.15
Surprisingly, only triethylammonium bromide was recovered from
the reaction mixture when using various temperatures and sol-
vents. Thus, commercially available (2-bromoethyl)trimethylam-
monium bromide was used to evaluate the proposed reaction
mechanism. On reaction with potassium 5-phenyl-1H-tetrazolate
in N,N-dimethylformamide, the quaternary ammonium intermedi-
ate trimethyl-2-(5-phenyl-2H-tetrazol-2-yl)ethylammonium bro-
mide (4) was obtained, isolated and characterized.16 Formation of
vinyl derivative 2a as a side product also occurred during this
reaction.
Figure 1. Tetrazole dimers 3a–c, side products of the reaction.
Compound 4 readily and quantitatively decomposed to vinyl
tetrazole 2a in boiling acetonitrile in the presence of triethylamine,
thereby confirming the suggested mechanism for the vinylation
(Scheme 3).
of 1,2-dibromoethane and triethylamine increased the yield of the
product 2a and decreased the yield of the dimers 3a–c. Surprisingly,
5-phenyl-1-vinyl-1H-tetrazole was formed in only a trace amount.
This result encouraged us to investigate the reaction mechanism.
Alkylation of 5-substituted tetrazoles is a well known process. Thus,
the alkylation of 5-substituted 1H-tetrazole with 1,2-dibromoeth-
ane would furnish an approximate 1:1 ratio of regioisomers and
the subsequent elimination would yield both 1- and 2-vinyl deriva-
tives of 5-substituted 1H-tetrazole. Also, an increasing amount of
both the alkylating agent and base would not significantly affect
the ratio of 1- and 2-substituted isomers. Therefore, alkylation of
the tetrazole with 1,2-dibromoethane is unlikely to be the first step
of this reaction. However, this mechanism may well explain the for-
mation of the tetrazole dimers 3a–c.
The requirement of a twofold molar amount of the base relative
to 1,2-dibromoethane suggests that the elimination step of the
reaction proceeds via a quaternary ammonium salt by a mecha-
nism similar to Hofmann elimination. This hypothesis was verified
by the reaction of tetrazole 1a with 1,2-dibromoethane in the pres-
ence of different organic bases. The reaction with diisopropylethyl-
amine as the base proceeded similarly to the reaction with
triethylamine, that is, vinyl derivative 2a was formed as the main
product. The same reaction using pyridine led to a mixture of qua-
ternary ammonium salts, and no vinyl derivative 2a was detected
in the reaction mixture.
We subsequently studied the effects of various solvents on the
yields of vinyl tetrazole 2a. It was found that the reaction pro-
ceeded in high yields almost regardless of the solvent used, which
is another advantage of this method (Table S1—Supplementary
data). However, to prevent increased formation of dimers, the or-
der of addition of the reagents is important. It is necessary to main-
tain an excess of dibromoethane in the reaction mixture. The
utility of this method was demonstrated by the preparation of sev-
eral new 5-aryl-2-vinyl-2H-tetrazoles 2a–h (Table 1).17,18
Moreover, 5-alkyl-2H-tetrazoles can also be converted into the
corresponding 5-alkyl-2-vinyl-2H-tetrazoles in moderate yields
(2i–k; Table 1).17,18 The lower yields can be attributed to the higher
nucleophilicity of 5-alkyl-2H-tetrazoles leading to easier formation
of tetrazole dimers, and to less steric hindrance from the 5-alkyl
groups. The low isolated yield of methyl derivative 2k (21%) was
due to the volatility of the product, however, examination of the
NMR spectra of the reaction mixture revealed that the 2-vinylation
proceeded in 53% yield, similar to the other alkyl derivatives.
Another advantage of this method is that the relatively lipo-
philic products can be easily isolated by column chromatography,
because they have markedly higher Rf values than other compo-
nents of the reaction mixture.
Thus, it is likely the reaction proceeds via the following pathway
(Scheme 2). In the first step, triethylamine reacted with 1,2-dibro-
In conclusion, we have developed a one-pot regioselective
method for the preparation of 5-substituted 2-vinyl-2H-tetrazoles
Scheme 2.
Scheme 3.

J. Roh et al. / Tetrahedron Letters 51 (2010) 1411–1414
1413
Table 1
6. Roh, J.; Artamonova, T. V.; Vavrova, K.; Koldobskii, G. I.; Hrabalek, A. Synthesis
2009, 13, 2175.
Preparation of 5-substituted 2-vinyl-2H-tetrazoles
7. (a) Koldobskii, G. I. Russ. J. Org. Chem. 2006, 42, 469; (b) Couri, M. R.; Luduvico,
I.; Santos, L.; Alves, R.; Prado, M. A.; Gil, R. F. Carbohydr. Res. 2007, 342, 1096; (c)
Efimova, J. A.; Mashkova, E. A.; Artamonova, T. V.; Koldobskii, G. I. Chem.
Heterocycl. Compd. 2008, 44, 498.
8. (a) Katritzky, A. R.; Cai, C.; Meher, N. K. Synthesis 2007, 1204; (b) Artamonova, T.
V.; Zhivich, A. B.; Dubinskii, M. Y.; Koldobskii, G. I. Synthesis 1996, 1428.
9. Davydov, D. V.; Beletskaya, I. P.; Gorovoy, M. S. Tetrahedron Lett. 2002, 43, 6221.
10. Koldobskii, G. I.; Kharbash, R. B. Russ. J. Org. Chem. 2003, 39, 453.
11. Vereshchagin, L. I.; Buzilova, S. R.; Mityukova, T. K.; Proidakov, A. G.;
Kizhnyaev, V. N. Zh. Org. Khim. 1986, 22, 1979.
12. (a) Finnegan, W.; Henry, R. J. Org. Chem. 1959, 24, 1565; (b) Moody, C. J. Chem.
Soc., Perkin Trans. 1 1991, 323; (c) Moody, C. J. Chem. Soc., Perkin Trans. 1 1991,
329.
Product
R-
Time (h)
4
Yield (%)
80
2a
13. Taillefer, M.; Ouali, A.; Renard, B.; Spindler, J.-F. Chem. Eur. J. 2006, 12, 5301.
14. Fleming, A.; Kelleher, F.; Mahon, M. F.; McGinley, J.; Prajapati, V. Tetrahedron
2005, 61, 7002.
2b
2c
4
4
75
79
15. Vidal, F. J .Org. Chem. 1959, 24, 680.
16. Preparation of trimethyl-2-(5-phenyl-2H-tetrazol-2-yl)ethylammonium bromide
(4): Potassium 5-phenyl-1H-tetrazolate (3.4 mmol) and (2-bromoethyl)trime-
thylammonium bromide (3.4 mmol) were added to 5 ml of N,N-dimeth-
ylformamide. The reaction mixture was stirred at 110 °C for 4 h, then cooled to
room temperature and the resulting solid was filtered, washed with CHCl3
(10 ml) and dried. The solid was dispersed in boiling ethanol (96%, 15 ml), KBr
was removed by filtration, the ethanolic filtrate was cooled and the product
crystallized by the addition of Et2O. Yield: 60%, mp 228–229 °C; 1H NMR
(300 MHz, D2O) d: 8.02–8.08 (m, 2H), 7.54–7.62 (m, 3H), 5.37 (t, J = 6.2 Hz, 2H),
4.21 (t, J = 6.2 Hz, 2H), 3.26 (s, 9H) ppm; 13C NMR (75 MHz, D2O) d: 164.9, 130.9,
128.8, 126.3, 125.3, 62.7, 53.2, 46.7 ppm; Anal. Calcd for C12H18BrN5: C, 46.16; H,
5.81; N, 22.43. Found: C, 45.77; H, 5.84; N, 22.43.
2d
2e
4
5
86
84
17. General method for the preparation of 5-substituted 2-vinyl-2H-tetrazoles: 1,2-
Dibromoethane (6 mmol) in MeCN (1.5 ml) was stirred at reflux. Then, a
solution of 5-substituted tetrazole (3 mmol) and Et3N (12 mmol) in MeCN
(2.5 ml) was added dropwise over 2 h. The mixture was heated at reflux for an
additional 2–3 h (overall reaction time is given in Table 1). The reaction was
monitored by TLC (mobile phase: hexane/Et2O). MeCN was removed under
reduced pressure, and the residue was dissolved in CHCl3 (30 ml) and washed
with H2O (3 Â 25 ml). The organic solution was dried over Na2SO4 and the
solvent was evaporated. The product was obtained by column
chromatography.
18. Data for compounds 2a–2k: 5-Phenyl-2-vinyl-2H-tetrazole (2a). Mobile phase:
hexane/Et2O, 15:1. Yield: 80%; mp 41 °C; 1H NMR (300 MHz, CDCl3) d: 8.17–
8.23 (m, 2H), 7.47–7.62 (m, 4H), 6.27 (dd, J = 15.6 and 1.5 Hz, 1H), 5.40 (dd,
J = 8.8 and 1.5 Hz, 1H) ppm; 13C NMR (75 MHz, CDCl3) d: 164.9, 130.6, 129.8,
128.9, 127.0, 126.9, 108.4 ppm; Anal. Calcd for C9H8N4: C, 62.78; H, 4.68; N,
32.54. Found: C, 62.55; H, 4.78; N, 32.64.
2f
4
77
78
2g
4.5
2h
2i
4.5
4
88
53
2j
CH3(CH2)10
–
4
4
54
5-p-Tolyl-2-vinyl-2H-tetrazole (2b): Mobile phase: hexane/Et2O, 10:1. Yield:
75%; mp 40–41 °C; 1H NMR (300 MHz, CDCl3) d: 8.08 (d, J = 8 Hz, 2H), 7.54 (dd,
J = 15.6 and 8.8 Hz, 1H), 7.31 (d, J = 8 Hz, 2H), 6.25 (dd, J = 15.6 and 1.5 Hz, 1H),
5.37 (dd, J = 8.8 and 1.5 Hz, 1H), 2.42 (s, 3H) ppm; 13C NMR (75 MHz, CDCl3) d:
164.9, 140.9, 129.8, 129.6, 127.0, 124.1, 108.2, 21.5 ppm; Anal. Calcd for
C10H10N4: C, 64.50; H, 5.41; N, 30.09. Found: C, 64.09; H, 5.45; N, 30.45.
5-(4-Nitrophenyl)-2-vinyl-2H-tetrazole (2c): Mobile phase: hexane/Et2O, 4:1.
Yield: 79%; mp 128–129 °C; 1H NMR (300 MHz, CDCl3) d: 8.28–8.48 (m, 4H),
7.59 (dd, J = 15.6 and 8.8 Hz, 1H), 6.32 (dd, J = 15.6 and 1.7 Hz, 1H), 5.48 (dd,
J = 8.8 and 1.7 Hz, 1H) ppm; 13C NMR (75 MHz, CDCl3) d: 163.0, 149.0, 132.8,
129.6, 127.9, 124.2, 109.5 ppm; Anal. Calcd for C9H7N5O2: C, 49.77; H, 3.25; N,
32.25. Found: C, 49.82; H, 3.52; N, 32.09.
2k
53/21a
a
NMR/isolated yield.
via a simple procedure without a metal catalyst or organocatalyst.
The resulting 5-substituted 2-vinyl-2H-tetrazoles can undergo
transformation of the double bond and can be used to prepare
3-substituted pyrazoles.12c
5-[4-(Trifluoromethyl)phenyl]-2-vinyl-2H-tetrazole (2d): Mobile phase: hexane/
Et2O, 10:1 Yield: 86%; mp 44 °C; 1H NMR (300 MHz, CDCl3) d: 8.32 (d,
J = 8.1 Hz, 2H), 7.77 (d, J = 8.1 Hz, 2H), 7.58 (dd, J = 15.6 and 8.8 Hz, 1H), 6.31
(dd, J = 15.6 and 1.6 Hz, 1H), 5.45 (dd, J = 8.8 and 1.6 Hz, 1H) ppm; 13C NMR
(75 MHz, CDCl3) d: 163.7, 132.4 (q, J = 32.8 Hz), 130.3, 129.7, 127.3, 125.9 (q,
J = 3.7 Hz), 123.8 (q, J = 272.3 Hz), 109.1 ppm; Anal. Calcd for C10H7F3N4: C,
50.01; H, 2.94; N, 23.33. Found: C, 49.99; H, 2.82; N, 23.05.
5-(4-Chlorophenyl)-2-vinyl-2H-tetrazole (2e): Mobile phase: hexane/Et2O, 15:1.
Yield: 84%; mp 81–82 °C; 1H NMR (300 MHz, CDCl3) d: 8.13 (d, J = 8.7 Hz, 2H),
7.55 (dd, J = 15.6 and 8.8 Hz , 1H), 7.47 (d, J = 8.7 Hz, 2H), 6.27 (dd, J = 15.6 and
1.6 Hz, 1H), 5.41 (dd, J = 8.8 and 1.6 Hz, 1H) ppm; 13C NMR (75 MHz, CDCl3) d:
164.0, 136.7, 129.7, 129.2, 128.3, 125.4, 108.7 ppm; Anal. Calcd for C9H7ClN4: C,
52.31; H, 3.41; N, 27.11. Found: C, 52.29; H, 3.34; N, 27.2.
Acknowledgements
This work was supported by the Ministry of Education of the
Czech Republic (Project No. MSM0021620822) and by the Czech
Science Foundation (203/07/1302). We thank Professor Jirí Kuneš
ˇ
for obtaining NMR spectra.
Supplementary data
Supplementary data (general experimental details, copies of
NMR spectra, Table S1) associated with this article can be found,
in the online version, at doi:10.1016/j.tetlet.2010.01.021.
N-[3-(2-Vinyl-2H-tetrazol-5-yl)phenyl]acetamide (2f): Mobile phase: Et2O/
hexane, 4:1. Yield: 77%; mp 153–154 °C; 1H NMR (300 MHz, CD3SOCD3) d:
10.18 (m, 1H), 8.41–8.45 (m, 1H), 7.89 (dd, J = 15.5 and 8.7 Hz, 1H), 7.70–7.80
(m, 2H), 7.45–7.52 (m, 1H), 6.18 (dd, J = 15.5 and 1.5 Hz, 1H), 5.56 (dd, J = 8.7
and 1.5 Hz, 1H), 2.07 (s, 3H) ppm; 13C NMR (75 MHz, CD3SOCD3) d: 168.8,
164.2, 140.3, 130.5, 130.0, 126.9, 121.3, 117.0, 109.7, 24.2 ppm; Anal. Calcd for
C11H11N5O: C, 57.63; H, 4.84; N, 30.55. Found: C, 57.49; H, 5.04; N, 30.47.
5-o-Tolyl-2-vinyl-2H-tetrazole (2g): Mobile phase: hexane/Et2O, 20:1. Yield:
78%; isolated as an oil; 1H NMR (300 MHz, CDCl3) d: 8.06–8.11 (m, 1H), 7.58
(dd, J = 15.6 and 8.8 Hz, 1H), 7.29–7.43 (m, 3H), 6.27 (dd, J = 15.6 and 1.5 Hz,
1H), 5.39 (dd, J = 8.8 and 1.5 Hz, 1H), 2.67 (s, 3H) ppm; 13C NMR (75 MHz,
CDCl3) d: 165.3, 137.7, 131.4, 130.2, 129.8, 129.6, 126.0, 125.9, 108.3,
21.7 ppm; HRMS (EI): m/z calcd for C10H10N4 [M]+: 186.0905; found: 186.0908.
5-(3,4-Dichlorophenyl)-2-vinyl-2H-tetrazole (2h): Mobile phase: hexane/Et2O,
References and notes
1. Herr, R. J. Bioorg. Med. Chem. 2002, 10, 3379.
2. Koldobskii, G. I.; Ostrovskii, V. A. Usp. Khim. 1994, 63, 847.
3. (a) Duncia, J. V.; Pierce, M. E.; Santella, J. B., III J. Org. Chem. 1991, 56, 2395; (b)
Amantini, D.; Beleggia, R.; Fringuelli, F.; Pizzo, F.; Vaccaro, L. J. Org. Chem. 2004,
69, 2896; (c) Aureggi, V.; Sedelmeier, G. Angew. Chem., Int. Ed. 2007, 46, 8440.
4. Demko, Z. P.; Sharpless, K. B. J. Org. Chem. 2001, 66, 7945.
5. Finnegan, W. G.; Henry, R. A.; Lofquist, R. J. Am. Chem. Soc. 1958, 80, 3908.

1414
J. Roh et al. / Tetrahedron Letters 51 (2010) 1411–1414
15:1. Yield: 88%; mp 116–117 °C; 1H NMR (300 MHz, CDCl3) d: 8.29 (d, J = 2 Hz,
54%; isolated as an oil; 1H NMR (300 MHz, CDCl3) d: 7.46 (dd, J = 15.7 and
8.8 Hz, 1H), 6.14 (dd, J = 15.7 and 1.5 Hz, 1H), 5.31 (dd, J = 8.8 and 1.5 Hz, 1H),
2.90 (t, J = 7.7 Hz, 2H), 1.74–1.85 (m, 2H), 1.20–1.40 (m, 16H), 0.87 (t, J = 6.6 Hz,
3H) ppm; 13C NMR (75 MHz, CDCl3) d: 166.9, 129.8, 107.8, 31.9, 29.6, 29.4,
29.3, 29.2, 29.1, 27.9, 25.4, 22.6, 14.1 ppm; HRMS (ESI): m/z calcd for C14H27N4
[M+H]+: 251.2230; found: 251.2229.
5-Methyl-2-vinyl-2H-tetrazole (2k): Mobile phase: hexane/Et2O, 4:1. Yield: 53%
(by NMR) / 21% (isolated); isolated as a volatile liquid; 1H NMR (300 MHz,
CDCl3) d: 7.46 (dd, J = 15.7 and 8.8 Hz, 1H), 6.15 (dd, J = 15.7 and 1.5 Hz, 1H),
5.32 (dd, J = 8.8 and 1.5 Hz, 1H), 2.55 (3H, s) ppm; 13C NMR (75 MHz, CDCl3) d:
162.9, 129.7, 107.9, 10.9 ppm; HRMS (ESI): m/z calcd for C4H7N4 [M+H]+:
111.0665; found: 111.0663.
1H), 8.02 (dd, J = 8.4 and 2 Hz, 1H), 7.50–7.62 (m, 2H), 6.28 (dd, J = 15.6 and
1.7 Hz, 1H), 5.43 (dd, J = 8.8 and 1.7 Hz, 1H) ppm; 13C NMR (75 MHz, CDCl3) d:
163.0, 134.9, 133.4, 131.0, 129.6, 128.8, 126.8, 126.1, 109.1 ppm; Anal. Calcd
for C9H6Cl2N4: C, 44.84; H, 2.51; N, 23.24. Found: C, 44.96; H, 2.77; N, 23.35.
5-Benzyl-2-vinyl-2H-tetrazole (2i): Mobile phase: hexane/Et2O, 10:1. Yield:
53%; isolated as an oil; 1H NMR (300 MHz, CDCl3) d: 7.46 (dd, J = 15.7 and
8.8 Hz, 1H), 7.20–7.40 (m, 5H), 6.16 (dd, J = 15.7 and 1.5 Hz, 1H), 5.33 (dd,
J = 8.8 and 1.5 Hz, 1H), 4.28 (s, 2H) ppm; 13C NMR (75 MHz, CDCl3) d: 165.5,
136.3, 129.7, 128.8, 128.7, 126.9, 108.3, 31.8 ppm; HRMS (EI): m/z calcd for
C10H10N4 [M]+: 186.0905; found: 186.0904.
5-Undecyl-2-vinyl-2H-tetrazole (2j): Mobile phase: hexane/Et2O, 15:1. Yield: