Silicon-mediated direct conversion of acyl chlorides to carbamoyl azides or/and tetrazolinones under mild conditions

Article abstract of DOI:10.1246/cl.2011.1149

A simple and mild one-pot procedure for the synthesis of carbamoyl azides from acyl chlorides utilizing a combination of tetrachlorosilane and sodium azide in acetonitrile at ambient temperature is reported. Under gentle heating 1-aryltetrazolin-5- ones were also obtained in one-pot process presumably via a [3 + 2] cycloaddition step.

Full text of DOI:10.1246/cl.2011.1149

doi:10.1246/cl.2011.1149
Published on the web September 28, 2011
1149
Silicon-mediated Direct Conversion of Acyl Chlorides to Carbamoyl Azides
or/and Tetrazolinones under Mild Conditions
Tarek A. Salama,*1,³ Saad S. Elmorsy,1 Abdel-Galil M. Khalil,1 and Mohamed A. Ismail2
1Chemistry Department, Faculty of Science, Mansoura University, 35516-Mansoura, Egypt
2Chemistry Department, College of Science, King Faisal University, P. O. Box 380, Hofuf 31982, Saudi Arabia
(Received July 11, 2011; CL-110588; E-mail: mismail@mans.edu.eg)
O
A simple and mild one-pot procedure for the synthesis of
carbamoyl azides from acyl chlorides utilizing a combination of
tetrachlorosilane and sodium azide in acetonitrile at ambient
temperature is reported. Under gentle heating, 1-aryltetrazolin-5-
ones were also obtained in one-pot process presumably via a
[3 + 2] cycloaddition step.
N
N
NH
Ar
Ar
+
2a-f +
N
N
H
H
N
O
4; Ar = 2,4-Cl2C6H3-
Ar
3a-d
3a; Ar = Ph
3b; Ar = 4-ClC6H4-
3c; Ar = 4-MeC6H4-
3d; Ar = 4-PhC6H4-
Carbamoyl azides are useful organic compounds having
wide applications in organic synthesis as well as in industry.1
They are used as key intermediates for synthesis of various
heterocyclic2 and medicinally important compounds.3 The
conventional methods for the preparation of carbamoyl azides
generally includes addition of azide species such as hydrazoic
acids4 or triarylbismuth diazides5 to isocyanates, nitrosation of
semicarbazides,6 and oxidation of aldehydes with pyridinium
chlorochromate7 or iodobenzene dichloride8 in the presence of
sodium azide. Aldehydes have been converted into carbamoyl
azides by using iodine azide either under reflux9 or under
continuous flow reaction conditions in microreactors.10 Carba-
moyl azides can also be prepared from tertiary amines using
triphosgene and sodium azide,11 from primary amines and
carbon dioxide with tetramethylphenylguanidine and diphenyl-
phosphoryl azide,12 or from carboxylic acids by means of the
Vilsmeier salt prepared from phosgene and DMF13 or by adding
PPh3/NCS and then NaN3/Me3N¢HCl.14 On the other hand,
tetrazolinone derivatives have gained intense interest due to their
applications in medicine15 and agriculture.16 Isocyanates repre-
sent in many cases the precursors for many tetrazolone
derivatives through their reaction with an azide source.17
Silyl azides particularly, trimethylsilyl azide (TMSN3)18
react with some carboxylic acid chlorides,19 anhydrides,20 esters,
and lactones21 to provide a facile synthetic route to a variety of
isocyanates, which in some cases directly cyclize to heterocyclic
compounds. A combination of tetrachlorosilane (SiCl4) and
sodium azide have been used for the conversion of aldehydes to
the corresponding nitriles,22 or to acyl azides in the presence
of MnO2.23 Ketones,24 including ¡,¢-unsaturated ketones,25
¢-chloroketones,26 and carboxylic acid amides27 were converted
to the corresponding tetrazoles utilizing this combination.
As a part of investigation of reactivity and potentiality of
this in situ reagent which provides an expedient source of azide
and in conjunction with our interest in exploring the utility of in
situ reagents based on tetrachlorosilane (TCS)28 in organic
synthesis, we report herein a facile and mild procedure for the
synthesis of carbamoyl azides through the reaction of carboxylic
acid chlorides with the inexpensive and readily available
tetrachlorosilane-sodium azide at room temperature. When the
same mixtures were gently heated, 1-aryltetrazolin-5-ones were
obtained as major products.
1. SiCl4, NaN3
CH3CN, 70-80°C
2. aq. NaHCO3
H
N
1. SiCl4, NaN3
O
CH3CN, r.t.
N3
Ar
Ar
Cl
1a-f
2. aq. NaHCO3
O
2a-f
1a, 2a; Ar = Ph
1b, 2b; Ar = 4-ClC6H4-
1c, 2c; Ar = 4-MeC6H4-
1d, 2d; Ar = 4-PhC6H4-
1e, 2e; Ar = 2,4-Cl2C6H3-
1f, 2f; Ar = 4-MeC6H4-CH=CH-
Scheme 1. Reaction of acyl chlorides with SiCl4-NaN3.
Stirring a mixture of carboxylic acid chloride (1 equiv) with
a combination of SiCl4 (2 equiv) and NaN3 (6 equiv) in dry
acetonitrile at room temperature affords the corresponding
carbamoyl azides in good yields after simple aqueous work-up
(Scheme 1 and Table 1). Identification of the carbamoyl azides
was carried out by their spectroscopic analyses as well as by
comparing their properties to those reported. Beside the -CO-
stretching bands, each product exhibited new characteristic IR
signals at 3269-3380 and 2146-2192 cm¹1 for the -NH and -N3
groups respectively. To improve our procedure for a time-saving
reaction, we carried out the reaction under gentle heating. Thus,
stirring a mixture of benzoyl chloride with SiCl4-NaN3 in
acetonitrile at 70-80 °C gave 1-phenyltetrazolin-5-one as a
major product, in addition to the expected phenylcarbamoyl
azide. Monitoring the reaction with TLC showed a complete
disappearance of the starting material within 2 h. This result led
us to investigate the reactions under gentle heating as a one-pot
process to tetrazolinones. Thus, various carboxylic acid chlo-
rides were reacted with SiCl4-NaN3 at 70-80 °C to give the
respective carbamoyl azides as minor products as well as the
tetrazolinone derivatives as major products in most cases
(Scheme 1 and Table 1).
Chem. Lett. 2011, 40, 1149-1151
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

1150
The structure of tetrazolinone derivatives was assigned
fragment, by loss of 28 mass units, giving the appropriate phenyl
nitrenium ion [PhN]+(m/z 91).19
based on their spectral analyses as well as by matching their
melting points with reported literature.17 For example, com-
pounds 3a and 3b showed carbonyl stretching absorption in the
IR spectra at ¯/cm¹1 1713 and 1720 as well as the NH stretching
at 3279 and 3213, respectively. The 1H NMR spectra of
compound 3a revealed the presence of a broad singlet for NH
at ¤ 14.6. Furthermore, its mass spectrum displayed the m/z
162 peak corresponding in mass to the molecular ion (M+) of
compound 3a as the base peak. Fragmentation of the tetrazo-
linone ring gives an intense peak at m/z 119, which provides
evidence for cycloreversion29 with formation of [PhNCO]+
(probably including [PhN3]+). Both these later radical ions
The generality of the process was examined through
applying the reaction to various aromatic acid chlorides. The
reaction tolerated several functional groups on the aromatic ring,
including chlorine, methyl, and phenyl (Table 1). Sterically
hindered acid chlorides such as 2¤,4¤-dichlorobenzoyl chloride
as well as ¡,¢-unsaturated acid chlorides such as 4¤-methyl-
cinnamoyl chloride gave the corresponding carbamoyl azides
as major products either at room temperature or under heating
for prolonged time even when using an excess reagent
(Table 1, Entries 9-12). Unfortunately, the reaction failed with
aliphatic acid chlorides. For example, acetyl chloride hardly
gave a minute amount of dimethyl urea and no other distinct
products were observed under the reaction conditions (Entry 13,
Table 1).
Table 1. Reaction of acyl chlorides with SiCl4-NaN3 combi-
nation
A plausible pathway for the present reaction is depicted in
Scheme 2. It is likely that the carbamoyl azides 2 are formed at
room temperature via addition of two moles of the silicon azide
chloride A, which was generated as a major triazidochlorosilane
from the reaction of SiCl4 and NaN3 in a molar ratio 1:330 to the
carbonyl group of 1. The reaction involves the formation of the
gem-diazide C which undergoes a Schmidt type rearrangement31
giving 2 after an aqueous work-up. Under gentle heating, an
alternative pathway may operate; formation of the siloxy azide
intermediate B in a similar 1,2-addition step of one mole of A to
1. B gives carbonyl azide D, which undergoes a Curtius reaction
to form the intermediate isocyanate E. Subsequent addition
of a second mole of A to E gives 1-aryltetrazolin-5-one 3 or
carbamoyl azide 2 via [3 + 2] cycloaddition or 1,2-addition,
respectively after aqueous work-up. Isolation of diarylurea 4
(Entry 10) after aqueous work-up indicates the formation of aryl
isocyanate through the reaction pathway. Moreover, carbamoyl
azides have proved resistant to both Curtius rearrangement32 and
base-induced cyclization to tetrazole derivatives.33 On the basis
Temp
/°C
Time
/h
Yield
Entry
Substrate
Product
/%a
1
2
3
4
5
6
7
8
9
1a
1a
1b
1b
1c
r.t.
70-80
r.t.
70-80
r.t.
70-80
r.t.
70-80
r.t.
70-80
r.t.
70-80
r.t.
12
2
13
3
14
3
12
4
16
5
22
7
22
15
2a
2a, 3a
2b
2b, 3b
2c
2c, 3c
2d
2d, 3d
2e
2e, 4
2f
84
26, 72
77
31, 67
81
22, 75
78
24, 70
88
78, 19
63
1c
1d
1d
1e
1e
1f
10
11
12
1f
Acetyl
2f
67
13
®
®
chloride 70-80
aIsolated yield.
MeCN
r.t.
SiCl4 + 3 NaN3
Si(N3)nCl4-n [(Si(N3)3Cl]
49%
A
H
OSi(N3)2Cl
N
OH
aq. NaHCO3
(H2O)
- N2
N
OSi(N3)2Cl
N
O
Ar
A, r.t.
Ar
Ar
Ar
Ar
N3
N3
N3
N3
N3
2 mol
- Si(N3)2Cl2
2
O
C
Ar
Cl
OSi(N3)2Cl
1
A, r.t.
O
H
N
H
N3
Cl
1 mol
Ar
C
4
N Ar
2
- Si(N3)2Cl2
B
aq. NaHCO3
(H2O)
aq. NaHCO3
O
Si(N3)2Cl2
Ar
Ar
N C O
Ar
N
C
OSi(N3)Cl2
Ar
N3
Curtius
reaction
1,2-addition
N3
E
D
A
[3+2] cycloaddition
Ar
O
O
aq. NaHCO3
(H2O)
N
N
N
NH
N
N
N
N
Si(N3)2Cl
3
Scheme 2. Plausible mechanism for the formation of 2, 3, and 4.
© 2011 The Chemical Society of Japan
Chem. Lett. 2011, 40, 1149-1151
www.csj.jp/journals/chem-lett/

1151
26 T. A. Salama, S. S. Elmorsy, Chin. Chem. Lett. 2011, 22, 1171.
27 A.-A. S. El-Ahl, S. S. Elmorsy, A. H. Elbeheery, F. A. Amer,
Tetrahedron Lett. 1997, 38, 1257.
of these considerations, it seems that the cyclization of carba-
moyl azides to the terazolinone 3 is not a pluasible pathway.
In conclusion, we have developed a new practical and
efficient route to carbamoyl azides as well to 1-aryltetrazolinone
derivatives from acyl chlorides utilizing the cheap and readily
available tetrachlorosilane and sodium azide.34 The mild
reaction conditions, easy work-up procedure and simple oper-
ation are advantages of this procedure. Moreover, the present
method provides an additional application of the in situ
generated SiCl4/NaN3 which represents a safer substitute to
the volatile and highly toxic hydrazoic acid as well as to the
relatively expensive TMSN3.
28 a) T. A. Salama, Z. Novák, Tetrahedron Lett. 2011, 52, 4026. b) T. A.
Salama, A.-A. S. El-Ahl, S. S. Elmorsy, A.-G. M. Khalil, M. A.
Ismail, Tetrahedron Lett. 2009, 50, 5933. c) T. A. Salama, S. S.
Elmorsy, A.-G. M. Khalil, M. A. Ismail, Tetrahedron Lett. 2007, 48,
6199. d) T. A. Salama, S. S. Elmorsy, A.-G. M. Khalil, Tetrahedron
Lett. 2007, 48, 4395. e) T. A. Salama, S. S. Elmorsy, A.-G. M. Khalil,
M. M. Girges, A.-A. S. El-Ahl, Synth. Commun. 2007, 37, 1313.
f) S. S. Elmorsy, A. G. M. Khalil, M. M. Girges, T. A. Salama,
Tetrahedron Lett. 1997, 38, 1071. g) S. S. Elmorsy, A. G. M. Khalil,
M. M. Girges, T. A. Salama, J. Chem. Res., Synop. 1997, 232.
29 G. Denecker, G. Smets, G. L’abbé, Tetrahedron 1975, 31, 765.
30 R. Herges, F. Starck, J. Am. Chem. Soc. 1996, 118, 12752.
31 For a review: S. Lang, J. A. Murphy, Chem. Soc. Rev. 2006, 35, 146.
32 F. L. Scott, Chem. Ind. 1954, 959.
References and Notes
³
Present address: Department of Chemistry, Faculty of Education,
Amran University, Amran, Yemen (E-mail: tasalama@yahoo.com)
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34 Typical procedure for the synthesis of arylcarbamoyl azides or/and
1-aryltetrazolinones: To a mixture of acid chloride (5 mmol) and
NaN3 (30 mmol) in CH3CN (20 mL), SiCl4 (10 mmol) was added and
the reaction mixture was stirred at room temperature or under heating
at 60-70 °C. On completion (the reaction was monitored by TLC),
the mixture was quenched with cold NaHCO3 (aq), extracted with
CH3COOEt, dried over anhydrous MgSO4 and the solvent was
evaporated under vacuum and the residue was chromatographed using
petroleum ether-ethyl acetate (5:1) as the eluent system to give pure 2
or 2 and 3 or 4 respectively. Data for some representative examples
are listed below:
1
2
3
4
5
6
7
2,4-Dichlorophenylcarbamoyl azide (2e): mp 121 °C; IR (KBr):
¯ = 3269 (NH), 2920, 2851, 2192, 2148 (-N3), 1681 (C=O), 1527
8
9
X.-Q. Li, X.-F. Zhao, C. Zhang, Synthesis 2008, 2589.
L. Marinescu, J. Thinggaard, I. B. Thomsen, M. Bols, J. Org. Chem.
2003, 68, 9453.
(N-C=O), 1472, 1383, 1253, 1237, 1101, 1053, 974, 789, 732,
¹1
664 cm
;
1H NMR (300 MHz, CDCl3): ¤ 7.43 (s, 1H), 7.37 (d,
J = 8.9 Hz, 1H), 7.23 (d, J = 8.9 Hz, 1H), 6.81 (s, 1H, NH); 13C NMR
(75 MHz, CDCl3): ¤ 158.1, 136.7, 133.8, 133.3, 129.4, 129.1, 127.3;
Anal. Calcd for C7H4Cl2N4O (231.04): C, 36.39; H, 1.75; N, 24.25%.
Found: C, 36.18; H, 1.82; N, 24.13%.
10 J. C. Brandt, T. Wirth, Beilstein J. Org. Chem. 2009, 5, 30.
11 V. K. Gumaste, A. R. A. S. Deshmukh, Tetrahedron Lett. 2004, 45,
6571.
12 E. García-Egido, M. Fernández-Suárez, L. Muñoz, J. Org. Chem.
2008, 73, 2909.
2-(4-Methylphenyl)vinylcarbamoyl azide (2f): mp 154 °C; IR
(KBr): ¯ = 3380 (NH), 2933, 2149 (-N3), 1688 (C=O), 1606
13 H. Affandi, A. V. Bayquen, R. W. Read, Tetrahedron Lett. 1994, 35,
2729.
(C=C), 1511 (N-C=O), 1462, 1380, 1341, 1295, 1250, 1177,
1113, 1030, 830 cm
¹1
;
1H NMR (300 MHz, CDCl3): 7.72 (d, J =
14 P. Frøyen, Synth. Commun. 1996, 26, 4549.
15 F. Janssens, J. Torremans, P. A. J. Janssen, J. Med. Chem. 1986, 29,
2290.
15.8 Hz, 1H), 7.43 (d, J = 8.1 Hz, 2H), 7.20 (d, J = 8.1 Hz, 2H), 6.95
(s, 1H), 6.38 (d, J = 15.8 Hz, 1H), 2.35 (s, 3H); 13C NMR (75 MHz,
CDCl3): ¤ 157.1, 146.7, 141.8, 131.1, 129.8, 128.6, 116.3, 22.1; Anal.
Calcd for C10H10N4O (202.21): C, 59.40; H, 4.98; N, 27.71%. Found:
C, 59.61; H, 5.13; N, 27.58%.
16 a) T. Goto, H. Hayakawa, Y. Watanabe, A. Yanaji, Eur. Pat. Appl. EP
572,855, 1994; T. Goto, H. Hayakawa, Y. Watanabe, A. Yanaji, Chem.
Abstr. 1994, 120, 164200n. b) K. Morimoto, M. Onari, H. Furusawa,
T. Teraji, K. Nishio, T. Nawamaki, K. Ishikawa, K. Nakahira, Jpn.
Kokai Tokkyo Koho 97,100,277, 1997; K. Morimoto, M. Onari, H.
Furusawa, T. Teraji, K. Nishio, T. Nawamaki, K. Ishikawa, K.
Nakahira, Chem. Abstr. 1997, 127, 17678r. c) T. Osumi, T. Hirose, M.
Hashizume, R. Matsunaga, Jpn. Kokai Tokkyo Koho 97,208,565,
1997; T. Osumi, T. Hirose, M. Hashizume, R. Matsunaga, Chem.
Abstr. 1997, 127, 234324b.
1-Phenyl-2-tetrazolin-5-one (3a): mp 189-190 °C (lit.17c mp 192-
193 °C); Rf = 0.68, petroleum ether (60-80 °C)-ethyl acetate: 3/1; IR
(KBr plate): ¯ = 3279 (NH), 1713 (C=O), 1605 (C=C), 1499, 1387,
¹1
1349, 1294, 1238, 1056, 969, 754, 687, 653 cm
.
1H NMR (300
MHz, DMSO-d6): ¤ 14.6 (br, 1H, NH), 7.86 (d, J = 8 Hz, 2H), 7.55
(m, 2H), 7.44 (m, 1H); MS (m/z, %): 162 (M+, 100), 163 (M+ + 1,
22), 119 (M+ ¹ HN3 or HNCO, 81), 91 (37), 77 (32).
1-(4-Methylphenyl)-2-tetrazolin-5-one (3c): mp 183-185 °C (lit.17b
mp 183.5-184.5 °C); Rf = 0.67, petroleum ether (60-80 °C)-ethyl
acetate: 3/1; IR (KBr plate): ¯ = 3198 (NH), 2920, 1706 (C=O),
17 a) J. Holt, A. Fiksdahl, J. Heterocycl. Chem. 2007, 44, 375. b) J. P.
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3076. c) O. Tsuge, S. Urano, K. Oe, J. Org. Chem. 1980, 45, 5130.
18 M. Jafarzadeh, Synlett 2007, 2144.
1605 (C=C), 1549, 1512, 1371, 1310, 1208, 1125, 1078, 920, 813,
¹1
738 cm
;
1H NMR (300 MHz, DMSO-d6): ¤ 8.50 (s, 1H), 7.33
19 M. Toselli, P. Zanirato, J. Chem. Soc., Perkin Trans. 1 1992, 1101.
20 a) J. D. Warren, J. H. MacMillan, S. S. Washburne, J. Org. Chem.
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21 H. R. Kricheldorf, Chem. Ber. 1973, 106, 3765.
22 S. S. Elmorsy, A.-A. S. El-Ahl, H. Soliman, F. A. Amer, Tetrahedron
Lett. 1995, 36, 2639.
(d, J = 8.4 Hz, 2H), 7.06 (d, J = 8.4 Hz, 2H), 2.24 (s, 3H); MS (m/z,
%): 176 (M+, 17), 133 (M+ ¹ HN3 or HNCO, 100), 106 (21), 104
(61), 91 (23), 78 (26).
1-(4-Biphenylyl)-2-tetrazolin-5-one (3d): mp 203-205 °C; Rf =
0.45, petroleum ether (60-80 °C)-ethyl acetate: 3/1; IR (KBr plate):
¯ = 3269 (NH), 1647 (C=O), 1600 (C=C), 1532 (N-C=O), 1492,
¹1
1398, 1325, 1283, 1089, 1013, 824, 754, 653 cm
.
1H NMR (300
23 S. S. Elmorsy, Tetrahedron Lett. 1995, 36, 1341.
24 A.-A. S. El-Ahl, S. S. Elmorsy, H. Soliman, F. A. Amer, Tetrahedron
Lett. 1995, 36, 7337.
25 T. A. Salama, A.-A. S. El-Ahl, A.-G. M. Khalil, M. M. Girges, B.
Lackner, C. Steindl, S. S. Elmorsy, Monatsh. Chem. 2003, 134, 1241.
MHz, DMSO-d6): ¤ 10.49 (s, 1H), 7.98 (d, J = 8.4 Hz, 2H), 7.81 (d,
J = 8.4 Hz, 2H), 7.62 (m, 2H), 7.42 (m, 3H); 13C NMR (75 MHz,
CDCl3): ¤ 164.51, 137.95, 136.56, 133.36, 129.66, 128.57, 128.51,
127.42, 121.88; Anal. Calcd for C13H10N4O (238.24): C, 65.54; H,
4.23; N, 23.52%. Found: C, 65.24; H, 4.58; N, 23.89%.
Chem. Lett. 2011, 40, 1149-1151
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/