Iodobenzene dichloride in combination with sodium azide for the effective synthesis of carbamoyl azides from aldehydes

Article abstract of DOI:10.1055/s-2008-1067196

Various aliphatic and aromatic aldehydes are converted into their corresponding carbamoyl azides in good to excellent yields with the use of a combined reagent system of iodobenzene dichloride and sodium azide in acetonitrile under nitrogen. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1067196

PAPER
2589
Iodobenzene Dichloride in Combination with Sodium Azide for the Effective
Synthesis of Carbamoyl Azides from Aldehydes
Carbamoyl
A
zide
s
i
from
A
a
ldehydes
U
o
sing PhICl
-
2-NaN3 Qiang Li, Xue-Fei Zhao, Chi Zhang*
The State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, P. R. of China
Fax +86(22)23499247; E-mail: zhangchi@nankai.edu.cn
Received 31 March 2008; revised 15 May 2008
of hypervalent iodine(III) reagent together with trimethyl-
Abstract: Various aliphatic and aromatic aldehydes are converted
into their corresponding carbamoyl azides in good to excellent
yields with the use of a combined reagent system of iodobenzene
dichloride and sodium azide in acetonitrile under nitrogen.
silyl azide, PhI(OAc)2-TMSN3.17 Chen et al. disclosed a
convenient procedure to convert aromatic aldehydes into
aroyl azides using a combined reagent of PhI(OAc)2-
NaN3. However, the reaction does not work on aliphatic
aldehydes.18 Bose et al. introduced another combined re-
agent of Dess–Martin periodinane and sodium azide to en-
able the conversion of aldehydes into acyl azides.19
Key words: aldehydes, carbamoyl azides, hypervalent iodine,
iodobenzene dichloride, oxidations
We have reported that iodobenzene dichloride (PhICl2)
can efficiently oxidize alcohols to their corresponding
carbonyl compounds with TEMPO as a catalyst together
with two very convenient as well as high yielding proce-
dures for the preparation of iodoarene dichlorides from io-
doarenes.20 As part of our ongoing program on
exploration of new reactivity of iodobenzene dichloride
which is the first reported hypervalent iodine reagent by
Willgerodt in 1886,21 we present herein a new, efficient,
and practical method for the conversion of aliphatic or ar-
omatic aldehydes into their corresponding carbamoyl
azides by using iodobenzene dichloride and sodium azide
in MeCN.
Carbamoyl azides are valuable synthetic intermediates in
organic synthesis.1 For example, N-alkylcarbamoyl azides
decompose readily to produce alkylamines under cold al-
kali conditions.2 And, carbamoyl azides react with prima-
ry amines to form urea derivatives.2,3 They also can be
converted into urethanes on refluxing with ethanol.4 Car-
bamoyl azides are usually synthesized from acyl azides,
which are generally prepared by the reaction of acid deriv-
atives with trimethylsilyl azide or sodium azide.5 More-
over, there have been a number of reports on direct
conversion of carboxylic acids into acyl azides mediated
by various acid activators such as phenyldichlorophos-
phate,6 ethyl chloroformate,7 SOCl2-DMF,8 NCS/PPh3,9
diphenylphosphoryl azide,10 triphosgene,11 and cyanuric
chloride.12 The pathway from acyl azides to carbamoyl
azides is well established, that is, the transformation of
acyl azides into isocyanates upon heating via a Curtius re-
arrangement and subsequent addition of hydrazoic acid
onto isocyanates to give carbamoyl azides (Scheme 1).2,5a
As depicted in Schemes 2, 2-phenylpropanal was convert-
ed into the corresponding carbamoyl azide, (1-phenyleth-
yl)carbamoyl azide, in an excellent yield.22
PhICl2 (2 equiv)
NaN3 (4 equiv)
O
MeCN (10 mL)
CHO
N
H
N3
O
O
0 °C (2 h)
HN3
heat
– N2
80 °C (8 h), N2
R
N C O
R
N3
R
N
N3
91%
H
acyl azides
carbamoyl azides
Scheme 2 Reaction of 2-phenylpropanal with PhICl2–NaN3
Scheme 1 Classical route for the preparation of carbamoyl azides
To test the generality and scope of this method, a variety
of aldehydes were tried and the results are summarized in
Table 1. Like 2-phenylpropanal, 3-phenylpropanal having
an isolated phenyl ring was also converted into its corre-
sponding carbamoyl azide in 97% yield (Table 1, entry 2).
Aliphatic linear aldehydes were excellent substrates under
the standard conditions (entries 3–6). Notably, n-butylcar-
bamoyl azide from the azidonation of pentanal (entry
6) was a key intermediate in the synthesis of an antidiabet-
ic drug, 1-butyl-3-p-tolylsulfonylurea.23 Aldehydes with
bulky groups such as cyclohexanecarboxaldehyde and
pivalaldehyde were also smoothly converted into their
corresponding carbamoyl azides in 99 and 89% yield, re-
spectively (entries 7 and 8). Moreover, various functional
Alternatively, the preparation of acyl azides can be ac-
complished from aldehydes by either chromic anhydride/
trimethylsilyl azide (CrO3/TMSN3)13 or triazidochlorosi-
lane-active manganese dioxide (SiCl4/NaN3-MnO2).14 In
addition, an efficient radical azidonation of aldehydes to
afford carbamoyl azides has been developed using iodine
azide as the source of azidyl radical.15 There are also a
couple of reports on the same transformation using either
polystyrene supported diazidoiodate16 or the combination
SYNTHESIS 2008, No. 16, pp 2589–2593
x
x.
x
x
.
2
0
0
8
Advanced online publication: 24.07.2008
DOI: 10.1055/s-2008-1067196; Art ID: F07908SS
© Georg Thieme Verlag Stuttgart · New York

2590
X.-Q. Li et al.
PAPER
Table 1 Screened Aldehydesa
Entry
1
Aldehydes
Products
Yield (%)b
91
O
CHO
N
H
N3
H
N
CHO
N3
2
97
O
H
N
N3
3
4
5
6
96
97
94
91
CHO
O
H
N
N3
CHO
O
H
N
N3
CHO
O
H
N
N3
CHO
O
H
N
CHO
N3
7c
99
O
H
N
8d
9e
89
72f
86
92
N3
CHO
O
H
Cl
N
N3
Cl
O
O
H
10e
11e
MeO
AcO
N
N3
MeO
AcO
O
O
O
H
N
N3
O
H
N
CHO
N3
12g
73
O
H
N
CHO
N3
13 g
14 g
53h
55i
O
Me
Me
H
N
MeO
CHO
MeO
N3
O
a Reaction conditions: aldehyde (1 mmol), PhICl2 (2 equiv), and NaN3 (4 equiv) in anhyd MeCN (10 mL) under N2; the reaction was run first
at 0 °C for 2 h and then followed by an additional stirring for 8 h at 80 °C.
b Isolated yields.
c The reaction was carried out first at 0 °C for 3 h and then followed by an additional stirring for 8 h at 80 °C.
d The reaction was carried out first at 0 °C for 4 h and then followed by an additional stirring for 8 h at 80 °C.
e The reaction was carried out first at 0 °C for 12 h and then followed by an additional stirring for 12 h at 80 °C.
f The conversion of starting chloroaldehyde was 81%.
g Reaction conditions: aromatic aldehyde (1 mmol), PhICl2 (3 equiv), and NaN3 (6 equiv) in anhyd MeCN (10 mL) under N2; the reaction was
performed first at 15 °C for 8 h and then followed by an additional stirring for 8 h at 80 °C.
h The conversion of 4-methylbenzaldehyde was 70%.
i The conversion of 3-methoxybenzaldehyde was 71%.
Synthesis 2008, No. 16, 2589–2593 © Thieme Stuttgart · New York

PAPER
Carbamoyl Azides from Aldehydes Using PhICl2-NaN3
2591
PhICl2
+
2 NaN3
PhI(N3)2
+
+
2 NaCl
groups such as chloro, ether, and acetate groups were well
tolerated under our conditions, affording the desired prod-
ucts in good to excellent yields (entries 9–11). Benzalde-
hyde was transformed to phenylcarbamoyl azide in 73%
yield with an increased amount of iodobenzene dichloride
(3 equiv) and sodium azide (6 equiv) compared with the
standard conditions (entry 12). Two more aromatic alde-
hydes such as 4-methylbenzaldehyde and 3-methoxy-
benzaldehyde were tried and the yields of the
corresponding carbamoyl azides were only moderate (en-
try 13 and 14).
•
•
PhI(N3)2
N3
PhIHN3
O
O
N3•
+
HN3
+
+
RCH
RC •
O
O
RC •
Ph•IHN3
PhI
+
RCN3
O
R
N
HN3
heat
O
C
RCN3
R
N
N3
O
H
Considering the mechanism of two PhI(OAc)2-related re-
action systems which effect the azidonation of aldehydes,
Scheme 3 Proposed mechanism
17
PhI(OAc)2-TMSN3 and PhI(OAc)2-NaN3,18 we hypothe-
sized that a key intermediate involved in these two sys-
tems, that is, bis(azido)iodobenzene [PhI(N3)2]24 might
still play a crucial role also in the present PhICl2-NaN3
system. PhI(N3)2 was believed to be formed by ligand ex-
change between PhICl2 and NaN3. This was supported by
NaN3 system to be an attractive route for the synthesis of
carbamoyl azides.
NaN3 was purchased from commercial suppliers. PhICl2 was pre-
the experimental observation that the yellowish color of pared according to method developed in our laboratory.20 MeCN
1
was distilled from anhyd CaH2 and degassed before use. The H
PhICl2 disappeared and white solids deposited after NaN3
NMR spectra were recorded at 400 MHz and 13C NMR spectra were
was added to the reaction flask containing a suspension of
measured at 100 MHz, using CDCl3 as the solvent. HRMS were
PhICl2 and an aldehyde in acetonitrile for about half an
measured at a Fourier Transform Ion Cyclotron Resonance mass
spectrometry (Ionspec 7.0T). IR spectra were recorded on a FT-IR
hour. Then azidyl radicals were formed from the decom-
position of bis(azido)iodobenzene. This is followed by
two radical steps giving the acyl azide as the key interme-
diate with the homolytic rupture of the aldehydic C–H
bond as the rate-limiting step (Scheme 3). Experimental
observations supported such an idea because aliphatic al-
dehydes were transformed to the corresponding acyl
azides completely at 0 °C while aromatic aldehydes could
not be converted into the corresponding acyl azides com-
pletely at 15 °C. The lower reaction efficiency for aromat-
ic aldehydes compared with the aliphatic aldehydes could
be interpreted by the much higher heats of formation of
aryl-substituted acyl radicals than that of alkyl-substituted
acyl radicals.25 Accordingly, in order to get a good yield
of phenylcarbamoyl azide from benzaldehyde in a reason-
ably short time period, 3 equivalents of PhICl2 and 6
equivalents of NaN3 and a temperature of 15 °C at the
stage of formation of acyl azide were required. Experi-
mentally, addition of 20 mol% of 2,2,6,6-tetramethylpip-
spectrometer in KBr pellets and only major peaks were reported in
cm–1. Elementary analysis was carried out by an elemental vario EL
analyzer.
Caution! Though no explosion took place in our laboratory during
our investigation of aldehyde azidonation by means of PhICl2-NaN3
system, azido compounds are hazardous and may explode when
heated. A safety shield, gloves, and eye-protection are highly rec-
ommended.
Carbamoyl Azides from Aldehydes; General Procedure
To a solution of the respective aldehyde (1 mmol) in anhyd MeCN
(10 ml) in a two-necked 25 mL rounded-bottomed flask was added
PhICl2 (550 mg, 2 mmol) and NaN3 (260 mg, 4 mmol) under N2 at
r.t. The reaction flask was immersed into an ice-water bath immedi-
ately and the reaction was allowed to run for 2 h. Subsequently, the
reaction flask was kept in an oil bath at 80 °C and stirred for 8 h. The
mixture was cooled to r.t. and diluted with EtOAc (50 mL). The re-
sulting mixture was washed with sat. aq Na2S2O3 (10 mL). The sep-
arated aqueous phase was extracted with EtOAc (20 mL). The
combined organic layers were washed with brine (10 mL), dried
(Na2SO4), and concentrated in vacuo to afford the crude product.
Purification by flash column chromatography [petroleum ether (bp
60–90 °C)–EtOAc, 9:1] afforded the corresponding carbamoyl
azide (Table 1). The known compounds were identified by compar-
eridin-1-yloxy (TEMPO),
a
widely used radical
scavenger, inhibited the reaction dramatically with the
yield of nonyl carbamoyl azide being 39% compared with
96% in the absence of TEMPO (Table 1, entry 3), which
indicated that a radical pathway was involved. The pro-
posed mechanism is depicted in Scheme 3.
1
ison to their literature melting points, H and 13C NMR data. The
new compounds were confirmed by IR (KBr), 1H and 13C NMR to-
gether with elementary analyses or HRMS (ESI) data.
In summary, iodobenzene dichloride, the first reported
hypervalent iodine reagent, was found to be capable of
converting aldehydes into their corresponding carbamoyl
azides in excellent yields together with sodium azide. Io-
dobenzene dichloride can be prepared in a quantitative
yield in five minutes by treating iodobenzene with sodium
hypochlorite in a dilute hydrochloric acid solution at room
temperature.20 The readily availability of iodobenzene
dichloride as well as the low cost of sodium azide com-
pared to that of TMSN3 make the present effective PhICl2-
1-Phenylethylcarbamoyl Azide (Table 1, Entry 1)9b
White solid; mp 86–87 °C.
1H NMR (400 MHz, CDCl3): d = 7.29–7.33 (m, 5 H), 6.01 (br s, 1
H), 4.92–4.95 (m, 1 H), 1.48 (d, J = 6.8 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 155.59, 142.32, 128.52, 127.40,
125.81, 50.64, 21.69.
2-Phenylethylcarbamoyl Azide (Table 1, Entry 2)15
White solid; mp 85–87 °C.
Synthesis 2008, No. 16, 2589–2593 © Thieme Stuttgart · New York

2592
X.-Q. Li et al.
PAPER
1H NMR (400 MHz, CDCl3): d = 7.19–7.35 (m, 5 H), 5.09 (br s, 1
H), 3.50 (q, J = 6.6 Hz, 2 H), 2.84 (t, J = 6.9 Hz, 2 H).
(9-Chlorononyl)carbamoyl Azide (Table 1, Entry 9)
White solid; mp 47–49 °C.
13C NMR (100 MHz, CDCl3): d = 156.26, 138.01, 128.40, 128.34,
IR (KBr): 3334, 2923, 2825, 2171, 2132, 1674, 1519, 1222 cm–1.
126.34, 42.00, 35.29.
1H NMR (400 MHz, CDCl3): d = 5.06 (br s, 1 H), 3.54 (t, J = 6.6
Hz, 2 H), 3.20 (q, J = 6.2 Hz, 2 H), 1.73–1.80 (m, 2 H), 1.49–1.53
(m, 2 H), 1.40–1.44 (m, 2 H), 1.30 (br s, 8 H).
13C NMR (100 MHz, CDCl3): d = 156.30, 45.05, 41.07, 32.55,
29.49, 29.23, 29.01, 28.71, 26.76, 26.57.
HRMS (ESI): m/z calcd for C10H19ClN4O + Na (M + Na+):
269.1140; found: 269.1137.
Nonylcarbamoyl Azide (Table 1, Entry 3)15
Colorless oil.
1H NMR (400 MHz, CDCl3): d = 5.12 (br s, 1 H), 3.23 (q, J = 6.8
Hz, 2 H), 1.49–1.52 (m, 2 H), 1.26–1.28 (m, 12 H), 0.88 (t, J = 6.8
Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 156.34, 40.97, 31.64, 29.29,
29.04, 26.53, 22.44, 13.81.
(9-Methoxynonyl)carbamoyl Azide (Table 1, Entry 10)
White solid; mp 34–36 °C.
Heptylcarbamoyl Azide (Table 1, Entry 4)15
IR (KBr): 3309, 2933, 2857, 2136, 1687, 1550, 1257, 1124, 937,
649 cm–1.
1H NMR (400 MHz, CDCl3): d = 5.18 (br s, 1 H), 3.36 (t, J = 6.6
Hz, 2 H), 3.33 (s, 3 H), 3.21 (q, J = 6.7 Hz, 2 H) 1.54–1.57 (m, 2 H),
1.49–1.52 (m, 2 H), 1.29 (br s, 10 H).
13C NMR (100 MHz, CDCl3): d = 156.23, 72.68, 58.19, 40.93,
29.35, 29.30, 29.20, 29.15, 28.92, 26.47, 25.86.
Colorless oil.
1H NMR (400 MHz, CDCl3): d = 5.87 (br s, 1 H), 3.14 (q, J = 6.7
Hz, 2 H), 1.43–1.46 (m, J = 6.7 Hz, 2 H), 1.20–1.22 (m, 8 H), 0.80
(t, J = 6.6 Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 156.35, 40.94, 31.48, 29.26,
28.68, 26.45, 22.33, 13.76.
HRMS (ESI): m/z calcd for C11H23N4O2 (M + H+): 243.1816; found:
243.1821.
Hexylcarbamoyl Azide (Table 1, Entry 5)
Colorless oil.
IR (KBr): 3305, 2927, 2140, 1693, 1234 cm–1.
1H NMR (400 MHz, CDCl3): d = 5.14 (br s, 1 H), 3.15 (q, J = 6.8
Hz, 2 H), 1.40–1.46 (m, 2 H), 1.22–1.26 (m, 6 H), 0.88 (t, J = 6.7
Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 156.33, 41.11, 31.33, 29.45,
26.30, 22.46, 13.92.
9-(Azidocarbonylamino)nonyl Acetate (Table 1, Entry 11)
White solid; mp 31–33 °C.
IR (KBr): 3316, 2915, 2177, 2142, 1727, 1683, 1544, 1043, 682
cm–1.
1H NMR (400 MHz, CDCl3): d = 5.09 (br s, 1 H), 4.05 (t, J = 6.7
Hz, 2 H), 3.22 (q, J = 6.7 Hz, 2 H), 2.05 (s, 3 H) 1.58–1.62 (m, 2 H),
1.49–1.53 (m, 2 H), 1.30 (br s, 10 H).
13C NMR (100 MHz, CDCl3): d = 170.96, 156.14, 64.28, 40.82,
29.16, 29.03, 28.80, 28.27, 26.35, 25.55, 20.61.
HRMS (ESI): m/z calcd for C12H23N4O3 (M + H+): 271.1764; found:
271.1765; m/z calcd for C12H22N4O3 + Na (M + Na+): 293.1584;
found: 293.1578.
MS (EI): m/z (%) = 170.0 (M+, 5), 128.0 (48), 99.0 (100), 71.0 (37),
43.0 (99), 29.0 (61).
Anal. Calcd for C7H14N4O: C, 49.39; H, 8.29; N, 32.92. Found: C,
49.22; H, 8.18; N, 32.78.
Butylcarbamoyl Azide (Table 1, Entry 6)22
Colorless oil.
IR (KBr): 3313, 2960, 2152, 1689, 1535, 1232 cm–1.
Phenylcarbamoyl Azide (Table 1, Entry 12)15
White solid; mp 106–107 °C.
1H NMR (400 MHz, CDCl3): d = 7.43–7.45 (m, 2 H), 7.32–7.36 (m,
2 H), 7.12–7.16 (m, 1 H), 6.82 (br s, 1 H).
13C NMR (100 MHz, CDCl3): d = 154.12, 136.81, 129.01, 124.54,
119.31.
1H NMR (400 MHz, CDCl3): d = 5.12 (br s, 1 H), 3.25 (q, J = 6.8
Hz, 2 H), 1.46–1.54 (m, 2 H), 1.30–1.40 (m, 2 H), 0.92 (t, J = 7.3
Hz, 3 H).
13C NMR (100 MHz, CDCl3): d = 156.37, 40.55, 31.20, 19.56,
13.29.
MS (EI): m/z = 142.0 (M+, 48), 100.0 (100), 71.0 (99), 57.0 (98),
27.0 (99).
4-Methylphenylcarbamoyl Azide (Table 1, Entry 13)15
White solid; mp 131–133 °C.
1H NMR (400 MHz, CDCl3): d = 7.31 (d, J = 8.4 Hz, 2 H), 7.13 (d,
J = 8.4 Hz, 2 H), 6.78 (br s, 1 H), 2.32 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 153.98, 134.30, 129.58, 119.40,
20.75.
Cyclohexylcarbamoyl Azide (Table 1, Entry 7)15
White solid; mp 105–106 °C.
1H NMR (400 MHz, CDCl3): d = 4.87 (br s, 1 H), 3.51–3.53 (m, 1
H), 1.84–1.88 (m, 2 H), 1.62–1.66 (m, 2 H), 1.53–1.57 (m, 2 H),
1.18–1.33 (m, 2 H), 1.07–1.10 (m, 2 H).
13C NMR (100 MHz, CDCl3): d = 155.37, 50.06, 32.90, 25.28,
24.61.
3-Methoxyphenylcarbamoyl Azide (Table 1, Entry 14)26
White solid; mp 95–96 °C.
1H NMR (400 MHz, CDCl3): d = 7.26–7.16 (m, 2 H), 6.91–6.89 (m,
tert-Butylcarbamoyl Azide (Table 1, Entry 8)15
Colorless oil.
1H NMR (400 MHz, CDCl3): d = 4.94 (br s, 1 H), 1.28 (s, 9 H).
13C NMR (100 MHz, CDCl3): d = 154.69, 51.56, 28.49.
1 H), 6.82 (br s, 1 H), 6.70–6.66 (m, 1 H), 3.80 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 160.19, 154.09, 138.07, 129.76,
111.55, 110.30, 105.25, 55.22.
Synthesis 2008, No. 16, 2589–2593 © Thieme Stuttgart · New York

PAPER
Carbamoyl Azides from Aldehydes Using PhICl2-NaN3
2593
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Acknowledgment
This work was financially supported by The National Natural
Science Foundation of China (No. 20572046 and No. 20421202),
the 111 Project (B06005), and the Ministry of Education of China.
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2.4 equiv of NaN3, the yield of hexylcarbamoyl azide
decreased to 75%, which was 19% lower than that with 2.0
equiv of PhICl2 and 4.0 equiv of NaN3 under the otherwise
same reaction conditions (Table 1, entry 5). Thus, in order to
obtain the excellent outcome within the shorter time period
and taking into account that both PhICl2 and NaN3 are
readily available and cost-effective, 2 equiv of PhICl2 and 4
equiv of NaN3 were used in the subsequent work.
(23) Bauer, V. J.; Fanshawe, W. J.; Safir, S. D. R. J. Org. Chem.
1966, 31, 3440.
(24) For the preparation and reactivity of PhI(N3)2, see:
(a) Fontana, F.; Minisci, F.; Yan, Y. M.; Zhao, L.
Tetrahedron Lett. 1993, 34, 2517. (b) Magnus, P.; Lacour,
J.; Weber, W. J. Am. Chem. Soc. 1993, 115, 9347. (c) Kita,
Y.; Tohma, H.; Mitoh, S.; Fujita, S.; Gyoten, M. Synlett
1994, 427.
(25) Chatgilialoglu, C.; Crich, D.; Komatsu, M.; Ryu, I. Chem.
Rev. 1999, 99, 1991.
(26) Swett, L. R.; Ratajczyk, J. D.; Darby, T. D. US Patent
3424844, 1967; Chem. Abstr. 1969, 71, 12793.
Synthesis 2008, No. 16, 2589–2593 © Thieme Stuttgart · New York