Chemoselective reduction of azides catalyzed by molybdenum xanthate by using phenylsilane as the hydride source

Article abstract of DOI:10.1016/j.tet.2009.10.093

A chemoselective, neutral, and efficient strategy for the reduction of azides to corresponding amines catalyzed by dioxobis(N,N,-diethyldithiocarbamato) molybdenum complex (1, MoO₂[S₂CNEt₂]₂) in the presence of phenylsilane is discovered. This chemoselective reduction strategy tolerates a variety of reducible functional groups.

Full text of DOI:10.1016/j.tet.2009.10.093

Tetrahedron 66 (2010) 329–333
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Tetrahedron
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Chemoselective reduction of azides catalyzed by molybdenum xanthate
by using phenylsilane as the hydride source
*
Mahagundappa R. Maddani, Saravana K. Moorthy, Kandikere R. Prabhu
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 August 2009
Received in revised form 26 October 2009
Accepted 27 October 2009
Available online 29 October 2009
A chemoselective, neutral, and efficient strategy for the reduction of azides to corresponding amines
catalyzed by dioxobis(N,N,-diethyldithiocarbamato) molybdenum complex (1, MoO2[S2CNEt2]2) in the
presence of phenylsilane is discovered. This chemoselective reduction strategy tolerates a variety of
reducible functional groups.
Ó 2009 Elsevier Ltd. All rights reserved.
Dedicated to Professor S. Chandrasekaran
on the occasion of his 64th birthday
Keywords:
Catalytic reduction
Chemoselectivity
Amines
Molybdenum
Silanes
1. Introduction
ketones,8 hydroaminomethylation of olefins9 and reduction of
amides.10 However, most of these methods suffer from limitations
Transition metal complexes with metal–oxygen multiple bonds
are well known catalysts for oxidation and oxo-transfer reactions.1
These classes of metal complexes are known for their unique redox
capabilities. However, their utility in organic transformations,
particularly in reductions of organic functional groups is rare.1,2
Additionally, several traditional metal catalysts, which are capable
of exhibiting redox reactions are sensitive to air and moisture.
Functional group incompatibility is another major drawback, which
limits the utility of such reagents.1a,3 Therefore, there is a necessity
to develop synthetically useful metal complexes for such catalytic
reactions.1
Amines are very important class of compounds, which are useful
in chemistry and biology.4,5 Their utility includes the synthesis of
a variety of natural products, pharmaceutical intermediates, and
medicinally important compounds.4a,5 Therefore, there is
a plethora of methods available for the synthesis of amines.6 Gen-
erally, amines are synthesized by reacting halides or alcohols with
ammonia under high pressure and elevated temperature.7 Amines
are also prepared by reductive aminations of aldehydes and
of requiring high temperature and pressure, using stoichiometric
amount of reagents and most importantly poor selectivity in the
presence of several other functional groups.11 Additionally, the se-
lective synthesis of terminal amines presents more challenges due
to their high reactivity.12 As aliphatic azides are synthesized easily
from their halides and sulfonates,13 the reduction of azides14 to the
corresponding amines14c,7,15 is one of the synthetically convenient
and attractive method. Unlike earlier, the ease of synthesizing ar-
omatic azides from aromatic bromides or iodides in a Cu-coupled
reaction with sodium azide under mild conditions makes the re-
duction protocols of azides to amines more attractive.16 Although,
there are several reagents available for this transformation such as
LAH, NaBH4, Na2S, Lindlar catalyst, etc.,17 their success varies from
substrate to subatrate.11b,18
Recently, we have demonstrated the utility of molybdenum
diethyl dithiocarbamate (MoO2(S2CNEt2)2,19 1) in organic trans-
formations.20 In continuation of our investigation, we initiated
a research program to utilize these metal complexes in organic
transformations, particularly in catalytic amounts. Herein, we re-
port successful reduction of several organic azides to the corre-
sponding amines by using catalytic amount of 1 in the presence of
phenylsilane under neutral reaction conditions. The present re-
action represents striking reversal of redox properties of Mo(VI)
* Corresponding author. Tel.: þ91 80 2360 2887; fax: þ91 80 2360 0529.
E-mail address: prabhu@orgchem.iisc.ernet.in (K.R. Prabhu).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.10.093

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M.R. Maddani et al. / Tetrahedron 66 (2010) 329–333
Table 2
complexes, which are involved in oxidation reaction. At this stage, it
is worth noting that the selective synthesis of amines is cumber-
some considering their high reactivity with several functional
groups like halides, aldehydes, ketones, etc.21 Quite interestingly,
the present reduction is very selective and tolerates a wide variety
of functional groups as presented in the following section.
Molybdenum catalyzed synthesis of primary aromatic amines
MoO2(S2CNEt2)2 (1, 10 mol%)
Ar-N3
PhSiH3
Ar-NH2
+
Toluene, 100 °C
Entry
Substrate
Timea
(h)
Products
Yieldsb,c
(%)
N3
NH2
2. Results and discussion
R
R
It is recently documented that the addition of Si–H bond to
1
2
3
4
R¼OCH3
R¼CI
2
3
4
5
5
3
3
3
2a
3a
4a
5a
78
84
83
89
metal carrying a ligand
hydride.22 Quite interestingly, this process of adding Si–H bond to
metal–ligand -bond converts strongly oxidizing M]O complex to
p-bond results in the production of metal
R¼CN
R¼NO2
p
silyloxy substituted metal hydride, which could potentially be
employed as a reductant. This concept has been employed in
hydrosilylation of aldehydes by using rhenium (V) dioxo complex
with silane to produce the corresponding trialkylsilyl ethers. In-
spired by this pioneering work, we became interested in applying
the similar concept to investigate the reactivities of Mo(VI) under
similar reaction conditions.23
O
O
5
6
6
7
4
3
6a 87
7a 88
N3
NH2
O
O
O
O
N3
N3
NH2
NH2
We initiated the present study by employing molybdenum
xanthate 1 as the catalyst, which is inexpensive, and easily syn-
thesized.19 In the preliminary experiments to screen the hydride
source, several silane derivatives as well as molecular hydrogen
have been tested (Table 1). After several experimental trials, it was
found that phenylsilane is the most suitable hydride source to re-
duce organic azide.24 Hence p-methoxyphenyl azide (2) with
10 mol % of 1 and phenylsilane (3 equiv) under refluxing condition
furnished the corresponding amine 2a in 78% in 5 h. Lowering the
catalyst loading to 2 mol % has resulted in longer reaction time
(40 h) to complete the reaction.
7
8
5
4
5
3
8a 92
9a 70
10a 65
11a 94
N
N
O
O
N3
CHO
N3
NH2
CHO
NH2
8
9
9
10
11
O
O
N3
NH2
10
With this present condition, the scope of this reduction was
studied extensively with several functionalized azides. As seen
from Tables 2 and 3, several azides with a variety of functional
groups underwent smooth reduction to furnish amines in good to
excellent yields. Table 2 presents several examples of aromatic
azides subjected to the present reduction conditions. Accordingly,
p-methoxyphenyl azide (2) with electron donating group on the
benzene ring reacted smoothly with the reagent 1 (10 mol %) in the
presence of excess of phenylsilane (3 equiv) to furnish the corre-
sponding amine 2a in good yield (entry 1, Table 2 and 5 h). Simi-
larly, the electron withdrawing group on the benzene ring (3) did
not pose any problem under the reaction condition and the cor-
responding amine (3a) was isolated in 84% (3 h, entry 2, Table 2).
Further, several reducible functional groups such as cyano (4) and
nitro (5) tolerated the reaction condition to furnish the respective
amines 4a and 5a in good to excellent isolated yields (entries 3 and
4, Table 2). Quite remarkably, the present reduction appears to be
OBn
O
OBn
O
O
O
11
12
12
13
4
3
12a 91
13a 71
N3
NH2
O
O
O
O
N3
NH2
N3
O
NHBoc
O
13
14
6
14a 64d
O
O
N3
NHBoc
O
14
15
15
16
6
6
15a 67d
16a 52
O
O
O
Table 1
HO
HO
N3
NH2
Molybdenum catalyzed reduction of azides: optimization of the reaction condition
MoO2(S2CNEt2)2 (1)
Hydride
Ph-N3
Ph-NH2
+
source
°
N3
NH2
Toluene, 100
C
16
17
5
17a 86
Entry Catalyst 1 (mol %) Hydride source Equiv
Timea (h) Yieldb (%)
1
2
3
4
5
6
7
6
7
10
10
10
10
10
2
5
10
10
(EtO)3SiH
(MeO)3SiH
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PhSiH3
PMHS
5
5
5
3
2
3
3
5
12
12
5
No reaction
No reaction
78
78
77
45
53
a
Reflux.
Isolated Yields.
b
c
All the products are characterized by IR, 1H NMR 13C NMR, mass spectroscopy.
Isolated as Boc derivative.
5
d
40
40
40
12
very selective, as several other sensitive functional groups were
unaffected. As seen from the Table 2, ketone (6), ester (7), and
amide (8) functionalities were unaffected during the reaction
conditions to produce the corresponding amines 6a, 7a, and 8a in
good yields (entries 5–7).
No reaction
No reaction
H2
Excess 12
a
Reflux.
Isolated Yields.
b

M.R. Maddani et al. / Tetrahedron 66 (2010) 329–333
331
Table 3
A number of experiments were carried out to understand the
mechanism of this reduction. In a reaction of p-methoxyphenyl
azide with reagent 1 under prolonged refluxing conditions did not
produce the corresponding amine but the starting material was
recovered unchanged. Similarly, an extended reaction of large ex-
cess of phenylsilane with p-methoxyphenyl azide did not furnish
any amine but the starting material was recovered. These two
control experiments indicate that phenylsilane and reagent 1 are
essential for the reduction. However, we do not have complete
proof to establish the activation of molybdenum xanthate, 1 by
phenylsilane. At this stage, we only believe that the reaction may
have some similarities with the reduction of aldehydes by dioxo-
rhenium system in presence of silane.22f However, additional in-
formation is required to eliminate the radical pathway.27
At this stage, the exact mechanism of this catalytic reduction is
not known. However, based on the literature precedence22 and our
control experiments we propose a speculative mechanism as
shown in Scheme 1. Reagent 1 reacts with phenylsilane to form
a metal hydride complex I, which in turn reacts with azide sub-
strate to give complex II along with liberation of nitrogen gas. Later
complex II furnishes aminosilane derivative, which produces the
amine during reaction conditions and regenerates reagent 1 and
the catalytic cycle continues.
Molybdenum catalyzed synthesis of aliphatic amines
MoO2(S2CNEt2)2 (1, 10 mol%)
R-NH2
R-N3
PhSiH3
+
Toluene, 100 °C
Entry
Substrates
Timea
(h)
Products
Yieldsb,c
(%)
1
2
18
19
3
3
18a 71
(CH2)10 N3
(CH2)10 NH2
19a 79d
20a 86d
(CH2)6
N3
N3
(CH2)6
NHBoc
NHBoc
3
4
20 3 h
21 7 h
N3
NHBoc
21a 74d
O
O
N3
OTs
NHBoc
OTs
5
6
22 10
23 3 h
22a 55d
23a 77d
O
O
O
O
N3
NHBoc
R-N3
N2
O
O
7
24
24a 76d
N3
NHBoc
a
H
Ph Si
H
Reflux.
Isolated Yields.
H
b
c
R
H
Ph Si
H
HN
All the products are characterized by IR, 1H NMR 13C NMR, mass spectroscopy.
Isolated as Boc derivative.
O
O
M
O
S
S
S
S
S
S
d
Et2N
M
NEt2
Et2N
NEt2
S
S
I
O
II
It is worth drawing the attention to the entry 8 of Table 2, in
which a remarkable selectivity is presented in the reduction of
azide in presence of aldehyde.13b Therefore, o-azido benzaldehyde
(9) in a reaction with 1 and phenylsilane has produced o-amino
benzaldehyde (9a) in good yield. It is important to recognize the
rare selectivity seen in obtaining 9a from 9, in which aldehyde and
amine functionalities are present in the same molecule and are
stable under the reaction condition. Allyl ethers (10) and benzyl
ethers (11) were found to be stable under reaction conditions to
produce the corresponding amines 10a and 11a in good yields
(entries 9 and 10, Table 2). Conjugated ester (12) and vinyl azides
(13) have also furnished the corresponding amines 12a and 13a in
good yields (entries 11 and 12, Table 2). Epoxide (14) and acetal
functionalities (15) (entry 13 and 14, Table 2) are stable under the
reaction conditions to furnish the corresponding amines 14a and
15b in good yields. This reduction appears to be general as 1-azi-
donapthalene (16) and the azide with alcohol functionalities (17)
underwent smooth reduction to furnish the respective amines 16a
and 17a in good yields (entries 15 and 16, Table 2).
PhSiH3
O
S
S
S
S
PhSiH2NH-R
RNH2
Et2N
Mo
NEt2
O
1
Scheme 1. Proposed catalytic cycle for the reduction of azide.
3. Conclusion
In conclusion, we have shown that catalytic amount of molyb-
denum xanthate (1) with PhSiH3 is an effective catalyst for the
reduction of azides to the corresponding amines. This method
tolerates a wide variety of reducible functional groups. To the best
of our knowledge, this kind of chemoselective reduction by dioxo
molybdenum (VI) complexes is rare. Further work is in progress to
develop additional Mo(VI) complexes catalyzed redox processes
and to uncover the reaction pathway.
Next, we investigated the scope of reagent 1 catalyzed reduction
with several aliphatic azides. As seen from Table 3,25,26 the present
strategy is useful in reducing several aliphatic azides in the presence
of a variety of functional groups. Primary and secondary azides un-
derwent a very smooth reduction in the presence of a variety of
functional groups (as isolation of several aliphatic amines was diffi-
cult, we converted them in to the corresponding N-Boc derivatives in
situ by adding Boc anhydride as presented in method B). As expected,
unfunctionalized primary azides 18–20 (entries 1–3, Table 3) and
secondaryazide (21, entry4, Table 3) produced correspondingamines
18a, 19a, 20a, and 21a in good yields. Very good chemoselectivity in
reduction of aliphatic azides is illustrated with azides 22–24. In these
examples, ketal, olefin, and enone functionalities were unaffected
under the reaction conditions and furnished the corresponding
amines 22a, 23a, and 24a in good yields (entries 5–7, Table 3).
4. Experimental
4.1. General
NMR spectra were recorded on a BRUKER-AV400 and JEOL LA-
300, spectrometer in CDCl3 and DMSO-d6. Tetramethylsilane (TMS;
d
¼0.00 ppm) and residual non-deuterated DMSO signal
(d
¼2.49 ppm) served as internal standards for 1H NMR. The cor-
responding residual non-deuterated solvent signal (CDCl3:
d
¼77.00 ppm; DMSO: ¼39.50 ppm) was used as internal stan-
d
dards for 13C NMR. IR spectra were measured using a JASCO FT/IR-
410 spectrometer, and Perkin–Elmer FT/IR Spectrum BX, GX. Mass
spectra were measured with Micromass Q-Tof (ESI-HRMS), and GC–
MS Shimadzu. Column chromatography was conducted on Silica gel

332
M.R. Maddani et al. / Tetrahedron 66 (2010) 329–333
230–400 mesh (Merck) and preparative thin-layer chromatography
was carried out using SILICA GEL GF-254. All melting points were
measured on a ‘Buchi Melting Point B-540’ apparatus and are un-
corrected. Elemental analysis was carried out at the Department of
Organic Chemistry, Indian Institute of Science, Bangalore, India by
using Thermo Finnigan Flash 1112 series analyzer.
d 115.9, 116.4, 118.8, 135.2, 135.7, 149.8, 194.1; HRESI-MS (m/z):
MþþH, found 122.0601. C7H7NO requires 122.0606.
4.2.5. tert-Butyl (3-phenylpropyl)carbamate (20a)32. Prepared by
the general method B; a colorless liquid; IR (Neat, cmꢁ1): 1694,
3351; 1H (400 MHz, CDCl3):
d
1.44 (9H, s, t-Bu), 1.80 (2H, m, CH2),
Aromatic azides were prepared by diazotization28 protocol and
aliphatic azides were prepared by nucleophilic substitution
reaction of halides or their equivalent with sodium azides.13 Dioxo-
bisdiethyldithiocabamate complex of molybdenum (1) was
prepared by the known method.19 The experimental procedures
adopted for reduction as well as the data for few selected products
are presented in the following section.
2.63 (2H, t, J¼7.7 Hz, CH2Ph), 3.10 (2H, m, CH2N), 4.50 (1H, br s, NH),
7.10–7.30 (5H, m, Arm); 13C (100 MHz, CDCl3):
d 28.3, 31.7, 33.0, 40.1,
79.0, 125.8, 128.3, 128.8, 141.5, 155.9; HRESI-MS (m/z): MþþNa,
found 258.1400. C14H21NO2 requires 258.1400.
4.2.6. tert-Butyl(3aR,5R,6S,6aR)-5-(aminomethyl)-2,2 dimethyltetra-
hydrofuro[2,3 d][1,3]dioxol-6-yl 4-methylbenzenesulfonate (22a).
Prepared by the general method B; a pale yellow viscous liquid; Rf
(20% EtOAc/Hexane) 0.50; IR (Neat, cmꢁ1): 1711; 1H (400 MHz,
4.2. General procedure for MoO2(S2CNEt2)2 catalyzed
reduction of azides to corresponding amines
CDCl3): d 1.28 (3H, s, CH3C), 1.43 (9H, s, t-Bu), 1.47 (3H, s, CH3C), 2.47
(3H, s, CH3Ts), 3.21–3.36 (2H, m, CH2N), 4.20–4.30 (1H, m, CHO),
4.65 (1H, br s, d, NH), 4.73–4.80 (2H m, CHO), 5.89 (1H, d, J¼3.6 Hz,
CHOTs), 7.40 (2H, d, J¼8.2 Hz, Arm), 7.82 (2H, d, J¼8.2 Hz, Arm); 13C
Method A
(100 MHz, CDCl3): d 21.7, 26.2, 26.5, 28.3, 38.7, 77.8, 79.6, 81.8, 83.4,
To a well stirred solution of aryl azide (1 mmol), and phenyl-
silane (3 mmol) in toluene (3 mL) was added molybdenum xan-
thate (1, 10 mol %), the reaction mixture was heated at reflux to
complete the reaction (TLC), cooled to room temperature and the
solvent evaporated in vacuo to give the crude product, which was
purified by column chromatography to give amine.
104.6, 112.5, 127.9, 130.2, 132.5, 145.8, 155.7; HRESI-MS (m/z):
MþþNa, found 466.1506. C20H29NO8S requires 466.1512.
4.2.7. tert-Butyl N-[(2E)-3-phenylprop-2-en-1-yl]carbamate (23a)33
Prepared by the general method B; a yellowish brown liquid; IR
(Neat, cmꢁ1): 1683, 1688, 3364; 1H (400 MHz, CDCl3):
1.40 (9H, s,
.
d
t-Bu), 3.90 (2H, br s, CH2N), 4.60 (1H, br s, NH), 6.10–6.20 (1H, m,
Method B
CHCH2N), 6.50 (1H, d, J¼15.8 Hz, CHPh), 7.10–7.40 (5H, m, Arm); 13
C
(100 MHz, CDCl3): d 28.3, 42.7, 79.4, 126.3, 127.5, 128.5, 131.4, 133.2,
Amines were isolated as N-Boc derivatives. To a well stirred
solution of alkyl azide (1 mmol), and phenylsilane (3 mmol) in
toluene (3 mL) was added molybdenum xanthate (1, 10 mol %)
followed by di-tert-butyl dicarbonate (2 mmol). The reaction mix-
ture was heated at reflux to complete the reaction (TLC) cooled to
room temperature and the solvent evaporated in vacuo to give the
crude product, which was purified by column chromatography to
give the N-Boc derivative of amine.
136.6, 155.7; HRESI-MS (m/z): MþþNa, found 256.1305. C14H19NO2
requires 256.1313.
Acknowledgements
The authors thank Indian Institute of Science and Ray Chemicals
Pvt. Ltd. for financial support of this investigation, Prof.
S. Chandrasekaran and Mr. Anjan Roy for encouragement and
Dr. A.R. Ramesha for useful discussions.
4.2.1. 4-Methoxyaniline (2a)29. Obtained by the general method A;
a pale yellow-brown solid; mp: 56 ꢀC; IR (Neat, cmꢁ1): 3312, 3386;
Supplementary data
1H (400 MHz, CDCl3):
d 3.42 (2H, br s, NH2), 3.74 (3H, s, CH3O), 6.65
(2H, d, J¼8.8 Hz, Arm), 6.75 (2H, d, J¼8.8 Hz, Arm); 13C (100 MHz,
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2009.10.093.
CDCl3):
d
55.7, 114.8, 116.4, 139.9, 152.8; HRESI-MS (m/z): MþþH,
found 124.0765. C7H9NO requires 124.0762.
4.2.2. 1-(4-Aminophenyl)ethanone (6a)29. Obtained by the general
References and notes
method A; a colorless solid; mp: 95–103 ꢀC; IR (Neat, cmꢁ1): 1651,
3335, 3396; 1H (400 MHz, CDCl3):
d 2.51 (3H, s, CH3), 4.16 (2H, br s,
1. (a) Kennedy- Smith, J. J.; Nolin, K. A.; Gunterman, H. P.; Toste, F. D. J. Am. Chem.
Soc. 2003, 125, 4056; (b) Handbook of Reagents for Organic Synthesis: Oxidizing
and Reducing Agents; Burke, S. D., Danheiser, R. L., Eds.; John Wiley & Sons: New
York, NY, 1999; See: Comprehensive Organic Synthesis; Trost, B. M., Fleming, I.,
Eds.; Pergamon: New York, NY, 1991; Vol. 7; (c) Nugent, W. A.; Mayer, J. M.
Metal–Ligand Multiple Bonds; Wiley: New York, NY, 1988.
NH2), 6.65 (2H, d, J¼8.6 Hz, Arm), 7.81 (2H, d, J¼8.6 Hz, Arm); 13C
(100 MHz, CDCl3):
d 26.1, 113.7, 127.8, 130.8, 151.1, 196.5; HRESI-MS
(m/z): MþþH, found 136.0758. C8H9NO requires 136.0762.
2. (a) Moloy, K. G. Inorg. Chem. 1988, 27, 677; (b) Tanaka, K.; Honjo, M.; Tanaka, T.
Inorg. Chem. 1985, 24, 2662; (c) Fernandes, A. C.; Ramao, C. C. Tetrahedron 2006,
62, 9650.
3. Nolin, K. A.; Ann, R. W.; Toste, F. D. J. Am. Chem. Soc. 2005, 127, 12462.
4. (a) Lawrence, S. A. Amines: Synthesis, Properties and Applications; Cambridge
University: Cambridge, 2005; (b) Rao, H.; Fu, H.; Jiang, Y.; Zhao, Y. Angew. Chem.,
Int. Ed. 2008, 48, 1114 and references therein; (c) Gunanathan, C.; Milstein, D.
Angew. Chem., Int. Ed. 2008, 47, 8661 and references therein.
5. (a) Weissermel, K.; Arpe, H. J. Industrial Organic Chemistry; Wiley-VCH: Wein-
heim, 1997; (b) Suwanprasop, S.; Nhujak, T.; Roengsumran, S.; Petsom, A. Ind.
Eng. Chem. Res. 2004, 43, 4973.
6. (a) Kadyrov, R.; Riermeier, T. H. Angew. Chem., Int. Ed. 2003, 42, 5472; (b) Gross,
T.; Seayad, A. M.; Ahmad, M.; Beller, M. Org. Lett. 2002, 4, 2055; (c) Lehmann, F.;
Scobie, M. Synthesis 2008, 1679; (d) Huang, X.; Ortiz-Marciales, M.; Huang, K.;
Stepanenko, V.; Merced, F. G.; Ayala, A. M.; Correa, W.; De Jesus, M. Org. Lett.
2007, 9, 1793.
4.2.3. 4-Amino-N,N-diethylbenzamide (8a)30. Prepared by the gen-
eral method A; a pale yellow solid; mp: 118–120 ꢀC; IR (Neat,
cmꢁ1): 1604, 3339, 3438; 1H (400 MHz, CDCl3):
d 1.17 (6H, t,
J¼6.8 Hz, CH3), 3.42 (4H, br s, CH2), 3.90–3.99 (2H, br s, NH2), 6.65
(2H, d, J¼8.4 Hz, Arm), 7.22 (2H, d, J¼8.4 Hz, Arm); 13C (100 MHz,
CDCl3):
d 13.6 (Weak intense), 114.2, 126.9, 128.2, 147.5, 171.7;
HRESI-MS (m/z): MþþNa, found 215.1153. C11H16N2O requires
215.1160.
4.2.4. 2-Aminobenzaldehyde (9a)31. Prepared by the general
method A; a pale yellow solid; mp: 38–40 ꢀC; IR (Neat, cmꢁ1): 1667,
3352, 3468; 1H (400 MHz, CDCl3):
d 6.11 (2H, br s, NH2), 6.65 (1H, d,
7. Larock, R. C. Comprehensive Organic Transformations; VCH: New York, NY, 1989;
pp 779 and 832.
8. Apodaka, R.; Xiao, W. Org. Lett. 2001, 3, 1745 and references therein.
J¼8 Hz, Arm), 6.73–6.77 (1H, m, Arm), 7.28–7.34 (1H, m, Arm), 7.48
(1H, d, J¼8 Hz, Arm) 9.87 (1H, s, CHO); 13C (100 MHz, CDCl3):

M.R. Maddani et al. / Tetrahedron 66 (2010) 329–333
333
9. Seayad, A.; Ahmed, M.; Klein, H.; Jackstell, R.; Gross, T.; Beller, M. Science 2002,
297, 1676.
18. (a) Kim, J.; Chang, S. Chem. Commun. 2008, 3052; (b) Kamal, A.; Ramana, K. V.;
Ankati, H. H. B.; Ramana, V. A. Tetrahedron Lett. 2002, 43, 6861.
19. (a) Moore, F. W.; Larson, M. L. Inorg. Chem. 1967, 6, 998; (b) Newton, W. E.;
Corbin, J. L.; Bravard, D. C.; Searles, J. E.; McDonald, J. W. Inorg. Chem. 1974, 13,
1100.
10. Magro, A. A. N.; Eastham, G. R.; Cole-Hamilton, D. J. Chem. Commun. 2007, 3154.
11. (a) White, E. H.; Eiliger, C. A. J. Am. Chem. Soc. 1965, 87, 5261; (b) Bartoli, G.;
Antonio, G. D.; Giovannini, R.; Giuli, S.; Lanari, S.; Paoletti, M.; Marcantoni, E.
J. Org. Chem. 2008, 73, 1919 and references therein; (c) Miriyala, B.; Bhatta-
charyyab, S.; Williamson, J. S. Tetrahedron 2004, 60, 1463.
20. (a) Maddani, M.; Prabhu, K. R. Tetrahedron Lett. 2007, 48, 7151; (b) Maddani, M.;
Prabhu, K. R. Tetrahedron Lett. 2008, 49, 4526.
12. Yamaguchi, R.; Kawagoe, S.; Asai, C.; Fujita, K. Org. Lett. 2008, 10, 181 and ref-
erences therein.
21. Hayes, K. S. Appl. Catal., A 2001, 221, 187.
22. (a) Du, G.; Fanwick, P. E.; Abu-omar, M. M. J. Am. Chem. Soc. 2007, 129, 5180; (b)
Ison, E. A.; Corbin, R. A.; Abu-Omar, M. M. J. Am. Chem. Soc. 2005, 127, 11938; (c)
Reis, P. M.; Coasta, P. J.; Ramao, C. C.; Fernandes, J. A.; Calhorda, M. J.; Roya, B.
Dalton Trans. 2008, 1727; (d) Fernandes, A. C.; Fernandes, J. A.; Paz, F. A. A.;
Ramao, C. C. Dalton Trans. 2008, 6686; (e) Hanada, S.; Motoyama, Y.; Naga-
shima, H. Eur. J. Org. Chem. 2008, 4097; (f) Nolin, K. A.; Krumper, J. R.; Bergman,
R. G.; Toste, F. D. J. Am. Chem. Soc. 2007, 129, 14684.
13. (a) Stevens, C. L.; Blumbergs, P.; Daniher, F. A.; Otterbach, D. H.; Taylor, K. G.
J. Org. Chem. 1966, 31, 2822; (b) Lichtenthaler, F. W.; Heidel, P. Angew. Chem.
1968, 80, 441; (c) Nakajima, M.; Shibata, H.; Kitahara, K.; Takahashi, S.;
Hasegawa, A. Tetrahedron Lett. 1968, 9, 2271; (d) Lawton, B. T.; Szarek, W. A.;
Jones, J. K. N. J. Chem. Soc., Chem. Commun. 1969, 787; (e) Horton, D.; Luetzow,
A. E. Carbohydr. Res. 1968, 7, 101.
14. (a) The Chemistry of the Azido Group; Patai, S., Ed.; Wiley: New York, NY, 1971;
(b) Azides and Nitrenes: Reactivity and Utility; Scriven, E. F. V., Ed.; Academic:
New York, NY, 1984; (c) Scriven, E. F. V.; Turnbull, K. Chem. Rev. 1988, 88, 297;
(d) Bra¨se, S.; Gil, C.; Knepper, K.; Zimmermann, V. Angew. Chem., Int. Ed. 2005,
44, 5188; (e) Amantini, D.; Fringuelli, F.; Pizzo, F.; Vaccaro, L. Org. Prep. Proced.
Int. 2002, 34, 109.
23. So far, we are successful in reducing the azides. Our attempts to reduce several
other functional groups have not produced any fruitful results so far.
24. Similar reaction of p-methoxyphenyl azide with molybdenum acetylacetonate
or ammonium molybdate or sodium molybdate under identical condition
failed to produce the corresponding amine and the starting material was re-
covered in almost quantitative yield.
15. (a) Bayley, H.; Standring, D. N.; Knowles, J. R. Tetrahedron Lett. 1978, 19, 3633;
(b) Mandville, G.; Ahmar, M.; Bloch, R. J. Org. Chem. 1996, 61, 1122; (c) Fringuelli,
F.; Pizzo, F.; Vaccaro, L. Synthesis 2000, 646; (d) Larock, R. C. Comprehensive
Organic Transformations; VCH: New York, NY, 1989; pp 815.
25. Yashuhara, A.; Kasano, A.; Sakamoto, T. J. Org. Chem. 1999, 64, 2301.
26. As isolation of several amines was difficult, we converted them in to the cor-
responding N-Boc derivatives insitu by adding Boc anhydride as presented in
method B.
16. (a) Feldman, A. K.; Colasson, B.; Fokin, V. V. Org. Lett. 2004, 6, 3897; (b)
Zhu, W.; Ma, D. Chem. Commun. 2004, 888; (c) Cai, Q.; Zhu, W.; Zhang.,
W. Y.; Ma, D. Synthesis 2005, 498; (d) Andersen, J.; Madsen, U.; Bjorkling,
F.; Liang, X. Synlett 2005, 2209; (e) Andersen, J.; Bolvig, S.; Liang, X. Synlett
2005, 2941.
27. Benati, L.; Benciveni, G.; Leardini, R.; Nanni, D.; Minozzi, M.; Spagnolo, P.;
Scialpe, R.; Zanardi, G. Org. Lett. 2007, 8, 2499.
28. Tanno, M.; Sueyoshi, S.; Kamiya, S. Chem. Pharm. Bull. 1982, 30, 3125.
29. Benati, L.; Bencivenni, G.; Leardini, R.; Minozzi, M.; Nanni, D.; Scialpi, R.;
Spagnolo, P.; Zanardi, G. J. Org. Chem. 2006, 71, 5822.
17. (a) Corey, E. J.; Nicolaou, K. C.; Balanson, R. D.; Machide, Y. Synthesis 1975, 590;
(b) Reddy, P. G.; Pratap, V. T.; Kumar, G. D. K.; Mohanty, S. K.; Baskaran, S. Eur. J.
Org. Chem. 2002, 3740; (c) Bose, A. K.; Kistner, J. F.; Farber, L. J. Org. Chem. 1962,
27, 2925; (d) Belinka, B. A.; Hassner, A. J. Org. Chem. 1979, 44, 4712; (e) Soai, K.;
Yokoyama, S.; Ookawa, A. Synthesis 1986, 48.
30. Huang, X.; Buchwald, S. L. Org. Lett. 2001, 3, 3417.
31. Smith, L. I.; Opie, J. W. Org. Synth. Coll. 1955, Vol. 3, 56.
32. Fujioka, H.; Hirose, H.; Ohba, Y.; Murai, K.; Nakahara, K.; Kita, Y. Tetrahedron
2007, 63, 625.
33. Berree, F.; Michelot, G.; Corre, M. L. Tetrahedron Lett. 1998, 39, 8275.