Simple and efficient AuI-based catalyst for hydroamination of alkynes

Article abstract of DOI:10.1016/j.mencom.2014.11.004

Hydroamination of terminal alkynes with anilines in the presence of (C₆F₅)₃PAuNTf₂ catalyst affords 2-aryliminoalkanes whose reduction in situ with sodium borohydride gives the corresponding secondary amines in

Full text of DOI:10.1016/j.mencom.2014.11.004

Mendeleev
Communications
Mendeleev Commun., 2014, 24, 332–333
Simple and efficient Aui-based catalyst for hydroamination of alkynes
Maksim V. Anokhin, Arina V. Murashkina, Alexei D. Averin and Irina P. Beletskaya*
Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation.
Fax: +7 495 939 1139; e-mail: beletska@org.chem.msu.ru
DOI: 10.1016/j.mencom.2014.11.004
Hydroamination of terminal alkynes with anilines in the presence of (C6F5)3PAuNTf2 catalyst affords 2-aryliminoalkanes whose
reduction in situ with sodium borohydride gives the corresponding secondary amines in high yields.
The establishment of an important fact that gold nanoparticles
(AuNPs) possess unique properties which are quite different from
those of bulk gold encouraged many researchers to investigate
catalytic properties of nano-gold. The majority of works dealing
with AuNPs study oxidation1 and reduction processes,2 making
an emphasis on the molecular structure of the gold clusters.3,4
There are some publications considering other reactions, usually
catalyzed by the complexes of Pd, Pt, etc. Among such works a
special place is occupied by the investigations dedicated to the
C–N bond formation in the course of hydroamination of alkynes.5
Other Au-catalyzed processes include the addition of HX to
carbon–carbon multiple bonds,6–8 however, hydroamination was
found to be most problematic9 but simultaneously one of the
most important in the atom-economy synthesis. Such processes
are attractive when the catalyst can be recycled, what depends
not only on the size and structure of AuNPs but also on the support
nature. The drawbacks of this approach include the unclear reac-
tion mechanism and the possibility of its different interpretation
when changing the reaction conditions and support nature.10
The attractiveness of gold as a catalyst evoked serious interest
in Aui and Auiii salts as Lewis acids. The first homogeneous
intermolecular hydroamination of alkynes was carried out by
Tanaka et al.11 who used aromatic amines in the presence of
(Ph3P)AuMe complex and acidic promoter like H3PW12O40. High
efficiency was manifested by Au complexes with N-heterocyclic
carbenes12–14 as well as AuNTf2 complexes with triphenylphos-
phine and 2-(dicyclohexylphosphino)-2',6'-dimethoxybiphenyl
ligands.15 In that study, 1-octyne was coupled with aliphatic
amines and chiral a-phenylethylamine which are usually less
active than aromatic ones. Supposing that the reaction proceeds
due to the activation of the triple bond with LAuNTf2, we have
chosen the complex of Aui with a weak donor ligand (C6F5)3P.
The complex was obtained from HAuCl4 and (C6F5)3P via
intermediate (C6F5)3PAuCl which was then subjected to the
anion exchange with AgNTf2.16,17 The reaction conditions were
optimized on coupling of phenylacetylene 1 with p-toluidine 2a
and 4-methoxyaniline 2b (Scheme 1, Table 1).
Table 1 Optimization of the Aui-catalyzed hydroamination conditions.
Entry Amine
Catalyst (mol%) Solvent
Imine
Yielda (%)
1
2
3
2a
2a
2b
2.5
1
CH2Cl2
neat
3a
3a
3b
84
88
80
1
neat
aYields after chromatographic isolation.
ketimine 3a (entry 1), while on application of 1 mol% catalyst
under neat conditions this product was obtained in 88% yield
(entry 2). The reaction of a more donor p-methoxyaniline 2b
resulted in 80% yield of 3b (entry 3). Note that we succeeded to
use fivefold lower quantity of catalyst at room temperature than
described in literature.15
As ketimines may always contain admixtures of the relative
ketones due to easy hydrolysis, further we reduced them in situ
with NaBH4 (Scheme 2, Table 2).† Intermediate imines were
synthesized under the optimized conditions, and the yields of
the secondary amines 4a,b were high enough (entries 1, 2). The
highest yield (98%) was achieved with the simplest aniline 3c
Ar
(C6F5)3PAuNTf2
N
+
R
C
CH
ArNH2
room temperature,
neat
R
Me
in situ
1 R = Ph
2a–g
5 R = 4-MeOC6H4
7 R = n-C5H11
MeOH NaBH4
a Ar = 4-MeC6H4
b Ar = 4-MeOC6H4
c Ar = Ph
d Ar = 4-ClC6H4
e Ar = 4-NO2C6H4
Ar
HN
R
Me
4a–d R = Ph
6b,d,f R = 4-MeOC6H4
8a,b R = n-C5H11
f
Ar = 3,5-Me2C6H3
g Ar = 3-NO2C6H4
Scheme 2
Reactions were run at ambient temperature using 20% excess
of alkyne. The reaction with 2a in the presence of 2.5 mol%
catalyst in CH2Cl2 provided 84% yield of the corresponding
†
Catalytic hydroamination of alkynes (general procedure). Alkyne 1, 5
or 7 (1.2 mmol), aniline derivative 2a–g (1 mmol) and (C6F5)3PAuNTf2
catalyst (10 mg, 1 mol%) were placed into a vial and stirred at ambient
temperature for ca. 24 h until the reaction was complete (TLC control).
The mixture was diluted with 3 ml MeOH, followed by addition of NaBH4
(2 mmol, 76 mg) and stirring for 3 h (TLC control). The mixture was
diluted with CH2Cl2 (15 ml), washed with water (15 ml) and saturated
NaCl aqueous solution (15 ml). The organic layer was separated, dried over
anhydrous Na2SO4, evaporated in vacuo and the residue was chromato-
graphed on silica gel using 3–5% EtOAc in light petroleum. 1H and 13
NMR spectroscopic data of compounds 3a,15 3b,18 4a–c,19 4d,20 6b,21
6d,22 6f,23 8a,24 8b25 are consistent with those described in the literature.
Ar
N
(C6F5)3PAuNTf2
Ph
C CH
+
ArNH2
room temperature
Ph
Me
3a,b
1
2a,b
a Ar = 4-MeC6H4
b Ar = 4-MeOC6H4
C
Scheme 1
© 2014 Mendeleev Communications. All rights reserved.
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Mendeleev Commun., 2014, 24, 332–333
Table 2 Synthesis of secondary amines via Aui-catalyzed hydroamination.
4 M. Boronat and A. Corma, J. Catal., 2011, 284, 138.
5 A. Corma, P. Concepcion, I. Dominguez, V. Fornes and M. J. Sabater,
J. Catal., 2007, 251, 39.
Entry
Alkyne
Amine
Product
Yielda (%)
6 X. Giner, C. Najera, G. Kovacs, A. Lledos and G. Ujaque, Adv. Synth.
Catal., 2011, 353, 3451.
7 T. E. Muller, K. C. Hultzsch, M. Yus, F. Foubelo and M. Tada, Chem.
1
1
1
1
1
1
5
5
5
5
7
7
2a
2b
2c
2d
2e
2b
2d
2f
4a
78
81
98
88
—
82
70
75
—
61
56
2
4b
3
4c
Rev., 2008, 108, 3795.
8 F. Alonso, I. P. Beletskaya and M. Yus, Chem. Rev., 2004, 104, 3079.
9 J. Seayad, A. Tillack, C. G. Hartung and M. Beller, Adv. Synth. Catal.,
2002, 344, 795.
4
4d
5
No reaction
6
6b
10 J. Zhao, Z. Zheng, S. Bottle, A. Chou, S. Sarina and H. Zhu, Chem.
7
6d
Commun., 2013, 49, 2676.
11 E. Mizushima, T. Hayashi and M. Tanaka, Org. Lett., 2003, 5, 3349.
12 V. Lavallo, G. D. Frey, B. Donnadieu, M. Soleilhavoup and G. Bertrand,
Angew. Chem. Int. Ed., 2008, 47, 5224.
8
6f
9
2g
2a
2b
No reaction
10
11
8a
8b
13 X. Zeng, G. D. Frey, S. Kousar and G. Bertrand, Chem. Eur. J., 2009,
15, 3056.
14 X. Zeng, G. D. Frey, R. Kinjo, B. Donnadieu and G. Bertrand, J. Am.
Chem. Soc., 2009, 131, 8690.
aYields after chromatographic isolation.
15 A. Leyva and A. Corma, Adv. Synth. Catal., 2009, 351, 2876.
16 C. Shu, L. Li, C.-B. Chen, H.-C. Shen and L.-W. Ye, Chem. Asian J.,
2014, 9, 1525.
17 J.-E. Kang and S. Shin, Synlett, 2006, 5, 717.
18 N. Senthilkumar, P. Gandeepan, J. Jayakumar and C.-H. Cheng, Chem.
Commun., 2014, 3106.
19 Q. Sun, Y. Wang, D. Yuan, Y. Yao and Q. Shen, Organometallics, 2014,
33, 994.
20 Q. Lei, Y. Wei, D. Talwar, C. Wang, D. Xue and J. Xiao, Chem. Eur. J.,
(entry 3), the use of a weak electron-withdrawing p-chloroaniline
2d also resulted in a high yield of product 4d (88%, entry 4).
However, in the case of stronger electron-withdrawing nitro-sub-
stituted reactant the reaction was completely cancelled (entry 5).
The presence of electron-donating methoxy group in alkyne 5
did not decrease its reactivity and amines 6b,d,f were isolated in
70–82% yields (entries 6–8). 3-Nitroaniline was essentially un-
reactive (entry 9). Aliphatic 1-heptyne 7 gave amines 8a,b in
lower yields, what is in good agreement with published data.15
The catalyst can be easily separated from product 4c by adding
hexane and can be used at least three times without substantial
loss in activity.
2013, 19, 4021.
21 W. Tang, C. Lau, X. Wu and J. Xiao, Synlett, 2014, 25, 81.
22 G. Ghattas, D. Chen, F. Pan and J. Klankermayer, Dalton Trans., 2012,
41, 9026.
23 N. Mrsic, L. Panella, E. G. IJpeij, A. J. Minnaard, B. L. Feringa and
J. G. de Vries, ChemCatChem, 2011, 3, 1139.
24 L. Rubio-Perez, F. J. Perez-Florez, P. Sharma, L. Velasco and A. Cabrera,
Org. Lett., 2009, 11, 265.
This work was supported by the Russian Science Foundation
(grant no. 14-23-00186).
25 C. Wang, A. Pettman, J. Bacsa and J. Xiao, Angew. Chem. Int. Ed., 2010,
49, 7548.
References
1 C. Della Pina, E. Faletta, L. Prati and M. Rossi, Chem. Soc. Rev., 2008,
37, 2077.
2 A. Corma and P. Serna, Nature, 2006, 313, 332.
3 A. A. Herzing, C. J. Kiely, A. F. Carley, P. Landon and G. J. Hutchings,
Science, 2008, 321, 1331.
Received: 13th October 2014; Com. 14/4483
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