Intermodular aerobic oxidative allylic amination of simple alkenes with diarylamines catalyzed by the Pd(OCOCF3)2/NPMoV/O 2 system

Article abstract of DOI:10.1021/ol100292g

Chemical Equation Presented Intermolecular aerobic oxidative allylic amination of simple alkyl alkenes with simple amines such as dlphenylamine was induced by a Pd(OCOCF₃)₂/NPMoV catalytic system, leading to the corresponding (E)-allylamines in good yield and selectivity through the formation of (n³-allyl)palladium(II) trifluoroacetate species as a possible key Intermediate.

Full text of DOI:10.1021/ol100292g

ORGANIC
LETTERS
2010
Vol. 12, No. 6
1372-1374
Intermolecular Aerobic Oxidative Allylic
Amination of Simple Alkenes with
Diarylamines Catalyzed by the
Pd(OCOCF3)2/NPMoV/O2 System
Yosuke Shimizu, Yasushi Obora,* and Yasutaka Ishii*
Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials
and Bioengineering, High Technology Research Center, and ORDIST, Kansai
UniVersity, Suita, Osaka 564-8680, Japan
obora@kansai-u.ac.jp; r091001@ipcku.kansai-u.ac.jp
Received February 3, 2010
ABSTRACT
Intermolecular aerobic oxidative allylic amination of simple alkyl alkenes with simple amines such as diphenylamine was induced by a
Pd(OCOCF3)2/NPMoV catalytic system, leading to the corresponding (E)-allylamines in good yield and selectivity through the formation of
(η3-allyl)palladium(II) trifluoroacetate species as a possible key intermediate.
A selective allylic C-H bond functionalization of alkenes
through allylic oxidation reactions is an important methodol-
ogy for the direct installation of functionality into hydro-
carbon frameworks.1 In particular, Pd(II)-catalyzed oxidative
allylic amination is an efficient methodology for preparing
nitrogen-containing unsaturated compounds such as enamines
and allylic amines.2 However, there have been limited works
on the reaction with nonsubstituted simple alkenes. Recently,
White and co-workers reported that Pd(II)-sulfide/Cr(III)-
catalyzed oxidative allylic amination of the simple alkenes
with tosylamides using 2 equiv of benzoquinone as a
reoxidant affords allylamides.3 Thereafter, the same group
presented that the Pd(II)/sulfoxide-catalyzed allylic amination
was promoted with dialkylamine bases.4 In addition, Liu and
co-workers reported the Pd(II)-catalyzed aerobic oxidative
allylic amination of the simple alkenes with tosylamides
under 6 atm of O2 pressure.5 On the other hand, Stahl and
co-workers reported a Pd(II)-catalyzed aza-Wacker-type
reaction of simple alkenes with imides or sulfamate esters
affording enamides as products.6 However, these previous
reports are limited to the reaction with nonbasic amides and
imides as nitrogen nucleophiles. Therefore, the development
of an innovative method for the intermolecular aerobic
oxidative allylic amination of simple alkenes with simple
amines under mild conditions is highly desired.7
(1) (a) Hansson, S.; Heumann, A.; Rein, T.; Åkermark, B. J. Org. Chem.
1990, 55, 975. (b) Heumann, A.; Reglier, M.; Waegell, B. Angew. Chem.,
Int. Ed. 1982, 21, 366. (c) Heumann, A.; Åkermark, B. Angew. Chem., Int.
Ed. 1984, 23, 453. (d) McMurry, J. E.; Kocovsky, P. Tetrahedron Lett.
1984, 25, 4187. (e) Åkermark, B.; Larsson, E. M.; Oslob, J. D. J. Org.
Chem. 1994, 59, 5729. (f) Macsari, I.; Szabo, K. J. Tetrahedron Lett. 1998,
39, 6345. (g) Yu, J.-Q.; Corey, E. J. J. Am. Chem. Soc. 2003, 125, 3232.
(h) Mitsudome, T.; Umetani, T.; Nosaka, N.; Mori, K.; Mizugaki, T.; Ebitani,
K.; Kaneda, K. Angew Chem., Int. Ed. 2006, 45, 481. Angew. Chem. 2006,
118, 495. (i) Chen, M. S.; White, M. C. J. Am. Chem. Soc. 2004, 126,
1346. (j) Chen, M. S.; Prabagaran, N.; Labenz, N. A.; White, M. C. J. Am.
Chem. Soc. 2005, 127, 6970. (k) Fraunhoffer, K. J.; Bachovchin, D. A.;
White, M. C. Org. Lett. 2005, 7, 223.
(3) Reed, S. A.; White, M. C. J. Am. Chem. Soc. 2008, 130, 3316.
(4) Reed, S. A.; Mazzotti, A. R.; White, M. C. J. Am. Chem. Soc. 2009,
131, 11701.
(2) Examples of intramolecular oxidative allylic amination: (a) Wu, L.;
Qiu, S.; Liu, G. Org. Lett. 2009, 11, 2707. (b) Scarborough, C. C.; Bergant,
A.; Sazama, G. T.; Guzei, I. A.; Spencer, L. C.; Stahl, S. S. Tetrahedron.
2009, 65, 5084. (c) Yu, H.; Fu, Y.; Guo, Q.; Lin, Z. Organometallics, 2009,
28, 4507. (d) Fraunhoffer, K. J.; White, M. C. J. Am. Chem. Soc. 2007,
129, 7274, and references cited therein.
(5) Liu, G.; Yin, G.; Wu, L. Angew. Chem., Int. Ed. 2008, 47, 4733.
(6) (a) Rogers, M. M.; Kotov, V.; Chatwichien, J.; Stahl, S. S. Org.
Lett. 2007, 9, 4331. (b) Brice, J. L.; Harang, J. E.; Timokhin, V. I.; Anastasi,
N. R.; Stahl, S. S. J. Am. Chem. Soc. 2005, 127, 2868.
10.1021/ol100292g  2010 American Chemical Society
Published on Web 02/16/2010

Table 1. Pd(II)/NPMoV-Catalyzed Oxidative Allylic Amination
of Diphenylamine (1a) with 1-Decene (2a) under Various
Conditionsa
We have recently found that the PdCl2(PhCN)2/molybdo-
vanadophosphate salt (NPMoV) system8 catalyzes efficiently
the aza-Wacker-type reaction of simple amines such as
diphenylamine with electron-deficient alkenes such as acry-
lates to afford enamines which have been difficult to obtain
as products so far.9
,
entry
Pd catalyst
solvent
yield of 3a/%b c
1
Pd(OCOCF3)2
Pd(OCOCF3)2
Pd(OCOCF3)2
Pd(OCOCF3)2
Pd(OCOCF3)2
Pd(OAc)2
PdCl2(PhCN)2
Pd(acac)2
PdCl2
Pd(OCOCF3)2
Pd(OCOCF3)2
Pd(OCOCF3)2
Pd(OCOCF3)2
Pd(OCOCF3)2
Pd(OCOCF3)2
Pd(OCOCF3)2
Pd(OCOCF3)2
Pd(OCOCF3)2
TFT
TFT
TFT
TFT
TFT
TFT
TFT
TFT
TFT
TFT
TFT
73 (62)
41
15
15
60
2d
3e
4f
In this study, we would like to report Pd(OCOCF3)2/
NPMoV-catalyzed intermolecular aerobic oxidative allylic
amination of simple aliphatic alkenes with simple amines such
as diphenylamine, leading to the corresponding (E)-allylamines
in good yields with high regio- and stereoselectivity (eq 1).
The reaction of diphenylamine (1a) with 1-decene (2a)
was chosen as a model reaction and carried out under various
conditions (Table 1). For instance, 1a (1 mmol) was reacted
with 2a (7 mmol) in the presence of Pd(OCOCF3)2 (0.1
mmol) and (NH4)5H4PMo6V6O40·23H2O (NPMoV) (0.02
mmol) in trifluorotoluene (TFT) (1 mL) under air (10 atm)
at 40 °C for 24 h to give (E)-1-diphenylamino-2-decene (3a)
in good yield (73%) in 78% conversion of 1a (entry 1). The
reaction proceeded with high stereo- and regioselectivity to
afford the E isomer, exclusively. In addition, no aza-Wacker-
type product was detected at all under these conditions. The
yield of 3a was high for the reaction of 1a when an excess
(7 equiv) of 2a was employed (entry 1). However, even if
the reaction of 1a with 2a was allowed to take place in a
1:3 molar ratio, the yield of 3a was still moderate (entry 2).
Removal of NPMoV from the catalytic system resulted in a
sluggish reaction (entry 3).
5g
6
4
7
8
9
n.d.h
n.d.h
n.d.h
19
10i
11j
12
13
14
15
16
17
18
37
73
74
55
35
6
7
30
perfluorohexane
FC-72k
toluene
DMF
DME
PhCN
tBuOH
a Conditions: 1a (1 mmol) was allowed to react with 2a (7 mmol) in
the presence of Pd catalyst (10 mol %) and NPMoV (2 mol %) in solvent
(1 mL) under air (10 atm) at 40 °C for 24 h. b GC yields based on 1a used.
The number in parentheses shows the isolated yield. c In this reaction,
2-decanone (5-20% based on 2a used) was obtained as byproduct. d 1a (1
mmol) and 2a (3 mmol) were used. e Reaction was performed in the absence
of NPMoV. f Reaction was performed under Ar. g Reaction was performed
under O2 (1 atm). h Not detected by GC. i H4PMo11VO40·23H2O was used
as a reoxidation catalyst. j H7PMo8V4O40·25H2O was used as a reoxidation
catalyst. k Perfluorohexanes, 3 M Company, St Paul, MN.
Needless to say, no reaction was induced in the absence
of Pd(II) catalyst. The reaction under argon resulted in a low
yield of 3a because of difficulty of regenerating Pd(II) from
the reduced Pd(0) during the reaction (entry 4). The reaction
proceeded under atmospheric oxygen (1 atm) and gave 3a
in moderate yield (entry 5). This is in sharp contrast to the
previously reported oxidative aminations with alkyl alkenes
which requires relatively high O2 pressure (4-6 atm).5,6a It
is important to note that Pd(OCOCF3)2 showed the highest
catalytic activity. In contrast, Pd(OAc)2 and Pd(acac)2, which
showed good catalytic performance in the Pd(II)/NPMoV/
O2 catalytic system reported previously,8 resulted in lower
catalytic activity in the present reaction (entries 6-9). The
yield of 3a was considerably decreased when molybdova-
nadophospholic acids (HPMoV) such as H4PMo11VO40·
23H2O and H7PMo8V4O40·25H2O were used as reoxidation
catalysts of the reduced Pd(0) because of the formation of
an amine salt of HPMoV with 1a (entries 10 and 11). This
shows that molbdovanadophosphate (NPMoV) partly re-
placed by ammonium cation of the HPMoV provides an
efficient reoxidation system in this reaction.
Among solvents examined in this reaction, fluorous solvents
such as TFT, perfluorohexane, and FC-72 were found to be
suitable for the formation of 3a, while the reaction in toluene,
DMF, DME, PhCN, and tBuOH under these reaction conditions
afforded 3a in low yields (entries 12-18).
Under optimized conditions, reactions of various diary-
lamines (1) with aliphatic alkenens (2) afforded the corre-
sponding allylamine derivatives in good yields (Table 2).
Thus, 1-octene (2b), 1-dodecene (2c), allylcyclohexane (2d),
allylbenzene (2e), and 4-phenyl-1-butene (2f) were allowed
to react with 1a affording the corresponding (E)-allyamine
derivatives (3b-f) in good yields (entries 1-5). An alkene
bearing ester group, methyl 5-hexenoate (2g) also reacted
with 1a to give the corresponding product (3g) in good yield
(entry 6). Secondary aromatic amines such as 3-methyl-
diphenylamine (1b) and 3-fluorodiphenylamine (1c) are
tolerated as substrates in the reaction with 2a to afford the
corresponding oxidative allylic amination products in moder-
ate to good yield (entries 7 and 8). Unfortunately, the reaction
with aliphatic amines such as hexylamine, dibutylamine, and
primary aromatic amines such as anilines were sluggish due
to the deactivation of palladium and NPMoV species by
strong coordination of these amines.
(7) Examples of allylic amination with hydroxyl amines: (a) Hogan,
G. A.; Gallo, A. A.; Nicholas, M. M.; Srivastava, R. S. Tetrahedron Lett.
2002, 43, 9505. (b) Adam, W.; Krebs, O. Chem. ReV. 2003, 103, 4131.
(8) Examples of the Pd/NPMoV/O2-catalyzed reactions: (a) Yokota, T.;
Fujibayashi, S.; Nishiyama, Y.; Sakaguchi, S.; Ishii, Y. J. Mol. Catal. A:
Chem. 1996, 114, 113. (b) Yokota, T.; Sakakura, A.; Tani, M.; Sakaguchi,
S.; Ishii, Y. Tetrahedron Lett. 2002, 43, 8887. (c) Yokota, T.; Sakaguchi,
S.; Ishii, Y. J. Org. Chem. 2002, 67, 5005.
(9) Obora, Y.; Shimizu, Y.; Ishii, Y. Org. Lett. 2009, 11, 5058.
Org. Lett., Vol. 12, No. 6, 2010
1373

1. First, Pd(II) reacts with alkene (2) to form an η3-
allylpalladium intermediate A through the allylic C-H bond
Table 2. Pd(OCOCF3)2/NPMoV-Catalyzed Oxidative Allylic
Amination of 1 and 2 Leading to Allylamine Derivatives (3)a b
,
Scheme 1. A Plausible Reaction Mechanism
activation.3-5 Then, the A is subjected to the nucleophilic
attack of amine (1) to afford the oxidative allylic amination
product 3 and Pd(0). Finally, Pd(0) is reoxidized by the
NPMoV/O2 system to generate Pd(II) (Scheme 2).8
Scheme 2
.
A Mechanism of Regeneration of Pd(II) from Pd(0)
under the Influence of NPMoV and O2
a Conditions: 1 (1 mmol) was allowed to react with 2 (7 mmol) in the
presence of Pd(OCOCF3)2 (0.1 mmol) and NPMoV (0.02 mmol) in TFT (1
mL) under air (10 atm) at 40 °C for 24 h. b GC yields. The numbers in
parentheses show isolated yields.
It is known that the reaction of alkenes with Pd(II) forms
an η3-allylpalladium intermediate through allylic C-H bond
activation.3-5 To obtain further insight of the Pd species in
this reaction, (η3-cinnamyl)palladium trifluoroacetate dimer
(4) and (η3-cinnamyl)palladium acetate dimer (5) were
independently prepared as model intermediates and the
stoichiometic reaction with 1a was carried out (eq 2). As a
result, the reaction of 4 with 1a produced 3e in substantial
yield along with unreacted 1a,10 while almost no coupling
product was obtained by the reaction with 5. These results
indicate that the electrophilicity of the η3-allylpalladium
species is an important factor to facilitate the present reaction.
It seems that the formation of more electrophilic η3-
allylpalladium trifluoroacetate is suitable for the present
reaction,11 which would be the key step in the reaction.
Unfortunately, the isolation of the expected palladium-
amine adducts and the direct observation of the amine
coordinating species by NMR are not successful at this point.
Therefore, another reaction pathway through aminopallada-
tion/ꢀ-hydride elimination (aza-Wacker process) cannot be
ruled out completely (Figure S1, Supporting Information).
In conclusion, we reported the Pd(II)/NPMoV/O2-catalyzed
oxidative allylic amination of simple alkenes with simple
amines to afford (E)-allylamines.
Further study on the detailed investigation of the scope
and the reaction mechanism is currently under investigation.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research from the Ministry of Educa-
tion, Culture, Sports, Science and Technology, Japan, and
Kansai University Research Grants: Grant-in Aid for En-
couragement of Scientists, 2009.
Therefore, although a detailed reaction mechanism is not
confirmed at this stage, a plausible path is shown in Scheme
Supporting Information Available: Experimental pro-
cedure and compound characterization data (1H NMR, 13C
NMR, IR, and MS) of the compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
(10) The yield of 3e was not improved even if the reaction was carried
out under air (10 atm) in the presence of NPMoV.
(11) (a) Obora, Y.; Ogawa, Y.; Imai, Y.; Kawamura, T.; Tsuji, Y. J. Am.
Chem. Soc. 2001, 123, 10489. (b) Hegedus, L. S.; Åkermark, B.; Zetterberg,
K.; Olsson, L. F. J. Am. Chem. Soc. 1984, 106, 7122.
OL100292G
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Org. Lett., Vol. 12, No. 6, 2010