Lewis acid catalyzed intermolecular olefin hydroamination: Scope, limitation, and mechanism

Article abstract of DOI:10.1002/ejoc.200701080

Intermolecular olefin hydroamination was studied by various Lewis acids. The results of ZrCl₄, FeCl₃, BiCl₃, and AlCl₃ catalyzed reactions of norbornene with aromatic amines were compared, and BiCl₃ was found to be the most effective catalyst to give high yields for various amines, whereas ZrCl₄ could promote the reactions at relatively low temperatures. The FeCl₃ catalyzed reactions were the most chemoselective and excellent yields could be achieved for certain amines by using AlCl₃. A carbocation mechanism was proposed, and the controllable syntheses of allylamine and tetrahydroquinoline from isoprene and 2,5-dichloroaniline were achieved by application of this mechanism. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200701080

FULL PAPER
DOI: 10.1002/ejoc.200701080
Lewis Acid Catalyzed Intermolecular Olefin Hydroamination: Scope,
Limitation, and Mechanism
Xiaojuan Cheng,[a] Yuanzhi Xia,[a,b] Hua Wei,[a] Bin Xu,[b] Chongguang Zhang,[a]
Yahong Li,*[a,b,c] Guimin Qian,[b] Xiaohua Zhang,[a] Kai Li,[a] and Wu Li[b]
Keywords: Hydroamination / Lewis acids / Amines / Catalysis / Mechanisms
Intermolecular olefin hydroamination was studied by various
Lewis acids. The results of ZrCl4, FeCl3, BiCl3, and AlCl3 cat-
alyzed reactions of norbornene with aromatic amines were
compared, and BiCl3 was found to be the most effective cata-
lyst to give high yields for various amines, whereas ZrCl4
could promote the reactions at relatively low temperatures.
The FeCl3 catalyzed reactions were the most chemoselective
and excellent yields could be achieved for certain amines by
using AlCl3. A carbocation mechanism was proposed, and
the controllable syntheses of allylamine and tetrahydroquin-
oline from isoprene and 2,5-dichloroaniline were achieved
by application of this mechanism.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
plexes have also been long investigated. Since the early
works of Livinghouse and Bergman,[5] many reports of tita-
nium- and zirconium-catalyzed hydroamination have been
reported in the literature, and the M=NR species was pro-
posed as the key intermediate in these reactions.[6]
Introduction
The synthesis of amines is of great academic and indus-
trial importance. Among the methods used for the genera-
tion of C–N bonds, hydroamination of unsaturated C–C
bonds has both the advantages of atom economy and
thermodynamic feasibility, and it was pursued by many re-
search groups worldwide.[1] Because of the high activation
barrier of the hydroamination reaction, the development of
catalytic transformations is necessary and has been the fo-
cus of numerous studies.
Depending on different catalysts used, the activation of
C–C and N–H bonds are the two major strategies in cata-
lytic reactions. So as to achieve efficient transformation, the
late transition metals such as Rh, Ru, Ir, Pd, Ni, and Pt
have been long used as catalysts for intra- and intermo-
lecular olefin hydroamination.[2] Recent work by He and
Che found that gold complexes are capable of catalyzing
intramolecular olefin hydroamination reactions through
C=C activation.[3] Later on, gold-catalyzed intermolecular
hydroaminations of allenes and 1,3-dienes were also
achieved by the Yamamoto and He groups.[4] Olefin hy-
droaminations catalyzed by early transition-metal com-
Organolanthanides have been used as effective catalysts
for both intra- and intermolecular olefin hydroaminations
since the pioneering work of Marks and coworkers in
1989.[7] The hydroamination reactions catalyzed by organo-
lanthanides possess the features of very high turnover fre-
quencies and excellent stereoselectivities, which makes this
methodology quite practical for the concise synthesis of
naturally occurring alkaloids and other polycyclic aza-
cycles, as exemplified by the successful total synthesis of
(+)-xenovenine, (+)-pyrrolidine 197B,[8] as well as other az-
acycle natural products.[9] The general accepted mechanism
for the organolanthanide-catalyzed hydroamination reac-
tions involves the insertion of the C–C multiple bond into
the Ln–N bond, followed by rapid protonolysis by other
amine substrates, and the insertion step is defined as the
rate-determining step. Because of the importance of stereo-
selectivity control in natural product synthesis, the asym-
metric olefin hydroamination reaction was also studied with
other metal catalysts, such as Ni, Rh, and Zn, by exploiting
various chiral ancillary ligands.[1c,10]
[a] Key Laboratory of Organic Synthesis of Jiangsu Province,
College of Chemistry and Chemical Engineering, Suzhou
University
In an attempt to find a cheap and ecofriendly hydro-
amination catalyst, many new catalytic processes have been
developed in recent years.[11] The scope of the catalyst was
greatly expanded by using main-group metals as catalysts.
The Hill group found that a calcium complex is an efficient
catalyst for both intra- and intermolecular olefin hydroami-
nations.[12] By using Bi(OTf)3, Shibasaki and coworkers
found that allylic amides could be formed in high yields
Suzhou, 215123, China
Fax: + 86-512-65880089
E-mail: liyahong@suda.edu.cn
[b] Qinghai Institute of Salt Lakes, Chinese Academy of Sciences
Xining, 810008, China
[c] State Key Laboratory of Applied Organic Chemistry, Lanzhou
University
Lanzhou 730000, China
Supporting information for this article is available on the
WWW under http://www.eurjoc.org/ or from the author.
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Y. Li et al.
FULL PAPER
from the hydroamination of 1,3-dienes with various acids, and the results are summarized in Table 1 (see Experi-
amides;[13] later on, the vinylarene hydroamination reaction mental Section for details).
was also accomplished with the same catalytic system.[14]
Table 1. Optimization of conditions for different Lewis acid cata-
lysts.
Brønsted acid catalyzed hydroaminations are also quite
remarkable. By using proton catalysts such as triflic acid,
sulfuric acid, proton-exchanged montmorillonite, HI, and
other forms of proton catalysts,[15] the intra- and intermo-
lecular hydroamination reaction can be accomplished under
relatively mild conditions.
Catalyst Cat. [mol-%]
Temp. [°C]
Time [h]
Yield [%][a]
The Lewis acid catalyzed hydroamination reaction was
firstly reported by Ackermann and coworkers in 2004.[16]
By using TiCl4, the intermolecular hydroamination of nor-
bornene and vinylarene with aromatic amines can be
achieved in excellent yields. The work of Komeyama et al.
found that the FeCl3 catalyst is quite efficient for the intra-
molecular hydroamination of unactivated olefins, and both
five- and six-membered nitrogen heterocycles are accessible
under ambient conditions.[17] On expanding the catalyst
scope, previous results of our group found that the reusable,
air- and moisture-tolerable BiCl3 catalyst is capable of cata-
lyzing the intermolecular hydroamination of norbornene
with aromatic amines.[18]
These newly developed Lewis acid catalytic systems have
the advantages of being readily available and easy to handle
and they are also ecofriendly. However, the reactions have
so far only been applied to a limited number of olefin sub-
strates.[16–18] Another problem with these reactions is that
the mechanism is still unknown. Whereas the oxidative-ad-
dition/reductive-elimination mechanism was defined for
most of the late-transition-metal catalysts, a metal amide
was the key intermediate in organolanthanide-catalyzed re-
actions, and a metal imido species was proposed as the
active intermediate for the early transition-metal-catalyzed
reactions. Little attention has been paid to the pathway of
the reaction catalyzed by commonly used Lewis acids.
Mechanistic understanding of these reactions would be cru-
cial to further improve and expand the Lewis acid catalyzed
olefin hydroamination reaction.
FeCl3
5
100
135
150
169
150
150
150
169
169
110
110
169
150
110
110
150
169
150
8
8
8
8
8
38
45
49
48
54
72
71
trace
60
61
trace
61
71
50
42
67
28
65
5
5
5
10
15
20
10
50
20
10
10
10
10
10
10
10
20
8
8
ZrCl4
24
4
24
24
4
4
8
8
8
BiCl3
AlCl3
8
8
[a] Isolated yields.
Optimization of the conditions revealed that the catalyst
loading, reaction temperature, and reaction time are dif-
ferent for different catalysts to achieve efficient transforma-
tion. When FeCl3 was used, a higher catalyst loading and a
higher temperature were needed to get a desirable yield, and
the optimal conditions of 15 mol-% catalyst loading at
150 °C gave 72% of hydroamination product 3a within 8 h.
However, the ZrCl4 catalyst was found to be less active:
10 mol-% catalyst loading at 169 °C only gave trace
amounts of 3a after 24 h. The reaction time was shortened
when the catalyst loading was increased to 50 mol-%, and
a moderate yield of 3a was obtained within 4 h at 169 °C.
A catalyst loading of 20 mol-% at 110 °C gave similar re-
sults, but a reaction time of 24 h was necessary. The higher
catalyst loading and low reaction rate of the ZrCl4-cata-
lyzed reaction may be attributed to the dimerization of
ZrCl4 when coordinated with aniline.[19] When the reaction
was catalyzed by BiCl3 and AlCl3, a catalyst loading of
10 mol-% at 150 °C gave moderate yield of the product, and
increased catalyst loading and/or higher temperature
showed no superiority.
As a continuation of our previous study,[18] the current
report aims at revealing the scope, limitation, and mecha-
nism of the intermolecular hydroamination of olefins cata-
lyzed by various Lewis acids. By conducting the hydroamin-
ation reactions of norbornene with aromatic amines, the
optimal reaction conditions for different Lewis acid cata-
lysts (FeCl3, ZrCl4, BiCl3, and AlCl3) are presented, and
the catalytic performances of these catalysts are compared.
The possible pathways for these reactions are discussed, and
a carbocation mechanism is most favorable, as supported
by the experimental results. This mechanistic insight further
leads to the controllable synthesis of allylamine and tetra-
hydroquinoline from isoprene and aromatic amines.
Scope and Limitations of the Lewis Acid Catalyzed
Hydroamination Reaction
With the optimized conditions for different catalysts, we
next expanded the reactions to various amines with dif-
ferent substituents on the phenyl ring, and the results are
shown in Table 2.
Results and Discussion
Optimization of the Conditions for Various Lewis Acid
Catalysts
The hydroamination of norbornene (1) with 3,4-dichlo-
For unsubstituted aniline (Table 2, Entry 1), it is interest-
roaniline (2a) was investigated with different kinds of Lewis ing that FeCl3 showed no catalytic activity at all, whereas
1930
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Lewis Acid Catalyzed Intermolecular Olefin Hydroamination
Table 2. Lewis acid catalyzed hydroamination of norbornene with various aromatic amines.
Entry Amine
Product
FeCl3
Selectivity[a]
ZrCl4
Selectivity[a]
BiCl3
AlCl3
Yield[b]
Yield[b]
Selectivity[a] Yield[b] Selectivity[a] Yield[b]
1
2
3
4
5
6
7
8
aniline
3b
3c
3d
3e
3f
3g
3h
0:0:0
0
88
93
86
82
26
18
88
39
30
Trace
71
0
72:28:0
100:0:0
100:0:0
100:0:0
94:5:1
82:8:10
100:0:0
100:0:0
100:0:0
87:10:3
78:22:0
100:0:0
0:0:0
43
61
67
69
72
66
55
86
63
74
59
67
0
58:42:0
100:0:0
100:0:0
98:2:0
83:13:4
82:8:10
100:0:0
100:0:0
100:0:0
87:10:3
78:22:0
100:0:0
0:0:0
45
68
68
80
84
68
57
92
70
81
64
81
0
76:24:0
100:0:0
100:0:0
100:0:0
82:15:4
91:4:5
100:0:0
100:0:0
92:8:0
52
Trace
69
44
75
49
30
82
70
44
66
82
0
4-nitroaniline
2-nitroaniline
3-nitroaniline
2-chloroaniline
3-chloroaniline
4-chloroaniline
100:0:0
100:0:0
100:0:0
97:3:0
94:6:0
100:0:0
100:0:0
100:0:0
98:2:0
100:0:0
100:0:0
0:0:0
2,5-dichloroaniline 3i
9
4-bromoaniline
2-fluoroaniline
4-fluoroaniline
2,4-dichloroaniline 3m
4-methoxyaniline 3n
3j
3k
3l
10
11
12
13
90:9:1
87:13:0
100:0:0
0:0:0
[a] Ratio of 3/4/5 determined by GC–MS. [b] Isolated yield of 3.
the other three catalysts gave hydroamination product 3b in and BiCl3. In almost all cases, the yields of the AlCl3 cata-
~50% yield and hydroarylation byproduct 4 in comparable lyzed reactions were not as good as those obtained by ZrCl4
yield.
and BiCl3 catalysis, and only a trace amount of the hydroa-
Without regard of the catalyst, enhanced selectivity and mination product was detected for the 4-NO2 aniline sub-
yield were found for most of the substituted anilines. When strate. The poorer activity of AlCl3 in these reactions may
the aniline is monosubstituted with an NO2 group, only the be the result of rapid hydrolysis, as all the reactions were
hydroamination products were obtained (Table 2, Entries 2, conducted under ambient conditions. High yields of the re-
3, and 4). The reactions of 4-chloroaniline, 4-bromoaniline, actions and the recoverable and reusable properties of BiCl3
as well as the dichloro-substituted anilines, were also quite make it the best catalyst choice for the current transforma-
selective (Table 2, Entries 7, 9, 8, and 12); the major prod- tion.[18]
ucts of type 3 were formed exclusively for all these sub-
It is interesting to find that no hydroamination or hy-
strates. However, a chlorine atom at C-2 or C-3, as well as droarylation occurred for 4-methoxyaniline, no matter
a fluorine atom at C-2 or C-4, of the phenyl ring of the which Lewis acid was used under various conditions
aniline (Table 2, Entries 5, 6, 10, and 11), resulted in lower (Table 2, Entry 13). These results indicate that the electronic
chemoselectivities relative to those of the above-mentioned structure of the phenyl ring influences the reactivity of the
reactions, but higher chemoselectivities than those obtained aniline most. Although all the electron-poor anilines proved
with the unsubstituted substrate.
to be effective nitrogen sources, we proposed that increased
The catalytic performances of the Lewis acids were found acidity of the amine hydrogen atom would be crucial for
to be different. The highest chemoselectivity was found in the occurrence of the reaction.[20] To test this idea, we con-
FeCl3 catalyzed reactions. Only the hydroamination prod- ducted more reactions of electron-donating-group-contain-
uct was formed in almost all the FeCl3 catalyzed reactions, ing anilines by using BiCl3 as a catalyst. No reaction was
and only one hydroarylation byproduct was formed in quite detected with the use of 4-methylaniline; reaction of 2-
low yield in limited cases. The FeCl3 catalyst was also found methylaniline with norbornene only gave 15% yield of hy-
to be quite substrate-dependent. Excellent yields were ob- droamination product 3o. However, introduction of an ad-
tained with substrates containing an NO2 group or a C-2 ditional NO2 group onto 4-methylaniline, namely, 4-methyl-
chloride atom and dichloride-substituted anilines also gave 2-nitroaniline, greatly improved the yield of hydroamination
good yields; however, the yields were lower than 40% when product 3p to 73%.
other halogen-substituted anilines were used as the nitrogen
source. Particularly for 2-fluoroaniline, as no reaction oc-
curred when FeCl3 was used as the catalyst.
Mechanistic Insight
The results show that the ZrCl4 and BiCl3 catalysts can
be applied to a wide range of amine substrates. Relative to
The mechanism of these reactions has not been explored.
the results of FeCl3 and AlCl3 catalyzed reactions, higher The metal–imido complex was proposed for the hydroamin-
yields were obtained for the reactions catalyzed by ZrCl4 ation reaction catalyzed by TiCl4.[16] However, the forma-
Eur. J. Org. Chem. 2008, 1929–1936
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1931

Y. Li et al.
FULL PAPER
tion of metal–imido species from TiCl4 and aniline is ques- nism postulated in Scheme 1b suggests that intermediate 12
tionable, and it is also difficult to use this mechanism for can be afforded by elimination of HCl from AlCl3–amine
the explanation of reactions catalyzed by various Lewis ac- complex 6, and insertion of the C=C bond of the olefin
ids.[21]
into the metal–N bond of this intermediate will finally give
The involvement of a proton catalyst in the reaction is 14 as the hydroamination product.[4a]
possible, as the metal chlorides used in the reactions would
Although both mechanisms are possible, we think the
be easily hydrolyzed under the ambient conditions. The re- carbocation mechanism is more favorable as supported by
sults are consistent with previous hydroamination reactions the experimental results. Firstly, these Lewis acid catalyzed
catalyzed by acidic zeolites, from which electron-poor ani- reactions have only been applied to a limited number of
lines were found to be more reactive.[15i] It should be noted cases so far. Despite the intramolecular hydroamination,
that the results of these Lewis acid catalyzed reactions are the unsaturated species investigated were generally limited
different from those of the proton-catalyzed ones in two to norbornene and styrene, as the generated carbocations
ways. The first one is that only trace amounts of product from these olefins are stabilized intramolecularly.[15a]
was detected when HCl was used as the catalyst.[18] Another Attempts to use other cyclic and acyclic olefins, such as
difference is that relative to the HI catalyzed reactions of cyclohexene and hex-1-ene, proved unsuccessful. Further
norbornene with aromatic amines,[15d] the Lewis acid cata- support of this mechanism can also be provided by the out-
lyzed reactions are much more chemoselective, and the hy- come that the electron-poor anilines are more reactive. It is
droamination products are formed exclusively in most cases. reasonable to propose that protonation of the olefin is more
Because the reactions can be catalyzed by various Lewis facile with increased acidity of the amine hydrogen atom.[20]
acids, two possible mechanisms are outlined in Scheme 1.
The carbocation mechanism prompted us to exam other
Scheme 1a illustrates that the reactions may be initiated by olefins that may generate relatively stable carbocations from
the Lewis acid–base interaction between the catalyst and protonation.[22] The results of isoprene were quite encour-
the amine substrate, and protonation of norbornene by 6 aging. As shown in Scheme 2, the reaction of isoprene (15)
or 9 to form cationic intermediate 7 is the key step of the with 2,5-dichloroaniline could be controlled by using dif-
hydroamination and hydroarylation reaction.[18] By using ferent solvents. When catalyzed by 10 mol-% of BiCl3, al-
AlCl3 as a representative Lewis acid, the alternative mecha- lylamine 16 was obtained in 40% yield in dioxane, and
Scheme 1. Plausible mechanisms for the hydroamination and hydroalkylation reactions of norbornene with aromatic amines.
1932
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Eur. J. Org. Chem. 2008, 1929–1936

Lewis Acid Catalyzed Intermolecular Olefin Hydroamination
1,2,3,4-tetrahydroquinoline 17 was formed selectively when yields in short reaction times. Optimization of the reaction
the reaction was carried out in toluene. The use of other conditions found that the ZrCl4 catalyzed reactions could
Lewis acids would give similar results.
be accomplished at relatively low temperatures, but a higher
catalyst loading and a longer reaction time were necessary
for desirable yields. The FeCl3 catalyzed reactions were the
most chemoselective and excellent yields were achieved for
certain amines when AlCl3 was used as the catalyst.
The reactivity of different functional-group-substituted
anilines was investigated, and it was found that increased
acidity of the amine hydrogen atom was crucial for a high
transformation yield. The possible mechanisms were pro-
posed, and a carbocation mechanism was supported by the
experiments. This mechanism was taken into consideration
in the controllable syntheses of allylamine and tetra-
hydroquinoline from isoprene and aromatic amines.
Scheme 2. Divergent reactions of isoprene with 2,5-dichloroaniline
in different solvents: (a) BiCl3 (10 mol-%), 150 °C, dioxane; (b)
BiCl3 (10 mol-%), 150 °C, toluene.
Experimental Section
Despite the drawback of low yields under the current
conditions, the reaction of isoprene with aromatic amines
is quite remarkable as a synthetic methodology, as the al-
lylamine derivatives are important synthetic precursors that
can be further transformed,[23] and tetrahydroquinoline is
the substructure of many naturally occurring substances.[24]
The different results of the isoprene reactions can be well
explained by the carbocation mechanism. As illustrated in
Scheme 3, the protonation of isoprene (15) will firstly give
more-stabilized tertiary cation 18, which may be in its reso-
General: All reactions were carried out in pressure tubes (45 mL,
150 psi) equipped with a magnetic stirring bar and capped with a
solid PTFE plug. All starting materials were purchased from com-
mercial suppliers and used without further purification. A Varian
Unity Plus 400 MHz spectrometer was used to obtain H and 13C
1
NMR spectra. GC–MS spectra were recorded with a GCMS-
QP2010 by using dodecane as an internal standard and MS spectra
were obtained by TOF-MS.
General Procedure: To a 45-mL pressure tube (ACEGLASS) was
nance form 19 upon reaction with a nitrogen source to give added norbornene (0.188 g, 2.00 mmol), BiCl3 (0.0630 g,
0.2 mmol), aniline (8.00 mmol), and anhydrous toluene (4 mL) (the
reactions catalyzed by other Lewis acids were conducted with sim-
ilar procedures according to the conditions optimized in Table 1).
The pressure tube was sealed, and the suspension was stirred at
150 °C for 6 h. After the pressure tube was cooled to room tem-
perature, the reaction mixture was transferred to a round-bottomed
flask (250 mL) and CH2Cl2 (20 mL) and H2O (20 mL) were added
to the flask. The organic layer was collected, and the aqueous phase
was extracted with CH2Cl2 (3ϫ25 mL). The combined organic
layer was dried with MgSO4 and concentrated in vacuo. Pure prod-
uct was obtained by column chromatography.
hydroamination product 16. In the presence of Lewis acid
and amine, the C=C bond of allylamine 16 could be pro-
tonated to give tertiary cation 20. When the reaction is con-
ducted in dioxane, this cation could be stabilized by the
polar solvent and further reaction is hindered. However, the
polarity of toluene is much lower, which enables more-reac-
tive 20 for the intramolecular hydroarylation reaction to
give 17 as the product.
N-(3,4-Dichlorophenyl)bicyclo[2.2.1]heptan-2-amine (3a): Product
3a (0.364 g, 71%, unless mentioned otherwise, all yields given in
this section are from the BiCl3 catalyzed reactions, yields of other
Lewis acid catalyzed reactions are given in Tables 1 and 2) was
obtained as a yellow oil after column chromatography (petroleum
1
ether/ethyl acetate, 100:1). H NMR (400 MHz, CDCl3): δ = 7.17
(dd, J = 5.2, 4.4 Hz, 1 H), 6.61 (m, 1 H), 6.39 (dd, J = 2.8, 2.4 Hz,
1 H), 3.74 (s, 1 H), 3.16 (m, 1 H), 2.30 (s, 1 H), 2.24 (s, 1 H), 1.83
(m, 1 H), 1.61–1.41 (m, 3 H), 1.24–1.14 (m, 4 H) ppm.[25]
Scheme 3. Mechanism for the formations of 16 and 17 from iso-
N-Phenylbicyclo[2.2.1]heptan-2-amine (3b): Product 3b (0.169 g,
45%) was obtained as a pale yellow oil after column chromatog-
raphy (petroleum ether/ethyl acetate, 50:1). 1H NMR (400 MHz,
CDCl3): δ = 7.18–7.14 (m, 2 H), 6.69–6.65 (m, 1 H), 6.58–6.56 (m,
2 H), 3.48 (s, 1 H, NH), 3.23–3.22 (m, 1 H), 2.27 (s, 2 H), 1.84–
1.79 (m, 1 H), 1.52–1.43 (m, 3 H),1.22–1.16 (m, 4 H) ppm.
prene and 2,5-dichloroaniline.
Conclusions
By conducting the hydroamination of norbornene with
aromatic amines, Lewis acid catalysts were expanded to sev-
eral commonly used metal halides, and the catalytic per-
formance of these catalysts was compared. Among the cata-
N-(4-Nitrophenyl)bicyclo[2.2.1]heptan-2-amine (3c): Product 3c
(0.316 g, 68%) was obtained as a pale yellow oil after column
chromatography (petroleum ether/ethyl acetate, 10:1). 1H NMR
(400 MHz, CDCl3): δ = 7.86 (t, J = 8.8 Hz, 2 H), 6.41 (d, J =
lysts, BiCl3 was the most effective and provided higher 8.8 Hz, 2 H), 4.61 (s, 1 H), 3.21 (s, 1 H), 2.25 (m, 2 H), 1.81–1.76
Eur. J. Org. Chem. 2008, 1929–1936
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Y. Li et al.
(dd, J = 8.0, 7.6 Hz, 1 H), 1.50–1.35 (m, 3 H), 1.21–1.09 (m, 4 H) J = 2.4, 4.4 Hz, 2 H), 3.63 (s, 1 H), 3.17 (m, 1 H), 2.32 (s, 1 H),
FULL PAPER
ppm.
2.28 (s, 1 H), 1.67–1.43 (m, 3 H), 1.34–1.13 (m, 4 H) ppm.
N-(2-Nitrophenyl)bicyclo[2.2.1]heptan-2-amine (3d): Product 3d
(0.316 g, 68%) was obtained as a yellow solid after column
chromatography (petroleum ether/ethyl acetate, 20:1). 1H NMR
(400 MHz, CDCl3): δ = 8.06 (d, J = 8.4 Hz, 1 H), 7.92 (s, 1 H),
7.35–7.31 (t, J = 7.2 Hz, 1 H), 6.75–6.73 (d, J = 8.8 Hz, 1 H), 6.55–
6.51 (t, J = 8.0 Hz, 1 H), 3.33 (m, 1 H), 2.37 (s, 2 H), 1.82 (ddd, J
= 2.0, 2.4, 22 Hz, 1 H), 1.58–1.45 (m, 3 H), 1.34–1.30 (m, 1 H),
1.22–1.10 (m, 3 H) ppm.
N-(2,4-Dichlorophenyl)bicyclo[2.2.1]heptan-2-amine (3m): Product
3m (0.415 g, 81%) was obtained as a yellow oil after column
chromatography (petroleum ether/ethyl acetate, 100:1). 1H NMR
(400 MHz, CDCl3): δ = 7.23–7.22 (d, J = 2.4 Hz, 1 H, 3-C6H3N),
7.09–7.06 (dd, J = 2.4, 2.4 Hz, 1 H, 5-C6H3N), 6.54–6.52 (d, J =
8.8 Hz, 1 H), 4.13 (s, 1 H, NH), 3.22 (s, 1 H, CH), 2.32–2.26 (d, J
= 21.6 Hz, 2 H), 1.87–1.82 (m, 1 H), 1.53–1.40 (m, 3 H), 1.22–1.07
(m, 4 H) ppm.
N-(3-Nitrophenyl)bicyclo[2.2.1]heptan-2-amine (3e): Product 3e
(0.371 g, 80%) was obtained as an orange solid after column
chromatography (petroleum ether/ethyl acetate, 20:1). 1H NMR
(400 MHz, CDCl3): δ = 7.41–7.39 (d, J = 8.0 Hz, 1 H), 7.26 (s, 1
H), 7.19–7.15 (m, 1 H), 6.75–6.72 (m, 1 H), 3.87 (s, 1 H, NH), 3.19
(s, 1 H, CH), 2.19–2.25 (m, 2 H, CH2), 1.82–1.77 (m, 1 H, CH),
1.56–1.36 (m, 3 H), 1.18–1.13 (m, 4 H) ppm.
N-o-Tolybicyclo[2.2.1]heptan-2-amine (3o): Product 3o (0.060 g,
15%) was obtained as a pale yellow oil after column chromatog-
1
raphy (petroleum ether/ethyl acetate, 100:1). H NMR (400 MHz,
CDCl3): δ = 7.13–7.09 (t, J = 7.6 Hz, 1 H, 6-C6H3N), 7.04–7.02 (d,
J = 7.2 Hz, 1 H, 3-C6H3N), 6.65–6.56 (m, 2 H), 3.34 (s, 1 H, NH),
3.28–3.27 (m, 1 H, CH), 2.29 (s, 2 H, CH2), 2.10 (s, CH3), 1.88–
1.82 (m, 1 H), 1.55–1.45 (m, 3 H), 1.24–1.17 (m, 4 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 145.75 (C), 130.24 (CH), 127.26
(CH), 121.91 (C), 116.65 (CH), 110.66 (CH), 56.72 (CH), 41.54
(CH), 41.43 (CH2), 35.85 (CH2), 35.62 (CH), 28.72 (CH2), 26.58
(CH2), 17.83 (CH3) ppm. HRMS (EI): calcd. for C14H19N
201.1517; found 201.1527.
N-(2-Chlorophenyl)bicyclo[2.2.1]heptan-2-amine (3f): Product 3f
(0.373 g, 84%) was obtained as a colorless oil after column
chromatography (petroleum ether/ethyl acetate, 200:1). 1H NMR
(400 MHz, CDCl3): δ = 7.19–7.15 (m, 1 H), 7.07–7.03 (m, 1 H),
6.65–6.57 (m, 2 H), 4.09 (s, 1 H), 3.19 (m, 1 H), 2.23–2.22 (m, 2
H), 1.78 (m, 1 H), 1.50–1.41 (m, 3 H), 1.23–1.10 (m, 4 H) ppm.
N-(3-Chlorophenyl)bicyclo[2.2.1]heptan-2-amine (3g): Product 3g
(0.302 g, 68%) was obtained as a colorless oil after column
chromatography (petroleum ether/ethyl acetate, 50:1). 1H NMR
(400 MHz, CDCl3): δ = 7.06–7.02 (t, J = 8.0 Hz, 1 H), 6.63–6.61
(d, J = 8.0 Hz, 1 H), 6.52 (s, 1 H), 6.42–6.40 (d, J = 8.4 Hz, 1 H),
3.63 (s, 1 H, NH), 3.20–3.18 (m, 1 H), 2.29–2.26 (m, 2 H), 1.85–
1.80 (m, 1 H), 1.53–1.41 (m, 3 H), 1.26–1.18 (m, 4 H) ppm.
N-(4-Methyl-2-nitrophenyl)bicyclo[2.2.1]heptan-2-amine (3p): Prod-
uct 3p (0.359 g, 73%) was obtained as an orange oil after column
chromatography (petroleum ether/ethyl acetate, 100:1). 1H NMR
(400 MHz, CDCl3): δ = 7.97 (s, 1 H), 7.91 (s, 1 H), 6.75–6.73 (d, J
= 8.8 Hz, 1 H), 3.40 (s, 1 H, NH), 2.36–2.34 (m, 2 H), 2.26 (s, 3
H, CH3), 1.93–1.87 (m, 1 H, CH), 1.58–1.53 (m, 4 H), 1.41–1.37
(m, 1 H), 1.26–1.20 (m, 3 H) ppm. 13C NMR (100 MHz, CDCl3):
δ = 141.99 (CH), 136.59 (C), 130.27 (C), 125.01 (C), 123.46 (CH),
113.69 (CH), 54.98 (CH), 40.66 (CH), 40.07 (CH2), 34.68 (CH2),
34.57 (CH), 27.35 (CH2), 25.28 (CH2), 18.94 (CH3) ppm. HRMS
(EI): calcd. for C14H18N2O2 246.1368; found 246.1376.
N-(4-Chlorophenyl)bicyclo[2.2.1]heptan-2-amine (3h): Product 3h
(0.253 g, 57%) was obtained as a pale yellow oil after column
chromatography (petroleum ether/ethyl acetate, 25:1). 1H NMR
(400 MHz, CDCl3): δ = 7.03–7.01 (m, 2 H), 6.42–6.40 (m, 2 H),
3.65 (s, 1 H), 3.09 (m, 1 H), 2.22 (s, 1 H), 2.18 (s, 1 H), 1.74 (dd,
J = 8.0, 7.6, Hz, 1 H), 1.51–1.35 (m, 3 H), 1.18–1.06 (m, 4 H) ppm.
2,5-Dichloro-N-(2-methylprop-1-enyl)aniline (16): Product 16
(0.184 g, 40%) was obtained as
a yellow oil after column
N-(2,5-Dichlorophenyl)bicyclo[2.2.1]heptan-2-amine (3i): Product 3i
chromatography (petroleum ether/ethyl acetate, 200:1). 1H NMR
(400 MHz, CDCl3): δ = 7.07–7.05 (d, J = 8.4 Hz, 1 H), 6.52–6.49
(m, 2 H), 5.25–5.22 (t, J = 6.4 Hz, 1 H), 4.2 (s, 1 H, NH), 3.63–
(0.471 g, 92%) was obtained as
a yellow oil after column
chromatography (petroleum ether/ethyl acetate, 60:1). 1H NMR
(400 MHz, CDCl3): δ = 7.26–7.11 (m, 1 H), 6.57 (s, 2 H), 4.22 (s,
1 H, NH), 3.22 (s, 1 H), 2.33–2.29 (m, 2 H), 1.89–1.84 (m, 1 H),
1.56–1.47 (m, 3 H), 1.26–1.20 (m, 4 H) ppm.
3.61 (t, J = 6.4 Hz, 2 H), 1.70–1.65 (d, J = 17.2 Hz, 6 H) ppm. 13
C
NMR (100 MHz, CDCl3): δ = 145.07 (1-C6H3NCl2), 137.02 (2-
C6H3NCl2), 133.74 (5-C6H3NCl2), 129.83 (6-C6H3NCl2), 120.52 (3-
C6H3NCl2), 117.38 (4-C6H3NCl2), 116.81 (C6H3NCl2NHCH2-
CHC), 111.28 (C6H3NCl2NHCH2CH), 41.78 (C6H3NCl2NHCH2),
25.95 (C6H3NCl2NHCH2CHCCH3), 18.29 (C6H3NCl2NHCH2-
CHCCH3) ppm. HRMS (EI): calcd. for C11H13NCl2 229.0425;
found 229.0434.
N-(4-Bromophenyl)bicyclo[2.2.1]heptan-2-amine (3j): Product 3j
(0.372 g, 70%) was obtained as an orange oil after column
chromatography (petroleum ether/ethyl acetate, 200:1). 1H NMR
(400 MHz, CDCl3): δ = 7.23–7.21 (d, J = 8.8 Hz, 2 H), 6.44–6.42
(d, J = 8.8 Hz, 2 H), 3.62 (s, 1 H, NH), 3.18–3.16 (m, 1 H, CH),
2.28–2.24 (m, 2 H, CH2), 1.84–1.80 (m, 1 H, CH), 1.53–1.41 (m, 3
H), 1.19–1.17 (m, 4 H) ppm.
5,8-Dichloro-1,2,3,4-tetrahydro-4,4-dimethylquinoline (17): Product
17 (0.174 g, 38%) was obtained as a pale yellow oil after column
chromatography (petroleum ether/ethyl acetate, 200:1). 1H NMR
(400 MHz, CDCl3): δ = 6.94–6.92 (d, J = 8.4 Hz, 1 H), 6.53–6.51
(d, J = 8.4 Hz, 1 H), 4.24 (s, 1 H, NH), 2.74–2.71 (t, J = 6.8 Hz, 2
H), 1.65–1.62 (t, J = 6.8 Hz, 2 H), 1.16 (s, 6 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 141.61 (C-9), 133.36 (C-10), 127.53 (C-5),
119.55 (C-7), 116.91 (C-8), 116.75 (C-6), 49.32 (C-3), 34.06 (C-2),
29.43 (C-4-CH3), 23.27 (C-4-CH3) ppm. HRMS (EI): calcd. for
C11H13NCl2 229.0425; found 229.0418.
N-(2-Fluorophenyl)bicyclo[2.2.1]heptan-2-amine (3k): Product 3k
(0.332 g, 81%) was obtained as
a yellow oil after column
chromatography (petroleum ether/ethyl acetate, 200:1). 1H NMR
(400 MHz, CDCl3): δ = 6.92–6.84 (m, 2 H), 6.61–6.50 (m, 1 H),
6.49–6.48 (d, J = 1.6 Hz, 1 H), 3.81 (s, 1 H, NH), 3.17–3.15 (t, J
= 3.6 Hz, 1 H), 2.21 (s, 2 H), 1.78–1.73 (m, 1 H), 1.53–1.39 (m, 3
H), 1.20–1.06 (m, 4 H) ppm.
N-(4-Fluorophenyl)bicyclo[2.2.1]heptan-2-amine (3l): Product 3l
(0.262 g, 64%) was obtained as an orange oil after column
chromatography (petroleum ether/ethyl acetate, 100:1). 1H NMR
(400 MHz, CDCl3): δ = 6.87 (dd, J = 6.4, 8.8 Hz, 2 H), 6.51 (dd,
Supporting Information (see footnote on the first page of this arti-
cle): Spectroscopic data for the products.
1934
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Eur. J. Org. Chem. 2008, 1929–1936

Lewis Acid Catalyzed Intermolecular Olefin Hydroamination
[10]
[11]
a) R. Dorta, P. Egli, F. Zurcher, A. Togni, J. Am. Chem. Soc.
1997, 119, 10857–10858; b) O. Lober, M. Kawatsura, J. F. Hart-
wig, J. Am. Chem. Soc. 2001, 123, 4366–4367; c) U. Nette-
koven, J. F. Hartwig, J. Am. Chem. Soc. 2002, 124, 1166–1167;
d) L. Fadini, A. Togni, Chem. Commun. 2003, 30–31.
a) V. Khedkar, A. Tillack, C. Benisch, J. P. Melder, M. Beller,
J. Mol. Catal. A Chem. 2005, 241, 175–183; b) M. Beller, C.
Breindl, Tetrahedron 1998, 54, 6359–6368; c) J. Seayad, A. Til-
lack, C. G. Hartung, M. Beller, Adv. Synth. Catal. 2002, 344,
795–813; d) Q. Ruo, E. M. Thomas, Tetrahedron 2001, 57,
6027–6033; e) J. J. Brunet, N. C. Chu, O. Diallo, E. Mothes, J.
Mol. Catal. A Chem. 2003, 198, 107–110; f) A. A. M. Lapis,
B. A. DaSilveira, J. D. Scholten, F. M. Nachtigall, M. N. Eber-
lin, J. Dupont, Tetrahedron Lett. 2006, 47, 6775–6779; g) A.
Ates, C. Quinet, Eur. J. Org. Chem. 2003, 1623–1626; h) B.-
L. Yin, T.-S. Hu, Y.-L. Wu, Tetrahedron Lett. 2004, 45, 2017–
2021.
Acknowledgments
The authors appreciate the financial support of the Chinese Acad-
emy of Sciences through the Hundreds of Talents Program
(2005012), the Natural Science Foundation of Jiangsu Province
(BK2005030), and Suzhou University. The authors would like to
thank Prof. Aaron L. Odom for editorial comments on a previous
version of the manuscript and for helpful scientific discussions.
[1] Recent reviews: a) K. C. Hultzsch, Org. Biomol. Chem. 2005,
3, 1819–1824; b) K. C. Hultzsch, Adv. Synth. Catal. 2005, 347,
367–391; c) P. W. Roesky, T. E. Mueller, Angew. Chem. Int. Ed.
2003, 42, 2708–2710; d) T. E. Muller, M. Beller, Chem. Rev.
1998, 98, 675–704; e) J. J. Brunet, D. Neibecker in Catalytic
Heterofunctionalization (Eds.: A. Togni, H. Grutzmacher),
Wiley-VCH, Weinheim, 2001, pp. 91–141.
[12]
[13]
[14]
[15]
M. R. Crimmin, I. J. Casely, M. S. Hill, J. Am. Chem. Soc.
2005, 127, 2042–2043.
H. Qin, N. Yamagiwa, S. Matsunaga, M. Shibasaki, J. Am.
Chem. Soc. 2006, 128, 1611–1614.
H. Qin, N. Yamagiwa, S. Matsunaga, M. Shibasaki, Chem.
Asian J. 2007, 2, 150–154.
[2] For recent examples of hydroamination reactions catalyzed by
late transition metals, see: a) T. E. Muller, M. Grosche, E.
Herdtweck, A.-K. Pleier, E. Walter, Y.-K. Yan, Organometallics
2000, 19, 170–183; b) H. M. Senn, P. E. BlGchl, A. Togni, J.
Am. Chem. Soc. 2000, 122, 4098–4107; c) L. Fadini, A. Togni,
Chem. Commun. 2003, 30–31; d) J. F. Hartwig, Pure Appl.
Chem. 2004, 76, 507–516; e) K. Li, P. H. Phua, K. K. Hii, Tet-
rahedron 2005, 61, 6237–6242; f) J. Takaya, J. F. Hartwig, J.
Am. Chem. Soc. 2005, 127, 5756–5757; g) L. D. Field, B. A.
Messerle, K. Q. Vuong, P. Turner, Organometallics 2005, 24,
4241–4250; h) T. Shimada, G. B. Bajracharya, Y. Yamamoto,
Eur. J. Org. Chem. 2005, 59–62; i) X. Li, A. R. Chianese, T.
Vogel, R. H. Crabtree, Org. Lett. 2005, 7, 5437–5440; j) R. A.
Windenhoefer, X. Han, Eur. J. Org. Chem. 2006, 4555–4563; k)
R. S. Robinson, M. C. Dovey, D. Gravestock, Eur. J. Org.
Chem. 2005, 505–511; l) M. Rodriguez-Zubiri, S. Anguille, J. J.
Brunet, J. Mol. Catal. A Chem. 2007, 271, 146–151; m) J.-J.
Brunet, N. C. Chu, O. Diallo, Organometallics 2005, 24, 3104–
3110. For early works of Brunet et al. on rhodium-catalyzed
hydroamination of norbornene with aromatic amines, see: n)
J. J. Bunet, G. Commenges, D. Neibecker, L. Rosenberg, J. Or-
ganomet. Chem. 1996, 522, 117–122; o) J. J. Bunet, D. Nei-
becker, K. Philippot, Tetrahedron Lett. 1993, 34, 3877–3880.
[3] a) J. Zhang, C.-G. Yang, C. He, J. Am. Chem. Soc. 2006, 128,
1798–1799; b) X. Y. Liu, C. H. Li, C. M. Che, Org. Lett. 2006,
8, 2707–2710.
[4] a) N. Nishina, Y. Yamamoto, Angew. Chem. Int. Ed. 2006, 45,
3314–3317; b) C. Brouwer, C. He, Angew. Chem. Int. Ed. 2006,
45, 1744–1747.
[5] a) R. D. Profilet, C. H. Zambrano, P. E. Fanwick, J. J. Nash,
I. P. Rothwell, Inorg. Chem. 1990, 29, 4364–4366; b) P. J. Walsh,
A. M. Baranger, R. G. Bergman, J. Am. Chem. Soc. 1992, 114,
1708–1719; c) P. L. McGrane, M. Jensen, T. Livinghouse, J.
Am. Chem. Soc. 1992, 114, 5459–5460.
[6] For recent reviews on hydroamination reactions catalyzed by
early transition metals, see: a) I. Bytschkov, S. Doye, Eur. J.
Org. Chem. 2003, 935–946; b) S. Doye, Synlett 2004, 1653–
1672; c) A. L. Odom, Dalton Trans. 2005, 225–233. For recent
examples catalyzed by Ti and Zr catalysts, see: d) C. Muller,
C. Loos, N. Schulenberg, S. Doye, Eur. J. Org. Chem. 2006,
2499–2503; e) M. C. Wood, D. C. Leitch, C. S. Yeung, J. A. Ko-
zak, L. L. Schafer, Angew. Chem. Int. Ed. 2007, 46, 354–358; f)
J. A. Bexrud, J. D. Beard, D. C. Leitch, L. L. Schafer, Org. Lett.
2005, 7, 1959–1962; g) R. K. Thomson, J. A. Bexrud, L. L.
Schafer, Organometallics 2006, 25, 4069–4071.
a) L. L. Anderson, J. Arnold, R. G. Bergman, J. Am. Chem.
Soc. 2005, 127, 14542–14543; b) D. C. Rosenfeld, S. Shekhar,
A. Takemiya, M. Utsunomiya, J. F. Hartwig, Org. Lett. 2006,
8, 4179–4182; c) B. Schlummer, J. F. Hartwig, Org. Lett. 2002,
4, 1471–1474; d) K. Marcsekova, S. Doye, Synthesis 2007, 145–
154; e) C. M. Haskins, D. W. Knight, Chem. Commun. 2002,
2724–2725; f) Z. Li, J. Zhang, C. Brouwer, C. G. Yang, N. W.
Reich, C. He, Org. Lett. 2006, 8, 4175–4178; g) K. Motokura,
N. Nakagiri, K. Mori, T. Mizugaki, K. Ebitani, K. Jitsukawa,
K. Kaneda, Org. Lett. 2006, 8, 4617–4620; h) K. Miura, T.
Honda, T. Nakagawa, T. Takahashi, A. Hosomi, Org. Lett.
2000, 2, 385–388; i) O. Jimenez, T. E. Muller, W. Schwieger,
J. A. Lercher, J. Catal. 2006, 239, 42–50; j) K. Miura, A. Ho-
somi, Synlett 2003, 143–155.
a) L. Ackermann, L. T. Kaspar, C. J. Gschrei, Org. Lett. 2004,
6, 2515–2518; b) L. T. Kaspar, F. Benjamin, L. Ackermann,
Angew. Chem. Int. Ed. 2005, 44, 5972–5974.
a) K. Komeyama, T. Morimoto, K. Takaki, Angew. Chem. Int.
Ed. 2006, 45, 2938–2941; b) J. Michaux, V. Terrason, S.
Marque, J. Wehbe, D. Prim, J.-M. Campagne, Eur. J. Org.
Chem. 2007, 2601–2603.
[16]
[17]
[18]
[19]
[20]
H. Wei, G. Qian, Y. Xia, K. Li, Y. Li, W. Li, Eur. J. Org. Chem.
2007, 4471–4474.
H. Wei, Y.-H. Li, Y. Zhang, Acta Crystallogr., Sect. E 2007,
63, 798–799.
For studies on the acidity of substituted anilines, see: a) B.
Hemmateenejad, M. Sanchooli, J. Chemometrics 2007, 21, 96–
107; b) U. A. Chaudry, P. L. A. Popelier, J. Org. Chem. 2004,
69, 233–241; c) K. C. Gross, P. G. Seybold, J. Org. Chem. 2001,
66, 6919–6925.
According to the suggestion of one of the referees, we con-
ducted the reactions by using TiCl4 as a catalyst under our
conditions. As expected, TiCl4 would be hydrolyzed rapidly un-
der the atmospheric conditions, and the reactions would be
quite inefficient. However, our TiCl4 catalyzed reactions do
give the hydroamination products for various amines, as char-
acterized by 1H NMR spectroscopy of the isolated products,
as well as by GC–MS analysis of the reaction mixtures. The
isolated yields of the hydroamination products from reactions
of norbornene with 4-bromoaniline, 2-chloroaniline, 2,4-
dichloroaniline, 2-fluoroaniline, and 4-chloroaniline are 5, 12,
43, 11, and 8%, respectively.
The reactions of allylsilane with aromatic amines only led to
mixtures inseparable by column chromatography. For selected
studies on the stability and reactivity of carbocations, see: a)
G. Hagen, H. Mayr, J. Am. Chem. Soc. 1991, 113, 4954–4961;
b) S. Minegishi, R. Loos, S. Kobayashi, H. Mayr, J. Am. Chem.
[21]
[7] a) M. R. Gagne, T. J. Marks, J. Am. Chem. Soc. 1989, 111,
4108–4109; b) S. Hong, T. J. Marks, Acc. Chem. Res. 2004, 37,
673–686.
[8] V. M. Arredondo, S. Tian, F. E. McDonald, T. J. Marks, J. Am.
Chem. Soc. 1999, 121, 3633–3639.
[9] G. A. Molander, E. D. Dowdy, S. K. Pack, J. Org. Chem. 2001,
66, 4344–4347.
[22]
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Y. Li et al.
FULL PAPER
Soc. 2005, 127, 2641–2649; c) H. Mayr, G. Lang, A. R. Ofial,
J. Am. Chem. Soc. 2002, 124, 4076–4083.
[23] a) S. Nomoto, S. Shiraishi, A. Shimoyama, Agric. Biol. Chem.
1991, 55, 2917–2918; b) C. M. Vogels, P. E. O’Connor, T. E.
Phillips, K. J. Watson, M. P. Shaver, P. G. Hayes, S. A.
Westcott, Can. J. Chem. 2001, 79, 1898–1905.
[24] a) X. F. Lin, Y. Li, D. W. Ma, Chin. J. Chem. 2004, 22, 932–
934; b) G. Savitha, P. T. Perumal, Tetrahedron Lett. 2006, 47,
3589–3593.
[25] The NMR spectra of known compounds 3a–m are compared
with the reported data in refs.[16a,18]
Received: November 15, 2007
Published Online: February 22, 2008
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Eur. J. Org. Chem. 2008, 1929–1936