Efficient C-N bond formations catalyzed by a proton-exchanged montmorillonite as a heterogeneous Bronsted acid

Article abstract of DOI:10.1021/ol0619821

Nucleophilic addition of sulfonamides and carboxamides to simple alkenes proceeded smoothly using a proton-exchanged montmorillonite catalyst. The spent catalyst was recovered easily from the reaction mixture and was reusable at least five times without any loss of activity. The unique acidity of the proton-exchanged montmorillonite (H-mont) catalyst was found to be applicable to additional reactions: substitution of hydroxyl groups of alcohols with amides and anilines.

Full text of DOI:10.1021/ol0619821

ORGANIC
LETTERS
2006
Vol. 8, No. 20
4617-4620
Efficient C−N Bond Formations
Catalyzed by a Proton-Exchanged
Montmorillonite as a Heterogeneous
Brønsted Acid
Ken Motokura,† Nobuaki Nakagiri,† Kohsuke Mori,‡ Tomoo Mizugaki,†
Kohki Ebitani,† Koichiro Jitsukawa,§ and Kiyotomi Kaneda*,†
Department of Materials Engineering Science, Osaka UniVersity, 1-3 Machikaneyama,
Toyonaka, Osaka 560-8531, Japan, DiVision of Materials and Manufacturing Science,
Osaka UniVersity, 1-2 Yamadaoka, Suita, Osaka 565-8071, Japan, Department of
Materials Science and Engineering, Nagoya Institute of Technology,
Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan
kaneda@cheng.es.osaka-u.ac.jp
Received August 9, 2006
ABSTRACT
Nucleophilic addition of sulfonamides and carboxamides to simple alkenes proceeded smoothly using a proton-exchanged montmorillonite
catalyst. The spent catalyst was recovered easily from the reaction mixture and was reusable at least five times without any loss of activity.
The unique acidity of the proton-exchanged montmorillonite (H-mont) catalyst was found to be applicable to additional reactions: substitution
of hydroxyl groups of alcohols with amides and anilines.
Heterogeneous acid catalysts based on montmorillonite
(mont) have received much attention as advanced materials
due to their unique properties, such as cation exchange ability
in the interlayer, expansible interlayer space, and tunable
acidity.1 Furthermore, the use of monts in liquid-phase
organic synthesis allows for easy catalyst separation and
reuse, which could provide more environmentally friendly
processes compared to homogeneous acids, such as H2SO4.
We have found metal ion species with unique structures in
the interlayers of the mont, which exhibited excellent
catalytic performances in various organic reactions.2
Hydroamination is an important reaction for construction
of new C-N bonds.3 Although various transition-metal
catalysts have been developed for hydroamination,4 there
† Department of Materials Engineering Science, Osaka University.
‡ Division of Materials and Manufacturing Science, Osaka University.
§ Nagoya Institute of Technology.
(1) (a) Pinnavaia, T. J. Science 1983, 220, 365. (b) Laszlo, P. Acc. Chem.
Res. 1986, 19, 121. (c) Izumi, Y.; Onaka, M. AdV. Catal. 1992, 38, 245.
(2) (a) Kawabata, T.; Mizugaki, T.; Ebitani, K.; Kaneda, K. J. Am. Chem.
Soc. 2003, 125, 10486. (b) Motokura, K.; Fujita, N.; Mori, K.; Mizugaki,
T.; Ebitani, K.; Kaneda, K. J. Am. Chem. Soc. 2005, 127, 9674. (c)
Kawabata, T.; Kato, M.; Mizugaki, T.; Ebitani, K.; Kaneda, K. Chem.-
Eur. J. 2005, 11, 288.
10.1021/ol0619821 CCC: $33.50
© 2006 American Chemical Society
Published on Web 09/08/2006

have been few reports on intermolecular reactions of unac-
tivated alkenes.5 Recently, the Au-catalyzed hydroamination
of unactivated alkenes with reactive benzenesulfonamides
was demonstrated6 and several examples for acid-catalyzed
hydroaminations were also reported.7 However, these reaction
systems have some disadvantages: the need for expensive
and toxic catalysts and the significant limitations of amide
groups as aminating reagents. As an alternative to homoge-
neous metal-catalyzed addition reactions to unactivated
alkenes, our group has reported proton-exchanged montmo-
rillonite (H-mont)-mediated addition reactions of 1,3-dicar-
bonyl compounds.8 In the course of our ongoing studies
exploring practical organic transformations, the H-mont
catalyst was proven to be efficient for the intermolecular
hydroamination of unactivated alkenes with various nitrogen
nucleophiles (eq 1). The H-mont catalyst, with its unique
acid sites, exhibits the promising advantages of a simple
workup procedure, reusability, and high catalytic activity.
This is the first report concerning the intermolecular
hydroamination of unactiVated alkenes with amides using
acid catalysts. This catalyst system was also applicable to
the substitution reaction of alcohols with amides and anilines
(eq 2).
Hydroamination of cyclohexene (1a) with p-toluene-
sulfonamide (2a) was carried out in the presence of various
heterogeneous and homogeneous acids, as summarized in
Table 1. The H-mont gave the highest yield of N-cyclohexyl
Table 1. Hydroamination of 1a with 2a Using Acid Catalystsa
yield of
3a (%)b
selectivity of
3a (%)b
entry
catalyst
H-mont
1
2
90
63
20
trace
trace
trace
n.r.
57
>99
>99
>99
-
-
-
H-USY
3
4
H-mordenite
H-ZSM-5
5
6
7
8
mont K10
SO42-/ZrO2
Na+-mont
p-TsOH‚H2Oc
-
90
c
9
H2SO4
44
nr
>99
-
10
none
a Reaction conditions: 1a (2.0 mmol), 2a (1.0 mmol), catalyst (0.1 g),
n-heptane (2 mL), 2 h, 150 °C. b Determined by GC analysis. c 0.1 mmol.
p-toluenesulfonamide (3a) (entry 1). A moderate yield of
the product was obtained in the H-USY-catalyzed reaction
(entry 2), and other solid acids, such as H-ZSM-5, mont K10,
SO42-/ZrO2, and H-mordenite, were less active (entries 3-6).
Notably, the H-mont catalyst showed higher activity than
the homogeneous acids, p-toluenesulfonic acid and H2SO4
(entries 7 and 8).
Table 2 shows the scope of the hydroamination reaction
of various alkenes with amides using the H-mont catalyst.
The hydroamination of norbornene (1b) with para-substituted
benzenesulfonamide derivatives proceeded successfully, af-
fording the corresponding adducts with toleration of func-
tional groups (entries 1-5). Both cyclic and acyclic unac-
tivated alkenes, such as cyclopentene and 1-hexene, were
found to be good acceptors in the reaction with 2a (entries
6-9).9 For hydroamination of inert alkenes with alkylsul-
fonamides, the addition reaction of methanesulfonamide to
1b proceeded to afford N-bicyclo[2.2.1]hept-2-yl methane-
sulfonamide in a 96% yield (entry 11). This H-mont catalyst
also worked well under a mild reaction temperature (entries
2 and 12). To extend the scope of the amides, aromatic,
heteroaromatic, and aliphatic carboxamides were investigated
as potential donors in the reaction of 1b (entries 13-17).
All of these carboxamides underwent hydroamination with
The H-mont was obtained via treatment of a Na+-mont
with aqueous hydrogen chloride. Elemental analysis showed
a 98.9% exchange degree of sodium cations to protons. It
was verified via XRD studies that the layered structure of
the H-mont was retained, and NH3 TPD analysis revealed
that the strength (∆H) and quantity of the acid sites in the
H-mont were 111 kJ mol-1 and 0.86 mmol g-1, respectively.8
(3) (a) Mu¨ller, T. E.; Beller, M. Chem. ReV. 1998, 98, 675. (b) Brunet,
J. J.; Neibecker, D. In Catalytic Heterofunctionalization; Togni, A.,
Gru¨tzmacher, H., Eds.; Wiley-VCH: New York, 2001; p 91. (c) Beller,
M.; Breindl, C.; Eichberger, M.; Hartung, C. G.; Seayad, J.; Thiel, O. R.;
Tillack, A.; Trauthwein, H. Synlett 2002, 1579. (d) Bystschkov, I.; Doye,
S. Eur. J. Org. Chem. 2003, 935. (e) Roesky, P. W.; Mu¨ller, T. E. Angew.
Chem., Int. Ed. 2003, 42, 2708. (f) Hong, S.; Marks, T. J. Acc. Chem. Res.
2004, 37, 673.
(4) For recent examples of metal-catalyzed hydroaminations, see: (a)
Tada, M.; Shimamoto, M.; Sasaki, T.; Iwasawa, Y. Chem. Commun. 2004,
2562. (b) Lauterwasser, F.; Hayes, P. G.; Bra¨se, S.; Piers, W. E.; Schafer,
L. L. Organometallics 2004, 23, 2234. (c) Hultzsch, K. C.; Hampel, F.;
Wagner, T. Organometallics 2004, 23, 2601. (d) Gribkov, D. V.; Hultzsch,
K. C. Angew. Chem., Int. Ed. 2004, 43, 5542. (e) Bender, C. F.;
Widenhoefer, R. J. Am. Chem. Soc. 2005, 127, 1070. (f) Crimmin, M. R.;
Casely, I. J.; Hill, M. S. J. Am. Chem. Soc. 2005, 127, 8294. (g) Waser, J.;
Nambu, H.; Carreira, E. J. Am. Chem. Soc. 2005, 127, 8294. (h) Karshtedt,
D.; Bell, A. T.; Tilly, T. D. J. Am. Chem. Soc. 2005, 127, 12640. (i)
Widenhoefer, R. Angew. Chem., Int. Ed. 2006, 45, 1747. (j) Qin, H.;
Yamagiwa, N.; Matsunaga, S.; Shibasaki, M. J. Am. Chem. Soc. 2006, 128,
1611. (k) Gribkov, D. V.; Hultzsch, K. C.; Hampel, F. J. Am. Chem. Soc.
2006, 128, 3748.
(7) For acid-catalyzed hydroamination, see: (a) Chauvel, A.; Delmon,
B.; Ho¨lderich, W. F. Appl. Catal. A General 1994, 115, 173. (b) Schlummer,
B.; Hartwig, J. F. Org. Lett. 2002, 4, 1471. (c) Anderson, L. L.; Arnold, J.;
Bergman, R. G. J. Am. Chem. Soc. 2005, 127, 14542. (d) Yin, Y.; Zhao,
G. Heterocycles 2006, 68, 23.
(8) Motokura, K.; Fujita, N.; Mori, K.; Mizugaki, T.; Ebitani, K.; Kaneda,
K. Angew. Chem., Int. Ed. 2006, 45, 2605.
(5) Intermolecular reaction with ethylene and propylene: (a) Brunet, J.-
J.; Cadena, M.; Chu, N. C.; Diallo, O.; Jacob, K.; Mothes, E. Organome-
tallics 2004, 23, 1264. (b) Wang, X.; Widenhoefer, R. A. Organometallics
2004, 23, 1649. With dienes: (c) Brouwer, C.; He, C. Angew. Chem., Int.
Ed. 2006, 45, 1744.
(9) Unfortunately, the reaction of styrene derivatives did not give desired
hydroamination products due to rapid oligomerization.
(6) Zhang, J.; Yang, C.-G.; He, C. J. Am. Chem. Soc. 2006, 128, 1798.
4618
Org. Lett., Vol. 8, No. 20, 2006

Table 2. Hydroamination of Alkenes with Nitrogen
Nucleophilesa
Table 3. Reuse of the H-Mont Catalyst for the
Hydroamination of 1b with 2aa
recycle number
fresh 1st 2nd 3rd 4th
5th
conversion of 2a [%]b >99 >99 >99 >99 >99 >99(94)c
a Reaction conditions: 1b (1.5 mmol), 2a (1.0 mmol), H-mont (0.1 g),
n-heptane (2 mL), 150 °C, 0.5 h. b Determined by GC analysis. c Isolated
yield of 3b.
of the spent catalyst, direct recrystallization of the filtrate
gave N-bicyclo[2.2.1]hept-2-yl p-toluenesulfonamide in 98%
isolated yield with a high TON of 570 and a TOF of 570
h-1. These TON and TOF values are much greater than those
reported for the homogeneous Ph3PAuCl/AgOTf system
(TON, 18; TOF, 1.2 h-1).6
Because of the high reactivity of amides as donors in the
H-mont catalyst system, we decided to explore the H-mont-
catalyzed substitution of hydroxyl groups of alcohols with
amide compounds (Table 4).10 For example, the reaction of
Table 4. Substitution of Alcohols with Amidesa
a Reaction conditions: alkene (2.0 mmol), amide (1.0 mmol), H-mont
(0.1 g), n-heptane (2 mL). b Yield of the isolated product based on the amide.
c 1b (1.5 mmol). d Alkene (1.0 mmol) and amide (1.5 mmol) were used.
Yield was based on alkene. e 1,4-Dioxane (2 mL) was used as a solvent.
f The alkene (4 mmol) was added in portions. g H-mont (0.15 g). h GC yield.
i Aniline (2.0 mmol) and 1b (1.0 mmol). Yield was based on 1b.
a Reaction conditions: amide (1.5 mmol), alcohol (1.0 mmol), H-mont
(0.1 g), 1,4-dioxane (2 mL), 100 °C, 2 h. b Yield of the isolated product
based on the alcohol. c Third reuse. d 20 h. e Amide (5 mmol) was used.
Alcohol was added in portions. f GC yield. g Alcohol (1.5 mmol), 2a (1
mmol). Yield was based on 2a.
good to excellent yields. Aniline derivatives also reacted,
giving both hydroamination and ortho-hydroarylation prod-
ucts (entries 18-20). Electron-withdrawing substituents on
the para position of aniline lead to an increasing selectivity
toward the hydroamination product.
The H-mont catalyst was reusable with maintenance of
high catalytic activity and selectivity: a 94% isolated yield
was obtained in the fifth recycle experiment (Table 3). The
simplicity and high performance of the workup of the H-mont
catalyst system are illustrated by the following example: the
hydroamination of 13 mmol of 1b with 10 mmol of 2a was
completed within 1 h in the presence of 0.02 g of the H-mont
catalyst (acid amount: 0.017 mmol). After simple filtration
2a with benzhydrol (4a) proceeded readily, giving a 94%
yield of N-(diphenylmethyl) p-toluenesulfonamide (entry 1).
Org. Lett., Vol. 8, No. 20, 2006
4619

Methanesulfonamide and benzamide were also found to be
good donors in the reaction with 4a (entries 3 and 4).
2-Cyclohexen-1-ol and 2-norborneol also reacted with 2a to
afford the corresponding products (entries 7 and 8). Notably,
this H-mont catalyst system was applicable to the allylic
substitution of allyl alcohols with aniline (eqs 3 and 4), which
is a powerful alternative candidate for traditional Pd catalyst
systems.11
anion coordination ability toward the H+ site,16 leading to
higher activity in the H-mont catalyst compared to that in
homogeneous acids (Table 1, entries 1 vs 8 and 9).
In summary, hydroamination of unactivated alkenes was
demonstrated in the presence of the proton-exchanged
montmorillonite. This catalyst system showed a high activity
and wide applicability with various substrates and easy
recycling. The unique acid sites in the montmorillonite
catalyst may also be useful for other novel reactions
involving cationic intermediates.
Addition of the radical trap 2,6-di-tert-butyl-p-cresol (10
mol % of the substrate) to the reaction medium hardly
influenced the reaction of 1b with 2a. The reactions of
terminal alkenes afforded C2 and C3 addition products
without formation of C1 adducts (Table 2, entries 8 and 9).
Furthermore, the catalytic activity of the H-mont was
significantly decreased by the addition of pyridine. Thus, it
is thought that this catalytic system does not involve free
radical intermediates.12 The H-mont and H-USY, with
Brønsted acidities (∆H) of 111 and 122 kJ mol-1, respec-
tively, showed higher activities than H-mordenite (∆H of
160 kJ mol-1),7 and then, the Brønsted acid site with suitable
strength may play an important role in the above hydroami-
nation.13 The density functional theory (DFT) calculations
reveal that a protonated cyclopentene intermediate is more
stable than a protonated methanesulfonamide intermediate;14
therefore, olefinic double bonds may be protonated in
preference to sulfonamide groups. From these results, a
plausible reaction pathway is proposed as follows: (i)
protonation of an alkene by the H+ site in the H-mont, (ii)
nucleophilic attack of an amide to the protonated alkene,
and (iii) formation of the hydroamination product and the
H+ site.15 The two-dimensional silicate sheets of the H-mont
effectively act as the macrocounteranions to decrease their
Acknowledgment. This investigation was supported by
a Grant-in-Aid for Scientific Research from the Ministry of
Education, Culture, Sports, Science, and Technology of
Japan. We thank the center of excellence (21COE; program
“Creation of Integrated Ecochemistry”, Osaka University).
We are also grateful to Dr. H. Takahashi (Graduate School
of Engineering Science, Osaka University) for density
functional theory calculations. K. Motokura thanks the JSPS
Research Fellowships for Young Scientists.
Supporting Information Available: Experimental pro-
cedure and characterization of new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
OL0619821
(12) Noji, M.; Ohno, T.; Fuji, K.; Futaba, N.; Tajima, H.; Ishii, K. J.
Org. Chem. 2003, 68, 9340.
(13) The presence of Brønsted acid sites in the H-mont catalyst was
confirmed by IR analysis of adsorbed pyridines; see ref 5.
(14) From density functional theory calculations (B3LYP/Aug-cc-pVDZ),
the energy change by adsorption of free H+ (∆E) of cyclopentene is -351.2
kcal mol-1, which is much lower than that of methanesulfonamide (O-
protonated, -199.0 kcal mol-1; N-protonated, -199.3 kcal mol-1).
(15) The reaction of an alcohol might proceed via activation of the
hydroxy group by the H+ site followed by nucleophilic attack of an amide.
(16) Bergman and co-workers reported that in reactions with aniline,
the activity of the protonic acid increased with decreasing anion coordination
(10) (a) Ozawa, F.; Okamoto, H.; Kawagishi, S.; Yamamoto, S.; Minami,
T.; Yoshifuji, M. J. Am. Chem. Soc. 2002, 124, 10968. (b) Kinoshita, H.;
Shinokubo, H.; Oshima, K. Org. Lett. 2004, 6, 4085.
(11) For radical addition, see: Kemper, J.; Studer, A. Angew. Chem.,
Int. Ed. 2005, 44, 4914.
ability (BPh4 < OTf- < NTf2 < B(C6F5)4-). See ref 7c.
-
-
4620
Org. Lett., Vol. 8, No. 20, 2006