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Brgnsted Acid Mediated Heterogeneous Addition Reaction of 1 3-Dicarbonyl Compounds to Alkenes and Alcohols.

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Angewandte
Chemie
Heterogeneous Catalysis
DOI: 10.1002/ange.200504609
Brønsted Acid Mediated Heterogeneous Addition
Reaction of 1,3-Dicarbonyl Compounds to
Alkenes and Alcohols**
Ken Motokura, Noriaki Fujita, Kohsuke Mori,
Tomoo Mizugaki, Kohki Ebitani, and
Kiyotomi Kaneda*
From the standpoint of atom efficiency,[1] nucleophilic additions to alkenes or alcohols instead of alkyl halides are
attractive salt-free methods (Scheme 1). Simple alkenes are
readily accessible and abundant carbon-atom sources, but
intermolecular additions of 1,3-dicarbonyl compounds to
simple alkenes remain problematic. In traditional acid- or
base-catalyzed Michael reactions of 1,3-dicarbonyl com-
[*] Dr. K. Motokura, N. Fujita, Dr. K. Mori, Dr. T. Mizugaki, Dr. K. Ebitani,
Prof. Dr. K. Kaneda
Department of Materials Engineering Science
Graduate School of Engineering Science
Osaka University
1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan)
Fax: (+ 81) 6-6850-6260
E-mail: kaneda@cheng.es.osaka-u.ac.jp
[**] This investigation was supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports, Science,
and Technology of Japan (16206078). We thank the Center of
Excellence (21COE; “Creation of Integrated Ecochemistry” program, Osaka University). We are also grateful to Prof. Dr. S. Namba
(Teikyo University) for catalyst preparation and Dr. K. Mori, Dr. Y.
Senga, and Dr. S. Yamakita (Bel Japan) for TPD measurement. K.M.
thanks the JSPS for a Research Fellowship for Young Scientists.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. 2006, 118, 2667 –2671
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2667
Zuschriften
Scheme 1. A comparison of nucleophilic additions to halides (with salt
formation) and to alkenes or alcohols (without salt formation).
pounds, only reactive, electron-deficient alkenes, such as a,bunsaturated ketones, have been utilized. Attempts to overcome this limitation have focused mainly on the development
of homogeneous metal catalysts to which the alkenes can
coordinate;[2, 3] however, these catalyst systems require expensive metals and halogenated solvents. We have pursued a new
concept that involves dual activation of the olefinic double
bond and the reacting C H bond of the nucleophile[4] by
catalytic sites to promote a highly efficient intermolecular
addition reaction.
Recently, solid acid catalysts based on montmorillonites
(monts)[5] and zeolites,[6] which have uniformly sized pores
and voids, have received attention. Their adjustable acidity
derived from enwrapped protons enables a variety of highly
selective organic reactions. The use of solid montmorillonite
and zeolite catalysts in liquid-phase organic synthesis also
allows a simple workup and the potential to recycle catalysts
in an environmentally acceptable process. Previously, we
reported that montmorillonites that enwrap metal cations
(Mn+-monts) act as strong solid acid catalysts for various
organic transformations.[7] Herein, we describe a novel
synthetic method in which montmorillonites are used in
addition reactions of 1,3-dicarbonyl compounds to alkenes
(Scheme 2). Not only does this heterogeneous catalytic
system enable a simple workup and the use of recyclable
catalysts, but it also has high activity owing to unique acid
sites in the montmorillonite. Furthermore, the catalytic
system can be used for the benzylation and allylation of 1,3dicarbonyl compounds with alcohols and for the nucleophilic
addition of carboxylic acids to alkenes.
Proton-exchanged montmorillonite (H-mont) was prepared from Na+-mont by using an aqueous solution of
Scheme 2. Use of a proton-exchanged montmorillonite as the catalyst
in addition reactions of 1,3-dicarbonyl compounds to alkenes.
2668
www.angewandte.de
hydrogen chloride (see Experimental Section). X-ray diffraction verified retention of a layered structure. The degree of
exchange of the sodium cations in the H-mont was 98.9 %.
NH3-TPD (temperature programmed desorption) analysis
revealed the strength (DH)[8, 9] and quantity of the acid sites in
the H-mont to be 111 kJ mol 1 and 0.86 mmol g 1, respectively. Other zeolites, such as H-USY, H-mordenite, and HZSM-5, were commercially available. Al-MCM-41, which has
large pores, was prepared according to the literature.[10]
The reaction of acetyl acetone (1 a) with norbornene (2 a)
was examined in the presence of several acid catalysts
(Table 1). The H-mont catalyst displayed excellent activity
and gave 3 a in 83 % yield (Table 1, entry 1). Substitution of
Table 1: Addition of 1 a to 2 a in the presence of various acid catalysts.[a]
Entry
Catalyst
Acid sites
ACHTUNGRE[mmol g 1][b]
Pore size
[F]
Conv.
2 a [%][c]
Yield
3 a [%][c]
1
2
3
4
5
6
7
8
9
10
11
H-mont
H-USY
mont K10
Al-MCM-41
H-mordenite
H-ZSM-5
SO42 /ZrO2
Na+-mont
H2SO4[e]
p-TsOH·H2O[e]
none
0.86
0.53
0.25
0.15
1.07
0.87
n.m.
n.m.
–
–
–
–
7.4 J 7.4
–
27 J 27
6.5 J 7.0
5.1 J 5.5
–
–
–
–
–
87
37
9
7
11
n.r.
n.r.
n.r.
29
n.r.
n.r.
83
37
8
5
trace[d]
n.r.
n.r.
n.r.
4
n.r.
n.r.
[a] Reaction conditions: 1 a (1.3 mmol), 2 a (1.0 mmol), catalyst (0.03 g),
n-heptane (2 mL), 0.5 h, 150 8C. [b] Estimated from the h and h+ peaks in
the NH3-TPD spectra. [c] Determined by GC analysis and 1H NMR
spectroscopy. [d] Oligomers of 2 a are the main products. [e] Quantity
used: 0.1 mmol. n.m. = not measured, n.r. = no reaction.
H-mont for H-USY led to just a moderate yield of the product
(Table 1, entry 2). Other solid acids, such as mont K-10, AlMCM-41, and H-mordenite, were significantly less active
(Table 1, entries 3–5). The reaction scarcely occurred in the
presence of H-ZSM-5 as a result of its restricted pore size
(Table 1, entry 6). The homogeneous acids H2SO4 and ptoluenesulfonic acid were not effective catalysts under these
reaction conditions (Table 1, entries 9 and 10).
The H-mont-catalyzed addition reaction was extended to
other 1,3-dicarbonyl compounds and alkenes, as shown in
Table 2. Compound 2 a reacted with a variety of b-diketones
to afford the addition products in excellent yields (Table 2,
entries 1–3 and 6). Notably, the reactions of b-ketoesters and
a b-lactone proceeded smoothly; the hydrodecarboxylation of
the ester groups was suppressed (Table 2, entries 4, 5, and
7).[11] Intermolecular additions of b-ketoesters to norbornene
were previously unknown. Interestingly, less reactive cyclic
alkenes, such as cyclopentene (2 b) and cyclohexene (2 c),
were good substrates for this H-mont catalyst system (Table 2,
entries 8–10). The reaction of the terminal aliphatic olefins 1pentene (2 d) and 1-hexene (2 e) gave the dione compounds in
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. 2006, 118, 2667 –2671
Angewandte
Chemie
Table 2: Addition reaction of 1,3-dicarbonyl compounds 1 to alkenes 2.[a]
Table 3: Reuse of the H-mont catalyst for the addition reaction of 1 a to
2 a.[a]
Recycle number
[b]
Yield of 3 a [%]
fresh
1
2
3
4
5
6
7
93
92
93
93
92
94
92
93
[a] Reaction conditions: 1 a (1 mmol), 2 a (1.3 mmol), H-mont (0.15 g),
n-heptane (2 mL), 1 h, 150 8C. [b] Determined by GC analysis.
Entry
1
2
t [h]
T [8C]
Yield [%][b]
1
2
3
4
5
6
7
8[c]
9[c]
10[c]
11[d,e]
12[d,e]
13[e,g]
14[i]
1a
1b
1c
1d
1e
1f
1g
1c
1b
1c
1c
1c
1e
1f
2a
2a
2a
2a
2a
2a
2a
2b
2c
2c
2d
2e
2f
2g
1
1
1
1
1
1
1
24
24
24
24
24
3
3
150
150
150
150
150
150
150
180
180
180
150
150
150
150
90
88
93
(71)
74
83
87
(66)
78
(80)
53, 9:1[f ]
60, 5:1[f ]
72[h]
72[h]
[a] Reaction conditions: 1 (1 mmol), 2 (1.3 mmol), H-mont (0.15 g), nheptane (2 mL). [b] Yield of the isolated product based on the dicarbonyl
starting material. Values in parentheses are yields as determined by GC
analysis. Diastereomers were formed in a 1:1 ratio from asymmetric
dicarbonyl compounds (1H NMR). Only the exo product was isolated in
the reaction of 2 a. [c] Quantity of 2: 5 mmol. [d] Quantity of 2: 15 mmol.
[e] The alkene was added in portions. [f ] Ratio of the 2-adduct to the 3adduct (1H NMR). [g] Quantity of 1 e: 3 mmol, 2 f: 1 mmol. [h] Yield of
the isolated product based on the alkene. [i] Quantity of 1 f: 1.3 mmol,
2 g: 1 mmol.
moderate yields along with small amounts of isomerization
products (Table 2, entries 11 and 12). Styrene derivatives also
functioned as good substrates in the H-mont-catalyzed
addition reaction (Table 2, entries 13 and 14).[12]
The high activity of the H-mont catalyst system and the
simplicity of the workup procedure are exemplified by the
following: After the reaction of dibenzoylmethane (1 c;
22.4 g, 0.10 mol) with 2 a (11.3 g, 0.12 mol) at 150 8C for 3 h
in the presence of the H-mont catalyst (0.3 g), the spent
catalyst was readily separated from the reaction mixture.
Direct recrystallization then gave pure 2-(bicycloACHTUNGRE[2.2.1]heptan-2-yl)-1,3-diphenylpropane-1,3-dione
(31.3 g,
98 % yield of the isolated product).[9] The turnover number
(TON) and turnover frequency (TOF) of this catalytic
reaction (TON: 380, TOF: 127 h 1, based on the active acid
sites of the H-mont) were considerably greater than those of a
previously reported homogeneous AuCl3/AgOTf catalyst
system (TON: 16, TOF: 3.2 h 1).[3a] Additionally, the recovered H-mont catalyst could be reused at least seven times
without any loss of its activity (Table 3). Dimethyl malonate,
which has a high pKa value, did not react.
The high reactivity of 1,3-dicarbonyl compounds in the Hmont-catalyzed reactions prompted investigations of the abenzylation and allylation of the 1,3-dicarbonyl compounds
by treatment with alcohols (Table 4). The reaction of 1 a with
1-phenylethanol in the presence of the H-mont catalyst gave
the a-benzylated product 3-(1-phenylethyl)pentane-2,4-dione
Angew. Chem. 2006, 118, 2667 –2671
Table 4: a-Benzylation and allylation of 1,3-dicarbonyl compounds 1 by
treatment with alcohols.[a]
1
Alcohol
R, R’
T [8C]
Yield [%][b]
1
2
3[c]
4
1a
1a
1a
1a
Ph, Me
p-Cl-C6H4, Me
2-naphthyl, Me
Ph, Ph
100
150
150
100
90
80
72
91
5
1a
6[e]
7[c]
8
9
1b
1f
1d
1e
Entry
10
Ph, Me
Ph, Me
Ph, Me
Ph, Me
1d
90
80[d]
100
150
100
100
86[f ]
86[f ]
88[f ]
51[f ]
90
48[f ]
[a] Reaction conditions: 1 (1.5 mmol), alcohol (1 mmol), H-mont
(0.15 g), n-heptane (2 mL), 1 h, 100 8C. [b] Yield of the isolated product
based on the alcohol. [c] Reaction time: 0.5 h. [d] Yield as determined by
GC analysis. [e] Quantity of 1 b: 1 mmol. [f ] Diastereomers were formed
in a 1:1 ratio (1H NMR).
in 90 % yield (Table 4, entry 1). The sterically hindered
alcohol 1-(2-napthyl)ethanol was also a good substrate for
this reaction (Table 4, entry 3). In the case of 2-cyclohexen-1ol, a-allylation proceeded efficiently (Table 4, entries 5 and
10). Furthermore, b-ketoesters underwent both benzylation
(Table 4, entries 8 and 9) and allylation (Table 4, entry 10).
Halides are usually used for the a-benzylation and allylation
of active methylene groups;[13] methods in which an alcohol is
used as a benzylating or allylating reagent are highly atom
efficient candidates.[14, 15] Unfortunately, reactions with primary alcohols resulted in low yields owing to the formation of
ethers under the present reaction conditions.
In the reaction of 1 a with 2 a, the addition of the radical
trap 2,6-di-tert-butyl-p-cresol to the reaction medium had
hardly any influence.[16] The IR spectrum of the H-mont upon
treatment with pyridine showed a new peak at 1543 cm 1 due
to protonated pyridine molecules.[9, 17] The catalytic activity of
a variety of Brønsted acids was shown not to depend on their
acidity, as determined by NH3-TPD (Table 1); H-mordenite,
which has strong Brønsted acidity (DH = 160 kJ mol 1) was
less active than the H-mont and H-USY catalysts, which have
DH values of 111 and 122 kJ mol 1, respectively.[8, 9] These
results suggest that a suitable strength of the Brønsted acid
sites is required for efficient addition reactions of 1,3dicarbonyl compounds to alkenes. In the intermolecular
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.de
2669
Zuschriften
competitive reaction of 2 a with an equimolar mixture of 1 a
(pKa = 9.0)[18] and nitroethane (pKa = 8.6),[18] the H-mont
catalyst favored the formation of 3 a (97 % yield) exclusively
(Scheme 3).
Furthermore, the higher activity of the H-mont catalyst
relative to that of the homogeneous acids can be attributed to
concentrated protonic acid sites in the interlayer space of the
H-mont.
The strong protonation ability of the H-mont catalyst is
further applicable to the addition reactions of carboxylic acids
to alkenes (Scheme 5). For example, the reaction of benzoic
Scheme 3. Intermolecular competitive reaction of 2 a with an equimolar mixture of 1 a and nitroethane under H-mont catalysis.
After treatment of the H-mont catalyst with 1 a, IR
absorptions due to both the keto and enol forms of 1 a
(1537ACHTUNGRE(enol), 1592ACHTUNGRE(enol), and 1698ACHTUNGRE(keto) cm 1)[9] were
detected, similar to those found for adsorbed 1 a onto the
Brønsted acid site of Z12H zeolite (1540ACHTUNGRE(enol), 1592ACHTUNGRE(enol),
and 1700ACHTUNGRE(keto) cm 1).[19] A proposed reaction path involves
the dual activation of the alkene and the 1,3-dicarbonyl
compound: 1) protonation of an alkene at an acid site and
coordination of a 1,3-dicarbonyl compound to a neighboring
H+ site;[20] 2) formation of an activated enol intermediate;
3) nucleophilic attack of the enol (Scheme 4). Kinetic studies
showed first-order dependence on 2 a and an inverse firstorder relationship with respect to 1 a,[9] and thus indicated that
alkene protonation may be a rate-determining step that is
impeded by adsorbed 1,3-dicarbonyl compounds. The negatively charged silicate layers are capable of acting as
delocalized counter anions to stabilize cationic intermediates.
Scheme 5. The H-mont-catalyzed addition of carboxylic acids to
alkenes. Tol = tolyl.
acid with 2 a in the presence of the H-mont catalyst gave 2benzoyloxynorbornane in 89 % yield. Even with less reactive
simple alkenes, such as cyclopentene and cyclohexene, the
corresponding esters were obtained in excellent yields.
Furthermore, the H-mont catalyst promoted the intramolecular reaction of 2-cyclopentene-1-acetic acid in excellent
yield.
In summary, environmentally benign addition reactions of
various 1,3-dicarbonyl compounds to alkenes and alcohols in
the presence of solid acid catalysts have been described.
Unique acid sites with delocalized counter anions of twodimensional silicate sheets will allow additional novel C C
bond-forming reactions.
Experimental Section
A mixture of the parent Na+-montmorillonite (3.0 g;
Na0.66(OH)4Si8(Al3.34Mg0.66Fe0.19)O20 ; Na 2.69, Al 11.8, Fe 1.46, Mg
1.97 %; Kunipia F, Kunimine Industry, Japan) and aqueous HCl
(1.1 wt %, 200 mL) was stirred at 90 8C for 24 h. The slurry obtained
was filtered and washed with distilled water (1 L) to remove chlorine,
then dried at 110 8C in air to afford the H-mont as a whitish-gray
powder. Elemental analysis: Na 0.03, Mg 1.73, Al 10.1, Fe 1.34 %.
Typical procedure: H-mont (0.15 g), n-heptane (2 mL), 1 a
(1 mmol), and 2 a (1.3 mmol) were placed in a pressure tube, and
the resulting mixture was stirred vigorously at 150 8C. After 1 h, the
catalyst was separated by filtration. GC analysis of the filtrate showed
that 3 a had formed in 93 % yield. The filtrate was concentrated by
evaporation, and the crude product was purified by column chromatography on silica (diethyl ether/n-hexane 1:9) to afford the pure
product (90 % yield). The recovered catalyst could be reused at least
seven times without appreciable loss of activity and selectivity: The
yields of the first, second, and seventh runs were 92, 93, and 93 %,
respectively.
Scheme 4. A proposed dual-activation reaction pathway for the addition of 1,3-dicarbonyl compounds to alkenes or alcohols in the
presence of the H-mont catalyst.
2670
www.angewandte.de
Received: December 29, 2005
Published online: March 17, 2006
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. 2006, 118, 2667 –2671
Angewandte
Chemie
.
Keywords: 1,3-dicarbonyl compounds · addition reactions ·
alcohols · alkenes · heterogeneous catalysis
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Angew. Chem. 2006, 118, 2667 –2671
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2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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