Ligand-accelerated cadmium-catalyzed allylation of aldehydes and ketones in aqueous media

Article abstract of DOI:10.1055/s-2002-20472

Cadmium perchlorate was found to catalyze allylation reactions using allyltributyltin in aqueous media very efficiently. These cadmium-catalyzed allylation reactions are accelerated by ligands such as N,N,N′,N,″N″ -pentamethyldiethylenetriamine or 2,9-dim

Full text of DOI:10.1055/s-2002-20472

LETTER
483
Ligand-Accelerated Cadmium-catalyzed Allylation of Aldehydes and Ketones
in Aqueous Media
L
S
igand-Accele
h
r
ate
d
Cadmi
u
u
¯
m-Catalyzed
A
llyla
K
tion obayashi,* Naohiro Aoyama, Kei Manabe
Graduate School of Pharmaceutical Sciences, The University of Tokyo, CREST, Japan Science and Technology Corporation (JST), Hongo,
Bunkyo-ku, Tokyo 113-0033, Japan
E-mail: skobayas@mol.f.u-tokyo.ac.jp
Received 11 December 2001
6
aqueous media. On the other hand, cadmium-catalyzed
Abstract: Cadmium perchlorate was found to catalyze allylation
reactions using allyltributyltin in aqueous media very efficiently.
These cadmium-catalyzed allylation reactions are accelerated by
ligands such as N,N,N ,N ,N -pentamethyldiethylenetriamine or
reactions (catalytic use of cadmium components) are rare
7
in synthetic reactions even in organic solvents, and, as far
as we know, the present system is the first example of cad-
2
,9-dimethylphenanthroline. This accelerated catalytic system gave mium-catalyzed allylation of carbonyl compounds.
allylation products of various aldehydes and ketones in high yields.
Table 1 Screening of Lewis Acids in Allylation in Aqueous Media
Key words: cadmium, allylation, allyltin, ligand acceleration,
aqueous media
Lewis acid (20 mol %)
OH
PhCHO + Bu3Sn
Ph
H2O/EtOH = 1/9
3
0 °C, 24 h
Allylation reactions of carbonyl compounds, which afford
synthetically useful homoallylic alcohols, have been a
subject of extensive investigation. On the other hand, the
Entry
Lewis acid
Sc(OTf)3
Y(OTf)3
Yield (%)
1
1
2
3
4
5
6
7
8
9
49
development of allylation reactions in aqueous media has
attracted great attention because of the easy handling, wa-
ter-tolerance, and unique reactivity of the methodology.2
Although several kinds of Lewis acid- or Brønsted acid-
catalyzed allylation reactions in aqueous media with allyl-
20
La(OTf)3
5
Cu(OTf)2
21
3
tributyltin have been reported, it is necessary to develop
AgOTf
5
more active and efficient catalysts. In the course of our in-
vestigations to exploit new synthetic reactions in aqueous
Zn(OTf)2
59
4
media, we have demonstrated scandium triflate-cata-
90 (85a)
34
lyzed allylation reactions of carbonyl compounds with tet-
Cd(ClO
4
)
2
5
raallyltin in aqueous media. To expand the utility and
Ga(OTf)3
In(ClO4)3
Sc(OTf)2
applicability of the allylation reactions, we have investi-
gated further to develop more efficient catalytic systems.
Herein, we report cadmium-catalyzed allylation reactions
with allyltributyltin in aqueous media. In this catalytic
89 (73a)
34
1
0
system, remarkable acceleration by ligands was observed, 11
Pb(ClO4)2
65
and not only aldehydes but also ketones reacted with allyl-
tributyltin to afford the corresponding allylated adducts in
high yields.
a
Reaction time is 6 h.
Next, we investigated the effect of ligands in the cadmi-
um-catalyzed allylation (Table 2), because ligand acceler-
ation is an interesting topic in metal-catalyzed organic
First, we screened several Lewis acids for the allylation
reaction of benzaldehyde (1 equiv) with allyltributyltin
(
(
1.2 equiv) in a typical aqueous media, H O–EtOH = 1:9
6 mL/1 mmol of benzaldehyde) (Table 1). Among Lewis
2
8
reactions. However, our initial attempts to realize ligand
acceleration failed. For example, addition of amines such
as 1a, 1b, and 1c led to lower yields (entries 2-4) than in
the case of no ligand (entry 1). Addition of methylated di-
amine 2a and tetramine 2c also led to lower yields (entries
acids tested, indium perchlorate and cadmium perchlorate
were found to catalyze allylation very effectively (entries
7
and 9). Furthermore, it is noteworthy that, when
quenched in 6 h, cadmium perchlorate gave the corre-
sponding allylation product in the highest yield (entry 7).
It has been reported that a stoichiometric amount of me-
tallic Cd promoted Barbier-type allylation reactions in
5
and 7). These ligands did not accelerate the reaction but
decelerated it. On the other hand, dramatic ligand acceler-
ation was observed in the case of N,N,N ,N ,N -pentame-
thyldiethylenetriamine (2b, entry 6), and the product was
obtained in excellent yield in 30 min. Figure shows the re-
action profiles for the cadmium perchlorate-catalyzed al-
lylation in the presence and absence of 2b, indicating that
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1
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437-2096,E;2002,0,03,0483,0485,ftx,en;Y24401ST.pdf.
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ISSN 0936-5214

4
84
S. Kobayashi et al.
LETTER
the ligand acceleration occurred. Using 2b, we also suc-
ceeded in decreasing the amount of the catalyst. Five
mol% of cadmium perchlorate and 2b gave the product in
8
8% yield after 16 h. In the case of pyridine-type biden-
tate ligands, 2,2 -dipyridyl (3) and 1,10-phenanthroline
4), the product was obtained in lower yields (entries 8
(
and 9). However, 2,9-dimethylphenanthroline (5) gave
excellent yield (entry 10). In this ligand acceleration, the
methyl groups of the ligands play a very important role,
and it should be noted that subtle structural differences in
the ligands greatly affected the catalytic activity of cadmi-
um. When this reaction was performed in dichlo-
romethane, the reaction proceeded much more slowly,
and ligand acceleration by 2b or 5 was not observed (with-
out ligand: 13% yield for 30 min; with 2b: 10% yield;
with 5: trace). This result indicates that the ligand acceler-
ation is a characteristic feature of the allylation reactions
in aqueous media. Although 2,6-lutidine (6) has been re-
ported to accelerate zinc triflate-catalyzed allylation of
9
ketones, it did not work well in the cadmium-catalyzed
allylation in aqueous media (entry 11).
Table 2 The Effect of Ligands in Cadmium-Catalyzed Allylation
Figure Reaction profiles for the cadmium perchlorate-catalyzed
reaction of benzaldehyde with allyltributyltin in H O–EtOH (1:9)
2
Cd(ClO4)2 (20 mol %)
at 30 °C.
ligand (20 mol %)
OH
PhCHO
+
Bu3Sn
Ph
H2O/EtOH = 1/9
These catalytic systems were applied to allylation of var-
ious aldehydes and ketones (Table 3). Aldehydes gave
30 °C, 30 min
their allylated adducts in excellent yields. In the case of
Entry
Ligand
Yield (%)
ketones,5
a,9,10
the allylated adducts were obtained in high
1
2
3
4
5
6
7
8
9
–
50
40
35
14
35
91
2
yields by increasing the equivalent of allyltributyltin. This
is the first example of catalytic allylation reactions of ke-
tones using allyltributyltin in aqueous media.
1a
1b
1c
2a
2b
2c
3
Considering toxicity of cadmium compounds, it is desir-
able to recover and reuse the cadmium catalyst. In the
present catalytic system using cadmium perchlorate and
2
b, the recovery of the cadmium salt was realized by ex-
traction with water (3 times) after diluting of a reaction
mixture with ether. ICP-MS determination of cadmium
amount in the organic phase showed that more than
9
9.999% cadmium was extracted with water. Further-
28
39
92
53
more, ligand 2b was also extracted with water. Thus, it is
possible, in principle, to reuse the catalyst and the ligand
after concentrating the aqueous phase.
4
1
1
0
1
5
The mechanism of the cadmium-catalyzed allylation in-
cluding the ligand acceleration has not yet been clarified.
It is known that allylation reactions proceed via a Lewis
acid pathway (activation of carbonyl compounds by metal
coordination) or via a transmetalation pathway (formation
6
H2N
nNH2
[N
]
N
N
N
N
H
1
1
1
a: n = 0
3
b: n = 1
c: n = 2
11
of allylmetals from allyltins and metal salts). The result
that Lewis bases such as 2b and 5 accelerate allylation re-
actions suggests that the allylation proceeds via the trans-
metalation pathway, because Lewis bases are likely to
Me2N
nNMe2
[N
Me
a: n = 0
b: n = 1
c: n = 2
]
R
R
2
2
2
4: R = H
5: R = Me
12
reduce the Lewis acidity of the cadmium cation. The re-
sult that scandium triflate, which is regarded as a much
stronger Lewis acid than cadmium salts, was inferior to
cadmium perchlorate would also imply the transmetala-
tion pathway.
Me
N
6
Me
Synlett 2002, No. 3, 483–485 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Ligand-Accelerated Cadmium-catalyzed Allylation
485
Table 3 Cadmium-Catalyzed Allylation of Aldehydes and Ketones
(2) For review see: (a) Lubineau, A.; Auge, J.; Queneau, Y. In
Organic Synthesis in Water; Grieco, P. A., Ed.; Blackie
Academic and Professional: London, 1998, 102. (b) Li, C.-
J.; Chan, T.-H. Organic Reactions in Aqueous Media; John
Wiley & Sons: New York, 1997.
Cd(ClO4)2 (20 mol %)
O
ligand (20 mol %)
OH
+
Bu3Sn
R'
R''
R'
R''
H2O/EtOH = 1/9
(
3) (a) Shibata, I.; Yoshimura, N.; Yabu, M.; Baba, A. Eur. J.
Org. Chem. 2001, 3207. (b) Loh, T.-P.; Xu, J.; Hu, Q.-Y.;
Vittal, J. J. Tetrahedron: Asymmetry 2000, 11, 1565.
30 °C
Entry Substrate
1
Time (h)
0.5
Ligand
Yield (%)
(
c) Loh, T.-P.; Zhou, J.-R. Tetrahedron Lett. 2000, 41,
5261. (d) Loh, T.-P.; Xu, J. Tetrahedron Lett. 1999, 40,
431. (e) Yanagisawa, A.; Morodome, M.; Nakashima, H.;
5
97
CHO
2
Yamamoto, H. Synlett 1997, 1309. (f) Yanagisawa, A.;
Nakashima, H.; Ishiba, A.; Yamamoto, H. J. Am. Chem. Soc.
2
0.5
10
2b
2b
86
98
1996, 118, 4723.
CHO
(
4) (a) Kobayashi, S.; Hamada, T.; Nagayama, S.; Manabe, K. J.
Brazil. Chem. Soc. 2001, 12, 627. (b) Kobayashi, S.;
O
3
CHO
OH
Hamada, T.; Nagayama, S.; Manabe, K. Org. Lett. 2001, 3,
165. (c) Nagayama, S.; Kobayashi, S. J. Am. Chem. Soc.
2000, 122, 11531. (d) Kobayashi, S.; Nagayama, S.;
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5) (a) Hachiya, I.; Kobayashi, S. J. Org. Chem. 1993, 58, 6958.
4
0.5
42
2b
5
91
93
CHO
O
(
(
b) Kobayashi, S.; Wakabayashi, T.; Oyamada, H. Chem.
5a
Lett. 1997, 831. (c) We have also developed allylation of
hydrazones or imines with allyltins in aqueous media:
Kobayashi, S.; Hamada, T.; Manabe, K. Synlett 2001, 1140.
(
d) See also: Kobayashi, S.; Busujima, T.; Nagayama, S.
6a
7b
48
48
2b
2b
94
90
Chem. Commun. 1998, 19.
O
O
(
6) Zheng, Y.; Bao, W.; Zhang, Y. Synth. Commun. 2000, 30,
3
517.
(
7) For example, see: (a) Prajapati, D.; Sandhu, J. S. J. Chem.
Soc., Perkin Trans. 1 1993, 739. (b) Baruah, B.; Boruah, A.;
Prajapati, D.; Sandhu, J. S. Tetrahedron Lett. 1997, 38,
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M.; Nakajima, M.; Hashimoto, S. Chem. Commun. 2000,
a
Allyltributyltin (2 equiv) was used.
Allyltributyltin (3 equiv) was used.
b
1851. (f) Saito, M.; Nakajima, M.; Hashimoto, S.
Tetrahedron 2000, 56, 9589.
8) For review, see: Berrisford, D. J.; Bolm, C.; Sharpless, K. B.
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10) For other examples of catalytic allylation reactions of
ketones with allyltins, see: (a) Kosugi, M.; Arai, H.;
Yoshino, A.; Migita, T. Chem. Lett. 1978, 795. (b) Yano,
K.; Hatta, Y.; Baba, A.; Matsuda, H. Synlett 1991, 555.
In conclusion, we have discovered that cadmium
perchlorate catalyzes allylation reactions using allyltribu-
tyltin in aqueous media very efficiently. These cadmium-
catalyzed allylation reactions are accelerated by ligands
such as 2b or 5. This accelerated catalytic system gave al-
lylation products of various aldehydes and ketones in high
yields. As far as we know, this is the first example of allyl-
ation of ketones using allyltributyltin in aqueous media.
Although the mechanism of the reaction and the ligand ac-
celeration is not clear, it must be emphasized that slight
changes of ligand structure drastically alter the catalytic
activity of the metal. Further investigation on diastereo-
and enantioselective allylation reactions in aqueous media
using this novel catalyst system and elucidation of the
mechanism of the ligand acceleration are currently in
progress in our laboratory.
(
(
(
c) Miyai, T.; Inoue, K.; Yasuda, M.; Baba, A. Synlett 1997,
699. (d) Shibata, I.; Fukuoka, S.; Yoshimura, N.; Matsuda,
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(
f) Yasuda, M.; Kitahara, N.; Fujibayashi, T.; Baba, A.
Chem. Lett. 1998, 743. (g) Kamble, R. M.; Singh, V. K.
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(
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Organic Synthesis; Yamamoto, H., Ed.; Wiley-VCH:
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12) There are a few examples of ligand-accelerated Lewis acid
catalysis in dry solvents, although the Lewis basicities of the
ligands used there are much lower than those of amine-based
ligands such as 2b and 5. See: (a) Denmark, S. E.; Fu, J. J.
Am. Chem. Soc. 2001, 123, 9488. (b) Kobayashi, S.;
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Acknowledgement
This work was partially supported by a Grant-in-Aid for Scientific
Research from Japan Society of the Promotion of Science.
(
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Synlett 2002, No. 3, 483–485 ISSN 0936-5214 © Thieme Stuttgart · New York