Solvent-free chelation-assisted intermolecular hydroacylation: Effect of microwave irradiation in the synthesis of ketone from aldehyde and 1-alkene by Rh(I) complex

Article abstract of DOI:10.1016/S0040-4039(01)00853-X

As a green alternative to classical homogeneous catalyst in toluene in closed vessels, the intermolecular hydroacylation of 1-alkenes with aldehydes by Rh(I) complex (Wilkinson catalyst) can be realized efficiently under solvent-free conditions. When coupled to microwave activation, it results in a serious improvement when compared to classical conditions.

Full text of DOI:10.1016/S0040-4039(01)00853-X

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 4803–4805
Solvent-free chelation-assisted intermolecular hydroacylation:
effect of microwave irradiation in the synthesis of ketone from
aldehyde and 1-alkene by Rh(I) complex
Chul-Ho Jun,a,* Jong-Hwa Chung,a Dae-Yon Lee,a Andre´ Loupyb,* and Saber Chattia
aDepartment of Chemistry, Yonsei University, Seoul 120-749, South Korea
bLaboratoire des Re´actions Se´lectives sur Supports, ICMO, CNRS UMR 8615, Baˆtiment 410, Universite´ Paris-Sud,
91405 Orsay Cedex, France
Received 13 March 2001; accepted 2 April 2001
Abstract—As a green alternative to classical homogeneous catalyst in toluene in closed vessels, the intermolecular hydroacylation
of 1-alkenes with aldehydes by Rh(I) complex (Wilkinson catalyst) can be realized efficiently under solvent-free conditions. When
coupled to microwave activation, it results in a serious improvement when compared to classical conditions. © 2001 Elsevier
Science Ltd. All rights reserved.
acid, which catalyzes the condensation of aldehyde and
4 accelerates the overall rate of the chelation-assisted
hydroacylation. Reactions can be now realized in tolu-
ene at 130°C within 4 h with high yields.8
Intermolecular hydroacylation is a useful synthetic
method for obtaining ketones from aldehydes and
olefins through CꢀH bond activation by transition
metal complexes.1–5 To suppress the decarbonylation
that results in catalytically inactive metal carbonyl spe-
cies, ethylene,3 carbon monoxide,4 or vinylsilane with a
Co(I) catalyst5 have been used. We have developed a
general intermolecular hydroacylation of 1-alkenes
using a Rh(I) complex and 2-amino-3-picoline 4 as a
cocatalyst (Eq. (1)).6 In this reaction, aldimine 5 is
assumed to be the key intermediate, which suppresses
decarbonylation as well as allows facile CꢀH bond
activation through cyclometallation.7
As a new development and to operate under ‘green
chemistry’ conditions, the reaction was next examined
in the absence of solvent.9 The effect of microwave
(MW) activation was also studied as of noticeable
interest under solvent-free conditions.
Two kinds of microwave equipments were used, either
a
domestic multimode oven or a more reliable
(1)
monomode reactor with focused electromagnetic field
and accurate control of temperature by infrared detec-
tion all along the reaction.10 The main results are given
in Table 1.
Recently, we found that the reactivity in hydroacylation
was improved when benzoic acid was added as a cata-
lyst. Since the formation of aldimine 5 is supposed to
be the rate determining step, the addition of benzoic
From Table 1, it is obvious to point out that hydro-
acylation of 1-alkenes with aldehydes can be considerably
enhanced using solvent-free conditions, preferentially
* Corresponding authors. E-mail: junch@yonsei.ac.kr; aloupy
@icmo.u-psud.fr
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00853-X

4804
C.-H. Jun et al. / Tetrahedron Letters 42 (2001) 4803–4805
Table 1. Intermolecular hydroacylation of 1-alkenes with
under microwave irradiation. The improvement is even
more important when using a monomode reactor due
to wave focusing, which induces a better homogeneity
in the electric field and subsequent need of a lower
aldehydes
1, R1
2, R2
Hydroacylated product 6 (%)a
Solvent-free MW
incident power. Such
a beneficial effect of the
Toluene 4 h
monomode system was previously described13 in some
comparative experiments.
130°Cb
Domestic,
10 min
Monomode
c
This new procedure involves safe conditions with
noticeable improvements in reactivity, cost and energy
reduction as well as simplicity of experimental
conditions.
Ph
n-C4H9
t-C4H9
n-C8H17 22
Me3Si
C6F5
CH2Ph
•
66
63
75
69
38
83
80
82
85
0
–
–
95 (30 min)
–
–
87
75
93
71
To check the possibility of intervention of specific
(non-purely thermal) microwave effects, control experi-
ments were done under the same conditions as under
MW but under conventional heating inside a thermo-
stated oil bath (Table 2).
84 (10 min)
–
n-C6H13 n-C8H17 13d
61 (10 min)d
d
a Yield in isolated products.
b See Ref. 11.
A rather important non-thermal MW effect is here
involved and leads to enhancements in yields. This
effect is evident when one considers the difference in
yields obtained under exactly the same conditions,
including comparable profiles of raise in temperature
for both kinds of activation (Fig. 1).
c See Ref. 12.
d A 74% yield in aldolization product was isolated in the case of
reaction in toluene and 37% for the solvent-free focused microwave-
assisted reaction.
This MW specific effect is consistent with the fact that
the rate-determining step of the reaction may be cer-
tainly the generation of aldimine 5 from aldehyde and
2-amino-3-picoline. As the transition state which devel-
ops a dipole (Scheme 1) is more polar than the ground
state of the reaction, it results in a reduction of the
activation energy due to enhanced dipole–dipole inter-
actions with the electric field when the reaction is in
progress.
Table 2. Solvent-free hydroacylation of 1-alkenes with
aldehyde for 30 min at 140°C
1, R1
2, R2
Reaction
Yield 6 (%)
time (min)
Microwave
Conventional
Ph
n-C8H17 30
CH2Ph 10
95
50
84
30
n-C6H13 n-C8H17 10
61a
30b
In summary, we have presented here an alternative
procedure to the classical homogeneous catalysis which
is generally performed in toluene in closed vessels for
a 37% of aldol product was formed.
b 13% of aldol product was formed.
Figure 1. Profiles of raising in temperature for the reaction PhCHO+1-decene under microwave (ꢀ) or conventional heating (ꢁ).

C.-H. Jun et al. / Tetrahedron Letters 42 (2001) 4803–4805
4805
Scheme 1. Evolution of the polarities during reaction progress.
rather long reaction times. This new efficient system
(solvent-free reactions and microwave activation under
‘green chemistry’ conditions) can be used for inter-
molecular hydroacylation. Further work is in progress
for the sake of generalization and directed toward a
better understanding of this reaction.
62, 1200–1201; (b) Jun, C.-H.; Lee, D.-Y.; Hong, J.-B.
Tetrahedron Lett. 1997, 38, 6673–6676.
7. Suggs, J. W. J. Am. Chem. Soc. 1979, 101, 489.
8. Jun, C.-H.; Lee, D.-Y.; Lee, H.; Hong, J.-B. Angew.
Chem., Int. Ed. 2000, 39, 3070–3072.
9. Loupy, A. Top. Curr. Chem. 1999, 206, 153–207.
10. Loupy, A.; Petit, A.; Hamelin, J.; Texier-Boullet, F.;
Jacquault, P.; Mathe´, D. Synthesis 1998, 1213–1234.
11. Typical procedure: Aldehyde (0.2 mmol), alkene (1.0
mmol), 2-amino-3-picoline (0.08 mmol), benzoic acid
(0.02 mmol) and RhCl(PPh3)3 (0.01 mmol) were dissolved
in toluene (100 mg) and then heated in the oil bath at
130°C (bath temperature) for 4 h. After the reaction, the
product was purified by column chromatography.
12. Typical procedure: Aldehyde (0.2 mmol), alkene (1.0
mmol), 2-amino-3-picoline (0.08 mmol), benzoic acid
(0.02 mmol) and RhCl(PPh3)3 (0.01 mmol) were mixed in
the absence of any organic solvent and then submitted
for 10 min to microwave irradiation inside a domestic
microwave oven (Samsung, RE-431H, 700 W) or in a
monomode Synthewave 402 Prolabo where power is
enslaved to temperature at 140°C. After the reaction, the
product was purified by column chromatography.
13. (a) Petit, A.; Loupy, A.; Maillard, P.; Momenteau, M.
Synth. Commun. 1992, 22, 1137–1142; (b) Loupy, A.; Le
Ngoc, T. Synth. Commun. 1993, 23, 2571–2577; (c)
Loupy, A.; Pigeon, P.; Ramdani, M.; Jacquault, P. J.
Chem. Res. (S) 1993, 36–37; (d) Loupy, A.; Pigeon, P.;
Ramdani, M.; Jacquault, P. Synth. Commun. 1994, 24,
159–165; (e) Castan, P.; Labiad, B.; Villemin, D.; Wim-
mer, F. L.; Wimmer, S. J. Organomet. Chem. 1994, 479,
153–157; (f) Jolivet, S.; Texier-Boullet, F.; Hamelin, F. J.
Heteroatom. Chem. 1995, 6, 469–474.
Acknowledgements
This work was supported by the National Research
Laboratory (2000-N-NL-01-C-271) Program adminis-
trated by the Ministry of Science and Technology, and
Brain Korea 21 project.
References
1. (a) Vora, K. P.; Lochow, C. F.; Miller, R. G. J.
Organomet. Chem. 1980, 192, 257–264; (b) Isnard, P.;
Denise, B.; Sneeden, R. P. A.; Cognion, J. M.; Durual, P.
J. Organomet. Chem. 1982, 240, 285–288.
2. Jun, C.-H.; Hong, J.-B.; Lee, D.-Y. Synlett 1999, 1–12.
3. Marder, T. B.; Roe, D. C.; Milstein, D. Organometallics
1998, 17, 1451–1453.
4. (a) Kondo, T.; Tsuji, Y.; Waranabe, Y. Tetrahedron Lett.
1987, 28, 6226–6230; (b) Kondo, T.; Akazome, M.; Tsuji,
Y.; Waranabe, Y. J. Org. Chem. 1990, 55, 1286–1291.
5. (a) Legens, C. P.; Brookhar, M. J. Am. Chem. Soc. 1997,
119, 3165–3166; (b) Legens, C. P.; Brookhar, M. J. Am.
Chem. Soc. 1998, 120, 6965–6979.
6. (a) Jun, C.-H.; Lee, H.; Hong, J.-B. J. Org. Chem. 1997,
.