and no strictly deoxygenated conditions are necessary. Moreover, a
simple combination of RhCl3/3 PPh3 showed the same efficiency
(entry 9) and that contributes to make of this reaction an easy
procedure for 1,4-diketone 3a synthesis from readily available
starting materials.
At this point of the study, it was important to check the generality
of the reaction. Various substituted arylboronic acids have been
successfully reacted using optimised conditions MeOH, 80 °C, 20
bars CO and 1% RhHCO(PPh3)3 with a 2:1 ratio of olefin to
boronic acid (Table 2; method A).
The selectivity was largely affected by the substituent on the aryl
group of the organoboronic acid used. High yields in the
corresponding carbonylated products 3 are obtained with para-
electrodonating substituents (entries 2–3). Derivatives of type 4 and
5 were obtained only in low yields and easily separated from 3 by
column chromatography on alumina giving an overall isolated yield
of 3 higher than 75%. Arylboronic acids with electro-withdrawing
groups are less easily converted into 3 and an unsatisfactory yield
of 38% is obtained with 3-chlorophenyl boronic acid (entry 4). This
is mainly due to the predominant noncarbonylative process yielding
4 in 42% yield. This suggests a disfavoured carbon monoxide
insertion step in the Rh–Ar bond in the case of para-electro-
withdrawing substituents. This is not surprising as similar observa-
tions were reported in cases of stoichiometric carbonylation
reactions of aryl-palladium, platinum and ruthenium complexes.9
Higher CO pressure and lower temperature conditions were
necessary to achieve better selectivities (Table 2; conditions B: 40
bars CO and 60 °C allowed the formation of the carbonylated
derivative 3 in 73 % yield). The same procedure was finally
successfully applied using various halo-substituted arylboronic
acids (entries 5–7). Sterically hindered ortho-substituted ar-
ylboronic acids were hardly used in this carbonylation reaction. o-
Tolylboronic acid furnished 3 in 47% yield under conditions B with
a significant amount of 4.
Activated olefins are necessary for the reaction to proceed and
simple a-olefins failed to react except ethylene which led to small
yields in propiophenone. Ethyl vinyl ketone was reacted in a similar
way and moderate yields were obtained with phenyl vinyl ketone,
probably because of its easy polymerisation (entries 9 and 10).
In conclusion, we have developed a new and efficient catalytic
process for acylation of enones yielding 1,4-diketones. The
acylation reagent is catalytically generated in situ from a combina-
tion of arylboronic acid, carbon monoxide and rhodium–triphenyl-
phosphine complex. Further studies aimed at the generalisation of
this new process to other unsaturated substrates are under
investigation.
Notes and references
† General procedure : A 100 mL stainless steel autoclave equipped with a
magnetic stirrer was charged with phenylboronic acid (1a, 0,183 g, 15
mmol) and RhH(CO)(PPh3)3 (13 mg, 0,15 mmol). The autoclave was
evacuated and filled with dinitrogen. A solution of methylvinylketone (2a,
0,244 mL, 3 mmol) and undecane (internal standard for GC analysis) in
MeOH (10 mL) was prepared in a Schlenk tube under dinitrogen. This was
then transferred to the stainless steel autoclave via a cannula and stirred
under dinitrogen for 2 min. CO was charged at the required pressure and the
mixture was warmed at the prerequisite temperature. At the end of the
reaction, the autoclave was cooled in an ice bath, vented, and the products
were analysed by gas chromatography analysis.
1 (a) W. C. Christopfel and L. Miller, J. Org. Chem., 1986, 51, 4169; (b)
F. Freeman and D. S. H. L. Kim, J. Org. Chem., 1992, 57, 172.
2 (a) B. C. Söderberg, D. C. York, E. A. Harriston, H. J. Caprara and A. H.
Flurry, Organometallics, 1995, 14, 3712; (b) J. Barluengua, F. Rodríguez
and F. J. Fañanás, Chem. Eur. J., 2000, 6, 1930; (c) L. S. Hegedus and R.
J. Perry, J. Org. Chem., 1985, 50, 4955; (d) D. Seyferth and R. C. Hui, J.
Am. Chem. Soc., 1985, 107, 4551; (e) M. F. Semmelhack, L. Keller, T.
Sato and E. Spiess, J. Org. Chem., 1982, 47, 4384.
3 (a) E. Shirakawa, Y. Yamamoto, Y. Nakao, T. Tsuchimoto and T.
Hiyama, Chem. Commun., 2001, 1926; (b) Y. Hanzawa, N. Tabuchi, K.
Narita, A. Kakuuchi, M. Yabe and T. Taguchi, Tetrahedron, 2002, 58,
7559; (c) Y. Hanzawa, N. Tabuchi, K. Saito, S. Noguchi and T. Taguchi,
Angew. Chem. Int. Ed., 1999, 38, 2395.
4 (a) T. Hayashi and K. Yamasaki, Chem. Rev., 2003, 103, 2829; (b) T.
Hayashi, Synlett, 2001, 879; (c) M. Sakai, H. Hayashi and N. Miyaura,
Organometallics, 1997, 16, 4229.
5 C. H. Oh, T. W. Ahn and R. Reddy, Chem. Commun., 2003, 2622.
6 T. Hayashi, N. Tokunaga, K. Yoshida and J. W. Han, J. Am. Chem. Soc.,
2002, 124, 5052.
Table 2 Rhodium catalysed aroylation reaction of a,b-unsaturated ketones
under CO pressure with various arylboronic acidsa
Entry
Ar
Method
R
3 (%)b
4 (%)b
5 (%)b
1
2
3
4
5
6
7
8
9
C6H5
A
A
A
A
B
B
B
B
A
B
Me
Me
Me
Me
Me
Me
Me
Me
78 (72)
81 (78)
80 (76)
38
73
73
9
6
6
42
8
5
7
3
3
4
5
2
2
< 2
nd
nd
4-MeC6H4
4-MeOC6H4
3-ClC6H4
3-ClC6H4
4-ClC6H4
4-FC6H4
2-MeC6H4
C6H5
71
47
7
35
nd
nd
C6H5 55
Et 76
10
C6H5
7 C. S. Cho, T. Ohe and S. Uemura, J. Organomet. Chem., 1995, 496,
221.
8 G. Zou, Z. Wang, J. Zhu and J. Tang, Chem. Commun., 2003, 2438.
9 (a) N. Sugita, J. V. Minkiewicz and R. F. Heck, Inorg. Chem., 1978, 17,
2809; (b) G. R. Clark, W. R. Roper, L. J. Wright and V. P. D. Yap,
Organometallics, 1997, 16, 5135.
a Reaction were carried out using arylboronic acid (1.5 mmol) and 1%
RhH(CO)(PPh3)3 in 10 mL MeOH for 18 h. Method A: 20 bars CO and 80
°C; Method B: 40 bars CO and 60 °C. b Yields were determined by GC
based on the arylboronic acid, isolated yields are given in parentheses.
C h e m . C o m m u n . , 2 0 0 4 , 1 5 2 0 – 1 5 2 1
1521