COMMUNICATION
ducted with the [{Pd
(cinnamyl)Cl}2]/nBuPAd2 catalyst
enhanced the selectivity (Table 1, entry 3). After an in-
creased reaction time of 20 h was found to be beneficial to
the yield, testing of different solvents did not show any posi-
tive effect (Table 1, entries 3–7). Nevertheless, the use of
2 mL of acetone improved the yield dramatically to 52%;
thus the use of additional solvent could be omitted (Table 1,
entry 8). Under these conditions several other inorganic
(K2CO3, K3PO4, KOH, CsF), as well as organic (KHMDS,
NaOtBu, KOtBu), bases were applied in the model system
but in all cases the desired 1,3-diketone was formed in only
12 to 25% yields (for further details, see the Supporting In-
formation). Other palladium precursors such as [Pd2dba3]
system, which has been used to promote a diverse array of
carbonylation reactions.[9] We have previously shown that
applying deoxybenzoin, as a comparatively acidic substrate,
under these conditions led to the formation of the corre-
sponding vinylbenzoate compound.[10] However, to our sur-
prise, the same catalyst system enabled the selective forma-
tion of the corresponding 1,3-diketone when acetone was
employed. Thus, when iodobenzene was reacted with ace-
tone under 10 bar of CO in the presence of [{Pd-
ACHTUNGTRENNUNG(cinnamyl)Cl}2]/nBuPAd2 and Cs2CO3 as base, 1-phenylbu-
tane-1,3-dione was obtained in a promising 19% yield
(Table 1, entry 1). At a reduced CO pressure of 5 bar, im-
proved product formation, resulting in a 27% yield, was ob-
served (Table 1, entry 2). Decreasing the reaction tempera-
ture to 608C had only a minor effect on the yield (24%) but
(dba=dibenzylideneacetone), PdCl2 or Pd
acetylacetonate) afforded 10 to 20% less product formation
than the [{Pd(cinnamyl)Cl}2] complex (for further details,
ACHTUNGTERNUN(NG acac)2 (acac=
AHCTUNGTRENNUNG
see the Supporting Information). Although the origins of
the beneficial reactivity achieved when using [{Pd-
AHCTUNGTRENG(UNN cinnamyl)Cl}2] in this chemistry have not been evaluated in
Table 1. Optimisation of the model system.[a]
detail, previous observations suggest that such precursors
are effective in providing access to the requisite Pd0 spe-
cies.[11]
Although 3 bar of carbon monoxide was found to be the
optimal pressure for the transformation (67% yield), it was
shown that even an atmospheric pressure of CO enables the
formation of the desired product in 62% yield (Table 1, en-
tries 9 and 10).
By extending the reaction time to 36 h, nearly full conver-
sion and a 71% yield of the desired diketone was achieved.
We then turned our attention to determining the influence
of different ligands on our model system (Table 1, entry 11).
The use of triphenylphosphine and tricyclohexylphosphine,
simple monodentate phosphines, afforded 53 and 36%
yields of the corresponding product, but tri-tert-butylphos-
phonium tetrafluoroborate did not promote the formation
of the product (Table 1, entries 12–14).
Since MorDalPhos (L5) had shown favourable activity in
noncarbonylative a-arylation protocols,[5a,b] this and several
structurally related di(1-adamanyl)phosphines (L1–L7) were
also tested; however, rather low yields (10–24%; Table 1,
entries 15–21) of the target 1,3-diketone product were ob-
tained. Considering that as electronically different ligands as
PPh3 and nBuPAd2 gave similar yields but sterically rather
different RPAd2 ligands were significantly less successful, a
very specific steric demand seems to be crucial for a selec-
tive reaction, especially since the majority of the tested li-
gands are known to enable oxidative addition and CO inser-
tion of aryl iodides.
Entry
Ligand
Solvent
pCO
[bar]
T
[8C]
Conv.
[%][b]
Yield
[%][b]
G
1
2
3
nBuPAd2
nBuPAd2
nBuPAd2
dioxane
dioxane
dioxane
10
5
5
100
100
60
>99
>99
i) 75
ii) 79[c]
>99
36
>99
87
87
80
65
95
>99
87
79
97
53
95
70
48
51
76
19
27
24
35[c]
11[c]
15[c]
9[c]
4
5
6
7
8
nBuPAd2
nBuPAd2
nBuPAd2
nBuPAd2
nBuPAd2
nBuPAd2
nBuPAd2
nBuPAd2
PPh3
DMF
5
5
5
5
5
3
1
3
3
3
3
3
3
3
3
3
3
3
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
toluene
DMSO
MeCN
11[c]
66[c]
67[c]
62[c]
71[d]
53[d]
36[d]
0[d]
acetone
acetone
acetone
acetone
acetone
acetone
acetone
acetone
acetone
acetone
acetone
acetone
acetone
acetone
9
10
11
12
13
14
15
16
17
18
19
20
21
PCy3
P
N
L1
L2
L3
L4
L5
L6
L7
24[d]
13[d]
11[d]
13[d]
10[d]
11[d]
14[d]
Thus, [{PdACHTNUGTRNEUNG(cinnamyl)Cl}2]/nBuPAd2 at 608C by using 3 bar
of CO and Cs2CO3 as base proved to be the optimal reac-
tion conditions for enabling this transformation (Table 1,
entry 11). Notably, in all optimisation reactions, no side
products derived either from the noncarbonylative a-aryla-
tion or multiple arylation reactions of acetone were detect-
ed. However, varying amounts of benzoic acid and benzal-
dehyde were observed, especially in cases of high conversion
but low yield, showing that side reactions involving iodoben-
[a] General reaction conditions: iodobenzene (1 mmol), acetone
(10 mmol; 2 mL in cases for which acetone is used as the solvent), [{Pd-
ACHTUNGTRENNUNG(cinnamyl)Cl}2] (1 mol%), ligand (4 mol%), Cs2CO3 (2 mmol), solvent
(2 mL), 1008C, 16 h. [b] Conversions and yields determined on the basis
of calibrated GC data by using hexadecane as an internal standard.
[c] 20 h. [d] 36 h.
Chem. Eur. J. 2013, 19, 12624 – 12628
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
12625