Pd-catalyzed α-allylation of 2-phenylpropanal and other carbonyl compounds with allyl alcohol and allyl acetates/carbonates in ionic liquids

Article abstract of DOI:10.1007/s00706-007-0710-6

The successful Pd-catalysed allylation of 2-phenylpropanal with allyl alcohol in ionic liquid is described and thus a simplier reaction composition catalytic system than in THF is possible. On the other hand, the Pd-catalyzed α-allylation of the same substrate with allyl acetate or allyl ethyl carbonate is proceeding nicely in ionic liquids. Allylation of different carbonyl derivatives was studied and it was found that the reaction is restricted to carbonyl derivatives from which a carbanion stabilized by an adjacent aromatic ring can be formed.

Full text of DOI:10.1007/s00706-007-0710-6

Monatshefte fu¨r Chemie 138, 1175–1179 (2007)
DOI 10.1007/s00706-007-0710-6
Printed in The Netherlands
Pd-Catalyzed a-Allylation of 2-Phenylpropanal and other Carbonyl
Compounds with Allyl Alcohol and Allyl Acetates=Carbonates
in Ionic Liquids
ꢀ
ˇ
Martin Hut’ka and Stefan Toma
Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia
Received April 24, 2007; accepted May 9, 2007; published online August 27, 2007
# Springer-Verlag 2007
Summary. The successful Pd-catalysed allylation of 2-phe-
al enolates [13, 14], or enol silyl ethers [4, 15], or
enamines [16].
nylpropanal with allyl alcohol in ionic liquid is described and
thus a simplier reaction composition catalytic system than in
THF is possible. On the other hand, the Pd-catalyzed ꢀ-allyla-
tion of the same substrate with allyl acetate or allyl ethyl
carbonate is proceeding nicely in ionic liquids. Allylation of
different carbonyl derivatives was studied and it was found
that the reaction is restricted to carbonyl derivatives from
which a carbanion stabilized by an adjacent aromatic ring can
be formed.
There are several papers on the Pd-catalyzed ally-
lation of acetylacetone [17], ꢁ-ketoesters [18], and
malonates [19] by simple allyl alcohols under drastic
conditions. On the other hand, Tamaru et al. have
found that the Pd-catalyzed allylation of methylene
active compounds by allyl alcohol can be efficiently
promoted by triethylborane [20]. Based on this find-
ing they have developed also Pd-catalyzed allylation
of 2-phenylpropanal by allyl alcohol [21]. The cata-
lytic system consisted of Pd(OAc)2, triphenylphos-
phine, triethylborane, triethylamine, and LiCl. Very
recently, also a paper has been published on the con-
version of allyl alcohol into allyl phenyl sulfones
[22]. Authors are using the same conditions as at
allylation of 2-phenylpropanal [21]. Overall the very
good yields were achieved after 12–15 h reaction
time in DMF at 80ꢁC.
Keywords. Pd-catalyzed; Ionic liquids; ꢀ-Allylation.
Introduction
Pd-catalyzed Tsuji-Trost allylations of active methy-
lene compounds are a well established method for
C–C bond formation [1]. As the potential nucleo-
philes dialkyl malonates, ꢁ-ketoesters [2, 3], and
allyl acetates or allyl carbonates are most frequently
used [4, 5]. An intramolecular version of this reac-
tion is used also for the synthesis of cyclic com-
pounds [6]. It is also frequently performed in an
asymmetric version [7–10] and we published papers
on an asymmetric version of the Tsuji-Trost reaction
in ionic liquids [11, 12].
The main aim of this work was to examine if ally-
lation of aldehydes by allyl alcohol or allyl acetates=
carbonates can be performed in ionic liquids.
Results and Discussion
ꢀ-Allylation of simple aldehydes and ketones has
been much less studied and these carbonyl com-
pounds in advance must be converted into their met-
To start our work on allylation of 2-phenylpropanal
with allyl alcohol, we decided to repeat the experi-
ment described in Ref. [21] (Scheme 1). As can be
seen from entry 2 in Table 1 we achieved the same
result as described. When the reaction was carried
ꢀ
Corresponding author. E-mail: toma@fns.uniba.sk

ˇ
M. Hut’ka and S. Toma
1176
Scheme 1
addition of base were performed (entries 7, 8) and
it was proven that allylation in an ionic liquid can be
performed without addition of any base while no
reaction was observed in THF.
Our next aim was to test the effect of the [Pd]-
source and ligand on the reaction course (Scheme 3).
Results are given in Table 3.
First of all it is necessary to point out that practi-
cally all reactions were proceeding with a full con-
version of the starting aldehyde. The isolated yields
of the products were very sensitive both to the [Pd]-
source as well as the ligand. Lower isolated yields
were caused by formation of several, not identi-
fied, side products. The best yields were achieved
with PdCl2(PPh3)2 and Pd2(dba)3 CHCl3 as the [Pd]-
source (entries 2, 5). The reaction was very clean
using P(o-tolyl)3 and P(2-furyl)3 as the ligands (en-
tries 6, 10). We were curious also if the structure of
ionic liquid would have some effect on the reaction
(Scheme 4) course and the corresponding results are
collected in Table 4.
Table 1. ꢀ-Allylation of 2-phenylpropanal with allyl alcohol
Entry
L
Solvent
Time= T=ꢁC Yield=
h
%
1
2
3
4
5
PPh3
PPh3
PPh3
PPh3
PPh3,
THF
THF
[bmim]PF6
[bmim]PF6
[bmim]PF6
12
12
12
36
36
50
50
50
RT
RT
87a
86
59
50
52
without LiCl
PPh3,
without BEt3
6
[bmim]PF6
36
RT
26
a
This yield was described in [21]
out in [bmim]PF6 a much lower yield was achieved.
Then attempts were made to simplify the composi-
tion of the reaction mixture (entries 4, 5). We found
that reaction proceeded also without addition of
LiCl, but reaction without Et3B gave much lower
yield, which is in accord with Ref. [20].
As the yield of allylation of 2-phenylpropanal
with allyl alcohol was low, we decided to examine
if it is not possible to perform its allylation with
another allylation agent, namely allyl acetate and
allyl ethyl carbonate (Scheme 2, Table 2). From the
results given in Table 2 one can see that the reaction
in [bmim]PF6 was proceeding nicely, in particular,
when triethylamine was used as the base. Practically
equal results were achieved in an allylation with al-
lyl acetate and allyl ethyl carbonate. Triethylamine
proved to be a more efficient base than potassium
carbonate. In our recent work [23] we have proved
that Michael addition of C-nucleophiles can be per-
formed in ionic liquids without addition of an ex-
ternal base. For that reason experiments without
From the results given in Table 4 it follows that
reaction proceeded very well in all ionic liquids, but
the most clean results were achieved using MERCK’s
[n-BuMePyrr](C2F5)3PF3 ionic liquid.
From the results given in Tables 2–4 it is possi-
ble to conclude that allylation of 2-phenylpropanal
in ionic liquid is possible without its interconver-
sion to its metal enolates or trimethylsilyl enolate.
We decided therefore to examine if allylation of oth-
er weak acidic substrates could undergo similar al-
lylation. Attempts were made on the allylation of
cyclohexanecarboxaldehyde, isobutyrylaldehyde,
2,6-dimethylcyclohexane-1-one, cyclohex-2-en-1-
one, as well as with ethyl phenylacetate, but prac-
Scheme 2

Pd-Catalyzed ꢀ-Allylation
1177
Table 2. Effect of leaving group and base on the ꢀ-allylation
of 2-phenylpropanal
We do not have any explanation for this fact at the
moment.
On the other hand, attempts to allylate diphenyla-
cetaldehyde and diethyl phenylmalonate were suc-
cessful, and high yields of the reaction products
(96 and 67%; structures 2 and 3 in Fig. 1) were
isolated. No allylation was going on with 2-methyl-
tetraline-1-one, while the product of a bis-allylation
and unreacted tetraline-2-one was isolated at reac-
tion with tetraline-2-one (Fig. 1, 4) (45%, with one
equivalent of allyl ethyl carbonate and 86% with two
equivalents of the reagent). These results point out
that for a successful allylation it is necessary that a
stable anion delocalised into benzene or other arene
rings can be formed.
Entry
X
Solvent
Base
Time= Yield=
h
%
1
2
3
4
5
6
7
8
OCOCH3 K2CO3
OCOCH3 [bmim]PF6 K2CO3
THF
20
20
5
5
5
34
69
83
51
85
0
OCOCH3 [bmim]PF6
OTs [bmim]PF6
OCOOEt [bmim]PF6
Br [bmim]PF6
OCOOEt [bmim]PF6
OCOOEt THF
Et3N
Et3N
Et3N
Et3N
–
5
5
5
63
0
–
tically no product was isolated even when we
prolonged the reaction time or rised the tempera-
ture. We assumed that this could be connected with
the low acidity of the substrate, and therefore in
attempts to react with isobutyraldehyde we changed
the base for potassium carbonate or BSA=LiOAc.
However, it provided no result on the reaction course.
In conclusion, our study proved that the Pd-cata-
lysed allylation of 2-penylpropanal in ionic liquids is
proceeding well even with free allyl alcohol. Better
yields were achieved when allyl acetate or allyl
ethyl carbonate was used as the allylation agent.
Scheme 3
Table 3. Effect of the Pd-source and ligand on the ꢀ-allylation of 2-phenylpropanal with allyl ethyl carbonate
Entry
[Pd] source (10 mol%)
L (20 mol%)
Time=h
Conversion=%
Isolated yield=%
1
2
3
4
5
6
7
8
9
10
Pd(OAc)2
PdCl2(PPh3)2
Pd(PPh3)4
Pd(dppf)2
Pd2(dba)3 ꢂ CHCl3
Pd2(dba)3 ꢂ CHCl3
Pd2(dba)3 ꢂ CHCl3
Pd2(dba)3 ꢂ CHCl3
Pd2(dba)3 ꢂ CHCl3
Pd2(dba)3 ꢂ CHCl3
PPh3
PPh3
PPh3
dppf
PPh3
5
5
5
5
5
5
2.5
2.5
2.5
2.5
100
100
100
100
100
100
85
100
100
100
68
83
40
80
80
83
70a
50
60
96
P(o-tolyl)3
P(o-tolyl)3
AsPh3
DPPF
P(2-furyl)3
a
Reactions were performed with 5 mol% of [Pd] and 10 mol% of L
Scheme 4

ˇ
M. Hut’ka and S. Toma
1178
Fig. 1. Structures of the products of ꢀ-allylations of different carbonyl compounds
0.6 mmol of the base. The reaction mixture was stirred at room
temperature for 5 h. The reaction mixture was then extracted
several times with diethyl ether ([bmim]PF6 as IL) or n-hex-
ane. Extracts were dried (Na2SO4), filtered, and the solvent
was evaporated on a RVO. The residue was purified by col-
umn chromatography on silica gel using an ethyl acetate:
isohexane (1:7) mixture as the eluent.
From the reaction with 2-phenylpropanal was isolated 2-
phenyl-4-butene-2-carboxaldehyde (Fig. 1, 1), an oil, NMR
spectra are identical with those described in Ref. [24].
From the reaction with diphenylacetaldehyde was isolated
2,2-diphenyl-3-propen-1-carboxaldehyde (Fig. 1, 2), an oil,
NMR spectra are identical with those described in Ref. [25].
From the reaction with diethyl phenylmalonate was isolated
diethyl allylphenylmalonate (Fig. 1, 3), an oil, NMR spectra
are identical with those described in Ref. [26].
Table 4. Ionic liquid ꢀ-allylation of 2-phenylpropanal with
allyl ethyl carbonatea
Entry
Ionic liquid
Conversion= Isolated
yield=%
%
1
2
3
4
5
6
[bmim]PF6
[bmim]PF6
[emim]SO4Et
100
90
100
100
90
95
60b
94
95
81
98
[n-Bu3EtP](EtO)2PO2
[i-Bu3MeP]Ts
[n-BuMePyrr](C2F5)3PF3
100
a
All reactions were carried out with 10 mol% of [Pd] and
20 mol% of L
b
1st recyclation
Allylation of different carbonyl compounds with
these reagents revealed that reaction in ionic liquids
is possible only in the case when the reagent has just
one C–H bond adjacent to the carbonyl group and
the formed carbanion is conjugated to an arene ring.
Bis-allylation products were isolated in the reactions
with reagents having two C–H bonds adjacent to the
carbonyl group.
1,1-Diallyltetraline-2-one (4, C16H18O)
From the reaction with tetraline-2-one 45% of an oil could
1
be isolated. H NMR (CDCl3, 300 MHz): ꢂ ¼ 7.35–7.14 (m,
4HAr), 5.44–5.30 (m, 2Hb), 4.94–4.85 (m, 4Ha), 2.80 (dd,
2He), 2.54 (m, 4Hc) ppm; 13C NMR (CDCl3, 75 MHz):
ꢂ ¼ 212.59, 138.11, 135.94, 132.33, 126.98, 125.90, 125.32,
117.26, 54.96, 44.05, 39.26, 26.82 ppm.
Acknowledgements
NMR measurements were performed on the equipment
supported by the Slovak State Program Project No.
2003SP200280203. Our thanks are due to Iveta Kmentova
PhD for preliminary experiments and to the Slovak Grant
Agency VEGA (grant No. 1=3569=06) for the financial
support.
Experimental
1H NMR spectra were measured at 300 MHz, 13C NMR at
75MHz, with a Varian Mercury Plus instrument as solution in
CDCl3 with tetramethylsilane as internal standard. Elemental
analysis was measured with a Carlo Erba Instrumentation
Analyzer. Measured data for the new compound are in accord
with the calculated data.
References
General Procedure for Allylation of Carbonyl Compounds
Palladium source (0.05 mmol of [Pd] and 0.1 mmol phos-
phine) were dissolved in 0.8cm3 ionic liquid and the solution
was stirred, under N2 atmosphere, at 80ꢁC for 20 min. The
solution of the pre-formed catalyst was cooled down to room
temperature and then was added 0.5 mmol allyl ethyl carbon-
ate or allyl acetate, 0.5mmol of carbonyl compound, and
[1] Godkleski SA (1991) Comprehensive Organic Synthe-
sis. In: Trost BM, Fleming I, Paquette LA (eds), vol. 4.
Pergamon Press, Oxford, p 585
[2] Consiglio G, Waymouth RM (1989) Chem Rev 89: 257
[3] Trost BM, Van Varken DL (1996) Chem Rev 96: 395
[4] Tsuji J, Minami I (1987) Acc Chem Res 20: 140
[5] Trost BM (1980) Acc Chem Res 13: 385

Pd-Catalyzed ꢀ-Allylation
1179
[6] Trost BM (1989) Angew Chem Int Ed Engl 28: 1173
[7] Trost BM, Lee C (2000) In: Ojima I (ed) Catalytic Asym-
metric Synthesis, Chapter 8E. Wiley-VCh, New York
[8] Trost BM, Weber L, Strenge PE, Fulleron TJ, Dietsche
TS (1978) J Am Chem Soc 100: 3426
[9] Hayashi T, Yamamoto A, Hagihara E, Ito Y (1986)
Tetrahedron Lett 27: 191
[10] Hayashi T, Kanechira K, Hagihara T, Kumada M (1988)
J Org Chem 53: 113
[11] Toma S, Gotov B, Kmentova I, Solcaniova E (2000)
Green Chem 2: 149
[12] Kmentova I, Gotov B, Solcaniova E, Toma S (2002)
Green Chem 4: 103
[13] Luo F-T, Negishi E (1985) Tetrahedron Lett 26: 2177
[14] Braun M, Laicher F, Meier T (2000) Angew Chem Int Ed
39: 3494
[15] Tsuji J, Minami I, Shimizu I (1983) Chem Lett 1325
[16] Hiroi K, Abe J, Suya K, Sato S, Komayama T (1994) J
Org Chem 59: 203
[17] Atkins KE, Walker WE, Manyik RM (1970) Tetrahedron
Lett 11: 3821
[18] Bergbreiter DE, Weatherford DA (1989) J Chem Soc
Chem Commun, 883
[19] Haudegong JP, Chauvin Y, Commereuc DJ (1979) J Org
Chem 44: 3063
[20] Kimura M, Mujai R, Tamigawa N, Tanaka S, Tamaru Y
(2003) Tetrahedron 59: 7767
[21] Kimura M, Horino Y, Mukai R, Tanaka S, Tamura Y
(2001) J Am Chem Soc 123: 10401
[22] Chandrasekhar S, Jagadeswar V, Sarith B, Narsihmulu C
(2005) J Org Chem 70: 6506
˘
˘
´
[23] Meciarova M, Toma S (2006) Chem Eur J 13: 1268
[24] Kulkarni MG, Davawala S, Anirudha K, Dhanjay S
(2004) 2919
[25] Bender CF, Widenhoefer RA (2005) J Am Chem Soc
127: 1070
[26] Necas D, Tursky M, Kotora M (2004) J Am Chem Soc
126: 10222