Solvent-controlled highly selective bis-and monoallylation of active methylene compounds by allyl acetate with palladium(0) nanoparticle

Article abstract of DOI:10.1021/ol702099v

(Chemical Equation Presented) Palladium(0) nanoparticle has been used as an efficient catalyst for the allylation of active methylene compounds. Very efficient bisallylation is achieved for a variety of active methylene compounds by allyl acetate and its derivatives in one stroke in THF solvent. The reaction in water provides monoallylated product selectively by allyl acetate only. The recovered Pd(0) nanoparticle is recycled. A probable mechanism is suggested.

Full text of DOI:10.1021/ol702099v

ORGANIC
LETTERS
2007
Vol. 9, No. 22
4595-4598
Solvent-Controlled Highly Selective Bis-
and Monoallylation of Active Methylene
Compounds by Allyl Acetate with
Palladium(0) Nanoparticle
Brindaban C. Ranu,* Kalicharan Chattopadhyay, and Laksmikanta Adak
Department of Organic Chemistry, Indian Association for the CultiVation of Science,
JadaVpur, Kolkata, 700 032, India
ocbcr@iacs.res.in
Received August 27, 2007
ABSTRACT
Palladium(0) nanoparticle has been used as an efficient catalyst for the allylation of active methylene compounds. Very efficient bisallylation
is achieved for a variety of active methylene compounds by allyl acetate and its derivatives in one stroke in THF solvent. The reaction in water
provides monoallylated product selectively by allyl acetate only. The recovered Pd(0) nanoparticle is recycled. A probable mechanism is
suggested.
Allylic substitution is a very useful reaction as it adds a
moiety that has much potential for further elaboration. The
palladium-catalyzed allylation by allylic alcohols or prefer-
ably its derivatives like acetate and carbonate is one of the
most efficient protocols for constructing C-C bonds in
organic synthesis.1 Usually a palladium derivative in com-
bination with a ligand is used.2 These procedures involved
Pd2(dba)3/PPh3,2a [Pd(η3-C3H5)Cl]2/tetraphosphine ligand,2b
Pd(0)/P(C6H4-m-SO3Na)3 [trisodium salt of tris(m-sul-
fonatophenyl)phosphine (tppts)],2c Pd-P(OC6H5)3,2d Pd(dba)2/
PPh3/Al2O3,2e PdCl2(CH3CN)2/[(HOCH2CH2NHCOCH2)2-
NCH2]2,2f and Pd[PPh3]4.2g A few procedures with other non-
palladium catalysts such as [CpRuCl(cod)]3a,b and Nio/dppp3c
were also reported. In recent times, interest in nanoparticle-
catalysis has increased considerably because of its improved
efficiency under mild and environmentally benign conditions
in the context of Green Chemistry.4,5 Palladium nanoparticles
have been found to be active species in various C-C bond
formation, namely Heck, Sonogashira, and Suzuki, coupling
reactions and thus showed great promise for further applica-
tions.5 However, the Tsuji-Trost reaction, i.e., allylic
substitution of active methylene compounds, has been less
studied and only recently, palladium and cobalt nanoparticles
immobilized on silica,6a montmorillonite entrapped sub-
(1) (a) Trost, B. M.; Van Vranken, D. L. Chem. ReV. 1996, 96, 395. (b)
Tsuji, J. Transition Metal Reagents and Catalysts; Wiley: New York, 2000.
(2) (a) Giambastiani, G.; Poli, G. J. Org. Chem. 1998, 63, 9608. (b)
Laurenti, D.; Feuerstein, M.; Pepe, G.; Doucet, H.; Santelli, M. J. Org.
Chem. 2001, 66, 1633. (c) Kinoshita, H.; Shinokubo, H.; Oshima, K. Org.
Lett. 2004, 6, 4085. (d) Kayaki, Y.; Koda, T.; Ikariya, T. J. Org. Chem.
2004, 69, 2595. (e) Ferroud, D.; Genet, J. P.; Muzart, J. Tetrahedron Lett.
1984, 25, 4379. (f) Chevrin, C.; Le Bras, J.; Henin, F.; Muzart, J.; Pla-
Quintana, A.; Roglans, A.; Pleixats, R. Organometallics 2004, 23, 4796.
(g) Schwartz, C. E.; Curran, D. P. J. Am. Chem. Soc. 1990, 112, 9272.
(3) (a) Yamamoto, Y.; Nakagai, Y.-i.; Itoh, K. Chem. Eur. J. 2004, 10,
231. (b) Renaud, J.-L.; Bruneau, C.; Demerseman, B. Synlett 2003, 408.
(c) Bricout, H.; Carpentier, J.-F.; Mortreux, A. Chem. Commun. 1997, 1393.
(4) (a) Lu, F.; Ruiz Aranzaes, J.; Astruc, D. Angew. Chem., Int. Ed. 2005,
44, 7399. (b) Moreno-Manas, M.; Pleixats, R. Acc. Chem. Res. 2003, 36,
638. (c) Crooks, R. M.; Zhao, M.; Sun, L.; Chechik, V.; Yeung, L. K. Acc.
Chem. Res. 2001, 34, 181.
(5) (a) Astruc, D. Inorg. Chem. 2007, 46, 1884. (b) Astruc, D.; Lu, F.;
Aranzaes, J. R. Angew. Chem., Int. Ed. 2005, 44, 7852. (c) Beletskaya, I.
P.; Cheprakov, A. V. Chem. ReV. 2000, 100, 3009.
10.1021/ol702099v CCC: $37.00
© 2007 American Chemical Society
Published on Web 09/29/2007

nanoordered Pd clusters,6b and palladium nanoparticle sta-
bilized by an asymmetric diphosphite6c were reported.
Allylation of amines6d and phenols6e by Pd nanoparticles was
also demonstrated. We report here a novel ligand-free
protocol for allylic substitution of active methylene com-
pounds by allyl acetate and its derivatives (Tsuji-Trost
reaction), catalyzed by palladium(0) nanoparticles. The
reaction in THF leads to bisallylation in one stroke, whereas
highly selective monoallylation by allyl acetate takes place
in H2O (Scheme 1).
Scheme 1
Figure 1. TEM image of Pd nanoparticles formed in the reaction
mixture.
Several structurally diverse active methylene compounds
underwent allylation by allyl acetate or its derivatives by in
situ generated palladium(0) nanoparticles in THF to produce
the corresponding allylated products in high yields. The
results are summarized in Table 1.
The experimental procedure is very convenient.7 A one-
pot reaction of active methylene compound and allyl acetate
in the presence of the PdCl2/TBAB/K2CO3 system in
refluxing THF provided the product. The formation of Pd-
(0) nanoparticles in situ from this reagent system was
detected by us from the analysis of the reaction mixture by
transmission electron microscope (TEM) and Energy Dis-
persive X-ray spectroscopy (EDS) (Figures 1 and 2). The
size of Pd nanoparticles was found to be 5-8 nm. In absence
of Pd nanoparticle no reaction was initiated.
(6) (a) Park, K. H.; Son, S. U.; Chung, Y. K. Org. Lett. 2002, 4, 4361.
(b) Mitsudome, T.; Nose, K.; Mori, K.; Mizugaki, T.; Ebitani, K.; Kitsukawa,
K.; Kaneda, K. Angew. Chem., Int. Ed. 2007, 46, 3288. (c) Jansat, S.;
Gomez, M.; Philippot, K.; Muller, G.; Guiu, E.; Claver, C.; Castillon, S.;
Chaudret, B. J. Am. Chem. Soc. 2004, 126, 1592. (d) Cortial, G.; Siutkowski,
M.; Goettmann, F.; Moores, A.; Boissiere, C.; Grosso, D.; Le Floch, P.;
Sanchez, C. Small 2006, 2, 1042. (e) Park, C. M.; Kwon, M. S.; Park, J.
Synthesis 2006, 3790.
(7) Representative Experimental Procedure for Allylation of Active
Methylene Compound (entry 1, Table 1). To a stirred mixture of
tetrabutylammonium bromide (323 mg, 1 mmol) and PdCl2 (7 mg, 0.04
mmol) in THF (4 mL) were added allyl acetate (250 mg, 2.5 mmol),
acetylacetone (100 mg, 1 mmol), and K2CO3 (414 mg, 3 mmol). The mixture
was then heated at reflux for 6 h (TLC). After being cooled THF was
evaporated and the residue was extracted with Et2O (3 × 10 mL). The
ether extract was washed with brine, dried (Na2SO4), and evaporated to
leave the crude product, which was purified by column chromatography
over silica gel (ether-hexane 10:90) to afford the pure product, 3,3-
diallylpentane-2,4-dione, as a yellow oil (150 mg, 82%); IR (neat) 2979,
1739, 1697, 1639 cm-1; 1H NMR (300 MHz, CDCl3) δ 2.06 (s, 6H), 2.61
(d, J ) 7.3 Hz, 4H), 5.04-5.11 (m, 4H), 5.42-5.53 (m, 2H); 13C NMR
(CDCl3, 75 MHz) δ 27.2 (2C), 35.0 (2C), 70.3, 119.3 (2C), 132.0 (2C),
205.7 (2C). These data were in agreement with the reported values.2c The
solid residue after organic extract containing Pd(0) nanoparticles was reused
for subsequent reactions (no loss of efficiency up to three runs).
(8) Muthusamy, S.; Gnanaprakasam, B. Tetrahedron Lett. 2005, 46, 635.
(9) Conrad, J. C.; Eelman, M. D.; Duarte Silva, J. A.; Monfette, S.;
Parnas, H. H.; Snelgrove, J. L.; Fogg, D. E. J. Am. Chem. Soc. 2007, 129,
1024.
Figure 2. Energy dispersive X-ray spectra with the use of a Cu-
grid.
As evident from the results all the substrates produced
bisallylated products under these conditions. The participating
active methylene compounds were acyclic and cyclic 1,3-
diketones, 1,3-keto esters, and 1,3-diester, and allylic agents
used were allyl acetate, crotyl acetate, and cinnamyl acetate
and its derivatives. The careful monitoring of the progress
of the reaction by TLC and 1H NMR at intermediate stages
indicated the presence of monoallylated compound in the
range of 5-7% together with the starting material and
bisallylated compound. It was also found that allylation of
monoallyl ethyl acetoacetate by this procedure was complete
within 1.5 h (entry 4, Table 1) compared to 7 h required for
(10) Bhar, S.; Chaudhuri, S. K.; Sahu, S. G.; Panja, C. Tetrahedron 2001,
57, 9011.
(11) Kondo, J.; Someya, H.; Kinoshita, H.; Shinokubo, H.; Yorimitsu,
H.; Oshima, K. Org. Lett. 2005, 7, 5713.
(12) Matlin, A. R.; McGarvey, D. J.; Leckta, T. C.; Jacob, P. W.; Picken,
H. A. Tetrahedron Lett. 1987, 28, 5087.
(13) Sigismondi, S.; Sinou, D. J. Mol. Catal. A: Chem. 1997, 116, 289.
4596
Org. Lett., Vol. 9, No. 22, 2007

Table 1. Allylation of Active Methylene Compounds by Allyl
Table 2. Comparative Results of Allylation in Different
Acetate Catalyzed by Pd(0) Nanoparticle in THF
Solvents
solvent
A:Ba
time (h)
yield (%)
THF
00:100
30:70
00:100
25:75
80:20
00:100
7
5
9
7
8
9
88
55
82
70
72
80
CH3CN
toluene
DMF
H2O
DCM
a The ratio of A and B was determined by integration of peaks in the 1H
NMR spectra.
nanoparticle was formed from the reduction of PdCl2 by the
alkene moiety of allyl acetate.5c The slurry of palladium
nanoparticles remaining after extraction of product was
evaporated under vacuum to leave a dust of residue, which
showed the presence of metallic Pd by XRD (Figure 3). This
Figure 3. Powder XRD pattern with characteristic dihedral angles
at 40.119° and 46.65° corresponding to Pd stabilized by TBAB in
the recovered Pd residue.
a Yields refer to those of purified products characterized by IR, 1H, and
1
13C NMR spectroscopic data. b Mixture of E and Z isomers (90:10 by H
NMR).
solid was equally effective for three subsequent runs without
any loss of efficiency (Figure 4).
bisallylation starting from ethyl acetoacetate (entry 2, Table
1). This indicates that bisallylation is much faster than the
monoallylation step, restricting accumulation of monoal-
lylated compound in the reaction mixture.
Interestingly, when the reaction was carried out in H2O
monoallylation took place selectively. The results are
reported in Table 3. However, this reaction was not very
general. The reaction proceeded successfully only with allyl
acetate; cinnamyl acetate and crotyl acetate failed to produce
any allylated product. However, the selectivity was quite
high; only in one example (entry 2, Table 3) was 20% of
the bisallylated product formed out of four types of sub-
strates.
The reactions were very clean and bisallylated products
were the only isolable compounds. The bisallylated com-
pounds are very useful synthons, and we showed a repre-
sentative example of the conversion of this compound to
spiro annulated product by Grubbs’ catalyst (eq 1). THF was
found to be the solvent of choice for the formation of
bisallylated product in high yields based on comparison of
reaction results with other solvents (Table 2). Palladium(0)
The analysis of results of allylation of all substrates
included in Tables 1 and 3 revealed that the additions were
highly regioselective. When allyl acetate was used terminal
Org. Lett., Vol. 9, No. 22, 2007
4597

Scheme 2. Possible Mechanism of Monoallylation in Water
and Bisallylation in THF
Figure 4. Recyclability Chart.
alkenes were produced (entries 1-9, Table 1 and entries
1-4, Table 3), whereas substituted allyl acetates provided
monoallylation in water is successful only for allyl acetate
and fails for other acetates. The steric factor may have a
role.
The present procedure has its own distinction from others.
The reaction is carried out in one pot including preparation
of nano Pd(0) by a very simple and convenient means. The
selective monoallylation and bisallylation were achieved by
using H2O and THF, respectively, and thus pure mono- and
bisallylated products were obtained. Usually either monoal-
lylated product or a mixture of mono- and bisallylated
products was obtained with other reagents except [Cp*RuCl-
(cod)],3a,b which provide bisallylated products.
Table 3. Allylation of Active Methylene Compounds by Allyl
Acetate Catalyzed by Pd(0) Nanoparticle in H2O
In conclusion, the present protocol using an in situ
prepared palladium(0) nanoparticle provides a convenient and
efficient procedure for allylation of active methylene com-
pounds by allyl acetate. The significant improvements offered
by this procedure are operational simplicity, achievement of
selective mono- or bisallylation in H2O or THF, respectively,
high regioselectivity in the formation of products, high
isolated yields, and reusibility of catalyst. To the best of our
knowledge, this strategy for the solvent controlled selective
allylation of active methylene compounds by allyl acetate
involving Pd(0) nanoparticles is novel and not reported
earlier.
a Yields refer to those of purified products characterized by IR, 1H, and
13C NMR spectroscopic data.
internal alkenes (entries 10-16, Table 1). We speculate that
Pd(0) nanoparticle combines with allyl acetate to form an
η3-allyl-Pd(II)-complex 1 which then reacts with an active
methylene compound to give an intermediate 2, which
provides the corresponding product by addition to the less-
substituted carbon end (Scheme 2).1a The difference in
reactivity of active methylene compounds in H2O and THF
leading to monoallylation and bisallylation, respectively, may
be explained by the fact that H2O hydrates2c the Pd(II) in
complex 1, weakening the coordination of Pd with CdO,
thereby decreasing the acidity at the methine center to go
for further allylation. However, in nonaqueous medium
having no such effect bisallylation is favored. THF was found
to be the best solvent toward bisallylation as mentioned
earlier (Table 2). However, it is not clear to us why the
Acknowledgment. We are pleased to acknowledge the
financial support from DST [Grant No. SR/S5/GC-02/2006]
for this investigation. K.C. and L.A. are thankful to CSIR
for their fellowship.
Supporting Information Available: Characterization (IR,
1H, and 13C NMR spectroscopic data and elemental analysis)
for the new compounds reported in Table 1 (listed in entries
1
11, 15, and 16) and H NMR and 13C NMR spectra of all
compounds listed in Tables 1 and 3. This material is available
free of charge via the Internet at http://pubs.acs.org.
OL702099V
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Org. Lett., Vol. 9, No. 22, 2007