Tandem β-boration/arylation of α,β-unsaturated carbonyl compounds by using a single palladium complex to catalyse both steps

Article abstract of DOI:10.1002/chem.200903095

Diphenyl(3-methyl-2-indolyl)phosphine (C₉H₈NPPh ₂, 1) gives stable dimeric palladium(II) complexes that contain the phosphine in P,Nbridging coordination mode. On treating 1 with [Pd(O ₂CCH₃)₂], the new complexes [Pd(μ-C ₉H₇NPPh₂)-(NCCH₃)]₂ (2) or [Pd(μ-C₉H₇NPPh₂)-(μ-O ₂CCH₃)]₂ (3) were isolated, depending on the solvent used, acetonitrile or toluene, respectively. Further reaction of 3 with the ammonium salt of 1 led to the substitution of one carboxylate ligand to afford [Pd(u-C₉H₇NPPh₂)₃(μ-O ₂CCH₃)] (4), in which the bimetallic unit is bonded by three C₉H₇NPPh₂^- moieties and one carboxylate group. Using this methodology, [Pd₂(μ-C ₆H₄PPh₂)₂(μ-C₉H ₇NPPh₂)(μ-O₂CCX₃)] (X = H (7); J. = F (8)) were synthesised from the ortho-metalated compounds [Pd(C ₆H₄PPh₂)(μO₂CCX3)], (X = H (5); J. = F (6)). Complexes 3, 4, 7, and 8 have been found to be active in the catalytic β-boration of α,β-unsaturated esters and ketones under mild reaction conditions. Hindrance of the carbonyl moiety has an influence on the reaction rate, but quantitative conversion was achieved in many cases. More remarkably, when aryl bromides were added to the reaction media, complex 7 induced a highly successful consecutive β-boration/crosscoupling reaction with dimethyl acrylamide as the substrate (99% conversion, 89 % isolated yield).

Full text of DOI:10.1002/chem.200903095

DOI: 10.1002/chem.200903095
Tandem b-Boration/Arylation of a,b-Unsaturated Carbonyl Compounds by
Using a Single Palladium Complex To Catalyse Both Steps
Amadeu Bonet,[a] Henrik Gulyꢀs,[a] Igor O. Koshevoy,[b] Francisco Estevan,[b]
Mercedes Sanaffl,[b] M. Angeles Úbeda,*[b] and Elena Fernꢀndez*[a]
Abstract: Diphenyl(3-methyl-2-indol-
yl)phosphine (C9H8NPPh2, 1) gives
stable dimeric palladium(II) complexes
that contain the phosphine in P,N-
bridging coordination mode. On treat-
C9H7NPPh2)
G
Complexes 3, 4, 7, and 8 have been
found to be active in the catalytic b-bo-
ration of a,b-unsaturated esters and ke-
tones under mild reaction conditions.
Hindrance of the carbonyl moiety has
an influence on the reaction rate, but
quantitative conversion was achieved
in many cases. More remarkably, when
aryl bromides were added to the reac-
tion media, complex 7 induced a highly
successful consecutive b-boration/cross-
coupling reaction with dimethyl acryl-
amide as the substrate (99% conver-
sion, 89% isolated yield).
R
the bimetallic unit is bonded by three
ꢀ
C9H7NPPh2 moieties and one carbox-
ylate group. Using this methodology,
[Pd2(m-C6H4PPh2)2(m-C9H7NPPh2)ACHTUNTGRNEUNG(m-
O2CCX3)] (X=H (7); X=F (8)) were
synthesised from the ortho-metalated
compounds
ing 1 with [Pd
A
complexes
G
N
O2CCX3)]2 (X=H (5); X=F (6)).
pending on the solvent used, acetoni-
trile or toluene, respectively. Further
reaction of 3 with the ammonium salt
of 1 led to the substitution of one car-
boxylate ligand to afford [Pd(m-
Keywords: arylation · domino reac-
tions
· heterogeneous catalysis ·
N,P ligands · palladium
Introduction
tionalisation protocol to have been explored so far.[3] We
became interested in the selective synthesis of b-boryl esters
as a platform for introducing a b-aryl functionality through
a subsequent cross-coupling reaction. We also attempted to
conduct both catalytic reactions, b-boration followed by ary-
lation, using the same palladium-based catalytic system
(Scheme 1).
Electronic directing effects give rise to regioisomeric orga-
noboronate formation in the metal-mediated b-boration of
a,b-unsaturated carbonyl substrates (Scheme 1, path a).[1]
This functionalisation creates a stereogenic centre at the b-
carbon, and enantioselectivity can be induced with an ap-
propriate catalyst.[2] Despite the selectivity of the C B bond
ꢀ
formation and the retention of configuration in the function-
alisation process by which the organoborane intermediates
are converted to the target products, to the best of our
knowledge the oxidation–acylation reaction is the only func-
[a] A. Bonet, Dr. H. Gulyꢀs, Dr. E. Fernꢀndez
Departament de Quꢁmica Fꢁsica i Inorgꢂnica
Universitat Rovira i Virgili, C/Marcel.lꢁ
Domingo s/n, 43007 Tarragona (Spain)
Fax : (+34)977-559563
Scheme 1. a) b-boration, b) arylation.
E-mail: mariaelena.fernandez@urv.cat
We were the first to demonstrate that palladium com-
plexes catalyse the diboration reaction of alkenes[4] despite
the unfavourable oxidative addition of the diboron reagent
to Pd0.[5] We also proposed the first palladium-mediated b-
boration of a,b-unsaturated esters, in which asymmetric in-
duction was achieved in the presence of appropriate chiral
[b] Dr. I. O. Koshevoy, Dr. F. Estevan, Dr. M. Sanaffl, Dr. M. A. Úbeda
Departament de Quꢁmica Inorgꢂnica, Universitat de Valencia
Dr. Moliner 50, 46100 Burjassot, Valencia (Spain)
E-mail: angeles.ubeda@uv.es
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200903095.
6382
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Chem. Eur. J. 2010, 16, 6382 – 6390

FULL PAPER
ligands.[6] An advantage of the palladium-catalysed B-addi-
ꢀ
tion reaction leading to the creation of a C B bond is that it
is possible to use the organoboronate intermediate to con-
duct a subsequent palladium-mediated reaction, for exam-
ple, a cross-coupling reaction[7] or borylative cyclisation of
enynes and enediynes.[8]
The tandem diboration/arylation of alkenes was first per-
formed asymmetrically by Morken et al.[9] A RhI complex
was employed for the catalytic diboration and a Pd complex
served favourably for the subsequent monoarylation of the
intermediate alkylboronic ester. In order to highlight the
benefit of using a single complex for both transformations,
Scheme 2. Synthesis of [Pd(m-C9H7NPPh2)
C9H7NPPh2)2A(m-O2CCH3)]2.
ACHTUNGTREN(UNGN NCCH3)]2 and [Pd(m-
we developed multifaceted palladium(II) and palladiumACHTUNTRGNEUNG(III)
CTHUNGTRENNUNG
complexes[10] that participated in both catalytic cycles (dibo-
ration and arylation) with equal success.[11]
The diphenyl(3-methyl-2-indolyl)phosphine ligand syn-
thesised by Browning et al.[12] contains an electron-rich het-
erocyclic indole substituent. Deprotonation of the indolyl ni-
trogen atom with a base gives rise to a second coordination
centre, yielding a bidentate ligand with two donor centres of
different Lewis basicity. This ligand may bridge two transi-
tion metal centres through the P and N atoms to afford di-
nuclear complexes favoured by the geometry and rigidity of
the ligand. There have been a few examples in the literature
of complexes with this phosphine, including dinuclear palla-
dium and trinuclear ruthenium compounds, in which the co-
ordination exclusively involves the phosphorus atom,[12,13]
{m3,h2-P
and [Ru3(CO)9ACHTUNGTRENNUNG(m-H)ACHTUNGTRNENGU ACHTUNGRETNN(GNU C6H5)2ACTHUNGTREN(NUNG C9H7N)}], in which the
ligand behaves as a novel and robust six-electron P,N-
donor.[13]
We present herein the synthesis and characterisation, as
well as electrochemical and catalytic studies, of new dinu-
clear palladium(II) complexes containing diphenyl(3-
methyl-2-indolyl)phosphine as a P,N-bridging coordination
ligand. The feasibility of a new b-boration/arylation tandem
approach has been demonstrated for all of these complexes.
Figure 1. ORTEP view of compound 2 with ellipsoids drawn at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
Results and Discussion
Palladium catalysts: Palladium acetate, [PdACHTUNRGTNEUNG(O2CCH3)2],
reacts smoothly under anaerobic conditions with diphenyl(3-
methyl-2-indolyl)phosphine (C9H8NPPh2, 1) to give dinu-
clear complexes with a P,N-bridging coordination mode. The
composition of the complex formed depends considerably
on the solvent used as the reaction medium. When [Pd-
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Figure 2. ORTEP view of compound 3 with ellipsoids drawn at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
AHCTUNGTRENNUNG
O2CCH3)]2 (3) was obtained (yield 84%) (Scheme 2). In the
synthesis of 2, a small amount of complex 3 was obtained,
along with decomposition products.
Both complexes were spectroscopically and structurally
characterised (Figures 1 and 2). Selected bond lengths and
angles are displayed in Table 1.
Compound 2 crystallised in the monoclinic space group
P2/c. Its structure is similar to those side-by-side palladi-
AHCTUNGTREGUNuNN m(I) compounds with metal–metal bonds of the type
Chem. Eur. J. 2010, 16, 6382 – 6390
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www.chemeurj.org
6383

E. Fernꢀndez, M. A. Úbeda et al.
Table 1. Selected bond lengths [Š] and angles [8] for different palladi-
um(I) and palladium(II) compounds.
ACHTUNGTRENNUNG
Compound
2[a]
3
4
7
ꢀ
Pd(1) Pd(2)
2.5459(8)
2.2275(18)
–
–
2.080(5)
2.164(6)
–
2.164
–
–
81.74(5)
91.15(14)
–
2.6884(8)
2.240(2)
2.240(2)
–
1.996(6)
1.973(6)
–
–
2.7521(4)
2.3619(11)
2.3619(11)
2.3435(11)
1.994(4)
2.034(4)
2.021(4)
–
2.7395(2)
2.3538(11)
2.3538(11)
2.3268(13)
–
2.091(4)
–
–
2.004(5)
2.016(5)
91.03(3)
86.95(3)
176.36(4)
ꢀ
Pd(1) P(1)
ꢀ
Pd(2) P(2)
ꢀ
Pd(1) P(3)
ꢀ
Pd(1) N(2)
Scheme 3. Synthesis of [Pd2(m-C9H7NPPh2)3ACHTNUGRTNEUNG(m-O2CCH3)].
ꢀ
Pd(2) N(1)
ꢀ
Pd(2) N(3)
ꢀ
Pd(2) N axial
ꢀ
Pd(1) C(42)
–
–
–
–
ꢀ
Pd(2) C(72)
P(1)-Pd(1)-Pd(2)
Pd(2)-Pd(1)-N(2)
P(1)-Pd(1)-P(3)
90.14(6)
90.14(6)
–
89.93(3)
90.45(10)
176.07(4)
[a] Pd(2)=Pd(1A); P(2)=P(1A); N(2)=N(1A).
[Pd2X
phenylphosphino)methane), with anionic ligands in axial po-
sitions,[14] and the cationic [Pd (BF4)2.[15]
2A(dppm)2A(CNtBu)2]
2ACHTUNGTRENNUNG(dppm)2] (X=Cl, Br, C6Cl5, CF3CO2; dppm=bis(di-
C
E
ACHTUNGTRENNUNG
The two palladium atoms are bridged by two phosphine li-
gands in the P,N coordination mode and show an approxi-
mately square coordination with Pd–Pd interaction. Two
molecules of acetonitrile in the axial positions complete the
coordination. The steric and orbital interactions are mini-
mised by a twisting about the Pd–Pd axis. The average dihe-
dral angle (F) between the two coordination least-square
planes formed by the two metal centres (PMMN) is 37.058.
Figure 3. ORTEP view of compound 4 with ellipsoids drawn at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
ꢀ
Compounds with the [Pd
N
The bimetallic unit is bonded by three C9H7NPPh2 li-
between 33 and 50.58.[14,15] The Pd–Pd distance is
gands and one carboxylate group. The palladium atoms
have different coordination environments in a square-planar
coordination mode. The substitution of one carboxylate
2.5459(8) Š, which is smaller than the corresponding dis-
tance in [Pd2X
2ACHTUNGTRENNUNG(dppm)2] compounds (2.594–2.699 Š) and
ꢀ
may indicate that acetonitrile has a weaker trans effect.[14]
group by a C9H7NPPh2 group increases the Pd–Pd distance
The Pd–Pd distance in [Pd
2.6186(12) Š.[15]
(dppm)
E
(BF4)2 is
in 4 (2.752(4) Š vs. 2.6884(8) Š in 3). Again, there is no Pd–
Pd interaction. The Pd(2)–P(2) (P trans to O) distance of
2.2525(1) Š is smaller than the Pd(1)–P(1) (2.3619(11) Š)
and Pd(1)–P(3) (2.3435(11) Š) distances when P is trans to
P. The Pd(1)–N(2) distance with N trans to O is also smaller
than the Pd(2)–N(1) and Pd(2)–N(3) distances (N trans to
N) (see Table 1).
Compound 3 crystallises in the monoclinic space group
P21/n. Each palladium atom is coordinated by one nitrogen
atom and one phosphorus atom, each from a different
ꢀ
C9H7NPPh2 ligand, and two different carboxylate anions
complete the square-planar coordination. The Pd–Pd dis-
tance of 2.6884(8) Š indicates the absence of a Pd–Pd inter-
action.
The same behaviour was observed when the ortho-meta-
lated compounds [Pd2ACTHNUTRGENNU(G C6H4PPh2)2CAHUTNGTRNE(NUGN m-O2CCX3)2] (X=H (5);
Compound 4 was obtained when 3 was treated with the
ammonium salt of 1, which was prepared by deprotonation
at the indolyl nitrogen of 1 by adding some drops of 1m
aqueous NH3 to a solution of this phosphine in CH2Cl2
(Scheme 3). Only one carboxylate anion was substituted by
a P,N-bridging coordination ligand. A second ligand could
not be introduced, even in the presence of an excess of the
ammonium salt of 1. Compound 4 was obtained in low yield
(17%) together with an insoluble compound that was not
characterised.
X=F (6)) were reacted with the ammonium salt of 1
(Scheme 4). Again, only one C9H7NPPh2 ligand was coordi-
nated. Compounds 7 and 8 were obtained in high yields (85
ꢀ
Compound 4 was structurally characterised by X-ray dif-
fraction techniques (Figure 3). It crystallises in the mono-
clinic space group P2(1). Selected bond lengths and angles
are displayed in Table 1.
Scheme 4. Synthesis of [Pd2(m-C6H4PPh2)2(m-C9H7NPPh2)
(X=H (7); X=F (8)).
ACHTUNGTERN(NUNG m-O2CCX3)]
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b-Boration/Arylation
FULL PAPER
Table 2. Potential values of the anodic and cathodic peaks and the A/C
couples.
and 80%, respectively). Both complexes were characterised
spectroscopically and 7 was also characterised by X-ray dif-
fraction analysis (Figure 4).
Compound Anodic peak poten-
tial, A [V]
Cathodic peak poten-
tial, C [V]
A/C couple
[V]
3
4
7
8
1.042
0.838
0.637
0.714
0.882
0.759
0.547
0.585
0.962
0.798
0.592
0.650
reversible single-electron transfer. The observed electro-
chemical behaviour can be described as a one-electron
transfer process. No second A/C couple was observed at the
potential values studied.
These values were compared with those obtained for com-
pounds 5 and 6 under the same conditions. In a previous
paper, we described how A/C couple potential values de-
crease with increasing electron-donating ability of the car-
boxylate group in compounds with two carboxylate bridging
ligands.[10c] The substitution of one carboxylate anion in 5
and 6 by one P,N-bridging coordination ligand considerably
decreased the A/C couple electrode potentials in com-
pounds 7 (0.592 vs. 0.898 V in 5) and 8 (0.650 vs. 0.678 V in
6). The same behaviour was observed when we compared
the electrochemical properties of 3 and 4. Again, the com-
pound with one carboxylate group, 4, showed a lower A/C
couple electrode potential (0.798 vs. 0.962 V). By comparing
the A/C couple potential data in Table 2, we were able to
propose the following order for the electron-donating abili-
ties of the ligands in compounds 3–8: [m-C6H4PPh2]ꢀ >[m-
Figure 4. ORTEP view of compound 7 with ellipsoids drawn at the 30%
probability level. Hydrogen atoms have been omitted for clarity.
¯
Compound 7 crystallises in the triclinic space group P1.
Selected bond lengths and angles are displayed in Table 1.
In this case, the two palladium atoms are bridged by two
ortho-metalated
triphenylphosphine
ligands,
one
ꢀ
C9H7NPPh2 ligand, and one carboxylate group. The Pd(1)–
Pd(2) distance of 2.7395(5) Š is similar to that observed in
compound 4. The Pd(2)–P(2) (P trans to O) distance is
smaller than the Pd(1)–P(1) and Pd(1)–Pd(3) distances (see
Table 1).
C9H7NPPh2]ꢀ >CH3CO2ꢀ >CF3CO2 .
ꢀ
PalladiumACTHNUGRTNEUNG(III) compounds: In spite of the reversible or
Electrochemical study: Cyclic voltammetry showed that the
dinuclear palladium(II) compounds 3, 4, 7, and 8 had one
A/C couple in their initial anodic scans between 1 and 1.5 V.
Figure 5 shows the cyclic voltammogram of 4 in 0.10m
Bu4NPF6 in CH2Cl2 (for the voltammograms of 3, 7, and 8,
see Figures S1, S2, and S3 in the Supporting Information).
Table 2 displays the potential values in volts of the anodic
and cathodic peaks and the A/C couples (half of the sum of
the anodic and cathodic peaks) versus AgCl/Ag. The A/C
couple can be described in terms of a reversible or pseudo-
pseudo-reversible electrochemical behaviour observed for 3,
4, 7, and 8, the oxidation reaction with PhI·Cl2 did not stabi-
lise palladium
tained. Whereas no reaction was observed with 3 and 4,
compounds 7 and 8 gave unstable palladium(III) complexes.
ACHTUNGTREN(NUNG III) complexes and different results were ob-
AHCTUNGTRENNUNG
The reactions of 4 and 8 with PhI·Cl2 were monitored by
31P NMR spectrometry between ꢀ60 and 258C and between
ꢀ60 and 358C, respectively. No changes in the spectrum of 4
at different temperatures were observed after the addition
of PhI·Cl2, indicating that no reaction took place. The spec-
trum of 8, on the other hand, recorded at ꢀ608C immediate-
ly after the addition of PhI·Cl2, showed two singlet signals at
d=28 and ꢀ10 ppm (1:2.5 ratio). The signal at d=28 ppm
did not disappear when the temperature was increased and
was attributed to the stable tetranuclear compound [Pd-
AHCTUNGTRENNUNG
A
N
CHTUNGTRENNUNG
evolve in solution at room temperature to this stable tetra-
nuclear product.[11] The minor signal at d=ꢀ10 ppm was no
longer seen in the spectrum recorded at 08C, and most
likely corresponded to an unstable palladium
pound[10d,11] that did not contain diphenyl(3-methyl-2-indol-
yl)phosphine as a P,N-bridging coordination ligand, probably
a palladium(III) derivative of [Pd(C6H4PPh2)Cl]4.
ACHTUNGTRENN(UNG III) com-
AHCTUNGTRENNUNG
Figure 5. Cyclic voltammogram of compound 4 in CH2Cl2.
N
ACHTUNGTRENNUNG
Chem. Eur. J. 2010, 16, 6382 – 6390
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6385

E. Fernꢀndez, M. A. Úbeda et al.
Catalytic b-boration of a,b-unsaturated carbonyl com-
pounds: In the course of studying the palladium-catalysed b-
boration of a,b-unsaturated carbonyl compounds, we select-
ed a,b-unsaturated esters, ketones, aldehydes, and amides as
suitable substrates. The catalytic influence was first estab-
lished when 2.5 mol% loadings of the dinuclear palladium
complexes 3, 4, 7, and 8 were used as catalytic precursors in
the reactions of ethyl acrylate or (E)-ethyl but-2-enoate
with bis(pinacolato)diboron (B2pin2) in toluene (Scheme 5).
In all cases, the b-boration was complete within 6 h at room
temperature (Table 3, entries 1–8). The presence of a base
and MeOH appeared to be crucial for high conversions[2a]
and THF could be used as the solvent with equal efficiency.
On the basis of the results obtained with these model sub-
strates, and with the aim of exploring the scope of these Pd
catalytic systems, we performed a series of experiments with
a range of substrates under the optimised conditions.
The substrate (E)-isobutyl but-2-enoate, with a bulkier
ester moiety, was also efficiently b-borated with catalytic
system 3, but less so with 4, 7, and 8 (Table 3, entries 9–13),
even after longer reaction times. A similar trend was ob-
served when a-substituted a,b-unsaturated esters were used
in the reaction, in that while (E)-methyl 2-methylbut-2-
enoate was conveniently transformed into the b-organobo-
rated product with catalytic system 3 (Table 3, entry 14), the
analogous substrates (E)-ethyl 2-methylbut-2-enoate and
(Z)-isobutyl 2-methylbut-2-enoate were only b-borated with
low or moderate conversions, even after reaction times of 16
or 24 h (Table 3, entries 15–19). Therefore, the nature of the
ester moiety seems to play an important role in the b-bora-
tion reaction as far as the substrate is concerned, and cata-
lytic system 3 seems to be the most efficient, probably be-
cause it contains only two P,N ligands. This behaviour could
also be observed when complexes 3 and 8 were used to me-
diate the b-boration of b-substituted ethyl 3-methylbut-2-
enoate, since complex 3 favoured complete conversion
while complex 8 only transformed 62% of the substrate into
the desired product (Table 3, entries 20 and 21).
Scheme 5. Pd-mediated b-boration of a,b-unsaturated esters.
We next explored the b-boration of related a,b-unsaturat-
ed ketones, which has only been explored previously in the
literature with CuI complexes as catalytic systems.[2c,16] Cata-
lytic complexes 3, 4, 7, and 8 were found to mediate the b-
boration of methyl vinyl ketone, both in toluene and THF
(Table 4, entries 1–4). However, when (E)-4-phenylbut-3-en-
2-one was used as substrate, the conversion and selectivity
diminished significantly, depending on the catalytic system
(Table 4, entries 5–10). It was observed that b-phenyl-substi-
tuted vinyl ketones favoured the formation of a non-borylat-
ed saturated byproduct (Scheme 6).
Table 3. Catalytic b-boration of a,b-unsaturated esters with B2pin2 medi-
ated by palladium complexes.[a]
Entry
Substrate
Catalytic system
t [h]
Conv. [%][b]
99
1
3
6
2
3
4
4
7
8
6
6
6
99
99
99
5
3
6
99
6
7
8
4
7
8
6
6
6
99
99
99
9
3
6
99
Table 4. Catalytic b-boration of a,b-unsaturated ketones with B2pin2
mediated by palladium complexes.[a]
10
11
12
13
4
7
7
8
6
6
24
6
64
47
57
81
Entry
1
Substrate
Catalytic system
3
Conv. [%][b]
99
Chem. [%][c]
100
2
3
4
4
7
8
99
99
99
100
100
100
14
15
3
3
6
94
50
16
5
3
85
65
16
17
18
4
7
8
16
16
16
51
51
33
6
7
4
7
31
80
77
76
8
3
93
64
19
3
24
27
9
10
4
8
22
93
66
71
20
21
3
8
6
6
99
62
[a] Standard conditions: substrate/Pd=1:0.05; B2pin2 (1.5 equiv), Cs2CO3
(1.5 equiv), H2O (1.5 equiv), MeOH (1 equiv); solvent: toluene (2 mL);
1
[a] Standard conditions: substrate/Pd 1:0.05; B2pin2 (1.5 equiv), Cs2CO3
(1.5 equiv), H2O (1.5 equiv), MeOH (1 equiv); solvent: toluene (2 mL);
T=258C. [b] Determined by H NMR spectrometry.
T=258C; t=6 h. [b] Determined by H NMR spectrometry. [c] Chemose-
lectivity in favour of the b-borated product, determined by 1H NMR
1
spectrometry.
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Chem. Eur. J. 2010, 16, 6382 – 6390

b-Boration/Arylation
FULL PAPER
The metal-catalysed b-boration of a,b-unsaturated amides
was first performed by Oshima[19] using NiII complexes. It
was revealed that amides reacted with B2pin2 much more
rapidly than the corresponding esters. Similarly, Molander
et al.[16] reported the preparation of trifluoroboratohomo-
AHCTUNGTREGeNNUN nolates from tertiary a,b-unsaturated amides by employing
CuI salts and KHF2. The asymmetric version was conducted
by Yun et al.[20] using CuI catalytic systems modified with
chiral bidentate ligands. In this context, this study has shown
for the first time that palladium complexes can efficiently
perform conjugate boration on a,b-unsaturated amides. As
can be seen in Scheme 8, the tertiary amide dimethyl acryl-
amide was quantitatively converted into the corresponding
b-borated product within a reasonable reaction time (6 h),
in both toluene and THF.
Scheme 6. Pd-mediated b-boration of a,b-unsaturated ketones.
Metal-catalysed b-boration of the most challenging a,b-
unsaturated aldehydes has hitherto only been reported in
two cases using Rh[17] and Pt[18] catalysts and by our group
using Cu complexes.[2d,e] Its difficulty stems from the fact
that there tends to be competing 1,2-diboron addition
(Scheme 7). Considering the benefits of palladium-mediated
Scheme 8. Pd-mediated b-boration of a,b-unsaturated amides.
Scheme 7. Pd-mediated b-boration of a,b-unsaturated aldehydes.
B-addition reactions,[4] we decided to examine the use of 3,
4, 7, and 8 as catalysts for the b-boration of acrolein as a
model substrate. As can be seen in Table 5, the transforma-
tion of the substrate into the desired organoborated product
was, depending on the catalytic system, achieved with mod-
erate to high levels of conversion (entries 1–3). Complex 3
was seen to be similarly effective in catalysing the b-bora-
tion of crotonaldehyde (Table 5, entries 4 and 5). However,
the b-boration of cinnamaldehyde was less chemoselective
when MeOH and H2O were added (Table 5, entries 6 and
7).
Catalytic Suzuki reaction: Finally, we checked whether pal-
ladium-based complexes could be used to catalyse single-pot
diboration/Suzuki–Miyaura cross-coupling when only
2.5 mol% of a given palladium dinuclear complex was pres-
ent throughout the tandem reaction (Scheme 9). We were
very pleased to observe that complex 7 catalysed both the
b-boration of ethyl acrylate or methyl vinyl ketone and the
subsequent cross-coupling with a range of aryl bromides, al-
though conversions were only moderate after 24 h of reac-
tion (Table 6, entries 1–5). However, the b-boration of di-
methyl acrylamide with B2pin2 was efficiently completed
after the addition of 3-bromoanisole with two equivalents of
Cs2CO3 and H2O. The b-arylation proceeded to completion
(Table 6, entry 6). THF was the solvent of choice for the
two consecutive reactions, because the use of toluene re-
duced the efficiency of the cross-coupling transformation.
Table 5. Catalytic b-boration of a,b-unsaturated aldehydes with B2pin2
mediated by palladium complexes.[a]
Entry
Subst.
Cat. system
Additives
Conv. [%][b] Sel. [%][c]
1
3
MeOH/H2O
94
98
2
3
4
8
MeOH/H2O
MeOH/H2O
82
97
74
87
4
5
6
7
3
3
3
3
MeOH/H2O
97
96
75
51
83
92
–
MeOH/H2O
–
23
100
[a] Standard conditions: substrate/Pd=1:0.05; B2pin2 (1.5 equiv), Cs2CO3
(1.5 equiv), H2O (1.5 equiv), MeOH (1 equiv); solvent: toluene (2 mL);
T=258C; t=6 h. [b] Determined by 1H NMR spectrometry. [c] Selectivi-
1
ty in favour of the b-borated product, determined by H NMR spectrom-
Scheme 9. Pd-mediated tandem single-pot diboration/Suzuki–Miyaura
etry.
cross-coupling. a) b-boration, b) arylation.
Chem. Eur. J. 2010, 16, 6382 – 6390
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6387

E. Fernꢀndez, M. A. Úbeda et al.
Table 6. Catalytic tandem sequence of b-boration/arylation of a,b-unsa-
turated carbonyl compounds mediated by palladium complex 7.[a]
mediating the tandem diboration–arylation reactions of al-
kenes by using a single catalyst. These examples show for
the first time the multifaceted properties of a palladium
complex in participating in different catalytic cycles through
organoborane intermediates with equal efficacy.
Entry
Subst.
ArX
Prod.
Conv. [%][b]
1
31
Conclusion
2
3
28
14
Stable dinuclear complexes with P,N-bridging coordination
have been synthesised in high yield. They showed high activ-
ity and selectivity in the catalytic b-boration of a,b-unsatu-
rated esters, ketones, aldehydes, and amides. More remarka-
bly, an “in situ” catalytic tandem reaction has been de-
4
5
55
46
ꢀ
signed, in which the Cb B bond is transformed into a target-
ꢀ
ed Cb Ar bond. Advantageously, the same catalyst pro-
motes both steps, with moderate to high conversion of the
substrate. In spite of the reversible or pseudo-reversible
electrochemical behaviour observed for all of the com-
pounds, no stabilised palladium
obtained.
ACHTUNGERTN(NUNG III) complexes have been
6
99 (89[c]
)
[a] Standard conditions for b-boration: substrate/Pd=1:0.05; B2pin2
(1.5 equiv), Cs2CO3 (1.5 equiv), H2O (1.5 equiv), MeOH (1 equiv); sol-
vent: THF (2 mL); T=258C; t=6 h. Standard conditions for cross-cou-
pling: ArX (2 equiv) and Cs2CO3 (3 equiv), reflux for 24 h. [b] Deter-
Experimental Section
1
mined by H NMR spectrometry. [c] Isolated yield.
General: Commercially available [Pd
Pressure Chemical. All solvents were of analytical grade. C9H8NPPh2
(1),[12] PhI·Cl2,[21] and [Pd (m-O2CCX3)]2 (X=H (5); F (6))[10a–c]
(C6H4PPh2)
ACHTNUGTRNEN(NUG O2CCH3)2] was purchased from
A
ACHTUNGTRENNUNG
The amide homoenolate cross-coupling reaction has only
been reported by Molander et al.,[16] and their yields were
moderate even when the potassium trifluoroboratohomo-
were synthesised according to the methods described in the literature.
Column chromatography was performed on silica gel (35–70 mesh). Sol-
vent mixtures are volume/volume mixtures, unless otherwise specified.
All reactions were carried out in oven-dried glassware under argon at-
mosphere using Schlenk techniques, although the isolated solids are air-
stable. 1H and 13C{1H} NMR (using the residual proton signal of CDCl3
as reference) and 19F{1H} NMR and 31P{1H} NMR (with standard referen-
ces) spectra were recorded on a Bruker Avance 400 MHz spectrometer
from samples in CDCl3 solutions at 258C, unless otherwise specified.
Chemical shifts are reported in ppm. Coupling constants (J) are given in
hertz (Hz). Elemental analyses were provided by the Centro de Micro-
analisis Elemental, Universidad Complutense de Madrid.
ACHTUNGTRENNUNGenolate analogue was used. While they required two differ-
ent catalytic systems (CuI/DPEPhos/NaOtBu and PdII/
RuPhos/K2CO3; DPEPhos=bis(2-diphenylphosphinophen-
yl) ether, RuPhos=(3-diethoxyphosphinothioylsulfanyl-1,4-
dioxan-2-yl)sulfanyldiethoxysulfanylidenephosphorane) to
perform the three steps (Scheme 10), we only needed the di-
nuclear palladium complex as a single catalytic system in a
one-pot protocol. Similar behaviour has been found for re-
Synthesis of [Pd(m-C9H7NPPh2)ACHTNUTRGENNUG(NCCH3)]2 (2): [PdACHTUNGTREN(NUNG O2CCH3)2] (100 mg,
6+
4+
0.446 mmol) was first suspended in acetonitrile (6 mL). The suspension
was degassed (two freeze–pump–thaw cycles), C9H8NPPh2 (140 mg,
0.444 mmol) was added in a flow of
lated Pd2 and Pd2 complexes as synthetic precursors for
argon, and the mixture was degassed
again. Upon reaching room tempera-
ture, the reaction mixture darkened
and an orange precipitate formed
within minutes. The mixture was then
stirred overnight in the absence of
light. Thereafter, the precipitate was
collected by filtration, washed with
acetonitrile (2”3 mL), and vacuum
dried. The crude complex was extract-
ed with
a CH2Cl2/CH3CN mixture
(5:1). The dark-red solution was twice
passed through a column filled with
cotton wool (1.5”10 cm). The result-
ing orange solution was layered with
CH3CN and set aside for evaporation
of the volatiles at room temperature in
the absence of light. Bright orange-red
crystals were obtained, which were
Scheme 10.
6388
www.chemeurj.org
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 6382 – 6390

b-Boration/Arylation
FULL PAPER
washed with acetonitrile and vacuum-dried (64 mg, 31%). Crystals suita-
ble for single-crystal X-ray diffraction analysis were obtained by slow
evaporation of the solvents from a solution of 2 in CH2Cl2/CH3CN at
room temperature. 1H NMR (CD2Cl2 + two drops of [D3]acetonitrile):
d=1.76 (s, 6H; CH3), 1.96 (s, unspecified amount, acetonitrile), 6.81 (t,
1J=7.8 Hz, 2H), 6.91 (t, 1J=8.0 Hz, 2H), 7.28 (m, 8H), 7.42 ppm (m,
16H); 31P{1H} (CD2Cl2 + two drops of [D3]acetonitrile): d=ꢀ2.5 ppm
(s); elemental analysis calcd (%) for C46H40N4P2Pd2: C 59.82, H 4.37, N
6.07; found: C 59.37, H 4.38, N 6.02.
(Carom), 182.0 ppm (d, J=3 Hz); 31P{1H} NMR: d=ꢀ0.9 (d, J=11 Hz),
1.3 ppm (t, J=11 Hz); elemental analysis calcd (%) for C65H54N3O2P3Pd2:
C 64.26, H 4.45, N 3.46; found: C 64.72, H 4.75, N 3.33.
X-ray
crystal
structure
data
for
compound
4:
C65H54Cl4N3O2P3Pd2·2CH2Cl2, monoclinic, space group P2(1), a=
15.1620(3), b=11.4900(2), c=17.4600(3) Š, b=92.5110(9)8, V=
3038.81(10) Š3, Z=2, crystal dimensions: 0.25”0.23”0.20 mm; MoKa ra-
diation, 273(2) K; 13059 reflections, 13059 independent; m=0.895 mmꢀ1
;
refinement (on F2) with SHELXTL (version 6.1), 730 parameters, 1 re-
X-ray crystal structure data for compound 2: C46H40N4P2Pd2·3H2O,
straint, R1 =0.0402 (I>2s) and wR2 (all data)=0.1166, GOF=1.128,
ꢀ3
monoACHTUNGTRENNUNGclinic, space group P2/c, a=13.8460(4), b=8.8460(3), c=
max/min residual electron density: 0.691/ꢀ1.172 eŠ
.
18.8590(6) Š, b=91.352(2)8, V=2309.24(13) Š3, Z=2, crystal dimen-
sions: 0.24”0.22”0.20 mm; MoKa radiation, 273(2) K; 8754 reflections,
5022 independent; m=0.889 mmꢀ1; refinement (on F2) with SHELXTL
(version 6.1), 259 parameters, 0 restraints, R1 =0.0659 (I>2s) and wR2
CCDC 771072 (4) contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
(all data)=0.2112, GOF=1.065, max/min residual electron density:
Synthesis of [Pd2(m-C6H4PPh2)2(m-C9H7NPPh2)
ACHTUNGTRENUN(NG m-O2CCX3)] (X=H (7);
ꢀ3
1.291/ꢀ1.386 eŠ
.
X=F (8)): [Pd2A(C6H4PPh2)2A(m-O2CCX3)2] (X=H (5); X=F (6))
C
CHTUNGTRENNUNG
CCDC 771070 (2) contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
(0.117 mmol) was dissolved in CH2Cl2 (15 mL) and a stoichiometric
amount of C9H8NPPh2 (40 mg, 0.117 mmol) in CH2Cl2 (3 mL) containing
two drops of 20% aqueous NH3 was added. The yellow reaction mixture
was stirred for 2 h, dried with Na2SO4, and filtered through siliceous
earth. Complexes 7 and 8 were obtained as yellow crystalline solids (7:
85%, 8: 80%). Crystals suitable for single-crystal X-ray diffraction analy-
sis were obtained by slow diffusion of hexane into a solution of 7 in
CH2Cl2 at ꢀ208C.
Synthesis of [Pd(m-C9H7NPPh2)ACHTUNTRGNEN(GU m-O2CCH3)]2 (3): [PdCAHTUNGTREN(NNGU O2CCH3)2]
(80 mg, 0.357 mmol) was suspended in toluene (10 mL), the suspension
was degassed (three freeze–pump–thaw cycles), and then C9H8NPPh2
(112 mg, 0.356 mmol) was added in a flow of argon. The reaction mixture
darkened immediately and the deep-red solution obtained was stirred for
10 h. The solvent was then removed under vacuum and the crude product
was extracted with diethyl ether (4”5 mL). The solvent was evaporated
from the combined extracts, and the brownish-red solid was briefly
washed with hexanes (2”3 mL) and recrystallised from a hexane/diethyl
ether mixture (145 mg, 84%). Crystals suitable for single-crystal X-ray
diffraction analysis were obtained by slow evaporation of the solvent
from a solution of 3 in hexane at room temperature. 1H NMR: d=1.08
(s, 6H; bridging acetate), 1.65 (s, 6H; methyl), 6.53 (brs, 4H), 6.65 (brs,
4H), 6.75 (m, 4H), 7.03 (t, J=7.2 Hz, 2H), 7.35 (dd, J=6.8 Hz, J=
4.2 Hz, 2H), 7.45 (m, 2H), 7.50 (m, 6H), 7.72 ppm (m, 4H); 13C{1H}
NMR: d=11.4 (s), 22.7 (s), 115.9 (s), 117.3 (s), 118.6 (s), 122.3 (s), 123.9,
124.7, 126.6, 127.2, 127.9, 128.4, 129.9, 130.7, 131.1, 131.5, 134.1, 145.3,
183.0 ppm; 31P{1H} NMR (161.9 MHz, CDCl3, 298 K): d=4.1 ppm (s); el-
emental analysis calcd (%) for C46H40N2O4P2Pd2: C 57.57, H 4.20, N 2.92;
found: C 57.42, H 4.30, N 2.94.
Compound 7: 1H NMR: d=0.75 (s, 3H), 1.54 (s, 3H), 6.53 (m, 2H),
6.61–6.75 (m, 6H), 6.80–7.00 (m, 8H), 7.05–7.15 (m, 6H), 7.18–7.22 (m,
4H), 7.30–7.38 (m, 6H), 7.40–7.50 (m, 10H), 8.45 ppm (d, J=8.2 Hz,
2H); 13C{1H} NMR: d=12.0 (s), 12.0 (s), 24.2 (s), 115–146 (Carom), 163.4
(s), 168 (s), 180 ppm (s); 31P{1H} NMR: d=2.6 (dd, J=365 Hz, J=
22 Hz), 13.8 (dd, J=365 Hz, J=28 Hz), 18.3 ppm (dd, J=28 Hz, J=
22 Hz); elemental analysis calcd (%) for C62H51N2O2P3Pd2: C 64.10, H
4.39, N 2.41; found: C 63.41, H 4.73, N 3.15.
X-ray crystal structure data for compound 7: Crystals suitable for single-
crystal X-ray diffraction analysis were obtained by slow diffusion of
hexane
C59H47Cl3NO2P3Pd2·(0.5C6H14, CHCl3), triclinic, space group P-1, a=
b=
into
a
solution
of
7
in
CH2Cl2
at
ꢀ208C.
12.9230(3),
b=14.2270(3),
c=18.3890(3) Š,
a=94.53708,
94.6850(13)8, g=116.14418, V=2999.74 Š3, Z=2, crystal dimensions:
0.26”0.25”0.20 mm; MoKa radiation, 273(2) K; 10153 reflections, 10153
independent; m=0.855 mmꢀ1; refinement (on F2) with SHELXTL (ver-
sion 6.1), 660 parameters, 0 restraints, R1 =0.0569 (I>2s) and wR2 (all
X-ray crystal structure data for compound 3: C46H40N2O4P2Pd2·C4H10O,
monoclinic, space group P21/n, a=11.5900(2), b=20.3330(4), c=
20.5630(5) Š, b=92.7330(7)8, V=92.7330 Š3, Z=4, crystal dimensions:
0.27”0.22”0.19 mm; MoKa radiation, 273(2) K; 8248 reflections, 8248 in-
dependent; m=0.855 mmꢀ1; refinement (on F2) with SHELXTL (ver-
sion 6.1), 555 parameters, 0 restraints, R1 =0.0750 (I>2s) and wR2 (all
data)=0.1900, GOF=1.137, max/min residual electron density: 1.010/
ꢀ3
ꢀ1.851 eŠ
.
CCDC 771073 (7) contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
data)=0.2141, GOF=1.098, max/min residual electron density: 1.478/
ꢀ3
ꢀ1.485 eŠ
.
Compound 8: 1H NMR: d=1.78 (s, 3H), 6.45 (m, 2H), 6.66 (m, 4H),
6.92 (m, 2H), 7.06 (m, 4H), 7.16 (m, 4H), 7.2 (m, 8H), 7.50 (m, 8H),
7.59 (m, 4H), 7.66 (m, 4H), 7.73 ppm (m, 2H); 13C{1H} NMR: d=12.0
(s), 12.0 (s), 24.2 (s), 115–146 (Carom), 163.4 (s), 168 (s), 180 ppm (s);
31P{1H} NMR: d=1.5 (dd, J=360 Hz, J=22 Hz), 11.4 (dd, J=360 Hz, J=
32 Hz), 19.5 ppm (dd, J=32 Hz, J=22 Hz); 19F{1H} NMR: d=ꢀ77.6 ppm
(s); elemental analysis calcd (%) for C62H48N2F3O2P3Pd2: C 61.25, H 3.95,
N 2.30; found: C 60.83, H 4.05, N 2.90.
CCDC 771071 (3) contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Synthesis of [Pd2(m-C9H7NPPh2)3ACHTNUTRGENNUG(m-O2CCH3)] (4): [Pd(m-C9H7NPPh2)ACHUTGNTREN(NUGN m-
O2CCH3)]2 (3) (50 mg, 0.052 mmol) was dissolved in CH2Cl2 (15 mL)
under an argon atmosphere and then a solution of C9H8NPPh2 (20 mg,
0.063 mmol) in CH2Cl2 (8 mL) containing two drops of 20% aqueous
NH3 was added. The reaction mixture was stirred overnight and then
dried with Na2SO4. The solvent was removed under vacuum. The residual
oil was dissolved in CH2Cl2/hexane (1:1; 5 mL) and chromatographed on
a column of silica (2”30 cm). Elution with CH2Cl2/hexane (1:1) led to
the separation of a red band, from which a red solid was crystallised
(11 mg, yield 17%). Crystals suitable for single-crystal X-ray diffraction
analysis were obtained by slow diffusion of hexane into a solution of 4 in
CH2Cl2 at room temperature. 1H NMR: d=0.63 (s, 3H), 1.40 (s, 3H),
1.56 (s, 6H), 6.56 (m, 5H), 6.64–6.74 (m, 16H), 6.87–6.92 (m, 5H), 6.99
(t, J=7 Hz, 2H), 7.15–7.19 (m, 4H), 7.55–7.33 (m, 6H), 8.44 ppm (d, J=
8 Hz, 2H); 13C{1H} NMR: d=11.4 (s), 12.0 (s), 23.2 (d, J=4 Hz), 115–146
Electrochemical measurements: Cyclic voltammetry was carried out in a
0.1m solution of Bu4NPF6 in CH2Cl2 at 258C, using a three-electrode con-
figuration (platinum disk as working electrode, platinum wire as counter
electrode, and an aqueous AgCl (3m KCl) Ag electrode separated from
the bulk solution by a salt bridge containing the solvent and supporting
electrolyte as reference electrode) on a 273A PAR potentiostat. The fer-
rocene/ferrocenium (Fc/Fc+) couple was used as an internal reference.
Typical catalytic b-boration of a,b-unsaturated compounds: The respec-
tive palladium complex (3, 4, 7, or 8) (0.003 mmol) was suspended in tol-
uene or THF (2 mL) under argon in a Schlenk flask. Bis(pinacolato)di-
boron (47.75 mg, 0.18 mmol) was added, the suspension was stirred for
Chem. Eur. J. 2010, 16, 6382 – 6390
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6389

E. Fernꢀndez, M. A. Úbeda et al.
10 min, and then Cs2CO3 (61 mg, 0.18 mmol) was added. A solution of
a,b-unsaturated ester, ketone, aldehyde, or amide (0.125 mmol) in tolu-
ene or THF (2 mL) was then added. Finally, MeOH (1.57 mmol) and
water (0.18 mmol) were added and the mixture was stirred at room tem-
[3] a) T. B. Marder, J. Organomet. Chem. 2008, 34, 46; b) L. Dang, Z.
Lin, T. B. Marder, Organometallics 2008, 27, 4443; c) V. Lillo, A.
Bonet, E. Fernꢀndez, Dalton Trans. 2009, 2899.
[4] V. Lillo, E. Mas-Marzꢀ, A. M. Segarra, J. J. Carbó, C. Bo, E. Fernꢀn-
dez, Chem. Commun. 2007, 338.
1
perature for 6 h. The products obtained were analysed by H NMR spec-
troscopy to determine their identity and the degree of conversion.
[5] a) Q. Cui, D. G. Musaev, K. Morokuma, Organometallics 1998, 17,
742; b) S. Sakaki, T. Kikuno, Inorg. Chem. 1997, 36, 226.
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Chem. 2009, 7, 4674.
[7] a) T. Ishiyama, N. Matsuda, M. Murata, N. Osawa, N. Miyaura, A.
Suzuki, Organometallics 1996, 15, 713; b) T. Ishiyama, M. Yamamo-
to, N. Miyaura, Chem. Lett. 1996, 1117; c) S. D. Brown, R. W. Arm-
strong, J. Am. Chem. Soc. 1996, 118, 6331.
[8] a) J. Marco-Martꢁnez, V. López-Carrillo, E. BuÇuel, R. Simancas,
D. J. Cꢀrdenas, J. Am. Chem. Soc. 2007, 129, 1874; b) J. Marco-Mar-
tꢁnez, E. BuÇuel, R. MuÇoz-Rodrꢁguez, D. J. Cꢀrdenas, Org. Lett.
2008, 10, 3619.
[9] a) S. P. Miller, J. B. Morgan, F. J. Nepveux, J. P. Morken, Org. Lett.
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Miyaura, A. Suzuki, Organometallics 1996, 15, 713; c) T. Ishiyama,
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Typical catalytic diboration, subsequent Suzuki reaction, and oxidation:
Bis(pinacolato)diboron (47.75 mg, 0.18 mmol) was added to a solution of
the palladium dimer (2.5 mol%, 0.003 mmol Pd) and Cs2CO3 (61 mg,
0.18 mmol, 1.5 equiv) in THF (2 mL) under argon. The solution was
stirred for 5 min, and then the a,b-unsaturated carbonyl substrate
(0.12 mmol) was added followed by MeOH (63 mL, 1.57 mmol) and water
(5 mL, 0.18 mmol), and stirring was continued for 6 h at room tempera-
ture. After heating to reflux, Cs2CO3 (122.18 mg, 0.37 mmol), the corre-
sponding halide (0.25 mmol), and water (degassed, 0.2 mL, 10% of the
solvent) were added and the reaction mixture was stirred for 24 h. After
cooling, the reaction mixture was extracted with ethyl acetate (3”20 mL)
and the combined organic phases were washed with brine (20 mL), dried
over magnesium sulfate, and dried in vacuo. The products obtained were
analysed by 1H NMR spectroscopy to determine their identity and the
degree of conversion.
3-Methoxyphenylpropanoic acid dimethyl amide: Purification by column
chromatography on silica eluting with petroleum ether/dichloromethane
(3:1) ! petroleum ether/ethyl acetate (1:1). 1H NMR: d=2.66 (t, 2H,
J=7.2 Hz; Ar-CH2-CH2-), 2.91 (m, 8H), 3.73 (s, 3H; OCH3), 6.80–6.70
(m, 2H), 7.20 (t, 1H, J=7.6 Hz), 7.25 ppm (s, 1H); 13C{1H} NMR: d=29
(CH2-CH2-N
ACHTUNGTRENNUNG(CH3)2), 35 (-NAHCTNUREGTN(GNNU CH3)2), 37 (-OCH3), 55 (CH2-CH2-NCATHNUGTREN(NGUN CH3)2),
111 (Carom), 114 (Carom), 120 (Carom), 129 (Carom), 143 (Carom), 159 (Carom
OMe), 172 ppm (CO); GC-MS: m/z: 177, 133, 120, 105, 91, 72, 58, 45.
–
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Acknowledgements
The authors are grateful for financial support from the MEC of Spain
(CTQ2007-60442/BQU, CTQ2008-06466) and Consolider Ingenio 2010
(CSD2006-0003). A.B. thanks the Generalitat de Catalunya for an FI
grant.
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Received: November 11, 2009
Revised: February 11, 2010
Published online: April 15, 2010
6390
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