Phase-transfer Tsuji—Trost allylation of CH-acids with the assistance of palladium complexes with bidentate PIII—N—PIII ligands

Article abstract of DOI:10.1007/s11172-017-1788-6

The Tsuji—Trost allylation of CH acids, in particular, those of the YCH₂CO₂Et type (Y = CO₂Et, C(O)Me, CN), with allylic acetates in the K₂CO₃—DMF system in the presence of palladium catalysts with ligands RN(PPh₂)₂ (R = Ph, Prⁱ, c-C₆H₁₁) is accomplished.

Full text of DOI:10.1007/s11172-017-1788-6

Russian Chemical Bulletin, International Edition, Vol. 66, No. 4, pp. 661—665, April, 2017
661
Phaseꢀtransfer Tsuji—Trost allylation of CHꢀacids with the assistance of
palladium complexes with bidentate PIII—N—PIII ligands
A. A. Vasil´ev,a, I. M. Aladzheva,b and O. V. Bykhovskayab
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: vasiliev@ioc.ac.ru
bA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6471. Eꢀmail: shipov@ineos.ac.ru
The Tsuji—Trost allylation of CH acids, in particular, those of the YCH2CO2Et type
(Y = CO2Et, C(O)Me, CN), with allylic acetates in the K2CO3—DMF system in the presence
of palladium catalysts with ligands RN(PPh2)2 (R = Ph, Pri, cꢀC6H11) is accomplished.
Key words: allylation, CH acids, palladium complexes, crossꢀcoupling, bis(diphenylꢀ
phosphino)amines, ligands, phase transfer, Tsuji—Trost reaction.
The Tsuji—Trost reaction (palladiumꢀcatalyzed crossꢀ
coupling of nucleophiles with allylic carboxylates) is
a convenient method to prepare functionalized unsaturated
compounds.1 Previously, we have studied2 this process
under phaseꢀtransfer conditions allowing deprotonation
of CH acids with nonꢀflammable, nonꢀhazardous, and
inexpensive alkali carbonates and phosphates instead of
traditional reagents such as sodium hydride or N,Oꢀbisꢀ
(trimethylsilyl)acetamide. In view of significance of this
name reaction, the search for new means to carry it out, in
particular, testing new ligands is topical.
Recently, we have reported3 on the Suzuki reaction
catalyzed by palladium complexes based on the bidentate
PIII—N—PIII ligands of bis(diphenylphosphino)amine
1a—c series, namely, complexes 2a—c. Complexes 2a—c
revealed moderate activity in crossꢀcoupling of model broꢀ
moarenes with phenylboronic acid. It is of note that
complexes with ligands of N—PIII type were previously
employed for catalysis of some processes, in particular,
asymmetric Tsuji—Trost reaction.4
Results and Discussion
The search for conditions to accomplish the Tsuji—
Trost process catalyzed by the bis(diphenylphosphino)ꢀ
amine ligandꢀbased complexes was performed on the model
reaction between allyl acetate (3) and diethyl malonate
(4a) (Scheme 1, Table 1). The catalysts were generated
in situ by mixing ligands 1a—c with Pd2dba3 (dba is dibenzꢀ
ylideneacetone), while in some cases the preꢀprepared
complexes 2a—c were used. Potassium carbonate was apꢀ
plied as the deprotonating agent, the reaction was carried
out in DMF at ambient temperature according to the proꢀ
cedure described by us previously.2a,b
Scheme 1
Y = CO2Et (a), C(O)Me (b), C≡N (c)
R = Ph (a), Pri (b), cꢀC6H11 (c)
Reagents and conditions: i. 2—4 mol.% [Pd], K2CO3, DMF,
20 °C, 18 h.
Herein, we have studied coupling between some model
CH acids and allylic acetates catalyzed by palladium comꢀ
plexes based on PIII—N—PIII ligands 1a—c.
The coꢀdissolution of ligands 1 and palladium source
(Pd2dba3) in a ratio corresponding to Pd : P = 1 : 4 in
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 0661—0665, April, 2017.
1066ꢀ5285/17/6604ꢀ0661 © 2017 Springer Science+Business Media, Inc.

662
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Vasil´ev et al.
Table 1. Coupling of CH acids 4a—c with allyl acetate 3. Dependence of the reaction mixture composiꢀ
tion on nature and amount of the catalysta
Entry
CH acid
Catalyst
Amount of
[Pd] (mol.%)b
Reaction mixture compositionc
(%)
4
5
6
1
2
3
4
5
6
7
8
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4b
4c
Pd2dba3+1a
Pd2dba3+1a
2
4
2
4
2
4
2
4
2
4
2
4
2
2
4
4
190
115
100
172
187
—
114
—
115
—
115
—
—
—
—
10
73
—
28
13
—
79
64
80
—
75
63
12
—
15
—
—
112
—
—
—
100
117
136
115
100
110
137
198
100
195
100
2a
2a
Pd2dba3+1b
Pd2dba3+1b
2b
2b
9
Pd2dba3+1c
Pd2dba3+1c
2c
10
11
12
13
14
15
16
2c
d
Pd2dba3+PPh3
Pd2dba3+dppm
Pd2dba3+1c
Pd2dba3+1c
—
a Reagents and conditions: K2CO3. DMF, 20 °C, 18 h. If not stated otherwise, 4 mol of RN(PPh)2
(based on Pd2dba3) were used. b Based on 4. c GC analysis data. d In the presence of 8 mmol PPh3 based
on Pd2dba3.
DMF or CH2Cl2 is accompanied by disappearance of dark
brown color of Pd2dba3 and the appearance of yellow colꢀ
or evidencing the in situ formation of Pd0 complex with
ligands 1. On the example of ligand 1b (whose phosphorus
atom in 31P NMR spectrum resonated at δ 48.2), we have
revealed that addition of calculated amount of Pd2dba3
shifts a new resonance upfield to δ 19.0. It is of note that
palladium(II) complex 2b with the same ligand manifested
phosphorus chemical shift at δP 28.3.3
the greatest size and highest +Iꢀeffect. Naturally, in the
case of ligand 1a with phenyl group the yields of products
were noticeably lower.
The similar phenomenon was observed upon the catalꢀ
ysis with complexes 2a—c having palladium atom in oxiꢀ
dation state 2+ (see Table 1, entries 3, 7, and 11). The
product yields in these cases were generally lower than
those for systems RN(PPh2)2—Pd2dba3. Obviously, poorly
soluble in DMF complexes 2 should serve as preꢀcataꢀ
lysts. To generate a soluble active species LnPd0 from them,
a certain time of contact of the reaction mixture comꢀ
ponents with partially dissolved and partially dispersed
compound 2 may have been required. Application of
equimolar amounts of ligands 1 and complexes 2 to proꢀ
vide Pd : P ratio of 1 : 4 did not result in improvement of
the yields of compounds 5 and 6.
Raising the catalyst amount from 2 to 4 mol.% [Pd]
allowed us to notably improve the conversion of malonate
4a (see Table 1, entries 2, 4, 6, 8, 10, and 12). Note that
with the use of systems Pd2dba3—1b,c exhaustive allylaꢀ
tion occurred with diallylmalonate 6a being the sole prodꢀ
uct (entries 6 and 10). In this way, diallyl derivatives 6b,c
were obtained in high yields from ethyl acetoacetate 4b
and cyanoacetate 4c (entries 15 and 16).
In view of our previous results,2 we applied amounts of
palladium source and ligand 1 providing an ultimate ratio
Pd : P = 1 : 4, i.e., we used 4 moles of RN(PPh2)2.
per 1 mole of Pd2dba3. At the same time, the Pd : P ratio
in the complexes 2a—c is equal to 1 : 2. In fact, employꢀ
ment of the catalysts based on ligands 1a,b in amount
2 mol.% relative to diethyl malonate (4a) (see Table 1,
entries 1 and 5) gives only monoallyl derivative 5a in low
yield. In the case of ligand 1c, yield of product 5a reaches
to 80% and some amount of diallyl compound 6a is also
formed (entry 9). For a comparison, in the case of comꢀ
mon triphenylphosphine (entry 13) and bis(diphenylꢀ
phosphino)methane CH2(PPh2)2 (dppm, entry 14) strucꢀ
turally related to ligands 1a—c, diallylmalonate 6a is
formed in the yields of 98—100%. Apparently, the negaꢀ
tive inductive effect of the amine nitrogen in ligands 1a—c
decreases the electron density at the adjacent phosphorus
atoms thus causing a decrease in the activity of the correꢀ
sponding catalysts. Among the ligands herein studied, the
most efficient was 1c with cyclohexyl substituent having
On using the system Pd2dba3—1c (4 mol.% [Pd]), couꢀ
pling of diethyl malonate (4a) with excess secꢀbutenyl
acetate (7) was carried out (Scheme 2) to give quantitaꢀ
tively only monosubstitution products 8a,b (~1 : 1). It is
of note that previously2a application of active diamidoꢀ

Allylation with P—N—P ligands
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 4, April, 2017
663
phosphite ligands onto these reactants caused easy formaꢀ
tion of the disubstitution products.
mers; while the "linear" isomer 11b was the 9 : 91 Z,Eꢀ
mixture. It is of note that the 11a,b mixture was earlier7
obtained in the reaction of substrate 9 with crotylstanꢀ
nane; however, these products were not characterized
therein. In this regard, we prepared herein the "linear"
isomer 11b by parallel alkylation of CH acid 9 with crotyl
bromide (see Scheme 3).
Scheme 2
Finally, the reaction of slight excess diethyl malonate
(4a) with 1,3ꢀdiphenylallyl acetate (12) afforded the
known8 diethyl [(2E)ꢀ1,3ꢀdiphenylpropꢀ2ꢀenꢀ1ꢀyl]malonꢀ
ate (13) (Scheme 4). The yield of compound 13 was 80%
on using Pd2dba3—1c system and 27% for the complex 2c
(4 mol.% [Pd] in both cases). This result confirms higher
efficiency of systems ligand 1—palladium source comꢀ
pared with complexes 2.
To sum up, palladium complexes with PIII—N—PIII
ligands of bis(diphenylphosphino)amineꢀtype were found
to be suitable to promote the Tsuji—Trost coupling of CH
acids with allylic acetates. Their activity, however, turned
to be somewhat lower than that of conventionally used
phosphines. The obtained results can be of interest for
fundamental knowledge of mechanistic insight of metalꢀ
catalyzed crossꢀcoupling reactions.
Reagents and conditions: Pd2dba3 (2 mol.%), cꢀC6H11N(PPh2)2
(1c) (8 mol.%), K2CO3, DMF, 20 °C, 18 h.
Coupling of rather CH acidic ethyl 2ꢀcyanoꢀ2ꢀphenylꢀ
acetate (9) (pKa ~ 7.5)5 with allyl acetate (3) afforded the
known6 ethyl 2ꢀcyanoꢀ2ꢀphenylpentꢀ4ꢀenoate (10)
(Scheme 3). Interestingly, the quantitative yield of this
product was achieved on using 4 mol.% [Pd] of both cataꢀ
lytic system Pd2dba3—1c and complex 2c. Coupling of
substrate 9 with secꢀbutenyl acetate 7 (Pd2dba3—1c sysꢀ
tem) brought about the mixture of regioisomers 11a,b
(52 : 48, 100% GC yield, 84% of isolated material), which
we failed to resolve (see Scheme 3). The "branched" regioꢀ
isomer 11a, in turn, was the 54 : 46 mixture of diastereoꢀ
Experimental
1
H and 13C NMR spectra were recorded on a Bruker AMꢀ300
instrument in CDCl3 at working frequencies of 300.13 and
75.47 MHz, respectively. The chemical shifts are referred to the
residual proton signal (1H) or deuterated solvent signal (13C).
Scheme 3
Reagents and conditions: i. Pd2dba3 (2 mol.%), cꢀC6H11N(PPh2)2 (1c) (8 mol.%), K2CO3, DMF, 20 °C, 18 h;
ii. [cꢀC6H11N(PPh2)2]PdCl2 (2c) (4 mol.%), K2CO3, DMF, 20 °C, 18 h; iii. K2CO3, acetone, 20 °C.
Scheme 4
Reagents and conditions: 4a (1.2 eqviv.), K2CO3, DMF, 20 °C, 18 h and Pd2dba3 (2 mol.%), cꢀC6H11N(PPh2)2 (1c) (8 mol.%) or
[cꢀC6H11N(PPh2)2]PdCl2 (2c) (4 mol.%).

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Russ. Chem. Bull., Int. Ed., Vol. 66, No. 4, April, 2017
Vasil´ev et al.
Electron impact (EI, 70 eV) mass spectra were measured on
Agilent 5977A quadrupole instrument with sample injection via
Agilent 7890 gas chromatograph.9 External calibration was perꢀ
formed with perfluorotributylamine (MS grade, Synquest Labꢀ
oratories) in automatic mode. Measurements were performed in
fullꢀscan (scan range from m/z 30 to m/z 400; 6.7 Hz) mode,
source temperature set at 230 °C, and transfer capillary temperaꢀ
ture set at 300 °C. Chromatography separation for mass spectra
was carried out on Agilent HPꢀ5ms fused silica capillary column
(30 m length; 250 μm diameter; 0.25 μm film thickness, 5%
(phenyl)methylpolysiloxane) using helium as a carrier gas with
flow rate of 1 mL min–1. Injection port temperature was set at
300 °C operating in a split mode at a 10 : 1 ratio with sample
injection volume of 1 μL. Temperature programing was as folꢀ
lows: 60 °C maintaining for 4 min, linear increase to 240 °C at
a heating rate of 10 deg min–1, linear increase to 300 °C at a heatꢀ
ing rate of 30 deg min–1, maintaining for 5 min. The spectra
were processed using Agilent MassHunter B.06.00 software package.
Gas chromatography analysis was performed using Chrom 5
chromatograph, injector and flame ionization detector temperaꢀ
tures were 240 °C, capillary column size was 0.2×25000 mm,
stationary phase was silicon SEꢀ30. Thermostat temperature was
raised from 100 to 230 °C (15 deg min–1). The mixture composiꢀ
tions were calculated using normalization method.
(207 mg, 1.5 mmol) was added, the mixture was evacuated three
times and refilled with argon followed by injection of allyl aceꢀ
tate (3) (125 mg, 1.25 mmol, ca. 0.15 mL). The mixture was
stirred at ambient temperature for 18 h and analyzed as in the
method A.
Diethyl (butꢀ3ꢀenꢀ2ꢀyl)malonate (8a) and diethyl (butꢀ2ꢀenꢀ
1ꢀyl)malonate (8b) (a ~1:1 mixture; compound 8b was also
a 12 : 88 Z,Eꢀmixture) was obtained by the general procedure A
from diethyl malonate (4a) and butꢀ3ꢀenꢀ2ꢀyl acetate (7). Their
spectra were in good accord with those reported by us earlier.2a
Diallylation products in this case were not detected.
Ethyl 2ꢀcyanoꢀ2ꢀphenylpentꢀ4ꢀenoate (10) was obtained by
the reaction of compounds 3 and 9 according to general proceꢀ
dures A and B using amounts of allyl acetate and potassium carbꢀ
onate reduced twice, since CH acid 9 is monoprotic. GC yields
in both cases were quantitative. 1H NMR, δ: 1.25 (t, 3 H, J = 7.1 Hz);
2.86 (dd, 1 H, J = 13.9 Hz, J = 7.0 Hz); 3.12 (dd, 1 H, J = 13.9 Hz,
J = 7.3 Hz); 4.24 (m, 2 H); 5.22 (d, 1 H, J = 9.9 Hz); 5.27 (d, 1 H
J = 16.3 Hz); 5.75 (m, 1 H); 7.32—7.45 (m, 3 H); 7.56 (d, 2 H,
J = 6.8 Hz). 13C NMR, δ: 13.7 (CH3), 42.2 (CH2), 54.0 (C), 63.1
(OCH2), 117.9 (CN), 121.1 (=CH2), 126.1 (CHarom), 128.8
(CHarom), 129.0 (CHarom), 130.6 (=CH), 134.1 (Carom), 167.0
(C=O). The spectral data are in agreement with the literature6a
and with those obtained by us earlier.6b
CHꢀacids 4a—c, 9, and allyl acetate (3) were commercially
available. Allylic acetates 7 and 12 were obtained by acylation of
the corresponding allylic alcohols with acetic anhydride in the
presence of DMAP as earlier described.10 Ligands 1a—c and
complexes 2a—c were synthesized by us previously.3 Potassium
carbonate (Reakhim, Russia) was calcined in air and kept in
a closed vessel; prior to each experiment, it was freshly powdered
in a mortar. N,NꢀDimethylformamide (99%+ purity) was used
as purchased from Acros Organics.
Compounds 11a and 11b. A Schlenk tube equipped with
a magnetic stirring bar and a rubber septum was charged with
ethyl 2ꢀcyanoꢀ2ꢀphenylacetate (9) (47 mg, 0.25 mmol) and DMF
(0.5 mL). The mixture was three times evacuated and refilled
with argon. Ligand 1c (ca. 9.5 mg, 0.02 mmol) and Pd2dba3
(ca. 4.6 mg, 0.005 mmol, 4 mol.%) were simultaneously added
and the mixture was stirred for ca. 5 min until dark brown color
turned yellow. Butꢀ3ꢀenꢀ2ꢀyl acetate (7) (37 mg, 0.37 mmol,
ca. 0.045 mL) was then injected and after 10 min stirring freshly
powdered potassium carbonate (52 mg, 0.38 mmol) was added.
Each opening of the tube was followed by evacuation and refillꢀ
ing with argon. The mixture was stirred at ambient temperature
for 18 h, treated with water, extracted with ether, and dried with
CaCl2. The chromatogram of the extract contained no peak of
the starting compound 9, but contained peaks of diastereomers
11a+11a* and isomers Zꢀ11b+Eꢀ11b in a ratio 28 : 24 : 4 : 44.
The extract was concentrated in vacuo and subjected to column
chromatography (gradient elution with 0→5% EtOAc in light
petroleum ether). Evaporation of the corresponding fractions
afforded 51 mg (84%) of the mixture of products 11a and 11b in
a ratio close to that before column chromatography.
Ethyl 2ꢀcyanoꢀ3ꢀmethylꢀ2ꢀphenylpentꢀ4ꢀenoate (11a), two
diastereomers in a ratio of ~54 : 46. 1H NMR (characteristic
signals), δ: 0.93 and 1.34 (both d, 3 H each, J = 6.9 Hz); 3.34
(two m, 1 H each); 4.95 (d, 1 H, J = 15.6 Hz); 4.96 (d, 1 H,
J = 11.4 Hz); 5.24 (d, 1 H, J = 10.1 Hz); 5.32 (d, 1 H, J = 16.9 Hz);
5.50 (m, 1 H); 5.96 (m, 1 H); signals of the Et and Ph groups are
overlapped with the signals of a "linear" isomer. 13C NMR, δ:
13.8 (CH3), 14.9 and 16.9 (HCCH3), 44.8 and 45.1 (CH), 59.9
and 60.1 (C), 62.9 and 60.1 (OCH2), 116.6 and 116.7 (CN),
118.1 and 118.5 (=CH2), 126.6 (CHarom), 126.7 (CHarom), 128.8
(CHarom), 133.0 and 133.4 (Carom), 135.9 and 137.3 (=CH),
167.2 and 167.3 (C=O). MS, m/z: 243 [M]+ (for both diaꢀ
stereomers).
Reaction of CH acids 4a—c with allyl acetate (3) (general
procedure). A. A Schlenk tube equipped with a magnetic stirring
bar and a rubber septum was charged with CH acid (0.5 mmol)
and DMF (1 mL). The mixture was evacuated three times and
refilled with argon. Ligand 1 (0.02 or 0.04 mmol) and Pd2dba3
(0.005 or 0.01 mmol) were simultaneously added, and the mixꢀ
ture was stirred for ca. 5 min until the dark brown color turned
yellow. Allyl acetate (3) (125 mg, 1.25 mmol, ca. 0.15 mL) was
then injected and after 10 min stirring freshly powdered potassiꢀ
um carbonate (207 mg, 1.5 mmol) was added. Each opening of
the tube was followed by evacuation and refilling with argon.
The mixture was stirred at ambient temperature for 18 h. In this
series of experiments, palladium black never precipitated. An
aliquot of the reaction mixture was treated with water, extracted
with diethyl ether, and analyzed by GC. The chromatograms
contained only peaks of the starting CH acids 4 and products of
their allylation 5 and 6. We supposed that under the mild reacꢀ
tion conditions highꢀboiling compounds and resins do not form
from the reactants and products, as well as no saponification of
ester groups occurs. Therefore, conversion of the starting reacꢀ
tant 4 was accepted equal to the yield of products 5 and 6. The
retention times of the known compounds 5a—c and 6a—c were
identical to those of the authentic samples, whose structures
were confirmed by us earlier in similar processes.2a,6b
B. A Schlenk tube was charged with CH acid (0.5 mmol),
palladium(II) complex 2a—c (0.01 or 0.02 mmol), and DMF
(1 mL). It was noted that complexes 2 were not fully dissolved in
these amounts of DMF. Freshly powdered potassium carbonate
Ethyl 2ꢀcyanoꢀ2ꢀphenylhexꢀ4ꢀenoate (11b) (parallel syntheꢀ
sis). To a stirred solution of ethyl 2ꢀcyanoꢀ2ꢀphenylacetate (9)
(567 mg, 3 mmol) in acetone (5 mL), crotyl bromide (486 mg,

Allylation with P—N—P ligands
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 4, April, 2017
665
3.6 mmol) was added followed by addition of freshly powdered
potassium carbonate (456 mg, 3.3 mmol). The mixture turned
slightly selfꢀwarmed up. Stirring was continued at ambient temꢀ
perature for 16 h. The GC analysis showed full completion of the
reaction and the absence of the "branched" isomers; the Z/Eꢀ11b
ratio was 79 : 21. The mixture was filtered, the filter cake was
washed with acetone, and the combined filtrates were concenꢀ
trated in vacuo. The residue was purified by column chromatogꢀ
raphy (gradient elution with 0→5% EtOAc in light petroleum
ether). Evaporation of the corresponding fractions afforded
591 mg (81%) of compound 11b. Analytically pure sample was
obtained by vacuum distillation, b.p. 115 °C (1 Torr), colorless
oil. Found (%): C, 74.30, 74.16; H, 7.11, 7.16; N, 5.79, 5.92.
C15H17NO2. Calculated (%): C, 74.05; H, 7.04; N, 5.76. MS,
m/z: 243 [M]+.
EꢀIsomer. 1H NMR, δ: 1.25 (t, 3 H, J = 6.9 Hz); 1.67 (d, 3 H,
J = 6.8 Hz); 2.76 (dd, 1 H, J = 13.7 Hz, J = 6.7 Hz); 3.06 (dd,
1 H, J = 13.7 Hz, J = 7.3 Hz); 4.23 (m, 2 H); 5.39 (dt, 1 H,
J = 15.1 Hz, J = 6.8 Hz); 5.70 (dq, 1 H, J = 15.1 Hz, J = 6.9 Hz);
7.34—7.43 (m, 3 H); 7.55 (d, 2 H, J = 8.2 Hz). 13C NMR, δ: 13.8
(CH3), 17.9 (=CCH3), 41.3 (=CCH2), 54.5 (C), 63.0 (OCH2),
118.2 (CN), 123.1 (MeCH=), 126.1 (CHarom), 128.7 (CHarom),
129.0 (CHarom), 132.2 (=CH), 134.3 (Carom), 167.2 (C=O).
ZꢀIsomer. 1H NMR (characteristic signals), δ: 2.88 (dd, 1 H,
J = 14.4 Hz, J = 7.3 Hz); 3.16 (dd, 1 H, J = 14.4 Hz, J = 7.8 Hz).
13C NMR (characteristic signals), δ: 13.0 (=CCH3), 35.6 (=CCH2),
53.9 (C), 63.1 (OCH2), 122.3 (MeCH=), 129.9 (=CH), the other
signals coincide with those of Eꢀisomer.
Diethyl [(2E)ꢀ1,3ꢀdiphenylpropꢀ2ꢀenꢀ1ꢀyl]malonate (13).
A. A Schlenk tube equipped with a magnetic stirring bar and
a rubber septum was charged with diethyl malonate (4a) (48 mg,
0.3 mmol) and DMF (0.5 mL). The mixture was three times
evacuated and refilled with argon. Ligand 1c (ca. 9.5 mg,
0.02 mmol) and Pd2dba3 (ca. 4.6 mg, 0.005 mmol, 4 mol.%)
were simultaneously added and the mixture was stirred for ca.
5 min until dark brown color turned yellow. 1,3ꢀDiphenylallyl
acetate (12) (63 mg, 0.25 mmol) was added and after 10 min
stirring freshly powdered potassium carbonate (69 mg, 0.5 mmol)
was added. Each opening of the tube was followed by evacuation
and refilling with argon. The mixture was stirred at ambient
temperature for 18 h, treated with water, extracted with diethyl
ether, and dried with CaCl2. Evaporation left a residue whose
aliquot was analyzed by 1H NMR spectroscopy. Spectral data
for product 13 were in agreement with those reported earlier.8
Ratio of components 12 and 13 was determined from integral
intensities of their characteristic signals, i.e., a singlet for the
C(O)CH3 group of 12 at δ 2.15, and a triplet for the more upꢀ
fieldꢀshifted methyl group of the CH(CO2CH2CH3)2 fragment
of 13 at δ 1.02. In this case, a ratio 12 : 13 was 20 : 80.
0.01 mmol). The mixture was three times evacuated and refilled
with argon. Diphenylallyl acetate (12) (63 mg, 0.25 mmol) was
added and after 10 min stirring freshly powdered potassium carbꢀ
onate (69 mg, 0.5 mmol) was added. Each opening of the tube
was followed by evacuation and refilling with argon. The process
was carried out as given in method A. In this case, the ratio
12 : 13 was 73 : 27.
References
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Trost, D. L. Van Vranken, Chem. Rev., 1996, 96, 395; (c) U. Kazꢀ
maier, M. Pohlman, in MetalꢀCatalyzed CrossꢀCoupling
Reactions, Eds A. de Meijere, F. Diedrich, WileyꢀVCH,
Weinheim, 2004, pp. 531—583.
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B. A Schlenk tube equipped with a magnetic stirring bar and
a rubber septum was charged with diethyl malonate (4a) (48 mg,
0.3 mmol), DMF (0.5 mL) and palladium complex 2c (6.5 mg,
Received July 11, 2016;
in revised form November 2, 2016