An improved catalytic system, Pd(PPh3)4/PhCOOH combined catalyst, for the allylation of carbon pronucleophiles with allenes

Article abstract of DOI:10.1055/s-2004-829178

The reaction of allenes with active methynes and methylenes proceeded smoothly in the presence of Pd(PPh₃)₄/PhCOOH combined catalyst to give the corresponding monoallylated products with E-stereoselectivity in good to high yields. Th

Full text of DOI:10.1055/s-2004-829178

2186
PAPER
An Improved Catalytic System, Pd(PPh3)4/PhCOOH Combined Catalyst, for
the Allylation of Carbon Pronucleophiles with Allenes
I
mprove
d
Catalytic
i
System
t
for th
i
e
A
lly
n
lation of
C
arbon Pr
T
onucleophile
s
w
.
ith
A
llenes Patil, Nirmal K. Pahadi, Yoshinori Yamamoto*
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
E-mail: yoshi@yamamoto1.chem.tohoku.ac.jp
Received 21 April 2004; revised 19 May 2004
Furthermore, the method suffered from a low yield, poor
Abstract: The reaction of allenes with active methynes and meth-
ylenes proceeded smoothly in the presence of Pd(PPh3)4/PhCOOH
combined catalyst to give the corresponding monoallylated prod-
ucts with E-stereoselectivity in good to high yields. This result is in
stereoselectivity and long reaction time. In the course of
our investigation, we found that the use of carboxylic acid
as an additive improved dramatically the drawbacks men-
marked contrast to the previous finding that the reaction of allenes tioned above.8a Now we wish to report that the reaction of
with active methynes, in the presence of Pd2(dba)3·CHCl3/dppb cat-
alyst, affords the allylation products in lower yield with lower ste-
reoselectivities.
phenyl allene (1a) with an activated methyne, methyl ma-
lononitrile (2), proceeds stereoselectively in a higher yield
(75%) with a shorter reaction time (12 h) by the use of
Pd(PPh3)4 (5 mol%) and benzoic acid (10 mol%) com-
Key words: palladium, carboxylic acids, catalysis, allenes, C-nu-
cleophiles
bined catalyst (Scheme 2), and that the reaction of various
allenes 1a–e with activated methylenes 4 under the com-
bined catalyst system proceeds very smoothly and gives
selectively the mono-allylation products 5 in good to high
yields with E-stereoselectivity (Scheme 2).
The formation of carbon-carbon bonds using transition
metal catalysts is an important process in organic synthe-
sis. The addition of a C-H bond to an unactivated C-C
multiple bond to form a new carbon-carbon bond, i.e. hy-
drocarbonation, is a desirable method since it is an eco-
chemical process with a high atom economy. Transition
metals have been shown to be effective catalysts for pro-
moting the addition of the C-H bond of carbon pronucleo-
philes to 1,3-dienes,1 alkynes,2 1,3-enyne,3 3,3-
dihexylcyclopropene,4 methyleneaziridines,5 methylene-
cyclopropanes6 and allenes.7 As a part of our continuing
program on the transition metal catalyzed carbon-carbon
bond formation, we previously reported the palladium cat-
alyzed allylation of active methynes with allenes
(Scheme 1).7a This new palladium-catalyzed transforma-
tion must become more useful, if the allylation of active
methylenes becomes feasible. However, we encountered
difficulties in the selective monoallylation of active meth-
ylenes; for example, a mixture of the mono- and diallylat-
ed products was obtained in the allylation of
malononitrile, since the C-H bond of monoallylated prod-
uct (allylmalononitrile) was more reactive than that of the
starting malononitrile.
H
Pd/PhCOOH
CN
C
C
CH2
Ph
CN
CN
CN
Ph
H
3
5
1a
2
E1
E2
Pd/PhCOOH
C
C
CH2
R
E1
E2
4
1a-e
R
E1
E2
: H2C(COOEt)2, H2C(COPh)(COOEt), H2C(COPh)2,
H2C(SO2Ph)(COPh)
Scheme 2
In an initial experiment, phenyl allene (1a) was treated
with 1 equivalent of methyl malononitrile (2), Pd(PPh3)4
(5 mol%) and benzoic acid (10 mol%) in dioxane at 100
°C to give the product 3 (E-isomer) in 75% yield
(Scheme 2). No formation of the Z-isomer was observed,
in contrast to the previous report7a in which a mixture of
E- and Z-isomers was obtained in a ratio of 57:43. It is
noteworthy that the addition of a catalytic amount of a
simple carboxylic acid dramatically enhanced the rate and
stereoselectivity of the reaction.8
R2
R2
H-Nu, Pd(0)
C
C
CH2
R1
Nu
THF, 100 °C, 48 h
R1
Having the optimized condition in hand, we turned our at-
tention towards active methylenes. As reported previous-
ly,7a the allylation of malononitrile with phenyl allene (1a)
proceeded well in the presence of Pd2(dba)3·CHCl3/dppb
catalyst, however a mixture of mono- and diallylated
products was obtained. At that stage, we believed that the
synthetically useful allylation with allenes was restricted
to active methynes only, and did not examine the allyla-
tion with other active methylenes. Later, it occurred to us
H-Nu = HC(Me)(CN)2, HC(Ph)(CN)(COOEt)
Scheme 1
SYNTHESIS 2004, No. 13, pp 2186–2190
x
x.
x
x
.
2
0
0
4
Advanced online publication: 27.07.2004
DOI: 10.1055/s-2004-829178; Art ID: F05804SS
© Georg Thieme Verlag Stuttgart · New York

PAPER
Improved Catalytic System for the Allylation of Carbon Pronucleophiles with Allenes
2187
that diethyl malonate, less reactive than malononitrile,
might react with 1a pertinently without forming the dou-
ble allylation product.
Ph
Nu
Pd(0)
PhCOOH
+
3 and 5
The reaction of diethyl malonate (4a) with phenyl allene
1a in the presence of Pd(PPh3)4 and PhCOOH (10 mol%)
in 1,4-dioxane at 100 °C for 12 hours afforded the
monoallylated product 5a in 90% isolated yield as a single
E-isomer (Table 1, entry 1). Formation of the diallylated
product was not observed at all under the conditions men-
tioned above. Similarly, the monoallylation of 4b, 4c and
4d with phenyl allene (1a) also proceeded smoothly to
give 5b, 5c, and 5d, respectively, in good yields (entries
2–4). It should be noted that the functional groups on the
aromatic ring of allenes did not affect the reaction effi-
ciency. Thus, the allenes 1b, 1c, and 1d with fluoro, chlo-
ro, and methyl substituents at the para position reacted
smoothly with diethyl malonate (4a) to give the corre-
HNu
2 and 4
H-Pd-OCOPh
6
Ph
H
C
C
CH2
Pd
Ph
OCOPh
1a
7
Scheme 3 Proposed mechanism for the allylation of C-nucleophiles
with allenes
Table 1 Pd(PPh3)4/Benzoic Acid Catalyzed Allylation of Active Methylenes with Allenesa
Entry
1
Allenes (1)
1a R = Ph
H-Nu (4)b
Product (5)
Yield (%)c
90
4a
COOEt
COOEt
Ph
E1 = E2 = COOEt
5a
2
3
1a R = Ph
4b
85
82
85
70
72
65
89
85
88
COPh
Ph
E1 = COPh
E2 = SOOPh
SOOPh
5b
1a R = Ph
4c
COPh
Ph
E1 = COPh
E2 = COOEt
COOEt
5c
4
1a R = Ph
4d
COPh
COPh
Ph
E1 = E2 = COPh
5d
5e
5f
5
1b R = p-F-C6H4
1c R = p-Cl-C6H4
1d R = p-Me-C6H4
1e R = COOEt
1e R = COOEt
1e R = COOEt
4a
4a
4a
4a
4b
4c
6
7
5g
8
COOEt
COOEt
EtOOC
5h
9
COPh
EtOOC
SOOPh
5i
10
COPh
EtOOC
COOEt
5j
a All reactions were carried out with 5 mol% Pd(PPh3)4 and 10 mol% benzoic acid in 1,4-dioxane at 100 °C for 12 h.
b 1.2 Equivalent of pronucleophiles was used.
c Isolated yield.
Synthesis 2004, No. 13, 2186–2190 © Thieme Stuttgart · New York

2188
N. T. Patil et al.
PAPER
2-(3-Phenyl-allyl)-malonic Acid Diethyl Ester (5a)10
Oil.
butadienoate (1e) also reacted with the active methylenes IR (KBr): 3029, 1740 cm–1.
sponding monoallylated products 5e, 5f and 5g in 70%,
72%, and 65% yield, respectively (entries 5–7). Ethyl 2,3-
1H NMR (300 MHz, CDCl3): d = 7.18–7.32 (m, 5 H), 6.46 (d, J =
15.9 Hz, 1 H), 6.14 (ddd, J = 15.9, 7.8, 7.8 Hz, 1 H), 4.18 (2 × q,
J = 7.3 Hz, 4 H), 3.47 (t, J = 7.5 Hz, 1 H), 2.78 (t, J = 7.5 Hz, 2 H),
1.24 (2 × t, J = 7.3 Hz, 6 H).
13C NMR (75 MHz, CDCl3) d = 168.6, 136.9, 132.6, 128.4, 128.3,
127.9, 127.2, 126.0, 125.4, 61.4, 51.9, 32.2, 14.09.
4a, 4b, and 4c to give the monoallylated products 5h, 5i,
and 5j, respectively, in high yields (entries 8–10). It
should be noted that the methodology reported herein is
only applicable to activated allenes and in the case of un-
activated allene such as deca-1,2-diene, starting material
is recovered quantitatively.
HRMS (EI): m/z [M+] calcd for C16H20O4: 276.1356; found:
276.1356.
A plausible mechanism for this allylation is illustrated in
Scheme 3. The initial step is the formation of the hydri-
dopalladium species 6 from Pd(0) and benzoic acid. The
hydropalladation of phenyl allene (1a) with 6 would pro-
duce the p-allylpalladium species 7. The p-allylpalladium
species would reacts with the pronucleophiles 2 and 4 to
give the products 3 and 5 with the liberation of Pd(0) and
benzoic acid.2 Another conceivable pathway is that the
Pd-catalyzed addition of benzoic acid to allene 1a takes
place first9 and then the resulting cinnamyl benzoate re-
acts with HNu in the Tsuji–Trost allylation manner to give
the products 3 and 5.
2-Benzenesulfonyl-1,5-diphenyl-pent-4-en-1-one (5b)11
Solid; mp 116–117 °C.
IR (KBr): 3061, 1686, 1596 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.91 (d, J = 8.0 Hz, 2 H), 7.78 (d,
J = 8.0 Hz, 2 H), 7.12–7.67 (m, 11 H), 6.39 (d, J = 16.0 Hz, 1 H),
5.91 (ddd, J = 16.0, 7.5, 7.5 Hz, 1 H), 5.18 (dd, J = 12.0, 4.0 Hz, 1
H), 2.89–3.03 (m, 2 H).
13C NMR (75 MHz, CDCl3): d = 191.6, 136.7, 136.3, 136.2, 134.1,
133.9, 133.8, 129.5, 128.7, 128.5, 128.2, 127.4, 125.9, 122.8, 69.3,
31.5.
HRMS (EI): m/z [M+] calcd for C23H20O3S: 376.1128; found [M –
SO2Ph]: 235.1117.
In conclusion, we have now improved our earlier allyla-
tion procedure for carbon pronucleophiles with allenes.
Nowadays, a variety of methods are known for the synthe-
sis of allenes, so we expect the present methodology can
prove a good alternative to the existing methods for the al-
lylation of carbon nucleophiles. Herein, we achieved se-
lective mono-allylation of active methylenes with E-
stereoselectivity and E-selective allylation of active meth-
ynes. The reason why the present catalytic system, Pd(0)/
PhCOOH, gives high E-stereoselectivity while the previ-
ous catalyst, Pd(0) only, produces a mixture of E and Z
stereomers is not clear at present. However, this differ-
ence may become a key for elucidating the precise mech-
anism for the previous reaction.7a Further investigation on
the mechanism for the allylation with allenes and on the
asymmetric allylation of carbon nucleophiles with allenes
are now underway in our laboratory.
2-Benzoyl-5-phenyl-pent-4-enoic Acid Ethyl Ester (5c)12
Oil.
IR (KBr): 3061, 1735, 1686 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.96 (d, J = 12 Hz, 2 H), 7.12–7.56
(m, 8 H), 6.42 (d, J = 15.5 Hz, 1 H), 6.18 (ddd, J = 15.5, 8.0, 8.0 Hz,
1 H), 4.41 (t, J = 8.0 Hz, 1 H), 4.11 (q, J = 7.5 Hz, 2 H), 2.86 (m, 2
H), 1.12 (t, J = 7.5 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 194.1, 169. 1, 136.8, 136.0, 133.3,
132.4, 128.5, 128.4, 128.4, 128.3, 128.0, 127.1, 125.9, 125.9, 61.33,
54.2, 32.3, 14.0.
HRMS (EI): m/z [M+] calcd for C20H20O3: 308.1407; found:
308.1407.
1,3-Diphenyl-2-(3-phenyl-allyl)-propane-1,3-dione (5d)11
Solid; mp 72–74 °C.
IR (KBr): 3085, 1690 cm–1.
The 1H NMR and 13C NMR spectra were recorded at 400 MHz us-
ing CDCl3 as solvent and are reported in ppm relative to CHCl3
(d = 7.26) for 1H NMR and relative to the central CDCl3 (d = 77.00)
1H NMR (300 MHz, CDCl3): d = 7.99 (d, J = 8 Hz, 4 H), 7.11–7.72
(m, 11 H), 6.48 (d, J = 16.0 Hz, 1 H), 6.26 (ddd, J = 16.0, 8.0, 8.0
Hz, 1 H), 5.37 (t, J = 8.0 Hz, 1 H), 3.04 (t, J = 8.0 Hz, 2 H).
13C NMR (75 MHz, CDCl3): d = 195.3, 136.8, 135.8, 133.4, 132.3,
128.8, 128.4, 128.3, 127.2, 126.6, 126.0, 57.0, 33.0.
HRMS (EI): m/z [M+] calcd for C24H20O2: 340.1458; found:
340.1455.
1
resonance for 13C NMR. Coupling constants in H NMR data are
given in Hz. The HRMS spectra were recorded at HITACHI M-
2500S instrument. Dehydrated 1,4-dioxane were purchased from
Wako Pure Chemical Inc. Structure of 5a,10 5b,11 5c,12 5d,11 were
confirmed by comparison with published spectral data. The allenes
1a,13 1b,14 1c,15 and 1d14 are known in literature. The allene 1e is
commercially available and was purchased from Aldrich.
2-[3-(4-Fluoro-phenyl)-allyl]-malonic Acid Diethyl Ester (5e)
Oil.
Allylation of Diethyl Malonate (4a) with Phenyl Allene (1a);
Typical Procedure
IR (KBr): 3030, 1741 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.25 (dd, J = 8.8, 5.2 Hz, 2 H),
6.95 (t, J = 8.0 Hz, 2 H), 6.41 (d, J = 15.9 Hz, 1 H), 6.05 (ddd, J =
15.9, 7.4, 7.4 Hz, 1 H), 4.17 (2 × q, J = 7.2 Hz, 4 H), 3.46 (t, J = 7.5
Hz, 1 H), 2.76 (t, J = 7.4 Hz, 2 H), 1.25 (2 × t, J = 7.3 Hz, 6 H).
13C NMR (75 MHz, CDCl3): d = 168.7, 160.8, 133.1, 133.0, 131.5,
127.5, 125.2, 115.4, 115.2, 61.4, 51.9, 32.2, 14.2.
To a mixture of phenyl allene (1a, 0.20 g, 1.72 mmol), diethyl ma-
lonate (4a, 0.33 g, 2.07 mmol), Pd(PPh3)4 (0.099 g, 0.086 mmol) in
anhyd 1,4-dioxane (5 mL) was added benzoic acid (0.021 g, 0.17
mmol), and the mixture was stirred for 12 h at 100 °C. The reaction
mixture was then filtered through a short silica gel column using
Et2O as an eluent, and the filtrate was concentrated. The residue was
purified by a silica gel column chromatography (hexane–EtOAc,
4:1) to give 5a (0.43 g, 90%).
HRMS (EI): m/z [M+] calcd for C16H19FO4: 294.1267; found:
294.1263.
Synthesis 2004, No. 13, 2186–2190 © Thieme Stuttgart · New York

PAPER
Improved Catalytic System for the Allylation of Carbon Pronucleophiles with Allenes
2189
2-[3-(4-Chloro-phenyl)-allyl]-malonic Acid Diethyl Ester (5f)
Oil.
13C NMR (75 MHz, CDCl3): d = 190.3, 168.5, 165.8, 144.1, 135.6,
133.9, 128.5, 123.6, 61.7, 60.2, 52.8, 31.08, 14.2, 13.9.
IR (KBr): 3025, 1745 cm–1.
HRMS (EI): m/z [M+] calcd for C17H20O5: 304.1305; found [M +
H]: 305.1384.
1H NMR (300 MHz, CDCl3): d = 7.08–7.23 (m, 4 H), 6.34 (d, J =
16.0 Hz, 1 H), 6.08 (ddd, J = 16.0, 7.4, 7.4 Hz, 1 H), 4.11 (2 × q,
J = 7.0 Hz, 4 H), 3.40 (t, J = 7.4 Hz, 1 H), 2.71 (t, J = 7.4 Hz, 2 H),
1.20 (2 × t, J = 7.0 Hz, 6 H).
Acknowledgment
NTP thanks the Japan Society for the Promotion of Science (JSPS)
for a postdoctoral research fellowship.
13C NMR (75 MHz, CDCl3): d = 168.7, 135.4, 132.9, 131.5, 128.6,
127.3, 126.3, 61.5, 51.9, 32.2, 14.2.
HRMS (EI): m/z [M+] calcd for C16H19ClO4: 310.0972; found:
310.0974.
References
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2-[3-(4-Methyl-phenyl)-allyl]-malonic Acid Diethyl Ester (5g)
Oil.
IR (KBr): 3029, 1743 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.25 (d, J = 8.0 Hz, 2 H), 7.12 (d,
J = 8.0 Hz, 2 H), 6.47 (d, J = 16.0 Hz, 1 H), 6.12 (dt, J = 16.0, 7.6
Hz, 1 H), 4.23 (2 × q, J = 7.0 Hz, 4 H), 3.51 (t, J = 7.6 Hz, 1 H), 2.83
(t, J = 7.6 Hz, 2 H), 2.33 (s, 3 H), 1.32 (t, J = 7.0 Hz, 6 H).
13C NMR (75 MHz, CDCl3): d = 168.8, 137.0, 134.2, 132.5, 129.1,
125.9, 124.4, 61.4, 52.1, 32.3, 21.2, 14.2.
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HRMS (EI): m/z [M+] calcd for C17H22O4: 290.1518; found:
290.1517.
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5-Ethoxycarbonyl-hex-2-enedioic Acid Diethyl Ester (5h)
Oil.
IR (neat): 3065, 1735, 1710 cm–1.
1H NMR (300 MHz, CDCl3): d = 6.85 (ddd, J = 12.9, 7.5, 7.5 Hz, 1
H), 5.85 (d, J = 12.9 Hz, 1 H), 4.18 (3 × q, J = 7.3 Hz, 6 H), 3.45 (t,
J = 7.5 Hz, 1 H), 2.77 (t, J = 7.5 Hz, 2 H), 1.25 (3 × t, J = 7.3 Hz, 9
H).
13C NMR (75 MHz, CDCl3): d = 167.9, 165.6, 143.5, 123.6, 61.5,
60.1, 50.5, 30.9, 14.1, 13.9.
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HRMS (EI): m/z [M+] calcd for C13H20O6: 272.1254; found [M +
H]: 273.1333.
5-Benzenesulfonyl-6-oxo-6-phenyl-hex-2-enoic Acid Ethyl
Ester (5i)
Oil.
IR (neat): 2931, 1710, 1690 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.89 (d, J = 8.0 Hz, 2 H), 7.74 (d,
J = 8.0 Hz, 2 H), 7.41–7.73 (m, 6 H), 6.65 (ddd, J = 12.8, 7.9, 7.9
Hz, 1 H), 5.78 (d, J = 12.8 Hz, 1 H), 5.15 (t, J = 8.0 Hz, 1 H), 4.07
(q, 7.3 Hz, 2 H), 2.95 (dd, J = 8.0, 7.9 Hz, 2 H), 1.19 (t, J = 7.3 Hz,
3 H).
13C NMR (75 MHz, CDCl3): d = 190.6, 165.2, 141.2, 136.3, 135.9,
134.3, 134.0, 129.4, 128.9, 128.8, 128.6, 124.8, 124.8, 68.1, 60.3,
30.2, 14.0.
HRMS (EI): m/z [M+] calcd for C20H20O5S: 372.1026; found [M +
H]: 373.1104.
5-Benzoyl-hex-2-enedioic Acid Diethyl Ester (5j)
Oil.
IR (neat): 3089, 1735, 1711, 1690 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.98 (d, J = 8.0 Hz, 2 H), 7.50–
7.59 (m, 1 H), 7.44–7.49 (m, 2 H), 6.89 (ddd, J = 12.7, 7.5, 7.5 Hz,
1 H), 5.88 (d, J = 12.7 Hz, 1 H), 4.42 (t, J = 8.0 Hz, 1 H), 4.14 (2 ×
q, J = 7.3 Hz, 4 H), 2.88 (m, 2 H), 1.25 (t, J = 7.3 Hz, 3 H), 1.15 (t,
J = 7.3 Hz, 3 H).
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