Pd(O)-PhCOOH catalyzed addition of oxygen pronucleophiles to allenes and internal alkynes

Article abstract of DOI:10.1139/v05-043

We have developed a catalytic system that enables the addition of alcohols to allenes using a combination of 5 mol% Pd(PPh₃)₄ and 10 mol% benzoic acid. Likewise, the addition reaction of carboxylic acids to alkynes is described. In all cases the reaction proceeded well, giving the corresponding allylation products in good-to-high yields with high regio- and stereoselectivities.

Full text of DOI:10.1139/v05-043

569
Pd(0)–PhCOOH catalyzed addition of oxygen
pronucleophiles to allenes and internal alkynes1
Nitin T. Patil, Nirmal K. Pahadi, and Yoshinori Yamamoto
Abstract: We have developed a catalytic system that enables the addition of alcohols to allenes using a combination
of 5 mol% Pd(PPh3)4 and 10 mol% benzoic acid. Likewise, the addition reaction of carboxylic acids to alkynes is de-
scribed. In all cases the reaction proceeded well, giving the corresponding allylation products in good-to-high yields
with high regio- and stereoselectivities.
Key words: addition, alcohols, carboxylic acids, allenes, alkynes, palladium.
Résumé : Nous avons développé un système catalytique qui utilise une combinaison de 5 mol% de Pd(PPh3)4 et de
10 mol% d’acide benzoïque et qui permet de réaliser l’addition d’alcools à des allènes. On décrit aussi la réaction
d’addition d’acides carboxyliques à des alcynes. Dans tous les cas, la réaction se produit bien et conduit aux produits
d’allylation correspondants avec des rendements allant de bons à élevés et avec des régio- et stéréosélectivités élevées.
Mots clés : addition, alcools, acides carboxyliques, allènes, alcynes, palladium.
[Traduit par la Rédaction] Patil et al. 573
Introduction
regioselectivity, in contrast to the previously reported cases
(4) wherein the addition of carbon nucleophiles proceeded
but the products were obtained in lower yields and consisted
of a mixture of E and Z stereoisomers. This difference in re-
action pathways in the case of carboxylic acid pronucleo-
philes and carbon pronucleophiles prompted us to study the
catalytic system closely. To our delight, we found that, in
this palladium catalyzed reaction, the addition of a catalytic
amount of carboxylic acid is crucial for obtaining the allyl-
ation products in high yields and in a regio- and stereo-
selective manner. Our unique finding (Pd(0)–RCOOH
combined catalyst) has also been successfully applied to the
addition of nitrogen (6) and carbon (7) nucleophiles. How-
ever, the addition of alcohols to allenes under the newly de-
veloped procedure remains to be disclosed.
The addition of various pronucleophiles to alkynes is also
a subject of interest in our laboratory (8). We recently re-
ported a new approach for the allylation of carbon (8a–8d)
and nitrogen (8d–8g) pronucleophiles with alkynes in the
presence of a Pd(0)–carboxylic acid combined catalyst.
Later we communicated the formal addition of alcohol to al-
kynes (eq. [2]) (8h). However, the addition of carboxylic
acid to alkynes has not been addressed until now by our
group. In the meantime, Zhang et al. (9) reported the addi-
tion of oxygen nucleophiles to alkynes using the catalytic
system developed by us without citing our (8h) reference. In
this paper we report, in detail, our efforts in the successful
implementation of our newly developed Pd(0)–PhCOOH
combined catalyst system for the addition of alcohols to
Transition metal catalyzed addition of nucleophiles to ac-
tivated C—C bonds is one of the most important processes
in organic synthesis. The addition of carbon pronucleophiles
to activated C—C bonds is commonly referred to as a hydro-
carbonation (1) reaction. Likewise, the addition reactions of
amines and alcohols across an activated C—C bond are re-
ferred to as hydroamination (2) and hydroalkoxylation (3),
respectively. All these processes are very important from the
synthetic point of view because, in principle, the addition re-
actions can be performed with 100% atom efficiency, with-
out any waste formation, and for this reason they fulfill the
requirements of green chemistry, in contrast to substitution
reactions. Although tremendous amounts of related work
have been carried out in the field of hydrocarbonation and
hydroamination reactions, very few reports have been found
for the hydroalkoxylation and hydrocarboxylation reactions,
partly because of the diminished nucleophilicity and the
softer Lewis base character of oxygen nucleophiles as com-
pared with amines.
Our interest in these type of addition reactions has
prompted us to investigate a catalytic system for the addition
of carbon and nitrogen pronucleophiles to allenes (2a, 4). As
part of our ongoing interest in this area, we extended this ap-
proach to the intermolecular addition of carboxylic acids (5)
to allenes (eq. [1]). In the latter case, it was found that the
reaction was completed in a shorter time period (4 h), giving
the allylation products in high yields with high stereo- and
Received 17 November 2004. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 2 June 2005.
N.T. Patil, N.K. Pahadi, and Y. Yamamoto.2 Department of Chemistry, Graduate School of Science, Tohoku University, Sendai
980-8578, Japan.
1This article is part of a Special Issue dedicated to Professor Howard Alper.
2Corresponding author (e-mail: yoshi@yamamoto1.chem.tohoku.ac.jp).
Can. J. Chem. 83: 569–573 (2005)
doi: 10.1139/V05-043
© 2005 NRC Canada

570
Can. J. Chem. Vol. 83, 2005
Table 1. Addition of alcohols to allenes.
allenes (eq. [3]) and the addition of carboxylic acids to al-
kynes in a regio- and stereoselective manner (eq. [4]).
Pd(0)–PhCOOH
1,4-diox ane
R1-OH
R
OR1
C
CH2
+
R
1
2
3
Pd(0)
R1-C OOH
R1-OH
C
CH2
+
OCOR1
OR1
[1]
[2]
R
R
R
Entry
Allene (1)
Alcohol (2)
Product (3) Yield (%)a
Pd (0)–R COOH
Pd (0)–R COOH
CH3
+
R
C
CH 2
1
2
BnOH
3a
3b
71
70
Ph
1a
OR1
C
CH2
+
[3]
[4]
R1-OH
R
1a
HO
R
R
Pd(0)
3
4
1a
1a
3c
3d
75
71
R1-COOH
R
OCOR1
+
C H3
HO
Results and discussion
HO
Heating a mixture of phenyl allene 1a and acetic acid in
the presence of Pd2dba3·CHCl3 and dppf in THF at 80 °C for
4 h under argon resulted in the formation of cinnamyl ace-
tate in 83% yield, with excellent regio- and stereoselectivity
(eq. [1], R = Ph, R1 = CH3) (5). However, when phenyl
allene was treated with carbon pronucleophiles (for instance,
methylmalononitrile) under similar conditions, the reaction
time was increased to 48 h (4a). Moreover, in most cases,
the products were obtained in lower yields and consisted of
a mixture of E and Z stereoisomers. At this stage the exact
reason behind the superiority of the addition of carboxylic
acid pronucleophiles to allenes over carbon pronucleophiles
was not known. After detailed investigation into the reaction,
we found that the combination of Pd(0) and carboxylic acid
was best (see mechanistic part mentioned later). A dramatic
change was observed when a catalytic amount of a
carboxylic acid was introduced into the reaction system. The
discovery of the unique role of a carboxylic acid as an addi-
tive allowed us to perform the addition of nitrogen (6) and
carbon (7) nucleophiles to allenes in a highly stereo- and
regioselective manner and in a shorter time. As a part of our
continuing interest in this area, we then decided to study the
intermolecular addition of alcohols to allenes. The results
are summarized in Table 1.
HO
5
1a
3e
75
6
7
1a
1a
3f
79
70
HO
Ph
3g
HO
8
1a
3h
75
HO
HO
9
1a
1a
3i
3j
65
75
Ph
10
HO
Ph
C
p-Me -C6H4 1b
CH2
11
BnOH
BnOH
3k
3l
68
72
C
CH2
1c
12
p-F-C6H 4
Treatment of phenyl allene 1a with benzyl alcohol 2a un-
der standard conditions gave the corresponding allylation
product 3a in 71% yield (entry 1). Likewise, in the hydro-
carbonation (7) and hydroamination (6) of allenes, the reac-
tion of phenyl allene 1a with various alcohols proceeded
smoothly to afford the products 3b–3j in good yields (entries
2–10). Substituents such as -CH3 and -F in the aromatic nu-
cleus of allenes do not affect the efficiency of the reaction.
Thus, when 1b and 1c were treated with benzyl alcohol, the
corresponding allylation products 3k and 3l were obtained in
68% and 72% yield, respectively (entries 11 and 12).
Next, we turned our attention towards the addition of car-
boxylic acids to alkynes. A mixture of 1-phenyl-1-propyne
(4a) and acetic acid (1.5 equiv.) in the presence of Pd(PPh3)4
(5 mol%) was heated in 1,4-dioxane at 100 °C for 12 h.
As anticipated, the starting materials were completely con-
sumed, giving the allylation product 6a in 81% isolated
yield as a single stereoisomer (Table 2, entry 1) (8a). Other
acids such as 2-furoic acid (5b), hexanoic acid (5c), 1-
naphthoic acid (5d), and 2,2-diphenylacetic acid (5e) reacted
Note: All reactions were carried out as per the general procedure de-
scribed in the Experimental section.
aIsolated yields.
well with alkyne 4a, giving the corresponding allylation
products in high yields (entries 2–5). The aryl alkynes bear-
ing -OMe and -Cl substituents at the para position, 4b and
4c, reacted well with 5e and 5c to give the products 6f and
6g, respectively, in excellent yields (entries 6 and 7).
The mechanism of this reaction is presumably similar to
those reported previously (8) and is shown in Fig 1. The ini-
tial step is the hydropalladation of alkynes 4 with the
hydridopalladium species 8 generated from Pd(0) and ben-
zoic acid (catalytic cycle I). The resulting vinyl palladium
species 7 would produce phenyl allene 1 and the active cata-
lyst 8 via β-elimination. Hydropalladation of 1 with 8 pre-
sumably gives the π-allylpalladium species 9, which reacts
with alcohols and carboxylic acids to give allylation prod-
ucts, along with the hydridopalladium species 8 (cycle II). In
© 2005 NRC Canada

Patil et al.
571
Table 2. Addition of carboxylic acids to alkynes.
thesized compounds 3f, 3i, 3k, 3l, and 6c–6g are given
below.
Pd (0)–PhCOOH
+
R1-COOH
R
OCOR 1
R
C H3
1,4-dioxane
4
5
6
3f
1
IR (neat) (cm–1): 1615. H NMR (CDCl3, 400 MHz) δ:
Entry
1
Product (6)
Yield (%)a
81
R1COOH(5)
Alkyne (4)
7.40–7.20 (m, 5H), 6.60 (d, J = 16.1 Hz, 1H), 6.30 (dt, J =
16.1, 6.1 Hz, 1H), 4.13 (dd, J = 6.1, 1.5 Hz, 2H), 3.55 (t, J =
7.6 Hz, 2H), 1.58 (t, J = 7.6 Hz, 2H), 0.92 (s, 9H). 13C NMR
(CDCl3, 100 MHz) δ: 136.6, 131.9, 128.4, 127.5, 126.4,
71.5, 67.8, 43.1, 29.8, 29.7. HR-MS calcd. for C15H22O
([M]+): 218.1671; found: 218.1665.
4a R = C6H5
CH3COOH (5a)
6a
2
3
4a
6b
6c
75
90
COOH
O
(5b )
3i
4a
4a
C OOH
1
IR (neat) (cm–1): 1622. H NMR (CDCl3, 400 MHz) δ:
(5c)
7.40–7.21 (m, 5H), 6.60 (d, J = 15.8 Hz, 1H), 6.30 (dt, J =
15.8, 6.01 Hz, 1H), 4.16 (dd, J = 6.01, 1.4 Hz, 2H), 3.33 (d,
J = 6.8 Hz, 2H), 1.16–1.06 (m, 1H), 0.62–0.51 (m, 2H),
0.26–0.22 (m, 2H). 13C NMR (CDCl3, 100 MHz) δ: 136.7,
132.2, 128.4, 127.5, 126.4, 126.3, 75.1, 71.2, 10.8. HR-MS
calcd. for C13H16O ([M]+): 188.1201; found: 188.1196.
COOH
4
5
6d
90
83
(5d )
Ph
4a
6e
Ph
COOH
(5e)
3k
1
IR (neat) (cm–1): 1606. H NMR (CDCl3, 400 MHz) δ:
7.35–7.01 (m, 9H), 6.55 (d, J = 15.8 Hz, 1H), 6.25 (dt, J =
15.8, 6.1 Hz, 1H), 4.5 (s, 2H), 4.15 (dd, J = 6.1, 1.2 Hz,
2H), 2.30 (s, 3H). 13C NMR (CDCl3, 100 MHz) δ: 138.2,
137.4, 133.8, 132.5, 129.2, 128.3, 127.7, 127.5, 126.3,
124.9, 72.0, 70.9, 21.3. HR-MS calcd. for C17H18O ([M]+):
238.1358; found: 238.1352.
4b R = C6H4-p-OMe
4c R = C6H4-p-Cl
6
7
5e
5c
6f
95
90
6g
Note: All reactions were carried out as per the general procedure de-
scribed in the Experimental section.
aIsolated yields.
3l
1
IR (neat) (cm–1): 1606. H NMR (CDCl3, 400 MHz) δ:
7.29–7.21 (m, 7H), 6.92 (t, J = 8.8 Hz, 2H), 6.51 (d, J =
16.1 Hz, 1H), 6.11 (dt, J = 16.1, 5.9 Hz, 1H), 4.50 (s, 2H),
4.10 (dd, J = 5.9, 1.5 Hz, 2H). 13C NMR (CDCl3, 100 MHz)
δ: 163.5, 138.1, 132.8, 131.2, 128.4, 127.9, 127.9, 127.7,
127.6, 125.7, 115.5, 72.3, 70.7. HR-MS calcd. for C16H15FO
([M]+): 242.1107; found: 242.1101.
short, in the case of alkynes both cycles I and II operate,
while in the case of allenes only cycle II operates.
In conclusion, the Pd(0)–benzoic acid catalyzed allylation
of alcohols and carboxylic acids with allenes and alkynes
provides a new route to allyl ethers and allyl carboxylates,
respectively. Although we proposed that a role of the
carboxylic acid in this catalytic system would be the forma-
tion of the hydridopalladium species (8), the precise nature
and a more detailed investigation on the catalytic species
should be carried out in future (10).
6c
IR (neat) (cm–1): 1735, 1598. 1H NMR (CDCl3,
400 MHz) δ: 7.35–7.11 (m, 5H), 6.56 (d, J = 15. 9 Hz, 1H),
6.20 (dt, J = 15.9, 6.3 Hz, 1H), 4.65 (dd, J = 6.3, 2.0 Hz,
2H), 2.27 (t, J = 7.5 Hz, 2H), 1.62–1.51 (m, 2H), 1.28–1.19
(m, 4H), 0.82 (t, J = 6.9 Hz, 3H). 13C NMR (CDCl3,
100 MHz) δ: 173.5, 136.2, 133.9, 128.5, 127.9, 126.5, 123.3,
64.8, 34.3, 31.4, 24.7, 22.4, 13.9. HR-MS calcd. for
C15H20O2 ([M + Na]): 255.1355; found: 255.1356.
Experimental section
General procedure for the addition of oxygen
pronucleophiles to allenes–alkynes
To a mixture of phenyl allene – 1-phenyl-1-propyne
(0.4304 mmol), alcohols – carboxylic acids (0.6456 mmol),
and tetrakis(triphenylphosphine)palladium (0.022 mmol) in
dry 1,4-dioxane (2 mL) was added acetic acid (0.043 mmol),
and the mixture was stirred at 100 °C for 12 h in a screw-
capped vial. The reaction mixture was then filtered through
a short silica gel column using ether as an eluent, and the fil-
trate was concentrated. The residue was purified by recy-
cling preparative HPLC (LC-918), using chloroform as an
eluent to give the allylated products. Structures of 3a–3e
(8h), 3g and 3h (8h), 3j (8h), 6a (9), and 6b (11) are known
in the literature. The characterization data for the newly syn-
6d
IR (neat) (cm–1): 1708, 1620. 1H NMR (CDCl3,
400 MHz) δ: 8.51 (s, 1H), 7.96 (dd, J = 8.6, 1.5 Hz, 1H),
7.78 (d, J = 8.0 Hz, 1H), 7.70 (t, J = 8.32 Hz, 2H), 7.43–
7.06 (m, 7H), 6.62 (d, J = 15.7 Hz, 1H), 6.30 (dt, J = 15.7,
6.3 Hz, 1H), 4.88 (dd, J = 6.3, 1.0 Hz, 2H). 13C NMR
(CDCl3, 100 MHz) δ: 166.3, 136.1, 135.4, 134.2, 132.3,
130.9, 129.2, 128.6, 128.5, 128.3, 128.1, 127.9, 127.6,
127.3, 126.5, 126.4, 125.1, 123.2, 65.6. HR-MS calcd. for
C20H16O2 ([M + Na]): 311.1045; found: 311.1043.
© 2005 NRC Canada

572
Can. J. Chem. Vol. 83, 2005
Fig. 1. A mechanism for the addition of O-nucleophiles to
allenes and alkynes.
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Nu
H 3C
R
3 or 6
4
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H-N u
2 or 5
OBz
H
R
Pd-OBz
H
Pd
H-Pd-OBz
II
I
H
R
8
H
7
9
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•
R
1
6e
IR (neat) (cm–1): 1732, 1598. 1H NMR (CDCl3,
400 MHz) δ: 7.27–7.15 (m, 15H), 6.49 (d, J = 15.9 Hz, 1H),
6.17 (dt, J = 15.9, 6.3 Hz, 1H), 4.50 (s, 1H), 4.72 (dd, J =
6.3, 1.2 Hz, 2H). 13C NMR (CDCl3, 100 MHz) δ: 172.1,
138.5, 136.1, 134.1, 128.6, 128.5, 128.4, 127.9, 127.2,
126.5, 122.8, 65.6, 57.1. HR-MS calcd. for C23H20O2 ([M +
Na]): 351.1354; found: 351.1356.
6f
IR (neat) (cm–1): 1732, 1606. 1H NMR (CDCl3,
400 MHz) δ: 7.24–7.12 (m, 12 H), 6.72 (d, J = 8.8 Hz, 2H),
6.41 (d, J = 15.8 Hz, 1H), 6.00 (dt, J = 15.8, 6.6 Hz, 1H),
4.96 (s, 1H), 4.66 (dd, J = 6.6, 1.0 Hz, 2H), 3.64 (s, 3H). 13
C
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NMR (CDCl3, 100 MHz) δ: 172.1, 159.4, 138.5, 133.9,
128.8, 128.5, 128.4, 127.7, 127.1, 120.4, 113.9, 65.9, 57.0,
55.2. HR-MS calcd. for C24H22O3 ([M + Na]): 381.1569;
found: 381.1584.
6g
IR (neat) (cm–1): 1735, 1633. 1H NMR (CDCl3,
400 MHz) δ: 7.32–7.25 (m, 4H), 6.59 (d, J = 15.9 Hz, 1H),
6.26 (dt, J = 15.9, 6.3 Hz, 1H), 4.72 (dd, J = 6.3, 1.2 Hz,
2H), 2.35 (t, J = 7.6 Hz, 2H), 1.69–1.56 (m, 2H), 1.36–1.27
(m, 4H), 0.89 (t, J = 6.8 Hz, 3H). 13C NMR (CDCl3,
100 MHz) δ: 173.4, 134.7, 133.6, 132.6, 128.7, 127.7, 124.0,
64.6, 34.3, 31.4, 24.7, 22.4, 13.9. HR-MS calcd. for
C15H19ClO2 ([M + O + Na]): 305.0914; found: 305.0915.
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Acknowledgements
N.T.P. thanks the Japan Society for the Promotion of Sci-
ence (JSPS) for a postdoctoral research fellowship.
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is also observed by other researchers, see: (a) B.M. Trost and
F. Rise. J. Am. Chem. Soc. 109, 3161 (1987); (b) B.M. Trost,
C. Jakel, and B. Plietker. J. Am. Chem. Soc. 125, 4438 (2003);
(c) K. Manabe and S. Kobayashi. Org. Lett. 5, 3241 (2003);
(d) for an excellent discussion related to this topic, see: B.M.
Trost. Chem. Eur. J. 4, 2405 (1998).
11. A.S. Gajare, M.S. Shingare, V.R. Kulkarni, N.B. Barhate, and
R.D. Wakharkar. Synth. Commun. 28, 25 (1998).
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