Novel Pd(II)- and Pt(II)-catalyzed regio- and stereoselective trans-hydroarylation of alkynes by simple arenes

Article abstract of DOI:10.1021/ja0005845

Efficient trans-hydroarylation of alkynes by simple arenes has been realized regio- and stereoselectively at room temperature in the presence of Pd(II) or Pt(II) catalysts and a mixed solvent containing trifluoroacetic acid (TFA). Various arenes undergo trans-hydroarylation selectively across terminal and internal C - C triple bonds - including those conjugated to CHO, COMe, CO₂H, and CO₂Et groups, affording kinetically controlled cis-arylalkenes predominantly in most cases, especially, in good yields for electron-rich arenes and activated alkynes. The formation of arene/alkyne 1/2 or 2/1 adducts as side products is dependent on the arenes' and alkynes' substituents, which can be suppressed in some cases by changing the catalyst, catalyst concentration, and reaction time. The Pt(II) system, PtCl₂/2AgOAc/TFA, shows lower catalytic activity than Pd(OAc)₂/TFA, but higher selectivity, giving higher yields of adducts at the same conversion. On the basis of several isotope experiments and control reactions, a possible mechanism involving electrophilic metalation of aromatic C - H bonds by in-situ-generated cationic Pd(II) and Pt(II) species leading to intermolecular trans-arylpalladation to alkyes has been discussed.

Full text of DOI:10.1021/ja0005845

7252
J. Am. Chem. Soc. 2000, 122, 7252-7263
Novel Pd(II)- and Pt(II)-Catalyzed Regio- and Stereoselective
trans-Hydroarylation of Alkynes by Simple Arenes
Chengguo Jia, Wenjun Lu, Juzo Oyamada, Tsugio Kitamura, Kenji Matsuda,
Masahiro Irie, and Yuzo Fujiwara*
Contribution from the Department of Chemistry and Biochemistry, Graduate School of Engineering,
Kyushu UniVersity, Hakozaki, Fukuoka, 812-8581, Japan
ReceiVed February 17, 2000
Abstract: Efficient trans-hydroarylation of alkynes by simple arenes has been realized regio- and stereose-
lectively at room temperature in the presence of Pd(II) or Pt(II) catalysts and a mixed solvent containing
trifluoroacetic acid (TFA). Various arenes undergo trans-hydroarylation selectively across terminal and internal
C-C triple bondssincluding those conjugated to CHO, COMe, CO2H, and CO2Et groups, affording kinetically
controlled cis-arylalkenes predominantly in most cases, especially, in good yields for electron-rich arenes and
activated alkynes. The formation of arene/alkyne 1/2 or 2/1 adducts as side products is dependent on the
arenes’ and alkynes’ substituents, which can be suppressed in some cases by changing the catalyst, catalyst
concentration, and reaction time. The Pt(II) system, PtCl2/2AgOAc/TFA, shows lower catalytic activity than
Pd(OAc)2/TFA, but higher selectivity, giving higher yields of adducts at the same conversion. On the basis of
several isotope experiments and control reactions, a possible mechanism involving electrophilic metalation of
aromatic C-H bonds by in-situ-generated cationic Pd(II) and Pt(II) species leading to intermolecular trans-
arylpalladation to alkynes has been discussed.
Introduction
triple bonds. This involves the coordination of an arene’s
substituent to a transition metal complex followed by oxidative
insertion into an ortho-aromatic C-H bond, resulting in the
addition to multiple C-C bonds (Scheme 1).2a These systems
are very useful in the activation of aromatic C-H bonds;
however, they are apparently limited to functionalized arenes
such as aromatic ketones at high reaction temperatures.
Catalytic activation of aromatic C-H bonds leading to useful
organic reactions such as new C-C bond formation is of
considerable interest for the chemical and pharmaceutical
industries, and remains a challenge to chemists.1 It would
provide simple, clean, and economic methods for making aryl-
substituted compounds directly from simple arenes since no
prefunctionalization such as halogenation is involved. The
catalytic systems for such a purpose have been sought for many
years, although there are many examples of stoichiometric
reaction of aromatic C-H bonds with transition metal
compounds.1b The few available catalytic systems1-3 based on
transition metals activate aromatic C-H bonds mainly through
the following routes:
(II) Electrophilic metalation of aromatic C-H bonds by Pd-
(II) complexes to give σ-aryl-Pd complexes (A in Scheme 2)
in oxidative coupling of arenes with olefins in acetic acid.3 The
σ-aryl-Pd complexes undergo cis-arylpalladation to C-C double
bonds followed by Pd â-hydride elimination to give trans-
arylalkenes in acetic acid (route a in Scheme 2). For this system,
in situ regeneration of Pd(II) from Pd(0) by oxidants is the
crucial step for the efficient catalysis, and turnover number
(TON) is still not high enough for possible industrial applica-
tions.
(I) Chelation-assisted insertion of low-valent metals such as
Ru(0)2a into aromatic C-H bonds in hydroarylation of C-C
(1) (a) Shilov, E.; Shul’pin, G. B. Chem. ReV. 1997, 97, 2879. (b)
Kakiuchi, F.; Murai, S. In ActiVation of UnreactiVe Bonds and Organic
Synthesis; Murai, S., Ed.; Springer: Berlin, 1999; pp 47-79. (c) Fujiwara,
Y.; Jintoku, T.; Takaki, K. CHEMTECH 1990, 636. (d) Dyker, G. Angew.
Chem., Int. Ed. 1999, 38, 1698. (e) Trost, B. M. Science 1991, 278, 1471.
(2) (a) Murai, S.; Kakiuchi, F.; Sekine, S.; Tanaka, Y.; Kamatani, A.;
Sonoda, M.; Chatani, N. Nature 1993, 366, 529. (b) Kakiuchi, F.;
Yamamoto, Y.; Chatani, N.; Murai, S. Chem. Lett. 1995, 681. (c) Hong,
P.; Cho, B.; Yamazaki, H. Chem. Lett. 1980, 507. (d) Hong, P.; Cho, B.;
Yamazaki, H.; Chem. Lett. 1979, 339. (e) Boese, W. T.; Goldman, A. S.
Organometallics 1991, 10, 782 (f) Christian, P. L.; Brookhart, M. J. Am.
Chem. Soc. 1999, 121, 6616.
(3) (a) Moritani, I.; Fujiwara, Y. Tetrahedron Lett. 1967, 1119. (b)
Fujiwara, Y.; Moritani, I.; Danno, S.; Teranishi, S. J. Am. Chem. Soc. 1969,
91, 7166. (c) Asano, R.; Moritani, I.; Fujiwara, Y.; Teranishi, S. Chem.
Commun. 1970, 1293. (d) Fujiwara, Y.; Asano, R.; Moritani, I.; Teranishi,
S. J. J. Org. Chem. 1976, 41, 1681. (e) Fujiwara, Y.; Takaki, K.; Taniguchi,
Y. Synlett 1996, 591. (f) Fuchita, Y.; Hiraki, K.; Kamogawa, Y.; Suenaga,
M.; Toggoh, K.; Fujiwara, Y. Bull. Chem. Soc. Jpn. 1989, 62, 1081. (g)
Lu, W.; Yamaoka, Y.; Taniguchi, Y.; Kitamura, T.; Fujiwara, Y. J.
Organomet. Chem. 1999, 586, 290. (h) Jia, C.; Lu, W.; Kitamura, T.;
Fujiwara, Y. Org. Lett. 1999, 1, 2097. (i) Jia, C.; Piao, D.; Oyamada, J.;
Lu, W.; Kitamura, T.; Fujiwara, Y. Science 2000, 287, 1992.
On continuing our search for efficient catalytic systems for
aromatic C-H bond activation and extending our coupling
reaction of arenes with olefins3 to the coupling with terminal
alkynes, we found the reaction of arenes with alkynes in the
presence of TFA as a solvent gives addition products instead
of the expected coupling product.3i
We report herein that efficient addition of arenes to terminal
and internal alkynes (route b in Scheme 2) has been realized
regio- and stereoselectively at room temperature in the presence
of Pd(II) or Pt(II) catalysts, and affording thermodynamically
unfavorable cis-arylalkenes predominantly in most cases. The
reaction may involve the formation of σ-aryl-Pd complexes
through metalation of aromatic C-H bonds by in-situ-generated
highly electrophilic Pd(II) and Pt(II) cationic species3,4 (possibly
as C in Scheme 2) in TFA. The reaction represents a useful
synthetic protocol to form cis-arylalkenes from simple electron-
rich arenes and alkynes in one step.
10.1021/ja0005845 CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/12/2000

trans-Hydroarylation of Alkynes by Simple Arenes
J. Am. Chem. Soc., Vol. 122, No. 30, 2000 7253
Table 1. Pd-Catalyzed Addition of 1a to Ethyl Propiolatea
Scheme 1. Chelation-Assisted Ru(0)-Catalyzed Addition
yield (%)b
entry
catalyst (mol %)
Pd(OAc)2 (0.1)
Pd(OAc)2 (1)
Pd(OAc)2 (5)
Pd(OAc)2 (5)
time (h) (Z)-2a (E)-2a 4a
1
2
3
4
180
45
27
70
48
45
68
72(56)
26
<3
58
4
6
15
5
3
7
5
2
(31)
3
6
5c Pd(OAc)2 (1)
Scheme 2. Pd-Catalyzed C-C Bond Formation Reactions
Involving Electrophilic Metalation of Aromatic C-H Bonds
6
Pd(OAc)2 (1) +
P[C6H3(OMe)2]3 (1)
70
5
7c Pd(OAc)2 (1) + PPh3 (4)
8
9
45
48
48
48
48
48
48
48
60
41
5
8
68
36
69
<3
10
trace
trace
trace
trace
3
3
5
Pd(PPh3)4 (2)
Pd (5%)/carbon (5)
Pd(acac)2 (1)
PdCl2 (1)
Pd(O2CCF3)2(PPh3)2 (1)
10
11
12
2
<1
6
13d Pd(O2CCF3)2(PPh3)2 (1)
trace
trace
14e PdCl2 (1) + AgO3SCF3 (2)
15
none
a Reaction conditions: 1a (30 mmol), ethyl propiolate (5 mmol),
TFA (4 mL), rt. b GC yield (isolated yields in parentheses) based on
the alkyne. c 10 mmol of the arene employed. d AcOH (4 mL) + TFA
(0.5 mL) used as the solvent and CF3CO2Na (0.025 mmol) added.
e CH2Cl2 (4 mL) + CF3SO3H (0.5 mL) used as the solvent.
Optimization of Reaction Conditions. Prior to surveying
the scope of this addition reaction, the reaction conditions were
optimized and results are listed in Table 1. Pd(II) catalysts such
as Pd(OAc)2, Pd(O2CCF3)(PPh3)2, and Pd(acac)2 showed higher
catalytic activity than Pd(0) catalysts such as Pd/carbon and
Pd(PPh3)4 (see entries 2, 8, 9, 10, and 12 in Table 1). The
reaction was enhanced greatly by increasing the amount of Pd-
(OAc)2, (from 0.1% to 1%, entries 1 and 2 in Table 1). When
it was increased to 5%, the 2/1 adduct 4a was obtained as the
main product (entry 4). This means whether the reaction gives
1/1 or 2/1 adducts as the main product can be controlled by the
concentration of Pd(OAc)2. Higher concentration of Pd(II)
facilitates the overall reaction. The tris(2,6-dimethoxyphenyl)-
phosphine was added (1 equiv to Pd, entry 6) to the system in
order to improve the addition reaction,5c,6 but very little effect
was found. However, adding more phosphine (4 equiv to Pd,
entry 7) decreased the catalytic activity of the system, presum-
ably because of blocking of the coordination sites of Pd(II).
The best results were obtained with Pd(OAc)2/TFA and Pd(O2-
CCF3)2(PPh3)2/TFA systems (entries 2 and 12). The attempts
to reduce the amount of TFA used in the reaction or to use
other Pd(II) cationic system such as PdCl2/CF3SO3Ag only
resulted in low yields (entries 13 and 14). Addition of a small
amount of CH2Cl2 (one-fourth to TFA by volume) to the reaction
system to improve the solubility of reactants had no detrimental
effect on the reaction.
Scheme 3. Pd-Catalyzed Reaction of p-Dimethoxybenzene
1a with Ethyl Propiolate in TFA
Results and Discussion
In the course of our studies of oxidative coupling of arenes
with olefins, the possibility to extend the coupling reaction to
terminal alkynes was investigated by reacting p-dimethoxyben-
zene (1a) with ethyl propiolate in the presence of an oxidant
and a catalytic amount of Pd(OAc)2 in TFA (Scheme 3). Instead
of the expected coupling product ethyl 3-(2,5-dimethoxyphenyl)-
propiolate, the reaction gave (2Z)-ethyl 3-(2,5-dimethoxyphen-
yl)-2-propenoate (Z-2a) (JH-H ) 12.3 Hz) as the main product,
together with small amounts of the corresponding E-isomer (E-
2a) (JH-H ) 16.2 Hz) and an arene/alkyne 2/1 adduct, ethyl
3-bis(2,5-dimethoxyphenyl)propionate (4a). Apparently, the
compounds Z-2a and E-2a (1/1 adducts) resulted from monoad-
dition of the arene to the alkyne, and 4a resulted from
subsequent addition of another molecular arene to 2a (this has
been confirmed by addition reaction of arenes to alkenes in
Table 5). The addtion reaction proceeds smoothly regardless
of whether oxidants such as t-BuOOH and benzoquinone were
employed. However, the reaction did not occur without either
TFA or Pd(OAc)2.
Hydroarylation of Terminal Acetylenes. The scope and
generality of this reaction have been explored first using various
commercially available arenes and several terminal acetylenes
(Scheme 4, Tables 2 and 3). The addition of the arenes to ethyl
(5) (a) Tsuji, J. Palladium Reagents and Catalysts; John Wiley & Sons:
New York, 1995; pp 1-18. (b) Carri, W.; Candiani, I. Acc. Chem. Res.
1995, 28, 2. (c) Trost, B. M.; Sorum, M. T.; Chan, C.; Harms, A. E.; Ruhter,
G. J. Am. Chem. Soc. 1997, 119, 698. (d) Little, A. F.; Fu, G. C. J. Org.
Chem. 1998, 64, 10. (e) Tao, W.; Nesbitt, S.; Heck, R. F. J. Org. Chem.
1990, 55, 66.
(4) (a) Brainard, M. W.; Nutt, W. R.; Lee, T. R.; Whitesides, G. M.
Organometallics 1988, 7, 2379. (b) Clark, F. R. S.; Norman, R. O. C.;
Thommas, C. B.; Willson, J. S. J. Chem. Soc., Perkin Trans. 1 1974, 1289.
(c) White, S.; Bennett, B. L.; Roddick, D. M. Organometallics 1999, 18,
2536. (d) Peters, R. G.; Shannon, S.; Roddick, D. M. Organometallics 1998,
17, 4493. (e) Holtcamp, M. W.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem.
Soc. 1997, 119, 848. (f) Swang, O.; Blom, R.; Ryan, O.; Faegri, K. J. Phys.
Chem. 1996, 100, 17334.
(6) (a) Zeijden, A.; Bosch, H. W.; Berke, H. Organometallics 1992, 11,
563. (b) Zargarrian, D.; Alper, H. Organometallics 1993, 12, 712. (c) Cacchi
S.; Fabrizi, G.; Marinelli F.; Moro L.; Pace P. Tetrahedron 1996, 10225.
(d) Cacchi, S.; Felici, M.; Pietroni, B. Tetrahedron Lett. 1984, 25, 3137.
(e) Cacchi, S.; Fabrizi, G.; Marinelli, F.; Moro, L.; Pace, P. Synlett 1997,
1367. (f) Yanagihara, N.; Lambert, C.; Iritani, K.; Utimoto, K.; Nozaki, H.
J. Am. Chem. Soc. 1986, 108, 2753. (g) Lu, X.; Zhu, G.; Ma, S. Tetrahedron
Lett. 1992, 33, 7205.

7254 J. Am. Chem. Soc., Vol. 122, No. 30, 2000
Jia et al.
a
Table 2. Pd- and Pt-Catalyzed Addition of Arenes to Ethyl
Table 3. Pd-Catalyzed Addition of Arenes to 3-Butyne-2-one
Propiolatea
a General procedure was followed: arenes (10 mmol), alkyne (5
mmol), TFA (4 mL), and CH2Cl2 (1 mL), rt. b Isolated yield (GC yield
in parentheses) based on acetylene. c Five times of reactants and solvents
employed except the catalyst. d Arene (5 mmol) and alkyne (10 mmol)
used, and the yield determined by 1H NMR and based on arene. e Arene
(5 mmol) and alkyne (7 mmol) used, and the yield based on arene was
1
determined by H NMR.
Scheme 4. Hydroarylation of Terminal Alkynes
a General procedure was followed: arene (10 mmol), ethyl propiolate
(5 mmol), Pd(OAc)2 (0.05 mmol), TFA (4 mL), and CH2Cl2 (1 mL) at
room temperature. b Isolated yield (GC yield in parentheses) based on
the acetylene. c PtCl2 (0.25 mmol) + AgOAc (0.5 mmol) used as
catalyst. d Yield determined by 1H NMR spectrum. e Arene (30 mmol)
added. f Arene (3.4 mmol) and alkyne (5 mmol) used, and the yield
based on the arene. g Arene (3.4 mmol) and alkyne (10 mmol) used,
and the yield based on the arene.
propiolate gave cis-adducts, (2Z)-ethyl 3-aryl-2-propenoates 2a-
c,e-i (JH-H ) 11.7 ( 0.6 Hz), predominantly in most cases
(entries 1-15 in Table 2). The corresponding trans-isomers as
the minor product were isolated (entry 15 in Table 2) or iden-
yne 2/1 adducts, ethyl 3-bisarylpropionates 4b,c, were found
to be the main products in some cases (entries 14 and
16 in Table 2).
1
tified in the mixture of adducts by H NMR (JH-H ) 15.9-
16.5 Hz) in some cases (entries 4 and 14 in Table 2). Arene/al-
kyne 1/2 adducts, (2E,4Z)-4-(ethoxycarbonyl)-5-aryl-2,4-pentadi-
enoates such as 3a-c, as the minor products were observed in
the reaction (e.g., entries 1, 6-9 in Table 2), and also arene/alk-
The reaction exhibited very good chemiselectivity with
unprotected OH and Br substituents in arenes, all proving to be
compatible (entries 10-13). A coumarin was obtained from the
reaction of p-tert-butyl phenol with ethyl propiolate (entries 10

trans-Hydroarylation of Alkynes by Simple Arenes
J. Am. Chem. Soc., Vol. 122, No. 30, 2000 7255
Scheme 5. Formation of Coumarins
Scheme 6. Formation of Dienes
and 11 in Table 2), apparently resulting from first addition of
the phenol to the alkyne followed by cyclization via ester
exchange (Scheme 5).7 When the ortho-positions of a phenol
were occupied by two methyl groups, the reactions gave a 1/1
adduct such as 2h (entry 12 in Table 2). The reaction of mesityl
bromide with ethyl propiolate afforded 1/1 adduct (2Z)-ethyl
3-(2,4,6-trimethyl-3-bromophenyl)-2-propenoate (entry 13 in
Table 2). No corresponding debrominated adduct or debromi-
Figure 1. Time dependence of monoaddition vs diaddition in the
reaction of 3,4-methylenedioxytoluene (2 equiv) with 3-butyn-2-one
in the presence of 1% Pd(OAc)2 in TFA at room temperature (GC yield
based on the alkyne).
substitution (para >75%): ethyl 3-bis(4-methoxyphenyl)pro-
pionate (4b) or 4-bis(4-methoxyphenyl)butan-2-one (6b), re-
spectively (entry 14 of Table 2 and entry 11 of Table 3).
In some cases, the reaction can be switched from giving
mainly 1/1 to 2/1 arene/alkyne adducts by controlling the
reaction time (entries 8 and 9 in Table 3) and the concentration
of Pd(OAc)2 (entries 2 and 4 in Table 1). Also the formation of
1/2 adduct such as 3a can be totally suppressed by employing
PtCl2/2AgOAc as catalyst (entry 2 in Table 2). The Pt(II)
catalyst showed lower activity compared with Pd(II) catalysts,
but better selectivity.
1
nated arene was isolated or observed by H NMR from the
reaction mixture, suggesting that the catalytic cycle may not
involve Pd(0) species.
A diene, (2Z)-ethyl 3-{2,4,6-trimethyl-3-[(Z)-2-ethoxycar-
bonylethylenyl)]phenyl]}propenoate (2f), was obtained from the
reaction of (2Z)-ethyl 3-mesitylpropenoate (2e) with 1.5 equiv
of ethyl propiolate (entry 5 in Table 2) or directly from the
reaction of mesitylene with ethyl propiolate (entry 8 in Table
2). This provides a new and simple route to the aryldienes from
simple arenes and alkynes (Scheme 6), and similar compounds
could be prepared from diiodoarenes by the Heck reaction.5e
The reactions of pentamethylbenzene with phenylacetylene
gave a Markovnikov-type adduct 1-pentamethylphenyl-1-phen-
ylethylene 7 as the only isolated product (eq 3 in Scheme 4).
No any other isomer was observed by analysis of the reaction
The reaction of the arenes with 3-butyn-2-one afforded
exclusively trans-adducts, (3E)-4-aryl-3-buten-2-ones 5a-e
(J
) 16.5 ( 0.3 Hz), as the only products in most cases
1
H-H
mixture with GC and H NMR.
(entries 1-8 and 10 in Table 3 and eq 2 in Scheme 4). The
arene/alkyne 2/1 adducts, 4-bisaryl-butan-2-ones 6a,b, were
found in the cases where alkoxyarenes were used (entries 8, 9,
and 11). The formation of arene/alkyne 1/1 to 2/1 adducts
occurred in a sequential fashion; further addition of the arene
to 1/1 adducts gave the 2/1 adducts as shown in Figure 1.
From the results shown in Tables 2 and 3, one can see that
the present reaction gives low to high yields of alkyne
hydroarylation products, depending on the reactivity of areness
the yield increases with increasing number of electron-donating
groups (e.g., compare entries 1-8 in Table 3). The electron-
rich arenes (having more than two electron-donating substitu-
ents) give good yields in general, showing characteristics of
electrophilic substitution.2,3,8 Also, the yield of 1/1 adducts can
be improved by using an excess of alkynes (entry 7 in Table 2,
and entries 5 and 7 in Table 3). It is also very interesting to
find that the steric hindrance of arenes is not a problem for this
reaction; therefore, the reaction of pentamethylbenzene is very
fast, affording adducts in the highest yield (entries 1-4 of Table
2 and entries 1-3 of Table 3). This is in marked contrast to
other Pd-catalyzed reactions such as the Heck reaction in which
the steric hindrance is a big obstacle.5a,d The present reaction is
A close comparison of the adducts (in Tables 2 and 3) and
the related arenes and alkynes reveals that whether the reaction
gives 1/1 or 2/1 adducts as the main products depends mainly
on the arenes’ substituents. The arenes having alkoxyl substit-
uents generally tend to proceed to 2/1 arene/acetylene adducts,
especially for less hindered arenes such as anisole. The reaction
of anisole with either ethyl propiolate or 3-butyn-2-one affords
mainly the 2/1 arene/alkyne adducts with methoxyl in the para-
(7) For related catalytic C-H bond activation reactions involving
phenolic functions as a directing group, see: (a) Kokubo, K.; Matsumasa,
K.; Nomura, M. J. Org. Chem. 1997, 62, 4564. (b) Trost, B. M.; Toste F.
D. J. Am. Chem. Soc. 1996, 118, 6305.
(8) March, J. AdVanced Organic Chemistry, 4th ed.; John Wiley &
Sons: New York, 1992; pp 501-521.

7256 J. Am. Chem. Soc., Vol. 122, No. 30, 2000
Jia et al.
a
Table 4. Transition Metal-Catalyzed Addition of Arenes to Internal Alkynes
a General procedure is followed: Arene (10 mmol), alkyne (5 mmol), TFA (4 mL), CH2Cl2 (1 mL), r.t. Pd, Pt, Rh, Ir, Ni, and Ru refer to
Pd(OAc)2, PtCl2/2AgOAc, Rh2(OAc)4, IrCl3/3AgOAc, Ni(OAc)2, and RuCl3/3AgOAc, all 0.25 mmol, respectively. b Isolated yield (GC yield in
c
parentheses) based on the alkyne. Trifluoroacetic anhydride (5 mmol) was added.
dictated by electronic effects of the substituents in arene rather
than steric effects.
we tested several other transition metals such as Rh(III), Ir-
(III), Ru(III), and Ni(II) in the reaction of pentamethylbenzene
with ethyl phenylpropiolate in order to screen catalytic systems
by comparison with Pd(II) and Pt(II) system (entries 19-26 in
Table 4). (2Z)-Ethyl 3-(pentamethylphenyl)cinnamate (19) and
corresponding hydrolyzed (2Z)-3-(pentamethylphenyl)cinnamic
acid (16) were isolated upon usual workup (entry 19 in Table
4). Compound 19 was hydrolyzed completely to 16 with
prolonged reaction time (entry 20 in Table 4). The results
summarized in Table 4 indicate that Pd(OAc)2 and PtCl2/AgOAc
as catalysts are superior to other transition metal systems (entries
19-26 in Table 4). Pd(OAc)2 has been found to be the most
active catalyst. The reaction with PtCl2/AgOAc is slower (slower
conversion of alkynes) than that with Pd(OAc)2 (entries 20 and
21), but gave higher yields at the same conversion levels (entries
7-16 in Table 4). The catalytic activity of the transition metals
decreases in the order Pd(II) > Pt(II) . Rh(III) > Ir(III) >
The efficiency of this reaction can be seen from the reaction
of pentamethylbenzene with 3-butyn-2-one in the presence of
0.02 mol % Pd(OAc)2 (entry 3 in Table 3). This reaction gave
(3E)-4-(pentamethylphenyl)-3-buten-2-one (5a) in 90% GC
yield, with a 4500 TON, in 96 h.
Hydroarylation of Internal Alkynes. The scope and gen-
erality of this reaction also have been explored by the reaction
of various commercially available internal alkynes with several
arenes (Table 4). Here we focus on the variety of alkynes which
bear functional groups such as CHO, COMe, CO2H, etc., all
proving to be compatible. The reaction affords thermodynami-
cally unfavorable cis-arylalkenes predominantly in most cases
(entries 3-17, 19-26), giving good yields of adducts especially
over the PtCl2/2AgOAc system.
Inspired by the higher selectivity of the PtCl2/2AgOAc system
(entries 1 and 2 of Table 2 and also entries 1-16 in Table 4),

trans-Hydroarylation of Alkynes by Simple Arenes
J. Am. Chem. Soc., Vol. 122, No. 30, 2000 7257
Scheme 7. The Possible Mechanism
and stereoselective fashion offers a valuable and unique method
for the preparation of cis-arylalkene, which cannot be easily
accessed by other reactions. The understanding of the effective-
ness of this reaction requires an understanding of the mechanism.
Mechanistic Considerations. The experimental findings and
their implications discussed already give us some information
about the possible mechanism of this reaction, which has been
outlined in Scheme 7.
Figure 2. Crystal structure of 12. Selected bond length (Å) and angles
(deg): C1-C2 1.341(5), C1-C9 1.491(5), C1-C15 1.496(5), C2-
C3 1.468(5), C9-C1-C2 120.7(3), C9-C1-C15 116.0(3), C2-C1-
C15 123.3(3), C1-C2-C3 131.3(4).
Ni(II), Ru (III), in accordance with the activity difference in
electrophilic metalation of aromatic C-H bonds by theses metal
ions.1a,9
(A) Formation of σ-Aryl-Pd Complexes via Electrophilic
Metalation of Aromatic C-H Bonds. It seems reasonable for
σ-arylpalladium complexes to be involved in the present reaction
on the basis of the reactivity order of both transition metals
and arenes in the present reaction (Tables 2-4). As mentioned
already, the reactivity order of transition metals in the present
reaction is consistent with the reactivity order of electrophilic
metalation of aromatic C-H bonds by these metal ions.1a,9
Formation of such σ-arylpalladium complexes also has been
partially confirmed by 1H NMR spectra with the disappearance
of the aryl hydrogen of pentamethylbenzene in the reaction with
1 equiv of Pd(OAc)2 in TFA in a few minutes at room
temperature. Such aryl-Pd(II) complexes have been known as
intermediates in the coupling of arenes with olefins, and in the
coupling of arenes with arenes.3f Similar aryl-Pt(II) complexes
have been synthesized from cationic Pt(II) complexes.4a,d The
facile formation of such Pd-aryl complexes (such as B in
Scheme 2) in TFA has been demonstrated by the coupling
reaction of arenes with arenes,4b and also by formation of
aromatic acid from simple arenes with carbon monoxide (route
c in Scheme 2),3g both at room temperature. Unfortunately, the
attempt to obtain the isotope effect in the reaction of mesitylene
plus mesitylene-d12 with 3-butyn-2-one in TFA was thwarted
by a rapid aryl H/D exchange, even in the absence of Pd(II)
The regio- and stereochemistry of all adducts (in Tables 2-4)
were unambiguously established on the basis of chemical shifts
and coupling constants in 1H NMR spectra, and differential NOE
experiments. The structures of 1-(pentamethylphenyl)-1-phenyl-
2-phenylethylene 12 (Figure 2) and 1-(pentamethylphenyl)-1-
phenylpropene 13 (see Supporting Information) were further
confirmed to be in the (Z)-configuration by X-ray crystal
structure analysis.
A close examination of all the results listed in Tables 2-4
reveals that the nature of the substituents in alkyne has a
considerable effect on the regiochemistry of the reaction
products and also on the reactivity of alkynes. The alkynes
conjugated to an electron-withdrawing group such as CHO,
CO2H, COMe, or CO2Et act as good acceptors of aryl
nucleophiles, providing â-aryl-substituted alkenes exclusively
and being cis-alkenes predominantly in most cases. The reaction
of the alkynes conjugated to a phenyl group provides the
1-arylalkenes with the aryl group substituted at the 1-position
selectively (eq 3 in Scheme 4 and entry 11 in Table 4). No
other stereo- or regioisomers were isolated or observed from
the reaction mixture. The regiochemistry of this reaction is
dominated by electronic effects of the substituents in alkyne
rather than steric effects, and similar to the effect of the
substituents in arenes. The reaction with internal alkynes is
slower than that with terminal alkynes. For instance, the
reactivity of acetylenes RCtCCO2Et decreases with the sub-
stituent R in the order R ) H > Ph > Me.
A possible side reaction is the addition of trifluoroacetic acid
to C-C triple bonds of alkynes followed by hydrolysis to give
ketones.6g,10 This has been also observed in a few cases under
our reaction conditions, especially in the absence of the arene
or in the presence of inactive arenes, while in the absence of
the Pd catalyst no such side reaction occurs.
Pd(0)-catalyzed hydroarylation of alkynes with aryl halides
in the presence of reductants such as sodium formate reported
by Cacchi et al.6c-e provides a mixture of regio- and stereo-
isomers in general. The present catalytic hydroarylation of
terminal or internal alkynes by simple arenes in a highly regio-
8
catalysts.
The present hydroarylation reaction fails in a hydrocarbon
solvent (hexane), ethereal solvent (THF), halogenated solvent
(CH2Cl2), or acetic acid, even in the presence of catalytic
amounts of TFA and Pd(O2CCF3)2. A reasonable explanation
is that the reaction requires highly cationic Pd(II) species to
facilitate the formation of stable σ-aryl-Pd complexes.4 It has
been proved that the acid loss from Pd or Pt trifluoroacetate
complexes is irreversible under the neutral or less acidic
conditions;4c thus, the presence of a large excess of TFA is
necessary to keep cationic Pd(II) species. The loose interaction
of labile trifluoroacetate anion with Pd(II) makes it highly
cationic and therefore highly active in the electrophilic substitu-
tion of arenes. Also, a strong acid like TFA would facilitate
the hydrolysis of vinyl-M complexes to give the final products.6a
(B) Formation of Vinyl-Pd(II) Species. The reaction of
pentamethylbenzene with two alkynes carried out in CF3CO2D
as the solvent (eqs 1 and 2 in Scheme 8) indicates that deuterium
atoms have been incorporated into adducts as vinyl atoms at
(9) Shul’pin, G. B. Organic Reactions Catalyzed by Metal Complexes;
Nauka: Moscow, 1988.
(10) Simonetta, M.; Gavezzotti, A. In The Chemistry of the Carbon-
Carbon Triple Bond; Patai, S., Ed.; John Wiley & Sons: New York, 1978;
Part 1, pp 1-73.

7258 J. Am. Chem. Soc., Vol. 122, No. 30, 2000
Jia et al.
Scheme 9. Formation of the Arene/Alkyne 1/2 Adducts
Scheme 8. Isotope Experiments (Ar ) Pentamethylphenyl)
incorporation at the â position may originate from the H/D
exchange of the terminal alkyne in CF3CO2D, indicating that
such an exchange reaction is very slow compared with the
hydroarylation reaction under the present reaction conditions.
This also implies that the present catalytic reaction does not
involve the insertion of Pd(II) into the C-H bonds of terminal
alkynes. Furthermore, the involvement of vinylidene Pd com-
plexes is not the case in the present reaction.5,13
The reaction of benzene-d6 with an internal alkyne (diphe-
nylacetylene) in TFA (undeuterated) gave the adduct 10-D5 with
almost no deuterium atoms incorporated in the vinyl positions
and almost 100% deuterium substitution at a phenyl group (m/z
M+• ) 261) (eq 3 in Scheme 8). This reveals that the vinyl
hydrogens originate completely from the solvent TFA.
It may also be possible that the vinyl deuteriums of 2b-D
could result from H/D-exchange of the vinyl hydrogens of 2b
in CF3CO2D in the presence of Pd(II) catalysts. The vinyl H/D
exchange has been excluded by a control reaction (eq 4 in
Scheme 8), which was carried out by stirring a solution of 2b
in CF3CO2D in the presence of 5% Pd(OAc)2 at room temper-
ature for 24 h, since no vinyl H/D exchange was observed by
1H NMR.
All these results provide very strong evidence for formation
of the vinyl-Pd(II) complexes. Further very strong evidence for
such vinyl-Pd(II) complexes is the formation of the 1/2 arene/
alkyne adducts such as 3a-D as a side product (eq 1 in Scheme
8). The impossiblity of the formation of 3a-D from 2b has been
proved by another control reaction, shown as eq 5 in Scheme
8. The only possible route to 3a-D is cis-addition of the vinyl-
Pd intermediate to another molecular alkyne, affording the
adduct 3a-D (JH-H ) 16.5 Hz) after hydrolysis by TFA (Scheme
9).
(C) trans-Addition of Aryl-Pd Complexes across the C-C
Triple Bond. On the basis of the generally accepted concept,
most transition metal-mediated carbometalation to C-C multiple
bonds proceeds in a cis-fashion, giving trans-adducts,5 but still
there are some reports of net trans-additions of M-H or M-R
across C-C triple bonds.2d,6 In some cases, trans-addition is
the preferred mode.6a Also, Pd(II)-catalyzed predominant trans-
addition of carboxylic acids to alkynes has been reported in an
inter- or intramolecular fashion.6f,g The occurrence of trans-
addition is not well understood, while the cis-addition is believed
to occur by a concerted process where the M-R bond
approaches the alkyne in a coplanar manner.11 The present
hydroarylation affords cis-arylalkene predominantly in most
cases, indicating the addition of aryl and hydrogen groups across
C-C triple bonds in a trans-fashion.
Figure 3. Part of 1H NMR spectra of 2b-D and 3a-D (Ar )
pentamethylphenyl).
1
the R positions predominantly, on the basis of H NMR and
GC/MS spectra of the adducts by comparison with those of the
adducts from TFA (undeuterated) as the solvent. Only traces
of the â-deuterium-incorporated adducts were detected in the
reaction of pentamethylbenzene with ethyl propiolate by GC/
1
MS. Two typical H NMR spectra for deuterium-containing
adducts 2b-D and 3a-D in eq 1 are shown in Figure 3. The
adduct 5a-DD (from the reaction of pentamethylbenzene with
3-butyn-2-one in CF3CO2D) with deuteriums incorporated at R
and â vinylic positions at different extents has been observed,
being 50% at R and 6% at â (eq 2 in Scheme 8). The GC/MS
spectra confirmed the formation of one- and two-deuterium-
incorporated adducts (m/z M+• ) 217, 218). The deuterium
The striking resemblance between our present trans-hy-
droarylation of alkynes and the stoichiometric trans-addition
of (CO)2(NO)(PMe3)2W-H to the same alkynes (Scheme 10)
(11) Thorn, D. L.; Hoffmann, R. J. Am. Chem. Soc. 1978, 100, 2079.
(12) Goldfinger, M. B.; Crawford, K. B.; Swager, T. M. J. Am. Chem.
Soc. 1997, 119, 4578.
(13) Bruneau, C.; Dixneuf, P. H. Acc. Chem. Res. 1999, 32, 311.

trans-Hydroarylation of Alkynes by Simple Arenes
J. Am. Chem. Soc., Vol. 122, No. 30, 2000 7259
Table 5. Pd-catalyzed Addition of Arenes to Alkenesa
Scheme 10. The Trans-Addition of the Tungsten Hydride to
Ethyl Phenylpropiolate and Thermal Isomerization6a
b
Scheme 11. Possible Route for Formation of Trans-Alkenes
reported by Berke et al.,6a from the reactivity order of different
alkynes to the regio- and stereochemistry of final products,
suggests that the arylpalladium complexes may undergo trans-
arylpalladation across C-C triple bonds to give the vinyl-Pd-
(II) complexes in a way similar to the trans-hydrotungstenation
in Scheme 10. The protonation of these vinyl-Pd(II) complexes
by TFA gives the final adducts. An overall possible mechanism
is shown in Scheme 7.
The cis-arylalkenes offered by the present reaction are
thermodynamically unfavorable; they are formed through trans-
hydroarylation of alkynes preferentially under kinetically con-
trolled conditions. They may undergo thermal isomerization
through a dipolar Pd intermediate D as suggested by Alper et
al.6 to give trans-arylalkenes in some cases (Scheme 11); this
may be the case in the reaction of arenes with 3-butyn-2-one.
This is the possible reason why the reactions of pentamethyl-
benzene with 4-phenyl-3-butyn-2-one and 3-butyn-2-one give
the cis-adduct 14 (entries 12 and 13 in Table 4) and the trans-
adduct 5a (entries 1-3 in Table 3), respectively. trans-
Arylpalladation of alkynes followed by thermal isomerization
may give thermodynamically favorable trans-arylalkenes such
as 5a.
a General procedure was followed: arene (5 mmol), alkene (5 mmol),
Pd(OAc)2 (0.05 mmol), TFA (3.5 mL), and CH2Cl2 (1.5 mL), at rt for
10 h. b Isolated yield based on the alkene.
Scheme 12. Possible Involvement of Carbocations in the
Addition of Alkoxyarenes to Alkenes
(D) The Formation of 2/1 Arene/Alkyne Adducts. As
mentioned already, the arenes having only alkoxyl substituents
tend to give 2/1 arene/alkyne adducts (see Tables 2 and 3). To
clarify the possible reasons for this, several reactions of
substituted cinnamates with arenes have been performed in order
to see the effects of the substituents in both arenes and alkenes
(Table 5). The addition of arenes to alkenes occurs only when
both arenes and cinnamates have alkoxyl substituents (entries
1-3 in Table 5), indicating that the presence of an alkyloxyl in
arenes and phenylethylenyl moiety of alkenes is critical to the
success of the reaction (Table 5). These results suggest the
possible involvement of carbocations in the reactions (Scheme
2). The electron-rich alkoxylphenyl group provides resonance
stabilization of the positive charge at the cations.12
Therefore, the possible mechanism has been outlined in
Scheme 7. The formation of σ-aryl-Pd complexes from elec-
trophilic metalation of aromatic C-H bonds by cationic Pd(II)
species would be followed by coordination of alkynes to Pd.
Also it is possible that the formation of σ-arylpalladium
complexes and the coordination of alkynes to Pd could occur
at the same time. trans-Insertion of C-C triple bonds to the
σ-aryl-Pd bonds would result in the vinyl-Pd complexes, and
the arene/alkyne 1/1 adduct would be released upon protonation
of the vinyl-Pd complexes. The possible involvement of Pd-
(II)-vinylidene and Pd(II)-allenyl complexes could be excluded
because of the nature of the adducts.13,14 The possible involve-
ment of the vinylcarbocations from alkynes (and subsequent
electrophilic substitution of arenes) in the present reaction cannot
be excluded, although we did not have enough evidence to
confirm it.
In summary, we have found a selective addition reaction of
simple arenes to the activated carbon-carbon triple bonds with
selective aromatic C-H bond cleavage in the presence of
catalytic amounts of palladium, platinum, or other transition
metal catalysts under mild conditions. A valuable and unique
character of the present reaction is the trans-addition of aryl
and hydrogen groups across C-C triple bonds (although the
specific mechanism of such addition is not necessarily clear),
giving predominantly cis-3-aryl-R,â-unsaturated acids, esters,
ketones, and aldehydes, since the known catalytic reactions
normally provide thermodynamically favorable trans-isomers.5,10
The present reaction constitutes a convenient and useful method
for the synthesis of cis-arylalkenes in one step from com-
mercially available alkynes and electron-rich arenes, and should
find wide applications in organic synthesis.
(14) Chen, J. T.; Hsu, R. H.; Chen, A. J. J. Am. Chem. Soc. 1998, 120,
3243.

7260 J. Am. Chem. Soc., Vol. 122, No. 30, 2000
Jia et al.
NMR (75 MHz, CDCl3): δ 14.01, 55.66, 55.95, 60.06, 111.25, 115.53,
115.97, 120.18, 124.63, 138.33, 151.50, 152.72, 166.19. IR (neat, cm-1):
1710 (CdO). Anal. Calcd for C13H16O4: C, 66.09; H, 6.84. Found:
C, 65.84; H, 6.78.
Experimental Section
General. All the reactions were performed in dry Pyrex tubes, and
only under argon atmosphere when Pd(0) catalysts were used. All
starting materials and solvents were used as received without further
purification unless otherwise indicated. 1H NMR and 13C NMR spectra
were recorded on a JEOL JNM-AL 300 FT-NMR (300 MHz) in CDCl3
solution (TMS as an internal standard). The methyl protons of sodium
2,2-dimethyl-2-silapentane-5-sulfonate in a sealed tube containing D2O
were used as an internal standard when the reaction mixture (containing
(2E)-Ethyl 3-(2,5-Dimethoxyphenyl)propenoate (E-2a). Light pink
1
oil. H NMR (300 MHz, CDCl3): δ 1.32 (t, J ) 7.2 Hz, 3H, CH3),
3.77 (s, 3H, OCH3), 3.82 (s, 3H, OCH3), 4.25 (q, J ) 7.2 Hz, OCH2),
6.49 (d, J ) 16.2 Hz, 1H, vinyl), 6.9 (m, 2H, aryl), 7.16 (d, J ) 2.7
Hz, 1H, aryl), 7.96 (d, J ) 16.2, 1H, vinyl). 13C NMR: δ 14.19, 55.53,
55.84, 60.19, 112.24, 113.06, 116.85, 118.78, 123.78, 139.56, 152.62,
153.33, 167.16. 1H NMR and 13C NMR spectra are in good agreement
with the reported values of chemical shifts and coupling constants.15a,d
1
TFA) was directly subjected to H NMR analysis. IR spectra were
recorded either neat or as a film on sodium chloride plates or as KBr
pellets on a HORIBA FT-200 spectrophotometer. Melting points were
measured with YANACO micro melting apparatus and are uncorrected.
The GC analysis was performed on a Shimadzu GC-8A using a 2.0-m
× 3-mm-diameter stainless steel column packed with Unisole 10T +
H3PO4 (5 + 0.5)% on 80-100 mesh Uniport HP with a flame ionization
detector. For thin-layer chromatography (TLC), Merck precoated
aluminum plates were used and detection was accomplished with an
UV lamp. Flash column chromatography employed Wako silica gel,
Wakogel C-300, 45-75 µm with a mixed solvent of hexane/EtOAc
(3/1 to 12/1, depending on the polarity of the reaction products) as
eluent. The elemental analysis and GC/MS were performed at the
Faculty of Science and at the Institute of Fundamental Research of
Organic Chemistry of Kyushu University, respectively.
(2Z)-Ethyl 3-(Pentamethylphenyl)propenoate (2b). White crystals,
1
mp 71.8-72.3 °C (hexane/EtOAc). H NMR (300 MHz, CDCl3): δ
1.09 (t, J ) 7.2 Hz, 3H, CH3), 2.14 (s, 6H, 2CH3), 2.19 (s, 6H, 2CH3),
2.22 (s, 3H, CH3), 4.01 (q, J ) 7.2 Hz, 2H, OCH2), 6.12 (d, J ) 12.0
Hz, 1H, vinyl), 7.12 (d, J ) 12.0 Hz, 1H, vinyl). 13C NMR (75 MHz,
CDCl3) δ 13.84, 16.22, 16.60, 17.46, 59.61, 122.01, 129.61, 131,72,
133.11, 133.79, 146.32, 165.23. IR (CHCl3, cm-1): 1724 (CdO). Anal.
Calcd for C16H22O2: C, 78.01; H, 9.00. Found: C, 77.89; H, 9.01.
(2E)-Ethyl 3-(1-Naphthyl)propenoate (2c). Colorless oil. 1H NMR
(300 MHz, CDCl3): δ 0.95 (t, J ) 7.2 Hz, 3H, CH3), 3.96 (q, J ) 7.2
Hz, 2H, OCH2), 6.19 (d, J ) 12.3 Hz, 1H, vinyl), 7.42 (m, 4H, aryl),
7.48 (d, J ) 12.3 Hz, 1H, vinyl), 7.8 (m, 3H, aryl). 13C NMR (75
MHz, CDCl3): δ 12.64, 59.95, 122.61, 124.22, 124.81, 125.65, 126.05,
126.38, 128.35, 128.53, 130.91, 132.85, 133.08, 141.63, 165.69. IR
(neat, cm-1): 1712 (CdO). Anal. Calcd for C15H14O2: C, 79.62; H,
6.24. Found: C, 79.45; H, 6.26.
The regio- and stereochemistry of all adducts (in Tables 2-5) were
unambiguously established on the basis of chemical shifts and coupling
constants in 1H NMR spectra, and differential NOE experiments.
Notably, the absorption of the R- and â-vinylic hydrogens for adducts
having vinylcarbonyl groups occurs at 6.0 ( 0.6 and 7.3 ( 0.7 ppm,
respectively. The coupling constants JHR-Hâ for cis- and trans-alkenes
are around 11.7 ( 0.6 and 16.5 ( 0.3 Hz, respectively. The vinyl
hydrogens of compounds 10, 10a, 11, 12, 13, 14, 16, 19, and 15 (Table
3) were assigned to be cis with phenyl and methyl groups respectively
by differential NOE study of the 1H NMR spectrum (irradiation of the
vinyl proton led to the respective enhancement of the signals of phenyl
and methyl groups). The vinyl protons at the 5-position of 3a, 3b, and
3c (singlet in 1H NMR spectra) were assigned to be cis with the vinyl
protons at the 3-position (doublet, J ) 15.9 Hz) also by differential
Ethyl 3-(2,5-Dimethylphenyl)-2-propenoate (2d). Colorless oil as
an inseparable mixture of (Z,E)-isomers (Z/E ) 2:1). The (Z)-2d and
(E)-2d have different coupling constants for their vinyl hydrogens and
1
are easily discernible from each other. H NMR (300 MHz, CDCl3):
δ 1.10 (t, J ) 7.2 Hz, 3H, CH3), 1.29 (t, J ) 7.2 Hz, 1.5H, CH3), 2.19
(s, 3H, CH3), 2.26 (s, 3H, CH3), 2.27 (s, 1.5H, CH3), 2.34 (s, 1.5H,
CH3), 4.05 (q, J ) 7.2 Hz, 2H, OCH2), 4.22 (q, J ) 7.2 Hz, 1H, OCH2),
5.96 (d, J ) 12.3 Hz, 1H, vinyl), 6.32 (d, J ) 15.9 Hz, 0.5H, vinyl),
6.98 (s, 1H, aryl), 7.02 (m, 3H, aryl), 7.07 (d, J ) 12.3 Hz, 1H, vinyl),
7.32 (s, 1H, 0.5H, aryl), 7.93 (d, J ) 15.9 Hz, 0.5H, vinyl). 13C NMR
(75 MHz, CDCl3): δ 13.74, 14.12, 19.03, 19.11, 20.67, 20.70, 59.79,
60.15, 118.71, 120.74, 126.70, 128.35, 128.91, 129.10 129.33, 130.48,
130.62, 132.38, 134.18, 134.38, 134.64, 135.43, 142.17, 142.68, 165.79,
166.83. IR (neat, cm-1): 1712 (CdO). Anal. Calcd for C13H16O2: C,
76.44; H, 7.90. Found: C, 76.52; H, 7.92.
(2Z)-Ethyl 3-Mesitylpropenoate (2e). Colorless oil. 1H NMR (300
MHz, CDCl3): δ 1.08 (t, J ) 6.9 Hz, 3H, CH3), 2.14 (s, 6H, 2CH3),
3.25 (s, 3H, CH3), 4.01 (q, J ) 6.9 Hz, OCH2), 6.10 (d, J ) 12.0 Hz,
1H, vinyl), 6.82 (s, 2H, aryl), 7.00 (d, J ) 12.0 Hz, 1H, vinyl). 13C
NMR (75 MHz, CDCl3): δ 13.77, 19.93, 20.83, 59.70, 122.59, 127.62,
132.62, 134.24, 136.43, 143.93, 165.22. IR (CHCl3, cm-1): 1729 (Cd
O). Anal. Calcd for C14H18O2: C, 77.03; H, 8.31. Found: C, 76.84; H,
8.39.
1
NOE of the H NMR spectrum.
General Procedure for Alkyne Hydroarylation. To a cold mixture
of the arene (10 mmol), the transition metal catalyst (0.02-5 mol %),
TFA (4 mL), and CH2Cl2 (1 mL) on an ice-water bath was added the
alkyne (5 mmol) with stirring. After continuous stirring at the same
temperature for 5 min, the mixture was warmed to room temperature.
Stirring continued until no further increase of the reaction products or
the disappearance of one starting material as monitored by GC, TLC,
or 1H NMR. When the yield was determined by GC, diethyl phthalate
was added to reaction mixture as an internal standard. The reaction
mixture was poured into a saturated NaCl aqueous solution and
extracted with ether. The ethereal layer was washed with saturated NaCl,
neutralized with Na2CO3 solution, and dried over anhydrous Na2SO4.
The solvent was removed in a vacuum, and the products were separated
by flash column chromatography.
(2Z)-Ethyl 3-{2,4,6-Trimethyl-3-[(1Z)-2-ethoxycarbonylethylenyl)]-
1
phenyl}propenoate (2f). Colorless oil. H NMR (300 MHz, CDCl3):
δ 1.11 (t, J ) 7.2 Hz, 6H, 2CH3), 2.05 (s, 3H, CH3), 2.15 (s, 6H,
2CH3), 4.03 (q, J ) 7.2 Hz, 4H, 2OCH2), 6.12 (d, J ) 11.7 Hz, 2H,
vinyl), 6.88 (s, 1H, aryl), 7.03 (d, J ) 11.7 Hz, 2H, vinyl). 13C NMR
(75 MHz, CDCl3): δ 13.82, 17.57, 20.08, 59.76, 122.60, 128.26, 130.87,
132.89, 133.35, 144.24, 165.24. IR (neat, cm-1): 1718 (CdO). Anal.
Calcd for C19H24O4: C, 72.13; H, 7.65. Found: C, 72.02; H, 7.60.
A Specific Example. Pentamethylbenzene (1.51 g, 10.2 mmol), Pd-
(OAc)2 (10 mg, 0.045 mmol), TFA (4 mL), and CH2Cl2 (1 mL) were
mixed in a 25-mL dry Pyrex tube on an ice-water bath, and then ethyl
propiolate (0.475 g, 4.9 mmol) was added to this mixture and the
mixture was stirred for 5 min. Then the mixture was warmed to room
temperature and stirred for 3 h. After workup according to the general
procedure and column chromatography with 8/1 hexane/EtOAc as
eluent, two compounds were isolated as white crystals: (2Z)-ethyl
3-(pentamethylphenyl)propenoate (2b) (1.05 g) in 88% yield and ethyl
(2E,4Z)-4-(ethoxycarbonyl)-5-(pentamethylphenyl)-2,4-pentadienoate
(3a) (0.05 g) in 6% yield, respectively.
Characterization Data. (2Z)-Ethyl 3-(2,5-Dimethoxyphenyl)-
propenoate (Z-2a). Light yellow oil. 1H NMR (300 MHz, CDCl3): δ
1.21 (t, J ) 7.2 Hz, 3H, CH3), 3.76 (s, 3H, OCH3), 3.78 (s, 3H, OCH3),
4.14 (q, J ) 7.2 Hz, 2H, OCH2), 5.97 (d, J ) 12.3 Hz, 1H, vinyl),
6.80 (d, J ) 8.7 Hz, 1H, aryl), 6.87 (dd, J ) 3.0 and 8.7 Hz, 1H, aryl),
7.12 (d, J ) 12.3 Hz, 1H, vinyl), 7.24 (d, J ) 3.0 Hz, 1H, aryl). 13C
(2Z)-Ethyl 3-(2,3,5,6-Tetramethylphenyl)-2-propenoate (2g). Light
1
yellow oil. H NMR (CDCl3, 300 MHz): δ 0.95 (t, J ) 6.9 Hz, 3H,
CH3), 1.97 (s, 6H, 2CH3), 2.10 (S, 6H, 2CH3), 3.88 (q, J ) 6.9 Hz,
2H, OCH2), 6.01 (d, J ) 11.7 Hz, 1H, vinyl), 6.77 (s, 1H, aryl), 6.94
(d, J ) 11.7 Hz, vinyl). 13C NMR (CDCl3, 75 MHz): δ 13.63, 16.20,
19.66, 59.50, 122.27, 129.95, 130.31, 132.72, 135.49, 145.23, 165.10.
(15) (a) Jalander, L. Finn. Chem. Lett. 1982, No. 5, 49. (b) Ricci, A.;
Buu-Hoi, N. P. Bull. Soc. Chim. Fr. 1967, 3634. (c) Ando, K. J. Org. Chem.
1997, 62, 1934. (d) Phillips, W. M.; Currie, D. Can. J. Chem. 1969, 47,
3137. (e) Heller, H. G.; Megit, R. M. J. Chem. Soc., Perkin Trans. 1 1974,
923.

trans-Hydroarylation of Alkynes by Simple Arenes
J. Am. Chem. Soc., Vol. 122, No. 30, 2000 7261
IR (neat, cm-1): 1714 (CdO). Anal. Calcd for C15H20O2: C, 77.55;
H, 8.68. Found: C, 76.28; H, 8.68.
6.74 (d, J ) 9.0 Hz, 2H, aryl), 6.76 (d, J ) 2.7 Hz, 2H, aryl). 13C
NMR (CDCl3, 75 MHz): δ 13.94, 35.32, 38.32, 55.42, 56.06, 59.98,
110.98, 111.76, 115.25, 132.47, 151.47, 153.28, 172.06. IR (CHCl3,
cm-1): 1729 (CdO). Anal. Calcd for C21H26O6: C, 67.36; H, 7.00.
Found: C, 67.43; H, 7.10.
(2Z)-Ethyl (2,4,6-Trimethyl-3-hydroxyphenyl)propenoate (2h).
White crystals, mp 58.7-59.6 °C (hexane/EtOAc). 1H NMR (300 MHz,
CDCl3): δ 1.10 (t, J ) 6.9 Hz, 3H, CH3), 2.04 (s, 3H, CH3), 2.07 (s,
3H, CH3), 2.08 (s, 3H, CH3), 4.03 (q, J ) 6.9 Hz, 2H, OCH2), 5.20 (s,
1H, OH), 6.11 (d, J ) 11.7 Hz, 1H, vinyl), 6.73 (s, 1H, aryl), 6.97 (d,
J ) 11.7 Hz, 1H, vinyl). 13C NMR (75 MHz, CDCl3): δ 12.79, 13.70,
15.65, 19.27, 59.90, 120.48, 122.23, 122.34, 125.56, 128.84, 133.81,
144.20, 149.84, 165.54. IR (CHCl3, cm-1): 3485 (OH), 1714 (CdO).
Anal. Calcd for C14H18O3: C, 71.77; H, 7.74. Found: C, 71.70; H,
7.70.
Ethyl 3-Bis(4-methoxyphenyl)propionate (4b). Colorless oil (>90%
1
of di-para-substitution as determined by GC). H NMR (300 MHz,
CDCl3): δ 1.10 (t, J ) 6.9 Hz, 3H, CH3), 2.98 (d, J ) 8.1 Hz, 2H,
OCH2), 3.73 (s, 6H, 2OCH3), 4.01 (q, J ) 6.9 Hz, 2H, OCH2), 4.50 (t,
J ) 8.1 Hz, 1H, CH), 6.80 (d, J ) 9.0 Hz, 2H, aryl), 7.13 (d, J ) 9.0
Hz, 2H, aryl). 13C NMR (75 MHz, CDCl3): δ 13.98, 41.11, 45.36,
55.01, 60.21, 113.73, 128.40, 135.90, 157.94, 171.79. IR (CHCl3, cm-1):
1733 (CdO). Anal. Calcd for C19H22O4: C, 72.59; H, 7.05. Found:
C, 72.49; H, 7.07.
(2Z)-Ethyl 3-(2,4,6-Trimethyl-3-bromophenyl)propenoate (2i). A
1
waxy solid, mp 29.5-30.6 °C (hexane/EtOAc). H NMR (300 MHz,
CDCl3): δ 1.09 (t, J ) 7.2 Hz, 3H, CH3), 2.11(s, 3H, CH3), 2.30 (s,
3H, CH3), 2.37 (s, 3H, CH3), 4.02 (q, J ) 7.2 Hz, 2H, OCH2), 6.13 (d,
J ) 12.0 Hz, 1H, vinyl), 6.93 (s, 1H, aryl), 7.02 (d, J ) 12.0 Hz, 1H,
vinyl). 13C NMR (CDCl3, 75 MHz): δ 12.85, 19.88, 21.21, 23.87, 60.04,
123.21, 124.99, 129.24, 133.14, 134.30, 134.55, 136.88, 143. 56, 165.14.
IR (CHCl3, cm-1): 1729 (CdO). Anal. Calcd for C14H17O2Br: C, 56.58;
H, 5.77. Found: C, 56.87; H, 5.81.
Ethyl 3-(2-Methoxyphenyl)-2-propenoate (2j). Light yellow oil as
an inseparable Z,E-mixture (Z:E ) 4:1). 1H NMR (300 MHz, CDCl3):
δ 1.11 (t, J ) 7.2 Hz, 3H, CH3), 1.24 (t, J ) 6.9 Hz, 0.8H, CH3), 3.70
(s, 0.8H, OCH3), 3.73 (s, 3H, OCH3), 4.04 (q, J ) 7.2 Hz, 2H, OCH2),
4.17 (q, J ) 6.9 Hz, 0.5H, OCH2), 5.87 (d, J ) 12.6 Hz, 1H, vinyl),
6.45 (d, J ) 15.9 Hz, 0.25H, vinyl), 6.83 (m, 2.5 H, aryl), 7.08 (d, 1H,
J ) 12.6 Hz, 1H, vinyl), 7.20 (m, 1.25 H, aryl), 7.41 (dd, J ) 1.8 and
7.5 Hz, 0.25H, aryl), 7.46 (dd, J ) 1.5 and 7.8 Hz, 1H, aryl), 7.91 (d,
J ) 15.9 Hz, 0.25H, vinyl). 13C NMR (CDCl3, 75 MHz): δ 13.98,
14.26, 55.08, 55.29, 59.97, 60.22, 111.12, 111.01, 118.67, 119.76,
119.88, 129.57, 123.32, 123.99, 128.80, 130.08, 130.62, 131.30, 138.90,
139.90, 156.99, 158.21, 166.25, 167.39. IR (CHCl3, cm-1): 1721 (Cd
O). Anal. Calcd for C12H14O3: C, 69.89; H, 6.84. Found: C, 69.70; H,
6.89.
(2E,4Z)-Ethyl 4-(Ethoxycarbonyl)-5-(pentamethylpenyl)-2,4-pen-
tadienoate (3a). Colorless crystals, mp 60.8-62.0 (hexane/EtOAc).
1H NMR (300 MHz, CDCl3): δ 0.87 (t, J ) 6.9 Hz, 3H, CH3), 1.32 (t,
J ) 6.9 Hz, 3H, CH3), 2.12 (s, 6H, 2CH3), 2.18 (s, 6H, 2CH3), 2.22 (s,
3H, CH3), 3.97 (q, J ) 6.9 Hz, 2H, OCH2), 4.25 (q, J ) 6.9 Hz, 2H,
OCH2), 6.17 (d, J ) 15.9 Hz, 1H, vinyl), 7.25 (s, 1H, vinyl), 7.50 (d,
J ) 15.9 Hz, 1H, vinyl). 13C NMR (CDCl3, 75 MHz): δ 13.40, 14.26,
16.19, 16.67, 17.78, 60.47, 60.53, 120.41, 130.37, 132.04, 132.44,
133.98, 134.44, 141.48, 145.25, 166.01, 166.84. IR (CHCl3, cm-1):
1734 (CdO), 1716 (CdO). Anal. Calcd for C21H28O4: C, 73.23; H,
8.19. Found: C, 73.35; H, 8.16.
Ethyl 3-Bis(2,4,6-trimethoxyphenyl)propionate (4c). Colorless
crystals, mp 106.4-107.3 °C (hexane/EtOAc ) 4). 1H NMR (CDCl3,
300 MHz): δ 1.16 (t, J ) 7.2 Hz, 3H, CH3), 3.05 (d, J ) 8.4 Hz, 2H,
CH2), 3.67 (s, 12H, 4OCH3), 3.75 (s, 6H, 2OCH3), 4.05 (q, J ) 7.2
Hz, 2H, OCH2), 5.18 (t, J ) 8.4 Hz, 1H, CH), 6.05 (s, 4H, aryl). 13C
NMR (CDCl3, 75 MHz): δ 14.25, 29.95, 37.80, 55.07, 55.67, 59.41,
91.06, 113.83, 158.72, 159.29, 173.58. IR (KBr, cm-1): 1735 (CdO).
Anal. Calcd for C23H30O8: C, 63.58; H, 6.96. Found: C, 63.56; H,
6.92.
2′-Ethylhexyl 3-(2,5-Dimethoxyphenyl)-3-(4-methoxyphenyl)pro-
1
pionate (4d). Light yellow oil. H NMR (CDCl3, 300 MHz): δ 0.79
(t, J ) 7.2 Hz, 3H, CH3), 0.87 (t, J ) 7.2 Hz, 3H, CH3), 1.18-1.35
(m, 9H, alkyl), 2.99 (m, 2H, CH2CdO), 3.69 (s, 3H, CH3O), 3.70 (s,
3H, CH3O), 3.71 (s, 3H, CH3O), 3.88 (d, J ) 5.4 Hz, 2H, CH2O), 4.86
(t, J ) 7.8 Hz, 1H, CH), 6.64 (dd, J ) 2.7, 9.0 Hz, 1H, aryl), 6.72 (s,
1H, aryl), 6.73 (d, J ) 8.7 Hz, 1H, aryl), 6.77 (d, J ) 8.7 Hz, 2H,
aryl), 7.17 (d, J ) 8.7 Hz, 2H, aryl). 13C NMR (CDCl3, 75 MHz): δ
10.76, 13.88, 22.81, 23.48, 28.78, 30.16, 38.59, 39.62, 39.84, 54.97,
55.41, 55.90, 66.45, 110.81, 111.62, 113.55, 114.56, 128.69, 133.57,
134.92, 151.00, 153.44, 157.88, 172.07. IR (neat, cm-1): 1737 (Cd
O). Anal. Calcd for C26H36O5: C, 72.87; H, 8.47. Found: C, 73.13; H,
8.42.
2′-Ethylhexyl 3-(2,4,6-Trimethoxyphenyl)-3-(4-methoxyphenyl)-
1
propionate (4e). Light yellow oil. H NMR (CDCl3, 300 MHz): δ
0.80 (t, J ) 7.2 Hz, 3H, CH3), 0.87 (t, J ) 7.2 Hz, 3H, CH3), 1.16-
1.45 (m, 9H, alkyl), 3.18 (m, 2H, CH2CdO), 3.62 (s, 3H, CH3O), 3.65
(s, 3H, CH3O), 3.67 (s, 6H, CH3O), 3.87 (m, 2H, CH2O), 5.11 (t, J )
7.5 Hz, 1H, CH), 6.06 (s, 2H, aryl), 6.70 (d, J ) 8.4 Hz, 2H, aryl),
7.22 (d, J ) 8.4 Hz, 2H, aryl). 13C NMR (CDCl3, 75 MHz): δ 10.50.
13.65, 22.56, 23.22, 28.54, 29.88, 31.19, 34.86, 37.77, 38.41, 54.44,
55.05, 65.74, 90.74, 112.51, 112.71, 128.05, 135.96, 157.15, 158.53,
159.43, 172.71. IR (neat, cm-1): 1729 (CdO). Anal. Calcd for
C27H38O6: C, 70.95; H, 8.48. Found: C, 70.72; H, 8.45.
(2E,4Z)-Ethyl 4-(Ethoxycarbonyl)-5-mesityl-2,4-pentadienoate
1
(3b). Colorless oil. H NMR (300 MHz, CDCl3): δ 0.79 (t, J ) 6.9
2′-Ethylhexyl 3-(2-Methyl-4,5-methylenedioxyphenyl)-3-(4-meth-
1
Hz, 3H, CH3), 1.22 (t, J ) 6.9 Hz, 3H, CH3), 2.05 (s, 6H, 2CH3), 2.16
(s, 3H, CH3), 3.90 (q, J ) 6.9 Hz, 2H, OCH2), 4.15 (q, J ) 6.9 Hz,
2H, OCH2), 6.15 (d, J ) 15.9 Hz, 1H, vinyl), 6.73 (s, 2H, aryl), 7.04
(s, 1H, vinyl), 7.37 (d, J ) 15.9 Hz, 1H, vinyl). 13C NMR (CDCl3, 75
MHz): δ 13.28, 14.09, 19.93, 20.78, 60.30, 60.52, 120.55, 127.66,
131.93, 134.27, 134.96, 137.09, 141.20, 142.93, 165.86, 166.58. IR
(CHCl3, cm-1): 1730 (CdO), 1722 (CdO). Anal. Calcd for C19H24O4:
C, 72.13; H, 7.65. Found: C, 72.40; H, 7.72.
oxyphenyl)propionate (4f). Light yellow oil. H NMR (CDCl3, 300
MHz): δ 0.80 (t, J ) 7.2 Hz, 3H, CH3), 0.87 (t, J ) 7.2 Hz, 3H,
CH3), 1.10-1.45 (m, 9H, alkyl), 2.22 (s, 3H, CH3), 2.92 (dd, J ) 1.2
and 7.8 Hz, 2H, CH2CdO) 3.74 (s, 3H, OCH3), 3.90 (d, J ) 5.4 Hz,
2H, OCH2), 4.61 (t, J ) 7.8 Hz, 1H, CH), 5.86 (q, J ) 2.4 Hz, 2H,
CH2O2), 6.73 (s, 1H, aryl), 6.60 (s, 1H, aryl), 6.78 (d, J ) 9.0 Hz, 2H,
aryl), 7.08 (d, J ) 9.0 Hz, 2H, aryl). 13C NMR (CDCl3, 75 MHz): δ
10.82, 14.03, 19.61, 22.87, 23.58, 28.83, 30.23, 38.65, 41.39, 42.01,
55.10, 66.68, 100.67, 106.81, 110.74, 113.82, 128.58, 129.10, 134.68,
135.26, 145.58, 145.83, 158.02, 171.99. IR (neat, cm-1): 1734 (Cd
O). Anal. Calcd for C26H34O5: C, 73.21; H, 8.03. Found: C, 73.42; H,
8.05.
(2E,4Z)-Ethyl 4-Ethoxycarbonyl-5-(2,3,5,6-tetramethylphenyl)-
2,4-pentadienoate (3c). Light yellow oil. 1H NMR (CDCl3, 300
MHz): δ 0.84 (t, J ) 6.9 Hz, 3H, CH3), 1.32 (t, J ) 6.9 Hz, 3H,
CH3), 2.06 (s, 6H, 2CH3), 2.20 (s, 6H, 2CH3), 3.95 (q, J ) 6.9 Hz, 2H,
OCH2), 4.25 (q, J ) 6.9 Hz, 2H, OCH2), 6.22 (d, J ) 15.9 Hz, 1H,
vinyl), 6.90 (s, 1H, aryl), 7.22 (s, 1H, vinyl), 7.48 (d, J ) 15.9 Hz,
1H, vinyl). 13C NMR (CDCl3, 75 MHz): δ 13.35, 14.26, 16.63, 19.78,
60.51, 60.55, 120.64, 130.88, 130.93, 133.27, 134.19, 134.95, 141.35,
144.42, 165.99, 166.84. IR (cm-1, neat): 1714 (CdO). Anal. Calcd
for C20H26O4: C, 72.77; H 7.93. Found: C, 73.58; H, 8.22.
(3E)-4-(Pentamethylphenyl)-3-buten-2-one (5a). Light yellow
1
crystals, mp 78.3-80.0 °C. H NMR (300 MHz, CDCl3): δ 2.20 (s,
12H, 4CH3), 2.23 (s, 3H, CH3), 2.38 (s, 3H, CH3), 6.16 (d, J ) 16.5
Hz, 1H, vinyl), 7.71 (d, J ) 16.5 Hz, 1H, vinyl). 13C NMR (CDCl3, 75
MHz): δ 16.24, 16.66, 17.71, 27.14, 130.85, 132.42, 132.59, 133.65,
135.07, 144.86, 197.94. IR (CHCl3, cm-1): 1685 (CdO). Anal. Calcd
for C15H20O: C, 83.28; H 9.32. Found: C, 83.26; H, 9.32.
Ethyl 3-Bis(2,5-dimethoxyphenyl)propionate (4a). Yellow crystals,
1
mp 88.3-89.5 °C (hexane/EtOAc). H NMR (300 MHz, CDCl3): δ
(3E)-4-(2,4,5,6-Tetramethylphenyl)-3-buten-2-one (5b). Colorless
1
1.09 (t, J ) 6.9 Hz, 3H, CH3), 3.00 (d, J ) 8.4 Hz, 2H, CH2), 3.70 (s,
6H, 2OCH3), 3.71 (s, 6H, 2OCH3), 4.01 (q, J ) 6.9 Hz, 2H, OCH2),
5.15 (t, J ) 8.4 Hz, 1H, CH), 6.65 (dd, J ) 2.7 and 9.0 Hz, 2H, aryl),
crystals, mp 77.4-78.1 °C (hexane/EtOAc). H NMR (CDCl3, 300
MHz): δ 2.18 (s, 3H, CH3), 2.25 (s, 3H, CH3), 2.26 (s, 3H, CH3), 2.27
(s, 3H, CH3), 2.39 (s, 3H, CH3), 6.24 (d, J ) 16.5 Hz, 1H, vinyl), 6.90

7262 J. Am. Chem. Soc., Vol. 122, No. 30, 2000
Jia et al.
(s, 1H, aryl), 7.69 (d, J ) 16.5 Hz, 1H, vinyl). 13C NMR (CDCl3, 75
MHz): δ 15.63, 17.53, 20.55, 20.58, 27.34, 129.63, 132.16, 132.96,
133.13, 133.18, 134.58, 136.83, 143.49, 198.39. IR (cm-1): 1662 (Cd
O). Anal. Calcd for C14H18O: C, 83.12; H, 8.97. Found: C, 83.25; H,
9.03.
4-Methyl-6-tert-butylcoumarin (8b). Light yellow crystals, mp
123.5-124.0 °C (hexane/EtOAc) (123 °C).15b 1H NMR (300 MHz,
CDCl3): δ 1.37 (s, 9H, 3CH3), 2.46 (d, J ) 1.5 Hz, 3H, CH3), 6.28 (d,
J ) 1.5 Hz, vinyl), 7.27 (d, J ) 8.7 Hz, 1H, aryl), 7.57 (s, 1H, aryl),
7.60 (d, J ) 8.7 Hz, 1H, aryl). 13C NMR (CDCl3, 75 MHz) δ 18.59,
31.33, 34.59, 114.84, 116.55, 119.20, 120.51, 129.33, 147.17, 151.46,
152.59, 161.01. IR (CHCl3, cm-1): 1729 (CdO).
(3E)-4-Mesityl-3-buten-2-one (5c). Light yellow crystals, mp 64.5-
1
65.1 °C. H NMR (300 MHz, CDCl3): δ 2.25 (s, 3H, CH3), 2.29 (s,
6H, 2CH3), 2.35 (s, 3H, CH3), 6.30 (d, J ) 16.5 Hz, 1H, vinyl), 6.86
(s, 2H, aryl), 7.64 (d, J ) 16.5 Hz, 1H, vinyl). 13C NMR (CDCl3, 75
MHz): δ 20.70, 20.73, 27.04, 128.96, 130.52, 131.99, 136.41, 138.11,
141.54, 197.89. The structure of this compound was confirmed by
converting it to (Z)-[(2E)-3-mesitylprop-2-enylidene]succinic anhydride,15e
mp 159.6-162 °C (160.0-161 °C).15e
(3E)-4-(2-Methyl-4,5-methylenedioxyphenyl)-3-buten-2-one (5d).
Colorless crystals, mp 112.4-114.3 °C (hexane/EtOAc ) 3). 1H NMR
(CDCl3, 300 MHz): δ 2.36 (s, 3H, CH3), 2.38 (s, 3H, CH3), 5.96 (s,
2H, O-CH2-O), 6.51 (d, J ) 15.9 Hz, 1H, vinyl), 6.68 (s, 1H, aryl),
7.05 (s, 1H, aryl), 7.75 (d, J ) 15.9 Hz, 1H, vinyl). 13C NMR (CDCl3,
75 MHz): δ 19.63, 27.76, 101.32, 105.43, 110.72, 125.68, 126.40,
133.45, 140.21, 146.48, 149.53, 198.14. IR (KBr, cm-1): 1664 (Cd
O). Anal. Calcd for C12H12O3: C, 70.57; H, 5.92. Found: C, 70.54; H,
5.95.
(2Z)-Ethyl 3-Mesitylcinnamate (10). Colorless oil. 1H NMR
(CDCl3, 300 MHz): δ 1.10 (t, J ) 6.9 Hz, 3H, CH3), 2.03 (s, 6H,
2CH3), 2.32 (s, 3H, CH3), 4.02 (q, J ) 6.9 Hz, 2H, OCH2), 6.61 (s,
1H, vinyl), 6.90 (s, 2H, aryl), 7.33 (m, 5H, aryl). 13C NMR (CDCl3,
75 MHz): δ 13.99, 19.74, 21.15, 59.85, 117.54, 126.94, 127.99, 128.64,
129.46, 134.62, 135.22, 136.68, 138.35, 155.06, 165.67. Anal. Calcd
for C20H22O2: C, 81.60; H, 7.53. Found: C, 81.44; H, 7.55.
(2Z)-3-Mesitylcinnamic Acid (10a). Colorless crystals, mp 195.0-
195.6 °C. 1H NMR (CDCl3, 300 MHz): δ 2.02 (s, 6H, 2CH3), 2.31 (s,
3H, CH3), 6.59 (s, 1H, vinyl), 6.89 (s, 2H, aryl), 7.30 (m, 5H, aryl).
13C NMR (CDCl3, 75 MHz): δ 19.71, 21.12, 116.94, 127.10, 128.19,
128.72, 129.84, 134.44, 134.68, 137.07, 138.19, 157.13, 169.75. IR
(CHCl3, cm-1): 3010 (wide and broad, COOH), 1697 (CdO). Anal.
Calcd for C 18H18O2: C, 81.87; H, 6.81. Found: C, 81.68; H, 6.66.
(2Z)-3-Pentamethylphenylcinnamaldehyde (11). Gray solid, mp
1
(3E)-4-(2,5-Dimethoxyphenyl)-3-buten-2-one (5e). Light yellow oil.
1H NMR (300 MHz, CDCl3): δ 2.38 (s, 3H, CH3), 3.78 (s, 3H, OCH3),
3.84 (s, 3H, OCH3), 6.71 (d, J ) 16.5 Hz, 1H, vinyl), 6.85 (d, J ) 9.0
Hz, aryl), 6.94 (dd, J ) 2.7 and 9.0 Hz, 1H, aryl), 7.07 (d, J ) 2.7 Hz,
1H, aryl), 7.86 (d, J ) 16.5 Hz, 1H, vinyl). 13C NMR (CDCl3, 75
MHz): δ 26.97, 55.61, 55.93, 112.29, 112.44, 117.43, 123.71, 127.71,
138.36, 152.63, 153.43, 198.89. IR (CHCl3, cm-1): 1675 (CdO). Anal.
Calcd for C12H14O3: C, 69.84; H, 6.84. Found: C, 69.65; H, 6.76.
4-Bis(2-methyl-4,5-methylenedioxyphenyl)-2-butanone (6a). Col-
orless crystals, mp 131.8-133.6 °C (hexane/EtOAc). 1H NMR (CDCl3,
300 MHz): δ 2.11 (s, 3H, CH3), 2.20 (s, 6H, 2CH3), 2.92 (d, J ) 7.8
Hz, 2H, CH2sCdO), 4.69 (t, J ) 7.8 Hz, 1H, CH), 5.87 (s, 4H, 2Os
CH2Os), 6.56 (s, 2H, aryl), 6.62 (s, 2H, aryl). 13C NMR (CDCl3, 75
MHz): δ 19.28, 30.30, 38.22, 49.02, 100.72, 107.06, 110.72, 128.91,
134.33, 145.59, 145.83, 206.67. IR (KBr, cm-1): 1720 (CdO). Anal.
Calcd for C20H20O5: C, 70.57; H, 5.92. Found: C, 70.33; H, 5.92.
4-Bis(4-methoxylphenyl)-2-butanone (6b). Yellow oil (75% di-
para-substitution as determined by GC in three isomers of p-, o-, m-).
1H NMR (CDCl3, 300 MHz): δ 2.04 (s, 3H, CH3), 3.09 (d, J ) 7.5
Hz, 2H, CH3), 3.73 (s, 6H, 2OCH3), 4.47 (t, J ) 7.5 Hz, 1H, CH),
6.80 (d, J ) 8.4 Hz, 4H, aryl), 7.11 (d, J ) 8.4 Hz, 4H, aryl). 13C
NMR (CDCl3, 75 MHz): δ 30.53, 44.47, 49.99, 55.10, 113.84, 128.44,
136.26, 157.94, 207.09. IR (neat, cm-1): 1714 (CdO). GC/MS: m/z
M+ for C18H20O3, 284. A small amount of the other two isomers in
this mixture is difficult to recognize, but GC/MS spectra show their
presence. GC/MS: m/z M+, 284.
114.0-115.2 °C H NMR (CDCl3, 300 MHz): δ 2.04 (s, 6H, 2CH3),
2.23 (s, 6H, 2CH3), 2.29 (s, 3H, CH3), 6.81 (d, J ) 7.2 Hz, 1H, vinyl),
7.32-7.40 (m, 5H, aryl), 9.30 (d, J ) 7.2 Hz, 1H, CHO). 13C NMR
(CDCl3, 75 MHz): δ 16.35, 16.70, 17.87, 126.24, 127.13, 128.77,
130.45, 131.12, 132.62, 132.85, 134.99, 137.74, 162.88, 194.10. IR
(CHCl3, cm-1): 1670 (CdO). Anal. Calcd for C20H22O: C, 86.29; H,
7.97. Found: C, 86.76; H, 7.53.
(2Z)-1-Pentamethylphenyl-1,2-bisphenylethylene (12). Colorless
1
crystals, mp 114.6-115.8 °C (hexane/EtOAc). H NMR (CDCl3, 300
MHz): δ 2.01 (s, 6H, 2CH3), 2.21 (s, 6H, 2CH3), 2.30 (s, 3H, CH3),
6.90-7.10 (m, 5H, aryl), 7.14 (s, 1H, vinyl), 7.18-7.36 (m, 5H, aryl).
13C NMR (CDCl3, 75 MHz): δ 16.62, 16.86, 17.18, 126.18, 126.71,
127.09, 127.82, 128.12, 128.35, 128.59, 131.11, 132.72, 133.90, 136.28,
137.63, 141.70, 142.18. Anal. Calcd for C25H26: C, 91.97; H, 8.03.
Found: C, 91.82; H, 8.03.
(2Z)-1-Pentamethylphenyl-1-phenylpropene (13). Colorless crys-
1
tals, mp 98.0-98.8 °C. H NMR (CDCl3, 300 MHz): δ 1.49 (d, J )
6.9 Hz, 3H, CH3), 2.04 (s, 6H, 2CH3), 2.23 (s, 6H, 2CH3), 2.27 (s, 3H,
CH3), 6.35 (q, J ) 6.9 Hz, 1H, vinyl), 7.20 (s, 5H, aryl). 13C NMR
(CDCl3, 75 MHz): δ 15.15, 16.63, 16.75, 17.17, 123.24, 125.73, 126.42,
128.22, 131.52, 132.19, 133.32, 135.96, 141.19, 141.79. Anal. Calcd
for C20 H24: C, 90.85; H, 9.15. Found: C, 90.58; H, 9.18.
(3Z)-4-(Pentamethylphenyl)-4-phenyl-3-buten-2-one (14). Brown
1
crystals, mp 49.2-50.5 °C. H NMR (CDCl3, 300 MHz): δ 1.69 (s,
1H, CH3), 2.04 (s, 6H, 2CH3), 2.23 (s, 6H, 2CH3), 2.29 (s, 3H, CH3),
6.83 (s, 1H, vinyl), 7.33 (m, 5H, aryl). 13C NMR (CDCl3, 75 MHz):
δ 16.46, 16.83, 17.67, 29.29, 127.30, 128.03, 128.65, 129.47, 130.37,
132.85, 134.84, 135.19, 139.18, 154.80, 200.18. IR (CHCl3, cm-1):
1654 (CdO). Anal. Calcd for C21H24O: C, 86.26; H, 8.27. Found: C,
85.90; H, 8.30.
1-Pentamethylphenyl-1-phenylethylene (7). Colorless crystals, mp
1
66.5-67.2 °C (hexane). H NMR (CDCl3, 300 MHz): δ 2.10 (s, 6H,
2CH3), 2.23 (s, 6H, 2CH3), 2.28 (s, 3H, CH3), 5.06 (d, J ) 1.5 Hz, 1H,
vinyl), 5.96 (d, J ) 1.5 Hz, 1H, vinyl), 7.23-7.28 (m, 5H, aryl). 13C
NMR (CDCl3, 75 MHz): δ 16.54, 16.75, 17.83, 114.29, 126.00, 127.42,
128.35, 131.56, 132.33, 133.70, 138.71, 140.02, 148.65. Anal. Calcd
for C19H22: C, 91.14; H 8.86. Found: C, 90.99; H, 8.85.
(2E)-Ethyl 3-(Pentamethylphenyl)-2-butenoate (15). Colorless oil.
1H NMR (300 MHz, CDCl3): δ 1.05 (t, J ) 6.9 Hz, 3H, CH3), 2.04
(d, J ) 1.5 Hz, 3H, CH3), 2.09 (s, 6H, 2CH3), 2.19 (s, 6H, 2CH3), 2.22
(s, 3H, CH3), 3.95 (q, J ) 6.9 Hz, 2H, OCH2), 6.04 (q, J ) 1.5 Hz,
1H, vinyl). 13C NMR (CDCl3, 75 MHz): δ 13.92, 16.33, 16.63, 16.93,
26.58, 59.31, 118.88, 127.90, 132.05, 133.30, 137.99, 158.08, 165.23.
IR (CHCl3, cm-1): 1733 (CdO). Anal. Calcd for C17H24O2: C, 78.42;
H, 9.29. Found: C, 78.43; H, 9.34.
(2Z)-3-(Pentamethylphenyl)cinnamic Acid (16). White crystals, mp
240.2-241.4 °C (hexane/EtOAc). 1H NMR (300 MHz, CDCl3): δ 2.00
(s, 6H, 2CH3), 2.20 (s, 6H, 2 CH3), 2.27 (s, 3H, CH3), 6.62 (s, 1H,
vinyl), 7.30 (m, 5H, aryl), 10.13 (br, 1H, COOH). 13C NMR (CDCl3,
75 MHz): δ 16.47, 16.84, 17.52, 117.13, 127.27, 128.66, 129.70,
130.13, 132.52, 134.26, 134.64, 138.78, 158.49, 169.51. IR (CHCl3,
cm-1): 3000 (wide and broad, COOH), 1697 (CdO). Anal. Calcd for
C20H22O2: C, 81.60; H 7.53. Found: C, 81.28; H, 7.65.
6-tert-Butylcoumarin (8). Light yellow crystals, mp 76.4-78.0 °C.
1H NMR (300 MHz, CDCl3): δ 1.36 (s, 9H, 3 CH3), 6.41 (d, J ) 9.6
Hz, 1H, vinyl), 7.27 (d, J ) 8.7 Hz, 1H, aryl), 7.45 (d, J ) 2.7 Hz,
1H, aryl), 7.60 (dd, J ) 2.7 and 8.7 Hz, 1H, aryl), 7.71 (d, J ) 9.6 Hz,
1H, vinyl). 13C NMR (CDCl3, 75 MHz): δ 31.27, 34.46, 116.31, 116.36,
118.21, 124.08, 129.45, 143.87, 147.53, 151.99, 161.14. IR (CHCl3,
cm-1): 1721 (CO). Anal. Calcd for C13H14O2; C, 77.20; H, 6.98.
Found: C, 77.05; H, 7.11.
4-Phenyl-6-tert-butylcoumarin (8a). Colorless crystals, mp 108.3-
1
109.0 °C (hexane/EtOAc). H NMR (300 MHz, CDCl3) δ: 1.27 (s,
9H, tert-butyl), 6.36 (s, 1H, vinyl), 7.35 (d, J ) 8.4 Hz, 1H, aryl),
7.54 (m, 6H, aryl), 7.60 (dd, J ) 2.4, 8.4 Hz, 1H, aryl). 13C NMR
(CDCl3, 75 MHz) δ: 31.2, 34.6, 115.0, 116.8, 118.2, 123.1, 128.4,
128.8, 129.5, 129.6, 135.4, 147.2, 152.2, 155.9, 161.0. IR (CHCl3,
cm-1): 1726 (CdO). Anal. Calcd for C19H18O2: C, 81.99; H, 6.52.
Found: C, 81.94; H, 6.55.
Diethyl 2-Pentamethylphenylfumarate (17). White crystals, mp
1
54.0-55.6 °C. H NMR (300 MHz, CDCl3): δ 1.02 (t, J ) 7.2 Hz,
3H, CH3), 1.25 (t, J ) 6.9 Hz, 3H, CH3), 2.03 (s, 6H, 2CH3), 2.17 (s,

trans-Hydroarylation of Alkynes by Simple Arenes
J. Am. Chem. Soc., Vol. 122, No. 30, 2000 7263
6H, 2CH3), 2.21 (s, 3H, CH3), 3.98 (q, J ) 7.2 Hz, 2H, CH2O), 4.24
(q, J ) 6,9 Hz, 2H, CH2O), 7.08 (s, 1H, vinyl). 13C NMR (CDCl3, 75
MHz): δ 13.73, 14.13, 16.40, 16.87, 17.66, 60.44, 61.65, 129.06,
130.38, 131.18, 131.82, 134.58, 146.33, 164.93, 166.46. IR (CHCl3,
cm-1): 1728 (CdO). Anal. Calcd for C19H26O4: C, 71.67; H, 8.23.
Found: C, 71.93; H, 8.28.
4-(Pentamethylphenyl)-4-octene (Z/E ) 1/1) (18). An inseparable
mixture of 4-(pentamethylphenyl)-4-octene (Z/E ) 1/1) and pentam-
ethylbenzene, as identified by GC/MS, 1H NMR, and 13C NMR
analyses. 1H NMR (300 MHz, CDCl3): δ 0.7-1.7 (m, 14 H), 2.18 (m,
15H), 5.48 (m, 1H, vinyl). 13C NMR (CDCl3, 75 MHz): δ 13.65, 13.94,
14.05, 14.27, 15.21, 16.52, 16.58, 17.40, 20.73, 22.40, 22.94, 24.88,
29.70, 30.6, 31.11, 32.25, 38.40, 41.14, 126.29, 127.63, 129.62, 130.47,
131.25, 132.08, 132.61, 136.71, 138.74, 138.80, 140.25, 140.76. GC/
MS: m/z M+ for 20, 258, calcd 258.
(2Z)-Ethyl 3-(Pentamethylphenyl)cinnamate (19). A colorless oil.
1H NMR (CDCl3, 300 MHz): δ 1.07 (t, J ) 7.2 Hz, 3H, CH3), 2.01
(s, 6H, 2CH3), 2.21 (s, 6H, 2CH3), 2.26 (s, 3H, CH3), 4.01 (q, J ) 7.2
Hz, 2H, CH2O), 6.62 (s, 1H, vinyl), 7.33 (m, 5H, aryl). 13C NMR
(CDCl3, 75 MHz): δ 13.89, 16.44, 16.79, 17.44, 59.65, 117.37, 127.09,
128.53, 129.24, 129.86, 131.89, 133.75, 135.47, 139.05, 156.88, 165.68.
IR (neat, cm-1): 1737 (CdO). Anal. Calcd for C22H26O2: C, 81.95;
H, 8.13. Found: C, 81.61; H, 7.95.
Standard workup gave 0.305 g of white crystals (in 92% % yield) as
5a-DD. The 1H NMR spectrum of 5a-DD is similar to that of 5a, except
for the occurrence of a singlet vinylic resonance at 7.71 ppm and the
unequal intensities of the vinylic resonances based on the integration
of protons in the methyl group connected to the carbonyl: δ 7.71 (s +
d, J ) 16.5 Hz, 0.94 H, 6% of D incorporation), 6.16 (d, J ) 16.5 Hz,
0.50H, 50% of D incorporation). GC/MS: m/z M+• for 5a-DD, 217
and 218; for 5a, 216.
Reaction of Benzene-d6 with Diphenylacetylene in TFA. The
general procedure was followed using PtCl2 (13.3 mg, 0.05 mmol),
AgOAc (16.6 mg, 0.10 mmol), PhCtCPh (0.18 g, 1 mmol), C6D6 (0.42
g, 5.0 mmol), CF3CO2H (2 mL), and CH2Cl2 (0.5 mL) with stirring
for 40 h at room temperature. Standard workup gave 0.16 g of colorless
oil (in 62% % yield) as 10-D5. The 1H NMR spectrum of 10-D5
indicated that the intensities of the vinyl proton (at 6.94 ppm as a singlet)
and aryl protons (at 7.05 ppm, multiplet, 5H and at 7.26, multiplet,
5H) are in a ratio of 1:10. GC/MS: m/z M+• for 10-D5, 261. All these
data suggest that there are five D’s in 10-D5, but no D has been
incorporated into the vinylic proton (TFA does not contain D).
H/D Exchange Reaction of (2Z)-Ethyl 3-(Pentamethylphenyl)-
propenoate (2b) in CF3CO2D. 2b (25 mg, 0.1 mmol), Pd(OAc)2 (1.1
mg, 0.005 mmol), and CF3CO2D (0.5 mL) were mixed in an NMR
tube, and then a sealed capillary tube containing sodium 2,2-dimethyl-
2-silapentane-5-sulfonate in D2O was inserted into the mixture. It is
concluded that no vinylic proton H/D exchange was found since no
Reaction of Pentamethylbenzene with Ethyl Propiolate in
CF3CO2D. The general procedure was followed using Pd(OAc)2 (3.3
mg, 0.015 mmol), HCtCCO2Et (0.15 g, 1.5 mmol), Me5C6H (0.45 g,
3.0 mmol), CF3CO2D (1.5 mL), and CH2Cl2 (0.5 mL) with stirring for
2 h at room temperature. Standard workup gave two white crystals as
1
decrease in the intensity of any peak in the H NMR spectrum was
observed. In fact, the spectrum of the reaction mixture was the same
as that of 2b in TFA.
1
2b-D (0.326 g in 86% yield) and 3a-D (18 mg in 6% yield). The H
Reaction of (2Z)-Ethyl 3-(Pentamethylphenyl)propenoate (2b)
and Ethyl Propiolate in CF3CO2D. 2b (25 mg, 0.1 mmol), HCt
CCO2Et (20 mg, 0.2 mmol), Pd(OAc)2 (1.1 mg, 0.005 mmol), and CF3-
CO2D (0.5 mL) were mixed in an NMR tube, and then a sealed capillary
tube containing sodium 2,2-dimethyl-2-silapentane-5-sulfonate in D2O
was inserted into the mixture. It is concluded that no reaction took
place after 24 h since no decrease in the intensity of any peak in the
1H NMR spectrum was observed.
NMR spectrum of 2b-D is similar to that of 2b except for the occurrence
of a singlet vinylic resonance at 7.12 ppm and the unequal intensities
of the vinylic resonances based on the integration of protons in the
ester group (Figure 3): δ 7.12 (s + d, J ) 12.0 Hz, 1H), 6.12 (d, J )
12.0 Hz, 0.43H, 57% of D incorporation). GC/MS: m/z M+• for 2b-D,
1
247; for 2b, 246, and a small amount of 2b-D2, 248. The H NMR
spectrum of 3a-D is similar to that of 3a except for the occurrence of
a singlet vinylic resonance at 7.50 ppm and the unequal intensities of
the vinylic resonances based on the integration of protons in the ester
group (Figure 3): δ 7.50 (s + d, J ) 15.9 Hz, 1H), 7.25 (s, J ) 15.9
Hz, 1H), 6.17 (d, J ) 15.9 Hz, 0.45H, 55% of D incorporation). GC/
MS: m/z M+• for 3a-D, 345; for 3a, 344; and for a small amount of
3a-D2, 346.
Reaction of Pentamethylbenzene with 3-Butyn-2-one in CF3CO2D.
The general procedure was followed using Pd(OAc)2 (3.3 mg, 0.015
mmol), HCtCCOMe (0.10 g, 1.5 mmol), Me5C6H (0.45 g, 3.0 mmol),
CF3CO2D (1.5 mL), and CH2Cl2 (0.5 mL) for 2 h at room temperature.
Acknowledgment. C.J. thanks Japan Society for the Promo-
tion of Science for a research fellowship (No. P98430).
Supporting Information Available: Details of the X-ray
structure determinations of compounds 12 and 13 (PDF). This
material is available free of charge via the Internet at
http://pubs.acs.org.
JA0005845