New synthetic applications of indium organometallics in cross-coupling reactions

Article abstract of DOI:10.1055/s-2004-834945

The use of indium organometallics in multifold and sequential cross-coupling reactions is reported. Triorganoindium reagents (R₃In) react, under palladium catalysis, with oligohaloarenes affording the multiple cross-coupling products in a single operation. In the reaction, the three organic groups (alkyl, aryl, alkenyl or alkynyl) attached to indium are efficiently transferred to the electrophile, with only a slight excess of organometallic reagent. We demonstrate that indium organometallics are useful reagents for sequential cross-coupling reactions. This reaction illustrates the high chemoselectivity of R₃In. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2004-834945

FEATURE ARTICLE
485
New Synthetic Applications of Indium Organometallics in Cross-Coupling
Reactions
N
M
ew
S
ynthetic Applica
i
tions
o
g
f
Indium Or
g
u
anometallic
e
s
l A. Pena, José Pérez Sestelo,* Luis A. Sarandeses*
Departamento de Química Fundamental, Universidade da Coruña, E-15071 A Coruña, Spain
Fax +34(981)165070; E-mail: qfsarand@udc.es
Received 19 July 2004
Dedicated to Professor Amos B. Smith, III on the occasion of his 60 birthday.
th
search groups and the synthetic scope was quickly
extended to include other indium reagents, such as tetraor-
Abstract: The use of indium organometallics in multifold and se-
quential cross-coupling reactions is reported. Triorganoindium re-
6k
ganoindates, different reaction conditions (aqueous me-
agents (R In) react, under palladium catalysis, with oligohaloarenes
3
6
b
5d,6i
affording the multiple cross-coupling products in a single operation. dia), and carbonylative cross-coupling reactions.
We
In the reaction, the three organic groups (alkyl, aryl, alkenyl or alky- describe here a full account of the use of triorganoindium
nyl) attached to indium are efficiently transferred to the electro-
compounds in multifold and sequential cross-coupling re-
phile, with only a slight excess of organometallic reagent. We
demonstrate that indium organometallics are useful reagents for se-
actions.8
quential cross-coupling reactions. This reaction illustrates the high
Pd or Ni catalyst
chemoselectivity of R In.
3 R1
3 R1
R
3
3
R In
X
THF
1
2
2
2
3
Introduction
R = Alkyl, vinyl, aryl, alkynyl
R1 = Aryl, vinyl, benzyl, acyl
Results and Discussion
Multifold Cross-Coupling Reactions
Sequential Cross-Coupling Reactions
Conclusion
.1
.2
X = Cl, Br, I, OTf
Scheme 1
Key words: atom economy, indium, organometallic reagents, mul-
tifold and sequential cross-coupling, palladium catalysis
Efficiency and economy are major goals in any chemical
transformation. In the field of organic synthesis, one im-
portant way to achieve efficiency in a reaction is through
a high level of conversion of the reagent into the reaction
product (atom economy). Another possibility is to per-
1
Introduction
Over the past decade, indium has received a great deal of form more than one reaction type, or several different re-
attention from organic chemists due to its location in the actions, in a single pot. The high conversion of R In in the
3
periodic table and the interesting chemical properties as- metal-catalyzed cross-coupling reaction prompted us to
1
sociated with it. Indium is today recognized as a useful explore its application to efficient reactions in which more
metal in organic synthesis and several synthetic applica- than one bond is formed in one step. For this purpose, oli-
2
3
tions, such as the allylation of carbonyls or triple bonds
gohaloarenes are useful partners to perform both multi-
in anhydrous or aqueous media, can be performed effi- fold cross-coupling reactions (multiple similar bonds
ciently under simple reaction conditions. Furthermore, in- formed in one step) or sequential cross-coupling reactions
dium organometallics have been shown to be useful (multiple different bonds formed in one step).
reagents in several fundamental organic transformations,
4
5,6
such as conjugate addition, cross-coupling and allylic
subtitution reactions.
7
2
2
Results and Discussion
In 1999, we discovered the metal-catalyzed cross-cou-
.1
Multifold Cross-Coupling Reactions
pling reaction of triorganoindium compounds (R In) with
3
5
a
organic halides. In this reaction, R In showed interesting
3
This particular type of reaction has been performed using
different organometallics and allows the synthesis of
highly unsaturated, conjugated p-systems, which are com-
chemical properties including high reactivity, efficiency,
versatility and chemoselectivity – all three organic groups
attached to the metal are efficiently transferred to the elec-
9
pounds of particular interest in materials science. Among
3
2
trophile and a wide variety of carbon types (sp , sp , sp)
can be bound to the metal (Scheme 1). Soon after our dis-
covery, this reaction drew the attention of various re-
the wide variety of conjugated architectures, polyphe-
nylene and polyphenylacetylene structures, as well as de-
rivatives bearing a heterocyclic unit in their structure, are
of particular interest. The utility of such compounds as
liquid crystals, core structures for dendrimers, building
blocks for two-dimensional carbon networks, electronic
1
0
11
SYNTHESIS 2005, No. 3, pp 0485–0492
x
x
.
x
x
.2
0
0
4
12
Advanced online publication: 03.12.2004
DOI: 10.1055/s-2004-834945; Art ID: Z14204SS
Georg Thieme Verlag Stuttgart · New York
©

4
86
M. A. Pena et al.
FEATURE ARTICLE
devices13 and molecular wires9b is a topic of current re- catalyzed cross-coupling reaction of 1,4-dibromobenzene
search.
(1a) with Ph In. After some experimentation, we found
3
that the double cross-coupling reaction product can be ob-
Despite the fact that various synthetic procedures have
been developed to prepare these interesting systems, met-
al-catalyzed cross-coupling reactions still represent the
tained in good yield when 100 mol% of Ph In is used in
3
THF (reflux for two hours) in the presence of 4 mol% of
9
a,14
Pd(dppf)Cl (Table 1, entry 1). Following the same exper-
2
most useful and straightforward methodology.
The
imental procedure, the reaction of tri(phenylethynyl)indi-
um or tris[(trimethylsilyl)ethynyl]indium with 1a
afforded the double cross-coupling products 2b or 2c in
cross-coupling reactions are usually performed between
an organometallic or acetylenic partner and an oligoha-
loarene to afford the desired multifold cross-coupling
products in one step. Typically, an efficient transforma-
tion requires a large excess of the organometallic reagent
and harsh reaction conditions (high temperatures and
8
3
4% and 60% yield, respectively (Table 1, entries 2 and
). The transfer of an alkyl group was also effective, using
only 70 mol% of n-Bu In (Table 1, entry 4).
3
pressure, long reaction times), and even in these cases the As demonstrated above, triorganoindium compounds are
1
5
yields are sometimes low. In an attempt to overcome the able to transfer efficiently all three aryl, alkynyl or alkyl
drawbacks outlined above, and encouraged by the partic- groups. These results can be improved using 1,4-diiodo-
ular advantages of triorganoindium compounds and the benzene (1b) as the electrophile. In this case, the cross-
potential uses of the final products, we developed a novel coupling reactions proceed in good yields using just 80
multiple palladium-catalyzed cross-coupling reaction us- mol% of R In. The reaction proceeds with triphenylindi-
3
ing triorganoindium compounds.
um, tri(phenylethynyl)indium or tris[(trimethylsilyl)ethy-
nyl]indium to give the twofold cross-coupling products
For our initial studies, we chose aryl and alkynyl triorga-
noindium reagents and dihalobenzenes as organic electro-
philes. In our first attempt, we studied the palladium-
2
a–2c in 60–76% yields. These yields can be further in-
creased to quantitative upon using 100 mol% of the trior-
Biographical Sketches
Miguel A. Pena was born in is currently working on his J. Pérez Sestelo. He spent a
Ferrol, Spain, in 1978. He Ph.D. thesis, as FPU fellow, predoctoral training period
studied chemistry at the on new developments of at the Max-Planck Institut
Universidade da Coruña, cross-coupling
reactions für Kohlenforschung in
Spain, where he obtained with indium organometal- Mülheim an der Ruhr, Ger-
his B.S. degree in 2001 and lics under the supervision of many, under the supervision
his M.S. degree in 2003. He Profs. L. A. Sarandeses and of Prof. A. Fürstner.
José Pérez Sestelo was studies with Prof. Amos B. ate professor. His main
born in Vigo (Spain) in Smith III at the University research topics are focused
1
966. He studied chemistry of Pennsylvania (1994–95) on the development of novel
at the Universidade de San- and Prof. T. Ross Kelly at metal-promoted organic re-
tiago de Compostela (B.S. Boston College (1996) he actions and their application
degree in 1989) where he joined the Universidade da to the synthesis of biologi-
got his Ph.D. in 1994 under Coruña (1997). After a peri- cally active natural prod-
the supervision of Profs. od as assistant professor ucts.
Antonio Mouriño and Luis (1998–2003) in the same in-
Castedo. After postdoctoral stitution, he became associ-
Luis A. Sarandeses was years (1990–1991) as a professor, and became asso-
born in Lugo, Spain, in NATO postdoctoral re- ciate professor in 1994. His
1
963. He studied chemistry searcher at the Université research interests are fo-
at the Universidade de San- Joseph Fourier de Grenoble, cused on the utilization of
tiago de Compostela, Spain, France, working with Dr. J.- transition metals in organic
(
B.S. degree in 1985) and L. Luche on the applications synthesis and in the synthe-
obtained his Ph.D. in 1989 of ultrasound in organic sis of natural products and
under the supervision of synthesis. In 1992, he joined pharmacologically active
Profs. L. Castedo and A. the
Universidade
da compounds.
Mouriño. He spent two Coruña, Spain, as assistant
Synthesis 2005, No. 3, 485–492 © Thieme Stuttgart · New York

FEATURE ARTICLE
New Synthetic Applications of Indium Organometallics
487
Table 1 Palladium-Catalyzed Twofold Cross-Coupling Reactions
with Triorganoindium Reagents
Table 2 Threefold Cross-Coupling Reactions of 1,3,5-Tribro-
mobenzene (3) with Indium(III) Organometallicsa
a
X
R
Br
R
Pd(dppf)Cl2 cat.
THF, reflux
R3In
Pd(dppf)Cl2 cat.
THF, reflux
X
R
3
R In
Br
Br
R
R
1
1
a, X = Br
b, X = I
2a–e
3
4a–f
Entry X
R
R In (mol%) Product Yield (%)b
Yield (%)b
3
Entry
R
R In (mol%) Product
3
1
2
3
4
5
6
7
8
Br (1a) Ph
PhC≡C
100
100
100
70
2a
2b
2c
2d
2a
2b
2c
2d
2e
70
1
2
3
4
5
Ph
130
130
150
130
130
130
4a
4b
4c
4d
4e
4f
97
99
80
90
70
76
84
PhC≡C
Me SiC≡C
60
3
Me SiC≡C
3
n-Bu
Ph
83
p-MeOC H
6
4
I (1b)
80
72
m-MeOC H
6
4
PhC≡C
80
76 (99)c
60 (92)c
70
6
n-Bu
a
Me SiC≡C
80
Reactions were performed with 4 mol% of Pd(dppf)Cl as catalyst in
3
2
refluxing THF for 2–4 h.
n-Bu
70
b
Isolated yield.
9
CH =CH
80
96
2
5c
dendrimers. The reaction with a trialkylindium species
also afforded the desired product in good yield (76%,
Table 1, entry 6). In all cases, the small excesses of trior-
ganoindium compound used and the short reaction times
required to construct three C–C bonds in a one-step, high
yielding sequence should be highlighted.
a
Reactions were carried out in refluxing THF for 2 h using 4 mol% of
Pd(dppf)Cl as catalyst.
2
b
Isolated yield.
c
The yield obtained using 100 mol% of R In is shown in parentheses.
3
ganoindium reagents (Table 1, entries 6 and 7). The
reaction of 1b with tributylindium afforded a similar re- At this point, we became interested in extending the scope
sult to that obtained previously (Table 1, entry 8), while of the multifold cross-coupling reactions to include aro-
the reaction of trivinylindium (80 mol%) gave an excel- matic compounds other than benzene. For this purpose,
lent yield of 2e (96%) after just two hours of reaction we selected an electron-deficient heteroaromatic com-
5
b
(
Table 1, entry 9). As previously reported, these results pound, 2,6-dibromopyridine (5), and an electron-rich het-
are in accordance with the higher reactivity of aryl iodides eroaromatic compound, 2,5-dibromothiophene (7).
than bromides towards triorganoindium reagents.
Aryl- and ethynyl-substituted pyridines have important
17
The utility of indium organometallics in multifold cou- applications as fluorescent chemosensors, as chelating
pling reactions was explored further by attempting to form agents in coordination chemistry, and as building blocks
1
8
19
three bonds in one step. 1,3,5-Triarylbenzenes and 1,3,5- in supramolecular structures. These compounds are usu-
triethynylbenzenes display interesting physical properties ally obtained in step-by-step cross-coupling reactions, but
as liquid crystals or non-linear optical materials and these these processes are associated with some synthetic diffi-
1
6
20
were chosen as our first targets. The reaction of 1,3,5-tri- culties. Following our methodology, we found that the
bromobenzene (3) with Ph In (130 mol%) in the presence reaction of 2,6-dibromopyridine (5) with just 80 mol% of
3
of catalytic amounts of Pd(dppf)Cl (4 mol%) under re- triphenylindium in the presence of catalytic amounts of
2
flux in THF afforded 1,3,5-triphenylbenzene (4a) in 97% Pd(dppf)Cl (4 mol%) afforded the twofold cross-cou-
2
yield (Table 2, entry 1). This result demonstrates the fea- pling product 6a in 91% yield (Table 3, entry 1). In the
sibility of using this type of organometallic reagent to same way, the reaction using tri(phenylethynyl)indium
form three C–C bonds on the same substrate in one pot, (80 mol%) as the organometallic component afforded the
and the efficient transfer of all three organic groups at- desired product, 2,6-bis(phenylethynyl)pyridine (6b), in
tached to indium(III).
90% yield (Table 3, entry 2). Other acetylenic, vinylic or
alkyl derivatives can also be efficiently synthesized using
the same experimental procedure, although larger
amounts of triorganoindium species were required (100
mol%, Table 3, entries 3–5). In particular, the lower reac-
tivity of the trialkylindium organometallics with respect
to the other compounds is evident in the reaction of
Under the same experimental conditions, the reaction of 3
with tri(phenylethynyl)indium gave the threefold cross-
coupling product 4b in quantitative yield (Table 2, entry
2
). When the reaction was performed with tris[(trimethyl-
silyl)ethynyl]indium, 150 mol% was needed to optimize
the yield (80%, Table 2, entry 3). Functionalized triarylin-
dium reagents can also be efficiently used (Table 2, en-
tries 4 and 5) and the cross-coupling products should
allow the synthesis of more complex compounds such as
n-Bu In with 5, which affords the cross-coupling product
3
in only 50% yield. In addition, in this reaction the use of
Pd(Ph P) as the catalyst gave the best results.
3
4
Synthesis 2005, No. 3, 485–492 © Thieme Stuttgart · New York

4
88
M. A. Pena et al.
FEATURE ARTICLE
Table 3 Synthesis of Disubstituted Pyridines Using Triorganoindi-
atom efficiency, with the three organic groups attached to
um Reagentsa
5d,6i
the metal transferred to the electrophile.
In our case,
under the reaction conditions previously reported5d [2.5
atm CO, 4 mol% of Pd(Ph P) in THF at 70 °C], 1,4-di-
Pd(dppf)Cl2 cat.
R3In
3
4
THF, reflux
Br
N
Br
R
N
R
iodobenzene (1b) reacted with triphenylindium (100
mol%) or tri(phenylethynyl)indium (80 mol%) to afford
the corresponding 1,4-diacylbenzene derivatives (9a or
9b) in moderate to good yields (78% and 50%, respective-
ly, Scheme 2).
5
6a–e
Entry
R
R In (mol%) Product
Yield (%)b
3
1
2
3
4
Ph
80
80
6a
6b
6c
6d
6e
91
PhC≡C
90 (99)c
82
O
CO (2.5 atm)
I
Pd(Ph3P)4 (4 mol%)
Me SiC≡C
100
100
100
R
3
R3In
THF, 70 °C
R
I
CH =CH
90
2
O
50d
1
b
9a, R = Ph, 78%
b, R = PhC≡C, 50%
5
n-Bu
9
a
Reactions were carried out in refluxing THF with Pd(dppf)Cl (4
2
Scheme 2
mol%).
b
Isolated yield.
c
The yield obtained by on using 100 mol% of R In is shown in paren-
3
A threefold carbonylative coupling was also achieved by
theses.
d
reaction of 1,3,5-triiodobenzene (10) with Ph In (160
Reaction performed with Pd(Ph P) (4 mol%) as catalyst.
3
3
4
mol%), under 2.5 atm of CO in the presence of 4 mol% of
Pd(Ph P) in THF at 70 °C, to afford the triacylbenzene 11
3
4
We next explored the reactivity of 2,5-dibromothiophene
in 70% yield (Scheme 3). These reactions demonstrate the
utility of indium organometallics in multifold cross-car-
bonylative coupling processes.
(
7). Aryl and alkynyl thiophene derivatives have interest-
9
b
ing properties as electronic devices and molecular wires.
Following our previously developed methodology, trior-
ganoindium reagents were able to efficiently transfer aryl,
alkenyl and alkynyl groups, although in this case it was
necessary to increase the ratio of indium organometallic
employed in order to optimize the yields (Table 4).
O
Ph
I
Ph3In (160 mol%)
CO (2.5 atm)
Pd(Ph3P)4 (4 mol%)
THF, 70 °C
Ph
O
I
I
O
Ph
Table 4 Synthesis of Disubstituted Thiophenes Using Triorganoin-
dium Reagentsa
10
11, 70%
Scheme 3
Pd(dppf)Cl2 cat.
R3In
Br
Br
R
R
S
THF, reflux
S
7
8a–d
2.2
Sequential Cross-Coupling Reactions
Entry
R
R In (mol%) Product
Yield (%)b
Once the behavior of indium organometallics in multifold
cross-coupling reactions was established, we decided to
explore the use of these reagents in sequential one-pot
metal-catalyzed cross-coupling reactions. The combina-
tion of several steps into a single-pot operation constitutes
an important way to improve the efficiency of a synthetic
methodology – an aspect also relevant from an economic
and environmental point of view. This methodology re-
quires high chemoselectivity, high levels of reagent con-
version, and the minimization of reaction byproducts.
Sequential cross-coupling reactions have already been
3
1
2
3
Ph
200
150
150
150
8a
8b
8c
8d
84 (40)c
91 (50)c
PhC≡C
Me SiC≡C
77
77
3
4
CH =CH
2
a
Reactions were carried out in refluxing THF using 4 mol% of
Pd(dppf)Cl .
2
b
Isolated yield.
c
The yield obtained on using 80 mol% of R In is shown in parenthe-
3
2
1
performed using different types of organometallics, and
ses.
2
2
some examples can be found based on bis-Suzuki cou-
2
3
plings or on a combination of two reaction types. In our
case, the efficiency of the cross-coupling reaction with in-
dium organometallics can be studied in the construction of
different C–C bonds in a one-step sequence by successive
addition of different triorganoindium reagents to a substi-
tuted oligohaloarene with different halogen atoms.
Having demonstrated the utility of indium organometal-
lics in multifold cross-coupling reactions with oligoha-
loarenes under palladium catalysis, we proceeded to study
the application of this methodology in carbonylative mul-
tifold coupling. The carbonylative coupling using triorga-
noindium compounds has proven to be an efficient
method to synthesize unsymmetrical ketones with high
Synthesis 2005, No. 3, 485–492 © Thieme Stuttgart · New York

FEATURE ARTICLE
New Synthetic Applications of Indium Organometallics
489
According to our previous studies, the aryl–iodide bond is cross-coupling processes involving triorganoindium com-
more reactive than the aryl–bromide bond in cross-cou- pounds allow the development of sequential cross-cou-
pling reactions with triorganoindium compounds.5c pling reactions that afford unsymmetrical alkyl-, aryl- and
Therefore, we selected 1-bromo-4-iodobenzene (12) as alkynyl-substituted aromatic compounds in one pot. In all
the first electrophile to study in sequential cross-coupling cases, the reaction proceeds in good yields with low cata-
reactions. A refluxing solution of 12 and Pd(Ph P) (4 lyst loading and short reaction times. The small excess of
3
4
mol%) was treated successively with triphenylindium (35 reagent employed shows that triorganoindium reagents
mol%) and tributylindium (50 mol%) and the sequential transfer their three organic groups to the electrophile with
cross-coupling product, 4-butylbiphenyl (13a, Table 5, high atom efficiency. These novel features make indium
entry 1), was obtained in 76% yield. This result illustrates organometallics useful alternatives to other organometal-
the chemoselectivity of the reaction and the utility of indi- lic reagents in organic synthesis and reveal them to be an
um organometallics in the one-pot preparation of unsym- important tool in modern organic synthesis.
metrically substituted aromatic compounds. In an effort to
extend the scope of the reaction, different organic groups
All reactions were conducted in flame-dried glassware in a well
were used as nucleophiles in this reaction. Aryl, alkynyl
ventilated hood. Reaction temperatures refer to external bath tem-
and alkyl groups could all be accommodated as organo- peratures. NMR spectra were obtained with a Bruker AC-200F (200
1
13
metallic counterparts, affording the corresponding 1,4-un- MHz for H NMR and 50 MHz for C NMR) spectrometer in
symmetrically substituted arenes 13b–h in good yields
1
CDCl using the residual solvent signal at d = 7.26 ppm ( H NMR)
3
1
3
or d = 77.0 ppm ( C NMR) as internal standard. DEPT was used to
assign carbon types. The electron-impact mass spectra were mea-
sured on a Fisons VG-Quattro spectrometer at 70 eV. Compounds
2a, 2c, 2d, 2e, 4a, 4b, 4d, 6a, 9a, and 13b are commercially avail-
able and were identified by comparison of their spectral data ( H
NMR, C NMR, IR, MS) and physical properties with authentic
(
40–95%, Table 5, entries 2–8).
Table 5 Sequential Cross-Coupling Reactions with Indium(III) Or-
ganometallicsa
1
1
1
2
)R 3In (35 mol%)
13
R1
I
Pd(Ph3P)4 (4 mol%)
samples.
2
)R 3In (50 mol%)
R2
Br
Triorganoindium Reagents; General Procedure
A 25 mL round-bottomed flask containing a stir bar was charged
12
13a–h
with InCl (0.40 mmol) and dried under vacuum with a heat gun.
Entry R1
R2
Yield (%)b
3
Product
The mixture was cooled, a positive argon pressure was established,
and anhydrous THF (4 mL) was added. The resulting solution was
cooled to –78 °C and a solution of RLi or RMgBr (1.1 mmol, 1.0–
1
2
3
4
5
6
7
8
Ph
n-Bu
Me
13a
13b
13c
13d
13e
13f
76
95
81
75
80
56
82
73
40
2.5 M in hexanes, THF, or Et O) was slowly added (15–30 min).
2
The mixture was stirred for 30 min, the cooling bath was removed,
and the reaction mixture was warmed to r.t.
PhC≡C
Ph
n-Bu
Me
Palladium-Catalyzed Multifold Cross-Coupling Reaction; Gen-
eral Procedure
A solution of R In (0.80 to 2.00 mmol, ca. 0.1 M in anhydrous THF)
3
was added to a refluxing mixture of the electrophile (1, 3, 5 or 7, 1
Me SiC≡C
Ph
3
mmol) and Pd(dppf)Cl (0.04 mmol) in anhydrous THF (4 mL). The
2
n-Bu
Ph
13g
13a
13h
mixture was heated under reflux until the starting material had been
consumed (2–4 h, TLC monitoring) and the reaction was quenched
by the addition of few drops of MeOH. The mixture was concentrat-
n-Bu
ed in vacuo and Et O (30 mL) was added. The organic phase was
2
9
Me
n-Bu
washed with sat. aq NH Cl (15 mL), dried (Na SO ), filtered, and
4
2
4
a
1
All reactions were carried out with 35 mol% of R In followed by 50
concentrated under vacuum. The residue was purified by flash chro-
matography to afford, after concentration and high-vacuum drying,
the multifold cross-coupling product.
3
2
3
mol% of R In in the presence of 4 mol% of Pd(Ph P) in refluxing
3
4
THF.
b
Isolated yield.
Palladium-Catalyzed Multifold Carbonylative Cross-Coupling
Reaction; General Procedure
In a Schlenk tube, a solution of R In (0.80 to 1.35 mmol, ca. 0.1 M
in anhydrous THF) was added to a mixture of the electrophile (1b
3
3
Conclusions
or 12, 1 mmol) and Pd(Ph P) (0.05 mmol) in anhydrous THF (5
3
4
Triorganoindium compounds can be efficiently employed mL). The tube was charged with CO (2.5 atm) and the resulting
mixture was heated at 70 °C for 6 h. The mixture was cooled, the
in multifold cross-coupling reactions using oligohalo-
pressure was released and the reaction was quenched by the addi-
tion of a few drops of MeOH. The mixture was concentrated in vac-
arenes and polyhalogenated aromatic heterocyclic com-
pounds. This methodology provides the possibility of
building several C–C bonds in a single operation. The
uo and Et O (20 mL) was added. The organic phase was washed
2
with sat. aq NH Cl (15 mL), dried (Na SO ), filtered, and concen-
4
2
4
multifold cross-coupling reaction can be performed under trated under vacuum. The residue was purified by flash chromatog-
a carbon monoxide atmosphere giving di- or triacylben- raphy (15% EtOAc–hexanes) to afford, after concentration and
high-vacuum drying, the multifold carbonylative cross-coupling
product.
zene derivatives in one pot. Furthermore, the high
chemoselectivity and atom efficiency in metal-catalyzed
Synthesis 2005, No. 3, 485–492 © Thieme Stuttgart · New York

4
90
M. A. Pena et al.
FEATURE ARTICLE
3
0
Palladium-Catalyzed Sequential Cross-Coupling Reactions;
2,6-Divinylpyridine (6d)
1
General Procedure
H NMR (CDCl ): d = 5.49 (dd, J = 10.7, 1.5 Hz, 2 H), 6.26 (dd,
J = 17.6, 1.5 Hz, 2 H), 6.84 (dd, J = 17.6, 10.7 Hz, 2 H), 7.22 (d,
J = 7.8 Hz, 2 H), 7.60 (t, J = 7.8 Hz, 1 H).
3
1
3
A solution of R In (0.35 mmol, ca. 0.1 M in anhydrous THF) was
added to a refluxing mixture of 9 (1 mmol) and Pd(Ph P) (0.04
3
4
mmol) in anhydrous THF (4 mL). After refluxing the mixture until
13
C NMR (CDCl ): d = 118.2 (2 × CH ), 119.9 (2 × CH), 136.8
3
2
the starting material had been consumed (2–4 h, TLC monitoring),
(
CH), 137.0 (2 × CH), 155.3 (2 × C).
2
a solution of R In (0.50 mmol, ca. 0.1 M in anhydrous THF) was
3
+
MS (FAB) m/z (%) = 132 [(M + 1), 100].
added. The resulting mixture was refluxed under the same condi-
tions until the intermediate product had been consumed (2–4 h) and
the reaction was quenched with a few drops of MeOH. The mixture
2
,6-Dibutylpyridine (6e)31
1
H NMR (CDCl ): d = 0.92 (t, J = 7.3 Hz, 6 H), 1.23–1.46 (m, 4 H),
1
2
was concentrated in vacuo, Et O (30 mL) was added and the organic
3
2
.60–1.75 (m, 4 H), 2.74 (m, J = 7.8 Hz, 4 H), 6.91 (d, J = 7.8 Hz,
H), 7.45 (t, J = 7.8 Hz, 1 H).
phase was washed with sat. aq NaCl (15 mL), dried (Na SO ), fil-
2
4
tered and concentrated under vacuum. The residue was purified by
flash chromatography (hexanes) to afford, after concentration and
high-vacuum drying, the sequential cross-coupling product.
13
C NMR (CDCl ): d = 13.9 (2 × CH ), 22.5 (2 × CH ), 32.3 (2 ×
3
3
2
CH ), 38.3 (2 × CH ), 119.5 (2 × CH), 136.2 (CH), 161.8 (2 × C).
2
2
+
+
,4-Bis(phenylethynyl)benzene (2b)24
MS (EI): m/z (%) = 191 (M , 4), 176 [(M – CH ), 8], 149 (100).
3
1
1
H NMR (CDCl ): d = 7.33–7.40 (m, 6 H), 7.51–7.58 (m, 8 H).
3
,5-Diphenylthiophene (8a)32
H NMR (CDCl ): d = 7.26–7.45 (m, 6 H), 7.31 (s, 2 H), 7.62–7.68
m, 4 H).
2
1
3
C NMR (CDCl ): d = 89.1 (2 × C), 91.2 (2 × C), 123.0 (2 × C),
1
3
3
1
1
23.1 (2 × C), 128.37 (2 × CH), 128.43 (2 × CH), 131.5 (4 × CH),
31.6 (4 × CH).
(
1
3
C NMR (CDCl ): d = 124.0 (2 × CH), 125.6 (4 × CH), 127.5 (2 ×
3
+
MS (EI): m/z (%) = 278 (M , 100), 139 (19).
CH), 128.9 (4 × CH), 134.3 (2 × C), 143.6 (2 × C).
+
,3,5-Tris[(trimethylsilyl)ethynyl]benzene (4c)25
MS (EI): m/z (%) = 236 (M , 100).
1
1
H NMR (CDCl ): d = 0.24 (s, 27 H), 7.50 (s, 3 H).
3
,5-Bis(phenylethynyl)thiophene (8b)32
H NMR (CDCl ): d = 7.17 (s, 2 H), 7.33–7.40 (m, 6 H), 7.50–7.57
m, 4 H).
2
1
3
C NMR (CDCl ): d = –10.9 (9 × CH ), 95.6 (3 × C), 103.1 (3 × C),
1
3
3
3
1
23.6 (3 × C), 134.9 (3 × CH).
(
+
+
MS (EI): m/z (%) = 366 (M , 32), 351 [(M – CH ), 100].
13
3
C NMR (CDCl ): d = 82.2 (2 × C), 94.0 (2 × C), 122.6 (2 × C),
3
1
1
24.6 (2 × C), 128.4 (4 × CH), 128.6 (2 × CH), 131.5 (4 × CH),
31.8 (2 × CH).
1
,3,5-Tris(3-methoxyphenyl)benzene (4e)26
1
H NMR (CDCl ): d = 3.91 (s, 9 H), 6.98 (br d, J = 7.9 Hz, 3 H),
7
3
+
MS (EI): m/z (%) = 284 (M , 19), 88 (100).
.28 (br s, 3 H), 7.32 (d, J = 7.6 Hz, 3 H), 7.44 (dd, J = 7.9, 7.6 Hz,
3
H), 7.82 (s, 3 H).
2
,5-Bis[(trimethylsilyl)ethynyl]thiophene (8c)33
1
3
C NMR (CDCl ): d = 55.4 (3 × CH ), 113.0 (3 × CH), 113.1 (3 ×
1
3
3
H NMR (CDCl ): d = 0.25 (s, 18 H), 7.05 (s, 2 H).
3
3
CH), 119.9 (3 × CH), 125.4 (3 × CH), 129.9 (3 × CH), 142.2 (3 ×
C), 142.6 (3 × C), 160.0 (3 × C).
1
C NMR (CDCl ): d = –0.2 (6 × CH ), 96.9 (2 × C), 99.9 (2 × C),
3
3
1
24.5 (2 × C), 132.2 (2 × CH).
+
MS (EI): m/z (%) = 396 (M , 100).
+
+
MS (EI): m/z (%) = 276 (M , 47), 261 [(M – CH ), 100].
3
1
,3,5-Tributylbenzene (4f)27
3
4
1
2,5-Divinylthiophene (8d)
H NMR (CDCl ): d = 0.95 (t, J = 7.3 Hz, 9 H), 1.28–1.47 (m, 6 H),
1
3
1
H NMR (CDCl ): d = 5.15 (d, J = 10.8 Hz, 2 H), 5.55 (d, J = 17.1
Hz, 2 H), 6.76 (dd, J = 17.1, 10.8, 2 H), 6.84 (s, 2 H).
3
.54–1.69 (m, 6 H), 2.57 (t, J = 7.3 Hz, 6 H), 6.83 (s, 3 H).
1
3
C NMR (CDCl ): d = 14.0 (3 × CH ), 22.5 (3 × CH ), 33.8 (3 ×
3
3
2
13
C NMR (CDCl ): d = 113.4 (2 × CH ), 126.3 (2 × CH), 130.0 (2 ×
3
2
CH ), 35.7 (3 × CH ), 125.8 (3 × CH), 142.6 (3 × C).
2
2
CH), 141.9 (2 × C).
+
MS (EI): m/z (%) = 246 (M , 43), 204 (100), 147 (77).
+
MS (EI): m/z (%) = 136 (M , 100).
2
,6-Bis(phenylethynyl)pyridine (6b)28
1,1¢-(1,4-Phenylene)bis[3-phenylprop-2-yn-1-one] (9b)3
5
1
H NMR (CDCl ): d = 7.35–7.41 (m, 6 H), 7.48 (d, J = 7.6 Hz, 2 H),
7
3
1
H NMR (CDCl ): d = 7.41–7.58 (m, 6 H), 7.70–7.76 (m, 4 H), 8.36
3
.59–7.64 (m, 4 H), 7.70 (d, J = 7.6 Hz, 1 H).
(
s, 4 H).
1
3
C NMR (CDCl ): d = 88.3 (2 × C), 89.6 (2 × C), 122.1 (2 × C),
3
13
C NMR (CDCl ): d = 86.8 (2 × C), 94.5 (2 × C), 119.7 (2 × C),
29.6 (4 × CH), 131.2 (2 × CH), 133.2 (4 × CH), 140.5 (2 × C),
3
1
1
26.2 (2 × CH), 128.4 (4 × CH), 129.1 (2 × CH), 132.1 (4 × CH),
36.4 (CH), 143.8 (2 × C).
1
1
77.0 (2 × C).
+
+
+
MS (EI): m/z (%) = 279 (M , 100), 278 [(M – 1), 43], 178 [(M –
C H ), 6].
+
MS (EI): m/z (%) = 334 (M , 34), 306 (15), 278 (26), 183 (22), 129
8
5
(
100).
2
,6-Bis[(trimethylsilyl)ethynyl]pyridine (6c)29
3
6
1
1,3,5-Tribenzoylbenzene (11)
H NMR (CDCl ): d = 0.26 (s, 18 H), 7.38 (d, J = 7.9 Hz, 2 H), 7.59
3
1
H NMR (CDCl ): d = 7.48–7.68 (m, 9 H), 7.83–7.89 (m, 6 H), 8.41
3
(
t, J = 7.9 Hz, 1 H).
(
s, 3 H).
1
3
C NMR (CDCl ): d = –0.4 (6 × CH ), 95.3 (2 × C), 103.1 (2 × C),
3
3
13
C NMR (CDCl ): d = 128.6 (6 × CH), 130.1 (6 × CH), 133.2 (3 ×
CH), 134.0 (3 × CH), 136.4 (3 × C), 138.2 (3 × C), 194.9 (3 × C).
3
1
26.6 (2 × CH), 136.2 (CH), 143.3 (2 × C).
+
+
+
MS (EI): m/z (%) = 271 (M , 38), 256 [(M – CH ), 100], 226 [(M
–
3
+
MS (EI): m/z (%) = 390 (M , 7), 105 (100).
C H ), 5].
2 6
Synthesis 2005, No. 3, 485–492 © Thieme Stuttgart · New York

FEATURE ARTICLE
-Butyl-1,1¢-biphenyl (13a)37
New Synthetic Applications of Indium Organometallics
491
4
Acknowledgment
1
H NMR (CDCl ): d = 0.98 (t, J = 7.3 Hz, 3 H), 1.30–1.54 (m, 2 H),
3
We are grateful to the Ministerio de Ciencia y Tecnología and Xun-
ta de Galicia of Spain and FEDER (BQU2003–00301 and
PGIDT04PXIC10308PN) for financial support. M.A.P thanks the
Ministerio de Educación Cultura y Deporte of Spain for a predocto-
ral fellowship (FPU).
1
.61–1.76 (m, 2 H), 2.69 (t, J = 7.3 Hz, 2 H), 7.29 and 7.55 (2 d, AB
system, J = 8.3 Hz, 4 H), 7.33–7.52 (m, 3 H), 7.60–7.66 (m, 2 H).
1
3
C NMR (CDCl ): d = 14.0 (CH ), 22.4 (CH ), 33.6 (CH ), 35.3
2
3
3
2
2
(
CH ), 127.0 (2 × CH), 127.16 (CH), 127.23 (CH), 128.68 (2 ×
CH ), 128.74 (2 × CH), 128.8 (2 × CH), 138.5 (C), 141.2 (C), 142.0
(
2
C).
+
+
+
References
MS (EI): m/z (%) = 210 (M , 31), 167 [(M – C H ), 100], 152 [(M
3
7
–
C H ), 19].
4 9
(
1) (a) Cintas, P. Synlett 1995, 1087. (b) Marshall, J. A.
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(e) Podlech, J.; Maier, T. C. Synthesis 2003, 633.
4
-(Phenylethynyl)-1,1¢-biphenyl (13c)38
1
H NMR (CDCl ): d = 7.35–7.71 (m, 14 H).
3
1
3
C NMR (CDCl ): d = 89.3 (C), 90.1 (C), 122.2 (C), 123.3 (C),
27.0 (2 × CH), 127.5 (CH), 127.6 (CH), 128.26 (2 × CH), 128.35
3
1
(
(
2 × CH), 128.9 (2 × CH), 131.6 (2 × CH), 132.0 (2 × CH), 140.4
C), 141.0 (C).
+
(2) (a) Li, C.-J.; Chan, T.-H. Tetrahedron 1999, 55, 11149.
MS (EI): m/z (%) = 254 (M , 100).
(
b) Ranu, B. C. Eur. J. Org. Chem. 2000, 2347. (c) Pae, A.
-Butyl-4-(phenylethynyl)benzene (13d)39
N.; Cho, Y. S. Curr. Org. Chem. 2002, 6, 715.
(3) (a) Araki, S.; Imai, A.; Shimizu, K.; Yamada, M.; Mori, A.;
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C.; Majee, A. Chem. Commun. 1997, 1225. (c) Fujiwara,
N.; Yamamoto, Y. J. Org. Chem. 1999, 64, 4095.
1
1
H NMR (CDCl ): d = 0.98 (t, J = 7.3 Hz, 3 H), 1.22–1.46 (m, 2 H),
3
1
.51–1.70 (m, 2 H), 2.64 (t, J = 7.3 Hz, 2 H), 7.18 and 7.45 (2 d, AB
system, J = 7.8 Hz, 4 H), 7.31–7.39 (m, 3 H), 7.52–7.53 (m, 2 H).
1
3
C NMR (CDCl ): d = 13.9 (CH ), 22.3 (CH ), 33.4 (CH ), 88.7
3
3
2
2
(d) Klaps, E.; Schmid, W. J. Org. Chem. 1999, 64, 7537.
(
(
C), 89.6 (C), 120.6 (C), 123.5 (C), 128.0 (CH), 128.2 (CH), 128.3
(e) Takami, K.; Yorimitsu, H.; Oshima, K. Org. Lett. 2002,
CH), 128.4 (2 × CH), 131.5 (2 × CH), 131.6 (2 × CH), 143.4 (C).
4, 2993.
+
+
(4) (a) Araki, S.; Shimizu, K.; Jin, S.-J.; Butsugan, Y. J. Chem.
Soc., Chem. Commun. 1991, 824. (b) Pérez, I.; Pérez
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J. Org. Chem. 1998, 63, 10074.
MS (EI): m/z (%) = 234 (M , 60), 191 [(M – C H ), 100].
3
7
-Methyl-4-(phenylethynyl)benzene (13e)40
1
1
H NMR (CDCl ): d = 2.40 (s, 3 H), 7.18 and 7.47 (2 d, AB system,
3
(5) For contributions from this group see: (a) Pérez, I.; Pérez
J = 7.8 Hz, 4 H), 7.33–7.40 (m, 3 H), 7.53–7.61 (m, 2 H).
Sestelo, J.; Sarandeses, L. A. Org. Lett. 1999, 1, 1267.
1
3
C NMR (CDCl ): d = 21.5 (CH ), 88.8 (C), 89.6 (C), 120.2 (C),
3
3
(b) Pérez, I.; Pérez Sestelo, J.; Sarandeses, L. A. J. Am.
1
23.5 (C), 128.1 (CH), 128.3 (2 × CH), 129.1 (2 × CH), 131.5 (2 ×
CH), 131.6 (2 × CH), 138.4 (C).
Chem. Soc. 2001, 123, 4155. (c) Pena, M. A.; Pérez, I.;
Pérez Sestelo, J.; Sarandeses, L. A. Chem. Commun. 2002,
2246. (d) Pena, M. A.; Pérez Sestelo, J.; Sarandeses, L. A.
Synthesis 2003, 780.
+
+
MS (EI): m/z (%) = 192 (M , 100), 115 [(M – C H ), 9].
6
5
1
-Phenyl-4-[(trimethylsilyl)ethynyl]benzene (13f)41
(6) (a) Nomura, R.; Miyazaki, S.-I.; Matsuda, H. J. Am. Chem.
Soc. 1992, 114, 2738. (b) Takami, K.; Yorimitsu, H.;
1
H NMR (CDCl ): d = 0.30 (s, 9 H), 7.33–7.51 (m, 3 H), 7.56 (s, 4
3
H), 7.59–7.66 (m, 2 H).
Shinokubo, H.; Matsubara, S.; Oshima, K. Org. Lett. 2001,
3, 1997. (c) Lee, P. H.; Sung, S.; Lee, K. Org. Lett. 2001, 3,
1
3
C NMR (CDCl ): d = 0.0 (3 × CH ), 94.8 (C), 105.0 (C), 122.0
3
3
3201. (d) Gotov, B.; Kaufmann, J.; Schumann, H.; Schmalz,
(
1
C), 126.8 (2 × CH), 127.0 (2 × CH), 127.6 (CH), 128.8 (2 × CH),
32.4 (2 × CH), 140.3 (C), 141.2 (C).
H.-G. Synlett 2002, 361. (e) Jaber, N.; Gelman, D.;
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2002, 1628. (f) Lee, K.; Lee, J.; Lee, P. H. J. Org. Chem.
+
+
MS (EI): m/z (%) = 250 (M , 56), 235 [(M – CH ), 100].
3
2
002, 67, 8265. (g) Lee, K.; Seomoon, D.; Lee, P. H. Angew.
-Butyl-4-[(trimethylsilyl)ethynyl]benzene (13g)42
Chem. Int. Ed. 2002, 41, 3901. (h) Takami, K.; Yorimitsu,
H.; Oshima, K. Org. Lett. 2002, 4, 2993. (i) Lee, P. H.; Lee,
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Org. Chem. 2003, 68, 6627. (k) Lee, P. H.; Lee, S. W.;
Seomoon, D. Org. Lett. 2003, 5, 4963.
1
3
C NMR (CDCl ): d = 0.0 (3 × CH ), 14.1 (CH ), 22.2 (CH ), 33.3
3
3
3
2
2
2
31.8 (2 × CH), 143.6 (C).
(7) (a) Lee, P. H.; Sung, S.-Y.; Lee, K.; Chang, S. Synlett 2002,
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+
+
3
J. Org. Chem. 2003, 68, 2518. (c) Baker, L.; Minehan, T. J.
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-Butyl-4-methylbenzene (13h)43
(
(
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3
C NMR (CDCl ): d = 14.0 (CH ), 21.0 (CH ), 22.4 (CH ), 33.8
3
3
3
2
2
2
(10) (a) Ebert, M.; Jungbauer, D. A.; Kleppinger, R.; Wendorff,
+
+
J. H.; Kohne, B.; Praefcke, K. Liq. Cryst. 1989, 4, 53.
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3
7
(
b) Kumar, S.; Varshney, S. K. Angew. Chem. Int. Ed. 2000,
9, 3140.
3
Synthesis 2005, No. 3, 485–492 © Thieme Stuttgart · New York

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FEATURE ARTICLE
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(
(
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