C(sp2)-C(sp) and C(sp)-C(sp) Coupling Reactions Catalyzed by Oxime-Derived Palladacycles

Article abstract of DOI:10.1002/adsc.200303067

Oxime-derived chloro-bridged palladacycle 8a, derived from 4,4′-dichlorobenzophenone, is an efficient pre-catalyst for the copper- and amine-free Sonogashira coupling between terminal acetylenes and aryl iodides and aryl and vinyl bromides achieving turnover numbers (TON) of up to 72000. Catalyst 8a has also been shown as a effective promoter for the sila-Sonogashira coupling between 1-(trimethylsilyl)alkynes and aryl iodides and bromides in the presence of CuI or Bu₄NBr as co-catalysts. This complex also catalyzes efficiently the homocoupling reaction (Glaser-type coupling) between 1-alkynes in NMP at room temperature with TONs of up to 1000. All the reactions can be performed under air and employing reagent-grade chemicals under very low loading conditions, which demonstrates the versatility and high activity of oxime-derived palladacycles.

Full text of DOI:10.1002/adsc.200303067

FULL PAPERS
C(sp2)-C(sp) and C(sp)-C(sp) Coupling Reactions Catalyzed by
Oxime-Derived Palladacycles
a
¬
Diego A. Alonso, Carmen Najera,* M Carmen Pacheco
¬
Departamento de QuÌmica Organica, Universidad de Alicante, Apartado 99, 03080 Alicante, Spain
Fax: ( ‡ 34)-965903549, e-mail: cnajera@ua.es
Received: April 10, 2003; Accepted: June 23, 2003
Abstract: Oxime-derived chloro-bridged palladacycle reaction (Glaser-type coupling) between 1-alkynes in
8a, derived from 4,4'-dichlorobenzophenone, is an NMP at room temperature with TONs of up to 1000.
efficient pre-catalyst for the copper- and amine-free All the reactions can be performed under air and
Sonogashira coupling between terminal acetylenes employing reagent-grade chemicals under very low
and aryl iodides and aryl and vinyl bromides achiev- loading conditions, which demonstrates the versatility
ing turnover numbers (TON) of up to 72000. Catalyst and high activity of oxime-derived palladacycles.
8a has also been shown as a effective promoter for the
sila-Sonogashira coupling between 1-(trimethylsil-
yl)alkynes and aryl iodides and bromides in the Keywords: alkynes; aryl halides; C C coupling; ho-
presence of CuI or Bu4NBr as co-catalysts. This mogeneous catalysis; metallacycles; N ligands; palla-
complex also catalyzes efficiently the homocoupling dium
À
Introduction
the methodologies that employ CuI as co-catalyst,
Buchwald and Fu,[5] have described Pd(PhCN)2Cl2/
Metal-catalyzed acetylenic homo- and cross-coupling CuI/P(t-Bu)3 as a versatile catalyst system for the
processes are currently under intensive study due to the Sonogashira reaction of aryl bromides at room temper-
presence of the alkynyl moieties in a wide range of ature (TON up to 200). Using an excess of a bulky and
natural and unnatural organic materials.[1] Two of the electron-donating ligand such as P(t-Bu)3 (6 mol %) and
most useful synthetic transformations of alkynes are the a high catalyst loading (3 mol % of Pd), these authors
Sonogashira Hagihara reaction[2] (palladium/copper- could effect the Sonogashira coupling using only an
catalyzed cross-coupling reactions of sp2-C to sp-C equimolar amount of amine. On the other hand, Mori
atoms) or the silane version of the process employing has carried out the Sonogashira coupling of terminal
alkynylsilanes (sila-Sonogashira reaction[3]), and the alkynes with aryl iodides and bromides at room temper-
palladium-catalyzed acetylenic oxidative homocoupling ature in the presence of Pd(PPh3)2Cl2 in THF with
reaction between their sp-carbon atoms, called the aqueous ammonia as base.[6] Very recently, Plenio and
Glaser-type process.[4]
colleagues[7] have presented a new and very efficient
The Sonogashira coupling of terminal acetylenes with catalytic system for the Sonogashira coupling of acti-
sp2-C atoms, provides a useful tool for the preparation of vated and non-activated aryl chlorides with terminal
alkyl-, aryl-, and diaryl-substituted acetylenes (Eq. 1, acetylenes, based on the combination Na2PdCl4/(1-
R2 ˆ H). The reaction is typically carried out in the Ad)2PBn/CuI (1-Ad ˆ 1-adamantyl, Bn ˆ benzyl). On
presence of copper(I) salts as co-catalysts, and employ- the other hand, N-heterocyclic carbene palladium(II)
ing amines as solvents. Most frequently, high loadings of complex 1,[8] has also been shown to mediate the
palladium (0.1 5 mol %) and varying amounts of CuI Sonogashira coupling of aryl bromides with different
are requiredwhen typicalcatalysts such as Pd(PPh3)2Cl2, alkynes at 80 0C in DMF under inert atmosphere, in the
Pd(PPh3)4 or Pd2(dba)3 are employed. With respect to presence of 2 mol % of CuI and 1 mol % of PPh3.
However, and in order to simplify the reaction protocol,
copper-free methodologies have lately attracted most
attention, as the use of copper(I) salts as co-catalysts
usually induces the homocoupling reaction (Glaser-
type[4]) of terminal alkynes to diynes in the presence of
oxygen as well as the precipitation of catalytically
inactive palladium black. Recent advances in this topic
have been reported employing amines as solvents
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C(sp2)-C(sp) and C(sp)-C(sp) Coupling Reactions
FULL PAPERS
cally diarylated acetylenes employing either trimethyl-
silylacetylene (TMSA) or bis(trimethylsilyl)acetylene
(BTMSA), which avoids the use of the toxic and tricky
to handle acetylene. The sila-Sonogashira reaction is
usually carried out in the presence of a palladium
catalystand afluorideionsource asactivator,[18] because
trimethylsilylated alkynes are usually inert to the
Sonogashira Hagihara reaction conditions. Lately, sil-
ver(I) salts have been shown as very effective co-
catalysts for the coupling of aryl iodides or vinyl triflates
with alkynylsilanes, employing different Pd(II) or Pd(0)
catalysts accompanied by phosphane ligands.[19] Mori
and co-workers have also shown that CuCl is a very
effective co-catalyst for the palladium-catalyzed reac-
tion of 1-trimethylsilylalkynes with aryl triflates in DMF
at 808C and under neutral conditions.[20] Yang and Nolan
have recently reported a very efficient sila-Sonogashira
reaction between aryl bromides and alkynylsilanes
catalyzed by the system Pd(OAc)2/imidazolium salt 6
(Figure 1).[21] Finally, Grieco et al. have used the system
PdCl2(PPh3)2/CuI in the presence of an amidine such as
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base, for
the one-pot synthesis of symmetrical and unsymmetrical
bisarylethynes employing TMSA under aqueous con-
ditions.[22]
Figure 1.
(piperidine or pyrrolidine) and palladium(0) complexes
Acetylenic homocoupling of terminal alkynes[4]
such as Pd(PPh3)4 as catalysts.[9] On the other hand, (Glaser reaction), is an atom economic and straightfor-
Herrmann and co-workers have recently found that the ward method for the synthesis of conjugated diynes,
catalytic system Pd2(dba)3/P(t-Bu)3 promotes the cop- polyynes and acetylenic arrays. These derivatives are
per-free Sonogashira-type reaction of aryl bromides at finding increasing applications as key structural ele-
room temperature.[10] Likewise, stoichiometric amounts ments of new materials with unusual electrical and
of silver(I) oxide for aryl iodides, and tetrabutylammo- optical properties, and are encountered in numerous
nium fluoride (Bu4NF) or tetrabutylammonium hydrox- natural and biologically active compounds. Since Rossi
ide (Bu4NOH) for aryl bromides, have also been used as in 1985 optimized the homocoupling reaction of termi-
activators in the first described copper- and amine-free nal alkynes as a synthetic method, employing palladium
procedure,[11] even though when using the ammonium as catalyst in the presence of CuI as co-catalyst and
salts as activators, the coupling reaction is rather slug- chloroacetone as terminal oxidant,[23] diverse modifica-
gish and CuI has to be added in a further improved tions of the procedure have appeared using different
procedure.[12] With respect to the use of palladacycles[13] oxidants such as DMSO,[24] iodine[25] or (diacetoxy)io-
as pre-catalysts for the copper-free Sonogashira-type dobenzene.[26] Palladium(II) complexes bearing N-het-
reaction, Herrmann×s phosphapalladacycle 2[14] and erocyclic carbenes modified with phosphines of the type
carbene-derived palladacycles 3[15] and 4[16] (Figure 1), 7 (Figure 1), have also been found to promote the
have been used in a copper-free protocol employing homocoupling of phenylacetylene in the presence of
triethylamine (TEA) as solvent at 908C with turnov er CuI as co-catalyst and TEA as solvent even in the
numbers (TON) of up to 8000 when using catalyst 2. With absence of added oxidant.[27] However, there are no
regard to the use of aryl chlorides as sp2 counterparts of reported examples, to the best of our knowledge, about
the reaction, Eberhard et al.[17] have established the first the use of palladacycles as catalysts for the homocou-
efficient palladium-based and copper-free catalytic sys- pling reaction of terminal acetylenes.
tem, which cross-couples efficiently a wide range of
We have recently reported that phosphane-free
activated and non-activated aryl chlorides with phenyl- oxime-based palladacycles 8 (Figure 1), are air- and
acetylene, employing the palladium PCP pincer complex water-stable pre-catalysts for a wide range of cross-
5(Figure 1) inthepresenceofcatalyticamounts ofZnCl2. coupling processes such as Heck, Suzuki, Stille, Sono-
The use of alkynylsilanes as sp components in the gashira and Ullmann-type reactions in organic[28] and
palladium-catalyzed cross-coupling reaction (sila-Sono- aqueous solvents.[29] In a preliminary communica-
gashira coupling3) (Eq. 1, R2 ˆ SiR3), has become a very tion,[28d] we have shown complexes 8 as very efficient
important tool in synthetic organic chemistry. This and versatile catalysts for amine- and copper-free
protocol has been used for the synthesis of symmetri- Sonogashira-type reactions of aryl iodides and aryl
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Diego A. Alonso et al.
FULL PAPERS
bromides with a variety of terminal acetylenes in air and zophenone 8a. Other palladacycles under study in our
using reagent-grade chemicals with turnovernumbers of group, derived from benzophenone, acetophenone,
up to 72000. Herein, we report the full account of oxime- pinacolone and 4,4'-dimethoxybenzophenone oximes,
derived complexes as efficient pre-catalysts not only for all gave in general similar or inferior results. In order to
the palladium-catalyzed Sonogashira-type coupling, but determine the optimum reaction conditions, we chose
also for the sila-Sonogashiraand homocoupling reactions the coupling between 1-chloro-4-iodobenzene and phe-
ofacetylenes under airatmosphere. Wedescribe first the nylacetylene in the presence of catalyst 8a (0.1
copper- and amine-free Sonogashira-type coupling of 0.5 mol % of Pd) as a model reaction (Scheme 1,
aryl iodides and vinyl and aryl bromides with different Table 1). As we have previously reported,[28d] the
terminal acetylenes in N-methylpyrrolidinone (NMP) coupling reaction, provided a good yield of the arylated
as solvent and tetrabutylammonium acetate (Bu4NOAc) acetylene 9a after 1 h (84%) when pyrrolidine was used
as base. Secondly, the synthesis of symmetrical diaryl- as solvent in the presence of CuI as co-catalyst (5 mol %)
ethynes from the palladium cross-coupling reaction of at 908C under air using 0.5 mol % of Pd (Table 1,
TMSA or BTMSAwith aryl iodides and bromides in the entry 1). Unexpectedly, when using NMP as solvent and
presence of CuI as co-catalyst is studied, as well as the only 2 equiv. of pyrrolidine as base in the absence of CuI
synthesis of monoarylated trimethylsilylalkynes from at 1108C (Table 1, entry 2), an excellent 96% yield of
the palladium cross-coupling reaction of TMSA or product was obtained. As a consequence of this result,
BTMSAwith aryl iodides and bromides in the presence we carried out a base study, which showed that inorganic
of tetrabutylammonium bromide (Bu4NBr) as co-cata- bases such as NaOAc or NH4OAc (150 mol %), only led
lyst. Finally, the palladium-catalyzed homocoupling to poor reaction yields (Table 1, entries 3 and 4). Other
reaction of terminal alkynes at room temperature in bases such as tetrabutylammonium fluoride (Bu4NF)
NMP as solvent and pyrrolidine as base to afford (150 mol %), gave an acceptable 86% yield after 3 h.
symmetrical conjugated diynes will be considered.
Aqueous tetrabutylammonium hydroxide (Bu4NOH)
did not promote the reaction coupling at all (Table 1,
entry 6). However, tetrabutylammonium acetate
(Bu4NOAc, 150 mol %) showed the best activity even
when the catalyst loading was reduced to 0.1 mol % of
Pd (Table 1, entry 7) and also in the presence of small
amounts of water (Table 1, entry 8). The reaction could
be carried out at lower temperature (80 0C) and using 1.1
equiv. of Bu4NOAc as well (Table 1, entry 9). Changing
Results and Discussion
Sonogashira-type Coupling of Aryl and Vinyl Halides
with Terminal Alkynes
The alkynylation reaction of aryl halides was evaluated the solvent from NMP to THF under reflux, resulted in a
with an oxime catalyst derived from 4,4'-dichloroben- lower yield and longer reaction times (Table 1, en-
Table 1. Sonogashira coupling: reaction conditions study.
Entry
Solvent
Additive [mol %]
T[a] [0C]
8a [mol % Pd]
t [h]
Yield[b] [%]
TON[c]
1
2
3
4
5
6
7
8
9
Pyrrolidine
NMP
NMP
NMP
NMP
NMP
NMP
NMP/H2O, 95/5
NMP
THF
CuI (5)
90
110
110
110
110
110
110
110
80
0.5
0.5
0.5
0.5
0.5
0.1
0.1
0.1
0.1
1
1
1
3.5
3
3
2
1
4
5
84
96
168
192
72
58
172
Pyrrolidine[d]
NaOAc[e]
36[f]
29[f]
86[f]
0
NH4OAc[e]
Bu4NF (150)
Bu4NOH (150)
Bu4NOAc (150)
Bu4NOAc (110)
Bu4NOAc (110)
Bu4NOAc (110)
Bu4NOAc (110)
Bu4NOAc (110)
> 99
> 99
> 99
89
97
72
990
990
990
890
9700
72000
[g]
10
11
12
-
0.1
NMP
NMP
110
110
10À2
10À3
24
24
[a]
Bath temperature.
[b]
[c]
[d]
[e]
[f]
Conversion determined by GLC using decane as internal standard and based on starting 1-chloro-4-iodobenzene.
TON ˆ turnover number (mol product mol PdÀ1).
2 equiv. were used.
1.5 equiv. were used.
Several non-identified enyne by-products were also obtained in variable yields as a result of the addition of the terminal
alkyne to the reaction product.
Under THF reflux.
[g]
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C(sp2)-C(sp) and C(sp)-C(sp) Coupling Reactions
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preparation of silylated alkynes (Table 2, entries 2 and
8), as trimethylsilylacetylene (TMSA), always gave
variable amounts of the sila-Sonogashira products. In
the case of employing 2-propyn-1-ol as the sp-counter-
part (Table 2, entry 5), a 60% isolated yield of the
corresponding alcohol 9e was obtained together with a
10% yield ofthe acetylated compound 9e×. As illustrated
in entries 7 and 8, the less reactive, electron-rich 4-
Scheme 1.
try 10). Higher TONs, 9700 and 72000, accompanied iodoanisole also coupled with similar good efficiency.
with very good yields could be obtained at 1108C, when Steric effects as in 2-iodotoluene (Table 2, entry 9), did
the catalyst loading was reduced to 10À2 and 10À3 mol % not influence the yield of the reaction. N-Acetyl-o-
of Pd, respectively (Table 1, entries 11 and 12).
iodoaniline, gave the alkylynated product 9j in 65%
Using NMP as solvent and Bu4NOAc as base, complex isolated yield. These types of substrates have been used
8a catalyzed the Sonogashira coupling of a wide variety in indole synthesis,[30] though in our case, no traces of
of aryl iodides with terminal acetylenes to afford the cyclization product were observed (Table 2, entry 10).
corresponding arylated alkynes 9 (Scheme 2, X ˆ I, We also found that an excess of 1-octyne reacted with
Table 2). Reaction conversions (determined by GLC
using decane as internal standard), were generally high
after short reaction times for all type of substrates, and
the chromatographic purification of the compounds
were carried out using either silica gel or florisil.
Activated substrates such as 1-chloro-4-iodobenzene
reacted with an array of aromatic and aliphatic alkynes
in good to excellent yields (Table 2, entries 1 5).
(Triisopropylsilyl)acetylene had to be used for the Scheme 2.
Table 2. Sonogashira-type coupling of aryl iodides catalyzed by 8a.
Entry
Aryl iodide
Alkyne
8a [mol % Pd]
T[a] [0C]
110
t [h]
1
Product
No.
Yield[b, c] [%]
1
0.1
9a
>99 (73)
2
3
4
5
6
0.5
0.5
0.1
0.1
0.1
110
110
110
110
110
1
1
5
1
1
9b
9c
9d
9e
9f
>99
100 [76]
85 (60)
99 (60)[d]
>99 [88]
7
0.1
110
1
9 g
89 [80]
8
9
0.1
0.1
110
110
1
1
9 h
9i
90
92 (80)
10
11
0.1
0.1
110
110
2
4
9j
100 (65)
80[e, f]
9k
[a]
Bath temperature.
[b]
Determined by GLC, based on ArI using decane as internal standard. In parenthesis isolated yield after flash
chromatography. In brackets isolated yield after florisil chromatography.
Reaction conditions: ArI (0.5 mmol), alkyne (0.6 mmol), Bu4NOAc (0.55 mmol), 8a, NMP (2 mL).
10% of acetylated alcohol, 9e×, was also obtained
Reaction conditions: ArI (0.5 mmol), alkyne (1.2 mmol), Bu4NOAc (1.1 mmol), 8a, NMP (2 mL).
14% of monoalkynylated compound, 9k×, was also obtained.
[c]
[d]
[e]
[f]
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Table 3. Sonogashira coupling of aryl and vinyl bromides catalyzed by 8a.
Entry
ArBr
Alkyne
8a [mol % Pd]
T[a] [0C]
t [h]
7.5
Product
No.
Yield[b, c] [%]
93 (90)[d]
1
0.5
110
9a
2
3
0.1
0.1
110
110
2
7
9b
9 l
78
66 (40)
4
0.1[e]
110
1
9 m
96 (75)
5
0.1
110
1
9n
81
6
7
0.1
0.1
110
110
3.5
1
9o
9p
79
96
8
0.25
0.25
0.1
130
130
110
4
1
3
9q
9 h
9r
81
9
85
10
45 [30]
11
0.1
130
23
9 s
89 (39) [52][f, g]
12
13
0.1
0.1
110
110
7.5
3
9 t
9k
73 (58)[f, h]
75 [60][f, i]
14
0.1
110
29
9u
86 [73][j, k]
15
16
[a]
0.1
0.1
110
110
3
1
9v
10
85 (40) [62]
63 (36)
Bath temperature.
[b]
Determined by GLC, based on ArBr using decane as internal standard. In parenthesis isolated yield after flash
chromatography. In brackets isolated yield after florisil chromatography.
[c]
[d]
[e]
[f]
[g]
[h]
[i]
Reaction conditions: ArBr (0.5 mmol), alkyne (0.6 mmol), Bu4NOAc (0.55 mmol), 8a, NMP (2 mL).
1
In parenthesis crude yield after work-up (pure by H and 13C NMR).
2.5 equiv. of 1-octyne were used.
Reaction conditions: ArBr (0.5 mmol), alkyne (1.5 mmol), Bu4NOAc (1.2 mmol), 8a, NMP (2 mL).
11% of pure monoalkynylated compound, 9 s×, was also obtained.
17% of pure monoalkynylated compound, 9 t×, was also obtained.
25% of pure monoalkynylated compound, 9k×, was also obtained.
Reaction conditions: ArBr (0.5 mmol), alkyne (2.5 mmol), Bu4NOAc (2.5 mmol), 8a, NMP (2 mL).
14% and 2% of pure di- and monoalkynylated compounds, 9u× and 9u∫ were also obtained, respectively
[j]
[k]
fairly good yield with 1,2-diiodobenzene to afford the acetylene and (triisopropylsilyl)acetylene to afford, in
bis-Sonogashira coupling product 9k (Table 2, entry 11). high yields (Table 3, entries 5 and 6), the corresponding
In order to evaluate the scope of this methodology, we 9-alkynylanthracenes 9n and 9o with no observable
also examined the Sonogashira-type coupling of diverse formation of aceanthrylenes.[31] Sterically hindered 2-
aryl bromides with alkyl- and aryl-substituted alkynes bromobenzonitrile also coupled with fairly good effi-
(Scheme 2, X ˆ Br, Table 3). Activated substrates such ciency with phenylacetylene at 1108C (Table 3, entry 7).
as 1-chloro-4-bromobenzene, 1-bromo-4-(trifluorome- However, in the case of less reactive electron-rich aryl
thyl)benzene and 1-bromonaphthalene reacted with bromides such as 4-bromotoluene and 4-bromoanisole,
phenylacetylene and 1-octyne in good yields (Table 3, 0.25 mol % of Pd and 1308C were used to achieve fast
entries 1 4). 9-Bromoanthracene, reacted with phenyl- conversions (Table 3, entries 8 and 9). 4-Bromobenzal-
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C(sp2)-C(sp) and C(sp)-C(sp) Coupling Reactions
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dehyde ethylene glycol acetal, gave the corresponding reaction between aryl halides and silylated alkynes
coupling product 9r after reaction with 1-octyne in a (Scheme 3, Table 4). In initial experiments, a catalytic
moderate 30% isolated yield, with no observable system consisting of 8a (0.5 mol % of Pd) and CuI
deprotection product (Table 3, entry 10). Polybromo- (5 mol %) in pyrrolidine as solvent at 90 0C (Method A),
benzenes, such as 1,2-dibromobenzene, 1,4-dibromo- was used to achieve with rather good yields the coupling
benzene and 1,3,5-tribromobenzene, reacted with an of 1-chloro-4-iodobenzene, 1-naphthalene and 4-iodo-
excess of the corresponding alkyne (3 or 5 equiv.), anisole with both TMSA (1.2 equiv.) and BTMSA (0.75
affording the resultant products in satisfactory yields equiv.) as synthetic equivalents of acetylene, to afford
(Table 3, entries 11 14). The yield of the corresponding the corresponding diarylated ethynes 11 (Table 4, en-
peralkynylated product could not be improved when the tries 1, 2, 6, 7 and 11). The reaction coupling with
amount of alkyne was considerably increased. Hetero- BTMSA could be carried out with similar levels of
cyclic 2-bromothiophene was likewise converted effi- efficiency employing NMP as solvent and 3 equiv. of
ciently to the corresponding cross-coupling product 9v pyrrolidine as base, by just increasing the temperature to
(Table 3, entry 15). In the case of the vinyl bromide 1108C (Method B) (Table 4, entries 3, 8 and 12).
trans-b-bromostyrene, the coupling with (triisopropyl-
When Bu4NBr, (20 mol %), was used as co-catalyst
silyl)acetylene, afforded the corresponding trans-enyne instead of CuI (Method C), the monosilylated alkynes
10 after 1 h at 1108C in a moderate 36% isolated yield 12, were isolated as the major products both in the case
(Table 3, entry 16). As described above, moderate to of using TMSA (Table 4, entries 4, 9 and 13), and
good yields were generally obtained, and these were BTMSA (Table 4, entries 5, 10 and 14).
usually higher when fluorisil was used instead of silica
gel in the chromatographic purification of the crude reacted sluggishly with TMSA and BTMSA. Again
products (see Table 3, entries 11 and 15). when using CuI as co-catalyst (Method B, Table 4,
As depicted in Table 4, entries 15 19, aryl bromides
The efficiency as catalyst in the Sonogashira-type reac- entries 16 and 17) diarylated acetylenes 11 were the
tion of oxime-derived palladacycle 8a, is apparent when main reaction products. On the contrary, in the presence
compared with Herrmann×s phosphapalladacycle 2,[14] of TBAB (Method C) the major products were the
which only works efficiently when phenylacetylene is used monoarylated silylalkynes 12 (Table 4, entries 15, 18
as sp counterpart, even employing triethylamine as solvent. and 19). Consequently, TMSA and BTMSA behaved as
acetylene equivalents when the coupling reaction was
carried out in the presence of CuI. However, in the
Sila-Sonogashira Coupling of Aryl Halides with
Silylated Alkynes
absence of CuI, TMSA gave only the Sonogashira
coupling products and BTMSA the monosila-Sonoga-
shira products.
During the course of our studies about the Sonogashira
The catalytic system was also competent for the sila-
Hagihara coupling of trimethylsilylacetylene (TMSA) Sonogashira coupling of 1-chloro-4-iodobenzene with
with different aryl halides, and contrary to the case of the other silylated alkynes such as 1-phenyl-2-(trimethylsi-
triisopropylsilyl moiety which remained stable under lyl)acetylene and 1-trimethylsilyl-1-pentyne, which
the reaction conditions (see Tables 2 and 3), we ob- gave after 7 h the asymmetrical substituted alkynes 9a
served the formation, in variable and small amounts, of and 9w in 76 and 50% yield, respectively, under the
the corresponding sila-Sonogashira coupling products. conditions of Method B (Scheme 4).
We then decided to carry out an investigation of the
With respect to the reaction mechanism, we observed
catalytic activity of complex 8a in the cross-coupling the fast formation of a 1:1 mixture of phenylacetylene
Scheme 3.
Scheme 4.
Adv. Synth. Catal. 2003, 345, 1146 1158
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1151

Diego A. Alonso et al.
Products
FULL PAPERS
Table 4. Sila-Sonogashira coupling of aryl halides catalyzed by 8a.
Entry
ArX
R
8a[a]
[mol % Pd]
Method[b]
A
t [h]
3
No. [Yield[c] %]
1
TMS
0.5
11a/12a: 61/0
2
3
4
5
6
H
TMS
H
TMS
H
1
A
B
C
C
A
7
6
2
8
6
11a/12a: 84/6
11a/12a: 88/0
11a/12a: 11/77
11a/12a: 11/53
11b/12b: 90/0
0.25
0.5
0.5
0.5
7
8
9
10
11
TMS
TMS
H
TMS
TMS
0.5
0.25
0.5
0.5
0.5
A
B
C
C
A
8
6
5
21
24
11b/12b: 99/0
11b/12b: 78/11
11b/12b: 15/61
11b/12b: 11/74
11c/12c: 75/0
12
13
14
15
TMS
H
TMS
0.25
0.5
0.5
B
C
C
C
6
5
8
5
11c/12c: 35/10
11c/12c: 5/45
11c / 12c: 0/54
11a/12a: 8/53
TMS
0.5
16
H
0.25
B
24
11b / 12b: 25/0
17
18
19
TMS
TMS
TMS
0.25
0.25
0.5
B
8
22
8
11b/12b: 28/6
11b/12b: 22/64
11c/12c: 6/59
C[d]
C
[a]
Mol % of Pd with respect to the aryl halide.
[b]
Method A: ArX (1 mmol), TMSA (1.2 mmol) or BTMSA (0.75 mmol), pyrrolidine (3 mL), CuI (5 mol %), 908C. Method
B: ArX (1 mmol), TMSA (0.75 mmol) or BTMSA (0.6 mmol), pyrrolidine (3 mmol), CuI (5 mol %), NMP (2 mL), 1108C.
Method C: ArX (1 mmol), alkyne (1.2 mmol), pyrrolidine (1 mmol), TBAB (20 mol %), NMP (2 mL), 1108C.
Determined by GLC, based on ArX using decane as internal standard.
[c]
[d]
The reaction was carried out at 1308C.
and the corresponding diyne (80% conversion after tion between phenylacetylene and iodobenzene, em-
30 min.), when 1-phenyl-2-(trimethylsilyl)acetylene was ploying other bases than pyrrolidine as solvent, such as
heated in NMP at 110 0C under Method B conditions. TEA and H¸nig×s base, in the presence of CuI as co-
However, in the absence of the palladium and copper catalyst,[28a] we found that significant amounts of 1,4-
catalysts, a 36% conversion to phenylacetylene was diphenylbuta-1,3-diyne were always obtained. Conse-
observed as well after 1 h. This result seems to indicate quently, we also decided to investigate and optimize the
that the reaction could proceed merely via protodesily- ability of catalyst 8a to promote the oxidative homo-
lation and coupling of the in situ formed terminal alkyne, coupling reaction of different terminal alkynes
though the fact that the desilylation is much faster in the (Scheme 5, Table 5).
presence of the catalysts (Method B), does not rule out
the possibility a simultaneous direct coupling of the silyl conjugated diynes 13 could be obtained by dimerization
alkynes through a transmetallation process. of 1-alkynes in the presence of oxime-derived catalyst 8a
As illustrated in Table 5, good isolated yields of
In conclusion, oxime-derived palladacycle 8a, has been (Scheme 5). We found that complex 8a can effectively
shown, to the best of our knowledge, to be the only catalyst promote the coupling of 1-octyne in the presence of CuI
of this type that is active in sila-Sonogashira couplings.
(5 mol %) as co-catalyst, using TEA as solvent and
pyrrolidine as base (1.1 equiv.) (Table 5, entry 1). As
mentioned above for the sila-Sonogashira reaction,
catalyst 8a avoids the use of the amine as solvent, and
the homocoupling reaction showed even higher levels of
Homocoupling Reactions of Terminal Alkynes
During the course of our initial studies about the effectiveness when the solvent was changed to NMP at
palladium-catalyzed Sonogashira cross-coupling reac- 1108C still employing pyrrolidine as base and under
1152
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C(sp2)-C(sp) and C(sp)-C(sp) Coupling Reactions
FULL PAPERS
Table 5. Homocoupling reactions of terminal alkynes catalyzed by 8a.
Product
Entry
R
8a[a] [mol % Pd]
Solvent
Base
T[b] [0C]
t [h]
No.
Yield[c],[d] [%]
1
2
3
4
5
6
7
8
C6H13
C6H13
C7H15
Ph
i-Pr3Si
C6H13
Me2(OH)C
Ph
Ph
Ph
Ph
Ph
0.5
TEA
Pyrrolidine
Pyrrolidine
Pyrrolidine
Pyrrolidine
Pyrrolidine
Bu4NOAc
Pyrrolidine
Pyrrolidine
Pyrrolidine
Pyrrolidine
90
8
3
2
2
2.5
9
23
2
6
6
13a
13a
13b
13c
13d
13a
13e
13c
13c
13c
13c
13c
99 (70)
99 (60)
99 (50)
99 (82)
90 (75)
73
25
99
92 (80)
58
87
0.05
0.05
0.05
0.05
0.1
0.05
0.5
0.05
0.05
0.5
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP[e]
i-Pr2NH[f]
NMP
110
110
110
110
110
110
rt
rt
rt
rt
rt
9
10
11
12
2
21
0.5
TEA[g]
11
[a]
Mol% of Pd with respect to the starting alkyne.
Bath temperature.
Determined by GLC, based on alkyne using decane as internal standard. In parenthesis isolated yield after flash
chromatography.
Reaction conditions: alkyne (1 mmol), CuI (5 mol %), base (pyrrolidine, Bu4NOAc or TEA 1.1 mmol.), solvent (2 mL).
The reaction was carried out under Ar atmosphere employing degassed NMP.
The reaction was carried out in the presence of 0.5 equiv. of I2.
[b]
[c]
[d]
[e]
[f]
[g]
The reaction was carried out in the presence of 1 equiv. of chloroacetone.
lower catalyst loadings (0.05 mol % of Pd, TON ˆ 1000) ble 5, entry 12). Therefore, oxime-derived palladacycle
(Table 5, entry 2). Under these conditions, 1-nonyne, 8a is a competent promoter of the palladium-catalyzed
phenylacetylene and (triisopropylsilyl)acetylene also homocoupling reaction of terminal alkynes at room
gave good yields of the corresponding dialkylated and temperature achieving turnover numbers of up to
diarylated diynes 13b, 13c and 13d, respectively (Ta- 1000.
ble 5, entries 3 5). Other bases such as Bu4NOAc
lengthened the reaction time and gave lower conver-
sions (Table 5, entry 6). The homocoupling of 2-methyl- Conclusion
3-butyn-2-ol (Table 5, entry 7), gave a poor 25% yield of
the corresponding homocoupled diol 13e. It is worthy to In summary, we have shown that the phosphane-free
note that the homocoupling process worked very oxime-derived palladacycle 8a, is an efficient and
efficiently (99% yield after 2 h, 0.5 mol % of Pd) at versatile pre-catalyst for the amine- and copper-free
room temperature (Table 5, entry 8). At this temper- Sonogashira-type reaction of aryl iodides and aryl- and
ature, reducing the catalyst loading to 0.05 mol % of Pd vinyl bromides with a variety of terminal acetylenes. The
(Table 5, entry 9), longer reaction times were necessary catalytic system has also been successfully applied to the
to completion. It was found that under these conditions cross-coupling of aryl iodides with alkynylsilanes. Tun-
the reaction proceeded sluggishly in the absence of ing the reaction conditions, it is possible to control the
oxygen (compare entries 9 and 10). However, the reaction outcome to obtain either the diarylated alkynes
presence of external oxidants such as iodine[25] did not (Methods A and B) or the silylated monoarylated
result in any significant improvement in rate or yield alkynes (Method C). Complex 8a also catalyzes very
(compare entries 8 and 11). Other oxidants such as efficiently, even at room temperature, the synthesis of
chloroacetone[23] seriously inhibited the reaction (Ta- conjugated diynes through the homocoupling of termi-
nal alkynes using copper iodide as co-catalyst. Conse-
quently, we have demonstrated that oxime-derived
palladacycles are extremely active pre-catalysts for
C(sp2)-C(sp) and C(sp)-C(sp) reaction couplings under
air and very low loading conditions employing reagent-
grade chemicals. Further studies on the applicability of
these systems in other organic transformations are
currently under investigation in our group.
Scheme 5.
Adv. Synth. Catal. 2003, 345, 1146 1158
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Diego A. Alonso et al.
FULL PAPERS
13C NMR: d ˆ 11.3, 18.6, 91.8, 105.8, 122.0, 128.5, 133.2, 134.3;
Experimental Section
‡
‡
MS: m/z (rel. int.) ˆ 294 (M ‡ 2, 3), 292 (M , 8), 251 (31), 249
‡
(M 43, 78), 223 (9), 221 (27), 209 (14), 207 (38), 195 (25), 193
General
(69), 181 (36), 179 (100), 165 (21), 163 (27), 139 (14), 97 (18), 63
(17); HRMS: calcd. for C17H25ClSi: 292.1414; found: 292.1429.
3-(4-Chlorophenyl)-1,1-dimethylprop-2-yn-1-ol (9d):[36] Rf:
0.12 (hexane/EtOAc, 9/1); mp 55 578C (toluene); IR (KBr):
n ˆ 3725 3026 cmÀ1 (OH); 1H NMR: d ˆ 1.61 (s, 6H, 2  CH3),
2.35 (s, 1H, OH), 7.25 7.35 (m, 4H, ArH); 13C NMR: d ˆ 31.3,
65.5, 81.0, 94.7, 121.2, 128.5, 132.8, 134.2; MS: m/z (rel. int.) ˆ
The reagents and solvents were obtained from commercial
sources and were generally used without further purification.
Palladacycle 8a can be purchased from MEDALCHEMYS. L.
Gas chromatographic analyses were performed on an HP-5890
instrument equipped with a WCOT HP-1 fused silica capillary
1
column using decane as internal standard. H NMR spectra
‡
‡
‡
196 (M ‡ 2, 7), 194 (M , 21), 181 (31), 179 (M 15, 100), 159
(12), 136 (28), 116 (13), 115 (24), 101 (12), 75 (12).
were recorded on a Bruker AC-300 MHz spectrometer.
Chemical shifts are reported in ppm using tetramethylsilane
(TMS, 0.00 ppm) as internal standard. 13C NMR spectra were
recorded at 75 MHz with CDCl3 as the internal reference. The
catalysts were weighed out in an electronic microscale
(Sartorius, XM1000P) with a precision of 1 mg. IR data were
collected on a Nicolet Impact 400D of FT. Solid products were
recrystallized in hexane/EtOAc unless otherwise stated, and
melting points were not corrected. When mentioned, the
reactions were set up with the aid of carousel reaction
equipment equipped with gas-tight threaded caps with a valve,
cooling reflux head system, and digital temperature controller.
Compound 9b, reported in Table 2 (entry 2), has been
previously reported[32] and was characterized by comparison of
the GLC/MS and 1H NMR spectra; the purity was confirmed
by GLC analysis. Compounds 9n,[31a] 9o[31a] and 9p[33] (Table 3,
entries 5, 6 and 7, respectively) and compounds 12a,[34] 11c[35]
and 12c[34] (Table 4), have been previously reported and were
3-(4-Chlorophenyl)prop-2-yn-1-ol (9e):[37] mp 76 788C
(Lit. 78.5 79 0C); IR (KBr): n ˆ 3617 2979, 2241 cmÀ1;
1H NMR: d ˆ 1.82 (s, 1H, OH), 4.49 (s, 2H, CH2), 7.28, 7.36
(2d, 4H, J ˆ 8.64 Hz, ArH); 13C NMR: d ˆ 51.6, 84.6, 88.1,
‡
121.0, 128.7, 132.9, 134.6; MS: m/z (rel. int.) ˆ 168 (M ‡ 2, 17),
‡
‡
167 (M ‡ 1, 14), 166 (M , 51), 165 (27), 149 (20), 138 (16), 137
(18), 136 (12), 132 (10), 131 (100), 114 (13), 113 (10), 103 (74),
102 (38), 101 (40), 77 (23), 75 (26), 74 (14), 63 (14), 51 (24).
3-(4-Chlorophenyl)prop-2-ynyl acetate (9e×): Rf: 0.22 (hex-
ane/EtOAc, 9/1); oil; IR (CH2Cl2): n ˆ 3086, 2237, 1748,
1223 cmÀ1; 1H NMR: d ˆ 2.13 (s, 3H, CH3), 4.89 (s, 2H, CH2),
7.29, 7.38 (2d, 4H, J ˆ 8.51 Hz, ArH); 13C NMR: d ˆ 20.8, 52.7,
83.9, 85.3, 120.6, 128.7, 133.1, 134.9, 170.3; MS: m/z (rel. int.) ˆ
‡
208 (M , 10), 193 (19), 151 (17), 150 (36), 149 (53), 148 (100),
145 (13), 137 (17), 131 (35), 114 (21), 113 (45), 102 (11), 101
(15), 75 (11), 63 (12); HRMS: calcd. for C11H9ClO2: 208.0291;
found: 208.0273.
1
characterized by comparison of their GLC/MS and H NMR
spectra; their purities were confirmed by GLC analyses.
1-(1-Naphthyl)-2-phenylacetylene (9f):[19] Rf: 0.22 (hexane);
oil; IR (film): n ˆ 3057, 2211 cmÀ1; 1H NMR: d ˆ 7.37 7.77 (m,
11H, ArH), 8.44 (d, 1H, J ˆ 8.22 Hz, ArH); 13C NMR: d ˆ 87.5,
94.3, 120.9, 123.4, 125.3, 126.2, 126.4, 126.8, 128.3, 128.36,
128.42, 128.7, 130.3, 131.6, 133.2, 133.3; MS: m/z (rel. int.) ˆ 229
Typical Procedure for Sonogashira-type Coupling of
Aryl Iodides and Bromides with 1-Alkynes
‡
‡
‡
‡
(M ‡ 1, 20), 228 (M , 100), 227 (M 1, 18), 226 (M 2, 40),
114 (16), 113 (18).
A reaction tube of the carousel reaction equipment, was
charged with 2-iodotoluene (65 mL, 0.5 mmol), decane (97 mL,
0.5 mmol), phenylacetylene (67 mL, 0.6 mmol), tetrabutylam-
monium acetate (171 mg, 0.55 mmol), 8a (0.204 mg,
0.00025 mmol, 0.1 mol % Pd) and NMP (2 mL). The mixture
was stirred at 1108C in air and the reaction progress was
analyzed by GLC. The crude reaction mixture was extracted
with water and EtOAc (3 Â 15 mL). The organic phases were
dried, evaporated (15 mm Hg) and the resulting crude material
was purified by flash chromatography (hexane) affording pure
1-(2-methylphenyl)-2-phenylacetylene (9i);[5] yield: 76.3 mg
(80%); Rf: 0.44 (hexane); oil; IR (film): n ˆ 3059, 3021,
2215 cmÀ1; 1H NMR: d ˆ 2.51 (s, 3H, CH3), 7.12 7.23 (m, 3H,
ArH), 7.31 7.34 (m, 3H, ArH), 7.48 7.55 (m, 3H, ArH);
13C NMR: d ˆ 20.7, 88.3, 93.3, 123.0, 123.5, 125.6, 128.1, 128.3,
1-(4-Methoxyphenyl)-2-phenylacetylene (9 g):[5] Rf: 0.15
(hexane); mp 51 53 0C (Lit. 52 54 0C); IR (KBr): n ˆ 3053,
2216, 1246, 1028 cmÀ1; 1H NMR: d ˆ 3.81 (s, 3H, CH3), 6.87 (d,
2H, J ˆ 8.52 Hz, ArH), 7.32 (m, 3H, ArH), 7.45 7.52 (m, 4H,
ArH); 13C NMR: d ˆ 55.3, 88.0, 89.3, 114.0, 115.3, 123.6, 127.9,
‡
128.3, 131.4, 133.0, 159.6; MS: m/z (rel. int.) ˆ 209 (M ‡ 1, 16),
‡
208 (M , 100), 193 (53), 165 (53), 164 (19), 163 (15), 139 (16).
1-(4-Methoxyphenyl)-2-(triisopropylsilyl)acetylene
(9 h):[38] Rf: 0.18 (hexane); oil; IR (film): n ˆ 3038, 3001, 2154,
1
1249, 1036 cmÀ1; H NMR: d ˆ 1.12 [s, 21H, 3  CH(CH3)2],
3.80 (s, 3H, OCH3), 6.81, 7.41 (2d, 4H, J ˆ 8.45 Hz, ArH);
13C NMR: d ˆ 11.4, 18.7, 55.3, 88.6, 107.1, 113.8, 115.8, 133.5,
‡
159.6; MS: m/z (rel. int.) ˆ 288 (M , 23), 246 (22), 245 (100), 217
(24), 203 (47), 189 (53), 176 (13), 175 (79), 161 (11), 159 (14),
135 (10), 94 (19).
‡
129.4, 131.5, 131.8, 140.1; MS: m/z (rel. int.) ˆ 193 (M ‡ 1, 15),
2-Phenylethynyl-N-acetylaniline (9j):[39] mp 120 122 0C
(Lit. 119 121 0C); IR (KBr): n ˆ 3305, 1661, 1532 cmÀ1;
1H NMR: d ˆ 2.24 (s, 3H, CH3), 7.07 (t, 1H, J ˆ 7.55 Hz,
ArH), 7.32 7.40 (m, 4H, ArH), 7.48 7.55 (m, 3H, ArH), 7.97
(s, 1H, NH), 8.41 (d, 1H, J ˆ 8.22 Hz, ArH); 13C NMR: d ˆ 24.9,
84.3, 96.4, 111.8, 119.3, 122.3, 123.4, 128.6, 128.9, 129.7, 131.5,
‡
‡
192 (M , 100), 191 (M 1, 92), 190 (18), 189 (34), 165 (28), 115
(13).
1-(4-Chlorophenyl)-2-phenylacetylene (9a):[10] mp 81 0C; IR
(KBr): n ˆ 3048 cmÀ1; 1H NMR: d ˆ 7.32 7.37 (m, 5H, ArH),
7.45 7.55 (m, 4H, ArH); 13C NMR: d ˆ 88.3, 90.3, 121.8, 123.0,
128.4, 128.5, 128.7, 131.6, 132.8, 134.3; MS: m/z (rel. int.) ˆ 214
‡
‡
‡
‡
131.6, 138.9, 168.1; MS: m/z (rel. int.) ˆ 235 (M , 40), 194 (16),
(M ‡ 2, 32), 213 (M ‡ 1, 16), 212 (M , 100), 176 (41), 151 (15),
193 (100), 192 (16), 165 (34), 90 (13), 89 (11).
150 (11), 106 (10), 88 (11).
1,2-Bis(1-octynyl)benzene (9k):[40] Rf: 0.17 (hexane); oil; IR
2-(4-Chlorophenyl)-1-(triisopropylsilyl)acetylene (9c): Rf:
0.65 (hexane); oil; IR (film): n ˆ 2157 cmÀ1; 1H NMR: d ˆ 1.12
[m, 21H, 3  CH(CH3)2], 7.26, 7.39 (2d, 4H, J ˆ 8.52 Hz, ArH);
1
(film): n ˆ 2228 cmÀ1; H NMR: d ˆ 0.93 (t, 6H, J ˆ 6.87 Hz,
2  CH3), 1.35 1.71 (m, 16H, 8  CH2), 2.49 (t, 4H, J ˆ
1154
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2003, 345, 1146 1158

C(sp2)-C(sp) and C(sp)-C(sp) Coupling Reactions
FULL PAPERS
7.00 Hz, 2 Â CCH2), 7.18 7.21 (m, 2H, ArH), 7.38 7.41 (m,
2H, ArH); 13C NMR: d ˆ 14.1, 19.7, 22.6, 28.6, 28.8, 31.4, 79.5,
2  CH3), 1.29 1.64 (m, 16H, 8  CH2), 2.40 (t, 4H, J ˆ
7.07 Hz, 2  CCH2), 7.29 (s, 4H, ArH); 13C NMR: d ˆ 14.0,
19.5, 22.6, 28.6, 28.7, 31.4, 80.4, 91.9, 123.2, 131.3; MS: m/z (rel.
int.) ˆ 295 (M ‡ 1, 15), 294 (M , 65), 251 (22), 225 (31), 223
(22), 183 (11), 181 (19), 179 (20), 178 (21), 169 (24), 168 (12),
167 (45), 166 (30), 165 (72), 157 (11), 156 (13), 155 (68), 154
(20), 153 (51), 152 (82), 151 (22), 143 (23), 142 (21), 141 (100),
139 (47), 130 (11), 129 (80), 128 (34), 127 (11), 126 (11), 115
(33), 109 (16), 91 (11), 79 (12), 67 (24), 55 (36).
‡
94.1, 126.3, 127.1, 131.8; MS: m/z (rel. int.) ˆ 294 (M , 29), 195
‡
‡
(17), 182 (13), 181 (68), 179 (21), 178 (23), 169 (28), 168 (18),
167 (90), 166 (35), 165 (70), 156 (12), 155 (55), 154 (25), 153
(48), 152 (62), 151 (20), 142 (24), 141 (100), 139 (13), 129 (30),
128 (29), 115 (18), 97 (11), 55 (48).
1-Bromo-2-(oct-1-ynyl)benzene (9k×): Rf: 0.40 (hexane); oil;
IR (film): n ˆ 2232 cmÀ1; 1H NMR: d ˆ 0.91 (t, 3H, J ˆ 6.53 Hz,
CH3), 1.24 1.68 (m, 8H, 4  CH2), 2.46 (t, 2H, J ˆ 6.86 Hz,
CCH2), 7.10 (dt, 1H, J ˆ 7.82, 1.65 Hz, ArH), 7.22 (dt, 1H, J ˆ
1-Bromo-4-(oct-1-ynyl)benzene (9 s×): Rf: 0.18 (hexane); oil;
IR (CH2Cl2): n ˆ 2204 cmÀ1; 1H NMR: d ˆ 0.89 (m, 3H, CH3),
1.30 1.68 (m, 8H, 4  CH2), 2.38 (t, 2H, J ˆ 7.07 Hz, CCH2),
ˆ
7.55, 0.96 Hz, ArH), 7.42 (dd, 1H, J 7.68, 1.65 Hz, ArH), 7.55
(dd, 1H, J ˆ 7.96, 0.96 Hz, ArH); 13C NMR: d ˆ 14.1, 19.6,
7.24, 7.40 (2d, 4H, J 8.51 Hz, ArH); MS: m/z (rel. int.) ˆ 266
ˆ
‡
‡
22.57, 28.3, 28.5, 31.3, 79.3, 95.6, 125.4, 126.1, 126.8, 128.6, 132.2,
(M ‡ 2, 17), 264 (M , 17), 223 (15), 221 (15), 197 (13), 195 (40),
193 (27), 182 (16), 180 (10), 171 (14), 169 (15), 156 (31), 143
(29), 142 (86), 141 (38), 130 (11), 129 (66), 128 (55), 127 (21),
117 (14), 116 (100), 115 (56), 114 (48), 113 (23), 102 (10), 101
(11), 95 (10), 88 (17), 63 (15); HRMS: calcd. for C14H17Br:
264.0514; found: 264.0535.
‡
‡
133.2; MS: m/z (rel. int.) ˆ 266 (M ‡ 2, 14), 264 (M , 12), 223
(19), 221 (18), 195 (27), 193 (20), 182 (20), 180 (15), 171 (22),
169 (22), 156 (40), 155 (11), 143 (26), 142 (87), 141 (45), 130
(16), 129 (81), 128 (64), 127 (23), 126 (10), 117 (16), 116 (100),
115 (77), 114 (63), 113 (25), 102 (12), 101 (12), 95 (40), 91 (12),
88 (20), 87 (10), 82 (10), 77 (10), 75 (13), 67 (15), 63 (16), 55 (11);
HRMS: calcd. for C14H17Br: 264.0514; found: 264.0513.
1,4-Bis(2-phenyl-1-ethynyl)benzene (9 t):[43] Rf: 0.20 (hex-
ane); mp 177 179 0C (Lit. 178 180 0C); IR (KBr): n ˆ 3048,
1595, 1516 cmÀ1; 1H NMR: d ˆ 7.34 7.36 (m, 6H, ArH), 7.51
7.55 (m, 8H, ArH); 13C NMR: d ˆ 89.1, 91.2, 123.0, 123.1,
1-Phenyl-2-(trifluoromethylphenyl)acetylene (9 l):[41] mp
103 0C; IR (KBr): n ˆ 2218 cmÀ1; 1H NMR: d ˆ 7.34 7.36 (m,
3H, ArH), 7.53 7.60 (m, 6H, ArH); 13C NMR: d ˆ 88.0, 91.8,
122.5, 123.9 (J ˆ 270.5 Hz), 125.3 (J ˆ 14.6 Hz), 127.1, 128.4,
128.8, 129.9 (J ˆ 31.5 Hz), 131.7, 131.8; MS: m/z (rel. int.) ˆ 247
‡
128.38, 128.45, 131.5, 131.6; MS: m/z (rel. int.) ˆ 279 (M ‡ 1,
‡
26), 278 (M , 100), 276 (17), 139 (19).
1,3,5-Tri(oct-1-ynyl)benzene (9u): Rf: 0.29 (hexane); oil; IR
(film): n ˆ 2229, 2200 cmÀ1; 1H NMR: d ˆ 0.902 (t, 9H, J ˆ
6.66 Hz, 3 Â CH3), 1.31 1.62 (m, 24H, 12 Â CH2), 2.37 (t, 6H,
J ˆ 6.93 Hz, 3  CCH2), 7.30 (s, 3H, ArH); 13C NMR: d ˆ 14.1,
19.3, 22.6, 28.56, 28.61, 31.4, 79.4, 91.2, 124.3, 133.5; MS: m/z
‡
‡
(M ‡ 1, 20), 246 (M , 100), 196 (12), 176 (14), 98 (31), 85 (12),
75 (13).
1-(Oct-1-ynyl)naphthalene (9 m): Rf: 0.38 (hexane); oil; IR
(film): n ˆ 3058, 2955, 2930, 2857, 2224 cmÀ1; 1H NMR: d ˆ 0.92
(t, 1H, J ˆ 6.87 Hz, CH3), 1.34 1.74 (m, 8H, 4  CH2), 2.55 (t,
2H, J ˆ 7.07 Hz, ꢀ CCH2), 7.38 (t, 1H, J ˆ 7.38 Hz, ArH),
7.45 7.57 (m, 2H, ArH), 7.61 (d, 1H, J ˆ 6.3 Hz, ArH), 7.75 (d,
1H, J ˆ 8.22 Hz, ArH), 7.81 (d, 1H, J ˆ 7.53 Hz, ArH), 8.25 (d,
1H, J ˆ 8.04 Hz, ArH); 13C NMR: d ˆ 14.1, 19.7, 22.6, 28.7,
28.9, 31.4, 78.6, 95.6, 121.8, 125.2, 126.2, 126.3, 126.4, 127.8,
‡
‡
(rel. int.) ˆ 403 (M ‡ 1, 11), 402 (M , 32), 359 (13), 333 (22),
219 (11), 216 (11), 215 (13), 209 (16), 208 (18), 207 (100), 205
(22), 203 (21), 202 (23), 193 (23), 191 (29), 190 (15), 189 (25),
179 (38), 178 (22), n167 (19), 165 (30), 153 (11), 152 (12), 133
(11), 109 (23), 96 (21), 95 (20), 81 (12), 79 (15), 73 (10), 69 (12),
67 (33), 55 (45); HRMS: calcd. for C30H42: 402.3287; found:
402.3278.
‡
128.2, 129.9, 133.2, 133.5; MS: m/z (rel. int.) ˆ 236 (M , 35), 207
(12), 193 (22), 179 (28), 178 (28), 167 (60), 166 (24), 165 (100),
164 (25), 163 (21), 153 (13), 152 (27), 141 (10); HRMS:calcd. for
C18H20: 236.1565; found: 236.1550.
1-Bromo-3,5-di(oct-1-ynyl)benzene (9u×): oil; MS: m/z (rel.
‡
‡
int.) ˆ 374 (M ‡ 2, 22), 372 (M , 21), 331 (12), 224 (20), 209
(21), 208 (28), 207 (99), 195 (19), 194 (17), 193 (22), 192 (13),
191 (18), 183 (10), 182 (33), 181 (34), 180 (27), 179 (49), 178
(49), 177 (12), 169 (15), 168 (22), 167 (62), 166 (45), 165 (100),
164 (19), 163 (21), 156 (16), 155 (54), 154 (22), 153 (52), 152
(60), 151 (34), 150 (30), 142 (20), 141 (48), 139 (23), 133 (12),
129 (16), 128 (27), 115 (14), 109 (14), 96 (19), 95 (48), 93 (16), 91
(11), 81 (13), 79 (26), 69 (14), 37 (30), 55 (39); HRMS: calcd. for
C22H29Br: 372.1453; found: 372.1458.
1-(4-Methylphenyl)-2-(triisopropylsilyl)acetylene (9q): Rf:
0.28 (hexane); oil; IR (film): n ˆ 3081, 3049, 3028, 2155 cmÀ1;
1H NMR: d ˆ 1.12 [m, 21H, 3  CH(CH3)2], 2.33 (s, 3H,
ArCH3), 7.09, 7.37 (2d, 4H, J ˆ 7.92 Hz, ArH); 13C NMR: d ˆ
11.3, 18.7, 21.5, 89.5, 107.3, 120.5, 128.9, 131.9, 138.4; MS: m/z
‡
(rel. int.) ˆ 272 (M , 7), 230 (16), 229 (70), 201 (22), 187 (41),
174 (11), 173 (60), 160 (16), 159 (100), 145 (16), 143 (29), 119
(19), 86 (20); HRMS: calcd. for C18H28Si: 272.1960; found:
272.1966.
1,3-Dibromo-5-(oct-1-ynyl)benzene (9u∫): oil; IR (CH2Cl2):
1
n ˆ 2227 cmÀ1; H NMR: d ˆ 0.91 (t, 3H, J ˆ 6.86 Hz, CH3),
2-[4-(Oct-1-ynyl)phenyl]-1,3-dioxolane (9r): Rf: 0.31 (hex-
1.24 1.61 (m, 8H, 4  CH2), 2.39 (t, 2H, J ˆ 6.99 Hz, CH2), 7.46
(d, 2H, J ˆ 1.77 Hz, ArH), 7.56 (d, 2H, J ˆ 1.77 Hz, ArH); MS:
1
ane/EtOAc, 9/1); oil; IR (film): n ˆ 2226 cmÀ1; H NMR: d ˆ
‡
‡
‡
0.90 (m, 3H, CH3), 1.26 1.65 (m, 8H, 4  CH2), 2.40 (t, 2H, J ˆ
7.07 Hz, CCH2), 4.00 4.14 (m, 4H, OCH2CH2O), 5.79 (s, 1H,
OCHO), 7.38, 7.51 (2d, 4H, J ˆ 8.37 Hz, ArH); 13C NMR: d ˆ
14.0, 19.4, 22.5, 28.6, 28.7, 31.3, 65.3, 80.3, 91.1, 103.4, 125.0,
m/z (rel. int.) ˆ 346 (M ‡ 4, 10), 344 (M ‡ 2, 20), 342 (M ,
10), 331 (15), 275 (10), 273 (18), 260 (15), 249 (10), 236 (14), 234
(13), 222 (20), 221 (10), 220 (17), 196 (18), 195 (15), 194 (28),
193 (15), 155 (24), 142 (26), 141 (50), 129 (16), 128 (100), 127
(25), 126 (23), 115 (32), 114 (23), 113 (53), 95 (33), 87 (13), 82
(13), 69 (29), 67 (24), 55 (15); HRMS calcd. for C14H16Br2:
341.9619; found: 341.9660.
‡
‡
126.3, 131.5, 137.0; MS: m/z (rel. int.) ˆ 258 (M , 53), 257 (M
1, 92), 213 (18), 187 (21), 157 (18), 144 (25), 143 (62), 142 (14),
141 (18), 131 (13), 130 (23), 129 (53), 128 (52), 127 (19), 117
(42), 116 (25), 115 (100), 104 (15), 102 (12), 91 (20), 73 (94);
HRMS: calcd. for C17H22O2: 258.1620; found: 258.1587.
1,4-Di(oct-1-ynyl)benzene (9 s):[42] Rf: 0.36 (hexane); oil; IR
2-(Oct-1-ynyl)thiophene (9v):[44] Rf: 0.48 (hexane); oil; IR
(film): n ˆ 2225 cmÀ1; H NMR: d ˆ 0.90 (t, 3H, J ˆ 6.80 Hz,
1
CH3), 1.29 1.62 (m, 8H, 4  CH2), 2.41 (t, 3H, J ˆ 7.07 Hz, ꢀ
CCH2), 6.93 (dd, 1H, J ˆ 5.07, 3.69 Hz, ArH), 7.11 (d, 1H, J ˆ
(film): n ˆ 2228 cmÀ1; H NMR: d ˆ 0.90 (t, 6H, J ˆ 6.86 Hz,
1
Adv. Synth. Catal. 2003, 345, 1146 1158
asc.wiley-vch.de
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1155

Diego A. Alonso et al.
FULL PAPERS
‡
‡
3.45 Hz, ArH), 7.16 (d, 1H, J ˆ 5.22 Hz, ArH); 13C NMR: d ˆ
132.7, 133.4; MS: m/z (rel. int.) ˆ 180 (M ‡ 2, 22), 178 (M ,
54), 163 (10), 151 (36), 150 (12), 149 (100), 143 (39), 142 (18),
141 (14), 136 (14), 128 (72), 127 (32), 115 (25), 114 (26), 113
(21), 99 (18), 98 (12), 75 (11), 63 (16); HRMS: calcd. for
C11H11Cl: 178.0549; found: 178.0539.
14.0, 19.7, 22.5, 28.5, 28.6, 31.3, 73.6, 94.6, 124.3, 125.8, 126.7,
‡
130.8; MS: m/z (rel. int.) ˆ 192 (M , 32), 163 (22), 150 (18), 149
(36), 136 (25), 135 (42), 134 (21), 124 (13), 123 (100), 122 (14),
121 (83), 116 (10), 115 (34), 110 (15), 108 (19), 97 (28), 91 (13),
79 (13), 77 (28), 69 (11), 63 (11).
Triisopropyl[(E)-4-phenyl-3-buten-1-ynyl]silane
(10):[45]
oil; IR (film): n ˆ 3081, 3061, 3029, 2165, 2118 cmÀ1;
1H NMR: d ˆ 1.11 [m, 21H, 3  CH(CH3)2], 6.21 and 6.99 (2d,
Typical Procedure for Sila-Sonogashira Coupling of
Aryl Iodides and Bromides to Afford Silylated
Alkynes
ˆ
2H, J ˆ 16.47 Hz, CH CH), 7.25 7.39 (m, 5H, ArH);
13C NMR: d ˆ 11.3, 18.6, 93.3, 106.2, 108.4, 126.2, 128.6, 128.7,
‡
136.2, 142.0; MS: m/z (rel. int.) ˆ 284 (M , 19), 242 (24), 241
Method C: A reaction tube of the carousel reaction equipment
was charged with 1-iodonaphthalene (295 mL, 2 mmol), decane
(390 mL, 2 mmol), bis(trimethylsilyl) acetylene (542 mL,
2.4 mmol) or trimethylsilylacetylene (340 mL, 2.4 mmol), tet-
rabutylammonium bromide (129 mg, 0.4 mmol), pyrrolidine
(177 mL, 2.1 mmol), catalyst 8a (4.079 mg, 0.005 mmol,
0.5 mol % Pd) and NMP (4 mL). The mixture was stirred at
110 0C in air and the reaction progress was analyzed by GLC.
The crude reaction mixture was extracted with water and
EtOAc (3 Â 15 mL). The organic phases were dried, evapo-
rated (15 mm Hg) and the resulting crude was purified by flash
chromatography (hexane/EtOAc) affording the correspond-
ing trimethyl[2-(1-naphthyl)-1-ethynyl]silane (12b);[47] oil; IR
(film): n ˆ 2147 cmÀ1; 1H NMR: d ˆ 0.34 (s, 9H, 3  CH3),
7.37 7.84 (m, 6H, ArH), 8.34 (d, 1H, J ˆ 7.89 Hz, ArH);
13C NMR: d ˆ 99.4, 103.1, 120.7, 125.1, 126.2, 126.3, 126.8,
‡
(M 43, 100), 213 (18), 199 (30), 186 (11), 185 (61), 183 (26),
172 (16), 171 (88), 169 (19), 167 (11), 157 (19), 155 (34), 145
(31), 131 (14), 129 (24), 105 (10), 92 (29), 59 (36).
Typical Procedure for Sila-Sonogashira Coupling of
Aryl Iodides and Bromides to Afford Diarylated
Alkynes
Method A: A 25-mL round-bottom flask was charged with 1-
iodonaphthalene (295 mL, 2 mmol), decane (194 mL, 1 mmol),
bis(trimethylsilyl)acetylene (345 mL, 1.5 mmol) or trimethyl-
silylacetylene (340 mL, 2.4 mmol), CuI (19.4 mg, 0.1 mmol), 8a
(4.079 mg, 0.005 mmol, 0.5 mol % Pd) and pyrrolidine (6 mL).
The mixture was stirred at 90 0C in air and the reaction progress
was analyzed by GLC. The crude reaction mixture was
extracted with water and EtOAc (3 Â 15 mL). The organic
phases were dried, evaporated (15 mm Hg) and the resulting
crude was purified by flash chromatography (hexane/EtOAc)
affording the corresponding 1,2-di(1-naphthyl)acetylene
(11b);[46] yield: 756.3 mg (54%); Rf: 0.23 (hexane/EtOAc, 99/
1); mp 125 0C (Lit. 127 129 0C); IR (KBr): n ˆ 3052,
‡
128.2, 129.0, 130.8, 133.1; MS: m/z (rel. int.) ˆ 224 (M , 36), 210
(20), 209 (100), 179 (10), 165 (23), 104 (11).
Typical Procedure for the Homocoupling Reaction of
Terminal Alkynes
1
3044 cmÀ1; H NMR: d ˆ 7.48 7.67 (m, 6H, ArH), 7.87 7.91
A reaction tube of the carousel reaction equipment was
charged with 1-octyne (152 mL, 1 mmol), decane (97 mL,
0.5 mmol), pyrrolidine (93 mL, 1.1 mmol), CuI (9.7 mg,
0.05 mmol), 8a (0.204 mg, 0.00025 mmol, 0.05 mol % Pd) and
NMP (2 mL). The mixture was stirred at the temperature
indicated in Table 5 (110 0C or rt) in air and the reaction
progress was analyzed by GLC. The crude reaction mixture
was extracted with water and EtOAc (3 Â 15 mL). The organic
phases were dried, evaporated (15 mm Hg) and the resulting
crude was purified by flash chromatography (hexane/EtOAc)
affording the corresponding 7,9-hexadecadiyne (13a);[19] yield:
65 mg (60%); oil; IR (film): n ˆ 2956, 2931, 2871, 2859,
2233 cmÀ1; 1H NMR: d ˆ 0.89 (t, 6H, J ˆ 6.8 Hz, 2  CH3),
1.22 1.56 (2 m, 16H, 8  CH2), 2.24 (t, 4H, J ˆ 7.0 Hz, 2 Â
ꢀ CCH2); 13C NMR: d ˆ 14.0, 19.2, 22.5, 28.3, 28.5, 31.3, 65.3,
(m, 6H, ArH), 8.57 (d, 2H, J ˆ 8.3 Hz, ArH); 13C NMR: d ˆ
92.4, 121.1, 125.3, 126.3, 126.5, 126.9, 128.4, 128.9, 130.6, 133.3;
‡
‡
‡
MS: m/z (rel. int.) ˆ 279 (M ‡ 1, 24), 278 (M , 100), 277 (M
‡
1, 23), 276 (M -2, 47), 139 (30), 138 (50), 137 (26), 125 (20).
Method B: A reaction tube of the carousel reaction equip-
ment was charged with 1-iodonaphthalene (148 mL, 1 mmol),
decane (194 mL, 1 mmol), bis(trimethylsilyl)acetylene
(136 mL, 0.6 mmol), pyrrolidine (253 mL, 3 mmol), CuI
(9.7 mg, 0.05 mmol), 8a (1.020 mg, 0.00125 mmol, 0.25 mol %
Pd) and NMP (2 mL). The mixture was stirred at 110 0C in air
and the reaction progress was analyzed by GLC. The crude
reaction mixture was extracted with water and EtOAc (3 Â
15 mL). The organic phases were dried, evaporated
(15 mm Hg) and the resulting crude was purified by flash
chromatography (hexane/EtOAc) affording the correspond-
ing 1,2-di(1-naphthyl)acetylene (11b).
‡
77.3; MS: m/z (rel. int.) ˆ 189 (M 29, 3), 147 (5), 133 (9), 119
(16), 105 (29), 91 (58), 79 (41), 77 (25), 67 (47), 55 (40), 44 (34),
41 (100).
1,2-Bis(4-chlorophenyl)acetylene (11a):[41] Rf: 0.52 (hexane/
EtOAc, 99/1); mp 176 0C (Lit. 174 176 0C); IR (KBr): n ˆ
8,10-Octadecadiyne (13b):[48] Rf: 0.58 (hexane); oil; IR
3078, 831 cmÀ1; H NMR: d ˆ 7.32 (d, 4H, J ˆ 8.3 Hz, ArH),
(film): n ˆ 2234 cmÀ1; H NMR: d ˆ 0.87 (t, 6H, J ˆ 6.72 Hz,
1
1
7.45 (d, 4H, J ˆ 8.3 Hz, ArH); 13C NMR: d ˆ 89.2, 121.4, 128.7,
2  CH3), 1.27 1.53 (m, 20H, 10  CH2), 2.23 (t, 4H, J ˆ
6.71 Hz, 2  CCH2); 13C NMR: d ˆ 14.0, 19.2, 22.6, 28.3,
‡
‡
132.8, 134.5; MS: m/z (rel. int.) ˆ 248 (M ‡ 2, 50), 246 (M ,
‡
100), 176 (47), 123 (22), 99 (10), 88 (19), 75 (17).
28.75, 28.78, 31.7, 65.2, 77.5; MS: m/z (rel. int.) ˆ 246 (M ,
1-Chloro-4-(pent-1-ynyl)benzene (9w): Rf: 0.52 (hexane);
oil; IR (film): n ˆ 3054, 3035, 2237 cmÀ1; 1H NMR: d ˆ 1.04 (t,
3H, J ˆ 7.41 Hz, CH3), 1.51 1.68 (m, 2H, CH3CH2), 2.37 (t,
2H, J ˆ 6.99 Hz, ꢀ CCH2), 7.24, 7.32 (2d, 4H, J ˆ 8.39 Hz,
ArH); 13C NMR: d ˆ 13.5, 21.4, 22.1, 79.6, 91.3, 122.6, 128.4,
0.1), 161 (12), 147 (20), 135 (14), 133 (36), 122 (11), 121 (30), 120
(13), 119 (51), 117 (18), 115 (12), 109 (19), 107 (38), 106 (13),
105 (60), 103 (12), 95 (28), 94 (15), 93 (48), 92 (21), 91 (100), 81
(51), 80 (14), 79 (60), 78 (28), 77 (33), 69 (16), 67 (56), 65 (16), 57
(10), 55 (49), 51 (11).
1156
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2003, 345, 1146 1158

C(sp2)-C(sp) and C(sp)-C(sp) Coupling Reactions
FULL PAPERS
1,4-Diphenyl-1,3-butadiyne (13c):[19] Rf: 0.33 (hexane/
EtOAc, 99/1); mp 87 0C (Lit. 87 0C); IR (KBr): n ˆ 3047 cmÀ1;
1H NMR: d ˆ 7.33 7.36 (m, 6H, ArH), 7.52 7.55 (m, 4H,
ArH); 13C NMR: d ˆ 73.9, 81.6, 124.8, 128.4, 129.2, 132.5; MS:
[7] A. Kˆllhofer, T. Pullmann, H. Plenio, Angew. Chem. Int.
Ed. 2003, 42, 1056 1057.
[8] R. A. Batey, M. Shen, A. J. Lough, Org. Lett. 2002, 4,
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Hirabayashi, Y. Nishihara, Org. Lett. 2000, 2, 2935 2937.
[12] A. Mori, T. Shimada, T. Kondo, A. Sekiguchi, Synlett
2001, 649 651.
[13] a) W. A. Herrmann, V. P. W. Bˆhm, C.-P. Reisinger, J.
Organomet. Chem. 1999, 576, 23 41; b) J. Dupont, M.
Pfeffer, J. Spencer, Eur. J. Inorg. Chem. 2001, #40#1917
1927.
‡
‡
m/z (rel. int.) ˆ 202 (M , 100), 200 (M 2, 25), 101 (15), 88 (9).
1,4-Bis(triisopropylsilyl)-1,3-butadiyne (13d):[49] mp 108
1
110 0C; IR (KBr): n ˆ 2061 cmÀ1; H NMR: d ˆ 1.09 [s, 42H,
6  CH(CH3)2]; 13C NMR: d ˆ 11.3, 18.6, 81.5, 90.2; MS: m/z
‡
‡
(rel. int.) ˆ 362 (M , 13), 321 (11), 320 (31), 319 (M -43, 100),
291 (18), 277 (17), 263 (14), 249 (24), 137 (12), 82 (27), 73 (12),
59 (13).
2,7-Dimethyl-3,5-octadiyne-2,7-diol (13e):[42] Rf: 0.83 (hex-
ane/EtOAc, 3/2); mp 131 133 0C (Lit. 133 0C); IR (KBr): n ˆ
3664 2663, 2144 cmÀ1; H NMR: d ˆ 1.53 (s, 12H, 4  CH3),
1
1.89 (s, 2H, CH2); 13C NMR: d ˆ 31.0, 65.6, 66.3, 84.0; MS: m/z
‡
(rel. int.) ˆ 166 (M , 4), 152 (11), 151 (100), 134 (13), 133 (85),
123 (52), 109 (24), 108 (15), 107 (15), 106 (19), 105 (80), 93 (35),
91 (33), 81 (10), 79 (30), 77 (47), 75 (11), 74 (11), 69 (33), 68 (12),
67 (19), 65 (27), 63 (26), 62 (11), 55 (27), 53 (22), 51 (24).
[14] W. A. Herrmann, C.-P. Reisinger, K. ÷fele, C. Bro˚mer,
M. Beller, H. Fischer, J. Mol. Cat. A: Chem. 1996, 108,
51 56.
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[18] Y. Hatanaka, T. Hiyama, J. Org. Chem. 1988, 53, 920
923.
Acknowledgements
¬
This work has been supported by the Direccion General de
¬
Investigacion of the Ministerio de Ciencia y TecnologÌa (MCyT)
(BQU2001 0724-CO2 01). D. A. A. thanks MCyT for a
contract under the program Ramon y Cajal. M. C. P. thanks
Generalitat Valenciana for a predoctoral fellowship.
¬
[19] a) Y. Koseki, K. Omino, S. Anzai, T. Nagasaka, Tetrahe-
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References and Notes
[1] a) L. Brandsma, S. F. Vasilevsky, H. D. Verkruijsse, in
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Synthesis, Springer-Verlag, Berlin, 1988, Chapter 10,
pp. 179 225; b) K. C. Nicolau, E. J. Sorensen, in Classics
in Total Synthesis, Wiley-VCH, Weinheim, 1996,
pp. 582 586; c) A. L. Rusanov, I. A. Khotina, M. M.
Begretov, Russ. Chem. Rev. 1997, 66, 1053 1068;
d) U. H. F. Bunz, Chem. Rev. 2000, 100, 1605 1644.
[2] a) K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron
Lett. 1975, 4467 4470; b) S. Takahashi, Y. Kuroyama, K.
Sonogashira, N. Hagihara, Synthesis 1980, 627 630; c) K.
Sonogashira, in Metal-Catalyzed Cross-Coupling Reac-
tions, (Eds.: F. Diederich, P. J. Stang), Wiley-VCH,
Weinheim, 1998, Chapter 5, pp. 203 209; d) K. Sonoga-
shira, J. Organomet. Chem. 2002, 653, 46 49; e) K.
Sonogashira, in Handbook of Organopalladium Chem-
istry for Organic Synthesis, (Eds.: E.-I. Negishi, A de
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