Palladium-catalyzed trimerizations of terminal arylalkynes: Synthesis of 1,3-diaryl-2-arylethynyl-1,3-butadienes

Article abstract of DOI:10.1002/adsc.200800182

Various 1,3-diaryl-2-arylethynyl-1,3-butadienes 7 have been prepared by the Pd-catalyzed trimerization of arylalkynes 4. Their structures and stereochemistry have been confirmed by X-ray crystal analyses. This procedure provides high regioselectivity to g

Full text of DOI:10.1002/adsc.200800182

FULL PAPERS
DOI: 10.1002/adsc.200800182
Palladium-Catalyzed Trimerizations of Terminal Arylalkynes:
Synthesis of 1,3-Diaryl-2-arylethynyl-1,3-butadienes[1]
Yao-Ting Wu,a,* Wei-Chih Lin,a Chia-Ju Liu,a and Chuan-Yi Wua
a
Department of Chemistry, National Cheng-Kung University, No.1 Ta-Hsueh Road, 70101 Tainan, Taiwan, R.O.C.
Fax : (+886)-6-274-0552; e-mail: ytwuchem@mail.ncku.edu.tw
Received: March 24, 2008; Revised: June 4, 2008; Published online: July 24, 2008
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: Various 1,3-diaryl-2-arylethynyl-1,3-buta- zation to form 2-(1-naphthalenyl)-3-(1-naphthalenyl-
dienes 7 have been prepared by the Pd-catalyzed tri-
merization of arylalkynes 4.Their structures and ste-
ACHTREUNG
AHCTREUNG
reochemistry have been confirmed by X-ray crystal 1,3-butadiene (Z-7a) was converted to 1-methyl-3-
analyses.This procedure provides high regioselectivi- phenyl-2-(2-phenyl-1-ethionyl)-2-indene (22) in 75%
ty to generate adducts Z-7 in moderate to excellent yield.
yields.The scope, limitations and regioselectivity of
this reaction have been investigated.In DMSO at
1808C, 1,3-di(1-naphthalenyl)-2-(1-naphthalenyleth- Keywords: alkynes; cross-coupling; enynes; hydroal-
ynyl)-1,3-butadiene (7m) underwent 6p-electrocycli- kynylation; palladium
Introduction
Alkynes are important building blocks and synthons
for the construction of interesting and useful mole-
cules.[2] The dual s and p nature of terminal acety-
lenes allows for various reaction types, particularly
À
for C C bond formation.In the presence of metal
catalysts, a terminal alkyne can be converted either to
a s-alkynyl, a h2-alkynyl or a h1-vinylidene (carbene)
complex.[3] The s-alkynyl complex is the key inter-
mediate for the generation of new internal alkynes.
For example, symmetrical 1,3-butadiynes 1 can be ac-
cessed from a terminal alkyne by an oxidative dimeri-
zation (Scheme 1).[4] This reaction can be classified as
Eglinton,[5] Glaser,[6] Hay,[7] or Pd-catalyzed[8] cou-
pling, depending on the metal complexes and catalysts
utilized.[9] A h2-alkynyl complex provides the possibil-
ity to generate a 1-metallaalkenyl species for further
transformation.Based on this reaction route, trisubsti-
Scheme 1. Metal-catalyzed oligomerizations of terminal al-
kynes.
tuted benzenes 2A and 2B can be prepared from an ducts E/Z-3 or 6 can be achieved by a suitable choice
alkyne by a formal [2+2+2]cycloaddition.[10] A h1-vi- of reaction conditions and catalysts.[16] In Pd-catalyzed
nylidene complex is able to exhibit several reaction protocols, terminal alkynes 4 usually undergo dimeri-
types due to the high reactivity of the carbene zations to form enynes 6.[14] Nolan[12h] and Gevorgy-
carbon.[11] Applying both the s and p nature of a ter- an[12i] independently developed new catalytic systems
minal alkyne, 1,4-disubstituted enynes E-3[12] and Z- for the regioselective generation of enynes E-3.More-
3,[12d,13] and 1,3-disubstituted enynes 6[13b,14] are formed over, linear trimerization adducts, such as dienynes
from the head-to-head and head-to-tail dimerization 5[17] and 8,[18] can be generated by several catalysts.
of alkynes, respectively.[15] Selective formation of ad- Compounds 5 should be formed by syn-hydroalkyny-
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Yao-Ting Wu et al.
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lation of the intermediate E-3.Formation of hexa-1,3-
roles.[19] PdCl2
G
N
dien-5-ynes 8 may involve a vinylidene intermediate. yield and regioselectivity relative to other Pd cata-
Recently, we observed that a new trimerization lysts, such as, PdCl2(acac)2, PdCl2(dppf), Pd(OAc)2
adduct 7 could be synthesized directly from alkynes 4. and PdCl2(PCy3)2.In contrast to other solvents, that
A
N
ACHTREUNG
AHCTREUNG
Herein, we have optimized the reaction conditions is, NMP, DMSO and toluene, acetonitrile and DMF
and studied their regioselectivity and applications in achieved excellent results, but the former with its low
organic synthesis.
boiling point has an advantage for the purification.In
the absence of a base, the desired product cannot be
furnished (entry 6 in Table 1).Of the bases used tri-
Results and Discussion
ACHTREUNG
AHCTREUNG
Upon heating phenylacetylene (4a) in acetonitrile ever, low regioselectivity was observed when triethyl-
with a mixture of PdCl2(PPh3)2, PPh3, NEt3 and CuI, amine was utilized as the solvent (entry 15 in
angular dienyne 7a can be synthesized with high re- Table 1).Suitable reaction temperature is 80 8C, since
gioselectivity in 94% yield (entry 16 in Table 1).To at 1108C the yield was slightly decreased, and at
AHCTREUNG
the best of our knowledge, this is the first example for room temperature 1,4-diphenyl-1,3-butadiyne (1a)
the generation of a dienyne with this skeleton by the was isolated as the major product.The cocatalyst CuI
trimerization of a terminal alkyne.Systematic studies
and the additive PPh3 can improve the regioselectivity
of the reaction conditions revealed that palladium cat- and yield (entries 4, 5 and 17 in Table 1), but CuI
alyst, base, solvent and temperature all play key does not have any critical influences in this reaction.
Table 1. Optimization of reaction conditions for the preparation of Z-7a.[a]
Entry
Catalyst
PdCl2(PPh3)2
Solvent
Temperature [8C]
Time [h]
E-3a:6a:E-7a:Z-7a[b]
Yield [%][c]
87
1
2
3
4
5
6
7
8
G
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
toluene
NMP
80
25
48
168
48
21
21
48
24
46
24
48
24
46
42
46
48
48
48
45
62
1:1:1:97
–
0:0:1:99
11:1:1:87
33:11:1:55
–
35:1:1:63
58:13:4:25
73:1:1:25
3:0:2:95
57:1:17:25
30:10:9:51
45:1:32:22
5:3:2:90
55:1:1:43
3:0:0:97
9:3:3:85
1:1:1:97
15:1:35:49
[d]
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(acac)2
PdCl2(dppf)
Pd(OAc)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
PdCl2(PPh3)2
Pd(PPh3)4
PdCl2(PCy3)2
G
–
84
C
110
110
110
110
110
80
110
80
110
80
110
80
80
80
80
[e]
U
–
–
–
–
[f]
R
[g]
R
[h]
U
[i]
E
–
9
H
–
–
–
–
–
–
–
10
11
12
13
14
15
16
17
18
19
N
G
N
N
E
N
NEt3
N
CH3CN
CH3CN
CH3CN
CH3CN
94
80[e]
87
G
E
80
80
[j]
C
–
[a]
3 mmol scale. 2.5 mL of solvent and 1.5 mL of base were used in this reaction.
The ratios were determined by the H NMR spectra of the crude products.The conversion cannot be analyzed.Starting
[b]
1
material 4a could be removed during the preparation of the sample for NMR study.
Isolated yield for Z-7a.
18% of 1,4-diphenylbutadiyne (1a) was isolated.
In the absence of CuI.
In the absence of PPh3.
In the absence of base.
i-Pr2NH was used as the base.
Pyridine was used as the base.
Instead of PPh3, PCy3 was used.
[c]
[d]
[e]
[f]
[g]
[h]
[i]
[j]
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Palladium-Catalyzed Trimerizations of Terminal Arylalkynes
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In its absence, Z-7a can also be obtained in 80% E/Z ratio of dienynes 7j and 7k could not be accurate-
yield.[20]
ly reported due to the random appearance of their
The reactivity of several alkynes has been examined values (entries 10 and 11 in Table 2).However, the
in this reaction.For example, phenylacetylene ( 4a) products provided by 3-ethynylanisole (4b) and 1-eth-
and alkynes 4b–h produced the corresponding dien- ynyl-3,5-dimethoxybenzene (4c) contained only traces
ynes 7 in good yields with Z-regioselectivity (Table 2). (less than 5%) of E-isomers.Angular trimerization of
In other examples, the electronic and steric properties an alkyne with a sterically congestive substituent led
of the aryl substituent in alkyne 4 affected the yield to the formation of a significant amount of intermedi-
and the regioselectivity.Methyl 4-ethynylbenzoate
ate 6 as well as the E-adduct.1-Ethynylnaphthalene
(4i) afforded the sole regioisomer Z-7i in very low (4m), 2-ethynylnaphthalene 4n and 9-ethynylphenan-
yield and left the starting material in large amounts. threne (4o) yielded the corresponding Z-7 as major
Although 4i was completely consumed at higher reac- products (entries 13–15 in Table 2).The two re-
tion temperature (1108C), the yield was only slightly gioisomers generated from 2-ethynyltoluene (4l) were
improved.In contrast to 4i, electron-rich alkynes fur- produced in approximately equal amounts.The more
nished the corresponding adducts 7 in moderate to bulky alkyne 4p exclusively underwent dimerization
excellent yields.Unlike other dienynes in Table 2, the
to give enyne 6p (R=9-anthracenyl) in 70% yield.In
Table 2. Preparation of various adducts 7 from alkynes 4.
Entry
Alkyne
Ar
Product
E/Z Ratio
Yield [%][a]
1
2
3
4
5
6
7
8
4a
4b
4c
4d
4e
4f
4g
4h
4i
Ph
Z-7a
Z-7b
E/Z-7c
Z-7d
Z-7e
Z-7f
Z-7g
Z-7h
Z-7i
–
–
94 (73[b])
66
62
70
66
80
60
65
23
3-OCH3-C6H4
3,5-(OCH3)2-C6H3
4-CH3-C6H4
3,5-(CH3)2-C6H3
4-t-Bu-C6H4
4-Ph-C6H4
4-F-C6H4
4-(CO2CH3)-C6H4
4-OCH3-C6H4
<5:95
–
–
–
–
–
–
9
10
11
12
4j
4k
4l
E/Z-7j
E/Z-7k
E/Z-7l
n.r.[c]
n.r.[c]
55:45
87
4-N
2-CH3-C6H4
A
55[e]
60[d]
13
14
4m
4n
E/Z-7m
E/Z-7n
12:88 (57:43[e])
83 (80[e])
<5:95
65
15
4o
4p
E/Z-7o
Z-7p
6:94
–
63[f]
16
0[g]
[a]
3 mmol scale.Each example was repeated at least twice.Traces of by-products 1 and 6 were also formed but neglected, if
not otherwise mentioned.The ratios of regioisomers were determined according to the 1H NMR spectra.
60 mmol scale.
[b]
[c]
[d]
[e]
[f]
This reaction has been repeated four times.The accurate value could not be reported.
Enyne 6l was isolated in 20% yield.
Instead of the combinations of PdCl2
Enyne 6o was isolated in 13% yield.
Enyne 6p was isolated in 70% yield.
G
N
[g]
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Yao-Ting Wu et al.
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Figure 1. The molecular structures of Z-7d (left) and Z-7o (right) showing 50% probability ellipsoids (Diamond version 3.0).
Hydrogen atoms except for 3-H have been omitted for clarity.[21]
addition, the ratio of E/Z-7m can also be influenced (Table 3).Addition of an alkyne to aryl-substituted
by the catalytic combinations of Pd
ACHTREUNG
PCy3 (entry 13 in Table 2).The skeleton, but not the
E/Z stereochemistry, of dienynes 7 could be assigned en-1-yne [9f (ꢀ6p)] did not participate in this reac-
by 2D-NMR spectra.Fortunately, Z-7d and Z-7o tion.The lack of reactivity of 9f possibly arises from
were crystallized from CHCl3/MeOH and their struc- the sterically congestive substituent.Triaryldienynes
tures were confirmed by the X-ray analyses 10 were afforded in lower yields in comparison to the
(Figure 1).[21]
direct formation of trimerization adducts 7 (entries 4–
Unlike arylethynes, 1-hexyne (4q),[22] trimethylsily- 6 and 8 in Table 3).The instability of 1,3-diphenyl-3-
lethyne, 3,3-dimethyl-1-butyne and 1-ethynyl-1-cyclo- buten-1-yne [9c (ꢀ 6a)] leads to lower yields.[24] In
hexene did not afford the corresponding adducts 7. our trimerization protocol 4a in situ generates enyne
This information led us to study the reaction between 6a, which can immediately undergo hydroalkynylation
enynes 9 and alkynes 4[23] because dienynes 7 should with an excess of alkyne 4a to furnish the stable cou-
be formed from enynes 6 by hydroalkynylation.It
pling adduct Z-7a in high yield.[25] Therefore, the
turned out that hydroalkynylation of enynes 9 did not yields for the formation of dienynes 10 mainly depend
give satisfactory results, but the scope, limitations and on the reactivity and stability of enynes 9.
regioselectivity of this reaction can be elucidated
Table 3. Palladium-catalyzed coupling reaction of an enyne 9 with an alkyne 4.[a]
Entry Enyne
R1
R2
Alkyne R3
Product
9:10[b] E/Z-10[b] Yield [%]
1
2
3
4
5
6
7
8
9
9a
9a
9b
Me
Me
Ph
Ph
Ph
n-Bu
Ph
Ph
4a
4q
4a
4a
4b
4j
Ph
n-Bu
Ph
10aa
10aq
10ba
43:57
12:88
21:79
44:56
67:33
38:62
0:100
2:98
41:59
76:24
17:83
29:71
–
44
75
32
40
44
46
34
33
9c (ꢀ6a) Ph
Ph
10ca (ꢀ7a) 0:100
9c
9c
9c
Ph
Ph
Ph
3-OCH3-C6H4 10cb
4-OCH3-C6H4 10cj
n-Bu
Ph
Ph
0:100
0:100
0:100
0:100
83:17
100:0
Ph
Ph
4q
10cq
10da
10ea
10fa
9d (ꢀ6j) 4-OCH3-C6H4 4-OCH3-C6H4 4a
9e (ꢀ6r) n-Hex n-Hex 4a
9f (ꢀ6p) 9-anthracenyl 9-anthracenyl 4a
traces
0
10
Ph
[a]
[b]
Starting materials enyne 9 and alkyne 4 (ratio 1:1.2) were utilized in this reaction.
The ratios were determined by the H NMR spectra of the crude products.
1
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Palladium-Catalyzed Trimerizations of Terminal Arylalkynes
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It has also been observed that alkynes 4 and enynes generation of 7 can be formulated as shown in
9 affected the stereochemistry of dienynes 10.Phenyl-
Scheme 2.Initially, s-complex 13 is formed,[26] and
acetylene (4a) and 1-hexyne (4q) provided different subsequently coordinates and inserts alkyne to afford
regioselectivities for the formation of dienynes 10, s-complex 15 by “syn-palladaalkynylation” (catalytic
and the former alkyne gave the Z-regioisomer as the cycle I).[27] Coupling adduct 6 is released after reduc-
major adduct.Reaction of enyne 9c with either phe- tive elimination of complex 15.However, enyne 6 has
nylacetylene (4a) or 3-ethynylanisole (4b) yielded the a higher affinity than alkyne 4 for complexes 11 and
corresponding adducts 10 with almost Z-regioselectiv- 13, and makes catalytic cycle II more efficient.Reac-
ity, but the same conditions using 4-ethynylanisole tion of enyne 6 with 13 forms h2-complex 16, which
(4j) afforded E/Z-10cj with a ratio of 41:59 (entries 4– yields E-7 by syn-palladaalkynylation and subsequent
6 in Table 3).In contrast to enyne 9c, electron-rich reductive elimination (Path A).Alternatively, Pd-
enyne 9d (ꢀ6j) formed a mixture of E/Z adducts (en- complexed enyne 18 offers the possibility to produce
tries 4 and 8 in Table 3).According to results of these
Z-7 by anti-hydroalkynylation (Path B).An alkynyl
studies, the random stereochemistry for the formation moiety in 12 or 13 and proton are concertedly or step-
of 7j and 7k can be elucidated (entries 10 and 11 in wisely transferred to 18 to give complex 19.Dienyne
Table 2).
Z-7 is accessed after reductive elimination.In general,
The results provided in Table 3 can be explained in Path B is the main reaction route in this protocol and
that enynes 6 are the key intermediates for the syn- dienynes Z-7 are obtained as the predominant prod-
thesis of dienynes 7.Based on this information and
ucts.A bulky phosphine ligand L, such as PCy , or an
3
literature processes, a putative mechanism for the alkyne with a sterically congestive substituent, espe-
Scheme 2. Proposed mechanism for the formation of a dienyne 7.
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Yao-Ting Wu et al.
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cially 2-ethynyltoluene (4l), perhaps makes complex allylic intermediate 23 and subsequently, the intramo-
18 less favorable and enhances the formation of E-7. lecular cyclization makes compound 24 accessible.
Moreover, the random appearance of the E/Z ratio of Further hydrolysis of the alkynyl moiety in 24 gener-
dienynes 7j and 7k perhaps arises from the intercon- ates 22 with a more stable conjugated enone form.
version process between complexes 17 and 19 via a
stable species 20 (entries 10 and 11 in Table 2 and
Scheme 2).
Conclusions
Thermal rearrangement of dienynes 7 does not
follow the same reaction type that 1,3-hexadien-5-yne We provide a new and simple procedure for generat-
does.[28] When a mixture of E/Z-7m (ratio 57:43) was ing trimerization adducts 7 from terminal arylalkynes
heated in DMSO at 1808C for 12 h, 2-(1-naphthalen- 4 in one pot.This protocol indicates that enynes 6 are
yl)-3-(1-naphthalenylethynyl)-1,2-dihydrophenanthr-
much more reactive than alkynes 4 towards hydroal-
ene (21; Figure 2) was generated in ca. 40% yield kynylation to yield dienynes Z-7.The scope, limita-
tions and regioselectivity for the formation of 2-eth-
ynyl-1,3-butadiene 7 and 10 have been elucidated.
Elaboration of this methodology and investigation of
other catalytic applications in the construction of
complex aromatic molecules and polymers are in
progress.
Experimental Section
General Remarks
1H and 13C NMR: Bruker 300 (300 and 75.5 MHz). Multi-
plicities were determined by the DEPT (distortionless en-
hancement by polarization transfer) sequence.The symbol
“+” is presented for CH or CH3, and “À” for CH2.MS:
Bruker Daltonics Apex II30.X-ray crystal structure deter-
mination: The data were collected on a Stoe-Siemens-AED
diffractometer.Melting points were determined with a
Büchi melting point apparatus B545 and are uncorrected.
Elemental analysis: Laboratory for elemental analyses at
National Cheng Kung University.1-Ethynyl-3,5-dimethoxy-
benzene (4c),[31] 1-ethynyl-3,5-dimethylbenzene (4e),[32]
methyl 4-ethynylbenzoate (4i),[33] 9-ethynylanthracene
(4p),[34] 1-phenyl-3-methylbut-3-en-1-yne (9a),[35] 2-phenyl-
oct-1-en-3-yne (9b),[36] 1,3-diphenylbut-3-en-1-yne (9c),[14d]
Figure 2. The molecular structure of 21 showing 50% proba-
bility ellipsoids (Diamond version 3.0). Hydrogen atoms
except for 1- and 2-H have been omitted for clarity.[29]
(based on E-7m) and 91% of Z-7m was recovered.
The structure of 21 has been analyzed by X-ray dif-
fraction.[29] Compound 21 should be formed from E-
7m by 6p-electrocyclization and subsequent 1,5-hy-
drogen shift.[30] Preparation of an indene derivative 22
and 1,3-di
(4-anisyl)but-3-en-1-yne (9d)[14d] were prepared ac-
A
is another synthetic application of dienynes
7
cording to or similar to published procedures.Other com-
pounds, which are not mentioned in the experimental sec-
tion, are commercially available.
(Scheme 3).Under acidic conditions, Z-7a converts to
General Procedure for the Preparation of Dienynes 7
(GP1)
To
a solution of the respective terminal alkyne 4
(3.00 mmol) in a solvent mixture of NEt3 (1.5 mL) and
CH3CN (2.5 mL) in a screw-capped Pyrex bottle PdCl2
A
PPh3 (15.7 mg, 60.0 mmol) were added at ambient tempera-
ture.The reaction mixture was purged with nitrogen for
5 min.The sealed bottle was heated at 80 8C for ca. 48 h.
After cooling to room temperature, the solvent was re-
moved under reduced pressure, and the residue subjected to
chromatography on silica gel (or alumina).Elution with
hexane/CH2Cl2 afforded the coupling product 7. Note: Al-
though compounds Z-7 are stable below 1808C under an N2
Scheme 3. Synthesis of indene 22 from dienyne Z-7a in
acidic conditions.
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Palladium-Catalyzed Trimerizations of Terminal Arylalkynes
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atmosphere, they easily decompose on contact with air at
room temperature.
[2] Acetylene Chemistry: Chemistry, Biology, and Material
Science (Eds:. P.J.Stang, R.R.Tykwinski, F.Dieder-
ich), Wiley-VCH, Weinheim, 2005.
[3] J.Tsuji, Transition Metal Reagents and Catalysts: Inno-
vations in Organic Synthesis, John Wiley & Sons, Chi-
chester, 2000, p 227.
[4] Review: P.Siemsen, RC. .Livingston, F.Diederich,
Angew. Chem. 2000, 112, 2740; Angew. Chem. Int. Ed.
2000, 39, 2632.
General Procedure for the Preparation of Dienynes
10 (GP2)
To
a solution of the respective terminal alkyne 4
(2.40 mmol) and enyne 9 (2.00 mmol) in a solvent mixture
of NEt3 (1.5 mL) and CH3CN (2.5 mL) in a screw-capped
Pyrex bottle PdCl2(PPh3)2 (14.0 mg, 20.0 mmol), CuI (3.8 mg,
G
[5] G.Eglinton, A.R.Galbraith,
J. Chem. Soc. 1959, 889.
20.0 mmol) and PPh3 (10.5 mg, 40 mmol) are added at ambi-
ent temperature.The reaction mixture is purged with nitro-
gen for 5 min.The sealed bottle is heated at 80 8C for 24 h.
After cooling to room temperature, the solvent is removed
under reduced pressure, and the residue is subjected to
chromatography on silica gel (or alumina).Elution with
hexane/CH2Cl2 affords the coupling product 10. Note: Com-
pounds 10 easily decompose on contact with air at room tem-
perature.
[6] a) C.Glaser, Justus Liebigs Ann. Chem. 1870, 154, 137;
b) C.Glaser, Ber. dtsch. chem. Ges. 1869, 2, 422.
[7] A.S.Hay, J. Org. Chem. 1962, 27, 3320.
[8] Selected examples, see: a) C.Ye, J-.C.Xiao, B.Twam-
ley, A.D. LaLonde, M.G. Norton, J.M. Shreeve,
J. Org. Chem. 2007, 5095; b) J.Yan, J.Wu, H.Jin,
Eur.
J.
Organomet. Chem. 2007, 692, 3636; c) F.Yang, X.Cui,
Y.-n. Li, J. Zhang, G.-r. Ren, Y. Wu, Tetrahedron 2007,
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Marder, A.C. Parsons, R.M. Ward, J. Zhu,
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A mixture of E/Z-7m (119 mg; E:Z=57:43) in DMSO
(2.5 mL) was heated at 1808C for 12 h.After cooling to
room temperature, the solution was diluted with CH2Cl2
(50 mL), washed with H2O (3”10 mL) and dried over
MgSO4.After removal of the solvent from the filtrate, the
residue was subjected to SiO2, eluting with hexane/CH2Cl2
(from 10:1 to 4:1) to afford 64 mg (40%, based on E-7m) of
21 and 43 mg (91%) of Z-7m.
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[9] More recently, two special protocols were reported.For
Synthesis of 1-Methyl-3-phenyl-2-(2-phenyl-1-ethion-
yl)-2-indene (22)
Au(III)-catalyzed coupling, see: a) C.Gonzµlez-Arella-
A
no, A.Abad, A.Corma, H.García, M.Iglesias, F.
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Int. Ed. 2007, 46, 1536; for homocoupling reactions of
an alkynylmagnesium chloride, see: b) A.Krasovskiy,
To a solution of Z-7a (202 mg) in CHCl3 (10 mL) at room
temperature was dropwise added concentrated H2SO4
(1 mL) and stirred at the same temperature for 3.5 h. This
reaction mixture was diluted with CHCl3 (50 mL), washed
with H2O (3”10 mL) and dried over MgSO4.After removal
of the solvent of the filtrate, the residue was subjected to
SiO2, eluting with hexane/CH2Cl2 (from 5:1 to 1:1) to afford
162 mg (75%) of 22.
A.Tishkov, V.del Amo, H.Mayr, P.Knochel,
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Acknowledgements
This work was supported by the National Science Council of
Taiwan (NSC 96-2113-M-006-008-MY2). We also thank Prof.
S.-L. Wang and Ms. C.-Y. Chen (National Tsing-Hua Univer-
sity, Taiwan) for the X-ray structure analyses and Dr. Arif
Karim (UCLA) for his careful proofreading of the final
manuscript.
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[21] Compound Z-7d: C27H24, monoclinic crystals of space
group C2/c, unit cell dimensions: a=18.673(3), b=
6.1099(9), c=36.375(6) Š, a=90, b=100.215(3), g=
908, V=4084.2(10) Š3, Z=8, Crystal size: 0.30”0.23”
0.10 mm3.Compound Z-7o: C48H30, triclinic crystals of
space group P1, unit cell dimensions: a=9.0868(18),
b=13.068(2), c=15.152(3) Š, a=65.804(8), b=
80.282(8), g=85.118(8)8, V=1617.4(5) Š3, Z=2, Crys-
tal size: 0.10”0.10”0.04 mm3.Crystallographic data
(excluding structure factors) for the structures reported
in this paper have been deposited with the Cambridge
Crystallographic Data Centre.CCDC 672448 ( Z-7d)
and 671872 (Z-7o) contain the supplementary crystallo-
graphic data for this paper.These data can be obtained
free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif
or on application to CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK [Fax: (internat.) + 44–1223–
336033; E-mail: deposit@ccdc.cam.ac.uk].
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À
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[22] Small amounts of compounds E/Z-7q (R=n-Bu) could
be prepared in accordance with our procedure.The
1H NMR spectra of these two regioisomers are very
similar to those of their analogues, (3E/3Z)-2-butyl-3-
(1-hexynyl)deca-1,3-diene, see: M.Kim, RL. .Miller,
D.Lee, J. Am. Chem. Soc. 2005, 127, 12818.
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[23] In these control experiments, only the reaction prod-
ucts of type 10 were isolated and characterized.Self-di-
merization and -trimerization adducts of alkynes 4 and
traces of other regioisomers were also formed but ne-
glected.
[18] Trimerization catalyzed by diiridium complexes, see:
[24] When enyne 9c was heated at 808C for 1 d in our cata-
lytic system, a complex mixture was generated and
only ca. 30% of the starting material was recovered.
[25] Product Z-7a is a stable species.It can be heated in 1,2-
dichlorobenzene at 1808C in an N2 atmosphere for 1 d
without obvious decomposition.Attempts at the prepa-
ration of a tetramer from the reaction of Z-7a and 4a
with our protocol were also not successful.
ref.[13g].
[19] GC analysis cannot provide accurate information for
determination of the products because compound Z-7a
generates one unknown product at ca. 2508C.
[20] Although it is well reported that copper(I) acetylides
are important reagents or intermediates for prepara-
tions of alkynyl derivatives, s-alkynyl Pd complexes
generated from terminal arylalkynes and Pd(0) cata-
lysts can also exhibit a similar function.There are sev-
eral examples for copper-free alkyne homocouplings
[26] Complex 13 can be directly formed from PdCl2(PPh3)2
A
and 4, or by the transmetallation from the correspond-
ing copper(I) acetylide.
1848
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Adv. Synth. Catal. 2008, 350, 1841 – 1849

Palladium-Catalyzed Trimerizations of Terminal Arylalkynes
FULL PAPERS
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1,3-hexadien-5-yne.It has been reported that 1,3-hexa-
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see: H.Hopf, H.Berger, G.Zimmermann, U.Nüchter,
P.G. Jones, I. Dix, Angew. Chem. 1997, 109, 1236;
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[29] Compound 21 (CCDC 671873): C36H24, monoclinic
crystals of space group P21/n, unit cell dimensions: a=
9.4820(17), b=14.912(2), c=17.501(2) Š, a=90, b=
99.524(8), g=908, V=2440.5(6) Š3, Z=4, Crystal size:
0.12”0.09”0.05 mm3.
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