Gold-catalyzed synthesis of 1,3-disubstituted benzenes through tandem allylation/cyclization reaction of alkynals

Article abstract of DOI:10.1016/j.jorganchem.2008.10.049

Treatment of alkynals with 2-substituted allylsilanes and PPh₃AuCl/AgOTf (5/3 mol%) catalyst led to formation of 1,3-disubstituted benzenes efficiently. This reaction sequence comprises an initial allylation of aldehyde, followed by cycloisomerization of enynes; PPh₃AuOTf is active in both steps.

Full text of DOI:10.1016/j.jorganchem.2008.10.049

Journal of Organometallic Chemistry 694 (2009) 566–570
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Gold-catalyzed synthesis of 1,3-disubstituted benzenes through tandem
allylation/cyclization reaction of alkynals
Sabyasachi Bhunia a, Shariar Md. Abu Sohel a, Chao-Chin Yang a, Shie-Fu Lush b, Fwu-Ming Shen c,
Rai-Shung Liu a,
*
a Department of Chemistry, National Tsing-Hua University, Hsinchu 30043, Taiwan, ROC
b Department of Biotechnology, Yuan-Pei University, Hsinchu, Taiwan, ROC
c Department of Medical Laboratory Science and Biotechnology, Yuan-Pei University, Hsinchu, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 August 2008
Received in revised form 10 October 2008
Accepted 29 October 2008
Available online 6 November 2008
Treatment of alkynals with 2-substituted allylsilanes and PPh3AuCl/AgOTf (5/3 mol%) catalyst led to for-
mation of 1,3-disubstituted benzenes efficiently. This reaction sequence comprises an initial allylation of
aldehyde, followed by cycloisomerization of enynes; PPh3AuOTf is active in both steps.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Allylation
Alkynal
Benzenes
Catalysis
Tandem reaction
1. Introduction
2. Results and discussion
Tandem reactions have been the subject of intensive investiga-
tions in organic synthesis [1]. The high efficiency and brief proce-
dures are the beneficial features of such reactions. With a single
workup, one can deliver a complicate molecule that would other-
wise have to be prepared over the course of several individual
steps. Transition-metal catalyzed cyclizations of enynes [2–6] have
emerged as powerful tools for the synthesis of carbocyclic com-
pounds, and Pt(II) and Au(I) catalysts are commonly used as the
catalysts because of their superior chemoselectivities and activi-
ties. Barriault has reported the gold catalyzed benzannulation of
3-hydroxy-1.5-enynes for the synthesis of tetrahydronaphthalenes
[7,8]. Scheme 1 shows an elegant example, reported by Fürstner
and coworkers [5e] for the synthesis of bicyclo[3.1.0]hexanones
via PtCl2 catalyzed cycloisomerization of 5-en-1-yn-3-ols, which
were prepared by Grignard reagents. As Ag(I) and Pt(II) catalysts
were also active in catalytic addition of allylsilanes to carbonyl
compounds [9], we sought to accomplish one-pot synthesis of such
ketones using suitable Ag(I), Pt(II) and Au(I) catalysts. Neverthe-
less, the outcome of our new attempts is the efficient production
of 1,3-disubstituted benzenes using a mixture of PPh3AuCl(5%)
and AgOTf (3%).
As shown in Table 1, we examined the cyclization of alkynal 1
and allylsilanes (2a–b) over various Ag(I), Pt(II) and Au(I) catalysts,
each at 5 mol% except for entries 6–7. Treatment of alkynal 1 with
allylsilane 2a and AuClPPh3/AgSbF6 led to a messy mixture of prod-
ucts (Table 1, entry 1). AuCl, AuClPPh3 and AuCl3 were not effective
to bring about any transformation (entries 2–4). AgOTf gave homo-
allylic alcohol 3a exclusively (93% yield) without a secondary
enyne cycloisomerization. However, the use of AuClPPh3(5 mol%)/
AgOTf(3 mol%) catalyst in CH2Cl2 at a brief time (2.0 h) gave homo-
allylic alcohol (3a) and biphenyl compound (4a) in 28% and 42%
yields, respectively, (entry 5). At a prolonged period (5 h), we only
obtained biphenyl 4a with the yield up to 84% (entry 6); this
observation confirms the intermediacy of 3a in this sequence.
We envisage that ‘‘PPh3AuOTf” generated here is active toward
both allylation and aromatization reaction because free AgOTf is
thought to be negligible in this catalyst composition (Au:Ag = 5:3).
PtCl2/CO [10] was not suitable to this reaction sequence even at
80 °C (entries 8 and 9). We extended this gold catalysis to unsub-
stituted allylsilane 2b, which led to the formation of 1-phenyl-
hex-5-en-1-yn-3-ol (3b) without any further cyclization.
Treatment of 1 and 2a with 5% TfOH for 24 h at room temperature
led to the protonation of allylsilane and the alkynal 1 was recov-
ered unreacted (entry 11) [11]. Similarly, 5% TMSOTf failed to give
desired 4a (entry 12).
* Corresponding author.
E-mail address: rsliu@mx.nthu.edu.tw (R.-S. Liu).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.10.049

S. Bhunia et al. / Journal of Organometallic Chemistry 694 (2009) 566–570
567
OH
O
OH
Cl2Pt
R
allylMgBr
R
CHO
R
R
OTMS
R
Au+, Ag+ or Pt(II)
R
R'
R
R'
SiMe3
Scheme 1.
Table 2
We studied the scope of this gold-catalyzed tandem catalysis
(Table 2). Entry 1 shows the applicability of this cyclization to 2-
phenylallylsilane 2c, which gave 1,3-diphenyl benzene 10 in 90%
Tandem allylation/cyclization of alkynals.
R1
PPh3AuCl
AgOTf
R2
R1
1, 5-9
yield (entry 1). We prepared alkynal 5–6 bearing
a p-and
+
O
m-methoxyphenyl groups 5–6, which gave the corresponding
1,3-disubstituted phenyl compounds 11–13 in 80–88% yields. Sub-
strates 7–8 bearing an electron-deficient p-nitro- and p-trifluoro-
methylphenyl group were very suitable for this tandem
sequence, giving 78–88% yields of resulting products 14–17.
Aliphatic alkynal 9 also worked well with allylsilanes 2a and 2c,
giving diphenyl compound in 82–86% yields.
We also examined the tandem cyclization of 3-phenylpropiolal-
dehyde (1) with various allylsilanes 2d–2h bearing various 2-
substituted R groups (Table 3). 2-arylallylsilanes 2d–2f (aryl = p-t-
BuC6H4, 2,4-dimethylphenyl, 2-benzothienyl) were very suitable
to this cyclization, giving desired biphenyl products 20–22 with
yields exceeding 81%. This tandem catalysis is extendible to allylsi-
lane 2g bearing a n-pentyl group (2e), giving compound 23 in 87%
yield. Carbomethoxy substituted allylsilane (2h) only led to its
exclusive recovery even for a prolonged reaction time; this is
obviously due to its low reactivity in allylation of carbonyl
compounds.
CH2Cl2, rt
5 h
SiMe3
2a, 2c
R2
10-19
Entrya
Alkynal (R1)
Ph (1)
Silane (R2)
Product
Yield (%)b
1
2
3
4
5
6
7
8
9
10
Ph (2c)
Me (2a)
Me (2a)
Ph (2c)
Me (2a)
Ph (2c)
Me (2a)
Ph (2c)
Me (2a)
Ph (2c)
10
11
12
13
14
15
16
17
18
19
90
88
80
88
78
80
85
88
82
86
p-MeOC6H4 (5)
m-MeOC6H4 (6)
m-MeOC6H4 (6)
p-O2NC6H4 (7)
p-O2NC6H4 (7)
p-F3CC6H4 (8)
p-F3CC6H4 (8)
n-C6H13 (9)
n-C6H13 (9)
a
[Substrate] = 0.22 M.
Yield of isolated product after silica gel column chromatography.
b
coordinates to aldehyde to activate the allylation, leading to the
formation of alcohol derivative B through intermediate A. We
envisage that the gold-alkoxy group of intermediate B tends to un-
dergo exchange with TMSOTf to regenerate active PPh3AuOTf be-
cause Si(IV) has a better affinity toward the alkoxy group than
Au(I). A subsequent electrophilic activation of the alkyne C by
Au+ gives rise to a 6-endo-dig ring closure, producing carbenoid
intermediate E, which is also represented by resonance form E0.
In contrast with the Fürstner pathway, as depicted in Scheme 1,
we envisage that tertiary carbocation E0 enhance the acidity of
the neighboring CH2 hydrogen that was readily deprotonated by
OTf anion to generate Au-cyclohexadienyl species. A final elimina-
tion of one molecule of TMSOH from species F led to gold-phenyl
species G, which undergoes protodemetallation to give the final
product. According to this proposed mechanism, it is clear that
the better stabilization of R2 = Ph, alkyl on the cationic intermedi-
ate E and E0 are crucial to realize the aromatization. This assess-
ment accounts for the failure to obtain aromatization product
from unsubstituted allylsilane 2b.
We propose a plausible mechanism to rationalize the course of
this allylation/aromatization cascade (Scheme 2). As depicted in
Scheme 1, ‘‘PPh3AuOTf” was shown to be catalytically active to-
ward allylation and cyclization. We previously reported that
[11a] treatment of ‘‘PPh3AuOTf” with allylSiMe3 did not generate
allylAuPPh3. Consequently we believe that PPh3AuOTf initially
Table 1
Catalyst screening over various acid catalysts
Ph
OH
O
5% catalyst
CH2Cl2
1
Ph
R
+
SiMe3
R
R
R = Me (4a); H (4b)
R = Me (3a); H (3b)
R = Me (2a); H (2b)
Entrya Catalyst
Allylsilane Condition
Products (yield %)b
In conclusion, we reported a facile synthesis of 1,3-disubsti-
tuted benzenes through cyclization of alkynyl aldehydes and 2-
substituted allylsilanes. This reaction sequence comprises a tan-
dem allylation and cyclization of enynes; the active species for
these two steps are PPh3AuOTf. A wide scope of alkynyl aldehydes
is applicable to this tandem sequence whereas the nature of the 2-
substituent of allylsilane is crucial for the both initial allylation and
the secondary aromatization. Evaluation of additional values of
such reactions is currently underway.
1
2
3
4
5% AuClPPh3/5% AgSbF6 2a
1 h, rt
Messy
N.R.c
5% AuCl
2a
2a
2a
2a
2a
2a
2a
2a
2b
2a
2a
10 h, rt
10 h, rt
24 h, rt
24 h, rt
2 h, rt
5.0 h, rt
10 h, rt
0.5 h, 80 °C messy
5% AuCl3
N.R.c
5% AuClPPh3
5% AgOTf
N.R.c
5
3a (93)
3a (28), 4a (42)
4a (84)
N.R.c
6d
7
5% AuClPPh3/3% AgOTf
5% AuClPPh3/3% AgOTf
5% PtCl2/CO
8
9
10
11
12
5% PtCl2/CO
5% AuClPPh3/5% AgOTf
5% TfOH
24 h, rt
24 h, rt
24 h, rt
3b (64)
N.R.c
5% TMSOTf
3a (33)
3. Experimental
a
[Substrate] = 0.22 M.
Yields are for products isolated after silica gel column chromatography.
No reaction.
b
c
Unless otherwise noted, all reactions were carried out under
nitrogen atmosphere in oven-dried glassware using standard
d
12% of unreacted alkynal 1 was recovered.

568
S. Bhunia et al. / Journal of Organometallic Chemistry 694 (2009) 566–570
Table 3
3.2. Experimental procedure for tandem allylation/gold-catalyzed
cyclization
Tandem allylation/cyclization of 3-phenylpropiolaldehyde
5% AuCl.PPh3
/ AgOTf
Ph
R
A long tube containing AuClPPh3 (19.0 mg, 0.0384 mmol) and
AgOTf (5.80 mg, 0.0225 mmol) was evacuated and backfilled with
N2. After repeating this procedure twice, the tube was charged
Ph
+
O
DCM / r.t
4.5h
SiMe3
1
20-24
R2
Yield (%)b
2d-2h
with alkynal
1 (0.1 g, 0.768 mmol), allylsilane 2a (0.108 g,
Entrya
Silane
Product
0.845 mmol) and CH2Cl2 (3.5 ml). The resulting mixture was stir-
red at 23 °C, 4.5 h, and filtered over a small silica bed. After re-
moval of the solvent in vacuo, the residues were purified on a
silica column (hexane) to give the 4a (0.1 g, 0.645 mmol, 84%) as
a colorless liquid.
1
2
p-tBu-C6H4 (2d)
20
21
94
92
(2e)
3-Methylbiphenyl 4a: Colorless oil, IR (nujol, cmꢀ1): 3028 (m),
(2f)
2906 (m), 685 (s), 778 (s); 1H NMR (600 MHz, CDCl3):
d
3
22
81
S
7.59 ꢁ 7.58 (m, 2H), 7.44 ꢁ 7.39 (m, 4H), 7.35 ꢁ 7.32 (m, 2H),
7.16 (d, J = 7.4 Hz, 2H), 2.42 (s, 3H); 13C NMR (150 MHz, CDCl3): d
141.3, 141.2, 138.3, 128.7 (ꢂ2CH), 128.6, 127.9, 127.1 (ꢂ2CH),
124.2, 21.5; HRMS Calc. for C13H12: 168.0939, found: 168.0941.
Compound 10: White solid, IR (nujol, cmꢀ1): 3039 (m), 2910(m),
683(s), 774(s); 1H NMR (600 MHz, CDCl3): d 7.86 ꢁ 7.85 (m, 1H),
7.69 ꢁ 7.68 (m, 4 H), 7.62 ꢁ 7.60 (m, 2H), 7.56 ꢁ 7.48 (m, 5H),
7.42 ꢁ 7.39 (m, 2H); 13C NMR (150 MHz, CDCl3): d 141.7, 141.1,
4
5
n-C5H11(2g)
CO2Me (2h)
23
24
87
N.R.c
a
Substrate = 0.22 M.
Yield of isolated product after silica gel column chromatography.
No reaction.
b
c
syringe, cannula and septa apparatus. Hexane was dried with so-
dium benzophenone and distilled before use. Dichloromethane
was dried over CaH2 and distilled before use. All the 1H NMR and
13C NMR were recorded in CDCl3 solution. Allylsilanes were pre-
pared according to the procedures reported in literature [12].
129.1, 128.8, 127.4, 127.2, 126.1, 126.0; HRMS Calc. for C18H14
230.1096, found: 230.1094.
:
40-Methoxy-3-methylbiphenyl 11: Colorless oil, IR (nujol, cmꢀ1):
3035 (m), 2904 (m), 1248 (s),1037 (s); 1H NMR (600 MHz, CDCl3):
d 7.54 ꢁ 7.52 (m, 2H), 7.39 (s, 1H), 7.36 ꢁ 7.34 (m, 1H), 7.29 (t,
J = 7.5 Hz, 1H), 7.12 (d, J = 7.5 Hz, 1H), 6.97 ꢁ 6.95 (m, 2H); 13C
NMR (150 MHz, CDCl3): d 159.4, 140.8, 138.6, 133.8, 128.8, 128.2,
127.6, 123.8, 114.3, 55.4, 21.4; HRMS Calc. for C14H14O:
198.1045, found: 198.1046.
3.1. Procedure for the synthesis of 3-phenylpropiolaldehyde (1)
To a mixture of Pd(PPh3)2Cl2 (0.344 g, 0.49 mmol) and CuI
(0.093 g, 0.49 mmol) was added a triethylamine (15 mL) solution
of iodobenzene (2.00 g, 9.80 mmol) at 0°, and the mixture was stir-
red for 10 min before addition of propargyl alcohol (0.549 g,
9.80 mmol). At the end of reaction, the resulting solution was fil-
tered, concentrated in vacuo, and partitioned between ethyl ace-
tate and water. The organic layer was washed with brine and
dried over MgSO4 and the residues were chromatographed through
a silica column (ethyl acetate/hexane, 1:9) to afford the compound
1 as light-yellow oil (1.14 g, 8.63 mmol, 88%). This product was dis-
solved in dichloromethane (20 mL), cooled to 0 °C, and treated
with a mixture (1:1 w/w) of PCC (2.42 g, 11.21 mmol) and celite.
The resulting suspension was stirred at 0 °C. for 1 h, and the reac-
tion mixture was filtered through a short silica pad. Concentration
of the solution gave the crude product which was then subjected to
a silica column chromatography (ethyl acetate–hexane, 0.5:9.5),
giving 3-phenylpropiolaldehyde (1) as oil. (0.808 g, 6.208 mmol,
72%).
3-Methoxy-30-methylbiphenyl 12: Colorless oil, IR (nujol, cmꢀ1):
3031 (m), 2901 (m), 1246 (s),1034 (s); 1H NMR (600 MHz, CDCl3):
d 7.45 ꢁ 7.33 (m, 4H), 7.22 ꢁ 7.15 (m, 3H), 6.92 ꢁ 6.90 (m, 1H),
3.87 (s, 3H), 2.44 (s, 3H); 13C NMR (150 MHz, CDCl3): d 160.2,
142.8, 141.0, 138.6, 129.9, 128.7, 128.3, 127.9, 124.3, 119.6,
112.8, 112.7, 55.3, 21.4; HRMS Calc. for C14H14O: 198.1045, found:
198.1043.
Compound 13: White solid; IR (neat, cmꢀ1): 3041 (m), 1252 (s),
1044 (s); 1H NMR (600 MHz, CDCl3): d 7.78 (t, J = 1.6 Hz, 1H),
7.64 ꢁ 7.63 (m, 2H), 7.57 ꢁ 7.55 (m, 2H), 7.51 ꢁ 7.44 (m, 3H),
7.38 ꢁ 7.35 (m, 2H), 7.24 ꢁ 7.17 (m, 2H), 6.92 ꢁ 6.90 (m, 1H),
3.86 (s, 3H); 13C NMR (100 MHz, CDCl3): d 159.9, 142.7, 141.7,
141.6, 141.1, 129.8, 127.4, 127.2, 126.3, 126.2, 126.1, 119.7,
112.9, 112.8, 55.3; HRMS Calc. for C19H16O: 260.1201, found:
260.1204.
3-Methyl-40-nitrobiphenyl 14: White solid; IR (neat, cmꢀ1): 2894
(m), 1532 (s), 1333 (s); 1H NMR (600 MHz, CDCl3): 8.25 ꢁ 8.23 (m,
OAuL
-OTf
LAuO
R2
R2
R1
R1
+
+
O
SiMe3
SiMe3
B
A
LAu+
Me3SiOTf
R2
R1
LAu+
OSiMe3
H
OSiMe3
R2
+
OSiMe3
Me3SiOTf
LAu
R1
LAu+
R1
6-endo-dig
C
D
R2
R1
LAuOTf
E
R2
OSiMe3
OSiMe3
H+
LAu
R1
Au
R1
LAu
R1
+
R2
R2
R1
R2
Au+
R2
Me3SiOH
G
HOTf
H
-OTf
F
E'
Scheme 2.

S. Bhunia et al. / Journal of Organometallic Chemistry 694 (2009) 566–570
569
2H), 7.70 ꢁ 7.68 (m, 2H), 7.41 ꢁ 7.35 (m, 3H), 7.24 (d, J = 7.8 Hz,
1H), 2.43 (s, 3H); 13C NMR (150 MHz, CDCl3): d 147.7, 146.9,
138.8, 138.6, 129.6, 128.9, 128.0, 127.6, 124.4, 123.9, 21.4; HRMS
Calc. for C13H11NO2: 213.079, found: 213.0792.
127.2, 127.1, 125.3 (ꢂ2CH), 124.5, 124.3, 123.6, 122.2, 119.7;
HRMS Calc. for C20H14S: 286.0816, found: 286.0813.
Acknowledgements
Compound 15: White solid; IR (neat, cmꢀ1): 3034 (m), 1536 (s),
1330 (s); 1H NMR (600 MHz, CDCl3): d 8.30 ꢁ 8.28 (m, 2H),
7.81 ꢁ 7.76 (m, 3H), 7.66 ꢁ 7.54 (m, 5H), 7.49 ꢁ 7.38 (m, 3H); 13C
NMR (150 MHz, CDCl3): d 147.5, 147.1, 142.2, 140.5, 139.2, 129.5,
128.9 (ꢂ2CH), 127.8, 127.7, 127.6, 127.1, 126.2, 124.1; HRMS Calc.
for C18H13NO2: 275.0946, found: 275.0948.
We thank the National Science Council, Taiwan for their gener-
ous financial support.
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3-Methyl-40-(trifluoromethyl)biphenyl 16: Colorless oil; IR (neat,
cmꢀ1): 3025 (m), 2902 (m), 678 (s), 772 (s); 1H NMR (600 MHz,
CDCl3) d 7.7 (s, 4H), 7.44 ꢁ 7.37 (m, 3H), 7.25 (d, J = 7.2 Hz, 1H),
2.46 (s, 3H); 13C NMR (150 MHz, CDCl3): d 144.8, 139.7, 138.6,
129.3 ꢁ 125.6 (ꢂ2C), 128.9, 128.8, 128, 127.4, 125.6, 124.3, 21.4;
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J = 7.4 Hz, 1H), 7.0 ꢁ 6.98 (m, 3H), 2.57 (t, J = 7.7 Hz, 2H), 2.34 (s,
3H), 1.62 ꢁ 1.29 (m, 8H), 0.89 (t, J = 7 Hz, 3H); 13C NMR
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d
(o) N.T. Patil, Y. Yamamoto, Chem. Rev. 108 (2008) 3395.
[4] (a) For gold-catalyzed cycloisomerizations of enynes, see selected examples:
C. Nieto-Oberhuber, P.M. Munoz, E. Bunuel, C. Nevado, D.J. Cardenas, A.M.
Echavarren, Angew. Chem., Int. Ed. 43 (2004) 2402;
7.68 ꢁ 7.67 (m, 2H), 7.52 ꢁ 7.48 (m, 4H), 7.43 ꢁ 7.39 (m, 2H),
7.23 (d, J = 7.6 Hz, 1H), 2.75 (t, J = 7.7 Hz, 2H), 1.77 ꢁ 1.72 (m,
2H), 1.47 ꢁ 1.39 (m, 6H), 0.98 (t, J = 6.8 Hz, 3H); 13C NMR
(150 MHz, CDCl3): d 143.4, 141.5, 141.2, 128.7, 128.6, 127.3
(ꢂ2CH), 127.2, 127.1, 124.5, 36.1, 31.7, 31.5, 29.1, 22.6, 14.1; HRMS
Calc. for C18H22: 238.1722, found: 238.1724.
(b) M.R. Luzung, J.P. Markham, F.D. Toste, J. Am. Chem. Soc. 126 (2004) 10858;
(c) Y. Horino, M.R. Luzung, F.D. Toste, J. Am. Chem. Soc. 128 (2006) 11364;
(d) L. Zhang, S.A. Kozmin, J. Am. Chem. Soc. 126 (2004) 11806;
(e) L. Zhang, J. Am. Chem. Soc. 127 (2005) 16804;
(f) J. Sun, M.P. Conley, L. Zhang, S.A. Kozmin, J. Am. Chem. Soc. 128 (2006)
9705;
(g) A. Buzas, F. Gagosz, J. Am. Chem. Soc. 128 (2006) 12614;
(h) S.F. Kirsch, J.T. Binder, B. Crone, A. Duschek, T.T. Haug, C. Liébert, H. Menz,
Angew. Chem., Int. Ed. 46 (2007) 2310.
Compound 20: White solid; IR (neat, cmꢀ1): 3044 (m), 686 (s),
776 (s); 1H NMR (600 MHz, CDCl3): d 7.89 (s, 1H), 7.72 (d,
J = 7.2 Hz, 2H), 7.68 ꢁ 7.61 (m, 4H), 7.57 ꢁ 7.50 (m, 5H),
7.57 ꢁ 7.50 (m, 5H), 7.43 (t, J = 7.2, 1H), 1.45 (s, 9H); 13C NMR
(150 MHz, CDCl3): d 150.4, 141.7, 141.6, 141.2, 138.2, 129.1,
128.7, 127.3, 127.2, 126.9, 126.0, 125.9, 125.8, 125.7, 34.5, 31.3;
HRMS Calc. for C22H22: 286.1722, found: 286.1724.
[5] (a) For PtCl2-catalyzed cycloisomerization of enynes, see selected examples:
N. Chatani, N. Furukawa, H. Sakurai, S. Murai, Organometallics 15 (1996) 901;
(b) B.M. Trost, G.A. Doherty, J. Am. Chem. Soc. 122 (2000) 3801;
(c) A. Fürstner, H. Szillat, F. Stelzer, J. Am. Chem. Soc. 122 (2000) 6785;
(d) M. Méndez, M.P. Munoz, C. Nevado, D.J. Cardenas, A.M. Echavarren, J. Am.
Chem. Soc. 123 (2001) 10511;
3-Pentylbiphenyl 21: Colorless oil; IR (neat, cmꢀ1): 3035 (m),
2896 (m), 682 (s), 782 (s); 1H NMR (600 MHz, CDCl3): d 7.62 (d,
J = 7.2 Hz, 2H), 7.47 ꢁ 7.35 (m, 6H), 7.19 (d, J = 7.6 Hz, 1H), 2.7 (t,
J = 7.6 Hz, 2H) 1.72 ꢁ 1.68 (m, 2H), 1.4 ꢁ 1.38 (m, 4H), 0.94 (t,
J = 6.4 Hz, 3H); 13C NMR (150 MHz, CDCl3): d 143.4, 141.4, 141.1,
128.7, 128.6, 127.4, 127.3, 127.2, 127.1, 124.5, 36.0, 31.5, 31.2,
22.5, 14.0; HRMS Calc. for C17H20: 224.1565, found: 224.1563.
Compound 22: White solid; IR (neat, cmꢀ1): 3021 (m), 2888 (m),
680 (s), 771 (s); 1H NMR (600 MHz, CDCl3): d 7.77 (s, 1H), 7.63 (d,
J = 7.6 Hz, 2H), 7.54 (d, J = 7.2 Hz, 2H), 7.49 ꢁ 7.43 (m, 3H), 7.35 (t,
J = 7.2, 1H), 7.25 (s, 2H), 7.0 (s, 1H), 2.38 (s, 6H); 13C NMR
(150 MHz, CDCl3): d 141.9, 141.6, 141.2, 141.1, 129.0, 128.9,
128.7, 127.3, 127.2 (ꢂ2CH), 126.1, 125.9, 125.1, 21.3; HRMS Calc.
for C20H18: 258.1409, found: 258.1408.
(e) V. Mamane, T. Gress, H. Krause, A. Fürstner, J. Am. Chem. Soc. 126 (2004)
8654;
(f) Y. Harrak, C. Blaszykowski, M. Bernard, K. Cariou, E. Mainetti, V. Mouriès,
A.-L. Dhimane, L. Fensterbank, M. Malacria, J. Am. Chem. Soc. 126 (2004) 8656;
(g) C. Blaszykowski, Y. Harrak, M.-H. Goncalves, J.-M. Cloarec, A.-L. Dhimane, L.
Fensterbank, M. Malacria, Org. Lett. 6 (2004) 3771;
(h) E. Soriano, J. Marco-Contelles, J. Org. Chem. 70 (2005) 9345;
(i) T.J. Harrison, B.O. Patrick, G.R. Dake, Org. Lett. 9 (2007) 367.
[6] (a) For cycloisomerization of enynes by other metals, see selected examples:
B.M. Trost, A.S.K. Hashmi, Angew. Chem., Int. Ed. 32 (1993) 1085;
(b) A. Goeke, M. Sawamura, R. Kuwano, Y. Ito, Angew. Chem., Int. Ed. 35 (1996)
662;
(c) P.A. Wender, D. Sperandio, J. Org. Chem. 63 (1998) 4164;
(d) N. Chatani, K. Kataoka, S. Murai, N. Furukawa, Y. Seki, J. Am. Chem. Soc. 120
(1998) 9104;
(e) B.M. Trost, F.D. Toste, J. Am. Chem. Soc. 122 (2000) 714;
(f) D. Sémeril, M. Cléran, C. Bruneau, P.H. Dixneuf, Adv. Synth. Catal. 343
(2001) 184;
2-(Biphenyl-3-yl)benzo[b]thiophene 23: White solid; IR (neat,
cmꢀ1): 3029 (m), 684 (s), 783 (s); 1H NMR (600 MHz, CDCl3): d
7.96 (s, 1H), 7.86 (d, J = 7.6 Hz, 1H), 7.81 (d, J = 7.6 Hz, 1H),
7.75 ꢁ 7.67 (m, 3H), 7.62 (s, 1H), 7.58 (d, J = 7.6 Hz, 1H), 7.5 (s,
J = 7.2 Hz, 3H), 7.47 ꢁ 7.31 (m, 3H); 13C NMR (150 MHz, CDCl3): d
144.08, 141.9, 140.7, 140.6, 139.5, 134.7, 129.3, 128.8, 127.6,
(g) N. Chatani, H. Inoue, T. Kotsuma, S. Murai, J. Am. Chem. Soc. 124 (2002)
10294;
(h) V. Michelet, P.Y. Toullec, J.-P. Genêt, Angew. Chem., Int. Ed. 47 (2008) 4268.
[7] (a) C.M. Grisé, L. Barriault, Org. Lett. 8 (2006) 5905;
(b) C.M. Grisé, L. Barriault, Tetrahedron 64 (2008) 797.
[8] (a) For benzannulation reactions of propargylic systems catalyzed by
transition metals, see: T. Kawasaki, S. Saito, Y. Yamamoto, J. Org. Chem. 67
(2002) 2653;

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(b) J. Zhao, C.O. Hughes, F.D. Toste, J. Am. Chem. Soc. 128 (2006) 7436;
[10] (a) A. Fürstner, P.W. Davies, T. Gress, J. Am. Chem. Soc. 127 (2005) 8244;
(b) A. Fürstner, F. Stelzer, J. Am. Chem. Soc. 123 (2001) 11863;
(c) M.-Y. Lin, A. Das, J. Am. Chem. Soc. 128 (2006) 9340;
(d) J.-M. Tang, S. Bhunia, S.M.A. Sohel, M.-Y. Lin, H.-Y. Liao, S. Datta, A. Das, R.-
S. Liu, J. Am. Chem. Soc. 129 (2007) 15677.
[11] (a) Y.-C. Hsu, S. Datta, C.-M. Ting, R.-S. Liu, Org. Lett. 10 (2008) 521;
(b) C.-C. Lin, T.-M. Teng, A. Odedra, R.-S. Liu, J. Am. Chem. Soc. 129 (2007)
3798;
(c) S. Wang, L. Zhang, J. Am. Chem. Soc. 128 (2006) 14274;
(d) A.S. Dudnik, T. Schwier, V. Gevorgyan, Org. Lett. 10 (2008) 1465;
(e) X. Huang, L. Zhang, Org. Lett. 9 (2007) 4627.
[9] (a) For addition of allylsilanes to carbonyl derivatives by using Ag (I) and Pt (II)
see selected examples: M. Wadamoto, N. Ozasa, A. Yanagisawa, H. Yamamoto,
J. Org. Chem. 68 (2003) 5593;
(b) A. Yanagisawa, H. Kageyama, Y. Nakatsuka, K. Asakawa, Y. Matsumoto, H.
Yamamoto, Angew. Chem. 111 (1999) 3916; Angew. Chem. Int. Ed. 38 (1999)
3701.;
(c) Ref. [9c].
[12] (a) K. Olofsson, M. Larhed, A. Hallberg, J. Org. Chem. 63 (1998) 5076;
(b) B.A. Narayanan, W.H. Bunnelle, Tetrahedron Lett. 28 (1987) 6261.
(c) S. Bhunia, K.-C. Wang, R.-S. Liu, Angew. Chem., Int. Ed. 47 (2008) 5063.