Generation of allenic/propargylic zirconium complexes and subsequent cross-coupling reactions: A facile synthesis of multisubstituted allenes

Article abstract of DOI:10.1021/jo9020419

(Chemical Equation Presented) The β-alkoxide elimination reaction of propargylic ether with Negishi reagent leads to allenes and/or alkynes after hydrolysis. The product distribution is highly dependent on the substitution pattern of starting propargylic

Full text of DOI:10.1021/jo9020419

pubs.acs.org/joc
Generation of Allenic/Propargylic Zirconium Complexes and Subsequent
Cross-Coupling Reactions: A Facile Synthesis of Multisubstituted Allenes
Hao Zhang,† Xiaoping Fu,† Jingjin Chen,† Erjuan Wang,‡ Yuanhong Liu,*,† and
Yuxue Li*,†
†State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, People’s Republic of China, and
‡Department of Chemistry, East China Normal University, 3663 North Zhongshan Road, Shanghai 200062,
People’s Republic of China
yhliu@mail.sioc.ac.cn
Received September 22, 2009
The β-alkoxide elimination reaction of propargylic ether with Negishi reagent leads to allenes and/or
alkynes after hydrolysis. The product distribution is highly dependent on the substitution pattern of
starting propargylic ethers; that is, aryl- or alkyl-substituted propargylic ethers favor the allene
products, whereas TMS-substituted propargylic ethers afford alkynes. DFT calculations revealed
that both the large steric effect and the β-effect of the TMS group favor the alkyne products, reversing
the selectivity. Subsequent coupling reactions of the allenic/propargylic zirconium intermediates with
aryl iodides in the presence of Pd(PPh3)4/CuCl provide a straightforward route for the synthesis of
multisubstituted allenes.
Introduction
low-valent zirconium induced β-alkoxide elimination reac-
tion is a particularly attractive protocol.2 Due to the oxo-
philic nature of zirconium metal, it can cause the elimination
of the alkoxy group at β-position of the zirconium metal to
form useful organometals such as allylic,3 γ-alkoxy allylic,4
γ,γ-dialkoxy allylic,5 allenic,3b,6 and alkenyl7 zirconium
Organozirconium compounds are attractive intermediates
in an impressive array of synthetic methodology and have
received much attention in recent years.1 Among various
possibilities for the generation of organozirconium reagents,
*To whom correspondence should be addressed. Fax: (þ86) 021-
64166128.
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(b) Ito, H.; Nakamura, T.; Taguchi, T.; Hanzawa, Y. Tetrahedron 1995, 51,
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DOI: 10.1021/jo9020419
r
Published on Web 11/18/2009
J. Org. Chem. 2009, 74, 9351–9358 9351
2009 American Chemical Society

Zhang et al.
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SCHEME 1
SCHEME 2
species. β-Alkoxide elimination from zirconacycles has also
been reported for the construction of allenes.8 Allenic/pro-
pargylic zirconium species can be conveniently prepared by
treatment of propargylic ethers with dibutylzirconocene
complex (Negishi reagent). However, the synthetic utility
of these intermediates has only been described in the reaction
with aldehydes, which affords mainly homopropargyl alco-
hols.3b,6 Nevertheless, the development of new C-C bond
formation reactions via these organometallic derivatives is
still highly demanding. In this paper, we report the substi-
tuent-dependent generation of the allenic zirconium com-
plexes and their coupling reactions with aryl halides
(Scheme 1). The coupling reaction of aryl halides with
organometals represents one of the most powerful methods
for C-C bond formation. Although the coupling reactions
of aryl iodides with various organozirconocenes such as vinyl
zirconocenes, zirconacyclopentenes, or zirconacyclopenta-
dienes are known,9 there is no report for the coupling
reactions with allenic/propargylic zirconium complexes to
the best of our knowledge. The present method could be
readily applied to the synthesis of multisubstituted allenes.
hydrolysis of the reaction mixture might form allenes, which
could also account for the existence of allenic zirconium
species. However, there are no such results in their report.
Here we found that quenching the reaction mixture by 3 N
HCl aqueous solution in the case of propargyl methyl ether
1a (R1 = Ph) bearing a cyclic ring at C-1 selectively afforded
allene 5a in 87% yield without contamination of any alkyne
6a (Scheme 2 and Table 1, entry 1). Alkyl-substituted
propargylic ethers 1b, 1d, and 1e afforded similar results,
although with lower yield compared with the phenyl-
substituted propargylic ether (entries 2, 4, and 5). The
substrate of 1f tethered with a phenyl group on the alkyne
substituent afforded allene 5f and alkyne 6f in 81% and 6%
yields, respectively (entry 6). C-1 substituted by two methyl
groups gave exclusively allene 5g in 64% yield (entry 7).
C-1-monosubstituted propargylic ethers 1h-j also gave rise
to allenes as major products (entries 8-10). The above
reactions also provided an efficient method for the synthesis
of allenes by simply quenching the zirconium intermedi-
ates.10 Interestingly, when R1 was a TMS group, the reaction
selectively generated alkynes 6k-n in 55-70% yields
(entries 11-14), whereas the allene products were not
t
Results and Discussion
detected. It is noteworthy that bulky Bu-substituted 1j
reacted completely differently with zirconocene-butene
complex compared with TMS-substituted one, in which
allene 5j was obtained as a major product (entry 10). In
addition to the steric effect caused by TMS group, the special
Hydrolysis of Allenic/Propargylic Zirconium Complexes
Generated from Propargylic Ether. Our investigation began
with an examination of the reaction between propargylic
ether 1 with Negishi reagent “Cp2ZrBu2” (Scheme 2). In
principle, both the allenic 3 and propargylic zirconium
species 4 could be formed under the reaction conditions,
and there exists an equilibrium between the two species. The
latter is suggested to be produced through a 1,3-metallotro-
pic rearrangement. As proposed by Taguchi et al.,3b,6 when
the propargylic ether contains a substituent at the pro-
pargylic position, the allenic zirconium will be formed pre-
ferentially due to the steric repulsion between R2/R3
substituent and the metal center. We envisioned that
ꢀ
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Bertozzi, F.; Crotti, P.; Macchia, F.; Pineschi, M.; Arnold, A.; Feringa, B. L.
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T.; Takaki, K.; Taniguchi, Y.; Fujiwara, Y. Tetrahedron Lett. 1995, 36, 6283.
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C.; Wibbeling, B.; Frohlich, R.; Hoppe, D. Org. Lett. 2001, 3, 1221. (h)
Nakamura, H.; Kamakura, T.; Ishikura, M.; Biellmann, J. J. Am. Chem. Soc.
2004, 126, 5958. (i) Ma, S. Eur. J. Org. Chem. 2004, 1175. (j) Zhou, Y.; Chen,
J.; Zhao, C.; Wang, E.; Liu, Y.; Li, Y. J. Org. Chem. 2009, 74, 5326. For
palladium-catalyzed coupling reactions of propargylic esters, mesylates, or
carbonates with Grignard or zinc reagents, etc., see: (k) Riveiros, R.;
(8) (a) Takahashi, T.; Hara, R.; Huo, S.; Ura, Y.; Leese, M. P.; Suzuki, N.
Tetrahedron Lett. 1997, 38, 8723. (b) Hara, R.; Ura, Y.; Huo, S.; Kasai, K.;
Suzuki, N.; Takahashi, T. Inorg. Chim. Acta 2000, 300-302, 741.
(9) (a) Negishi, E.; Van Horn, D. E. J. Am. Chem. Soc. 1977, 99, 3168–
3170. (b) Negishi, E.; Takahashi, T.; Baba, S.; Van Horn, D. E.; Okukado, N.
Rodrıguez, D.; Sestelo, J. P.; Sarandeses, L. A. Org. Lett. 2006, 8, 1403. (l)
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Ma, S.; Wang, G. Angew. Chem., Int. Ed. 2003, 42, 4215. (m) Riveiros, R.;
Sestelo, J. P.; Sarandeses, L. A. Synthesis 2007, 3595. (n) Jeffery-Luong, T.;
Linstrumelle, G. Tetrahedron Lett. 1980, 21, 5019. (o) Ruitenberg, K.; Kleijn,
H.; Elsevier, C. J.; Meijer, J.; Vermeer, P. Tetrahedron Lett. 1981, 22, 1451.
(p) Konno, T.; Tanikawa, M.; Ishihara, T.; Yamanaka, H. Chem. Lett. 2000,
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Commun. 1997, 2083.
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P. D.; Takahashi, T. Tetrahedron Lett. 1997, 38, 447–450. (d) Takahashi, T.;
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TABLE 1. Formation of Allenes and/or Alkynes by the Reaction of Cp2ZrBu2 with Propargyl Ethers
aIsolated yields. Unless noted, all the reactions were carried out using 1.6 equiv of Negishi reagent at room temperature for 3 h. b1.25 equiv of Negishi
reagent was used. c2.0 equiv of Negishi reagent was used.
electronic effects of the TMS group might also be respon-
sible for the observed experimental results. These unusual
results prompted us to investigate the in situ NMR of
the reaction with TMS-substituted propargylic ethers. Sur-
prisingly, it was found that the allenic zirconium species 3n
(R1 = TMS, R2, R3 = -(CH2)5-) was formed as a
major zirconium species (90% NMR yield) according to
1H and 13C NMR spectra in the case of propargylic
ether 1n.11 In 13C NMR, the low-field signal (195.4 ppm)
is characteristic for sp carbon in allene skeleton. The in situ
NMR of allenic zirconium 3m (R1= TMS, R2, R3= nPr) has
also been investigated, which is similar to that of 3n.12
To better understand the structure of intermediates 3 and 4,
density functional theory (DFT)13 studies have been per-
formed with the Gaussian03 program14 using the B3LYP15
(14) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci,
B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Frisch, M. J.; Nakai, H.; Klene, M.; Li, X.; Knox,
J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannengerg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain,
M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski,
J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision C.02;
Gaussian, Inc.: Wallingford, CT, 2004.
(11) NMR data of allenic zirconium species derived from (3-methoxy-4-
methylpent-1-ynyl)benzene 1h has been reported; see ref 3b.
(12) See the Supporting Information.
(13) (a) Hohenberg, P.; Kohn, W. Phys. Rev. 1964, 136, B864. (b) Kohn,
W.; Sham, L. J. Phys. Rev. 1965, 140, A1133.
(15) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang, W.;
Parr, R. G. Phys. Rev. 1988, B37, 785.
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FIGURE 1. Optimized allenic structures 3g (R1 = Ph, R2 = R3 = Me), 3m0 (R1 = TMS, R2 = R3 = Me) and 3g0 (R1 = Ph, R2 = R3 = H),
the propargylic structures 4g, 4m0, and 4g0, the rearrangement transition states TS-3g-4g, TS-3m0-4m0, and TS-3g0-4g0. The selected bond
lengths are in angstroms, and the relative free energies ΔG are in kcal/mol. Calculated at B3LYP/6-311þG**/Lanl2DZ level.
method. For C, H, O, Cl, and Si, the 6-311þG** basis set was
used; for Zr the Lanl2DZ basis set with Effective Core
Potential (ECP)16 was used. The optimized structures were
all checked with harmonic vibration frequency calculations.
The structures of allenic zirconium species 3g (R1 = Ph, R2 =
R3 = Me), propargylic zirconium species 4g and the transition
states for their rearrangement TS-3g-4g have been fully
optimized with complete models (Figure 1). For the TMS
substituted propargylic ether 1m, the simplified model 3m0
with R2 = R3 = Me was used. To find out the effect of the R2
and R3 group, the model 3g0 with R1 = Ph and R2 = R3 = H
was also studied.17
The results indicate that the allenic structure 3g is more
stable than the propargylic structure 4g by about 11.4 kcal/
mol. Therefore, the allenic structure 3g should be dominant
under room temperature. The barrier of the rearrangement
from 3g to 4g (TS-3g-4g) is 23.3 kcal/mol. For 3m0, the
situation is similar. Therefore, R1 has small effect on the
equilibrium of 3 and 4. The barriers of the rearrangement are
over 23 kcal/mol, which indicates a reaction being completed
within hours. Since the hydrolysis of 3g and 3m by 3 N HCl
can be completed within minutes, the hydrolysis via the
(16) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284.
(17) For the reaction of propargyl ether without substituent at the C-1
carbon such as (3-(benzyloxy)prop-1-ynyl)benzene with 2 equiv of Negishi
reagent, see ref 3b. The reaction produced (Z)-β-methylstyrene as a sole
product, which was explained by addition of “Cp2Zr” to propargyl zirco-
nium species.
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Zhang et al.
JOCArticle
well consistent with the experimental observations: 3g favors
the allenic product, whereas 3m0 favors the alkyne product.
Generally, in the allenic zirconium complexes 3g and 3m0,
the carbon atom which is connected with the Zr center (Ca)
possesses a greater negative charge. In 3g, the NBO charges
on Ca and Cc are -0.465 and -0.158, respectively; in 3m0, the
NBO charges on Ca and Cc are -0.901 and -0.198, respec-
tively. Consequently, Ca is more easily attacked by the
proton. This is the case for 3g. However, the situation may
be changed by the steric effect of R1, R2, and R3. Obviously,
in TS-3g-allene the flat phenyl group causes small steric
energy on the attack of the proton, whereas in TS-3m0-allene
the bulky TMS group will cause large steric repulsion. 3g or
3m0 will be distorted on the attack of the proton. This
distortion is to some extent caused by the steric effect of
R1, R2, R3, and the Cp rings. Therefore, the steric energies in
the four transition states were estimated by the distortion
energy (DE).22 DE was calculated by this way: for the four
transition states shown in Figure 3, the HCl and the two H2O
molecules were deleted with the rest part unchanged, and
then the single-point energies were calculated. Using the
undistorted 3g and 3m0 as the zero-point references, the
relative distortion energies for the four transition states were
obtained. As shown in Figure 3, the DE of TS-3m0-allene is
3.3 kcal/mol higher than that of TS-3m0-alkyne, whereas the
DE of TS-3g-allene is nearly the same as that of TS-3g-
alkyne. Thus, the steric effect is one of the important factors
to determine the selectivity.
On the other hand, for the transition states to form alkyne
products, the attack of the proton on Cc will arouse positive
charges on Cb. The calculated NBO atomic charges of Cb in
TS-3m0-alkyne is 0.203. It is smaller than that of Cb in TS-3g-
alkyne (0.257), indicating that TMS group can stabilize the
positive charges on Cb. This can be explained by the well-
known β-effect23 of the TMS group; i.e., the hyperconjuga-
tion of the Ca-Si σ bond with the partially positive charged p
orbital on the β position (Cb). Thus, both the large steric
effect and the β-effect of the TMS group favor the alkyne
product, reversing the selectivity.
Cross-Coupling Reactions of Allenic/Propargylic Zirco-
nium Complexes with Aryl Halides. We next proceeded to
investigate the coupling reactions of the allenic/propargylic
zirconium species with aryl iodides. Here, we found that
treatment of the reaction mixture of 1c and Cp2ZrBu2 with
1.2 equiv of CuCl9 and 1.2 equiv of PhI in the presence of 5
mol % of Pd(PPh3)4 at room temperature for 2 h afforded
arylated allene 7a in 72% yield (Scheme 3 and Table 2,
entry 1). Aryl iodides bearing electron- donating or electron-
withdrawing substituents could be used, furnishing the cor-
responding products 7b-d in 64-71% yields (Table 2, en-
tries 2-4). It should be noted that in some cases, addition of 2
equiv of DMAP and stirring for 1 h before coupling reactions
would afford better yields of the desired products and also
result in a cleaner reaction. For example, in the case of alkyl-
substituted propargylic ether 1e, the allene 7e was formed in
a higher yield of 79% in the presence of DMAP (Table 2,
entry 5). DMAP was suggested to be coordinated with the
excess amount of the low-valent zirconium species, which
FIGURE 2. Optimized structure of 3n, the selected 13C chemical
shifts (regular font for experimental values, and italic for calculated
results), and bond lengths (in angstroms). Both the geometry
optimization and the NMR studies were calculated at B3LYP/6-
311þG**/Lanl2DZ level.
propargylic pathway can be excluded safely. Interestingly,
the propargylic structure 4g0 is more stable than the allenic
structure 3g0 by 1.5 kcal/mol, and the rearrangement barrier
(TS-3g0-4g0) is also dropped to 12.7 kcal/mol, indicating
that R2 and R3 have great effect on the relative stabilities of 3
and 4. The C-Zr bond length in 4g (2.437 A) and 4m0 (2.434
A) are much longer than those in 4 g0 (2.364 A), 3g (2.347 A),
and 3m0 (2.327 A). This indicates that the large repulsion
between the R2/R3 and the Cp rings decreases the interaction
of the carbanion and the metal center. Consequently the
energies of the propargylic structures are increased.3b,6
To further confirm that the allenic structure 3 is dominant
under room temperature, the 13C chemical shifts of 3n
were calculated by gauge including atomic orbital (GIAO)
method.18 The selected results are shown in Figure 2. The
calculated NMR shifts are in good agreement with the
experimental values.19
The mechanisms of the hydrolysis of 3g and 3m0 by 3N
HCl have been studied with the models shown in Figure 3. In
these models, both the proton Hþ and the Cl- ion were
solvated by an explicit water molecule. The long rang solvent
effect was estimated with IEFPCM20 (UAHF atomic radii)
method in water (ε = 78.39) using the gas-phase optimized
structures. The atomic charges were calculated by NBO
natural bonding analysis.21 As shown in Figure 3, in transi-
tion states TS-3g-alkyne and TS-3m0-alkyne, the protons
attack Cc and lead to alkyne products, whereas in transition
states TS-3g-allene and TS-3m0-allene, the protons attack Ca
and lead to allene products. TS-3g-allene is 6.8 kcal/mol
lower in energy than TS-3g-alkyne; however, TS-3m0-allene
is 4.7 kcal/mol higher in energy than TS-3m0-alkyne, which is
(18) Ditchfield, R. Mol. Phys. 1974, 27, 789–807.
(19) The experimental NMR shift of C6 might be overlapped with Cp
impurities in the range of 110.3-114.1 ppm.
ꢁ
(20) (a) Cances, E.; Mennucci, B.; Tomasi, J. J. Chem. Phys. 1997, 107,
3032. (b) Cossi, M.; Barone, V.; Mennucci, B.; Tomasi, J. Chem. Phys. Lett.
1998, 286, 253.
(21) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899–
(22) Legault, C. Y.; Garcia, Y.; Merlic, C. A.; Houk, K. N. J. Am. Chem.
Soc. 2007, 129, 12664–12665.
(23) Lambert, J. B. Tetrahedron 1990, 46, 2677.
926.
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FIGURE 3. Optimized transition states for the hydrolysis reaction. The selected NBO charges for Ca, Cb, and Cc are given in the box. The
selected bond lengths (bold) are in angstroms, and the relative free energies including solvent effect ΔGsol (bold) and the relative distortion
energies (DE, italic underlined) are in kcal/mol. Calculated at the B3LYP/6-311þG**/Lanl2DZ level.
may give a negative effect on the coupling process. When C-
1-monosubstituted substrates 1h-j were employed, the cor-
responding allenes 7i-k were formed in good to high yields
(entry 9-11). In these cases, DMAP had little influence on
the reaction. Interestingly, in the cases of TMS-substituted
propargylic ether 1k-n, the coupling reactions with ArI still
generated the allene type of products 7l-o in 46-73% yields
(entries 12-15). The results indicated that the coupling
precursor of the metal intermediate was an allenic
zirconium. These coupling reactions are also quite different
with that of the Pd-catalyzed coupling reaction of allenic/
propargylic zinc species with phenyl iodide,24 in which a
TMS substituent results in the formation of both arylated
alkyne and allene.
SCHEME 3
between the R2/R3 group and the zirconium atom in 4.
Transmetalation of both of the Zr-C bonds in 3 and 4 to a
Cu-C bond affords allenic/propargylic copper species 8 and
9; however, the equilibrium leaves largely on the side of
allenic copper 8. This is followed by transmetalation with an
arylpalladium intermediate generated from ArI and a Pd(0)
catalyst, and then reductive elimination to form the desired
arylated products.
To further demonstrate the utility of allenic/propargylic
zirconium species, the coupling reactions with allylic halides
were carried out. The allylic allenes were obtained cleanly in
54-76% yields in the presence of CuCl (Table 3). Without
CuCl, no allylation occurred.
A plausible reaction mechanism is shown in Scheme 4.
First, an allenic zirconium 3 and propargylic zirconium 4 are
formed in the reaction mixture through β-alkoxide elimina-
tion. In all of the cases, the allenic zirconium 3 is formed as a
predominant zirconium species due to the steric interaction
(24) Ma, S.; Zhang, A. J. Org. Chem. 2002, 67, 2287.
9356 J. Org. Chem. Vol. 74, No. 24, 2009

Zhang et al.
JOCArticle
TABLE 2. Coupling Reactions of Allenic/Propargylic Zirconium Species with Aryl Iodides
aIsolated yields. The yields with 2.0 equiv of DMAP are shown in parentheses. Unless noted, all the reactions were carried out using 1.6 equiv of
Negishi reagent. b1.25 equiv of Negishi reagent was used. c2.0 equiv of Negishi reagent was used.
SCHEME 4
selectively by tuning the substituents on the alkyne terminus of
the propargylic ether. The subsequent coupling reactions with
aryl iodides in the presence of Pd/CuCl provided a straightfor-
ward route for the synthesis of multisubstituted allenes.
Experimental Section
General Procedure for the Synthesis of Allenes 5 and/or
Alkynes 6 via the β-Alkoxide Elimination Reaction of Propargylic
Methyl Ethers with Negishi Reagent. To a solution of Cp2ZrCl2
(0.234 g, 0.8 mmol) in THF (5 mL) was added n-BuLi (1.6 M
solution in hexanes, 1.0 mL, 1.6 mmol) at -78 °C. After the
mixture was stirred for 1 h at the same temperature, propargylic
methyl ether (0.5 mmol) was added, and then the mixture was
warmed to room temperature and stirred for 3 h. The reaction
mixture was quenched with 3 N HCl aqueous solution and
extracted with ethyl ether. The extract was washed with satu-
rated NaHCO3 solution and dried over MgSO4. The solvent
was evaporated in vacuo, and the residue was purified by
chromatography on silica gel to afford allenes 5 and/or
Conclusion
In summary, we have shown that the β-alkoxide elimination
reaction of propargylic ether with Negishi reagent leads to
allenes and/or alkynes after hydrolysis, which can be obtained
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Zhang et al.
JOCArticle
TABLE 3. Reactions of Allenic Zirconium with Allyl Halides
0.8 mmol) in THF (5 mL) was added n-BuLi (1.6 M solution in
hexanes, 1.0 mL, 1.6 mmol) at -78 °C. After the mixture was
stirred for 1 h at the same temperature, propargylic methyl ether
(0.5 mmol) was added, and then the mixture was warmed to
room temperature and stirred for 3 h. Aryl iodides (0.6 mmol),
Pd(PPh3)4 (29 mg, 0.025 mmol), and CuCl (60 mg, 0.6 mmol)
were added, and the mixture was stirred at room temperature for
2 h. In some cases, the addition of 2 equiv of DMAP and stirring
for 1 h before coupling reactions was performed. The reaction
mixture was quenched with 3 N HCl aqueous solution and
extracted with ethyl ether. The extract was washed with satu-
rated NaHCO3 solution and dried over MgSO4. The solvent was
evaporated in vacuo, and the residue was purified by chroma-
tography on silica gel to afford aryl-substituted allenes 7. 1-(2-
Cyclohexylidene-1-phenylvinyl)-4-methylbenzene (7b). Column
chromatography on silica gel (petroleum ether) afforded the
title product in 71% isolated yield: 1H NMR (CDCl3, Me4Si) δ
1.56-1.58 (m, 2H), 1.66-1.67 (m, 4H), 2.27-2.30 (m, 4H),
2.34 (s, 3H), 7.12 (d, J = 8.1 Hz, 2H), 7.19-7.25 (m,
3H), 7.27-7.36 (m, 4H); 13C NMR (CDCl3, Me4Si) δ 21.1,
26.1, 27.6, 31.5, 105.4, 107.3, 126.5, 128.1, 128.4, 128.9, 135.2,
136.3, 138.4, 200.2; HRMS (EI) for C21H22 calcd 274.1722,
found 274.1721.
Acknowledgment. We thank the National Natural Science
Foundation of China (Grant No. 20672133, 20732008,
20702059), Chinese Academy of Science, Science and Tech-
nology Commission of Shanghai Municipality (Grant No.
08QH14030, 07JC14063), and the Major State Basic Re-
search Development Program (Grant No. 2006CB806105)
for financial support.
aIsolated yields. b2.0 equiv DMAP was added and the mixture stirred
for 1 h before addition of allyl chloride.
alkynes 6. (2-Cyclopentylidenevinyl)benzene (5a). Column chro-
matography on silica gel (petroleum ether) afforded the title
product in 87% isolated yield: 1H NMR (CDCl3, Me4Si) δ
1.69-1.79 (m, 4H), 2.40-2.57 (m, 4H), 6.06-6.11 (m, 1H),
7.11-7.18 (m, 1H), 7.26-7.30 (m, 4H); 13C NMR (CDCl3,
Me4Si) δ 27.2, 31.1, 94.8, 107.5, 126.3, 126.6, 128.4, 136.0,
198.6; HRMS (EI) for C13H14 calcd 170.1096, found 170.1104.
General Procedure for the Synthesis of Arylated Allenes 7
through the Coupling Reactions of Allenic Zirconium Com-
plexes with Aryl Iodides. To a solution of Cp2ZrCl2 (0.234 g,
Supporting Information Available: General methods and
spectroscopic characterization of all new compounds calculated
total energies and geometrical coordinates. This material is
available free of charge via the Internet at http://pubs.acs.org.
9358 J. Org. Chem. Vol. 74, No. 24, 2009