Synthesis of sterically hindered biaryls by Zr-mediated Co-cyclotrimerization of alkynes

Article abstract of DOI:10.1002/ejoc.200400881

Treatment of zirconacyclopentadienes with ortho-substituted arylpropynoates in the presence of stoichiometric amounts of CuCl or NiBr ₂(PPh₃)₂ represents a novel approach to the synthesis of biaryls, formed in good yields. The CuCl-mediated reaction proceeded through two reaction mechanisms, also affording Dewar benzenes together with the corresponding biaryls Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.

Full text of DOI:10.1002/ejoc.200400881

FULL PAPER
Synthesis of Sterically Hindered Biaryls by Zr-Mediated Co-cyclotrimerization
of Alkynes
[a]
[a,b]
and Ivana Císa rˇ ová[c]
Lenka Dufková, Martin Kotora,*
Keywords: Biaryls / Zirconium / Benzene / Cyclotrimerization / Dewar benzene
Treatment of zirconacyclopentadienes with ortho-substituted
also affording Dewar benzenes together with the correspond-
arylpropynoates in the presence of stoichiometric amounts
ing biaryls.
2 3 2
of CuCl or NiBr (PPh ) represents a novel approach to the
synthesis of biaryls, formed in good yields. The CuCl-medi-
ated reaction proceeded through two reaction mechanisms,
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Introduction
tion with the other two alkynes to complete the desired
molecule. An ideal reaction for such a process is [2+2+2]
cyclotrimerization of alkynes. As for the ortho-substituted
arylalkyne, it would be beneficial if it could bear functional
groups that would ensure its synthetic flexibility with regard
to further organic transformations.
Hindered biaryl compounds have numerous applications
in organic synthesis. Biaryl backbones constitute important
moieties in many natural compounds[ and are also used
as chiral scaffolds in many chiral ligands (phosphanes, pyri-
1]
[
2]
dines, etc). Biaryls are most frequently prepared by transi-
tion metal-catalyzed cross-coupling reactions between aryl
[
2,3]
metals and aryl halides or esters (e.g., triflates).
Al-
though this approach has its merits and has been exten-
sively studied, it may suffer drawbacks in cases of coupling
of heavily substituted partners in which steric hindrance
may severely retard the course of the cross-coupling reac-
tion. In view of this, it is of general synthetic interest to
develop new pathways for the preparation of highly substi-
tuted biaryls, and one possible approach is outlined in
Scheme 1. Retrosynthetic analysis of the upper benzene ring
of the biaryl compound clearly shows that it could be con-
structed from different alkynes: an ortho-substituted arylal-
kyne containing the necessary functional groups (A, B, C)
and two other alkynes bearing between them the rest of
the substituents (D). In this way the whole problem of the
preparation of the substituted biaryl is reduced to the prep-
aration of the ortho-substituted arylalkyne and its combina-
Scheme 1. Retrosynthetic analysis of biaryl formation by cyclo-
trimerization.
Although cyclotrimerization of alkynes has been a well
[
4]
known reaction for 30 years, its application for the con-
[
a] Department of Organic and Nuclear Chemistry, Faculty of Sci- struction of chiral centers has started to gain attention only
ence, Charles University,
[5]
recently. However, because of selectivity problems these
Albertov 2030, 12843 Prague 2, Czech Republic
Fax: +420-221-951-326
approaches are usually applied to cyclotrimerization of α,ω-
diynes with alkynes. As for the cyclotrimerization of three
alkynes to highly substituted arenes with potential atropo-
isomeric properties, one convenient method is based on the
E-mail: kotora@natur.cuni.cz
[
b] Institute of Organic Chemistry and Biochemistry, Czech Acad-
emy of Sciences, Flemingovo nám eˇ stí 2, 166 10 Prague 6, Czech
Republic
[
6]
Fax: +420-220-183-560
treatment of zirconacyclopentadienes with alkynes in the
[
c] Department of Inorganic Chemistry, Faculty of Science,
Charles University,
[7]
presence of stoichiometric amount of CuCl,
NiBr2-
[
8]
[9]
Albertov 2030, 128 43 Prague 2, Czech Republic
Fax: +420-221-951-253
(PPh
3
)
2
,
or NiBr
2
(PMe
3
)
2
.
This method has been suc-
cessfully applied for the synthesis of polysubstituted aro-
matic compounds such as benzoheterocycles containing
E-mail: cisarova@natur.cuni.cz
Supporting information for this article is available on the
WWW under http://www.eurioc.com
[
10]
[11]
group 14 elements,
haloterphenyls,
haloterphenyls
Eur. J. Org. Chem. 2005, 2491–2499
DOI: 10.1002/ejoc.200400881
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2491

L. Dufková, M. Kotora, I. Císa rˇ ová
FULL PAPER
[
12]
with chiral backbones,
perfluoroalkyl-substituted ter-
[
13]
[14]
[15]
phenyls,
polyacenes,
and ferrocenylalkynes.
There
are several factors that favor the above method: firstly, zir-
conacyclopentadienes are easily prepared with a great vari-
ety of substituents and they are stable at room temperature,
and secondly, arylalkynes can be easily prepared from com-
monly accessible starting material. Additionally, both CuCl
and NiBr (PPh ) are stable and cheap compounds. Al-
2
3 2
though there are plenty of examples of reactions between
zirconacyclopentadienes and arylalkynes proceeding in
good to excellent yields, no data are available on how ortho-
substitution in the aromatic rings in the arylalkynes will
affect the course of the reaction. It is reasonable to assume
that ortho-substitution might cause undesirable steric hin-
drance that would result in a slower reaction rate. Although
there had previously been a lack of information on the in-
fluence of the ortho-effect on the course of the reactions of
ortho-substituted alkynes in transition metal-induced reac-
tions, this topic has recently started to gain attention.
Knowledge of this effect is important in the search for new
synthetic methods for the preparation of potentially atropo-
isomeric biaryls, such as in the Dötz reaction between or-
[
16]
tho-substituted arylalkynes and chromium carbenes.
Results and Discussion
In this study we focused on reactions between alkyl-sub-
stituted zirconacyclopentadienes and various ortho-substi-
tuted arylpropynotes in an approach to substituted biaryls
with potentially atropoisomeric properties. To compare the
synthetic suitabilities of these methods we carried out the
reactions in the presence of CuCl and NiBr (PPh ) . The
2
3 2
choice of arylpropynoates as the arylalkyne representatives
was based on three facts: firstly, the presence of the ester
Scheme 2. Reactions between zirconacyclopentadienes and ortho-
group next to the triple bond is a prerequisite for the suc- substituted arylpropynoates.
[
7]
cessful course of the reaction in the presence of CuCl,
secondly, the ester group can easily be converted into other
functional groups, and, last but not least, the arylpropy- tures, the Dewar benzenes 5a and 5b were formed in 32 and
noates can readily be prepared in great structural variety by 20% yields, respectively. However, the Dewar benzenes 5a
simple synthetic procedures. Tetramethyl- (1) and tetraeth- and 5b probably decomposed during isolation and only the
ylzirconacyclopentadiene (2) were chosen as typical repre- biaryls 4a and 4b were isolated. Interestingly, in the cases
sentatives of zirconacycles (Scheme 2).
The results of Cu-mediated reactions of tetramethylzirco-
nacyclopentadiene (1) and tetraethylzirconacyclopentadiene
2) are summarized in Table 1. The reactions proceeded CuCl.
Table 1. Reactions between zirconacyclopentadienes 1 and 2 and
arylpropynoates 3 in the presence of stoichiometric amounts of
(
with various levels of success in all cases; in addition to the
Yield [%][a]
Zirconacycle
Propynoate
Products
[17]
expected biaryls, Dewar benzenes
were also formed as
1
2
1
2
1
2
1
2
1
2
2
3a
3a
3b
3b
3c
3c
3d
3d
3e
3e
3e
4a + 5a
6a + 7a
4b + 5b
6b + 7b
4c
6c + 7c
4d
6d + 7d
4e + 5e
6e + 7e
6f
60 + 32 (57)
59 + 38 (52)
36 + 20 (32)
48 + 15 (38)
50 (47)
32 + 12 (30 + 10)
55 (40)
17 + 15 (30)
22 + 10 (16 + 6)
26 + 25 (23 + 20)
10 (7)
minor side-products (Scheme 2). Generally, the reaction
rates were slow in all cases and reaction times of 148 h (1
week) were necessary in order to achieve reasonable yields
of the products. This is in sharp contrast to the reaction
with unsubstituted phenylpropynoate, which proceeded in
excellent yield (85%) within a reasonable reaction time of
[
7b]
4
8 h. The reactions between tetramethylzirconacyclopen-
tadiene (1) and ortho-halophenylpropynoates 3a and 3b
gave the corresponding biaryls 4a and 4b in 60 and 36%
yields. According to NMR analysis of the reaction mix- [a] H NMR yields, isolated yields are in parentheses.
1
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Sterically Hindered Biaryls by Zr-Mediated Co-cyclotrimerization of Alkynes
FULL PAPER
of the ortho-methoxy- and methylphenylpropynoates 3c and other in the solid state (Figure 1). The orientation of the
d, only the formation of the biaryls 4c and 4d was ob- carboxyl plane is affected by extensive weak intermolecular
served, in 50 and 55% yields. The reaction with the ortho- hydrogen bonding O..H–C between the carbonyl oxygen
trifluoromethyl)phenylarylpropynoate 3e again furnished a and the methyl groups of the ester moiety or the hydrogen
3
(
mixture of the biaryl 4e and Dewar benzene 5e.
of the less substituted aromatic ring.
Treatment of the tetraethylzirconacyclopentadiene 2 with
The reactions between the tetraethylzirconacyclopentadi-
the arylpropynoates 3 afforded mixtures of biaryls and De- ene (2) and the arylpropynoates 3a–f carried out in the pres-
war benzenes in all the cases but one. The reactions with ence of stoichiometric amounts of NiBr (PPh ) complex
2
3 2
the haloarylpropynoates 3a and 3b thus gave mixtures of proceeded in most cases with good yields to give only the
the biaryls and Dewar benzenes 6a and 7a (59 and 38%) biaryls 6a–f (Table 2). In this case no formation of the De-
and 6b and 7b (48 and 15%), respectively. Also, as in the war benzenes was observed, and obviously they would not
previous two instances, the Dewar benzenes 7a and 7b be able to form because of the reaction mechanism.[ In
probably decomposed during isolation and only the biaryls addition, the reaction between 2 and 3c was carried out in
8]
6
a and 6b were isolated. Analogously, the reactions with the presence of NiBr (PBu ) , because it had recently been
2 3 2
the methoxy, methyl, and trifluoromethyl ortho-substituted shown that the use of Ni complexes with alkylphosphanes
[
9]
arylpropynoates 3c, 3d, and 3e resulted in mixtures of the was advantageous in certain cases. Nonetheless, the biaryl
corresponding biaryls and Dewar benzenes 6c and 7c (32 6c was formed in only 42% yield.
and 12%), 6d and 7d (17 and 15%), and 6e and 7e (26
and 25%), respectively. Finally, treatment with methyl 2-
methoxynaphthylpropynoate (3f) gave a rather disappoint-
ing low yield of the biaryl 6f (10%). Several general trends
Table 2. Reactions between tetraethylzirconacyclopentadiene (2)
and arylpropynoates 3 in the presence of stoichiometric amounts
can be inferred from the results presented in Table 1. Firstly,
higher yields were obtained with 1 then with 2; the observed
difference might be caused by the greater size of the Et
group than the Me group. Secondly, the yields of products
2 3 2
of NiBr (PPh ) .
Zirconacycle
Propynoate
Product
Yield [%][a]
2
2
2
2
2
2
3a
3b
3c
3d
3e
3f
6a
6b
6c
6d
6e
6f
67 (45)
71 (46)
90 (52)
53 (33)
44 (23)
24 (20)
[
18]
decrease roughly with the size of the ortho-substituents,
increasing steric hindrance of which may have negative ef-
fects on the course of the reaction.
A single-crystal X-ray structure of the biaryl 4c showed
that the two phenyl rings are almost perpendicular to each [a] H NMR yields, isolated yields are in parentheses.
1
Figure 1. View of part of the network of 4c with atom numbering. The dihedral angle of the least-squares planes of the aromatic rings
i
i
i
i
i
ii
ii
ii
is 74.29(4)°. The parameters of hydrogen bonds C4 –H4 ···O1: C4 ···O1 3.230(2) Å, C4 –H4 ···O1 131.5° and C12 -H12C ···O1: C12 ···O1
ii
ii
3
.449(2) Å, C12 –H12C ···O1 171.5°, symmetry codes (i) –x, –y, 1 – y, (ii) –x, 1 – y, 1 – y. The displacement ellipsoids are drawn at the
50% probability level (PLATON).
Eur. J. Org. Chem. 2005, 2491–2499
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L. Dufková, M. Kotora, I. Císa rˇ ová
FULL PAPER
In the next step we attempted to carry out a diastereo- between cyclobutadienes and alkynes,[19] so their formation
selective reaction between tetramethylzirconacyclopentadi- indicates that a cyclobutadiene must be formed in one of
ene (1) and the (–)-menthyl ester 8 in the presence of a stoi- the reaction steps. In view of this, we assume that the for-
chiometric amount of CuCl (Scheme 3). However, the result mation of the Dewar benzenes proceeds as follows: radical
was rather disappointing: the corresponding product 9 was decomposition of the dicopper intermediate, formed after
obtained in unimpressive yield (19%) and the diastereose- the transmetallation of the zirconacyclopentadiene with
lectivity was also low (2:1). The diastereoselectivity ratio CuCl, results in the formation of the tetraethylcyclobutadi-
1
was determined by integration of H NMR signals of each ene, which immediately reacts with the present arylpropy-
diastereoisomer. The major diastereoisomer was obtained noate to give the corresponding Dewar benzene (path B,
as a single compound by HPLC. (However, the configura- Scheme 4). In an attempt to confirm this assumption, the
tion of the biaryl moiety remains unknown, because it was unsymmetrically substituted 4,5-diethyl-2,3-diphenylzir-
not possible to grow crystals suitable for X-ray analysis and conacyclopentadiene was treated with the propynoate 3c to
the use of other methods also did not provide clearcut in- check whether regioisomeric Dewar benzenes could be
formation.) The obtained diastereoisomer was tested for formed, but unfortunately only an intractable reaction mix-
configurational stability by heating it at different tempera- ture was obtained. Nevertheless, the cyclobutadiene path-
tures for various periods of times, but we did not observe way is supported by the fact that the formation of tetraeth-
any indication of racemization (i.e., lost of axial chirality ylcyclobutadiene from tetraethylzirconacyclopentadiene—
about the C–C bond connecting the two aryl rings) even on as well as its cycloaddition reaction—under similar condi-
[
20]
heating it at 200 °C. This indicates that the ortho-substitu- tions has been reported previously.
tion provides considerable steric hindrance to block rota-
tion about the C–C bond connecting the both aryl rings.
Scheme 3. Reaction between the zirconacyclopentadiene 1a and the
(–)-menthyl ester 8.
As far as a reaction mechanism is concerned, it is worth
noting that the formation of the Dewar benzenes in CuCl-
mediated reactions between zirconacyclopentadienes and
activated alkynes has not been observed previously. There
is some evidence, and it has been generally accepted, that
the mechanism of the CuCl-mediated reaction with acti-
vated alkynes proceeds through a conjugated addition of
Scheme 4. Mechanisms of the reactions of zirconacyclopentadienes
to afford biaryls and Dewar benzenes.
Further supportive information for the above reaction
the C–Cu bond to the triple bond of the activated alkyne mechanism appeared at just about the same time as we were
followed by ring closure to the aryl compound through rad- concluding this study. An article reported on the generation
ical decomposition of the unstable dicopper intermediate of a cyclobutadiene from a zirconacyclopentadiene,[ and
21]
path A, Scheme 4).[ However, it was obvious that this re- the authors showed that the organodicopper species formed
7]
(
action mechanism cannot explain the formation of the De- by the reaction between a zirconacyclopentadiene and CuCl
war benzenes and that there must be a concomitantly op- underwent fast reductive elimination of copper in the pres-
erating alternative reaction pathway. Generally, Dewar ben- ence of benzoquinone to give a cyclobutadiene dimerization
zenes have usually been prepared by cycloaddition reactions product. Cyclobutadiene was regarded as the reactive inter-
2494
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2005, 2491–2499

Sterically Hindered Biaryls by Zr-Mediated Co-cyclotrimerization of Alkynes
FULL PAPER
Scheme 5. Reaction between 2 and 3c in the presence of CuCl and benzoquinone.
mediate. Although it was not stated in the report, the role of modifications; for details see Supporting Information. Hex-3-yne
and nBuLi (1.6 m solution in hexanes) were purchased from Ald-
benzoquinone is quite unambiguous: it supports reductive
elimination of copper from the intermediate[
22]
rich. But-2-yne was purchased from Fluka, Buchs. All other chemi-
cals and solvents were of commercial purity and were used without
further purification.
thus en-
hancing the formation of cyclobutadiene. We reasoned that
application of these conditions to our system might give us
access to reaction mixtures with higher proportions of De-
war benzenes, so the reaction between tetraethylzirconacy-
clopentadiene (1) and the propynoate 3c in the presence of
CuCl and benzoquinone was carried out at 50 °C
1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were re-
corded on a Varian Unity Inova 400 spectrometer with tetrameth-
ylsilane as an internal standard. Infrared spectra were recorded on
a PE-640 Perkin–Elmer spectrometer. Mass spectra were obtained
on a ZAB-SEQ VG Analytical spectrometer. Elemental analyses
were obtained on a Perkin–Elmer 2400 elemental analyzer. TLC
was performed on Merck Silica Gel 60 F254 aluminium sheets and
column chromatography was performed on Fluka Silica Gel 60.
(Scheme 5). However, the result was not encouraging: the
biaryl 6c was formed in 30% yield and the formation of the
corresponding Dewar benzene 7c was observed only in
trace amounts in the initial stages of the experiment. Proba-
bly it decomposed under the reaction conditions, as we also
observed its decomposition into a complex mixture of prod-
ucts even on standing at room temperature (20 °C). As for
General Procedure for Reactions between Zirconacylopentadienes
and Arylpropynoates in the Presence of Stoichiometric Amounts of
CuCl: nBuLi in hexanes (1.6 m, 1.25 mL, 2 mmol) was added at
–78 °C to a solution of zirconocenene dichloride (292 mg, 1 mmol)
other products, compounds such as the tricyclooctadiene 10 in THF (5 mL) and the reaction mixture was stirred for 1 h. The
and the cyclooctatetraene 11 were detected in the reaction alkyne (2 mmol) was then added and the reaction mixture was al-
mixture by their characteristic NMR signals.[
21]
lowed to warm to 20 °C within 1 h. After that the arylpropynoate
1.5 mmol) and CuCl (200 mg, 2 mmol) were added, and the reac-
(
tion mixture was stirred for 148 h (1 week) at 20 °C. The reaction
mixture was quenched with 3 m HCl and extracted with diethyl
ether (3×10 mL), and combined organic fractions were dried over
Conclusions
4
In conclusion, we have shown that the zirconocene-based MgSO . Removal of solvents under reduced pressure, followed by
methodology provides a simple, convenient, and one-pot column chromatography on silica gel, afforded the corresponding
products.
procedure for coupling of two alkynes with an ortho-substi-
tuted arylpropynoate to provide highly substituted biaryls General Procedure for Reactions between Zirconacylopentadienes
under mild reaction conditions. In this regard, the reaction and Arylpropynoates in the Presence of Stoichiometric Amounts of
of the intermediate zirconacyclopentadienes proceeds une- NiBr
2
(PPh
3 2 2 3 2
) : The arylpropynoate (1.5 mmol) and NiBr (PPh )
(
742 mg, 1 mmol) were added to a solution of tetraethylzirconacy-
ventfully in the presence of the Ni complex to give solely
the corresponding biaryls. On the other hand, the reaction
in the presence of CuCl apparently proceeds by two dif-
ferent pathways: one resulting in the formation of biaryls
and the other in the formation of Dewar benzenes.
clopentadiene (1 mmol) in THF (5 mL), and the reaction mixture
was stirred for 24 h at 20 °C. The reaction mixture was diluted with
diethyl ether (10 mL), filtered, and evaporated with silica gel. Col-
umn chromatography on silica gel afforded the corresponding
products.
Methyl 2-(2-Fluorophenyl)-3,4,5,6-tetramethylbenzoate (4a). Reac-
tion with CuCl: Column chromatography on silica gel (hexane/
Experimental Section
EtOAc, 10:1) afforded the title compound (163 mg, 57%) as color-
1
General Remarks: All reactions were carried out under inert atmo-
less crystals: m.p. 76–79 °C. H NMR (400 MHz, CDCl
3
, Me
4
Si):
sphere (Ar). THF was distilled from benzophenone and sodium
δ = 2.01 (s, 3 H), 2.25 (s, 3 H), 2.26 (s, 3 H), 2.27 (s, 3 H), 3.42,
1
3
prior to use. NiBr
2
(PPh
3
)
2
, the propynoates 3, and the (–)-menthyl
7.08–7.16 (m, 3 H), 7.28–7.34 (m, 1 H) ppm. C NMR (100 MHz,
CDCl , Me Si): δ = 16.27, 16.72, 17.33, 17.61, 51.49, 115.07 (d, J
ester 8 were prepared by previously reported methods or by their
3
4
Eur. J. Org. Chem. 2005, 2491–2499
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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L. Dufková, M. Kotora, I. Císa rˇ ová
FULL PAPER
=
8
22 Hz), 123.61 (d, J = 4 Hz), 127.73 (d, J = 18 Hz), 129.25 (d, J =
Hz), 129.86, 130.00, 131.42 (d, J = 3 Hz), 132.88, 135.49, 136.60,
Compound 5e: M.p. 51–53 °C. 1H NMR (400 MHz, CDCl
Me Si): δ = 1.20 (s, 3 H), 1.36 (s, 3 H), 1.66 (d, J = 1.4 Hz, 3 H),
3
,
4
1
1
2
58.68, 161.12, 170.53 ppm. IR (CHCl
3
): ν˜ = 1720, 1455, 1436,
297, 1201, 1176, 1100, 1010 cm . HRMS calcd. for C18
86.13691; found 286.13774; R (hexane/EtOAc, 9:1) = 0.31.
1.70 (d, J = 1.4 Hz, 3 H), 3.57 (s, 3 H), 7.18 (d, J = 7.6 Hz, 1 H),
7.40 (t, J = 7.5 Hz, 1 H), 7.52 (t, J = 7.6 Hz, 1 H), 7.68 (d, J =
–1
H19FO :
2
1
3
f
7.9 Hz, 1 H) ppm. C NMR (100 MHz, CDCl
3
, Me
4
Si): δ = 9.76,
2
1
2
1
0.54, 11.11, 11.20, 50.80, 55.25, 59.34, 123.84 (q,
(C–F)
J =
Methyl 2-(2-Chlorophenyl)-3,4,5,6-tetramethylbenzoate (4b). Reac-
tion with CuCl: Column chromatography on silica gel (hexane/
EtOAc, 10:1) afforded the title compound (97 mg, 32%) as color-
less crystals: m.p. 102–104 °C. H NMR (400 MHz, CDCl
4
3
72 Hz), 126.28 (q,
J(C–F) = 5 Hz), 127.61 (q, J(C–F) = 31 Hz),
27.63, 127.95, 131.10, 134.05, 141.50, 142.66, 144.31, 162.63,
): ν˜ = 3016, 2957, 1710, 1647, 1436, 1317,
1
163.71 ppm. IR (CHCl
216, 1212, 1170, 1133, 1115, 1037 (cm ). HRMS calcd. for
: 336.13372; found 336.13442; R (hexane/EtOAc, 9:1)
3
3
,
–
1
1
Me
4
Si): δ = 1.97 (s, 3 H), 2.26 (s, 3 H), 2.27 (s, 3 H), 2.28 (s, 3 H),
.41 (s, 3 H), 7.14–7.17 (m, 1 H), 7.25–7.28 (m, 2 H), 7.42–7.45 (m,
H) ppm. 13C NMR (100 MHz, CDCl
, Me Si): δ = 16.32, 16.71,
C
19
H
19
F
3
O
2
f
3
1
1
1
= 0.25.
3
4
7.10, 17.69, 51.43, 126.24, 128.62, 128.95, 129.81, 131.22, 132.19, Methyl 3,4,5,6-Tetraethyl-3-(2-fluorophenyl)benzoate (6a). Reaction
32.48, 133.67, 134.37, 135.35, 136.56, 139.03, 170.42 ppm. IR with CuCl: Column chromatography on silica gel (hexane/EtOAc,
(CHCl
3
): ν˜ = 3009, 1721, 1436, 1296, 1201, 1176, 1060, 1054,
10:1) afforded the title compound (178 mg, 52%) as a yellow oil:
–1
1
1010 cm . HRMS calcd. for C18
H19ClO
2
: 302.10736; found
H NMR (400 MHz, CDCl , Me Si): δ = 0.91 (t, J = 7.5 Hz, 3 H),
3
4
3
02.10779; R (hexane/EtOAc, 9:1) = 0.45.
f
1.20 (t, J = 7.5 Hz, 3 H), 1.21 (t, J = 7.5 Hz, 3 H), 1.22 (t, J =
7
7
.5 Hz, 3 H), 2.40–2.75 (m, 8 H), 3.38 (s, 3 H), 7.08–7.14 (m, 2 H),
Methyl 2-(2-Methoxyphenyl)-3,4,5,6-tetramethylbenzoate (4c). Re-
action with CuCl: Column chromatography on silica gel (hexane/
1
3
.16 (td, J = 7.3, 1.8 Hz, 1 H), 7.28–7.34 (m, 1 H) ppm. C NMR
, Me Si): δ = 15.02, 15.66, 15.74, 15.95, 21.90,
22.21, 23.33, 23.98, 51.31, 115.09 (d, J = 22 Hz), 123.33 (d, J =
Hz), 127.33 (d, J = 18 Hz), 129.24 (d, J = 8 Hz), 130.62, 132.24
d, J = 3 Hz), 133.59, 135.88, 138.84, 140.46, 141.64, 158.64,
161.08, 170.60 ppm. IR (CHCl ): ν˜ = 2970, 1722, 1493, 1451, 1438,
(100 MHz, CDCl
3
4
EtOAc, 4:1) afforded the title compound (140 mg, 47%) as color-
1
less crystals: m.p. 85–86 °C. H NMR (400 MHz, CDCl
3
, Me
4
Si):
4
(
δ = 1.97 (s, 3 H), 2.24 (s, 3 H), 2.25 (s, 3 H), 2.26 (s, 3 H), 3.40 (s,
3
1
Me
1
1
1
H), 3.75 (s, 3 H), 6.90–6.96 (m, 2 H), 7.05 (dd, J = 7.3, 1.8 Hz,
H), 7.28–7.30 (m, 1 H) ppm. 1 C NMR (100 MHz, CDCl
Si): δ = 16.24, 16.70, 17.22, 17.66, 51.30, 55.59, 110.43, 120.06,
28.68, 129.17, 129.53, 130.85, 132.77, 132.94, 133.03, 134.61,
36.21, 157.08, 170.81 ppm. IR (CHCl ): ν˜ = 2947, 1727, 1660,
581, 1495, 1462, 1434, 1293, 1245, 1197, 1027, 756 cm . HRMS
: 298.16096; found 298.15968; elemental anal.
: C 76.48, H 7.43, O 16.09; found C 76.41, H 7.67.
(hexane/EtOAc, 4:1) = 0.35.
3
3
,
3
–
1
1279, 100, 1173, 1056, 1028 cm . HRMS calcd. for C22
2
H27FO :
4
342.19951; found 342.19892; R (hexane/EtOAc, 9:1) = 0.40.
f
3
Reaction with NiBr
(PPh : Column chromatography on silica gel
hexane/EtOAc, 9:1) afforded the title compound (154 mg, 45%) as
a viscous oil.
3 2
)
2
–1
(
calcd. for C19
calcd. C19H O
R
22 3
H O
22 3
Methyl 3-(2-Chlorophenyl)-3,4,5,6-tetraethylbenzoate (6b). Reaction
with CuCl: Column chromatography on silica gel (hexane/EtOAc,
f
Methyl 3,4,5,6-Tetramethyl-2-(2-methylphenyl)benzoate (4d). Reac-
tion with CuCl: Column chromatography on silica gel (hexane/
1
0:1) afforded the title compound (136 mg, 38%) as a yellow oil:
1
H NMR (400 MHz, CDCl
1
7
3
, Me
.20 (t, J = 7.4 Hz, 3 H), 1.21 (t, J = 7.4 Hz, 3 H), 1.23 (t, J =
.5 Hz, 3 H), 2.28 (q, J = 7.6 Hz, 2 H), 2.50–2.75 (m, 6 H), 3.37
4
Si): δ = 0.90 (t, J = 7.6 Hz, 3 H),
EtOAc, 10:1) afforded the title compound (113 mg, 40%) as color-
1
less crystals: m.p. 86–89 °C. H NMR (400 MHz, CDCl
3
, Me
4
Si):
δ = 1.91 (s, 3 H), 2.03 (s, 3 H), 2.24 (s, 3 H), 2.27 (s, 6 H), 3.37 (s,
H), 7.00 (dt, J = 7.2, 1.2 Hz, 1 H), 7.14–7.18 (m, 1 H), 7.20 (d,
13
(
(
2
1
s, 3 H), 7.23–7.26 (m, 3 H), 7.40–7.44 (m, 1 H) ppm. C NMR
100 MHz, CDCl , Me Si): δ = 15.01, 15.73, 15.78, 15.99, 21.91,
2.16, 23.16, 23.97, 51.20, 125.80, 128.58, 128.96, 132.05, 132.87,
34.12, 134.34, 135.90, 138.28, 138.60, 140.26, 141.68, 170.48 ppm.
3
3
4
1
3
J = 1.2 Hz, 1 H), 7.21–7.23 (m, 1 H) ppm. C NMR (100 MHz,
CDCl , Me Si): δ = 16.18, 16.67, 16.97, 17.60, 19.78, 51.29, 125.15,
27.25, 129.30, 129.35, 129.54, 131.98, 132.45, 134.36, 135.69,
36.35, 136.93, 139.60, 170.81 ppm. IR (CHCl ): ν˜ = 3005, 2951,
3
4
1
1
1
–1
IR (CHCl
3
): ν˜ = 2970, 1723, 1437, 1281, 1199, 1174, 1059 cm .
27ClO : 358.16996; found 358.16893; R
hexane/EtOAc, 9:1) = 0.48.
3
HRMS calcd. for C22
(
H
2
f
–
1
722, 1435, 1295, 1201, 1176, 1176, 1010 cm . HRMS calcd. for
: 282.16198; found 282.16229; R (hexane/EtOAc, 10:1) =
C
19
H
22
O
2
f
2 3 2
Reaction with NiBr (PPh ) : Column chromatography on silica gel
0
.40.
Methyl
4e) and Methyl 1,4,5,6-Tetramethyl-3-[2-(trifluoromethyl)phenyl]bi-
(
hexane/EtOAc, 9:1) afforded the title compound (165 mg, 46%) as
3,4,5,6-Tetramethyl-2-[2-(trifluoromethyl)phenyl]benzoate
a viscous oil.
(
cyclo[2.2.0]hexa-2,5-diene-2-carboxylate (5e). Reaction with CuCl: Methyl 3,4,5,6-Tetraethyl-3-(2-methoxyphenyl)benzoate (6c) and
Column chromatography on silica gel (hexane/EtOAc, 10:1) af-
forded 4e (54 mg, 16%) as a colorless solid and 5e (20 mg, 6%) as
a colorless oil, which upon further recrystallization from n-hexane
afforded colorless crystals.
Methyl 1,4,5,6-Tetraethyl-3-(2-methoxyphenyl)bicyclo[2.2.0]hexa-
2,5-diene-2-carboxylate (7c): Reaction with CuCl. Column
chromatography on silica gel (hexane/EtOAc, 9:1) afforded 6c
(106 mg, 30%) and 7c (35 mg, 10%) as viscous oils. Reaction with
2 3 2
NiBr (PPh ) . Column chromatography on silica gel (hexane/
EtOAc, 9:1) afforded 186 mg (52%) of the title compound 6c as a
viscous oil.
Compound 4e: M.p. 59–61 °C. 1H NMR (400 MHz, CDCl
Me Si): δ = 1.88 (s, 3 H), 2.25 (s, 3 H), 2.26 (s, 3 H), 2.27 (s, 3 H),
,
3
4
3
.38 (s, 3 H), 7.19 (d, J = 7.6 Hz, 1 H), 7.45 (t, J = 7.6 Hz, 1 H),
7
.52 (t, J = 7.4 Hz, 1 H), 7.70 (d, J = 7.7 Hz, 1 H) ppm. 13C NMR
Compound 6c: H NMR (400 MHz, CDCl
1
3
, Me
4
Si): δ = 0.90 (t, J
(
100 MHz, CDCl
3
, Me
4
Si): δ = 16.32, 16.65, 17.79, 17.99, 51.28, = 7.5 Hz, 3 H), 1.20 (t, J = 7.5 Hz, 3 H), 1.21 (t, J = 7.5 Hz, 3 H),
2
(C–F) = 273 Hz), 126.07 (q, 4
1
1
1
1
23.96 (q,
J
J
(C–F) = 5 Hz), 127.55,
29.28 (q, J(C–F) = 30 Hz), 129.74, 130.99, 131.99, 132.06, 132.24,
33.67, 135.24, 136.50, 138.62, 170.25 ppm. IR (CHCl ): ν˜ = 2950,
723, 1436, 1316, 1296, 1174, 1153, 1129, 1060, 1035, 908 cm .
: 336.13372; found 336.13303; R
1.22 (t, J = 7.5 Hz, 3 H), 2.34 (q, J = 7.5 Hz, 1 H), 2.45 (q, J =
7.5 Hz, 1 H), 2.56 (q, J = 7.5 Hz, 1 H), 2.62 (q, J = 7.5 Hz, 1 H),
2.64–2.80 (m, 4 H), 3.34 (s, 3 H), 3.74 (s, 3 H), 6.92 (t, J = 7.6 Hz,
3
3
–
1
13
1 H), 7.08 (dd, J = 7.6, 1.8 Hz, 1 H), 7.26 (m, 2 H) ppm. C NMR
HRMS calcd. for C19
H
19
F
3
O
2
f
(100 MHz, CDCl
3 4
, Me Si): δ = 14.96, 15.72, 15.81, 16.00, 21.92,
(hexane/EtOAc, 10:1) = 0.40.
22.25, 23.25, 24.17, 51.13, 55.53, 110.48, 119.76, 128.63, 128.82,
2496
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 2491–2499

Sterically Hindered Biaryls by Zr-Mediated Co-cyclotrimerization of Alkynes
FULL PAPER
1
1
1
31.79, 133.50, 133.69, 135.56, 138.94, 139.55, 141.30, 157.07,
Reaction with NiBr
(hexane/EtOAc, 9:1) afforded 90 mg (23%) of the title compound
6e as a viscous oil.
2
(PPh
3
)
2
: Column chromatography on silica gel
70.91 ppm. IR (neat): ν˜ = 2950, 1704, 1595, 1487, 1466, 1434,
–1
270, 1248, 1192, 1173, 1069, 1026, 753 cm . HRMS calcd. for
C
=
23
H
0.43.
30
O
3
: 354.219495; found 354.220534. R
f
(hexane/EtOAc, 9:1)
1
Compound 6e: H NMR (400 MHz, CDCl
=
3
, Me
4
Si): δ = 0.86 (t, J
7.5 Hz, 3 H), 1.18 (t, J = 7.5 Hz, 3 H), 1.19 (t, J = 7.5 Hz, 3 H),
1.22 (t, J = 7.5 Hz, 3 H), 2.15 (dq, J = 14.0, 7.5 Hz, 2 H), 2.50 (dq,
1
Compound 7c: H NMR (400 MHz, CDCl
3
, Me Si): δ = 0.88 (t, J
4
=
7.5 Hz, 3 H), 0.98 (t, J = 7.5 Hz, 3 H), 1.00 (t, J = 7.5 Hz, 3 H), J = 14.0, 7.5 Hz, 2 H), 2.62 (dq, J = 14.0, 7.5 Hz, 2 H), 2.68–2.74
1
3
.02 (t, J = 7.5 Hz, 3 H), 1.84–2.03 (m, 4 H), 2.05–2.24 (m, 4 H),
.68 (s, 3 H), 3.78 (s, 3 H), 6.80 (dd, J = 7.4, 1.0 Hz, 1 H), 6.94
(m, 2 H), 3.34 (s, 3 H), 7.29 (d, J = 7.5 Hz, 1 H), 7.41–7.52 (m, 2
H), 7.68 (d, J = 7.6 Hz, 1 H) ppm. C NMR (100 MHz, CDCl3,
1
3
(
td, J = 7.5, 1.1 Hz, 1 H), 7.24–7.30 (m, 1 H), 7.58 (dd, J = 7.6,
Me Si): δ = 15.15, 15.68, 15.74, 16.00, 21.84, 22.05, 23.46, 23.94,
4
.6 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl
, Me Si): δ = 10.71,
2
4
1
1
1
1
1
1
3
3
4
51.06, 123.93 (q, J(C–F) = 272 Hz), 126.15 (q, J(C–F) = 5 Hz),
3
0.75, 11.22, 11.42, 20.53, 21.00, 21.15, 21.17, 50.69, 54.75, 110.31,
20.10, 121.65, 124.77, 130.71, 132.17, 128.87, 136.88, 142.90,
44.19, 157.11, 162.45, 164.92 ppm. IR (neat): ν˜ = 2969, 1729,
601, 1581, 1487, 1495, 1460, 1435, 1281, 1244, 1194, 1172, 1113,
129.37 (q, J
C–F)
= 31 Hz), 130.45, 132.04, 132.36, 132.66, 133.87,
(
135.75, 137.87, 138.10, 140.19, 141.55, 170.40 ppm. IR (CHCl ): ν˜
3
= 3016, 2974, 2938, 1721, 1453, 1316, 1289, 1275, 1263, 1213, 1176,
–
1
1131, 1035 cm . HRMS calcd. for C H F O : 392.19632; found
2
3
27
3
2
–1
052,1027 cm . HRMS calcd. for C23
H
30
O
3
354.219495; found
92.19565; R (hexane/EtOAc, 9:1) = 0.38.
f
54.220534. R (hexane/EtOAc, 4:1) = 0.35.
f
1
Compound 7e: H NMR (400 MHz, CDCl
3
, Me
4
Si): δ = 0.86 (t, J
Methyl 3,4,5,6-Tetraethyl-3-(2-methoxyphenyl)benzoate (6d) and
Methyl 1,4,5,6-Tetraethyl-3-(2-methoxyphenyl)bicyclo[2.2.0]hexa-
= 7.3 Hz, 3 H), 1.05 (t, J = 7.5 Hz, 3 H), 1.01 (t, J = 7.5 Hz, 3 H),
1.07 (t, J = 7.3 Hz, 3 H), 1.85–1.91 (m, 4 H), 2.10–2.22 (m, 2 H),
2,5-diene-2-carboxylate (7d): Reaction with CuCl: Column 2.30 (dq, J = 7.5 Hz, 2 H), 3.55 (s, 3 H), 7.20 (dt, J = 7.6, 0.9 Hz,
chromatography on silica gel (hexane/EtOAc, 9:1) afforded a in-
separable mixture of 6d and 7d (108 mg, 30%) in 1:0.8 ratio as a
viscous oil.
1 H), 7.37–7.42 (t, J = 7.5 Hz, 1 H), 7.75 (t, J = 7.6 Hz, 1 H), 7.67
1
3
(d, J = 7.6 Hz, 1 H) ppm. C NMR (100 MHz, CDCl , Me Si): δ
3
4
= 10.62, 10.86, 11.79, 12.92, 20.51, 20.55, 20.65, 21.88, 50.73, 60.15,
2
1
1
64.77, 124.43 (q, J
= 272 Hz), 125.15 (q, J
(C–F)
= 362 Hz),
Compound 6d: H NMR (400 MHz, CDCl
3
, Me
4
Si): δ = 0.88 (t, J
(C–F)
4
1
1
2
26.10 (q, J(C–F) = 5 Hz), 127.44, 127.58, 130.99, 135.05, 141.06,
46.62, 149.67, 163.15, 163.91 ppm. IR (CHCl
939, 1711, 1437, 1317, 1265, 1218, 1213, 1172 cm . HRMS calcd.
=
7.3 Hz, 3 H), 1.19 (t, J = 7.3 Hz, 3 H), 1.21 (t, J = 7.3 Hz, 3 H),
3
): ν˜ = 3016, 2973,
1
1
2
.23 (t, J = 7.3 Hz, 3 H), 2.01 (s, 3 H), 2.17 (dq, J = 13.5, 7.4 Hz,
–
1
H), 2.48 (dq, J = 13.5, 7.4 Hz, 1 H), 2.60 (q, J = 7.5 Hz, 2 H),
1
3
23 27 3 2 f
for C H F O : 392.19632; found 392.19291; R (hexane/EtOAc,
.66–2.80 (m, 4 H), 3.32 (s, 3 H), 7.10–7.20 (m, 4 H) ppm.
, Me Si): δ = 15.14, 15.82, 15.91, 16.08,
0.02, 21.84, 22.17, 22.96, 23.97, 51.10, 124.73, 127.21, 129.28,
C
9:1) = 0.38.
NMR (100 MHz, CDCl
3
4
2
1
1
Methyl 3,4,5,6-Tetraethyl-2-(2-methoxynaphthyl)benzoate (6f). Re-
action with NiBr (PPh : Column chromatography on silica gel
hexane/EtOAc, 9:1) afforded the title compound (85 mg, 20%) as
30.27, 133.05, 135.63, 136.16, 136.94, 137.86, 139.18, 139.40,
41.56, 170.89 ppm.
2
3 2
)
(
1
1
Compound 7d: H NMR (400 MHz, CDCl
3
, Me
4
Si): δ = 0.88 (t, J
3 4
a viscous oil: H NMR (400 MHz, CDCl , Me Si): δ = 0.79 (t, J
=
7.6 Hz, 3 H), 1.00 (t, J = 7.6 Hz, 3 H), 1.01 (t, J = 7.6 Hz, 3 H), = 7.5 Hz, 3 H), 1.21 (t, J = 7.5 Hz, 3 H), 1.25 (t, J = 7.5 Hz, 3 H),
1
6
.02 (t, J = 7.3 Hz, 3 H), 1.91 (q, J = 7.4 Hz, 2 H), 2.05–2.20 (m,
1.28 (t, J = 7.5 Hz, 3 H), 2.19 (dq, J = 13.8, 7.5 Hz, 1 H), 2.35 (dq,
J = 13.8, 7.5 Hz, 1 H), 2.63 (q, J = 7.5 Hz, 2 H), 2.76 (q, J =
7.5 Hz, 2 H), 2.78 (q, J = 7.5 Hz, 2 H), 3.03 (s, 3 H), 3.85 (s, 3 H),
7.18–7.22 (m, 1 H), 7.25–7.33 (m, 3 H) 7.73–7.77 (m, 1 H), 7.84 (d,
1
3
H), 2.26 (s, 3 H), 3.63 (m, 3 H), 7.10–7.20 (m, 4 H) ppm.
, Me Si): δ = 10.58, 10.95, 11.96, 12.78,
9.91, 20.49, 20.77, 20.81, 21.36, 50.71, 60.15, 64.03, 124.91,
C
NMR (100 MHz, CDCl
3
4
1
1
1
1
1
3
26.56, 127.66, 130.17, 133.30, 134.73, 135.89, 139.43, 146.25,
3 4
J = 9 Hz, 1 H) ppm. C NMR (100 MHz, CDCl , Me Si): δ =
49.92; 165.97 ppm. IR (neat): ν˜ = 2971, 2937, 2878, 1708, 1634,
14.78, 15.83, 15.96, 16.11, 22.00, 22.31, 23.60, 24.19, 50.75, 56.35,
113.13, 122.70, 123.25, 125.74, 126.03, 127.36, 128.52, 129.20,
131.19, 134.04, 134.15, 136.00, 139.57, 139.69, 141.66, 154.39,
–
1
488, 1455, 1437, 1379, 1301, 1284, 1274, 1200, 1174, 1057 cm .
338.22458; found 338.22517. R (hex-
HRMS calcd. for C23
ane/EtOAc, 9:1) = 0.44.
Reaction with NiBr (PPh
hexane/EtOAc, 9:1) afforded 6d (112 mg, 33%) as a viscous oil:
H
30
O
2
f
3
170.67 ppm. IR (CHCl ): ν˜ = 2968, 2935, 1718, 1507, 1274, 1262,
–
1
1
243, 1198, 1173, 1058, 908, 809 cm . HRMS calcd. for C27
32 3
H O :
2
3 2
) : Column chromatography on silica gel
4
04.23515; found 404.23648; R (hexane/EtOAc, 9:1) = 0.20.
f
(
1
H NMR (400 MHz, CDCl
3
, Me
4
Si): δ = 0.88 (t, J = 7.3 Hz, 3 H),
Reaction with CuCl: Column chromatography on silica gel (hexane/
EtOAc, 9:1) afforded the title compound 6f (30 mg, 7%) as a vis-
.3 Hz, 3 H), 2.01 (s, 3 H), 2.17 (dq, J = 13.5, 7.4 Hz, 1 H), 2.48 cous oil.
1
7
.19 (t, J = 7.3 Hz, 3 H), 1.21 (t, J = 7.3 Hz, 3 H), 1.23 (t, J =
(
(
(
2
1
1
1
1
dq, J = 13.5, 7.4 Hz, 1 H), 2.60 (q, J = 7.5 Hz, 2 H), 2.66–2.80
(
–)-Menthyl
3,4,5,6,2Ј-Pentamethylbiphenyl-2-carboxylate
(9):
13
m, 4 H), 3.32 (s, 3 H), 7.08–7.22 (m, 4 H) ppm. C NMR
100 MHz, CDCl , Me Si): δ = 15.14, 15.82, 15.91, 16.08, 20.02,
1.84, 22.17, 22.96, 23.97, 51.10, 124.73, 127.21, 129.28, 130.27,
33.05, 135.63, 136.16, 136.94, 138.86, 139.18, 139.40, 141.56,
70.89 ppm. IR (CHCl ): ν˜ = 3014, 2973, 2938, 2878, 1723, 1453,
438, 1379, 1332, 1303, 1286, 1273, 1219, 1216, 1199, 1174, 1083,
nBuLi in hexanes (1.6 m, 1.25 mL, 2 mmol) was added at –78 °C to
a solution of zirconocenene dichloride (292 mg, 1 mmol) in THF
(
(
3
4
5 mL) and the reaction mixture was stirred for 1 h. But-2-yne
314 μL, 4 mmol) was then added and the reaction mixture was
3
allowed to warm up to 20 °C within 1 h. The menthyl ester 8
298 mg, 1.5 mmol) and CuCl (200 mg, 2 mmol) were added, and
(
–1
056, 1040, 1028 cm . HRMS calcd. for C23
30 2
H O : 338.22458;
the reaction mixture was stirred for 148 h (1 week) at 20 °C. The
reaction mixture was quenched with 3 m HCl and extracted with
found 338.22517. R
f
(hexane/EtOAc, 9:1) = 0.44.
Methyl 3,4,5,6-Tetraethyl-3-[2-(trifluoromethyl)phenyl]benzoate (6e) diethyl ether (3×10 mL), and the combined organic fractions were
and Methyl 1,4,5,6-Tetraethyl-3-[2-(trifluoromethyl)phenyl]bicy-
clo[2.2.0]hexa-2,5-diene-2-carboxylate (7e). Reaction with CuCl:
Column chromatography on silica gel (hexane/EtOAc, 9:1) afforded
4
dried over MgSO . Removal of solvents under reduced pressure
followed by column chromatography on silica gel (hexane/EtOAc,
1
10:1) afforded the title compound (77 mg, 19%) as a yellow oil: H
6e (90 mg, 23%) and 7e (78 mg, 20%) as viscous oils.
NMR (400 MHz, CDCl
3
, TMS): δ = 0.57 (d, J = 7.0 Hz, 3 H),
Eur. J. Org. Chem. 2005, 2491–2499
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2497

L. Dufková, M. Kotora, I. Císa rˇ ová
FULL PAPER
ˇ
0
2
1
.77 (d, J = 6.4 Hz, 3 H), 0.78 (d, J = 7.0 Hz, 3 H), 0.89–0.98 (m, [2] For application of biaryls as ligands, see: a) P. Ko cˇ ovský, S.
H), 1.14–1.20 (m, 1 H), 1.19–1.28 (m, 2 H), 1.55–1.60 (m, 3 H),
.76–1.84 (m, 1 H), 1.80 (s, 3 H), 2.01 (m, 3 H), 2.26 (s, 3 H), 2.27
Vysko cˇ il, M. Smr cˇ ina, Chem. Rev. 2003, 103, 3213–3246; b) Y.
Chen, S. Yekta, A. K. Yudin, Chem. Rev. 2003, 103, 3155–3212;
c) T. Hayashi, Acc. Chem. Res. 2000, 33, 354–362; d) S. Akuta-
gawa, App. Cat. A: General 1995, 128, 171–207; e) Chiral Auxil-
iaries and Ligands in Asymmetric Synthesis (Ed.: J. Seyden-
Penne); John Wiley & Sons: New York, 1995; f) Asymmetric
Catalysis in Organic Synthesis (Ed.: R. Noyori); Wiley Europe:
Weinheim, 1994.
(
s, 3 H), 2.28 (s, 3 H), 4.50–4.60 (m, 1 H), 7.02 (d, J = 7.3 Hz, 1
13
H), 7.12–7.22 (m, 3 H) ppm. C NMR (100 MHz, CDCl
3
, TMS):
δ = 15.82, 16.28, 16.70, 16.87, 17.48, 20.03, 20.81, 21.89, 22.93,
5.65, 31.11, 34.10, 39.31, 46.62, 74.56, 125.44, 127.31, 129.18,
29.42, 129.81, 132.04, 132.91, 134.38, 135.40, 136.05, 137.37,
2
1
1
1
4
39.70, 169.93 ppm. IR (CHCl
3
): ν˜ = 2957, 2927, 1709, 1456, 1294,
195, 998, 953 cm . HRMS calcd. for C28 : 406.28718; found
06.28701; R (hexane/EtOAc, 9:1) = 0.50.
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CDCl
5
= –30.8 (c = 1, CHCl
, TMS): δ = 0.64 (d, J = 7.0 Hz, 3 H), 0.74 (d, J = 6.4 Hz,
1
D
3
). H NMR (400 MHz,
3
3
1
1
H), 0.80 (d, J = 7.0 Hz, 3 H), 0.89–0.98 (m, 2 H), 1.14–1.20 (m,
H), 1.21–1.28 (m, 2 H), 1.52–1.60 (m, 3 H), 1.76–1.84 (m, 1 H),
.88 (s, 3 H), 2.05 (m, 3 H), 2.25 (s, 3 H), 2.26 (s, 3 H), 2.27 (s, 3
H), 4.52 (dt, J = 10.9, 4.4 Hz, 1 H), 7.02 (d, J = 7.3 Hz, 1 H), 7.12–
.22 (m, 3 H) ppm.
7
¯
22 3
H O , M = 298.37, triclinic, P1 (No, 2),
Crystal Data for 3c: C19
a = 7.9730(3) Å, b = 9.0650(3) Å, c = 12.3800(4) Å, α = 74.960(2)°,
2000, 100, 2901–2916.
3
x
β = 72.121(2)°, γ = 73.285(2)°, V = 801.06(5) Å , Z = 2, D =
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Acknowledgments
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This work was supported by the Grant Agency of the Czech Re-
public (grant No. 203/01/0863 and is a part of long-term Research
Plan of the Faculty of Science, Charles University. The authors
thank Mirek Kvasnica for measurement of IR spectra.
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2498
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 2491–2499

Sterically Hindered Biaryls by Zr-Mediated Co-cyclotrimerization of Alkynes
FULL PAPER
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Received: December 13, 2004
Eur. J. Org. Chem. 2005, 2491–2499
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2499