Nickel/magnesium-lanthanum mixed oxide catalyst in the Kumada-coupling

Article abstract of DOI:10.1039/b919246h

A new, heterogeneous, magnesium-lanthanum mixed oxide solid base-supported nickel(ii) catalyst was developed. The catalyst was used successfully in the Kumada coupling of aryl halides, especially aryl bromides. The optimal reaction conditions of the coupling were determined.

Full text of DOI:10.1039/b919246h

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COMMUNICATION
www.rsc.org/obc | Organic & Biomolecular Chemistry
Nickel/magnesium–lanthanum mixed oxide catalyst in the Kumada-coupling
a
a
b
´
Arpa´d Kiss, Zolta´n Hell* and Ma´ria Ba´lint
Received 16th September 2009, Accepted 31st October 2009
First published as an Advance Article on the web 10th November 2009
DOI: 10.1039/b919246h
A new, heterogeneous, magnesium–lanthanum mixed oxide
solid base-supported nickel(II) catalyst was developed. The
catalyst was used successfully in the Kumada coupling of
aryl halides, especially aryl bromides. The optimal reaction
conditions of the coupling were determined.
inate the product, which is unacceptable e.g. in pharmaceutical
syntheses. This induced a considerable research effort to develop
new, heterogeneous catalytic systems. Lipshutz described the use
of Ni on activated charcoal (DARCO) in the Kumada coupling.
He obtained good conversions even with aryl chloride, but only
in the presence of an equimolar amount of anhydrous LiBr.
The other disadvantage of his method is that a large amount
(ca. 20 mol%) of triphenyl phosphine (free or polymer-bound)
has to be added into the reaction mixture. Without this ligand
the yield decreased significantly and a considerable amount of
homocoupled product was detected.11 Styring12 bound a nickel
chelate complex to Merrifield-resin and this modified resin was
used as catalyst. The disadvantage of this method is that a
great excess (3 moles) of Grignard compound is necessary to
obtain a good yield. Very recently Richardson13 examined the
coupling of phenylmagnesium chloride and 4-bromoanisole using
nickel(II)acetylacetonato complex supported on either polymer-
bound ethylenediamine or on modified mesoporous silica. He
found that the leached nickel promoted the catalysis.
Recently our research group has developed a new heterogeneous
catalyst, Pd on magnesium–lanthanum mixed oxide, and applied
it successfully in the Heck, Sonogashira and Suzuki reaction.14–16
Based on these results we investigated the applicability of related,
heterogeneous catalyst systems in the Kumada coupling.
The coupling of a Grignard reagent with halides can be effected
without catalyst via nucleophilic substitution, if the halide is
activated, such as allyl bromide or benzyl bromide. Alkyl halides
react weakly and the reactivity, of course, further decreases
towards vinyl and aryl halides. The Kumada reaction can be a
useful method for the coupling of these unactivated halides. To
investigate the applicability of a heterogeneous catalyst for the
coupling we chose the reaction of phenylmagnesium bromide with
bromobenzene (Scheme 1) as a model reaction.
The reaction of organomagnesium halides with carbonyl com-
pounds discovered by Barbier1 and improved by Grignard2 has
became a very important synthetic method even in industrial
syntheses. A number of modifications of the original method were
elaborated aiming to improve the functional group tolerance or
the yield. Thus e.g. Kharasch3 examined the effect of different
metal salts on the coupling reaction of Grignard compounds
with the weakly reactive aryl halides. He observed that in the
reaction of bromobenzene and 4-bromotoluene the formation
of homocoupled products was determinant. He suggested an
interesting redox mechanism. Based on his considerations this
reaction could only be used for the preparation of homocoupled
products. He described the formation of polymer-like byproducts
(terphenyl, etc.), too. He found that anhydrous cobalt chloride was
the best catalyst.
Later Kumada and his coworkers4 described the coupling of
Grignard reagents in a homogeneous, nickel complex-catalyzed
reaction. Their suggestion for the reaction mechanism is more
similar to the mechanism described for today’s metal-catalyzed
carbon–carbon coupling reactions (e.g. Negishi, Stille, etc.). It was
found that nickel was the best catalyst, but if the halide was iodide,
Pd was also efficient. In some cases Fe-complexes also proved to
be applicable.5 In the last years new methods were described using
iron catalysts.6
Kumada used nickel(II) phosphine complexes in a homogeneous
process with bidentate ligands such as dppe, dppp and others.4
The advantage of these ligands is that in some cases (e.g. dppf,
DIOP, tert-Leuphos) they can induce enantioselectivity.7 Besides
the phosphine compounds some other ligands were also used
such as acetylacetone (Kumada–Corriu coupling).8 Very recently
Hu described the use of nickel(II) pincer complexes as good
catalysts for the coupling of nonactivated aryl halides with aryl
and heteroaryl nucleophiles.9 Butadiene was also found to be a
good ligand.10
In recent years the importance of the different carbon–carbon
coupling reactions has increased significantly. Nowadays various
methods are used even on an industrial scale thanks to their good
yield and selectivity. The main disadvantage of these reactions is
that when homogeneous catalysts are used, the metal can contam-
Scheme 1
As it was described, the coupling can be catalyzed by different
metals. Nickel has been used most frequently, but palladium,
iron and other metals were also applied. Thus, we first examined
the efficiency of different metals. These metals were placed onto
different supports having basic properties namely Mg : Al 2 : 1 or
3 : 1 hydrotalcite (HT), Mg : La 3 : 1 mixed oxide (MgLaO), and
˚
4 A molecular sieve (4A).
As was expected the reaction without catalyst gave a poor yield
(Table 1, entry 1), and most of this product has already been
formed during the formation of the Grignard reagent. It is well
known, that the commercial Grignard-reagents always contain
aDepartment of Organic Chemistry and Technology, Budapest University of
Technology and Economics, H-1521, Budapest, Hungary. E-mail: zhell@
mail.bme.hu; Fax: (+36 1) 463-3648; Tel: (+36 1) 463-1414
bBa´lint Analitika Kft, H-1116 Budapest, Fehe´rva´ri u´t, 144, Hungary
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Table 1 Effect of the metal and the support on the coupling of
bromobenzene
Entry
Catalysta
Yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
—
16
30
26
49
30
22
28
<5
<5
<5
72
26
66
86c
67
66
18
67
Pd2+–MgLaO
Pd0–MgLaO
Co2+–HT 2 : 1
Cu2+–MgLaO
Cu2+HT 2 : 1
Cu0–HT 2 : 1
Fe3+–HT 2 : 1
Fe3+–HT 3 : 1
Fe3+–4A
Fig. 1 SEM image of a catalyst particle (left) and distribution of the
nickel on the particle (right) (magnification: 4000¥).
Ni2+–HT 2 : 1
Ni2+–HT 2 : 1 (calc.)
Ni2+-4A
Ni2+–MgLaO
Ni2+–MgO
Ni2+–La2O3
MgLaO
d
anhydrous NiCl2
Fig. 2 Standard quantitative analysis of the catalyst.
Table 2 Effect of the amount of nickel on the couplinga
Nickel concentration
a 1 mmol metal/g support, 10 ml Et2O, 0.2 g catalyst/10 mmol substrate,
reflux. b Isolated yield, the purity is checked by GC-MS. c Using THF
instead of diethyl ether the same yield was obtained. d 4% metal (Kharasch
method)
on the catalyst/
Catalyst
amount/g mol%
Nickel amount/ Yieldb
Entry mmol g-1
(%)
a certain amount of coupled product as contaminant which is
explained by a reaction of one Grignard compound with another.
In agreement with Kumada’s statement, the best yield was
obtained with nickel. Palladium, both in the form of Pd(II)
and Pd(0) gave poor yield. Cobalt, which had been described
by Kharasch as the best metal for this type of coupling, gave
moderate yield. Copper, which is also known as efficient catalyst
or co-catalyst for several coupling reactions17 showed no high
activity. Although Fe(acac)3 has been described as a catalyst for
1
2
3
4
5
6
7
0.8
0.4
0.08
0.08
0.04
0.016
0.016
0.2
0.2
0.2
0.1
0.2
0.2
0.4
1.6
0.8
0.16
0.08
0.08
0.032
0.064
86
87
88 (88)c
42
42
39
77
a 10 mmol substrate, 6 h. b Isolated yield, the purity is checked by GC-MS.
c Reaction time: 12 h.
˚
the coupling, when we used iron(III) on hydrotalcite or on 4 A
molecular sieves (entries 8–10), the product was no the required
biphenyl but a complex mixture was obtained. The best result
was obtained with MgLa mixed oxide support (entry 14). This
would suggest that – since this mixed oxide is a quite strong Lewis
base – the efficiency of the support would be determined by its
into the surface structure of the mixed oxide support, as can be
seen in Fig. 1 (right). This is supported by the ICP-OES results
which showed a slight decrease in the Mg : La ratio comparing
the pure support and the catalyst. Additionally, the presence of
chlorine and magnesium was shown in the filtrate obtained during
the workup in the preparation process of the catalyst. The amount
of the nickel on the support was also determined by ICP-OES and
was found to be 0.8 mmol g-1.
To avoid the contamination of the product and/or the environ-
ment, the amount of the heavy metal used in an organic synthesis
should be as low as possible. Thus we examined the effect of the
amount of the nickel on the coupling. As is shown in Table 2,
the optimal amount of nickel was 0.16 mol%. In the cases when
the yield was lower, the reaction mixture contained the unreacted
starting materials. In the published experiments the amount of
nickel varied between 0.34 and 3 mol%.9 Thus, our catalyst requires
a smaller amount of nickel for a good yield than the published
methods.
˚
basicity. But in this case 4 A molecular sieves (entry 13) which are
also a strong Lewis base, should give a similar result as MgLaO.
Thus the support would seem to have another effect. The simple
oxides, MgO and La2O3 (entries 15 and 16, resp.) showed weaker
activity. Calcination of Mg : Al 2 : 1 hydrotalcite impregnated with
nickel chloride (Ni2+–HT 2 : 1) decreased the activity of the catalyst
significantly (entry 12). The MgLa mixed oxide without nickel
showed no activity e.g. the same yield was obtained as without
any additive (entry 17 vs. entry 1). In all of the cases, when
the supports HT and MgLaO were compared with the same
metal, the MgLaO proved to be more efficient. When the original
Kharasch-experiment was reproduced, GC-MS investigation of
the products showed the presence of higher polymeric species
(entry 18) according to the mechanism proposition of Kharasch.3
The structure of the Ni2+–MgLaO catalyst was investigated by
scanning electron microscopy. The nickel is evenly distributed on
the surface of the support (Fig. 1). The low intensity of chlorine
(Fig. 2) possibly indicates that during the preparation of the
catalyst it is not a simple surface adsorption that occurs. The nickel
has exchanged probably with magnesium and been incorporated
The use of this type of solid catalyst system generally induces
dispute over whether the reaction takes place on the solid surface
or with the metal leached into the solution. We used the hot
filtration test to choose from these two possibilities. Thus, after
2 h the reaction mixture was filtered, and the filtrate was examined
by X-ray fluorescence. This showed that there was about 1–
2 ppm nickel in the solution which might verify a capture–release
332 | Org. Biomol. Chem., 2010, 8, 331–335
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mechanism. The X-ray fluorescence investigation of the isolated
products showed the absence of nickel.
In the preliminary experiments the reaction time was 6 h. We
examined the effect of the reaction time and found, that the yield
increased significantly with the reaction time, but after 3 h it had
no longer effect as is shown in Fig. 3.
Scheme 3
Table 4 Results of the cross-coupling reactionsa
Entry
R1
R2
Yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
H
H
H
H
H
H
H
p-Me
p-Me
p-Me
p-Me
p-OMe
p-CF3
p-Me
86
73
81
83
23
78
84
25
69
29
55
11
21
Fig. 3 Effect of the reaction time on the yield.
o-OMe
m-OMe
p-OMe
o-CF3
m-CF3
p-CF3
o-CF3
m-CF3
p-CF3
p-OMe
p-Me
The nature of the coupling aryl halide influences the reactivity
significantly. The reaction of different halobenzenes and phenyl-
magnesium halides were investigated in the presence of Ni2+–
MgLaO (10 mmol of each reactant, diethyl ether, reflux, 3 h,
Scheme 2). The results (Table 3) show the general reactivity of
the aryl halides. Nevertheless, the Y halogen plays the key role. If
it is iodine, then an excellent yield can be expected. But the bromo
derivative gave also good results. The chloro derivative gave a
moderate yield even after a longer reaction time.
With the optimal reaction conditions we examined the scope
of the cross-coupling (Scheme 3). In the reaction of phenylmag-
nesium bromide and p-bromotoluene 61% of the desired product
was obtained, but the two homocoupled products, biphenyl and
p,p¢-bitolyl were also obtained. When the ratio of the R1-aryl
bromide : magnesium was changed to 1.3 : 1.15 in the Grignard
reaction, no p,p¢-bitolyl was formed, but near the 86% 4-methyl-
biphenyl 15% biphenyl was also obtained. Thus, this way the
formation of the R2-homocoupled product can be avoided since
there is no residual magnesium in the mixture which could
form a Grignard reagent from R2-aryl halide. With this modified
conditions we examined the reaction of different aryl bromides.
Using higher excess of Grignard compounds the yield did not
increased. The results are summarized in Table 4.
m-CF3
a Conditions: 11.5 mmol Grignard compound, 10 mmol aryl bromide, 0.2 g
Ni2+–MgLaO, 10 ml diethyl ether, 3 h. b Isolated yield based on R2-aryl
bromide, ca. 15% R1-C6H4–C6H4-R1 was also formed which was shown by
GC-MS.
reagent obtained from p-bromotoluene had poorer reactivity
than bromobenzene. Entries 11 and 12 gave surprisingly weak
results. When the reaction of p-tolylmagnesium bromide with
p-bromoanisole (entry 11) was investigated by GC-MS the pres-
ence of a great amount of unreacted p-bromoanisole and the lack
of p-bromotoluene showed that the formation of the Grignard
compound occurred, but the coupling took place weakly.
Contrarily when the Grignard compound was formed from
p-bromoanisole and this was coupled with p-bromotoluene (en-
try 12), GC-MS of the product showed the presence of a lot
of anisole, which was formed from the unreacted Grignard
compound during the workup of the reaction mixture. These
results show that the methoxy group can inhibit the reaction,
although this is not verified by the results obtained in entries 2–4.
The investigation of the crude products by GC-MS showed
that the amount of other byproducts, such as phenol (formed by
reaction of the Grignard compound with oxygen from the air and
subsequent hydrolysis) or 2-phenylethanol (formed by a radical
reaction between the Grignard reagent and the solvent diethyl
ether) did not exceed 0.2% in any of the cases.
As it is shown, generally good results were obtained when the
Grignard reagent was formed from bromobenzene, except when
the coupling aryl halide was o-trifluoromethyl-bromobenzene.
This latter gave a poor yield in every reaction. The Grignard
Scheme 2
Table 3 Effect of the halogen on the yielda
The recyclability of the catalyst was investigated in the reaction
of bromobenzene and p-bromotoluene. Thus in the first reaction
the yield obtained was 86%. The catalyst was filtered out from the
Entry
X
Y
Yield (%)
1
2
3
4
Br
Br
Br
I
Cl
Br
I
50 (51)b
86
99
◦
mixture and after washing it with toluene and drying at 120 C
for 1 h it was reused in the same reaction. In the second run the
yield obtained was 70%. The quite big decrease in the yield can be
explained with the precipitation of magnesium bromide – which
is formed in the reaction of necessity – onto the surface of the
I
94
a Reaction time: 6 h. b Reaction time: 18 h.
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catalyst. Its separation from the catalyst cannot be effected easily
because of its low solubility in organic solvents.
128.8, 133.9, 141.0, 159.5; MS m/z(%): 184 (M+, 100), 169 (54), 141 (61),
115 (43). Anal. Calcd. for C13H12O: C 84.78, H 6.52%, found: C 84.76, H
6.54%.
Thus a new, efficient catalytic method was elaborated for the
coupling of arylmagnesium bromides or iodides with aryl halides
(especially bromides) using nickel(II) on Mg–La mixed oxide as
catalyst with good yield. The catalyst is easy separable from the
reaction mixture, thus the nickel contamination of the product can
be avoided.†
2-Trifluoromethyl-biphenyl:24 colorless liquid, 1H NMR (300 MHz,
CDCl3) d (ppm): 7.28–7.34 (m, 3H), 7.36–7.49 (m, 4H), 7.51–7.59 (m,
1H), 7.74 (d, 1H); 13C NMR (75 MHz, CDCl3) d (ppm): 124.3 (q), 125.9,
127.4, 127.6, 127.7, 128.6, 129.2, 131.2, 132.1, 140,1, 141.4; MS m/z(%):
222 (M+, 100), 201 (34), 153 (9). Anal. Calcd. for C13H9F3: C 70.27, H
4.05%, found: C 70.12, H 3.89%.
3-Trifluoromethyl-biphenyl:25 yellowish liquid, 1H NMR (300 MHz,
CDCl3) d (ppm): 7.36–7.67 (m, 6H), 7.76 (d, 1H), 7.81 (s, 1H); 13C NMR
(75 MHz, CDCl3) d (ppm): 124.0 (q), 127.3, 127.4, 128.2, 129.0, 129.1,
129.4, 130.6 ppm; MS m/z(%): 222 (M+, 100), 203 (6.1), 201 (13), 153
(24.7). Anal. Calcd. for C13H9F3: C 70.27, H 4.05%, found: C 70.21, H
3.96%.
Acknowledgements
The authors are grateful to Chinoin Pharmaceutical and Chemical
Works Ltd., member of the Sanofi-Aventis Group for the technical
4-Trifluoromethyl-biphenyl: white solid, m.p. 69–70 ◦C (lit.: 70–70,5 ◦C26),
13C NMR (75 MHz, CDCl3) d (ppm): 125.8 (q), 127.2, 127.4, 127.5, 128.3,
128.8, 129.1, MS m/z(%): 222 (M+, 100), 203 (7.9), 153 (22.8). Anal. Calcd.
for C13H9F3: C 70.27, H 4.05%, found: C 70.20, H 4.08%.
´
support, A. K. for the financial support as well.
4-Methyl-2¢-(trifluoromethyl)-biphenyl:27 colorless liquid, 1H NMR
(300 MHz, CDCl3) d (ppm): 2.43 (s, 3H), 7.21–7.25 (m, 4H), 7.33 (d,
1H), 7.46 (t, 1H), 7.56 (t, 1H), 7.78 (d, 1H); 13C NMR (75 MHz, CDCl3)
d (ppm): 21.2, 124.3 (q), 126.8, 127.4, 128.6, 128.8, 131.3, 132.3, 137.1,
137.5, 141.4; MS m/z(%): 236 (M+, 100), 201 (21), 165 (26), 91 (15). Anal.
Calcd. for C14H11F3: C 71.19, H 4.61%, found: C 71.28, H 4.57%.
4-Methyl-3¢-(trifluoromethyl)-biphenyl:28 colorless liquid, 1H NMR
(300 MHz, CDCl3) d (ppm): 2.41 (s, 3H), 7.28 (d, 2H), 7.46–7.64 (m,
4H), 7.74-7.81 (m, 1H), 7.85 (s, 1H); 13C NMR (75 MHz, CDCl3) d (ppm):
21.2, 123.8 (q), 124.3, 127.2, 129.0, 129.8, 130.3, 131.5, 137.8, 141.6; MS
m/z(%): 236 (M+, 100), 217 (6), 165 (31), 91 (13). Anal. Calcd. for C14H11F3:
C 71.19, H 4.61%, found: C 71.05, H 4.73%.
Notes and references
† Preparation of nickel(II)/magnesium-lanthanum mixed oxide:
Magnesium–lanthanum mixed oxide was prepared as described in
Reference 14. This mixed oxide (3.0 g) was suspended in 300 ml of
deionized water and 0.714 g nickel(II)-chloride hexahydrate was added
into the mixture. The suspension was stirred at room temperature for
24 h, then the light greenish solid was filtered out, washed with deionized
water and dried at 120 ◦C for 4 h. The catalyst was stored under argon
atmosphere. Before the experiments it was dried at 100 ◦C for 1 h. The
other catalysts were prepared analogously.
Reaction of phenylmagnesium bromide with bromobenzene: 0.25 g
(10 mmol) of magnesium turnings were added to 10 ml of diethyl ether,
then 1.06 ml (1.57 g, 10 mmol) of bromobenzene was added to the mixture
under vigorous stirring. After the complete dissolution of magnesium 0.2 g
of the catalyst and then another 1.06 ml of bromobenzene were added
and the mixture was stirred for 6 h under reflux. Then the mixture was
cooled, diluted with ether, the solid was filtered out, washed with ether or
with toluene, the filtrate was treated with 10 ml of water, the layers were
separated, the aqueous was washed with ether, the combined organic phase
was dried over anhydrous sodium sulfate, the solvent was evaporated. The
residue was examined by GC-MS.
4-Methyl-4¢-(trifluoromethyl)-biphenyl:29 colorless solid, m.p. 120 ◦C (lit.:
◦
1
121 C28), H NMR (300 MHz, CDCl3) d (ppm): 2.45 (s, 3H), 7.28 (m,
2H), 7.53 (m, 2H), 7.68 (s, 4H); 13C NMR (75 MHz, CDCl3) d (ppm):
21.1, 125.6 (q), 125.8, 127.2, 127.3, 129.2, 129.7, 137.1, 138.3, 144.6; MS
m/z(%): 236 (M+, 100), 217 (7), 165 (40), 152 (13), 91 (11). Anal. Calcd.
for C14H11F3: C 71.19, H 4.61%, found: C 71.25, H 4.59%.
4-Methoxy-4¢methyl-biphenyl: 1H NMR (300 MHz, CDCl3) d (ppm): 2.39
(s, 3H), 3.83 (s, 3H), 7.01 (m, 2H), 7.23 (m, 2H), 7.48 (m, 2H), 7.53 (m,
2H); 13C NMR (75 MHz, CDCl3) d (ppm): 21.1, 55.3, 114.3, 126.6, 127.7,
129.5, 133.7, 136.4, 138.1, 158.7; MS m/z(%): 198 (M+, 100), 183 (56), 128
(13), 77 (7). Anal. Calcd. for C14H14O: C 84.85, H 7.07%, found: C 84.75,
H 6.99%.
General procedure of the cross-coupling: 0.28 g (11.5 mmol) of magnesium
turnings were added to 20 ml of diethyl ether, then 13 mmol of aryl bromide
was added to the mixture under vigorous stirring. After the complete
dissolution of magnesium half the amount of the solvent was evaporated,
to the residue 0.2 g of the catalyst and then 10 mmol of the coupling
aryl bromide were added and the mixture was stirred for 3 h under reflux.
Then the mixture was cooled, diluted with ether, the solid was filtered out,
washed with ether or with toluene, the filtrate was treated with 10 ml of
water, the layers were separated, the aqueous layer was washed with ether,
the combined organic phase was dried over anhydrous sodium sulfate, the
solvent was evaporated. The residue was purified or examined by GC-MS.
Selected spectroscopic data:
3,4¢-Bis-(trifluoromethyl)-biphenyl: MS m/z(%): 290 (M+, 100), 271 (22),
241 (13), 221 (7), 219 (6), 201 (20), 152 (16), 145 (10), 120 (6), 95 (8). Anal.
Calcd. for C14H8F6: C 57.93, H 4.76%, found: C 57.75, H 4.56%.
1 P. Barbier, C. R. Acad. Sci., 1899, 128, 110–111.
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Biphenyl: white crystals, m.p.: 66–67 ◦C (hexane) (lit.: 67–68 C18); 1H
◦
NMR (300 MHz, CDCl3) d (ppm): 7.27–7.58 (m, 10H); 13C NMR
(75 MHz, CDCl3) d (ppm): 127.1, 127.2, 128.6, 141.1. Anal. Calcd. for
C12H10: C 93.51, H 6.49%, found: C 93.46, H 6.53%.
4-Methyl-biphenyl: white crystals, m.p.: 42–43 ◦C (diethyl ether) (lit.: 44–
◦
1
46 C19); H NMR (300 MHz, CDCl3) d (ppm): 2.38 (s, 3H), 7.24–7.41
(m, 5H), 7.48–7.57 (m, 4H); 13C NMR (75 MHz, CDCl3) d (ppm): 21.7,
127.2, 129.3, 129.8, 137.2, 139.0, 141.4. Anal. Calcd. for C13H12: C 92.86,
H 7.14%, found: C 93.01, H 7.08%.
9 O. Vechorkin, V. Proust, and X. Hu, J. Am,. Chem. Soc. 2009,
10.1021/ja9027378.
2-Methoxy-biphenyl:20 colorless oil, 1H NMR (300 MHz, CDCl3) d (ppm):
3.80 (s, 3H), 7.23–7.61 (m, 9H); 13C NMR (75 MHz, CDCl3) d (ppm):
55.2, 111.5, 120.3, 127.0, 127.9, 128.8, 129.9, 130.7, 130.9, 138.4, 156.5;
MS m/z(%): 184 (M+, 100), 169 (54), 141 (51). Anal. Calcd. for C13H12O:
C 84.78, H 6.52%, found: C 84.86, H 6.50%.
10 J. Terao, H. Watanabe, A. Ikumi, H. Kuniyasu and N. Kambe, J. Am.
Chem. Soc., 2002, 124, 4222.
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