Oxovanadium(V)-Induced Cross-Coupling Reaction between Two Ligands of Organozinc Compounds

Article abstract of DOI:10.1021/jo9919106

Oxovanadium(V) compounds such as VO(OEt)Cl₂ serve as useful oxidants for organozinc compounds, providing the corresponding cross-coupling products derived from two ligands of organozinc compounds. In particular, triorganozincates undergo selective cross-coupling smoothly by the action of oxovanadium(V).

Full text of DOI:10.1021/jo9919106

J . Org. Chem. 2000, 65, 1511-1515
1511
Oxova n a d iu m (V)-In d u ced Cr oss-Cou p lin g Rea ction betw een Tw o
Liga n d s of Or ga n ozin c Com p ou n d s
Toshikazu Hirao,* Takashi Takada, and Akiya Ogawa
Department of Applied Chemistry, Faculty of Engineering, Osaka University,
Yamada-oka, Suita, Osaka 565-0871, J apan
Received December 14, 1999
Oxovanadium(V) compounds such as VO(OEt)Cl2 serve as useful oxidants for organozinc compounds,
providing the corresponding cross-coupling products derived from two ligands of organozinc
compounds. In particular, triorganozincates undergo selective cross-coupling smoothly by the action
of oxovanadium(V).
Sch em e 1
In tr od u ction
Organozinc compounds, which can tolerate a broad
range of functionalities,1 are useful synthetic intermedi-
ates, and their chemistry has been developed intensively
in recent years.2 In particular, cross-coupling reactions
of organozinc reagents catalyzed by transition metal salts
provide versatile synthetic tools in organic syntheses.3
In these reactions, the substituents on zinc couple with
electrophilic species such as organic halides; however,
examples of the selective cross-coupling of two ligands
of organozinc compounds are limited to a few cases, which
include effective carbon-carbon bond forming reaction
via 1,2-migration of zincate carbenoids and intramolecu-
lar coupling reaction of organozinc compounds by orga-
nocopper reagents.4 Thus, the development of such a
selective coupling of the ligands of zinc reagents is one
of the most challenging subjects in organozinc chemistry.
To accomplish this transformation, oxidation of orga-
nozinc compounds has been investigated in detail, and
the desired coupling of organozinc compounds, which was
found to take place by the action of oxovanadium(V)
compounds as the oxidants (Scheme 1), is described in
this paper.
Ta ble 1. Cou p lin g Rea ction of Or ga n ozin c Com p ou n d
2a w ith Oxid a n ts
Resu lts a n d Discu ssion
Cr oss-Cou p lin g Rea ction of Or ga n ozin c Com -
p ou n d s 2 w ith Oxid a n ts. Table 1 represents the results
of the reaction of the organozinc compound 2a with a
variety of oxidants. Owing to the property that orga-
nozinc compounds are subject to undergo the Schlenk
(1) (a) Guijarro, A.; Rosenberg, D. M.; Rieke, R. D. J . Am. Chem.
Soc. 1999, 121, 4155. (b) Thorn, S. N.; Gallagher, T. Synlett 1996, 185.
(c) Lipshutz, B. H.; Wood, M. R.; Tiroda, R. J . Am. Chem. Soc. 1995,
117, 6126.
(2) For recent reviews of syntheses of organozinc compounds, see:
(a) Knochel, P.; Langer, F.; Longeau, A.; Rottla¨nder, M.; Stu¨demann,
T. Chem. Ber. 1997, 130, 1021. (b) Knochel, P.; Singer, R. D. Chem.
Rev. 1993, 93, 2117.
(3) (a) Oshima, K. Transition Metal Catalyzed Reactions of Orga-
nozinc Compounds, In Advance in Organometallic Chemistry; Liebi-
skind, L. S., Ed.; J AI Press: London, 1991; Vol. 2, p 101. (b) Erdik, E.
Tetrahedron 1992, 48, 9577.
(4) (a) Iyoda, M.; Kabir, S. M. H.; Vorasingha, A.; Kuwatani, Y.;
Yosihda, M. Tetrahedron Lett. 1998, 39, 5393. For coupling reactions
of substituents on zinc via 1,2-migration of zincate carbenoids, see:
(b) Harada, T.; Iwazaki, K.; Hara, D.; Hattori, K.; Oku, A. J . Org. Chem.
1997, 62, 8966. (c) Harada, T.; Katsuhira, T.; Katsuhira, T.; Osada,
A.; Iwazaki, K.; Maejima, K.; Oku, A. J . Am. Chem. Soc. 1996, 118,
11377 and references therein.
equilibrium,5 isolation of mixed diorganozinc compounds
such as 2a was very difficult, and therefore the orga-
nozinc compound was prepared in situ by transmetala-
tion of the corresponding alkylzinc halide with the
aryllithium. The reaction of (2-methoxyphenyl)methyl-
zinc (2a ) with Cp2FePF6 afforded the homo-coupling
(5) For discussion of the Schlenk equilibrium of organozinc com-
pounds, see: (a) Charette, A. B.; Marcoux, J .-F. J . Am. Chem. Soc.
1996, 118, 4539 and references therein. (b) Andre´, B. C.; Andre´ B.;
Marcoux, J .-F. J . Am. Chem. Soc. 1998, 120, 5114.
10.1021/jo9919106 CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/12/2000

1512 J . Org. Chem., Vol. 65, No. 5, 2000
Hirao et al.
Ta ble 2. Cou p lin g Rea ction of Or ga n ozin c Com p ou n d s
2 w ith Oxova n a d iu m (V) Com p ou n d s
Sch em e 2
compound 4a selectively. The result prompted us to
investigate the coupling by use of other oxidants. Among
the oxidants employed, AgBF4 served as a useful oxidiz-
ing agent to give the desired cross-coupling compound
3a , probably via a one-electron oxidation process. More
6
interestingly, the use of VO(OEt)Cl2 instead of AgBF4
dramatically improved the yield of 3a (Table 1). The
present coupling reaction of organic ligands of organozinc
compounds also proceeded successfully in the Schlenk
equilibrium between two kinds of diorganozinc com-
pounds (Scheme 2). Whether this reaction occurs by
intramolecular or intermolecular process is not clear, but
this result indicates that the cross-coupling reaction
proceeds in preference to the homo-coupling one.
Oxova n a d iu m (V)-In d u ced Cr oss-Cou p lin g Rea c-
tion of Dior ga n ozin c Com p ou n d s 2. The oxidative
coupling of organozinc compounds 2a and 2b was exam-
ined by using oxovanadium(V) compounds. In the case
of the reaction of 2 with VO(OEt)Cl2, the cross-coupling
compound 3 was obtained as the major product with high
selectivity (Table 2, entry 3). Moreover, when 3.0 equiv
of VO(OEt)Cl2 was used, the best yield of 3 was attained,
whereas the reaction using isopropoxy oxovanadium(V)
reagents was accompanied by the formation of the homo-
coupling product 4 (entries 4 and 5). The oxidative
reaction with a combination of VO(OEt)Cl2 and Me3-
SiOTf 7 gave a complex mixture, and the coupling com-
pound 3 was produced in a lower yield (entry 6).
This method was successfully applied to various orga-
nozinc compounds, affording the corresponding coupling
products in good yields (Table 3). The coupling reaction
of organozinc compounds bearing an o-methoxy, o-phenyl,
or o-methylthio group on the arene ring proceeded
smoothly at room temperature to give good yields of the
cross-coupling products (Table 3, entries 1, 2, 5, and 9).
In contrast, o-cyano-substituted aryl alkylzinc compound
2d exhibited lower reactivity toward the oxidative cou-
pling with VO(OEt)Cl2 (entry 6). However, while an
organoaluminum compound having an electron-with-
drawing substituent did not undergo oxidative coupling
with oxovanadium(V), the corresponding organozinc com-
pound was oxidized to the cross-coupling compound 3d
exclusively. The cross-coupling reaction of organozinc
compounds having an ortho-substituent proceeded ef-
ficiently, whereas the oxidative reaction of 2e and 2i,
with less steric hindrance, preferentially gave a substan-
tial amount of the homo-coupling compounds 4e and 4i,
respectively (entries 7 and 13). The reaction of 2f having
an m-methoxy group led to the recovery of the starting
material, because the bromine-lithium exchange reac-
tion did not take place and the corresponding organozinc
compound could not be prepared (entry 8). It should be
noted that, in addition to the methyl group, an n-butyl
or 1-alkynyl group could couple with the aryl group
successfully, as shown in Table 3 (entries 3, 4, 10, and
11). On the other hand, the cross-coupling with a vinyl
group was inefficient, and sterically hindered sec- and
tert-butyl groups could not couple with aryl groups at all.
Oxid a tive Cr oss-Cou p lin g Rea ction of Tr ior ga -
n ozin ca tes 6. It is expected that triorganozincates 6 may
undergo the more facile oxidation with oxovanadium(V)
compounds, compared with diorganozinc compounds 2.
Actually, as shown in Table 4, the cross-coupling reaction
of triorganozincates using VO(OEt)Cl2 proceeded very
smoothly to give the corresponding cross-coupling com-
pounds 3 in high yields. When diethylzinc was used, gas
evolution was observed with the moderate yield of 3.
Selective cross-coupling reaction between alkyl groups
and o-methoxy-substituted aryl groups occurred when 6.0
equiv of AgBF4 was used instead of the oxovanadium(V)
compound. In this case, an excess of AgBF4 seems to be
essential because AgBF4 is less soluble in ether. After
the reaction was complete, Ag(0) was detected in the
reaction mixture. The result suggests that the cross-
coupling reaction is induced by one-electron oxidation
with Ag(I).
(6) (a) Ishikawa, T.; Ogawa, A.; Hirao, T. J . Am. Chem. Soc. 1998,
120, 5124. (b) Ishikawa, T.; Nonaka, S.; Ogawa, A.; Hirao, T. Chem.
Commun. 1998, 1209. (c) Ishikawa, T.; Ogawa, A.; Hirao, T. J .
Organomet. Chem. 1999, 575, 76.
(7) The order of the reactivity of vanadium reagents is VO(OR)Cl2-
AgOTf or Me3SiOTf > VO(OR)Cl2 > VO(OR)3 > VO(acac)2. Hirao, T.;
Mori, M.; Ohshiro, Y. Bull. Chem. Soc. J pn. 1989, 62, 2399. Hirao, T.;
Mori, M.; Ohshiro, Y. J . Org. Chem. 1990, 55, 358. Hirao, T.; Mori,
M.; Ohshiro, Y. Chem. Lett. 1991, 783.
More interestingly, the preparation of the zincate
complexes by the halogen-zinc exchange reaction with
triorganozincates8 dramatically improved the product
selectivity: when zincate complex 6, prepared by iodine-
zinc exchange reaction with Me3-ZnLi, was oxidized by

Oxovanadium(V) Cross-Coupling of Organozinc Ligands
J . Org. Chem., Vol. 65, No. 5, 2000 1513
a
Ta ble 3. Cr oss-Cou p lin g Rea ction of Or ga n ozin c Com p ou n d s 2 w ith VO(OEt)Cl2
Ta ble 4. Cr oss-Cou p lin g Rea ction of Tr ior ga n ozin ca tes 6 w ith VO(OEt)Cl2 or AgBF 4
VO(OEt)Cl2, the corresponding cross-coupling compound
reagents in the preparation step of the zincates 6. When
the organozinc compounds were prepared from organo-
lithiums and zinc halides or dialkylzincs, most probably,
the homo-coupling may proceed via the oxidation of
was obtained exclusively in high yield without formation
of any homo-coupling products (Table 5). This reaction
does not involve the aryllithium derivatives as starting

1514 J . Org. Chem., Vol. 65, No. 5, 2000
Hirao et al.
Ta ble 5. Cr oss-Cou p lin g Rea ction of Tr ior ga n ozin ca tes
then quickly replaced with a distillation head, and the solvent
was removed at atmospheric pressure. The product was
distilled under reduced pressure to give the corresponding
oxovanadium(V) compound as a yellow/orange liquid.
Dich lor o(eth oxy)oxova n a d iu m (V), 78%, bp 55-60 °C/5
mmHg [1801-77-0]; d ich lor o(isop r op oxy)oxova n a d iu m (V),
75%, bp 59-62 °C/3 mmHg [1636-01-7]; ch lor o(d iisop r o-
p oxy)oxova n a d iu m (V), 83%, bp 55-58 °C/1 mmHg [1636-
00-6].
a
6 P r ep a r ed fr om Ar yl Iod id es 7 w ith VO(OEt)Cl2
P r ep a r a tion of 2-Meth oxy-1-m eth yln a p h th a len e (1g).
To a solution of 1-bromo-2-naphthol (2.23 g, 10.0 mmol) in dry
THF (50 mL) was added sodium hydride (0.36 g, 15.0 mmol)
followed by methyl iodide (5.7 g, 40.0 mmol) at room temper-
ature. The mixture was stirred for 24 h at room temperature,
the reaction mixture was quenched with water. The mixture
was extracted with ether, which was dried over MgSO4 and
evaporated under reduced pressure. The residue was purified
by column chromatography over silica gel eluting with hex-
ane-ether (9:1) to give 1g (1.70 g, 72%, Rf ) 0.7).
Rep r esen ta tive P r oced u r e for Oxid a tive Cou p lin g
Rea ction of Dior ga n ozin c Der iva tive 2 (Ta ble 3). To a
stirred solution of the aryl bromide 1a (187 mg, 1.0 mmol) in
dry ether (2.0 mL) under argon at room temperature was
added n-BuLi (1.1 mmol, 0.71 mL, 1.54 M in hexane) to
generate the corresponding aryllithium. After the mixture
stirred for 10 min at room temperature, MeZnCl (1.5 mmol,
0.75 mL, 2.0 M in THF) was added dropwise to the resulting
solution at 0 °C. After stirring for 30 min at 0 °C, the resulting
solution of 2a was added to a solution of VO(OEt)Cl2 (549 mg,
3.0 mmol) in dry ether (2.0 mL) at room temperature. The
mixture was stirred for 3 h at room temperature, and then
ether and 1.5 M aqueous HCl were added to the reaction
mixture. After extraction with ether, the combined organic
layer was washed with brine, dried over MgSO4, and concen-
trated under reduced pressure. The residue was purified by
column chromatography on silica gel eluting with hexane-
ether (4:1) to give 3a (63 mg, 52%, Rf ) 0.6) and 4a (27 mg,
25%, Rf ) 0.4). The products were identified by comparison of
spectral data with those of the authentic samples. 1-Octynyl-
zinc chloride was prepared from 1-octynyllithium (1.1 mmol),
which was prepared from 1-octyne (121 mg, 1.1 mmol) and
n-BuLi (1.1 mmol, 0.71 mL, 1.54 M in hexane) in dry ether
(2.0 mL), and ZnCl2 (217 mg, 1.5 mmol) in dry THF (1.0 mL).
Trimethylsilylethynylzinc chloride was similarly prepared.
n-Butylzinc chloride was prepared from n-BuLi (1.5 mmol, 0.97
mL, 1.54 M in hexane) and ZnCl2 (217 mg, 1.5 mmol) in dry
THF (1.0 mL).
organolithium compounds remaining in situ.9 Thus, the
selective synthesis of cross-coupling compounds was
accomplished, where the coupling reaction of aryl com-
pounds having functional groups such as isopropoxycar-
bonyl and nitro groups was found to proceed efficiently.
Con clu sion
In summary, we have demonstrated that organozinc
compounds undergo oxovanadium(V)-promoted cross-
coupling reactions. This novel approach for selective
cross-coupling of organozinc compounds realizes the
carbon-carbon bond formation between sp2 carbon (aryl
group) and sp carbon (alkynyl group) or sp3-carbon (alkyl
group). Although the mechanism of these coupling reac-
tions is still ambiguous, we are presuming that the
reactions proceed by either a process of one-electron
transfer between organozinc compounds and oxovanadi-
um(V) or transmetalation. We are currently developing
the application of these reactions to some other organo-
metallics and investigating several reactions for consid-
ering the reaction mechanism.
2-Meth yla n isole (3a ), [578-58-5]; 2,2′-d im eth oxybip h e-
n yl (4a ), [4877-93-4]; 2-p h en yltolu en e (3b), [643-58-3];
o-qu a ter p h en yl (4b), [641-96-3]; 1-m eth yl-2-(m eth ylth io)-
ben zen e (3c), [14092-00-3]; o-t olu n it r ile (3d ), [529-19-1];
4-m eth yl-a n isole (3e), [104-93-8]; 4,4′-d im eth oxybip h en yl
(4e), [2132-39-0]; 2-m eth oxy-1-m eth yln a p h th a len e (3g),
[1130-80-9]; 1-m eth yln a p h th a len e (3h ), [90-12-0]; 1,1′-bi-
n a p h th yl (4h ), [604-53-5]; 2-m eth yln a p h th a len e (3i), [91-
57-6]; 2,2′-b in a p h t h yl (4i), [612-78-2]. 2-(1-Oct yn yl)-1-
p h en ylben zen e (3j): colorless oil; 1H NMR (300 MHz, CDCl3)
δ 7.58-7.62 (m, 2 H), 7.51-7.54 (m, 1 H), 7.24-7.45 (m, 6 H),
2.23 (t, 2 H, J ) 6.9 Hz), 1.43-1.52 (m, 2 H), 1.19-1.35 (m, 6
H), 0.90 (t, 3 H, J ) 6.9 Hz); 13C NMR (75 MHz, CDCl3) 143.6,
140.8, 133.0, 129.4, 129.3, 127.7, 127.6, 127.2, 126.9, 122.4,
Exp er im en ta l Section
Gen er a l Meth od s. All reagents are of commercial quality.
All solvents were freshly distilled under argon over an ap-
propriate drying agent before use. The bromonaphthalene
derivative 1g was prepared according to the standard proce-
dure.10
Gen er a l P r oced u r e for P r ep a r a tion of Oxova n a d iu m -
(V) Com pou n ds.11 To a 200 mL round-bottomed flask equipped
with a condenser, magnetic stirring bar, and septum was
added hexane (20 mL) under argon, followed by trichlorooxo-
vanadium(V) (100 g, 54.3 mL, 0.58 mol). Then, the dry
corresponding alcohol (1.1 or 2.2 equiv) was added dropwise
to the solution. During the addition, argon was flowed to
remove HCl evolved from the reaction. After the addition was
complete, the mixture was stirred for 1 h. The condenser was
93.5, 80.2, 31.6, 28.7, 28.6, 22.7, 19.7, 14.3; IR (neat) 2227 cm-1
MS (EI) m/z 262 (94, M+), 191 (100), 178 (48). Anal. Calcd for
20H22: C, 91.28; H, 8.33. Found: C, 91.55; H, 8.45. 1-P h en yl-
;
C
2-{2-(tr im eth ylsilyl)eth yn yl}ben zen e (3k ), [147492-79-
2]; 1-b u t yl-2-m et h oxyn a p h t h a len e (3l), [99287-89-5].
2-Meth oxy-1-(1-octyn yl)n a p h th a len e (3m ): pale yellow oil;
1H NMR (300 MHz, CDCl3) δ 8.17-8.21 (m, 1 H), 7.67-7.70
(m, 2 H), 7.41-7.46 (m, 1 H), 7.25-7.31 (m, 1 H), 7.15 (d, 1 H,
J ) 9.0 Hz), 3.93 (s, 3 H), 2.56 (t, 2 H, J ) 6.9 Hz), 1.62-1.71
(m, 2 H), 1.45-1.54 (m, 2 H), 1.26-1.32 (m, 4 H), 0.83-0.87
(m, 3 H); 13C NMR (75 MHz, CDCl3) 158.4, 134.8, 129.1, 128.6,
128.0, 127.0, 125.4, 124.0, 112.7, 107.2, 100.5, 74.7, 56.7, 31.6,
(8) For the preparation of zincate complex by halogen-zinc exchange
reactions, see: Kondo, Y.; Takazawa, N.; Yamazaki, C.; Sakamoto, T.
J . Org. Chem. 1994, 59, 4717.
(9) Ishikawa, T.; Ogawa, A.; Hirao, T. Organometallics, 1998, 17,
5713.
(10) Onoda, M.; Kawai, M.; Izumi, Y. Bull. Chem. Soc. J pn. 1986,
59, 1761.
(11) (a) Funk, H.; Weiss, W.; Zeising, M. Z. Anorg. Allg. Chem. 1958,
36, 296. (b) Hirao, T.; Mori, M.; Ohshiro, Y. Bull. Chem. Soc. J pn. 1989,
62, 2399.
29.2, 28.9, 22.8, 20.4, 14.3; IR (neat) 2223, 1272, 1065 cm-1
MS (EI) m/z 266 (100, M+), 251 (4), 197 (32), 181 (11), 158
;

Oxovanadium(V) Cross-Coupling of Organozinc Ligands
J . Org. Chem., Vol. 65, No. 5, 2000 1515
(13). Anal. Calcd for C19H22O: C, 84.81; H, 8.32. Found: C,
84.67; H, 8.42.
mixture was stirred for 2 h at room temperature, and then
ether and 1.5 M aqueous HCl were added to the reaction
mixture. After extraction with ether, the combined organic
layer was washed with brine, dried over MgSO4, and concen-
trated under reduced pressure. The residue was purified by
column chromatography on silica gel eluting with hexane-
ether (3:1) to give 3n (65 mg, 70%, Rf ) 0.7, [14804-32-1]) and
4a (3 mg, 4%).
1-Eth yl-2-m eth oxyn a p h th a len e (3p ), [17295-03-3].
Rep r esen ta tive P r oced u r e for Oxid a tive Cou p lin g
Rea ction of Tr ior ga n ozin ca te 6 P r ep a r ed fr om Ar yl
Iod id e 7 (Ta ble 5). To a stirred solution of the aryl iodide 7a
(117 mg, 0.5 mmol) in dry THF (1.0 mL) under argon at 0 °C
was added Me3ZnLi, which was prepared from MeLi (2.25
mmol, 2.25 mL, 1.02 M in ether) and ZnCl2 (102 mg, 0.75
mmol) in dry THF (1.0 mL). After stirring for 2 h at 0 °C, VO-
(OEt)Cl2 (549 mg, 3.0 mmol) was added to the resulting
solution of 6a at 0 °C. The mixture was stirred for 10 h at
room temperature, and then ether and 1.5 M aqueous HCl
were added to the reaction mixture. After extraction with
ether, the combined organic layer was washed with brine, dried
over MgSO4, and concentrated under reduced pressure. The
residue was purified by column chromatography on silica gel
eluting with hexane-ether (4:1) to give 3a (101 mg, 83%, Rf
) 0.5). The products were identified by comparison of spectral
data with those of the authentic samples.
Rep r esen ta tive P r oced u r e for Oxid a tive Cou p lin g
Rea ction s of Dior ga n ozin c Der iva tive 6 (Ta ble 4). To a
stirred solution of the aryl bromide 1a (187 mg, 1.0 mmol) in
dry ether (2.0 mL) under argon at room temperature was
added n-BuLi (1.1 mmol, 0.71 mL, 1.54 M in hexane) to
generate the corresponding aryllithium. After the solution
stirred for 10 min at room temperature, Me2Zn (1.2 mmol, 1.2
mL, 1.0 M in hexane) was added dropwise to the resulting
solution at 0 °C. After stirring for 30 min at 0 °C, the resulting
solution of 6a was added to a solution of VO(OEt)Cl2 (549 mg,
3.0 mmol) in dry ether (2.0 mL) at room temperature. The
mixture was stirred for 3 h at room temperature, and then
ether and 1.5 M aqueous HCl were added to the reaction
mixture. After extraction with ether, the combined organic
layer was washed with brine, dried over MgSO4, and concen-
trated under reduced pressure. The residue was purified by
column chromatography on silica gel eluting with hexane-
ether (4:1) to give 3a (72 mg, 59%) and 4a (23 mg, 22%). The
products were identified by comparison of spectral data with
those of the authentic samples. Di-n-butylzinc was prepared
from n-BuLi (2.2 mmol, 1.4 mL, 1.5 M in hexane) and ZnCl2
(136 mg, 1.0 mmol) in dry THF (2.0 mL).
Bip h en yl-2,2′-d ica r bon itr ile (4d ), [4341-02-0]; 2-bu tyl-
a n isole (3o), [18272-72-5].
Rep r esen ta tive P r oced u r e for Oxid a tive Cou p lin g
Rea ction w ith AgBF 4. To a stirred solution of the aryl
bromide 1a (0.68 mmol) in dry ether (1.4 mL) under argon at
room temperature was added n-BuLi (0.75 mmol, 0.49 mL,
1.54 M in hexane) to generate the corresponding aryllithium.
After the solution stirred for 10 min at room temperature, Et2-
Zn (0.75 mmol, 0.75 mL, 1.0 M in hexane) was added dropwise
to the resulting solution at 0 °C. After stirring for 10 min at 0
°C, the resulting solution of 6n was added to a solution of
AgBF4 (801 mg, 4.1 mmol, 6.0 equiv) in dry ether at 0 °C. The
Isop r op yl 2-m eth ylben zoa te (3q), [943-13-2]; 4-n itr o-
tolu en e (3r ), [99-99-0].
Ack n ow led gm en t. The use of the facilities of the
Analytical Center, Faculty of Engineering, Osaka Uni-
versity is acknowledged. This work was partly sup-
ported by a Grant-in-Aid for Scientific Research from
the Ministry of Education, Science, and Culture, J apan.
J O9919106