Communications
DOI: 10.1002/anie.200801447
Cross-Coupling Reactions
Nickel-Catalyzed Cross-Coupling of Aryl Methyl Ethers with Aryl
Boronic Esters**
Mamoru Tobisu,* Toshiaki Shimasaki, and Naoto Chatani*
Palladium- and nickel-catalyzed cross-coupling reactions
have been recognized as an indispensable tool for current
organic synthesis.[1] Among these reactions, Suzuki–Miyaura
coupling[2–7] is, arguably, of the greatest practical importance
of these methods because of the attractive features of
organoboronic acids: widespread availability, stability to air
and moisture, and low toxicity. Recently, tremendous progress
has been made in the development of more elaborate catalyst
systems that allow the couplings to be conducted at room
temperature,[3] to use unreactive chlorides,[4] and to use alkyl
electrophiles.[5,6] Despite these significant advances, the
electrophilic coupling partner for use in Suzuki–Miyaura
coupling remains limited, for the most part, to organic halides
and sulfonates; although the use of less available electro-
philes, including diazonium salts,[7a] ammonium salts,[7b] aryl-
triazene/BF3,[7c] azoles,[7d] and phosphonium salts[7e] has been
reported. Aryl methyl ethers, which are as readily available as
aryl halides, have never been used in the Suzuki–Miyaura
coupling reaction, except for the ruthenium-catalyzed
system,[8] which requires a ligating group at the ortho position
for the reaction to proceed. Herein, we describe a method for
the nickel-catalyzed cross-coupling of aryl methyl ethers with
boronic esters [Eq. (1)].
Wenkert[9a,b] and Dankwardt[9c] in the nickel-catalyzed reac-
tion with Grignard reagents (i.e., Kumada–Tamao–Corriu-
type coupling). Although functional-group compatibility and
availability of the starting Grignard reagents for these initial
methods are rather limited, these pioneering studies offer a
starting point for the development of cross-coupling reactions
between aryl methyl ethers and organoboron reagents. Thus,
we investigated the reaction of 2-methoxynaphthalene (1a)
with organoboron compounds in the presence of a catalytic
amount of [Ni(cod)2] (cod = cycloocta-1,5-diene) and PCy3
(Table 1). Whereas attempts with boronic acid (Table 1,
entry 1) and borates (Table 1, entries 2 and 3) were unsuc-
cessful, cross-coupling with boronic ester 2a furnished the
product in modest yield (Table 1, entry 4). Although the
Table 1: Optimization of reaction conditions.[a]
Entry Organoboron compd. Base
T [8C] Solvent Yield [%][b]
1[c]
2
3
PhB(OH)2
PhBF3K
NaBPh4
2a
2a
2a
NaOH 80
NaOEt 80
NaOEt 80
NaOEt 80
dioxane
dioxane
dioxane
dioxane 64
dioxane 54
dioxane 47
toluene 89
toluene 93
0
0
8
The advantages of using aryl alkyl ethers in the metal-
catalyzed cross-coupling reaction have been documented by
4
5
CsF
CsF
CsF
CsF
80
80
80
120
6[d]
7[d]
8[d]
2a
2a
[*] Dr. M. Tobisu, Dr. T. Shimasaki
[a] Reaction conditions: 1a (0.5 mmol), organoboron compound
(0.6 mmol), [Ni(cod)2] (0.05 mmol), PCy3 (0.10 mmol), NaOEt
(0.75 mmol) or CsF (2.25 mmol), toluene (1.5 mL) in a sealed tube.
[b] Yields of 2-phenylnaphthalene measured by GC. [c] Toluene/H2O=
3:1 was used as a solvent. [d] PCy3 (0.20 mmol) and 2a (0.75 mmol)
were used.
Frontier Research Base for Global Young Researchers
Graduate School of Engineering, Osaka University
Suita, Osaka 565-0871 (Japan)
Fax: (+81)6-6879-7396
E-mail: tobisu@chem.eng.osaka-u.ac.jp
Prof. Dr. N. Chatani
Department of Applied Chemistry
Faculty of Engineering, Osaka University
Suita, Osaka 565-0871 (Japan)
Fax: (+81)6-6879-7396
reaction did not proceed in the absence of base, the use of a
mild base (CsF) proved reasonably effective (Table 1,
entry 5). Ligand screening did not lead to a fruitful result
(none: 0%, PtBu3: 0%, PtBu2Me: 22%, P(cylopentyl)3: 13%,
PMe3: 0%, PPh3: 0%, dmpe: 0%, binap: 0%, IPr·HCl: 0%;
E-mail: chatani@chem.eng.osaka-u.ac.jp
[**] This work was carried out on the Program of Promotion of
Environmental Improvement to Enhance Young Researchers’
Independence, the Special Coordination Funds for Promoting
Science and Technology, Ministry of Education, Culture, Sports,
Science and Technology (MEXT) (Japan). We also thank the
Instrumental Analysis Center, Faculty of Engineering, Osaka
University, for their assistance with the MS, HRMS, and elemental
analyses.
dmpe = 1,2-bis(dimethylphosphanyl)ethane,
binap = 2,2’-
bis(diphenylphosphanyl)-1,1’-binaphthyl). However, product
yield was improved when toluene was used as the solvent:
89% at 808C (Table 1, entry 7) and 93% at 1208C (Table 1,
entry 8).
Steric bulk of the substituents at the ether oxygen atom
had a significant effect on the efficiency of the cross-coupling
Supporting information for this article is available on the WWW
4866
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2008, 47, 4866 –4869