914
OCOMe
O
Table 2. Cross-coupling of arylboronic acids with aryl carbon-
OAc
atesa
+
+
Ph B(OH)2
2a
(0.10 mmol)
Et
[Ni(cod)2] (10%), DCyPF (10%)
Ar1 OCOMe
1d (0.40 mmol)
[Ni(cod)2] (10 µmol)
1c' (0.40 mmol)
2
Ar B(OH)2
Ar1 Ar2
+
K2CO3, Toluene, 60 °C
O
1
2
3
Ph
Ph
Ligand (10 or 20 µmol)
2a: Ar2 = Ph
1a: Ar1 = 4-(MeO)C6H4
1b: Ar1 = 4-(t-BuO2C)C6H4
1c: Ar1 = 2-naphthyl
+
2b: Ar2 = 4-(MeO)C6H4
2c: Ar2 = 4-(F3C)C6H4
2d: Ar2 = 2-MeC6H4
K2CO3 (0.20 mmol)
Toluene, 60 °C
Et
3h
3c
Ligand = PCy3 (24 h)
4%
25%
6%
Entry
1
1
2
Time/h
96
Product (3)
Yield/%b
46
Ligand = DCyPF (30 min)
22%
3a
1a 2a
1b 2a
MeO
Scheme 1. Competitive experiment of the cross-coupling
reaction.
3bc
2
72
71
EWG
In the precedent work,5,10 PCy3 is the preferable ligand
to the nickel-catalyzed cross-coupling reaction involving the
cleavage of the inert C(sp2)-O bond. However, the results of
Table 1 indicate that the monophosphine is useless for the
reaction of aryl carbonates. The aryl carbonates were allowed to
couple with the arylboronic acids by using bidentate ligand,
DCyPF. In order to clarify the difference in reactivity between
PCy3- and DCyPF-nickel catalyst, we conducted a set of
competitive experiments using an equimolar mixture of carbon-
ate 1d and acetate 1c¤ (Scheme 1). In the competitive experiment
with PCy3, formation of 3c prevailed over that of 3h. However,
use of DCyPF ligand led to preferential formation of 3h. The
observations indicate that the PCy3-nickel complex is favorable
for the C-O bond cleavage of aryl acetates but cannot activate
the C-O bond of aryl carbonates. In contrast, coordination
of DCyPF ligand enables the nickel catalyst to undergo the
oxidative addition of aryl carbonates, but the reaction with the
acetates might be restrained by use of the bidentate bisphos-
phine.14 Although the detailed mechanism of the reaction is
unclear, the chemoselectivities of the nickel catalysts may be
governed by the number of phosphorus atoms on the nickel atom
in the active catalyst species.5d
3
1c 2a
1c 2a
24
96
83
80
4d
3c
5e
6
1b 2b
1c 2b
1c 2c
1c 2d
72
48
48
96
EWG
OMe
3dc
82
95
64
63
OMe
3e
7
CF3
3f
Me
8
3g
aReactions were conducted on a 0.50 mmol scale in 1.0 mL
of toluene. The ratio of 1:2:[Ni(cod)2]:ligand:base was
10:12:1:1:20. bIsolated yields. cEWG- = t-BuO2C-. dThe
reaction was conducted with 5% catalyst loading. eThe
reaction was conducted on a 0.20 mmol scale.
1a to phenol 4. The side reaction took precedence over the
desired cross-coupling, when the reaction was conducted in
polar solvent (Entries 11-14) as well as with a stronger and/or
more soluble base (Entries 15-20). Raising the reaction temper-
ature also facilitated the undesirable formation of 4 and
disfavored the cross-coupling (Entry 21). The cross-coupling
product 3a was obtained in 46% isolated yield from the reaction
carried out for 96 h (Table 2, Entry 1).
The [Ni(cod)2]-DCyPF catalyst was applied to the synthesis
of various biaryl compounds (Table 2). As with typical cross-
coupling reactions, electron-deficient aryl carbonates 1b and 1c
were more reactive than electron-rich 1a, affording the coupling
products 3b and 3c in good yields (Entries 2 and 3). The reaction
of 1c with 2a proceeded without significant loss of the yield of
3c when the catalyst loading was reduced to 5 mol % (Entry 4).
In contrast to the electrophilic substrate, the reactivity of
arylboronic acid was increased by the electron-donating group
on the aromatic ring. p-Methoxyphenylboronic acid (2b) reacted
with 1c to give the product 3e in 95% yield (Entry 6).
Meanwhile, the trifluoromethyl group of 2c seemed to cause
decrease in the yield of cross-coupling product (Entry 7).
o-Substituted arylboronic acid 2d worked as a coupling partner
of aryl carbonates (Entry 8).
In summary, we have developed a new effective catalyst for
the Suzuki-Miyaura reaction of aryl carbonates. The carbonate
electrophiles couple with arylboronic acids through [Ni(cod)2]-
DCyPF catalyst, giving biaryl compounds in good yields. The
nickel catalyst enables the organoborons to react with non-
benzo-fused aryl carbonates.15
This work was supported by Grant-in-Aid for the Grobal
COE Program, “Science for Future Molecular Systems” from
MEXT.
This paper is in celebration of the 2010 Nobel Prize
awarded to Professors Richard F. Heck, Akira Suzuki, and
Ei-ichi Negishi.
References and Notes
1
a) Metal-Catalyzed Cross-Coupling Reactions, Second Com-
pletely Revised and Enlarged Edition, ed. by A. de Meijere,
F. Diederich, Wiley-VCH, Weinheim, 2004, Vols. 1-2. b)
Cross-Coupling Reactions. A Practical Guide, ed. by N.
Miyaura, Springer-Verlag, Berlin, 2002. c) J. Hassan, M.
Sévignon, C. Gozzi, E. Schulz, M. Lemaire, Chem. Rev.
Chem. Lett. 2011, 40, 913-915
© 2011 The Chemical Society of Japan
Kuwano, Ryoichi
