788
Bull. Chem. Soc. Jpn. Vol. 84, No. 7, 788-790 (2011)
Short Articles
Table 1. Screening of Reaction Parameters for Copper(I)-
Catalyzed O-Arylation of p-Bromoanisole and p-Cresol
Bis(®-iodo)bis[(¹)-sparteine]-
dicopper: A Versatile Catalyst for
Direct O-Arylation and O-Alkylation
of Phenols and Aliphatic Alcohols
with Haloarenes
Br
OH
Catalyst
H3CO
O
+
Base (2 equiv)
Solvent, 80° C, 12 h
OMe
Entry Catalyst
Solvent
Base
Yield/%d)
1
2
3
4
5
6
7
8
9
CuIa)
DMSO
DMSO
DMSO
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Cs2CO3
K3PO4
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
85
58
55
50
93
85
75
42
NDe)
NDe)
NDe)
NDe)
Cu2Oa)
CuBra)
CuCla)
Ponnam Satyanarayana,1
Hariharasarma Maheswaran,*1
Mannepalli Lakshmi Kantam,1
and Suresh Bhargava2
DMSO
b)
[CuI{(¹)-spa}]2
[CuI{(¹)-spa}]2
[CuI{(¹)-spa}]2
[CuI{(¹)-spa}]2
[CuI{(¹)-spa}]2
[CuI{(¹)-spa}]2
[CuI{(¹)-spa}]2
CuIc)
DMSO
DMSO
DMSO
DMF
b)
b)
b)
b)
b)
b)
NMP
10
11
12
1,4-Dioxane
Toluene
DMSO
1Inorganic and Physical Chemistry Division, Indian Institute
of Chemical Technology, Hyderabad-500007, India
2School of Applied Sciences, RMIT University,
Melbourne, Australia
a) Reactions (Entries 1-4) were performed on a 1.0 mmol scale
with catalyst (0.1 mmol), (¹)-sparteine (0.1 mmol), p-bromoanisole
(1.0 mmol), p-cresol (1.0 mmol), base (2.0 mmol) in 3 mL solvent
at 80 °C for 12 h. b) Reactions (Entries 5-11) were performed on
a 1.0 mmol scale with preformed bis(®-iodo)bis[(¹)-sparteine]-
dicopper(I) complex (5.0 mol %), p-bromoanisole (1.0 mmol),
p-cresol (1.0 mmol), base (2.0 mmol) in 3 mL solvent at 80 °C for
12 h. c) Reaction (Entry 12) was carried out with cuprous iodide
(0.1 mmol) without (¹)-sparteine. d) Isolated yields after silica gel
column chromatography. e) Product not detected.
Received January 5, 2011
E-mail: maheswaran_dr@yahoo.com
The easy to prepare dimeric bis(®-iodo)bis[(¹)-sparteine]-
dicopper ([CuI{(¹)-spa}]2 complex) is shown to be versatile
catalyst for O-arylation and O-alkylation with various aryl
halides with phenols and aliphatic alcohols respectively,
including less reactive aryl chlorides, such as chlorobenzene
under mild conditions.
many researchers showed copper-catalyzed O-arylation reactions
in the presence of organic additives such as ethylene glycol
diacetate,7a 8-hydroxyquinoline,7b 1-naphthoic acid,7c triphenyl-
phosphine,7d 2,9-dimethyl-1,10-phenanthroline,7e 2,2,6,6-tetra-
methylheptane-3,5-dione,7f (2S,4R)-4-hydroxyproline,7g the tripod
ligand such as 1,1,1-tris(hydroxymethyl)ethane,7h chelating li-
gands like Chxn-Py-Al, salicylaldoxime, dimethyldioxime,7i
silica-supported Cu(II),7j 1,10-phenanthroline,7k ¢-ketoester,7l
phosphazene P4-t-Bu base,7m bipyridyl complex,7n 1,1¤-binaph-
thyl-2,2¤-diol,7o 1,1¤-binaphthyl-2,2¤-diamine (BINAM),7p and
N,N-dimethylglycine,7q,7r and tetraethyl orthosilicate as solvent.8
The above advances in the field of Ullmann coupling are not
sufficient as most of the reactions still require long reaction times,
high reaction temperatures (>120 °C), and in some cases, very
high catalytic loading. In particular, the coupling of aryl bromides
with aliphatic alcohols does not provide the alkyl aryl ether at all
or only provides poor yields or the relative catalyst amount or the
temperature has to be increased to improve the yields.7k,7r Thus,
there are greater needs to develop new and improved catalytic
processes for O-arylation and O-alkylation reactions with aryl
halide and phenol or alcohols as coupling partners to further
improve the efficiency and generality of the copper-catalyzed
coupling of phenols and alcohols with aryl halides.
Many synthetically challenging and biologically important
compounds, for example isodityrosin family and derivatives such
as vancomycin and antitumoral bouvardin contain diaryl ether and
aryl alkyl ether groups in their skeletal framework.1 Both diaryl
ether and aryl alkyl ether moieties have been shown to be prevalent
in agrochemicals, pesticides, fragrances, cosmetics, solvents, and
materials.2,3
Traditionally, copper-catalyzed Ullmann coupling reaction has
been used for the synthesis of diaryl ethers by using aryl alcohols
and aryl halides. Unfortunately, these Ullmann coupling reactions
require stoichiometric amounts of copper, high temperatures, and
harsh reaction conditions.4 In addition, these Ullmann reactions are
very sensitive to the substituent groups on the aryl halides and often
give poor yields for the desired products.4 Other protocols involves
palladium-catalyzed synthesis of diaryl ethers from corresponding
aryl halides and aryl alcohols or their sodium salts.5 However, this
methodology suffers from disadvantages such as moisture sensi-
tivity, high oxophilicity associated with phosphine ligands, the use
of expensive palladium metal catalyst, and environmental toxicity.
These disadvantages have rendered palladium-based protocols
unpopular, in particular, for large-scale reactions.6
We have recently identified (¹)-sparteine as new efficient
supporting ligand for copper-catalyzed direct N-arylation reactions
of various NH-heterocycles and aryl halides.9 It is to be noted that
(¹)-sparteine contains tertiary nitrogen atoms, which makes N-
donor site poor ·-donors; which is well-known to result in larger
thermodynamic stabilization of catalytically active lower-valent
Cu(I) species.10 It is very likely that such poor ·-donor character-
istics of the (¹)-sparteine ligand additive play an important role in
During last few years, significant improvements have been
made for the synthesis of diaryl ethers using more attractive
copper-catalyzed Ullmann type O-arylation/O-alkylation methods
using external supporting ligand additives. These external addi-
tives are thought to act as ligands to copper, and increase the
efficiency of the Ullmann reaction by increasing the solubility of
the copper salts by preventing their aggregation. In this direction,