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Published on the web June 5, 2010
Microwave-assisted Synthesis of Diaryl Selenides.
Elucidation of Cu(I)-catalyzed Reaction Mechanism
Irina P. Beletskaya,*1 Alexander S. Sigeev,1 Alexander S. Peregudov,2 Pavel V. Petrovskii,2 and Victor N. Khrustalev2
1Department of Chemistry, Moscow State University, GSP-3, Moscow 119899, Russia
2A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Science,
Vavilova str. 28, V-344, Moscow 119991, Russia
(Received April 12, 2010; CL-100355; E-mail: beletska@org.chem.msu.ru)
Table 1. Cross-coupling of arylbromides with 1a: Conven-
tional heating vs. microwave assistance
A novel microwave-assisted cross-coupling of trialkyltin
arylselenides 1 with arylbromides using [(phen)CuI]2 afforded un-
symmetrical diarylselenides 3 in high to excellent yields. A plau-
sible catalytic cycle for Cu(I)-catalysed cross-coupling has been
proposed. A key intermediate in this catalytic cycle was synthe-
sized and its structure was determined by X-ray diffractometry.
SeSnBu3 Br
SeAr(Het)
5% [(phen)CuI]2
DMF
+
X
Cl
Cl
1a
2a-l
3a-l
The microwave-assisted organic synthesis has received wide
recognition in recent years since it provides drastic decrease in
reaction times.1 This can significantly influence the selectivity
and yields of products in some reactions.2
X = 4-NO2 (a), 4-CN (b), 3,4,5-Cl3 (c), 4-Ac (d)
3-CF3 (e), 4-NMe2 (g), 4-NH2 (h), 2-Me-4-NH2 (i)
Br
Br
Br
,
Br
N
,
,
ArBr =
N
N
S
Compounds containing arylchalcogenide structural motif
have attracted considerable attention due to their various prac-
tical and scientific applications. They include substances of
pharmaceutical3 and material4 interest. Earlier, we have shown
that easily available trialkyltin arylselenides ArSeSnAlk35 are an
excellent source of ArSe-group in the cross-coupling reactions
with aryl,6 alkyl,7 and acylhalogenides.8 At the same time these
compounds can disproportionate in the presence of palladium
complexes at temperatures more than 90 °C with formation of
Ar2Se and (Alk3Sn)2Se.
N
t-Bu
(f)
(j)
(k)
(l)
MW, 140 °C
t/min
110 °C
t/h
Yielda/%
Entry
Ar(Het)
Yielda/%
1
2
3
4
5
4-NO2C6H4
4-NCC6H4
12
96
93
97
91
90
6
6
90
89
95
—
—
15
3,4,5-Cl3C6H2
4-AcC6H4
15
6
15
—
—
3-CF3C6H4
20
½Mꢁ;ꢀ
ArSeSnBu3 ꢀꢀꢀꢀ! Ar2Se þ ðBu3SnÞ2Se
ð1Þ
6
18
87
—
—
In contrast, Cu(I) complexes with bidentate N,N-ligands
(2,2¤-bipyridine (bpy), 1,10-phenanthroline (phen)) turned out to
be excellent catalysts for this reaction leading to unsymmetrical
diarylselenides in high yields.6b
7
8
4-Me2NC6H4
4-NH2C6H4
25
25
25
15
20
87
82b
65
88
88
14
16
18
5
72
56c
31
81
—
9
4-NH2-2-MeC6H3
3-Thienyl
3-Py
In the present work we have carried out the reaction of 4-
ClC6H4SeSnBu3 (1a) with various aryl and hetarylbromides
in the presence of 5% [(phen)CuI]2 under microwave (MW)
irradiation (Table 1).10 The microwave activation drastically
decreased the reaction time: from 6-30 h to 15-50 min.
The yields of diarylselenides were also higher in the case of
the microwave-assisted reactions. If for active ArBr 2a-2c the
increase in yield was not more than 2-6% (Entries 1-3), for
deactivated aryl bromides 2g and 2h it was more significant (15-
26%) (Entries 7 and 8). In the case of 4-bromoaniline (2h), the
difference in results of MW and conventional heating was
connected with ammonolysis of 1a by aniline with formation
of ArSeH which was unreactive under conventional heating
conditions (Entry 8).
10
11
—
N
N
12
50
48
30
(15)d
N
t-Bu
aIsolated yield. The GC yield is given in parentheses. b<4% of
(4-ClC6H4Se)2 by GC. cca. 12% of (4-ClC6H4Se)2 by GC.
d>30% (4-ClC6H4)2Se by GC.
of cross-coupling product 3l was very low (<15%, GC)
(Entry 12).
In the case of several bromine atoms in arylbromide,
selective substitution can be performed (Table 2).10
The selective monosubstitution in 2,6-dibromopyridine
(2m) in the microwave-assisted reaction proceeds with high
selectivity (Entry 1) with the use of 0.95 equiv of 1a vs. 1.1
equiv in the standard protocol and leads to a monosubstituted
product in 85% yield. Although under the conventional heating
conditions the overall substitution yield being almost the same,
For deactivated arylbromides 2i and 2l with steric hindran-
ces the increase in yields was more than 30% (Entries 9 and 12).
Even for very unreactive 3-bromo-2-tert-butylimidazo[1,2a]pyr-
imidine (2l), diarylselenide 3l was obtained in moderate yield
(48%) after 50 min of MW heating.
In contrast, conventional heating leads mainly to the
disproportion product: (4-ClC6H4)2Se (>30%, GC). The yield
Chem. Lett. 2010, 39, 720-722
© 2010 The Chemical Society of Japan