Tetrahedron Letters
Facile chemoselective carbonyl allylation of chalcones
with allyltributylstannane catalyzed by CuI
⇑
Pabitra Kumar Kalita, Prodeep Phukan
Department of Chemistry, Gauhati University, Guwahati 781014, Assam, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Chemoselective allylation of carbonyl functionality of chalcones with allyltributylstannane was accom-
plished in the presence of CuI as catalyst. This reaction works well in DMF at 70 °C with exclusive forma-
tion of 1,2-addition product. Interesting feature of this reaction is that no conjugate addition product was
produced. Various types of chalcones undergo carbonyl allylation in excellent yield.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 6 May 2013
Revised 6 June 2013
Accepted 10 June 2013
Available online 14 June 2013
Keywords:
Allylation
Allyltributylstannane
Chalcones
1,2-Addition
The chemoselective functionalization of organic compounds is
synthetically important, both in the laboratory and in industry.
Allylation of carbonyl compounds is a useful method for the syn-
thesis of homoallylic alcohols,1 which has been widely applied in
the synthesis of natural products and other complex targets.2 In
To our knowledge, there are only a few reports of allylation
reaction of chalcones with exclusive formation of 1,2-addition
product.4–6 In continuation of our investigations on various allyla-
tion reactions7 and CuI catalyzed reactions,7e–g,8 we present herein
a new method for chemoselective carbonyl allylation of chalcones
with allyltributylstannane using CuI as catalyst in the presence of
K2CO3 in DMF medium (Scheme 1).
In a typical reaction, chalcones (1 mmol), allyltributylstannane
(1 mmol), K2CO3 (1 mmol), and CuI (10 mol %) were added succes-
sively in DMF (1.5 mL) at room temperature. The reaction was
monitored by TLC. The results are presented in Table 1. Initial
experiment without K2CO3 failed to produce any product both at
room temperature (Table 1, entry 1) and at 70 °C (Table 1, entry
2). Another experiment without CuI also produced negative result
both at room temperature and at 70 °C (Table 1, entries 3 and 4,
respectively). When the reaction was examined using both K2CO3
(1 mmol) and CuI (10 mol %), it produced 48% of the 1,2-addition
product after 24 h at room temperature (Table 1, entry 5). The
reaction with increasing the concentration of the catalyst gradually
increases the yield of the reaction up-to 62%. However, the reaction
rate as well as yield of the product increased significantly, when
the temperature of the reaction was increased from room temper-
ature to 70 °C. In this case, the reaction produced corresponding
alcohol in 62% yield just after 10 h of reaction. An improvement
general, addition of allyl metals to
a,b-unsaturated ketones such
as chalcones, leads to conjugate addition of allyl metals to chal-
cones, which is referred to as the Sakurai-type Michael reaction.3
In many cases, a mixture of 1,4-and 1,2-addition products was
formed during the reaction with predominant formation of the
1,4-product. In 2001, Lee3a has successfully studied the regioselec-
tivity on the reactions of
a,b-enones with allyl indium reagents
generated in situ by the reaction of allyl iodide with indium metal
in the presence of chlorotrimethylsilane (TMSCl). They found that
the regioselectivity (1,4-addition vs 1,2-addition) is dependent on
the type of substrate used. Kelly and Gilheany4 investigated the ef-
fect of InCl3 on the addition of Grignard reagents to chalcones,
where they found that the presence of 5 mol % InCl3 can signifi-
cantly alter the amount of 1,2-addition product. But the reaction
needs 16 h for completion. Cho and co-workers5 reported indium
mediated 1,2-addition of allyl iodide to
a,b-unsaturated carbonyl
compounds. In this method, they used indium trichloride as an
activator along with indium powder to accomplish the reaction.
Very recently, Li et al.6 reported a Barbier-type allylation method
by using Mg powder under solvent-free condition where in case
of chalcones, 1,2-addition products were obtained regioselectively
in good yields.
CuI,
OH
O
K2CO3
R1
R2
R1
R2
+
SnBu3
DMF, 70 o
C
1
+_
3
)
2
(
⇑
Corresponding author. Tel.: +91 361 2570535; fax: +91 361 2700311.
Scheme 1. 1,2-Allylation of chalcones.
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.