Journal of Fluorine Chemistry
Short Communication
The regioselective trifluoromethylation of 1,3-bis(vinyl triflates) in the
absence of external trifluoromethyl sources
a,⁎
a
a
b
Takuji Kawamoto , Rio Sasaki , Akio Kamimura , Hiroshi Matsubara
a
Department of Applied Chemistry, Yamaguchi University, Ube, Yamaguchi 755-8611, Japan
b
Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8511, Japan
A R T I C L E I N F O
A B S T R A C T
Keywords:
We report the regioselective trifluoromethylation of 1,3-bis(vinyl triflates) via an allyl radical intermediate. In
this reaction, the trifluoromethyl radical exclusively attacks the 4-position of the 1,3-diketone derivatives. The
observed regioselectivity can be rationalized on the basis of DFT calculations, which suggest that the attack at
the 4-position is more favorable than that at the 2-position. We have also developed a one-pot procedure for the
regioselective trifluoromethylation of 1,3-diketones.
Trifluoromethylation
Radicals
1
,3-Bis(vinyl triflates)
One-pot reaction
1
. Introduction
fluoromethylation of bis(vinyl triflates) in the absence of external tri-
fluoromethyl sources.
1
,3-Dicarbonyl dianions and related compounds represent useful
building blocks in organic synthesis [1,2]. The terminal carbon atom in
these species can react regioselectively with electrophiles due to its
high basicity and reactivity, and reactions involving numerous elec-
trophiles have been developed. However, to the best of our knowledge,
reports on the radical addition and trifluoromethylation of 1,3-di-
carbonyl dianions and equivalents remain elusive.
2. Results and discussion
Initially, we examined the reactivity of 1a toward the tri-
fluoromethyl radical. When a dichloromethane solution of 1a was
treated with BEt and 2,6-di-tert-butyl pyridine (2,6-DTBP) at room
3
temperature, the expected regioselective trifluoromethylated product
(2a) was obtained in 35% yield, together with regio isomer 2a’ (13%)
(Scheme 2), while the corresponding 2-trifluoromethylated product was
not observed.
Trifluoromethylated compounds are ubiquitous in a variety of
pharmaceuticals, agrochemicals, and organic materials with potential
applications in optical, magnetic, and electronic materials [3], and the
radical trifluoromethylation is a powerful tool for the synthesis of tri-
fluoromethyl-containing structures [4]. Recently, we have reported a
method for the synthesis of α-trifluoromethylated ketones from vinyl
Encouraged by the initial findings, we investigated different com-
binations of radical initiators, additives, and solvents [10]. Treating 1a
with 2,6-DTBP in the presence of 2,2′-azobis(2-methylpropionitrile)
(AIBN) as a radical initiator afforded the desired products in 46% yield
(2a:2a’ = 76:24) (Table 1, entry 1). The yield was slightly improved
triflates in the presence of BEt as a radical initiator (Scheme 1, eq. 1)
3
[
5–7]. This reaction proceeds chemoselectively toward the conjugated
vinyl triflates (Scheme 1, eq. 2), and we speculated that 1,3-bis(vinyl
triflates), which can be generated from the corresponding 1,3-dike-
tones,[8] should regioselectively afford the product substituted at the 4-
position via an allyl radical intermediate (path A, Scheme 1, eq. 2) [9].
when K
2
HPO was used as an additive (entry 2). Interestingly, we found
4
that the reaction also proceeded in the absence of additives (entry 3).
Then, we carried out the trifluoromethylation of 1,3-bis(vinyl tri-
flates) and 1,3-bis(vinyl perfluoroalkyl sulfonates) (Table 2). The re-
action of 1,3-bis(vinyl perfluoroalkyl sulfonate) 1b furnished the cor-
Herein, we report
a new strategy for the regioselective tri-
⁎
Received 7 January 2019; Received in revised form 3 April 2019; Accepted 4 April 2019
Available online 06 April 2019
0022-1139/ © 2019 Elsevier B.V. All rights reserved.
Kawamoto, Takuji
