Palladium-catalyzed fluoroacylation of (Hetero)arylboronic acid with fluorothioacetates at ambient temperature

Article abstract of DOI:10.1016/j.tetlet.2020.151780

A palladium-catalyzed fluoroacylation of (hetero)aryl boronic acid with the fluorothioacetates is described at ambient temperature. A variety of aryl, and heteroaryl boronic acids are compatible in the reaction, affording the corresponding fluoroalkyl ketones in moderate to good yields. Further late-stage di-, and trifluoroacylation of drug molecule clofibrate and estrone demonstrated the synthetic practicability of this protocol.2009 Elsevier Ltd. All rights reserved.

Full text of DOI:10.1016/j.tetlet.2020.151780

Journal Pre-proofs
Palladium-Catalyzed Fluoroacylation of (Hetero)arylboronic Acid with Fluo‐
rothioacetates at Ambient Temperature
Xing Yi, Ya-Fang Cao, Xing Wang, Hui Xu, Shu-Rong Ban, Hui-Xiong Dai
PII:
S0040-4039(20)30212-4
DOI:
Reference:
https://doi.org/10.1016/j.tetlet.2020.151780
TETL 151780
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
18 January 2020
19 February 2020
24 February 2020
Please cite this article as: Yi, X., Cao, Y-F., Wang, X., Xu, H., Ban, S-R., Dai, H-X., Palladium-Catalyzed
Fluoroacylation of (Hetero)arylboronic Acid with Fluorothioacetates at Ambient Temperature, Tetrahedron
Letters (2020), doi: https://doi.org/10.1016/j.tetlet.2020.151780
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Graphical Abstract
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Palladium-Catalyzed Fluoroacylation of (Hetero)arylboronic Acid with Fluorothioacetates at Ambient
Temperature
Xing Yi, Ya-Fang Cao, Xing Wang, Hui Xu, Shu-Rong Ban, Hui-Xiong Dai
O
.
.
Mild reaction conditions
Broad substrate scope
Compatibility with heterocycle
Late-state of diversification of drugs
.
O
O
B(OH)2
+
Pd2dba3, TFP, CuTC
Rf
.
R
R
THF, 30 o
C
t-BuS
Rf
Rf : -CHF2, -CF3, -C2F5
O
O
O
Rf
Rf
H
H
Rf
O
Rf
EtO
O
H
O
Rf
N
H
S
O
Me
O
from Estrone
from Clofibrate

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Palladium-Catalyzed Fluoroacylation of (Hetero)arylboronic Acid with
Fluorothioacetates at Ambient Temperature
Xing Yia, Ya-Fang Caod, Xing Wangb,c, Hui Xub, Shu-Rong Bana, and Hui-Xiong Daib,c
a School of Pharmaceutical Science, Shanxi Medical University, 56 Xinjian South Road, Taiyuan 030001, China
b Chinese Academy of Sciences Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Shanghai 201203, China
c University of Chinese Academy of Sciences, Beijing 100049, China
d Nano Science and Technology Institute, University of Science and Technology of China, Suzhou, Jiangsu 215123, China
———
ARTICLE INFO
ABSTRACT
 Corresponding author. e-mail: xuhui2018@simm.ac.cn
 Corresponding author. e-mail: shurongban@sxmu.edu.cn
Article history:
A palladium-catalyzed fluoroacylation of (hetero)aryl boronic acid with the fluorothioacetates
is described at ambient temperature. A variety of aryl, and heteroaryl boronic acid are
compatible in the reaction, affording the corresponding fluoroalkyl ketones in moderate to good
yields. Further late-stage di-, and trifluoroacylation of drug molecule clofibrate and estrone
demonstrated the synthetic practicability of this protocol.
Received
 Corresponding author. e-mail: hxdai@simm.ac.cn
Received in revised form
Accepted
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
Fluoroacylation
Arylboronic acid
Cross coupling
Late-stage diversification of drugs
The incorporation of fluorine atom into organic molecular has
drawn much attentions in pharmaceuticals, organic materials, and
agrochemicals research due to the unique role of enhancing
molecular properties and functionality.1 For example, fluorinated
drug are more lipophilic and metabolically stable than the
nonfluorinated analogues, thus could enhance the interaction
strength between the drug molecular and target protein.2 Among
the various fluorinated compounds, fluoroalkyl ketones have
been well exploited as the potent enzyme inhibitors as well as
valuable synthetic intermediates for constructing fluoroalkylated
compounds.3 Many synthetic methodologies have been
developed, such as oxidation of fluoroalkyl alcohols,4
arylboronic acid with corresponding phenyl perfluorinate.12
Skrydstrup and Zhang independently reported the
difluoroacylation of arenes by palladium-catalyzed carbonylation
of difluoroalkyl bromides with aryl boron reagent.13 In 2018,
Skrydstrup realized the Pd-catalyzed difluoroacylation of alkyl-9-
BBN using the same strategy.14 Very recently, Zhang reported
the first example of nickel-catalyzed carbonylative
difluoroalkylation of arylboronic acids under 1 atm of CO.15
Despite those undisputable advances, these protocols often
suffered from high temperature, toxic CO, multistep reaction
sequence and incompatibility of heterocyclic substrates in some
cases.
electrophilic
phenyllithium6
fluoroacylation
or Grignard
of
electro-rich
reagents,7
nucleophilic
arene,5
Transition-metal-catalyzed C–S bond activations to construct C–
C and C–X bond has garnered widespread interest.16 In 2000,
Liebeskind and coworkers reported a mechanistically unique and
unprecedented ketone synthesis via Pd-catalyzed base-free cross
coupling of thiolesters with boronic acids in the presence of
copper(I) thiophene-2-carboxylate (CuTC), namely Liebeskind-
fluoroalkylation of carboxylic derivatives,8 and direct
electrophilic fluorination with F+ reagent.9 Recently, transition-
metal-catalyzed cross coupling reaction paves a new road for the
synthsis of fluoroalkyl ketone. In 2016, Yang developed
palladium-catalyzed carbonylative coupling of aryl iodides with
(trifluoromethyl)copper reagent for the synthesis of aryl
trifluoromethyl ketones.10 Weng and Yan respectively reported
the trifluoroacetylation of arenediazonium salts and C–H of
Srogl
cross-coupling
reaction.17
One
example
of
trifluoroacylation of electro-deficient 3-nitrophenyl boronic acid
was reported. However, other types of polyfluoroacylation of
indole
via
a
copper-mediated
decarboxylation
of
ethyltrifluoropyruvate.11 Direct fluoroacylation of broadly
accessible and low toxic organoboron reagent would be a
powerful alternative. In 2001, Yamamoto reported the
trifluoromethyl, pentafluoroethyl, and heptafluoropropyl ketone
synthesis via palladium-catalyzed cross-coupling reaction of

2
Yamamoto12
B(OH)2
phosphinoxanthene. TFP = tri(2-furyl)phosphine. CuTC = Copper(I)
thiophene-2-carboxylate. b 1a (0.20 mmol), 2 (0.40 mmol).
O
Pd(OAc)2/PnBu3
O
Rf
R1
R1
Rf : -CF3, -C2F5, -C3F7
+
PhO
O
Rf
NMP, 80 o
C
Trifluoromethylketones (TFMKs) are especially important due to
their unique substructure in medicinal chemistry. So we
commenced our studies by treating phenyl boronic acid 1a with
Skrydstrup, Zhang13-15
BX2
CO
O
Pd or Ni
R2
trifluoroacylation
reagent
2a
under
Liebeskind’s
CF2
+
R2
R3
CF2Br
O
1) Carbonylation
trifluoroacylation conditions.17 However, only 28% yields of
desired product 3a was formed (entry 1, Table 1). After screening
of the various phosphine ligands, we found that TFP was the
optimal choice (entries 2-5). Bidentate phosphorus ligands, such
as dppe, Xantphos were totally inefficient. The yields decreased
when Pd2dba3 was replaced with other Pd catalyst (entries 6-9).
Next, we turned our attention to screen a range of electronically
diverse S-aryl and S-alkyl in the thioester 2 (entries 10-13). In
sharp contrast to the thioester 2a and 2b, only trace amounts of
product was formed when thioester 2c was employed. To our
delight, the yield could be improved to 48% by using 2d as the
trifluoroacylation reagent (entry 12, Table 1). Lowering the
reaction temperature could improve the yield to 92% by using 2
equiv. of 2d (entries 14-17).
2) Decarboxylation
Liebeskind17
B(OH)2
O
Pd2dba3, CuTC
CF3
+
50 o
C
p-Tol-S
t-BuS
CF3
NO2
NO2
This work:
O
O
B(OH)2
Pd2dba3, CuTC
30 o
Rf
R4 Het
R4 Het
+
Rf
C
Rf : -CHF2, -CF3, -C2F5
Scheme 1 Fluoroacylation of aryl boron reagent
(hetero)aryl boronic acids with thiolester have not been
demonstrated. Herein, we reported a general protocol for
palladium-catalyzed room-temperature di-, tri-, and penta-
fluoroacylation
corresponding thioesters.
of
(hetero)aryl boronic acids
with
the
Scheme 2 Substrates scope for the trifluoroacylation of
(hetero)arylboronic acidsa
O
Table 1 Optimization of the reaction conditionsa
O
B(OH)2
+
Pd2dba3, TFP
CF3
O
Pd catalyst (1 mol%)
CuTc, Ligand
R
Het
R
Het
1
B(OH)2
O
t-BuS
2d
CF3
O
CuTC, THF, 30 o
C
CF3
+
RS
CF3
THF, Temp (oC)
3
O
1a
2
3a
O
O
MeO
CF3
Me
MeO
Temp
Yield
CF3
CF3
CF3
Entry
2
Pd catalyst
Ligand
(oC)
50
50
50
50
50
50
50
50
50
50
50
50
50
100
80
30
30
(%)
28
21
0
OMe
3d
3a
3b
3c, 68%
, 85%
, 65%
, 80%
1
2
2a
2a
2a
2a
2a
2a
Pd2dba3
Pd2dba3
Pd2dba3
Pd2dba3
Pd2dba3
Pd(OAc)2
TFP
PPh3
dppe
dcype
XantPhos
TFP
O
O
O
O
CF3
CF3
CF3
CF3
3
Me
MeO
TMS
Ph
4
0
b
b
3e
3f
3g
, 64%
, 80%
, 85%
3h
, 82%
5
0
O
O
CF3
O
O
6
23
16
20
8
CF3
CF3
CF3
7
2a Pd(MeCN)2Cl2
TFP
Cl
O2N
Br
3j, 67%b
b
8
2a
2a
2b
2c
2d
2e
2d
2d
2d
2d
Pd(PPh3)4
Pd(dppf)Cl2
Pd2dba3
Pd2dba3
Pd2dba3
Pd2dba3
Pd2dba3
Pd2dba3
Pd2dba3
Pd2dba3
TFP
3i
, 71%
3k
, 58%
3l
, 85%
O
9
TFP
O
O
CF3
O
CF3
10
11
12
13
14
15
16
17b
TFP
20
trace
48
26
22
26
52
CF3
O
CF3
N
H
TFP
TFP
3m
, 95%
3n
, 90%
3o
, 78%
3p
, 72%
a
1a
2d
(0.40 mmol), Pd2dba3 (1 mol%), TFP (3 mol%), CuTC (0.3
Reaction conditions:
mmol), THF (2 mL), 30 oC, 18 h. b CuTC (0.4 mmol).
(0.20 mmol),
TFP
TFP
TFP
Having identified the optimal conditions for trifluoroacylation,
we next explored the scope of various arylboronic acids. As
shown in Scheme 2, our protocol appeared to be quite general
with respect to the substituents in aryl boronic acids 1. A variety
of aryl boronic acids with electron-donating methyl-, methoxy-,
and phenyl substituents could be furnished smoothly, giving the
corresponding products in moderate to good yields (3a-3h).
Moreover, electron-deficient aryl boronic acids 1k could also be
compatible in the reaction, providing the trifluoroacylated
product 3k in 58% yield. It was noting that very sensitive -Cl, -
Br, and -TMS could be tolerated, which could be further
functionalized by metal-catalyzed cross coupling (3g, 3i, 3j). For
polycyclic aromatic compound, such as naphthyl, phenanthrenyl,
TFP
TFP
92 (85)
R
O
O
O
2a
R = -Me,
R = -OMe,
2c
2b
F3C
S
F3C
S
F3C
S
R = -CF3,
2a-2c
2d
2e
a
Reaction conditions: 1a (0.22 mmol), 2 (0.20 mmol), Pd catalyst (1
mol%), ligand (3 mol%), CuTC (0.15 mmol), THF (2 mL). The yield
was determined by GC-MS analysis of crude product using C16H34 as
internal standard. dppe = 1,2-bis(diphenylphosphino)ethane, dcype = 1,2-
bis(dicyclohexylphosphino)ethane. XantPhos
= dimethylbisdiphenyl-

3
O
trifluoroacylated products 3l-3n were obtained in isolated yields
of 85-95%. It is worth noting that the protocol could be
compatible with heteroaryl boronic acids. 1o and 1p could
produce the expected products 3o and 3p in 78% and 72% yields,
respectively.
Considering the high importance of difluoromethyl ketone in
many pharmaceuticals and materials, we question whether this
success protocol with trifluoroacylation could be applied to the
difluoroacylation of arylboronic acid (Scheme 3). To our delight,
regardless of electronic properties of the substituents, aryl,
polycyclic aryl, and heteroaryl boronic acids could be tolerated,
giving the corresponding difluoroacylated product in 60-85%
yields. The obtained difluoroacylated products are useful
synthons and could be further transformed to the fluorinated
alcohols and α-aryl-α, α-difluoroketones via Rh-, and Pd-
catalyzed arylation.18
B(OH)2
O
Pd2dba3, TFP
Rf
O
R
R
H
+
CuTC, THF, 30 o
C
t-BuS
2d
Rf
4
3
5
or
or
1
O
CHF2
H
H
Rf
3q
, Rf = CF3, 76%
EtO
O
5n
, Rf = CHF2, 77%
5o
, 70%
O
Me
O
from Clofibrate
from Estrone
a
1a
2d
4
Reaction conditions:
mol%), CuTC (0.4 mmol), THF (2 mL), 30 oC, 18 h.
(0.20 mmol),
or (0.40 mmol), Pd2dba3 (1 mol%), TFP (3
Based on the previous reports,16,17 we proposed a plausible
mechanism for the fluoroacylation of arylboronic acid as depicted in
Scheme 6. Initially, oxidative addition of CuTC-bound thiolester I to
Pd(0) formed the Pd(II) complex II, which then underwent
transmetallation with arylboronic acid 1a to afford the complex III.
CuTC was proposed to facilitate the transmetallation process by
Scheme 3 Substrates scope for the difluoroacylation of
forming
a stronger Cu-S bond, or acting as a reactive
arylboronic acidsa
transmetallation center. The subsequent reductive elimination of III
gave the desired trifluoroacylated product 3a with the regeneration
of Pd(0) species.
O
B(OH)2
+
O
Pd2dba3, TFP
CHF2
R
Het
R
Het
t-BuS
CHF2
O
CuTC, THF, 30 o
C
1
4
5
Scheme 6. Possible Mechanism
O
O
O
MeO
CuTC
CHF2
CHF2
Ac
CHF2
OMe
CHF2
F3C
S
Pd0
t-Bu
F3C
t-Bu
5b
OMe
O
5a
, 65%
5c
, 79%
O
5d
O
, 70%
, 85%
CHF2
I
O
3a
O
O
Oxidative
addition
Reductive
elimination
CHF2
CHF2
CHF2
MeO
TMS
Ph
5f
5h
, 71%
, 70%
5e
, 63%
5g
, 63%
F3C
PdII
PdII
O
t-Bu
F3C
O
O
CHF2
S
O
CHF2
O
O
III
CHF2
CuTC
CHF2
II
N
H
X
Transmetallation
5m
, 72%
5k
5l
, X = O, 60%
, X = S, 73%
5i
, 74%
5j
, 80%
B(OH)2
1a
a
t-BuSCu
TC-B(OH)2
1a
4
(0.20 mmol), (0.40 mmol), Pd2dba3 (1 mol%), TFP (3 mol%), CuTC
Reaction conditions:
(0.4 mmol), THF (2 mL), 30 oC, 18 h.
In summary, we have developed a palladium-catalyzed room-
temperature di-, tri-, and pentafluoroacylation of (hetero)
aryl boronic acids with the corresponding thioesters. This
protocol has high functional group tolerance, and a variety of
hetero(aryl) boronic acid could be well compatible, giving the
corresponding product in good to excellent yield. We further
explored the synthetic practicability of this strategy in the late-
stage di- and trifluoroacylation of medicinal drugs clofibrate and
estrone.
Furthermore, pentafluoropropionylation of arylboronic acid could
also be achieved, giving the desired product 7 in 70% yields by
using the similar protocol (Scheme 4).
Scheme 4 Pentafluoropropionylation of 1-naphthylboranic
acid
O
C2F5
B(OH)2
O
Pd2dba3, TFP
+
CuTC, THF, 30 o
C
t-BuS
C2F5
1h
7,
70 %
6
Acknowledgments
To explore the synthetic practicability of this strategy, we applied
this protocol to the late-stage diversification of medicinal drugs
clofibrate and estrone, and obtained the corresponding di- and
trifluoroacylated product 3q, 5n, 5o in 70-77% isolated yields
(Scheme 5).
We gratefully acknowledge the Shanghai Institute of Materia
Medica, the Chinese Academy of Sciences, the NSFC
(21772211), the Youth Innovation Promotion Association CAS
(No. 2014229 and 2018293), the Science and Technology
Commission of Shanghai Municipality (17JC1405000), the
Scheme 5 Late-stage diversification of drugs moleculesa
Program
of
Shanghai
Academic
Research
Leader
(19XD1424600), Primary Research & Developement Plan of
Shanxi Province (201903D321110), the National Science &
Technology Major Project “Key New Drug Creation and
Manufacturing Program”, China (2018ZX09711002-006) for
financial support.

4
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