Rhodium-Catalyzed Direct Ortho C-H Arylation Using Ketone as Directing Group with Boron Reagent

Article abstract of DOI:10.1021/acs.orglett.7b02931

A general method for selective ortho C-H arylation of ketone, with boron reagent enabled by rhodium complexes with excellent yields, is developed. The transformation is characterized by the use of air-stable Rh catalyst, high monoarylation selectivity, and excellent yields of most of the substrates.

Full text of DOI:10.1021/acs.orglett.7b02931

Letter
Cite This: Org. Lett. XXXX, XXX, XXX-XXX
pubs.acs.org/OrgLett
Rhodium-Catalyzed Direct Ortho C−H Arylation Using Ketone as
Directing Group with Boron Reagent
Bing Zhang, Huai-Wei Wang, Yan-Shang Kang, Ping Zhang, Hua-Jin Xu, Yi Lu,* and Wei-Yin Sun*
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering,
Nanjing National Laboratory of Microstructures, Collaborative Innovation Center of Advanced Microstructures, Nanjing University,
Nanjing 210023, China
*
S Supporting Information
ABSTRACT: A general method for selective ortho C−H
arylation of ketone, with boron reagent enabled by rhodium
complexes with excellent yields, is developed. The trans-
formation is characterized by the use of air-stable Rh catalyst,
high monoarylation selectivity, and excellent yields of most of
the substrates.
he biaryl structural motif plays an increasingly important
Scheme 1. C−H Arylation Assisted by Ketone
T
role in biologically active molecules and photonic
1
materials. However, biaryl compounds have mainly been
synthesized by using aryl halides and aryl metal compounds,
2
releasing equivalent byproducts. Due to the ubiquitous nature of
C−H bonds, transition-metal-catalyzed C−H functionalization
3
has emerged as a useful method to build aryl−aryl stocks.
4
Inspired by the pioneering work of Murai and co-workers,
direct synthesis of carbon−carbon and carbon−heteroatom
bonds using transition-metal-catalyzed C−H functionalization
5
has attracted increasing attention. As a result, a wide range of
coordinating moieties have been utilized to efficiently activate6
the C−H bonds. Among these directing groups, pyridyl,
7
8
9
amino, azo, and amide groups have been applied to facilitate
various reactions described in the literature; however, other
13
1
0
11
12
functional groups, such as thio, hydroxy, carbonyl, ester,
1
4
15
aldehyde, and carboxy groups, were less reported.
Ketone-assisted C−H functionalization (e.g., alkylation,
amination, hydroxylation, and olefination) catalyzed by Ru, Pd,
16,17
Rh, and Ir has been well-documented.
However, arylation of
aromatic C−H bonds assisted by ketone has seldom been
1
8
described. Murai et al. have reported ortho arylation of aromatic
18a
ketones catalyzed by Ru and Pd (Scheme 1, eq 1). Cheng et al.
ketone (Table 1). Among silver salts, copper salts, and other
have reported Pd catalyzed ketone assisted arylation with
18c
organic oxidants, only AgF, AgOAc, and Ag O were effective
relatively low yield (Scheme 1, eq 2). In addition, they have
2
(
Table 1, entries 5, 8, 9, and 10), and Ag O gave the highest yield
reported ketone-assisted dual C−H functionalization (Scheme 1,
2
1
9
(Table 1, entry 9). As to the solvents, DCE gave the desired
products with high yield (85%) in 3 h (Table 1, entry 9), while
the other solvents, such as methanol and toluene, afforded no
desired products (Table 1, entries 11 and 12). The yield was
further elevated to 95% when the reaction time was prolonged to
eq 3). Inspired by our previous study on weak coordinating
2
0
group amide directed C−H arylation catalyzed by Rh catalyst,
as well as others concerning Rh-catalyzed olefination and
21
hydroxylation directed by ketones, we aimed to establish a
more efficient and site-selective synthetic method to build
decorated biphenyl derivatives catalyzed by Rh catalyst using
ketone as the directing group, with moderate to high yields.
Herein, we report an interesting synthesis of biaryl derivatives
from sec-alkyl aryl ketones and boron reagent by Rh-catalyzed
C−H activation.
6
h (Table 1, entry 13). Unfortunately, adding ligands, bases, or
acids lowered the yield dramatically (see the Supporting
Information). In addition, catalysts also evidently affected the
reaction (see Table S5). The reaction of 1-(2-methoxyphenyl)-2-
At the outset of our studies, we tested various reaction
parameters for the envisioned Rh-catalyzed C−H arylation of
Received: September 19, 2017
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b02931
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
,
a b
Table 1. Optimization of Reaction Conditions
Scheme 2. Scope of Ketone Substrates.
b
entry
oxidant
BQ
solvent
yield (%)
1
2
3
4
5
6
7
8
9
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCM
MeOH
toluene
DCE
NR
NR
NR
NR
52
O2
PhI(OAc)2
Cu(OAc)2
AgF
Ag CO
2
NR
NR
53
3
Ag PO
3
4
AgOAc
Ag O
2
85
1
1
1
1
0
1
2
3
Ag O
2
65
Ag O
2
NR
NR
95
Ag O
2
c
Ag O
2
a
Conditions: 1a (0.1 mmol), 2a (0.3 mmol), [RhCp*(MeCN) ]-
3
(
SbF ) (10 mol %), oxidant (0.2 mmol), solvent (2 mL), N , 3 h, 120
6 2 2
b
1
°C. The yield was determined by H NMR analysis of crude product
c
using CH Br as an internal standard. Reaction time 6 h.
2
2
methylpropan-1-one (1a) with 4-methoxycarbonylphenylbor-
onic acid pinacol ester (4-CO Me-Ph-Bpin) (2a) in the presence
2
a
of a more reactive Rh catalyst [RhCp*(MeCN) ](SbF ) (10
Conditions: 1a−t (0.1 mmol), 2a (0.3 mmol), [RhCp*(MeCN)
]-
3
3
6 2
(
SbF ) (10 mol %), Ag O (0.2 mmol), DCE (2 mL), N , 6 h, 120 °C.
mol %) and Ag O (0.2 mmol) in DCE (2 mL) at 120 °C for 6 h
6
2
2
2
2
b
Isolated yield.
generated a biphenyl derivative 3a in 95% yield. Control
experiments revealed that no desired product 3a was obtained in
the absence of Rh catalyst or silver salt (see Table S5).
,
a b
Scheme 3. Scope of Arylating Reagents
Having identified these optimized conditions, we set out to
evaluate the scope for this new reaction. A variety of substituted
substrates were surveyed (Scheme 2). Various substrates were
smoothly transformed into the corresponding ortho-arylated
products in moderate to high yields. Substrates with electron-
donating groups in the ortho, meta, and para sites afforded the
desired products in excellent yields (3a−g) (Scheme 2). In
particular, the regioselectivity was high, and only monosub-
stituted product was generated for each substrate. As
demonstrated by the reaction of 1 bearing halogen groups, the
functional group tolerance was high, although the yields were
modest (3h−m) (Scheme 2), which allowed additional
modification reactions in the halogenated positions. Moreover,
reactions of other sec-alkyl aryl ketones, such as tertiary butyl,
ethyl, propyl, cyclohexyl, and phenyl aryl ketones, afforded the
desired products with excellent yields (3n−s) (Scheme 2). α-
Tetralone gave moderate yield (53%), which can be attributed to
its restricted structure (3t). Notably, benzophenone (3s)
(Scheme 2) was also tolerated, which has rarely been reported
until now.
Afterward, this C−H bond functionalization reaction was
successfully extended to various arylboronic acid pinacol esters
with 1a under the optimized conditions (Scheme 3). Non-
substituted arylboronic acid pinacol ester (2j) (Scheme 3) gave
the desired product with excellent yield (93%). Likewise,
substrates with halogens in para positions (2e−g) (Scheme 3)
also did so. In particular, arylboronic acid pinacol esters with a
nitro group (2h) (Scheme 3) gave the desired products in 70%
yield. We also prepared 3e on gram scale to demonstrate the
further application of this transformation (Scheme 4).
a
Conditions: 1a (0.1 mmol), 2b−j (0.3 mmol), [RhCp*(MeCN) ]-
3
(
SbF ) (10 mol %), Ag O (0.2 mmol), DCE (2 mL), N , 6 h, 120 °C.
6
2
2
2
b
Isolated yield.
To gain insights into the mechanism, deuterium-labeling
experiments were conducted to determine the kinetic isotope
B
DOI: 10.1021/acs.orglett.7b02931
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 4. Gram-Scale Synthesis
AUTHOR INFORMATION
Corresponding Authors
■
*
*
E-mail: luyi@nju.edu.cn.
E-mail: sunwy@nju.edu.cn.
ORCID
Yi Lu: 0000-0002-8767-7801
Wei-Yin Sun: 0000-0001-8966-9728
Notes
effect (KIE). The observed intermolecular KIE of 3.7 and parallel
KIE of 2.3 revealed that the ortho C−H bond cleavage may be the
rate-determining step (see the SI). On the basis of the results, a
possible reaction mechanism was proposed for this catalytic
reaction (Scheme 5). Coordination of the carbonyl of 1 to the Rh
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Scheme 5. Proposed Reaction Mechanism
We gratefully thank the National Natural Science Foundation of
China (21671097, 21331002, 21201100) and the Fundamental
Research Funds for the General University (020514380071) for
financial support.
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DOI: 10.1021/acs.orglett.7b02931
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