Amide-Directed Cobalt(III)-Catalyzed C-H Amidation of Ferrocenes

Article abstract of DOI:10.1021/acs.orglett.8b03938

The amide-directed cobalt(III)-catalyzed C-H amidation of ferrocene carboxamides using 1,4,2-dioxazol-5-ones as robust and efficient amidating reagents has been developed. This reaction proceeds efficiently under mild reaction conditions with good functional group tolerance, providing expedient access to a broad range of ferrocenes containing a nitrogen group on the Cp ring.

Full text of DOI:10.1021/acs.orglett.8b03938

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Amide-Directed Cobalt(III)-Catalyzed C−H Amidation of Ferrocenes
Dan-Ying Huang,† Qi-Jun Yao,§ Shuo Zhang,§ Xue-Tao Xu,*,†,‡ Kun Zhang,*,†,‡ and Bing-Feng Shi*,§
†School of Biotechnology and Health Sciences, Wuyi University, Jiangmen, 529020, China
‡International Healthcare Innovation Institute (Jiangmen), Jiangmen 529040, China
§Department of Chemistry, Zhejiang University, Hangzhou 310027, China
S
* Supporting Information
ABSTRACT: The amide-directed cobalt(III)-catalyzed C−H
amidation of ferrocene carboxamides using 1,4,2-dioxazol-5-
ones as robust and efficient amidating reagents has been
developed. This reaction proceeds efficiently under mild
reaction conditions with good functional group tolerance,
providing expedient access to a broad range of ferrocenes
containing a nitrogen group on the Cp ring.
Scheme 1. Transition Metal-Catalyzed C−H Amidation of
Ferrocene Derivatives
errocene and its derivatives have attracted much attention
due to their important applications in asymmetric
F
synthesis,1 molecular switches,2 and pharmaceuticals.3 There-
fore, tremendous efforts have been devoted to the synthesis of
functionalized ferrocenes. Traditionally, functionalized ferro-
cenes were prepared via either Friedel−Crafts type electro-
philic aromatic substitution or directed ortho-lithiation using
stoichiometric alkyllithium reagents.4 However, the use of air-
sensitive, stoichiometric alkyllithium reagents imposes great
limitations.
Transition metal-catalyzed C−H functionalization has
emerged as one of the most straightforward strategies to
access these skeletons.5 However, these elegant methods have
mainly focused on the formation of C−C bonds, such as
alkylation,6 arylation,7 alkenylation,8 alkynylation,9 and acyla-
tion.10 To the best of our knowledge, C−N bond formation via
C−H amination of ferrocene derivatives has not been realized
until recently. You and co-workers reported the first Rh(III)-
catalyzed C−H amidation of ferrocenes using pyridyl as a
directing group (Scheme 1a).11a Very recently, You et al.11b
and Ackermann et al.11c elegantly demonstrated the Co(III)-
catalyzed C−H amidation of ferrocenes using pyridyl and
thiocarbonyl as directing groups, respectively. Meanwhile, C−
H functionalization of ferrocenes heavily rely on precious
transition metal catalysts, prominently featuring iridium,
rhodium and palladium complexes.5−10,11a In sharp contrast,
C−H functionalization of ferrocenes with earth-abundant,
inexpensive base metal catalysts continues to be scar-
ce.11b,c,12,8i,13 Yu, Dai, and co-workers reported the first
reagents.14 Shortly after, the same group elegantly revealed that
dioxazolones could also be utilized as a new type of amidating
reagent in Co(III)-catalyzed C−H amidation reactions.15
Inspired by these pioneering work and our continuous interests
in Co(III)-catalyzed C−H functionalization,16,17 herein we
report a Co(III)-catalyzed C−H amidation of ferrocene
carboxamides with 1,4,2-dioxazol-5-ones under mild con-
ditions (Scheme 1b).
We commenced our investigations by using 1-(pyrrolidine-
1-carbonyl) ferrocene (1a) as a model substrate to react with
3-phenyl-1,4,2-dioxazol-5-one (2a) for the optimization of
Co(III)-catalyzed C−H amidation reaction conditions. Nota-
bly, the choice of 1,4,2-dioxazol-5-ones as amidating reagent
has several advantages: (1) they can be easily prepared from
the corresponding hydroxamic acids;18 (2) they can be used or
stored without special precautions; (3) the reaction is oxidant
copper-mediated C−H thiolation of ferrocenes.13 Butenschon
̈
and co-workers reported a Co-catalyzed ortho-C−H alkenyla-
tion of ferrocenes.8i The incorporation of a nitrogen atom onto
ferrocene via base-metal-catalyzed C−H amination using
synthetically useful functional groups, such as amides, as
directing groups would be highly desirable.
In 2015, Chang and co-workers demonstrated a pioneering
work on Rh(III)-catalyzed C−H amidation of arenes with
1,4,2-dioxazol-5-ones as robust and highly efficient amidating
Received: December 10, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b03938
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Organic Letters
Letter
ab
free and CO2 is released as the single byproduct. We were
delighted to find that the desired amidation product 3a was
obtained in 55% yield using [Cp*Co(CO)I2] as the catalyst in
combination with AgNTf2 in DCE under nitrogen (Table 1,
Scheme 2. Scope of Various Dioxazolones
a
Table 1. Optimization of the Reaction Conditions
T
yield
b
entry
solvent
DCE
additive (mol %)
(°C) silver salt
(%)
1
2
3
4
5
6
7
8
PivOH (20)
PivOH (20)
PivOH (20)
PivOH (20)
PivOH (20)
PivOH (20)
PivOH (20)
PivOH (20)
PhCO2H (20)
1-AdCO2H (20)
AcOH (20)
PivOH (40)
none
60
60
60
60
60
60
60
60
60
60
60
60
60
40
80
AgNTf2
AgNTf2
AgNTf2
AgNTf2
AgNTf2
AgBF4
AgOTf
AgSbF6
AgNTf2
AgNTf2
AgNTf2
AgNTf2
AgNTf2
AgNTf2
AgNTf2
55
62
64
54
73
dioxane
ethyl acetate
toluene
acetone
acetone
acetone
acetone
acetone
acetone
acetone
acetone
acetone
acetone
acetone
c
c
60
42
65
46
65
47
41
14
70
64
9
10
11
12
13
14
15
a
Reaction conditions: 1a (0.1 mmol), 2 (0.15 mmol), [Cp*Co-
(CO)I2] (0.01 mmol, 10 mol %), AgNTf2 (0.02 mmol), PivOH (0.02
mmol) in 1.0 mL acetone at 60 °C for 24 h. Isolated yield.
b
PivOH (20)
PivOH (20)
a
Reaction conditions: 1a (0.1 mmol), 2a (0.15 mmol), [Cp*Co-
desired amidation product in relatively higher yields.
Importantly, halides, such as chloride (3f and 3l), bromide
(3g, 3n, and 3o), and iodide (3h), survived under the
optimized conditions, giving the desired products in moderate
to good yields. These groups could be further elaborated via
conventional cross-coupling reactions. Alkyl substituent could
also be tolerated, affording the desired product in moderate
yield (3o, 43%). Dioxazolone bearing a heteroarene sub-
stituent at the 3-position also reacted smoothly with 1a to give
the desired product in good yields (thiophene, 3p, 76%; furan,
3q, 82%). It is worth mentioning that ferrocene-derived
dioxazolone 2r also acted as a good aminating reagent and the
desired product (3r) was obtained in 69% yield. Of particular
significance is the fact that [2.2]paracyclophane, an important
scaffold widely applied in organic synthesis and materials
science, is compatible with this protocol (3s, 53%).
Encouraged by the results above, the scope of ferrocene
derivatives was examined next. As shown in Scheme 3,
ferrocene derivatives bearing various different amides could
react smoothly with 2a to give the desired products in
moderate to good yields (3aa−3ad). but the yield will not
change much when the pyrrole ring is opened (3ad).
Ferrocenes bearing a substituent on the other Cp ring were
tested next. An isopropyl group was tolerated to give 3ae in
66% yield. 1-(Furan-2-yl)ethyl group was also compatible with
this reaction, albeit in reduced yield (3af, 22%). The yield
could be significantly increased when 1-phenylethyl was
attached on the other Cp ring (3ag, 83%). Subsequently, the
electronic effect of benzyl substituent was investigated,
however, both electron-withdrawing and electron-donating
groups led to reduced yields (3ah−3aj). When methyl
prolinate was introduced to ferrocene carboxamide, it could
act as a chiral auxiliary to give moderate diastereoselectivity
(CO)I2] (0.01 mmol, 10 mol %), AgNTf2 (0.02 mmol), PivOH (0.02
b
mmol), solvent (1.0 mL), 60 °C, 24 h. 1H NMR yield using
c
mesitylene as the internal standard. Isolated yield. 1-AdCO2H = 1-
adamantanecarboxylic acid.
entry 1). Acetone turned out to be the optimal solvent (entry
5, 73% isolated yield), while protic solvents or strong
coordinating solvents, such as DMF, DMSO, MeCN, and
alcohols, totally inhibit the reaction (see the Supporting
Information). After the screening of a variety of silver salts,
AgNTf2 was found to be the most suitable additive for this
transformation (entries 5−8). The judicious choice of
carboxylic acids could significantly affect the efficiency and
PivOH was proved to be the best (entries 9−13). We
speculated that a bulky carboxylic acid, such as PivOH, could
act as proper ligand in the C−H cleavage step via concerted
metalation deprotonation (CMD) mechanism and suppress
the aggregation of the cobalt by steric effect to maintain the
activity. The reaction proceeded most efficiently at 60 °C, and
increasing or lowering the temperature resulted in reduced
yield (entries 14 and 15). The structure of 3a was
unambiguously confirmed by X-ray crystallographic analysis
(Scheme 2; also see the Supporting Information for details).
With the optimal reaction conditions in hand, we set out to
explore the generality of this amidation reaction. In general, the
amidation reaction proceeded smoothly over a wide range of 3-
substituted-1,4,2-dioxazol-5-ones (Scheme 2). Both electron-
donating groups (e.g., Me, MeO, t-Bu) and electron-with-
drawing groups (e.g., F, Cl, Br, I, CF3) in substituted benzene
are compatible with this reaction protocol (3b−3n).
Dioxazolones bearing electron-withdrawing substituents on
the aromatic ring are generally more efficient, giving the
B
DOI: 10.1021/acs.orglett.8b03938
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Letter
ab
Scheme 3. Scope of Ferrocenes
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b03938.
Experimental details and spectral data for all new
compounds and X-ray crystallography/CIF for 3a
(PDF)
Accession Codes
CCDC 1871963 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: wyuchemxxt@126.com (X.X.)
*E-mail: kzhang@gdut.edu.cn (K.Z.)
*E-mail: bfshi@zju.edu.cn (B.-F.S.)
ORCID
Bing-Feng Shi: 0000-0003-0375-955X
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from Department of Education of
Guangdong Province (No. 2017KTSCX185, 2017KSYS010,
2016KCXTD005) is gratefully acknowledged.
a
Reaction conditions: 4 (0.1 mmol), 2a (0.15 mmol), [Cp*Co-
(CO)I2] (0.01 mmol, 10 mol %), AgNTf2 (0.02 mmol), PivOH (0.02
mmol) in 1.0 mL acetone at 60 °C for 24 h. Isolated yield. The dr
value was determined by H NMR.
b
c
1
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