Intermolecular Electrochemical C(sp3)-H/N-H Cross-coupling of Xanthenes with N-alkoxyamides: Radical Pathway Mediated by Ferrocene as a Redox Catalyst

Article abstract of DOI:10.1002/adsc.201701536

Efficient intermolecular dehydrogenative cross-coupling of N-alkyloxyamides with xanthenes is reported. The protocol is carried out in an undivided cell under constant current conditions employing simple, cheap and readily available ferrocene (Fc) as a redox catalyst. Cyclic voltammetry and control experiments disclosed that the dehydrogenative cross-coupling reaction may proceed via an amidyl radical. (Figure presented.).

Full text of DOI:10.1002/adsc.201701536

Title: Intermolecular electrochemical C(sp3)-H/N-H cross-coupling of
xanthenes with N-alkoxyamides: radical pathway mediated by
ferrocene as a redox catalyst
Authors: mengying lin, kun Xu, yangye jiang, yongguo liu, baoguo sun,
and Cheng-Chu Zeng
This manuscript has been accepted after peer review and appears as an
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201701536
Link to VoR: http://dx.doi.org/10.1002/adsc.201701536

Advanced Synthesis & Catalysis
10.1002/adsc.201701536
FULL PAPER
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
3
Intermolecular electrochemical C(sp )-H/N-H cross-coupling of
xanthenes with N-alkoxyamides: radical pathway mediated by
ferrocene as a redox catalyst
a
a
a
b
b
Meng-Ying Lin, Kun Xu, Yang-Ye Jiang, Yong-Guo Liu, Bao-Guo Sun and
a,
Cheng-Chu Zeng *
a
Beijing Key Laboratory of Environmental and Viral Oncology, College of Life Science & Bioengineering, Beijing
University of Technology, Beijing 100124, China.
Corresponding author: zengcc@bjut.edu.cn
Beijing Key Laboratory of Flavor Chemistry, Beijing Technology and Business University, Beijing 100048, China
b
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Abstract. Efficient intermolecular dehydrogenative cross-
coupling of N-alkyloxyamides with xanthenes is reported. Keywords: Electrochemical oxidative amination; C-N
The protocol is carried out in an undivided cell under constant formation; Ferrocene; Redox mediator
current conditions employing simple, cheap and readily
available ferrocene (Fc) as a redox catalyst. Cyclic
voltammetry and control experiments disclosed that the
dehydrogenative cross-coupling reaction may proceed via an
amidyl radical.
traces of transition metal in products, from the
Introduction
employed catalysts or oxidants, is highly concerned.
Consequently, mild, metal-free and atom economic
The cross dehydrogenative coupling to form new C-
oxidative C-N bonds formation is highly desirable.
heteroatom bonds has emerged as a profound method
Electrochemistry
provides
an
alternative,
in organic synthesis due to its step- and atom economy
environmentally benign method to generate nitrogen-
centred radical for the formation of C-N bonds, either
through direct electrolysis or via a redox catalyst
playing the role of the electron transfer agent (indirect
electrolysis). For example, a direct intramolecular
anodic oxidation of olefins tethering a nitrogen
trapping group was proceeded to synthesize nitrogen-
containing heterocycles by Moeller et al. (Scheme
characteristics
as
well
as
avoiding
the
[
1]
prefunctionlization of substrates. Among various C-
heteroatom bonds, the C-N bond has been in the
central position since C-N bonds are important
structural moieties (such as amines, amides, and
peptides) in natural products, pharmaceuticals,
[2]
agrochemicals and material sciences. As a result,
efficient and selective construction of a new C-N bond
has always been paid much attention in the industrial
and academic setting. Although it is taught in a college
textbook that the C-N bond could be formed from a
nucleophilic substitution reaction of an alkyl halide
with a nitrogen-nucleophile, the transition-metal
catalyzed ionic type cross couplings for forming C-N
bonds are more popular and have been widely
employed in the synthesis of natural products,
[6]
1
a). Xu and co-workers achieved the electrocatalytic
hydroamidation and aminooxygenation of unactivated
alkenes using Fc or TEMPO as redox catalysts
[7]
(
Scheme 1b).
Mechanistically, these processes
reported above involves the electrochemical
generation of a nitrogen-centred radical and its
subsequent intramolecular addition to unsaturated C-C
2
3
bonds, thus constructing C(sp , sp )-N bonds. Herein,
we describe an intermolecular radical substitution
[
3]
polymers, and
pharmaceutical compounds.
3
between C(sp )-H and N-H bond via electrochemical
Alternatively, oxidative radical processes have also
been developed for the formation of C(sp )-N and
cross
dehydrogenative
coupling
of
N-
2
[4]
[8]
[9]
methoxyamides and xanthenes using cheap Fc as
the redox catalyst (Scheme 1c). The process is
conveniently carried out in an undivided cell under
constant current conditions. To the best of our
3
[5]
C(sp )-N bonds. Despite these advances, most of
these strategies mentioned above require either
prefunctionalized substrates, such as alkyl halides or
sulfonates as nucleophilic partners, or a combination
of a transition metal catalyst and an excess amount of
chemical oxidant. Moreover, the toxicity of residual
knowledge, this work represents the first example of
intermolecular
3
electrochemical
C(sp )-H/N-H
1
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Advanced Synthesis & Catalysis
10.1002/adsc.201701536
dehydrogenative cross-coupling using
mediator.[
a
redox
mol % decreased the yield of product 3a to 38% (entry
20). Notably, the redox catalyst Fc could be recovered
in almost quantitatively after column chromatography.
Finally, other anodes and cathodes were also examined,
however, the results showed that none of the ones
tested gave better yield than that of with carbon as the
anode and cathode (entries 21-22 vs 14).
10]
Scheme 2. Electrochemical dehydrogenative cross-
coupling of 1a and 2a.
[
a]
Table 1. Optimization of the reaction conditions .
Anode
Yield
Entry
Catalyst
Additive
Supporting electrolyte
MeOH
b
/
Cathode
(%)
1
2
3
4
5
NaBr
NaBr
NaBr
NaBr
NaBr
-
-
-
-
-
C/C
20
14
C/C
LiClO
LiClO
LiClO
4
4
4
3
/CH CN
Scheme 1. Electrochemically oxidative cross-coupling for
the formation of C-N bonds.
C/C
/EtOH
18
C/C
/THF:MeOH (5:1)
trace
22
C/C
MeOH:CH
LiClO
4:1)
LiClO
2:1)
LiClO
2:1)
LiClO
2:1)
LiClO
2:1)
LiClO
2:1)
2
Cl
2
(2:1)
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
/CH
/CH
/CH
/CH
/CH
/CH
/CH
/CH
/CH
/CH
/CH
/CH
/CH
/CH
/CH
/CH
/CH
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
CN:H
2
O
Results and Discussion
6
7
8
9
NaBr
NaBr
NaBr
-
-
-
-
-
-
C/C
C/C
C/C
C/C
C/C
C/C
C/C
C/C
C/C
C/C
C/C
C/C
C/C
C/C
C/C
Pt/C
C/Fe
12
34
(
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
CN:CH
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
To prove the concept described above, N-
methoxyamide 1a and xanthene 2a were chosen as
model substrates to optimize the reaction conditions
(
40
(
(
Scheme 2 and Table 1). The electrochemical cross-
coupling reaction of 1a with 2a was performed in an
undivided cell equipped with a carbon anode and a
carbon cathode. When NaBr was used as a mediator,
initial screening of supporting electrolyte/solvent
Et
4
NBr
23
(
1
1
1
1
1
1
1
1
1
1
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
n-Bu
4
NI
trace
12
(
system indicates that LiClO
4
in CH
3
CN/CH
2
Cl (v: v
2
NH
4
I
(
=
2: 1) was the best (entries 1-7). Based on our
LiClO
(2:1)
experience in the halide mediated electrochemical
NH
4
Br
Na
Na
2
CO
3
51
formation of chemical bonds,[
11]
various halide-
LiClO
containing salts as a redox catalyst in the optimal
Fc
Fc
Fc
Fc
Fc
Fc
---
Fc
Fc
Fc
-
46
(
2:1)
LiClO
2:1)
LiClO
2:1)
LiClO
2:1)
LiClO
2:1)
LiClO
2:1)
LiClO
2:1)
LiClO
2:1)
LiClO
2:1)
LiClO
2:1)
solution were then screened (entries 8-11). After some
attempts, NH Br was proved to be the best halide-
4
2
CO
3
62
(
based catalyst (entry 8); the electrochemical cross-
coupling led to the formation of product 3a in 40%
yield, along with the generation of xanthone, 4, and
another side-product. Based on the spectroscopic
analysis, the side product should derive from 1a, but
its structure could not be identified at this stage. The
NaOH
Pyridine
DBU
58
(
trace
46
(
(
yield of 3a increased to 51% in the presence of Na
2
CO
3
as an additive (entry 12). By switching the catalyst to
Et
3
N
42
(
Fc, the yield of product 3a increased to 46% and 62%
before and after the addition of Na
2
CO (entries 13 and
3
Na
2
2
2
2
CO
CO
CO
CO
3
3
3
3
23
(
1
4). These results indicate that additive plays an
important role, as a result, different additives were
examined in the next. However, other commonly
Na
Na
Na
38
(
used bases such as NaOH, pyridine, DBU, and Et N,
3
60
(
failed to give better yields (entries 15-18). Control
experiment revealed that Fc is essential for this
electrochemical cross-coupling reaction, while only
55
(
[
a]
Reaction conditions: 1a (1.0 mmol), 2a (1.2 mmol),
catalyst (0.5 mmol) and additive (1.0 mmol) in an undivided
cell, J = 5 mA/cm , room temperature. Xanthone and an
2
3% yield of product 3a was obtained in the absence
of Fc along with the formation of the unidentified side
product (entry 19). Lowering the catalyst loading to 25
2
2
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Advanced Synthesis & Catalysis
10.1002/adsc.201701536
unidentified material were also formed in different amounts.
Isolated yields. Along with xanthone in 15% yield.
Fc (0.25 mmol).
To further examine the limitation of this reaction,
other substrates were also investigated. As shown in
[
b]
[c]
[d]
Scheme
3,
when
isochromane,
9,10-
dihydroanthracene, diphenylmethane and 1,2-
methylenedioxybenzene were subjected to react with
1a under the standard conditions, the desired
corresponding products were not detected and most of
the starting 1a was decomposed, although the exact
reason was not clear yet.
Under the optimized conditions, the substrate scope
of this electrochemical cross-coupling reaction with
various N-methoxyamides 1 was investigated. As
shown in Table 2, reactions with all of the N-
methoxyamides bearing electron-donating or electron-
withdrawing substituents gave the corresponding
products in good to moderate yields. For para-
substituted N-methoxyamides, strong electron-
donating group (such as methoxyl) and the electron-
withdrawing nitro-group were not compatible with the
optimized conditions, leading to the formation of 3c
and 3g in much lower yields. N-Methoxyamides with
meta-substituents were also good substrates for theses
electrochemical cross-coupling reactions, giving
corresponding products 3h and 3i in 51% and 63%
yields, respectively. In addition, ortho-methyl
substituted substrate 1j gave corresponding cross-
coupling product 3j in up to 73%. It is noteworthy that
heteroarene amides and 2-naphthamide also tolerated
well to give cross-coupling products 3k-3m in 64-77%
yields. In addition to aromatic amides, aliphatic
amides, such as 2n, also worked well to give the
3
Scheme 3. Molecular structures of C(sp )-H–containing
reagents that failed to react under the optimized reaction
conditions.
The large-scale preparation of product 3a highlights
the utility of this procedure (Scheme 4). Upon scaling
up the electrochemical reaction to 6.0 mmol, the
product 3a was obtained in 37% yield.
2
corresponding 3n in 45% yield. For the R group,
when the methyl group was replaced by an ethyl group,
the corresponding product 3o was obtained in 63%
yield.
Scheme 4. Gram-scale synthesis.
Next, some substituted xanthenes were tested under
the optimized conditions. As shown in Table 2, acyl-
substituted xanthenes 1p-1r were well tolerated to give
corresponding products 3p-3r in 50-53% yields.
As mentioned above, apart from the most effective
ferrocene, NH Br also mediated the cross-coupling of
4
1
a with 2a, although in a slightly lower yield (See
[
a]
Table 2. Substrate scope of amides and xanthenes .
Table 1, entry 12 vs entry 14). Therefore, the
electrochemical cross-coupling of N-alkyloxy amides
and xanthenes was also investigated to demonstrate the
generality of NH Br as the redox catalyst. As shown in
4
Table 3, when xanthene 2a was subjected to
electrolysis with 1f under the standard conditions but
using NH Br as the mediator, the adduct 3f was
4
generated in 32% yield, less than with ferrocene (56%
yield). A similar trend was also observed for other
substrates. For example, NH Br-mediated cross
4
coupling gave 3i, 3j, 3m, and 3o in 51%, 59%, 29%
and 48% yields, respectively, whereas slightly higher
yields were obtained using ferrocene as the mediator.
[
a]
Reaction conditions: N-alkyloxy amides 1 (1.0 mmol),
xanthenes 2 (1.2 mmol), Fc (0.5 mmol) and Na CO (1.0
mmol) in a mixed solvent CH CN/CH CH (2: 1 = v: v),
undivided cell, J = 5 mA/cm , room temperature.
2
3
Table 3. Cross-coupling of N-alkyloxy amides and
[a,b]
3
2
2
4
xanthenes mediated by NH Br.
2
3
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Advanced Synthesis & Catalysis
10.1002/adsc.201701536
Figure 1. Cyclic voltammograms of Fc and related
4 3 2 2
compounds in 0.1 M LiClO /CH CN: CH Cl (2: 1 = v/ v)),
[
a]
Reaction conditions: N-alkyloxy amides 1 (1.0 mmol),
xanthenes 2 (1.2 mmol), NH Br (0.5 mmol) and Na CO
1.0 mmol) in a mixed solvent CH CN/CH CH (2: 1 = v:
using Pt working electrode, Pt wire and Ag/AgNO (0.1 M
3
4
2
3
in CH CN) as counter and reference electrode at 20 mV/s
3
(
3
2
2
scan rate. a: 1a (1.0 mmol/L), b: 1a (1.0 mmol/L) and t-
BuOK (20.0 mmol/L), c: 2a (1 mmol/L); d: 2a (1.0 mmol/L)
and t-BuOK (20.0 mmol/L), e: Fc (1 mmol/L), f: Fc (1
mmol/L) and 1a (2.0 mmol/L), g: Fc (1 mmol/L) and t-
BuOK (20.0 mmol/L), h: Fc (1 mmol/L) and 1a (2.0
mmol/L) in the presence of t-BuOK (40.0 mmol/L).
2
[b]
v), undivided cell, J = 5 mA/cm , room temperature. The
yields using ferrocene as mediator are shown in parentheses
for a comparison
To better understand the mechanism for the
electrochemical dehydrogenative cross-coupling of N-
alkoxyamides and xanthenes, cyclic voltammetry was
initially employed. As shown in Figure 1, N-
alkoxyamide 1a was redox inactive in the range of 0.0
In addition, when the electrolysis was repeated
under the standard conditions in the presence of 2
equiv of butylated hydroxytoluene (BHT), a trapping
adduct 5 was isolated in 23% yield, along with trace
amount of product 3a. This result indicates that the
cross-coupling may involve a radical process via an
alkoxyamidyl radical as the intermediate (Scheme 5).
V – 2.0 V vs Ag/AgNO
whereas it afforded an irreversible oxidation wave at
.73 V vs Ag/AgNO (0.1 M in CH CN) when
3
(0.1 M in CH
3
CN) (curve a),
0
3
3
stoichiometric amount of t-BuOK was added to
prepare its corresponding anion (curve b). This result
indicates that 1a is easily oxidized in the presence of a
base. In a contrast, xanthene 2a give an obvious
oxidation wave at 1.61 V vs Ag/AgNO
CH CN) in the absence and presence of t-BuOK
curves c and d). Curve e was CV of Fc, giving a
reversible oxidation peak at 0.48 V and reduction peak
at 0.40 V vs. Ag/AgNO (0.1 M in CH CN). The CV
3
(0.1 M in
3
(
Scheme 5. Control experiment.
3
3
of Fc did not change when either 1a (curve f) or t-
BuOK was added (curve g). However, an obvious
catalytic current was observed in the presence of 1a
and t-BuOK, along with complete disappear of
reduction current (curve h), or decrease of intensity of
cathodic peak current at 100 mV/s scan rate (see
Figure S1 in Supporting Information for details).
These results drop a hint that a homogeneous electron
transfer occurs between Fc at its oxidized form and 1a
with the assistance of t-BuOK. This observation is
reasonable when one takes note of only 0.25 V of peak
potential gap between Fc and 1a in the presence of a
base (0.73 for 1a in the presence of t-BuOK vs. 0.48 V
for Fc). Notably, the homogeneous electron transfer
did not occur between Fc and 2a in the absence and
presence of t-BuOK, due to a large potential gap (1.61
V for 2a vs. 0.48 V for Fc).
Based on CV results and control experiment, as well
as previous reports, a possible reaction mechanism for
the electrochemical dehydrogenative cross-coupling
of N-methoxyamides with xanthenes is proposed and
depicted in Scheme 6. The anodic oxidation of Fc (II)
affords Fc (III), which undergoes homogeneous
electron transfer with N-alkoxyamide anion 6,
generated from the reaction of N-alkoxyamide with a
base, to give alkoxyamidyl radical, 7. Alkoxyamidyl
radical abstracts a benzylic hydrogen atom from
xanthene to afford xanthene radical 8. Then, the
xanthene radical 8 loses an electron to generate cation
9.
Trapping cation 9 with N-alkoxyamide anion 6
gives product 3. On the other hand, the cathodic
reduction of a proton gives hydrogen. It is reported that
[
12]
pK
CH
a
for xanthene in DMSO is 30.0
and
[13]
3
CONHOMe is 17.1, which indicates that the
acidity of hydroxamic acid is much stronger than that
of xanthene. Consequently, we believe that the
homogeneous electron transfer occurs between Fc (III)
and N-alkoxyamide anion 6, instead of the conjugated
base of xanthene.
4
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Advanced Synthesis & Catalysis
10.1002/adsc.201701536
1
were recorded using a 400 MHz spectrometer (400 MHz H
frequency, 100 MHz 13C frequency). Chemical shifts are
given as δ values (internal standard: TMS). Coupling
constants are reported in Hz. Amides were synthesized
[
14]
according to known procedure.
derivatives 1-(9H-xanthen-2-yl)ethan-1-one, phenyl(9H-
xanthen-2-yl)methanone, and p-tolyl(9H-xanthen-2-
yl)methanone) were prepared according to literature
Various xanthene
[
15]
procedures.
Other starting materials and solvents were
Scheme 6. A plausible mechanism for the electrochemical
dehydrogenative cross-coupling of N-methoxyamides with
xanthenes.
obtained from commercial sources and used without further
purification. Products were purified by chromatography on
silica gel (petroleum ether/EtOAc).
Cyclic voltammetry
A plausible mechanism mediated by NH Br is
4
illustrated in the Scheme 7. The reaction sequence
begins with the anodic oxidation of bromide to form
bromine and its subsequent reaction with N-
alkoxyamide 1 to afford 10. Then, a homolytic
cleavage of intermediate 10 affords alkoxyamidyl
radical 7. Radical 7 abstracts a benzylic hydrogen atom
from xanthene 2 to afford xanthene radical 8. Then, the
xanthene radical 8 loses an electron to generate cation
Cyclic voltammograms were measured using a Princeton
Applied Research 273A Potentiostat/Galvanostat equipped
with electrochemical analysis software, using
a
conventional three-electrode cell. The working electrode
was a platinum disk electrode (ca. φ= 3 mm). The auxiliary
and reference electrodes consisted of a Pt wire and
3 3
Ag/AgNO (0.1 M in CH CN), respectively. Platinum was
polished with a polishing cloth before each measurement.
All electrodes for CV experiments were obtained from CH
Instruments, Inc. USA. The concentration of all tested
compounds was 1 mmol/L, while that of the supporting
electrolyte was 0.1 mol/L.
9.
Trapping cation 9 with N-alkoxyamide 1 gives
product 3.
Typical procedure for the electrochemical cross-
coupling of N-alkoxyamides and xanthenes
An undivided cell was equipped with a carbon anode
2
2
(
2.5×2.0 cm ) and a carbon cathode (2.5×2.0 cm ) and
connected to a DC regulated power supply. To the cell was
added amide (1 mmol), xanthene (1.2 mmol) , Fc (0.5
mmol) , Na
2
CO
3
(1.0 mmol) and 15 mL of 0.1 M
Cl (2: 1 = v/ v). The mixture was
4
Scheme 7. The plausible mechanism mediated by NH Br
LiClO /CH CN:CH
4
3
2
2
2
electrolyzed using constant current conditions (~5 mA/cm )
at room temperature under magnetic stirring. When TLC
analysis indicated that the electrolysis was complete
Conclusion
(
witnessed by the disappearance of the amide), the solvent
In conclusion, we have developed a novel
electrochemical protocol to generate N-alkoxyamidyl
radical from N-methoxyamides using Fc as the
mediator. By virtue of this strategy, the first example
of intermolecular dehydrogenative cross-coupling of
was removed under reduced pressure. The residue was
purified by column chromatography on silica gel using a
mixture of petroleum ether/EtOAc (v: v = 8: 1) as eluent to
afford the desired pure product.
3
C(sp )-H and N-H was realized via mediated
N-Methoxy-4-methyl-N-(9H-xanthen-9-yl)benzamide (3a)
electrolysis. The protocol proceeds in an undivided
cell under constant current conditions employs simple,
cheap and readily available Fc as the redox catalyst,
rather than the combination of transition metals and
excess amounts of external oxidant, thereby providing
an environmentally benign method to generate amidyl
radical. Further application in organic synthesis of this
electrochemical generation of amidy radical from N-
alkoxyamides is underway in our laboratory
Yield: 213 mg, 62%; Yellow oil; Reaction time: 7 h; Flash
chromatography (Petroleum ether/EtOAc, 8/1). H NMR
1
(
400 MHz, CDCl
3
) δ 2.36 (s, 3H), 2.94 (s, 3H), 7.08 (s, 1H),
7
1
.12-7.19 (m, 6H), 7.33-7.37 (m, 2H), 7.56 (dd, J = 7.7 Hz,
13
.3 Hz, 2H), 7.60 (d, J = 8.2 Hz, 2H); C NMR (100 MHz,
) δ 21.5, 52.7, 64.5, 116.8, 118.8, 123.5, 128.5, 128.8,
29.5, 129.6, 131.2, 141.2, 152.8, 169.9; HRMS (ESI-TOF)
CDCl
1
3
+
m/z calcd for C22
68.1257.
3
H19NNaO (M+Na) : 368.1251, found:
3
N-Methoxy-N-(9H-xanthen-9-yl)benzamide (3b) Yield:
Experimental Section
o
2
05 mg, 62%; Yellow solid; mp: 86-89 C; Reaction time: 6
1
Instruments and reagents
h; Flash chromatography (Petroleum ether/EtOAc, 8/1). H
NMR (400 MHz, CDCl ) δ 2.92 (s, 3H), 7.08 (s, 1H), 7.12-
7.19 (m, 4H), 7.33-7.42 (m, 5H), 7.57 (dd, J = 7.7 Hz, 1.2
3
All melting points were measured with an electrothermal
melting point apparatus and are uncorrected. NMR spectra
13
Hz, 2H), 7.65-7.67 (m, 2H); C NMR (100 MHz, CDCl ) δ
3
5
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Advanced Synthesis & Catalysis
10.1002/adsc.201701536
1
3
5
1
C
2.7, 64.5, 116.8, 118.8, 123.5, 128.1, 128.2, 129.5, 129.7,
3
(m, 3H), 7.64-7.65 (m, 1H); C NMR (100 MHz, CDCl ) δ
30.7, 134.2, 152.8, 170.0; HRMS (ESI-TOF) m/z calcd for
52.6, 64.8, 116.9, 118.5, 123.7, 126.4, 128.4, 129.5, 129.8,
130.8, 134.1, 135.8, 152.8, 168.4; HRMS (ESI-TOF) m/z
+
21
H
17NNaO
3
(M+Na) : 354.1101, found: 354.1109.
+
calcd for C21
388.0715.
H
16ClNNaO
3
(M+Na) : 388.0711, found:
N,4-Dimethoxy-N-(9H-xanthen-9-yl)benzamide (3c) Yield:
45 mg, 40%; Yellow oil; Reaction time: 7.5 h; Flash
1
1
chromatography (Petroleum ether/EtOAc, 8/1). H NMR
400 MHz, CDCl ) δ 2.96 (s, 3H), 3.83 (s, 3H), 6.88 (d, J =
.8 Hz, 2H), 7.11 (s, 1H), 7.12-7.20 (m, 4H), 7.34-7.38 (m,
H), 7.56 (dd, J = 7.7 Hz, 1.2 Hz, 2H), 7.73 (d, J = 8.8 Hz,
N-Methoxy-3-methyl-N-(9H-xanthen-9-yl)benzamide (3i)
Yield: 218 mg, 63%; Yellow solid; mp: 64-66 C; Reaction
time: 5.5 h; Flash chromatography (Petroleum ether/EtOAc,
8/1). H NMR (400 MHz, CDCl
o
(
3
8
2
2
1
1
1
3
) δ 2.39 (s, 3H), 2.98 (s,
13
H); C NMR (100 MHz, CDCl
3
) δ 52.7, 55.3, 64.4, 113.4,
3H), 7.11 (s, 1H), 7.17-7.23 (m, 4H), 7.29-7.31 (m, 2H),
16.7, 118.9, 123.4, 126.1, 129.5, 129.5, 130.6, 152.8, 161.7, 7.37-7.41 (m, 2H), 7.48 (d, J = 6.4 Hz, 1H), 7.52 (s, 1H),
13
69.2; HRMS (ESI-TOF) m/z calcd for C22
H
19NNaO
4
7.60 (d, J = 7.6 Hz, 2H); C NMR (100 MHz, CDCl
52.6, 64.5, 116.8, 118.8, 123.5, 125.2, 128.0, 128.7, 129.5,
29.6, 131.5, 134.2, 137.9, 152.8, 170.2; HRMS (ESI-TOF)
3
)δ 21.4,
+
(
M+Na) : 384.1206, found: 384.1209.
1
+
4
-Fluoro-N-methoxy-N-(9H-xanthen-9-yl)benzamide (3d)
m/z calcd for C22
368.1257.
3
H19NNaO (M+Na) : 368.1257, found:
Yield: 163 mg, 47%; Yellow oil; Reaction time: 7 h; Flash
chromatography (Petroleum ether/EtOAc, 8/1). H NMR
1
(
400 MHz, CDCl
3
) δ 2.91 (s, 3H), 7.03-7.07 (m, 2H), 7.13-
N-Methoxy-2-methyl-N-(9H-xanthen-9-yl)benzamide (3j)
7
7
6
1
1
.21 (m, 5H), 7.35-7.39 (m, 2H), 7.56 (d, J = 7.6 Hz, 2H),
Yield: 253 mg, 73%; Yellow oil; Reaction time: 7 h; Flash
chromatography (Petroleum ether/EtOAc, 8/1). H NMR
1
3
1
.70-7.73 (m, 2H); C NMR (100 MHz, CDCl
3
) δ 52.5,
4.6, 115.2 (d, J = 21.8 Hz), 116.8, 118.7, 123.6, 129.5,
29.7, 130.0 (d, J = 3.8 Hz), 130.9 (d, J = 8.3 Hz), 152.8,
(400 MHz, CDCl
7.14-7.19 (m, 6H), 7.24-7.25 (m, 2H), 7.33-7.38 (m, 2H),
7.61 (d, J = 7.5 Hz, 2H); 13C NMR (100 MHz, CDCl
) δ
19.1, 52.0, 64.4, 116.8, 118.8, 123.5, 125.2, 126.4, 129.2,
29.7, 130.1, 134.9, 135.2, 153.1, 171.7; HRMS (ESI-TOF)
3
) δ 2.20 (s, 3H), 2.78 (s, 3H), 7.12 (s, 1H),
64.1 (d, J = 249.8 Hz), 168.6; HRMS (ESI-TOF) m/z calcd
3
+
for C21
H
16FNNaO
3
(M+Na) : 372.1006, found: 372.1007.
1
+
4
-Chloro-N-methoxy-N-(9H-xanthen-9-yl)benzamide (3e)
m/z calcd for C22
368.1257.
3
H19NNaO (M+Na) : 368.1257, found:
Yield: 214 mg, 59%; Yellow oil; Reaction time: 6 h; Flash
chromatography (Petroleum ether/EtOAc, 8/1). H NMR
1
(
(
2
400 MHz, CDCl
m, 4H), 7.31-7.38 (m, 4H), 7.55 (dd, J = 7.6 Hz, 1.2 Hz,
H), 7.62 (d, J = 8.6 Hz, 2H); C NMR (100 MHz, CDCl
3
) δ 2.90 (s, 3H), 7.10 (s, 1H), 7.12-7.19
N-Methoxy-N-(9H-xanthen-9-yl)furan-2-carboxamide (3k)
Yield: 248 mg, 77%; White solid; mp: 108-109 C; Reaction
o
1
3
3
)
time: 5.5 h; Flash chromatography (Petroleum ether/EtOAc,
1
δ 52.6, 64.7, 116.9, 118.6, 123.6, 128.4, 129.5, 129.8, 129.9,
32.4, 137.0, 152.8, 168.7; HRMS (ESI-TOF) m/z calcd for
8/1). H NMR (400 MHz, CDCl
3
) δ 3.23 (s, 3H), 6.50 (d, J
1
C
= 2.0 Hz, 1H), 7.09 (d, J = 2.8 Hz, 1H), 7.14 (t, J = 7.2 Hz,
2H), 7.21 (d, J = 8.8 Hz, 3H), 7.37 (t, J = 8.0 Hz, 2H), 7.54
+
21
H
16ClNNaO
3
(M+Na) : 388.0711, found: 388.0710.
(
d, J = 7.6 Hz, 2H), 7.64 (s, 1H); 13C NMR (100 MHz,
4
-Bromo-N-methoxy-N-(9H-xanthen-9-yl)benzamide (3f)
3
CDCl ) δ 52.5, 65.0, 111.8, 116.7, 118.3, 118.6, 123.6,
Yield: 229 mg, 56%; Yellow oil; Reaction time: 6 h; Flash
chromatography (Petroleum ether/EtOAc, 8/1). H NMR
129.7, 129.8, 145.8, 152,9, 159.7; HRMS (ESI-TOF) m/z
1
+
calcd for C19
344.0895.
H
15NNaO
4
(M+Na) : 344.0893, found:
(
(
(
6
1
400 MHz, CDCl
m, 4H), 7.33-7.37 (m, 2H), 7.49 (d, J = 8.8 Hz, 2H), 7.54
3
) δ 2.90 (s, 3H), 7.10 (s, 1H), 7.12-7.19
1
3
d, J = 8.8 Hz, 4H); C NMR (100 MHz, CDCl
3
) δ 52.6,
4.8, 116.9, 118.6, 123.6, 125.4, 129.5, 129.8, 130.1, 131.4,
32.9, 152.8, 168.8; HRMS (ESI-TOF) m/z calcd for
N-Methoxy-N-(9H-xanthen-9-yl)thiophene-2-carboxamide
o
(3l) Yield: 216 mg, 64%; Yellow solid; mp: 109-111 C;
Reaction time: 7 h; Flash chromatography (Petroleum
+
1
C
21
H
16BrNNaO
3
(M+Na) : 432.0206, found: 432.0210.
ether/EtOAc, 8/1). H NMR (400 MHz, CDCl
3
) δ 3.25 (s,
3
H), 7.09-7.14 (m, 3H), 7.18 (d, J = 1.2 Hz, 1H), 7.20 (d, J
N-Methoxy-4-nitro-N-(9H-xanthen-9-yl)benzamide (3g)
= 1.2 Hz, 1H), 7.22 (s, 1H), 7.33-7.38 (m, 2H), 7.51-7.54
Yield: 158 mg, 42%; Yellow oil; Reaction time: 6 h; Flash
chromatography (Petroleum ether/EtOAc, 8/1). H NMR
(m, 2H), 7.56 (dd, J = 5.2 Hz, 1.2 Hz, 1H), 7.99 (dd, J = 4.0
1
13
Hz, 1.6 Hz, 1H); C NMR (100 MHz, CDCl
3
) δ 50.2, 62.9,
(
(
(
400 MHz, CDCl3) δ 2.91 (s, 3H), 7.16 (s, 1H), 7.18-7.25
m, 4H), 7.40-7.44 (m, 2H), 7.59 (d, J = 7.2 Hz, 2H), 7.78
114.3, 116.2, 121.2, 124.6, 127.3, 127.3, 130.6, 131.2, 132.6,
150.3, 160.8; HRMS (ESI-TOF) m/z calcd for
1
3
+
d, J = 8.8 Hz, 2H), 8.24 (d, J = 8.8 Hz, 2H); C NMR (100
) δ 52.8, 65.0, 117.0, 118.3, 123.3, 123.7, 129.2,
29.4, 130.0, 140.1, 148.9, 152.9, 168.0; HRMS (ESI-TOF)
C
19
H
15NNaO
3
S (M+Na) : 360.0665, found: 360.0666.
MHz, CDCl
1
3
N-Methoxy-N-(9H-xanthen-9-yl)-2-naphthamide
(3m)
+
Yield: 248 mg, 65%; Yellow solid; mp: 173-175 oC;
16 2 5
m/z calcd for C21H N NaO (M+Na) : 399.0951, found:
3
3
99.0950.
Reaction time: 7 h; Flash chromatography (Petroleum
1
ether/EtOAc, 8/1). H NMR (400 MHz, CDCl
3
) δ 2.97 (s,
-Chloro-N-methoxy-N-(9H-xanthen-9-yl)benzamide (3h)
3H), 7.19-7.25 (m, 5H), 7.39-7.43(m, 2H), 7.52-7.59 (m,
Yield: 185 mg, 51%; Yellow oil; Reaction time: 5.5 h; Flash
chromatography (Petroleum ether/EtOAc, 8/1). H NMR
2H), 7.66 (d, J = 7.6 Hz, 2H), 7.75-7.78 (m, 1H), 7.85-7.91
1
13
(m, 3H), 8.27 (s, 1H); C NMR (100 MHz, CDCl
3
) δ 52.7,
(
(
400 MHz, CDCl
m, 4H), 7.28-7.32 (m, 1H), 7.34-7.41 (m, 3H), 7.52-7.56
3
) δ 2.92 (s, 3H), 7.10 (s, 1H), 7.14-7.20
64.7, 116.8, 118.8, 123.6, 125.0, 126.5, 127.5, 127.7, 127.8,
128.8, 128.9, 129.6, 129.7, 131.4, 132.5, 134.3, 152.9,
6
This article is protected by copyright. All rights reserved.

Advanced Synthesis & Catalysis
10.1002/adsc.201701536
1
69.8; HRMS (ESI-TOF) m/z calcd for C25
H
19NNaO
3
135.0, 141.1, 143.3, 152.3, 155.7, 170.0, 194.8; HRMS
+
+
(
M+Na) : 404.1257, found: 404.1255.
(ESI-TOF) m/z calcd for C30
found: 486.1678.
H
25NNaO
4
(M+Na) : 486.1676,
N-Methoxy-N-(9H-xanthen-9-yl)cyclohexanecarboxamide
3n) Yield: 151 mg, 45%; Yellow oil; Reaction time: 6.5 h;
[
14]
(
Xanthone (4) Yield: 30 mg, 15%; White solid; mp:177-
1
o
Flash chromatography (Petroleum ether/EtOAc, 8/1). H
NMR (400 MHz, CDCl ) δ 1.16-1.31 (m, 3H), 1.46-1.55 (m,
H), 1.65-1.83 (m, 5H), 2.48-2.55 (m, 1H), 3.15 (s, 3H),
178 C; Reaction time: 6.5 h; Flash chromatography
(Petroleum ether/EtOAc, 8/1). H NMR (400 MHz, CDCl
1
3
3
)
2
6
7
δ 7.41 (t, J = 7.6 Hz, 2H), 7.53 (d, J = 8.4 Hz, 2H), 7.74-
.99 (s, 1H),7.07-7.11 (m, 2H), 7.14-7.16 (m, 2H), 7.30-
7.78 (m, 2H), 8.37 (dd, J = 8.0 Hz, 1.6 Hz, 2H); 13C NMR
.34 (m, 2H), 7.42 (dd, J = 7.7 Hz, 1.3 Hz, 2H); 13C NMR
3
(100 MHz, CDCl ) δ 118.0, 121.8, 123.9, 126.7, 134.8,
(
100 MHz, CDCl
3
) δ 25.7, 25.8, 28.7, 40.7, 51.4, 65.1, 116.6, 156.2, 177.2.
1
19.3, 123.3, 129.4, 129.6, 152.8, 178.9; HRMS (ESI-TOF)
+
m/z calcd for C21
H
23NNaO
3
(M+Na) : 360.1570, found:
N-(3,5-di-tert-butyl-1-methyl-4-oxocyclohexa-2,5-dien-1-
yl)-N-methoxy-4-methylbenzamide (5) Yield: 88 mg, 23%;
3
60.1569.
Yellow oil; Reaction time: 7 h; Flash chromatography
1
N-Ethoxy-4-methyl-N-(9H-xanthen-9-yl)benzamide (3o)
(Petroleum ether/EtOAc, 8/1). H NMR (400 MHz, CDCl
3
)
Yield: 224 mg, 63%; Orange solid; mp: 100-102 oC;
δ 1.25 (s, 18H), 1.74 (s, 3H), 2.39 (s, 3H), 3.42 (s, 3H), 6.95
Reaction time: 6.5 h; Flash chromatography (Petroleum
(s, 2H), 7.19 (d, J = 7.6 Hz, 2H), 7.56 (d, J = 7.6 Hz, 2H);
C NMR (100 MHz, CDCl ) δ 21.5, 26.2, 29.4, 34.7, 62.5,
3
1
13
ether/EtOAc, 8/1). H NMR (400 MHz, CDCl
3
) δ 0.58 (t, J
=
7.2 Hz, 3H), 2.34 (s, 3H), 3.06 (q, J = 7.2 Hz, 2H), 7.08(s,
64.5, 128.3, 128.6, 132.4, 140.7, 141.1, 145.1, 172.1, 186.0;
+
1
H), 7.11-7.17 (m, 6H), 7.31-7.35 (m, 2H), 7.55 (d, J = 7.6
HRMS (ESI-TOF) m/z calcd for C24
406.2353, found: 406.2358.
H
3
33NNaO (M+Na) :
1
3
Hz, 2H), 7.60 (d, J = 8.0 Hz, 2H); C NMR (100 MHz,
CDCl ) δ 13.3, 21.5, 52.8, 72.9, 116.7, 119.1, 123.5, 128.5,
28.7, 129.5, 129.6, 131.4, 141.0, 153.0, 170.0; HRMS
3
Supporting Information Available: Copies of H NMR, 13C
1
1
+
(
ESI-TOF) m/z calcd for C23
H
21NNaO
3
(M+Na) : 382.1414, NMR spectral and HRMS.
found: 382.1418.
Acknowledgements
N-(2-Acetyl-9H-xanthen-9-yl)-N-methoxy-4-
methylbenzamide (3p) Yield: 194 mg, 50%; Yellow oil;
This work was supported by grants from the National Key
Technology R&D Program (2017YFB0307502,
011BAD23B01) and the National Natural Science
Foundation of China (No. 21472011). ZCC also thank
financial support from the Open Project Program of Beijing
Key Laboratory of Flavor Chemistry, Beijing Technology
and Business University (BTBU)
Reaction time: 7 h; Flash chromatography (Petroleum
1
ether/EtOAc, 8/1). H NMR (400 MHz, CDCl
3
) δ2.36 (s,
2
3
5
H), 2.58 (s, 3H), 2.97 (s, 3H), 7.04 (s, 1H), 7.17-7.23 (m,
H), 7.35-7.39 (m, 1H), 7.58-7.61 (m, 3H), 7.98 (dd, J = 8.4
1
3
Hz, 1.8 Hz, 1H), 8.16 (s, 1H); C NMR (100 MHz, CDCl
3
)
δ 21.5, 26.5, 52.6, 64.5, 116.9, 117.1, 118.6, 118.9, 124.2,
1
1
C
28.4, 128.9, 129.4, 129.8, 129.9, 130.7, 131.0, 132.8, 141.4,
52.2, 156.2, 170.1, 196.3; HRMS (ESI-TOF) m/z calcd for
+
24
H
21NNaO
4
(M+Na) : 410.1363, found: 410.1367.
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This article is protected by copyright. All rights reserved.

Advanced Synthesis & Catalysis
10.1002/adsc.201701536
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Advanced Synthesis & Catalysis
10.1002/adsc.201701536
FULL PAPER
3
Intermolecular electrocatalytic C(sp )-H/N-H
cross-coupling of xanthenes with N-alkoxyamides:
radical pathway mediated by ferrocene as a redox
catalyst
Adv. Synth. Catal. Year, Volume, Page – Page
Meng-Ying Lin, Kun Xu, Yang-Ye Jiang,
Yong-Guo Liu, Bao-Guo Sun and Cheng-Chu
Zeng*
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