Electrogenerated-bases promoted electrochemical synthesis of N-bromoamino acids from imines and carbon dioxide

Article abstract of DOI:10.1016/j.tet.2014.01.054

In this paper, the one-step synthesis of N-bromoamino acids has been developed by electrolyzing imines and carbon dioxide (4 MPa). The electrosynthesis was performed in an undivided cell with Ni cathode and Al sacrificial anode containing n-Bu₄NBr-DMF as supporting electrolyte with a constant current at room temperature. The N-bromoamino acids were afforded in moderate to good yields rather than traditional α-amino acids. To explore the truth, some influenced factors (cathode materials, supporting electrolyte, and electricity etc.) were investigated. The experimental results indicated that the NH group of the α-amino acid could be deprotonated by alkyl anion R^- (carbanion, a strong base), followed by the oxidation of hypobromous acid resulted from the two-step oxidation of the bromide ion at the anode, and produced the N-bromoamino acid. Finally, the reaction mechanism was briefly discussed.

Full text of DOI:10.1016/j.tet.2014.01.054

Tetrahedron 70 (2014) 1855e1860
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Electrogenerated-bases promoted electrochemical synthesis
of N-bromoamino acids from imines and carbon dioxide
,
b
,
a
b
b
b
Chuan-Hua Li a , Xiang-Zhi Song , Li-Ming Tao , Qiang-Guo Li , Jin-Qi Xie ,
*
Meng-Na Peng b, Lan Pan b, Chao Jiang b, Zhi-Yu Peng b, Man-Fen Xu b
a School of Chemistry and Chemical Engineering, Central South University, Changsha, 410083 Hunan, PR China
b Department of Chemistry and Life Science, Xiangnan University, Chenzhou, 423000 Hunan, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 August 2013
Received in revised form 17 January 2014
Accepted 23 January 2014
Available online 28 January 2014
In this paper, the one-step synthesis of N-bromoamino acids has been developed by electrolyzing imines
and carbon dioxide (4 MPa). The electrosynthesis was performed in an undivided cell with Ni cathode
and Al sacrificial anode containing n-Bu4NBreDMF as supporting electrolyte with a constant current at
room temperature. The N-bromoamino acids were afforded in moderate to good yields rather than
traditional
electrolyte, and electricity etc.) were investigated. The experimental results indicated that the NH group
of the
-amino acid could be deprotonated by alkyl anion Rꢀ (carbanion, a strong base), followed by the
a-amino acids. To explore the truth, some influenced factors (cathode materials, supporting
Keywords:
The electrogenerated bases (EGBs)
Electrosynthesis
Benzylideneaniline
Carbon dioxide
a
oxidation of hypobromous acid resulted from the two-step oxidation of the bromide ion at the anode,
and produced the N-bromoamino acid. Finally, the reaction mechanism was briefly discussed.
Ó 2014 Elsevier Ltd. All rights reserved.
N-Bromoamino acid
1. Introduction
haloamino acids continues to attract the interest of synthetic
chemists.
a
-Amino acids are a class of the major building blocks of living
Carbon dioxide (CO2) as one of the greenhouse gases was mainly
produced by human activities and has given rise to a series of se-
rious environmental problems. Considerable attention has been
directed towards the transformation and utilization of carbon di-
oxide. Carbon dioxide as an abundant and renewable raw material
has received extensive attention in both academia and industry.
The electrochemical approach is one of efficient routes for CO2
fixation, in which CO2 can be reduced directly at the cathode9 or
indirectly activated by using metal catalysts, such as Ni, Co, and Pd
complexes.10e12 In the past decades, the electrochemical method
associated with sacrificial anodes in undivided cells has been de-
veloped.13,14 Al and Mg were regarded as the efficient sacrificial
anode materials. Some investigations indicated that Al3þ or Mg2þ
ions resulted from the anode and carbon dioxide pressure could
strongly influence the process of electrocarboxylation.15e19 Elec-
trocarboxylations of CO2 with some organic compounds, including
ketones,20e22 alkenes,23,24 alkynes,25,26 halides,27e31 amines,32,33
epoxides,34 and heterocyclic compounds,35,36 could afford valu-
able compounds for the production of fine chemicals, polymers,
and pharmaceuticals. In particular, electrochemically activated in-
systems, being the principal components of all naturally occurring
peptides and proteins. They have been proved to exhibit quite
diverse physiological and pharmaceutical activities.1 The N-hal-
oamino acids, which could be formed by halogenating agents, such
as hypobromite and N-bromosuccinimide (NBS),2e6 have played an
important role in water quality control processes and in the de-
fense of the organisms against infection. However, several toxic
compounds have been detected among the reaction products of N-
haloamino acids, some of them being characterized as carcinogenic
and/or mutagenic.7 Some work has been focused on the de-
composition of N-haloamino acids because their decomposition
was of environmental interest. The oxidation of amino acids by
halogenating agents could only afford an unstable N-haloamino
acid, which subsequently decarboxylates to give the corresponding
aldehyde or nitrile, depending on the reaction conditions. It is also
worth mentioning that some N-substituted amino acids have been
found to effectively treat the microbe infections of the skin or
mucous membranes, e.g., infections caused by bacteria or fungi.8
Thus, searching the effective approach for the synthesis of N-
sertion of carbon dioxide to the C]N bond can result in a-amino
acids.37e40
Most importantly, the electrochemical method has significant
advantage over the classical syntheses because the electrons as
* Corresponding author. Tel.: þ86 0735 2653129; fax: þ86 0735 2653128; e-mail
address: lichuanhua0526@126.com (C.-H. Li).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.01.054

1856
C.-H. Li et al. / Tetrahedron 70 (2014) 1855e1860
Table 1
a ‘reagent’ allow the formation of highly reactive intermediates
(such as the electrogenerated bases, EGBs). These EGBs are pro-
duced under mild conditions and can replace toxic and harmful
reagents (phosgene, isocyanates, etc.) with low environmental
impact. Molecules, containing a CH or NH group, that is acidic
enough, may be activated versus electrophilic substrates by direct
cathodic reduction or by deprotonation via electrogenerated bases.
Many target compounds, such as oxazolidin-2-ones, carbamates, 5-
Effect of various electrodes on the electrocarboxylation of benzylideneaniline with
a
CO2
Entry
Electrode
Conversionb (%)
Yield 1bc (%)
h
d (%)
1
2
3
4
5
6
Ag
Pt
Cu
31
34
40
43
69
70
25
32
37
41
66
68
12.5
16
18.5
20.5
33
Stainless steel
Zn
Ni
methylene-1,3-oxazolidin-2-ones, and
b-lactams were conve-
34
niently synthesized via the use of the EGBs.41e44 In this context, we
have considerably concerned about the green synthetic method. In
our previous work, an efficient electrochemical method has been
developed for the electrocarboxylation of unsaturated hydrocar-
bons and CO2 with Ni as the cathode without additional catalysts, in
which Ni exhibits good catalytic activation.18,19,45,46 Moreover, we
a
Experimental conditions: benzylideneaniline (2 mmol), DMF (35 mL), CO2
4 MPa, room temperature, n-Bu4NBr (2.5 mmol), electricity (4 F molꢀ1), current
density 10 mA cmꢀ2, Al as sacrificial anode.
b
Conversion was calculated on starting benzylideneaniline.
Isolated yield based on benzylideneaniline.
c
d
h¼Q1/Q2
(h: current efficiency; Q1: quantity of electricity consumed in forming
product; Q2: total electricity quantity in the electrolysis).
also successfully applied the EGBs to synthesize the
a-alkylidene
cyclic carbonates47 and heterocyclic compounds.48
In this work, we attempted to explore the possibility of the one-
step synthesis of N-substituted amino acids from imines and car-
bon dioxide. The idea originated from the previous work.18,19,45e48
In the experiments, a phenomenon was always observed when the
sufficient charges were employed to electrolyze tetrabutylammo-
nium bromide (TBAB)/DMF solution. The electrolyte was found to
slowly become a brown solution. The hypobromous acid in the
electrolyzed solution was detected by UV spectrometry at
330 nm.49 The formation of the hypobromous acid was further
confirmed by using the potential sweep and rotating ring-disc
electrode methods. The reason is that bromide ions undergo
respectively. In comparison, Ni was a more effective cathode for the
formation of 1b, conversely, Ag was the worst one (Table 1, entries 1
and 6). The difference may be related to the nature of cathode
materials.52 One reason for various cathode materials has different
ability on the adsorption of substrates, which could affect the
subsequent electrochemical and chemical processes. In the case of
Ag as cathode, it exhibited pronounced specific absorption toward
imines, which could produce the complex compounds on the
electrode surface and cause the potential shifts to a less cathodic
field for the reduction of imines.53 The specific adsorption could
provide an increase in the imines concentration on the electrode
surface and to accelerate the dimers formation rates, which de-
creased the yields of carboxylation product.37e40In our experi-
ments, the amount of dimers of starting imine formed with Ag as
cathode was much more than that of other cathode materials (the
dimers were confirmed by GC/MS analysis, m/z¼364).
a
two-step oxidation to hypobromous acid at the anode
(Brꢀþe/Brad, BradþH2O/HBrOþHþ).50,51 Considering that the
oxidation of amino acids by halogenating agents can afford the N-
haloamino acids, we tried to electrolyze benzylideneaniline and
CO2. Unexpectedly, the N-bromoamino acid was obtained rather
than the a-amino acid. In the same conditions, other derivatives
have similar property (Scheme 1). The experimental results show
that the electrochemical mechanism is apparently different from
that of the previous work.37e40 Finding the truth has the theoretical
and practical significance of the conversion and utilization of CO2.
To the best of our knowledge, such work has not been reported in
literatures.
2.2. Effect of other electrochemical parameters
When the electrolysis was carried out with Et4NBr to be dis-
solved in DMF as supporting electrolyte, product 1b was also ob-
tained (Table 2, entry 1). With KBr as conducting salt (instead of
a R4Nþ salt), product 1b was not formed (Table 2, entry 2). The
Table 2
Electrocarboxylation of benzylideneaniline influenced by various reaction
conditionsa
Entry
Conducting salt
Conversionb (%)
Yield 1bc (%)
h
d (%)
1
2
Et4NBr
KBr
58
0
53
0
26.5
0
10.5
22
34
35
9
11.5
33
3e
4f
5
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
27
48
70
71
26
25
68
57
21
44
68
70
18
23
66
54
6g
7h
8i
9j
10k
Scheme 1. Electrosynthesis of the N-bromoamino acids from imines and carbon
dioxide.
27
2. Results and discussion
a
Experimental conditions: benzylideneaniline (2 mmol), DMF (35 mL), CO2
4 MPa, room temperature, conducting salts (2.5 mmol), electricity (4 F molꢀ1),
current density 10 mA cmꢀ2, Ni cathode, and Al anode.
2.1. Effect of cathode materials
b
Conversion was calculated on starting benzylideneaniline.
Isolated yield based on benzylideneaniline.
Current efficiency.
Two Faradays per mol of benzylideneaniline supplied to the electrodes.
Three Faradays per mol of benzylideneaniline supplied to the electrodes.
Five Faradays per mol of benzylideneaniline supplied to the electrodes.
n-Bu4NBr (1 mmol).
CH3CN was used as solvent.
It is known that electrode materials, especially cathode mate-
rials, could strongly influence the experience of electro-
carboxylation reaction and resulted in different products.
Therefore, we firstly investigated the influence of cathode mate-
rials. Benzylideneaniline was selected as model molecule. The ob-
tained results were listed in Table 1. With Ag, Pt, Cu, stainless steel,
Zn, and Ni employed as the cathodes, N-bromoamino acid (1b) was
obtained in the yields of 25%, 32%, 37%, 41%, 66%, and 68%,
c
d
e
f
g
h
i
j
Carbon dioxide pressure was 5 MPa.
k
The electrolysis temperature was 10 ꢁC.

C.-H. Li et al. / Tetrahedron 70 (2014) 1855e1860
1857
experimental results indicated that the formation of the N-bro-
moamino acid was related to tetraalkylammonium cations (R4Nþ).
The yields were strongly dependent on the amount of electricity
supplied during the electrolyses (Q). When the electricity increased
from 2 to 4 F molꢀ1, the yield of 1b increased to 68% (Table 2, entries
3e5). Further increasing the electricity, the yield of the target
product increased slightly (Table 2, entry 6). Decreasing the amount
of the conducting salt (n-Bu4NBr), the yield of 1b was decreased
the main products, which indicated the formation of the N-hal-
oamino acids might be related to the property of halogen anion.
2.3. Electrocarboxylation of benzylideneaniline derivatives
with CO2
Under optimal conditions (Ni cathode and Al anode, n-Bu4NBr-
DMF as supporting electrolyte, the electricity 4 F molꢀ1 of starting
substrates, CO2 pressure 4 MPa), we further investigated the elec-
trocarboxylation of benzylideneaniline derivatives with CO2. The
experimental results were listed in Table 3. For different benzyli-
deneaniline derivatives, the corresponding N-bromoamino acids
could be obtained (Table 3, entries 1e7). The property of
substituted groups in benzylideneaniline derivatives could in-
fluence the yield of the N-bromoamino acids. For the substrates
with electron-donating groups, the yield of the target products
increased (Table 3, entries 2e4). Conversely, the electron-
withdrawing groups decreased the yield of the target products
(Table 3, entries 5e7). The experimental results indicated the
electron-donating groups contributed to the formation of the
N-bromoamino acids. The reason may be that the present electro-
chemical reaction involved the free radical process. The electron-
donating groups might enable the substrate free radicals more
and the small amount of the a-amino acid was produced (Table 2,
entry 7). Especially, at the end of the electrolysis, the surplus gases
in high-pressure electrochemical cell were detected by GCeMS
analysis and a certain amount of n-butane was existed. According to
the published work,54 it is reasonable to infer that the R4Nþ at
the cathode in DMF was reduced and provided R3N and Rꢀ
(R4Nþþeꢀ/R4Nꢂ, R4Nꢂ/RꢂþR3N, Rꢂþeꢀ/Rꢀ). Alkyl anion Rꢀ
could deprotonate the NH group of the
RH.43
a-amino acid and produced
The yields were also depended on the solvent. With CH3CN as
the solvent,1b was isolated in 23% yield (Table 2, entry 8). Changing
CO2 pressure and temperature, the yields of 1b were increased to
66%, 54%, respectively (Table 2, entries 9 and 10). In addition, with
n-Bu4NCl or n-Bu4NI as supporting electrolyte, only a small amount
of N-haloamino acids was obtained, while the
a
-amino acids were
Table 3
a
Electrocarboxylation of benzylideneaniline and its derivatives with CO2
Entry
1
Aryl
Product
Conversionb (%)
70
Yieldc (%)
68
hd (%)
Ar1¼Ph, Ar2¼Ph (1a)
34
2
3
Ar1¼p-MeOeC6H4, Ar2¼Ph (2a)
Ar1¼p-MeeC6H4, Ar2¼Ph (3a)
75
72
74
70
37
35
4
Ar1¼Ph, Ar2¼C6H4ep-Me (4a)
74
72
36
5
6
Ar1¼p-CleC6H4, Ar2¼Ph (5a)
Ar1¼Ph, Ar2¼C6H4ep-Cl (6a)
55
52
52
49
26
24.5
7
Ar1¼p-FeC6H4, Ar2¼Ph (7a)
49
45
22.5
a
Experimental conditions: DMF (35 mL), n-Bu4NBr (2.5 mmol), substrate (2 mmol), CO2 4 MPa, room temperature, electricity (4 F molꢀ1), current density 10 mA cmꢀ2, Ni
cathode, and Al anode.
b
Conversion was calculated on starting substrate.
Isolated yield based on substrate (2 mmol).
Current efficiency.
c
d

1858
C.-H. Li et al. / Tetrahedron 70 (2014) 1855e1860
stable than the electron-withdrawing groups did during the elec-
trolysis. Above all, the electron-donating groups were more favor-
able for increasing the nucleophilic ability of the substrates and
resulted in the higher yield. Of course, details are needed to study
further. Based on the above investigated scope of substrates, we
could conclude that the electrochemical approach has wide range
of scope for the synthesis of N-bromoamino acids from imines and
carbon dioxide.
2.4. The electrochemical reaction mechanism
To further elucidate the electrochemical mechanism, the CV
behavior of benzylideneaniline (model compound) and CO2 was
recorded at an Auto LAB (PGSTAT 30) electrochemical workstation
with Ni as a working electrode and a saturated calomel electrode
(SCE) as a reference electrode (as shown in Fig. 1). When the re-
duction potential was about ꢀ1.7 V versus SCE, the reduction cur-
rent of CO2 was still zero (Fig.1a). However, the reduction current of
benzylideneaniline appeared (Fig. 1b). In our previous work,45
a blank experiment (only containing n-Bu4NBr and DMF) in the
Ni working electrode was performed under the same conditions,
where the reduction peak was not observed at ꢀ1.7 V versus SCE.
Thus, in our present CV experiment, the reduction peak at ꢀ1.7 V
versus SCE was attributed to the reduction of benzylideneaniline
rather than that of the R4Nþ. The CV results indicated that benzy-
lideneaniline was preferentially reduced into anion radicals than
carbon dioxide on the surface of the cathode, which was in
agreement with literature data.37e40
Scheme 2. The electrochemical mechanism for the synthesis of the N-bromoamino
acid.
water. It is possible that bromide free radicals generated from the
oxidation of bromide ions are very active and easily combine with
residual water to produce hydrogen bromide. About the source of the
residual water, it is easy to understand that in our electrochemical
system, there is more or less water because it is very difficult to keep
an absolute anhydrous state. The real reason is still unclear for us in
the present stage. Further study is needed to carry out.
3. Experimental
3.1. Chemicals
All solvents and conducting salts were analytical reagent (AR)
and were purchased from Sinopharm Chemical Reagent Co., Ltd.
Imines were purchased from Alfa Aesar and used without further
purification. Tetrabutylammonium bromide (n-Bu4NBr, TBAB) was
dried at 60 ꢁC under vacuum for 10 h. N,N-Dimethylformamide
(DMF) was kept over anhydrous MgSO4 for several days.
3.2. Instrumentation
FTIR spectra were determined by a TENSOR27 spectrometer.
Mass spectra analyses were performed on a Shimadzu QP5050A
spectrometer. 1H NMR and 13C NMR were recorded at 400 MHz and
100 MHz, respectively, with a Bruker DRX-400 spectrometer using
DMSO-d6 as a solvent. Chemical shifts were given in ppm down
Fig. 1. Cyclic voltammograms of a 0.07 mol Lꢀ1 n-Bu4NBreDMF solution (35 mL) at
room temperature at the scan rate 50 mV sꢀ1 on a Ni working electrode: (a) only in the
presence of saturated CO2 (0.1 MPa); (b) only in the presence of benzylideneaniline
(2 mmol).
field (d) from Me4Si (TMS) as an internal standard. The electrolytic
cell and the parameters of the CV experiment were the same as
those reported in our published works.18,19,45,46
Based on the above results and the previous literatures,37e40 the
electrochemical mechanism was proposed in Scheme 2. Benzylide-
neaniline was firstly reduced into radical anion at the cathode and
then reacted with carbon dioxide to afford carboxylate anion A. A
was further reduced to B with a proton. As proposed in the litera-
ture,25 the proton may originate from three different sources (i.e.,
residual water, ammonium salt, and DMF solvent). Under normal
3.3. General procedure
In a typical experimental procedure, a mixture of imine
(2 mmol) and TBAB (2.5 mmol) in dry DMF (35 mL) was taken into
an undivided electrochemical cell equipped with a nickel plate
cathode (2ꢃ3 cm2) and an aluminum plate anode (2ꢃ3 cm2). Se-
quentially, the electrolytic cell was assembled and CO2 was charged
into the cell up to 4 MPa pressure. The solution was electrolyzed at
a constant current of 10 mA cmꢀ2 until electricity of 4 F molꢀ1 of
substrate was passed at room temperature. After the electrolyzed
solution was distilled off at reduced pressure, the residue was
acidified with HCl (1.0 mol Lꢀ1) and continuously stirred for 30 min.
The crude product was obtained by extracting with diethyl ether
(3ꢃ35 mL). The combined ether extracts were washed successively
conditions, acid treatment of B can produce the
a-amino acid.
However, in our present electrochemical system, the tetrabuty-
lammonium cations (R4Nþ) at the cathode could further be reduced
to alkyl anion Rꢀ. The alkyl anions Rꢀ could deprotonate the imino
group of B and produce C.43 At the same time, bromide ion was ox-
idized to the hypobromous acid at the anode by a two-step pro-
cess.50,51 C could combine with hypobromous acid and provide
D.55,56 After D was acidified, product 1b was obtained. It should be
pointed out that the formation of hypobromous acid was involved in

C.-H. Li et al. / Tetrahedron 70 (2014) 1855e1860
1859
with water (2ꢃ25 mL). Evaporation of the solvent in vacuo afforded
the crude product. Further purification could be performed through
re-crystallization or thin layer chromatography and column chro-
matography, with the suitable ratio of petroleum ethereethyl ac-
etate as an eluent, and then dried at 60 ꢁC in a vacuum oven.
and carbon dioxide. Nickel as cathode displays the better catalytic
activity. The imines with different substituted groups on the ben-
zene ring have obvious impact on the yield of the desired products.
The formation of the N-bromoamino acids was suggested to be
involving the deprotonation of the imino groups by the electro-
generated bases (Rꢀ), and then reacted with hypobromous acids
from the two-step oxidation of bromide ions. The present approach
provides a valuable and competitive procedure for the synthesis of
the N-bromoamino acids, which has a certain reference value for
the conversion and utilization of CO2.
3.4. Characterizations of products
3.4.1. 2-(N-Bromo-N-phenylamino)-2-phenylacetic acid (1b). 1H
NMR (DMSO-d6, 400 MHz):
7.37e7.33 (m, 2H), 7.30e7.28 (m,1H), 7.04e7.00 (m, 2H), 6.63 (m, 2H),
6.54e6.51 (m,1H), 5.06 (s,1H).13C NMR (DMSO-d6,100 MHz):
173.0,
146.9, 138.5, 128.7, 128.4, 127.7, 127.5, 116.5, 113.0, 59.7. IR (KBr):
1713 cmꢀ1. HRMS: calcd for C14H12BrNO2 305.0050, found 305.0053.
d 12.42 (s, 1H), 7.51e7.49 (m, 2H),
d
Acknowledgements
n:
The authors thank the Postdoctoral Foundation of Central South
University, the National Natural Science Foundation of China (Nos.
20973145, 21273190), the Opening Topic Fund for Hunan Provincial
Key Laboratory of Xiangnan Rare-Precious Metals Compounds and
Applications (2012XGJSYB02), Hunan Provincial Natural Science
Foundation of China (No. 11JJ3019), and the Construct Program of
the Key Discipline in Hunan Province for financial support.
3.4.2. 2-(N-Bromo-N-phenylamino)-2-(4-methoxyphenyl)
acetic
acid (2b). 1H NMR (DMSO-d6, 400 MHz):
d
12.35 (s, 1H), 7.41e7.36
(m, 2H), 7.04e7.00 (m, 2H), 6.93e6.90 (m, 2H), 6.64e6.58 (m, 2H),
6.54e6.51 (m, 1H), 4.99 (s, 1H), 3.72 (s, 3H). 13C NMR (DMSO-d6,
100 MHz):
59.0, 55.1. IR (KBr):
d
173.2, 158.8, 147.0, 131.2, 130.3, 128.7, 116.5, 115.0, 113.0,
: 1710 cmꢀ1. HRMS: calcd for C15H14BrNO3
n
335.0140, found 335.0138.
Supplementary data
3.4.3. 2-(N-Bromo-N-phenylamino)-2-p-tolylacetic acid (3b). 1H
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2014.01.054.
These data include MOL file and InChiKey of the most important
compounds described in this article.
NMR (DMSO-d6, 400 MHz):
d 12.38 (s, 1H), 7.39e7.37 (m, 2H),
7.01e6.97 (m, 2H), 6.87e6.79 (m, 2H), 6.62e6.58 (m,1H), 6.35e6.24
(m, 2H), 4.92 (s, 1H), 2.37 (s, 3H). 13C NMR (DMSO-d6, 100 MHz):
d
173.1, 147.2, 137.3, 129.2, 127.5, 127.3, 126.7, 115.5, 112.9, 58.6, 25.5.
IR (KBr):
n
: 1708 cmꢀ1. HRMS: calcd for C15H14BrNO2 319.0200,
References and notes
found 319.0201.
3.4.4. 2-(N-Bromo-N-p-tolylamino)-2-phenylacetic acid (4b). 1H
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d 12.41 (s, 1H), 7.43e7.39 (m, 2H),
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100 MHz):
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d
172.9, 147.0, 137.4, 129.1, 127.6, 127.1, 126.9, 115.7, 112.8,
: 1707 cmꢀ1. HRMS: calcd for C15H14BrNO2
n
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ꢀ
ꢁ
ꢀ
(5b). 1H NMR (DMSO-d6, 400 MHz):
d 12.50 (s, 1H), 7.58e7.51 (m,
213.
ꢀ
ꢁ
ꢀ
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found 338.9658.
n
: 1714 cmꢀ1. HRMS: calcd for C14H11BrClNO2 338.9660,
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7.41e7.36 (m, 2H), 7.23e7.16 (m, 2H), 7.06e7.01 (m, 2H), 6.55e6.51
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173.9, 146.7,
d
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ꢀ
~
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In conclusion, we have developed a new strategy for the one-
step synthesis of N-bromoamino acids by electrolyzing imines

1860
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