Electrocatalytic Synthesis of Non-Symmetric Biphenols Mediated by Tri(p-bromophenyl)amine: Selective Oxidative Cross-Coupling of Different Phenols and Naphthols

Article abstract of DOI:10.1002/cjoc.201800560

An efficient electrochemical access to the non-symmetric biphenols using tri(p-bromophenyl)amine (TBPA) as a redox mediator has been developed. The electrochemical protocol features highly selective cross-coupling products in up to 83% yield, instead of f

Full text of DOI:10.1002/cjoc.201800560

Electrocatalytic synthesis of non-symmetric biphenols mediated by
tri(p-bromophenyl)amine (TBPA): selective oxidative cross-coupling of
different phenols and naphthols
Qing-Qing Wang,a,b Yang-Ye Jiang,b Cheng-Chu Zeng*,b Bao-Guo Sun*,a
a Beijing advanced innovation center for food nutrition and human health, School of Food and Chemical Engineering, Beijing Technology and Business
University, Beijing 100048, China
b Beijing Key Laboratory of Environmental and Viral Oncology, College of Life Science & Bioengineering, Beijing University of Technology, Beijing 100124,
China
Cite this paper: Chin. J. Chem. 2019, 37, XXX—XXX. DOI: 10.1002/cjoc.201900XXX
An efficient electrochemical access to the non-symmetric biphenols using tri(p-bromophenyl)amine (TBPA) as a redox mediator has been developed.
The electrochemical protocol features highly selective cross-coupling products in up to 83% yield, instead of forming homo-coupling ones.
biphenols using FeCl3 /t-BuOOt-Bu system or catalytic amount of
Introduction
meso-tetraphenylporphyrion iron chloride (Fe[TPP]Cl) in
Efficient synthesis of biphenols has emerged as a prevalent
research field in organic chemistry since these structural motifs
are widely found in natural products, pharmaceutical molecules
and materials, as well as serving as ligands in asymmetrical
synthesis and for other applications.1 To this end, various methods
have been developed to construct the biphenol structural scaffold,
among which the direct oxidative coupling of two unprotected
phenolic molecules has attracted much attention due to its atom-
and step-economic character, and much advances have been
addressed in the oxidative homo-coupling of two phenols,
especially successful in their selectivity and efficiency.2
1,1,1,3,3,3-hexafluoropropano-2-ol (HFIP) using t-BuOOH as the
oxidant.5 Right recently, K2S2O8 in CF3COOH has also been
employed to realize the cross-coupling of phenol-phenol or
phenol-naphthol in the presence of Bu4NHSO3 (10 mol%).6
Moreover, Kita and coworkers have developed an
organo-iodine(III)-catalyzed oxidative cross-coupling reaction of
phenol-phenol using oxone as the terminal oxidant in HFIP
solvent.7 In spite of these progresses, expensive transition-metal
catalysts, such as Fe[TPP]Cl, and excess terminal oxidant are
required, which leads to producing large amount of waste
(Scheme 1a).
However, the cross coupling of two different phenols is not
well studied and still a challenge because of the competitive side
reactions, such as homo-coupling of phenol, oligomerization,
formation of quinone and C-O bond between two phenols.3 In this
context, the cross-coupling of substituted 2-naphthols employing
Electrochemistry uses electron as a traceless reagent to avoid
the producing of waste, thereby emerging as an environmentally
benign means for the C-H functionalization and C-C formation.8 By
separating the electrochemical and chemical processes
independently, Yoshida et al. has developed a versatile and
powerful “cation-pool” method to get access to biaryls.9 However,
this approach could not extend to synthesis of biphenols.10 To
address this issue, Waldvogel and coworkers have made extensive
effects and found that the combination of boron doped diamond
(BDD) anode and HFIP solvent could provide non-symmetric
stoichiometric CuCl2•4H2O
/
benzylamine system was first
4
reported by Hovorka, Zavada, and later by Kocovsky et al. Later
on, Cr-salen-Cy catalyst has been developed for the cross-coupling
of phenols using O2 as a terminal oxidant.3 Recently, Pappo and
coworkers reported the efficient synthesis of non-symmetric
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biphenols in high selectivity and satisfactory yields (Scheme 1b).11
In continuation to our interest in the oxidative
functionalization of C-H bonds via indirect electrolysis using a
redox catalyst as the electron transfer agent.12 we herein reported
the electrocatalytic cross-coupling of phenols with naphthols or
phenols using TBPA as the mediator (Scheme 1c). The protocol
features high chemical selectivity (cross-coupling vs
out. As shown in Figure 1 and Table 1, TBPA gave a well-defined
reversible anodic peak at 0.84 V vs Ag/AgNO3 (0.1 M in CH3CN)
and a cathodic peak at 0.76 V vs Ag/AgNO3 (0.1 M in CH3CN) with
an anodic to cathodic peak current ratio of about 1.0. This
observation corresponds to the oxidation of TBPA to its cation
radical and its reduction, back to TBPA. On the other hand, each
phenol and naphthol exhibits an irreversible oxidation peak in the
homo-coupling), broad scope of substrates and coupling efficiency. range of 0.84 - 1.35 V vs Ag/AgNO3 (Table 1). For example, the
To the best of our knowledge, this work represents the first
example using TBPA as the mediator for the synthesis of
non-symmetric biphenols.
CVs of 1a and 2a were observed to be oxidized irreversibly at 0.90
V and 1.05 V vs Ag/AgNO3, respectively (Figure 1). Higher peak
potentials of 1a with 2a than TBPA indicates that TBPA is easier to
be oxidized over 1a and 2a.
a) Chemical cross-coupling of two different phenols:
OH
Table 1. Peak potentials of TBPA and related compounds
OH
R1
compound
EOX1 (V)
0.84
1.14
0.87
1.37
1.26
1.21
0.84
compound
EOX1 (V)
0.90
0.93
1.35
1.15
1.05
1.13
OH
Conditions
R2
R1
+
OH
TBPA
1b
1a
1c
1e
1g
2a
2c
R2
Conditions:
Hovorka , Zavada and Kocovsky: CuCl2.4H2O, benzylamine, MeOH
Kozlowski et al: Cr-Salen-Cy, O2, DCE, 50-80oC
Pappo et al: FeCl3 (5 mol%), t-BuOOt-Bu, rt
Pappo et al: Fe[TPP]Cl (1 mol%), t-BuOOH, HFIP, rt
Jeganmohan et al: K2S2O8, Bu4NHSO3, CF3COOH, rt
Kita et al:organic catalyst, oxone, 18-crown-6, AcOH, HFIP, rt
1d
1f
1h
2b
b) Electrochemical cross-coupling of two different phenols:
OH
2d
OH
R1
OH
BDD anode, Ni net cathode
Conditions: Cyclic voltammetry was measured in 0.1 M LiClO4/CH3CN
using Pt disk working electrode, Ag wire, and Ag/AgNO3 (0.1 M in CH3CN)
as counter and reference electrode at a scan rate of 100 mA/s.
R1
+
R2
j = 2.8 mA/cm, undivided
OH
R2
cell, HFIP, 50 o
C
c) This work:
When the solution of TBPA was added substrate 1a, the
anodic peak current of TBPA increased from 9.1 μA to 108.1 μA,
along with a complete disappear of cathodic peak current of TBPA,
which proves a catalytic current occurred. Since the oxidation
peak potential of TBPA is less positive than that of 1a, it is
believed that the catalytic current of TBPA results from the
homogeneous electron transfer of TBPA cation radical (TBPA+•)
with 1a. On the other hand, catalytic current of TBPA in the
presence of 2a also existed, but the multitude of peak current is
less than that with 1a (9.1 μA to 30.2 μA). These results are
reasonable when one realizes that the anodic peak potential of 1a
is less positive than that of 2a, resulting into lower oxidation peak
OH
OH
TBPA (10 mol%)
LiClO4 / CH3CN
R1
OH
R1
+
R2
Pt anode
graphite cathode
R2
OH
Scheme 1 Oxidative cross-coupling for the synthesis of non-symmetric
biphenols
Results and Discussion
2.1 Electrochemical analysis of TBPA and related phenols
and naphthols by cyclic voltammetry
To probe the possibility of the TBPA-mediated cross-coupling
reactions of different phenols, cyclic voltammetry analyses of
TBPA and related phenols 1 and naphthols 2 in CH3CN containing
0.1 M LiClO4 as the supporting electrolyte were initially carried
ox
potential gap between TBPA and 1a (ΔEp = 0.06 V) than that
with 2a (ΔEpox = 0.21 V). The smaller the peak potential difference
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between the mediator and a substrate, the larger the catalytic
current. In a word, cyclic voltammetry analysis discloses that
TBPA could be used to mediate the anodic oxidation of 1a and 2a,
but superior for phenol 1a due to its lower oxidation potential
than that of 2a.
2a increased to 1:1.5 from 1:1, product 3a was afforded in 83%
yield (entry 2). Further enhance of the ratio to 1:3 proved to be
unbeneficial; the yield of 3a decreased slightly to 65% (entry 3).
Solvent screening disclosed that CH3CN was preferable since the
commonly used solvents, such as a mixture of CH3CN and CH2Cl2
or CF3CH2OH gave product 3a in moderate yield (entries 4 and 5).
In particular, when methanol or ethanol were used as the solvent,
very poor yield of 3a was isolated due to their low solubility in
these solvents (entries 6 and 7).
The reaction temperature also play an important role for the
dehydrogenative cross-coupling reaction of 1a and 2a. When the
o
reaction was performed at 0 C, only traces of 3a was detected
o
(entry 8), while 60% yield of 3a was isolated at 60 C (entry 9).
Evaluation of electrode materials indicated that a combination of
Pt anode and graphite cathode is beneficial because DSA or
graphite anode with Al or Fe cathode gave lower yields (entries
10-14). When the reaction was carried out in the absence of TBPA,
65% yield of 3a was also isolated (entry 15). Notably, without the
assistance of TBPA, the cross-coupling reaction of 1a with 2a
proceeded slowly, only 2.2 mA of initial current could achieved,
whereas, more than 8.3 mA of initial current was observed in the
presence of TBPA. In addition, when the loading of TBPA
increased to 20%, a comparable yield (80%) of 3a was afforded
(entry 16). When the electrochemical reaction was conducted in
an undivided cell, the desired product 3a was not observed (entry
17). In addition, only 14% yield of 3a was isolated when
tri(p-tolyl)amine was used as a redox catalyst. Based on these
results described above, we concluded that the optimized
conditions allows for using LiClO4/CH3CN as supporting electrolyte,
Pt anode and graphite cathode. The cross-coupling reaction
prefers to be carried out at a controlled-potential of 0.8 V vs
Figure 1. Cyclic voltammograms of TBPA and related compounds in
0.1 M LiClO4/CH3CN using Pt disk working electrode, Ag wire, and
Ag/AgNO3 (0.1 M in CH3CN) as counter and reference electrode at a scan
rate of 100 mA/s.
2.2. Preparative scale of electrolysis
OH
MeO
OMe
OH
OH
OH
MeO
OMe
TBPA
+
0.1 M LiClO4
divided cell
2a
1a
3a
Scheme 2. Electrochemical dehydrogenative cross-coupling of 1a and
2a
The appearance of catalytic current in CVs of TBPA in the
presence of 1a or 2a determines that the preparative electrolysis
of 1a with 2a mediated by TBPA is possible. To confirm such an
idea, we then carried out controlled potential electrolysis of 1a
with 2a in an H-type divided cell using Pt plate as an anode and
graphite plate as a cathode in the presence of 10 mol % of TBPA
as the redox catalyst. When the electrolysis was performed at 0.8
V vs Ag/AgNO3, the oxidation peak potential of TBPA, the
cross-coupling product 3a was afforded exclusively in 75% yield,
without observing the formation of homo-coupling products from
1a or 2a (Scheme 2 and Table 2, entry 1). When the ratio of 1a to
Ag/AgNO3 using 10 mol% of TBPA as the mediator.
Table 2. Optimization of reaction conditions a
entry ratio of anode /
solvent
TBPA temperature yield
1a:2a cathode
(mol%)
10
(%)b
75
1
2
3
4
5
1:1
1:1.5
1:3
Pt/C
Pt/C
Pt/C
CH3CN
CH3CN
CH3CN
r.t.
r.t.
r.t.
r.t.
r.t.
10
10
83
65
55
45
1:1.5
1:1.5
Pt/C CH3CN:DCM(3:1) 10
Pt/C CF3CH2OH 10
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6
7
1:1.5
1:1.5
1:1.5
1:1.5
Pt/C
Pt/C
Pt/C
Pt/C
MeOH
CH3CH2OH
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
10
10
10
10
10
10
10
10
10
-
r.t.
r.t.
0
8
6
and 3l were not detected; and all the starting material were
recovered.
Table 3. Cross-coupling of phenols and naphthols a,b
8
trace
60
9
60
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
OMe
OH
1a
Me
OMe
OH
MeO
10
11
12
13
14
15
16
17c
1:1.5 DSA/C
72
MeO
MeO
OMe
OH
OH
OH
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
C/C
Pt/Al
Pt/Fe
Pt/Pt
Pt/C
Pt/C
Pt/C
Pt/C
65
OH
1c
1d
1b
36
OH
OH
HO
OH
39
HO
2a
2b
2c
2d
78
OH
OMe
OH
OH
65
MeO
OMe
MeO
MeO
OMe
OH
MeO
HO
OMe
20
20
10
80
OH
OH
OH
OH
OH
n.d.
14
OH
18d
3d (58%)
3b (42%)
3c (34%)
3a (83%)
OMe
a
Reaction conditions: 0.5 mmol of 1a with 2a in 10 mL of solvent
Me
OMe
Me
OMe
Me
OMe
MeO
OH
OH
dissolving LiClO4 (0.1 M) as the conducting salt in a H-type divided cell,
controlled potential at 0.8 V vs Ag/AgNO3. 3 F/mol.
b Isolated yield.
OH
OH
OH
OH
OH
OH
HO
HO
OH
3h (39%)
3g (32%)
3e (55%)
3f (42%)
MeO
c under undivided cell.
MeO
MeO
MeO
OH
OH
OH
OH
OH
OH
OH
OH
d Tri(p-tolyl)amine, instead of TBPA was used as redox catalyst.
HO
Br
HO
3j (76%)
3k (0%)
3l (0%)
3i (53%)
With the optimal electrolytic conditions in hand, we then
turned to examine the scope of the substrates and generality of
the reaction. As shown in Table 3, when phenol 1a was subjected
to indirect electrolysis with dihydroxynaphthalene 2b and 2c in
the presence of TBPA as the mediator, corresponding coupling
products 3b and 3c were afforded in 42% and 34%, respectively.
Although the yields of the cross-coupling products were moderate,
the reactions were clear; only cross-coupling products and the
remaining starting materials were detected from TLC, without
formation of homo-coupling products. In addition, it was
observed that these products were formed from the
cross-coupling of para-C-H bond of 1a and one of the α-C-H bond
of 2b and 2c. The electrochemical coupling of
3,4-dimethoxyphenol, 1b, with naphthols 2b or 2c also proceeded
smoothly to give corresponding coupling products 3d and 3e in 58%
and 55% yields, respectively. For 2-methoxy-4-methylphenol 1c,
its reaction with naphthols also worked well, but gave moderate
yields of 3f, 3g and 3h. In the reactions of 4-methoxyphenol 1d
with naphthols, corresponding products 3i and 3j were afforded in
53% and 76% yields, whereas other cross-coupling products, 3k
a
Reaction conditions: phenols 1a-1d (1.0 mmol), naphthols 2a-2d
(1.5 mmol) and TBPA (0.1 mmol) in a H-type divided cell containing 10 mL
of CH3CN/LiClO4 (0.1 M), Pt plate anode and graphite plate as cathode,
room temperature, controlled potential at 0.8 V vs Ag/AgNO3.
b Isolated yield.
A scale-up experiment proved the protocol to be practicable.
As shown in Scheme 3, when 7 mmol of 1a with 2a were
subjected to electrolysis under the standard conditions, 3a (1.18 g)
was isolated in 57% yield and 80% yield based on the recovered
1a.
OH
OH
MeO
OMe
OH
OH
MeO
OMe
standard conditions
+
1a (7 mmol)
2a (1.5 equiv)
3a (1.18 g)
57% isolated yield
80% yield based on recovered 1a
Scheme 3. Scale up
Notably, for naphthanlene-2,3-diol (2b), two OH groups are
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present on the aromatic ring, therefore, bis-arylation reaction of
2b to install two phenol moieties on the α-C-H of the
corresponding OH groups might occur. As shown in Scheme 4,
when 2b with excess amounts of 1a or 1c (2.2 equiv) were
subjected to electrolysis under the standard conditions,
corresponding cross-coupling products 4a or 4b were exclusively
afforded in 62% and 54% yields, respectively, without producing
the homo-coupling products from 1a or 1c, although partial 1a
and 1c were observed remaining and could be recovered.
OH
Me
Me
OMe
OH
MeO
OMe
OH
OH
1e
1b
1g
1a
OH
Me
OH
OH
Me
t-Bu
1f
1h
OH
OH
OH
MeO
OMe
OH
MeO
Me
OMe
MeO
Me
OMe
OH
OH
t-Bu
OMe
5b (18%, 85% c
)
5a (27%)
5c (25 %, 67% c
)
Me
OMe
Me
OMe
OH
Me
OMe
Me
Me
OMe
OMe
OH
OMe
MeO
HO
MeO
OH
OH
standard conditions
OH
OH
OH
OH
+
1a
2b
2.2 equiv
1.0 equiv
OH
4a (62%)
HO
Me
OH
t-Bu
Me
OH
5g (35%)
5d (35%)
5e (39%)
5f (39%)
a
MeO
OMe
Reaction conditions: equivalent amount of phenols (1.0 mmol) and
standard conditions
2b
1c
+
TBPA (0.1 mmol) in a H-type divided cell containing 10 mL of CH3CN/
LiClO4 (0.1 M), Pt plate anode and graphite plate as cathode, room
temperature, controlled potential at 0.8 V vs Ag/AgNO3.
b Isolated yield.
2.2 equiv
1.0 equiv
HO OH
OH
OH
4b (54%)
Scheme 4. Bis-arylation of naphthol 2b
c Isolated yield based on the recovered 1a.
Next, the electrochemical protocol was extended to the
cross-coupling of two different phenols, of which proved to be
difficult and corresponding homo-coupling reaction occurs
predominantly because of their similar oxidation potential values.
To our delight, our mediated electrochemical cross-coupling
reaction of various phenols also worked, although in low yields
(Table 4). For example, the reaction of tri-substituted 1a with
tri-substituted 1b afforded cross-coupling products 5a in 27%
yield. When tri-substituted 1a with di-substituted phenols 1e and
1f were subjected to anodic oxidation under standard conditions,
5b and 5c were isolated after column chromatograph in 18% and
25% yields (85% and 67% yields based on the recovered 1b),
respectively. Notably, the reactions were clear and highly selective,
only cross-coupling products and remaining starting materials
were detected by TLC analysis. Similarly, cross-coupling of 1b with
1e, 1f, 1g and 1h afforded corresponding products 4d, 4e, 4f and
4g in 35%, 39%, 39% and 35%, respectively.
Based on the CV analyses and preparative electrolysis results
described above,
a
TBPA-mediated mechanism for the
cross-coupling of phenol-naphthol or phenol-phenol was
proposed (Scheme 5). Taking the cross-coupling of 1a with 2a as
an example, the reaction sequence starts from an electrochemical
oxidation of TBPA at the surface of anode to generate its cation
radical TBPA+•. Subsequent homogeneous electron transfer of
TBPA+• with less positive oxidation potential of 1a, instead of 2a,
forms corresponding cation radical 6a, which under nucleophilic
addition with 2a, followed by deprotonation and oxidation to give
the final product 3a.
Table 4. Cross-coupling of two different phenols a,b
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three-electrode cell. The working electrode was
a Pt disk
Anode
Cathode
OH
1a
OH
TBPA
MeO
OMe
electrode (ca. φ= 1.0 mm). The auxiliary and reference electrodes
consisted of a Pt wire and Ag/AgNO3 (0.1 M in CH3CN),
respectively. Pt disk electrode 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-1, while that of the
supporting electrolyte was 0.1 mol L-1
MeO
OMe
OH
H2
OH
3a
- e, - 2 H+
.
+
MeO
OMe
TBPA
2 H+
.
+
OH
6a
2a
General procedures for the in-cell electrolysis
Scheme 5.
A
proposed mechanism for the TBPA-mediated
An H-type cell equipped with a 4G porosity glass frit to
separate the anode and cathode compartments was used. A
platinum mesh (2 × 3 cm) served as the working electrode, a
graphite plate served as the counter electrode and an Ag/AgNO3
(0.1 M) electrode was used as the reference electrode. The
electrochemical cross-coupling of phenol 1a and naphthol 2a
Conclusions
In summary, we have developed an efficient electrochemical
access to the non-symmetric biphenols from cross-coupling of
phenols or naphthols using TBPA as the redox mediator. The
electrochemical protocol provides highly selective cross-coupling
products in up to 83% yield, instead of forming homo-coupling
ones. Compared with the previous reports on the conventional
chemical synthesis of non-symmetric biphenols, this
electrochemically dehydrogenative cross-coupling method avoids
the use of transition metals and external oxidants, thus providing
an appealing alternative to the synthesis of non-symmetric
biphenols.
solution of 0.1
M LiClO4/CH3CN was added to the two
compartments (10 mL × 2), each equipped with a magnetic stir
bar. Then the substrate 1a (1.0 mmol), 2a (1.5 mmol), and the
mediator, TBPA (10 mol %), were added to the anodic
compartment. After connection to the constant voltage power
supply, the electrolysis was performed at a potential of 0.8 V (vs
Ag/AgNO3), and terminated when TLC analysis showed that the
starting 1a had been consumed. Then the solvent was removed
under reduced pressure and extraction was carried out using
CH2Cl2 (3 × 15 mL). The combined organic layers were washed
with a saturated aqueous NaCl and dried over MgSO4. Purified
product was obtained after column chromatography on silica gel
using a solvent mixture of petroleum ether and ethyl acetate.
Experimental
Instruments and reagents
1-(4-Hydroxy-3,5-dimethoxyphenyl)naphthalen-2-ol
(3a)6
All melting points were measured with an Electrothermal
melting point apparatus and are uncorrected. NMR spectra were
Yellow liquid; 1H NMR (400 MHz, CDCl3) δ 3.91 (s, 6H), 5.33 (s, 1H),
5.73 (s, 1H), 6.65 (s, 2H), 7.27 (d, J = 8.8 Hz, 1H), 7.34-7.41 (m, 2H),
7.49 (d, J = 8.0 Hz, 1H), 7.81-7.84 (m, 2H); 13C NMR (100 MHz,
CDCl3) δ 56.4, 107.5, 117.2, 121.1, 123.3, 124.7, 126.6, 128.1,
128.9, 129.5, 133.5, 134.8, 148.0, 150.4.
1-(4-Hydroxy-3,5-dimethoxyphenyl)naphthalene-2,3-diol (3b)6
Yellow liquid; 1H NMR (400 MHz, CDCl3) δ 3.75 (s, 6H), 6.52 (s, 2H),
7.10 (d, J = 7.6 Hz, 1H), 7.13-7.20 (m, 2H), 7.31 (d, J = 8.0 Hz, 1H),
7.62 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, DMSO-d6) δ 56.5,
108.7, 123.0, 123.3, 124.7, 126.3, 126.6, 128.8, 129.0, 135.0,
144.0, 146.6,148.3.
1
recorded with 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.
Other chemicals and solvents were obtained from commercial
resource and used without further purification.
Cyclic voltammetry
Cyclic voltammograms were measured using a Princeton
Applied Research 273A Potentiostat/Galvanostat equipped with
electrochemical analysis software, using
a
conventional
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1-(4-Hydroxy-3,5-dimethoxyphenyl)naphthalene-2,7-diol (3c)6
1-(2-Hydroxy-3-methoxy-5-methylphenyl)naphthalene-2,7-dio
1
Yellow liquid; 1H NMR (400 MHz, CDCl3) δ 3.88 (s, 6H), 5.30 (s, 1H), l (3h) Yellow liquid; H NMR (400 MHz, CDCl3) δ 2.37 (s, 3H), 3.96
5.46 (s, 1H), 5.73 (s, 1H), 6.63 (s, 2H), 6.80 (d, J = 2.2 Hz, 1H), 6.97
(dd, J = 8.3 Hz, 2.4 Hz, 1H), 7.12 (d, J = 8.8 Hz, 1H), 7.71-7.74 (m,
2H); 13C NMR (100 MHz, CDCl3) δ 56.4, 106.9, 107.5, 114.7, 115.1,
119.8, 124.2, 125.0, 129.3, 129.9, 134.6, 135.1, 147.9, 150.9,
154.6.
(s, 3H), 5.38 (s, 1H), 5.59 (s, 1H), 6.71 (s, 1H), 6.76 (s, 1H), 6.83 (s,
1H), 6.93-6.95 (m, 1H), 7.13 (d, J = 8.8 Hz, 1H), 7.69-7.74 (m, 2H);
13C NMR (100 MHz, CDCl3) δ 20.8, 55.7, 106.6, 111.7, 114.6, 114.7,
114.9, 118.9, 123.8, 124.2, 129.4, 129.8, 130.1, 134.2, 141.3,
146.9, 151.1, 153.9,; IR (KBr) (cm-1): ν 1461, 1492, 1513, 1624,
1698, 2850, 2919, 3423. HRMS (ESI): calcd for C18H18O4 (M+H)
1-(2-Hydroxy-4,5-dimethoxyphenyl) naphthalene-2,3-diol (3d)
Yellow liquid; 1H NMR (400 MHz, CDCl3) δ 3.97 (s, 3H), 3.98 (s, 3H), 297.1119, found 297.1121.
5.62 (s, 1H), 6.15 (s, 2H), 7.07 (d, J = 6.0 Hz, 2H), 7.21 (s, 2H),
7.28-7.30 (m, 2H), 7.33 (s, 1H), 7.60-7.62 (m, 2H); 13C NMR (100
MHz, CDCl3) δ 56.3, 60.7, 102.0, 104.1, 110.0, 117.2, 124.0, 126.2,
129.5, 142.2, 144.5, 145.7, 146.0, 148.6, 150.6, 171.8; IR
(KBr)(cm-1): ν 3445, 3095, 2922, 2851, 1636, 1474, 1283, 1073;
HRMS(ESI): calcd for [(C18H15O5)] (M-H) 311.0927, found:
311.0925.
1-(2-Hydroxy-5-methoxyphenyl) naphthalen-2-ol (3i)13 Yellow
1
liquid; H NMR (400 MHz, CDCl3) δ 3.79 (s, 3H), 4.65 (s, 1H), 5.42
(s, 1H), 6.81-6.82 (m, 1H), 6.99-7.02 (m, 1H), 7.09 (d, J = 8.9 Hz,
1H), 7.30 (d, J = 8.9 Hz, 1H), 7.39-7.43 (m, 3H), 7.84-7.89 (m, 2H);
13C NMR (100 MHz, CDCl3) δ 60.5, 115.8, 117.9, 118.0, 118.4,
122.6, 123.6, 124.5, 126.9, 128.2, 129.2, 130.2, 133.3, 146.5,
151.2, 154.1
1-(2-Hydroxy-4,5-dimethoxyphenyl) naphthalene-2,7-diol (3e)
Yellow liquid; 1H NMR (400 MHz, CDCl3) δ 3.98 (s, 3H), 3.99 (s, 3H),
5.10 (s, 1H), 5.60 (s, 1H), 6.92-6.95 (m, 1H), 6.99 (s, J = 2.4 Hz, 1H),
7.08 (d, J = 4.4 Hz, 3H), 7.33 (s, 1H), 7.65 (d, J = 8.8 Hz, 1H); 13C
NMR (100 MHz, CDCl3) δ 56.3, 60.7, 102.0, 104.1, 110.0, 117.2,
124.0, 126.2, 129.5, 142.2, 144.5, 145.7, 146.0, 148.6, 150.6,
171.8; IR (KBr)(cm-1): ν 3445, 3095, 2922, 2851, 1636, 1474, 1283,
1073; HRMS (ESI): calcd for C18H15O5 (M-H) 311.2958, found:
311.2955.
6-bromo-1-(4-hydroxy-3,5-dimethoxyphenyl)naphthalen-2-ol
(3j)11d Yellow solid，mp 186oC; 1H NMR (400 MHz, d6-DMSO) δ
3.74 (s, 6H), 6.51 (s, 2H), 7.28 (d, J = 9.2 Hz, 1H), 7.35-7.44 (m, 2H),
7.75 (d, J = 5.6 Hz, 1H), 8.06 (d, J = 1.6 Hz, 1H), 8.44 (s, 1H),9.51(s,
1H),; 13C NMR (100 MHz, d6-DMSO) δ 56.5×2, 108.7×2, 115.8,
120.0, 122.3, 125.9, 127.3, 128.0, 129.3, 129.5, 129.9, 133.0,
135.2, 148.4×2, 152.7.
1,4-Bis(4-hydroxy-3,5-dimethoxyphenyl)naphthalene-2,3-diol
(4a) 6 Brick red solid; 1H NMR (400 MHz, CDCl3) 3.93 (s, 12H), 5.71
(s, 4H), 6.70 (s, 4H), 7.28-7.32 (m, 2H), 7.54 (dd, J = 6.3 Hz, 3.3 Hz,
2H); 13C NMR (100 MHz, CDCl3) δ 51.7, 102.7, 117.0, 119.4, 120.2,
120.4, 123.8, 130.0, 136.0, 143.0.
1-(2-Hydroxy-4-methoxy-5-methylphenyl)
naphthalen-2-ol
1
(3f)13 Yellow liquid; H NMR (400 MHz, CDCl3) δ 2.38 (s, 3H), 3.99
(s, 3H), 5.43 (s, 1H), 5.62 (s, 1H), 6.74 (s, 1H), 6.86 (s, 1H),
7.28-7.42 (m, 3H), 7.48 (d, J = 7.9 Hz, 1H), 7.82-7.84 (m, 2H); 13C
NMR (100 MHz, CDCl3) δ 21.2, 56.1, 112.0, 117.8, 119.3, 123.3,
124.4, 124.8, 126.5, 128.1, 128.4, 129.2, 129.8, 130.4, 133.1,
141.7, 147.2, 150.8.
1,4-Bis(2-hydroxy-5-methoxyphenyl)naphthalene-2,3-diol (4b)
Yellow liquid; 1H NMR (400 MHz, CDCl3) δ 3.79 (s, 6H), 5.20 (s, 2H),
6.34 (s, 1H), 6.78-6.83 (m, 6H), 7.22 (s, 1H), 7.30-7.32 (m, 1H),
7.59-7.62 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 55.9, 110.1, 115.0,
116.1, 124.1, 126.2, 129.5, 144.3, 149.5, 153.7; IR (KBr)(cm-1): ν
3385, 3095, 2925, 1649, 1511, 1473, 1473, 1262,1163; HRMS (ESI):
calcd for C24H19O6 (M-H)+ 403.1192, found 403.1187.
1-(2-Hydroxy-4-methoxy-5-methylphenyl)naphthalene-2,3-dio
13
1
l (3g) Yellow liquid; H NMR (400 MHz, CDCl3) δ 2.38 (s, 3H),
4.00 (s, 3H), 5.86 (s, 1H), 5.98 (s, 1H), 6.07 (s, 1H), 6.77 (s, 1H),
6.85 (s, 1H), 7.24 (d, J = 7.2 Hz, 1H), 7.35-7.31 (m, 2H), 7.50 (d, J =
8.4 Hz, 1H), 7.71 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ
20.7, 55.6, 109.4, 111.3, 117.7, 119.1, 123.4, 123.7, 124.1, 124.5,
126.3, 127.3, 129.8, 129.8, 140.3, 140.4, 144.6, 146.5.
3,3',5'-Trimethoxy-5-methyl-[1,1'-biphenyl]-2,4'-diol
(5a)6
Yellow semisolid; 1H NMR (400 MHz, CDCl3) δ 2.25 (s, 3H), 3.90 (s,
6H), 3.93 (s, 3H), 5.55 (s, 2H), 6.53 (s, 2H), 6.77 (s, 1H), 6.86 (s, 1H);
13C NMR (100 MHz, CDCl3) δ 20.1, 56.1, 56.3, 56.4, 106.2, 112.7,
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116.0, 126.8, 132.8, 133.5, 134.9, 143.2, 145.5, 146.6.
Supporting Information
3',5'-Dimethoxy-5-methyl-[1,1'-biphenyl]-2,4'-diol (5b)11d 1H
NMR (400 MHz, CDCl3) δ 2.34 (s, 3H), 3.93 (s, 6H), 5.22 (s, 1H),
5.62 (s, 1H), 6.67 (s, 2H), 6.90 (d, J = 8.4 Hz, 1H), 7.06-7.13 (m, 2H);
13C NMR (100 MHz, CDCl3) δ 20.5, 56.4, 105.7, 115.5, 127.9, 128.1,
129.5, 129.9, 130.4, 134.4, 147.6, 150.2.
The supporting information for this article is available on the
WWW under https://doi.org/10.1002/cjoc.2018xxxxx.
Acknowledgement
This work was supported by grants from the National Key
Technology R&D Program (2016YFD0400801) and the National
Natural Science Foundation of China (No. 21871019).
5-(tert-Butyl)-3',5'-dimethoxy-[1,1'-biphenyl]-2,4'-diol (5c)11d
o
1
Brown solid; mp 138-140 C; H NMR (400 MHz, CDCl3) δ 1.35 (s,
9H), 3.94 (s, 6H), 5.21 (s, 1H), 5.62 (s, 1H), 6.69 (s, 2H), 6.95 (d, J =
8.4 Hz, 1H), 7.24 (d, J = 2.4 Hz, 1H), 7.32 (dd, J = 8.8 Hz, 2.4 Hz, 1H);
13C NMR (100 MHz, CDCl3) δ 31.6, 34.2, 56.4, 105.9, 115.1, 126.0,
126.8, 127.5, 128.4, 134.5, 143.4, 147.6, 150.2.
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3-Methoxy-5,5'-dimethyl-[1,1'-biphenyl]-2,2'-diol (5d)6 Yellow
1
syrup; H NMR (400 MHz, CDCl3) δ 2.35 (s, 3H), 2.37 (s, 3H), 3.96
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1
(5e)6 Yellow liquid; H NMR (400 MHz, CDCl3) δ 1.35 (s, 9H), 2.38
(s, 3H), 3.96 (s, 3H), 6.22 (s, 1H), 6.28 (s, 1H), 6.75 (m, 2H),
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3-Methoxy-3',5,5'-trimethyl-[1,1'-biphenyl]-2,2'-diol
(5f)6
Yellow semisolid; 1H NMR (400 MHz, CDCl3) δ 2.23 (s, 3H), 2.25 (s,
3H), 2.33 (s, 3H), 3.91 (s, 3H), 6.15 (s, 1H), 6.21 (s, 1H), 6.71 (s, 1H),
6.74 (s, 2H), 6.86 (s, 1H), 7.05 (s, 1H); 13C NMR (100 MHz, CDCl3) δ
18.9, 19.6, 21.3, 56.2, 110.8, 118.9, 122.6, 123.8, 124.0, 129.1,
130.5, 131.7, 138.0, 139.3, 146.3, 151.4.
3-Methoxy-5-methyl-[1,1'-biphenyl]-2,3',4'-triol (5g)6 Yellow
1
liquid; H NMR (400 MHz, CDCl3) δ 2.21 (s, 3H), 3.91 (s, 3H), 5.24
(s, 1H), 5.44 (s, 1H), 6.73 (s, 1H), 6.74 (d, J= 1.88 Hz, 1H), 6.80 (s,
1H), 6.81 (d, J = 1.9 Hz, 1H), 6.88 (d, J = 8.0 Hz, 1H); 13C NMR (100
MHz, CDCl3) δ 20.1, 56.0, 112.7, 115.0, 116.0, 116.6, 122.1, 127.1,
134.3, 134.7, 142.4, 143.0, 143.2, 145.4.
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(The following will be filled in by the editorial staff)
Manuscript received: XXXX, 2019
Manuscript revised: XXXX, 2019
Manuscript accepted: XXXX, 2019
Accepted manuscript online: XXXX, 2019
Version of record online: XXXX, 2019
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Entry for the Table of Contents
Page No.
Electrocatalytic synthesis of non-symmetric
biphenols
mediated
by
OH
OH
tri(p-bromophenyl)amine (TBPA): selective
oxidative cross-coupling of different phenols
and naphthols
TBPA (10 mol%)
LiClO4 / CH3CN
R1
OH
R1
+
R2
Pt anode
graphite cathode
R2
OH
18 examples
up to 83%
Electrochemical cross-coupling of unprotected phenol with naphthols and phenols using TBPA as
mediator has reported.
Author, Qing-Qing Wang, Yang-Ye Jiang,
Cheng-Chu Zeng,* Bao-Guo Sun*
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