Oxidant-Free C(sp2)-H Functionalization/C-O Bond Formation: A Kolbe Oxidative Cyclization Process

Article abstract of DOI:10.1021/acs.joc.8b00089

An anodic oxidation/cyclization of 2-arylbenzoic acids for the synthesis of dibenzopyranones has been developed. The reaction proceeds at room temperature with no oxidant or electrolyte required and exhibits a high atom economy with H₂ being th

Full text of DOI:10.1021/acs.joc.8b00089

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Article
2
Oxidant-Free C(sp)-H Functionalization/C-O Bond
Formation: A Kolbe Oxidative Cyclization Process
Lei Zhang, Zhenxing Zhang, Junting Hong, Jian Yu, Jianning Zhang, and Fanyang Mo
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b00089 • Publication Date (Web): 23 Feb 2018
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The Journal of Organic Chemistry
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Oxidant-Free C(sp )−H Functionalization/C−O Bond Formation: A
Kolbe Oxidative Cyclization Process
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†
†
Lei Zhang, Zhenxing Zhang, Junting Hong, Jian Yu, Jianning Zhang, Fanyang Mo*
Department of Energy and Resources Engineering, College of Engineering, Peking University, Beijing 100871, China
ABSTRACT: An anodic oxidation/cyclization of 2ꢀarylbenzoic acids for dibenzopyranones synthesis has been developed. The
reaction proceeds at room temperature with no oxidant or electrolyte required, and exhibits high atomꢀeconomy as H being the
only byꢀproduct. A series of dibenzopyranones were obtained in good to excellent yields. Urolithin A, B and C are formally syntheꢀ
sized by adopting this method as a key step to demonstrate its synthetic utility.
2
ꢀ
Kolbe dimer R−R. However, aryl carboxylates (ArCO ) canꢀ
not be applied in Kolbe dimerization due to the challenging
2
INTRODUCTION
Oxygenꢀcontaining heterocycles are privileged motifs found in
numerous bioactive natural products, organic materials, agroꢀ
chemicals, and pharmaceuticals. The traditional approaches
for constructing such heterocyclic scaffolds mainly rely on the
addition of a nucleophile to a carbonyl group, to a halide or
other leaving groups, electrocyclic reactions, etc. However,
most of these approaches involve the use of expensive reaꢀ
gents, harsh conditions, and generate large amounts of waste.
Although much progress has been made in recent decades in
the transition metalꢀcatalyzed cyclization of acyclic substrates
Scheme 1. Intramolecular Anodic Oxidative C−O Bond
Formation and Kolbe Electrolysis
1
2
3
for heterocycles synthesis, the high cost, toxicity, and
air/moisture sensitivity of some catalysts are major concerns.
Consequently, new compatible and more sustainable synthetic
approaches are urgently needed for the synthesis of heterocyꢀ
cles.
The prosperous development of organic electrochemistry
has dramatically expanded chemists’ toolboxes that provide a
variety of opportunities to solve synthetic challenges in unique
4
ways. For example, intramolecular anodic oxidative C−O
bond formation can serve as a powerful tool for the construcꢀ
tion of oxygenꢀcontaining heterocycles (Scheme 1A). Moeller
and coworkers pioneered a series of intramolecular anodic
5
cyclization of electronꢀrich olefins with alcohols. Intramolecꢀ
ular electrochemical nucleophilic attack of oxygen nucleoꢀ
philes on Schiff bases reported by Zeng and other groups also
provide straightforward routes to constructing oxygenꢀ
decarboxylation of aroyloxy radicals. In fact, Barton has cateꢀ
6
containing heterocycles. The Okimoto and Lee groups deꢀ
gorized ArCO • as “nondecarboxylating acyloxy radicals”,
2
scribed the anodic oxidation of amides or tertiary amines to
generate reactive Nꢀacyliminium cations or iminium cations
which were trapped by alcohol nucleophiles to afford cyclic
N,Oꢀacetals. Very recently, the Waldvogel and Xu groups
reported on the intramolecular anodic dehydrogenative couꢀ
pling of aromatic C−H bonds and amide groups for the syntheꢀ
noting that it does not decarboxylate at temperatures below
o
10
1
20ꢀ130 C. Thus, compared with alkyl carboxylic acids,
there have been far fewer investigations of aryl carboxylic
acids for the Kolbe oxidation reaction (Scheme 1B). These
previous results give four reasons that the preparation of benꢀ
zolactones is an ideal process for the use of Kolbe electrolysis
of 2ꢀarylbenzoic acids. First, although this has been less invesꢀ
tigated, anodic oxidation of aromatic carboxylic acid is feasiꢀ
7
8
sis of benzoxazoles and benzoxazines, respectively.
The anodic oxidation of carboxylic acid, also known as
Kolbe electrolysis (or Kolbe oxidation, Kolbe dimerization)9
11
ble. Second, the formed aroyloxy radical does not undergo
has a long history of development since its discovery in 1849.
decarboxylation at ambient temperature. Third, the two conꢀ
secutive electron transfer between the electrode and the subꢀ
strate taking place on the same electrode (double anodic oxiꢀ
The coupling reaction of alkyl radicals generated from elecꢀ
trodecarboxylation of alkyl carboxylates (RCO ) gives the
ꢀ
2
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1
4m
dation) favor implementation of the reaction. Finally, the conꢀ
comitant cathodic proton reduction to hydrogen gas exactly
balances the redox of the overall reaction. In this paper, we
report a Kolbe electrolysis for the lactonization of 2ꢀ
arylbenzoic acids at room temperature in an oxidantꢀfree manꢀ
ner (Scheme 1C).
group
independently reported a photoredox and cobalt coꢀ
2
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catalyzed C(sp )–H functionalization/C–O bond formation
reaction towards biaryl lactone synthesis with no oxidant inꢀ
volved. However, the catalysis system is somewhat complicatꢀ
ed. The most known methods use stoichiometric oxidants,
since the overall process involves the removal of two hydroꢀ
gens from the substrate. This will cause excessive waste genꢀ
eration and poor atom economy. We envisage that oxidantꢀ
free conditions might be possible if the two hydrogens can be
properly handled. In this case, the generation of hydrogen gas
(H ) gives an ideal solution for the two hydrogen atoms
(Scheme 3).
Scheme 3. Rationale of Kolbe Electrolysis for Cyclization
of 2ꢀArylbenzoic Acid
RESULTS AND DISCUSSION
Biaryl lactones and their derivatives are common structure
motifs found in a wide variety of bioactive molecules ranging
1
2
from natural products to drugs (Scheme 2). They also serve
as versatile building blocks for the synthesis of various pharꢀ
maceuticals, as well as agrochemicals, fragrances, and materiꢀ
2
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als. In light of the importance of these biaryl lactone comꢀ
pounds, a variety of methods have been developed for their
synthesis.
Scheme 2. Natural Products and Pharmaceuticals Containꢀ
ing Biaryl Lactones
O
HO
O
OH
O
O
OH
O
Urolithin A
O
HO
O
O
O
Sarolactone
O
OH
O
OH
OH
Urolithin B
O
HO
HO
Core structure
HO
HO
O
O
7843 targeted at SciFinder
by Dec 2017
O
Ellagic acid
anti-tumor activity)
(
OH
HO
Urolithin C
O
O
HO
O
O
O
H
O
O
HO
OH
OMe
OH
Chartreusin
O
Table 1. Reaction development and optimization
Among those methods, the oxidative cyclization of 2ꢀ
arylbenzoic acids via a C−H bond activation/C−O bond forꢀ
14
mation process is a commonly used cyclization method. For
example, Togo and Yokoyama reported on (diacetoxyꢀ
iodo)arene and iodine coꢀmediated cyclization of 2ꢀaryl (or
b
entry
deviation from the standard conditions
MeCN instead of MeOH, 2.8 h
Acetone instead of MeOH, 2.8 h
DMF instead of MeOH, 11 h
THF instead of MeOH, 7 h
yield (%)
1
4bꢀd
alkyl) benzoic acids under photo irradiation.
In 2013, Marꢀ
1
69
2
52
tin and coꢀworkers reported on Cuꢀcatalyzed C−H functionaliꢀ
zation/C−O bond formation assisted by carboxylic acids with
3
34
1
4e
4
32
dibenzoyl peroxide as the oxidant. Later, they also reported
on the iodine (III)ꢀcatalyzed cyclization of 2ꢀarylbenzoic acid
i
5
PrOH instead of MeOH, 4 h
34
1
4i
6
HFIP instead of MeOH, 3 h
79
with peroxyacetic acid as the terminal oxidant. Wang and
coꢀworkers developed a Pdꢀcatalysis for the same transforꢀ
7
2
Under N , 1.8 h
80 (86)
76
1
4f
8
1 mmol scale, 0.3 M conc., 3.3 h
mation using PhI(OAc) as the oxidant. Gevorgyan reported
o
2
9
50 C, 16 h
76
a Cu(II)ꢀcatalyzed title transformation using tertꢀbutyl peroxꢀ
10
cc 10 mA, 5 h
76
1
4g
ybenzoate as the oxidant. Xu also achieved the same goal
1
1
w/o NaOH, cv 60V, current ca. 3~7 mA, 2 d
No electricity, 2 d
76
14j
using a Ag(I) catalyst with (NH ) S O as the oxidant. In
4
2
2
8
12
0
a
addition, the Wei group demonstrated visible lightꢀinduced
Reaction conditions: 1a 0.5 mmol, MeOH 3 mL, H O 0.3 mL, Pt net elecꢀ
2
cyclization of 2ꢀarylbenzoic acids with Nꢀiodosuccinimide as
trode, 1cm×1cm, 52 mesh. cc constant current, cv constant voltage. HFIP
1,1,1,3,3,3ꢀhexafluoroꢀ2ꢀpropanol. Reaction time varies in each entry. The
14h
the oxidant, whereas the GonzalezꢀGomez group reported
on the metalꢀfree dehydrogenative lactonization of 2ꢀ
b
completion of the reaction is monitored by TLC and voltage. Yield determined
1
by H NMR using 1,3,5ꢀtrimethoxybenzene. Isolated yield in parentheses.
arylbenzoic acids at room temperature under visible light irraꢀ
+
diation with [Acr ꢀMes] as the photocatalyst and (NH ) S O
4
2
2
8
We initially studied the anodic oxidation of 2ꢀ
phenylbenzoic acid (Table 1). The reaction conditions were
14k
14l
as the oxidant. Very recently, the Luo group and the Zhu
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optimized to give the desired cyclization product 2a with 84%
NMR yield and 88% isolated yield in the presence of 10%
with a current of 23 mA. The Kolbe reaction is usually perꢀ
formed with constant current density with the anode potential
seldom needing to be controlled by a potentiostat.
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9e
NaOH in a MeOH/H O mixed solvent. Platinum was used as
2
the electrode with the reaction using the constant current mode
2
a
Table 2. Kolbe Anodic Cyclization via C(sp )−H Functionalization/C−O Formation
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Reaction conditions: 1a 0.5 mmol, MeOH 3 mL, H O 0.3 mL, Pt net electrode, 1cm×1cm, 52 mesh. cc constant current. Isolated yield are reported.
The reaction proceeds quite fast as monitored by TLC and the
voltage variations with the voltage starting at 10~15 V and
rising to over 20 V on completion of the reaction. Other solꢀ
vents, such as MeCN, acetone, and DMF, proved to be less
efficient (entries 1ꢀ5), while HFIP gave a comparable yield
(entry 6). The reaction is not sensitive to air or concentration
withdrawing substituents worked well on both aromatic rings.
Substituents in the ortho position to the targeted C−H bond
hindered the reaction, providing 2j in relatively low yield.
2
metaꢀsubstitution on Ar ring cause site selectivity, as shown
in the case of 2k. The reaction gave a roughly 1.25:1 mixure
of isomers in 90% total yield. In another example, a single
isomer 2z was obtained with the naphthalene backbone. Hetꢀ
erocycles could also be accommodated under our electrochemꢀ
ical condition as exemplified by 2aa.
(entries 7 and 8). Normally, the reaction temperature is slightꢀ
ly higher than room temperature, since the reaction is exoꢀ
thermic. Interestingly, the reaction still works well, but slower
o
at 50 C (entry 9). An applied current of 10 mA required a
longer reaction time with a good yield (entry 10). The reaction
media became less conductive (60V, 3ꢀ7 mA) when no base
was added. The yield did not drop much after two days’ elecꢀ
trolysis (entry 11). The results show that the reaction is unamꢀ
biguously driven by the electrical current (entry 12).
Scheme 4. Comparison of 10 Gram Scale with 0.1 Gram
Scale Reactions
The optimal reaction conditions were then used for substrate
scope studies with the results shown in Table 2. A series of1
benzoic acid substrates bearing substitutions on both the Ar
2
and Ar rings were examined with the corresponding cyclizaꢀ
tion products isolated with good to excellent yields. This anodꢀ
ic oxidation reaction tolerates a variety of functional groups,
such as ketone, ester, ether, alkene, halides, trifluoromethyl,
and trifluoromethoxyl groups. Both electronꢀdonating and ꢀ
Furthermore, a 10 gramꢀscale experiment was conducted to
examine the scalability of this electrochemical protocol. Runꢀ
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ning the reaction at a 60 mmol scale with larger electrodes in a a radical cation. Homolytic cleavage of this radical cation afꢀ
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higher concentration (0.5 M) in constant voltage mode (60 V)
gave 2a with 75% isolated yield (Scheme 4).
fords 2ꢀphenylbenzoic acid radical and TEMPO cation. The
compound 2a can be formed by subsequent radical trapping
+
Three compounds in the Urolithin family are suitable targets
for demonstrating the synthetic utility of this Kolbe oxidative
cyclization reaction. Starting from the easily available substiꢀ
tuted benzoic acid or ester, the electrochemical precursors are
obtained by means of a Pdꢀcatalyzed cross coupling reaction
or the C−H arylation reaction. An electrochemical technique
was then applied to convert compounds 5 to cyclized products
and reꢀoxidation either by TEMPO or the anode. At the cathꢀ
+
ode, reduction of TEMPO back to TEMPO and hydrogen
evolution are two possible reactions to balance the overall
transformation. To get more insight into this reaction, we have
also performed two competitive reactions between 1a and 5b,
5b and 1w, respectively (Scheme 6C). It was shown that 5b is
predominantly oxidized when competing with 1a, while 5b
and 1w are equally oxidized to give 6b and 2w in a ca. 1:1
ratio. These competitive experiments demonstrated that the
Kolbe oxidation of benzoic acid is not likely a rateꢀ
determining step.
6
. Finally, compounds 6a, 6b and 6c can be easily transformed
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to Urolithin A, B and C following a reported procedure
15
(Scheme 5).
Scheme 5. Kolbe Oxidative Cyclization for the Synthesis of
the Urolithin Family of Natural Products
Scheme 6. Control Experiments
To probe the mechanism of this reaction, 2,2,6,6ꢀ
tetramethylꢀ1ꢀpiperidinyloxy (TEMPO), a free radical scavenꢀ
ger, was introduced as an additive to the standard reaction. We
found that the reaction was suppressed to a great extent. As
shown in Scheme 6A, product 2a was formed with less than
5
% yield in 2 h and 17% yield in 6 h. These results support the
Kolbe oxidation mechanism. Interestingly, the compound 7,
which was synthesized by adopting a procedure reported by
16
Zeng, can be converted to the cyclized product 2a in a decent
yield under the standard conditions (Scheme 6B). We proꢀ
posed that compound 7 be oxidized at the anode first to deliver
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CONCLUSION
The Journal of Organic Chemistry
(0.167 M, 0.05mmol). Two platinum net electrodes (1.0 cm ×
.0 cm) were set up in the tube. Make sure that the electrodes
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1
In summary, we have developed a general, practical intraꢀ
molecular Kolbe oxidative cyclization method for the syntheꢀ
sis of dibenzopyranones. This method is oxidantꢀfree, does
not involve electrolytes, has high yields, works at ambient
temperature and is scalable. Urolithins are formally syntheꢀ
sized by adopting this method as a key step to demonstrate its
synthetic utility.
be totally immersed. The resulting mixture was electrolyzed at
constant current mode with a current of 23 mA under ambient
temperature. The reaction was monitored by TLC. After 3 h 50
min, the reaction mixture was concentrated under reduced
pressure. The residue was chromatographed through silica gel
eluting with PE/EA to give the desired product 2a, 106 mg,
25
8
6
2% yield.
Hꢀbenzo[c]chromenꢀ6ꢀone (2a). White solid, using PE/EA
14f
(
10:1 v/v) as eluent. Isolated yield: 88% (86 mg); mp 90ꢀ91 °C
EXPERIMENTAL SECTION
0
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14e 1
(lit 88ꢀ89 °C). H NMR (400 MHz, CDCl ): δ 8.39 (d, 1H, J
3
General Information. Unless otherwise noted, chemicals
and solvents were purchased with the highest purity grade
available and were used without further purification. Purificaꢀ
tion of products was conducted by column chromatography on
silica gel (200ꢀ300 mesh, from Qingdao, China). NMR spectra
=
7
=
7.9 Hz), 8.10 (d, 1H, J = 8.1 Hz), 8.04 (d, 1H, J = 7.9 Hz),
.81 (t, 1H, J = 7.7 Hz), 7.57 (t, 1H, J = 7.6 Hz), 7.47 (t, 1H, J
7.7 Hz), 7.35 (d, 1H, J = 6.5 Hz), 7.33 (t, 1H, J = 8.1
13
Hz). C NMR(101 MHz, CDCl ): 161.1, 151.2, 134.8, 134.6,
1
3
using PE/EA (10:1 v/v) as eluent. Isolated yield: 90% (95 mg);
mp 129ꢀ130 °C (lit 125ꢀ126 °C). H NMR (400 MHz,
CDCl ): δ 8.38 (d, 1H, J = 7.9 Hz), 8.07 (d, 1H, J = 8.1 Hz),
7.93 (d, 1H, J = 8.0 Hz), 7.79 (dd, 1H, J = 3.9 Hz, J = 11.4
Hz), 7.54 (t, 1H, J = 7.6 Hz), 7.17 (s, 1H), 7.15 (d, 1H, J = 8.2
Hz), 2.45 (s, 3H). C NMR (101 MHz, CDCl ): δ 161.4,
3
30.4, 130.4, 128.8, 124.5, 122.7, 121.6, 121.1, 117.9, 117.6.
1
13
were measured on a Bruker ARX400 ( H at 400 MHz, C at
01 MHz) magnetic resonance spectrometer. Chemical shifts
δ) are reported in ppm using tetramethylsilane as internal
14f
ꢀMethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2b).
White solid,
1
(
16
1
standard (s = singlet, d = doublet, t = triplet, q = quartet, dd =
doublet of doublets, td = triplet of doublets, dt = doublet of
triplets, ddd = doublet of doublet of doublets, m = multiplet),
and coupling constants (J) were reported in Hertz (Hz). Infraꢀ
red spectra were recorded on a Thermal Fisher Nicolet iS50
Fourier transform spectrometer (FTꢀIR) and were reported in
3
13
3
1
1
3
51.3, 141.3, 135.0, 134.7, 130.6, 128.4, 125.6, 122.5, 121.4,
21.0, 117.9, 115.5, 21.4.
ꢀ(Trifluoromethoxy)ꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone
ꢀ
1
wave numbers (cm ). HRMS data were obtained on a VG
ZABꢀHS mass spectrometer, Brucker Apex IV FTMS specꢀ
trometer.
14g
(2c).
White solid, using PE/EA (10:1 v/v) as eluent. Isolated yield:
8
MHz, CDCl ): δ 8.41 (dd, 1H, J = 7.9, 1.4 Hz), 8.09 (dd, 2H, J
=
17
1
6% (120 mg); mp 77ꢀ78 °C (lit 86ꢀ87 °C). H NMR (400
Characterization Data. General Procedure for the electroꢀ
chemical experiments: To a 15 mL test tube with a stir bar was
charged with 0.5 mmol 2ꢀarylbenzoic acid 1, followed by 3mL
MeOH and 0.3 mL aqueous NaOH solution (0.167 M,
3
8.5, 2.3 Hz), 7.86 (ddd, 1H, J = 8.2, 7.3, 1.4 Hz), 7.62 (ddd,
13
1
H, J = 8.2, 7.4, 1.1 Hz), 7.26 – 7.17 (m, 2H). C NMR (101
MHz, CDCl ): δ 160.5, 151.8, 150.2, 135.2, 133.8, 130.8,
1
110.2.
3ꢀPhenylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2d).
using PE/EA (10:1 v/v) as eluent. Isolated yield: 74% (100
mg); mp 84ꢀ86 °C. H NMR (400 MHz, CDCl ): δ 8.42 (dd, J
=
=
3
0
.05mmol). Two platinum net electrodes (1.0 cm × 1.0 cm)
29.4, 124.2, 121.8, 120.9, 120.4 (q, J = 259 Hz), 117.0, 116.8,
were set up in the tube. Make sure that the electrodes be totalꢀ
ly immersed. The resulting mixture was electrolyzed at conꢀ
stant current mode with a current of 23 mA under ambient
temperature. The reaction was monitored by TLC or GC. Upꢀ
on completion, the reaction mixture was concentrated under
reduced pressure. The residue was chromatographed through
silica gel eluting with PE/EA to give the desired product 2.
General Procedure for the 10 gram scale electrochemical
experiment: To a 150 mL conical flask with a stir bar was
charged with 60 mmol 2ꢀarylbenzoic acid 1a, followed by 100
mL MeOH and 20 mL aqueous NaOH solution (0.3 M, 6
mmol). Two platinum net electrodes (1.5 cm × 1.0 cm) were
set up in the conical flask. Make sure that the electrodes be
totally immersed. The resulting mixture was electrolyzed at
constant potential mode with a potential of 60 V under ambiꢀ
ent temperature. Note, the reaction is exothermic. Ice water
14j
White solid,
1
3
7.9, 1.4 Hz, 1H), 8.13 (dd, J = 10.7, 8.5 Hz, 2H), 7.84 (td, J
7.7, 1.4 Hz, 1H), 7.66 (d, J = 7.1 Hz, 2H), 7.63 – 7.56 (m,
13
3
H), 7.49 (t, J = 7.5 Hz, 2H), 7.42 (t, J = 7.3 Hz, 1H).
C
NMR (101 MHz, CDCl ): δ 161.2, 151.6, 143.4, 139.2, 134.8,
3
1
1
3
34.6, 130.6, 129.1, 128.8, 128.3, 127.0, 123.3, 123.2, 121.7,
21.1, 116.9, 115.7.
14f
ꢀAcetylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2e). White solid, usꢀ
ing PE/EA (10:1 v/v) as eluent. Isolated yield: 79% (94 mg);
mp 189ꢀ191 °C. H NMR (400 MHz, CDCl ): δ 8.46 (dd, J =
7
7
1
3
.9, 1.4 Hz, 1H), 8.18 (t, J = 8.4 Hz, 2H), 7.97 – 7.92 (m, 2H),
.90 (ddd, J = 8.2, 7.4, 1.4 Hz, 1H), 7.72 – 7.65 (m, 1H), 2.68
13
(s, 3H). C NMR (101 MHz, CDCl ): δ 196.5, 160.6, 151.2,
3
bath was used to maintain reaction temperature between
138.4, 135.1, 133.7, 130.9, 130.1, 123.9, 123.2, 122.4, 122.0,
121.8, 118.0, 26.8.
Methyl
White solid, using PE/EA (10:1 v/v) as eluent. Isolated yield:
9
o
1
5~30 C. The reaction was monitored by TLC. Upon compleꢀ
tion, the reaction mixture was poured into saturated Na CO3
2
6ꢀoxoꢀ6Hꢀbenzo[c]chromeneꢀ3ꢀcarboxylate
(2f).
aqueous solution. Large amount of solid product precipitated
out. The solid product was filtered and washed by water. The
residue was dried under heating and vacuum to give analytical
pure product 2a, 8.81 g, 75% yield.
1
0% (114 mg); mp 160ꢀ162 °C. H NMR (400 MHz, CDCl ):
3
δ 8.43 (dd, 1H, J = 7.9, 1.3 Hz), 8.17 (d, 1H, J = 8.1 Hz), 8.13
d, 1H, J = 8.3 Hz), 7.99 (d, 2H, J = 7.6 Hz), 7.91 – 7.84 (m,
(
1
Electrolysis of compound 7: The compound 7 was syntheꢀ
13
H), 7.69 – 7.63 (m, 1H), 3.98 (s, 3H). C NMR (101 MHz,
1
6
sized by adopting a procedure reported by Zeng. To a 15 mL
test tube with a stir bar was charged with 0.66 mmol 2,2,6,6ꢀ
tetramethylpiperidinꢀ1ꢀyl [1,1'ꢀbiphenyl]ꢀ2ꢀcarboperoxoate 7,
followed by 3mL MeOH and 0.3 mL aqueous NaOH solution
CDCl ): δ 165.8, 160.6, 151.0, 135.1, 133.7, 131.9, 130.8,
1
2
3
30.0, 125.3, 122.9, 122.4, 121.9, 121.8, 119.1, 52.6. IR: ν =
ꢀ1
948, 1735, 1717, 1606, 1304, 1267, 1097, 751 cm . HRMS
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 10
+
+
13
(
ESI): calcd for C H O
[M+H] : 255.0652; found:
8.0 Hz, 1H), 7.34 (t, J = 7.6 Hz, 1H), 2.91 (s, 3H). C NMR
1
5
11
4
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2
55.0646.
(101 MHz, CDCl ): δ 151.2, 139.1, 135.0, 133.6, 129.6, 129.2,
3
1
4f
3ꢀBromoꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2g).
using PE/EA (10:1 v/v) as eluent. Isolated yield: 77% (105
mg); mp 134ꢀ136 °C (lit 136ꢀ138 °C). H NMR (400 MHz,
CDCl ): δ 8.39 (dd, 1H, J = 8.0, 1.4 Hz), 8.11 – 8.04 (m, 1H),
7
7
7
1
1
3
White solid,
128.3, 127.2, 124.0, 122.8, 119.7, 118.0, 25.41.
9ꢀMethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2m).
4f
White solid,
1
6
1
using PE/EA (10:1 v/v) as eluent. Isolated yield: 92% (97 mg);
16
1
mp 84ꢀ86 °C (lit 86ꢀ88 °C). H NMR (400 MHz, CDCl ): δ
3
3
.91 (d, 1H, J = 8.5 Hz), 7.84 (ddd, 1H, J = 8.2, 7.4, 1.5 Hz),
.61 (ddd, 1H, J = 8.2, 7.3, 1.1 Hz), 7.53 (d, 1H, J = 2.0 Hz),
.46 (dd, 1H, J = 8.5, 2.0 Hz). C NMR (101 MHz, CDCl ): δ
60.5, 151.5, 135.1, 134.0, 130.8, 129.3, 127.9, 124.0, 123.7,
21.7, 121.0, 120.9, 117.1.
ꢀ(Trifluoromethyl)ꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2h). White
8.26 (d, 1H, J = 8.1 Hz), 8.02 (dd, 1H, J = 7.9, 1.5 Hz), 7.91 –
7.85 (m, 1H), 7.46 (ddd, 1H, J = 8.5, 7.2, 1.6 Hz), 7.37 (ddd,
1H, J = 8.2, 1.6, 0.7 Hz), 7.35 – 7.33 (m, 1H), 7.33 – 7.29 (m,
1
3
3
13
1H), 2.55 (s, 3H). C NMR (101 MHz, CDCl ): δ161.2, 151.4,
3
145.9, 134.6, 130.4, 130.2, 130.1, 124.4, 122.7, 121.8, 118.7,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
14f
118.0, 117.6, 22.2.
8ꢀMethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2n).
14f
solid, using PE/EA (10:1 v/v) as eluent. Isolated yield: 93%
White solid,
14e
1
(123 mg); mp 127ꢀ129 °C (lit 123.1ꢀ124.1 °C) H NMR
using PE/EA (10:1 v/v) as eluent. Isolated yield: 90% (95 mg);
16 1
(400 MHz, CDCl ): δ 8.45 (d, 1H, J = 7.9 Hz), 8.18 (t, 2H, J =
mp 128ꢀ129 °C (lit 114ꢀ115 °C). H NMR (400 MHz,
3
8
.1 Hz), 7.89 (t, 1H, J = 7.7 Hz), 7.68 (t, 1H, J = 7.6 Hz), 7.63
CDCl ): 8.11 (s, 1H), 7.99 – 7.87 (m, 2H), 7.56 (dd, J = 8.2,
3
1
3
(s, 1H), 7.59 (d, 1H, J = 8.4 Hz). C NMR (101 MHz,
2.1 Hz, 1H), 7.46 – 7.36 (m, 1H), 7.28 (t, J = 8.1 Hz, 2H), 2.44
13
CDCl ): δ 160.2, 151.0, 135.2, 133.4, 132.4, 132.1, 130.9,
130.1, 124.6, 123.6, 122.2, 122.0, 121.7, 121.2, 121.11,
121.08, 121.0, 115.3, 115.3, 115.24, 115.20.
3ꢀ(Allyloxy)ꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2i). White solid,
using PE/EA (10:1 v/v) as eluent. Isolated yield: 66% (83 mg);
(s, 3H). C NMR (101 MHz, CDCl ): δ 150.9, 139.2, 136.0,
3
3
132.1, 130.2, 129.8, 124.4, 122.5, 121.6, 121.0, 118.1, 117.6,
21.3.
1
4j
14f
9ꢀMethylꢀ3ꢀpentylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2o). White
solid, using PE/EA (10:1 v/v) as eluent. Isolated yield: 86%
1
16
1
mp 93ꢀ94 °C. H NMR (400 MHz, CDCl ): δ 8.31 (dd, 1H, J =
(120mg); mp 60ꢀ61 °C (lit 61ꢀ63 °C). H NMR (400 MHz,
3
7
7
1
.9, 1.3 Hz), 7.98 – 7.92 (m, 1H), 7.88 (d, 1H, J = 8.8 Hz, 1H),
.75 (ddd, 1H, J = 8.4, 7.3, 1.5 Hz), 7.47 (ddd, 1H, J = 8.2, 7.3,
.1 Hz), 6.90 (dd, 1H, J = 8.8, 2.6 Hz), 6.82 (d, 1H, J = 2.6
CDCl ): δ 8.24 (dd, 1H, J = 8.1, 2.1 Hz), 7.91 (dd, 1H, J = 8.0,
3
2.3 Hz), 7.83 (s, 1H), 7.33 (dt, 1H, J = 8.0, 1.5 Hz), 7.13 (dd,
2H, J = 9.6, 1.6 Hz), 2.68 (t, 2H, J = 7.7 Hz), 2.53 (s, 3H),
1
3
Hz), 6.06 (ddt, 1H, J = 17.3, 10.5, 5.3 Hz), 5.45 (dq, 1H, J =
1.66 (m, 2H), 1.40 – 1.30 (m, 4H), 0.94 – 0.86 (m, 3H). C
1
5
1
1
1
7.2, 1.6 Hz), 5.34 (dq, 1H, J = 10.5, 1.4 Hz), 4.58 (dt, 2H J =
.3, 1.6 Hz). C NMR (101 MHz, CDCl ): δ 161.4, 160.4,
52.5, 135.1, 134.8, 132.4, 130.5, 127.7, 123.7, 121.0, 119.9,
18.4, 112.9, 111.2, 102.5, 69.2.
ꢀMethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2j).
NMR (101 MHz, CDCl ): δ 161.5, 151.5, 146.1, 145.8, 130.5,
3
13
129.6, 124.8, 122.4, 121.6, 118.4, 117.2, 115.6, 35.7, 31.4,
30.7, 22.5, 22.3, 14.0.
3
9ꢀtertꢀButylꢀ3ꢀmethoxyꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone
(2p).
1
4f
White solid,
White solid, using PE/EA (10:1 v/v) as eluent. Isolated yield:
1
using PE/EA (10:1 v/v) as eluent. Isolated yield: 43% (45 mg);
mp 159ꢀ161 °C (lit 161 °C). H NMR (400 MHz, CDCl ): δ
91% (128 mg); mp 150ꢀ151 °C. H NMR (400 MHz, CDCl ):
3
1
8
1
δ 8.28 (d, 1H, J = 8.4 Hz), 7.99 (dd, 2H, J = 5.3, 3.5 Hz), 7.56
(dd, 1H, J = 8.4, 1.8 Hz), 6.92 (dd, 1H, J = 8.8, 2.6 Hz), 6.86
3
8.50 (d, 1H, J = 7.9 Hz), 8.39 (d, 1H, J = 8.4 Hz), 7.83 (t, 1H,
J = 7.8 Hz), 7.60 (t, 1H, J = 7.6 Hz), 7.36 (t, 1H, J = 7.8 Hz),
7.28 (d, 1H, J = 8.5 Hz), 7.17 (d, 1H, J = 7.4 Hz), 2.90 (s, 3H).
13
(d, 1H, J = 2.5 Hz), 3.88 (s, 3H), 1.43 (s, 9H). C NMR (101
MHz, CDCl ): δ 161.6, 161.3, 158.8, 152.8, 134.9, 130.4,
3
1
3
C NMR (101 MHz, CDCl ): δ 161.3, 152.2, 136.2, 136.1,
34.2, 130.8, 129.3, 128.8, 128.1, 126.2, 122.2, 117.5, 116.2,
5.5.
125.7, 123.6, 117.5, 117.3, 112.4, 111.6, 101.6, 55.7, 35.6,
3
1
2
2
31.1. IR: ν = 2961, 2908, 1727, 1612, 1409, 1277, 1106, 1040,
ꢀ
1
+
+
776, 692 cm . HRMS (ESI): calcd for C H O [M+H] :
18 19
3
1
4g
ꢀMethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2k).
White solid,
283.1329; found: 283.1329.
9ꢀChloroꢀ3ꢀmethoxyꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone
2
0
using PE/EA (10:1 v/v) as eluent. Isolated 53 mg; mp 124ꢀ125
(2q).
19
1
°
C (lit 126ꢀ128 °C). H NMR (400 MHz, CDCl ): δ 8.36 (d,
White solid, using PE/EA (10:1 v/v) as eluent. Isolated yield:
3
1
1
H, J = 7.9 Hz), 8.05 (d, 1H, J = 8.1 Hz), 7.78 (m, 2H), 7.54
85% (110 mg); mp 190ꢀ192 °C. H NMR (400 MHz, CDCl ):
3
13
(t, 1H, J = 7.6 Hz), 7.23 (m, 2H), 2.44 (s, 3H). C NMR (101
δ 8.28 (d, J = 8.5 Hz, 1H), 7.96 (d, J = 2.1 Hz, 1H), 7.87 (d, J
= 8.9 Hz, 1H), 7.45 (dd, J = 8.5, 2.0 Hz, 1H), 6.93 (dd, J = 8.9,
MHz, CDCl ): δ 161.3, 149.3, 134.8, 134.7, 134.1, 131.3,
3
13
1
7
4
30.5, 128.7, 122.7, 121.6, 121.2, 117.6, 117.4, 77.4, 77.1,
6.8, 21.1.
ꢀMethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2k’). Isolated 42 mg,
2.6 Hz, 1H), 6.86 (d, J = 2.6 Hz, 1H), 3.89 (s, 3H). C NMR
(101 MHz, CDCl ): δ 162.1, 160.7, 153.0, 141.8, 136.7, 132.2,
3
1
4g
128.1, 123.9, 121.1, 118.2, 112.7, 110.0, 101.7, 55.8.
8ꢀChloroꢀ3ꢀmethoxyꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2r). White
1
9
1
white solid; mp 120ꢀ122 °C (lit 132ꢀ134 °C). H NMR (400
MHz, CDCl ): δ 8.37 (d, 1H, J = 7.9 Hz), 8.07 (d, 1H, J = 8.1
Hz), 7.85 (d, 1H, J = 7.9 Hz), 7.78 (dt, 1H, J = 1.2 Hz, J = 7.8
Hz), 7.54 (t, 1H, J = 7.6 Hz), 7.30 (d, 1H, J = 7.3 Hz), 7.19 (t,
1H, J = 7.7 Hz), 2.47 (s, 3H). C NMR (101 MHz, CDCl ) δ
1
1
1
using PE/EA (10:1 v/v) as eluent. Isolated yield: 46% (48 mg);
mp 119ꢀ120 °C (lit
CDCl ): δ 8.38 (d, J = 7.8 Hz, 1H), 8.32 (d, J = 8.3 Hz, 1H),
7
solid, using PE/EA (10:1 v/v) as eluent. Isolated yield: 83%
3
1
(108 mg); mp 160ꢀ161 °C. H NMR (400 MHz, CDCl ): δ
3
8.31 (d, J = 2.3 Hz, 1H), 7.94 (d, 1H, J = 8.6 Hz), 7.89 (d, 1H,
J = 8.9 Hz), 7.72 (dd, 1H, J = 8.6, 2.3 Hz), 6.92 (dd, 1H, J =
1
3
3
1
3
61.2, 149.6, 135.1, 134.7, 131.8, 130.4, 128.6, 127.0, 124.0,
21.8, 121.1, 120.4, 117.6, 77.4, 77.1, 76.8, 16.0.
0ꢀMethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2l).
8.8, 2.6 Hz), 6.86 (d, 1H, J = 2.6 Hz), 3.89 (s, 3H). C NMR
(101 MHz, CDCl ): δ 161.8, 160.4, 152.5, 135.2, 133.6, 130.0,
3
1
4f
White solid,
123.8, 122.8, 121.2, 112.8, 110.4, 101.7, 55.8. IR: ν = 2939,
ꢀ
1
2839, 1728, 1623, 1604, 1474, 1263, 1168, 775 cm . HRMS
1
4h
1
+ +
122ꢀ124 °C). H NMR (400 MHz,
(ESI): calcd for C H ClO [M+H] : 261.0313; found:
14 10 3
261.0312.
3
.65 (d, J = 7.5 Hz, 1H), 7.48 (t, J = 7.6 Hz, 2H), 7.41 (d, J =
ACS Paragon Plus Environment

Page 7 of 10
The Journal of Organic Chemistry
1
9
ꢀBromoꢀ3ꢀmethoxyꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2s). White
(100 mg); mp 220ꢀ222 °C. H NMR (400 MHz, CDCl ): δ
3
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
solid, using PE/EA (10:1 v/v) as eluent. Isolated yield: 77%
8.56 (d, 1H, J = 1.5 Hz), 8.45 (d, 1H, J = 8.2 Hz), 8.05 (d, 1H,
J = 8.9 Hz), 8.00 (dd, 1H, J = 8.2, 1.6 Hz), 6.96 (dd, 1H, J =
8.9, 2.6 Hz), 6.88 (d, 1H, J = 2.5 Hz), 3.90 (s, 3H), 2.74 (s,
1
(117 mg); mp 188ꢀ190 °C. H NMR (400 MHz, CDCl ): δ
3
8.18 (d, 1H, J = 8.5 Hz), 8.10 (d, 1H, J = 1.8 Hz), 7.84 (d, 1H,
J = 8.9 Hz), 7.59 (dd, 1H, J = 8.5, 1.8 Hz), 6.90 (dd, 1H, J =
13
3H). C NMR (101 MHz, CDCl ): δ 197.4, 162.0, 160.7,
3
13
8.8, 2.6 Hz), 6.83 (d, 1H, J = 2.6 Hz), 3.89 (s, 3H). C NMR
101 MHz, CDCl ): δ 162.1, 160.8, 153.0, 136.7, 132.2, 131.0,
152.8, 141.6, 135.6, 131.2, 126.7, 124.1, 122.9, 121.0, 112.8,
(
110.7, 101.8, 55.8, 27.1. IR: ν = 3075, 2841, 1734, 1684, 1611,
3
ꢀ
1
1
2
30.6, 124.2, 123.9, 118.6, 112.7, 109.9, 101.7, 55.8. IR: ν =
1420, 1282, 1270, 1235, 1038 cm . HRMS (ESI): calcd for
ꢀ
1
+ +
918, 1731, 1625, 1600, 1590, 1277, 1169, 1034, 768 cm .
C H O [M+H] : 269.0808; found: 269.0808.
16 13 4
+
+
HRMS (ESI): calcd for C H BrO [M+H] 304.9808; found:
10Hꢀtribenzo[c,f,h]chromenꢀ10ꢀone(2y). White solid, using
1
4
10
3
3
9
04.9809.
ꢀFluoroꢀ3ꢀmethoxyꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2t). White
PE/EA (10:1 v/v) as eluent. Isolated yield: 62% (92 mg); mp
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
154ꢀ156 °C. H NMR (400 MHz, CDCl ): δ 8.70 (dd, 1H, J =
3
solid, using PE/EA (10:1 v/v) as eluent. Isolated yield: 77%
3.4, 6.2 Hz), 8.67 (dd, 1H, J = 3.4, 6.2 Hz), 8.63 (d, 2H, J =
8.2 Hz), 8.55 (d, 1H, J = 8.3 Hz), 8.51 (d, 1H, J = 7.9 Hz),
7.86 (dt, 1H, J = 1.1, 7.7 Hz), 7.75 (m, 1H), 7.72 (dd, 1H, J =
1
(
94 mg); mp 188ꢀ189 °C. H NMR (400 MHz, CDCl ): δ 8.38
3
(dd, 1H, J = 8.8, 5.8 Hz), 7.84 (d, 1H, J = 8.9 Hz), 7.61 (dd,
13
1
1
H, J = 9.9, 2.4 Hz), 7.19 (td, 1H, J = 8.5, 2.4 Hz), 6.92 (dd,
5.7, 6.5 Hz), 7.66 (m, 2H), 7.62 (m, 1H). C NMR (101 MHz,
13
H, J = 8.9, 2.6 Hz), 6.86 (d, 1H, J = 2.5 Hz), 3.89 (s, 3H).
C
CDCl ): δ 161.2, 146.7, 135.5, 134.2, 131.3, 130.6, 128.9,
3
NMR (101 MHz, CDCl ): δ 167.1 (d, J = 256.1 Hz), 162.1,
128.92, 128.89, 127.7, 127.6, 127.1, 126.5, 126.1, 126.0,
3
160.6, 153.1, 138.2 (d, J = 10.7 Hz), 133.9 (d, J = 10.3 Hz),
124.0, 116.4 (d, J = 2.5 Hz), 115.9 (d, J = 23.4 Hz), 112.7,
110.5 (d, J = 2.9 Hz), 107.4 (d, J = 23.5 Hz), 101.7, 55.8. IR: ν
= 2957, 2849, 1746, 1614, 1600, 1278, 1267, 1193, 1099, 832,
123.7, 123.1, 122.51, 122.49, 110.1. IR: ν = 3066, 1735, 1496,
ꢀ
1
1479, 1312, 1200, 1113, 1084, 763, 699 cm . HRMS (ESI):
+
+
calcd for C H O [M+H] : 297.0910; found: 297.0909.
21
13
2
14g
6Hꢀdibenzo[c,h]chromenꢀ6ꢀone (2z).
White solid, using
ꢀ
1
+
+
6
2
3
19 cm . HRMS (ESI): calcd for C H FO [M+H] :
PE/EA (10:1 v/v) as eluent. Isolated yield: 90% (111 mg); mp
14 10 3
14e
1
45.0608; found: 245.0607.
ꢀMethoxyꢀ9ꢀmethylꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2u). White
182ꢀ184 °C (lit 181ꢀ182 °C). H NMR (400 MHz, CDCl ): δ
3
8.61 (dd, 1H, J = 8.1, 1.7 Hz), 8.48 (dd, 1H, J = 7.9, 1.3 Hz),
8.21 (d, 1H, J = 8.1 Hz), 8.08 (d, 1H, J = 8.8 Hz), 7.88 (td, 2H,
solid, using PE/EA (10:1 v/v) as eluent. Isolated yield: 81%
1
(
97 mg); mp 155ꢀ157 °C. H NMR (400 MHz, CDCl ): δ 8.24
J = 7.6, 1.4 Hz), 7.78 (d, 1H, J = 8.7 Hz), 7.67 – 7.58 (m, 3H).
3
13
(d, 1H, J = 8.1 Hz), 7.94 (dd, 1H, J = 8.9, 1.0 Hz), 7.79 (s, 1H),
C NMR (101 MHz, CDCl ): δ 161.2, 147.2, 135.3, 134.9,
3
7
.36 – 7.29 (m, 1H), 6.91 (ddd, 1H, J = 8.8, 2.6, 0.7 Hz), 6.86
134.2, 130.6, 128.6, 127.8, 127.6, 127.1, 124.5, 123.8, 122.3,
122.0, 121.1, 119.1, 113.0.
5Hꢀthieno[2,3ꢀc]isochromenꢀ5ꢀone (2aa). White solid, using
13
(dd, 1H, J = 2.6, 0.9 Hz), 3.88 (s, 3H), 2.54 (s, 3H). C NMR
(
101 MHz, CDCl ): δ 161.6, 161.4, 152.8, 145.9, 135.2, 130.6,
3
1
29.1, 123.7, 121.2, 117.6, 112.3, 111.2, 101.6, 55.7, 22.3. IR:
PE/EA (10:1 v/v) as eluent. Isolated yield: 55% (56 mg); mp
1
ν = 3007, 2943, 1736, 1616, 1279, 1265, 1198, 1038, 831, 771
116ꢀ117 °C. H NMR (400 MHz, CDCl ): δ 8.35 (dd, 1H, J =
3
ꢀ
1
+
+
cm . HRMS (ESI): calcd for C H O [M+H] : 241.0859;
0.6, 8.0 Hz), 7.80 (ddd, 1H, J = 1.3, 7.0, 8.3 Hz), 7.75 (m, 1H),
7.51 (ddd, 1H, J = 1.4, 7.1, 8.4 Hz), 7.31 (d, 1H, J = 5.9 Hz),
1
5
13
3
found: 241.0858.
3ꢀMethoxyꢀ6Hꢀnaphtho[2,3ꢀc]chromenꢀ6ꢀone (2v). White
13
6.99 (d, 1H, J = 5.9 Hz). C NMR (101 MHz, CDCl ): δ
3
solid, using PE/EA (10:1 v/v) as eluent. Isolated yield: 89%
161.7, 156.1, 135.3, 134.4, 131.1, 127.6, 122.2, 119.2, 118.3,
1
(123 mg); mp 181ꢀ183 °C. H NMR (400 MHz, CDCl ): δ
117.0, 116.0. IR: ν = 2921, 2850, 1736, 1610, 1305, 1200,
3
ꢀ
1
+
+
8
2
7
.90 (s, 1H), 8.32 (s, 1H), 8.03 (d, 1H, J = 8.8 Hz), 7.94 (dd,
H, J = 12.7, 8.3 Hz), 7.63 (ddd, 1H, J = 8.3, 6.8, 1.3 Hz),
.52 (ddd, 1H, J = 8.1, 6.8, 1.1 Hz), 6.91 (dd, 1H, J = 8.8, 2.6
1014, 710 cm . HRMS (ESI): calcd for C H O S [M+H] :
11 7 2
203.0161; found: 203.0161.
4,4'ꢀDimethoxybiphenylꢀ2ꢀcarboxylic acid (5a). This comꢀ
1
3
Hz), 6.81 (d, 1H, J = 2.5 Hz), 3.87 (s, 3H). C NMR (101
pound was synthesized following the procedure as reported by
21
22
1
MHz, CDCl ): δ 161.7, 161.2, 152.0, 136.4, 132.8, 131.8,
Su. Isolated yield: 57%; mp 155ꢀ156 °C (lit 156 °C). H
3
1
1
1
30.0, 129.5, 129.5, 127.8, 126.6, 123.9, 119.5, 118.5, 112.4,
NMR (400 MHz, CDCl ): δ 7.44 (d, J = 2.8 Hz, 1H), 7.29 –
3
11.3, 101.8, 55.6. IR: ν = 2841, 1728, 1628, 1301, 1288,
7.19 (m, 3H), 7.08 (dd, J = 8.5, 2.8 Hz, 1H), 6.90 (d, J = 8.6
ꢀ1
+
13
273, 1165, 771, 470 cm . HRMS (ESI): calcd for C H O
Hz, 2H), 3.86 (s, 3H), 3.83 (s, 3H). C NMR (101 MHz,
18
13
3
+
[
M+H] : 277.0859; found: 277.0859.
CDCl ): δ 173.5, 158.8, 158.3, 135.6, 133.1, 132.5, 130.0,
3
Methyl
3ꢀmethoxyꢀ6ꢀoxoꢀ6Hꢀbenzo[c]chromeneꢀ9ꢀ
129.7, 118.6, 115.1, 113.6, 55.6, 55.3.
carboxylate (2w). White solid, using PE/EA (10:1 v/v) as eluꢀ
4'ꢀmethoxybiphenylꢀ2ꢀcarboxylic acid (5b). This compound
was synthesized following the procedure as reported by
1
ent. Isolated yield: 87% (123 mg); mp 128ꢀ130 °C. H NMR
1
4f
23
(400 MHz, CDCl ): δ 8.68 (d, 1H, J = 1.5 Hz), 8.42 (d, 1H, J
Wang. Isolated yield: 86%; mp 146ꢀ147 °C (lit 146ꢀ
3
1
= 8.2 Hz), 8.10 (dd, 1H, J = 8.2, 1.5 Hz), 8.05 (d, 1H, J = 8.9
Hz), 6.96 (dd, 1H, J = 8.8, 2.6 Hz), 6.89 (d, 1H, J = 2.5 Hz),
148 °C). H NMR (400 MHz, CDCl ): δ 7.92 (dd, J = 7.8, 1.4
3
Hz, 1H), 7.54 (td, J = 7.5, 1.5 Hz, 1H), 7.43 – 7.37 (m, 1H),
1
3
4.02 (s, 3H), 3.90 (s, 3H). C NMR (101 MHz, CDCl ): δ
7.37 – 7.33 (m, 1H), 7.30 – 7.26 (m, 2H), 6.97 – 6.89 (m, 2H),
3
13
1
1
1
66.0, 162.0, 160.8, 152.8, 135.7, 135.4, 130.9, 127.8, 124.2,
3.84 (s, 3H). C NMR (101 MHz, CDCl ): δ 173.4, 159.1,
3
22.9, 122.8, 112.8, 110.7, 101.7, 55.8, 52.8. IR: ν = 2959,
142.9, 133.4, 132.0, 131.2, 130.7, 129.7, 129.4, 126.9, 113.6,
55.3.
ꢀ
1
732, 1629, 1422, 1302, 1281, 1253, 1107, 1040, 751 cm .
+
+
HRMS (ESI): calcd for C H O [M+H] : 285.0758; found:
4,4',5ꢀtrimethoxybiphenylꢀ2ꢀcarboxylic acid (5c). This comꢀ
pound was synthesized following the procedure as reported by
1
6
13
5
2
9
85.0756.
ꢀAcetylꢀ3ꢀmethoxyꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (2x). White
21
1
Su. Isolated yield: 56%; mp 198ꢀ199 °C. H NMR (400 MHz,
solid, using PE/EA (10:1 v/v) as eluent. Isolated yield: 75%
CDCl ): δ 7.52 (s, 1H), 7.24 (d, J = 8.6 Hz, 2H), 6.92 (d, J =
3
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.7 Hz, 2H), 6.76 (s, 1H), 3.95 (s, 3H), 3.92 (s, 3H), 3.85 (s,
Page 8 of 10
8
3
(4) (a) Moeller, K. D. Tetrahedron 2000, 56, 9527; (b) Jutand,
1
3
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
A. Chem. Rev. 2008, 108, 2300; (c) Yoshida, J.ꢀi.; Kataoka, K.;
Horcajada, R.; Nagaki, A. Chem. Rev. 2008, 108, 2265; (d)
Francke, R.; Little, R. D. Chem. Soc. Rev. 2014, 43, 2492; (e)
Horn, E. J.; Rosen, B. R.; Baran, P. S. ACS Cent. Sci. 2016, 2,
02; (f) Jiang, Y.; Xu, K.; Zeng, C. Chem. Rev.
0.1021/acs.chemrev.7b00271; (g) Yan, M.; Kawamata, Y.;
Baran, P. S. Angew. Chem. Int. Ed., 10.1002/anie.201707584; (h)
Yan, M.; Kawamata, Y.; Baran, P. S. Chem. Rev. 2017, 117,
13230.
(5) For seminal, see: (a) Sutterer, A.; Moeller, K. D. J. Am.
Chem. Soc. 2000, 122, 5636; For recent, see: (b) Redden, A.;
Perkins, R. J.; Moeller, K. D. Angew. Chem. Int. Ed. 2013, 52,
12865; (c) Smith, J. A.; Moeller, K. D. Org. Lett. 2013, 15, 5818;
H). C NMR (101 MHz, CDCl ): δ 172.4, 158.9, 151.9,
3
147.5, 138.3, 133.7, 129.8, 120.3, 114.0, 113.6, 113.4, 56.2,
56.1, 55.3.
3,8ꢀDimethoxyꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (6a). White solꢀ
id, using PE/EA (10:1 v/v) as eluent. Isolated yield: 63%
81mg); mp 147ꢀ148 °C (lit 156 °C). H NMR (400 MHz,
1
5
3
1
1
5
1
(
CDCl ): δ 7.93 (d, J = 8.9 Hz, 1H), 7.87 (d, J = 8.8 Hz, 1H),
3
7
(
3
1
1
3
.77 (d, J = 2.8 Hz, 1H), 7.37 (dd, J = 8.8, 2.8 Hz, 1H), 6.91
dd, J = 8.7, 2.6 Hz, 1H), 6.87 (d, J = 2.5 Hz, 1H), 3.93 (s, 3H),
.88 (s, 3H). C NMR (101 MHz, CDCl ): δ 161.6, 160.7,
59.2, 151.7, 128.7, 124.5, 123.2, 122.8, 121.0, 112.4, 111.3,
11.0, 101.6, 55.8, 55.7.
ꢀMethoxyꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (6b). White solid,
using PE/EA (10:1 v/v) as eluent. Isolated yield: 88% (99mg);
mp 128ꢀ130 °C (lit 133ꢀ135 °C). H NMR (400 MHz,
13
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
15
(
d) Campbell, J. M.; Smith, J. A.; Gonzalez, L.; Moeller, K. D.
Tetrahedron Lett. 2015, 56, 3595.
1
6
1
(6) (a) Li, W.ꢀC.; Zeng, C.ꢀC.; Hu, L.ꢀM.; Tian, H.ꢀY.; Little, R.
D. Adv. Synth. Catal. 2013, 355, 2884; (b) Shih, Y.; Ke, C.; Pan,
C.; Huang, Y. RSC Advances 2013, 3, 7330; (c) Gao, W.ꢀJ.; Li,
W.ꢀC.; Zeng, C.ꢀC.; Tian, H.ꢀY.; Hu, L.ꢀM.; Little, R. D. J. Org.
Chem. 2014, 79, 9613; (d) Singh, S.; Sharma, L. K.; Saraswat, A.;
Srivastava, M. K.; Siddiqui, I. R.; Singh, R. K. P. Chemistry of
Heterocyclic Compounds 2014, 49, 1508; (e) Xiao, H.ꢀL.; Zeng,
C.ꢀC.; Tian, H.ꢀY.; Hu, L.ꢀM.; Little, R. D. J. Electroanal. Chem.
2014, 727, 120; (f) Röse, P.; Emge, S.; Yoshida, J.ꢀi.; Hilt, G.
Beilstein J. Org. Chem. 2015, 11, 174; (g) Kang, L.ꢀS.; Xiao, H.ꢀ
l.; Zeng, C.ꢀC.; Hu, L.ꢀM.; Little, R. D. J. Electroanal. Chem.
CDCl ): δ 8.34 (d, J = 8.0 Hz, 1H), 7.98 (d, J = 8.1 Hz, 1H),
3
7
.92 (d, J = 8.8 Hz, 1H), 7.77 (t, J = 7.6 Hz, 1H), 7.49 (t, J =
7.6 Hz, 1H), 6.90 (dd, J = 8.5, 2.0 Hz, 1H), 6.84 (s, 1H), 3.88
(s, 3H). C NMR (101 MHz, CDCl ): δ 161.5, 161.4, 152.7,
135.2, 134.8, 130.6, 127.7, 123.8, 121.0, 120.0, 112.4, 111.2,
101.7, 55.7.
,8,9ꢀtrimethoxyꢀ6Hꢀbenzo[c]chromenꢀ6ꢀone (6c).
solid, using PE/EA (10:1 v/v) as eluent. Isolated yield: 26%
37mg); mp 176ꢀ177 °C (lit 178 °C). H NMR (400 MHz,
13
3
15
3
White
2
4
1
(
2
016, 767, 13.
7) (a) Okimoto, M.; Yoshida, T.; Hoshi, M.; Hattori, K.;
CDCl ): δ 7.82 (d, J = 8.8 Hz, 1H), 7.68 (s, 1H), 7.31 (s, 1H),
3
(
6
3
1
1
.89 (dd, J = 8.8, 2.6 Hz, 1H), 6.84 (d, J = 2.6 Hz, 1H), 4.08 (s,
H), 3.99 (s, 3H), 3.88 (s, 3H). C NMR (101 MHz, CDCl ): δ
61.4, 160.9, 155.2, 152.3, 149.3, 130.5, 123.1, 113.0, 112.3,
11.2, 110.4, 102.1, 101.5, 56.3, 56.2, 55.7.
13
Komata, M.; Numata, K.; Tomozawa, K. Heterocycles 2006, 68,
2563; (b) Lee, D.ꢀS. Tetrahedron: Asymmetry 2009, 20, 2014; (c)
Okimoto, M.; Ohashi, K.; Yamamori, H.; Nishikawa, S.; Hoshi,
M.; Yoshida, T. Synthesis 2012, 44, 1315.
3
(
8) (a) Gieshoff, T.; Kehl, A.; Schollmeyer, D.; Moeller, K. D.;
Waldvogel, S. R. Chem. Commun. 2017, 53, 2974; (b) Gieshoff,
T.; Kehl, A.; Schollmeyer, D.; Moeller, K. D.; Waldvogel, S. R. J.
Am. Chem. Soc. 2017, 139, 12317; (c) Xu, F.; Qian, X.ꢀY.; Li, Y.ꢀ
J.; Xu, H.ꢀC. Org. Lett. 2017, 19, 6332.
ASSOCIATED CONTENT
Supporting Information
1
13
Copies of H and C NMR spectra
(9) (a) Kolbe, H. Justus Liebigs Ann. Chem. 1849, 69, 257; (b)
Vijh, A. K.; Conway, B. E. Chem. Rev. 1967, 67, 623; (c) Schäfer,
H.ꢀJ., Recent contributions of kolbe electrolysis to organic
synthesis. In Electrochemistry IV, Steckhan, E., Ed. Springer
Berlin Heidelberg: Berlin, Heidelberg, 1990; pp 91; (d) Wang, Z.,
Kolbe Electrolysis. In Comprehensive Organic Name Reactions
and Reagents, John Wiley & Sons, Inc.: 2010; (e) Tanaka, H.;
Kuroboshi, M.; Torii, S., Oxidation of Carboxylic Acids and
Derivatives. In Organic Electrochemistry, Fifth Edition Revised
and Expanded, Hammerich, O.; Speiser, B., Eds. CRC Press:
Boca Raton, 2015; pp 1267.
AUTHOR INFORMATION
Corresponding Author
*
fmo@pku.edu.cn
Author Contributions
†
These authors contributed equally.
Notes
(
10) (a) H.R. Barton, D.; Lacher, B.; Zard, S. Z. Tetrahedron
The authors declare no competing financial interest.
1
987, 43, 4321; (b) Barton, D. H. R.; Ramesh, M. Tetrahedron
Lett. 1990, 31, 949.
ACKNOWLEDGMENT
(11) (a) Bunyan, P. J.; Hey, D. H. J. Chem. Soc. (Resumed)
1960, 3787; (b) Wilshire, J. Aust. J. Chem. 1963, 16, 432; (c)
Kikuhiko, K.; Kunihisa, Y.; Shigeru, T. Bull. Chem. Soc. Jpn.
1966, 39, 516.
(12) (a) Ishiguro, K.; Yamaki, M.; Kashihara, M.; Takagi, S.;
Isoi, K. Phytochemistry. 1990, 29, 1010; (b) Koch, K.; Podlech,
J.; Pfeiffer, E.; Metzler, M. J. Org. Chem. 2005, 70, 3275; (c)
Weissman, K. Chem. Biol. 2005, 12, 512; (d) Tibrewal, N.;
Pahari, P.; Wang, G.; Kharel, M. K.; Morris, C.; Downey, T.;
Hou, Y.; Bugni, T. S.; Rohr, J. J. Am. Chem. Soc. 2012, 134,
The project was supported by the Natural Science Foundation of
China (Grant Nos. 21502003 and 21772003). We also thank the
“1000ꢀYouth Talents Plan” and Peking University for startup
funds.
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0
1
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5
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
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