Copper(II)-promoted C-C bond formation by oxidative coupling of two C(sp3)-H bonds adjacent to carbonyl group to construct 1,4-diketones and tetrasubstituted furans

Article abstract of DOI:10.1002/ejoc.201403274

The copper(II)-promoted C-C bond formation from the coupling of two C(sp³)-H bonds that are adjacent to a carbonyl group was achieved. This protocol offers a simple and efficient approach to 2,3-disubstituted 1,4-diketones and tetrasubstituted furans. This method features a wide substrate scope and high functional group tolerance.

Full text of DOI:10.1002/ejoc.201403274

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FULL PAPER
DOI: 10.1002/ejoc.201403274
Copper(II)-Promoted C–C Bond Formation by Oxidative Coupling of Two
C(sp3)–H Bonds Adjacent to Carbonyl Group to Construct 1,4-Diketones and
Tetrasubstituted Furans
Shuai Mao,[a] Ya-Ru Gao,[a] Shao-Liang Zhang,[a] Dong-Dong Guo,[a] and
Yong-Qiang Wang*[a]
Keywords: Synthetic methods / C–C coupling / Oxidation / Copper / Oxygen heterocycles
The copper(II)-promoted C–C bond formation from the cou-
pling of two C(sp3)–H bonds that are adjacent to a carbonyl
ficient approach to 2,3-disubstituted 1,4-diketones and tetra-
substituted furans. This method features a wide substrate
group was achieved. This protocol offers a simple and ef- scope and high functional group tolerance.
(NaHMDS)] to produce the enolate followed by an oxidat-
Introduction
ive coupling reaction (see Scheme 1).[8] Herein, we report
an effective copper(II)-promoted direct oxidative coupling
reaction of two C(sp3)–H bonds that are adjacent to a carb-
onyl group to produce 2,3-disubstituted 1,4-diketones.
The formation of a carbon-carbon (C–C) bond from the
coupling of two simple carbon-hydrogen (C–H) bonds is of
great interest because of its intrinsic advantages with regard
to atom-economy and step-economy.[1] In general, this
transformation proceeds under transition-metal-mediated
oxidative conditions.[2] However, the coupling of two
C(sp3)–H bonds is challenging, as these bonds do not have
an empty low-energy orbital or a filled high-energy orbital,
and, thus, it is difficult for a metal atom to activate them
through an orbital interaction.[3] Although great progress
has been made with regard to C–C bond formation from
the activation of C(sp3)–H bonds,[4] the coupling of two
C(sp3)–H bonds adjacent to a carbonyl group has not yet
been documented, despite the fact that the carbonyl group
plays a particularly important role in organic synthesis.
2,3-Disubstituted 1,4-dicarbonyl compounds are ubiqui-
tous substructures of natural products and pharmaceuti-
cals[5,6] as well as highly useful synthetic building blocks of
various carbocyclic and heterocyclic compounds.[7] Gen-
erally, the direct and convergent synthesis of 2,3-disubsti-
tuted-1,4-dicarbonyl compounds from two carbonyl sub-
units is extremely difficult. One typical method to synthe-
size such compounds is by using an enolate coupling
reaction. However, this approach suffers from the use of a
stoichiometric amount of a strong base [e.g., lithium diiso-
propylamide (LDA) and sodium hexamethyldisilazide
Scheme 1. Synthesis of 1,4-dicarbonyl compounds (M = metal).
Results and Discussion
Initially, we utilized deoxybenzoin (1a) as a standard
substrate to evaluate the coupling of two C(sp3)–H bonds
adjacent to a carbonyl group. We chose copper salts as the
oxidant because they are inexpensive, readily available, and
easy to handle, and they possess a distinct advantage in
oxidative coupling reactions.[9] To our delight, the desired
product 2a was obtained in 35% yield when the reaction
was carried out with copper chloride as the oxidant in tolu-
ene at reflux (see Table 1, Entry 1). A variety of other oxi-
dants from copper sources were then investigated. The ex-
periments revealed that CuII species provided better results
than CuI species. Cu(OAc)2 was most effective oxidant and
afforded the product in 75% isolated yield (see Table 1, En-
tries 2–10). After a careful screening, xylene was chosen as
the solvent, (see Table 1, Entries 11–15). Finally, hydrated
Cu(OAc)2 was as efficient an oxidant as anhydrous
[a] Key Laboratory of Synthetic and Natural Functional
Molecule Chemistry of Ministry of Education, Department of
Chemistry & Materials Science, Northwest University,
Xi’an 710069, P.R. China
E-mail: wangyq@nwu.edu.cn
http://www.nwu.edu.cn/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201403274.
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S. Mao, Y.-R. Gao, S.-L. Zhang, D.-D. Guo, Y.-Q. Wang
FULL PAPER
Cu(OAc)2 and afforded 2a in 90% yield (see Table 1, (not shown). Substrates that contained electron-with-
Entry 16). In contrast, a catalytic amount of either drawing substituents on either side of the aromatic ring
Cu(OAc)2 or Cu(OAc)2·H2O (e.g., 20 mol-%) led to an in- underwent the reaction faster than those that were substi-
complete reaction.
tuted by electron-donating groups. This difference implies
the possibility of a cross-coupling reaction. Consequently,
we examined the cross-coupling reactions of 1b with 1e and
1g with 1i as typical reactions that would provide two dif-
ferent substitution patterns (see Scheme 2). Delightedly, the
cross-coupling reactions proceeded well when the substrates
with the electron-withdrawing group (i.e., 1e and 1i) were
added slowly to their corresponding reaction system to pro-
vide cross-coupling products 2r and 2s in 50 and 66% iso-
lated yield, respectively.
Table 1. Optimization of conditions for the oxidative coupling of
1a.[a]
Entry
Oxidant
Solvent
Yield [%][b]
1
2
3
4
5
6
7
8
CuCl2
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
xylene
35
30
75
27
40
18
15
16
10
5
92
78
60
0
CuBr2
Cu(OAc)2
CuO
Cu(OTf)2
Cu2O
CuCl
CuBr
[c]
9
CuI
CuOAc
10
11[d]
12[d]
13[d]
14[e]
15[e]
16[d]
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2·H2O
DMF[c]
DMSO[c]
CH3CN
1,4-dioxane
xylene
10
Scheme 2. Cross-coupling reactions.
90[f]
[a] Reagents and conditions: Unless otherwise noted, the reaction
was carried out with 1a (0.5 mmol), oxidant (0.5 mmol), and sol-
vent (1.5 mL) at reflux. [b] Isolated yield. [c] OTf = trifluoro-
methanesulfonate, DMF = N,N-dimethylformamide, DMSO = di-
methyl sulfoxide. [d] At 140 °C. [e] At reflux temperature. [f] Dia-
stereomeric ratio (dr, 0.75:1) was determined by H NMR spectro-
scopic analysis.
Surprisingly, when 1.0 equiv. of trifluoroacetic acid
(TFA) was introduced into the reaction system of deoxy-
benzoin (1a), we attained tetrasubstituted furan 3a (con-
firmed by single-crystal X-ray analysis[13]) in 70% yield (see
Scheme 3). Encouraged by this result, we tried to develop
a direct method to synthesize polysubstituted furans from
ketones in one step. It is well-known that polysubstituted
furans are an important class of five-membered hetero-
cycles that are prevalent in natural products, pharmaceuti-
1
Next, we applied the optimized reaction conditions to
investigate other substrates in the copper(II)-promoted oxi-
dative coupling reaction. Pleasingly, all of the reactions pro-
ceeded smoothly and afforded the 2,3-disubstituted-1,4-di-
carbonyl compounds in good to excellent yields (see
Table 2). Various substituents such as the methyl, methoxy,
fluoro, chloro, bromo, and nitro group were tolerated under
the reaction conditions. The steric hindrance from the sub-
stituent on the aromatic group had no effect on the reaction
(see Table 2, compounds 2l–2n). In addition, the deoxyben-
zoin derivative that contained a 4-phenyl group was also
suitable for the reaction and provided the desired product
in 95% yield (see Table 2, compound 2o). The structure of
the product 2j was confirmed by single-crystal X-ray analy-
sis.[13] Remarkably, dialkyl ketones, for example, benzyl
butyl ketone (1p) and 2-bromophenylacetone (1q) also were
suitable substrates and afforded the corresponding products
in excellent yields (see Table 2, compounds 2p and 2q).
However, 3-pentanone did not provide the desire product Scheme 3. Synthesis of tetrasubstituted furan 3a.
2
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Cu(II)-Promoted Coupling of Two C(sp3)–H bonds
Table 2. Scope of substrates for the oxidative coupling reaction.[a–c]
[a] Reagents and conditions: 1 (0.5 mmol), Cu(OAc)2·H2O (0.5 mmol), and xylene (1.5 mL) at 140 °C. [b] Isolated yield. [c] Diastereomeric
1
ratios were determined by H NMR spectroscopic analysis.
cals, and agrochemicals. In addition, they are useful build- of oxygen as the oxidant, the reaction rate and yield de-
ing blocks in organic synthesis.[10] Accordingly, a new and creased (see Table 3, Entry 20). After carefully screening
efficient process for the region-defined synthesis of polysub- various parameters, Cu(OAc)2·H2O (20 mol-%), Ag2O
stituted furans is highly desirable.[11]
(10 mol-%), O2 (1 atm), TFA (1.6 equiv.), and xylene as the
We then screened different acids in the reaction system as solvent at 140 °C were chosen as the optimal reaction con-
well as the amount of TFA that was employed (see Table 3, ditions.
Entries 1–13). These results showed that TFA (1.6 equiv.)
The optimized conditions were then applied to a broad
gave the best results and afforded 3a in 87% yield. When range of substrates, and the tetrasubstituted furans were ef-
the amount of Cu(OAc)2·H2O was reduced to 0.5 equiv. ficiently obtained in all cases (see Table 4). Electron-donat-
and oxygen was employed as the terminal oxidant, 3a was ing and electron-withdrawing groups on both aromatic
obtained in 65% yield (see Table 3, Entry 14). This rings were compatible under the reaction conditions, and
result inspired us to explore a catalytic approach to this these groups were uniformly furnished in the desired prod-
process. It has been reported that silver(I) species can pro- ucts. Carbon-halogen bonds such as C–F, C–Cl, C–Br, and
mote the oxidation of CuI into CuII.[12] Therefore, a cata- C–I were well-tolerated in the reaction system and provided
lytic amount of a variety of silver(I) species were added to the possibility for further functionalization of the polysub-
the reaction system (see Table 3, Entries 16–19). Ag2O was stituted furans, enabling these products to be used as core
shown to be the best additive. When air was used instead structures for polymers and functional materials. Dialkyl
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FULL PAPER
Table 3. Optimization of conditions for the synthesis of tetrasubsti- ketones also provided the desired products in good yields
tuted furan.[a]
(see Table 4, compounds 3p and 3q), whereas 3-pentanone
was unsuccessful. The structure of the product 3e was con-
firmed by single-crystal X-ray analysis.[13]
Finally, we investigated the corresponding cross-coupling
reaction (see Scheme 4). Two typical reactions were exam-
ined. The substrates with an electron-withdrawing substitu-
ent, 1e and 1i, were added to the standard reaction systems
of 1b and 1g, respectively, to afford the corresponding
cross-coupling products in good yields.
Entry Oxidant [equiv.]
Acid [equiv.]
Additive Yield [%][b]
1
2
3
4
5
6
7
8
Cu(OAc)2·H2O (1.0) TFA (1.0)
Cu(OAc)2·H2O (1.0) HCO2H (1.0)
Cu(OAc)2·H2O (1.0) CH3COOH (1.0)
Cu(OAc)2·H2O (1.0) PhCOOH (1.0)
Cu(OAc)2·H2O (1.0) TsOH (1.0)[c]
Cu(OAc)2·H2O (1.0) H3BO3 (1.0)
Cu(OAc)2·H2O (1.0) CH2(COOH)2 (1.0)
Cu(OAc)2·H2O (1.0) maleic acid (1.0)
Cu(OAc)2·H2O (1.0) fumaric acid (1.0)
Cu(OAc)2·H2O (1.0) TFA (0.4)
Cu(OAc)2·H2O (1.0) TFA (0.8)
Cu(OAc)2·H2O (1.0) TFA (1.6)
Cu(OAc)2·H2O (1.0) TFA (2.0)
Cu(OAc)2·H2O (0.5) TFA (1.6)
Cu(OAc)2·H2O (0.2) TFA (1.6)
Cu(OAc)2·H2O (0.2) TFA (1.6)
Cu(OAc)2·H2O (0.2) TFA (1.6)
Cu(OAc)2·H2O (0.2) TFA (1.6)
Cu(OAc)2·H2O (0.2) TFA (1.6)
Cu(OAc)2·H2O (0.2) TFA (1.6)
–
–
–
–
–
–
–
–
70
50
41
13
47
18
35
4
A single-electron transfer (SET) is an obvious consider-
ation with regard to the mechanism of the copper-promoted
oxidative coupling reaction.[9] To gain insight into the
mechanism, a radical-trapping experiment was carried out.
The radical inhibitor TEMPO (2,2,6,6-tetramethylpiper-
idine-1-oxyl) was introduced into the standard reaction sys-
tem of deoxybenzoin (1a, see Scheme 5). The oxidative cou-
pling reaction did not occur. Instead, the coupling reaction
of deoxybenzoin (1a) with TEMPO occurred, and 4a was
produced in 40% yield. The structure of 4a was confirmed
by single-crystal X-ray analysis.[13] Thus, a possible mecha-
nism is proposed in Scheme 6. Substrate 1 undergoes an
oxidative SET by the reduction of CuII and deprotonation
to generate carbonyl alkyl radical A followed by the cou-
pling reaction with the other partner to give 1,4-dicarbonyl
product 2. Under acid conditions, 2 then produces tetrasub-
stituted furan 3. CuI is then oxidized by Ag2O/O2 to regen-
erate CuII.[12]
9
–
6
10
11
12
13
14[d]
15[d]
16[d]
17[d]
18[d]
19[d]
20
–
–
–
–
–
30
58
87
85
65
40
85
58
66
78
70
–
Ag2O
AgNO3
Ag2CO3
AgOAc
Ag2O
[a] Reagents and conditions: 1a (0.5 mmol), Cu(OAc)2·H2O, acid,
additive (0.05 mmol), and xylene (1.5 mL) at 140 °C under air
(1 atm). [b] Isolated yield. [c] TsOH = p-toluenesulfonic acid.
[d] Under O2 (1 atm). [e] Under air (1 atm).
Table 4. Scope of substrates for the synthesis of tetrasubstituted furans.[a,b]
[a] Reagents and conditions: Unless otherwise noted, the reaction was carried out with 1 (0.5 mmol), Cu(OAc)2·H2O (20 mol-%), Ag2O
(10 mol-%), O2(1 atm), and TFA (1.6 equiv.) in xylene (1.5 mL) at 140 °C. [b] Isolated yield.
4
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Cu(II)-Promoted Coupling of Two C(sp3)–H bonds
Scheme 4. Synthesis of tetrasubstituted furans by cross-coupling reactions.
process. Further mechanistic studies and applications of
these approaches are in progress.
Experimental Section
General Methods: All reactions were carried out under oxygen or
air. All reagents and solvents were obtained from commercial sup-
pliers and used without further purification. The progress of the
reactions was monitored by TLC with silica gel plates (GF254),
1
and the visualization was carried out under UV light. The H and
the 13C NMR spectroscopic data were recorded with a Varian
Unity Inova-400 spectrometer (1H and 13C NMR at 400 and
100 MHz, respectively). CDCl3 was used as the NMR solvent, un-
less otherwise noted. Infrared (IR) data were recorded as films on
potassium bromide plates with a Bruker Tensor 27 FT-IR spec-
trometer. Absorbance frequencies are reported in reciprocal centi-
meters (cm–1). High resolution mass spectra were acquired with a
Bruker Daltonics MicroTof-Q II mass spectrometer. X-ray crystal
structure analyses were measured on a Bruker Smart APEXIICCD
instrument using Mo-Kα radiation. The structures were solved and
refined by using the SHELXTL software package.
Scheme 5. Radical-trapping experiment.
Typical Procedure for the Synthesis of 1,4-Diketone: A mixture of
deoxybenzoin (1a, 1.0 mmol) and Cu(OAc)2·H2O (1.0 mmol) in
xylene (3 mL) was stirred at 140 °C. Upon completion of the reac-
tion, the mixture was cooled to room temp. and filtered through a
small pad of silica gel. The filtrate was concentrated in vacuo, and
the residue was purified by chromatography on a silica gel column
to afford product 2a.
1,2,3,4-Tetraphenylbutane-1,4-dione (2a):[14] White solid (90% iso-
1
lated yield; dr 0.75:1). H NMR (400 MHz, CDCl3): δ = 7.99 (d, J
Scheme 6. Proposed mechanism.
= 8.0 Hz, 4 H, C6H5), 7.43 (d, J = 8.0 Hz, 2 H, C6H5), 7.35 (t, J
= 6.0 Hz, 4 H, C6H5), 7.09 (s, 6 H, C6H5), 7.02 (d, J = 5.3 Hz, 4
H, C6H5), 5.40 (s, 2 H, CH) ppm. 13C NMR (100 MHz, CDCl3): δ
= 199.5, 136.4, 136.4, 133.0, 129.0, 128.9, 128.7, 128.5, 127.3,
58.5 ppm. HRMS (ESI): calcd. for C28H22O2Na [M + Na]+
413.1512; found 413.1517.
Conclusions
In summary, we have developed the coupling of two
C(sp3)–H bonds that are adjacent to a carbonyl group to
provide direct and efficient access to 2,3-disubstituted-1,4-
dicarbonyl compounds. In addition, an unusually simple
approach to produce tetrasubstituted furans directly from
ketones was achieved by using the copper-catalyzed oxidat-
ive coupling reaction with oxygen as a terminal oxidant.
2,3-Diphenyl-1,4-di-p-tolylbutane-1,4-dione (2b):[15] White solid
1
(91% isolated yield; dr 0.65:1). H NMR (400 MHz, CDCl3): δ =
7.79 (d, J = 8.0 Hz, 4 H, H-Ar), 7.53 (d, J = 4.0 Hz, 4 H, H-Ar),
7.18 (d, J = 8.0 Hz, 4 H, H-Ar), 7.13–7.08 (m, 6 H, H-Ar), 5.77 (s,
2 H, CH), 2.30 (s, 6 H, CH3) ppm. 13C NMR (100 MHz, CDCl3):
The two economic approaches feature a wide substrate δ = 198.1, 143.9, 137.2, 134.4, 129.2, 129.1, 128.8, 128.7, 127.3,
55.9, 21.6 ppm.
scope and a high functional group tolerance. Tentative
mechanistic studies suggest that the coupling reaction is
1,4-Bis(4-methoxyphenyl)-2,3-diphenylbutane-1,4-dione
(2c):[16]
likely to proceed through a single-electron transfer (SET) White solid (83% isolated yield; dr 0.83:1). 1H NMR (400 MHz,
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CDCl3): δ = 7.98 (d, J = 8.0 Hz, 4 H, H-Ar), 7.10 (d, J = 8.0 Hz, Ar), 7.32–7.39 (m, 7 H, H-Ar), 6.99 (t, J = 6.0 Hz, 4 H, H-Ar),
6 H, H-Ar), 7.01 (d, J = 8.0 Hz, 4 H, H-Ar), 6.84 (d, J = 8.0 Hz, 6.90 (q, J = 8.0 Hz, 3 H, H-Ar), 6.84 (t, J = 8.0 Hz, 4 H, H-Ar),
4 H, H-Ar), 5.34 (s, 2 H, CH), 3.80 (s, 6 H, OCH3) ppm. 13C NMR 5.72 (s, 1.5 H, CH), 5.36 (s, 2 H, CH) ppm. 13C NMR (100 MHz,
(100 MHz, CDCl3): δ = 197.9, 163.3, 137.0, 131.3, 129.5, 128.8, CDCl3, major isomer): δ = 199.3, 162.0 (d, JF,C = 245 Hz), 136.1,
128.6, 127.1, 113.7, 58.1, 55.5 ppm.
133.2, 132.1 (d, JF,C = 3.0 Hz), 130.3 (d, JF,C = 8.0 Hz), 128.9,
128.6, 116.0, 57.6 ppm. 13C NMR (100 MHz, CDCl3, minor iso-
mer): δ = 198.3, 162.1 (d, JF,C = 245 Hz), 136.6, 133.3, 132.5 (d,
JF,C = 3.0 Hz), 130.7 (d, JF,C = 8.0 Hz), 128.7, 128.5, 115.8,
1,4-Bis(4-fluorophenyl)-2,3-diphenylbutane-1,4-dione (2d): White so-
1
lid (86% isolated yield; dr 0.81:1). H NMR (400 MHz, CDCl3): δ
= 8.00 (s, 4 H, H-Ar), 7.12 (s, 6 H, H-Ar), 7.04 (t, J = 10.0 Hz, 4
H, H-Ar), 6.99 (s, 4 H, H-Ar), 5.31 (s, 2 H, CH) ppm. 13C NMR
(100 MHz, CDCl3): δ = 198.0, 165.7 (d, JF,C = 250 Hz), 136.1,
132.8 (d, JF,C = 3.0 Hz), 131.6 (d, JF,C = 9.0 Hz), 128.84, 128.76,
55.4 ppm. IR (KBr): ν = 3069, 2924, 1670, 1598, 1578, 1508, 1449,
˜
1377, 1323, 1291, 1225, 1160, 1099, 1013, 938, 814, 750, 690 cm–1.
HRMS (ESI): calcd. for C28H20F2O2Na [M + Na]+ 449.1324;
found 449.1338.
127.5, 115.7 (d, JF,C = 22.0 Hz), 58.5 ppm. IR (KBr): ν = 3065,
˜
3032, 2927, 2854, 1672, 1596, 1232, 1155, 860, 842, 738, 700 cm–1.
HRMS (ESI): calcd. for C28H20F2O2Na [M + Na]+ 449.1324;
found 449.1332.
2,3-Bis(4-chlorophenyl)-1,4-diphenylbutane-1,4-dione (2k):[14] White
1
solid (88% isolated yield; dr 0.88:1). H NMR (400 MHz, CDCl3):
δ = 7.95 (d, J = 8.0 Hz, 4 H, H-Ar), 7.84 (d, J = 8.0 Hz, 3.6 H, H-
Ar), 7.50–7.42 (m, 7.7 H, H-Ar), 7.40–7.32 (m, 7.7 H, H-Ar), 7.18
(d, J = 8.0 Hz, 3.6 H, H-Ar), 7.12 (d, J = 8.0 Hz, 4 H, H-Ar), 6.96
(d, J = 8.0 Hz, 3.8 H, H-Ar), 5.70 (s, 1.7 H, CH), 5.34 (s, 2 H,
CH) ppm. 13C NMR (100 MHz, CDCl3): δ = 198.9, 197.9, 136.5,
136.0, 135.2, 134.7, 133.6, 133.52, 133.47, 133.3, 130.4, 130.1,
129.2, 129.2, 128.9, 128.72, 128.66, 128.5, 57.6, 55.5 ppm.
1,4-Bis(4-chlorophenyl)-2,3-diphenylbutane-1,4-dione (2e):[17] White
solid (81% isolated yield; dr 0.17:1). H NMR (400 MHz, CDCl3):
δ = 7.91 (d, J = 8.0 Hz, 4 H, H-Ar), 7.34 (d, J = 8.0 Hz, 4 H, H-
Ar), 7.12 (s, 6 H, H-Ar), 6.97 (s, 4 H, H-Ar), 5.29 (s, 2 H, CH) ppm.
13C NMR (100 MHz, CDCl3): δ = 197.1, 139.7, 136.5, 135.1, 129.9,
129.0, 128.91, 127.7, 56.3 ppm.
1
2,3-Bis(4-bromophenyl)-1,4-diphenylbutane-1,4-dione (2l):[19] White
solid (92% isolated yield; dr 0.30:1). H NMR (400 MHz, CDCl3):
1,4-Bis(4-bromophenyl)-2,3-diphenylbutane-1,4-dione (2f): White so-
lid (80% isolated yield; dr 0.16:1). H NMR (400 MHz, CDCl3): δ
1
1
δ = 7.92 (d, J = 8.0 Hz, 4 H, H-Ar), 7.44 (d, J = 8.0 Hz, 2 H, H-
Ar), 7.34 (t, J = 8.0 Hz, 4 H, H-Ar), 7.25 (d, J = 8.0 Hz, 4 H, H-
Ar), 6.89 (d, J = 8.0 Hz, 4 H, H-Ar), 5.32 (s, 2 H, CH) ppm. 13C
NMR (100 MHz, CDCl3): δ = 198.8, 136.0, 135.2, 133.3, 132.1,
130.4, 128.9, 128.6, 121.7, 57.6 ppm.
= 7.83 (d, J = 8.0 Hz, 4 H, H-Ar), 7.46 (d, J = 8.0 Hz, 4 H, H-
Ar), 7.10 (s, 6 H, H-Ar), 6.97 (s, 4 H, H-Ar), 5.31 (s, 2 H, CH) ppm.
13C NMR (100 MHz, CDCl3): δ = 198.4, 135.8, 135.0, 131.8, 130.4,
128.8, 128.7, 128.2, 127.5, 58.4 ppm. IR (KBr): ν = 3057, 3031,
˜
2924, 2853, 1665, 1585, 1564, 1485, 1453, 1253, 1205, 1174, 1071,
1008, 850, 821, 800, 728, 705 cm–1. HRMS (ESI): calcd. for
C28H21Br2O2 [M + H]+ 546.9903; found 546.9905.
2,3-Bis(3-bromophenyl)-1,4-diphenylbutane-1,4-dione (2m): White
1
solid (90% isolated yield; dr 0.49:1). H NMR (400 MHz, CDCl3):
1,4-Diphenyl-2,3-di-p-tolylbutane-1,4-dione (2g):[14] White solid
δ = 7.97 (d, J = 8.0 Hz, 4 H, H-Ar), 7.46 (t, J = 6.0 Hz, 2 H, H-
Ar), 7.37 (t, J = 6.0 Hz, 4 H, H-Ar), 7.26–7.23 (m, 4 H, H-Ar),
7.01–6.97 (m, 2 H, H-Ar), 6.93 (d, J = 7.0 Hz, 2 H, H-Ar), 5.34 (s,
2 H, CH) ppm. 13C NMR (100 MHz, CDCl3): δ = 198.5, 138.3,
135.9, 133.4, 131.4, 130.7, 130.4, 128.9, 128.6, 127.6, 122.8,
1
(89% isolated yield; dr 0.62:1). H NMR (400 MHz, CDCl3): δ =
7.89 (d, J = 8.0 Hz, 4 H, H-Ar), 7.42 (d, J = 8.0 Hz, 6 H, H-Ar),
7.32 (t, J = 8.0 Hz, 4 H, H-Ar), 7.01 (d, J = 8.0 Hz, 4 H, H-Ar),
5.75 (s, 2 H, CH), 2.17 (s, 6 H, CH3) ppm. 13C NMR (100 MHz,
CDCl3): δ = 198.5, 137.0, 136.9, 134.0, 132.9, 129.6, 129.0, 128.6,
128.5, 55.7, 21.0 ppm. HRMS (ESI): calcd. for C30H26O2Na [M +
Na]+ 441.1825; found 441.1825.
57.8 ppm. IR (KBr): ν = 3056, 2925, 1668, 1593, 1576, 1473, 1447,
˜
1425, 1285, 1250, 1200, 1178, 1074, 1006, 972, 780, 713, 686 cm–1.
HRMS (ESI): calcd. for C28H20Br2O2Na [M + Na]+ 568.9722;
found 568.9699.
2,3-Bis(4-methoxyphenyl)-1,4-diphenylbutane-1,4-dione
(2h):[14]
White solid (90% isolated yield; dr 0.53:1). 1H NMR (400 MHz,
CDCl3): δ = 7.97 (d, J = 4.0 Hz, 4 H, H-Ar), 7.45 (d, J = 8.0 Hz,
2 H, H-Ar), 7.36 (t, J = 6.0 Hz, 4 H, H-Ar), 6.93 (d, J = 8.0 Hz, 4
H, H-Ar), 6.67 (d, J = 8.0 Hz, 4 H, H-Ar), 5.30 (s, 2 H, CH), 3.70
(s, 6 H, OCH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 199.9,
158.6, 136.5, 132.9, 130.2, 129.9, 128.9, 128.5, 114.1, 57.7,
55.1 ppm.
2,3-Bis(2-bromophenyl)-1,4-diphenylbutane-1,4-dione (2n): White
solid (90% isolated yield; dr 1.0:1). H NMR (400 MHz, CDCl3):
1
δ = 8.09 (d, J = 8.0 Hz, 4 H, H-Ar), 7.96 (d, J = 8.0 Hz, 3 H, H-
Ar), 7.62 (t, J = 10.0 Hz, 4 H, H-Ar), 7.47–7.39 (m, 10 H, H-Ar),
7.31 (t, J = 8.0 Hz, 6 H, H-Ar), 7.18–7.13 (m, 4 H, H-Ar), 6.98–
6.94 (m, 4 H, H-Ar), 6.19 (s, 1.5 H, CH), 6.11 (s, 2 H, CH) ppm.
13C NMR (100 MHz, CDCl3): δ = 199.0, 198.0, 136.7, 135.9, 135.7,
134.1, 133.4, 133.3, 133.2, 133.1, 131.5, 130.4, 129.2, 129.1, 128.9,
128.8, 128.6, 128.4, 127.8, 127.6, 125.8, 125.4, 55.2, 54.3 ppm. IR
2,3-Bis(4-nitrophenyl)-1,4-diphenylbutane-1,4-dione (2i):[18] White
1
solid (90% isolated yield; dr 0.51:1). H NMR (400 MHz, CDCl3):
(KBr): ν = 3060, 2958, 2851, 1673, 1595, 1469, 1445, 1285, 1249,
˜
δ = 8.06 (d, J = 8.0 Hz, 2 H, H-Ar), 7.98 (d, J = 8.0 Hz, 4 H, H-
Ar), 7.91 (d, J = 4.0 Hz, 4 H, H-Ar), 7.80 (d, J = 8.0 Hz, 2 H, H-
Ar), 7.69 (d, J = 12.0 Hz, 2 H, H-Ar), 7.51–7.44 (m, 5 H, H-Ar),
7.39–7.31 (m, 8.2 H, H-Ar), 7.22 (s, 9 H, H-Ar), 5.84 (s, 1 H, CH),
5.56 (s, 2 H, CH) ppm. 13C NMR (100 MHz, CDCl3): δ = 197.6,
196.8, 147.4, 143.6, 143.2, 135.8, 135.5, 134.2, 133.9, 130.1, 129.6,
129.00, 128.97, 128.9, 128.6, 124.3, 124.2, 57.7, 56.0 ppm. HRMS
(ESI): calcd. for C28H20N2O6Na [M + Na]+ 503.1214; found
503.1217.
1202, 1023, 1003, 973, 749, 703, 687 cm–1. HRMS (ESI): calcd. for
C28H21Br2O2 [M + H]+ 546.9903; found 546.9908.
2,3-Di(biphenyl-4-yl)-1,4-diphenylbutane-1,4-dione (2o): White solid
1
(95% isolated yield; dr 0.68:1). H NMR (400 MHz, CDCl3): δ =
8.04 (d, J = 8.0 Hz, 4 H, H-Ar), 7.48 (s, 6.7 H, H-Ar), 7.38 (d, J
= 8.0 Hz, 12.5 H, H-Ar), 7.32–7.22 (m, 3.6 H, H-Ar), 7.13 (d, J =
8.0 Hz, 4 H, H-Ar), 5.48 (s, 2 H, CH), 5.28 (s, 1.3 H, CH) ppm.
13C NMR (100 MHz, CDCl3): δ = 199.5, 140.3, 139.9, 136.4, 135.4,
133.1, 129.3, 129.0, 128.8, 128.6, 127.4, 126.9, 58.1 ppm. IR (KBr):
2,3-Bis(4-fluorophenyl)-1,4-diphenylbutane-1,4-dione (2j): White so-
1
lid (93% isolated yield; dr 0.74:1). H NMR (400 MHz, CDCl3): δ
ν = 3060, 3029, 2922, 2853, 1665, 1597, 1579, 1486, 1447, 1280,
˜
= 7.97 (d, J = 8.0 Hz, 4 H, H-Ar), 7.86 (d, J = 8.0 Hz, 3 H, H-
Ar), 7.51 (t, J = 6.0 Hz, 4 H, H-Ar), 7.45 (d, J = 8.0 Hz, 3 H, H-
1247, 1176, 1009, 842, 815, 764, 693 cm–1. HRMS (ESI): calcd. for
C40H30NaO2 [M + Na]+ 565.2138; found 565.2143.
6
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O43274
/KAP1
Date: 17-12-14 14:11:59
Pages: 11
Cu(II)-Promoted Coupling of Two C(sp3)–H bonds
6,7-Diphenyldodecane-5,8-dione (2p): White solid (91% isolated 2,3,4,5-Tetraphenylfuran (3a):[20] White solid (85% isolated yield);
yield; dr 0.71:1). 1H NMR (400 MHz, CDCl3): δ = 7.39 (d, J = m.p. 170–171 °C. 1H NMR (400 MHz, CDCl3): δ = 7.52 (d, J =
8.0 Hz, 4 H, C6H5), 7.31 (t, J = 8.0 Hz, 4 H, C6H5), 7.27–7.21 (m, 4.0 Hz, 4 H, C6H5), 7.27–7.23 (m, 12 H, C6H5), 7.16 (s, 4 H,
2 H, C6H5), 4.61 (s, 2 H, CH), 2.32–2.20 (m, 2 H, CH2), 2.11–1.99
C6H5) ppm. 13C NMR (100 MHz, CDCl3): δ = 147.8, 133.2, 130.9,
(m, 2 H, CH2), 1.29–1.10 (m, 4 H, CH2), 0.93–0.85 (m, 4 H, CH2), 130.5, 128.4, 128.4, 127.4, 127.2, 125.9, 125.2 ppm. HRMS (ESI):
0.64 (t, J = 8.0 Hz, 6 H, CH3) ppm. 13C NMR (100 MHz, CDCl3): calcd. for C28H20ONa [M + Na]+ 395.1406; found 395.1405.
δ = 208.7, 136.6, 129.0, 128.8, 127.6, 60.6, 43.2, 25.3, 21.8,
3,4-Diphenyl-2,5-di-p-tolylfuran (3b):[21] White solid (60% isolated
13.7 ppm. IR (KBr): ν = 3061, 2957, 2869, 1710, 1600, 1495, 1457,
˜
yield); m.p. 154–155 °C. 1H NMR (400 MHz, CDCl3): δ = 7.36 (d,
J = 8.0 Hz, 4 H, H-Ar), 7.18 (s, 6 H, H-Ar), 7.11 (s, 4 H, H-Ar),
7.03 (d, J = 8.0 Hz, 4 H, H-Ar), 2.27 (s, 6 H, CH3) ppm. 13C NMR
(100 MHz, CDCl3): δ = 147.7, 137.1, 133.4, 130.5, 129.1, 128.4,
128.3, 127.1, 125.9, 124.4, 21.4 ppm. HRMS (ESI): calcd. for
C30H24ONa [M + Na]+ 423.1719; found 423.1726.
1368, 1239, 1126, 1043, 747, 702 cm–1. HRMS (ESI): calcd. for
C24H30O2Na [M + Na]+ 373.2138; found 373.2134.
3,4-Bis(2-bromophenyl)hexane-2,5-dione (2q): White solid (86% iso-
1
lated yield; dr 0.81:1). H NMR (400 MHz, CDCl3): δ = 7.63 (d, J
= 8.0 Hz, 2 H, C6H4), 7.42 (d, J = 8.0 Hz, 2 H, C6H4), 7.31 (t, J
= 8.0 Hz, 2 H, C6H4), 7.14 (t, J = 8.0 Hz, 2 H, C6H4), 5.31 (s, 2
H, CH), 1.96 (s, 6 H, CH3) ppm. 13C NMR (100 MHz, CDCl3): δ
= 204.9, 135.8, 133.7, 129.3, 128.8, 128.1, 126.5, 58.8, 30.5 ppm.
2,5-Bis(4-methoxyphenyl)-3,4-diphenylfuran (3c):[15] White solid
(64% isolated yield); m.p. 123–124 °C. 1H NMR (400 MHz,
CDCl3): δ = 7.34 (d, J = 8.0 Hz, 4 H, H-Ar), 7.13 (s, 6 H, H-Ar),
7.06 (s, 4 H, H-Ar), 6.71 (d, J = 8.0 Hz, 4 H, H-Ar), 3.68 (s, 6 H,
OCH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 158.8, 147.4, 133.5,
130.5, 128.4, 127.3, 127.0, 123.9, 123.5, 113.9, 55.3 ppm.
IR (KBr): ν = 3053, 2917, 2850, 1702, 1555, 1463, 1415, 1350, 1262,
˜
1214, 1145, 1018, 953, 748, 661, 627, 538, 475 cm–1. HRMS (ESI):
calcd. for C24H30O2Na [M + Na]+ 444.9409; found 444.9424.
Typical Procedure for the Synthesis of 1,4-Diketone by Using a
2,5-Bis(4-fluorophenyl)-3,4-diphenylfuran (3d):[22] Red solid (73%
isolated yield); m.p. 173–174 °C. 1H NMR (400 MHz, CDCl3): δ =
7.47–7.43 (m, 4 H, H-Ar), 7.22 (s, 6 H, H-Ar), 7.12 (s, 4 H, H-Ar),
6.96 (t, J = 8.0 Hz, 4 H, H-Ar) ppm. 13C NMR (100 MHz, CDCl3):
δ = 162.1 (d, JF,C = 246 Hz), 147.0, 132.9, 130.3, 128.6, 127.7 (d,
JF,C = 8.0 Hz), 127.4, 127.1 (d, JF,C = 3.0 Hz), 124.7, 115.5 (d, JF,C
= 21 Hz) ppm. HRMS (ESI): calcd. for C28H18F2ONa [M + Na]+
431.1218; found 431.1214.
Cross-Coupling Reaction:
A solution of 1b (0.5 mmol) and
Cu(OAc)2·H2O (1.0 mmol) in xylene (1.5 mL) was stirred at 140 °C.
A solution of 1e (0.5 mmol) in xylene (1.5 mL) was then slowly
added to the mixture. The progress of the reaction was monitored
by TLC analysis. When the reaction reached completion, the crude
mixture was cooled to room temperature and filtered through a
small pad of silica gel. The filtrate was concentrated in vacuo, and
the residue was purified by chromatography on a silica gel column
to afford product 2r.
2,5-Bis(4-chlorophenyl)-3,4-diphenylfuran (3e):[23] White solid (77%
isolated yield); m.p. 155–156 °C. 1H NMR (400 MHz, CDCl3): δ =
7.44 (d, J = 12.0 Hz, 4 H, H-Ar), 7.27–7.23 (m, 10 H, H-Ar), 7.18–
7.13 (m, 4 H, H-Ar) ppm. 13C NMR (100 MHz, CDCl3): δ = 147.0,
133.2, 132.6, 130.3, 129.2, 128.7, 128.6, 127.5, 127.0, 125.6 ppm.
HRMS (ESI): calcd. for C28H19Cl2O [M + H]+ 441.0807; found
441.0811.
1-(4-Chlorophenyl)-2,3-diphenyl-4-p-tolylbutane-1,4-dione
(2r):
White solid (50% isolated yield; dr 1.2:1). 1H NMR (400 MHz,
CDCl3): δ = 7.93–7.87 (m, 8 H, H-Ar), 7.77 (d, J = 8.0 Hz, 2 H,
H-Ar), 7.31–7.25 (m, 6 H, H-Ar), 7.19–7.16 (m, 2 H, H-Ar), 7.15–
7.11 (m, 6 H, H-Ar), 7.09–7.06 (m, 6 H, H-Ar), 7.00 (s, 6 H, H-
Ar), 5.35 (s, 2 H, CH), 5.33 (s, 2 H, CH), 2.31 (s, 6 H, CH3) ppm.
13C NMR (100 MHz, CDCl3): δ = 198.9, 198.3, 143.8, 139.2, 136.5,
136.1, 134.8, 133.7, 131.4, 130.3, 129.7, 129.2, 129.1, 128.9, 128.8,
2,5-Bis(4-bromophenyl)-3,4-diphenylfuran (3f):[24] White solid (87%
isolated yield); m.p. 190–191 °C. 1H NMR (400 MHz, CDCl3): δ =
7.37 (q, J = 8.0 Hz, 8 H, H-Ar), 7.26 (s, 6 H, H-Ar), 7.13 (d, J =
4.0 Hz, 4 H, H-Ar) ppm. 13C NMR (100 MHz, CDCl3): δ = 147.0,
132.6, 131.6, 130.2, 129.6, 128.6, 127.6, 127.3, 125.8, 121.5 ppm.
HRMS (ESI): calcd. for C28H18Br2ONa [M + Na]+ 550.9617;
found 550.9618.
128.7, 127.4, 127.2, 58.4, 21.6 ppm. IR (KBr): ν = 3029, 2922, 2854,
˜
1665, 1568, 1489, 1453, 1399, 1289, 1256, 1172, 1090, 1007, 847,
810, 737, 699 cm–1. HRMS (ESI): calcd. for C29H24ClO2 [M +
H]+ 439.1459; found 439.1459.
2-(4-Nitrophenyl)-1,4-diphenyl-3-p-tolylbutane-1,4-dione (2s): White
1
solid (66% isolated yield; dr 1.2:1). H NMR (400 MHz, CDCl3):
2,5-Diphenyl-3,4-di-p-tolylfuran (3g):[25] White solid (71% isolated
yield); m.p. 174–175 °C. 1H NMR (400 MHz, CDCl3): δ = 7.44 (d,
J = 8.0 Hz, 4 H, H-Ar), 7.18 (t, J = 8.0 Hz, 4 H, H-Ar), 7.12 (d, J
= 4.0 Hz, 2 H, H-Ar), 6.97 (s, 8 H, H-Ar), 2.24 (s, 6 H, CH3) ppm.
13C NMR (100 MHz, CDCl3): δ = 147.6, 136.7, 131.1, 130.3, 130.2,
129.2, 128.4, 127.2, 125.9, 125.2, 21.4 ppm. HRMS (ESI): calcd.
for C30H24ONa [M + Na]+ 423.1719; found 423.1723.
δ = 8.00–7.95 (d, J = 8.0 Hz, 10 H, H-Ar), 7.50–7.44 (m, 4 H, H-
Ar), 7.42–7.34 (m, 10 H, H-Ar), 7.26–7.20 (m, 4 H, H-Ar), 6.94–
6.91 (m, 8 H, H-Ar), 5.54 (d, J = 8.0 Hz, 2 H, CH), 5.39 (d, J =
8.0 Hz, 2 H, CH), 2.20 (s, 6 H, CH3) ppm. 13C NMR (100 MHz,
CDCl3): δ = 198.7, 198.6, 147.1, 144.3, 137.5, 136.0, 133.5, 133.2,
132.4, 129.8, 129.7, 129.0, 128.9, 128.7, 128.6, 128.5, 128.5, 58.1,
57.8, 21.1, 21.0 ppm. IR (KBr): ν = 3061, 2923, 2855, 1918, 1743,
˜
3,4-Bis(4-methoxyphenyl)-2,5-diphenylfuran (3h):[26] Colorless gum
1680, 1599, 1516, 1455, 1343, 1202, 1106, 997, 583, 807, 759, 691,
569 cm–1. HRMS (ESI): calcd. for C29H23NO4Na [M + Na]+
472.1519; found 472.1522.
1
(62% isolated yield). H NMR (400 MHz, CDCl3): δ = 7.53 (d, J
= 8.0 Hz, 4 H, H-Ar), 7.27 (t, J = 8.0 Hz, 4 H, H-Ar), 7.21 (d, J
= 4.0 Hz, 2 H, H-Ar), 7.07 (d, J = 8.0 Hz, 4 H, H-Ar), 6.80 (d, J
= 8.0 Hz, 4 H, H-Ar), 3.80 (s, 6 H, OCH3) ppm. 13C NMR
(100 MHz, CDCl3): δ = 158.7, 147.5, 131.5, 131.1, 128.4, 127.2,
125.8, 125.4, 124.9, 113.9, 55.2 ppm.
Typical Procedure for the Synthesis of Tetrasubstituted Furans: De-
oxybenzoin (1a, 1.0 mmol), Ag2O (23.2 mg, 0.1 mmol), and
Cu(OAc)2·H2O (39.8 mg, 0.2 mmol) were added to a round-bottom
flask (10 mL), and then xylene (3 mL) and TFA (0.12 mL,
1.6 mmol) were added to the mixture. The flask was evacuated and
backfilled with O2, and the reaction mixture was stirred at 140 °C.
Upon completion of the reaction, the mixture was cooled, and the
solvent was evaporated in vacuo. The residue was purified by
chromatography on a silica gel column to afford product 3a.
3,4-Bis(4-nitrophenyl)-2,5-diphenylfuran (3i):[27] Yellow gum (90%
1
isolated yield). H NMR (400 MHz, [D6]DMSO): δ = 8.40 (d, J =
12.0 Hz, 4 H, H-Ar), 8.20 (d, J = 8.0 Hz, 4 H, H-Ar), 7.99 (d, J =
8.0 Hz, 4 H, H-Ar), 7.82 (t, J = 8.0 Hz, 2 H, H-Ar), 7.64 (t, J =
8.0 Hz, 4 H, H-Ar) ppm. 13C NMR (100 MHz, [D6]DMSO): δ =
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7

Job/Unit: O43274
/KAP1
Date: 17-12-14 14:11:59
Pages: 11
S. Mao, Y.-R. Gao, S.-L. Zhang, D.-D. Guo, Y.-Q. Wang
FULL PAPER
193.2, 192.7, 151.0, 136.7, 135.8, 131.9, 131.3, 130.0, 129.5, 121.2, 31.1, 26.3, 22.6, 14.0 ppm. IR (KBr): ν = 3055, 3033, 2957,
˜
124.4 ppm. HRMS (ESI): calcd. for C28H18N2O5Na [M + Na]+
485.1108; found 485.1110.
2927, 2864, 1947, 1881, 1675, 1607, 1578, 1524, 1493, 1460, 1379,
1346, 1182, 1102, 1072, 1001, 983, 912, 763, 699 cm–1. HRMS
(ESI): calcd. for C24H28ONa [M + Na]+ 355.2032; found 355.2036.
3,4-Bis(4-fluorophenyl)-2,5-diphenylfuran (3j): White solid (76% iso-
lated yield); m.p. 195–196 °C. 1H NMR (400 MHz, CDCl3): δ =
7.49 (d, J = 8.0 Hz, 4 H, H-Ar), 7.30–7.23 (m, 6 H, H-Ar), 7.11 (t,
J = 8.0 Hz, 4 H, H-Ar), 6.96 (t, J = 8.0 Hz, 4 H, H-Ar) ppm. 13C
NMR (100 MHz, CDCl3): δ = 162.2 (d, JF,C = 245 Hz), 148.0,
132.0 (d, JF,C = 8.0 Hz), 130.6, 129.0 (d, JF,C = 3.0 Hz), 128.5,
3,4-Bis(2-bromophenyl)-2,5-dimethylfuran (3q): White solid (70%
isolated yield); m.p. 92–93 °C. 1H NMR (400 MHz, CDCl3): δ =
7.52 (t, J = 9.0 Hz, 3.5 H, H-Ar), 7.20–6.99 (m, 10.8 H, H-Ar),
2.24 (s, 4.5 H, CH3), 2.20 (s, 6 H, CH3) ppm. 13C NMR (100 MHz,
CDCl3): δ = 146.9, 146.8, 134.5, 134.4, 133.0, 132.7, 132.39, 132.35,
128.7, 128.5, 127.0, 126.8, 125.0, 124.9, 121.8, 121.7, 13.0,
127.6, 125.9, 124.0, 115.7 (d, JF,C = 22.0 Hz) ppm. IR (KBr): ν =
˜
3052, 2921, 2852, 1897, 1599, 1560, 1502, 1218, 1155, 841, 761,
686 cm–1. HRMS (ESI): calcd. for C28H18F2ONa [M + Na]+
431.1218; found 431.1238.
12.9 ppm. IR (KBr): ν = 3055, 2921, 2853, 1920, 1613, 1582, 1472,
˜
1429, 1378, 1262, 1208, 1060, 1026, 996, 928, 752 cm–1. HRMS
(ESI): calcd. for C18H14Br2ONa [M + Na]+ 426.9304; found
426.9281.
3,4-Bis(4-chlorophenyl)-2,5-diphenylfuran (3k): White solid (76%
isolated yield); m.p. 181–182 °C. 1H NMR (400 MHz, CDCl3): δ =
7.40 (d, J = 4.0 Hz, 4 H, H-Ar), 7.21–7.15 (m, 10 H, H-Ar), 6.98
(d, J = 8.0 Hz, 4 H, H-Ar) ppm. 13C NMR (100 MHz, CDCl3):
δ = 148.2, 133.4, 131.7, 131.4, 130.4, 128.9, 128.6, 127.8, 126.0,
Typical Procedure for the Synthesis of Tetrasubstituted Furans by
Using a Cross-Coupling Reaction: Compound 1b (0.50 mmol),
Ag2O (23.2 mg, 0.1 mmol), and Cu(OAc)2·H2O (39.8 mg,
0.2 mmol) were added to a round-bottom flask (10 mL). The flask
was then evacuated and backfilled with O2, and the reaction mix-
ture was stirred at 140 °C. A solution of 1e (0.5 mmol) in xylene
(1.5 mL) and TFA (0.12 mL, 1.6 mmol) was slowly added to the
mixture. The progress of the reaction was monitored by TLC analy-
sis. Upon completion, the crude mixture was cooled to room tem-
perature and filtered through a small pad of silica gel. The filtrate
was concentrated in vacuo, and the residue was purified by
chromatography on a silica gel column to afford product 3r.
123.5 ppm. IR (KBr): ν = 3052, 2920, 2851, 1897, 1593, 1484, 1391,
˜
1083, 1011, 944, 831, 759, 691 cm–1. HRMS (ESI): calcd. for
C28H19Cl2O [M + H]+ 441.0807; found 441.0791.
3,4-Bis(4-bromophenyl)-2,5-diphenylfuran (3l):[28] White solid (78%
isolated yield); m.p. 209–210 °C. 1H NMR (400 MHz, CDCl3): δ =
7.46 (s, 4 H, H-Ar), 7.35 (d, J = 4.0 Hz, 4 H, H-Ar), 7.24 (d, J =
8.0 Hz, 6 H, H-Ar), 6.97 (d, J = 4.0 Hz, 4 H, H-Ar) ppm. 13C
NMR (100 MHz, CDCl3): δ = 148.1, 132.0, 131.8, 130.3, 128.5,
127.8, 126.0, 123.4, 121.6 ppm.
2-(4-Chlorophenyl)-3,4-diphenyl-5-p-tolylfuran (3r): White solid
(54% isolated yield); m.p. 150–152 °C. 1H NMR (400 MHz,
CDCl3): δ = 7.40 (dd, J = 12.1, 8.4 Hz, 4 H, H-Ar), 7.28–7.19 (m,
8 H, H-Ar), 7.17–7.11 (m, 4 H, H-Ar), 7.07 (d, J = 8.0 Hz, 2 H,
H-Ar), 2.32 (s, 3 H, CH3) ppm. 13C NMR (100 MHz, CDCl3): δ =
148.3, 146.4, 137.5, 133.1, 133.0, 132.9, 130.4, 130.3, 129.5, 129.2,
128.63, 128.56, 128.4, 128.0, 127.4, 127.2, 127.0, 126.0, 125.5,
3,4-Bis(3-bromophenyl)-2,5-diphenylfuran (3m): White solid (67%
isolated yield); m.p. 132–133 °C. 1H NMR (400 MHz, CDCl3): δ =
7.50 (d, J = 8.0 Hz, 4 H, H-Ar), 7.41 (d, J = 4.0 Hz, 2 H, H-Ar),
7.33–7.26 (m, 8 H, H-Ar), 7.16 (t, J = 8.0 Hz, 2 H, H-Ar), 7.08 (d,
J = 8.0 Hz, 2 H, H-Ar) ppm. 13C NMR (100 MHz, CDCl3): δ =
148.3, 135.0, 133.2, 130.6, 130.3, 130.2, 129.1, 128.6, 127.9, 126.0,
124.6, 21.4 ppm. IR (KBr): ν = 2985, 1740, 1448, 1374, 1242, 1100,
˜
123.3, 122.5 ppm. IR (KBr): ν = 3053, 2922, 2853, 1744, 1674,
˜
1047, 937, 847, 738, 633 cm–1. HRMS (ESI): calcd. for
C29H21ClONa [M + Na]+ 443.1173; found 443.1170.
1546, 1459, 1069, 1024, 756, 690 cm–1. HRMS (ESI): calcd. for
C28H18Br2ONa [M + Na]+ 550.9617; found 550.9618.
3-(4-Nitrophenyl)-2,5-diphenyl-4-p-tolylfuran (3s): White solid (63%
isolated yield); m.p. 183–185 °C. 1H NMR (400 MHz, CDCl3): δ =
8.08 (d, J = 8.0 Hz, 2 H, H-Ar), 7.51 (d, J = 8.0 Hz, 2 H, H-Ar),
7.46 (d, J = 4.0 Hz, 2 H, H-Ar), 7.33–7.21 (m, 8 H, H-Ar), 7.09
(d, J = 8.0 Hz, 2 H, H-Ar), 7.02 (d, J = 8.0 Hz, 2 H, H-Ar), 2.35
(s, 3 H, CH3) ppm. 13C NMR (100 MHz, CDCl3): δ = 148.7, 148.5,
146.9, 140.7, 137.5, 131.3, 130.5, 130.19, 130.16, 129.6, 129.3,
128.7, 128.5, 128.2, 127.7, 126.4, 125.9, 124.3, 123.7, 123.0,
3,4-Bis(2-bromophenyl)-2,5-diphenylfuran (3n): White solid (62%
isolated yield); m.p. 136–137 °C. 1H NMR (400 MHz, CDCl3): δ =
7.54 (t, J = 4.0 Hz, 2 H, H-Ar), 7.46 (d, J = 8.0 Hz, 4 H, H-Ar),
7.39 (d, J = 8.0 Hz, 2 H, H-Ar), 7.26 (t, J = 8.0 Hz, 4 H, H-Ar),
7.20 (t, J = 8.0 Hz, 4 H, H-Ar), 7.10 (t, J = 4.0 Hz, 2 H, H-
Ar) ppm. 13C NMR (100 MHz, CDCl3): δ = 147.6, 134.4, 134.0,
133.3, 132.7, 132.4, 130.9, 130.7, 129.5, 129.3, 128.6, 128.5, 127.6,
127.5, 127.1, 125.4, 125.3, 125.2, 124.8, 124.2 ppm. IR (KBr): ν =
˜
3054, 2922, 2853, 1950, 1595, 1490, 1431, 1024, 755, 680 cm–1.
HRMS (ESI): calcd. for C28H18Br2ONa [M + Na]+ 550.9617;
found 550.9609.
21.4 ppm. IR (KBr): ν = 2923, 2855, 1727, 1599, 1517, 1453, 1343,
˜
1265, 1109, 1027, 948, 856, 820, 765, 693 cm–1. HRMS (ESI): calcd.
for C29H21NO3Na [M + Na]+ 454.1414; found 454.1409.
2,5-Bis(4-iodophenyl)-3,4-diphenylfuran (3t):[29] White solid (78%
isolated yield); m.p. 206–207 °C. 1H NMR (400 MHz, CDCl3): δ =
7.50 (d, J = 8.0 Hz, 4 H, H-Ar), 7.16 (d, J = 4.0 Hz, 6 H, H-Ar),
7.13 (d, J = 8.0 Hz, 4 H, H-Ar), 7.04 (d, J = 4.0 Hz, 4 H, H-
Ar) ppm. 13C NMR (100 MHz, CDCl3): δ = 147.1, 137.6, 132.6,
130.2, 130.1, 128.6, 127.6, 127.5, 126.0, 93.1 ppm.
3,4-Di(biphenyl-4-yl)-2,5-diphenylfuran (3o): White solid (81% iso-
lated yield); m.p. 246–247 °C. 1H NMR (400 MHz, CDCl3): δ =
7.56–7.48 (m, 8 H, H-Ar), 7.44 (d, J = 8.0 Hz, 4 H, H-Ar), 7.34 (t,
J = 8.0 Hz, 4 H, H-Ar), 7.28–7.11 (m, 12 H, H-Ar) ppm. 13C NMR
(100 MHz, CDCl3): δ = 148.0, 140.6, 139.7, 132.2, 130.91, 130.86,
128.8, 128.5, 127.5, 127.4, 127.1, 127.0, 126.1, 124.6 ppm. IR
(KBr): ν = 3028, 2922, 2853, 1885, 1592, 1481, 1439, 1393, 1109,
˜
The Control Experiment for the Reaction Mechanism: A mixture of
deoxybenzoin (1a, 1.0 mmol), Cu(OAc)2 (1.0 mmol), and 2,2,6,6-
tetramethylpiperidine-1-oxyl (1.0 mmol) in xylene (3 mL) was
761, 685 cm–1. HRMS (ESI): calcd. for C40H28ONa [M + Na]+
547.2032; found 547.2030.
2,5-Dibutyl-3,4-diphenylfuran (3p): Colorless gum (77% isolated stirred at 140 °C for 0.5 h. The mixture was cooled to room tem-
yield). 1H NMR (400 MHz, CDCl3): δ = 7.27–7.15 (m, 6 H, H- perature and filtered through a small pad of silica gel. The filtrate
Ar), 7.06 (s, 4 H, H-Ar), 2.66 (s, 4 H, CH2), 1.67 (s, 4 H, CH2), was concentrated in vacuo, and the crude residue was purified by
1.36 (d, J = 8.0 Hz, 4 H, CH2), 0.96–0.84 (m, 6 H, CH3) ppm. 13C chromatography on a silica gel column to afford the corresponding
NMR (100 MHz, CDCl3): δ = 150.6, 133.9, 129.8, 128.0, 126.1,
product 4a.
8
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Job/Unit: O43274
/KAP1
Date: 17-12-14 14:11:59
Pages: 11
Cu(II)-Promoted Coupling of Two C(sp3)–H bonds
Baran, J. Am. Chem. Soc. 2008, 130, 11546–11560; b) E. J. Yoo,
1,2-Diphenyl-2-(2,2,6,6-tetramethylpiperidin-1-yloxy)ethanone
(4a):[30] White solid (40% isolated yield); m.p. 170–171 °C. 1H
NMR (400 MHz, CDCl3): δ = 8.11 (d, J = 4.0 Hz, 2 H, H-Ar),
7.53 (d, J = 4.0 Hz, 2 H, H-Ar), 7.48 (d, J = 8.0 Hz, 1 H, H-Ar),
7.41 (t, J = 8.0 Hz, 2 H, H-Ar), 7.30 (t, J = 8.0 Hz, 2 H, H-Ar),
7.21 (t, J = 8.0 Hz, 1 H, H-Ar), 6.03 (s, 1 H, CH), 1.47 (s, 4 H,
CH2), 1.31 (d, J = 16.0 Hz, 2 H, CH2), 1.21 (s, 6 H, CH3), 1.02 (s,
3 H, CH3), 0.84 (s, 3 H, CH3) ppm. 13C NMR (100 MHz, CDCl3):
δ = 198.3, 137.8, 135.2, 132.9, 129.3, 128.4, 127.5, 127.2, 93.2, 60.0,
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59.8, 40.2, 33.6, 33.3, 20.3, 20.2, 17.0 ppm. IR (KBr): ν = 3088,
˜
3068, 2973, 2947, 2925, 2846, 1669, 1596, 1579, 1492, 1448, 1377,
1359, 1264, 1225, 1178, 1132, 1084, 1044, 1025, 765, 737, 697,
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374.2091; found 374.2102.
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Acknowledgments
The authors are grateful for financial support from the National
Natural Science Foundation of China (NSFC) (grant numbers
NSFC-20972126 and 21272185).
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Eur. J. Org. Chem. 0000, 0–0
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Date: 17-12-14 14:11:59
Pages: 11
S. Mao, Y.-R. Gao, S.-L. Zhang, D.-D. Guo, Y.-Q. Wang
FULL PAPER
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Published Online: ᭿
10
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Job/Unit: O43274
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Date: 17-12-14 14:11:59
Pages: 11
Cu(II)-Promoted Coupling of Two C(sp3)–H bonds
C–C Bond Formation
S. Mao, Y.-R. Gao, S.-L. Zhang,
D.-D. Guo, Y.-Q. Wang* ................. 1–11
Copper(II)-Promoted C–C Bond Forma-
tion by Oxidative Coupling of Two C(sp3)–
H Bonds Adjacent to Carbonyl Group to
Construct 1,4-Diketones and Tetrasubsti-
tuted Furans
Coupling of two C–H bonds adjacent to a
carbonyl group: The copper(II)-promoted
coupling of two C(sp3)–H bonds that are
adjacent to a carbonyl group was carried
out for the preparation of 2,3-disubstituted
1,4-diketones and tetrasubstituted furans.
This economic approach features a wide
Keywords: Synthetic methods / C–C cou-
pling / Oxidation / Copper / Oxygen hetero-
cycles
substrate scope and
group tolerance.
a high functional
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11