Synthesis of 1,2-Diketones via a Metal-Free, Visible-Light-Induced Aerobic Photooxidation of Alkynes

Article abstract of DOI:10.1021/acs.joc.6b00097

1,2-Diketones were synthesized by the oxidation of corresponding alkynes using air as the oxidant under metal-free conditions upon irradiation of blue light. A cheap and readily available organic dye, eosin Y, was used as the photocatalyst. For various substituents on the aryl ring, the reaction proceeded smoothly to give the dicarbonylation products in moderate to good yields. Some oxidation-sensitive groups, such as formyl and the carbon-carbon double bond, were tolerated under the developed reaction conditions.

Full text of DOI:10.1021/acs.joc.6b00097

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Note
Synthesis of 1,2-Diketones via A Metal-free, Visible-
light Induced Aerobic Photooxidation of Alkynes
Xu Liu, Tiantian Cong, Ping Liu, and Peipei Sun
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b00097 • Publication Date (Web): 08 Apr 2016
Downloaded from http://pubs.acs.org on April 13, 2016
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Synthesis of 1,2-Diketones via A Metal-free, Visible-light Induced
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Aerobic Photooxidation of Alkynes
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Xu Liu, Tiantian Cong, Ping Liu and Peipei Sun*
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College of Chemistry and Materials Science, Jiangsu Provincial Key Laboratory of Material Cycle
Processes and Pollution Control, Jiangsu Collaborative Innovation Center of Biomedical
Functional Materials, Nanjing Normal University, Nanjing 210023, China
sunpeipei@njnu.edu.cn
ABSTRACT: 1,2ꢀDiketones were synthesized by the oxidation of corresponding alkynes using air
as the oxidant under metalꢀfree conditions upon irradiation of blue light. A cheap and readily
available organic dye, eosin Y, was used as the photocatalyst. For various substituents on the aryl
ring, the reaction proceeded smoothly to give the dicarbonylation products in moderate to good
yields. Some oxidation sensitive groups such as formyl and carbonꢀcarbon double bond tolerated
under the developed reaction conditions.
1,2ꢀDiketones are very important precursors in organic synthesis. The construction of azacyclic
compounds from 1,2ꢀdiketones are wellꢀknown.1 These compounds also play an important role in
pharmaceutical chemistry. For example, they were used as the basic materials to synthesize
anticonvulsant and antimicrobial drugs.2 The oxidation of various compounds such as olefins,
methylene ketones, and alkynes are generally employed for the preparation of 1,2ꢀdiketones,3 in
which the oxidations of alkynes are considered to be one of the most straightforward and practical
strategies. Alkynes can be oxidized by ordinary oxidants such as potassium permanganate to the
corresponding 1,2ꢀdiketones, but the tolerance to the functional groups is very limited. Mn(III) or
Cu mediated oxidative decarboxylative coupling of arylboronic acids or aryl iodides with
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arylpropiolic
acids provided
new protocols for
the preparation of these
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compounds.4 Other than that, many efforts focused on the transitionꢀmetal catalyzed direct
oxidation of alkynes to 1,2ꢀdiketones in recent years. Pd,5 Ru,6 Au7, Cu,8 etc were employed as the
catalysts, and DMSO, Oxone, K2S2O8 and Ph2SO behaved as the oxidants in these transformations.
Alkynes could also be oxidized to αꢀketoesters, esters or amides by hypervalent iodines in the
presence of alcohol or amine.9 It is obvious that to construct chemical bonds under
transitionꢀmetalꢀfree conditions to fulfill the classic transitionꢀmetalꢀcatalyzed reactions is highly
desired, especially in pharmaceuticals industry. Thus, developing more efficient and high selective
oxidation pathways is still a challenging task.
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Visible light photoredox catalysis for the activation of organic molecules has received much
attention in recent years.10 Several electronꢀrich functional groups have enabled the oxidation via
the singleꢀelectron oxidation pathways with visible light in the presence of photocatalysts. For
example, alcohols,11 αꢀhaloesters,12 arylboronic acids13 and thiobenzanilides14 can be oxidized to
corresponding aldehydes, αꢀketoesters, phenols and benzothiazoles respectively upon irradiation
of visible light in the presence of photocatalysts. Recently, a nitrate radical NO3̇ was found to
oxidize diphenylacetylene to generate dibenzoyl under visible light photooxidation conditions.15
What is more, organic dyes have been introduced as photocatalysts in many visible light
photoredox catalysis, and drawn greater attention.16 In this work, we wish to report an efficient
method for the synthesis of 1,2ꢀdiketones via visible light photooxidation of alkynes, in which O2
was employed as the oxidant, and eosin Y as the photoꢀcatalyst.
In our initial study, we selected diphenylethyne (1a) as a model substrate for the optimization
of reaction conditions (Table 1). To our delight, using eosin Y as the photocatalyst upon irradiation
of blue light, and in the presence of 4ꢀchlorobenzenethiol, an oxidation product
1,2ꢀdiphenylethaneꢀ1,2ꢀdione was obtained in 55% yield at room temperature in THF after 8 h
(entry 1). However, if the reaction was carried out in dark environment, only trace product was
found (entry 2). In the absence of 4ꢀchlorobenzenethiol, photocatalyst or air (O2), no product was
generated (entries 3ꢀ5). Then, a screen of different solvents such as MeCN, DCE, DMF, toluene
and DMSO were tested and MeCN was proved to be the best, and a good yield of 83% was
obtained (entries 6–10). Other photocatalysts were then examined. With the transitionꢀmetal
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complexes such as Ru(bpy)3Cl2·6H2O and Ir(ppy)3, the moderate yields were given (entries 11 and
12). Other organic dyes (rose bengal, fluorescein and rhodamine B) did not show better effect than
that of eosin Y (entries 13–15). The presence of 2 equiv 4ꢀchlorobenzenethiol was essential. The
decrease of the amount of 4ꢀchlorobenzenethiol to 1 equiv resulted in the lower yields (entry 16).
When 4ꢀmethoxybenzenethiol was used to replace 4ꢀchlorobenzenethiol, a lower yield of 74%
was obtained (entry 17). Compared with that in air, when the reaction took place in O2, the yield
was not considerably enhanced (entry 18). The appropriate amount of the photocatalyst was 2
mol %. Increasing it to 4 mol % did not bring the obvious change of the yield, but reducing the
dosage of the photocatalyst to 1 mol % led to a lower yield of 72% (entries 19 and 20). Upon
irradiation of green light instead of blue light, the yield was slightly decreased (entry 21).
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Table 1. Optimization of Reaction Conditionsa
entry
1
photocatalyst (mol %)
eosin Y (2)
solvent
THF
yield (%)
55
2b
3c
eosin Y (2)
THF
trace
0
eosin Y (2)
THF
4
ꢀ
THF
0
5d
eosin Y (2)
THF
0
6
eosin Y (2)
MeCN
DCE
83
7
eosin Y (2)
26
8
eosin Y (2)
DMF
19
9
eosin Y (2)
toluene
DMSO
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
31
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12
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15
16e
17f
eosin Y (2)
13
Ru(bpy)3Cl2·6H2O (2)
Ir(ppy)3 (2)
53
61
rose bengal (2)
fluorescein (2)
rhodamine B (2)
eosin Y (2)
37
65
69
70
eosin Y (2)
74
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18g
19
eosin Y (2)
eosin Y (4)
eosin Y (1)
eosin Y (2)
MeCN
MeCN
MeCN
MeCN
84
82
72
75
20
21h
aReaction conditions (unless otherwise specified): 1a (0.2 mmol), 4ꢀchlorobenzenethiol (0.4
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mmol), photocatalyst, solvent (2 mL), irradiation under air atmosphere at room temperature
b
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d
using 5 W blue LED for 8 h. In the dark. Without 4ꢀchlorobenzenethiol. In Ar atmosphere.
e4ꢀChlorobenzenethiol (0.2 mmol). f4ꢀMethoxybenzenethiol was used instead of
h
4ꢀchlorobenzenethiol. gUnder O2 atmosphere (1 atm). Using 5 W green LED as the light
source.
Having established the optimized reaction conditions, we then explored the generality and
scope of the reaction across a series of alkynes (Table 2). As that can been seen from Table 2,
different 1,2ꢀdisubstituted alkynes were oxidized to the corresponding diketones in moderate to
good yields. It was showed that the diarylethynes containing electronꢀdonating substitutes, such as
methyl, tertꢀbutyl, methoxyl had a high reactivity and afforded the corresponding diaryldiketones
in good yields (2a–2f, 2s–2v), but the presence of electronꢀwithdrawing groups, such as halogens,
nitro, cyano, trifluoromethyl, ester and carbonyl led to moderate yields, which might be because
that the electronꢀdeficiency of the triple bonds reduced their reactivity (2g–2r). It was nice to
see that the easily oxidized formyl group could be preserved in this oxidation process (2r), this
result revealed that the reaction had very good selectivity. Moreover, for naphthyl and thienyl
substituted ethynes, the corresponding 1,2ꢀdiketones were also afforded in 72% and 70% yield
respectively (2w and 2x). In addition, from the reaction of 1,4ꢀdiphenylbutaꢀ1,3ꢀdiyne, only a
monoalkynyl oxidized product was obtained (2y). And for 1,4ꢀdiphenylbutꢀ1ꢀenꢀ3ꢀyne, the
carbonꢀcarbon double bond was preserved (2z). The reaction was suitable for various diaryl
alkynes or other large conjugated alkynes. For the substrate phenylacetylene or 1ꢀphenylꢀ1ꢀhexyne,
however, the complex mixture was obtained. Although the exact reason was not clear, it should be
related to the stability of the intermediates.
Table 2. Visible-Light-Induced Synthesis of 1,2-Dikeonesa
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2d, 81%
2h, 69%
2a, 83%
2b, 84%
2c, 82%
2g, 66%
2f, 85%
2j, 65%
2n, 67%
2e, 85%
2i, 63%
2k, 70%
2o, 74%
2l, 65%
2m, 63%
2q, 55%
2p, 71%
2t, 82%
2x, 70%
2s, 89%
2r, 77%
2v, 81%
2w, 72%
2u, 86%
2y, 77%
2z, 68%
aReaction conditions: 1 (0.2 mmol), 4ꢀchlorobenzenethiol (0.4 mmol), eosin Y (2 mol %), MeCN
(2 mL), irradiation under air atmosphere at room temperature using 5 W blue LED for 8 h. All
yields are isolated ones.
In order to study the possible mechanism of the transformation, a radical scavenger TEMPO
(2,2,6,6ꢀtetramethylꢀ1ꢀpiperidinyloxy) was added under the standard reaction conditions. No
desired product was found from the reaction mixture in the presence of 2 equiv TEMPO,
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meanwhile, an adduct of 4ꢀchlorophenylthio radical with TEMPO was detected by LCꢀMS
(Scheme 1), which indicated that the transformation might undergo through a radical pathway. By
using DMPO (5,5ꢀdimethylꢀ1ꢀpyrrolineꢀNꢀoxide) as the radical trapping agent, a characteristic
signal of a superoxide radical anion (O2ꢁ˙) was clearly observed by EPR spectra (see Supporting
Information).17 This radical anion was obviously generated from the molecular oxygen by a
singleꢀelectron transfer (SET) under the current reaction conditions.18
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Scheme 1. Control Experiment
It was found by Wille et al that a thiylperoxyl radical could be generated by a reversible
oxidation of thiophenyl radical with O2.19 Inspired by this report, and based on our observations as
well as other related works,16ꢀ18 a plausible reaction mechanism is described in Scheme 2. Initially,
eosin Y was converted to excited state eosin Y* upon irradiation of visible light, and this eosin Y*
underwent reductive quenching by thiophenol to afford the radical cation A and form an eosin Y
radical anion. The eosin Y radical anion was oxidized to the ground state by aerobic oxygen to
complete the photoredox cycle and a superoxide radical anion (O2ꢁ˙) was generated
simultaneously.18 The resulting radical cation A was deprotonated by O2ꢁ˙ to give the thiophenyl
radical B. Subsequently, a thiylperoxyl radical C was formed through the reversible trapping of B
with O2. The addition of radical C to 1,2ꢀdiphenylethyne (1a) generated an vinyl radical D. The
rearrangement of D via the homolytic O−O bond cleavage and the radical transfer formed radical
intermediate E. The desired product 1,2ꢀdiphenylethaneꢀ1,2ꢀdione 2a was finally produced by the
elimination of thiophenyl radical B from E. In addition, a byproduct di(4ꢀchlorophenyl) disulfide
F which came from the homocoupling of radical B was also separated from the reaction mixture.
Scheme 2. Plausible Reaction Mechanism
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In summary, we have discovered a convenient pathway for the oxidation of diarylalkynes into
corresponding 1,2ꢀdiketones using air as the oxidant under metalꢀfree conditions upon irradiation
of visible light. A cheap and readily available organic dye, eosin Y, was used as the photocatalyst.
The reaction has a very good selectivity, various substituents on the aryl ring, including some
oxidation sensitive groups such as formyl and carbonꢀcarbon double bond tolerated under the
developed reaction conditions and the dicarbonylation products were obtained in moderate to good
yields.
Experimental Section
General.
All reactions were run in ovenꢀdried flasks under air. Chemicals were commercially available
and were used without purification. Diarylethynes and other alkynes were prepared according to
the literature procedures.20 NMR spectra were recorded at 400 MHz (1H), 100 MHz (13C) in
CDCl3 using TMS as an internal standard. The following abbreviations were used to explain the
multiplicities: s = singlet, d = doublet, dd = doublet of doublet, t = triplet, dt = doublet of triplet, td
= triplet of doublet, q = quartet, m = multiplet, ddd = doublet of doublet of doublet. Melting points
are uncorrected. QꢀTOF was used for the HRMS measurement.
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General Experimental Procedure for the Synthesis of 1,2-Diphenylethane-1,2-dione (2a).
1,2ꢀDiphenylethyne (1a) (0.2 mmol, 35.6 mg), 4ꢀchlorobenzenethiol (0.4 mmol, 57.4 mg), and
eosin Y (2 mol %, 2.8 mg) were added in MeCN (2 mL). The mixture was stirred under blue LED
irradiation for 8 h under ambient air. After completion of the reaction, the reaction mixture was
extracted with DCM (15 mL × 3). The combined organic phases were washed with brine (15 mL),
dried over anhydrous Na2SO4, filtered and concentrated in vacuo. The residue was purified by
silica gel chromatography using petroleum ether/ethyl acetate (20:1) to afford the pure product 2a.
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1,2ꢀDiphenylethaneꢀ1,2ꢀdione (2a).4b Yellow solid (34.9 mg, 83% yield); mp 94−95 °C; 1H NMR
(CDCl3, 400 MHz): δ (ppm) 8.00 (d, J = 7.1 Hz, 4H), 7.67 (t, J = 7.4 Hz, 2H), 7.53 (t, J = 7.7 Hz,
4H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 194.6, 134.9, 133.0, 129.9, 129.1.
1ꢀPhenylꢀ2ꢀ(pꢀtolyl)ethaneꢀ1,2ꢀdione (2b).4b Yellow solid (37.6 mg, 84% yield); mp 93−94 °C; 1H
NMR (CDCl3, 400 MHz): δ (ppm) 7.99 (dt, J = 8.5, 1.5 Hz, 2H), 7.89 (d, J = 8.3 Hz, 2H), 7.67 (t,
J = 7.4 Hz, 1H), 7.53 (t, J = 7.8 Hz, 2H), 7.33 (d, J = 8.0 Hz, 2H), 2.46 (s, 3H); 13C NMR (CDCl3,
100 MHz): δ (ppm) 194.8, 194.3, 146.2, 134.8, 133.1, 130.6, 130.0, 129.9, 129.8, 129.0, 21.9.
1ꢀPhenylꢀ2ꢀ(mꢀtolyl)ethaneꢀ1,2ꢀdione (2c).4b Yellow solid (36.7 mg, 82% yield); mp 56−57 °C; 1H
NMR (CDCl3, 400 MHz): δ (ppm) 7.99 (d, J = 7.1 Hz, 2H), 7.80 (dt, J = 9.7, 4.8 Hz, 2H), 7.68 (t,
J = 7.4 Hz, 1H), 7.57–7.47 (m, 3H), 7.42 (t, J = 7.5 Hz, 1H), 2.43 (s, 3H); 13C NMR (CDCl3, 100
MHz): δ (ppm) 194.9, 194.7, 139.0, 135.8, 134.9, 133.1, 133.0, 130.2, 129.9, 129.0, 128.9, 127.2,
21.3.
1ꢀPhenylꢀ2ꢀ(oꢀtolyl)ethaneꢀ1,2ꢀdione (2d).4b Yellow solid (36.3 mg, 81% yield); mp 55−56 °C; 1H
NMR (CDCl3, 400 MHz): δ (ppm) 8.00 (d, J = 7.1 Hz, 2H), 7.71–7.64 (m, 2H), 7.57–7.50 (m, 3H),
7.37 (d, J = 7.6 Hz, 1H), 7.29 (t, J = 7.6 Hz, 1H), 2.73 (s, 3H); 13C NMR (CDCl3, 100 MHz): δ
(ppm) 196.8, 194.9, 141.4, 134.7, 133.8, 133.1, 133.1, 132.6, 131.8, 130.0, 129.0, 126.1, 21.9.
1
1ꢀ(4ꢀ(Tertꢀbutyl)phenyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2e).4b Yellow oil (45.3 mg, 85% yield); H
NMR (CDCl3, 400 MHz): δ (ppm) 8.00 (d, J = 7.1 Hz, 2H), 7.93 (d, J = 8.6 Hz, 2H), 7.67 (t, J =
7.4 Hz, 1H), 7.59–7.48 (m, 4H), 1.36 (s, 9H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 194.8, 194.3,
159.1, 134.8, 133.1, 130.5, 129.9, 129.0, 126.1, 35.4, 31.0.
1ꢀ(4ꢀMethoxyphenyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2f).4b Yellow oil (40.8 mg, 85% yield); 1H NMR
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(CDCl3, 400 MHz): δ (ppm) 7.98 (t, J = 8.6 Hz, 4H), 7 .66 (t, J = 7.4 Hz, 1H), 7.52 (t, J = 7.8 Hz,
2H), 7.00 (d, J = 9.0 Hz, 2H), 3.90(s, 3H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 194.9, 193.2,
165.0, 134.7, 133.2, 132.4, 129.9, 129.0, 126.1, 114.4, 55.7.
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1ꢀ(4ꢀFluorophenyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2g).8 Yellow solid (30.1 mg, 66% yield); mp
69−70 °C; 1H NMR (CDCl3, 400 MHz): δ (ppm) 8.06–8.02 (m, 2H), 8.00 (dt, J = 8.5, 1.5 Hz, 2H),
7.69 (t, J = 7.5 Hz, 1H), 7.54 (t, J = 7.7 Hz, 2H), 7.24–7.17 (m, 2H); 13C NMR (CDCl3, 100 MHz):
δ (ppm) 194.1, 192.7, 166.8 (d, J = 256.7 Hz), 135.0, 132.9, 132.8 (d, J = 9.8 Hz), 130.0, 129.5,
129.1, 116.4 (d, J = 22.1 Hz).
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1ꢀ(4ꢀChlorophenyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2h).4b Yellow solid (33.8 mg, 69% yield); mp
1
72−73 °C; H NMR (CDCl3, 400 MHz): δ (ppm) 8.00–7.93 (m, 4H), 7.71–7.67 (m, 1H), 7.56–
7.50 (m, 4H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 193.9, 193.1, 141.6, 135.1, 132.8, 131.4,
131.2, 130.0, 129.5, 129.1.
1
1ꢀ(3ꢀChlorophenyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2i).6b Yellow oil (30.8 mg, 63% yield); H NMR
(CDCl3, 400 MHz): δ (ppm) 8.02–7.96 (m, 3H), 7.87–7.85 (m, 1H), 7.72–7.67 (m, 1H), 7.66–7.63
(m, 1H), 7.54 (tt, J = 7.6, 1.4 Hz, 2H), 7.50–7.44 (m, 1H); 13C NMR (CDCl3, 100 MHz): δ (ppm)
193.6, 193.0, 135.4, 135.2, 134.8, 134.5, 132.7, 130.4, 130.0, 129.6, 129.1, 128.1.
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1ꢀ(2ꢀChlorophenyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2j).6b Yellow oil (31.8 mg, 65% yield); H NMR
(CDCl3, 400 MHz): δ (ppm) 8.05 (dd, J = 8.3, 1.1 Hz, 2H), 7.92 (dd, J = 8.1, 1.6 Hz, 1H), 7.71 –
7.64 (m, 1H), 7.58–7.53 (m, 3H), 7.45 (t, J = 7.5 Hz, 2H); 13C NMR (CDCl3, 100 MHz): δ (ppm)
193.7, 192.1, 134.6, 134.6, 134.0, 133.9, 132.5, 132.1, 130.5, 130.2, 128.9, 127.4.
1ꢀ(4ꢀBromophenyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2k).6b Yellow solid (40.5 mg, 70% yield); mp
86−87 °C; 1H NMR (CDCl3, 400 MHz): δ (ppm) 8.00ꢀ7.97 (m, 2H), 7.88ꢀ7.85 (m, 2H), 7.72ꢀ7.67
(m, 3H), 7.56ꢀ7.52 (m, 2H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 193.9, 193.3, 135.1, 132.8,
132.5, 131.8, 131.3, 130.5, 130.0, 129.1.
1ꢀ(4ꢀNitrophenyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2l).4b Yellow solid (33.2 mg, 65% yield); mp
137−138 °C; 1H NMR (CDCl3, 400 MHz): δ (ppm) 8.38 (d, J = 9.0 Hz, 2H), 8.19 (d, J = 9.0 Hz,
2H), 8.01 (dd, J = 8.4, 1.3 Hz, 2H), 7.73 (t, J = 7.5 Hz, 1H), 7.57 (t, J = 7.8 Hz, 2H); 13C NMR
(CDCl3, 100 MHz): δ (ppm) 192.9, 192.1, 151.2, 137.3, 135.5, 132.4, 131.0, 130.1, 129.2, 124.1.
4ꢀ(2ꢀOxoꢀ2ꢀphenylacetyl)benzonitrile (2m).4b Yellow solid (29.6 mg, 63% yield); mp 98−99 °C;
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1H NMR (CDCl3, 400 MHz): δ (ppm) 8.11 (d, J = 8.5 Hz, 2H), 8.00 (d, J = 7.1 Hz, 2H), 7.84 (d, J
= 8.5 Hz, 2H), 7.72 (t, J = 7.5 Hz, 1H), 7.56 (t, J = 7.8 Hz, 2H); 13C NMR (CDCl3, 100 MHz): δ
(ppm) 193.0, 192.4, 135.9, 135.4, 132.8, 132.5, 130.2, 130.0, 129.2, 117.9, 117.6.
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1ꢀPhenylꢀ2ꢀ(4ꢀ(trifluoromethyl)phenyl)ethaneꢀ1,2ꢀdione (2n).6b Yellow solid (37.3 mg, 67% yield);
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mp 44−45 °C; H NMR (CDCl3, 400 MHz): δ (ppm) 8.13 (d, J = 8.1 Hz, 2H), 8.00 (dd, J = 8.4,
1.3 Hz, 2H), 7.80 (d, J = 8.2 Hz, 2H), 7.71 (t, J = 7.5 Hz, 1H), 7.59–7.52 (m, 2H); 13C NMR
(CDCl3, 100 MHz): δ (ppm) 193.5, 193.0, 135.9 (q, J = 32.7 Hz), 135.6, 135.3, 132.6, 130.2,
130.0, 129.2, 126.1 (q, J = 3.7 Hz), 123.3 (q, J = 271.3 Hz).
1ꢀ(4ꢀAcetylphenyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2o) 4a
70 72 °C
1H NMR (CDCl3, 400 MHz): δ (ppm) 8.06 (s, 4H), 7.97 (d, J = 7.1 Hz, 2H), 7.68 (t, J
. Yellow solid (37.3 mg, 74% yield); mp
−
;
= 7.5 Hz, 1H), 7.53 (t, J = 7.8 Hz, 2H), 2.65 (s, 3H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 197.2,
193.8, 193.6, 141.3, 136.0, 135.2, 132.7, 130.1, 130.0, 129.1, 128.7, 27.0.
Ethyl 4ꢀ(2ꢀoxoꢀ2ꢀphenylacetyl)benzoate (2p).21 Yellow solid (40.1 mg, 71% yield); mp 75−76 °C;
1H NMR (CDCl3, 400 MHz): δ (ppm) 8.18 (d, J = 8.7 Hz, 2H), 8.05 (d, J = 8.7 Hz, 2H), 7.99 (dd,
J = 8.4, 1.3 Hz, 2H), 7.69 (t, J = 7.5 Hz, 1H), 7.54 (t, J = 7.7 Hz, 2H), 4.43 (q, J = 7.1 Hz, 2H),
1.42 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 193.8, 193.7, 165.4, 136.0, 135.7,
135.1, 132.7, 130.1, 130.0, 129.8, 129.1, 61.7, 14.3.
4ꢀ(2ꢀ(4ꢀMethoxyphenyl)ꢀ2ꢀoxoacetyl)benzonitrile (2q).6b Yellow oil (29.2 mg, 55% yield); H
1
NMR (CDCl3, 400 MHz): δ (ppm) 8.11 (d, J = 8.6 Hz, 2H), 7.98 (d, J = 9.0 Hz, 2H), 7.83 (d, J =
8.6 Hz, 2H), 7.02 (d, J = 9.0 Hz, 2H), 3.93 (s, 3H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 192.7,
191.5, 165.4, 136.2, 132.7, 132.6, 130.2, 125.5, 117.7, 117.7, 114.6, 55.7.
4ꢀ(2ꢀOxoꢀ2ꢀphenylacetyl)benzaldehyde (2r).4b Yellow solid (36.7 mg, 77% yield); mp 186−187 °C;
1H NMR (CDCl3, 400 MHz): δ (ppm) 10.15 (s, 1H), 8.16 (d, J = 8.3 Hz, 2H), 8.05–7.99 (m, 4H),
7.74–7.66 (m, 1H), 7.56 (t, J = 7.8 Hz, 2H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 193.6, 193.5,
191.3, 140.0, 137.0, 135.3, 132.6, 130.4, 130.0, 130.0, 129.2.
1,2ꢀBis(4ꢀmethoxyphenyl)ethaneꢀ1,2ꢀdione (2s).8 Yellow solid (48.1 mg, 89% yield); mp
1
99−101 °C; H NMR (CDCl3, 400 MHz): δ (ppm) 7.96 (d, J = 8.9 Hz, 4H), 6.99 (d, J = 8.9 Hz,
4H), 3.90 (s, 6H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 193.5, 164.9, 132.4, 126.3, 114.3, 55.6.
1ꢀ(4ꢀMethoxyphenyl)ꢀ2ꢀ(pꢀtolyl)ethaneꢀ1,2ꢀdione (2t).8 Yellow solid (41.7 mg, 82% yield); mp
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98−99 °C; 1H NMR (CDCl3, 400 MHz): δ (ppm) 7.96 (d, J = 8.9 Hz, 2H), 7.88 (d, J = 8.2 Hz, 2H),
7.31 (d, J = 8.0 Hz, 2H), 6.98 (d, J = 9.0 Hz, 2H), 3.90 (s, 3H), 2.45 (s, 3H); 13C NMR (CDCl3,
100 MHz): δ (ppm) 194.6, 193.4, 164.9, 146.0, 132.4, 130.8, 130.0, 129.7, 126.2, 114.3, 55.6,
21.9.
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1ꢀ(3,5ꢀDimethylphenyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2u). Yellow oil (41.0 mg, 86% yield); 1H NMR
(CDCl3, 400 MHz): δ (ppm) 7.99 (dd, J = 8.3, 1.2 Hz, 2H), 7.71−7.63 (m, 1H), 7.60 (s, 2H), 7.53
(t, J = 7.8 Hz, 2H), 7.31 (s, 1H), 2.38 (s, 6H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 195.1, 194.9,
138.9, 136.7, 134.8, 133.1, 133.1, 129.9, 129.0, 127.6, 21.1; HRMSꢀESI (m/z): calcd for
C16H14O2Na [M + Na]+ 261.0886, found 261.0882.
1
1ꢀ(3,4ꢀDimethylphenyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2v).22 Yellow oil (38.6 mg, 81% yield); H
NMR (CDCl3, 400 MHz): δ (ppm) 7.99 (dd, J = 8.4, 1.3 Hz, 2H), 7.77 (s, 1H), 7.72 (d, J = 7.8 Hz,
1H), 7.67 (t, J = 7.4 Hz, 1H), 7.52 (t, J = 7.8 Hz, 2H), 7.28 (d, J = 7.8 Hz, 1H), 2.36 (s, 3H), 2.33
(s, 3H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 194.9, 194.7, 145.1, 137.6, 134.8, 133.2, 131.0,
130.8, 130.3, 129.9, 129.0, 127.8, 20.3, 19.7.
1ꢀ(Naphthalenꢀ1ꢀyl)ꢀ2ꢀphenylethaneꢀ1,2ꢀdione (2w).4b Yellow solid (37.5 mg, 72% yield); mp
101−102 °C; 1H NMR (CDCl3, 400 MHz): δ (ppm) 9.33 (dd, J = 8.6, 0.8 Hz, 1H), 8.15 (d, J = 8.2
Hz, 1H), 8.10–8.01 (m, 2H), 7.99–7.88 (m, 2H), 7.77 (ddd, J = 8.6, 6.9, 1.4 Hz, 1H), 7.71–7.64 (m,
2H), 7.57–7.51 (m, 3H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 197.2, 194.6, 136.0, 135.1, 134.8,
134.1, 133.4, 131.0, 130.0, 129.5, 129.1, 128.8, 128.6, 127.1, 126.0, 124.4.
1
1ꢀPhenylꢀ2ꢀ(thiophenꢀ2ꢀyl)ethaneꢀ1,2ꢀdione (2x).4b Yellow oil (30.3 mg, 70% yield); H NMR
(CDCl3, 400 MHz): δ (ppm) 8.07 (dt, J = 8.5, 1.5 Hz, 2H), 7.86 (dd, J
= 4.9, 1.1 Hz, 1H), 7.83 (dd, J
=
3.9, 1.1 Hz, 1H), 7.71–7.64 (m, 1H), 7.54 (t, J = 7.8 Hz, 2H), 7.21 (dd, J = 4.9, 3.9 Hz, 1H); 13
C
NMR (CDCl3, 100 MHz): δ (ppm) 192.1, 185.6, 139.9, 136.9, 136.8, 134.9, 132.6, 130.3, 128.9,
128.8.
1
1,4ꢀDiphenylbutꢀ3ꢀyneꢀ1,2ꢀdione (2y).6b Yellow oil (36.1 mg, 77% yield); H NMR (CDCl3, 400
MHz): δ (ppm) 8.11 (dt, J = 8.5, 1.5 Hz, 2H), 7.70–7.67 (m, 3H), 7.58–7.51 (m, 3H), 7.45–7.42
(m, 2H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 188.5, 178.6, 134.9, 133.7, 131.7, 131.6, 130.5,
128.9, 128.8, 119.2, 99.2, 87.1.
1
(E)ꢀ1,4ꢀDiphenylbutꢀ3ꢀeneꢀ1,2ꢀdione (2z).23 Yellow oil (32.1 mg, 68% yield); H NMR (CDCl3,
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δ
8.07 (dd, J = 8.4, 1.3 Hz, 2H), 7.74 (d, J = 16.4 Hz, 1H), 7.68 (d, J = 7.5 Hz,
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1H), 7.63 (dd, J = 7.5, 1.8 Hz, 2H), 7.58–7.51 (m, 2H), 7.48–7.44 (m, 3H), 7.17 (d, J = 16.4 Hz,
1H); 13C NMR (CDCl3, 100 MHz): δ (ppm) 193.3, 192.8, 148.9, 134.7, 134.0, 132.8, 131.6, 130.2,
129.1, 128.9, 128.9, 122.4.
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■ ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI:
Copies of 1H NMR and 13C NMR spectra for all products (PDF).
■ AUTHOR INFORMATION
Corresponding Author
*Eꢀmail: sunpeipei@njnu.edu.cn
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This work was supported by the National Natural Science Foundation of China (Project 21272117,
21502097), the Key International (Regional) Joint Research Program of NSFC (Grant No.
21420102002), the Natural Science Foundation of the Education Department of Jiangsu province
(15KJB150015), and the Priority Academic Program Development of Jiangsu Higher Education
Institutions. The authors also thank Mr. Hailong Liu for the determination of HRMS.
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