Study on comparison of reducing ability of three organic hydride compounds

Article abstract of DOI:10.1016/j.tet.2012.04.047

Selective reduction of three kinds of substrates were studied to evaluate the reducing abilities of N,N-dimethyl-benzimidazolidine (DMBI), 2-phenylbenzimidazoline (PBI) and 2-phenylbenzothiazoline (PBT). As hydride donors, these three five-membered heterocyclic compounds performed different reducing abilities depending on the substrates.

Full text of DOI:10.1016/j.tet.2012.04.047

Tetrahedron 68 (2012) 5053e5059
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Study on comparison of reducing ability of three organic hydride compounds
,
Yi-Si Feng a, Chun-Yan Yang a, Qiang Huang b, Hua-Jian Xu b
*
a School of Chemical Engineering, Hefei University of Technology, Hefei 230009, PR China
b School of Medical Engineering, Hefei University of Technology, Tunxi Road 193, Hefei 230009, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Selective reduction of three kinds of substrates were studied to evaluate the reducing abilities of N,N-
dimethyl-benzimidazolidine (DMBI), 2-phenylbenzimidazoline (PBI) and 2-phenylbenzothiazoline (PBT).
As hydride donors, these three five-membered heterocyclic compounds performed different reducing
abilities depending on the substrates.
Received 13 January 2012
Received in revised form 9 April 2012
Accepted 12 April 2012
Available online 21 April 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Organic hydride compounds
Reducing ability
Irradiation
1. Introduction
phenylbenzimidazoline (PBI) and 2-phenylbenzothiazoline (PBT),
to compare their abilities in reducing three kinds of substrates,
a,b-
Organic hydride compounds are one kind of substances, which
can transfer hydrogen to the surrounding substrates in the form of
hydride anions in chemical and biochemical reactions.1 As we all
know, there are many natural organic hydride donors in different
forms in nature, such as NAD(P)H,2 FADH2,3 Vitamin C4 and tetra-
hydrofolate.5 Many biomimetic hydrogen sources were synthesized
by chemists in which the most widely studied were three six-
membered heterocyclic compounds Hantzsch ester (HEH), 1-
benzyl-1,4-dihydronicotinamide (BNAH) and 9,10-dihydroacridine
(AcrH2) with 1,4-dihydropyridine as active centre. They have been
extensively studied by chemical workers as reducing agents, such
as MacMillan,6 List,7 Rueping8 and You.9 At the same time, many
five-membered heterocyclic compounds have been synthesized to
epoxy ketones, electron-deficient olefins and -unsaturated ke-
a,b
tones. On the basis of exploring their reaction scope and properties,
we committed to find the relationship between structure and ac-
tivity. It will provide some protocols for designing the organic hy-
dride compounds with more efficiently reducing abilities in future.
transfer hydrogen to
a,b
-unsaturated compounds,10 imines11 and
a,b
-epoxy ketones.12 Although these five-membered hydride
compounds don’t have 1,4-dihydropyridine structure, the proxim-
ity of hydride dissociation energy to NADH and high efficient hy-
dride donating abilities they have also generated great interest of
many chemists. However, although the theoretical data about five-
membered heterocyclic hydride compounds have been reported,13
such as the thermodynamic data of capacity of providing hydride
anions, experimental studies on the comparison of their reducing
abilities are lacking.
2. Results and discussion
2.1. Reduction of a,b-epoxy ketones
Chemoselective reduction of
much attention for several decades because the reduction product
-hydroxy ketones) were very important intermediates in organic
synthesis.12,14 Thus, in initial experiments we chose
-epoxy ke-
a,b-epoxy ketones have attracted
(b
Herein, we chose three different five-membered heterocyclic
hydride compounds, N,N-dimethylbenzimidazoline (DMBI), 2-
a,b
tones as the reactive substrate to investigate the different catalytic
efficiency of three hydride donors. At first, DMBI was used as hy-
dride anion donor and the reaction parameters, such as solvent,
time and loadings of DMBI were summarized in Table 1. In the
* Corresponding author. Tel.: þ86 551 2904353; fax: þ86 551 2904405; e-mail
address: hjxu@hfut.edu.cn (H.-J. Xu).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.04.047

5054
Y.-S. Feng et al. / Tetrahedron 68 (2012) 5053e5059
Table 1
Table 2
Hydrogenation of epoxy ketone 1a with DMBI
Reduction of a,b-epoxy ketones by DMBI, PBI and PBT
Entry
Substrate
Product
Yield (%)
1a
2b
3c
Yielda (%)
1
2
3
4
5
6
7
8
9
1a: Ar1¼Ph, Ar2¼Ph
4a
4b
4c
4d
4e
4f
4g
4h
4i
89
37
92
88
62
69
87
41
78
42
88
70
89
92
81
76
87
77
91
79
87 (91)d
40
65
52
42
58
83
45
96
Entry
Loadings (equiv)
Time (h)
Solvent
1b: Ar1¼p-FeC6H4, Ar2¼Ph
1c: Ar1¼p-CleC6H4, Ar2¼Ph
1d: Ar1¼p-Br, Ar2¼Ph
1
2
3
4
5
6
7
8
1.5
1.5
1.5
1.5
1.0
2.0
2.5
2.0
2.0
2.0
2.0
24
24
24
24
24
24
24
12
36
24
24
CH3OH
THF
CH3CN
Toluene
THF
THF
THF
THF
THF
d
75
68
70
30
89
87
56
88
d
1e: Ar1¼p-OCH3eC6H4, Ar2¼Ph
1f: Ar1¼p-CH3eC6H4, Ar2¼Ph
1g: Ar1¼Ph, Ar2¼p-CleC6H4
1h: Ar1¼Ph, Ar2¼o-CleC6H4
1i: Ar1¼Ph, Ar2¼p-BreC6H4
1j: Ar1¼Ph, Ar2¼p-OCH3eC6H4
10
4j
76
9
10b
11c
THF
THF
90
11
12
4k
4l
47
33
80
83
57
49
a
Isolated yield.
b
c
50 ꢀC, without hv.
With 10 mol % AlCl3.
selective reduction of
a
,
b-epoxy ketone 1a to b-hydroxy ketones 4a,
the optimum reaction condition was irradiating at room tempera-
ture in THF (Table 1, entry 6). As shown, addition of Lewis acid could
not significantly promote the yield. It was noteworthy that no
product was obtained using proton solvent ethanol or without
irradiation.
2-Phenylbenzimidazoline (PBI) is unstable in the air and easily
oxidized to 2-pheny-benzimidazole according to the previous
report.10a Therefore, in situ generation of PBI with o-phenylenedi-
13
4m
45
85
43
a
amine and benzaldehyde as raw materials, was used to reduce
epoxy ketone. The optimum conditions about reduction of 1a to
a
,
b
b
-
-
Isolated yield. The reaction was reduced by DMBI.
Isolated yield. The reaction condition was reduced by PBI.
Isolated yield. The reaction condition was: PBT (2 equiv), THF (5 mL), hv, rt, 24 h.
Isolated yield. The reaction was carried out in THF at ambient temperature for
b
c
hydroxy ketones 4a were obtained by using PBI in 2.0 equiv under
irradiation at room temperature for 24 h in THF (Table 2, entry 1).
2-phenylbenzothiazoline (PBT), as a reducing agent, was used to
d
36 h.
transform hydrogen to 1a to form b-hydroxy ketone 4a. Among the
selection of solvents, THF was also the best solvent and proton
solvent ethanol was ineffective. Employing 2.0 equiv PBT under
irradiation for 36 h was sufficient to complete the reaction in 91%
yield (Table 2, entry 1).
2.2. Reduction of electron-deficient olefins
From above, relatively satisfactory results were observed on the
reducing abilities of three kinds of hydride donors by selective re-
Through the above studies we concluded that the reduction of
duction of a,b-epoxy ketones. Then reduction of electron-deficient
a
,
b
-epoxy ketones by organic hydride compounds didn’t need
Lewis acid as catalyst. Reactions accomplished sufficiently under
irradiation at room temperature. Nevertheless, corresponding
olefins carried with electron-withdrawing substituents by the
three organic hydride compounds were investigated in this part.
For optimizing the conditions, reduction of 2-(4-nitrobenzylidene)
malononitrile 2a by DMBI was chosen as model reaction. As shown,
93% yield was obtained by employing 1.5 equiv of DMBI in THF for
24 h (Table 3, entry 13). It was noteworthy that the amount of
solvent became an important factor that using 7 mL solvent was
better than 5 mL. However, the yields dropped unexpectedly as the
solvent continuing to increase (Table 3, entries 11, 13e15).
Accordingly, a series of selection were carried out in order to
find the appropriate conditions in reduction of electron-deficient
olefin 2a by PBI and PBT. The results showed that 2a was reduced
in the yield of 78% by PBI at room temperature in ethanol and
was reduced by PBT in the yield of 81% at 80 ꢀC in ethanol (Table 4,
entry 1).
After optimized the reaction conditions, a range of cyano-
substituted alkenes 2aek were reduced by DMBI, PBI and PBT in
the same conditions. As presented in Table 4, when using DMBI as
reductant, the substrates with phenyl, which was activated by
strong electron-withdrawing group, such as nitro gave the corre-
sponding reductive products in good yields (Table 4, entries 1e3).
However, the substrates with halogen-substituted benzene 2h and
b
-
hydroxy ketone couldn’t be obtained without irradiation because
a possible mechanism was a photoinduced electron transfer pro-
cess, which to be a useful way to generate ketyl radicals.15 High-
pressure mercury lamp can provide UV irradiation (l>300 nm) to
promote the hydride compounds to be excited and became radical
cations. At the same time substrates converted to the correspond-
ing radical anions via photoinduced electron transfer.16 In the
choice of solvent, employing a nonpolar solvent, such as THF could
achieve good yields. However, proton solvent ethanol was in-
efficient. The potential reason was that the reaction process re-
quired two electrons and two protons, thereby protonic solvents
would trap the radical and prevent the electron transfer and
resulted in no target product.12a
As shown in Table 2, a series of
to the corresponding -hydroxy ketones by DMBI, PBI and PBT,
respectively, in the uniform conditions. In contrast to DMBI and
PBT, the reduction of -epoxy ketones by PBI generated in situ
a,b-epoxy ketones were reduced
b
a,b
obtained more satisfactory results because of the comparatively
stable yields (70e92%).

Y.-S. Feng et al. / Tetrahedron 68 (2012) 5053e5059
5055
Table 3
Optimization of reaction conditions for reduction of 2a by DMBI
Table 4
Reduction of electron-deficient olefins by DMBI
Entry
Substrate
Product
Yield (%)
1a
2b
3c
1
2
2a
2b
5a
5b
93
86
d
(81)e
(88)d
Entry
Loadings (equiv)
Solvent (mL)
Time (h)
Yielda (%)
1
2
3
4
0.5
1.0
1.5
2.0
2.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
MeCN (5)
MeCN (5)
MeCN (5)
MeCN (5)
MeCN (5)
MeCN (5)
MeCN (5)
MeCN (5)
MeCN (5)
EtOH (5)
THF (5)
12
12
12
12
12
12
12
24
36
24
24
24
24
24
24
67
73
81
83
81
82
74
87
86
79
91
85
93
89
81
87
84
84
80
d
5
6b
7c
8
3
2c
5c
d
9
10
11
12
13
14
15
4
5
2d
2e
5d
5e
85
89
26
d
d
Benzene (5)
THF (7)
THF (9)
THF (11)
d
a
Isolated yield.
React with hv.
React at 50 ꢀC.
b
c
6
2f
5f
78
75
d
2i or alkenes jointed with furan 2e or two phenyls 2j or methyl and
phenyl 2k could hardly be reduced to the target products. As
shown, olefins were reduced by PBI in comparatively good yields in
THF or ethanol. However, reduction of electron-deficient olefins by
PBT in this condition couldn’t afford satisfactory results. Heating to
80 ꢀC could effectively improve the yields. Apparently, we can
conclude that reduction of electron-deficient olefins by DMBI and
PBI proceed more easily than by PBT. Heating was an effective
method to ensure high yields in reduction of olefins by PBT.
7
8
2g
2h
5g
5h
86
83
21
(85)d
(91)e
d
52
95
d
d
d
d
d
d
9
2i
5i
d
d
d
2.3. Reduction of a,b-unsaturated ketones
Selective hydrogenation of carbonecarbon double bond of
unsaturated carbonyl compounds is a very important process in
organic synthesis.17 Therefore, reduction of
-unsaturated ke-
a,b-
10
2j
5j
a,b
tones to the corresponding saturated ketones by three hydride
donors was studied. Compound 3i was chosen as reaction substrate
to find the optimized conditions. As shown in Table 5, a series of
reaction parameters, such as the amount of DMBI, solvent, tem-
perature, reaction time and Lewis acid were investigated. Among
the catalyst tested, anhydrous magnesium perchlorate gave the
best results (entries 3, 5e7). The optimal reaction conditions were
utilizing 1.5 equiv of DMBI in toluene at 80 ꢀC for 24 h (Table 5,
entry 8). In our further study, only 48% 6i was obtained with PBI as
a reductant and zinc chloride as a catalyst (Table 6, entry 9). In
contrast, 3i was reduced in the yield of 75% by PBT with aluminium
chloride as catalyst (Table 6, entry 9). In this process, Lewis acid
played an important role and the possible course was that the metal
ions of Lewis acid and the carbonyl oxygen of the substrates gen-
erated to a complex, which induced polarization of the carbon-
ecarbon double bond.10c
11
2k
5k
a
Isolated yield. The reaction was reduced by DMBI.
Isolated yield. The reaction was reduced by PBI.
Isolated yield. The reaction was reduced by PBT.
The solvent was C2H5OH.
b
c
d
e
Heat at 80 ꢀC in C2H5OH.
heterocycle could give satisfactory yields. However, if the phenyl
connected to carbonyl group was replaced by methyl, the ketone 3k
couldn’t be reduced to the corresponding product 6k (entry 11). In
contrast, no products were obtained by using PBI and PBT as re-
ducing donors in this reaction conditions. In order to prove the
above reactions were not suitable for this system, reduction of 3a
and 3d in their optimal conditions were studied. As a result, the
reduction yields by using PBT as hydride donors were better than
using PBI.
As presented in Table 6, a series of a,b-unsaturated ketones were
reduced to corresponding saturated ketones by three hydride do-
nors in the same conditions. When using DMBI as reductant,
the yields were 70e87% except 6k. The substrates with phenyl
carrying substituent and those of carbonyl group connected with
For testifying the method of optimization conditions was
objective, we made a kinetic analysis.
a,b-epoxy ketone 1a was

5056
Y.-S. Feng et al. / Tetrahedron 68 (2012) 5053e5059
Table 5
Table 6
Optimization of reaction conditions for reduction of 3h by DMBI
Reduction of a,b-unsaturated ketones by DMBI
Entry
Substrate
Product
Yield (%)
Entry
Loadings
(equiv)
Solvent
(mL)
Time
(h)
Temp
(ꢀC)
Lewis acid
Yield
(%)
1a
2b
3c
1
2
3
4
5
6
7
8
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.0
2.0
1.5
1.5
1.5
1.5
Benzene
Benzene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
12
12
12
12
12
12
12
24
36
24
24
24
24
24
24
25
50
80
100
80
80
80
80
80
80
80
80
80
80
80
Mg(ClO4)2
Mg(ClO4)2
Mg(ClO4)2
Mg(ClO4)2
FeCl3
AlCl3
ZnCl2
Mg(ClO4)2
Mg(ClO4)2
Mg(ClO4)2
Mg(ClO4)2
d
d
48
73
74
64
61
63
86
86
69
87
d
1
3a
3b
6a
6b
78
d
(45)d
d
(69)e
2
3
4
75
79
75
d
d
d
d
9
10
11
12
13a
14b
15c
Mg(ClO4)2
Mg(ClO4)2
Mg(ClO4)2
62
87
43
3c
6c
a
Mg(ClO4)2 (5 mol %).
Mg(ClO4)2 (20 mol %).
Under air.
b
c
3d
6d
d
(42)d
d
(65)e
reduced by using PBT as reductant to find the reactivity under ir-
radiation. We sampled the reaction solution quantitatively every
3 h during 48 h. Each sample was detected by HPLC and the results
were presented in Fig. 1. To begin with, the yield of 4a was in-
creasing to 94% until 36 h as time went by. In contrast, the yield of
4a was decreased when reaction duration was lengthened to 48 h.
The possible cause was the happening of side reaction during long-
period irradiation.
5
3e
6e
70
d
d
3. Conclusion
In summary, we studied the reduction of
a,b-epoxy ketones,
6
7
8
9
3f
6f
82
79
76
86
d
d
d
d
d
electron-deficient olefins and -unsaturated ketones by three
a,b
organic hydride compounds DMBI, PBI and PBT. Differences in re-
ducing abilities of these hydride compounds were observed
depending on the substrates. Base on the yields of product, we
would like to conclude that reduction of a,b-epoxy ketones by PBI
was more effective than the other two, but in the hydrogenation of
3g
3h
3i
6g
6h
6i
electron-deficient olefins, DMBI and PBI achieved higher yields
than PBT. In the selective reduction of
a,b-unsaturated ketones,
DMBI gained better results than the other two. Accordingly, all of
these studies will make for the design of some new five-membered
heterocyclic hydride compounds and would be a foundation for
other people’s research.
4. Experimental
4.1. General remarks
d
(48)d
d
(75)e
All the reduction reactions were carried out in oven-dried flasks
of Schlenk tubes and conducted under a positive pressure of argon.
DMBI13b and PBT10c were prepared by previously reported
methods. In situ generation of PBI was processed directly by o-
10
11
3j
6j
80
d
d
d
d
phenylenediamine and benzaldehyde.10a The
a,b-epoxy ketones 1
were prepared from corresponding unsaturated ketones using al-
kaline hydrogen peroxide.18 The olefins 2 were prepared by corre-
sponding aldehydes and malononitrile with basic alumina.19 The
a
,b
-unsaturated ketones were prepared by corresponding aceto-
3k
6k
d
phenone (3aej) or acetone (3k) or heterocyclic ketones (3l, 3m)

Y.-S. Feng et al. / Tetrahedron 68 (2012) 5053e5059
5057
Table 6 (continued )
benzaldehyde (0.5 mmol) or PBT (0.5e1.5 mmol) with or without
Lewis acid in tetrahydrofuran (5 mL) or other solvents was irradi-
ated with a 450 W high-pressure mercury lamp in a Schlenk tubes
under an argon atmosphere at room temperature for 12e36 h. The
irradiated reaction was monitored by TLC. After completion of the
reaction, 1 mL HCl (0.1 mol/L) was added to the solution and stirred
for 10 min, and then the solvent was evaporated under reduced
pressure and the residue was purified by column chromatography
Entry
Substrate
Product
Yield (%)
1a
2b
3c
12
3l
6l
87
d
d
on silica gel and the obtained corresponding b-hydroxy ketones
were identified by 1H and 13C NMR.
13
3m
6m
86
d
d
4.2.1. 3-Hydroxy-1,3-diphenylpropan-1-one(4a).21 1HNMR(300MHz,
CDCl3)
d
7.96 (d, J¼7.2 Hz, 2H), 7.59 (t, J¼7.4 Hz,1H), 7.53e7.22 (m, 7H),
5.35 (t, J¼6.0 Hz, 1H), 3.61 (s, 1H), 3.38 (d, J¼6.0 Hz, 2H). 13C NMR
a
Isolated yield. The reaction was reduced by DMBI.
Isolated yield. The reaction was reduced by PBI.
Isolated yield. The reaction was reduced by PBT.
Reaction was carried out in the presence of 40 mol % ZnCl2 in C2H5OH.
Reaction was carried out in the presence of 40 mol % AlCl3 in C2H5OH.
b
c
(75 MHz, CDCl3)
128.20, 127.74, 125.80, 70.06, 47.43.
d 200.27, 144.93, 136.56, 133.73, 128.76, 128.63,
d
e
4.2.2. 1-(4-Fluorophenyl)-3-hydroxy-3-phenylpropan-1-one (4b).21 1H
NMR (300 MHz, CDCl3) d 8.01e7.97 (m, 2H), 7.45e731 (m, 5H), 7.14 (t,
J¼8.6 Hz, 2H), 5.42e5.29 (m, 1H), 3.50 (s, 1H), 3.38e3.32 (m, 2H). 13C
100
90
80
70
60
50
40
30
20
10
0
NMR (75 MHz, CDCl3) d 198.42, 167.78, 142.94, 130.94, 130.82, 128.62,
127.76, 125.75, 116.01, 115.71, 70.08, 47.38.
4.2.3. 1-(4-Chlorophenyl)-3-hydroxy-3-phenylpropan-1-one
(4c).21 1H NMR (300 MHz, CDCl3)
d
7.88 (d, J¼8.7 Hz, 2H), 7.45e7.25
(m, 7H), 5.36e5.32 (m, 1H), 3.49 (s, 1H), 3.33 (t, J¼6.4 Hz, 2H). 13C
NMR (75 MHz, CDCl3)
d 198.79, 142.88, 140.17, 134.98, 129.60,
129.06, 128.64, 127.80, 125.74, 70.03, 47.46.
4.2.4. 1-(4-Bromophenyl)-3-hydroxy-3-phenylpropan-1-one (4d).21 1H
NMR (300 MHz, CDCl3)
7.49e7.27 (m, 5H), 5.37e5.33 (m, 1H), 3.76 (br s, 1H), 3.34 (t, J¼8.4 Hz,
2H). 13C NMR (75 MHz, CDCl3)
199.04, 142.83, 135.32, 132.08, 130.08,
d
7.82 (d, J¼8.6 Hz, 2H), 7.61 (d, J¼8.6 Hz, 2H),
d
129.70, 128.67, 127.83, 125.76, 70.00, 47.46.
0
3
6
9
12 15 18 21 24 27 30 33 36 39 42 45 48 51
time(h)
4.2.5. 3-Hydroxy-1-(4-methoxyphenyl)-3-phenylpropan-1-one
(4e).21 1H NMR (300 MHz, CDCl3)
d
7.94 (d, J¼9.0 Hz, 2H), 7.52e7.26
(m, 5H), 6.93 (d, J¼9.0 Hz, 2H), 5.35e5.31 (m, 1H), 3.87 (s, 3H), 3.76
(br s, 1H), 3.33e3.30 (m, 2H). 13C NMR (75 MHz, CDCl3)
200.31,
Fig. 1. Relations between yield and time in reduction of 1a by PBT.
d
165.46, 144.56, 132.02, 131.14, 130.05, 129.12, 127.27, 115.36, 71.67,
57.03, 48.42.
and benzaldehyde with NaOH at room temperature.20 Other re-
agents and solvents were purchased and used without further
purification. Analytical thin layer chromatography (TLC) was per-
formed using Merck silica gel GF254 plates. Flash column chroma-
tography was performed with silica gel (200e300 mesh). Gas
chromatographic (GC) analysis was performed on a Shimadzu GC-
2014 Series GC System. High performance liquid chromatography
(HPLC) was performed on a Waters 2487 UV detector. The 1H and
13C NMR spectra were recorded in CDCl3 on a 300 MHz instrument
with TMS as internal standard.
4.2.6. 3-Hydroxy-3-phenyl-1-p-tolylpropan-1-one (4f).21 1H NMR
(300 MHz, CDCl3)
(d, J¼8.9 Hz, 2H), 5.35e5.31 (m, 1H), 3.90 (s, 1H), 3.87 (s, 3H),
3.33e3.30 (m, 2H). 13C NMR (75 MHz, CDCl3)
198.84, 143.95,
d
7.94 (d, J¼8.9 Hz, 2H), 7.49e7.28 (m, 5H), 6.93
d
143.09, 132.04, 130.54, 128.58, 127.65, 125.80, 113.89, 70.19, 55.56,
46.95.
4.2.7. 3-(4-Chlorophenyl)-3-hydroxy-1-phenylpropan-1-one (4g).21 1H
NMR (300 MHz, CDCl3)
1H), 7.47 (t, J¼7.4 Hz, 2H), 7.42e7.30 (m, 4H), 5.34e5.30 (m, 1H),
3.69 (s, 1H), 3.38e3.31 (m, 2H). 13C NMR (75 MHz, CDCl3)
200.02,
141.46, 136.42, 133.85, 133.36, 128.80, 128.73, 128.18, 127.20, 69.43,
47.27.
d
7.95 (d, J¼7.2 Hz, 2H), 7.60 (t, J¼7.4 Hz,
4.1.1. N,N-Dimethylbenzimidazoline (DMBI).13 1H NMR (300 MHz,
CDCl3)
d
6.62 (dd, J¼3.3, 5.4 Hz, 2H), 6.35 (dd, J¼3.3, 5.4 Hz, 2H),
d
4.27 (s, 2H), 2.67 (s, 6H). 13C NMR (75 MHz, CDCl3)
112.66, 80.23, 33.61.
d 143.15, 119.12,
4.1.2. 2-Phenylbenzothiazoline (PBT).10c 1H NMR (300 MHz, CDCl3)
7.56e7.53 (m, 2H), 7.40e7.29 (m, 3H), 7.05 (d, J¼7.5 Hz, 1H), 6.95
(t, J¼7.6 Hz, 1H), 6.76 (t, J¼7.2 Hz, 1H), 6.66 (d, J¼7.7 Hz, 1H), 6.38 (s,
1H), 4.33 (br s, 1H). 13C NMR (101 MHz, CDCl3)
146.26, 141.66,
129.02, 128.76, 128.72, 126.54, 125.48, 121.62, 120.65, 109.71, 69.98.
4.2.8. 3-(2-Chlorophenyl)-3-hydroxy-1-phenylpropan-1-one (4h).21 1H
d
NMR (300 MHz, CDCl3)
7.60 (t, J¼7.2 Hz, 1H), 7.47 (t, J¼7.8 Hz, 2H), 7.34 (t, J¼7.2 Hz, 2H),
7.21e7.26 (m, 1H), 5.69 (d, J¼9.6 Hz, 1H), 3.80 (br s, 1H), 3.60e3.10 (m,
d
7.97 (d, J¼7.2 Hz, 2H), 7.72 (d, J¼7.8 Hz, 1H),
d
2H). 13C NMR (75 MHz, CDCl3)
d 200.37, 140.35, 136.43, 133.80, 131.19,
129.38, 128.77, 128.64, 128.25, 127.30, 66.85, 45.39.
4.2. General procedure for reduction of a,b-epoxy ketones
4.2.9. 3-(4-Bromophenyl)-3-hydroxy-1-phenylpropan-1-one(4i).22 1H
A solution of a
a
,
b
-epoxy ketone substrate (0.5 mmol) and DMBI
NMR (300 MHz, CDCl3)
7.32 (d, J¼8.1 Hz, 2H), 5.33e5.29 (m, 1H), 3.65 (br s, 1H), 3.38e3.28
d
7.95 (d, J¼8.4 Hz, 2H), 7.60e7.45 (m, 5H),
(0.5e1.25 mmol) or o-phenylenediamine (0.5 mmol) and

5058
Y.-S. Feng et al. / Tetrahedron 68 (2012) 5053e5059
(m, 2H). 13C NMR (75 MHz, CDCl3)
131.67, 128.80, 128.20, 127.57, 121.46, 69.46, 47.24.
d
199.96, 142.03, 136.40, 133.85,
(d, J¼7.2 Hz, 2H). 13C NMR (75 MHz, CDCl3)
d 149.57, 143.09, 114.45,
110.92, 109.98, 29.77, 22.66.
4.2.10. 3-Hydroxy-3-(4-methoxyphenyl)-1-phenylpropan-1-one
4.3.6. 2-(9H-Fluoren-9-yl)malononitrile (5f).24 1H NMR (300 MHz,
(4j).21 1H NMR (300 MHz, CDCl3)
d
7.96 (d, J¼7.2 Hz, 2H), 7.59 (t,
CDCl3)
d
7.82e7.75 (m, 4H), 7.51 (t, J¼7.5 Hz, 2H), 7.41 (t, J¼7.5 Hz,
J¼7.2 Hz, 1H), 7.46 (t, J¼7.8 Hz, 2H), 7.37 (d, J¼8.7 Hz, 2H), 6.91 (d,
2H), 4.40 (d, J¼5.1 Hz, 1H), 4.24 (d, J¼5.3 Hz, 1H). 13C NMR (75 MHz,
J¼8.7 Hz, 2H), 5.36e5.23 (m,1H), 3.81 (s, 3H), 3.56 (s,1H), 3.40e3.31
CDCl3)
27.84.
d 141.45, 139.66, 129.77, 128.15, 124.71, 120.83, 111.52, 46.02,
(m, 2H). 13C NMR (75 MHz, CDCl3)
d 200.30, 159.15, 136.62, 135.17,
133.67, 128.74, 128.20, 127.08, 113.96, 69.71, 55.34, 47.38.
4.3.7. 2-Benzylmalononitrile (5g).10a 1H NMR (400 MHz, CDCl3)
4.2.11. 3-Hydroxy-1-(naphthalen-2-yl)-3-phenylpropan-1-one
d
7.41e7.38 (m, 3H), 7.33e7.31 (m, 2H), 3.91 (t, J¼6.9 Hz, 1H), 3.28
(4k).21 1H NMR (300 MHz, CDCl3)
d
8.45 (s, 1H), 7.94e7.86 (m, 4H),
(d, J¼6.9 Hz, 2H). 13C NMR (101 MHz, CDCl3)
d 133.27, 129.64,
7.60e7.35 (m, 7H), 5.41 (t, J¼6.0 Hz, 1H), 3.66 (br s, 1H), 3.51 (d,
129.46, 129.16, 112.49, 37.07, 25.31.
J¼6.0 Hz, 2H). 13C NMR (75 MHz, CDCl3)
d 200.07, 144.78, 133.94,
132.45, 130.18, 129.62, 128.98, 128.60, 127.81, 127.71, 126.93, 126.79,
125.80, 123.56, 70.18, 47.50.
4.3.8. 2-(4-Chlorobenzyl)malononitrile (5h).23 1H NMR (400 MHz,
CDCl3)
d
7.50 (d, J¼7.5 Hz, 2H), 7.23 (d, J¼7.5 Hz, 2H), 3.90 (t,
J¼6.9 Hz, 1H), 3.25 (d, J¼6.9 Hz, 2H). 13C NMR (101 MHz, CDCl3)
4.2.12. 4-Hydroxy-4-phenylbutan-2-one (4l).21 1H NMR (400 MHz,
d 134.89, 130.96, 129.78, 128.88, 111.81, 35.39, 24.63.
CDCl3)
1H), 3.37 (br s,1H), 2.91e2.76 (m, 2H), 2.17 (s, 3H). 13C NMR (101 MHz,
CDCl3) 209.12, 142.90, 128.62, 127.75, 125.72, 69.94, 52.08, 30.83.
d
7.34 (d, J¼4.4 Hz, 4H), 7.29e7.26 (m,1H), 5.13 (dd, J¼3.3, 9.0 Hz,
4.3.9. 2-(4-Bromobenzyl)malononitrile (5i).23 1H NMR (400 MHz,
d
CDCl3)
d
7.46 (d, J¼7.3 Hz, 2H), 7.38 (d, J¼5.7 Hz, 2H), 3.96 (t,
J¼7.0 Hz, 1H), 3.34 (d, J¼7.0 Hz, 2H). 13C NMR (101 MHz, CDCl3)
4.2.13. 1-(2-Furyl)-3-hydroxy-3-phenylpropan-1-one
NMR (300 MHz, CDCl3)
(4m).21 1H
7.61 (s, 1H), 7.49e7.19 (m, 6H), 6.56e6.55
(m, 1H), 5.40e5.24 (t, J¼6.0 Hz, 1H), 3.43 (s, 1H), 3.30e3.21 (m, 2H).
13C NMR (75 MHz, CDCl3)
188.69, 147.02, 142.86, 128.60, 127.77,
d 132.59, 131.95, 130.78, 123.48, 112.80, 36.35, 24.73.
d
4.4. General procedure for reduction of
ketones
a,b-unsaturated
d
125.76, 118.12, 112.53, 70.06, 47.03.
A solution of the a,b-unsaturated ketone (0.5 mmol) and DMBI
4.3. General procedure for reduction of electron-deficient
olefins
(0.5e1.0 mmol) or o-phenylenediamine (0.5 mmol) and benzalde-
hyde (0.5 mmol) or PBT (0.5e1.5 mmol) in benzene (7 mL) or tol-
uene (7 mL) in the presence of a Lewis acid (5e20 mol %) was
stirred in a Schlenk tubes at 25e80 ꢀC for 12e48 h under an argon
atmosphere. The reaction was monitored by TLC. After completion
of the reaction, 1 mL HCl (0.1 mol/L) was added to the solution and
stirred for 10 min, and then the resulted aqueous mixture was
concentrated under reduced pressure and the residue followed by
column chromatography on silica gel and the obtained corre-
sponding saturated ketones were identified by 1H and 13C NMR.
A solution of the olefin (0.5 mmol) and DMBI (0.25e1.25 mmol)
or o-phenylenediamine (0.5 mmol) and benzaldehyde (0.5 mmol)
or PBT (0.5e1.5 mmol) in acetonitrile (5 mL) or other solvent
(5e11 mL) at room temperature or other conditions was stirred in
a Schlenk tubes for 12e36 h under an argon atmosphere. The re-
action was monitored by GC. After completion of the reaction, ap-
propriate amount of HCl (0.1 mol/L) was added to the solution and
stirred for 10 min, and then the resulted solution was concentrated
under reduced pressure and the residue followed by column
chromatography on silica gel and the obtained corresponding
malononitriles were identified by 1H and 13C NMR.
4.4.1. 1,3-Diphenylpropan-1-one (6a).10c 1H NMR (300 MHz, CDCl3)
d
7.96 (d, J¼9.6 Hz, 2H), 7.61e7.50 (m, 1H), 7.49e7.39 (m, 2H),
7.35e7.18 (m, 5H), 3.30 (t, J¼7.2 Hz, 2H), 3.14e2.99 (m, 2H). 13C NMR
(75 MHz, CDCl3)
d 198.17, 140.28, 135.88, 132.01, 127.58, 127.50,
4.3.1. 2-(4-Nitrobenzyl)malononitrile (5a).23 1H NMR (300 MHz,
127.40, 127.02, 125.11, 39.41, 29.13.
CDCl3)
d
8.26 (d, J¼9.0 Hz, 2H), 7.51 (d, J¼9.0 Hz, 2H), 4.04 (t,
J¼6.0 Hz, 1H), 3.41 (d, J¼6.6 Hz, 2H). 13C NMR (75 MHz, CDCl3)
4.4.2. 3-Phenyl-1-p-tolylpropan-1-one (6b).25 1H NMR (300 MHz,
d
145.2, 145.1, 130.45, 124.54, 111.50, 36.09, 24.46.
CDCl3)
2H), 3.04e2.92 (m, 2H), 2.32 (s, 3H). 13C NMR (75 MHz, CDCl3)
197.80,142.75,140.38,133.41,128.24,127.47,127.39,127.13,125.06,
d
7.78 (d, J¼8.1 Hz, 2H), 7.23e7.11 (m, 7H), 3.19 (t, J¼7.8 Hz,
4.3.2. 2-(3-Nitrobenzyl)malononitrile (5b).23 1H NMR (300 MHz,
d
CDCl3)
d
8.27 (t, J¼9.0 Hz, 2H), 7.63e7.74 (m, 2H), 4.04 (t, J¼6.8 Hz,
39.28, 29.20, 20.57.
1H), 3.44 (d, J¼9.0 Hz, 2H). 13C NMR (75 MHz, CDCl3)
d 147.47,
140.03, 135.43, 130.56, 124.27, 124.06, 111.52, 36.07, 24.61.
4.4.3. 1-(4-Chlorophenyl)-3-phenylpropan-1-one (6c).25 1H NMR
(300 MHz, CDCl3) d 7.95e7.75 (m, 2H), 7.64e7.29 (m, 3H), 7.28e7.06
4.3.3. 2-(2-Nitrobenzyl)malononitrile (5c).23 1H NMR (300 MHz,
(m, 4H), 3.19 (t, J¼7.8 Hz, 2H), 2.98 (t, J¼7.5 Hz, 2H). 13C NMR
CDCl3)
d
8.14 (d, J¼7.1 Hz, 1H), 7.74e7.53 (m, 3H), 4.42 (t, J¼7.8 Hz,
(75 MHz, CDCl3) d 197.98, 141.10, 139.52, 135.20, 130.79, 129.96,
129.49, 128.95, 128.61, 128.45, 126.26, 40.45, 30.08.
1H), 3.57 (d, J¼7.8 Hz, 2H). 13C NMR (75 MHz, CDCl3)
d
148.69,
134.63, 133.97, 130.51, 128.35, 126.04, 112.10, 35.02, 23.68.
4.4.4. 1-(4-Methoxyphenyl)-3-phenylpropan-1-one (6d).25 1H NMR
4.3.4. 2-(Pyridin-3-ylmethyl)malononitrile
(5d).23 1H
NMR
(300 MHz, CDCl3)
d
7.94 (d, J¼8.4 Hz, 2H), 7.37e7.12 (m, 5H), 6.92 (d,
(300 MHz, CDCl3)
d
8.78e8.50 (m, 2H), 7.72 (d, J¼7.8 Hz, 1H), 7.37 (t,
J¼8.4 Hz, 2H), 3.86 (s, 3H), 3.32e3.19 (m, 2H), 3.13e2.98 (m, 2H). 13C
J¼9.0 Hz, 1H), 3.99 (t, J¼6.6 Hz, 1H), 3.32 (d, J¼6.6 Hz, 2H). 13C NMR
NMR (75 MHz, CDCl3) d 197.86, 163.48, 141.51, 130.35, 129.97,
(75 MHz, CDCl3)
33.95, 24.74.
d
150.36, 150.28, 143.01, 136.90, 124.03, 111.71,
128.55, 128.48, 126.13, 113.76, 55.50, 40.17, 30.35.
4.4.5. 3-Phenyl-1-o-tolylpropan-1-one (6e).26 1H NMR (300 MHz,
4.3.5. 2-(Furan-2-ylmethyl)malononitrile (5e).23 1H NMR (300 MHz,
CDCl3)
7.43 (s, 1H), 6.46e6.32 (m, 2H), 4.07 (t, J¼7.2 Hz, 1H), 3.38
CDCl3)
d
7.50 (d, J¼7.5 Hz, 1H), 7.21e7.06 (m, 8H), 3.13 (t, J¼7.2 Hz,
d
2H), 2.95 (t, J¼7.8 Hz, 2H), 2.38 (s, 3H). 13C NMR (75 MHz, CDCl3)

Y.-S. Feng et al. / Tetrahedron 68 (2012) 5053e5059
5059
d
202.29, 140.16, 137.02, 136.91, 130.91, 130.17, 127.46, 127.38, 127.31,
Supplementary data
125.07, 124.61, 42.17, 29.30, 20.17.
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2012.04.047. These data in-
clude MOL files and InChiKeys of the most important compounds
described in this article.
4.4.6. 3-(4-Chlorophenyl)-1-phenylpropan-1-one (6f).25 1H NMR
(300 MHz, CDCl3)
d
7.85 (d, J¼7.2 Hz, 2H), 7.46 (t, J¼7.2 Hz, 1H), 7.35
(t, J¼7.5 Hz, 2H), 7.21e7.12 (m, 2H), 7.08 (d, J¼8.4 Hz, 2H), 3.18 (t,
J¼7.5 Hz, 2H), 2.95 (t, J¼7.5 Hz, 2H). 13C NMR (75 MHz, CDCl3)
d
197.73, 138.72, 135.75, 132.10, 130.83, 128.79, 127.59, 127.55,
References and notes
126.96, 39.06, 28.34.
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d
7.95 (d, J¼7.2 Hz, 2H), 7.55 (t, J¼7.2 Hz, 1H), 7.45
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3H), 3.27 (t, J¼7.5 Hz, 2H), 3.01 (t, J¼7.5 Hz, 2H). 13C NMR (75 MHz,
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d 199.41, 158.04, 136.94, 133.35, 133.07, 129.40, 128.64,
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198.22, 137.16, 135.89, 134.55, 131.95, 128.16, 127.54, 127.25,
d
7.85 (d, J¼8.1 Hz, 2H), 7.36e7.12 (m, 8H), 3.27 (t, J¼7.5 Hz,
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126.99, 39.53, 28.69, 19.95.
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4.4.9. 3-(4-Nitrophenyl)-1-phenylpropan-1-one (6i).28 1H NMR
(300 MHz, CDCl3)
d
8.16 (d, J¼8.6 Hz, 2H), 7.96 (d, J¼7.2 Hz, 2H),
7.72e7.35 (m, 5H), 3.37 (t, J¼7.5 Hz, 2H), 3.19 (t, J¼7.2 Hz, 2H). 13C
NMR (75 MHz, CDCl3)
d 198.19, 149.27, 136.92, 136.51, 133.44,
129.41, 128.76, 128.02, 123.79, 39.42, 29.74.
4.4.10. 3-(2-Chlorophenyl)-1-phenylpropan-1-one (6j).27 1H NMR
(300 MHz, CDCl3)
J¼7.5 Hz, 2H), 7.36e7.29 (m, 2H), 7.22e7.10 (m, 2H), 3.33e3.27 (m,
2H), 3.21e3.15 (m, 2H). 13C NMR (75 MHz, CDCl3)
197.89, 137.82,
d
8.01e7.90 (m, 2H), 7.54 (t, J¼7.2 Hz, 1H), 7.44 (t,
d
135.76, 132.91, 132.05, 129.76, 128.52, 127.56, 127.02, 126.69, 125.93,
37.40, 27.31.
4.4.11. 1-(2-Furyl)-3-phenylpropan-1-one (6l).26 1H NMR (300 MHz,
CDCl3)
6.52e6.61 (m, 1H), 3.22e3.10 (m, 2H), 3.07e3.01 (m, 2H). 13C NMR
(75 MHz, CDCl3) 188.58, 152.63, 146.45, 140.99, 128.57, 128.46,
d
7.57 (d, J¼0.9 Hz, 1H), 7.51e7.37 (m, 1H), 7.37e7.12 (m, 5H),
d
126.23, 117.20, 112.29, 40.19, 29.98.
4.4.12. 3-Phenyl-1-(thiophen-2-yl)propan-1-one (6m).26 1H NMR
(300 MHz, CDCl3)
1H), 7.27e7.07 (m, 5H), 7.04e7.01 (m, 1H), 3.20e3.10 (m, 2H),
3.04e2.93 (m, 2H). 13C NMR (75 MHz, CDCl3)
191.06, 143.13,
d
7.60 (d, J¼4.8 Hz, 1H), 7.53 (dd, J¼0.9, 4.8 Hz,
d
139.95, 132.49, 130.77, 127.50, 127.38, 127.05, 125.16, 40.06, 29.34.
4.5. Kinetic measurement
A solution of a a,b-epoxy ketone substrate 1a (1 mmol) and PBT
(2 mmol) in tetrahydrofuran (10 mL) was irradiated with a 450 W
high-pressure mercury lamp in a Schlenk tubes under an argon
atmosphere at room temperature for 48 h. Every 3 h 0.5 mL re-
action solution was took out under the protection of argon atmo-
sphere. The yield of corresponding
monitored by HPLC.
b-hydroxy ketone 4a was
Acknowledgements
25. Bagal, D. B.; Qureshi, Z. S.; Dhake, K. P.; Khan, S. R.; Bhanage, B. M. Green Chem.
2011, 13, 1490.
We gratefully acknowledge financial support from the National
Natural Science Foundation of China (Nos. 20802015, 21072040,
21071040) and the Program for New Century Excellent Talents in
University of the Chinese Ministry of Education (NCET-11-0627).
26. Gooben, L. J.; Ghosh, K. Angew. Chem., Int. Ed. 2001, 40, 3458.
27. Kumar, A.; Kumar, S.; Kapoor, K. K. Aust. J. Chem. 2007, 60, 621.
28. Zengin, M.; Genc, H.; Demirci, T.; Arslan, M.; Kucukislamoglu, M. Tetrahedron
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