Acidic-functionalized ionic liquid as an efficient, green and reusable catalyst for hetero-Michael addition of nitrogen, sulfur and oxygen nucleophiles to α,β-unsaturated ketones

Article abstract of DOI:10.1039/c1ob06346d

A series of acidic-functionalized ionic liquids were synthesized and applied to the hetero-Michael addition of nitrogen, sulfur and oxygen nucleophiles to α,β-unsaturated ketones under solvent-free conditions. Notably, 1-methylimidazolium p-toluenesulfoni

Full text of DOI:10.1039/c1ob06346d

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PAPER
Acidic-functionalized ionic liquid as an efficient, green and reusable catalyst
for hetero-Michael addition of nitrogen, sulfur and oxygen nucleophiles to
a,b-unsaturated ketones†
Feng Han,a,b Lei Yang,*a Zhen Lia and Chungu Xia*a
Received 8th August 2011, Accepted 26th September 2011
DOI: 10.1039/c1ob06346d
A series of acidic-functionalized ionic liquids were synthesized and applied to the hetero-Michael
addition of nitrogen, sulfur and oxygen nucleophiles to a,b-unsaturated ketones under solvent-free
conditions. Notably, 1-methylimidazolium p-toluenesulfonic ([Hmim]OTs) was found to be the most
efficient catalyst and could realize “homogeneous catalysis, two-phase separation”. Additionally, the
catalytic system has wide substrate scope and good to excellent yields (up to 99%) could be obtained at
room temperature.
metal chlorides,8 phosphines and their derivatives,9 Me4NF,10
Introduction
BF3·OEt2,11 borax,12 VO(OTf)2 and so on. On the other hand,
13
silica@copper (SiO2@Cu) core–shell nanoparticles,14 nafionꢀ
Ionic liquids (ILs) are salts being composed of distinct cations
R
SAC-13 perfluorinated resin sulfonic acid,15 KF/Al2O3,16 various
cation-exchanged faujasite zeolites with different Si/Al ratios,17
Amberlyst-15,18 perchloric acid adsorbed on silica gel (HClO4–
SiO2)19 as numerous heterogeneous catalysts were also exploited.
Both homogeneous catalysis and heterogeneous catalysis have
their own advantages and disadvantages. To preserve the benefits
of a homogeneous catalyst while co-opting the primary benefits
of a heterogeneous catalyst, one strategy is to use functionalized
ionic liquids as the catalyst, whereby the system could realize
“homogeneous catalysis, two-phase separation”.
and anions that are capable of facilely tuning, whereby they can
be designed for task-specific applications through smart choice
of the respective cation and/or anion. In addition, ILs also have
some favorable properties, such as negligible vapor pressure, non-
flammability, high thermal and chemical stability, and adjustable
solvent power for organic and inorganic substances.1 Based on
the above attractive properties, various ILs have been extensively
investigated. Especially, some functionalized ILs, such as acidic,
basic and other ionic liquids have been synthesized and used to
catalyze various chemical reactions.2
Michael and hetero-Michael addition are powerful reactions
for the formation of carbon–carbon and carbon–hetero atom
bonds.3 Moreover, the addition products such as b-amino, b-
thio and b-oxy ketone functionalities are important synthetic
intermediates.4 Normally, either the donor or the acceptor compo-
nent needs to be activated in hetero-Michael addition reactions.
The classical method to achieve this has been deprotonation of
the nucleophile with strong bases.5 And important advances have
been made with Lewis acid catalysts, which activate the acceptor
components and allow hetero-Michael addition to proceed under
much milder conditions. In this respect, numerous homogeneous
catalysts have currently been developed, such as bismuth nitrate,6
bis(trifluoromethanesulfon)imide,7 [Pd(CH3CN)2Cl2] over noble
Although several kinds of ionic liquids have been used for the
transformation,20 most are non-functionalized ILs and the ILs
were usually used as solvents or their usage amount was too large
for the catalytic system. Moreover, rarely reported catalysts were
applied to investigate three different types of nucleophiles in detail.
The success of conjugate addition reactions lies in the use of either
acidic or basic conditions which, if not selected judiciously, can
be detrimental to the desired synthesis allowing unwanted side-
reactions to contaminate the product. In addition, the possibility
of poisoning metal-based catalysts with thiols, alkyl- or arylamines
cannot be completely ruled out. Moreover, weak nucleophiles such
as carbamates and alcohols usually show low activity. Therefore,
a milder, environmentally benign catalyst system that can tolerate
more nucleophile classes for functionalized Michael acceptors still
remains to be explored.
In our continuing effort on developing an efficient catalytic
system for this reaction,9,15,21 we synthesized and applied a series of
acidic-functionalized ionic liquids (Fig. 1) as metal-free, recyclable
and efficient catalysts for the hetero-Michael reaction of N-
containing substrates, thiols, and alcohols as nucleophiles with
a,b-unsaturated ketones at room temperature (Scheme 1). No-
tably, 1-methylimidazolium p-toluenesulfonic ([Hmim]OTs) was
aState Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences, and Graduate
School of the Chinese Academy of Sciences, Lanzhou, 730000, P. R. China.
E-mail: lyang@licp.cas.cn, cgxia@licp.cas.cn; Fax: 86 931 827 7088; Tel: 86
931 496 8129
bGraduate School of the Chinese Academy of Sciences, Beijing, 100039,
China
† Electronic supplementary information (ESI) available. CCDC reference
numbers 836789, 836790. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1ob06346d
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Table 1 Screening the activities of the ionic liquidsa
Entry
Ionic liquid
Yield (%)b
1
2
3
4
5
6
7
8
9
—
NRc
NRc
NRc
53
62
50
70
89
71
[Bmim]BF4
[Bmim]PF6
[Bmim]HSO4
[Bsmim]HSO4
PyHSO4
[Hmim]HSO4
[Hmim]OTs
[Hmim]BF4
Fig. 1 Acidic-functionalized ionic liquids used in the hetero-Michael
reaction.
a Reaction conditions: cyclohexenone 0.5 mmol, ethyl carbamate 0.6 mmol,
ionic liquid 1 mL, rt, t = 24 h. b GC yield using n-decane as internal
standard. c No reaction occurred.
Scheme 1 Hetero-Michael reactions of nitrogen, sulfur, oxygen nucle-
ophiles with a,b-unsaturated enones.
found to be the most efficient catalyst and the catalytic system suc-
cessfully realized “homogeneous catalysis, two-phase separation”.
Results and discussion
Fig. 2 The influence of the catalyst amount on the reaction. Reaction
conditions: cyclohexenone 0.5 mmol, ethyl carbamate 0.6 mmol, rt, 24 h,
cat. [Hmim]OTs.
Initial studies were carried out using cyclohexenone (1a) and ethyl
carbamate (2a) as a model partner catalyzed by a series of ionic liq-
uids derived from 1-methylimidazolium, pyridine and the results
were summarized in Table 1. Obviously, the reaction could not
occur without any catalyst (Table 1, entry 1). Neutral ionic liquids
such as [Bmim]BF4 and [Bmim]PF6 were also found to be inactive
for the reaction (entries 2 and 3). Subsequently, the activities were
To examine the utility and generality of this methodology for
hetero-Michael addition, we applied the present catalyst system
to a series of a,b-unsaturated ketones with nitrogen, sulfur
and oxygen nucleophiles (Tables 2–5). Firstly, hetero-Michael
addition of a,b-unsaturated ketones with nitrogen nucleophiles
catalyzed by [Hmim]OTs was examined. Using ethyl carbamate
as the nitrogen nucleophile, cyclohexenone and all kinds of linear
enones could react smoothly to obtain above 80% yields except
1e (Table 2, entries 1–5). Additionally, some control experiments
were done to compare the catalytic activities between traditional
acids and [Hmim]OTs possessing similar pKa under an analogical
determination method (see ESI†). To our delight, [Hmim]OTs
exhibited the best activity (entries 6–8).
Then all kinds of nitrogen nucleophiles were also investigated
using pent-3-en-2-one as the acceptor and the results were
summarized in Table 3. As we know, imidazoles unsubstituted
in the 1-position are weak acids. The pKa values of imidazole,
pyrazole, benzimidazole, benzotriazole and 5-phenyl-1H-tetrazole
are respectively 14.52, 14.21, 12.75, <9.3 and <4.89.22 That’s to say,
the N–H acidity becomes stronger with the increase of the number
of N atoms. The results revealed that the reactivity decreased
in the order of 5-phenyl-2H-tetrazole > 1H-benzo[1,2,3]triazole
-
compared with ionic liquids employing HSO4 as the anion and
[Bmim]+, [Bsmim]+, Py+ or [Hmim]+ as cations (entries 4–7). As
a result, the catalytic efficiency increased in the order of Py+
<
[Bmim]+ < [Bsmim]+ < [Hmim]+. Then the anion’s effects on the
reaction of a series of acidic-functionalized ionic liquids based on
1-methylimidazolium were examined (entries 7–9). Interestingly,
the acidic-functionalized IL with OTs- showed excellent perfor-
mance to give 89% yield (entry 8). Therefore, [Hmim]OTs was
chosen as the model catalyst for further investigation.
Subsequently, the influence of the amount of the catalyst on the
reaction was also evaluated under identical reaction conditions, as
listed in Fig. 2. The yield of the product was just 57% in the pres-
ence of 10 mmol% [Hmim]OTs and the yield markedly increased to
82% with 30 mmol% catalyst present. However, the yield changed
only slightly when further increasing the amount of [Hmim]OTs
from 30 mmol% to 100 mmol%. Therefore, 30 mmol% was the
optimal amount for the reaction from an economical standpoint.
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Table 2 Hetero-Michael addition of a,b-unsaturated ketones with ethyl
carbamate (2a) catalyzed by [Hmim]OTsa
Table 3 Hetero-Michael addition of a,b-unsaturated substrates with
nitrogen-containing heterocycles catalyzed by [Hmim]OTsa
Entry Enone
1
Product
t (h) Yield (%)b
Entry Nucleophile
1
Product
t (h) Yield (%)b
24 82
24
24
24
65
76
79
2
2
3
16 98
16 95
3c
4
5
24 87
24 56
4c
3
92
82
5c,d
12
6c
7d
8e
24 86
24 80
24 76
6c
1
95
a Reaction conditions: pent-3-en-2-one 0.5 mmol, nitrogen-containing
heterocycle 0.6 mmol, cat. = [Hmim]OTs, 30 mmol%, rt. b Isolated yield.
c 2 mL CH2Cl2 was added. d (E)-(2-nitrovinyl)benzene (1k) as the substrate,
60 ◦C, 12 h.
benzo[1,2,3]triazole as the acceptor respectively. Unfortunately,
the reactions did not work at room temperature in most cases (see
ESI†, Table S2, entries 1–8). Only an 82% yield could be obtained
employing 1H-benzo[1,2,3]triazole and (E)-(2-nitrovinyl)benzene
as the substrates by improving the temperature to 60 ◦C (Table 3,
entry 5).
a Reaction conditions: a,b-unsaturated ketones 0.5 mmol, ethyl carbamate
0.6 mmol, cat. = [Hmim]OTs, 30 mmol%, rt. b Isolated yield. c 2 mL DMSO.
d cat. HCl 30 mmol%, 2 mL DMSO. e cat. H2SO4 30 mmol%, 2 mL DMSO.
> 1H-benzo-imidazole > 1H-pyrazole > 1H-imidazole (Table
3, entries 1–5), which was occasional in accordance with the
order of the acidity.22 Notably, using 5-phenyl-2H-tetrazole as
the nitrogen nucleophile, a nearly quantitative yield could be
obtained within 1 h (entry 6). In addition, the activities of several
nitrogen nucleophiles were also examined employing 1-phenylbut-
2-en-1-one as the acceptor and the results were summarized
in Table S1†. And X-ray analysis has been used to establish
some crystal structures and prove the N-substituted position
(see ESI†). Besides, several other a,b-unsaturated electrophiles
such as methyl acrylate, acrylamide, acrylonitrile and (E)-(2-
nitrovinyl)benzene were also tested using ethyl carbamate or 1H-
As we know, thiols are notoriously difficult to use in the presence
of Lewis acidic metals due to their strong tendency to poison these
catalysts, although recent advances have been made.23 Therefore,
developing a more efficient catalytic system for addition of thiols
with a,b-unsaturated ketones would be important. Fortunately,
further experiments revealed that [Hmim]OTs could be applied
successfully to thiols (Table 4). Benzenethiol and cyclohex-2-
en-1-one could afford almost quantitative yield within 18 h. In
addition, the results indicated that the yield was lower than
using benzenethiol as the sulfur nucleophiles, either benzenethiol
with withdrawing substitute or with donating substitute (Table 4,
entries 1, 2, 4–6). Moreover, the steric hindrance of the substitute
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Table 4 Hetero-Michael addition of a,b-unsaturated substrates with sulfur nucleophiles catalyzed by [Hmim]OTsa
Entry
1
Nucleophile
Product
t (h)
Yield (%)b
87/97
12/18
2c
24
32
24
28
24
24
86
93
92
93
82
69
3
4
5c
6c
7
8
24
61
9c
4
4
91
99
10
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Table 4 (Contd.)
Entry
11
Nucleophile
Product
t (h)
Yield (%)b
78
6
12d
13e
4
4
85
89
a Reaction conditions: substrate 0.5 mmol, thiophenol 0.6 mmol, cat. [Hmim]OTs 30 mmol%, rt. b Isolated yield. c 2 mL CH2Cl2 was added. d methyl
acrylate (1h) as the substrate. e acrylonitrile (1j) as the substrate.
also has some influence on the reaction. However, a good yield
could also be obtained by prolonging the reaction time when
using o-methyl benzenethiol (3c) as the sulfur nucleophile (entry
3). Besides, aliphatic thiols were also active for the addition,
acquiring moderate yield within 24 h (entries 7 and 8). Then several
Scheme 2 The reaction used for testing the recyclability of the acidic–
functionalized ionic liquid.
kinds of a,b-unsaturated substrates were examined employing
p-CH3O benzenethiol as the corresponding sulfur nucleophile
(entries 4, 9, 10, 11). Interestingly, above 90% yield could be
en-2-one and 5-phenyl-1H-tetrazole as the substrates (Scheme 2).
obtained within 4 h when N-phenylmaleimide or pent-3-en-2-one
When the reaction was completed, the reaction mixture was
was used (entries 9 and 10). However, when using 4-phenylbut-3-
extracted with ethyl acetate, the ionic liquid left in the reaction
en-2-one as the acceptor, only good yield (78%) was obtained by
vessel was rinsed with ethyl acetate and dried under vacuum at
prolonging the reaction time to 6 h and the phenomena may be
90 ◦C for 8 h to eliminate any water trapped from moisture
ascribed to the steric hindrance effect (entry 11). Fortunately, the
and reused for subsequent reactions. The results shown in Fig.
reactions of benzenethiol with methyl acrylate and acrylonitrile
3 indicated that the isolated yield of the product 2bf was almost
could smoothly occur and obtain excellent yields (85% and 89%
respectively) within 4 h (entries 12, 13). Trace or no product could
be acquired using acrylamide or (E)-(2-nitrovinyl)benzene as the
consistent after five runs and [Hmim]OTs could be reused at least
five times.
electrophile (Table S2, entries 9, 10†).
Generally, alcohols are less reactive than the above nucleophiles
for the hetero-Michael addition, only acquiring poor yields with
a,b-unsaturated substrates. Gratifyingly, we found the ionic liquid
[Hmim]OTs was also a good catalyst for oxa-Michael addition
and the results were summarized in Table 5. Simple alcohols such
as methanol, alcohol and so on were suitable nucleophiles with
above 60% yields (Table 5, entries 1–4). Fortunately, aromatic
alcohols usually exhibiting competitive interference of Friedel–
Crafts-type reactions reacted with pent-3-en-2-one to give 60%
yield of the Michael product by prolonging the reaction time to
48 h (entry 5). Besides, other a,b-unsaturated ketones with the
phenyl ring of the carbonyl side such as 1-phenyl-but-2-en-1-one
furnished the addition product in 78% yield (entry 6). And the
reaction of methanol and N-phenylmaleimide was very slow and
just 23% yield could be acquired at the same conditions. However,
improving the temperature to 60 ◦C led to 65% yield just after 12 h.
It is well-known that the stability and reusability of a catalyst
system are the two key factors that identify whether it finds
potentially application in industry. To test the catalyst reusability,
the reaction was carried out in the presence of a catalytic amount
of [Hmim]OTs under the optimal reaction conditions with pent-3-
Fig. 3 Recyclability of the catalyst. Reaction conditions: pent-3-en-2-one
0.5 mmol, 5-phenyl-1H-tetrazole 0.6 mmol, t = 1 h, [Hmim]OTs 30 mmol%.
Conclusions
In conclusion, three kinds of hetero-Michael addition including
nitrogen, sulfur and oxygen nucleophiles with a,b-unsaturated
substrates have been successfully realized using the synthesized
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Table 5 Hetero-Michael addition of a,b-unsaturated ketones with oxy-
obtained as solutions in either CDCl3 or D2O. Chemical shifts
were reported in parts per million (ppm, d) and referenced to
CHCl3 (d 7.27) or D2O (d 4.88). Gas chromatographic analyses
were performed using an Agilent 6850 system (FID). Silica gel
(200–300 microns) was used for all chromatographic separations.
Anhydrous organic solvents were dried and stored under nitrogen.
All other chemicals used for synthetic procedures were reagent
grade or better. Solutions were concentrated in vacuo with a rotary
evaporator and the residue was purified using a silica gel column
unless specified otherwise. All reactions were monitored by TLC
with silica gel-coated plates. Detection was conducted by UV
absorption (254 nm) and fuming with iodine in a jar.
gen nucleophiles catalyzed by [Hmim]OTsa
Entry Nucleophile
Product
t (h) Yield (%)b
1
2
3
4
5
6c
7
CH3OH 4a
12
12
12
12
48
48
48
85
76
61
66
60
78
23
CH3CH2OH 4b
ClCH2CH2OH 4c
The synthetic procedure for 1-methylimidazolium p-toluenesulfonic
([Hmim]OTs)
1-Methylimidazole (6.15 g, 0.075 mol) was placed in a three necked
flask, which was provided with a stirrer and cooled to 0 ◦C.
Then p-toluenesulfonic acid (0.075 mol, 12.9 g; 40% solution in
water, 33 mL) was added slowly over a period of 30 min while
stirring and cooling to maintain the temperature at 0–5 ◦C. After
that, the reaction mixture was stirred for an additional period
of 2 h. Water was removed in vacuum to give the product as a
colorless liquid, which solidified on cooling. 1-Methylimidazolium
p-toluenesulfonic (19.0 g, 98% yield) was obtained after drying in
vacuo for 24 h.
IR: 3417, 3149, 2659, 2855, 2642, 2072, 1924, 1628, 1587, 1552,
1495, 1451, 1392, 1311, 1281, 1192, 1126, 1038, 1011, 904, 819,
757, 688, 626, 567. 1H NMR (400 MHz, D2O) d = 2.21 (s,
3H), 3.71 (s, 3H), 7.15–7.23 (m, 4H), 7.50 (s, 1H), 7.53 (s, 1H),
8.42 (s, 1H). 13C NMR (100 MHz, D2O) d = 20.4, 35.3, 119.4,
122.8, 125.3, 129.3, 134.8, 139.5, 142.3. MS (ESI): [m/z]+ = 82.8,
[m/z]- = 170.6.
PhCH2OH 4e
CH3OH 4a
CH3OH 4a
8c
CH3OH 4a
12
65
General procedure for hetero-Michael addition
To a well stirred mixture of nucleophile (0.6 mmol) and catalyst
([Hmim]OTs 30 mol%, 38.1 mg) was added a,b-unsaturated
substrate (0.5 mmol) and then the reaction mixture was stirred
for the designated reaction time. After completion of the reaction,
the mixture was extracted with ethyl acetate (5 mL ¥ 3), the
organic layer was washed with brine, dried (Na2SO4), evaporated
and purified by using column chromatography to obtain the pure
product. The products were characterized by measuring melting
point, IR, 1H NMR,13C NMR and HRMS.
a Reaction conditions: substrate 0.5 mmol, alcohol 2.0 mmol, Cat. =
[Hmim]OTs, 30 mmol%, rt. b Isolated yield. c T = 60 ◦C.
acidic-functionalized ionic liquids under metal-free and solvent-
free conditions. Notably, 1-methylimidazolium p-toluenesulfonic
was found to be the most efficient catalyst. Additionally, the
catalytic system successfully realized “homogeneous catalysis,
two-phase separation” and has wide substrate scope including
aromatic and aliphatic nucleophiles. Moreover, good to excellent
yields (up to 99%) could be obtained for the three kinds of hetero-
Michael addition reactions at room temperature. This process thus
represents a greener pathway for the hetero-Michael reactions.
Developing a new catalytic system for the reaction or applying the
catalytic system for new reactions are in progress in our laboratory.
Characterization of the products
Ethyl 3-oxocyclohexylcarbamate (2aa). 75.9 mg, 82% yield as
yellow liquid. IR: 3324, 2949, 2870, 1708, 1534, 1276, 1248, 1219,
1
1049, 780, 651. H NMR (400 MHz, CDCl3) d = 1.24 (t, J = 6.8
Hz, 3H), 1.67–1.77 (m, 2H), 1.99–2.03 (m, 1H), 2.08–2.18 (m, 1H),
2.27–2.40 (m, 3H), 2.27–2.40 (m, 1H), 2.70 (dd, J = 4.8, 14.0 Hz,
1H), 3.97 (s, 1H), 4.10 (t, J = 2.0 Hz, 2H), 5.09 (d, J = 7.2 Hz,
1H). 13C NMR (100 MHz, CDCl3) d = 14.6, 22.0, 31.2, 40.8, 48.0,
50.1, 60.8, 155.7, 209.0. HRMS-ESI: Calcd. For C9H15NNaO3:
208.0944. Found: 208.0936.
Experimental
General
NMR spectra were recorded on BRUKER DRX 400 spectrome-
ters. 1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were
Ethyl 4-oxopentan-2-ylcarbamate (2ba). 84.8 mg, 98% yield as
yellow liquid. IR: 3330, 2967, 2934, 1716, 1533, 1369, 1259, 1098,
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1073, 1018, 799. 1H NMR (400 MHz, CDCl3) d = 1.16 (t, J = 6.4
Hz, 6H), 2.09 (s, 3H), 2.53 (dd, J = 6.4, 16.8 Hz, 1H), 2.65 (dd,
J = 5.2, 16.8 Hz, 1H), 3.98–4.02 (m, 3H), 5.09 (s, 1H). 13C NMR
(100 MHz, CDCl3) d = 13.6, 19.6, 29.5, 42.6, 48.3, 59.6, 154.9,
206.6. HRMS-ESI: Calcd. For C8H15NNaO3: 196.0944. Found:
196.0949.
30.5, 47.5, 49.4, 110.2, 122.2, 122.8, 132.7, 141.2, 144.0, 204.8.
HRMS-ESI: Calcd. For C12H15N2O: 203.1179. Found: 203.1180.
4-(1H-Benzo[d][1,2,3]triazol-1-yl)pentan-2-one (2be). 93.4 mg,
92% yield as yellow liquid. IR: 2982, 2935, 1717, 1369, 1166, 749.
1H NMR (400 MHz, CDCl3) d = 1.66 (d, J = 7.2 Hz, 3H), 2.12 (s,
3H), 2.98 (dd, J = 7.2, 17.6 Hz, 1H), 3.16 (dd, J = 5.6, 18.0 Hz, 1H),
5.01–5.10 (m, 1H), 7.27–7.32 (m, 2H), 7.46 (d, J = 6.8 Hz, 1H),
7.81 (d, J = 6.4 Hz, 1H), 7.99 (s, 1H). 13C NMR (100 MHz, CDCl3)
d = 20.6, 30.5, 47.5, 49.4, 110.2, 122.2, 122.8, 132.7, 141.2, 144.0,
204.8. HRMS-ESI: Calcd. For C11H13N3NaO: 226.0951. Found:
226.0945.
Ethyl 3-oxopentylcarbamate (2ca). 75.5 mg, 95% yield as
yellow liquid. IR: 3551, 2980, 2940, 1710, 1530, 1376, 1254, 111,
1
1036, 779, 617. H NMR (400 MHz, CDCl3) d = 1.06 (t, J = 7.6
Hz, 3H), 1.22 (t, J = 7.2 Hz, 3H), 2.44 (q, J = 7.2, Hz, 2H), 2.66 (t,
J = 5.6 Hz, 2H), 3.41 (q, J = 5.6 Hz, 2H), 4.08 (q, J = 6.4 Hz, 2H),
5.21 (s, 1H). 13C NMR (100 MHz, CDCl3) d = 7.6, 14.5, 35.5, 36.1,
41.9, 60.6, 156.6, 210.8. HRMS-ESI: Calcd. For C8H15NNaO3:
196.0944. Found: 196.0944.
1-(2-Nitro-1-phenylethyl)-1H-benzo[1,2,3]triazole (2ke). 146.6
mg, 82% yield as light yellow solid. mp: 92–93 ◦C IR: 1559, 1376,
747, 705. 1H NMR (400 MHz, CDCl3) d = 5.15 (dd, J = 4.8, 14.8
Hz, 1H), 5.95 (q, J = 9.6 Hz, 1H), 6.58 (q, J = 4.8 Hz, 1H), 7.34–7.47
(m, 8H), 8.08 (d, J = 8.4 Hz, 1H). 13C NMR (100 MHz, CDCl3)
d = 59.8, 76.6, 109.3, 120.3, 124.6, 126.9, 128.0, 129.6, 129.8, 132.7,
134.0, 146.2. HRMS-ESI: Calcd. For C14H12N4NaO2: 291.0852.
Found: 291.0854.
Ethyl 4-oxohexan-2-yl carbamate (2da). 80.4 mg, 87% yield as
yellow liquid. IR: 3334, 2978, 2938, 1712, 1532, 1254, 1079, 1027,
1
832. H NMR (400 MHz, CDCl3) d = 0.97 (t, J = 7.2 Hz, 3H),
1.14–1.17 (m, 6H), 2.37 (q, J = 7.2 Hz, 2H), 2.51 (dd, J = 5.2, 16.4
Hz, 1H), 2.63 (dd, J = 4.8, 16.4 Hz, 1H), 3.96–4.01 (m, 3H), 5.16
(s, 1H). 13C NMR (100 MHz, CDCl3) d = 6.6, 13.6, 19.6, 35.5,
42.7, 59.6, 154.9, 209.3. HRMS-ESI: Calcd. For C9H17NNaO3:
210.1101. Found: 210.1093.
4-(5-Phenyl-2H-tetrazol-2-yl) pentan-2-one (2bf). 109.3 mg,
95% yield as light liquid. IR: 2987, 1720, 1465, 1450, 1363, 1026,
1
733, 694. H NMR (400 MHz, CDCl3) d = 1.59 (d, J = 6.8 Hz,
3H), 2.13 (s, 3H), 2.96 (dd, J = 6.4, 18.0 Hz, 1H), 3.38 (dd, J = 7.2,
18.0 Hz, 1H), 5.34–5.42 (m, 1H), 7.36–7.41 (m, 3H), 8.05 (dd, J =
2.0, 8.0 Hz, 2H). 13C NMR (100 MHz, CDCl3) d = 19.8, 29.3, 47.3,
54.9, 125.8, 126.4, 127.8, 129.2, 163.8, 203.1. HRMS-ESI: Calcd.
For C12H14N4NaO: 253.1060. Found: 253.1064.
Ethyl (1-methyl-3-oxo-3-phenylpropyl)carbamate (2ea). 65.8
mg, 56% yield as light yellow liquid. IR: 2977, 2925, 1741, 1680,
1425, 1256, 1057, 1030, 760, 694. 1H NMR (400 MHz, CDCl3) d =
1.23 (t, J = 7.2 Hz, 3H), 1.30 (d, J = 6.8 Hz, 3H), 3.06 (dd, J = 6.4,
16.8 Hz, 1H), 3.38 (d, J = 14.0 Hz, 1H), 4.10 (q, J = 7.2 Hz, 2H),
4.19–4.26 (m, 1H), 5.21 (s, 1H), 7.47 (t, J = 7.2 Hz, 2H), 7.58 (t, J =
7.6 Hz, 1H), 7.97 (d, J = 7.2 Hz, 2H). 13C NMR (100 MHz, CDCl3)
d = 14.6, 20.4, 44.2, 44.3, 60.7, 128.1, 128.7, 133.3, 136.9, 155.9,
198.8. HRMS-ESI: Calcd. For C13H17NNaO3: 258.1101. Found:
258.1105.
3-Phenylthiocyclohexan-1-one (3aa). 99.9 mg, 97% yield as
yellow liquid. IR: 2943, 2867, 1713, 1581, 1477, 1442, 1314, 1280,
1222, 1097, 1027, 972, 746, 695. 1H NMR (400 MHz, CDCl3) d =
1.67–1.79 (m, 2H), 2.11–2.18 (m, 2H), 2.30–2.41 (m, 3H), 2.68 (dd,
J = 4.4, 14.4 Hz, 1H), 3.39–3.46 (m, 1H), 7.28–7.34 (m, 3H), 7.42
(dd, J = 1.6, 7.2 Hz, 2H). 13C NMR (100 MHz, CDCl3) d = 24.0,
31.2, 40.8, 46.1, 47.7, 127.8, 129.0, 133.0, 133.2, 208.7. HRMS-
ESI: Calcd. For C12H14NaOS: 229.0658. Found: 229.0651.
4-(1H-Imidazol-1-yl)pentan-2-one (2bb). 49.4 mg, 65% yield
as yellow liquid. IR: 3115, 2960, 2929, 2857, 1719, 1500, 1457,
1
1413, 1370, 1285, 1077, 745, 665. H NMR (400 MHz, CDCl3)
d = 1.49 (d, J = 6.8 Hz, 3H), 2.09 (s, 3H), 2.80 (dd, J = 6.4, 17.6
Hz, 1H), 2.93 (dd, J = 6.8, 17.6 Hz, 1H), 4.70–4.79 (m, 1H), 6.93
(s, 1H), 7.03 (s, 1H), 7.53 (s, 1H). 13C NMR (100 MHz, CDCl3)
d = 21.7, 30.5, 48.7, 51.0, 116.6, 129.4, 135.8, 204.8. HRMS-ESI:
Calcd. For C8H13N2O: 153.1022. Found: 153.1022.
3-(4-Methylphenylthio) cyclohexan-1-one (3ab). 94.6 mg,
86% yield as yellow liquid. IR: 3021, 2940, 2865, 1713.
1491. 1449. 1421. 1342. 1313. 1280. 1220. 1096. 1023.
971. 810. 1H NMR (400 MHz, CDCl3)
d = 1.57–1.67
(m, 2H), 2.01–2.09 (m, 2H), 2.19–2.29 (m, 6H), 2.57 (dd,
J = 4.4, 14.0 Hz, 1H), 3.22–3.29 (m, 1H), 7.04 (d, J = 8.0 Hz,
2H), 7.05 (d, J = 8.0 Hz, 2H). 13C NMR (100 MHz, CDCl3) d =
20.1, 23.0, 30.2, 39.8, 45.4, 46.7, 128.1, 128.8, 132.9, 137.1, 207.8.
HRMS-ESI: Calcd. For C13H16NaOS: 243.0814. Found: 243.0809.
4-(1H-Pyrazol-1-yl)pentan-2-one (2bc). 57.8 mg, 76% yield as
1
yellow liquid. IR: 3203, 2982, 1716, 1399, 1366, 757. H NMR
(400 MHz, CDCl3): d 1.52 (d, J = 6.8 Hz, 3H), 2.07 (s, 3H), 2.81
(dd, J = 6.0 Hz, 17.2 Hz, 1H), 3.25 (dd, J = 7.2 Hz, 17.2 Hz, 1H),
4.88–4.80 (m, 1H), 6.20 (t, J = 2.4 Hz, 1H), 7.43 (d, J = 2.0 Hz,
1H), 7.53 (d, J = 1.6 Hz, 1H). 13C NMR (100 MHz, CDCl3): d
21.2, 30.5, 49.8, 53.2, 104.8, 139.3, 206.0. HRMS-ESI: Calcd. For
C8H13N2O: 153.1022. Found: 153.1023.
3-(o-Tolylthio)cyclohexanone (3ac). 102.3 mg, 93% yield as
yellow liquid. IR: 2942, 1713, 1588, 1464, 1451, 1219, 1178, 1062,
1
751, 601. H NMR (400 MHz, CDCl3) d = 1.69–1.82 (m, 2H),
2.11–2.17 (m, 2H), 2.32–2.40 (m, 3H), 2.43 (s, 3H), 2.68 (dd,
J = 4.4, 14.0 Hz, 1H), 3.39–3.45 (m, 1H), 7.14–7.23 (m, 3H), 7.39
(dd, J = 1.6, 7.2 Hz, 1H). 13C NMR (100 MHz, CDCl3) d = 20.9,
24.1, 31.3, 40.9, 45.6, 47.7, 126.5, 127.7, 130.5, 132.6, 133.2, 140.5,
208.7. HRMS-ESI: Calcd. For C13H16NaOS: 243.0814. Found:
243.0816.
4-(1H-Benzo[d]imidazol-1-yl)pentan-2-one (2bd). 79.8 mg,
79% yield as yellow liquid. IR: 3400, 3087, 2979, 7934, 1716, 1490,
1457, 1364, 1284, 1227, 1169, 1113, 1032, 773, 747. 1H NMR (400
MHz, CDCl3) d = 1.66 (d, J = 7.2 Hz, 3H), 2.12 (s, 3H), 2.98 (dd,
J = 7.2, 17.6 Hz, 1H), 3.16 (dd, J = 5.6, 18.0 Hz, 1H), 5.01–5.10
(m, 1H), 7.27–7.32 (m, 2H), 7.46 (d, J = 6.8 Hz, 1H), 7.81 (d, J =
6.4 Hz, 1H), 7.99 (s, 1H). 13C NMR (100 MHz, CDCl3) d = 20.6,
3-(4-Methoxyphenylthio)cyclohexanone (3ad). 108.6 mg, 92%
yield as white solid. mp: 47–48 ◦C. IR: 2942, 2938, 1709, 1592,
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1
1494, 1447, 1284, 1247, 1177, 1099, 1030, 832, 805, 640, 531. H
124.0, 127.3, 127.7, 128.4, 136.3, 141.2, 159.9, 205.7. HRMS-ESI:
Calcd. For C17H18NaO2S: 309.0920. Found: 309.0920.
NMR (400 MHz, CDCl3) d = 1.64–1.69 (m, 2H), 2.09–2.15 (m,
2H), 2,24–2.34 (m, 3H), 2.61 (dd, J = 4.4, 14.4 Hz, 1H), 3.19–3.25
(m, 1H), 3.78 (s, 3H), 6.84 (d, J = 8.8 Hz, 2H), 7.38 (d, J = 8.8
Hz, 2H). 13C NMR (100 MHz, CDCl3) d = 24.0, 31.1, 40.7, 46.9,
47.7, 55.2, 114.5, 122.8, 136.4, 159.9, 209.0. HRMS-ESI: Calcd.
For C13H16NaO2S: 259.0763. Found: 259.0768.
Methyl 3-(phenylthio)propanoate (3ha). 102.8 mg, 85% yield
as yellow liquid. IR: 2950, 1738, 1438, 1245, 743, 694. H NMR
1
(400 MHz, CDCl3) d = 3.14 (d, J = 6.4 Hz, 1H), 3.27 (dd, J =
5.6, 14.4 Hz, 1H), 3.39 (dd, J = 4.0, 14.0 Hz, 1H), 3.61 (s, 3H),
4.39–4.43 (m, 1H), 7.20–7.24 (m, 1H), 7.28–7.31 (m, 2H), 7.43 (d,
J = 7.2 Hz, 2H). 13C NMR (100 MHz, CDCl3) d = 39.1, 52.5, 69.3,
126.9, 129.0, 130.7, 134.8, 173.1. EI-MS (m/z): 191.27.
3-(4-Chlorophenylthio)cyclohexanone (3ae). 111.6 mg, 93%
yield as white solid. mp: 65–66 ◦C. IR: 2954, 2880, 826, 743.
1H NMR (400 MHz, CDCl3) d = 1.63–1.78 (m, 2H), 2.12–2.17
(m, 2H), 2.31–2.39 (m, 3H), 2.67 (dd, J = 4.4, 14.4 Hz, 1H),
3.37–3.44 (m, 1H), 7.29 (d, J = 8.4 Hz, 2H), 7.36 (d, J = 8.4
Hz, 2H). 13C NMR (100 MHz, CDCl3) d = 24.0, 31.1, 40.8, 46.4,
47.6, 129.3, 131.5, 134.1, 134.6, 208.4. HRMS-ESI: Calcd. For
C12H13ClNaOS: 263.0268. Found: 263.0264.
3-(Phenylthio)propanenitrile (3ja). 72.6 mg, 89% yield as yel-
1
low liquid. IR: 3057, 2932, 2250, 1581, 1478, 1436, 744, 694. H
NMR (400 MHz, CDCl3) d = 2.58 (t, J = 7.2 Hz, 2H), 3.12 (t, J
= 7.2 Hz, 2H), 7.28–7.36 (m, 3H), 7.42 (dd, J = 0.8, 8.8 Hz, 2H).
13C NMR (100 MHz, CDCl3) d = 18.1, 30.1, 117.9, 127.6, 129.3,
131.3, 133.1. EI-MS (m/z): 163.24.
3-(Naphthalen-2-ylthio)cyclohexanone (3af). 105.0 mg, 82%
yield as white solid. mp: 48 ◦C IR: 2934, 2859, 1713, 821, 748.
1H NMR (400 MHz, CDCl3) d = 1.64–1.81 (m, 2H), 2.08–2.20 (m,
2H), 2.24–2.44 (m, 3H), 2.69–2.74 (m, 1H), 3.49–3.56 (m, 1H),
7.44–7.50 (m, 3H), 7.75–7.81 (m, 3H), 7.89 (d, J = 0.8 Hz, 1H).
13C NMR (100 MHz, CDCl3) d = 30.3, 39.8, 45.1, 46.7, 125.4,
125.6, 126.4, 126.7, 127.6, 129.2, 129.4, 131.1, 131.5, 132.6, 207.6.
HRMS-ESI: Calcd. For C16H16NaOS: 279.0814. Found: 279.0814.
4-Methoxypentan-2-one (4ba). 49.3 mg, 85% yield as yellow
liquid. IR: 1637, 1369, 1236, 664. 1H NMR (400 MHz, CDCl3): d
1.15 (d, J = 6.4 Hz, 3H), 2.15 (s, 3H), 2.41 (dd, J = 5.6 Hz, 16.0
Hz, 1H), 2.70 (dd, J = 7.2 Hz, 16 Hz, 1H), 3.29 (s, 3H), 3.73–3.81
(m, 1H). 13C NMR (100 MHz, CDCl3): d 19.1, 30.9, 50.5, 56.2,
73.1, 207.4. EI-MS (m/z): 116.16.
4-Ethoxypentan-2-one (4bb). 49.4 mg, 76% yield as yellow
liquid. IR: 3587, 3004, 2967, 2929, 2252, 1712, 1422, 1092, 919,
735, 531. 1H NMR (400 MHz, CDCl3): d 1.12–1.15 (m, 6H), 2.15
(s, 3H), 3.34–3.41 (m, 1H), 3.49–3.57 (m, 1H), 3.29 (s, 3H), 3.82–
3.89 (m, 1H). 13C NMR (100 MHz, CDCl3): d 15.4, 19.9, 31.0,
50.7, 63.9, 71.5, 207.6 EI-MS (m/z): 130.18.
3-Benzylthio-cyclohexan-1-one (3ag). 75.9 mg, 69% yield as
yellow liquid. IR: 2941, 2867, 1711, 1454, 1421, 1315, 1282, 1223,
767, 704, 510. 1H NMR (400 MHz, CDCl3) d = 1.62–1.74 (m, 2H),
2.06–2.10 (m, 2H), 2.29–2.34 (m, 2H), 2.37 (t, J = 4.0 Hz, 1H),
2.66 (dd, J = 4.4, 14.4 Hz, 1H), 2.89–2.96 (m, 1H), 3.75 (d, J = 2.0
Hz, 1H), 7.22–7.25 (m, 1H), 7.30 (d, J = 4.4 Hz, 4H). 13C NMR
(100 MHz, CDCl3) d = 24.0, 31.2, 34.8, 40.8, 41.8, 47.7, 127.0,
128.5, 128.6, 137.8, 208.5. HRMS-ESI: Calcd. For C13H16NaOS:
243.0814. Found: 243.0806.
4-(2-Chloroethoxy)pentan-2-one (4bc). 50.0 mg, 61% yield as
1
yellow liquid. IR: 2970, 2930, 1715, 1372, 1136, 1111, 666. H
NMR (400 MHz, CDCl3) d = 1.15 (d, J = 6.0 Hz, 3H), 2.13 (s,
3H), 2.40 (dd, J = 5.2, 16.4 Hz, 1H), 2.71 (dd, J = 7.6, 16 Hz,
1H), 3.51–3.61 (m, 3H), 3.68–3.74 (m, 1H), 3.87–3.95 (m, 1H).
13C NMR (100 MHz, CDCl3) d = 19.7, 31.1, 43.1, 50.5, 68.9, 72.3,
207.2. HRMS-ESI: Calcd. For C7H13ClNaO2: 187.0496. Found:
187.0483.
3-(Hexylsulfanyl)cyclohexanone (3ah). 65.3 mg, 61% yield as
1
yellow liquid. IR: 2928. 2857, 1714, 1451, 1314, 1221. H NMR
(400 MHz, CDCl3) d = 0.84 (t, J = 6.8 Hz, 3H), 1.21–1.27 (m,
4H), 1.29–1.37 (m, 2H), 1.49–1.56 (m, 2H), 1.64–1.72 (m, 2H),
2.07–2.14 (m, 2H), 2.27–2.37 (m, 3H), 2.50 (t, J = 7.2 Hz, 2H),
2.66 (dd, J = 4.4, 14.0 Hz, 1H), 2.99–3.04 (m, 1H). 13C NMR (100
MHz, CDCl3) d = 13.9, 22.4, 24.2, 28.5, 29.6, 30.4, 31.3, 31.6, 40.9,
42.7, 48.1, 208.8. HRMS-ESI: Calcd. For C12H22NaOS: 237.1284.
Found: 237.1274.
4-Isopropoxypentan-2-one (4bd). 47.5 mg, 66% yield as yellow
liquid. IR: 2929, 1715, 1371, 1773. 1H NMR (400 MHz, CDCl3):
d 1.07–1.15 (m, 9H), 2.16 (s, 3H), 2.39 (dd, J = 5.6 Hz, 15.6 Hz,
1H), 2.68 (dd, J = 7.2 Hz, 15.2 Hz, 1H), 3.60–3.66 (m, 1H), 3.90–
3.98 (m, 1H). 13C NMR (100 MHz, CDCl3): d 20.9, 22.2, 23.2,
31.3, 51.2, 69.2, 69.4, 207.9. HRMS-ESI: Calcd. For C8H16NaO2:
167.1043. Found: 167.1045.
4-(4-Methoxyphenylthio) pentan-2-one (3bi). 110.9 mg, 91%
yield as light yellow liquid. IR: 2964, 17144, 1592, 1493, 1246,
1
1031, 830. H NMR (400 MHz, CDCl3) d = 1.24 (d, J = 6.8 Hz,
4-(Benzyloxy)pentan-2-one (4be). 57.6 mg, 60% yield as yellow
liquid. IR: 3451, 2971, 2929, 2872, 1715, 1453, 1371, 1092, 740,
699. 1H NMR (400 MHz, CDCl3) d = 1.22 (d, J = 6.0 Hz, 3H), 2.13
(s, 3H), 2.46 (dd, J = 5.6, 16.0 Hz, 1H), 2.77 (dd, J = 7.2, 16.0 Hz,
1H), 3.98–4.06 (m, 1H), 4.43 (d, 1H), 4.55 (d, 1H), 7.24–7.28 (m,
1H), 7.30–7.34 (m, 4H). 13C NMR (100 MHz, CDCl3) d = 19.8,
31.0, 50.8, 65.1, 70.8, 71.6, 127.7, 128.4, 138.5, 207.5. HRMS-ESI:
Calcd. For C12H16NaO2: 215.1043. Found: 215.1035.
3H), 2.12 (s, 3H), 2.51 (dd, J = 8.4, 16.8 Hz, 1H), 2.71 (dd, J
= 5.2, 17.2 Hz, 1H), 3.46–3.55 (m, 1H), 3.80 (m, 3H), 6.85 (d,
J = 8.4 Hz, 2H), 7.39 (d, J = 8.8 Hz, 2H). 13C NMR (100 MHz,
CDCl3) d = 21.0, 30.5, 39.4, 50.4, 55.3, 114.5, 124.0, 136.0, 159.7,
206.7 HRMS-ESI: Calcd. For C12H16NaO2S: 247.0763. Found:
247.0756.
4-(4-Methoxyphenylthio)-4-phenylbutan-2-one
(3gi). 111.5
mg, 78% yield as white solid. mp: 76 ◦C. IR: 3409, 2961, 1711,
1591, 1472, 1287, 1271, 1175, 1027, 829, 699. 1H NMR (400 MHz,
CDCl3) d = 2.07 (s, 3H), 3.03 (dd, J = 2.0, 7.6 Hz, 2H), 3.77 (s,
3H), 4.53 (t, J = 7.6 Hz, 1H), 6.76 (d, J = 8.8 Hz, 2H), 7.17–7.25
(m, 7H). 13C NMR (100 MHz, CDCl3) d = 30.7, 49.1, 55.3, 114.3,
3-Methoxy-1-phenylbutan-1-one (4ea). 69.4 mg, 78% yield as
white solid. mp: 120–121 ◦C. IR: 1370, 1300, 1217, 1187, 1356,
1093, 998, 755, 693. 1H NMR (400 MHz, CDCl3) d = 1.26
(d, J = 6.4 Hz, 3H), 2.92 (dd, J = 6.0, 16.4 Hz, 1H), 3.34 (s,
3H), 3.34(dd, J = 6.8, 16.4 Hz, 1H), 3.96–4.04 (m, 1H), 7.46 (t,
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J = 7.6 Hz, 2H), 7.56 (t, J = 7.6 Hz, 1H), 7.97 (d, J = 7.2 Hz, 2H).
13C NMR (100 MHz, CDCl3) d = 19.5, 45.4, 56.4, 73.5, 128.1,
128.5, 133.0, 137.2, 198.6. HRMS-ESI: Calcd. For C11H14NaO2:
201.0886. Found: 201.0888.
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Chim. Acta, 2007, 90, 425; (f) M. Meciarova, M. Cigan and S. Toma,
Eur. J. Org. Chem., 2008, 4408; (g) R. R. Schmidt and Y. D. Vankar,
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Song, Synthesis, 2010, 2935.
3-Methoxy-1-phenylpyrrolidine-2,5-dione (4fa). 66.6 mg, 65%
yield as white solid. mp: 80–81 ◦C. IR: 3287, 3135, 3054, 1730,
1668, 1631, 1560, 1546, 1441, 1320, 1172, 756, 693. 1H NMR (400
MHz, CDCl3): d 3.95 (s, 3H), 6.22 (d, J = 13.2 Hz, 1H), 6.44 (d,
J = 13.6 Hz, 1H), 7.13 (t, J = 7.6 Hz, 1H), 7.34 (t, J = 8.4 Hz,
2H), 7.67 (d, J = 7.6 Hz, 2H), 10.83 (s, 1H). 13C NMR (100 MHz,
CDCl3): d 52.8, 120.1, 124.6, 124.9, 129.0, 137.8, 140.3, 161.4,
167.2. HRMS-ESI: Calcd. For C11H11NNaO3: 228.0631. Found:
228.0637.
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7 T. C. Wabnitz and J. B. Spencer, Org. Lett., 2003, 5, 2141.
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45, 4507.
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Org. Chem., 2007, 374.
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5195.
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3279.
Acknowledgements
We gratefully acknowledge the National Key Basic Research
Project of China (2011CB201404) for financial support.
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