Facile synthesis of tetrahydroimidazolpyridinones via an MCR involving 6-Cl-PMNI, aldehydes, and meldrum's acid

Article abstract of DOI:10.1080/00397911003797791

Tetrahydroimidazolpyridinones 2, which are new, highly bioactive potential insecticides, were prepared in 30-96% yield through a multicomponent reaction (MCR) of 6-Cl-PMNI, aldehydes, and Meldrum's acid using catalytic Et ₃N or K₂CO<

Full text of DOI:10.1080/00397911003797791

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Facile Synthesis of
Tetrahydroimidazolpyridinones via an
MCR Involving 6-Cl-PMNI, Aldehydes, and
Meldrum's Acid
Bin Hu a , Yi-Yue Zhou a , Wenting Du a , Xiaoyong Xu a , Zhong Li a &
Wei-Ping Deng a b
a School of Pharmacy, East China University of Science and
Technology , Shanghai , China
b Department of Pharmacy , Zhejiang Medical College , Hangzhou ,
China
Published online: 21 Mar 2011.
To cite this article: Bin Hu , Yi-Yue Zhou , Wenting Du , Xiaoyong Xu , Zhong Li & Wei-Ping Deng
(2011) Facile Synthesis of Tetrahydroimidazolpyridinones via an MCR Involving 6-Cl-PMNI, Aldehydes,
and Meldrum's Acid, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 41:8, 1112-1118, DOI: 10.1080/00397911003797791
To link to this article: http://dx.doi.org/10.1080/00397911003797791
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Synthetic Communications1, 41: 1112–1118, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911003797791
FACILE SYNTHESIS OF
TETRAHYDROIMIDAZOLPYRIDINONES VIA AN MCR
INVOLVING 6-Cl-PMNI, ALDEHYDES, AND
MELDRUM’S ACID
Bin Hu,1 Yi-Yue Zhou,1 Wenting Du,1 Xiaoyong Xu,1
Zhong Li,1 and Wei-Ping Deng1,2
1School of Pharmacy, East China University of Science and Technology,
Shanghai, China
2Department of Pharmacy, Zhejiang Medical College, Hangzhou, China
GRAPHICAL ABSTRACT
Abstract Tetrahydroimidazolpyridinones 2, which are new, highly bioactive potential insec-
ticides, were prepared in 30–96% yield through a multicomponent reaction (MCR) of
6-Cl-PMNI, aldehydes, and Meldrum’s acid using catalytic Et3N or K2CO3 in anhydrous
CH3CN at refluxing temperature.
Keywords 6-Cl-PMNI; insecticide; Meldrum’s acid; multicomponent reaction; tetrahy-
droimidazolpyridinone
INTRODUCTION
Nitromethylene neonicotinoids 1 (Fig. 1) were recently found in our laboratory
to be potential new insecticides possessing greater activity against imidacloprid-
resistant brown planthopper than imidacloprid.[1] Its synthesis proceeded through
Michael addition of b-nitroketeneaminal (6-Cl-PMNI) 3 to a,b-unsaturated
aldehydes and subsequent ring closure.[1,2] However, this reaction suffers from
relatively poor yield, low reactivities to cinnamic aldehyde and its analogs, and
limited availability of corresponding a,b-unsaturated aldehydes. On the other
hand, because of the chemical instability of 1 arising from the dehydration of the
2-hydroxyl group, we envisaged that a more stable tetrahydroimidazolpyridinone 2
might be a potential skeleton as a potent insecticide. It has been reported[3] that
tetrahydroimidazolpyridinones can be prepared through Michael addition of
Received December 13, 2009.
Address correspondence to Wenting Du, School of Pharmacy, East China University of Science
and Technology, 130 Meilong Road, Shanghai 200237, China. E-mail: duwt@ecust.edu.cn
1112

TETRAHYDROIMIDAZOLPYRIDINONES
1113
Figure 1. The structures of neonicotinoids 1, tetrahydroimidazolpyridinone 2, and b-nitroketeneaminal 3.
2-(nitromethylene)imidazolidine with ethyl acrylate and subsequent ring closure.
However, the reaction of N-methyl-2-(nitromethylene)imidazolidine with methyl
acrylate provided the corresponding product in 32% yield,[4] and notably no other
b-substituted a,b-unsaturated substrates were reported to perform this reaction,
probably because of the low reactivity of both N-substituted 2-(nitromethylene)imi-
dazolidine and b-substituted a,b-unsaturated carboxylate. As a matter of fact, the
reaction of 3 with methyl cinnamate (or crotonate) turned out to give only a trace
amount of the desired products under the same reaction condition.[5] Therefore, to
further develop our newly discovered insecticide and its analogs, a versatile and
efficient synthetic protocol was highly demanded.
Recently, Yu and coworkers[6] reported a Meldrum’s acid–involved one-pot
reaction of heterocyclic ketene aminals (HKAs) and aldehydes that smoothly pro-
vided a similar imidazolpyridinone skeleton, presumably via an aza-ene pathway.
It is noted that, in this case, N-unprotected HKAs with a,b-unsaturated ketone or
ester were used, which are normally more reactive than N-protected HKAs, such
as the 6-Cl-PMNI used in our case. However, it was still believed that the more
reactive alkylidene Meldrum’s acids generated in situ facilitate the Michael addition
to the N-protected HKAs. Therefore, we describe herein our preliminary results
on the synthesis of 2 by a multicomponent reaction (MCR) of Meldrum’s acid,
aldehydes, and 3.
RESULTS AND DISCUSSION
For nitromethylene neonicotinoids 1, insecticidal activity was found to be opti-
mal when R is methyl group. Therefore, we initially employed acetaldehyde as sub-
strate to test the MCR. Unfortunately, no desired product was found under the
optimal reaction condition reported by Yu et al. We then turned our attention to
using aromatic aldehyde to test our idea. A series of aromatic aldehydes were thus
employed for this reaction using catalytic (0.1 equiv.) triethylamine in anhydrous
acetonitrile at refluxing temperature, and the results are summarized in Table 1. It
is encouraging that (hetero) aromatic aldehydes with both electron-withdrawing
and electron-donating groups proceeded smoothly and resulted in good to excellent
yields without apparent difference (entries 1–11). Substrate salicylaldehyde 4h with
an unprotected OH group also gave corresponding product 2h in 78% yield (entry
8). With such a positive result with aromatic aldehyde, we came back to solving
the problem with aliphatic aldehydes. According to the mechanism proposed by
Yu et al., the key intermediate would be enzylidene–Meldrum’s acid, and the role

1114
B. HU ET AL.
Table 1. Three-component reaction of various aldehydes, Meldrum’s acid, and 3
Entry
Aldehyde
R
Product
Base (amount)
Reaction time (h)
Yield (%)a
1
2
4a
4b
4c
4d
4e
4f
Ph
4-BrPh
2a
2b
2c
Et3N (0.1 eq)
Et3N (0.1 eq)
Et3N (0.1 eq)
Et3N (0.1 eq)
Et3N (0.1 eq)
Et3N (0.1 eq)
Et3N (0.1 eq)
Et3N (0.1 eq)
Et3N (0.1 eq)
Et3N (0.1 eq)
Et3N (0.1 eq)
Et3N (0.1 eq)
Et3N (1 eq)
12
12
12
12
12
12
12
12
12
12
12
12
24
24
24
24
24
24
89
85
3
4-NO2Ph
2-NO2Ph
2-MePh
4-MeOPh
3,4-CH2O2Ph
2-OHPh
3-Indole
2-Furan
2-thiophene
Ethyl
90
91
4
2d
2e
5
96
90
6
2f
7
4g
4h
4i
2g
2h
2ib
2jb
2k
2lb
2lb
2lb
2lb
2m
2m
2n
94
78
8
9
85
79
10
11
12
13
14
15
16
17
18
4j
4k
4l
72
Trace
Trace
16
4l
Ethyl
Ethyl
Ethyl
4l
Et3N (2 eq)
K2CO3 (2 eq)
Et3N (2 eq)
4l
53
15
4m
4m
4n
BnOCH2
BnOCH2
Me
K2CO3 (2 eq)
K2CO3 (2 eq)
30
31
aYield of isolated and purified products.
bShowing high insecticidal activities against pea aphids.[5]
of base is to form the key intermediate. Therefore, a base screening was carried out
to find the proper reaction condition for aliphatic aldehydes. It is interesting that
16% yield of corresponding product 4l was obtained, when the amount of triethyla-
mine was increased to 2 equiv. (entries 12–14). To our amazement, further optimiza-
tion of various bases showed that 2 equiv. of K2CO3 was the optimal condition and
gave corresponding products in moderate yields (entries 15, 17, and 18, up to 53%).
On the other hand, the reaction of preprepared benzylidene–Meldrum’s acid with 3
under the same reaction condition resulted in comparable yield (90%), as expected,
which further provided experimental evidence for the aza–ene mechanism.[6]
CONCLUSIONS
In summary, we have developed a facile synthesis of tetrahydroimidazolpyri-
dinones 2 in 30–94% yields through an MCR of 6-Cl-PMNI, aldehydes, and
Meldrum’s acid using catalytic Et3N or K2CO3 in anhydrous CH3CN at refluxing
temperature. Taking account of the high efficiency of this MCR and the ready avail-
ability of various aldehydes, we believe that our synthetic protocol would be of great

TETRAHYDROIMIDAZOLPYRIDINONES
1115
help in synthesizing a library of tetrahydroimidazolpyridinones with various substi-
tuents to seek out new potent insecticides. Further work is currently ongoing in our
laboratory to extend the synthetic application of this new method and to test the
insecticidal activities against insects, especially the resistant strains.
EXPERIMENTAL
All solvents were distilled under standard procedures prior to use under a
nitrogen atmosphere. (For example, CH3CN was distilled from CaH2). 1H
1
(400 MHz) chemical shifts are reported in CDCl3 7.27 ppm for H, and standards
and coupling constants (J) are reported in hertz (Hz). The following abbreviations
are used to designate signal multiplicity: s, singlet; d, doublet; t, triplet; q, quartet;
m, multiplet; and br, broad.
General Procedure for the MCR of Various Aldehydes, Meldrum’s
Acid, and 6-Cl-PMNI 3
Compound 3 was prepared according to previously reported procedures.[2,7]
Compound 3 (0.39 mmol), Meldrum’s acid (0.47 mmol), and aldehyde 4 (0.47 mmol)
were added to anhydrous acetonitrile (1 mL) respectively with Et3N (0.1 eq) or
K2CO3 (2 eq) as a catalyst under the nitrogen atmosphere. After stirring under reflux
for 12 or 24 h, the reaction mixture was concentrated in vacuo, and the residue was
purified via column chromatography (EtOAc–petroleum ether).
All products gave satisfactory analytical data.
Representative Data
All products gave satisfactory analytical data.
Characterization data of product 2a (entry 1, R ¼ Ph). Mp 219–220 ꢀC. IR
(KBr): 3440.38, 1701.39, 1590.15, 1392.21, 1319.92, 1273.09, 1216.87 cmꢁ1. 1H NMR
(400 MHz, CDCl3): d ¼ 8.27 (d, J ¼ 2.4 Hz, 1H), 7.49 (dd, J ¼ 2.4, 8.0 Hz, 1H),
7.27–7.26 (m, 3H), 7.18 (d, J ¼ 8.0 Hz, 1H), 7.11–7.09 (m, 2H), 4.90–4.81 (m, 3H),
4.15–4.09 (m, 1H), 3.96–3.79 (m, 2H), 3.73–3.67 (m, 1H), 3.06 (d, J ¼ 4.4 Hz, 2H);
13C NMR (100 MHz, CDCl3): d ¼ 167.62, 151.72, 151.53, 149.11, 140.98, 138.61,
129.32, 128.95, 127.37, 125.95, 124.69, 110.23, 51.90, 50.14, 41.12, 38.36, 37.33.
HRMS (EI): m=z [Mþ] calcd. for C19H17ClN4O3: 384.0989; found: 384.0990.
Characterization data of product 2b (entry 2, R ¼ 4-BrPh). Mp
1
108–111 ꢀC. H NMR (400 MHz, CDCl3): d 8.27 (s, 1H), 7.51 (d, J ¼ 8.4 Hz, 1H),
7.37 (d, J ¼ 8.4 Hz, 2H), 7.21 (d, J ¼ 8.4 Hz, 1H), 6.95 (d, J ¼ 8.4 Hz, 2H),
4.88–4.79 (m, 3H), 4.12–4.08 (m, 1H), 3.95–3.84 (m, 2H), 3.76–3.73 (m, 1H), 3.04
(m, 2H).
Characterization data of product 2c (entry 3, R ¼ 4-NO2Ph). Mp
1
233–237 ꢀC. H NMR (400 MHz, DMSO-d6): d 8.30 (d, J ¼ 1.6 Hz, 1H), 8.07 (d,
J ¼ 8.8 Hz, 2H), 7.74 (dd, J ¼ 2.8, 2.4 Hz, 1H), 7.40 (d, J ¼ 8.4 Hz, 1H), 7.21

1116
B. HU ET AL.
(d, J ¼ 8.4 Hz, 2H), 4.90 (s, 2H), 4.74 (d, J ¼ 6.8 Hz, 1H), 4.05–3.86 (m, 4H), 3.25 (dd,
J ¼ 8.0, 7.2 Hz, 1H), 2.80 (d, J ¼ 17.2 Hz, 1H).
Characterization data of product 2d (entry 4, R ¼ 2-NO2Ph). Mp
1
107–109 ꢀC. H NMR (400 MHz, CDCl3): d 8.39 (s, 1H), 7.91 (s, 1H), 7.68 (d,
J ¼ 7.2 Hz, 1H), 7.41 (s, 2H), 7.28 (d, J ¼ 6.0 Hz, 1H), 6.81 (s, 1H), 5.27 (d,
J ¼ 8.8 Hz, 1H), 4.90 (dd, J ¼ 15.6 Hz, 2H), 4.14–3.89 (m, 4H), 3.24 (dd, J ¼ 9.2,
8.8 Hz, 1H), 2.93 (d, J ¼ 17.6 Hz, 1H).
Characterization data of product 2e (entry 5, R ¼ 2-MePh). Mp
1
122–125 ꢀC. H NMR (400 MHz, CDCl3): d 8.32 (s, 1H), 7.60 (s, 1H), 7.19–6.90
(m, 4H), 6.42 (s, 1H), 4.80 (s, br, 3H), 4.03–3.72 (m, 4H), 2.98 (d, J ¼ 6.4 Hz, 1H),
2.61 (d, J ¼ 16.3 Hz, 1H), 2.34 (s, 3H).
Characterization data of product 2f (entry 6, R ¼ 4-MeOPh). Mp
1
164–166 ꢀC. IR (KBr): 3440.38, 1704.76, 1596.77, 1292.07, 1224.58 cmꢁ1. H NMR
(400 MHz, CDCl3): d ¼ 8.27 (s, 1H), 7.50 (d, J ¼ 8.0 Hz, 1H), 7.19 (d, J ¼ 8.4 Hz,
1H), 6.97 (d, J ¼ 8.4 Hz, 2H), 6.78 (d, J ¼ 8.8 Hz, 2H), 4.89–4.80 (m, 3H),
4.13–4.07 (m, 1H), 3.96–3.81 (m, 2H), 3.79 (s, 3H), 3.74–3.69 (m, 1H), 3.01 (s,
2H); 13C NMR (100 MHz, CDCl3): d ¼ 167.68, 158.74, 151.55, 151.48, 149.16,
138.64, 132.98, 129.51, 127.03, 124.60, 114.23, 110.50, 55.28, 51.85, 50.33, 41.14,
37.73, 37.56. HRMS (EI): m=z [Mþ] calcd. for C20H19ClN4O4: 414.1095; found:
414.1097.
Characterization data of product 2g (entry 7, R ¼ 3,4-CH2O2Ph). Mp
1
218–221 ꢀC. H NMR (400 MHz, CDCl3): d 8.32 (s, 1H), 7.78 (d, J ¼ 6.4 Hz, 1H),
7.44 (d, J ¼ 7.2 Hz, 1H), 6.68 (d, J ¼ 6.8 Hz, 1H), 6.57 (s, 1H), 6.30 (d, J ¼ 6.80 Hz,
1H), 5.96 (s, 2H), 4.89 (s, 2H), 4.52 (d, J ¼ 4.4 Hz, 1H), 3.94–3.82 (m, 4H), 3.11
(dd, J ¼ 5.6 Hz, 1H), 2.71 (d, J ¼ 16.4 Hz, 1H).
Characterization data of product 2h (entry 8, R ¼ 2-OHPh). Mp
1
239–240 ꢀC. H NMR (400 MHz, DMSO-d6): d 9.69 (s, 1H), 8.39 (s, 1H), 7.84 (d,
J ¼ 8.0 Hz, 1H), 7.49 (dd, J ¼ 8.4 Hz, 1H), 7.01 (t, J ¼ 7.2 Hz, 1H), 6.77 (d,
J ¼ 7.6 Hz, 1H), 6.52 (t, J ¼ 7.2 Hz, 1H), 6.30 (d, J ¼ 7.2 Hz, 1H), 4.94 (s, 2H), 4.71
(d, J ¼ 7.6 Hz, 1H), 4.03–3.75 (m, 4H), 3.08 (dd, J ¼ 7.6, 8.0 Hz, 1H), 2.61 (d,
J ¼ 16.4 Hz, 1H).
Characterization data of product 2i (entry 9, R ¼ 3-Indole). Mp
206–211 ꢀC. IR (KBr): 3417.24, 1693.19, 1602.56, 1398.14, 1284.36, 1216.86 cmꢁ1
.
1H NMR (100 MHz, DMSO-d6): d ¼ 10.86 (s, 1H), 8.37 (s, 1H), 7.67 (dd, J ¼ 2.0 Hz,
8.0 Hz, 1H), 7.57 (d, J ¼ 8.0 Hz; 1H), 7.35 (d, J ¼ 8.0 Hz, 1H), 7.26 (d, J ¼ 8.4 Hz,
1H), 7.09 (t, J ¼ 7.6 Hz, 1H), 6.97 (t, J ¼ 7.6 Hz, 1H), 6.83 (s, 1H), 4.98–4.80 (m,
3H), 3.98–3.75 (m, 4H), 3.16 (dd, J ¼ 6.4 Hz, 1H), 2.90–2.86 (m, 1H); 13C NMR
(100 MHz; DMSO-d6): d ¼ 168.59, 153.21, 149.86, 149.66, 139.46, 137.19, 131.40,
126.24, 124.27, 121.82, 121.57, 119.14, 119.08, 115.33, 112.01, 108.95, 51.82, 50.50,
41.71, 38.29, 32.03. HRMS (EI): m=z [Mþ] calcd. for C21H18ClN5O3: 423.1098;
found: 423.1105.
Characterization data of product 2j (entry 10, R ¼ 2-Furan). Mp
1
86–90 ꢀC. H NMR (400 MHz, CDCl3): d 8.28 (s, 1H), 7.53 (d, J ¼ 8.4 Hz, 1H),

TETRAHYDROIMIDAZOLPYRIDINONES
1117
7.27–7.24 (m, 1H), 6.28 (s, 1H), 6.57 (s, 1H), 6.03 (d, J ¼ 2.8 Hz, 1H), 4.92–4.89 (m,
2H), 4.81 (d, J ¼ 15.6 Hz, 1H), 4.13–4.08 (m, 1H), 3.92–3.84 (m, 2H), 3.72–3.69 (m,
1H), 2.99 (d, J ¼ 3.2 Hz, 2H).
Characterization data of product 2k (entry 11, R ¼ 2-Thiophene). Mp
86–88 ꢀC. 1H NMR (400 MHz, CDCl3): d 8.28 (d, J ¼ 1.6 Hz, 1H), 7.53 (d,
J ¼ 2.0 Hz, 1H), 7.23 (d, J ¼ 8.0 Hz, 1H), 7.16 (d, J ¼ 5.2 Hz, 1H), 6.91 (t, J ¼ 3.6,
5.2 Hz, 1H), 6.78 (d, J ¼ 3.2 Hz, 1H), 5.08 (t, J ¼ 4.8, 3.2 Hz, 1H), 4.84 (s, 2H),
4.11 (m, 1H), 3.90–3.83 (m, 2H), 3.66–3.65 (m, 1H), 3.08 (d, J ¼ 5.6 Hz, 2H).
Characterization data of product 2 l (entry 12, R ¼ Ethyl). Mp
1
132–135 ꢀC. H NMR (400 MHz, CDCl3): d 8.33 (s, 1H), 7.73 (d, J ¼ 8.4 Hz, 1H),
7.34 (d, J ¼ 8.4 Hz, 1H), 4.89 (dd, J ¼ 15.2, 15.6 Hz, 2H), 4.10–4.06 (m, 1H),
3.94–3.84 (m, 2H), 3.75–3.72 (m, 1H), 3.47 (dd, J ¼ 6.0, 6.8 Hz, 1H), 2.76 (dd,
J ¼ 6.4, 6.8 Hz, 1H), 2.63 (d, J ¼ 17.2 Hz, 1H), 1.47–1.36 (m, 2H), 0.84 (t, J ¼ 7.2 Hz,
3H).
Characterization data of product 2 m (entry 16, R ¼ BnOCH2). Mp
1
53–55 ꢀC. H NMR (400 MHz, CDCl3): d 8.21 (s, 1H), 7.52 (dd, J ¼ 2.4 Hz, 1H),
7.37–7.27 (m, 5H), 7.13 (d, J ¼ 8.0 Hz, 1H), 4.77 (dd, J ¼ 15.6 Hz, 2H), 4.41 (dd,
J ¼ 11.2 Hz, 2H), 3.93 (m, 1H), 3.80–3.75 (m, 2H), 3.61–3.57 (m, 2H), 3.47–3.44
(m, 2H), 2.86–2.84 (m, 1H), 2.72 (d, J ¼ 17.2 Hz, 1H).
Characterization data of product 2n (entry 19, R ¼ Methyl). Mp
204–207 ꢀC. IR (KBr): 3436.53, 1706.69, 1585.20, 1396.21, 1309.43, 1197.58,
1
1141.65 cmꢁ1. H NMR (100 MHz, CDCl3): d ¼ 8.33 (d, J ¼ 2.4 Hz, 1H), 7.72 (dd,
J ¼ 2.4, 8.4 Hz, 1H), 7.35 (d, J ¼ 8.0 Hz, 1H), 4.89 (d, J ¼ 15.6 Hz, 1H), 4.78 (d,
J ¼ 15.6 Hz, 1H), 4.16–4.05 (m, 1H), 3.94–3.82 (m, 2H), 3.73–3.64 (m, 2H), 2.81
(dd, J ¼ 6.8, 17.2 Hz, 1H), 2.53 (dd, J ¼ 1.6, 17.2 Hz, 1H), 1.12 (d, J ¼ 7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3): d ¼ 167.79, 151.61, 150.48, 149.00, 138.77, 129.68,
124.62, 111.58, 52.03, 50.08, 41.10, 38.50, 29.31, 19.19. HRMS (EI): m=z [Mþ] calcd.
for C14H15ClN4O3: 322.0833; found: 322.0836.
ACKNOWLEDGMENTS
This work was financially supported by the Shanghai Committee of Science
and Technology (No. 064319022), the New Century Excellent Talents in University,
the Ministry of Education, China (No. NCET-07-0283), the Natural Science Foun-
dation of China (No. NSFC 20602011), and the ‘‘111’’ Project (No. B07023).
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