One-pot microwave-assisted synthesis of novel substituted N-dichloroacetyl-4,5-dimethyl-1,3-oxazolidines

Article abstract of DOI:10.1002/jhet.951

A one-pot and efficient synthesis of substituted N-dichloroacetyl-4,5- dimethyl-1,3-oxazolidines utilizing the reaction of alkamine with aldehyde or ketone in refluxing benzene under microwave irradiation was described. The N-acylation was followed with dichloroacetyl chloride and NaOH acting as the attaching acid agent. All compounds were characterized by IR, ¹H NMR, ¹³C NMR, and element analysis. Additionally, the absolute configuration of 4a was determined by X-ray crystallography. All the compounds were tested for their herbicide safeners activity of protecting the maize from the injury of acetochlor.

Full text of DOI:10.1002/jhet.951

September 2012
One-Pot Microwave-Assisted Synthesis of Novel Substituted
1235
N-Dichloroacetyl-4,5-dimethyl-1,3-oxazolidines
*
Ying Fu, Lei Yang, Fei Ye, and Shuang Gao
Department of Applied Chemistry, College of Science, Northeast Agricultural University,
Harbin, 150030, Heilongjiang, P.R. China
*
E-mail: yefei@neau.edu.cn
Received January 26, 2011
DOI 10.1002/jhet.951
Published online 26 October 2012 in Wiley Online Library (wileyonlinelibrary.com).
A one-pot and efficient synthesis of substituted N-dichloroacetyl-4,5-dimethyl-1,3-oxazolidines utilizing
the reaction of alkamine with aldehyde or ketone in refluxing benzene under microwave irradiation was de-
scribed. The N-acylation was followed with dichloroacetyl chloride and NaOH acting as the attaching acid
1
agent. All compounds were characterized by IR, H NMR, 13C NMR, and element analysis. Additionally,
the absolute configuration of 4a was determined by X-ray crystallography. All the compounds were tested
for their herbicide safeners activity of protecting the maize from the injury of acetochlor.
J. Heterocyclic Chem., 49, 1235 (2012).
INTRODUCTION
for the synthesis of oxazolidines have been modified under
microwave irradiation [21,22]. However, these techniques
all had their own inherent disadvantages, for example, the
employment of expensive catalyst in the case of catalytic
treatment. In continuation of our interest for the synthesis
of N-dichloroacetyl oxazolidines [23–25], we reported
herein the synthesis of oxazolidines with different substitu-
ents via two components synthesis by using microwave
technique (Scheme 1). The structures of compounds were
listed in Table 1.
Since the first study on the use of microwave irradiation
in organic chemistry, the accelerated process has been a
lure for chemists to further apply this technology to new
reactions. Microwave-assisted reactions have received
great interest because of their simplicity in operation,
enhanced reaction rates, products with high purity, and
better yields compared to those conducted by conventional
heating [1,2]. Therefore, microwave-assisted synthesis has
been used as an effective and powerful technique to
promote a lot of chemical reactions [3–6].
Oxazolidine derivatives are important target com-
pounds with their biological activities, pharmacological
activity and their extensive use as chiral auxiliaries for
synthesis of many chiral compounds [7–12]. In addition,
N-dichloroacetyl oxazolidines have been used as herbicide
safeners in recent years [13]. The literature survey reveals
that N-dichloroacetyl compounds acted as herbicide safener
by increasing the activities of glutathione-S-transferase
(GST) and some herbicidal target enzymes have drawn
widespread attention in agricultural biochemistry [14,15].
The synthesis of oxazolidine derivatives has received much
attention from organic chemists. Oxazolidines were usually
prepared from β-hydroxy amines by a [4+1] ring synthesis
[16,17], and a few examples were reported from the [3+2]
cycloaddition of azomethine ylides and carbonyl
compounds (mostly benzaldehyde) [18,19], and in other
ways [20]. There has been extensive effort to adopt green
technologies in synthetic organic chemistry, so as to mini-
mize waste production, material and energy consumption,
and the use of hazardous compounds. Several methods
RESULTS AND DISCUSSION
The synthesis of oxazolidines under conventional heat-
ing technique required prolonged reaction time and
afforded moderate yields of products. Conducting a two-
component synthesis of these target molecules under
microwave irradiation, to the best of our knowledge, has
never been published before. To establish the general
validity of our newly developed method, several microwave-
assisted syntheses were carried out by changing irradiating
time and microwave power. This method appeared to
be rapid and economical, with a wide range of applications.
A mixture of 3-amino-2-butanol 1 and aldehyde or ketone
2 in benzene was stirred for 15min under room tempera-
ture, then refluxed to remove water irritated by MW
800W for 20 min at 80°C, the corresponding oxazolidine
derivatives 3 were obtained. The reaction was found to
proceed smoothly under microwave irradiation. For the
condensation was reversible, water should be removed from
© 2012 HeteroCorporation

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Y. Fu, L. Yang, F. Ye, and S. Gao
Vol 49
Scheme 1
the mixture. The microwave power was 800W to increase
the temperature fast, and the microwave irradiation was
20min to remove all water. Then the mixture was time
cooled and dichloroacetyl chloride was added dropwise
with NaOH aq. acted as the attaching acid agent.
To examine the aldehyde or ketone substrate effect on
the rate and overall yields, seven aldehydes and ketones
were used under the aforementioned reaction conditions.
Under the alkaline condition, oxazolidine easily transferred
to the imine especially for the substitute was H at the
second position. The steric hindrance effect also hindered
the acylation of dichloroacetyl chloride with 3. The yields
of 4c, 4f, and 4g were lower than other compounds
(Table 1).
The molecular structure of 4a was also confirmed by
X-ray crystallography. Single crystals of 4a were obtained
by dissolving it in the solvent of ethyl acetate and light
petroleum, followed by slow evaporation at ambient
temperature. A structural view with atom-numbering
scheme is shown in Figure 1 and selected bond lengths
and bond angles are listed in Table 2.
one-dimensional chains (Fig. 2), which stabilized the
crystal structure.
The safener activity of the newly synthesized oxazolidine
derivatives was carried out by protecting the maize from the
injury of acetochlor. The results of the safener activity were
showed in Table 3. The recovery rates of the growth levels
could be attained over 50% with 25 mg/kg of the 4a–g
when the concentration of acetochlor in the soil was
20 mg/kg. Among the compounds tested, 4f showed the
best activity against the injury of acetochlor.
In conclusion, this method provided an excellent approach
for the safe, rapid, inexpensive, and simple synthesis of
substituted N-dichloroacetyl-4,5-dimethyl-1,3-oxazolidines
containing alkyl and phenyl at position 2 in one-pot reaction
under microwave irradiation. The compound 3 was a valuable
synthon for the preparation of a variety of heterocycle-fused
oxazolidines. The biological evaluation showed that all the
compounds have safety activity of protecting the maize from
the injury of acetochlor in some extent.
EXPERIMENTAL
The colorless crystal with a dimension of 0.48 × 0.42 ×
0.40 mm3 was selected for X-ray diffraction analysis. The
bond lengths and bone angles of the oxazolidine ring were
both normal with the average bond length being 1.465 Å
(Table 2). The C2—O1 bond length of 1.216(5) Å
was indicative of a double bond C═O (1.21–1.23 Å).
The p-π conjunction between N1 and C2—O1 resulted
in shorter bond length of C2—N1 (1.339(5) Å) than
the typical C—N bond length (1.472 Å).
The infrared (IR) spectra were taken on a KJ-IN-27G infrared
1
spectrophotometer (KBr). The H NMR and 13C NMR spectra
were recorded on a Bruker AVANVE 300MHz nuclear magnetic
resonance spectrometer with CDCl3 as the solvent and TMS as
the internal standard. The elemental analysis was performed on
In the crystal structure, molecules were linked by
weak intermolecular C—O···H hydrogen bonds to form
Table 1
Compound structure.
Compound no.
R1
R2
Total yield (%)
4a
4b
4c
4d
4e
4f
CH3
CH3
H
CH3
CH3
H
CH3
CH2CH3
CH2CH2CH3
CH2CH2CH3
CH2CH(CH3)2
C6H5
87.2
79.5
48.9
66.8
64.8
59.6
54.7
Figure 1. A view of 4a showing the atom‐numbering scheme. Thermal
ellipsoids are shown at the 30% probability level.
4g
CH3
CH2CH2C6H5
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

September 2012 One-Pot Microwave-Assisted Synthesis of Novel Substituted N-Dichloroacetyl-4,5-
1237
dimethyl-1,3-oxazolidines
Table 2
Selected bond lengths (Å) and angles (°) for 4a.
Bond lengths (Å)
Bond angles (°)
C(1) C(2)
1.537(5)
1.731(5)
1.769(5)
1.216(5)
1.339(5)
1.470(4)
1.492(7)
1.525(7)
1.414(6)
1.518(7)
1.422(5)
1.495(5)
1.505(7)
1.519(7)
C(2) C(1) Cl(1)
108.9(3)
110.3(2)
124.6(4)
119.8(4)
115.6(3)
99.1(3)
115.0(4)
103.1(4)
102.0(3)
111.8(3)
128.1(3)
121.5(3)
110.3(3)
108.9(3)
C(1) Cl(1)
C(1) Cl(2)
C(2) O(1)
C(2) N(1)
C(3) N(1)
C(3) C(4)
C(3) C(5)
C(5) O(2)
C(5) C(6)
C(7) O(2)
C(7) N(1)
C(7) C(9)
C(7) C(8)
Cl(1) C(1) Cl(2)
O(1) C(2) N(1)
O(1) C(2) C(1)
N(1) C(2) C(1)
N(1) C(3) C(5)
C(4) C(3) C(5)
O(2) C(5) C(3)
O(2) C(7) N(1)
N(1) C(7) C(8)
C(2) N(1) C(3)
C(2) N(1) C(7)
C(3) N(1) C(7)
C(5) O(2) C(7)
Figure 2. Packing view of 4a.
NMR δC(CDCl3, 75MHz): 160.13, 97.92, 72.27, 65.39, 55.
83, 30.52, 21.20, 16.25, 14.13, 8.29; Anal. Calcd. for
C10H17Cl2NO2: C 47.42, H 6.77, N 5.53; found: C 47.38, H
6.72, N 5.50.
FLASH EA1112 elemental analyzer. The automatic microwave
synthesizer was XH-100B of Beijing Xianghu Company. The
melting points were determined on Beijng Taike melting point ap-
paratus (X-4) and uncorrected. All the reagents were of analytical
reagents grade.
The starting 3-amino-2-butanol 1 was prepared by the litera-
ture procedure using nitroethane and acetaldehyde to produce
3-nitro-2-butanol, which was reduced by iron powder and hydro-
chloric acid [26].
Typical procedure for the preparation of substituted N-
dichloroacetyl-4,5-dimethyl-1,3-oxazolidines. 3-Amino-2-butanol
(0.026 mol), aldehyde or ketone (0.026 mol), and benzene (25 mL)
were stirred for 15 min under room temperature. Then, the mixture
was heated to reflux under microwave irradiation (800 W and 80°C)
for 20 min and water was stripped off, followed by cooling to 0–4°C
and addition of 3 mL of 33% sodium hydroxide solution. Afterward
3 mL (0.031 mol) of dichloroacetyl chloride was added dropwise
with stirring and cooling in an ice bath. Stirring was continued for
1.5 h. The organic phase was washed until pH = 7. The organic
layer was dried over magnesium sulfate anhydrous and vacuum
distillation solvent. Compound 4b, 4d, 4f, and 4g were separated on
silica gel by column chromatography. The crude products 4a and 4e
were recrystallized with ethyl acetate and light petroleum until the
white crystals were obtained.
N-Dichloroacetyl-4,5-dimethyl-2-n-propyl-1,3-oxazolidine(4c).
Yield:48.9%; Yellow oil; IR(KBr)ν:2962–2870 (C—H), 1649
1
(C═O), 1417 (Cl2HC—CO—), 1118 (N—C—O); H NMR δH
(CDCl3, 300 MHz): 6.08 (s, 1H, Cl2CH-), 5.13–5.18 (m, 1H,
N—CH—O), 4.01–4.10 (m, 1H, N—CH—C), 3.61–3.62
(m, 1H,C—CH—O), 2.28–2.34 (m, 2H, C—CH2—C—C),
1.65–1.70 (m, 2H, C—CH2—C), 1.22–1.29 (m, 6H, CH3—C—N
and CH3—C—O), 0.95–0.96 (m, 3H, CH3—C—C); 13C NMR δC
(CDCl3, 75MHz): 174.94, 90.35, 73.50, 62.15, 46.04, 36.47, 19.41,
18.48, 14.20, 12.37; Anal. Calcd. for C10H17Cl2NO2: C 47.42,
H 6.77, N 5.53; found: C 47.38, H 6.72, N 5.60.
N-Dichloroacetyl-2,4,5-trimethyl-2-n-propyl-1,3-oxazolidine(4d).
Yield:66.8%; White crystal; mp:81–82°C; IR(KBr)ν:3035–2875
(C—H), 1658 (C═O), 1415 (Cl2HC—CO—), 1110 (N—C—O);
1H NMR δH(CDCl3, 300MHz): 6.13 (s, 1H, Cl2CH—), 3.88–3.94
(m, 1H, N—CH—C), 3.47–3.53 (m, 1H, C—CH—O), 1.21–1.61
(m, 13H, C—CH2—CH2—C, CH3—C—N, CH3—C—O, CH3—C),
0.83–0.91 (q, J = 7.3Hz, 3H, CH3—C—C); 13C NMR
δC(CDCl3, 75MHz): 160.06, 99.01, 78.71, 65.32, 59.54, 39.22,
24.34, 20.74, 18.33, 16.06, 14.06; Anal. Calcd. for C11H19Cl2NO2:
C 49.42, H 7.17, N 5.24; found: C 49.48, H 7.12, N 5.23.
N-Dichloroacetyl-2,2,4,5-tetramethyl-1,3-oxazolidine(4a).
Yield:87.2%; white crystal; mp:108–109°C; IR(KBr)ν:3030–2875
(C—H) , 1663 (C═O), 1411 (Cl2HC—CO—), 1145 (N—C—O);
1H NMR δH(CDCl3, 300MHz): 6.13 (s, 1H, Cl2CH—), 4.24–4.32
(m, 1H, N—CH—C), 3.94–4.00 (m, 1H, C—CH—O), 1.67 (s, 3H,
CH3-—C), 1.59 (s, 3H, CH3—C), 1.22–1.42 (m, 6H, CH3—C—N,
CH3—C—O); 13C NMR δC(CDCl3, 75MHz): 159.94, 95.40, 72.68,
65.49, 56.27, 26.78, 22.73, 16.22, 14.17; Anal. Calcd. for
C9H15Cl2NO2: C 45.18, H 6.32, N 5.86; found: C 45.20, H 6.38, N 5.90.
N-Dichloroacetyl-2,4,5-trimethyl-2-ethyl-1,3-oxazolidine(4b).
Yield:79.5%; White crystal; mp:62–63°C; IR(KBr)ν:3030–2880
(C—H), 1660 (C═O), 1413 (Cl2HC—CO—), 1124 (N—C—
Table 3
Effect of detoxification of compounds 4a–g to growth maize.
Recovery
of plant
weight
(%)
Recovery
of root
length
(%)
Recovery
of root
weight
(%)
Recovery
of plant
height (%)
Compound
4a
4b
4c
4d
4e
4f
86.61
86.42
84.06
77.95
69.09
92.13
67.91
84.30
81.77
76.78
68.37
63.54
84.58
61.97
94.03
91.11
87.37
78.88
73.29
95.65
71.84
82.04
77.71
74.93
64.37
55.79
82.62
54.69
1
O); H NMR δH(CDCl3, 300MHz): 6.15 (s, 1H, Cl2CH—), 4.29–
4.35 (q, J = 6.2Hz, 1H, N—CH—C), 3.94–4.01 (q, J = 6.7Hz,
1H, C—CH—O), 1.98–2.20 (m, 2H, C—CH2—C), 1.56–1.64
(m, 3H, CH3—C), 1.36–1.43 (m, 3H, CH3—C—N), 1.22–1.28
(m, 3H, CH3—C—O), 0.85–0.94 (m, 3H,CH3—C—C); 13C
4g
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

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Y. Fu, L. Yang, F. Ye, and S. Gao
Vol 49
N-Dichloroacetyl-2,4,5-trimethyl-2-isobutyl-1,3-oxazolidine(4e).
Acknowledgments. This work was supported by China Postdoctoral
Science Foundation funded project (20100471243), the Heilongjiang
Province Foundation for Young Scholar (No.QC2009C44), the
Research Science Foundation in Technology Innovation of Harbin
(2010RFQYN108), and Northeast Agricultural University Doctor
Foundation funded project.
Yield:64.8%; White crystal; mp:105–106°C; IR(KBr)ν:3051–2869
(C—H), 1666 (C═O), 1413 (Cl2HC—CO—), 1110 (N—C—O);
1H NMR δH(CDCl3, 300MHz): 6.14 (s, 1H, Cl2CH—), 3.94–4.00
(q, J = 5.8Hz, 1H, N—CH—C), 3.63–3.67 (t, J = 5.9Hz, 1H,
C—CH—O), 1.69 (s, 3H, CH3—C), 1.36–1.44 (m, 6H, CH3—C—N
and CH3—C—O), 1.24–1.28 (m, 2H, C—CH2—C), 0.93–1.00
(m, 7H, (CH3)2CH—); 13C NMR δC(CDCl3, 75MHz): 160.89,
99.48, 78.24, 65.56, 59.33, 44.91, 24.75, 24.02, 23.89, 20.87,
19.34, 18.49; Anal. Calcd. for C12H21Cl2NO2: C 51.23, H 7.53,
N 4.98; found: C 51.27, H 7.51, N 4.92.
N-Dichloroacetyl-4,5-dimethyl-2-benzyl-1,3-oxazolidine(4f).
Yield:59.6%; White crystal; mp:62–63°C; IR(KBr)ν:3020–2850
(C—H), 1677 (C═O), 1411 (Cl2HC—CO—), 1095 (N—C—O);
1H NMR δH(CDCl3, 300MHz): 7.33–7.45 (m, 5H, C6H5—C),
6.35 (s, 1H, Cl2CH—), 5.69 (s, 1H, CH—C6H5), 3.78–3.90 (m,
2H, N—CH—CH—O), 1.31–1.45 (m, 6H, CH3—C—N and
CH3—C—O); 13C NMR δC(CDCl3, 75MHz): 161.72, 137.13,
129.86, 129.18, 129.18, 126.70, 126.70, 88.99, 78.46, 64.90,
60.25, 17.28, 16.72; Anal. Calcd. for C13H15Cl2NO2: C
54.35, H 5.27, N 4.88; found: C 54.31, H 5.30, N 4.92.
N-Dichloroacetyl-2,4,5-trimethyl-2-phenylethyl-1,3-oxazolidine
(4g). Yield:54.7%; White crystal; mp:58–59°C; IR (KBr)ν:
3030–2875 (C—H), 1677 (C═O), 1419 (Cl2HC—CO—), 1159
(N—C—O); 1H NMR δH(CDCl3, 300MHz): 7.19–7.29 (m, 5H,
C6H5—C), 6.18 (s, 1H, Cl2CH—), 4.32–4.38 (m, 1H, N—CH—C),
3.99–4.03 (t, J = 6.1Hz, 1H, C—CH—O), 2.53–2.74 (m, 4H,
C—CH2—CH2—C), 1.62–1.74 (m, 3H, CH3—C), 1.27–1.47
(m, 6H, CH3—C—N and CH3—C—O); 13C NMR δC (CDCl3,
75MHz): 160.09, 141.62, 128.51, 128.42, 128.42, 128.38,
125.90, 97.05, 73.36, 65.55, 56.16, 37.30, 30.59, 24.84, 16.59,
14.44; Anal. Calcd. for C16H21Cl2NO2: C 58.34, H 6.43, N 4.26
found: C 58.39, H 6.41, N 4.22.
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet