Solvent-free synthesis of N-Aryl-?β-Enaminones under microwave irradiation

Article abstract of DOI:10.14233/ajchem.2014.15524

A series of N-Aryl-?β-enaminones were efficiently prepared by acetylacetone reacted with substituted anilines in high yields without additional solvent under microwave irradiation. The most yields can reach over 80 %. Compared with traditional routes, thi

Full text of DOI:10.14233/ajchem.2014.15524

Asian Journal of Chemistry; Vol. 26, No. 3 (2014), 937-938
http://dx.doi.org/10.14233/ajchem.2014.15524
NOTE
Solvent-Free Synthesis of N-aryl-β-Enaminones Under Microwave Irradiation
1
,2,3,*
2
2
2
2
GUANGYONG XIE
, LONG LI , GONGYI LIU , LU LEI and AIQING ZHANG
1
Key Laboratory of Rubber-Plastics of Ministry of Education/Shandong Provincial Key Laboratory of Rubber -plastics, Qingdao University
of Science & Technology, Qingdao 266042, P.R. China
2
Key Laboratory of Catalysis and Materials Science of Hubei Province, College of Chemistry and Materials Science, South-Central University
for Nationalities, Wuhan 430074, P.R. China
3
Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei University, Wuhan 430062,
P.R. China
*
Corresponding author: Tel: +86 27 67842752; E-mail: xxgyy@hotmail.com
Received: 22 March 2013; Accepted: 9 July 2013;
Published online: 30 January 2014;
AJC-14672
A series of N-aryl-β-enaminones were efficiently prepared by acetylacetone reacted with substituted anilines in high yields without
additional solvent under microwave irradiation. The most yields can reach over 80 %. Compared with traditional routes, this method
needs only 15 min and simpler after-treatment procedures while owns higher yields.
Keywords: N-aryl-β-enaminones, Acetylacetone, Microwave, Solvent-free Synthesis.
β-Enaminone compounds are very important intermediates
other traditional routes, this method needs less reaction time,
easier after-treatment and can obtain higher yields.
for organic synthesis and have received considerable attentions
in recent years, which can be used for the synthesis of some
compounds having biological or pharmacological activity, such
NH
2
1-3
R
1
as α- or β-amino acids, polypeptide, alkaloid, pyrazole, etc. .
β-Enaminone with aryl group on N-atom, i.e. N-aryl-β-
enaminone, can also chelate with transition metals to obtain
complexes, which can usually be used for the catalysts of olefin
NH
O
Microwave
O
O
R2
a-1e
R
2
R
1
1
2a-2e
4
polymerization or oligomerization .
Traditionally, β-enaminone compounds can be prepared
by the condensation of β-diketones with amines catalyzed by
a: R
d: R
1
=CH
=F, R
3
, R
2
=H; b: R
=Cl, R
2
1
=F, R
2 1 2
=H; c: R =H, R =F
1
2
=F; e: R
1
=H
Scheme-I: Synthesis of N-aryl-β-enaminones under microwave irradiation
5,6
proton acid catalysts , which usually needs organic solvents
and high temperature to reflux and remove the generated
water. These methods would lead to low yield, complicated
after-treatment, high energy consumption and serious environ-
mental pollution, etc. Better results can be obtained when solid
Acetylacetone and substituted anilines were purchased
fromAcros Organics orAldrich Chemical Co. without further
purification. The melting points were determined on a X6
1
microscopic warming apparatus and are uncorrected. H NMR
7
-9
Lewis acid catalysts were used, but the yields for N-aryl-β-
enaminones are much lower.
spectra of the compounds were recorded on a Bruker Avance
III 400 MHz spectrometer with tetramethylsilane as an internal
standard. IR spectra of the compounds were collected on a
Nicolet Nexus470 FT-IR spectrometer. Elemental analyses
were carried out using Vario EL 111.
Microwave has been widely adopted for the synthesis of
organic compounds. Since the mid-1980s, a large number of
studies have demonstrated that an acceleration of chemical
rates can be achieved by employing high-density microwave
irradiation instead of traditional sources of heat. Recently we
synthesized a series of N-aryl-β-enaminones in good yields
without any supernumerary solvents under microwave irra-
diation, which was followed as Scheme-I. Compared with
General procedure for the synthesis of N-aryl-β-
enaminones (2a-2e): The mixtures of acetylacetone (10
mmol), substituted aniline (10 mmol) and three drops acetic
acid in the 100 mL flask were reacted 15 min under controlled
microwave heating, then the mixtures were diluted with 10 mL

938 Xie et al.
Asian J. Chem.
dilute hydrochloric acid and extracted three times with 10 mL
diethyl ether. The collected solutions of diethyl ether were
would decrease as increasing or decreasing reaction times
(Entry 1-3). Secondly, the microwave powers can also affect
the reaction activities. When the power increases from 490
watt to 700 watt, a little reduction of yield would appear.
Thirdly, the substituted groups on amines have great influences
upon the yields of N-aryl-β-enaminones. From entry 2 and
5-8, it can be found that the N-aryl-β-enaminones with
electron-donating groups would obtain higher yields, while
the electron-withdrawing groups would decrease the yields of
N-aryl-β-enaminones greatly. Furthermore, the ortho electron-
withdrawing groups have more obvious reduction upon the
yields than the para-ones and more electron-withdrawing
groups can reduce the yields further.
2 4
dried over anhydrous Na SO and then the solvent was evapo-
rated to obtain crude product, which was further purified by
recrystal in methanol. Experiments results are presented in
Table-1. Spectroscopic data of 2a-2e are given below.
1
2
a: m.p. 38-40 °C, H NMR (400 MHz, CDCl
3
), δ12.35
(
s, 1H, NH), 7.19 (m, 4H, Ph), 5.21 (s, 1H, CH), 2.29 (s, 3H,
PhCH ), 2.12 (s, 3H, CHCOCH ), 1.88 (s, 3H, CHCNCH ).
IR (KBr, νmax, cm ): 3432 (N-H), 1597 (C=O), 1560 (C=C).
Anal. calcd. (%) for C12 15NO: C, 76.16; H, 7.99; N, 7.40.
Found (%): C, 76.07; H, 7.78; N, 7.44.
3
3
3
-1
H
1
2
b: m.p. 47-49 °C, H NMR (400 MHz, CDCl ), δ12.25
3
(
CHCOCH
s,1H, NH), 7.18 (m, 4H, Ph), 5.26 (s, 1H, CH), 2.11 (s, 3H,
-1
3 3
), 1.94 (s, 3H, CHCNCH ). IR (KBr, νmax, cm ):
TABLE-1
SYNTHESIS OF N-ARYL-β-ENAMINONES
UNDER MICROWAVE IRRADIATION
3
439 (N-H),1616 (C=O), 1569 (C=C). Anal. calcd. (%) for
12NOF: C, 68.38; H, 6.26; N, 7.25. Found (%): C, 68.12;
H, 6.28; N, 7.34.
c: m.p. 44-45 °C, HNMR (400 MHz, CDCl
s, 1H, NH), 7.07 (m, 4H, Ph), 5.20 (s, 1H, CH), 2.10 (s, 3H,
11
C H
Power
Time
(min)
Entry
Product
Yield (%)
(
watt)
490
490
490
700
490
490
490
490
1
2
3
), δ12.26
1
2
3
4
5
6
7
8
2a
2a
2a
2a
2b
2c
2d
2e
10
15
20
15
15
15
15
15
78.3
84.1
79.7
81.2
66.4
80.5
62.6
59.9
(
-1
3 3
CHCOCH ), 1.93 (s, 3H, CHCNCH ). IR (KBr, νmax, cm ):
3
447 (N-H), 1609 (C=O), 1570 (C=C). Anal. calcd. (%) for
12NOF: C, 68.38; H, 6.26; N, 7.25. Found (%): C, 68.43;
H, 6.18; N, 7.20.
d: m.p. 44-46 °C, HNMR (400 MHz, CDCl
s, 1H, NH), 6.84-7.16 (m, 3H, Ph), 5.26(s, 1H, CH), 2.10 (s,
11
C H
1
2
3
), δ12.08
(
-1
3
H, CHCOCH
439 (N-H), 1609 (C=O), 1568 (C=C). Anal. calcd. (%) for
: C, 62.55; H, 5.25; N, 6.63. Found (5): C, 62.66;
H, 5.37; N, 6.45.
e: m.p. 65-66 °C, HNMR (400 MHz, CDCl
s, 1H, NH), 7.13-7.44 (m, 4H, Ph), 5.26 (s, 1H, CH), 2.12 (s,
3 3
), 1.88 (s, 3H, CHCNCH ). IR (KBr, νmax, cm ):
3
ACKNOWLEDGEMENTS
11 2
C H11NOF
The authors are grateful for the financial support from
the Natural Sciences Foundation of China (21172269), the
Open Fund of Key Laboratory of Rubber-Plastics of Ministry
of Education /Shandong Provincial Key Laboratory of Rubber
plastics (KF2010001) and the Open Fund of Ministry of
Education Key Laboratory for the Green Preparation and
Application of Functional Materials.
1
2
3
), δ12.41
(
-1
3
H, CHCOCH
447 (N-H), 1604 (C=O), 1558 (C=C). Anal. calcd. For
12NOCl: C, 63.01; H, 5.77; N, 6.68. Found: C, 63.21; H,
.82; N, 6.83.
The title compounds were characterized by H NMR, IR
3 3
), 1.94 (s, 3H, CHCNCH ). IR(KBr), ν, cm :
3
11
C H
5
1
and element analysis and the structures were confirmed.
From Table-1, it can be seen that N-aryl-β-enaminones
can be prepared easily in a short time promoted by microwave
with the yields up to 84 %. Compared with other traditional
routes, this method needs less reaction time and simpler after-
treatment while obtains higher yields. The powers of micro-
wave, reaction times and substituted groups can affect the
yields of products. Firstly, the reaction times can be condensed
greatly in comparison with the traditional methods, which
usually need several hours and thus the energy can be saved
greatly. For o-methyl substituted N-aryl-β-enaminones, the
yield of 2a can reach 84.1 % with only 15 min and the yields
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