Synthesis and Cation Recognition Study of Novel Benzo Crown Ether Functionalized Enamine Derivatives

Article abstract of DOI:10.1080/00397911.2015.1053146

A novel series of benzo crown ether (dibenzo 18-crown-6 ether, benzo 18-crown-6 ether, and benzo 15-crown-5 ether) functionalized enamines derivatives from amino benzo crown ether (4-amino dibenzo 18-crown-6 ether, 4-amino benzo 18-crown-6 ether, 4-amino

Full text of DOI:10.1080/00397911.2015.1053146

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Synthesis and Cation Recognition Study of Novel Benzo
Crown Ether Functionalized Enamine Derivatives
a
a
a
Dayanand R. Patil , Dattatraya R. Chandam , Abhijeet Ganpatrao Mulik , Suryabala D.
a
a
a
Jagdale , Prasad P. Patil & Madhukar B. Deshmukh
a
Department of Chemistry, Shivaji University, Kolhapur, India
Accepted author version posted online: 27 May 2015.
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To cite this article: Dayanand R. Patil, Dattatraya R. Chandam, Abhijeet Ganpatrao Mulik, Suryabala D. Jagdale, Prasad P.
Patil & Madhukar B. Deshmukh (2015): Synthesis and Cation Recognition Study of Novel Benzo Crown Ether Functionalized
Enamine Derivatives, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, DOI: 10.1080/00397911.2015.1053146
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Synthesis and cation recognition study of novel benzo crown ether functionalized
enamine derivatives
1
1
1
Dayanand R Patil , Dattatraya R. Chandam , Abhijeet Ganpatrao Mulik , Suryabala D.
1
1
1
Jagdale , Prasad P. Patil , Madhukar B. Deshmukh
Department of Chemistry, Shivaji University, Kolhapur, India
1
Corresponding Author: Madhukar B. Deshmukh, Department of Chemistry, Shivaji
University, Vidyanagar, Kolhapur 415311, India. Email: shubhlaxmi111@gmail.com
Abstract
A novel series of benzo crown ether (dibenzo 18 -crown- 6 ether, benzo 18-crown-6
ether and benzo 15 -crown -5 ether) functionalized enamines derivatives from amino
benzo crown ether (4-amino dibenzo 18-crown-6 ether, 4-amino benzo 18-crown-6 ether,
4
-amino benzo 15- crown- 5 ether) and substituted 3-(dimethylamino)-1-phenylprop-2-
en-1-one compounds have been synthesized. All the synthesized compounds were
1
13
characterized by IR, H NMR, C NMR, DEPT 135, Mass and Elemental analysis
techniques. The cation recognition property for benzo crown ether enamine 8a was
studied by absorption and fluorescence spectroscopy.
1

Graphical Abstract:
KEYWORDS: Benzo 15-crown-5 ether, Benzo 18-crown-6 ether, benzo crown ether
enamine, photo physical properties, 4-amino dibenzo 18- crown- 6 ether.
INTRODUCTION
Crown ethers are the significant macrocyclic compounds containing several oxygens or
hetero atoms separated by ethylene moieties which reveal selective and sensitive binding
[
1,2]
properties of ionic or neutral molecules . Since their discovery by Pederson in 1967,
Crown ether are popular host compounds in host-guest chemistry along with their
remarkable properties to complex metal cations have useful as synthetic ionophores,
chromatographic stationary phase, ability to solubilize inorganic compound in organic
solvent to increase their reactivity, phase transfer catalysts in organic synthesis,
therapeutic reagents in chelate therapy as well as effective complexing reagents for the
2

[3–7]
cations of alkaline earth and transition metal ions . In addition, crown ether has
extensive application in the field of science and technology and analytical chemistry such
as pH sensors, construction of chemical switches, molecular recognition, metal ion
[
8–11]
probes, laser dyes, ion-selective electrode and organic conductors
.
The selectivity and binding ability of crown ethers depend on size of hetero atom of the
crown ether, metal ion radius, nature of donor atom, conformation, polarity of the solvent
[
12, 2]
etc.
. Recently cation recognition, sensing of metal ions and anions have been
[
13,14]
energetic area in supramolecular chemical research
. The selectively recognition and
metal binding with polyether cavity of crown ether have been studied by amperometry,
potentiometry and fluorescence technique. Among these, the fluorescence spectroscopy
which estimates quality and quantity of recognition. Consequently the synthesis of
functionalized crown ethers are important due to the sensitivity of resulting chemosensors
[
15,16]
with change in optical signal is screened with respect to metal ion binding
.
Nowdays, enamine and enamine like compounds have important building blocks
employed as nucleophile in Michael type addition for the synthesis of natural product,
[
17-
fused heterocycles and precursors of chiral amines upon asymmetric transformations
2
0]
.
Amongst them β-enaminones represent a useful moiety for the synthesis of
[
21-25]
heterocyclic scaffolds such as pyrrole, dihydropyridine, piperidine, pyrimidine etc.
.
In prolongation of our efforts for the synthesis of novel crown ether functionalized
[
26-29]
molecules and their photo physical study
, we report herein synthesis of new benzo
3

crown ether enamine derivatives from amino benzo crown ether and substituted 3-
dimethylamino)-1-phenylprop-2-en-1-one compounds (Scheme 1). Subsequently the
(
absorption and fluorescence study of the benzo crown ether enamine 8a was done with
distinct metal cation.
RESULTS AND DISCUSSION
Herein, we have explained the synthesis of new benzo crown ether functionalized
enamines from amino benzo crown ether and substituted 3-(dimethylamino)-1-
phenylprop-2-en-1-one compounds in acetonitrile at RT (Scheme 1).
Initially, the synthesis of starting materials 4-amino benzo dibenzo 18-crown-6 ether (3)
and 4-amino benzo 18-crown-6 ether (6) from dibnezo 18-crown-6 ether and benzo 18-
[
26,30]
crown-6 ether were carried out respectively
.
An amination of dibenzo 18-crown-6 ether was carried in single step using sodium azide
and polyphosphoric acid at 100°C to afford 4-amino dibenzo 18-crown-6 (3) in 62%
yield. While the nitration of the benzo 18-crown-6 ether occurred in HNO (70%) and
3
CH COOH at RT for 24 hr to obtained yellow colored 4-nitro benzo 18-crown-6 (5) in
3
7
7% yield which on further reduction by using NH Cl and fresh Fe in ethanol at reflux
4
condition to obtained 4-amino benzo 18-crown-6 ether (6) as a brownish solid in 67%
yield. After that, we have synthesized substituted 3-(dimethylamino)-1-phenylprop-2-en-
1
-one compounds with excellent yield by using substituted acetophenone and dimethyl
[31,32]
formamide dimethyl acetal in toluene under reflux condition
.
4

Next, the key step for synthesis of benzo crown enamines is depicted in scheme 1, the
amino benzo crown ether (3/6/7) reacted with various substituted 3-(dimethylamino)-1-
phenylprop-2-en-1-one compounds in acetonitrile under RT condition. The benzo crown
ether enamines were afforded in good yield (Table 1) and which were confirmed by
1
13
spectroscopic technique IR, H NMR, C NMR, DEPT 135 and Mass analysis.
The IR spectrum of compound 1-(phenyl)-3-(amino dibenzo-18-crown-6) prop-2-en-1-
one (8a) observed a characteristics absorption band at frequency 3354, 2885, 1627 and
-1
1
583 cm due to N-H stretching, aromatic C-H stretching, >C=O stretching and C=C
1
stretching respectively. In H NMR spectrum the proton of ethylene oxy unit (-OCH -
2
CH -) showed multiplet at up field region between δ 4.04 to 4.19 ppm whereas the two
2
olefinic proton (-CH=CH-) showed two doublet at δ 5.99-6.01 and 6.65-6.68 ppm
respectively. The entire aromatic protons (Ar-H) observed multiplet between the range δ
6
.65 to 7.96 ppm and the characteristics peak of N-H proton observed doublet far
downfield at δ 12.17 -12.21 ppm due to intramolecular hydrogen bonding with oxygen.
1
3
The C NMR reveals that peak of the carbon for ethylene oxy unit (-OCH -CH -)
2
2
observed between δ 68.72 to 70.00 ppm while the olefinic carbon peak (=CH-C=O) and
=CH-NH) showed at δ 93.08 and 145.70 ppm. All the aromatic carbon appears in the
(
range δ 103.49 to 149.84 ppm as well as characteristic peak of carbonyl carbon (>C=O)
appear at δ 190.64 ppm. Final affirmation of the compound (8a) was obtained from mass
5

analysis that showed precise most intense molecular ion peak at 595.2 m/z whereas
elemental analysis well matched with the theoretical value of the compound.
The plausible mechanism for formation of the benzo crown enamine 10 is depicted in
scheme 2. The nucleophilic attack of benzo amino crown 7 on electrophilic carbon of
compound 1 to form carbanion intermediate 11. However the carbanion abstract proton
from iminium cation to give an intermediate 12 which afford Schiff base 13 by
elimination of dimethyl amine 14. Finally the Schiff base 13 undergoes imine - enamine
tautomerization to form a benzo crown enamine 10 scaffolds.
Absorption Spectra
Fluorophore groups have concerned the binding of various fluorescent dyes to the crown
and aza crown ethers due to the complex reactions. These compounds are commonly
considered functional cages because of their ability and selectivity to heavy or alkali
metal sensors by using light. Furthermore, dibenzo 18 crown-6 ether derivatives proposed
2
+
3+[33-35]
as effective highly selective chemosensor for Hg and Al
.
Based on the above mentioned findings, we have studied UV- visible and fluorescence
analyses for a compound 8a.
-4
Absorption spectra of compound 8a (1x10 M) was measured in DMSO: H O (80:20,
2
v/v) with 20 ppm metal cation solution in water and the results are summarized in Fig. 1.
-4
The compound 8a (1x10 M) shows absorption peak at 392 nm. Afterward addition of
6

2
+
-4
Hg (20 ppm) solution in to 8a (1x10 M) solution, the absorption peak shows at 394 nm
indicates there is no remarkable change in the shifting of wavelength. Similar results
2
+
2+
+
2+
2+
2+
2+
were observed in case of the other metal cation (Ba , Ca , K , Na , Pb , Cd , Zn )
solution added in to 8a solution.
Fluorescence Spectra
The binding ability of selected metal cations with compound 8a was measured by
fluorescent emission responses in DMSO: H O (80:20, v/v). The absorption fluorescent
2
correlated spectrum of 8a showed that a maximum fluorescent emission response
-4
appeared with an excitation 392 nm. Thus the emission spectra of 8a (1x10 M) with a 20
-4
2+
2+
2+
+
2+
2+
2+
2+
ppm (1x10 M) metal cations (Hg , Ba , Ca , K , Na , Pb , Cd , Zn ) were
examined at an excitation 392 nm and the results are tabulated in Table 2.
2
+
After the addition of Hg cation solutions, the fluorescent intensity of compound 8a
λem= 475 nm) quenching and the position of emission maximum moves to longer
wavelength (λ = 545 nm, Fig. 2.). These results indicates that the binding of compound
(
em
2
+
2+
8
a with Hg induces quenching to 70 nm red shift operated by co-ordination of Hg to
crown ether cavity.
2
+
A close interaction of Hg with ‘O’ atom of the crown cavity stabilize excited state of
2
+
complex between 8a and Hg than that of 8a itself, so that which leads to red shift in the
2
+
2+
+
2+
2+
2+
2+
emission. Similar type of behavior found in Ba , Ca , K , Na , Pb , Cd , Zn with
7

similar quenching intensities. Thus compound 8a shows a binding affinity towards metal
cations and it bind with ‘O’ in the crown cavity.
CONCLUSION
In summary, we have synthesized a series of novel benzo crown ether functionalized
enamine derivatives from amino benzo crown ether (4-amino dibenzo 18-crown-6 ether,
4
-amino benzo 18-crown-6 ether, 4-amino benzo 15-crown-5 ether) and substituted 3-
(dimethylamino)-1-phenylprop-2-en-1-one compounds with good yields. The
fluorescence spectrum result of compound 8a shows binding affinity of metal cations
towards crown cavity with quenching of 70 nm wavelength.
EXPERIMENTAL
All the chemicals were purchased from Sigma Aldrich, SD Fine Chem. Limited, Himedia
and Thomas Baker used as received without further purification. All the melting point
check on Labstar melting apparatus was uncorrected. The IR spectra was run on a UV
3
600 Shimadzu UV-VIS-NIR spectrophotometer with the use of a 1.0 cm quartz cell and
-1 1
13
expressed in cm . H NMR and C NMR spectra were recorded on Bruker Avance (300
MHz & 75 MHz) spectrometer in CDCl using TMS as the internal standard. The
3
chemical shifts (δ) are expressed in ppm and coupling constant ‘J’ expressed in Hz. Mass
spectra were recorded on a Performa spectrometer equipped with electron spray
ionization interface. Elemental analyses were performed on a Elemental EURO analyzer.
The absorption spectrum was acquired at room temperature on UV-Specord-210 + UV-
VIS NIR Spectrophotometer with the use of 1.0 cm quartz cell. Fluorescence
8

measurements of solution were made with PC best spectrofluorophotometer (FP-8300
JASCO, JAPAN equipped with Xenon lamp source and 1.0 cm quartz cell.
General Procedure For The Synthesis Of Benzo Crown Ether Enamine Derivatives
(8a-8b, 9a-9d, 10a-10b)
A mixture of substituted 3 -(dimethylamino) -1-phenylprop-2-en-1-one compounds 1 (1
mmol), amino benzo crown ether 3/6/7 (1 mmol) and acetonitrile (5 ml) were charged in
2
5 ml round bottom flask. The reaction mixture was stirred at RT up to completion of
reaction as monitored by TLC (Chloroform: Methanol, 9.5:0.5). After completion of
reaction, a thick precipitated solid was obtained. The generated solid was filtered off and
wash with cold acetonitrile to afford pure product. In those cases, where a solid was not
formed after cooling, the solvent was evaporated by rotary evaporation and the crude
product obtained was purified by column chromatography on silica gel (Chloroform:
Methanol, 9.5: 0.5) to get pure benzo crown ether enamine (Table 1, entries 3,4,5,7,8).
Characterization Data For (1-(Phenyl)-3-(Amino Dibenzo-18-Crown-6 Ether) Prop-
2
-En-1-One (8a). (Table 1, Entry 1)
Yellow solid; Yield 79%; m.p. 197-199°C; IR: 3054, 2925, 2885, 1627, 1583, 1499,
-1 1
1
471, 1226, 1127, 1018, 940 cm ; H NMR (300 MHz, CDCl ): δ 4.04-4.05 (m, 8H,
3
OCH ), 4.18-4.19 (m, 8H, OCH ), 5.99- 6.01 (d, 1H, CH), 6.65-6.68 (s, 1H, CH), 6.85-
2
2
6
1
.94 (m, 6H, Ar-H), 7.41-7.51 (m, 4H, Ar-H), 7.93-7.96 (d, 2H, Ar-H), 12.17-12.21 (d,
1
3
H, NH); C NMR (75 MHz, CDCl ): δ 68.72, 68.81, 68.88, 69.42, 69.80, 70.00, 93.08,
3
9

1
1
6
1
03.49, 108.38, 113.56, 114.91, 121.32, 127.24, 128.41, 131.43, 134.56, 139.29, 145.51,
45.70, 148.75, 149.84, 190.64; DEPT 135 (75 MHz, CDCl3): δ 68.46, 68.53, 68.65,
9.09, 69.65, 69.87, 93.04, 103.18, 108.21, 113.12, 114.34, 121.18, 127.23, 128.41,
+
31.43, 145.69; ESI-MS: Calcd for C H NO [M] : 505.559; Found: 506.2. Anal.
2
9
31
7
Calcd. for C H NO (505.559): C, 68.90; H, 6.18; N, 2.77. Found: C, 68.82; H, 6.11; N,
2
9
31
7
2
.84.
FUNDING
The authors are thankful to Department of Chemistry, Shivaji University, Kolhapur for
spectral measurements. One of the authors D. R. Patil is grateful to the UGC New Delhi
for awarding him a Junior Research Fellowship [F.No.41-211/2012 (SR)].
SUPPLEMENTAL MATERIAL
Supplemental data for this article can be accessed on the publisher’s website.
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1
3

a
Table 1. Synthesis of benzo crown ether enamines (8a-8b, 9a-9d, 10a-10b)
1
Entry R in 1 R in R-NH
Product
Time Yield m.p.°C
2
b
(
hr)
(%)
79
1
2
H
Dibenzo 18-crown -6
8a
8b
2
197-
199
O
O
O
ether (3)
NH
O
O
O
O
4-CH3 Dibenzo 18-crown -6
1.5
75
181-
183
O
O
O
ether (3)
NH
O
O
O
O
3
4
5
6
H
Benzo 18-crown-6
9a
9b
9c
9d
1.5
77
78
72
73
-
-
-
O
O
ether (6)
NH
O
O
O
O
O
4-CH3 Benzo 18-crown-6
1
O
O
ether (6)
NH
O
O
O
O
O
F
4-F
Benzo 18-crown-6
1
O
O
O
ether (6)
NH
O
O
O
O
Cl
4-Cl
Benzo 18-crown-6
1
207-
210
O
O
O
ether (6)
NH
O
O
O
O
1
4

O N
2
7
8
4-NO2 Benzo 15-crown-5
10a 1.5
75
71
-
-
O
ether (7)
O
O
NH
O
O
O
F
4-F
Benzo 15-crown-5
10b 1.5
O
ether (7)
O
NH
O
O
O
O
a
Reaction condition: amino benzo crown ether 3/6/7 (1 mmol), substituted 3-
(dimethylamino)-1-phenylprop-2-en-1-one 1 (1 mmol) in acetonitrile (5 ml) stirred at RT.
b
Isolated yield.
1
5

-4
Table 2. Emission (λ ) responses of 8a (1x10 M) upon the addition of the various metal
em
ion solution 20 ppm at excitation (λ = 392 nm)
ex
Compound (8a)
Metal ion
Ion-Free
λex (nm)
392
λem (nm)
475
2
+
Hg
392
545
2
+
Ba
Ca
392
545
2
+
392
545
+
K
392
545
+
Na
392
545
2
+
Pb
392
545
2
+
Cd
392
545
2
+
Zn
392
545
1
6

Scheme 1. Synthesis of benzo crown ether enamine.
1
7

Scheme 2. Plausible mechanism for the formation of benzo crown ether enamine.
1
8

-4
Figure 1. UV-visible absorption spectrum of (1x 10 M) of 8a and metal cation.
1
9

-4
Figure 2. Fluorescence spectrum of (1x 10 M) of 8a and metal cation 20 ppm in
DMSO: Water (80:20, V/V). 20 ppm in DMSO: Water (80:20, V/V).
2
0