Synthesis of a novel class of azacrown macrocycles and lariat crown ethers containing two 1,2,4-triazole rings as subunits

Article abstract of DOI:10.1055/s-0029-1217398

Azacrown macrocycles were prepared in 70-76% yield by the condensation reaction of 1,2-, 1,3-, and 1,4-bis(4-amino-5-mercapto-4H-1,2,4-triazol-3-yl) alkanes with bisaldehydes in acetic acid under reflux. Reaction of two of these azacrown macrocycles with

Full text of DOI:10.1055/s-0029-1217398

PAPER
2557
Synthesis of a Novel Class of Azacrown Macrocycles and Lariat Crown Ethers
Containing Two 1,2,4-Triazole Rings as Subunits
Synthesis of
A
zacr
a
ow
n
M
acro
s
cycles an
e
d
Lariat Cro
r
wnEthers Foroughifar,* Akbar Mobinikhaledi, Sattar Ebrahimi
Department of Chemistry, Faculty of Sciences, Arak University, Arak 38156-879, Iran
Fax +98(861)4173406; E-mail: n_foroughifar@yahoo.com
Received 26 March 2009; revised 7 April 2009
properties of natural ionophores.12 In connection with
Abstract: Azacrown macrocycles were prepared in 70–76% yield
by the condensation reaction of 1,2-, 1,3-, and 1,4-bis(4-amino-5-
mercapto-4H-1,2,4-triazol-3-yl)alkanes with bisaldehydes in acetic
acid under reflux. Reaction of two of these azacrown macrocycles
these findings, and in a continuation of our interest in syn-
thesizing macrocyclic crown compounds containing het-
erocyclic moieties,13 we report here the synthesis of a
with iodomethane and benzyl chloride furnished exclusively the tar- series of 18–21-membered azacrown macrocycles fused
get lariat macrocycles in good yields.
with two 1,2,4-triazole rings, containing N and O inside
the macrocyclic ring as donor atoms and possessing pen-
dent thiol groups as precursors for the synthesis of lariat
thioether macrocycles.
Key words: azacrown macrocycles, 1,2,4-triazole, thiols, bistri-
azoles, lariat crown ethers
Several synthetic methods have been developed for the
synthesis of macrocyclic compounds. Among these meth-
ods, the high dilution technique is often used as the most
versatile procedure.14 On the other hand, Sharghi and
others15–18 have reported the synthesis of macrocycles
without the use of high dilution techniques.
Since Pedersen’s discovery in 1967 of crown ethers and
their ability to bind strongly with metal ions,1,2 the study
of crown ethers has grown at an incredible rate. Syntheses
of many different types of crown ethers (e.g., crown ether
diesters, azacrown ethers, thiacrown ethers, and chiral
crown ethers) have been documented in the literature and
the binding properties of crown ethers, such as binding
strength and selectivity toward a wide range of metal ions,
nonmetal ions, and neutral molecules, have been investi-
gated.3 The incorporation of oxygen, nitrogen, and sulfur
donor atoms in these macrocycles also markedly affects
the complexing properties because of the hard (O, N) and
soft (S) character of the donor atoms and the exodentate
tendency of the sulfide linkages.4 Other changes involve
the insertion of aromatic and/or heterocyclic ring systems
into the macrocycles;5 heterocyclic groups provide rigidi-
ty and are able, in some cases, to form complexes through
their soft donor atoms.6 The wide interest in the construc-
tion of synthetic macrocyclic compounds containing five-
and six-membered heterocyclic rings as subunits has led
to the preparation of a range of such compounds, which
have been shown to possess very interesting properties in
a variety of fields.7 These macrocycles were found to ex-
hibit interesting host–guest complexation characteristics8
and have shown antibacterial activities,9 in which the bio-
logical activity is highly dependent upon the side-chain
substitution pattern. Lariat ethers are compounds with a
macrocyclic ring and a side arm which bears a donor
group. Lariat ethers have been designed as cation com-
plexing agents which exhibit complexation behavior sim-
ilar to crown ethers, but with a three-dimensional binding
character.10,11 Also, as efficient organic ligands, lariat
crown ethers meet the requirement of rapid, strong, and
three-dimensional cation binding, and can mimic the
This project describes the synthesis of novel azacrown
ethers and lariat ethers containing two triazole rings as
subcyclic units, as shown in Schemes 1 and 2. The synthe-
sis of azacrown ethers containing 1,2,4-triazole rings has
not been reported previously. The synthetic strategy in-
volves cyclocondensation between bis(aminotriazoles)
and the appropriate bisaldehydes to give the correspond-
ing Schiff bases. The starting 1,2-, 1,3-, and 1,4-bis(4-
amino-5-mercapto-4H-1,2,4-triazol-3-yl)alkanes
2a–c
were prepared by heating aliphatic diacids with 2 molar
equivalents of carbonothioic dihydrazide in an oil bath at
170 °C.19 Reaction of the bis(4-amino-5-mercapto-4H-
1,2,4-triazol-3-yl)alkanes 2a–c with 1 equivalent of the
bisaldehydes 1a–c20 in refluxing acetic acid under high di-
lution conditions afforded the corresponding azacrown
ether compounds 3a–g. The expected compounds were
obtained in reasonable yields, as reported in Table 1.
Table 1 Azacrown Macrocycles 3a–g
Product
3a
X
Y
Yielda (%)
(CH2)2
(CH2)3
(CH2)4
(CH2)2
(CH2)4
(CH2)2
(CH2)3
(CH2)2
(CH2)2
(CH2)2
(CH2)3
(CH2)3
(CH2)4
(CH2)4
76
73
71
72
71
76
70
3b
3c
3d
3e
3f
SYNTHESIS 2009, No. 15, pp 2557–2560
x
x.
x
x
.
2
0
0
9
3g
Advanced online publication: 22.06.2009
DOI: 10.1055/s-0029-1217398; Art ID: Z04909SS
© Georg Thieme Verlag Stuttgart · New York
a Isolated yields.

2558
N. Foroughifar et al.
PAPER
N
N
N
N
N
N
Y
SH
HS
CHO
CHO
N
N
N
N
N
N
AcOH
N
N
O
X
O
Y
+
SH
HS
O
O
NH2 H2N
X
1a–c
2a–c
3a–g
Scheme 1
N
N
N
N
N
N
N
N
N
N
N
N
Y
Y
R
R
S
S
MeI or BnCl
EtO–Na+
SH
HS
N
N
N
N
O
O
O
O
X
X
3a,b
4a–d
R = Me, Bn
Scheme 2
Lariat ethers can be divided into two categories depending In conclusion, we have established a simple and efficient
on the nature of the secondary binding site: lariat ethers method for the preparation of azacrown macrocycles con-
with a pendent neutral side arm and lariat ethers with a taining two 1,2,4-triazole subunits. These macrocycles
pendent proton-ionizable arm. With the new Schiff base with pendent thiol groups are a key intermediate for the
macrocycles 3a–g available, we were stimulated to study synthesis of novel lariat macrocycles.
their transformation into lariat azacrown ethers containing
two triazole rings as subcyclic units and thioether groups
1H and 13C NMR spectra were recorded on a Bruker spectrophoto-
as the side chain. Thus, the novel lariat compounds 4a–d
meter operating at 300 and 75 MHz, respectively, with DMSO-d6 as
with neutral side arms were prepared by reaction of the
corresponding azacrown macrocycles 3a,d with two
equivalents of benzyl chloride or iodomethane in ethanol
at room temperature for five hours (Scheme 2). The ex-
pected compounds were obtained in reasonable yields, as
reported in Table 2.
solvent. IR spectra were recorded on a Galaxy series FT-IR 5000
spectrophotometer using KBr discs. Mass spectra were recorded on
an Agilent Technologies (HP) 5973 Network mass selective detec-
tor under electron impact (EI).
Azacrown Macrocycles 3a–g; General Procedure
To a soln of a bis(aminotriazole) 2a–c (0.3 mmol) in glacial AcOH
(100 mL) was added a soln of the appropriate bisaldehyde 1a–c (0.3
mmol) in glacial AcOH (50 mL). The reaction mixture was then
heated under reflux for 8 h. The solvent was removed under reduced
pressure, the residue was washed with H2O, and the solid obtained
was collected and crystallized from an appropriate solvent to give
the azacrown macrocycles 3a–g.
The IR spectra of the bis(4-amino-5-mercapto-4H-1,2,4-
triazol-3-yl)alkanes 2a–c showed absorption bands at
3161 and 3286 cm–1 due to the NH2 groups, bands which
were absent in the IR spectra of the azacrown compounds
1
3a–g. Similarly, the H NMR spectra of the bistriazoles
2a–c showed a broad signal at d = 5.56 ppm attributed to
the NH2 groups, a signal which was not present in the 1H
NMR spectra of compounds 3a–g. The absence of the IR
absorptions and 1H NMR signals due to the SH groups of
compounds 3a,d clearly confirmed the formation of the
lariat crown macrocycles 4a–d.
2,3:14,15-Dibenzo-6,7:10,11-bis[3-mercapto-4H-1,2,4-triazo-
lo][1,16,5,6,11,12]dioxatetraazacyclooctadeca-4,12-diene (3a)
IR (KBr): 3038 (aromatic CH stretch), 2742 (SH stretch), 1595
(C=N) cm–1.
1H NMR (300 MHz, DMSO-d6): d = 13.66 (s, 2 H, 2 × SH), 9.70 (s,
2 H, 2 × CH=N), 7.70 (d, J = 7.2 Hz, 2 H, Harom), 7.58 (t, J = 7.3 Hz,
2 H, Harom), 7.19 (d, J = 8.3 Hz, 2 H, Harom), 7.05 (t, J = 7.5 Hz, 2 H,
Table 2 Lariat Ethers 4a–d
Harom), 4.46 (s, 4 H, 2 × OCH2), 3.03 (s, 4 H, 2 × CH2).
Product
4a
X
Y
R
Yielda (%)
13C NMR (75 MHz, DMSO-d6): d = 22.8, 68.7, 114.7, 121.0, 121.9,
126.9, 135.1, 149.8, 159.6, 162.2, 163.0.
(CH2)2
(CH2)2
(CH2)2
(CH2)2
(CH2)2
(CH2)3
(CH2)2
(CH2)3
Me
Me
Bn
Bn
85
79
90
84
MS (EI): m/z = 492 [M+], 346, 264, 228, 196, 146 (base peak), 120,
91.
4b
4c
2,3:14,15-Dibenzo-6,7:10,11-bis[3-mercapto-4H-1,2,4-triazo-
lo][1,16,5,6,11,12]dioxatetraazacyclononadeca-4,12-diene (3b)
IR (KBr): 3042 (aromatic CH stretch), 2754 (SH stretch), 1597
(C=N) cm–1.
4d
a Isolated yields.
Synthesis 2009, No. 15, 2557–2560 © Thieme Stuttgart · New York

PAPER
Synthesis of Azacrown Macrocycles and Lariat Crown Ethers
2559
1H NMR (300 MHz, DMSO-d6): d = 13.50 (s, 2 H, 2 × SH), 10.25
(s, 2 H, 2 × CH=N), 7.60 (d, J = 7.2 Hz, 2 H, Harom), 7.54 (t, J = 7.3
Hz, 2 H, Harom), 7.26 (d, J = 8.3 Hz, 2 H, Harom), 7.01 (t, J = 7.5 Hz,
2 H, Harom), 4.41 (t, J = 5.1 Hz, 4 H, 2 × OCH2), 3.14 (s, 4 H, 2 ×
CH2), 2.20 (t, J = 5.0 Hz, 2 H, CH2).
MS (EI): m/z = 520 [M+], 374, 264, 256, 146 (base peak), 120, 91.
2,3:16,17-Dibenzo-6,7:12,13-bis[3-mercapto-4H-1,2,4-triazo-
lo][1,18,5,6,13,14]dioxatetraazacyclohenicosa-4,14-diene (3g)
IR (KBr): 3044 (aromatic CH stretch), 2768 (SH stretch), 1600
(C=N) cm–1.
13C NMR (75 MHz, DMSO-d6): d = 23.6, 28.6, 67.8, 116.2, 121.7,
122.1, 126.0, 134.8, 151.1, 157.1, 159.6, 161.2.
1H NMR (300 MHz, DMSO-d6): d = 13.51 (s, 2 H, 2 × SH), 9.98 (s,
2 H, 2 × CH=N), 7.73 (d, J = 7.7 Hz, 2 H, Harom), 7.54 (t, J = 7.4 Hz,
2 H, Harom), 7.28 (d, J = 8.4 Hz, 2 H, Harom), 7.00 (t, J = 7.6 Hz, 2 H,
Harom), 4.42 (br, 4 H, 2 × OCH2), 2.73 (br, 4 H, 2 × CH2), 2.02 (br,
2 H, CH2), 1.53 (br, 4 H, 2 × CH2).
MS (EI): m/z = 506 [M+], 346, 278, 228, 196, 160 (base peak), 134,
132, 102, 77.
2,3:14,15-Dibenzo-6,7:10,11-bis[3-mercapto-4H-1,2,4-triazo-
lo][1,16,5,6,11,12]dioxatetraazacycloicosa-4,12-diene (3c)
IR (KBr): 3057 (aromatic CH stretch), 2781 (SH stretch), 1599
(C=N) cm–1.
13C NMR (75 MHz, DMSO-d6): d = 22.9, 25.1, 25.5, 68.6, 115.1,
121.2, 122.2, 126.8, 135.1, 150.8, 158.8, 160.3, 161.4.
MS (EI): m/z = 534 [M+], 374, 274, 256, 238, 224, 160 (base peak),
120, 91.
1H NMR (300 MHz, DMSO-d6): d = 13.48 (s, 2 H, 2 × SH), 10.10
(s, 2 H, 2 × CH=N), 7.72 (d, J = 7.5 Hz, 2 H, Harom), 7.55 (t, J = 7.7
Hz, 2 H, Harom), 7.10 (d, J = 8.3 Hz, 2 H, Harom), 7.02 (t, J = 7.4 Hz,
2 H, Harom), 4.10 (br, 4 H, 2 × OCH2), 3.10 (s, 4 H, 2 × CH2), 2.20
(br, 4 H, 2 × CH2).
Lariat Ethers 4a–d; General Procedure
To a soln of the azacrown macrocycle 3a or 3d (0.1 mmol) in EtOH
(5 mL) was added NaOEt (0.25 mmol), the mixture was stirred for
2 min, and MeI or BnCl (0.2 mmol) was added. The reaction mix-
ture was stirred at r.t. for 5 h and then poured onto n-hexane (5 mL).
The solid obtained was collected by filtration and crystallized
(EtOH–n-hexane, 3:1) to give compounds 4a–d.
13C NMR (75 MHz, DMSO-d6): d = 23.8, 25.3, 68.5, 113.7, 120.5,
121.0, 126.8, 134.9, 150.2, 159.7, 159.9, 161.4.
MS (EI): m/z = 520 [M+], 346, 288, 228, 196, 174 (base peak), 102,
77.
2,3:14,15-Dibenzo-6,7:10,11-bis[3-(methylthio)-4H-1,2,4-triaz-
olo][1,16,5,6,11,12]dioxatetraazacyclooctadeca-4,12-diene (4a)
IR (KBr): 3035 (aromatic CH stretch), 2930 (aliphatic CH stretch),
1599 (C=N) cm–1.
2,3:15,16-Dibenzo-6,7:11,12-bis[3-mercapto-4H-1,2,4-triazo-
lo][1,17,5,6,12,13]dioxatetraazacyclononadeca-4,13-diene (3d)
IR (KBr): 3052 (aromatic CH stretch), 2778 (SH stretch), 1605
(C=N) cm–1.
1H NMR (300 MHz, DMSO-d6): d = 9.05 (s, 2 H, 2 × CH=N), 7.90
(d, J = 7.1 Hz, 2 H, Harom), 7.63 (t, J = 7.1 Hz, 2 H, Harom), 7.23 (d,
J = 8.4 Hz, 2 H, Harom), 7.10 (t, J = 7.5 Hz, 2 H, Harom), 4.44 (s, 4 H,
2 × OCH2), 3.08 (s, 4 H, 2 × CH2), 2.50 (s, 6 H, 2 × CH3).
1H NMR (300 MHz, DMSO-d6): d = 13.66 (s, 2 H, 2 × SH), 9.61 (s,
2 H, 2 × CH=N), 7.70 (d, J = 7.6 Hz, 2 H, Harom), 7.57 (t, J = 7.7 Hz,
2 H, Harom), 7.22 (d, J = 8.4 Hz, 2 H, Harom), 7.06 (t, J = 7.5 Hz, 2 H,
Harom), 4.48 (s, 4 H, 2 × OCH2), 2.73 (br, 4 H, 2 × CH2), 2.02 (br, 2
H, CH2).
13C NMR (75 MHz, DMSO-d6): d = 14.6, 23.4, 67.5, 113.4, 120.2,
121.6, 127.4, 135.7, 148.1, 151.1, 159.4, 165.0.
13C NMR (75 MHz, DMSO-d6): d = 22.6, 24.2, 68.9, 114.9, 121.4,
122.2, 126.4, 135.1, 150.6, 159.1, 160.7, 161.5.
MS (EI): m/z = 520 [M+], 473, 264, 256, 242, 146 (base peak), 120,
102, 91.
MS (EI): m/z = 506 [M+], 360, 264, 242, 210, 146 (base peak), 91.
2,3:15,16-Dibenzo-6,7:11,12-bis[3-(methylthio)-4H-1,2,4-triaz-
olo][1,17,5,6,12,13]dioxatetraazacyclononadeca-4,13-diene (4b)
IR (KBr): 3030 (aromatic CH stretch), 2928 (aliphatic CH stretch),
1601 (C=N) cm–1.
2,3:15,16-Dibenzo-6,7:11,12-bis[3-mercapto-4H-1,2,4-triazo-
lo][1,17,5,6,12,13]dioxatetraazacyclohenicosa-4,13-diene (3e)
IR (KBr): 3045 (aromatic CH stretch), 2772 (SH stretch), 1601
(C=N) cm–1.
1H NMR (300 MHz, DMSO-d6): d = 8.74 (s, 2 H, 2 × CH=N), 7.70
(d, J = 6.5 Hz, 2 H, Harom), 7.63 (t, J = 6.8 Hz, 2 H, Harom), 7.26 (d,
J = 7.9 Hz, 2 H, Harom), 7.07 (t, J = 7.1 Hz, 2 H, Harom), 4.51 (s, 4 H,
2 × OCH2), 2.74 (t, J = 5.5 Hz, 4 H, 2 × CH2), 2.38 (s, 6 H, 2 × CH3),
2.03 (t, J = 5.4 Hz, 2 H, CH2).
1H NMR (300 MHz, DMSO-d6): d = 13.69 (s, 2 H, 2 × SH), 9.73 (s,
2 H, 2 × CH=N), 7.72 (d, J = 7.5 Hz, 2 H, Harom), 7.54 (t, J = 7.5 Hz,
2 H, Harom), 7.15 (d, J = 8.3 Hz, 2 H, Harom), 7.02 (t, J = 7.5 Hz, 2 H,
Harom), 4.17 (br, 4 H, 2 × OCH2), 2.75 (br, 4 H, 2 × CH2), 2.00 (br,
2 H, CH2), 1.89 (br, 4 H, 2 × CH2).
13C NMR (75 MHz, DMSO-d6): d = 15.3, 22.9, 24.9, 68.8, 114.9,
120.4, 121.9, 127.0, 135.5, 146.7, 152.7, 159.5, 160.7.
13C NMR (75 MHz, DMSO-d6): d = 22.7, 22.9, 25.7, 68.4, 113.9,
120.9, 121.4, 127.7, 134.7, 150.2, 158.9, 161.7, 161.8.
MS (EI): m/z = 534 [M+], 491, 270, 264, 256, 146 (base peak), 120,
102, 91, 77.
MS (EI): m/z = 534 [M+], 360, 278, 242, 210, 174 (base peak), 134,
102, 77.
2,3:14,15-Dibenzo-6,7:10,11-bis[3-(benzylthio)-4H-1,2,4-triazo-
lo][1,16,5,6,11,12]dioxatetraazacyclooctadeca-4,12-diene (4c)
IR (KBr): 3100 (CH=N stretch), 3030 (aromatic CH stretch), 2933
(aliphatic CH stretch), 1601 (C=N) cm–1.
2,3:16,17-Dibenzo-6,7:12,13-bis[3-mercapto-4H-1,2,4-triazo-
lo][1,18,5,6,13,14]dioxatetraazacycloicosa-4,14-diene (3f)
IR (KBr): 3033 (aromatic CH stretch), 2784 (SH stretch), 1605
(C=N) cm–1.
1H NMR (300 MHz, DMSO-d6): d = 8.97 (s, 2 H, 2 × CH=N), 7.88
(d, J = 7.4 Hz, 2 H, Harom), 7.63 (t, J = 7.0 Hz, 2 H, Harom), 7.23–7.30
(m, 12 H, Harom), 7.09 (t, J = 6.8 Hz, 2 H, Harom), 4.41 (s, 4 H, 2 ×
OCH2), 4.31 (s, 4 H, 2 × CH2Ph), 3.05 (s, 4 H, 2 × CH2).
1H NMR (300 MHz, DMSO-d6): d = 13.58 (s, 2 H, 2 × SH), 9.92 (s,
2 H, 2 × CH=N), 7.71 (d, J = 7.3 Hz, 2 H, Harom), 7.56 (t, J = 7.0 Hz,
2 H, Harom), 7.21 (d, J = 8.0 Hz, 2 H, Harom), 7.01 (t, J = 7.1 Hz, 2 H,
Harom), 4.49 (s, 4 H, 2 × OCH2), 2.72 (s, 4 H, 2 × CH2), 1.52 (s, 4 H,
2 × CH2).
13C NMR (75 MHz, DMSO-d6): d = 23.4, 36.2, 67.3, 113.5, 120.2,
121.5, 127.6, 127.8, 128.8, 129.4, 135.7, 137.5, 146.7, 151.0, 159.4,
165.4.
13C NMR (75 MHz, DMSO-d6): d = 25.1, 25.4, 69.9, 115.3, 121.2,
122.0, 125.9, 135.0, 151.0, 158.7, 159.9, 161.7.
MS (EI): m/z = 672 [M+], 434, 408, 317, 264, 91 (base peak), 77.
Synthesis 2009, No. 15, 2557–2560 © Thieme Stuttgart · New York

2560
N. Foroughifar et al.
PAPER
2,3:15,16-Dibenzo-6,7:11,12-bis[3-(benzylthio)-4H-1,2,4-triazo-
lo][1,17,5,6,12,13]dioxatetraazacyclononadeca-4,13-diene (4d)
IR (KBr): 3104 (CH=N stretch), 3040 (aromatic CH stretch), 2943
(aliphatic CH stretch), 1597 (C=N) cm–1.
(8) (a) Bradshaw, J. S.; Huszthy, P.; McDaniel, C. W.; Zhu, C.
Y.; Dalley, N. K.; Izatt, R. M.; Lifson, S. J. Org. Chem.
1990, 55, 3129. (b) Bradshaw, J. S.; Thompson, P. K.; Izatt,
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1H NMR (300 MHz, DMSO-d6): d = 8.67 (s, 2 H, 2 × CH=N), 7.68
(d, J = 7.4 Hz, 2 H, Harom), 7.58 (t, J = 7.3 Hz, 2 H, Harom), 7.21–7.25
(m, 12 H, Harom), 7.06 (t, J = 7.2 Hz, 2 H, Harom), 4.48 (s, 4 H, 2 ×
OCH2), 4.17 (s, 4 H, 2 × CH2Ph), 2.75 (br, 4 H, 2 × CH2), 2.01 (br,
2 H, CH2).
13C NMR (75 MHz, DMSO-d6): d = 23.1, 25.0, 37.1, 68.5, 114.6,
120.4, 121.9, 127.2, 127.9, 128.8, 129.3, 135.5, 137.1, 145.2, 152.7,
159.5, 161.6.
MS (EI): m/z = 686 [M+], 448, 422, 331, 91 (base peak), 77.
(11) Weber, E.; Vögtle, F. Top. Curr. Chem. 1981, 98, 14.
(12) Gokel, G. W.; Trafton, J. E. Cation Binding by Lariat Ethers,
In Cation Binding by Macrocycles; Inoue, Y.; Gokel, G. W.,
Eds.; Marcel Dekker: New York, 1990, 253; see also p. 279.
(13) Foroughifar, N.; Mobinikhaledi, A.; Ebrahimi, S.;
Moghanian, H.; Bodaghi Fard, M. A.; Kalhor, M.
Tetrahedron Lett. 2009, 50, 836.
Acknowledgment
We gratefully acknowledge the financial support from the Research
Council of Arak University.
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