Synthesis of ferrocenyl-1-(4-pyridylmethyl)- and ferrocenyl-1-[2-hydroxy-1, 2-bis(4-pyridyl)ethyl]pyrazoles

Article abstract of DOI:10.1055/s-2004-831204

Pyridine-4-carbaldehyde reacts with ferrocenyl-4,5-dihydropyrazoles to yield ferrocenyl-1-(4-pyridylmethyl)pyrazoles and ferrocenyl-1-[2-hydroxy- 1,2-bis(4-pyridyl)ethyl]pyrazoles. The structures of the compounds obtained were established based on spectroscopic (IR, mass, ¹H and ¹³C NMR) data. X-ray diffraction data for 4-[3-(p-bromophenyl)-5-ferrocenyl-l-(4- pyridyl)-methylpyrazole corroborate its structure.

Full text of DOI:10.1055/s-2004-831204

PAPER
2471
Synthesis of Ferrocenyl-1-(4-pyridylmethyl)- and Ferrocenyl-1-[2-hydroxy-
1,2-bis(4-pyridyl)ethyl]pyrazoles
S
ynthesisof Fe
r
d
rocenylpyra
u
zoles ardo A. Vázquez López,a Elena I. Klimova,*a Tatiana Klimova,a Cecilio Alvarez Toledano,b Lena Ruíz Ramírez,a
Ruben Alfredo Toscano,b Marcos Martínez Garcíab
a
Facultad de Química, Universidad Nacional Autónoma de México, Cd. Universitaria, Coyoacán, C.P. 04510, México D.F., México
b
Instituto de Química, Universidad Nacional Autónoma de México, Cd. Universitaria, Coyoacán, C.P. 04510, México D.F., México
Fax +52(5)556225371; E-mail: klimova@servidor.unam.mx
Received 9 April 2004; revised 9 June 2004
zoles. However, the use of conventional oxidation proce-
Abstract: Pyridine-4-carbaldehyde reacts with ferrocenyl-4,5-di-
dures is inapplicable in this case, as it can result in
hydropyrazoles to yield ferrocenyl-1-(4-pyridylmethyl)pyrazoles
destruction of the metallocene structure of ferrocene.
and
ferrocenyl-1-[2-hydroxy-1,2-bis(4-pyridyl)ethyl]pyrazoles.
The structures of the compounds obtained were established based
on spectroscopic (IR, mass, 1H and 13C NMR) data. X-ray diffrac-
tion data for 4-[3-(p-bromophenyl)-5-ferrocenyl-1-(4-pyridyl)-
methylpyrazole corroborate its structure.
In this connection, it is of interest to develop procedures
for the synthesis of pyrazoles with ferrocenyl substituents
and to study their chemical and pharmacological proper-
ties. The aim of the present study was the study of an in-
tramolecular redox process that takes place in the reaction
of ferrocenyl-4,5-dihydropyrazoles with pyridine-4-car-
baldehyde.
Key words: a,b-unsaturated ketones, ferrocenylpyrazolines, ferro-
cenyl-1-(4-pyridylmethyl)pyrazoles, ferrocenyl-1-[2-hydroxy-1,2-
bis(4-pyridyl)ethyl]pyrazoles
Ferrocenyl-4,5-dihydropyrazoles 1a–d and 2a–e were
used as the starting compounds (Figure 1).
Studies of pharmacological properties and metabolism of
biologically active heterocyclic compounds are currently
focused on pyrazole derivatives. Being non-steroidal
pharmaceuticals, these often possess a complex of valu-
able medicinal characteristics and do not injure living or-
ganisms.1–5 Medicines of the pyrazole series manifest
anti-inflammatory, analgesic, antiviral, antithrombotic
and anti-psychotic activities and are also favorable for
cardiovascular and gastrointestinal systems.
It is known that the introduction of ferrocene substituents
into molecules of organic compounds leads to an enhance-
ment (or to the appearance) of biological activity of the re-
sulting compounds and to a decrease in their toxicity
compared to the initial compounds.6 Thus ferrocenyl-sub-
stituted 4,5-dihydropyrazoles also belong to pharmaco-
logically active compounds. In particular, 4-acetyl-3-
ferrocenyl-2,4,5-triazatricyclo[5.2.2.02,6]undec-5-ene ex-
hibits high antiviral activity.7 One would expect that the
introduction of additional ferrocenilic fragments into mol-
ecules of pyrazoles of this class will afford products pos-
Figure 1
Compounds 1a–d and 2a–e were prepared by condensa-
tion of hydrazine hydrate with ferrocenyl a,b-enones 3a–
d and 4a–e, respectively (Figure 2).
sessing
a broader spectrum of useful biological
characteristics.
Pyrazoles with ferrocenyl substituents are virtually unex-
plored, since ferrocenyl 1,3-diketones, which are the start-
ing compounds for their synthesis, are usually hardly
accessible.8 Ferrocenyl-4,5-dihydropyrazoles, which can
easily be prepared from ferrocene-containing a,b-enones
and hydrazine,8,9 are the most available compounds of the
ferrocene series suitable for the access to ferrocenylpyra-
Figure 2
SYNTHESIS 2004, No. 15, pp 2471–2478
x
x.
x
x
.
2
0
0
4
Advanced online publication: 02.09.2004
DOI: 10.1055/s-2004-831204; Art ID: M02304SS
© Georg Thieme Verlag Stuttgart · New York

2472
E. A. V. López et al.
PAPER
Dihydropyrazoles 1a–d and 2a–e are yellow or orange by abstracting a proton from water (to yield compounds 5
crystalline compounds that are sufficiently stable in the and 7) or by reacting with the second molecule of pyri-
dry state. We have found that dihydropyrazoles react with dine-4-carbaldehyde (to yield compounds 6 and 8). The
pyridine-4-carbaldehyde (ca 120 °C, ca 20 min) to yield formation of double addition products 6 and 8 is in favor
mixtures of two types of products, namely, 5a–d + 6a–d of the suggested scheme.
and 7a–e + 8a–e (Scheme 1).
An alternative mechanism involving a 1,3-hydride shift
The structures of compounds 5–8 were established based from the carbon atom 5 in the cation 9 was ruled out ex-
1
on the data from mass spectrometry, IR and H and 13C perimentally (Scheme 3).
NMR spectroscopy, and elemental analysis (see experi-
mental section).
Thus we have found that the reaction product of deuterat-
ed 3-phenyl-4,5-dihydro-2H-benzo[g]indazole (2f-D)
The spatial structure of one of the reaction products, viz., with pyridine-4-carbaldehyde contained virtually no deu-
compounds 5b, was determined using X-ray diffraction terium atoms.
analysis of a single crystal prepared by crystallization
from CHCl3. The general view of the molecule 5b is given
in Figure 3a, the crystal packing is shown in Figure 3b.
The biological activity of compounds 5–8 is being re-
searched.
The five-membered ring in the molecule 5b is a planar and
The 1H and 13C NMR spectra were recorded on a Unity Inova Vari-
an spectrometer (at 300 MHz and 75 MHz, respectively) for solu-
tions in CDCl3 with tetramethylsilane as the internal standard. The
mass spectra were obtained on a Varian MAT CH-6 instrument (EI
MS, 70 eV). An Elemental Analysis system GmbH was used for el-
emental analyses. IR spectra were obtained for KBr pellets on a
Specord IR-75 instrument. Chromatographic separations were car-
ried out on columns with alumina (Brockmann activity III). The unit
virtually equilateral pentagon, the ferrocenyl substituent
1
being in the eclipsed conformation. According to H
NMR data, compounds 6a–d and 8a–e were formed as
single diastereomeric forms. We could not elucidate their
spatial structures because no crystals suitable for the X-
ray diffraction analysis could be prepared.
Thus, the reaction of 4,5-dihydropyrazoles 1 and 2 with cell parameters and the X-ray diffraction intensities were recorded
on a Bruker Smart Apex CCD diffractometer. The principal geo-
pyridine-4-carbaldehyde proceeds with intramolecular
metrical parameters of the molecule 5b are listed in the legend to
oxidation of the pyrazoline ring (→ pyrazole) and con-
Figure 1. The structure of compound 5b was solved by the direct
comitant reduction of an exocyclic functionality into the
method (SHELXS) and refined using full-matrix least-squares on
methylene group.
F2.
A putative reaction scheme may be suggested, which
gives a rationale for the transformations observed. Initial-
ly, the dihydropyrazole with a free 1-NH group adds to
pyridine-4-carbaldehyde to yield a cation 9 (Scheme 2).
The following reagents were purchased from Aldrich: ferrocenecar-
baldehyde, 99%; acetylferrocene, 98%; 4-bromobenzaldehyde,
99%; 4-bromoacetophenone, 98%; p-anisaldehyde, 98%; 4-meth-
oxyacetophenone, 99%; a-tetralone, 98%; 5-methoxy-1-tetralone,
97%; 6-methoxy-1-tetralone, 99%; 7-methoxy-1-tetralone, 99%;
5,7-dimethyl-1-tetralone, 97%; 4-pyridinecarboxaldehyde, 97%;
benzaldehyde-d, 98 atom% D.
Presumably, this is followed by an intramolecular shift of
the electron pairs leading to a bipolar mesomeric interme-
diate 10 and then to a carbanion 11. The latter is stabilized
Scheme 1
Synthesis 2004, No. 15, 2471–2478 © Thieme Stuttgart · New York

PAPER
Synthesis of Ferrocenyl Pyrazoles
2473
Figure 3 (a) Molecular structure of 5b. Selected bond lengths (Å): N(7)–N(8) = 1.356(3); N(7)–C(11) = 1.361(3); C(10)–C(11) = 1.363(4);
N(7)–C(12) = 1.448(3); C(9)–C(10) = 1.399(4); C(9)–N(8) = 1.330(3); C(9)–C(13) = 1.473(4); C(11)–C(19) = 1.463(4); C(16)–Br(1) =
1.901(3). Selected bond angles (°): C(11)–N(7)–N(8) = 112.1(2); N(8)–N(7)–C(12) = 117.5(2); N(8)–C(9)–C(10) = 110.5(2); N(8)–C(9)–
C(13) = 119.8(3); C(11)–N(7)–C(12) = 130.4(2); C(9)–N(8)–N(7) = 105.1(2); C(11)–C(10)–C(9) = 106.5(3); N(7)–C(11)–C(10) = 105.8(2);
N(7)–C(11)–C(19) = 125.7(2). (b) Crystal packing of 5b.
Scheme 2
Synthesis 2004, No. 15, 2471–2478 © Thieme Stuttgart · New York

2474
E. A. V. López et al.
PAPER
Scheme 3
3-Aryl-1-ferrocenylprop-2-enones 3a,d and 3b,c; General Pro-
cedure
J = 6.0 Hz, 2 H, ArH), 7.17 (d, J = 8.4 Hz, 2 H, ArH), 7.53 (d, J =
8.4 Hz, 2 H, ArH), 8.53 (d, J = 6.0 Hz, 2 H, ArH).
These compounds were prepared by condensation of acetylfer-
rocene with arenecarbaldehydes or acetophenones with ferrocene-
carbaldehyde in aqueous-ethanolic alkali.9–11
13C NMR (CDCl3): d = 51.93 (CH2), 66.61, 68.68 (C5H4), 69.60
(C5H5), 77.80 (CipsoFc), 104.55 (CH=), 121.21, 130.09, 132.00,
150.06 (ArH), 123.16, 129.04, 144.09, 146.73, 151.27 (C).
MS: m/z = 498 [M]+.
2-Ferrocenylmethylidenetetralones 4a–e and 2-Benzylidene-
tetralone 4f; General Procedure
Anal. Calcd for C25H20BrFeN3: C, 60.28; H, 4.04; Br, 16.04; Fe,
11.21; N, 8.43. Found: C, 60.46; H, 3.91; Br, 16.21; Fe, 11.40; N,
8.27.
These compounds were prepared by condensation of ferrocenecar-
baldehyde and benzaldehyde-d with tetralones in aqueous-ethanolic
alkali.13 The physical and 1H NMR spectroscopic characteristics of
compounds 3a–d and 4a–e were in accord with the literature da-
ta.12,13
3-(4-Bromophenyl)-5-ferrocenyl-1-(4-pyridylmethyl)pyrazole
(5b)
Yield: 40%; mp 172–173 °C.
Ferrocenyl-4,5-dihydropyrazoles 1a–d and 2a–f; General Pro-
cedure
IR (KBr): 3082, 3031, 2936, 1650, 1599, 1562, 1464, 1444, 1413,
1357, 1310, 1219, 1105, 1070, 1006, 956, 882, 831, 787 cm–1.
1H NMR (CDCl3): d = 4.13 (s, 5 H, C5H5), 4.29 (m, 2 H, C5H4), 4.31
(m, 2 H, C5H4), 5.54 (br s, 2 H, CH2), 6.69 (s, 1 H, CH=), 7.00 (d,
J = 6.0 Hz, 2 H, ArH), 7.54 (d, J = 8.7 Hz, 2 H, ArH), 7.72 (d, J =
8.7 Hz, 2 H, ArH), 8.57 (d, J = 6.0 Hz, 2 H, ArH).
13C NMR (CDCl3): d = 52.36 (CH2), 68.30, 69.19 (C5H4), 69.68
(C5H5), 74.01 (CipsoFc), 103.32 (CH=), 121.20, 127.17, 131.69,
150.14 (ArH), 121.69, 132.08, 143.50, 146.79, 146.84 (C).
These compounds were obtained according to the known
procedure10,11 by reactions of the enones 3a–d and 4a–f, respective-
ly, with hydrazine hydrate in EtOH. The reaction products that pre-
cipitated (1a–d and 2a–f) were filtered off, washed with EtOH and
dried in vacuo. Their yields ranged from 60% to 70% and the melt-
ing points corresponded to the literature data.11–13
Reaction of Pyridine-4-carbaldehyde with Ferrocenyl-4,5-dihy-
dropyrazoles 1a–d; General Procedure
MS: m/z = 498 [M]+.
The dihydropyrazole 1a–d (2.0 mmol) was added with stirring to
pyridine-4-carbaldehyde (0.32 g, 3.0 mmol) at 120 °C. The mixture
was stirred at 100–120 °C for 20 min, and excess of pyridinecarbal-
dehyde was steam-distilled. The residue was chromatographed on
alumina (hexane–CH2Cl2, 4:1) to yield ferrocenyl-1-(4-pyridyl-
methyl)pyrazoles 5a–d and ferrocenyl-1-[2-hydroxy-1,2-bis(4-py-
ridyl)ethyl]pyrazoles 6a–d.
Anal. Calcd for C25H20BrFeN3: C, 60.28; H, 4.04; Br, 16.04; Fe,
11.21; N, 8.43. Found: C, 60.35; H, 4.23; Br, 15.85; Fe, 11.02; N,
8.62.
3-(4-Methoxyphenyl)-5-ferrocenyl-1-(4-pyridylmethyl)pyra-
zole (5c)
Yield: 34%; mp 163–165 °C.
5-(4-Bromophenyl)-3-ferrocenyl-1-(4-pyridylmethyl)pyrazole
(5a)
Yield: 35%; mp 165–166 °C.
IR (KBr): 3077, 2934, 2835, 1601, 1566, 1531, 1462, 1437, 1359,
1292, 1253, 1173, 1107, 1032, 997, 957, 832, 828, 789 cm–1.
1H NMR (CDCl3): d = 3.85 (s, 3 H, CH3), 4.13 (s, 5 H, C5H5),4.28
(m, 2 H, C5H4), 4.31 (m, 2 H, C5H4), 5.54 (br s, 2 H, CH2), 6.65 (s,
1 H, CH=), 6.96 (d, J = 9.0 Hz, 2 H, ArH), 7.01 (d, J = 6.0 Hz, 2 H,
ArH), 7.78 (d, J = 9.0 Hz, 2 H, ArH), 8.56 (d, J = 6.0 Hz, 2 H, ArH).
IR (KBr): 3090, 3026, 2954, 1654, 1598, 1561, 1472, 1447, 1409,
1379, 1317, 1295, 1103, 1068, 1031, 968, 873, 828, 779 cm–1.
1H NMR (CDCl3): d = 4.10 (s, 5 H, C5H5), 4.30 (m, 2 H, C5H4), 4.72
(m, 2 H, C5H4), 5.31 (br s, 2 H, CH2), 6.43 (s, 1 H, CH=), 6.93 (d,
13C NMR (CDCl3): d = 52.24 (CH2), 55.31 (CH3), 68.29, 69.09
(C5H4), 69.68 (C5H5), 74.35 (CipsoFc), 102.97 (CH=), 114.02,
Synthesis 2004, No. 15, 2471–2478 © Thieme Stuttgart · New York

PAPER
Synthesis of Ferrocenyl Pyrazoles
2475
121.24, 126.88, 150.12 (ArH), 125.92, 143.09, 147.16, 151.12,
159.44 (C).
Anal. Calcd for C31H25BrFeN4O: C, 61.52; H, 4.16; Br, 13.20; Fe,
9.23; N, 9.25. Found: C, 61.74; H, 4.01; Br, 13.41; Fe, 9.39; N, 9.12.
MS: m/z = 449 [M]+.
3-(4-Methoxyphenyl)-5-ferrocenyl-1-[2-hydroxy-1,2-bis(4-py-
ridyl)ethyl]pyrazole (6c)
Yield: 25%; mp 179–181 °C.
Anal. Calcd for C26H23FeN3O: C, 69.50; H, 5.16; Fe, 12.43; N, 9.35.
Found: C, 69.71; H, 5.32; Fe, 12.64; N, 9.16.
IR (KBr): 3333, 3081, 2956, 2835, 1941, 1599, 1563, 1531, 1465,
1415, 1384, 1292, 1249, 1177, 1107, 1069, 1031, 1003, 959, 835,
790 cm–1.
5-(4-Methoxyphenyl)-3-ferrocenyl-1-(4-pyridylmethyl)pyra-
zole (5d)
Yield: 36%; mp 135–136 °C.
1H NMR (CDCl3): d = 3.89 (s, 3 H, CH3), 4.08 (s, 5 H, C5H5), 3.94
(m, 1 H, C5H4), 4.25 (m, 3 H, C5H4), 5.40 (dd, J = 4.2, 9.0 Hz, 1 H,
CH), 5.60 (d, J = 4.2 Hz, 1 H, CH), 6.08 (d, J = 9.0 Hz, 1 H, OH),
6.55 (s, 1 H, CH=), 7.02 (d, J = 8.7 Hz, 2 H, ArH), 7.06 (d, J = 6.3
Hz, 2 H, ArH), 7.20 (d, J = 6.3 Hz, 2 H, ArH), 7.81 (d, J = 8.7 Hz,
2 H, ArH), 8.45 (d, J = 6.3 Hz, 2 H, ArH), 8.61 (d, J = 6.3 Hz, 2 H,
ArH).
13C NMR (CDCl3): d = 55.40 (CH3), 65.01 (CH), 68.18, 69.12,
69.20, 69.30 (C5H4), 69.75 (C5H5), 73.86 (CipsoFc), 75.91 (CHOH),
103.17 (CH=), 114.21, 121.14, 122.15, 127.00, 149.73, 150.21
(ArH), 121.60, 123.30, 125.03, 145.04, 147.01, 159.93 (C).
IR (KBr): 3083, 2936, 2837, 1601, 1562, 1538, 1485, 1413, 1348,
1295, 1251, 1173, 1101, 1069, 1028, 996, 945, 830, 779, 720 cm–1.
1H NMR (CDCl3): d = 3.83 (s, 3 H, CH3), 4.10 (s, 5 H, C5H5),4.29
(m, 2 H, C5H4), 4.72 (m, 2 H, C5H4), 5.32 (br s, 2 H, CH2), 6.39 (s,
1 H, CH=), 6.91 (d, J = 8.7 Hz, 2 H, ArH), 6.94 (d, J = 6.6 Hz, 2 H,
ArH), 7.24 (d, J = 8.7 Hz, 2 H, ArH), 8.52 (d, J = 6.6 Hz, 2 H, ArH).
13C NMR (CDCl3): d = 51.82 (CH2), 55.34 (CH3), 66.62, 68.59
(C5H4), 69.48 (C5H5), 78.23 (CipsoFc), 104.14 (CH=), 114.19,
121.33, 129.22, 150.01 (ArH), 122.13, 145.12, 147.18, 150.63,
160.46 (C).
MS: m/z = 449 [M]+.
MS: m/z = 556 [M]+.
Anal. Calcd for C26H23FeN3O: C, 69.50; H, 5.16; Fe, 12.43; N, 9.35.
Found: C, 69.29; H, 5.03; Fe, 12.28; N, 9.49.
Anal. Calcd for C32H28FeN4O2: C, 69.07; H, 5.07; Fe, 10.04; N,
10.07. Found: C, 68.87; H, 4.89; Fe, 10.19; N, 10.23.
5-(4-Bromophenyl)-3-ferrocenyl-1-[2-hydroxy-1,2-bis(4-py-
ridyl)ethyl]pyrazole (6a)
Yield: 22%; mp 235–237 °C.
5-(4-Methoxyphenyl)-3-ferrocenyl-1-[2-hydroxy-1,2-bis(4-py-
ridyl)ethyl]pyrazole (6d)
Yield: 18%; mp 172–173 °C.
IR (KBr): 3500–3040, 2861, 2723, 1913, 1599, 1563, 1474, 1412,
1352, 1315, 1219, 1101, 1069, 999, 877, 816, 805, 714 cm–1.
IR (KBr): 3335, 3082, 2935, 2837, 1940, 1654, 1599, 1563, 1538,
1489, 1412, 1349, 1288, 1250, 1178, 1105, 1062, 1032, 998, 877,
825, 792, 721 cm–1.
1H NMR (CDCl3): d = 3.83 (s, 3 H, CH3), 4.12 (s, 5 H, C5H5), 4.29
(m, 2 H, C5H4), 4.74 (m, 2 H, C5H4), 5.12 (dd, J = 3.2, 8.1 Hz, 1 H,
CH), 5.53 (d, J = 3.2 Hz, 1 H, CH), 6.15 (d, J = 8.1 Hz, 1 H, OH),
6.30 (s, 1 H, CH=), 6.84 (d, J = 6.0 Hz, 2 H, ArH), 6.90 (d, J = 8.7
Hz, 2 H, ArH), 7.03 (d, J = 6.3 Hz, 2 H, ArH), 7.35 (d, J = 8.7 Hz,
2 H, ArH), 8.43 (d, J = 6.3 Hz, 2 H, ArH), 8.51 (d, J = 6.0 Hz, 2 H,
ArH).
1H NMR (CDCl3): d = 4.14 (s, 5 H, C5H5), 4.37 (m, 2 H, C5H4), 4.77
(m, 2 H, C5H4), 5.16 (d, J = 3.6 Hz, 1 H, CH), 5.64 (d, J = 3.6 Hz, 1
H, CH), 6.18 (br s, 1 H, OH), 6.36 (s, 1 H, CH=), 6.88 (d, J = 6.0
Hz, 2 H, ArH), 6.92 (d, J = 8.1 Hz, 2 H, ArH), 7.07 (d, J = 5.4 Hz,
2 H, ArH), 7.50 (d, J = 8.1 Hz, 2 H, ArH), 8.43 (d, J = 5.4 Hz, 2 H,
ArH), 8.48 (d, J = 6.0 Hz, 2 H, ArH).
13C NMR (CDCl3): d = 66.40 (CH), 66.70, 66.85, 68.98, 69.00
(C5H4), 69.54 (C5H5), 74.59 (CipsoFc), 74.61 (CHOH)), 104.37
(CH=), 121.35, 123.19, 130.38, 132.07, 149.48, 149.76 (ArH),
123.70, 128.30, 144.38, 144.51, 148.32, 151.30 (C).
MS: m/z = 556 [M]+.
Anal. Calcd for C32H28FeN4O2: C, 69.07; H, 5.07; Fe, 10.04; N,
10.07. Found: C, 69.24; H, 4.92; Fe, 9.87; N, 9.86.
MS: m/z = 605 [M]+.
Anal. Calcd for C31H25BrFeN4O: C, 61.52; H, 4.16; Br, 13.20; Fe,
9.23; N, 9.25. Found: C, 61.37; H, 4.25; Br, 13.05; Fe, 9.37; N, 9.44.
Reaction of Pyridine-4-carbaldehyde with 3-Ferrocenyl-
3,3a,4,5-tetrahydro-2H-benzo[g]indazoles 2a–e; General Proce-
dure
The condensation of compound 4a–e (2 mmol) with pyridine-4-car-
baldehyde (0.53 g, 5 mmol) was carried out at 110–120 °C for 30
min. Subsequent work-up of the reaction mixture as described
above and column chromatography (Al2O3, hexane–CH2Cl2, 4:1)
afforded 3-ferrocenyl-2-(4-pyridylmethyl)-4,5-dihydro-2H-ben-
zo[g]indazoles 7a–e and 3- ferrocenyl-2-[2-hydroxy-1,2-bis(4-py-
ridyl)ethyl]-4,5-dihydro-2H-benzo[g]indazole 8a–e.
3-(4-Bromophenyl)-5-ferrocenyl-1-[2-hydroxy-1,2-bis(4-py-
ridyl)ethyl]pyrazole (6b)
Yield: 20%; mp 224–225 °C.
IR (KBr): 3419, 3084, 2938, 2720, 1943, 1599, 1563, 1458, 1415,
1376, 1311, 1223, 1187, 1104, 1067, 1003, 885, 805, 713 cm–1.
1H NMR (CDCl3): d = 4.09 (s, 5 H, C5H5), 4.02 (m, 2 H, C5H4), 4.29
(m, 2 H, C5H4), 5.46 (dd, J = 4.0, 8.1 Hz, 1 H, CH), 5.71 (d, J = 4.0
Hz, 1 H, CH), 6.10 (d, J = 8.1 Hz, 1 H, OH), 6.60 (s, 1 H, CH=),
7.05 (d, J = 8.7 Hz, 2 H, ArH), 7.12 (d, J = 6.3 Hz, 2 H, ArH), 7.26
(d, J = 6.3 Hz, 2 H, ArH), 7.90 (d, J = 8.7 Hz, 2 H, ArH), 8.47 (d,
J = 6.3 Hz, 2 H, ArH), 8.65 (d, J = 6.3 Hz, 2 H, ArH).
3-Ferrocenyl-2-(4-pyridylmethyl)-4,5-dihydro-2H-benzo[g]in-
dazole (7a)
Yield: 37%; mp 162–163 °C.
1H NMR (CDCl3, D2O): d = 4.08 (s, 5 H, C5H5), 4.02 (m, 2 H, C5H4),
4.30 (m, 2 H, C5H4), 5.44 (d, J = 4.0 Hz, 1 H, CH), 5.71 (d, J = 4.0
Hz, 1 H, CH), 6.60 (s, 1 H, CH=), 7.04 (d, J = 8.5 Hz, 2 H, ArH),
7.12 (d, J = 6.3 Hz, 2 H, ArH), 7.27 (d, J = 6.3 Hz, 2 H, ArH), 7.90
(d, J = 8.5 Hz, 2 H, ArH), 8.47 (d, J = 6.3 Hz, 2 H, ArH), 8.61 (d,
J = 6.3 Hz, 2 H, ArH).
IR (KBr): 3078, 2923, 2843, 1946, 1626, 1594, 1554, 1495, 1462,
1414, 1371, 1307, 1233, 1103, 1066, 1030, 991, 884, 813, 793, 767,
726 cm–1.
1H NMR (CDCl3): d = 3.00 (m, 4 H, CH2), 4.14 (s, 5 H, C5H5), 4.30
(m, 4 H, C5H4), 5.71 (br s, 2 H, CH2), 7.02 (d, J = 6.0 Hz, 2 H, ArH),
7.65 (d, J = 6.3 Hz, 1 H, ArH), 7.73 (m, 1 H, ArH), 7.85 (d, J = 6.6
Hz, 2 H, ArH), 8.43 (d, J = 6.0 Hz, 2 H, ArH).
MS: m/z = 605 [M]+.
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E. A. V. López et al.
PAPER
13C NMR (CDCl3): d = 20.46, 29.76 (CH2), 52.49 (CH2), 67.74,
68.89 (C5H4), 69.40 (C5H5), 74.38 (CipsoFc), 121.12, 122.13,
150.16, 156.59 (ArH), 129.60, 136.44, 137.13, 140.59, 147.73,
160.45 (C).
MS: m/z = 475 [M]+.
Anal. Calcd for C28H25FeN3O: C, 70.75; H, 5.30; Fe, 11.75; N, 8.84.
Found: C, 70.61; H, 5.38; Fe, 12.00; N, 8.71.
MS: m/z = 445 [M]+.
3-Ferrocenyl-6,8-dimethyl-2-(4-pyridylmethyl)-4,5-dihydro-
2H-benzo[g]indazole (7e)
Yield: 27%; mp 235–237 C.
Anal. Calcd for C27H23FeN3: C, 72.82; H, 5.20; Fe, 12.55; N, 9.43.
Found: C, 72.61; H, 5.37; Fe, 12.36; N, 9.24.
IR: 3078, 3019, 2936, 2917, 2836, 1944, 1641, 1597, 1571, 1505,
1466, 1413, 1380, 1314, 1302, 1264, 1216, 1161, 1102, 1063, 1033,
991, 912, 850, 827, 797, 743 cm–1.
3-Ferrocenyl-6-methoxy-2-(4-pyridylmethyl)-4,5-dihydro-2H-
benzo[g]indazole (7b)
Yield: 33%; mp 188–189 °C.
1H NMR (CDCl3): d = 2.32 (s, 3 H, CH3), 2.34 (s, 3 H, CH3), 2.97
(m, 4 H, CH2), 4.05 (s, 5 H, C5H5), 4.30 (m, 4 H, C5H4), 5.70 (br s,
2 H, CH2), 6.96 (br s, 1 H, ArH), 7.00 (d, J = 6.3 Hz, 2 H, ArH), 7.60
(br s, 1 H, ArH), 8.57 (d, J = 6.3 Hz, 2 H, ArH).
IR (KBr): 3084, 2929, 2831, 1949, 1607, 1593, 1528, 1461, 1415,
1360, 1308, 1248, 1229, 1158, 1101, 1067, 1033, 975, 869, 814,
790 cm–1.
1H NMR (CDCl3): d = 2.97 (m, 4 H, CH2), 3.87 (s, 3 H, CH3), 4.18
(s, 5 H, C5H5), 4.35 (m, 2 H, C5H4), 4.41 (m, 2 H, C5H4), 5.75 (br s,
2 H, CH2), 6.90 (dd, J = 0.9, 8.1, Hz, 1 H, ArH), 7.11 (d, J = 6.0 Hz,
2 H, ArH), 7.21 (t, J = 8.1 Hz, 1 H, ArH), 7.43 (dd, J = 0.9, 8.1 Hz,
1 H, ArH), 8.56 (d, J = 6.0 Hz, 2 H, ArH).
13C NMR (CDCl3): d = 20.47, 22.55 (2 × CH2), 53.26 (CH2), 55.81
(CH3), 68.50, 69.59 (C5H4), 70.16 (C5H5), 75.44 (CipsoFc), 110.33,
115.51, 122.10, 150.90, 151.00 (ArH), 115.75, 125.11, 127.83,
131.96, 141.58, 148.84, 157.83 (C).
13C NMR (CDCl3): d = 19.98, 29.31 (2 × CH2), 20.87, 25.13 (2 ×
CH3), 52.51 (CH2), 67.72, 68.85 (C5H4), 69.41 (C5H5), 74.54
(CipsoFc), 120.74, 121.12, 130.47, 150.17 (ArH), 115.19, 129.26,
131.68, 135.56, 135.79, 136.92, 147.80, 148.75 (C).
MS: m/z = 473 [M]+.
Anal. Calcd for C29H27FeN3: C, 73.58; H, 5.75; Fe, 11.80; N, 8.87.
Found: C, 73.74; H, 5.52; Fe, 11.59; N, 8.67.
3-Phenyl-2-(4-pyridylmethyl)-4,5-tetrahydro-2H-benzo[g]in-
dazole (7f)
MS: m/z = 475 [M]+.
Yield: 35%; mp 143–145 °C.
Anal. Calcd for C28H25FeN3O: C, 70.75; H, 5.30; Fe, 11.75; N, 8.84.
Found: C, 70.93; H, 5.08; Fe, 11.93; N, 8.99.
1H NMR (CDCl3): d = 2.90–3.21 (m, 4 H, CH2), 5.75 (br s, 1.86 H,
CH2), 7.10 (d, J = 6.0 Hz, 2 H, ArH), 7.35–7.64 (m, 5 H, ArH), 7.72
(m, 2 H, ArH), 7.85 (d, J = 6.6 Hz, 2 H, ArH), 8.43 (d, J = 6.0 Hz,
2 H, ArH).
3-Ferrocenyl-7-methoxy-2-(4-pyridylmethyl)-4,5-dihydro-2H-
benzo[g]indazole (7c)
Yield: 31%; mp 206–207 °C.
MS: m/z = 337 [M]+.
IR (KBr): 3025, 2929, 2831, 1946, 1625, 1607, 1593, 1528, 1461,
1439, 1415, 1360, 1308, 1248, 1232, 1158, 1109, 1033, 1003, 869,
814, 790 cm–1.
Anal. Calcd for C23H19N3: C, 81.88; H, 5.68; N, 12.44. Found: C,
81.51; H, 5.97; N, 12.17.
1H NMR (CDCl3): d = 2.98 (m, 4 H, CH2), 3.84 (s, 3 H, CH3), 4.13
(s, 5 H, C5H5), 4.30 (m, 4 H, C5H4), 5.67 (br s, 2 H, CH2), 6.83 (d,
J = 2.7 Hz, 1 H, ArH), 6.85 (d, J = 1.5 Hz, 1 H, ArH), 7.02 (d, J =
6.0 Hz, 2 H, ArH), 7.70 (dd, J = 1.5, 2.7 Hz, 1 H, ArH), 8.75 (d, J =
6.0 Hz, 2 H, ArH),.
13C NMR (CDCl3): d = 19.94, 21.65 (2 × CH2), 53.44 (CH2), 55.51
(CH3), 67.85, 68.69 (C5H4), 69.38 (C5H5), 74.86 (CipsoFc), 109.48,
115.04, 125.90, 127.17, 128.71 (ArH), 124.54, 127.05, 130.99,
136.75, 138.56, 147.66, 156.76 (C).
3-Ferrocenyl-2-[2-hydroxy-1,2-bis(4-pyridyl)ethyl]-4,5-dihy-
dro-2H-benzo[g]indazole (8a)
Yield: 24%; mp 222–223 °C.
IR (KBr): 3334, 3082, 2931, 2845, 1949, 1647, 1598, 1562, 1464,
1415, 1344, 1299, 1217, 1164, 1104, 1067, 1003, 952, 876, 817,
777, 731 cm–1.
1H NMR (CDCl3): d = 2.92 (m, 2 H, CH2), 3.01 (m, 2 H, CH2), 4.07
(s, 5 H, C5H5), 4.03 (m, 1 H, C5H4), 4.16 (m, 1 H, C5H4), 4.26 (m, 1
H, C5H4), 4.31 (m, 1 H, C5H4), 5.45 (dd, J = 4.5, 8.7 Hz, 1 H, CH),
5.89 (d, J = 4.5 Hz, 1 H, CH), 6.02 (d, J = 8.7 Hz, 1 H, OH), 7.07
(d, J = 6.0 Hz, 2 H, ArH), 7.22 (d, J = 6.0 Hz, 2 H, ArH), 7.20–7.39
(m, 4 H, ArH), 8.44 (d, J = 6.0 Hz, 2 H, ArH), 8.62 (d, J = 6.0 Hz,
2 H, ArH).
MS: m/z = 475 [M]+.
Anal. Calcd for C28H25FeN3O: C, 70.75; H, 5.30; Fe, 11.75; N, 8.84.
Found: C, 70.57; H, 5.49; Fe, 11.57; N, 8.67.
3-Ferrocenyl-8-methoxy-2-(4-pyridylmethyl)-4,5-dihydro-2H-
benzo[g]indazole (7d)
Yield: 24%; mp 226–227 °C.
1H NMR (CDCl3, D2O): d = 2.91 (m, 2 H, CH2), 3.00 (m, 2 H, CH2),
4.06 (s, 5 H, C5H5), 4.03 (m, 1 H, C5H4), 4.17 (m, 1 H, C5H4), 4.26
(m, 1 H, C5H4), 4.31 (m, 1 H, C5H4), 5.45 (d, J = 4.5 Hz, 1 H, CH),
5.90 (d, J = 4.5 Hz, 1 H, CH), 7.07 (d, J = 6.0 Hz, 2 H, ArH), 7.22
(d, J = 6.0 Hz, 2 H, ArH), 7.20–7.39 (m, 4 H, ArH), 8.44 (d, J = 6.0
Hz, 2 H, ArH), 8.62 (d, J = 6.0 Hz, 2 H, ArH).
IR (KBr): 3084, 3021, 2937, 2846, 1943, 1597, 1569, 1503, 1478,
1451, 1427, 1372, 1301, 1244, 1207, 1163, 1104, 1039, 1007, 905,
823, 800, 748 cm–1.
1H NMR (CDCl3): d = 2.96 (m, 4 H, CH2), 3.85 (s, 3 H, CH3), 4.13
(s, 5 H, C5H5), 4.31 (m, 4 H, C5H4), 5.71 (br s, 2 H, CH2), 6.82 (dd,
J = 2.7, 8.1 Hz, 2 H, ArH), 7.02 (dd, J = 1.5, 6.0 Hz, 1 H, ArH), 7.18
(d, J = 8.1 Hz, 1 H, ArH), 7.42 (d, J = 2.7 Hz, 1 H, ArH), 8.58 (dd,
J = 1.5, 6.0 Hz, 2 H, ArH).
13C NMR (CDCl3): d = 20.71, 28.95 (2 × CH2), 52.51 (CH2), 55.53
(CH3), 67.76, 68.90 (C5H4), 69.41 (C5H5), 74.38 (CipsoFc), 106.50,
114.52, 121.10, 129.24, 150.21 (ArH), 115.71, 128.69, 130.52,
137.23, 147.71, 148.39, 158.72 (C).
MS: m/z = 552 [M]+.
Anal. Calcd for C33H28FeN4O: C, 71.75; H, 5.11; Fe, 10.11; N,
10.14. Found: C, 71.49; H, 4.95; Fe, 10.30; N, 9.97.
3-Ferrocenyl-6-methoxy-2-[2-hydroxy-1,2-bis(4-pyridyl)ethyl]-
4,5-dihydro-2H-benzo[g]indazole (8b)
Yield: 19%; mp 235 °C (decomp.).
IR (KBr): 3399, 3081, 3023, 2931, 2832, 1945, 1612, 1596, 1567,
1499, 1453, 1414, 1375, 1343, 1301, 1260, 1212, 1101, 1044, 1002,
925, 876, 821, 793, 727 cm–1.
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Synthesis of Ferrocenyl Pyrazoles
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1H NMR (CDCl3): d = 2.90 (m, 2 H, CH2), 3.11 (m, 2 H, CH2), 3.90
(s, 3 H, CH3), 4.05 (s, 5 H, C5H5), 4.03 (m, 1 H, C5H4), 4.16 (m, 1
H, C5H4), 4.26 (m, 1 H, C5H4), 4.30 (m, 1 H, C5H4), 5.44 (dd, J =
4.2, 9.0 Hz, 1 H, CH), 5.89 (d, J = 4.2 Hz, 1 H, CH), 6.07 (d, J = 9.0
Hz, 1 H, OH), 6.90 (dd, J = 0.9, 8.4 Hz, 1 H, ArH), 7.08 (d, J = 6.0
Hz, 2 H, ArH), 7.21 (d, J = 6.0 Hz, 2 H, ArH), 7.32 (t, J = 8.4 Hz, 1
H, ArH), 7.58 (dd, J = 0.9, 8.4, Hz, 1 H, ArH), 8.45 (d, J = 6.0 Hz,
2 H, ArH), 8.62 (d, J = 6.0 Hz, 2 H, ArH).
13C NMR (CDCl3): d = 19.59, 21.44 (2 × CH2), 55.59 (CH3), 65.50
(CH), 67.09, 68.40, 68.77, 69.09 (C5H4), 69.42 (C5H5), 73.72
(CHOH), 76.18 (CipsoFc), 110.23, 115.05, 121.28, 122.23, 127.31,
149.70, 150.25 (ArH), 114.97, 125.0, 129.97, 139.18, 147.43,
148.51, 149.60, 156.95 (C).
IR (KBr): 3337, 3090, 3034, 2937, 2858, 1944, 1645, 1600, 1563,
1506, 1417, 1372, 1300, 1197, 1169, 1106, 1073, 1036, 1001, 961,
881, 851, 813, 745 cm–1.
1H NMR (CDCl3): d = 2.35 (s, 3 H, CH3), 2.40 (s, 3 H, CH3), 2.93
(m, 4 H, 2 × CH2), 4.05 (s, 5 H, C5H5), 4.02 (m, 1 H, C5H4), 4.15 (m,
1 H, C5H4), 4.26 (m, 1 H, C5H4), 4.29 (m, 1 H, C5H4), 5.45 (dd, J =
4.2, 8.7 Hz, 1 H, CH), 5.87 (d, J = 4.2 Hz, 1 H, CH), 6.18 (d, J = 8.7
Hz, 1 H, OH), 7.03 (s, 1 H, ArH), 7.07 (d, J = 6.0 Hz, 2 H, ArH),
7.22 (d, J = 6.0 Hz, 2 H, ArH), 7.64 (s, 1 H, ArH), 8.43 (d, J = 6.0
Hz, 1 H, ArH), 8.62 (d, J = 6.0 Hz, 2 H, ArH).
1H NMR (CDCl3, D2O): d = 2.35 (s, 3 H, CH3), 2.40 (s, 3 H, CH3),
2.93 (m, 4 H, 2 × CH2), 4.06 (s, 5 H, C5H5), 4.02 (m, 1 H, C5H4),
4.14 (m, 1 H, C5H4), 4.26 (m, 1 H, C5H4), 4.30 (m, 1 H, C5H4), 5.45
(d, J = 4.2 Hz, 1 H, CH), 5.87 (d, J = 4.2 Hz, 1 H, CH), 7.03 (s, 1 H,
ArH), 7.08 (d, J = 6.0 Hz, 2 H, ArH), 7.21 (d, J = 6.0 Hz, 2 H, ArH),
7.64 (s, 1 H, ArH), 8.42 (d, J = 6.0 Hz, 1 H, ArH), 8.63 (d, J = 6.0
Hz, 2 H, ArH).
MS: m/z = 582 [M]+.
Anal. Calcd for C34H30FeN4O2: C, 70.11; H, 5.19; Fe, 9.59; N, 9.61.
Found: C, 70.28; H, 5.40; Fe, 9.38; N, 9.49.
3-Ferrocenyl-7-methoxy-2-[2-hydroxy-1,2-bis(4-pyridyl)ethyl]-
4,5-dihydro-2H-benzo[g]indazole (8c)
Yield: 23%; mp 271 °C (decomp.).
13C NMR (CDCl3): d = 19.95 (CH3), 20.01 (CH3), 21.04, 24.96 (2 ×
CH2), 65.38 (CH), 67.06, 68.37, 68.76, 69.08 (C5H4), 69.41 (C5H5),
73.81 (CHOH), 76.20 (CipsoFc), 114.67, 120.88, 121.27, 122.24,
149.70, 150.25 (ArH), 128.31, 128.59, 131.07, 131.97, 135.85,
135.95, 139.08, 147.50, 148.99 (C).
IR (KBr): 3426, 3089, 2937, 2834, 1940, 1614, 1589, 1529, 1464,
1433, 1371, 1347, 1304, 1257, 1152, 1106, 1032, 1004, 864, 820,
759 cm–1.
MS: m/z = 580 [M]+.
1H NMR (CDCl3): d = 2.90 (m, 2 H, CH2), 2.97 (m, 2 H, CH2), 3.86
(s, 3 H, CH3), 4.03 (s, 5 H, C5H5), 4.01 (m, 1 H, C5H4), 4.25 (m, 1
H, C5H4), 4.28 (m, 1 H, C5H4), 4.33 (m, 1 H, C5H4), 5.63 (t, J = 6.0
Hz, 1 H, CH), 5.95 (d, J = 6.0 Hz, 1 H, CH), 6.27 (d, J = 6.0 Hz, 1
H, OH), 6.87 (m, 2 H, ArH), 7.15 (d, J = 4.5 Hz, 2 H, ArH), 7.25 (d,
J = 6.0 Hz, 2 H, ArH), 7.85 (d, J = 8.1 Hz, 1 H, ArH), 8.43 (d, J =
6.0 Hz, 2 H, ArH), 8.52 (d, J = 6.0 Hz, 2 H, ArH).
13C NMR (CDCl3): d = 19.33, 29.03 (2 × CH2), 54.34 (CH3), 65.08
(CH), 67.20, 68.34, 68.81, 69.12 (C5H4), 69.39 (C5H5), 73.19
(CHOH), 73.23 (CipsoFc), 111.38, 112.85, 120.42, 122.83, 137.43,
148.32, 148.37 (ArH), 113.22, 121.43, 122.62, 136.86, 145.69,
146.08, 149.40, 158.37 (C).
Anal. Calcd for C35H32FeN4O: C, 72.42; H, 5.56; Fe, 9.62; N, 9.65.
Found: C, 72.56; H, 5.36; Fe, 9.49; N, 9.88.
3-Phenyl-2-[2-hydroxy-1,2-bis(4-pyridyl)ethyl]-4,5-dihydro-
2H-benzo[g]indazole (8f)
Yield: 32%; mp 199–202 °C.
1H NMR (CDCl3): d = 2.97 (m, 2 H, 2 × CH2), 3.10 (m, 2 H, CH2),
5.49 (dd, J = 4.8, 9.0 Hz, 1 H, CH), 5.98 (d, J = 4.8 Hz, 1 H, CH),
6.11 (d, J = 9.0 Hz, 1 H, OH), 7.12 (d, J = 6.3 Hz, 2 H, ArH), 7.20
(d, J = 6.3 Hz, 2 H, ArH), 7.22–7.79 (m, 9 H, ArH), 8.41 (d, J = 6.3
Hz, 2 H, ArH), 8.64 (d, J = 6.3 Hz, 2 H, ArH).
MS: m/z = 444 [M]+.
MS: m/z = 582 [M]+.
Anal. Calcd for C29H24N4O: C, 78.36; H, 5.44; N, 12.60. Found: C,
78.60; H, 5.22; N, 12.38.
Anal. Calcd for C34H30FeN4O2: C, 70.11; H, 5.19; Fe, 9.59; N, 9.61.
Found: C, 69.97; H, 5.02; Fe, 9.76; N, 9.45.
3-Phenyl-3,3a,4,5-tetrahydro-2H-benzo[g]indazole (2f)
3-Ferrocenyl-8-methoxy-2-[2-hydroxy-1,2-bis(4-pyridyl)ethyl]-
4,5-dihydro-2H-benzo[g]indazole (8d)
Yield: 20%; mp 268 °C (decomp).
Yield: 74%; mp 121–123 °C.
1H NMR (acetone-d6): d = 3.07 (m, 4 H, 2 × CH2), 3.61 (t, J = 4.8
Hz, 1 H, CH), 6.99 (br s, 1 H, NH), 7.16–7.49 (m, 9 H, ArH).
IR (KBr): 3369, 3078, 2924, 2848, 1945, 1612, 1597, 1563, 1500,
1467, 1411, 1297, 1267, 1209, 1167, 1103, 1035, 1001, 876, 811,
750 cm–1.
Crystallographic data for the structural analysis have been deposit-
ed with the Cambridge Crystallographic Data Centre, CCDC no.
234759 for compound 5b. Copies of this information may be ob-
tained free of charge from: The Director, CCDC, 12 Union Road,
Cambridge CB2 IEZ, UK [Fax: +44(1223)336033; e-mail: depos-
it@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk].
1H NMR (CDCl3): d = 2.87 (m, 4 H, 2 × CH2), 3.89 (s, 3 H, CH3),
4.18 (s, 5 H, C5H5), 4.20 (m, 1 H, C5H4), 4.32 (m, 1 H, C5H4), 4.36
(m, 1 H, C5H4), 4.38 (m, 1 H, C5H4), 5.71 (t, J = 6.6 Hz, 1 H, CH),
6.02 (d, J = 6.6 Hz, 1 H, CH), 6.25 (d, J = 6.6 Hz, 1 H, OH), 6.82
(dd, J = 2.7, 8.4 Hz, 1 H, ArH), 7.20 (d, J = 6.3 Hz, 2 H, ArH), 7.23
(d, J = 6.3 Hz, 2 H, ArH), 7.46 (d, J = 2.7 Hz, 1 H, ArH), 7.51 (d,
J = 8.4 Hz, 1 H, ArH), 8.40 (d, J = 6.3 Hz, 2 H, ArH), 8.47 (d, J =
6.3 Hz, 2 H, ArH).
Acknowledgment
This work was supported by the grant DGAPA–UNAM (Mexico,
grant IN 207102-3). Thanks are due to Messrs M. L. Velasco, J. Pe-
rez, H. Rios, and E. R. Patiño for their technical assistance.
MS: m/z = 582 [M]+.
Anal. Calcd for C34H30FeN4O2: C, 70.11; H, 5.19; Fe, 9.59; N, 9.61.
Found: C, 70.29; H, 5.39; Fe, 9.80; N, 9.79.
References
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