Construction of five- and six-membered heterocycles on both Cp rings of the ferrocene moiety of α-oxoketene-S,S-acetal and β-oxodithioester via heteroaromatic annulation

Article abstract of DOI:10.1039/c2ra21744a

1,1′-Bis(1,1-dimethylsulfanyl-3-oxo-1-propene)ferrocene and 1,1′-Bis(methyl-3-hydroxy-prop-2-ene-dithioate)ferrocene have been shown to be useful three-carbon synthons for the efficient synthesis of hitherto unreported and synthetically demanding Fc-heter

Full text of DOI:10.1039/c2ra21744a

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Construction of five- and six-membered heterocycles on
both Cp rings of the ferrocene moiety of a-oxoketene-
S,S-acetal and b-oxodithioester via heteroaromatic
annulation3
Cite this: RSC Advances, 2013, 3, 245
Girijesh Kumar Verma, Rajiv Kumar Verma and Maya Shankar Singh*
1,19-Bis(1,1-dimethylsulfanyl-3-oxo-1-propene)ferrocene
and
1,19-Bis(methyl-3-hydroxy-prop-2-ene-
Received 9th August 2012,
Accepted 24th October 2012
dithioate)ferrocene have been shown to be useful three-carbon synthons for the efficient synthesis of
hitherto unreported and synthetically demanding Fc-heterocycles. Five-membered (pyrazole, isoxazole,
and thiophene) and six-membered (pyrimidine, coumarin, and quinoline) heterocycles have been
constructed on both Cp rings of the ferrocene matrix via regioselective heteroaromatic annulation.
DOI: 10.1039/c2ra21744a
www.rsc.org/advances
Furthermore, several mono- and bis-urea substituted ferrocene
receptors are synthesized and utilized for anion recognition
Introduction
Since the accidental discovery of ferrocene1 in 1951 (an
isostere of benzene), the fascinating metallocene has experi-
enced a renaissance, and captured the attention of synthetic,
materials, as well as medicinal chemists. Ferrocene appended
scaffolds are important synthetic targets for both the
pharmaceutical industry and academic laboratories, owing to
their rich chemistry and numerous applications in organic
synthesis,2,3 asymmetric catalysis,4 development of new
materials,5 non-linear optics,6 and in bio-organometallic
chemistry.7 In particular, ferrocene grafted compounds play
a key role as scaffolds for ligands in asymmetric synthesis,8
and display a wide range of biological activities, such as
anticancer9 (ferrocifen I, ferrocenyl acridine II), antimalarial10
(ferrochloroquine III), anti-proliferative,11 and inhibitors of
enzymes12 (Chart 1). Incorporation of a ferrocene moiety into
the skeleton of an organic compound often leads to enhanced
activity or unexpected biological properties,13 which is due to
their different membrane permeation properties and anom-
alous metabolism.14 There are many examples in the literature
where a phenyl or alkyl group has been replaced by a ferrocene
moiety as a drug design strategy.
and sensing.18 Recently, a ferrocene-functionalized polydiace-
tylene liposome has been developed,19 which has the
propensity to respond colorimetrically and electrochemically
upon binding to a cyclodextrin oligomer. Hence, there has
been renewed interest in the synthesis of ferrocene based
heterocycles with potential applications.
Functionalized a-oxoketene-S,S-acetals, due to their highly
polarized push (MeS)–pull (CLO) interaction on the CLC bond,
have been proved to be versatile three-carbon building
blocks20 for the construction of various heterocyclic systems,
such as pyrazole,21a,b isoxazole,21c thiophene,21d,e pyrimidi-
ne,22a–c coumarin,22d,e and quinoline22f,g derivatives. Due to
their broad array of applications in biology, materials science,
and chemistry, there has been an ever increasing demand for
Apart from the above properties, ferrocene based com-
pounds have also been widely utilized as organic conductors15
(ferrocene-p-extended-dithiafulvalenes IV), redox-active coor-
dination polymers16 (V), and as ligands in metal-catalyzed
cyclopropanation and Diels–Alder reactions17 (VI) (Chart 1).
Department of Chemistry (Centre of Advanced Study), Faculty of Science, Banaras
Hindu University, Varanasi-221005, India. E-mail: mssinghbhu@yahoo.co.in;
Fax: +91-542-2368127; Tel: +91-542-6702502
Electronic Supplementary Information (ESI) available: original 1H, 13C NMR
3
Chart 1 Some important ferrocene appended scaffolds.
RSC Adv., 2013, 3, 245–252 | 245
and HRMS spectra of compounds. See DOI: 10.1039/c2ra21744a
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ferrocene appended heterocycles. Recently, few synthetic
approaches toward ferrocene-based heterocycles have been
developed.23 The scarcity of resourceful synthetic methods for
ferrocene-heterocycles synthesis, and the significant limita-
tions of existing procedures prompted us to develop an
efficient and more viable route for the synthesis of ferrocene
grafted heterocycles.
To the best of our knowledge, there is no report available
for the synthesis of ferrocene derivatives with 5- and
6-membered heterocycles installed on both Cp rings of a
ferrocene matrix, utilizing a ferrocene based a-oxoketene-
S,S-acetal and b-oxodithioester. As part of our ongoing studies
on the chemistry of functionalized a-oxoketene acetals24 and
b-oxodithioesters,25 we wish to report herein a highly efficient
regioselective heteroannulation of ferrocene based a-oxoke-
tene-S,S-acetal and b-oxodithioester to furnish hitherto unre-
ported ferrocene-heterocycles containing five-/six-membered
and fused heterocycles on both Cp rings.
reactivity of these ambident electrophiles toward unsymme-
trical heterobinucleophiles by variation of reaction conditions
to afford substituted five-/six-membered heterocycles in a
highly regiocontrolled fashion.21–26
Our first attempt was to synthesize five-membered hetero-
cyclic rings over both the Cp rings of ferrocene template via
b-oxodithioester 2 and a-oxoketene dithioacetal 3 (Schemes 2–
4). Thus, when b-oxodithioester 2 was treated with phenylhy-
drazine in refluxing ethanol, the corresponding 1,19-bis(3-
methylsulfanyl-1-phenyl-pyrazol-5-yl)ferrocene 4 was obtained
in moderate yield (45%). Similarly, treatment of a-oxoketene
dithioacetal 3 with hydrazine hydrate in refluxing ethanol
furnished 1,19-bis(3-methylsulfanyl-pyrazol-5-yl)ferrocene 5 in
73% yield. Further, when 3 was treated with phenylhydrazine
in the presence of potassium tert-butoxide in refluxing tert-
butanol provided 1,19-bis(5-methylsulfanyl-1-phenyl-pyrazol-3-
yl)ferrocene 6 in 63% yield. Only one regioisomeric pyrazole 6
was observed and no trace of the corresponding 1,19-bis(3-
methylsulfanyl-1-phenyl-pyrazol-5-yl)ferrocene 4 could be iso-
lated from the reaction mixture, making the protocol highly
regioselective (Scheme 2).
Results and discussion
The isoxazole ring is widely present in numerous natural
products and synthetic pharmaceuticals. With a view to
synthesize isoxazole rings over the ferrocene platform, the
ketene dithioacetal 3 was next subjected to treatment with
hydroxylamine hydrochloride in the presence of barium
hydroxide and ethanol under reflux to give the corresponding
The utility of a-oxoketene acetals20–22 and b-oxodithioesters25,26
as versatile intermediates in organic synthesis has been well
recognized. The desired ferrocene appended b-oxodithioester 2
and a-oxoketene dithioacetal 3 were not commercially sourced,
and prepared in good yields according to reported procedures.27
The methodology involved reaction of the 1,19-diacetylferrocene
1 with S,S-dimethyltrithiocarbonate in the presence of NaH in a
mixture of N,N-dimethylformamide (DMF) and benzene (1 : 10)
at reflux temperature to yield 1,19-bis(methyl-3-hydroxy-prop-2-
ene-dithioate)ferrocene 2 in 65% yield. The b-oxodithioester 2
was further treated with methyl iodide, 50% solution of NaOH
and tetrabutyl ammonium bromide (TBAB) in benzene to
furnish 1,19-bis(1,1-dimethylsulfanyl-3-oxo-1-propene)ferrocene
3 in 83% yield (Scheme 1).
1,19-bis(5-methylsulfanyl-isoxazol-3-yl)ferrocene
7
in 50%
yield. Our attempt to prepare 1,19-bis(5-ethoxy-isoxazol-3-
yl)ferrocene 8 by the treatment of ketene dithioacetal 3 with
hydroxylamine hydrochloride in the presence of sodium
Substituted pyrazoles are important synthetic targets for
the synthesis of several commercial drugs and functional
materials. Recent studies have shown that incorporation of a
ferrocenyl group into such structures may improve their
biological activities or create new medicinal properties.28
Earlier studies have shown that it is possible to tune the
Scheme 1 The synthesis of ferrocene-based b-oxodithioester 2 and a-oxoke-
tene dithioacetal 3.
Scheme 2 The synthesis of ferrocene appended pyrazoles.
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Scheme 5 The synthesis of a ferrocene appended pyrimidine.
midin-6-yl) ferrocene 11 in 70% yield (Scheme 5). Compound
11 was found to be insoluble in common NMR solvents, such
as CDCl3, CD2Cl2, CD3COCD3, and DMSO-d6, so the structure
was assigned with the help of IR and LC-HRMS study. The
versatility of heteroaromatic annulation was further demon-
strated by the synthesis of ferrocene grafted coumarin 12, as
shown in Scheme 6. Thus, (4 + 2) cycloaddition of ketene
dithioacetal 3 with 5-bromo-2-hydroxybenzaldehyde in pre-
sence of InCl3 at 80 uC under solvent-free conditions produced
1,19-bis(6-bromochromene-3-carbonyl)ferrocene 12 in 70%
yield.
In order to get more insight into this type of annulation
chemistry, in an another strategy, we further extended (4 + 2)
cyclocondensation studies of ketene dithioacetal 3 for the
synthesis of ferrocene appended quinoline derivatives to add
further points of diversity. Thus, the annulation of 3 with
Scheme 3 The synthesis of ferrocene appended isoxazoles.
ethoxide under refluxing ethanol yielded a complex insepar-
able reaction mixture (Scheme 3).
Redox-active molecules containing p-conjugated thiophene
fragments have attracted increasing interest in materials
science from the viewpoint of the fabrication of organic
semi-conducting materials.29 To further add diversity to the
ferrocene platform, ketene dithioacetal 3 was subjected to
cyclocondensation with ethylthioglycolate in the presence of
potassium carbonate in ethanol to afford 1,19-bis(5-methylsul-
fanyl-2-carboethoxy-thiophen-3-yl) ferrocene 9 in moderate
yield (45%). Similarly, addition of 2-bromo-1-(4-chloropheny-
l)ethanone to a stirred solution of b-oxodithioester 2 and
potassium carbonate in acetone produced 1,19-bis(2-(4-chlor-
obenzoyl)-5-methylsulfanyl-thiophen-3-yl) ferrocene 10 in 41%
yield (Scheme 4).
The successful use of 1,2-binucleophiles to construct five-
membered heterocycles over the ferrocene platform prompted
us to use 1,3-heterobinucleophiles with a view to construct six-
membered heterocycles on the ferrocene matrix. Substituted
pyrimidines not only represent an important class of six-
membered heterocycles prevalent in bioactive natural pro-
ducts and pharmaceuticals, but also represent useful inter-
mediates in organic synthesis. Thus, heterocyclization of 3
with guanidine nitrate in presence of sodium tert-butoxide in
tert-butanol furnished 1,19-bis(2-amino-4-methylsulfanyl-pyri-
o-aminobenzophenone/o-aminoacetophenone
produced
1,19-bis(4-phenyl/methyl-2-methylsulfanyl-quinoline-3-carbo-
nyl)ferrocenes 13 in good yields (Scheme 7).
In another alternative pathway, 3 was added to lithiated 3,4-
dimethoxyaniline (prepared by drop wise addition of n-BuLi to
a solution of 3,4-dimethoxyaniline in dry THF at room
temperature under an argon atmosphere) at room temperature
to produce the respective N,S-acetal 1,19-bis(1-(3,4-dimethox-
yamino)-1-methylsulfanyl-3-oxo-1-propene)ferrocene 14 in
35% yield. The N,S-acetal 14 thus obtained was treated with
polyphosphoric acid (PPA) at 90 uC for 6 h to afford
1,19-bis(6,7-dimethoxy-2-methylsulfanyl-quinoline-4-yl)ferro-
cene 15 in 70% yield (Scheme 7). The structural determina-
1
tions of all the new compounds were done by IR, H and 13C
NMR, and HRMS studies.
In summary, we have developed an efficient and regiose-
lective protocol for the synthesis of ferrocene grafted five- and
six-membered heterocycles via heteroaromatic annulation of
b-oxodithioester and a-oxoketene acetal. Here, we have
efficiently installed the five-/six-membered heterocycles over
the ferrocene matrix. The methodology has been further
elaborated to the corresponding N,S-acetal, leading to ferro-
Scheme 6 The synthesis of a ferrocene grafted coumarin.
Scheme 4 The synthesis of ferrocene appended thiophenes.
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Synthesis of starting materials and final compounds
1,19-BIS(METHYL-3-HYDROXY-PROP-2-ENE-DITHIOATE)FERROCENE (2). A
solution of 1,19-diacetylferrocene 1 (1.0 g, 3.7 mmol) in
benzene (20 mL) was added dropwise to a stirred suspension
of NaH (60%, 0.74 g, 18.5 mmol) and dimethyltrithiocarbonate
(1.27 g, 9.2 mmol) in a solution of benzene (40 mL) and DMF
(4 mL) at reflux temperature over a period of 40 min. After
addition was over, the refluxing was continued for 8 h
(monitored by TLC). The reaction mixture was cooled to room
temperature and poured into saturated aqueous ammonium
chloride solution (40 mL). The organic layer was separated and
washed with water (3 6 40 mL) followed by brine (40 mL) and
dried over anhydrous Na2SO4. The solvent was evaporated
under reduced pressure and the residue obtained was purified
by column chromatography over neutral alumina using
n-hexane–ethyl acetate (5 : 1) as eluent to give 2 as a shiny
violet solid (1.1 g, 65%). mp 155–156 uC. IR (KBr): 3437, 1668,
1568, 1455, 1233, 1095 cm21 1H NMR (300 MHz, CDCl3): d
.
14.76 (s, 2H, 2 6 OH, D2O exchangeable), 6.41 (s, 2H, 2 6
CH), 4.79 (s, 4H, HCp), 4.54(s, 4H, HCp), 2.60 (s, 6H, 2 6 SCH3).
13C NMR (75 MHz, CDCl3): d 213.6, 171.5, 107.9, 79.2, 73.3,
69.4, 16.8.
Scheme 7 The synthesis of ferrocene appended quinolines.
1,19-BIS(1,1-DIMETHYLSULFANYL-3-OXO-1-PROPENE)FERROCENE (3). To a
well stirred solution of b-oxodithioester 2 (1.0 g, 2.2 mmol) in
benzene (20 mL), methyl iodide (0.68 mL, 11.0 mmol), phase
transfer catalyst TBAB (n-Bu4N+Br2) (0.35 g, 1.1 mmol), and
50% aq. NaOH (10 mL) were added slowly at 15 uC. On
completion of the reaction (monitored by TLC), the organic
layer was separated, washed with water (3 6 40 mL) followed
by brine (40 mL), and dried over anhydrous Na2SO4. The
solvent was evaporated under reduced pressure and the crude
product was purified by column chromatography over neutral
alumina using n-hexane–ethyl acetate (3 : 1) as eluent to give 3
as red solid (0.9 g, 83%). mp 186–187 uC. IR (KBr): 1608, 1494,
cene appended quinoline, providing a further point of
diversity in the newly synthesized heterocyclic frameworks.
In view of the broad range of biological activities displayed by
ferrocene grafted heterocycles, these newly synthesized com-
pounds will prove useful for preliminary pharmacological
screening. Our further efforts to improve the yields of
5-membered heterocycles and optimization of more annula-
tion reactions on 1,19-bis(1,1-dimethylsulfanyl-3-oxo-1-prope-
ne)ferrocene are in progress.
1
1374, 1250, 1100 cm21. H NMR (300 MHz, CDCl3): d 6.18 (s,
2H, 2 6 CH), 4.74 (s, 4H, HCp), 4.46 (s, 4H, HCp), 2.55 (s, 6H, 2
6 SCH3), 2.50 (s, 6H, 2 6 SCH3). 13C NMR (75 MHz, CDCl3): d
188.0, 162.9, 110.7, 83.0, 72.7, 70.7, 17.3, 15.0. LC-HRMS [ESI,
(M + H)+]: C20H22FeO2S4, Calcd: 478.9930, Found 478.9925.
1,19-BIS(3-METHYLSULFANYL-1-PHENYL-PYRAZOLE-5-YL)FERROCENE (4). A
solution of b-oxodithioester 2 (0.450 g, 1.0 mmol) and
phenylhydrazine (0.32 mL, 3.0 mmol) in absolute ethanol (10
mL) was refluxed for 8 h (monitored by TLC). The solvent was
evaporated under reduced pressure and the residue obtained
was treated with water followed by extraction with EtOAc (2 6
25 mL). The organic layer was washed with water (2 6 30 mL)
followed by brine (30 mL) and dried over anhydrous Na2SO4.
After evaporating the solvent, the crude product was purified
over neutral alumina using n-hexane–ethyl acetate (10 : 1) as
eluent to give 4 as an orange colored solid (0.253 g, 45%). mp
Experimental
General
Commercially available reagents were purchased from Merck,
Aldrich, and Fluka, and used as received without further
purification. b-Oxodithioester 2 and a-oxoketene acetal 3 were
prepared according to the protocol described in the litera-
ture26 and displayed in Scheme 1. Solvents were dried before
use by standard procedures. 1H and 13C NMR spectra were
recorded on a JEOL AL 300 FT-NMR spectrometer operating at
300 and 75 MHz, respectively. Chemical shifts are given as d
values with reference to tetramethylsilane (TMS) as the
internal standard. J values are given in Hz. The IR spectra
were recorded on a Varian 3100 FT-IR spectrophotometer.
Mass spectra were recorded on a micro TOF-Q II 10330,
WATERS-Q-Tof Premier-HAB213 and Q-Tof micro (YA-105)
instruments. All the reactions were monitored by TLC using
precoated sheets of silica gel G/UV-254 of 0.25 mm thickness
160–161 uC. IR (KBr): 3059, 2923, 1595, 1499, 1356, 1195 cm21
.
1H NMR (300 MHz, CDCl3): d 7.38–7.27 (m, 10H, ArH), 6.26 (s,
2H, ArH), 4.09 (s, 4H, HCp), 3.97 (s, 4H, HCp), 2.58 (s, 6H, 2 6
SCH3). 13C NMR (75 MHz, CDCl3): d 147.8, 142.0, 139.8, 128.9,
128.1, 128.0, 126.0, 106.2, 75.4, 70.4, 15.7. HRMS [ESI, (M +
H)+]: C30H26FeN4S2, Calcd: 563.1026, Found: 563.1157.
(Merck 60 F254) using UV light (254 nm/365 nm) for
visualization. Melting points were determined with a Bu¨chi
B-540 melting point apparatus and are uncorrected.
1,19-BIS(3-METHYLSULFANYL-PYRAZOLE-5-YL) FERROCENE (5). To a
stirred solution of ferrocenyl dithioacetal 3 (0.479 g, 1.0 mmol)
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in EtOH (15 mL), hydrazine hydrate (0.13 mL, 3.0 mmol) was
added and the reaction mixture was refluxed for 12 h
(monitored by TLC). The solvent was removed under reduced
pressure. The residue was washed with chloroform (2 6 10
mL) to give NMR pure orange solid 5 (0.30 g, 73%). mp
decomposes over 250 uC. IR (KBr): 3441, 2924, 2853, 1633,
1384, 1028 cm21. 1H NMR (300 MHz, DMSO-d6): d 12.72 (s, 2H,
2 6 NH, D2O exchangeable), 6.17 (s, 2H, ArH), 4.55 (s, 4H,
followed by extraction with CHCl3 (2 6 20 mL). The organic
layer was washed with water (2 6 25 mL) followed by brine (30
mL), and dried over anhydrous Na2SO4. The solvent was
evaporated in vacuo and the residue thus obtained was
purified over neutral alumina using n-hexane–EtOAc (9 : 1)
as eluent to yield 9 as a red solid (0.264 g, 45%). mp 179–180
uC. IR (KBr): 2924, 2858, 1700, 1507, 1420, 1284, 1090 cm21. 1H
NMR (300 MHz, CDCl3): d 6.85 (s, 2H, ArH), 4.77 (s, 4H, HCp),
4.29–4.21 [m, 8H, (4H, HCp and 2 6 CH2)], 2.56 (s, 6H, 2 6
SCH3), 1.33 (t, J = 6.9 Hz, 6H, 2 6 CH3). 13C NMR (75 MHz,
CDCl3): d 161.3, 145.0, 143.5, 130.3, 124.4, 80.2, 71.9, 70.2,
60.7, 19.3, 14.2. HRMS [ESI, (M + Na)+]: C26H26FeO4S4, Calcd:
608.9961, Found: 608.9960.
1,19-BIS(2-(4-CHLOROBENZOYL)-5-METHYLSULFANYL-THIOPHENE-3-
YL)FERROCENE (10). To a stirred solution of K2CO3 (0.278 g, 2.0
mmol) in acetone (4 mL), b-oxodithioester 2 (0.450 g, 1.0
mmol) was added and stirred for 1 h, followed by drop wise
addition of 4-chlorophenacylbromide (0.466 g, 2.0 mmol)
solution in acetone (6 mL). The reaction mixture was refluxed
for 3 h (monitored by TLC). After completion of the reaction,
solvent was evaporated under reduced pressure and residue
was treated with water (15 mL) followed by extraction with
CHCl3 (2 6 20 mL). Organic layer was washed with water (2 6
20 mL), brine (20 mL) and dried over anhydrous Na2SO4. The
solvent was evaporated under reduced pressure and purified
over neutral alumina using n-hexane-EtOAc (49 : 1) as eluent
to yield 10 as a red solid (0.294 g, 41%). mp 194–195 uC. IR
(KBr): 3094, 2922, 2852, 1670, 1607, 1409, 1284, 1086 cm21. 1H
NMR (300 MHz, CDCl3): d 7.54 (d, J = 8.4 Hz, 4H, ArH), 7.21 (d,
J = 8.4 Hz, 4H, ArH), 6.88 (s, 2H, ArH), 4.20 (s, 4H, HCp), 4.03 (s,
4H, HCp), 2.60 (s, 6H, 2 6 SCH3). 13C NMR (75 MHz, CDCl3): d
187.2, 145.7, 143.9, 138.5, 136.5, 134.5, 131.0, 129.5, 128.2,
81.4, 71.0, 70.3, 19.4. HRMS [ESI, (M + H)+]: C34H24Cl2FeO2S4,
Calcd: 718.9464, Found: 718.9474.
H
Cp), 4.18 (s, 4H, HCp), 2.50 (s, 6H, 2 6 SCH3). 13C NMR (75
MHz, DMSO-d6): d 111.0, 82.4, 74.6, 70.3, 70.1, 67.5, 16.5.
HRMS [ESI, (M + H)+]: C18H18FeN4S2, Calcd: 411.0400, Found:
411.0403.
1,19-BIS(5-METHYLSULFANYL-1-PHENYL-PYRAZOLE-3-YL)FERROCENE (6).
To a stirred suspension of ButOK (0.448 g, 4.0 mmol) and
ferrocenyl dithioacetal 3 (0.479 g, 1.0 mmol) in ButOH,
phenylhydrazine (0.32 mL, 3.0 mmol) was added dropwise.
The reaction mixture was refluxed for 12 h (monitored by TLC).
The solvent was removed under reduced pressure and the
residue obtained was treated with saturated aqueous solution
of NH4Cl followed by extraction with EtOAc (2 6 30 mL). The
organic layer was washed with water (2 6 30 mL) followed by
brine (30 mL) and dried over anhydrous Na2SO4. The solvent
was evaporated under vacuum, and the residue obtained was
purified by column chromatography over neutral alumina
using n-hexane–ethyl acetate (19 : 1) as eluent to give 6 as an
orange solid (0.349 g, 62%). mp 175–176 uC. IR (KBr): 2922,
1
2854, 1658, 1595, 1498, 1420, 1364, 1030 cm21. H NMR (300
MHz, CDCl3): d 7.62 (d, J = 7.5 Hz, 4H, ArH), 7.47–7.35 (m, 6H,
ArH), 6.26 (s, 2H, ArH), 4.62 (s, 4H, HCp), 4.26 (s, 4H, HCp), 2.31
(s, 6H, 2 6 SCH3). 13C NMR (75 MHz, CDCl3): d 139.6, 138.0,
128.8, 127.4, 124.5, 105.9, 79.0, 69.8, 68.1, 17.9. HRMS [ESI, (M
+ H)+]: C30H26FeN4S2, Calcd: 563.1026, Found: 563.1023.
1,19-BIS(5-METHYLSULFANYL-ISOXAZOLE-3-YL)FERROCENE (7). A mix-
ture of Ba(OH)2 (2.273 g, 12.0 mmol) and NH2OH.HCl (0.556 g,
8.0 mmol) in EtOH (15 mL) was stirred for 10 min. Ferrocenyl
dithioacetal 3 (0.479 g, 1.0 mmol) was added and the reaction
mixture was refluxed for 12 h (monitored by TLC). Solvent was
evaporated under reduced pressure and the crude product was
treated with ice-cold water (30 mL) followed by extraction with
ethyl acetate (2 6 30 mL). The combined organic layer was
washed with water (3 6 30 mL) followed by brine (30 mL) and
dried over anhydrous Na2SO4. The solvent was evaporated
under reduced pressure and the residue obtained was purified
by recrystallization to yield 7 as an orange solid (0.206 g, 50%).
mp 149–150 uC. IR (KBr): 2924, 2855, 1559, 1436, 1393, 1033
1,19-BIS(2-AMINO-4-METHYLSULFANYL-PYRIMIDINE-6-YL)FERROCENE (11).
Guanidine nitrate (0.269 mg, 2.2 mmol) was added to a stirred
solution of ButONa (4.4 mmol, prepared in situ from 102 mg of
Na metal in 4 mL of ButOH) in ButOH (8 mL) at room
temperature and stirred for 15 min. Ketene dithioacetal 3
(0.479 mg, 1.0 mmol) was added and the reaction mixture was
refluxed for 8 h (monitored by TLC). The solvent was
evaporated under reduced pressure. The residue was treated
with water (20 mL), the solid obtained was filtered and washed
with water (20 mL) followed by chloroform (2 6 15 mL) to give
a dark brown solid (0.325 g, 70%). mp . 275 uC (decomp.). IR
1
cm21. H NMR (300 MHz, CDCl3): d 5.93 (s, 2H, ArH), 4.65 (s,
(KBr): 3421, 2926, 1424, 1025, 872 cm21 1H and 13C NMR
.
4H, HCp), 4.35 (s, 4H, HCp), 2.61 (s, 6H, 2 6 SCH3). 13C NMR
(75 MHz, DMSO-d6): d 167.2, 161.1, 100.6, 73.9, 71.0, 68.5, 15.2.
HRMS [ESI, (M + Na)+]: C18H16FeN2O2S2, Calcd: 434.9900,
Found 434.9902.
could not be recorded due to insolubility in common NMR
solvents like CDCl3, CD2Cl2, CD3COCD3, and DMSO-d6. LC-
HRMS [ESI, (M + H)+]: C20H20FeN6S2, Calcd: 465.0618, Found:
465.0613.
1,19-BIS(5-METHYLSULFANYL-2-CARBOETHOXY-THIOPHENE-3-
YL)FERROCENE (9). Ethylthioglycolate (0.20 mL, 2.0 mmol) was
added drop wise to a suspension of K2CO3 (0.276 g, 2.0 mmol)
in EtOH (5 mL) and stirred for 20 min. A solution of ferrocenyl
dithioacetal 3 (0.479 g, 1.0 mmol) in EtOH (5 mL) was added to
the reaction mixture and the solution was refluxed for 8 h
(monitored by TLC). Solvent was evaporated under reduced
pressure and the crude residue was treated with water (25 mL)
1,19-BIS(6-BROMOCHROMENE-3-CARBONYL)FERROCENE (12). A mixture
of ferrocenoyl dithioacetal 3 (0.479 g, 1 mmol), 5-bromo-2-
hydroxybezaldehyde (0.402 g, 2 mmol), and InCl3 (0.044 g, 20
mol %) was heated in an oil bath at 80 uC for 2 h (monitored by
TLC). Reaction mixture was dissolved in EtOAc (30 mL),
washed with water (2 6 20 mL), brine (20 mL) and dried over
anhydrous Na2SO4. The crude product thus obtained was
purified by recrystallization with EtOH to yield 12 as a dark
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brown solid (0.481 g, 70%). mp . 250 uC (decomp.). IR (KBr):
2922, 2852, 1725, 1645, 1556, 1451, 1288, 1170, 1022 cm21. 1H
NMR (300 MHz, CDCl3): d 7.96 (s, 2H, ArH), 7.76–7.69 (m, 4H,
PPA (0.500 g) and N,S-acetal 14 (0.240 g, 0.35 mmol) was
mixed well and heated at 90 uC for 6 h. After the completion of
reaction (monitored by TLC), the reaction mixture was care-
fully neutralized by saturated aqueous solution of NaHCO3
(400 mL). The reaction mixture was extracted with EtOAc (2 6
25 mL), washed with water (3 6 20 mL) followed by brine (20
mL), and dried over anhydrous Na2SO4. The crude product was
purified over neutral alumina using 20% EtOAc in n-hexane to
yield the red colored compound 15 (0.457 g, 70%). mp 197–198
uC. IR (KBr): 2957, 2924, 2853, 1579, 1485, 1464, 1248, 1103,
1006 cm21. 1H NMR (300 MHz, DMSO-d6): d 8.31 (s, 2H, ArH),
7.56 (s, 2H, ArH), 7.19 (s, 1H, ArH), 7.15 (s, 1H, ArH), 4.97 (s,
4H, HCp), 4.54 (s, 4H, HCp), 3.90 (s, 6H, 2 6 OMe), 3.88 (s, 6H,
2 6 OCH3), 2.54 (s, 6H, 2 6 SCH3). 13C NMR (75 MHz, CDCl3):
d 156.6, 151.9, 148.2, 146.0, 142.5, 119.5, 119.1, 107.8, 103.9,
ArH), 7.22 (s, 2H, ArH), 4.94 (s, 4H, HCp), 4.73 (s, 4H, HCp). 13
C
NMR (75 MHz, DMSO-d6): d 192.4, 156.8, 152.4, 141.4, 135.2,
131.2, 126.9, 119.6, 118.1, 115.9, 78.3, 74.8, 72.0. HRMS [ESI,
(M + Na)+]: C30H16Br2FeO6, Calcd: 708.8560, Found: 708.8669.
General procedure for the synthesis of 13
A
mixture of 2-aminoaryl/alkyl ketone (2.0 mmol) and
a-oxoketene dithioacetal 3 (1.0 mmol) was heated at 80 uC in
the presence of InCl3 (20 mol %, 0.2 mmol, 44 mg) for the
stipulated period of time (1.5–2.0 h) until the completion of
the reaction (monitored by TLC). The mixture was treated with
water (20 mL) and extracted with EtOAc (2 6 20 mL). The
combined organic extract was washed with water (2 6 20 mL)
followed by brine (15 mL) and dried over anhydrous Na2SO4.
The solvent was evaporated under vacuum. The crude product
thus obtained was purified by column chromatography on
silica gel (ethyl acetate/n-hexane, 1 : 19).
84.6, 71.7, 71.3, 56.0, 14.1. HRMS [ESI, (M
C34H32FeN2O4S2, Calcd: 653.1231, Found: 653.1238.
+
H)+]:
Acknowledgements
1,19-BIS(2-METHYLSULFANYL-4-PHENYL-QUINOLINE-3-CARBONYL)FERROCENE
(13A). Orange solid (0.533 g, 72%): mp 242–243 uC. IR (KBr): 2923,
We gratefully acknowledge the generous financial support
from the Council of Scientific and Industrial Research (CSIR)
and the Department of Science and Technology (DST), New
Delhi. The authors (G.K.V. & R.K.V.) are thankful to UGC and
CSIR, New Delhi for senior research fellowships.
1
1651, 1537, 1450, 1249, 1070 cm21. H NMR (300 MHz, CDCl3): d
8.03 (d, J = 8.1 Hz, 2H, ArH), 7.69 (t, J = 8.1 Hz, 2H, ArH), 7.56 (d, J =
8.4 Hz, 2H, ArH), 7.36 (t, J = 7.8 Hz, 2H, ArH), 7.21–7.19 (m, 10H,
ArH), 4.37 (s, 4H, HCp), 4.32 (s, 4H, HCp), 2.55 (s, 6H, 2 6 SCH3). 13
C
NMR (75 MHz, CDCl3): d 200.2, 156.2, 148.0, 144.9, 134.8, 131.0,
130.6, 130.3, 128.4, 128.3, 127.9, 126.5, 125.7, 124.1, 80.8, 74.3, 71.8,
13.3. HRMS [ESI, (M + Na)+]: C44H32FeN2O2S2, Calcd: 763.1152,
Found: 763.1161.
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CENE (13B). Orange solid (0.395 g, 64%): mp decomposes over
230 uC. IR (KBr): 2961, 2871, 1584, 1476, 1433, 1234, 1094
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.
ArH), 7.88 (d, J = 8.1 Hz, 2H, ArH), 7.70 (t, J = 7.5 Hz, 2H, ArH),
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Na)+ 639.0839, Found 639.0849.
SYNTHESIS OF 1,19-BIS(6,7-DIMETHOXY-2-METHYLSULFANYL-QUINOLINE-4-YL)
FERROCENE (15). n-BuLi (2 M in cyclohexane, 2.0 mL, 4.0 mmol) was
added drop wise to a solution of 3,4-dimethoxyaniline (0.307 g, 2.0
mmol) in THF (5 mL) over a period of 25 min under argon
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EtOAc (2 6 20 mL). The extract was washed with water (3 6 25
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dried over anhydrous Na2SO4 and evaporated under vacuum to
give the crude product. The product was purified over neutral
alumina using 20% EtOAc in n-hexane followed by 1% MeOH in
DCM to yield 1,19-bis(1-(3,4-dimethoxyamino)-1-methylsulfanyl-3-
oxo-1-propene)ferrocene 14 in 35% yield.
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