Synthesis and characterization of fluorene tethered benzo[c]thiophene/ benzo[c]- selenophene analogs

Article abstract of DOI:10.1016/j.tet.2010.05.060

Synthesis of 9 9-dialkyl/diarylfluorene based benzo[c]thiophene/benzo[c] selenophenes is presented. The synthesis of benzo[c]thiophene analogs is also realized with fluorene containing one or two thiophene units. The optical and electrochemical studies of

Full text of DOI:10.1016/j.tet.2010.05.060

Tetrahedron 66 (2010) 5660e5670
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and characterization of fluorene tethered benzo[c]thiophene/benzo[c]-
selenophene analogs
*
Natarajan Senthil Kumar, Arasambattu K. Mohanakrishnan
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 April 2010
Received in revised form 13 May 2010
Accepted 15 May 2010
Available online 11 June 2010
Synthesis of 9,9-dialkyl/diarylfluorene based benzo[c]thiophene/benzo[c]selenophenes is presented. The
synthesis of benzo[c]thiophene analogs is also realized with fluorene containing one or two thiophene
units. The optical and electrochemical studies of fluorenyl benzo[c]heterocycles are correlated with their
structures.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Disubstituted fluorene
Benzo[c]thiophene
Lawesson’s reagent
Woollins reagent
Cyclic Voltamogram
Band gap
1. Introduction
film transistors.10 Huang and co-workers outlined the synthesis of
2,7-dipyrenyl-9-phenyl-9-pyrenyl fluorene moiety as blue emitters
Conjugated thienyl oligomers attract much attention by their
unique optical and semiconducting properties.1 They can be used as
Organic Light Emitting Diodes (OLEDs)2 and Organic Field Effect
Transistors (OFETs).3 Oligomers can be easily tuned to the desired
properties by changing the structure, by inserting various func-
tional groups like 2-n-hexylfluorene, 9,9-diphenyl fluorene,4 and
oligothiophene/functionalized truxene.5 Polythiophene and its
derivatives are often used as optoelectonic materials because of
their high electrical conductivity and thermal stability in both
neutral and doped states.6 The fluorene incorporated poly-
thiophene materials exhibit relatively high photo and electrolu-
minescence quantum efficiency than polythiophene materials.7
Perepichka and co-workers synthesized poly star shaped tris-
EDOT coupled terthienobenzene, which showed switching be-
tween red- and blue-colored stable states.8 Now a days plenty of
fluorene incorporated materials have been synthesized and used in
electronic application especially ortho-linked spirobifluorene have
unique photophysical properties and high triplet energy because of
in nondoped OLEDs without the need for hole-injection layers for
simplifying device fabrication.11
Ding and co-workers reported the synthesis of copolymers of
fluorene and oxadiazole as Polymer Light Emitting Diodes
(PLEDs).12 Lee and co-workers outlined the synthesis of oligo(9,9-
dihexyl-2,7-fluoreneethynylene)s as blue light emitting diodes.13
Beifield and Yao reported the synthesis of two-photon absorbing
unsymmetrical branched chromophores containing fluorene moi-
ety.14 Recently, Yang and co-workers synthesized novel oligo-9,90-
spirobifluorenes through ortho-linkage as full hydrocarbon phos-
phorescent OLEDs.15 Wong and co-workers reported the synthesis
of novel (9,9-di-p-tolylfluorene) analogs containing thiophene and
pyridine rings.16
Rodriguez and co-workers reported the synthesis and optical
characterization of thiophene and fluorene derivatives containing
ethynyl spacers.17 Promarak and co-workers reported the synthesis
of conjugated fluorenyl oligothiophenes and showed the decrease
in oxidation potential and increase in absorption maxima with in-
creasing the number of thiophene rings on fluorene moiety.18 They
have also synthesized N-carbazole end-capped oligothiophene-
fluorenes as potential hole-transporting and light-emitting layers
in OLED devices.19 Indenofluorenes are known to have good fluo-
rescence properties and have also been investigated for their OLED
applications.20 Recently, linear and star shaped rigid conjugated
fluorene and truxene molecules containing terpyridine units are
the p
-conjugation interruption between spirobifluorene units.9 Bao
and co-workers reported the synthesis of fluorene coupled oligo-
thiophenes as high performance semiconductors for organic thin
* Corresponding author. Tel.: þ91 44 22202813; fax: þ91 44 22300488; e-mail
address: mohan_67@hotmail.com (A.K. Mohanakrishnan).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.05.060

N.S. Kumar, A.K. Mohanakrishnan / Tetrahedron 66 (2010) 5660e5670
5661
reported, and their photophysical properties showed that they emit
strong blue color in solutions, which provides potential for such
materials as the hosts to construct novel functionalized materials
for understanding the energy and electron transfer processes.21
quenching led to the isolation of respective keto-alcohols. The DCM
solution of keto-alcohols upon thionation using 0.5 equiv of Law-
esson’s reagent (LR) followed by workup and column chromato-
graphic purification afforded respective benzo[c]thiophene analogs
9aeq in 42e62% yields (Scheme 1). As expected, the trans-
formation of the lactones 8aec into the respective benzo[c]thio-
phenes can be smoothly performed via ring-opening of the lactones
with variety of aryl as well as heteroaryl Grignards to afford the
respective heterocycles in moderate yields. With the exception of
heterocycles 9a and 9def, all other benzo[c]thiophenes are found
to be either orange or yellow liquids. The fluorenyl benzo[c]thio-
phenes 9aeq are found to be highly soluble in common organic
solvents.
R1
S
S
X
S
S
S
2 X = O, R1 = C6H13
3 X = S, R1 = C6H13
4 X = NC6H13, R1 = H
1
O
O
R1
6
O
S
S
S
X
S
S
CO2H
AlCl3/DCM
4 h, rt
O
2 X = O, R1 = C6H13
3 X = S, R1 = C6H13
4 X = NC6H13, R1 = H
R1
1
R1
5a-c
R2
7a R1 = R2 = n-C2H5
7b R1 = R2 = n-C6H13
7c R1 = R2 = p-tolyl
R2
NaBH4/EtOH-THF
reflux, 10 h
The smaller band gap of 1,3-dithienylbenzo[c]thiophene 1 is
a result of the increased contribution of the quinoid resonance
structure due to the stabilization achieved by the aromatization of
the benzene ring.22 Over the years, the synthesis and character-
ization of benzo[c]thiophene analogs are well explored due to the
low band gap properties associated with their polymer.23 The
benzo[c]thiophene analogs are explored as fluorescent labels,24
components in OLEDs,25 as well as photovoltaics.26 Recently, Kis-
selev and Thelakkat achieved the synthesis of polymer containing
benzo[c]thiophene and triaryl amine groups as a new class of light
harvesting dyes.27 Very recently, Swager and co-workers reported
the synthesis and characterization of push/pull-type near-IR fluo-
rophores containing benzo[c]furan/benzo[c]thiophene units.28
Thus, the exciting photophysical properties along with enormous
application potential of benzo[c]thiophenes prompted us to explore
the synthesis and characterization of various types of symmetrical
as well as unsymmetrical 1,3-diarylbenzo[c]thiophenes.29 In con-
tinuation of the preliminary report on synthesis of fluorene capped
benzo[c]thiophenes30 and dibenzoheterocycle tethered benzo[c]
thiophenes 2e4,29e we reported herein a detailed study on syn-
thesis and characterization of 9,9-disubstituted fluorenyl benzo[c]
thiophenes.
i) Ar1MgBr
ii) NH4Cl
Ar1
S
O
R2
R1
iii) L.R (0.5 eq.)
42-62%
R2
9a-q
O
R1
8a R1 = R2 = n-C2H5
8b R1 = R2 = n-C6H13
8c R1 = R2 = p-tolyl
Compound R1/R2
Ar1
Yield
)
ethyl
ethyl
ethyl
ethyl
ethyl
ethyl
ethyl
hexyl
hexyl
hexyl
hexyl
hexyl
hexyl
hexyl
p-tolyl
thiophen-2-yl
57
57
45
50
47
52
52
62
57
50
57
58
57
55
45
42
47
9a
9b
9c
9d
9e
9f
9g
9h
9i
9j
9k
9l
9m
9n
9o
9p
9q
3-hexylthiophen-2-yl
5-hexylthiophen-2-yl
phenyl
p-anisyl
p-tolyl
1-naphthyl
thiophen-2-yl
3-hexylthiophen-2-yl
5-hexylthiophen-2-yl
phenyl
p-anisyl
p-tolyl
1-naphthyl
thiophen-2-yl
2. Results and discussion
p-tolyl 3-hexylthiophen-2-yl
p-tolyl 5-hexylthiophen-2-yl
Cava and Lorcy achieved the synthesis of 1,3-dithienylbenzo[c]
thiophene 1 via ring-opening of 2-thienylphthalide with 2-thi-
enylmagnesium bromide followed by thionation.23b The required
2-thienylphthalide was prepared using FriedeleCrafts phthaloyla-
tion of thiophene with phthalic anhydride followed by reductive
cyclization using NaBH4 in aq NaHCO3 solution. Following the
Cava’s procedure, 9,9-dialkyl/diarylfluorene 5aec12,31 upon Frie-
deleCrafts phthaloylation with phthalic anhydride in the presence
of anhydrous AlCl3 led to keto-acids 7aec.
The usual NaBH4 reduction of the keto-acids 7aec in aq NaHCO3
found to be problematic, producing only trace amount of lactones
8aec. However, the reduction of keto-acids, using NaBH4 in THF/
EtOH (2:5) at reflux for 10 h afforded required lactones in 37e60%
yields. Next, ring-opening of the lactones 8aec using freshly pre-
pared 2-thienyl/arylmagnesium bromides followed by aq NH4Cl
Scheme 1.
Having achieved the synthesis of fluorene capped benzo[c]
thiophenes 9aeq, next the preparation of similar heterocycles with
2-(2-thienyl)-9,9-dihexyl fluorene 10a as well as 2,7-bis(2-thienyl)-
9,9-dihexyl fluorene 10b was planned. The known oligothiophene/
fluorene 10a and 10b were prepared using a Pd-mediated Stille
coupling of respective mono/dibromo-9,9-dihexyl fluorene with
2-tributylstannylthiophene. As expected, FriedeleCrafts phthaloy-
lation of 10a followed by reductive cyclization produced the lactone
12a in 35% overall yield. Similarly, FriedeleCrafts phthaloylation of

5662
N.S. Kumar, A.K. Mohanakrishnan / Tetrahedron 66 (2010) 5660e5670
10b with phthalic anhydride in the presence of anhydrous AlCl3 led
to keto-acid 11b in 51% yield. Reductive cyclization of the keto-acid
11b using NaBH4 in THF/EtOH at reflux led to the isolation of lac-
tone 12b in 69% yield as a thick yellow liquid (Scheme 2).
comparatively better yields from the corresponding benzo[c]furans
rather than the keto-alcohols.31 Hence, the ring-opening of the
lactone 8b with various 2-thienylmagnesium bromides followed by
acidic workup, and subsequent selenation of crude benzo[c]furans
with 0.25 equiv of Woollins reagent in DCM afforded benzo[c]
selenophene derivatives 15aec in 55e62% yields, (Scheme 4).
n
S
S
C6H13
C6H13
i)
10a (n = 0)
MgBr
S
10b (n = 1)
O
O
O
8a/8b
ii) HCl
R1
AlCl3/DCM
4 h, rt
S
R2
14a R1/R2 = C2H5
14b R1/R2 = C6H13
6
O
S
n
i) Ar1MgBr
Ar1
S
Se
C6H13
8b
C6H13
O
CO2H
ii) HCl
11a (n = 0)
iii) Woollins reagent
(0.25 eq.)
11b (n = 1)
C6H13
C6H13
15a-c
NaBH4
EtOH/THF
reflux, 10 h
Compound
15a
Ar1
thiophen-2-yl
Yield (
59
)
3-hexylthiophen-2-yl
5-hexylthiophen-2-yl
62
55
15b
15c
S
n
R2
O
Scheme 4.
R1
S
12a (n = 0)
12b (n = 1)
O
Interaction of monomeric benzo[c]thiophene 9a/9h with an-
hydrous FeCl3 in DCM at room temperature for 6 h followed by
quenching with dilute solution of hydrazine hydrate and sub-
sequent column chromatographic purification led to the isolation
of corresponding dimer 16a/16b (Scheme 5). Similar dimerization
of benzo[c]thiophene 9i using anhydrous FeCl3 did form the
expected dimer. However, the attempted purification of the dimer
was unsuccessful. It should be noted that the dimerization of 9a/9h
proceeded selectively at the thiophene-2-position rather than the
fluorene-7-position.
Scheme 2.
Interaction of the fluorene/oligothiophene lactones 12a and 12b
with freshly prepared aryl/heteroarylmagnesium bromides fol-
lowed by thionation and subsequent column chromatographic
purification led to the isolation of benzo[c]thiophene analogs
13aeg (Scheme 3).
Next, the synthesis of push/pull-type benzo[c]thiophene ana-
logs is planned. Accordingly, Vilsmeier/Haack formylation of 9a/9h
i) Ar1MgBr
ii) NH4Cl
S
12a/b
n
S
C6H13
S
C6H13
S
S
iii) L.R
13a-g
Ar1
S
45-57%
i) FeCl3/DCM
S
9a/9h
ii) NH2NH2.H2O
Compound
13a
n
Ar
thiophen-2-yl
3-hexylthiophen-2-yl
5-hexylthiophen-2-yl
phenyl
thiophen-2-yl
3-hexylthiophen-2-yl
5-hexylthiophen-2-yl
Yield (
51
)
R2
R1
R2
R1
0
0
0
0
1
1
1
13b
13c
13d
13e
13f
13g
47
45
49
55
57
50
16a R1 = R2 = C2H5 (45%)
16b R1 = R2 = C6H13 (40%)
Scheme 5.
Scheme 3.
at room temperature for 10 h followed by workup and column
chromatographic purification afforded aldehyde 17a/17b as red
solid and dark red liquids in 57% and 61% yields, respectively. It
should be noted that formylation has taken place selectively at
thiophene rather than the fluorene portion. As expected, conden-
sation of the aldehyde 17a/17b with malononitrile/thiophene-2-
acetonitrile in the presence of piperidine or t-BuOK afforded the
corresponding conjugated cyano-vinylenes 18aec as black solids
(Scheme 6).
Treatment of phthalide 8a/8b with freshly prepared 2-thi-
enylmagnesium bromides followed by acidic workup and column
chromatographic purification gave the respective benzo[c]furans
14a/14b as an orange solid. The 1H NMR spectral analysis of bright
yellow fluorescent solution of benzo[c]furans 14a/14b confirmed
that these compounds are highly unstable as the solutions turned
red when exposed to white light. Our earlier observation has con-
firmed that always benzo[c]selenophenes can be prepared in

N.S. Kumar, A.K. Mohanakrishnan / Tetrahedron 66 (2010) 5660e5670
5663
backbone. Surprisingly, the incorporation of
case of 9a/9h also reduced the
a
-hexyl unit in the
p
-conjugation, which indicates that
the planarity of skeletal framework may be perturbed. The lmax
values of fluorenyl benzo[c]thiophenes 9a/9h as well as hetero-
cycles 2e429e were more or less same. This confirms that the non-
bonded electron pair of heterocycles 2e4 is not significantly
DMF/POCl3
rt, 10 h
S
9a/9h
S
O
R2
R1
H
17a R1 = R2 = C2H5 (57%)
contributing for the observed
p-conjugation. The addition of one
17b R1 = R2 = C6H13 (61%)
or two thiophene unit into the benzo[c]thiophene (9a/13a/13e)
induced red shift in the lmax value. As observed earlier,32 com-
paratively benzo[c]selenophenes 15aec displayed higher lmax
values than the corresponding benzo[c]thiophenes. The presence
of electron-withdrawing aldehyde function at one end of benzo[c]
thiophene 9a/9h caused 55 nm red shift of absorption, which
Ar1
CN
S
CN
Ar1
17a/17b
S
piperidine
confirmed the enhancement in the
p-electron delocalization. The
R2
(or)
R1
dimerization of benzo[c]thiophene (9a/9h/16a/16b) also red
shifted the lmax value (Table 1).
H
t-BuOK
18a-c
The qualitative emission data of fluorenyl heterocycles were
recorded in DCM solution and the emission values are also given in
Table 1. The monomeric benzo[c]thiophenes showed emission
values in the range of 490e550 nm. As observed in the case of
absorption spectra, the emission values of these benzo[c]thio-
Compound
Ar1
CN
thiophen-2-yl
thiophen-2-yl
R1/R2 Yield (
)
18a
18b
18c
hexyl
ethyl
hexyl
40
45
47
phenes are also red shifted with increasing p-conjugation.
Scheme 6.
A complete summary on physical properties of representative
fluorenyl heterocycles are listed in Table 1. The HOMO and LUMO
energy levels of these heterocycles were calculated from the ab-
sorption and the onset oxidation potential. The Eg, HOMO, and
LUMO values obtained for representative benzo[c]thiophenes and
benzo[c]selenophenes are presented in Table 1. The monomeric
benzo[c]thiophenes 9aec, 9hej, 9o, and 9p showed Eg values in
the range of 2.7e3.0 eV. The replacement of one thiophene ring of
parent 1,3-dithienylbenzo[c]thiophene 1 with 9,9-disubstituted
fluorene has slightly increased the band gap value (1/9aec,
9hej, 9o, 9p). The observed band gap values of 9a/9h and het-
erocycles 2e4 are in the same range, which indicated the mini-
mum non-bonded electron pair influence in the heterocycles 2e4.
The incorporation of one or two thiophene unit into the benzo[c]
thiophene (9a/13a/13e) has not caused any appreciable change
in its band gap value. As observed earlier,31 the Eg values for
benzo[c]selenophenes 15aec are less compared to the respective
benzo[c]thiophenes 9hej. The dimerization of benzo[c]thio-
phenes (9a/9h/16a/16b) has reduced its band gap value. In-
troduction of electron withdrawing aldehyde function at one end
of the benzo[c]thiophene (9a/9h/17a/17b) has also reduced
band gap value. The monomeric benzo[c]thiophenes displayed
HOMO energy level in the range of 5.2e5.4 eV and the corre-
sponding LUMO energy level lie in the region of 2.4e2.5 eV. It is
clear that during the dimerization, the HOMO energy levels are
more or less unaffected. However, the dimerization has signifi-
cantly increased the LUMO energy levels, which led to the de-
crease in their band gap value. Introduction of electron
withdrawing aldehyde function at one end of the benzo[c]thio-
phenes portrayed similar effect on the HOMO and LUMO energy
levels.
3. Photophysical and electrochemical studies
The UVevis spectra of monomeric benzo[c]thiophenes exhibi-
ted a strong absorption in the region of 415e455 nm due to the
*
pep electronic transition of the conjugated backbone system.
The exact absorption lmax values of some representative benzo[c]
thiophenes as well as benzo[c]selenophenes are given in Table 1.
As expected, the replacement of thiophene ring by 9,9-di-
substituted fluorene (1/9a/9h) has increased its lmax value.
Similar to earlier observation,29d the presence of
b
-hexyl group on
the thiophene unit of the fluorenyl benzo[c]thiophene (9a/
9h/9b/9i) reduced its
p-conjugation due to the twist in their
Table 1
Physical data for some selected benzo[c]thiophenes
Compound
lmax
llum
Egc (V)
E
ox
HOMOe
(eV)
LUMOf
(eV)
a
b
onsetd
(nm)
(nm)
(eV)
9a
9b
9c
9h
9i
9j
9o
9p
13a
13b
13e
13f
15a
15b
15c
16a
16b
17a
17b
18a
18c
455
430
435
445
425
430
430
415
460
450
475
455
465
445
435
495
480
510
500
545
530
550
520
525
539
512
515
500
490
555
545
570
540
553
541
545
597
592
605
600
635
625
2.72
2.88
2.85
2.78
2.92
2.88
2.88
2.99
2.69
2.75
2.61
2.72
2.66
2.78
2.85
2.50
2.58
2.43
2.48
2.27
2.33
0.81
0.85
0.83
0.82
0.91
0.85
0.89
0.93
0.80
0.81
0.71
0.72
0.72
0.76
0.77
0.67
0.71
0.69
0.72
0.65
0.67
5.25
5.29
5.27
5.26
5.35
5.29
5.33
5.37
5.24
5.25
5.15
5.16
5.17
5.21
5.22
5.12
5.16
5.14
5.17
5.10
5.12
2.53
2.41
2.42
2.48
2.43
2.41
2.45
2.38
2.55
2.50
2.54
2.44
2.51
2.43
2.37
2.62
2.58
2.71
2.69
2.83
2.79
4. Conclusion
In summary, the synthesis of a variety of fluorenyl benzo[c]
thiophene analogs has been achieved in reasonable yields. The
physical data of representative fluorenyl benzo[c]thiophenes are
correlated with their structure. The synthesis of fluorenyl benzo[c]
thiophene based push/pull system was also achieved. The highly
soluble nature of the fluorenyl benzo[c]thiophenes may make them
suitable for transistor applications through spin-coating tech-
niques. Additionally, the higher-lying HOMO energy levels of these
benzo[c]thiophenes (w5.1e5.3 eV) may find them as suitable
a
Measured in dilute dichloromethane solution.
Excited at the absorption maxima.
b
c
d
e
f
Estimated from the absorption (Eg¼1240/lmax).
The onset of oxidation potential determined using CV.
Calculated using the empirical equation: HOMO¼(4.44þEooxnset).
Calculated from LUMO¼HOMOꢀEg.

5664
N.S. Kumar, A.K. Mohanakrishnan / Tetrahedron 66 (2010) 5660e5670
candidates for application as hole-transporting materials in dou-
ble-layer OLEDs.
127.85, 126.98, 125.69, 123.21, 123.08, 120.75, 55.26, 40.08, 31.43,
29.59, 23.71, 22.54, 13.97; MS (EI): m/z (%)¼482 [M]þ.
5.2.2. 3-((5-(9,9-Dihexyl-2-thiophen-2-yl)-9H-fluoren-7-yl)thio-
phen-2-yl)benzoic acid (11b). Following the above-mentioned
procedure (A), keto-acid 11b was obtained using 2,7-bis(2-thienyl)-
9,9-dihexyl fluorene 10b (5 g, 10.00 mmol), phthalic anhydride
(1.78 g, 12.02 mmol), and AlCl3 (2.40 g, 18.02 mmol) as a thick yel-
low liquid (3.30 g, 51%); [found: C, 75.9; H, 6.4; S, 10.1. C41H42O3S2
requires C, 76.12; H, 6.54; S, 9.91%]; Rf (20% EA/hexane) 0.31; nmax
5. Experimental
5.1. General
All melting points are uncorrected. IR spectra were recorded on
a SHIMADZU FT-IR 8300 instrument. 1H and 13C NMR spectra were
recorded in CDCl3 using TMS as an internal standard on a Bruker-
300 spectrometer. Mass spectra were recorded on a JEOL DX 303 HF
spectrometer. Elemental analyses were carried out on a Per-
kinseElmer series II 2400 (IIT Madras) instrument. All UVevis
spectra were recorded in CH2Cl2 solution. The emission spectra
were recorded on PerkineElmer LS-45 spectrophotometer. The
cyclic-Voltammogram of 10ꢀ3 M solution of benzo[c]thiophenes
was carried out on a CHI 600C electrochemical analyzer. All the
measurements were carried out under oxygen free condition using
three electrode cells in which glassy carbon electrode was working
electrode, saturated Ag/AgCl electrode was reference electrode, and
platinum wire was used as an auxiliary electrode. Tetrabuty-
lammonium hexafluoro phosphate (TBAPF6) was used as support-
ing electrolyte and its concentration was 10ꢀ1 M.
(KBr) 3365, 2911, 1681, 1667, 1595 cmꢀ1
; dH (300 MHz, CDCl3) 8.10
(1H, d, J 7.2 Hz, ArH), 7.70e7.48 (10H, m, ArH), 7.40e7.38 (1H m,
ArH), 7.32e7.29 (2H, m, ArH), 7.26e7.25 (1H, m, ArH), 7.13 7.10 (1H,
m, ArH), 2.04e1.99 (4H, m, CH2), 1.08e1.04 (12H, m, CH2),
0.76e0.71 (10H, m, CH2CH3); dC (75.6 MHz, CDCl3) 188.89, 170.02,
154.52, 151.96, 151.93, 144.98, 142.40, 141.92, 141.73, 139.75, 135.66,
133.83, 132.86, 132.07, 131.07, 129.79, 128.10, 127.86, 125.50, 125.10,
124.74, 123.72, 123.09, 120.58, 120.43, 120.26, 120.21, 55.40, 40.35,
31.43, 29.62, 23.75, 22.53, 13.96; MS (EI): m/z (%)¼646 [M]þ.
5.2.3. 3-(9,9-Diethyl-9H-fluoren-2-yl)isobenzofuran-1(3H)-one
(8a). Following the above-mentioned procedure (A), lactone 8a was
obtained using 9,9-diethyl fluorene 5a (5 g, 22.5 mmol), phthalic
anhydride (4 g, 27.02 mmol), AlCl3 (5.4 g, 40.5 mmol), and NaBH4
(4.28 g,112 mmol) as a colorless solid (4.0 g, 50%); mp 102 ꢁC; [found:
C, 84.5; H, 6.5. C25H22O2 requires C, 84.72; H, 6.26%]; Rf (10% EA/
5.1.1. Preparation of compounds 10a/b. Compound 10a was syn-
thesized in 63% yield from 2-bromo-9,9-dihexyl fluorene12
(1 equiv), tributylstannylthiophene (1 equiv), and 1 mol % of Pd
(PPh3)4 in dry toluene at reflux for 24 h. Similarly compound 10b
was also synthesized in 50% yield from 2,7-dibromo-9,9-dihexyl
fluorene12 (1 equiv), tributylstannylthiophene (2 equiv), and 2 mol
% of Pd(PPh3)4 in dry toluene at reflux for 24 h.
hexane) 0.41; nmax (KBr) 2857, 1759, 1600, 1511 cmꢀ1
; dH (300 MHz,
CDCl3) 7.77 (1H, d, J 12 Hz, ArH), 7.47e7.41 (2H, m, ArH), 7.36e7.27
(2H, m, ArH),7.10e7.09(4H, m,ArH),7.04e6.97(2H,m, ArH), 6.26(1H,
m, ArH),1.83e1.73 (4H, m, CH2), 0.22e0.10(6H,m,CH3);dC (75.6 MHz,
CDCl3) 170.70, 150.79, 150.15, 150.01, 142.80, 140.61, 135.00, 134.37,
129.36, 127.60, 126.97, 125.89, 125.73, 125.64, 122.97, 122.87, 121.65,
120.04, 119.94, 83.29, 56.24, 32.61, 8.51; MS (EI): m/z (%)¼354 [M]þ.
5.2. General procedure(A) for preparation of lactones (8aec
and 12a/b)
5.2.4. 3-(9,9-Dihexyl-9H-fluoren-2-yl)isobenzofuran-1(3H)-one
(8b). Following the above-mentioned procedure (A), lactone 8b
was obtained using 7b (5 g, 22.5 mmol) and NaBH4 (4.28 g,
112 mmol) as a colorless solid (2.2 g, 60.1%); mp 98 ꢁC; [found: C,
84.7; H, 8.4. C33H38O2 requires C, 84.94; H, 8.21%]; Rf (10% EA/
To a stirred suspension of phthalic anhydride (1.2 equiv) in dry
DCM (100 mL), anhydrous aluminum chloride (1.5 equiv with re-
spect to phthalic anhydride) was added and stirred for 0.5 h at
room temperature to get yellow solution. To this solution fluorene
(5aec and 10a/b) (1 equiv) in DCM (25 mL) was slowly added
(20 min) at 0 ꢁC. The resulting dark-green solution was stirred for
4 h at room temperature. Then it was poured into ice water con-
taining concd HCl. The organic layer was separated and dried over
Na2SO4. Removal of solvent in vacuo afforded crude keto-acid
(7aec and 11a/b), which was dissolved in THF/EtOH (2:5). To this
solution NaBH4 (5 equiv) was added in portions and refluxed for
10 h. The reaction mixture was poured into water and concd HCl
was added dropwise under stirring (pH¼1e2). The precipitated
solid was washed with ethanol to afford the required lactones 8aec
and 12a/b. (only 7b, 11b compounds were isolated and other keto-
acids were used as such in reduction step. Compounds 12a/b were
obtained by column chromatography).
hexane) 0.42; nmax (KBr) 2875,1759,1600,1500 cmꢀ1
; dH (300 MHz,
CDCl3) 7.91 (1H, d, J 7.2 Hz, ArH), 7.59e7.56 (2H, m, ArH), 7.52 (1H, d,
J 7.39 Hz, ArH), 7.40 (1H, t, J 7.37 Hz, ArH), 7.27e7.19 (4H, m, ArH),
7.14e7.10 (2H, m, ArH), 6.40 (1H, s, CH), 1.89e1.78 (4H, m, CH2),
1.09e0.82 (12H, m, CH2), 0.71e0.43 (10H, m, CH2CH3); dC
(75.6 MHz, CDCl3) 170.70, 151.60, 150.94, 150.12, 142.40, 140.21,
134.95, 134.24, 129.31, 127.56, 126.87, 125.74, 125.73, 125.67, 122.92,
122.80, 121.56, 120.06, 119.94, 83.26, 55.21, 40.24, 31.33, 29.60,
23.71, 22.53, 13.98; MS (EI): m/z (%)¼466 [M]þ.
5.2.5. 3-(9,9-Dip-tolyl-9H-fluoren-2-yl)isobenzofuran-1(3H)-one
(8c). Following the above-mentioned procedure (A), lactone 8c
was obtained using 9,9-dip-tolyl fluorene 5c (5 g, 14.45 mmol),
phthalic anhydride (2.57 g, 17.36 mmol), AlCl3 (3.47 g, 26.05 mmol),
and NaBH4 (2.74 g, 72.10 mmol) as a colorless solid (2.6 g, 37%); mp
115 ꢁC; [found: C, 88.1; H, 5.7. C35H26O2 requires C, 87.84; H, 5.48%];
5.2.1. 2-(9,9-Dihexyl fluorenyl)benzoic acid (7b). Following the
above-mentioned procedure (A), keto-acid 7b was obtained using
9,9-dihexyl fluorene 5b (5 g, 14.9 mmol), phthalic anhydride
(2.66 g, 17.9 mmol), and AlCl3 (3.60 g, 27.02 mmol) as a colorless
solid (5.19 g, 71%); mp 142 ꢁC; [found: C, 81.9; H, 7.7. C33H38O3 re-
quires C, 82.12; H, 7.94%]; Rf (20% EA/hexane) 0.22; nmax (KBr) 3365,
Rf (10% EA/hexane) 0.41; nmax (KBr) 2925, 1759, 1611, 1500 cmꢀ1
; dH
(300 MHz, CDCl3) 7.89e7.87 (1H, m, ArH), 7.65e7.47 (4H, m, ArH),
7.32e7.07 (8H, m, ArH), 6.95e6.89 (6H, m, ArH), 6.31 (1H, s, CH),
2.23 (6H, s, CH3); dC (75.6 MHz, CDCl3) 170.22,151.60,150.97, 150.12,
147.17, 145.95, 142.40, 141.55, 140.21, 134.95, 134.24, 129.31, 127.56,
126.87, 125.74, 125.73, 125.67, 122.92, 122.80, 121.56, 120.06, 119.94,
83.26, 62.91, 21.01; MS (EI): m/z (%)¼478 [M]þ.
2911,1691,1672,1595 cmꢀ1
; dH (300 MHz, CDCl3) 8.06e8.03 (1H, m,
ArH), 7.96e7.91 (1H, m, ArH), 7.75e7.72 (1H, m, ArH), 7.69e7.64
(2H, m, ArH), 7.57e7.48 (2H, m, ArH), 7.44e7.34 (4H, m, ArH),
2.06e1.97 (4H, m, CH2),1.13e1.06 (12H, m, CH2), 0.79e0.61 (10H, m,
CH2CH3); dC (75.6 MHz, CDCl3) 197.06, 170.35, 152.16, 151.01, 146.17,
143.03, 139.76,136.00,135.65, 133.01,130.85,129.86,129.33,128.43,
5.2.6. 3-(5-(9,9-Dihexyl-9H-fluoren-2-yl)thiophen-2-yl)iso-
benzofuran-1(3H)-one (12a). Following the above-mentioned
procedure (A), lactone 12a was obtained using 2-(2-thienyl)-9,9-

N.S. Kumar, A.K. Mohanakrishnan / Tetrahedron 66 (2010) 5660e5670
5665
dihexyl fluorene 10a (3 g, 7.2 mmol), phthalic anhydride (1.28 g,
8.65 mmol), AlCl3 (1.73 g, 13.00 mmol), and NaBH4 (1.37 g,
36.00 mmol) as a thick yellow liquid (1.4 g, 35%); [found: C, 80.7; H,
7.6; S, 5.7. C37H40O2S requires C, 80.98; H, 7.35; S, 5.84%]; Rf (10% EA/
m, ArH), 7.38e7.35 (4H, m, ArH), 7.38e7.29 (1H, m, ArH), 7.11e7.06
(3H, m, ArH), 2.65 (2H, t, J 8.25 Hz, CH2), 2.08 (4H, q, J 7.4 Hz, CH2),
1.63e1.55 (2H, m, CH2), 1.25e1.21 (6H, m, CH2), 0.83e0.79 (3H, m,
CH3), 0.41 (6H, t, J 7.35 Hz, CH3); dC (75.6 MHz, CDCl3) 150.84,150.21,
142.34, 141.14, 141.02, 139.23, 138.01, 136.24, 134.33, 132.84, 129.25,
128.22, 128.16,127.28,127.00,125.85,124.20, 124.05, 123.66, 123.00,
121.79,121.02,120.18,119.83, 56.27, 32.78, 31.60, 30.84, 29.09, 29.03,
22.56, 14.05, 8.62; MS (EI): m/z (%)¼520 [M]þ.
hexane) 0.47; nmax (KBr) 2875, 1755,1600,1500 cmꢀ1
; dH (300 MHz,
CDCl3) 7.99 (1H, d, J 7.5 Hz, ArH), 7.71e7.67 (2H, m, ArH), 7.57e7.51
(3H, m, ArH), 7.45e7.35 (2H, m, ArH), 7.28e7.26 (2H, m, ArH),
7.16e7.08 (3H, m, ArH), 6.67 (1H, s, CH), 2.03e1.96 (4H, m, CH2),
1.11e1.03 (12H, m, CH2), 0.75e0.63 (10H, m, CH2CH3); dC (75.6 MHz,
CDCl3) 170.11, 151.79, 151.75, 148.61, 145.06, 140.85, 139.98, 137.61,
134.41, 133.55, 132.53, 129.89, 128.10, 126.00, 125.77, 125.04, 124.64,
123.21, 122.99, 122.61, 120.23, 120.15, 78.27, 55.33, 40.40, 31.45,
29.64, 23.73, 22.56, 14.00; MS (EI): m/z (%)¼548 [M]þ.
5.3.3. 1-(9,9-Diethyl-9H-fluoren-2-yl)-3-(5-hexylthiophen-2-yl)
benzo[c]thiophene (9c). Following the above-mentioned procedure
(B), benzo[c]thiophene 9c was obtained using the lactone 8a (0.7 g,
1.97 mmol), 5-hexyl-2-thienylmagnesium bromide [prepared from
2-bromo-5-hexylthiophene (0.97 g, 3.95 mmol) and Mg (0.11 g,
4.58 mmol)], and Lawesson’s reagent (0.40 g, 1.00 mmol) as a thick
orange liquid (0.46 g, 45%); [found: C, 80.9; H, 7.1; S, 12.1. C35H36S2
requires C, 80.72; H, 6.97; S, 12.31%]; Rf (100% hexane) 0.89; nmax
5.2.7. 3-((5-(9,9-Dihexyl-2-thiophen-2-yl)-9H-fluoren-7-yl)thio-
phen-2-yl)isobenzofuran-1(3H)-one (12b). Following the above-
mentioned procedure (A), lactone 12b was obtained using 11b
(3.3 g, 5.11 mmol) and NaBH4 (0.97 g, 25.5 mmol) as a thick yellow
liquid (2.2 g, 68.7%); [found: C, 77.8; H, 7.0; S, 9.9. C41H42O2S2 re-
quires C, 78.05; H, 6.71; S, 10.16%]; Rf (10% EA/hexane) 0.51; nmax
(KBr) 2915, 1595, 1500 cmꢀ1
; dH (300 MHz, CDCl3) 7.85e7.79 (1H,
m, ArH), 7.74e7.73 (1H, m, ArH), 7.65e7.59 (2H, m, ArH), 7.55e7.49
(1H, m, ArH), 7.41e7.35 (4H, m, ArH), 7.31e7.29 (1H, m, ArH),
7.15e7.07 (3H, m, ArH), 2.67 (2H, t, J 8.17 Hz, CH2), 2.05 (4H, q, J
7.4 Hz, CH2), 1.59e1.51 (2H, m, CH2), 1.25e1.21 (6H, m, CH2),
0.83e0.79 (3H, m, CH3), 0.45 (6H, t, J 7.29 Hz, CH3); dC (75.6 MHz,
CDCl3) 150.55, 149.27, 142.30, 141.11, 141.00, 139.22, 138.05, 136.25,
134.37, 132.83, 129.37, 128.12, 127.32, 127.00, 125.98, 124.22, 124.01,
123.77, 123.03, 121.89, 121.00, 120.22, 119.88, 56.37, 32.86, 31.55,
30.79, 29.07, 22.61, 14.11, 8.62; MS (EI): m/z (%)¼520 [M]þ.
(KBr) 2875,1759,1600,1500 cmꢀ1
; dH (300 MHz, CDCl3) 8.00 (1H, d,
J 7.5 Hz, ArH), 7.74e7.63 (4H, m, ArH), 7.60e7.50 (4H, m, ArH), 7.47
(1H, s, ArH), 7.37 (1H, d, J 3.3 Hz, ArH), 7.28e7.26 (2H, m, ArH), 7.16
(1H, d, J 3.6 Hz, ArH), 7.10e7.08 (1H, m, ArH), 6.66 (1H, s, CH),
2.03e1.96 (4H, m, CH2), 1.11e1.03 (12H, m, CH2), 0.75e0.63 (10H, m,
CH2CH3); dC (75.6 MHz, CDCl3) 169.76, 151.80, 151.75, 148.61, 147.55,
145.06, 140.85, 139.98, 137.61, 134.41, 133.51, 132.53, 129.89, 129.16,
128.10, 126.00, 125.77, 125.04, 124.93, 124.64, 123.21, 122.99, 122.61,
120.23, 120.15, 78.27, 55.33, 40.40, 31.45, 29.64, 23.73, 22.56, 14.00;
MS (EI): m/z (%)¼630 [M]þ.
5.3.4. 1-(9,9-Diethyl-9H-fluoren-2-yl)-3-phenylbenzo[c]thiophene
(9d). Following the above-mentioned procedure (B), benzo[c]
thiophene 9d was obtained using the lactone 8a (0.7 g, 1.97 mmol),
phenylmagnesiumbromide [prepared from bromobenzene (0.62 g,
3.95 mmol) and Mg (0.11 g, 4.58 mmol)], and Lawesson’s reagent
(0.40 g, 1.00 mmol) as a yellow solid (0.40 g, 50%); mp 55 ꢁC;
[found: C, 86.7; H, 6.3; S, 7.2. C31H26S requires C, 86.47; H, 6.09; S,
5.3. A representative procedure for the preparation of benzo
[c]thiophene (9a) from lactone (8a) (procedure B)
5.3.1. 1-(9,9-Diethyl-9H-fluoren-2-yl)-3-(thiophen-2-yl)benzo[c]-
thiophene (9a). To a solution of lactone 8a (0.7 g, 1.97 mmol) in
anhydrous THF (25 mL) was added 2-thienylmagnesium bromide
[prepared from 2-bromothiophene (0.64 g, 3.92 mmol) and mag-
nesium turnings (0.11 g, 4.58 mmol)] at 0 ꢁC under N2. The reaction
mixture was slowly raised to room temperature and stirred for 4 h.
It was then quenched with aq NH4Cl solution, extracted with DCM
(2ꢂ20 mL), and dried (Na2SO4). The DCM solution was then stirred
with Lawesson’s reagent (0.40 g, 1.00 mmol) at room temperature
for 4 h. Solvent was evaporated in vacuo to give the crude product,
which was purified by column chromatography (100% hexane) to
give the title compound 9a (0.49 g, 57%) as an orange solid; mp
56 ꢁC; [found: C, 79.6; H, 5.6; S, 14.8. C29H24S2 requires C, 79.77; H,
5.54; S, 14.69%]; Rf (100% hexane) 0.85; nmax (KBr) 2891, 1601,
7.45%]; Rf (100% hexane) 0.81; nmax (KBr) 2905, 1595, 1501 cmꢀ1
; dH
(300 MHz, CDCl3) 7.99e7.89 (1H, m, ArH), 7.84e7.71 (4H, m, ArH),
7.61 (1H, s, ArH), 7.35e7.28 (5H, m, ArH), 7.15e7.09 (3H, m, ArH),
7.03e7.01 (2H, m, ArH), 2.10e2.03 (4H, m, CH2), 0.43e0.37 (6H, m,
CH3); dC (75.6 MHz, CDCl3) 150.70, 150.22, 144.25, 141.14, 140.60,
140.09, 133.80, 130.25, 127.90, 127.20,127.00,125.64,125.44, 125.22,
124.00, 123.84, 123.00, 122.25, 121.81, 120.33, 120.22, 120.10, 119.74,
119.00, 56.30, 32.91, 8.62; MS (EI): m/z (%)¼430 [M]þ.
5.3.5. 1-(9,9-Diethyl-9H-fluoren-2-yl)-3-(4-methoxyphenyl)benzo[c]-
thiophene (9e). Following the above-mentioned procedure (B),
benzo[c]thiophene 9e was obtained using the lactone 8a (0.7 g,
1.97 mmol), p-anisylmagnesiumbromide [prepared from 4-bro-
moanisole (0.74 g, 3.95 mmol) and Mg (0.11 g, 4.58 mmol)], and
Lawesson’s reagent (0.40 g, 1.00 mmol) as a yellow solid (0.47 g,
47%); mp 59 ꢁC. [found: C, 83.2; H, 6.3; S, 7.2. C32H28OS requires C,
83.44; H, 6.13; S, 6.96%]; Rf (100% hexane) 0.71; nmax (KBr) 2855,
1500 cmꢀ1
; dH (300 MHz, CDCl3) 7.92e7.70 (6H, m, ArH), 7.53 (1H,
d, J 3 Hz, ArH), 7.36e7.29 (5H, m, ArH), 7.14 (1H, t, J 3 Hz, ArH), 7.01
(1H, m, ArH), 2.15e2.06 (4H, m, CH2), 0.40 (6H, t, J 3.6 Hz, CH3); dC
(75.6 MHz, CDCl3) 150.70, 150.19, 144.21, 141.14, 140.58, 140.09,
133.74, 130.24, 127.88, 127.16, 126.99, 125.44, 125.22, 123.96, 123.84,
122.96, 122.25, 121.81, 120.33, 120.22, 120.06, 119.74, 118.97, 56.27,
32.86, 8.62; MS (EI): m/z (%)¼436 [M]þ.
1595, 1501 cmꢀ1
; dH (300 MHz, CDCl3) 7.97e7.85 (2H, m, ArH),
7.85e7.73 (3H, m, ArH), 7.39e7.27 (5H, m, ArH), 7.15e7.11 (3H, m,
ArH), 7.03e6.95 (2H, m, ArH), 3.75 (3H, s, OCH3), 2.01e1.95 (4H, m,
CH2), 0.45e0.39 (6H, m, CH3); dC (75.6 MHz, CDCl3) 151.01, 150.45,
144.25, 141.14, 140.60, 140.09, 133.80, 130.25, 127.90, 127.20, 127.05,
125.64,125.44,125.22,124.00,123.84,123.00,122.25,121.81,121.43,
120.22, 120.10, 119.74, 119.22, 56.31, 40.57, 32.91, 8.62; MS (EI): m/z
(%)¼460 [M]þ.
5.3.2. 1-(9,9-Diethyl-9H-fluoren-2-yl)-3-(3-hexylthiophen-2-yl)
benzo[c]thiophene (9b). Following the above-mentioned procedure
(B), benzo[c]thiophene 9b was obtained using the lactone 8a (0.7 g,
1.97 mmol), 3-hexyl-2-thienylmagnesium bromide [prepared from
2-bromo-3-hexylthiophene (0.97 g, 3.95 mmol) and Mg (0.11 g,
4.58 mmol)], and Lawesson’s reagent (0.40 g, 1.00 mmol) as a thick
orange liquid (0.58 g, 57%); [found: C, 80.5; H, 6.8; S, 12.6. C35H36S2
requires C, 80.72; H, 6.97; S, 12.31%]; Rf (100% hexane) 0.89; nmax
5.3.6. 1-(9,9-Diethyl-9H-fluoren-2-yl)-3-(4-methylphenyl)benzo[c]-
thiophene (9f). Following the above-mentioned procedure (B),
benzo[c]thiophene 9f was obtained using the lactone 8a (0.7 g,
1.97 mmol), p-tolylmagnesiumbromide [prepared from 4-bromo-
toluene (0.68 g, 3.95 mmol) and Mg (0.11 g, 4.58 mmol)], and
(KBr) 2915,1595,1500 cmꢀ1
ArH), 7.74e7.73 (1H, m, ArH), 7.68e7.64 (2H, m, ArH), 7.60e7.57 (1H,
; dH (300 MHz, CDCl3) 7.85e7.82 (1H, m,

5666
N.S. Kumar, A.K. Mohanakrishnan / Tetrahedron 66 (2010) 5660e5670
Lawesson’s reagent (0.40 g, 1.00 mmol) as a yellow solid (0.46 g,
52%); mp 55 ꢁC; [found: C, 86.2; H, 6.4; S, 7.0. C32H28S requires C,
86.44; H, 6.35; S, 7.21%]; Rf (100% hexane) 0.75; nmax (KBr) 2855,
(B), benzo[c]thiophene 9j was obtained using the lactone 8b (0.7 g,
1.50 mmol), 5-hexyl-2-thienyl magnesiumbromide [prepared from
2-bromo-5-hexylthiophene (0.74 g, 3.00 mmol) and Mg (0.08 g,
3.61 mmol)], and Lawesson’s reagent (0.30 g, 0.74 mmol) as a thick
orange liquid (0.47 g, 50%); [found: C, 81.8; H, 8.0; S, 10.4. C43H52S2
requires C, 81.59; H, 8.28; S, 10.13%]; Rf (100% hexane) 0.85; nmax
1595, 1501 cmꢀ1
; dH (300 MHz, CDCl3) 7.76e7.69 (3H, m, ArH),
7.67e7.56 (3H, m, ArH), 7.35e7.30 (7H, m, ArH), 7.19e6.93 (2H, m,
ArH), 2.62 (3H, s, CH3), 2.12e2.00 (4H, m, CH2), 0.42e0.30 (6H, m,
CH3); dC (75.6 MHz, CDCl3) 151.21, 151.00, 150.00, 146.63, 144.37,
140.19, 139.94, 136.01, 135.05, 134.80, 133.72, 130.72, 130.46, 129.86,
128.99, 128.45, 127.94, 127.07, 123.90, 123.10, 120.75, 119.24, 56.28,
32.50, 29.70, 8.44; MS (EI): m/z (%)¼444 [M]þ.
(KBr) 2885, 1595, 1500 cmꢀ1
; dH (300 MHz, CDCl3) 7.81e7.64 (4H,
m, ArH), 7.42e7.40 (2H, m, ArH), 7.19e7.14 (2H, m, ArH), 6.98e6.89
(3H, m, ArH), 6.84e6.83 (2H, m, ArH), 2.91e2.71 (2H, m, CH2),
2.10e2.05 (4H, m, CH2), 1.81e1.66 (8H, m, CH2), 1.45e1.33 (12H, m,
CH2CH3), 0.98e0.82 (13H, m, CH2CH3); dC (75.6 MHz, CDCl3)
151.52, 151.08, 147.66, 145.89, 140.75, 140.62, 137.56, 135.69, 135.40,
134.77, 129.41, 128.63, 127.29, 126.94, 126.64, 125.59, 124.94,
123.91, 122.72, 122.37, 121.92, 120.17, 119.87, 55.23, 40.38, 31.64,
31.57, 30.38, 29.98, 29.75, 28.93, 28.86, 28.71, 23.90, 22.64, 14.12;
MS (EI): m/z (%)¼632 [M]þ.
5.3.7. 1-(9,9-Diethyl-9H-fluoren-2-yl)-3-(naphthalen-1yl)benzo[c]-
thiophene (9g). Following the above-mentioned procedure (B),
benzo[c]thiophene 9g was obtained using the lactone 8a (0.7 g,
1.97 mmol), 1-naphthalenylmagnesiumbromide [prepared from
1-bromonaphthalene (0.82 g, 3.95 mmol) and Mg (0.11 g,
4.58 mmol)], and Lawesson’s reagent (0.40 g, 1.00 mmol) as a thick
yellow liquid (0.49 g, 52%); [found: C, 87.2; H, 5.6; S, 6.9. C35H28
requires C, 87.46; H, 5.87; S, 6.67%]; Rf (100% hexane) 0.81; nmax
(KBr) 2875,1601,1501 cmꢀ1
dH (300 MHz, CDCl3) 7.79e7.76 (4H, m,
ArH), 7.75e7.72 (6H, m, ArH), 7.66 (1H, d, J 6 Hz, ArH), 7.60 (1H, d, J
4.8 Hz, ArH), 7.47e7.33 (5H, m, ArH), 7.05 (1H, t, J 4.2 Hz, ArH),
2.01e1.94 (4H, m, CH2), 0.24 (6H, t, J 7.2 Hz, CH3); dC (75.6 MHz,
CDCl3) 150.70, 150.22, 147.22, 145.71, 144.25, 143.11, 141.14, 140.60,
140.09, 133.80, 131.91, 130.25, 127.90, 127.20, 127.00, 125.64, 125.44,
125.22, 124.00,123.84,123.00,122.25,121.81,120.33, 120.22, 120.10,
119.74, 119.00, 56.30, 32.91, 8.62; MS (EI): m/z (%)¼480 [M]þ.
S
5.3.11. 1-(9,9-Dihexyl-9H-fluoren-2-yl)-3-phenylbenzo[c]thiophene
(9k). Following the above-mentioned procedure (B), benzo[c]
thiophene 9k was obtained using the lactone 8b (0.7 g,
1.50 mmol), phenylmagnesiumbromide [prepared from bromo-
benzene (0.47 g, 3.00 mmol) and Mg (0.08 g, 3.61 mmol)], and
Lawesson’s reagent (0.30 g, 0.74 mmol) as a thick yellow liquid
(0.46 g, 57%); [found: C, 86.5; H, 7.6; S, 5.7. C39H42S requires C,
86.29; H, 7.80; S, 5.91%]; Rf (100% hexane) 0.81; nmax (KBr) 2905,
;
1595, 1501 cmꢀ1
; dH (300 MHz, CDCl3) 7.95e7.89 (4H, m, ArH),
7.84e7.66 (4H, m, ArH), 7.55e7.51 (2H, m, ArH), 7.43e7.33 (4H, m,
ArH), 7.16e7.02 (2H, m, ArH), 2.12e2.01 (4H, m, CH2), 1.20e1.18
(12H, m, CH2), 0.82e0.78 (10H, m, CH2CH3); dC (75.6 MHz, CDCl3)
150.89, 150.41, 143.67, 140.13, 139.59, 139.49, 133.15, 129.60,
127.24, 126.54, 126.30, 124.81, 124.63, 124.59, 123.30,123.24,
122.28, 121.58, 121.20, 119.69, 119.65, 119.45, 119.17, 118.37,
54.63, 39.89, 30.94, 29.15, 23.25, 22.00, 13.44; MS (EI): m/z (%)¼
542 [M]þ.
5.3.8. 1-(9,9-Dihexyl-9H-fluoren-2-yl)-3-(thiophen-2-yl)benzo[c]-
thiophene (9h). Following the above-mentioned procedure (B),
benzo[c]thiophene 9h was obtained using the lactone 8b (0.7 g,
1.50 mmol), 2-thienylmagnesium bromide [prepared from 2-bro-
mothiophene (0.49 g, 3.00 mmol) and Mg (0.08 g, 3.61 mmol)], and
Lawesson’s reagent (0.30 g, 0.74 mmol) as a thick orange liquid
(0.51 g, 62%); [found: C, 80.8; H, 7.3; S, 11.9. C37H40S2 requires C,
80.97; H, 7.35; S, 11.68%]; Rf (100% hexane) 0.85; nmax (KBr) 2895,
5.3.12. 1-(9,9-Dihexyl-9H-fluoren-2-yl)-3-(4-methoxyphenyl)benzo
[c]thiophene (9l). Following the above-mentioned procedure (B),
benzo[c]thiophene 9l was obtained using the lactone 8b (0.7 g,
1.50 mmol), p-anisylmagnesiumbromide [prepared from 4-bro-
moanisole (0.56 g, 3.00 mmol) and Mg (0.08 g, 3.61 mmol)], and
Lawesson’s reagent (0.30 g, 0.74 mmol) as a thick yellow liquid
(0.49 g, 58%); [found: C, 83.8; H, 7.8; S, 5.7. C40H44OS requires C,
83.87; H, 7.74; S, 5.60%]; Rf (100% hexane) 0.71; nmax (KBr) 2905,
1601, 1505 cmꢀ1
; dH (300 MHz, CDCl3) 8.02e7.92 (3H, m, ArH),
7.88e7.80 (3H, m, ArH), 7.62e7.61 (1H, m, ArH), 7.47e7.36 (4H, m,
ArH), 7.22e7.10 (3H, m, ArH), 2.18e2.10 (4H, m, CH2), 1.24e1.08
(12H, m, CH2), 0.89e0.79 (10H, m, CH2CH3); dC (75.6 MHz, CDCl3)
151.55, 151.07, 144.33, 140.78, 140.25, 140.15, 133.80, 130.26, 127.90,
127.20, 126.96, 125.47, 125.36, 125.25, 123.97, 123.90, 122.94, 122.24,
121.86, 120.35, 120.31, 120.10, 119.83, 119.03, 55.29, 40.55, 31.60,
29.81, 23.91, 22.66, 14.10; MS (EI): m/z (%)¼548 [M]þ.
1595, 1501 cmꢀ1
; dH (300 MHz, CDCl3) 7.73e7.49 (8H, m, ArH),
7.24e7.20 (3H, m, ArH), 6.98e6.95 (4H, m, ArH), 3.71 (3H, s, OCH3),
1.83e1.80 (4H, m, CH2),1.11e0.89 (12H, m, CH2), 0.65e0.62 (10H, m,
CH2CH3); dC (75.6 MHz, CDCl3) 158.85, 151.51, 151.01, 143.91, 140.86,
139.89, 130.64, 130.48, 127.06, 126.91, 126.36, 125.10, 124.87, 124.71,
123.69, 122.91, 122.03, 121.33, 120.33, 120.24, 119.86, 119.73, 118.87,
114.60, 55.40, 55.26, 40.56, 31.58, 29.79, 23.89, 22.64, 14.07; MS
(EI): m/z (%)¼572 [M]þ.
5.3.9. 1-(9,9-Dihexyl-9H-fluoren-2-yl)-3-(3-hexylthiophen-2-yl)
benzo[c]thiophene (9i). Following the above-mentioned procedure
(B), benzo[c]thiophene 9i was obtained using the lactone 8b (0.7 g,
1.50 mmol), 3-hexyl-2-thienyl magnesiumbromide [prepared from
2-bromo-3-hexylthiophene (0.74 g, 3.00 mmol) and Mg (0.08 g,
3.61 mmol)], and Lawesson’s reagent (0.30 g, 0.74 mmol) as a thick
orange liquid (0.54 g, 57%); [found: C, 81.8; H, 8.0 ; S, 10.3.
C43H52S2 requires C, 81.59; H, 8.28; S, 10.13%]; Rf (100% hexane)
5.3.13. 1-(9,9-Dihexyl-9H-fluoren-2-yl)-3-(4-methylphenyl)benzo[c]-
thiophene (9m). Following the above-mentioned procedure (B),
benzo[c]thiophene 9m was obtained using the lactone 8b (0.7 g,
1.50 mmol), p-tolylmagnesiumbromide [prepared from 4-bromo-
toluene (0.51 g, 3.00 mmol) and Mg (0.08 g, 3.61 mmol)], and
Lawesson’s reagent (0.30 g, 0.74 mmol) as a thick yellow liquid
(0.47 g, 57%); [found: C, 86.1; H, 8.2; S, 6.0. C40H44S requires C,
86.28; H, 7.96; S, 5.76%]; Rf (100% hexane) 0.75; nmax (KBr) 2855,
0.89; nmax (KBr) 2915, 1595, 1500 cmꢀ1
; dH (300 MHz, CDCl3)
7.85e7.82 (1H, m, ArH), 7.81e7.75 (2H, m, ArH), 7.70e7.64 (2H, m,
ArH), 7.45e7.39 (5H, m, ArH), 7.13e7.00 (3H, m, ArH), 2.73e2.68
(2H, m, CH2), 2.10e2.05 (4H, m, CH2), 1.32e1.27 (8H, m, CH2),
1.20e1.15 (12H, m, CH2CH3), 0.90e0.80 (13H, m, CH2CH3); dC
(75.6 MHz, CDCl3) 151.61, 151.10, 146.10, 142.00, 141.00, 140.61,
136.60, 134.81, 132.85, 130.63, 129.22, 128.70, 127.30, 127.00,
125.90, 124.01, 123.80, 123.77, 123.00, 122.44, 121.60, 120.20,
119.90, 55.27, 40.40, 31.65, 31.50, 30.80, 29.73, 29.14, 29.10, 23.90,
22.61, 14.10, 14.05; MS (EI): m/z (%)¼632 [M]þ.
1595, 1501 cmꢀ1
; dH (300 MHz, CDCl3) 7.85e7.79 (6H, m, ArH),
7.77e7.61 (2H, m, ArH), 7.33e7.29 (5H, m, ArH), 7.05e7.01 (2H, m,
ArH), 2.41 (3H, s, CH3), 2.10e2.00 (4H, m, CH2), 1.11e1.01 (12H, m,
CH2), 0.74e0.72 (10H, m, CH2CH3); dC (75.6 MHz, CDCl3) 151.46,
151.00, 144.30, 143.94, 140.79, 140.01, 136.80, 130.51, 130.09, 129.68,
127.05, 126.86, 125.03, 124.90, 124.83, 123.78, 122.88, 122.01, 121.88,
5.3.10. 1-(9,9-Dihexyl-9H-fluoren-2-yl)-3-(5-hexylthiophen-2-yl)
benzo[c]thiophene (9j). Following the above-mentioned procedure

N.S. Kumar, A.K. Mohanakrishnan / Tetrahedron 66 (2010) 5660e5670
5667
120.36, 120.19, 119.70, 118.98, 55.23, 40.49, 31.52, 29.73, 23.82,
142.01, 141.02, 140.61, 137.62, 136.62, 134.80, 132.87, 130.65, 129.23,
128.71, 127.32, 127.00, 125.91, 124.01, 123.82, 123.79, 123.00, 122.45,
121.62, 120.22, 119.60, 62.72, 40.41, 29.11, 23.97, 22.62, 20.91, 14.01 ;
MS (EI): m/z (%)¼644 [M]þ.
22.57, 21.36, 14.00; MS (EI): m/z (%)¼556 [M]þ.
5.3.14. 1-(9,9-Dihexyl-9H-fluoren-2-yl)-3-(naphthalen-1-yl)benzo[c]-
thiophene (9n). Following the above-mentioned procedure (B),
benzo[c]thiophene 9n was obtained using the lactone 8b (0.7 g,
1.50 mmol), 1-naphthalenylmagnesiumbromide [prepared from
1-bromonaphthalene (0.62 g, 3.00 mmol) and Mg (0.08 g,
3.61 mmol)], and Lawesson’s reagent (0.30 g, 0.74 mmol) as a thick
5.3.18. 1-(5-(9,9-Dihexyl-9H-fluoren-2-yl)thiophen-2-yl)-3-(thio-
phen-2-yl)benzo[c]thiophene (13a). Following the above-men-
tioned procedure (B), benzo[c]thiophene 13a was obtained using
the lactone 12a (0.6 g, 1.10 mmol), 2-thienylmagnesium bromide
[prepared from 2-bromothiophene (0.53 g, 3.30 mmol) and Mg
(0.09 g, 3.90 mmol)], and Lawesson’s reagent (0.22 g, 0.55 mmol) as
a thick red liquid (0.35 g, 51%); [found: C, 78.3; H, 7.0; S,
15.0C41H42S3 requires C, 78.05; H, 6.71; S, 15.25%]; Rf (100% hexane)
yellow liquid (0.49 g, 55%); [found: C, 86.9; H, 7.6; S, 5.6. C43H44
requires C, 87.11; H, 7.48; S, 5.41%]; Rf (100% hexane) 0.81; nmax
(KBr) 2855, 1595, 1500 cmꢀ1
dH (300 MHz, CDCl3) 8.08e7.83 (9H,
S
;
m, ArH), 7.60 (2H, t, J 7.5 Hz, ArH), 7.47e7.39 (5H, m, ArH), 7.15e7.12
(2H, m, ArH), 2.20e2.18 (4H, m, CH2), 1.21e1.11 (12H, m, CH2),
0.90e0.85 (10H, m, CH2CH3); dC (75.6 MHz, CDCl3) 151.58, 151.10,
144.86, 144.77, 143.66, 142.57, 142.11, 140.84, 140.28, 139.77, 136.51,
131.85, 130.51, 129.04, 127.23, 127.00, 126.91, 125.33, 125.16, 124.88,
124.02, 122.97, 122.45, 122.17, 120.52, 120.33, 119.87, 119.18, 55.34,
40.60, 31.65, 29.85, 23.95, 22.70, 14.14; MS (EI): m/z (%)¼592 [M]þ.
0.85; nmax (KBr) 2915, 1601, 1505 cmꢀ1
; dH (300 MHz, CDCl3)
8.43e8.41 (1H, m, ArH), 7.87 (1H, d, J 9 Hz, ArH), 7.80e7.75 (2H, m,
ArH), 7.71e7.67 (2H, m, ArH), 7.64e7.54 (7H, m, ArH), 7.46e7.43
(3H, m, ArH), 1.91e1.86 (4H, m, CH2), 1.25e0.97 (12H, m, CH2),
0.76e0.53 (10H, m, CH2CH3); dC (75.6 MHz, CDCl3) 152.17, 150.89,
146.03, 141.54, 139.71, 135.68, 135.33, 132.72, 131.09, 131.03, 130.78,
130.43, 129.97, 129.92, 129.09, 128.40, 127.89, 127.76, 127.01, 126.50,
125.96, 125.82, 123.94, 123.13, 120.73, 119.23, 55.18, 39.98, 31.48,
29.66, 23.77, 22.58, 14.01; MS (EI): m/z (%)¼630 [M]þ.
5.3.15. 1-(9,9-Dip-tolyl-9H-fluoren-2-yl)-3-(thiophen-2-yl)benzo[c]-
thiophene (9o). Following the above-mentioned procedure (B),
benzo[c]thiophene 9o was obtained using the lactone 8c (0.7 g,
1.48 mmol), 2-thienylmagnesium bromide [prepared from 2-bro-
mothiophene (0.48 g, 2.97 mmol) and Mg (0.08 g, 3.61 mmol)], and
Lawesson’s reagent (0.30 g, 0.74 mmol) as a thick orange liquid
(0.37 g, 45%); [found: C, 83.8; H, 5.2; S, 11.2. C39H28S2 requires C,
83.53; H, 5.03; S, 11.44%]; Rf (100% hexane) 0.82; nmax (KBr) 2925,
5.3.19. 1-(5-(9,9-Dihexyl-9H-fluoren-2-yl)thiophen-2-yl)-3-(3-hex-
ylthiophen-2-yl)benzo[c]thiophene (13b). Following the above-
mentioned procedure (B), benzo[c]thiophene 13b was obtained
using the lactone 12a (0.6 g, 1.10 mmol), 3-hexyl-2-thienyl mag-
nesiumbromide [prepared from 2-bromo-3-hexylthiophene
(0.87 g, 3.30 mmol) and Mg (0.09 g, 3.90 mmol)], and Lawesson’s
reagent (0.22 g, 0.55 mmol) as a thick red liquid (0.37 g, 47%);
[found: C, 78.7; H, 7.8; S, 13.7. C47H54S3 requires C, 78.94; H, 7.61; S,
1601, 1505 cmꢀ1
; dH (300 MHz, CDCl3) 7.70e7.66 (2H, m, ArH),
7.47e7.46 (2H, m, ArH), 7.37e7.31 (2H, m, ArH), 7.27e7.25 (3H, m,
ArH), 7.10e6.98 (13H, m, ArH), 2.27 (6H, s, CH3); dC (75.6 MHz,
CDCl3) 154.61, 152.45, 141.90, 141.25, 139.77, 136.79, 136.57, 136.27,
135.14, 134.95, 133.41, 130.61, 129.10, 128.98, 127.86, 127.76, 127.67,
127.55, 127.37, 126.17, 125.96, 125.47, 124.05, 122.95, 122.31, 121.90,
119.84, 119.28, 62.77, 20.99; MS (EI): m/z (%)¼560 [M]þ.
13.45%]; Rf (100% hexane) 0.85; nmax (KBr) 2915, 1601, 1505 cmꢀ1
;
dH (300 MHz, CDCl3) 8.43e8.41 (1H, m, ArH), 7.87 (1H, d, J 9 Hz,
ArH), 7.80e7.75 (2H, m, ArH), 7.71e7.67 (3H, m, ArH), 7.64e7.54
(3H, m, ArH), 7.46e7.43 (2H, m, ArH), 7.33e7.30 (3H, m, ArH),
2.77e2.71 (2H, m, CH2), 1.92e1.85 (4H, m, CH2), 1.69e1.60 (2H, m,
CH2), 1.35e1.12 (18H, m, CH2), 0.90e0.81 (13H, m, CH2CH3); dC
(75.6 MHz, CDCl3) 152.93, 150.25, 147.57, 143.70, 139.99, 137.16,
132.94, 131.62, 130.30, 130.12, 129.80, 129.63, 129.33, 128.89, 128.29,
127.42, 126.88, 126.84, 126.07, 125.13, 124.74, 124.29, 122.82, 122.11,
121.10,120.98, 120.15, 119.71, 55.32, 40.26, 31.49, 31.45, 31.39, 30.30,
29.62, 28.63, 23.64, 22.55, 14.06, 13.98; MS (EI): m/z (%)¼714 [M]þ.
5.3.16. 1-(9,9-Dip-tolyl-9H-fluoren-2-yl)-3-(3-hexylthiophen-2-yl)
benzo[c]thiophene (9p). Following the above-mentioned procedure
(B), benzo[c]thiophene 9p was obtained using the lactone 8b (0.7 g,
1.48 mmol), 3-hexyl-2-thienyl magnesiumbromide [prepared from
2-bromo-3-hexylthiophene (0.73 g, 2.97 mmol) and Mg (0.08 g,
3.61 mmol)], and Lawesson’s reagent (0.30 g, 0.74 mmol) as a thick
orange liquid (0.40 g, 42%); [found: C, 83.6; H, 6.1 ; S, 10.1. C45H40S2
requires C, 83.80; H, 6.25; S, 9.94%]; Rf (100% hexane) 0.87; nmax
5.3.20. 1-(5-(9,9-Dihexyl-9H-fluoren-2-yl)thiophen-2-yl)-3-(5-hex-
ylthiophen-2-yl)benzo[c]thiophene (13c). Following the above-
mentioned procedure (B), benzo[c]thiophene 13c was obtained
using the lactone 12a (0.6 g, 1.10 mmol), 5-hexyl-2-thienyl mag-
nesiumbromide [prepared from 2-bromo-5-hexylthiophene
(0.87 g, 3.30 mmol) and Mg (0.09 g, 3.90 mmol)], and Lawesson’s
reagent (0.22 g, 0.55 mmol) as a thick red liquid (0.36 g, 45%);
[found: C, 78.7; H, 7.9; S, 13.7. C47H54S3 requires C, 78.94; H, 7.61; S,
(KBr) 2900, 1595, 1501 cmꢀ1
; dH (300 MHz, CDCl3) 7.45e7.42 (5H,
m, ArH), 7.38e7.16 (3H, m, ArH), 7.11e7.00 (13H, m, ArH), 2.72 (2H,
t, J 7.5 Hz, CH2), 2.28 (6H, s, CH3), 1.63e1.59 (2H, m, CH2), 1.35e1.25
(6H, m, CH2), 0.85e0.75 (3H, m, CH3); dC (75.6 MHz, CDCl3) 154.59,
152.61, 147.15, 146.10, 145.61, 144.93, 142.00, 141.00, 140.61, 137.61,
136.60, 134.81, 132.85, 130.63, 129.22, 128.70, 127.30, 127.02, 125.90,
124.03, 123.80, 123.79, 123.01, 122.45, 121.60, 120.20, 119.90, 62.73,
40.40, 29.10, 23.95, 22.61, 20.93, 14.05; MS (EI): m/z (%)¼644 [M]þ.
13.45%]; Rf (100% hexane) 0.85; nmax (KBr) 2911, 1600, 1505 cmꢀ1
;
dH (300 MHz, CDCl3) 8.42e8.41 (1H, m, ArH), 7.85 (1H, d, J 8.5 Hz,
ArH), 7.82e7.75 (2H, m, ArH), 7.73e7.67 (3H, m, ArH), 7.63e7.51
(3H, m, ArH), 7.43e7.41 (2H, m, ArH), 7.33e7.30 (3H, m, ArH),
2.77e2.71 (2H, m, CH2), 1.93e1.82 (4H, m, CH2), 1.71e1.60 (2H, m,
CH2), 1.37e1.12 (18H, m, CH2), 0.90e0.81 (13H, m, CH2CH3); dC
(75.6 MHz, CDCl3) 152.17, 150.89, 146.03, 141.54, 139.71, 135.68,
135.33, 132.72, 131.09, 131.03, 130.78, 130.43, 129.97, 129.92, 129.09,
128.40, 127.89, 127.76, 127.01, 126.50, 125.96, 125.82, 123.94, 123.13,
120.73, 119.23, 55.18, 39.98, 31.48, 31.43, 31.37, 30.22, 29.66, 28.61,
23.77, 22.58, 14.01, 13.97; MS (EI): m/z (%)¼714 [M]þ.
5.3.17. 1-(9,9-Dip-tolyl-9H-fluoren-2-yl)-3-(5-hexylthiophen-2-yl)
benzo[c]thiophene (9q). Following the above-mentioned procedure
(B), benzo[c]thiophene 9q was obtained using the lactone 8b (0.7 g,
1.48 mmol), 5-hexyl-2-thienyl magnesiumbromide [prepared from
2-bromo-5-hexylthiophene (0.73 g, 2.97 mmol) and Mg (0.08 g,
3.61 mmol)], and Lawesson’s reagent (0.30 g, 0.74 mmol) as a thick
orange liquid (0.44 g, 47%); [found: C, 83.6; H, 6.1 ; S, 10.2. C45H40S2
requires C, 83.80; H, 6.25; S, 9.94%]; Rf (100% hexane) 0.87; nmax
(KBr) 2900, 1595, 1501 cmꢀ1
; dH (300 MHz, CDCl3) 7.65e7.62 (4H,
m, ArH), 7.45e7.35 (3H, m, ArH), 7.32e7.25 (2H, m, ArH), 7.13e7.00
(12H, m, ArH), 2.73e2.68 (2H, m, CH2), 2.27 (6H, s, CH3), 1.63e1.57
(2H, m, CH2), 1.30e1.23 (6H, m, CH2), 0.82e0.71 (3H, m, CH3); dC
(75.6 MHz, CDCl3) 154.60, 152.65, 147.13, 146.10, 145.60, 144.93,
5.3.21. 1-(5-(9,9-Dihexyl-9H-fluoren-2-yl)thiophen-2-yl)-3-phenyl-
benzo[c]thiophene (13d). Following the above-mentioned pro-
cedure (B), benzo[c]thiophene 13d was obtained using the lactone

5668
N.S. Kumar, A.K. Mohanakrishnan / Tetrahedron 66 (2010) 5660e5670
12a (0.6 g, 1.10 mmol), phenylmagnesiumbromide [prepared from
bromobenzene (0.51 g, 3.30 mmol) and Mg (0.09 g, 3.90 mmol)],
and Lawesson’s reagent (0.22 g, 0.55 mmol) as a thick orange liquid
(0.33 g, 49%); [found: C, 82.5; H, 6.9; S, 10.5. C43H44S2 requires C,
82.64; H, 7.10; S, 10.26%]; Rf (100% hexane) 0.81; nmax (KBr) 2905,
d, J 9 Hz, ArH), 7.73e7.63 (4H, m, ArH), 7.49e7.41 (7H, m, ArH),
7.28e6.99 (4H, m, ArH), 2.77e2.71 (2H, m, CH2), 1.92e1.85 (4H, m,
CH2), 1.69e1.60 (2H, m, CH2), 1.35e1.11 (18H, m, CH2), 0.90e0.81
(13H, m, CH2CH3); dC (75.6 MHz, CDCl3) 152.97, 150.28, 147.56,
143.75, 137.21, 132.98, 131.67, 130.81, 130.33, 130.20, 129.93, 129.86,
129.67, 129.39, 128.96, 128.92, 128.34, 128.03, 127.86, 127.50, 126.97,
126.14, 125.22, 124.78, 124.66, 122.56, 122.20, 121.58, 121.18, 121.06,
120.21, 119.80, 55.37, 40.35, 31.57, 31.45, 31.39, 30.30, 29.71, 28.62,
23.63, 22.64, 14.10, 13.91; MS (EI): m/z (%)¼796 [M]þ.
1601, 1505 cmꢀ1
; dH (300 MHz, CDCl3) 7.92e7.89 (1H, m, ArH),
7.87e7.83 (2H, m, ArH), 7.79e7.74 (2H, m, ArH), 7.73e7.70 (2H, m,
ArH), 7.67e7.52 (2H, m, ArH), 7.37e7.23 (4H, m, ArH), 7.16e7.03
(3H, m, ArH), 7.07e7.02 (2H, m, ArH), 2.07e2.00 (4H, m, CH2),
1.14e1.06 (12H, m, CH2), 0.77e0.72 (10H, m, CH2CH3); dC (75.6 MHz,
CDCl3) 152.91, 150.22, 14.55, 143.71, 139.97, 137.11, 132.95, 131.62,
130.31, 130.15, 129.81, 129.63, 129.35, 128.91, 128.31, 127.41, 126.89,
126.85, 126.05, 125.11, 124.75, 124.27, 122.81, 122.11, 121.11, 120.97,
120.15, 119.72, 55.23, 40.48, 31.45, 29.74, 23.83, 22.59, 13.99; MS
(EI): m/z (%)¼624 [M]þ.
5.4. A representative procedure for the preparation of benzo
[c]selenophene (15a) from lactone (8b) (procedure C)
5.4.1. 1-(9,9-Dihexyl-9H-fluoren-2-yl)-3-(thiophen-2-yl)benzo[c]se-
lenophene (15a). To a solution of lactone 8b (0.7 g, 1.50 mmol) in
anhydrous THF (25 mL) was added 2-thienylmagnesium bromide
[prepared from 2-bromothiophene (0.49 g, 3.00 mmol) and mag-
nesium turnings (0.08 g, 3.61 mmol)] at 0 ꢁC under N2. The reaction
mixture was slowly raised to room temperature and stirred for 4 h.
It was then quenched with 3 M HCl solution, extracted with DCM
(2ꢂ20 mL), and dried (Na2SO4). The DCM solution of benzo[c]furan
was then stirred with Woollins reagent (0.20 g, 0.37 mmol) at room
temperature for 4 h. Solvent was evaporated in vacuo to give the
crude product, which was purified by column chromatography
(100% hexane) to give the title compound 15a (0.53 g, 59%) as an
orange liquid; [found: C, 74.4; H, 6.5; S, 5.5. C37H40SSe requires C,
74.60; H, 6.77; S, 5.38%]; Rf (100% hexane) 0.81; nmax (KBr) 2895,
5.3.22. 1-(5-(9,9-Dihexyl-2-(thiophen-2-yl)-9H-fluoren-2-yl)thio-
phen-2-yl)-3-(thiophen-2-yl)benzo[c]thiophene (13e). Following the
above-mentioned procedure (B), benzo[c]thiophene 13e was
obtained using the lactone 12b (0.7 g, 1.11 mmol), 2-thie-
nylmagnesium bromide [prepared from 2-bromothiophene (0.54 g,
3.33 mmol) and Mg (0.09 g, 3.90 mmol)], and Lawesson’s reagent
(0.22 g, 0.55 mmol) as a thick red liquid (0.43 g, 55%); [found: C,
75.6; H, 6.5; S, 17.7. C45H44S4 requires C, 75.79; H, 6.22; S, 17.99%]; Rf
(100% hexane) 0.85; nmax (KBr) 2915, 1601, 1505 cmꢀ1
; dH
(300 MHz, CDCl3) 8.53 (1H, d, J 9 Hz, ArH), 7.89 (1H, d, J 9 Hz, ArH),
7.73e7.63 (4H, m, ArH), 7.49e7.41 (7H, m, ArH), 7.28e6.99 (5H, m,
ArH), 1.91e1.85 (4H, m, CH2), 1.11e1.03 (12H, m, CH2), 0.78e0.56
(10H, m, CH2CH3); dC (75.6 MHz, CDCl3) 152.60, 140.85, 140.71,
140.19, 139.77, 139.65, 139.10, 136.77, 133.84, 130.19, 129.91, 127.97,
127.09, 126.20, 126.08, 125.40, 125.34, 125.04, 125.00, 124.34,
123.86, 122.85, 122.78, 122.29, 121.99, 121.53, 121.19, 120.90, 119.89,
119.79, 55.72, 40.21, 31.51, 29.62, 23.70, 22.63, 14.07; MS (EI): m/z
(%)¼712 [M]þ.
1601, 1505 cmꢀ1
; dH (300 MHz, CDCl3) 7.87 (1H, d, J 8.4 Hz, ArH),
7.77e7.66 (3H, m, ArH), 7.57e7.55 (2H, m, ArH), 7.36e7.29 (5H, m,
ArH), 7.14e7.11 (1H, m, ArH), 7.04e6.94 (2H, m, ArH), 2.0 (4H, q, J
5.23 Hz, CH2), 1.09e1.07 (12H, m, CH2), 0.79e0.74 (10H, m,
CH2CH3); dC (75.6 MHz, CDCl3) 151.55,151.09,144.31,140.88,140.55,
138.27, 137.90, 137.54, 134.58, 134.37, 128.63, 127.92, 127.32, 126.94,
125.89, 125.64, 124.36, 124.02, 123.97, 122.97, 122.14, 121.97, 120.18,
119.88, 55.23, 40.34, 31.52, 29.73, 23.87, 22.60, 14.04; MS (EI): m/z
(%)¼596 [M]þ.
5.3.23. 1-(5-(9,9-Dihexyl-2-(thiophen-2-yl)-9H-fluoren-2-yl)thio-
phen-2-yl)-3-(3-hexylthiophen-2-yl)benzo[c]thiophene
(13f). Fol-
lowing the above-mentioned procedure (B), benzo[c]thiophene 13f
was obtained using the lactone 12b (0.7 g, 1.11 mmol), 3-hexyl-2-
thienyl magnesiumbromide [prepared from 2-bromo-3-hexylth-
iophene (0.82 g, 3.33 mmol) and Mg (0.09 g, 3.90 mmol)], and
Lawesson’s reagent (0.22 g, 0.55 mmol) as a thick red liquid (0.50 g,
57%); [found: C, 76.5; H, 6.9; S, 16.3. C51H56S4 requires C, 76.83; H,
7.08; S, 16.09%]; Rf (100% hexane) 0.85; nmax (KBr) 2915, 1601,
5.4.2. 1-(9,9-Dihexyl-9H-fluoren-2-yl)-3-(3-hexylthiophen-2-yl)
benzo[c]selenophene (15b). Following the above-mentioned pro-
cedure (C), benzo[c]selenophene 15b was obtained using the lac-
tone 8b (0.7 g, 1.50 mmol), 3-hexyl-2-thienyl magnesiumbromide
[prepared from 2-bromo-3-hexylthiophene (0.74 g, 3.00 mmol)
and Mg (0.08 g, 3.61 mmol)], and Woollins reagent (0.20 g,
0.37 mmol) as a thick orange liquid (0.63 g, 62%); [found: C, 76.1; H,
7.7; S, 4.7. C43H52SSe requires C, 75.96; H, 7.71; S, 4.72%]; Rf (100%
1505 cmꢀ1
; dH (300 MHz, CDCl3) 8.47e8.43 (1H, m, ArH), 7.87 (1H,
d, J 8.5 Hz, ArH), 7.83e7.75 (3H, m, ArH), 7.71e7.67 (3H, m, ArH),
7.64e7.52 (4H, m, ArH), 7.46e7.41 (2H, m, ArH), 7.37e7.31 (3H, m,
ArH), 2.77e2.69 (2H, m, CH2), 1.95e1.85 (4H, m, CH2), 1.69e1.61
(2H, m, CH2), 1.35e1.15 (18H, m, CH2), 0.92e0.81 (13H, m, CH2CH3);
dC (75.6 MHz, CDCl3) 152.71, 150.22, 145.53, 143.77, 140.71, 140.19,
139.77, 139.65, 139.10, 136.77, 133.84, 130.19, 129.91, 129.39, 127.97,
127.09, 126.20, 126.08, 125.40, 125.34, 125.04, 124.34, 123.86,
122.85, 122.78, 122.29, 121.99, 121.53, 121.19, 120.90, 120.22, 119.79,
55.37, 40.22, 31.53, 31.47, 31.37, 30.32, 29.62, 23.71, 22.63, 14.01,
13.93; MS (EI): m/z (%)¼796 [M]þ.
hexane) 0.85; nmax (KBr) 2895, 1601, 1505 cmꢀ1
; dH (300 MHz,
CDCl3) 7.85e7.74 (3H, m, ArH), 7.66e7.63 (2H, m, ArH), 7.48e7.37
(5H, m, ArH), 7.12 (1H, d, J 5.4 Hz, ArH), 7.04e7.00 (2H, m, ArH), 2.71
(2H, t, J 7.8 Hz, CH2), 2.10e2.05 (4H, m, CH2),1.68e1.61 (2H, m, CH2),
1.32e1.15 (18H, m, CH2), 0.90e0.81 (13H, m, CH2CH3); dC
(75.6 MHz, CDCl3) 151.53, 151.08, 146.09, 141.96, 140.80, 140.60,
136.60, 134.81, 132.81, 130.62, 129.21, 128.65, 127.30, 126.94, 125.88,
124.01, 123.78, 123.74, 122.97, 122.43, 121.55, 120.16, 119.87, 55.24,
40.38, 31.65, 31.53, 30.79, 29.73, 29.14, 29.07, 23.88, 22.60, 14.09,
14.04; MS (EI): m/z (%)¼680 [M]þ.
5.3.24. 1-(5-(9,9-Dihexyl-2-(thiophen-2-yl)-9H-fluoren-2-yl)thio-
phen-2-yl)-3-(5-hexylthiophen-2-yl)benzo[c]thiophene (13g). Fol-
lowing the above-mentioned procedure (B), benzo[c]thiophene
13g was obtained using the lactone 12b (0.7 g, 1.11 mmol), 5-hexyl-
2-thienyl magnesiumbromide [prepared from 2-bromo-5-hex-
ylthiophene (0.82 g, 3.33 mmol) and Mg (0.09 g, 3.90 mmol)], and
Lawesson’s reagent (0.22 g, 0.55 mmol) as a thick red liquid (0.44 g,
50%); [found: C, 76.6; H, 6.9; S, 16.3. C51H56S4 requires C, 76.83; H,
7.08; S, 16.09%]; Rf (100% hexane) 0.87; nmax (KBr) 2915, 1611,
5.4.3. 1-(9,9-Dihexyl-9H-fluoren-2-yl)-3-(5-hexylthiophen-2-yl)
benzo[c]selenophene (15c). Following the above-mentioned pro-
cedure (C), benzo[c]selenophene 15c was obtained using the lac-
tone 8b (0.7 g, 1.50 mmol), 5-hexyl-2-thienyl magnesiumbromide
[prepared from 2-bromo-5-hexylthiophene (0.74 g, 3.00 mmol)
and Mg (0.08 g, 3.61 mmol)], and Woollins reagent (0.20 g,
0.37 mmol) as a thick orange liquid (0.56 g, 55%); [found: C, 76.2; H,
7.9; S, 4.5. C43H52SSe requires C, 75.96; H, 7.71; S, 4.72%]; Rf (100%
hexane) 0.85; nmax (KBr) 2895, 1601, 1505 cmꢀ1
CDCl3) 7.84e7.73 (4H, m, ArH), 7.65e7.62 (2H, m, ArH), 7.47e7.37
; dH (300 MHz,
1501 cmꢀ1
; dH (300 MHz, CDCl3) 8.51 (1H, d, J 9 Hz, ArH), 7.81 (1H,

N.S. Kumar, A.K. Mohanakrishnan / Tetrahedron 66 (2010) 5660e5670
5669
(4H, m, ArH), 7.11 (1H, d, J 5.4 Hz, ArH), 7.04e7.00 (2H, m, ArH), 2.69
(2H, t, J 7.8 Hz, CH2), 2.09e2.03 (4H, m, CH2), 1.67e1.62 (2H, m,
CH2), 1.30e1.16 (18H, m, CH2), 0.93e0.77 (13H, m, CH2CH3); dC
(75.6 MHz, CDCl3); 151.52, 151.07, 146.09, 141.95, 140.79, 140.59,
136.58, 134.79, 132.80, 130.61, 129.21, 128.64, 127.29, 126.93, 125.88,
124.00, 123.77, 123.74, 122.96, 122.42, 121.54, 120.15, 119.87, 55.23,
40.37, 31.64, 31.52, 30.79, 29.72, 29.13, 29.07, 23.87, 22.60, 14.07,
14.04; MS (EI): m/z (%)¼680 [M]þ.
182.28, 151.03, 150.25, 146.50, 141.99, 141.52, 140.72, 138.81, 137.13,
136.53, 135.65, 131.87, 128.33, 127.59, 127.07, 126.30, 124.91, 124.78,
123.77, 123.04, 121.93, 121.30, 120.31, 119.98, 56.33, 32.73, 8.59; MS
(EI): m/z (%)¼464 [M]þ.
5.6.2. 5-((3-(9,9-Dihexyl-9H-fluoren-2-yl)benzo[c]thiophen-1-yl)-
thiophene-2-yl)carbaldehyde (17b). Following the above-men-
tioned procedure (E), aldehyde 17b was obtained using the benzo
[c]thiophene 9h (0.7 g, 1.27 mmol), DMF (1 mL), and POCl3 (0.29 g,
1.90 mmol) as a red liquid (0.45 g, 61%); [found: C, 79.4; H, 7.2; S,
11.0. C38H40OS2 requires C, 79.12; H, 6.99; S, 11.12%]; Rf (5% EA/
5.5. A representative procedure for the preparation of
compound 16a (procedure D)
hexane) 0.67; nmax (KBr) 2895, 1675, 1601, 1505 cmꢀ1
; dH (300 MHz,
To a stirred solution of 9a (0.4 g, 0.92 mmol) in dry DCM (20 mL)
was added FeCl3 (0.30 g, 1.85 mmol) under N2 atmosphere. The
reaction mixture was stirred for 6 h at room temperature and
quenched with dilute solution of N2H4.H2O. Then, it was filtered
through Celite, extracted with DCM, and dried (Na2SO4). Evapora-
tion of solvent followed by column chromatographic purification
afforded 16a as a semi solid (0.18 g, 45%).
CDCl3) 9.61 (1H, s, CHO), 7.81 (1H, d, J 8.3 Hz, ArH), 7.81e7.67 (3H,
m, ArH), 7.66e7.61 (5H, m, ArH), 7.41 (1H, d, J 3.9 Hz, ArH),
7.37e7.27 (3H, m, ArH), 2.22e2.17 (4H, m, CH2), 1.31e1.15 (12H, m,
CH2), 0.95e0.81 (10H, m, CH2CH3); dC (75.6 MHz, CDCl3) 181.71,
150.73, 147.15, 141.72, 141.50, 140.51, 138.47, 137.69, 136.11, 135.51,
133.87, 132.09, 128.53, 127.69, 126.91, 125.11, 124.67, 123.93, 123.11,
121.52, 121.42, 120.69, 119.12, 55.13, 40.67, 31.89, 29.49, 23.07, 22.71,
14.22; MS (EI): m/z (%)¼576 [M]þ.
5.5.1. 5,50-Bis(3-(9,9-diethyl-9H-fluoren-2-yl)benzo[c]thiophen-1-
yl)-2,20bithiophene (16a). Semi solid; [found: C, 80.1; H, 5.4; S, 14.6.
C58H46S4 requires C, 79.96; H, 5.32; S, 14.72%]; Rf (100% hexane)
5.6.3. 2-((5-(1-(9,9-Dihexyl-9H-fluoren-2-yl)benzo[c]thiophen-3-yl)
thiophen-2-yl)methylene)malononitrile (18a). Few drops of piperi-
dine was added to the solution of 17b (0.3 g, 0.53 mmol), malono-
nitrile (0.10 g, 1.56 mmol) in ethanol and stirred for 10 h. The
reaction mixture was poured into water. The precipitated solid was
filtered off and purified by column chromatography to afford 18a
(0.13 g, 40%) as a black solid. Mp 151 ꢁC; [found: C, 79.0; H, 6.7; N,
4.8; S, 10.0. C41H40N2S2 requires C, 78.80; H, 6.45; N, 4.48; S,
10.26%]; Rf (5% EA/hexane) 0.55; nmax (KBr) 2895, 2215, 1675, 1601,
0.65; nmax (KBr) 2891, 1595, 1500 cmꢀ1
; dH (300 MHz, CDCl3) 7.98
(2H, d, J 8.7 Hz, ArH). 7.80e7.61 (4H, m, ArH), 7.52e7.51 (2H, m,
ArH), 7.31e7.00 (14H, m, ArH), 6.89e6.86 (4H, m, ArH), 2.00 (8H, q, J
7.4 Hz, CH2), 0.35 (12H, t, J 7.4 Hz. CH3); dC (75.6 MHz, CDCl3)
150.90, 150.22, 141.33, 140.93, 136.55, 135.44, 135.30, 135.15, 132.54,
128.15, 127.35, 127.01, 126.95, 126.30, 126.05, 125.77, 124.89, 124.53,
124.30, 123.65, 123.00, 121.69, 120.22, 119.86, 56.28, 32.77, 8.62; MS
(EI): m/z (%)¼870 [M]þ.
1505 cmꢀ1
; dH (300 MHz, CDCl3) 7.63e7.61 (2H, m, ArH), 7.59e7.49
(5H, m, ArH), 7.39e7.35 (1H, m, ArH), 7.31e7.23 (3H, m, ArH),
7.14e7.05 (3H, m, ArH), 2.15e2.03 (4H, m, CH2), 1.30e1.17 (12H, m,
CH2), 0.91e0.81 (10H, m, CH2CH3); dC (75.6 MHz, CDCl3) 152.13,
151.64, 151.04, 140.84, 140.56, 136.09, 135.49, 135.14, 134.93, 132.58,
130.09, 129.93, 129.02, 128.12, 127.89, 127.32, 126.93, 125.35,125.29,
124.66, 124.37, ,123.65, 122.96, 121.57, 121.43, 120.26, 119.89, 55.26,
40.38, 31.53, 29.73, 23.86, 22.62, 14.06; MS (EI): m/z (%)¼624 [M]þ.
5.5.2. 5,50-Bis(3-(9,9-hexyl-9H-fluoren-2-yl)benzo[c]thiophen-1-yl)-
2,20bithiophene (16b). Following the above-mentioned procedure
(D), dimer 16b was obtained using the benzo[c]thiophene 9h (0.7 g,
1.50 mmol) and FeCl3 (0.36 g, 2.29 mmol) as a red liquid (0.28 g,
40%); [found: C, 80.9; H, 7.4; S, 11.5. C74H78S4 requires C, 81.12; H,
7.18; S, 11.71%]; Rf (100% hexane) 0.77; nmax (KBr) 2891, 1595,
1500 cmꢀ1
; dH (300 MHz, CDCl3); 7.67e7.64 (4H, m, ArH), 7.60e7.54
(10H, m, ArH), 7.37e7.36 (4H, m, ArH), 7.27 (4H, d, J 5.1 Hz, ArH),
7.10e7.07 (4H, m, ArH), 2.04e1.99 (8H, m, CH2), 1.11e1.05 (24H, m,
CH2), 0.76e0.71 (20H, m, CH2CH3); dC (75.6 MHz, CDCl3) 151.60,
151.07, 144.31, 140.78, 140.25, 140.15, 133.80, 130.26, 127.90, 127.20,
126.96, 125.47, 125.36, 125.25, 123.97, 123.90, 122.94, 122.24, 121.86,
120.35, 120.31, 120.10, 119.83, 119.03, 55.29, 40.55, 31.60, 29.81,
23.91, 22.66, 14.10; MS (EI): m/z (%)¼1094 [M]þ.
5.7. A representative procedure for the preparation of
compound 18b (procedure F)
To the solution of 17a (0.3 g, 0.64 mmol) and thiophene-2-ace-
tonitrile (0.16 g, 1.29 mmol) in dry THF, a solution of t-BuOK (0.14 g,
1.29 mmol) in THF was added dropwise and stirred for 10 h under
nitrogen atmosphere. The reaction mixture was poured into water,
extracted with DCM followed by column chromatographic purifi-
cation gave 18b (0.16 g, 45%) as a black solid.
5.6. A representative procedure for the preparation of
compound 17a (procedure E)
5.7.1. 3-(5-(1-(9,9-Diethyl-9H-fluoren-2-yl)benzo[c]thiophen-3-yl)
thiophen-2-yl)-2-(thiophen-2-yl)acrylonitrile (18b). Mp 137 ꢁC;
[found: C, 76.1; H, 4.9; N, 2.2; S, 17.1. C36H27NS3 requires C, 75.88; H,
4.78; N, 2.46; S, 16.88%]; Rf (5% EA/hexane) 0.55; nmax (KBr) 2895,
To a stirred solution of DMF (1 mL) in dry DCM, POCl3 (0.37 g,
2.42 mmol) was added to get yellow solution. To this solution 9a
(0.7 g, 1.60 mmol) was added slowly and stirred overnight at room
temperature. Then, the reaction mixture was quenched with water,
extracted with DCM, and dried. Evaporation solvent followed by
column chromatographic purification gave 17a (0.42 g, 57%) as
a red solid.
2220, 1675, 1601, 1505 cmꢀ1
; dH (300 MHz, CDCl3) 8.52e8.49 (1H,
m, ArH), 7.90e7.81 (3H, m, ArH), 7.80e7.73 (1H, m, ArH), 7.67e7.61
(4H, m, ArH), 7.55e7.51 (2H, m, ArH), 7.43e7.33 (4H, m, ArH),
7.23e7.15 (2H, m, ArH), 2.12e2.01 (4H, m, CH2), 0.81e0.73 (6H, m,
CH3); dC (75.6 MHz, CDCl3) 151.22, 151.05, 144.61, 144.17, 141.78,
140.11, 134.35, 131.07, 130.59, 128.66, 128.56, 127.90, 127.35, 127.22,
126.89,126.61,126.29,126.22,125.83,125.50,125.27,124.82,124.39,
123.73, 122.91, 121.47, 120.48, 120.27, 120.11, 119.24, 118.97, 55.25,
32.75, 8.61; MS (EI): m/z (%)¼569 [M]þ.
5.6.1. 5-((3-(9,9-Diethyl-9H-fluoren-2-yl)benzo[c]thiophen-1-yl)-
thiophene-2-yl)carbaldehyde (17a). Mp 95 ꢁC; [found: C, 77.3; H,
5.5; S, 13.6. C30H24OS2 requires C, 77.55; H, 5.21; S, 13.80%]; Rf (5%
EA/hexane) 0.63; nmax (KBr) 2891, 1670, 1601, 1500 cmꢀ1
; dH
(300 MHz, CDCl3) 9.91 (1H, s, CHO), 8.09 (1H, d, J 8.7 Hz, ArH),
7.86e7.78 (3H, m, ArH), 7.69 (2H, d, J 6.0 Hz, ArH), 7.67e7.61 (3H, m,
ArH), 7.47 (1H, d. J 4.2 Hz, ArH), 7.37e7.36 (3H, m, ArH), 2.09 (4H, q,
J 7.35 Hz, CH2), 0.41 (6H, t, J 7.35 Hz, CH3); dC (75.6 MHz, CDCl3)
5.7.2. 3-(5-(1-(9,9-Dihexyl-9H-fluoren-2-yl)benzo[c]thiophen-3-yl)
thiophen-2-yl)-2-(thiophen-2-yl)acrylonitrile (18c). Following the
above-mentioned procedure (F), compound 18c was prepared

5670
N.S. Kumar, A.K. Mohanakrishnan / Tetrahedron 66 (2010) 5660e5670
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hexane) 0.57; nmax (KBr) 2895, 2217, 1675, 1601, 1505 cmꢀ1
; dH
(300 MHz, CDCl3) 8.52e8.49 (1H, m, ArH), 7.90e7.81 (3H, m, ArH),
7.80e7.73 (1H, m, ArH), 7.66e7.59 (4H, m, ArH), 7.55e7.51 (2H, m,
ArH), 7.43e7.33 (4H, m, ArH), 7.13 (1H, t, J 8.7 Hz, ArH), 7.10 (1H, t, J
8.4 Hz, ArH), 2.12e2.01 (4H, m, CH2), 1.20e1.18 (12H, m, CH2),
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Acknowledgements
We thank the Department of Science and Technology (DST),
New Delhi for financial support. N.S. thanks CSIR, New Delhi for SRF
fellowship. The authors thank the Department of Science and
Technology (DST-FIST) for a 300 MHz NMR spectrometer. The
University of Madras is also acknowledged for financial support
through DST-PURSE program.
References and notes
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