Synthesis of β-pyrrole and β-thiophene substituted 21,23-dithia and 21-monothiaporphyrins

Article abstract of DOI:10.1016/j.tet.2004.03.047

A series of β-pyrrole and β-thiophene substituted porphyrins with N₂S₂ and N₃S porphyrin cores were synthesized and characterized. The introduction of substituents at β-pyrrole and β-thiophene carbons resulted in significant shifts in ¹H NMR, absorption and fluorescence maxima. These effects were attributed to alteration of the porphyrin ring current caused by substituents at β-positions.

Full text of DOI:10.1016/j.tet.2004.03.047

Tetrahedron 60 (2004) 4739–4747
Synthesis of b-pyrrole and b-thiophene substituted 21,23-dithia
and 21-monothiaporphyrins
*
Neeraj Agarwal and Mangalampalli Ravikanth
Department of Chemistry, Indian Institute of Technology, Powai, Mumbai 400076, India
Received 30 September 2003; revised 19 February 2004; accepted 11 March 2004
Abstract—A series of b-pyrrole and b-thiophene substituted porphyrins with N2S2 and N3S porphyrin cores were synthesized and
characterized. The introduction of substituents at b-pyrrole and b-thiophene carbons resulted in significant shifts in 1H NMR, absorption and
fluorescence maxima. These effects were attributed to alteration of the porphyrin ring current caused by substituents at b-positions.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
Both electron withdrawing and electron releasing sub-
stituents has been introduced and detailed spectral and
electrochemical properties investigated.3 Porphyrins bear-
ing electron withdrawing substituents such as –Br, –NO2 at
b-pyrrole carbons have considerable potential as catalysts
for epoxidation of alkenes and hydroxylation of alkanes.4
Although there is extensive literature on b-substitution of
porphyrins with an N4 core, except a couple of reports by
us,5 there is no other report on b-substituted core modified
porphyrins. The core-modified porphyrins resulting from
the replacement of pyrrole with heterocycles such as
thiophene, furan, selenophene and tellurophene have
received less attention in spite of their novel properties
such as stabilization of metals in unusual oxidation states.6
We have been interested in the synthesis and the chemistry
of new core-modified porphyrins for use in bioorganic
and materials chemistry applications7 and in this paper we
Porphines have two potential positions: meso- and
b-positions at which substituents can be introduced. The
electronic properties of porphyrins can be tuned at will by
introducing suitable substituents at meso- or at b-positions.
Generally, most of the porphyrins synthesized possess aryl
groups at meso positions because they can be synthesized
easily and they are very stable to handle for various
applications.1 Further introduction of substituents on meso-
aryl groups does not much alter the electronic properties of
the porphyrin ring since the substituents are not in direct
conjugation with the porphyrin macrocycle. However, the
introduction of substituents at the b-positions alters the
electronic properties tremendously since these substituents
are in direct conjugation with the porphyrin ring.2 There are
several reports on b-substituted porphyrins with an N4 core.
Chart 1.
Keywords: b-Substituted porphyrins; Core-modified porphyrins; Bathochromic shifts; Non-planarity.
*
Corresponding author. Fax: þ91-22-576-7152; e-mail address: ravikanth@chem.iitb.ac.in
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.03.047

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N. Agarwal, M. Ravikanth / Tetrahedron 60 (2004) 4739–4747
Scheme 1. Synthetic scheme for b-pyrrole substituted 21,23-dithiaporphyrin 1.
report the synthesis and characterization of a series of
b-substituted thiaporphyrins with N2S2 and N3S porphyrin
cores. The thiaporphyrins have two types of b-positions:
b-pyrroles and b-thiophenes at which the substituents can
be introduced. We successfully synthesized b-substituted
thiaporphyrins in which the substituents were introduced at
b-pyrrole as well as b-thiophene carbons independently
(Chart 1) and investigated the effect of substituents on the
spectral properties of the porphyrins.
characteristic Mþ and M2Brn (n¼1–4) peaks. The
introduction of bromines at b-pyrrole carbons resulted in
large red shifts and broadening of absorption bands (Table
1). This is because of the presence of bulky substituents at
the b-pyrrole carbons which reduce the energy gap between
HOMO and LUMO. The emission bands of 1 also
experienced similar red shifts compared to S2TPP. How-
ever, 1 was more weakly fluorescent than S2TPP because of
the presence of heavy halogens at the b-pyrrole carbons. To
introduce aryl groups at b-pyrrole carbons, 1 was reacted
with substituted phenyl boronic acids under Suzuki coupling
conditions. This resulted in a complicated mixture of
products and no attempts were made to separate and
identify the products. We then diverted our attention to
synthesize 3,4-disubstituted pyrroles for using them to
synthesize b-substituted porphyrins. The 3,4-disubstituted
pyrrole synthesis available in the literature is generally a
multi-step process with low yields. However, Ono et al.8
recently reported an easy and faster method of synthesizing
3,4-disubstituted pyrroles and then converting them to
b-substituted porphyrins. Thus we prepared 3,4-diphenyl
pyrrole following their method and condensed it with
2,5-bis(a-hydroxymethylphenyl)thiophene using BF3·OEt2
in chloroform to obtain (b-Ph)4S2TPP, 2, in 25% yield
(Scheme 2). Ono et al.8 reported that 3,4-diphenyl pyrrole
was not reactive enough to form porphyrins with aromatic
aldehydes. Hence they formylated and reduced it to the
hydroxymethyl group and tetramerized it under acidic
conditions to form porphyrins. However, in the present case
the 3,4-diphenyl pyrrole reacted easily. The reactive
functionality of 2,5-bis(hydroxymethyphenyl)thiophene9
helped in the formation of 2 under normal porphyrin
2. Results and discussion
2.1. b-Pyrrole substituted 21,23-dithiaporphyrins
Our initial goals were to introduce bromines at b-pyrrole
carbons and use them as synthons for the synthesis of other
b-substituted dithiaporphyrins via Suzuki coupling. Thus,
we investigated the possibility of tetrabrominating the
5,10,15,20-tetraphenyl-21,23-dithiaporphyrin (S2TPP).
Treatment of S2TPP with 4.2 equiv. of N-bromosuccinimide
in chloroform gave (b-Br)4S2TPP, 1, in 70% yield (Scheme
1). The tetrabrominated porphyrin, 1, was purified by silica
gel column using dichloromethane and characterized with
1H NMR, mass, absorption and emission spectroscopies.
The absence of the pyrrole signal in 1H NMR indicated that
the hydrogens were replaced by bromines at the b-positions
of two pyrrole rings. The b-thiophene protons appeared as
singlet indicating the symmetric nature of 1. The thiophene
protons in 1 experienced an upfield shift of 0.26 ppm
compared to S2TPP due to the change in ring current caused
by the bromines at b-pyrrole carbons. The mass showed
Table 1. Absorption and emission data of porphyrins 1–11 along with S2TPP and STPPH in toluene
Porphyrin
Soret band lmax (nm) (1£1024
)
Absorption Q-bands, lmax (nm) (1£1024
)
Fluorescence lmax
(lex¼440 nm)
IV
III
II
I
Q(0,0)
Q(0,1)
f
S2TPP
1
2
3
4
435 (25.0)
440 (19.2)
440 (21.2)
449 (18.1)
438 (17.5)
446 (16.9)
444 (13.0)
454 (2.90)
429 (18.7)
428 (23.7)
430 (15.9)
433 (14.3)
433 (17.2)
519 (2.60)
521 (1.9)
519 (1.9)
547 (0.70)
—
—
—
—
—
—
—
547 (0.44)
546 (sh)
550 (sh)
549 (sh)
549 (sh)
633 (0.22)
633 (0.15)
637 (0.22)
649 (0.18)
637 (0.13)
646 (0.25)
640 (0.13)
654 (0.17)
618 (0.19)
614 (0.32)
618 (0.21)
619 (0.17)
619 (0.46)
696 (0.45)
698 (0.22)
700 (0.31)
717 (0.23)
701 (0.32)
714 (0.31)
707 (0.21)
715 (0.12)
678 (0.30)
674 (0.34)
678 (0.41)
680 (0.19)
679 (0.42)
706
740
735
802
706
744
722
736
678
682
693
688
693
781
—
—
—
—
—
—
—
760
—
—
—
—
0.0076
,1024
0.0009
,1024
0.0015
0.0005
0.0020
0.0003
0.0168
0.0044
0.0025
0.0036
0.0014
530 (1.70)
520 (2.07)
527 (1.80)
524 (1.37)
524 (0.69)
513 (1.71)
513 (2.07)
516 (1.43)
517 (1.37)
517 (2.65)
5
6
7
STPPH
8
9
10
11

N. Agarwal, M. Ravikanth / Tetrahedron 60 (2004) 4739–4747
4741
Scheme 2. Synthetic scheme for b-pyrrole substituted 21,23-dithiaporphyrin 2.
forming conditions. The porphyrin 2 was characterized by
1H NMR, mass, absorption and emission spectroscopies. In
1H NMR, the pyrrole protons were absent as expected. The
thiophene protons were also upfield shifted by 0.44 ppm
compared to S2TPP.6 The product was further confirmed by
the presence of the molecular ion peak in the mass spectrum.
The absorption (Fig. 1) and emission bands (Fig. 2) were
broadened and also red shifted compared to S2TPP6 (Table
Figure 1. UV–visible spectra S2TPP (—), 2 (- - -) and 7 (· · ·) recorded in toluene.
Figure 2. Fluorescence spectra of S2TPP (—), 2 (- - -) and 7 (· · ·) recorded in toluene at lex¼440 nm.

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N. Agarwal, M. Ravikanth / Tetrahedron 60 (2004) 4739–4747
Scheme 3. Synthetic scheme for diols 12, 13, 14 and 15.
1) indicating that the phenyl substituents at b-pyrrole
carbons alter the energy levels. The molar absorption
coefficients and fluorescence yields of 1 and 2 were reduced
compared to S2TPP. Similarly we prepared 3-phenyl-4-
nitropyrrole following Ono’s method8 and condensed it with
2,5-bis(a-hydroxymethylphenyl) thiophene in the presence
of BF3·OEt2 in chloroform to obtain (b-Ph)(b-NO2)S2TPP,
3, in 4.8% yield. The crude porphyrin 3 was purified by
silica gel column chromatography using dichloromethane as
spectral properties. However, there is no report to under-
stand the effect of substituents on ring current if the
substituents are present at b-thiophene carbons instead of b-
pyrrole carbons. Our preliminary study5c indicated that the
substituents at b-thiophene carbons alter the porphyrin ring
more effectively when compared to the same substituents at
the b-pyrrole carbons. Thus we synthesized N2S2 porphyr-
ins 4 and 5 containing two and four methyl groups,
respectively, at the b-thiophene carbons. The required
thiophene precursors, 3-methyl thiophene and 3,4-dimethyl
thiophene were synthesized following known method-
ology.10 The unknown diols 12 and 13 were synthesized
as shown in Scheme 3 following Ulman and Manassen’s
method.9 The 3-methyl or 3,4-dimethyl thiophene was first
reacted with n-butyl lithium in n-hexane in the presence of
TMEDA, followed by treatment with benzaldehyde in THF
at 0 8C. The tlc analysis indicated the formation of diol 12 or
13 with small amounts of mono-ol and unreacted benzal-
dehyde. The diols 12 and 13 were purified by silica gel
column chromatography using petroleum ether/ethyl acetate
and to afford 12 as a semi-white solid in 22% and 13 as a
1
an eluent. The H NMR spectrum of 3 varied with the
concentration since porphyrins with electron withdrawing
substituents have a high tendency to aggregate. The mass
spectrum showed an Mþ ion peak, hence confirming the
product. The absorption and emission bands of 3 were
broader and also red shifted with lower absorption
coefficients and quantum yields than 1 and 2.
2.2. b-Thiophene substituted 21,23-dithiaporphyrins
The substituents at the b-pyrrole carbons altered the
porphyrin ring current which was reflected in the observed
Scheme 4. Synthetic scheme for b-thiophene substituted 21,23-dithiaporphyrin 5.

N. Agarwal, M. Ravikanth / Tetrahedron 60 (2004) 4739–4747
4743
crystalline white solid in 17% yield. The N2S2 porphyrins 4
and 5 were synthesized by condensing the appropriate diol
12 and 13, respectively, with pyrrole in CH2Cl2 in the
presence of BF3·OEt2 at room temperature, followed by
oxidation with DDQ (Scheme 4). The crude porphyrins 4
and 5 were purified by silica gel column chromatography
using petroleum ether/CH2Cl2 and the pure crystalline
purple solids of porphyrins 4 and 5 were obtained in 8–9%
yields. The porphyrins 4 and 5 were characterized by NMR,
compared to S2TPP. Porphyrin 7 did not show any
thiophene signal as expected due to the presence of phenyl
groups at b-thiophenes. The pyrrole protons in 6 appeared
as three separate signals because of the unsymmetric
substitution pattern whereas the pyrrole protons in 7
appeared as singlet, due to the symmetric substitution.
Furthermore, the pyrrole protons in 7 experienced the
maximum upfield shifts compared to any other b-substi-
tuted 21,23-dithiaporphyrin reported in this paper. This
suggests that the four phenyl groups at b-thiophene carbons
in 7 altered the porphyrin ring current more effectively
compared to 21,23-dithiaporphyrins having four phenyl
substituents at b-pyrrole carbons or any other b-substituted
21,23-dithiapophyrins. The absorption (Fig. 1) and emission
bands (Fig. 2) of 7 also exhibited maximum red shifts
(Table 1) and reduction in absorption coefficients and
fluorescence yield.
1
mass, absorption and fluorescence spectroscopies. The H
NMR spectrum of 4 in which one methyl group is present at
the b-thiophene carbons showed a very interesting feature.
The two thiophene protons, one on each thiophene of 4,
appeared as a singlet which was upfield shifted compared to
S2TPP.6 Unlike in S2TPP where pyrrole protons appear as a
singlet, the pyrrole protons of 4 appeared as four separate
signals: two doublets and two singlets indicating that the
protons were not equivalent. The pyrrole protons of 4 were
upfield shifted compared to S2TPP. In porphyrin 5, the
thiophene protons disappeared due to the substitution of
thiophene hydrogens by methyl groups. The pyrrole protons
in 5 appeared as singlet and upfield shifted than pyrrole
protons of S2TPP. The absorption and emission bands of 4
and 5 were shifted bathochromically with low absorption
coefficients and fluorescence yields compared to S2TPP
(Table 1). However, the magnitude of red shifts was larger
for 5 than 4 due to the presence of more methyl groups at the
b-thiophene carbons in 5 than in 4.
2.3. b-Thiophene substituted 21-monothiaporphyrins
The thiophene diols 12 and 13 were also used to synthesize
b-thiophene substituted 21-monothiaporphyrins 8 and 9,
respectively. The condensation of 1 equiv. of 12 with
2 equiv. of benzaldehyde and 3 equiv. of pyrrole gave a
crude porphyrin mixture (Scheme 5). The tlc analysis
showed the formation of three porphyrins: meso-5,10,15,20-
tetraphenyl-b-2,12-dimethyl-21,23-dithiaporphyrin (N2S2
porphyrin 4), the required meso-5,10,15,20-tetraphenyl-b-
2-methyl-21-monothiaporphyrin (N3S porphyrin 8) and
meso-5,10,15,20-tetraphenyl porphyrin (N4 porphyrin).
The mixture of three porphyrins was separated by silica
gel column chromatography and the desired N3S porphyrin
8 was collected as the second band using petroleum ether/
CH2Cl2 in 12% yield. Similarly the condensation of 1 equiv.
of diol 13 with 2 equiv. of benzaldehyde and 3 equiv. of
pyrrole followed by column chromatography gave por-
phyrin 9 in 12% yield. Both porphyrins 8 and 9 were
characterized by NMR, mass, absorption and fluorescence
The porphyrins with phenyl groups substituted at b-thio-
phene carbons 6 and 7 were synthesized using correspond-
ing unknown diols 14 and 15, respectively. The diols 14
and 15 were synthesized using 3-phenylthiophene and
3,4-diphenylthiophene, respectively, under identical n-butyl
lithium conditions mentioned for diols 12 and 13 (Scheme
3). The diols 14 and 15 were purified by silica gel column
chromatography and afforded as white solids in 28–29%
yields. To prepare porphyrins 6 and 7, 1 equiv. of diol 14
and 15, respectively, was condensed with 1 equiv. of pyrrole
under mild acidic conditions followed by oxidation with
DDQ. The crude porphyrinic mixture was subjected twice to
silica gel column chromatography to provide 6 in 4.8% and
7 in 2.3% yields as purple solids. The porphyrins 6 and 7
were confirmed by 1H NMR and the molecular ion peak in
mass spectra. In 1H NMR, porphyrin 6 showed a singlet for
thiophene protons which was upfield shifted by 0.11 ppm
1
spectroscopic techniques. The thiophene proton of 8 in H
NMR appeared as a singlet and it was upfield shifted by
0.35 ppm compared to b-unsubstituted meso-5,10,15,20-
tetraphenyl-21-monothiaporphyrin (STPPH).6 The thio-
phene protons of 9 were absent as expected. The pyrrole
protons of 8 and 9 appeared as five and three separate signals,
respectively, and they were slightly upfield shifted compared
to STPPH. The absorption spectra of porphyrins 8 and 9
Scheme 5. Synthetic scheme for b-thiophene substituted 21- monothiaporphyrin 8.

4744
N. Agarwal, M. Ravikanth / Tetrahedron 60 (2004) 4739–4747
showed four Q-bands and one Soret band with negligible
shifts in peak maxima compared to STPPH (Table 1).
CH2Cl2 in a 100 ml one-necked round bottomed flask fitted
with an argon bubbler. Trifluoroacetic acid (96.3 ml) was
added to initiate the condensation. The reaction mixture was
stirred under argon at room temperature. The progress of the
reaction was monitored using absorption spectroscopy.
Aliquots of the reaction mixture were taken at regular
intervals and oxidized with DDQ and the formation of the
porphyrin was checked using absorption spectroscopy. The
reaction was very slow and it took 10 h for completion.
DDQ (100 mg, 0.440 mmol) was then added and the
reaction mixture was stirred in air for 2 h. The solvent
was removed under vacuum and the crude compound was
dissolved in minimum amount of CH2Cl2 to prepare slurry
powder by adding silica gel. The slurry was loaded on a
silica gel column and eluted with CH2Cl2. The desired
compound eluted very slowly and was collected and
subjected to second silica gel column chromatography
using CH2Cl2 as solvent to afford 2 in 25% yield. Mp
Porphyrins 10 and 11 were synthesized similarly by
condensing 1 equiv. of diol 14 and 15, respectively, with
2 equiv. of benzaldehyde and 3 equiv. of pyrrole under
porphyrin forming conditions. The crude porphyrins were
subjected to silica gel column chromatography and pure
1
porphyrins 10 and 11 were obtained in ,6% yields. In H
NMR, the thiophene proton appeared as singlet in 10 and it
was absent in 11 due to substitution by phenyl groups. The
pyrrole protons appeared as three signals in both 10 and 11
indicating the low symmetric nature of porphyrins. The
absorption and emission peaks also experienced slight red
shifts with a reduction in intensity compared to STPPH
(Table 1).
1
.300 8C. H NMR (CDCl3, d in ppm) 6.90 (m, 8H, Ar),
3. Conclusions
7.06 (m, 4H, Ar), 7.21 (m, 8H, Ar), 7.52 (m, 8H, Ar), 7.71
(m, 8H, Ar), 7.80 (m, 4H, Ar), 9.23 (m, 4H, b-thiophene).
LD-MS C68H44N2S2 calcd mass, 953.2. Obsd m/z 953.9
(Mþ). Anal. calcd: C, 85.68; H, 4.65; N, 2.94. Found: C,
85.84; H, 4.56; N, 3.03. IR (KBr, n (cm21)) 3420, 3230,
2963, 741.
In conclusion, we have prepared a series of b-pyrrole and
b-thiophene substituted thiaporphyrins with N2S2 and
N3S porphyrin cores. The introduction of substituents at
b-pyrrole and b-thiophene carbons alters the electronic
properties of the porphyrins. The magnitude of the effect
depends on the number of substituents. The substituents at
b-positions of thiaporphyrins cause upfield shifts of
4.1.3. meso-5,10,15,20-Tetraphenyl-b-7,17-diphenyl-b-
8,18-dinitro-21,23-dithia porphyrin (3). In a 500 ml one-
necked round bottomed flask, 2,5-bis(hydroxyphenyl-
methyl) thiophene (500 mg, 1.687 mmol) and 2-nitro-3-
phenylpyrrole (400 mg, 2.123 mmol) were dissolved in
250 ml CHCl3 and argon was purged for 10 min. BF3·OEt2
(660 ml of 2.5 M stock solution) was added and the reaction
mixture was stirred for 1 h under argon at room temperature.
The formation of porphyrin was confirmed with absorption
spectroscopy by taking small amounts of reaction mixture
and oxidizing with DDQ in toluene. DDQ (425 mg,
1.872 mmol) was added and the reaction mixture was
stirred in air for 2 h. The solvent was removed on a rotary
evaporator and the crude compound was purified twice by
silica gel column chromatography using CH2Cl2 as solvent
to afford a dark purple solid (35 mg, 4.6%). Mp .300 8C 1H
NMR (CDCl3, d in ppm) 7.10–7.30 (m, 30H, Ar), 7.50–
7.70 (m, 4H, b-thiophene). LD-MS C56H34N4S2O4 calcd
mass 891.0, obsd m/z 892.7. Anal. calcd: C, 75.49; H, 3.85;
N, 6.29. Found: C, 75.86; H, 3.79; N, 6.58; IR (KBr, n
(cm21)) 3414, 2915, 1550, 741.
1
thiophene and pyrrole protons in H NMR, bathochromic
shifts in absorption bands, and large red shifts with
reduction in quantum yields of fluorescence bands com-
pared to unsubstituted thiaporphyrin counterparts. We are
presently investigating the metallation and electrochemical
properties of these porphyrins.
4. Experimental
4.1. Data for compounds
4.1.1. meso-5,10,15,20-Tetraphenyl-b-7,8,17,18-tetra-
bromo-21,23-dithiaporphyrin (1). 5,10,15,20-Tetraphenyl-
21,23-dithiaporphyrin (80 mg, 0.123 mmol) was dissolved
in 20 ml of CHCl3 in 100 ml one-necked round bottomed
flask and 4.2 equiv. of freshly recrystallized N-bromosuc-
cinimide (336 mg, 0.516 mmol) was added to it. The
reaction mixture was refluxed for 2 h. The progress of the
reaction was monitored with tlc and absorption spectro-
scopy. The solvent was removed on a rotary evaporator and
the crude compound was purified by silica gel column
chromatography using CH2Cl2 as eluent (74 mg, 70%). Mp
4.1.4. 2,5-Bis(hydroxymethylphenyl)-3-methylthiophene
(12). In a 100 ml three-necked round bottomed flask fitted
with a gas inlet tube, a reflux condenser and a rubber
sept0um, d0r00ied and distilled n-hexane (10 ml) was placed.
(TMEDA)
1
.300 8C H NMR (CDCl3, d in ppm) 7.80 (m, 12H, Ar),
8.06 (m, 8H, Ar), 9.39 (s, 4H, b-thiophene). 13C NMR
(CDCl3, d in ppm) 14.21, 29.45, 32.01, 113.03, 127.92,
133.62, 140.09, 149.30. LD-MS C44H24N2S2Br4 calcd
mass, 964.4. Obsd m/z 964.7 (Mþ), 885.7 (M21Br), 805.9
(M22Br), 725.2 (M23Br), 645 (M24Br). Anal. calcd: C,
54.80; H, 2.51; N, 2.90. Found: C, 54.93; H, 2.42; N, 2.78.
IR (neat, n (cm21)) 3276, 2934, 2861, 741.
N,N ,N00,N -Tetramethylethylene
diamine
(0.42 ml, 0.32 g, 2.76 mmol) and n-butyl lithium (4 ml of
a 1.6 M solution in hexane) were injected into the stirred
solution. 2-Methylthiophene (0.200 g, 2.04 mmol) was
injected and the solution was refluxed gently for 1 h. In
another three-necked 100 ml round bottomed flask fitted
with gas inlet and outlet tube and septum, benzaldehyde
(0.53 ml, 0.550 g, 5.20 mmol) was dissolved in 10 ml dry
THF. The solution was cooled in an ice bath and nitrogen
was bubbled for 15 min. The 2,5-dilithio-3-methyl-
thiophene suspension from the first flask was added to
4.1.2. meso-5,10,15,20-Tetraphenyl-b-7,8,17,18-tetra-
phenyl-21,23-dithia-porphyrin (2). 2,5-Bis(a-hydroxy-
phenylmethyl)thiophene (100 mg, 0.337 mmol) and 3,4-di-
phenylpyrrole (80 mg, 0.365 mmol) were dissolved in 25 ml

N. Agarwal, M. Ravikanth / Tetrahedron 60 (2004) 4739–4747
4745
benzaldehyde solution in THF through siphon apparatus
over a period of 10 min. After the addition was complete,
the mixture was allowed to attain room temperature. An ice
cold saturated NH4Cl solution was added and the mixture
was then extracted with ether (3£50 ml). The organic
layers were combined, washed with brine and dried
over anhydrous Na2SO4. The crude product obtained on
evaporation of the solvent was subjected to silica gel
column chromatography using petroleum ether/ethyl acetate
mixture (4:1), which afforded the pure diol 12 as a semi-
white solid (140 mg, 22%). Mp 125–127 8C. 1H NMR
(CDCl3, d in ppm) 2.10 (s, 3H, CH3), 2.42 (s, 2H, OH), 5.51
(s, 2H, CH), 7.18 (1H, thiophene) 7.32–7.51 (m, 10H,
phenyl). 13C NMR (CDCl3, d in ppm) 65.15, 70.70, 79.73,
126.81, 128.95, 139.59. ES-MS C19H18O2S calcd av. mass,
310.4. Obsd m/z 293.0 (M2OH). Anal calcd: C, 73.52; H,
5.84. Found:C, 73.97;H, 6.03. IR(KBr, n (cm21))3395(OH),
2925, 1715, 1649, 1458, 1268, 1185, 1008, 750, 696, 530.
phene (15). 3,4-Diphenyl thiophene (0.236 g, 1.00 mmol)
and n-butyl lithium (2 ml of a 1.6 M solution in hexane)
were stirred in dry diethylether (10 ml) for 1 h at room
temperature to get the dilithio salt of 3,4-diphenyl
thiophene. The dilithiated salt of 3,4-diphenyl thiophene
was added to the solution of benzaldehyde (0.230 ml,
0.243 g, 2.30 mmol) in 10 ml THF solution followed by
similar work as mentioned for compound 12. Column
chromatography on silica gel using petroleum ether/ethyl
acetate mixture (3:1) afforded pure 15 as a white solid
1
(0.130 g, 29%). Mp 130–131 8C. H NMR (CDCl3, d in
ppm) 2.32 (s, 2H, OH), 5.95 (s, 2H, CH), 7.04 (t, J¼2.2 Hz,
4H, phenyl), 7.25–7.35 (m, 16H, phenyl). 13C NMR
(CDCl3, d in ppm) 70.80, 126.28, 127.04, 127.23, 127.73,
127.92, 128.38, 130.20, 135.48, 143.10. ES-MS C30H24O2S
calcd av. mass, 448.5. Obsd m/z 449.0. Anal calcd: C, 80.33;
H, 5.39. Found: C, 80.56; H, 5.44. IR (KBr, n (cm21)) 3348
(OH), 3060, 3028, 2920, 1602, 1492, 1449, 1274, 1133,
1010, 912, 768, 731, 700, 640.
4.1.5. 2,5-Bis(hydroxymethylphenyl)-3,4-dimethylthio-
phene (13). 2,5-Dilithio-3,4-dimethyl thiophene was
synthesized by lithiating 3,4-dimethyl thiophene (500 mg,
4.46 mmol) with n-butyl lithium (8.0 ml of 1.6 M solution
in hexane) in dry hexane (25 ml) in the presence of TMEDA
(1.6 ml, 1.24 g, 10.7 mmol) under similar reaction con-
ditions as mentioned for compound 12. The dilithiated salt
of 3,4-dimethyl thiophene was then added to the solution
of benzaldehyde (1.20 ml, 1.24 g, 11.6 mmol) in dry THF
(25 ml) followed by similar work-up as mentioned for
compound 12 gave crude diol 13. Column chromatography
on silica gel using petroleum ether/ethyl acetate mixture
(4:1) and afforded pure diol 13 as a white solid (248 mg,
4.1.8. meso-5,10,15,20-Tetraphenyl-b-2,12-dimethyl-
21,23-dithiaporphyrin (4). A stream of argon was passed
through dichloromethane (30 ml) in a 100 ml round-
bottomed flask for 10 min. The diol 12 (0.100 g,
0.320 mmol) and pyrrole (25 ml, 0.360 mmol) were added
and argon purging was continued for an additional 10 min.
BF3·OEt2 (20 ml of 2.5 M stock solution in CH2Cl2) was
added and the reaction mixture was stirred for 1 h. The
progress of the reaction was monitored by TLC and
absorption spectroscopy. After 2 h stirring, DDQ (50 mg,
0.220 mmol) was added and the reaction was stirred in air
for additional 1 h. The solvent was removed in vacuo and
the crude compound was purified by silica column using
petroleum ether/CH2Cl2 (3:7) mixture as eluent. The desired
compound 4 was obtained as a purple solid (18 mg, 8.6%).
1
17%). Mp 141–1438C. H NMR (CDCl3, d in ppm) 2.05
(s, 6H, –CH3), 2.32 (s, 2H, –OH), 6.01 (s, 2H, –CH), 7.24–
7.41 (m, 10H, phenyl). 13C NMR (CDCl3, d in ppm) 13.11,
71.03, 126.35 127.71, 128.38, 134.32, 139.63, 142.68. FAB-
MS C20H20O4S calcd av. mass, 324.4. Obsd m/z 324.0. Anal
calcd: C, 74.04; H, 6.21. Found: C, 74.36; H, 6.53. IR (KBr,
n (cm21)) 3293 (OH), 3062, 3027, 2915, 2860, 1493, 1452,
1198, 1080, 1007, 914, 852, 697, 582.
1
Mp .300 8C. H NMR (CDCl3, d in ppm) 2.87 (s, 6H,
CH3), 7.72–7.80 (m, 12H, m,p-phenyl), 8.03–8.06 (m, 4H,
o-phenyl), 8.20–8.22 (m, 4H, o-phenyl), 8.37 (s, 1H,
b-pyrrole.), 8.44 (d, J¼4.57 Hz, 1H, b-pyrrole), 8.56 (d,
J¼4.39 Hz, 1H, b-pyrrole), 8.63 (s, 1H, b-pyrrole), 9.40
(s, 2H, b-thiophene). 13C NMR (CDCl3, d in ppm) 20.29,
29.78, 42.90, 127.71, 128.69, 133.42, 134.42, 134.38,
139.54. FAB-MS C46H32N2S2 calcd av. mass, 678.8. Obsd
m/z 677.0. Anal. calcd: C, 81.62; H, 4.77; N, 4.14. Found: C,
81.91; H, 4.53; N, 3.89. IR (KBr, n (cm21)) 3396, 2922,
2857, 703.
4.1.6. 2,5-Bis(hydroxymethylphenyl)-3-phenylthiophene
(14). 2,5-Dilithio-3-phenyl thiophene was synthesized by
stirring 3-phenyl thiophene (0.320 g, 2.00 mmol) with
n-butyl lithium (4.0 ml of 1.6 M solution in hexane) in dry
diethylether (15 ml) at room temperature. The dilithiated
salt of 3-phenyl thiophene was added to the solution of
benzaldehyde (0.460 ml, 0.439 g, 4.14 mmol) in dry THF
(15 ml) followed by similar work-up as mentioned for
compound 12 gave crude diol 14. Column chromatography
on silica gel using petroleum ether/ethyl acetate mixture
(3:1) as eluent afforded pure 14 as a white solid (210 mg,
28%). Mp 128–130 8C 1H NMR (CDCl3, d in ppm) 2.40 (s,
2H, –OH), 5.93 (d, J¼7.2 Hz, 1H –CH), 6.04 (s, 1H, –CH),
6.75 (s, 1H, b-thiophene), 7.30–7.61 (m, 15H, phenyl). 13C
NMR (CDCl3, d in ppm) 19.60, 49.30, 59.52, 97.06, 128.05,
129.71, 129.97, 130.79, 131.53. ES-MS C24H20O2S calcd
av. mass, 372.4. Obsd m/z 355.1 (M2OH). Anal calcd: C,
77.39; H, 5.41. Found: C, 77.52; H, 5.76. IR (KBr, n
(cm21)) 3314 (OH), 3057, 3028, 2876, 1600, 1495, 1447,
1285, 1194, 1155, 1008, 847, 700, 533.
4.1.9. meso-5,10,15,20-Tetraphenyl-b-2,3,12,13-tetra-
methyl-21,23-dithiaporphyrin (5). A solution of diol 13
(0.100 g, 0.306 mmol) and pyrrole (25 ml, 0.360 mmol) in
30 ml CH2Cl2 was treated with BF3·OEt2 (10 ml of 2.5 M
stock solution) under an argon atmosphere to initiate the
condensation. After 1 h, DDQ (0.040 g, 0.176 mmol) was
added and stirring was continued for an additional 1 h.
Column chromatography on silica with petroleum ether/
CH2Cl2 (3:7) gave solid purple colored porphyrin 5 (20 mg,
9%). Mp .300 8C 1H NMR (CDCl3, d in ppm) 2.61 (s, 12H,
CH3), 7.74 (m, 12H, phenyl), 8.12 (m, 8H, phenyl), 8.26 (s,
4H, b-pyrrole). 13C NMR (CDCl3, d in ppm) 18.44, 29.87,
32.10, 127.23, 127.35, 132.19, 133.75, 143.07, 144.67.
ES-MS C48H36N2S2 calcd av. mass: 704.9. Obsd m/z 704.8.
Anal. calcd: C, 81.78; H, 5.15; N, 3.97. Found: C, 81.42, H,
5.27, N, 3.95. IR (KBr, n (cm21)) 3435, 3059, 2929, 703.
4.1.7. 2,5-Bis(hydroxymethylphenyl)-3,4-diphenylthio-

4746
N. Agarwal, M. Ravikanth / Tetrahedron 60 (2004) 4739–4747
4.1.10. meso-5,10,15,20-Tetraphenyl-b-2,12-diphenyl-
21,23-dithiaporphyrin (6). In a 100 ml round bottomed
flask, thiophene diol 14 (0.200 g, 0.534 mmol) and pyrrole
(40 ml, 0.038 g, 0.56 mmol) were mixed in 50 ml CH2Cl2
under an argon atmosphere. BF3·OEt2 (40 ml of 2.5 M stock
solution) was added and the reaction was stirred for 1 h at
room temperature. DDQ (90 mg, 0.396 mmol) was added
and the reaction mixture was stirred in air for an additional
1 h. The solvent was removed on a rotary evaporator and the
crude compound was purified twice using silica gel column
chromatography with CH2Cl2 as solvent to afford 6 as a
purple solid (21 mg, 4.8%). Mp .300 8C. 1H NMR (CDCl3,
d in ppm) 7.28–7.34 (m, 4H, Ar), 7.42–7.58 (m, 6H, Ar),
7.72–7.84 (m, 12H, Ar), 8.21–8.38 (m, 8H, Ar), 8.48 (d,
J¼5.20 Hz, 2H, b-pyrrole), 8.53 (d, J¼4.80 Hz, b-pyrrole),
8.66 (s, 1H, b-pyrrole), 9.56 (s, 2H, b-thio-phene). 13C
NMR (CDCl3, d in ppm) 29.89, 127.98, 128.33, 129.14,
129.51, 130.06, 131.18, 133.37, 134.69, 135.60, 136.44,
140.41. ES-MS C56H36N2S2 calcd av. mass, 801.0. Obsd
m/z 801.3. Anal. calcd: C, 83.97; H, 4.53; N, 3.50: Found: C,
83.65; H, 4.67; N, 3.77. IR (KBr, n (cm21)) 3414, 3059,
2929, 697.
in ppm) 14.33, 20.47, 29.90, 126.77, 127.18, 127.63,
128.01, 128.69, 132.87, 133.47, 134.33, 134.54, 134.91,
135.71, 137.87, 139.11, 141.39, 142.60, 143.79, 145.98,
154.99. FAB-MS C45H31N3S calc av. mass, 645.8. Obsd
m/z: 646. Anal. calcd: C, 83.69; H, 4.84; N, 6.51. Found: C,
83.93; H, 5.05; N, 6.30. IR (KBr, n (cm21)) 3325, 3039,
2923, 707.
4.1.13. meso-5,10,15,20-Tetraphenyl-b-2,3-dimethyl-21-
monothiaporphyrin (9). Diol 13 (200 mg, 0.617 mmol),
benzaldehyde (140 ml, 148 mg, 1.40 mmol) and pyrrole
(140 ml, 135 mg, 2.02 mmol) in CH2Cl2 (70 ml) were
treated with BF3·OEt2 (30 ml of 2.5 M stock solution)
under an argon atmosphere. After 1 h, DDQ (110 mg,
0.484 mmol) was added and the reaction mixture was stirred
for 1 h in air. Chromatography on silica gel with petroleum
ether/CH2Cl2 (6:4) gave the desired compound 9 as a purple
solid which moved as the second band (50 mg, 12%). Mp
.300 8C. 1H NMR (CDCl3, d in ppm) 22.37 (s, 1H, –NH),
2.80 (s, 6H, –CH3), 7.72–7.77 (m, 12H, m,p-phenyl), 8.08–
8.21 (m, 8H, o-phenyl), 8.45 (d, J¼4.39 Hz, 2H, b-pyrrole),
8.52 (d, J¼4.39 Hz, 2H, b-pyrrole), 8.87 (m, 2H, b-pyr-
role), 13C NMR (CDCl3, d in ppm) 18.36, 29.79, 32.02,
53.49, 123.72, 126.66, 127.16, 128.38, 129.99, 133.17,
133.87, 134.46, 138.78, 142.51, 144.94, 154.48, 158.80.
ES-MS C46H33N3S calc av. mass, 659.8, obsd m/z 660.
Anal. calcd: C, 83.73; H, 5.04; N, 6.37. Found: C, 84.11; H,
5.32; N, 6.16. IR (KBr, n (cm21)) 3322, 3059, 2929, 710.
4.1.11. meso-5,10,15,20-Tetraphenyl-b-2,3,12,13-tetra-
phenyl-21,23-dithiaporphyrin (7). In a 100 ml round
bottomed flask, diol 15 (0.200 g, 0.446 mmol) and pyrrole
(40 ml, 0.038 g, 0.5 mmol) were dissolved in 45 ml CH2Cl2
and argon was purged for 10 min. BF3·OEt2 (40 ml of 2.5 M
stock solution) was added and the reaction was stirred for
1 h under argon at room temperature. DDQ (80 mg,
0.352 mmol) was added and the reaction mixture was
stirred for 1.5 h in air. The solvent was removed on a rotary
evaporator and the crude compound was purified twice by
silica gel column chromatography using CH2Cl2 as solvent
to give 7 as a purple solid (10 mg, 2.3%). Mp .300 8C. 1H
NMR (CDCl3, d in ppm) 7.04–7.91 (m, 40H, phenyl), 8.10
(s, 4H, b-pyrrole). 13C NMR (CDCl3, d in ppm) 14.31,
29.88, 128.66, 130.41, 132.06, 138.55. ES-MS C68H44N2S2
calcd av. mass: 953.2. Obsd m/z. 953.33. Anal. calcd: C,
85.68; H, 4.65; N, 2.94. Found: C, 85.37; H, 4.93; N, 3.13.
IR (KBr, n (cm21)) 3321, 3063, 2931, 703.
4.1.14. meso-5,10,15,20-Tetraphenyl-b-2-phenyl-21-
monothiaporphyrin (10). 2,5-Bis(hydroxymethylphenyl)-
3-phenylthiophene 14 (250 mg, 0.679 mmol), benzaldehyde
(150 ml, 1.42 mmol) and pyrrole (150 ml, 2.17 mmol) were
dissolved in 60 ml CH2Cl2. BF3·OEt2 (40 ml of 2.5 M stock
solution) was added to initiate the condensation and the
reaction mixture was stirred for 1 h. DDQ (0.115 g,
0.509 mmol) was added and the reaction left stirring for
1 h in air. The solvent was removed on a rotary evaporator
and the crude porphyrin was purified by silica gel column
chromatography with petroleum ether/CH2Cl2 (1:1) to give
the desired porphyrin 10 as a purple solid (30 mg, 6.3%).
1
Mp .300 8C. H NMR (CDCl3, d in ppm) 22.51 (s, 1H,
4.1.12. meso-5,10,15,20-Tetraphenyl-b-2-methyl-21-
monothiaporphyrin (8). A solution of diol 12 (312 mg,
1 mmol), benzaldehyde (0.220 ml, 2.05 mmol) and pyrrole
(212 mg, 3.17 mmol) in 100 ml of CH2Cl2 were treated with
BF3·OEt2 (30 ml of 2.5 M stock solution) and stirred for 1 h
under an argon atmosphere. DDQ (180 mg, 0.792 mmol)
was added and reaction mixture was stirred for 1 h in air.
The solvent was removed under reduced pressure. The TLC
analysis of crude product showed the formation of three
porphyrins as expected. The crude compound was loaded
on silica and eluted with a mixture of petroleum ether/
dichloromethane. The desired compound was collected as
the second band using petroleum ether/CH2Cl2 (1:1). The
solvent was removed on a rotary evaporator to afford 8 as a
dark purple crystalline solid (78 mg, 12%). Mp .300 8C. 1H
NMR (CDCl3, d in ppm) 22.56 (s, 1H, NH), 2.93 (s, 3H,
CH3), 7.77–7.80 (m, 12H, m,p-phenyl), 8.03–8.20 (m, 8H,
o-phenyl), 8.43 (d, J¼4.57 Hz, 1H, b-pyrrole), 8.52
(d, J¼4.57 Hz, 1H, b-pyrrole.), 8.58 (d, J¼4.57 Hz, 1H,
b-pyrrole), 8.65 (d, J¼4.57 Hz, 1H, b-pyrrole), 8.88 (s, 2H,
b-pyrrole), 9.46 (s, 1H, b-thiophene). 13C NMR (CDCl3, d
NH), 7.10–7.30 (m, 5H, aryl), 7.44 (m, 2H, o-phenyl),
7.75–7.83 (m, 12H, m,p-phenyl), 8.21–8.26 (m, 6H,
o-phenyl), 8.49 (s, 2H, b-pyrrole), 8.62 (d, J¼4.80 Hz, 2H,
b-pyrrole), 8.70 (d, J¼3.60 Hz, 1H, b-pyrrole), 8.92 (s, 1H,
b-pyrrole), 9.65 (s, 1H, b-thiophene). 13C NMR (CDCl3, d in
ppm) 29.88, 123.72, 124.29, 126.82, 127.61, 128.05, 130.89,
132.54, 133.56, 134.37, 134.71, 135.13, 138.68, 139.65,
140.44, 141.21, 142.46, 144.47, 149.54, 155.09, 157.80.
ES-MS C50H33N3S calcd av. mass, 707.8, obsd m/z 708.3.
Anal. calcd: C, 84.84; H, 4.70; N, 5.94. Found: C, 84.98; H,
4.92; N, 6.12. IR (KBr, n (cm21)) 3332, 3059, 3923, 703.
4.1.15. meso-5,10,15,20-Tetraphenyl-b-2,3-diphenyl-21-
monothiaporphyrin (11). 2,5-Bis(hydroxymethyl)-3,4-
diphenylthiophene 15 (0.080 g, 0.178 mmol), benzaldehyde
(40 ml, 0.398 mmol) and pyrrole (40 ml, 0.579 mmol) were
dissolved in 30 ml CH2Cl2. BF3·OEt2 (40 ml of 2.5 M stock
solution) was added to initiate the cyclization and reaction
mixture was stirred for 1 h. DDQ (0.115 g, 0.506 mmol)
was added and stirred the reaction mixture in air for an
additional 1 h. The solvent was removed on a rotary

N. Agarwal, M. Ravikanth / Tetrahedron 60 (2004) 4739–4747
4747
(e) D’Souza, F.; Villard, A.; Camelbecke, E. V.; Franzen,
M.; Boschi, T.; Tagliatesta, P.; Kadish, K. M. Inorg. Chem.
1993, 32, 4042–4048. (f) Ochsenbein, P.; Mandon, D.;
Fischer, J.; Weiss, R.; Austin, R. N.; Jayaraj, K.; Gold, A.;
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evaporator and the crude porphyrin mixture was purified by
column chromatography with petroleum ether/CH2Cl2 (1:4)
to afford the desired porphyrin 11 as a purple solid (9 mg,
6.4%). Mp .300 8C. 1H NMR (CDCl3, d in ppm) 22.29 (s,
1H, NH), 6.80–7.40 (m, 22H, aryl), 7.66–7.80 (m, 8H,
aryl), 8.20 (m, 3H, b-pyrrole) 8.32 (m, 1H, b-pyrrole), 8.46
(m, 1H, b-pyrrole), 8.88 (s, 1H, b-pyrrole). 13C NMR
(CDCl3, d in ppm) 14.44, 22.70, 29.37, 29.70, 31.93,
123.54, 125.78, 125.94, 126.46, 126.64, 126.81, 127.83,
128.69, 132.03, 134.08, 134.43, 138.56, 139.11, 141.17,
141.73, 142.31, 150.01, 155.09, 159.18. ES-MS C56H37N3S
calcd av. mass, 783.9. Obsd m/z 784.3. Anal. calcd: C,
85.79; H, 4.76; N, 5.36. Found: C, 85.96; H, 4.89; N, 5.54.
(KBr, n (cm21)) 3319, 3053, 2858, 702.
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Acknowledgements
This research was supported by Department of Atomic
Energy (No. 2001/37/21/BRNS/797) and Department of
Science and Technology, Government of India, New Delhi.
Mass spectra were obtained at CDRI, Lucknow and IIT—
Bombay and NMR spectra were obtained in IIT—Bombay.
6. Latos-Grazynski, L. The porphyrin handbook; Kadish, K. M.,
Smith, K. M., Guilard, R., Eds.; Academic: New York, 2000;
Vol. 2, pp 361–416 and references cited therein.
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Perkin Trans. 1 2001, 1644–1648. (c) Ravikanth, M.;
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