Highly efficient synthesis of 21-thia-5,10,15,20-tetraarylporphyrins and 21,23-dithia-5,10,15,20-tetraarylporphyrins in presence of acidic ionic liquid catalyst

Article abstract of DOI:10.1016/j.tetlet.2014.05.005

The reaction of 2,5-bis-(α-arylhydroxymethyl)thiophenes with 5-aryldipyrromethanes in the presence of acidic ionic liquid gives 21-thia-5,10,15,20-tetraarylporphyrins in 30% yield whereas the reaction of 2,5-bis-(α-arylhydroxymethyl)thiophenes with 5,10-d

Full text of DOI:10.1016/j.tetlet.2014.05.005

Accepted Manuscript
Highly efficient synthesis of 21-thia-5,10,15,20-tetraarylporphyrins and 21,23-
dithia-5,10,15,20-tetraarylporphyrins in presence of acidic ionic liquids catalyst
Amit Kumar Rawat, Soumee Bhattacharya, S.M.S. Chauhan
PII:
S0040-4039(14)00781-3
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.05.005
TETL 44595
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
6 March 2014
2 May 2014
3 May 2014
Please cite this article as: Rawat, A.K., Bhattacharya, S., Chauhan, S.M.S., Highly efficient synthesis of 21-
thia-5,10,15,20-tetraarylporphyrins and 21,23-dithia-5,10,15,20-tetraarylporphyrins in presence of acidic ionic
liquids catalyst, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.2014.05.005
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Graphical Abstract
Highly efficient synthesis of 21-thia-porphyrins
Leave this area blank for abstract info.
and 21,23-dithia-5,10,15,20-tetraarylporphyrins in presence of acidic ionic liquids catalyst
Amit Kumar Rawat, Soumee Bhattacharya and S.M.S. Chauhan*
N
H
S
S
AILs/
DCM, DDQ
AILs/
DCM, DDQ
N
N
N
N
+
+
S
S
OH
OH
N
NHHN
S
OH
OH
H
Tetrahedron Letters
journal homepage: www.elsevier.com
Highly efficient synthesis of 21-thia-5,10,15,20-tetraarylporphyrins and 21,23-dithia-5,10,15,20-
tetraarylporphyrins in presence of acidic ionic liquids catalyst
*
Amit Kumar Rawat, Soumee Bhattacharya and S.M.S. Chauhan
Bioorganic Research Laboratory, Department of Chemistry, University of Delhi, Delhi-110007, India;
—
——
*
correspondence Author Tel.: +; Fax : +91-11-27666845
E-Mail: smschauhan@chemistry.du.ac.in;

2
ARTICLE INFO
ABSTRACT
Article history:
Received
The reaction of 2,5-bis-(α-arylhydroxymethyl)thiophenes with 5-
aryldipyrromethanes in the presence of acidic ionic liquid gives 21-
thia-5,10,15,20-tetraarylporphyrins in 30 % yield whereas the
reaction of 2,5-bis-(α-arylhydroxymethyl)thiophenes with 5,10-
diaryltripyrromethane or pyrrole gives 21,23-dithia-5,10,15,20-
tetraarylporphyrins in 35 % yield. Acidic ionic liquids are better
catalyst and reaction media than acid catalyzed reaction in organic
solvents for the synthesis of core modified porphyrins.
Received in revised form
Accepted
Available online
Keywords:
Acidic
ionic
liquids,
dipyrromethane,
2,5-Bis-(α-
2
009 Elsevier Ltd. All rights reserved.
arylhydroxymethyl)thiophene, 21-
thiaporphyrins,
dithiaporphyrins
21,23-
1
0
The replacement of one or two pyrrole NH group observed for monoheteroatom
substituted
with O, S, Se and Te atoms in porphyrins forms 21- porphyrins. The heteroatom porphyrins are easy to
1,2
heteroatom and 21,23-heteroatom core modified reduce and difficult to oxidize compared to regular
3
-5
11
porphyrins,
respectively. The core modified
porphyrins.
bifunctionalized (2 or 5 position) five membered
heterocycles with aromatic aldehydes,
The reaction of mono or
porphyrins result in an altered electronic structure
6
7
with interesting optical , chemical, photochemical
8
and electrochemical properties. The introduction
of a heteroatom in place of “N” results in large red
shift in both Soret and Q-bands. The maximum red
shift was observed with “S”, “Se” and “Te”
dipyrromethanes and tripyrromethane in presence of
protic or Lewis acid in organic solvents gives core
modified porphyrins in moderate yields. The
synthesis of core modified porphyrins have been
containing heteroporphyrins and minimum for “O” examined in the presence of strong acids such as
9
.
containing heteroporphyrins. Furthermore, the red
BF O(Et) , TFA, methylsulfuric acid and propionic
3
2
1
2-14
shift of absorption bands of diheteroatom acid.
In order to avoid the use of corrosive acid
substituted porphyrins were greater than those and to minimize the amount of harmful organic

3
solvents, the development of a new method for the
synthesis of core modified porphyrins catalyzed by
acidic ionic liquids would be highly desirable.
imidazolium trifluoromethylacetate acidic ionic
liquid as compared to that with longer alkyl chains in
dichloromethane (Table 1). This is adroit to the short
chain length of methylene groups, hence, drop off in
hydrophobicity and +I effect of ionic liquid leading
to an increase in acidic nature. Primarily 1a was
screened under a variety of experimental conditions
to optimize the product distribution at room
temperature. The equivalent amount of 5-
The acidic ionic liquids have gained special
attention as a catalyst in organic synthesis because
of many advantages such as their outstanding
flexibility,
heat
resistance,
non-volatility,
noncorrosiveness, negligible vapour pressure,
tunable polarity, operationally simplicity and high
1
5,16
reactivity with common organic solvents.
arydipyrromethanes
and
2,5-bis-(
α-
Acidic ionic liquids have been used in the synthesis
arylhydroxymethyl)thiophenes were taken up in
dichloromethane. Acidic ionic liquid 1a (0.1 mol
equiv.) was added into the reaction mixture. The
progress of the reaction was monitored by TLC
17,18
of porphyrins in moderate yield
whereas, they
are not been used as catalyst and solvents for the
synthesis of core modified porphyrins. Herein, we
report the high yield synthesis of core modified
porphyrins in the condensation of 2,5-bis-(α-
(
complete consumption of dipyrromethane). The
core modified porphyrin was isolated in 21% yield.
The formation of 21-heteroporphyrins was possible
arylhydroxymethyl)thiophenes
with
5-
19,20
aryldipyrromethanes, tripyrromethanes
or pyrrole
when the scrambling occurred in dipyrromethanes.
in different reaction conditions (Scheme 1, Figure
).
The 21-heteroporphyrins (4) were formed in 28-30%
1
yields, using 0.3-0.5 equivalents of acid catalyst.
The starting materials 5-arydipyrromethanes However, the core modified porphyrins (4) were
(
2a-2h)
arylhydroxymethyl)thiophenes
prepared by minor modification of known literature
and
2,5-bis-(α- formed in 20 % yields, using 1 equivalent of acid
(3a-3d)
were
catalyst, the time required for the completion of
reaction was comparatively more, which is attributed
2
1-23
procedure.
The different acidic ionic liquids to different extent of acidolysis under different
were used for the synthesis of core modified
porphyrins and the better yields were obtained in the thiaporphyrins under reaction conditions suggested
presence of 1-methyl-3-(4-sulfopropyl)-
that the acidolysis of 5-aryldipyrromethanes
reaction conditions. The exclusive formation of 21-

Tetrahedron Letters
4
24,25
occurred in the presence of acidic ionic liquids.
dependent upon the steric bulk of 5-substituent in
This type of acidolysis of 5-aryldipyrromethane is dipyrromethane. Moreover, the yields of core
2
6
also reported in literature. Results obtained by the
modified porphyrins (4) were also dependent on the
nature of dipyrromethane; dipyrromethane with
electron donating groups at para position gave better
yield as compared to electron withdrawing groups.
variation of catalyst concentration suggested that
0
.5 mol equivalent concentration found to be
rational concentration for the acidolysis of
dipyrromethane and its conversion into 21- The reactions of 5-(mesityl)dipyrromethane (2e)
thiaporphyrins.
with 2,5-bis-( α-arylhydroxymethyl)thiophenes (3d)
gave corresponding core modified 21-thiaporphyrin
(12 % yield) and porphyrin at ambient temperature.
With respect to the appealing results obtained from
the catalyst concentrations screening, we framed
the general protocol for the synthesis of 21- The observed time required for the conversions was
thiaporphyrins
by
treating
and
several
5- too long (Table 2, Entry 5). This could be ascribed
aryldipyrromethanes
2,5-bis-(α- to steric hindrance of bulky methyl substituents.
arylhydroxymethyl)thiophene using acidic ionic The reaction of 5-aryldipyrromethane with 2,5-bis-
liquid 1a (0.5 mol equiv.) followed by DDQ (α-arylhydroxymethyl)thiophenes, in the presence
oxidation in dichloromethane (Table 2). The of
1-methyl-3-(4-sulfopropyl)-imidazolium
structure of 21-thia-5,10,15,20-tetraarylporphyrins hydrogen sulphate, afforded core modified
was characterized by UV-Visible spectroscopy and porphyrins and porphyrin in poorer yields. Apart
1
confirmed by H NMR spectroscopic and mass from this, a black tarry third isomer was also
spectrometric techniques (data in the supplementary observed; but due to less availability of sample and
information). Nevertheless, the reaction of 5- poor solubility in organic solvents a detailed
substituted dipyrromethanes (2) also showed similar structural characterization was not possible.
behaviour in ionic liquids and the yields were

5
R4
R4
S
OH
OH
3
3
3
3
a. R = H
4
b. R = CH
4
3
c. R = OCH
4
3
d. R = C(CH )
4
3 3
R
R1
2 (c)
(b
(a)
)
R3
2a. R1 = R2 = R3 = H
R2
R2 2b. R1 = R2 = H, R =CH3
R1 R2
3
AILs/
DCM, DDQ
AILs/
2c. R1 = R2 = H, R3 = (C(CH3)3
R1 2d. R1 = R2 = H, R3 = OCH3
AILs/
DCM, DDQ
S
DCM, DDQ R1
N
H
NH HN
6
2e. R1 = R3 = CH3, R2 = H
NHHN
2
2f. R1 = H, R2 = OCH3, R3 = OH
g. R1 = R2 = H, R = Br
2
3
R2
2h. R1 = R2 = R3 = F
R4
R4
R4
R1
R2
R3
R2
R1
S
S
R2
R1
N
N
S
R1
N
N
HN
N
N
R2
R1
S
R1
S
R2
R1
R4
R4
R4
R4
R4
b.R = R = R = C(CH3)3
R3
R2
1
2
5
5
5
5a. R = R = R = H
4a. R1 = R2 = R3 = R4 = H
4b. R1 = R = R = H, R3 = C(CH3)3
2 4
1
2
4
4
1
2
e.R = R = C(CH ) , R = OCH
5b. R = C(CH ) , R = R = H
1
2
3 3
4
3
4
3 3
1
2
4c. R1 = R2 = H, R3 = OCH3, R4 = C(CH3)3
d. R1 = R = H, R = CH , R = C(CH3)3
f. R = R = C(CH ) , R = CH3
5c. R4 = CH , R = R = H
1
2
3 3
4
3
4
1
2
3
3
4
5
d. R = C(CH ) , R = C H ,
4
2
3 3
6
5
4e. R1 = H, R2 = OCH , R = OH, R4 = C(CH3)3
3 3
R = COOC H
4f. R1 = R2 = H, R = R = C(CH3)3
3 4
2
5
4
4
g. R1 = R = R = F, R = H
2 3 4
X
h. R1 = R = H, R = OCH , R = CH3
4i. R1 = R = R = H, R4 = Br
2
3
3
4
R
N
N
2 3
AILs =
1
a. R = -(CH ) SO H, X = CF COO
e. R = -CH COOH, X = CF COO
2 3
2
3
3
3
i. R = -(CH ) SO H, X = CF COO
2 4 3 3
b. R = -(CH ) SO H, X = CF SO
f. R = -CH COOH, X = CF SO
2 3 3
2
3
3
3
3
j. R = -(CH ) SO H, X = CF SO
2 4 3 3 3
c. R = -(CH ) SO H, X = CH SO
g. R = -CH COOH, X = CH SO
2 3 3
2
3
3
3
3
k.R = -(CH ) SO H, X = CH SO
2 4 3 3 3
d. R = -(CH ) SO H, X = HSO
h. R = -CH COOH, X = HSO
2
3
3
4
2
4
l. R = -(CH ) SO H, X = HSO
2 4 3 4
Scheme 1

Tetrahedron
Synthesis of 21-thiaporphyrins in
6
Table 1:
Entry 1a (Mol
equiv.)/Tim
e (min)
DPMs 2,5-Bis-(α- Yield
c
a
arylhydrox (%)
presence of different acidic ionic liquids
ymethyl)th
iophenes
4
/lit[1]
Entry AILs DPMs 2,5-Bis-(α- Time Yield
b
arylhydrox (min) (%) 4
1
2
3
4
5
0.1/70
0.2/70
0.3/60
0.5/40
1.0/90
2a
2a
2a
2a
2a
3a
3a
3a
3a
3a
19/17
21/17
28/17
30/17
20/17
ymethyl)thi
ophenes
1
1a
2a
3a
40
30
2
3
4
5
6
7
8
9
1b
1c
1d
1e
1f
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
45
40
45
40
40
40
40
40
40
40
27
22
26
25
23
24
22
25
25
25
6
7
8
9
0.5/40
0.5/40
0.5/40
0.5/40
0.5/40
2b
2c
2d
2e
2f
3d
3d
3d
3d
3d
3d
3b
25/15
27
20/14
12/8
16
1g
1h
1i
1
0
1
2
0
.5/40
.5/40
1
1
2h
2d
18
10
1j
0
20
1
1
1
1k
ab
Reaction conditions: reaction temperature 25 °C,
2
1l
2a
3a
40
25
dipyrromethanes (0.45 mmol), Diols (0.45 mmol);
a
Reaction conditions: reaction temperature 25 °C,
AILs (1a) (0.22 mmol); reaction time: 40 min.
dipyrromethanes (0.45 mmol), Diols (0.45 mmol);
acidic ILs (0.22 mmol); solvent (10 mL)
c
dichloromethane (10 mL); Isolated yields
The
were prepared and characterized as above. The
1,23-diheteroporphyrins (5) were isolated in 35%
21,23-dithia-5,10,15,20-tetraarylporphyrins
b
dichloromethane; Isolated yields
Table 2: Condensation of dipyrromethane and 2,5-
2
bis-(α-arylhydroxymethyl)thiophenes in presence
yield using 0.1equivalent of acid catalyst 1a. Higher
amounts of acid concentration did not improve the
result to a greater extent. The equimolar amount of
ab
of acidic ionic liquids 1a

7
2
,5-bis-(α-arylhydroxymethyl)thiophene
and
Entry
2,5-Bis-(α-
arylhydroxymethyl
TPM
s
Yield
(%) 5
b
pyrrole were taken up in dry dichloromethane.
Acidic ionic liquids (0.1 mol equiv.) was added into
the reaction mixture for appropriate time (Table 3)
followed by the oxidation with DDQ gave core
modified 21,23-dithiaporphyrins in upto 35 % yields
)
thiophenes
4
5
6
7
3d
3d
3b
3c
-
30%
45%
42%
40%
6
6
6
a
(Scheme 1b Table 3). The same reactions, performed
Reaction conditions: reaction temperature 25 °C,
in the presence of p-toluene sulfonic acid in pyrrole (0.45 mmol), diols (0.45 mmol); acidic ILs
dichloromethane gave the 9-20 % yield while in (0.11 mmol); dichloromethane (10 mL); reaction
.
3
b
presence of BF OEt maximum yields of 10-13 % time: 30 min; Isolated yield
2
27
were obtained . The yields of the products were Acidolysis of dipyrromethane in acidic ionic
observed to be increased upto ~10 % by following liquids:
3+1] strategy. The reaction of 2,5-bis-(α-
The synthesis of core modified porphyrinoids
arylhydroxymethyl)thiophenes with
[
has been obtained by the acidolysis of at least one
of the precursors, either dipyrromethanes or
tripyrromethanes followed by the reaction of
tripyrromethane in presence of acidic ionic liquid
followed by DDQ oxidation in dichloromethane
gave core modified porphyrins in upto ~45 % yields resulting species with other components leading to
(
Scheme 1c, Table 3, Entry 6-8)
porphyrinogen, which on oxidation with DDQ gave
the final product as core modified porphyrins. The
acidolysis of 5-aryldipyrromethanes were observed
in the presence of inorganic acid, organic acids and
selected acidic ionic liquids depending upon their
Table 3: Synthesis of 21,23-dithiaporphyrins by
the reaction of 2,5-bis-(α-
a
arylhydroxymethyl)thiophenes
Entry
2,5-Bis-(α-
arylhydroxymethyl
TPM
s
Yield
(%) 5
b
concentrations,
temperatures
The reaction of two moles of 5-
aryldipyrromethanes forms scrambled
tripyrromethanes catalyzed by acidic ionic liquids,
and
reaction
)
thiophenes
28,29
conditions.
1
2
3
3a
3b
3c
-
-
-
32%
35%
33%

Tetrahedron
8
which
on
further
reaction
with
form
2,5- studies together provide an insight into the origin
bis(arylhydroxymethyl)thiophene
21- of scrambling with different types of substrates
under different reaction conditions in the
dipyrromethane with 2,5-bis-(α-
arylhydroxymethyl)thiophenes route to 21-
The heteroatom-porphyrins.
condensation of dipyrromethane and 2,5-bis-(α-
arylhydroxymethyl)thiophenes is common
method for the synthesis of 21-thia porphyrins,
thiaporphyrinogen (Figure 2). The oxidation of
porphyrinogens or 21-thiaporphyrinogens by DDQ
or other oxidizing agent produced corresponding
porphyrins
and
21-heteroporphyrins.
The major product of 21-thia-5,10,15,20-
tetraarylporphyrins (4) apparently formed as a result
of the acidic ionic liquids-driven cleavage of
dipyrromethane and subsequent recombination of
the fragments with another equivalent of 2,5-bis-(α-
arylhydroxymethyl)thiophenes (3). This side
a
3
0,31
but it is often overwhelmed by scrambling
processes leading to a mixture of porphyrins. The
problem of scrambling is more prominent in
unhindered
dipyrromethanes
(e.g.,
5-
reaction, leading to scrambling of substituents, is
phenyldipyrromethane) than that in hindered
dipyrromethanes (e.g., 5-mesityldipyrromethane).
Scrambling can be suppressed by inhibiting the
reaction of oligomer fragments generated by acidic
ionic liquid-induced cleavage of dipyrromethane,
rather than by inhibiting acidolysis itself. However,
such reaction conditions were also found to inhibit
the condensation, leading to low yields (<10%) of
core modified porphyrin. The absence of
scrambling in 5-mesityldipyrromethane and 2,5-bis-
32,33
often observed in porphyrin synthesis.
In some
cases, scrambling can be controlled to prepare the
34,35
scrambled porphyrins
selectively. The easy
availability of this catalyst and its superiority over
the existing methods should make the present
protocol an attractive addition to conventional
procedures.
(
α-arylhydroxymethyl)thiophenes
was due to the resistance
mesityldipyrromethane towards acidolysis. These
condensations
of 5-

9
References and notes
H
N
H
NH HN
1.
Srinivasan, A.; Sridevi, B.; Reddy, M. V. R.;
H+
HN
HN
+
NH HN
HN
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Broadhurst, M. J.; Grigg, R.; A. Johnson,
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H
N
N
H
H
2.
NH
HN
OH2
NH
H
HN
2H+
H+
H
S
OH2
S
3
4
.
.
Latos-Grażyński, L.; Pacholska, E.;
Chmielewski, P. J.; Olmstead, M. M.;
Balch, A. L. Angew. Chem. Int. Ed. 1995,
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H
N
H
DDQ
N
N
NH
HN
S
S
3
4, 2252.
Chmielewski, P. J.; Latos-Grażyński, L.;
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Figure 2: Plausible mechanism for the synthesis of
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5
6
7
8
.
.
.
.
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2
1,23-dithiaporphyrins. The high yield, operational
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3
3
4.
5.

X
R
N
N
1
a. R = -(CH ) SO H, X = CF COO
2
e. R = -CH COOH, X = CF COO
2 3
3
3
3
i. R = -(CH ) SO H, X = CF COO
2 4 3 3
b. R = -(CH ) SO H, X = CF SO
3
f. R = -CH COOH, X = CF SO
2 3 3
2
3
3
3
j. R = -(CH ) SO H, X = CF SO
2 4 3 3 3
c. R = -(CH ) SO H, X = CH SO
2
g. R = -CH COOH, X = CH SO
2 3 3
3
3
3
3
k.R = -(CH ) SO H, X = CH SO
2 4 3 3 3
d. R = -(CH ) SO H, X = HSO
3
2
h. R = -CH COOH, X = HSO4
2
3
4
l. R = -(CH ) SO H, X = HSO
2 4 3 4
Figure 1: Structures of Brønsted acidic ionic liquids