One-Pot Synthesis of Butadiyne-Bridged Bipyrrole Derivatives and Bisporphyrin

Article abstract of DOI:10.1002/ejoc.201700891

Butadiyne-bridged bipyrroles were prepared from 2-iodopyrroles and trimethylsilylacetylene through a facile one-pot synthesis involving a modified Sonogashira coupling reaction and in situ aerobic oxidative coupling of the acetylenic pyrroles; the products were obtained in yields of 31–72 % depending on the substituents on the pyrrole. The acetylene-bridged diacids obtained from the hydrolysis of the corresponding ester derivatives are highly stable, unlike most reported oligopyrrolic diacids. This protocol could be easily extended towards the synthesis of butadiyne-bridged bisporphyrins.

Full text of DOI:10.1002/ejoc.201700891

A Journal of
Accepted Article
Title: One Pot Syntheses of Butadiyne bridged Bipyrrole derivatives
and Bisporphyrin
Authors: Nanda Kishore M. V. and Pradeepta K. Panda
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10.1002/ejoc.201700891
European Journal of Organic Chemistry
COMMUNICATION
One Pot Syntheses of Butadiyne bridged Bipyrrole derivatives
and Bisporphyrin
M. V. Nanda Kishore and Pradeepta K. Panda*[a]
Abstract: A facile one-pot synthesis of butadiyne bridged bipyrroles
could be achieved from 2-iodopyrroles and trimethylsilylacetylene via
a modified Sonogashira coupling and in-situ aerial oxidative coupling
of the acetylenic pyrroles in 31-72% yields, depending upon the
substituents on pyrrole. The acetylene bridged diacids obtained from
hydrolysis of the corresponding ester derivatives were highly stable,
unlike most of the reported oligopyrrolic diacids. This protocol could
be easily extended towards the synthesis of butadiyne bridged
bisporphyrin.
viz. as photosensitizers for two photon photodynamic therapy,[2d-
tracking molecular motion, create artificial protein-like
molecules, etc. However, there are only very few reports
regarding their efficient synthesis.[1a,6]
While most of the synthetic approaches, consist of multiple steps
involving Pd/Cu-cocatalyzed Sonogashira coupling of iodo
arenes (i.e. pyrroles or porphyrins) with trimethylsilylacetylene
(TMSA), followed by deprotection of the silyl protecting group
and then either another Sonogashira coupling to generate the
monoacetylene bridged bipyrrole (or bisporphyrin) derivatives or
else Pd-catalyzed oxidative coupling to yield the diacetylene
(butadiyne) bridged bipyrrole (or bisporphyrin) derivatives.
Herewith, we report a very efficient one pot synthesis of
butadiyne bridged bipyrroles and bisporphyrin.
e]
Introduction
Acetylene bridged biaryls, in particular bipyrroles has emerged
as an attractive building block for the synthesis of new class of
expanded porphyrins e.g. 1-2 possessing interesting
[1]
Results and Discussion
photophysical properties (Figure 1).
Whereas, bisporphyrins
such as 3 bridged via acetylene(s) also emerged as potential
nonlinear optical materials (Figure 1), [2] along with their utility as
The motivation towards this work came during our attempts to
synthesize acetylene bridged bipyrrolic systems following the
one-pot synthetic protocol for symmetrical bisarylethynes
reported by Mio et al. via modified Sonogashira coupling
reaction.[7] Interestingly, during our attempt to synthesize the
acetylene bridged bipyrrole derivative (Scheme 1), the TLC
Scheme 1. Synthesis of acetylene bridged bipyrroles
analysis revealed
a
small amount of starting material,
iodopyrrole 5a (never got consumed completely, in spite of
extended reaction time or higher temperature), along with
another yellow fluorescent spot close to the desired blue
fluorescent product 6a (Table 1, entry 1). Even modulation of
reaction conditions via change of solvent and addition of water
after some time could not help suppressing the formation of the
latter product 7a completely (Table S1). Successful isolation of
Figure 1. Some examples of acetylene bridged bipyrrole derivatives,
bisporphyrins and porphyrin nanorings.
Table 1. Yields of compounds 6 and 7 from Scheme 1
a platform to synthesize novel multiporphyrinic derivatives,[3]
porphyrin nanorings 4,[4] supramolecular nesting[5a] and charge
storage/transport,[5b-e] which display many interesting properties,
Scheme 1 (% yield)
entry
R
6
7
7
1
2
3
4
5
OEt (a)
OBn (b)
Ph (c)
Me (d)
H (e)
71
65
58
52
44
[a]
School of Chemistry, University of Hyderabad
Hyderabad-500046, India
13
22
18
-
E-mail: pkpsc@uohyd.ernet.in, predeepta.panda@uohyd.ac.in
http://chemistry.uohyd.ac.in/~pkp/
ORCID: Pradeepta K. Panda: 0000-0002-3243-5071
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/ejoc.201700891
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1
this compound via column chromatography revealed similar H
NMR spectrum as the desired acetylene bridged bipyrrole
derivative 6a (Figure S16 and S25). However, 13C NMR
spectrum (Figure S26) displayed an additional carbon signal (at
achieve our desired target, we increased the quantity of TMSA
to 1.2 equivalents and exposed the reaction mixture to air after
1
74.85 ppm for C≡C). The similarity in H NMR spectra and the
additional carbon signal in 13C NMR spectrum, led us to believe
presence of one more alkyne bond in the molecule, which was
confirmed by mass analysis showing peak at 459.2260 (Figure
S27) for the corresponding [M + Na]+ species. Finally, the
identity of the compound could be unequivocally resolved
through single crystal X-ray diffraction analysis (obtained by
slow evaporation of dichloromethane solution of 7a). The
structure shows both pyrroles are in opposite direction, yet in
same plane, whereas, in case of 6a (crystals obtained under
similar condition) the pyrroles are pointed towards the same
direction (Figure 2). While, the presence of unreacted starting
material can be attributed to the formation of diacetylene (or
butadiyne) bridged bipyrroles, the formation of the latter may be
Scheme 2. Synthesis of butadiyne bridged bipyrroles
the regular modified Sonogashira coupling (Scheme 2).
Reaction of 5a under this condition resulted in the exclusive
formation of the desired bipyrrole 7a in 72% yield. Similarly,
other iodopyrrole derivatives 5b-e (Table 2, entry 2-5) also
produced quite good yields of diacetylene bridged bipyrrole
derivatives 7b-e (31 - 67%). The decrease in yield in case of 7e
(Table 2, entry 5) can be attributed to strong deactivating nature
Table 2. Yields of compounds 7 from Scheme 2
entry
R
7 (% yield)
1
2
3
4
5
OEt (a)
OBn (b)
Ph (c)
Me (d)
H (e)
72
67
61
54
31
of the formyl substituent at the α-position of the pyrrole moiety.
The reaction could be easily performed upto 10 g scale in case
of 5a to synthesize 7a in good yield (60%). The plausible
mechanism for the diacetylene bridged bipyrrole synthesis
involves a general Sonogashira coupling of TMSA in first step, a
base mediated deprotection of TMS group in the second step
and oxidative Glaser coupling of thus formed acetylenic pyrrole
in presence of palladium and copper.[10]
Versatility of this approach could be verified by employing it
towards the synthesis of acetylene and butadiyne bridged
porphyrins. Here, following the route in Scheme 1, we could
obtain the acetylene-bridged bisporphyrin 9 as the minor product,
on the other hand to our surprise, the butadiyne bridged
bisporphyrin 10 formed as the major product (Scheme 3). This
may be attributed to the relatively dilute condition we need to
Figure 2. ORTEP diagrams of 6a (top) and 7a (bottom). Thermal ellipsoids are
scaled up to 35% probability level. Color code: grey = Carbon, white =
Hydrogen, blue = Nitrogen and red = Oxygen.
ascribed to the presence of trace amount of oxygen in the
reaction medium, which might have promoted the oxidative
coupling. While we are working on this theme, Graça H. Vicente
and co-workers reported synthesis of 1,2-dipyrrolylethynes
following this strategy.[8] However, comparatively lower yields
reported by them do not rule out the formation of the butadiyne
derivatives in their cases also. Following this protocol several
functionalized acetylene bridged bipyrrole derivatives 6a-e could
be synthesized in varying yields depending on the nature of the
substituents on the α-position of the 3,4-diethylpyrrole moiety
(Table 1, entry 1-5). In most of the cases, we could able to
isolate minor quantities of butadiyne bridged bipyrroles 7.
Encouraged by the above results and owing to the importance of
the butadiyne bridged derivatives,[1,9] we wished to explore if
they can be exclusively synthesized in one-pot. In order to
Scheme 3. Synthesis of acetylene and butadiyne bridged bisporphyrins.
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10.1002/ejoc.201700891
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COMMUNICATION
the reported procedures. NMR spectra were recorded on a Bruker
Avance-400 and 500 MHz FT NMR spectrometers using
adopt for this reaction in order to solubilize the porphyrin in
benzene (reaction in THF resulted in much reduced yield) and
this may led to the presence of relatively increased oxygen
concentration and hence promoting the formation of latter via
oxidative coupling. We believe, if carried out in larger scale and
also presence of longer alkyl/alkoxy chain(s) at porphyrin
periphery to enhance its solubility should result in increased
yield of the monoacetylene bridged bisporphyrin (our reaction is
not rigorously optimized). However, second route (as in Scheme
2) exclusively yielded the butadiyne-bridged bisporphyrin 10 in
quite good yield (65%). To our knowledge, this is the most
versatile method for the synthesis of these important bipyrrole
based precursors having no protecting group on pyrrolic N and
bisporphyrin derivatives.[6,10]
tetramethylsilane (TMS,
δ = 0) as an internal standard at room
temperature. Mass spectral determinations were carried out by Bruker
Maxis Spectrometer by ESI technique. Melting points were determined
on MR-Vis+ visual melting point range apparatus from LABINDIA
instruments private limited. IR spectra were recorded on a JASCO-FT-IR
model 5300 and NICOLET 5700 FT-IR spectrometers. All UV-Vis spectra
were recorded using Perkin Elmer Lambda-750 UV-VIS spectrometer
and fluorescence spectra were recorded in Fluorolog-3-221
spectrofluorometer. Fluorescence spectra were recorded by exciting all
acetylene bridged bipyrroles and bisporphyrins in the wavelength range
of 265-269 nm and 497-502 nm, respectively. Quantum yield (ϕf)
calculations were done using 9,10-diphenylanthracene in ethanol as
reference for acetylene bridged bipyrroles and tetraphenylporphyrin in
toluene for bisporphyrins.[16]
Hydrolysis of 6a and 7a resulted in almost quantitative isolation
of 11 and 12 (Scheme 4). Unlike other oligopyrrolic diacids,[11]
these diacids were found to be very stable under ambient
condition and hence could be rigorously characterized (Figure
S57-S62). We could also successfully demonstrate coupling
between two differently substituted pyrroles to isolate bipyrrole
13 in moderate yield (Scheme 4).
Crystallographic data for 6a and 7a were collected on BRUKER SMART-
APEX CCD diffractometer. Mo α ( = 0.71073 Å) radiation was used to
collect X-ray reflections on the single crystal. Data reduction was
performed using Bruker SAINT software.[17] Intensities for absorption
were corrected using SADABS[18] and refined using SHELXL-2014/7[19]
with anisotropic displacement parameters for non-H atoms. Hydrogen
atoms on O and N were experimentally located in difference electron
density maps. A check of the final CIF file using PLATON[20] did not show
any missed symmetry. Crystallographic data (including the structure
factor) for structures 6a and 7a in this paper have been deposited in the
Cambridge Crystallographic Data Centre as supplementary publication
numbers CCDC 1500784-1500785. Copies of the data can be obtained
free of charge on application to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: +44(0)-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk).
General procedure for the synthesis of 2-benzoyl/acyl substituted
3,4-diethylpyrroles 15c and 15d (Scheme S1).[21] To a three neck
round bottom flask having a dropping funnel and a reflux condenser N,N-
dimethylbenzamide (DMBz) (3.3 g, 22 mmol)/ N,N-DMAc (3.1 mL, 33
mmol) was added. The flask was immersed in an ice bath, POCl3 (2 mL,
22 mmol)/ (3.1 mL, 33 mmol) was added slowly through syringe. The ice
bath was removed and the complex was stirred for another 24 h/15
min at room temperature. DCE (5 mL) was added and the ice bath was
Scheme 4. Synthesis of acetylene bridged bipyrrole acid derivatives and
differently substituted acetylene bridged bipyrrole.
Conclusions
°
replaced. When the internal temperature has been lowered to 5 C,
In conclusion, we have demonstrated a simple approach
towards the synthesis of several butadiyne bridged bipyrrole
derivatives, along with their acetylene bridged counterparts. The
protocol not only could be easily scaled up, but also could be
successfully extended to porphyrinic system, indicating its
versatility. As all the bipyrrolic derivatives are without N-
protection and also endowed with useful functional groups at
their α-positions, they can be used directly or with minimal
synthetic manipulation as building blocks towards synthesis of
novel π-extended porphyrinoids, retaining the acetylene bridged
conjugation. Presently, our efforts are underway in this direction.
3,4-diethylpyrrole (2.46 g, 20 mmol)/ (3.69 g, 30 mmol) dissolved in DCE
(20 mL) was added slowly to cooled reaction mixture. After the
addition was complete, the ice bath was replaced with heating mantle.
The mixture was refluxed for 4 h, then cooled to 25-30 °C and
a
saturated solution of sodium acetate (9 g, 110 mmol)/ (13.5 g, 165
mmol) was added slowly to the reaction mixture. The reaction
mixture was again refluxed for 4 h, during which there is a copious
evolution of HCl gas. After the completion of reaction it was extracted
thrice with DCM. The combined organic layers were washed with
saturated aq sodium carbonate solution and dried over anhyd sodium
carbonate. The crude product was purified using silica gel via column
chromatography with 20% EtOAc + 80% Hexane as eluent to get the
desired products.
15c: 3.8 g, 84%; pale yellow liquid; FTIR data (in cm-1): 3246, 2963,
1617; 1H NMR (400 MHz, CDCl3 δ in ppm): 8.76 (s, 1H), 7.66 (m, 2H),
7.52 (m, 1H), 7.46 (m, 2H), 6.81 (d, J = 2.8 Hz, 1H), 2.50 (m, 4H), 1.22 (t,
J = 7.6 Hz , 3H), 1.01 (t, J = 7.6 Hz, 3H); 13C NMR (100 MHz, CDCl3 δ in
ppm): 186.5, 140.2, 134.1, 131.0, 128.3, 128.0, 121.6, 18.3, 18.0, 15.4,
14.7; HRMS m/z calculated for [M+Na]+ C15H17NONa: 250.1208, found
250.1210.
Experimental Section
General Information. Commercially available solvents were distilled
before use. Reagents were purchased from Sigma Aldrich and used as
received without further purification unless otherwise stated. Solvents for
the reaction were dried according to literature methods. Compounds
ethyl
5-iodo-3,4-diethylpyrrole-2-carboxylate
15b,[13]
5a,[12]
5-iodo-3,4-diethylpyrrole-2-
benzyl
3,4-
diethylpyrrole-2-carboxylate
°
carboxaldehyde 5e,[6a] 3,4-diethylpyrrole 14,[14] and 5-iodo-10,20-Bis(3,5-
di-tert-butylphenyl) porphyrinato Zinc (II) 8[15] were prepared according to
15d: 4.7 g, 95%; off-white crystalline solid; mp 96-98 C ; FTIR data (in
1
cm-1): 3203, 2967, 1615; H-NMR (400 MHz, CDCl3 δ in ppm) : 9.04 (s,
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10.1002/ejoc.201700891
European Journal of Organic Chemistry
COMMUNICATION
1H), 6.76 (d, J = 3.2 Hz, 1H), 2.76 (q, J = 7.6 Hz, 2H), 2.47 (s, 3H), 2.45
(q, J = 7.6 Hz, 2H), 1.2 (m, 6H); 13C NMR (100 MHz, CDCl3 δ in ppm):
187.6, 131.6, 128.9, 127.3, 121.0, 27.2, 18.6, 17.8, 15.8, 14.7; HRMS
m/z calculated for [M+H]+ C10H16NO:166.1232 found 166.1229.
6b Eluent:10% EtOAc + 90% Hexane, Yield: 174 mg, 65%; light brown
solid; UV-Vis data (CHCl3), max (in nm): 265 (4.25), 346 (4.57), 371
(4.49) ; Fluorescence (CHCl3), max (in nm): 384, 401; ϕf : 0.01. All data
matched with previously reported compound, except the emission studies
which was not reported earlier.[1b]
General procedure for the synthesis of iodopyrrole derivatives 5(b-
d) (Scheme S2):[12] To sodium bicarbonate solution (3.125 g, 38 mmol in
58.5 mL water) in a two neck round bottom flask bearing a reflux
condenser with a nitrogen inlet and a pressure equalizing dropping funnel,
6c Eluent:15% EtOAc + 85% Hexane, Yield: 138 mg, 58%; yellow solid;
°
mp 196-197 C; FTIR data (in cm-1): 3300, 2966, 1593, 1414; 1H NMR
(400 MHz, CDCl3 δ in ppm): 8.83 (s, 2H), 7.69 (d, J = 6.8 Hz, 4H), 7.55 (t,
J = 7.2 Hz, 2H), 7.48 (t, J = 7.2 Hz, 4H), 2.58 (m, 8H), 1.22 (t, J = 7.6 Hz,
6H), 1.05 (t, J = 7.6 Hz, 6H); 13C NMR (100 MHz, CDCl3 δ in ppm): 185.8,
139.6, 134.0, 133.5, 131.5, 128.5, 128.3, 128.1, 115.8, 86.1, 18.4, 18.1,
15.7, 15.5; HRMS m/z calcd. for [M+H]+ C32H33N2O2:477.2542, found
477.2546. UV-Vis data (CHCl3), max (in nm): 254 (4.40), 393 (4.57);
Fluorescence (CHCl3), max (in nm): 448; ϕf : 0.003.
°
the pyrrole derivative (10 mmol) in DCE was added and heated at 90 C.
To this, KI3 solution (KI - 3.65 g, 22 mmol + I2 - 2.79 g, 11 mmol in 30 mL
°
water) was added dropwise and stirred for 90 min at 80 C. Later the
reaction mixture was extracted twice with DCM. The organic layer was
washed with saturated sodium thiosulphate solution and dried over
anhyd sodium sulfate. The solvent was evaporated on
a rotary
evaporator and the crude product was subsequently purified by column
chromatography using silica gel and 10% EtOAc + 90% Hexane as
eluent to obtain the pure compounds.
6d Eluent:15-30% EtOAc in Hexane, Yield: 92 mg, 52%; brown solid; mp
°
233-234 C; FTIR data (in cm-1): 3237, 2962, 1610, 1427; 1H NMR (400
MHz, DMSO-d6 δ in ppm): 11.93 (s, 2H), 2.69 (q, J = 7.6 Hz, 4H), 2.51 (q,
J = 7.6 Hz, 4H), 2.40 (s, 6H), 1.09 (m, 12H); 13C NMR (100 MHz, DMSO-
d6 δ in ppm): 187.8, 132.2, 131.7, 129.1, 114.7, 85.7, 28.1, 18.4, 17.8,
16.4, 16.0; HRMS m/z calcd. for [M+H]+ C22H29N2O2:353.2229, found
353.2232. UV-Vis data (CHCl3), max (in nm): 256 (4.18), 281 (4.13), 373
(4.55), 393 (4.52); Fluorescence (CHCl3), max (in nm): 413, 433; ϕf :
0.379.
5b Yield: 3 g, 78%; white solid; mp 94-95 °C; FTIR data (in cm-1): 3265,
2964, 1671; H NMR (400 MHz, CDCl3 δ in ppm): 8.94 (s, 1H), 7.38 (m,
5H), 5.31, (s, 2H), 2.77 (q, J = 7.6 Hz, 2H), 2.38 (q, J = 7.6 Hz, 2H), 1.13
(t, J = 7.6 Hz, 3H), 1.08 (t, J = 7.6 Hz, 3H); 13C NMR (100 MHz, CDCl3 δ
in ppm): 160.0, 136.1, 133.7, 131.7, 128.6, 128.3, 122.8, 73.1, 66.0, 19.8,
18.8, 15.8, 15.5; HRMS calcd. for [M+H]+ C16H19NO2I:384.0461, found
384.0461.
1
6e Eluent:15-30% EtOAc in Hexane, Yield: 141 mg, 44%; yellow solid;
UV-Vis data (CHCl3), max (in nm): 257 (4.08), 287 (4.13), 384 (4.56), 403
(4.56); Fluorescence (CHCl3), max (in nm): 421, 439; ϕf : 0.43. All data
matched with previously reported compound, except the emission studies,
which was not reported earlier.[1a]
°
5c Yield: 2.9 g, 83%; yellow solid; mp 120-121 C ; FTIR data (in cm-1):
3236, 2962, 1604; 1H NMR (400 MHz, CDCl3 δ in ppm): 9.05 (s, 1H),
7.66 (m, 2H), 7.54 (m, 1H), 7.46 (m, 2H), 2.52 (q, J = 7.6 Hz, 2H), 2.42 (q,
J = 7.6 Hz, 2H), 1.11 (t, J = 7.6 Hz, 3H), 0.99 (t, J = 7.6 Hz, 3H); 13C
NMR (100 MHz, CDCl3 δ in ppm): 185.3, 139.5, 134.3, 132.4, 131.3,
128.4, 128.1, 76.8, 19.8, 18.8, 15.8, 15.3; HRMS calcd. for [M+H]+
C15H17NOI:354.0355, found 354.0359.
General procedure for the synthesis of dipyrrolyl butadiynes 7(a-e):
To an oven dried two necked round bottom flask PdCl2(PPh3)2 (42 mg,
0.06 mmol), CuI (19 mg, 0.1 mmol) and iodopyrrole derivative (1 mmol)
were added and flushed with N2 gas. Nitrogen purged THF (5 mL) and
DBU (0.9 mL, 6 mmol) were added and the reaction mixture was kept for
freeze-pump thaw cycle for 3 times. To this reaction mixture TMSA (170
µL, 1.2 mmol) was added and stirred in dark for 16 h. Water (18 µL) was
added and again stirred in dark for 24 h at room temperature under
aerobic condition. After completion of the reaction product was
partitioned between ethyl acetate and dilute HCl. The organic layer was
washed with brine and dried over anhyd sodium sulfate. Evaporation of
solvent under reduced pressure provided crude product, which was
purified by silica gel column chromatography using 20-40% EtOAc in
Hexane to yield the desired compounds.
5d Yield: 2.4 g, 83%; off-white solid; mp 118-120 °C; FTIR data (in cm-1):
3238, 2964, 1621; 1H NMR (400 MHz, CDCl3 δ in ppm): 9.29 (s, 1H),
2.77 (q, J = 7.6 Hz, 2H), 2.46 (s, 3H), 2.39 (q, J = 7.6 Hz, 2H), 1.20 (t, J =
7.6 Hz, 3H), 1.09 (t, J = 7.6 Hz, 3H); 13C NMR (100 MHz, CDCl3 δ in
ppm): 186.4, 133.4, 132.0, 131.8, 76.8, 27.0, 19.7, 19.2, 16.3, 15.4;
HRMS calcd. for [M+H]+ C10H15NOI:292.0198, found 292.0199.
General procedure for the synthesis of dipyrrolyl ethynes 6(a-e):[7]
To an oven dried two necked round bottom flask PdCl2(PPh3)2 (42 mg,
0.06 mmol), CuI (19 mg, 0.1 mmol) and iodopyrrole derivative (1 mmol)
were added and flushed with N2. Nitrogen purged acetonitrile (5 mL) and
DBU (0.9 mL, 6 mmol) were added and the reaction mixture was kept for
freeze-pump thaw cycle for 3 times. To this reaction mixture TMSA (71
µL, 0.5 mmol) and water (7 µL, 40 mol%) were added and stirred in dark
for 24 h at room temperature. After completion of the reaction, the
product was partitioned between ethyl acetate and dil. HCl. The organic
layer was washed with brine and dried over anhyd sodium sulfate.
Evaporation of solvent under reduced pressure gave crude product,
which was purified by silica gel column chromatography to yield the titled
compounds.
7a Yield: 156 mg, 72%; yellow solid; mp 208-209 °C; FTIR data (in cm-1):
3273, 2966, 2129, 1666; 1H NMR (400 MHz, CDCl3 δ in ppm): 9.02 (s,
2H), 4.34 (q, J = 7.2 Hz, 4H), 2.73 (q, J = 7.2 Hz, 4H), 2.56 (q, J = 7.2 Hz,
4H), 1.37 (t, J = 7.2 Hz, 6H), 1.16 (m, 12H); 13C NMR (100 MHz, CDCl3 δ
in ppm): 160.4, 135.1, 132.4, 120.3, 113.1, 79.0, 74.9, 60.4, 18.2, 15.8,
15.6, 14.4; HRMS m/z calcd. for [M+Na]+ C26H32NaN2O4:459.2260, found
459.2260. UV-Vis data (CHCl3), max (in nm): 320 (4.51), 334 (4.62), 360
(4.59), 389 (4.50); Fluorescence (CHCl3), max (in nm): 443, 471; ϕf :
0.005.
6a Eluent:10% EtOAc + 90% Hexane, Yield: 146 mg, 71%; off-white
°
solid; mp 180-181 C; FTIR data (in cm-1): 3290, 2962, 2199, 1660; 1H
7b Yield: 188 mg, 67%; yellow solid; mp 175-176 °C; FTIR data (in cm-1):
3287, 2958, 2131, 1666; 1H NMR (400 MHz, CDCl3 δ in ppm): 9.08 (s,
2H), 7.38 (m, 10H), 5.31 (s, 4H), 2.72 (q, J = 7.6 Hz, 4H), 2.53 (q, J = 7.6
Hz, 4H), 1.14 (m, 12H); 13C NMR (100 MHz, CDCl3 δ in ppm): 160.1,
135.9, 135.2, 133.0, 128.6, 128.3, 119.9, 113.4, 79.0, 74.8, 66.3, 18.2,
18.1, 15.7, 15.7; HRMS m/z calcd. for [M+H]+ C36H37N2O4:561.2753,
found 561.2754. UV-Vis data (CHCl3), max (in nm): 257 (4.42), 283
NMR (400 MHz, CDCl3 δ in ppm): 8.87 (s, 2H), 4.33 (q, J = 7.6 Hz, 4H),
2.75 (q, J = 7.6 Hz, 4H), 2.56 (q, J = 7.6 Hz, 4H), 1.37 (t, J = 7.6 Hz, 6H),
1.17 (m, 12H); 13C NMR (100 MHz, CDCl3 δ in ppm): 160.7, 132.6, 132.5,
119.4, 114.1, 85.1, 60.2, 18.2, 18.1, 15.7, 14.5; HRMS m/z calcd. for
[M+H]+ C24H33N2O4:413.2440, found 413.2442. UV-Vis data (CHCl3), max
(in nm): 265 (4.20), 344 (4.59), 369 (4.51); Fluorescence (CHCl3), max (in
nm): 382, 400; ϕf : 0.005.
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10.1002/ejoc.201700891
European Journal of Organic Chemistry
COMMUNICATION
(4.41), 336 (4.68), 362 (4.65), 391 (4.56); Fluorescence (CHCl3), max (in
nm): 408, 424, 481, 503; ϕf : 0.004.
mixture was cooled and 2N NaOH (400 mg, 10 mmol) solution was
added and again refluxed under nitrogen atmosphere for 10-12 h until a
clear solution was obtained. The reaction mixture was cooled and diluted
with water. To the ice cooled reaction mixture, dilute HCl was added
dropwise under constant stirring to obtain clear precipitate, which was
filtered and dried overnight under vacuum to provide the titled
compounds.
7c Yield: 153 mg, 61%; yellow solid; mp 210-212 °C; FTIR data (in cm-1):
3233, 2966, 1595; 1H NMR (400 MHz, CDCl3 δ in ppm): 8.89 (s, 2H),
7.68 (d, J = 7.2 Hz, 4H), 7.56 (t, J = 6.8 Hz, 2H), 7.48 (t, J = 7.2 Hz, 4H),
2.58 (q, J = 7.6 Hz, 8H), 1.21 (t, J = 7.6 Hz, 6H), 1.05 (t, J = 7.6 Hz, 6H);
13C NMR (100 MHz, CDCl3 δ in ppm): 185.7, 139.3, 136.0, 133.8, 131.7,
128.8, 128.6, 128.2, 114.7, 79.7, 75.2, 18.4, 18.1, 15.6; HRMS m/z calcd.
for [M+H]+ C34H33N2O2:501.2542, found 501.2545. UV-Vis data (CHCl3),
max (in nm): 261 (4.43), 389 (4.68), 419 (4.59); Fluorescence (CHCl3),
11 Yield: 322 mg, 91%; grey solid; mp > 250°C (decomposes); FTIR data
(in cm-1): 3300, 2961, 2930, 1660; 1H NMR (400 MHz, Methanol-d4, δ in
ppm): 2.76 (q, J = 7.2 Hz, 4H), 2.58 (q, J = 7.2 Hz, 4H), 1.16 (m, 12H);
13C NMR (100 MHz, CDCl3 δ in ppm): 162.5, 132.4, 131.1, 119.0, 114.5,
84.5, 17.6, 17.5, 14.9; HRMS m/z calcd. for [M+Na]+ C20H24N2NaO4:
379.1634 found 379.1635. UV-Vis data (MeOH), max (in nm): 262 (4.09),
338 (4.46), 360 (4.40); Fluorescence (MeOH), max (in nm): 393; ϕf :
0.007.

max (in nm): 458; ϕf : 0.003.
7d Yield: 102 mg, 54%; yellow solid; mp 266-268 °C; FTIR data (in cm-1):
3269, 2972, 1620; 1H NMR (400 MHz, DMSO-d6 δ in ppm): 12.15 (s, 2H),
2.67 (q, J = 7.2 Hz, 4H), 2.48 (q, J = 7.2 Hz, 4H), 2.39 (s, 6H), 1.11 (t, J =
7.2 Hz, 6H), 1.05 (t, J = 7.2 Hz, 6H); 13C NMR (100 MHz, DMSO-d6 δ in
ppm): 188.0, 134.7, 131.5, 129.9, 112.9, 78.7, 76.4, 28.1, 18.3, 17.8,
16.3, 15.9; HRMS m/z calcd. for [M+H]+ C24H29N2O2:377.2229, found
377.2230. UV-Vis data (CHCl3), max (in nm): 287 (4.21), 359 (4.61), 377
(4.62), 406 (4.53); Fluorescence (CHCl3), max (in nm): 448; ϕf : 0.006.
12 Yield: 366 mg, 96%; light brown solid; mp > 250°C (decomposes);
FTIR data (in cm-1): 3300, 2962, 1661; 1H NMR (400 MHz, Methanol-d4,
δ in ppm): 2.74 (q, J = 7.2 Hz, 4H), 2.55 (q, J = 7.6 Hz, 4H), 1.17 (t, J =
7.6 Hz, 6H), 1.12 (t, J = 7.6 Hz, 6H); 13C NMR (100 MHz, CDCl3 δ in
ppm):163.5, 135.3, 133.5, 121.6, 114.4, 79.2, 75.9, 18.9, 18.9, 16.2,
16.2; HRMS m/z calcd. for [M+Na]+ C22H24N2NaO4: 403.1634 found
403.1633. UV-Vis data (MeOH), max (in nm): 314 (4.47), 329 (4.52), 354
(4.46), 381 (4.36); Fluorescence (MeOH), max (in nm): 470, 498; ϕf :
0.004.
7e Yield: 54 mg, 31%; yellow solid; UV-Vis data (CHCl3), max (in nm):
281 (4.29), 368 (4.61), 385 (4.61); Fluorescence (CHCl3), max (in nm):
430; ϕf : 0.256. All data matched with previously reported compound,
except the emission studies, which was not reported earlier.[1c]
Synthesis of differently substituted acetylene bridged bipyrrole 13:
To an oven dried two necked round bottom flask PdCl2(PPh3)2 (42 mg,
0.06 mmol), CuI (19 mg, 0.1 mmol) and 5a (1 mmol) were added and
flushed with N2 gas. Nitrogen purged THF (5 mL) and triethylamine (0.9
mL) were added and the reaction mixture was kept for freeze-pump thaw
cycle for 3 times. To the reaction mixture TMSA (170 µL, 1.2 mmol) was
added and stirred in dark for 16 h. To the reaction mixture 5c, DBU (1.8
mL) and water (14 µL) were added and again stirred for 24 h at rt.
Subsequently, the reaction mixture was partitioned between ethyl acetate
and dil. HCl. The organic layer was washed with brine and dried over
anhyd sodium sulfate. Evaporation of solvent under reduced pressure
provided crude product, which was purified by silica gel column
chromatography using 10% EtOAc in hexane to yield the desired
compound along with 7a (24%).
Preparation of acetylene bridged porphyrin dimer 9: To a Schlenk
flask fitted with a tight rubber septum was added Zn(II) complex of
iodoporphyrin (88 mg, 0.1 mmol), PdCl2(PPh3)2 (4 mg, 6 mol%), CuI (2
mg, 10 mol%). Dry benzene (5 mL) and DBU (5 mL) were added and the
solution was degassed by freeze-pump thaw cycles. TMSA (7 µL, 0.05
mmol) and water (1 µL, 40 mol%) were added and stirred under inert
°
atmosphere for 48 h at 60 C. The mixture was washed with water and
the organic layer was evaporated in vacuum to obtain the crude product,
which was subjected to column chromatography using silica gel and
DCM-Hexane-Et3N (1:1:0.01) mixture as eluent to obtain both mono and
diacetylene bridged dimers. The pure compound 9 was obtained as a
green solid using preparative TLC (14 mg, 18%), along with 10 (27 mg,
35%). UV-Vis data (CHCl3), max (nm): 415 (5.03), 478 (5.17), 551 (4.21),
652 (4.33), 690 (4.39); Fluorescence (1% pyridine in toluene), max (nm):
735; ϕf : 0.094. All data matched with previously reported compound,
except the quantum yield, which is measured in different solvent and is of
similar order.[22]
Yield: 141 mg, 32%; yellow solid; mp 188-190°C ; FTIR data (in cm-1):
3282, 2972, 1660, 1593; 1H NMR (400 MHz, CDCl3, δ in ppm): 8.91 (s,
1H), 8.86 (s, 1H), 7.70 (d, J = 4 Hz, 2H), 7.56 (t, J = 4 Hz, 1H), 7.48 (t, J
= 8 Hz, 2H), 4.33 (q, J = 6.8 Hz, 2H), 2.75 (q, J = 8 Hz, 2H), 2.58 (m, 6H),
1.37 (t, J = 6 Hz, 3H), 1.19 (m, 9H), 1.05 (t, J = 6 Hz, 3H); 13C NMR (100
MHz, CDCl3 δ in ppm): 185.8, 160.6, 139.7, 134.0, 133.3, 132.8, 132.6,
131.4, 128.5, 128.1, 119.6, 116.2, 113.8, 86.2, 85.0, 60.3, 18.4, 18.2,
18.1, 15.7, 15.5, 14.4; HRMS m/z calcd. for [M+H]+ C28H33N2O3:
445.2491 found 445.2490. UV-Vis data (CHCl3), max (in nm): 253 (4.31),
300 (4.28), 377 (4.54); Fluorescence (CHCl3), max (in nm): 446; ϕf :
0.002.
Preparation of butadiyne bridged porphyrin dimer 10: To a Schlenk
flask fitted with a tight rubber septum was added Zn(II) complex of
iodoporphyrin (44 mg, 0.05 mmol), PdCl2(PPh3)2 (2 mg, 6 mol%), CuI (1
mg, 10 mol%). THF (4 mL) and DBU (0.5 mL) were added and the
solution was degassed by freeze-pump thaw cycles. TMSA (11 µL, 0.075
mmol) was added and stirred in dark for 16 h. Water (2 µL) was added
and the reaction mixture was stirred under aerobic condition for 24 h at
room temperature. The reaction mixture was washed with water and the
organic layer was evaporated in vacuum to obtain the crude product. It
was further subjected to silica gel column chromatography using DCM-
Hexane (1:2) as eluent to obtain the desired dimer 10 as a green solid
(25 mg, 65%). UV-Vis data (CHCl3), max (in nm): 448 (5.07), 480 (4.90),
562 (4.06), 634 (4.19), 679 (4.33); Fluorescence (toluene), max (in nm):
682; ϕf : 0.12. All data matched with previously reported compound,
except the quantum yield, which so far is not reported precisely.[2c,6b]
Acknowledgements
This work is supported by the Science and Engineering
Research Board (SERB), India (Project no. SR/S1/IC-56/2012).
Financial and infrastructure support from the University Grants
Commission, New Delhi (through the UPE and CAS programs)
and the Department of Science and Technology, New Delhi
(through the PURSE and FIST programs) are gratefully
General procedure for the synthesis of acetylene bridged bipyrrole
acid derivatives 11 and 12: To a two neck round bottomed flask fitted
with a rubber septum 6a or 7a (1 mmol) was added and dissolved in
minimum amount of ethanol by refluxing. Subsequently, the reaction
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COMMUNICATION
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crystal structures.
Keywords: Alkynes • Biaryls • C-C coupling • Porphyrinoids •
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Entry for the Table of Contents (Please choose one layout)
COMMUNICATION
Butadiyne bridged bipyrroles were
obtained from the corresponding iodo
pyrroles in one pot strategy which was
subsequently applied to synthesize
butadiyne bridged bisporphyrin in
good yield.
Butadiyne bridged bipyrroles*
M. V. Nanda Kishore, Pradeepta K.
Panda*
Page No.1 – Page No.6
One Pot Syntheses of Butadiyne
bridged Bipyrrole derivatives and
Bisporphyrin
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