A simple route to prepare monofunctionalised 21-thia-, 21,23-dithia-, and 21-thia-23-oxaporphyrins from unsymmetrical thiophene diols and their use in the synthesis of covatently linked unsymmetrical porphyrin dimers

FULL PAPER

A Simple Route to Prepare Monofunctionalised 21-Thia-, 21,23-Dithia-, and

21-Thia-23-oxaporphyrins from Unsymmetrical Thiophene Diols and Their Use

in the Synthesis of Covalently Linked Unsymmetrical Porphyrin Dimers

Sokkalingam Punidha,^[a]Neeraj Agarwal,^[a]and Mangalampalli Ravikanth*^[a]

Keywords: Thiophene diols / Porphyrins / Synthetic methods

A series of unsymmetrical thiophene diols has been prepared

in two steps from thiophene in 16–46% yields. The unsym-

metrical thiophene diols containing functionalised aryl

groups were then used as key synthons for the synthesis of

a series of monofunctionalised 21-thia (N₃S), 21,23-dithia

(N₂S₂) and 21-thia-23-oxaporphyrins (N₂SO). Condensation

of one equivalent of unsymmetrical diol with either two

equivalents of aldehyde and three equivalents of pyrrole, one

equivalent of symmetrical 16-thiatripyrrane or one equiva-

thia-, 21,23-dithia- or 21-thia-23-oxaporphyrins in decent

yields. This unsymmetrical diol method is simple, versatile

and gives an access for the first time to any desired mono-

functionalised porphyrins with N₃S, N₂S₂and N₂SO porphy-

rin cores. The use of monofunctionalised N₃S, N₂S₂and

N₂SO porphyrins is further demonstrated by synthesising the

first examples of three new covalently linked diarylethyne-

bridged unsymmetrical dimers containing two different por-

phyrin cores such as N₂S₂-N₄, N₂S₂-N₃S and N₂S₂-N₂SO.

lent of symmetrical 16-oxatripyrrane under standard porphy- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,

rin-forming conditions resulted in monofunctionalised 21-

Germany, 2005)

(N₄core) or an assembly of two different heteroatom-sub-

stituted porphyrins would offer unique dimers which are

expected to have unusual electronic structure and interest-

ing properties. However, very few examples of unsymmetri-

cal porphyrin arrays containing heteroatom-substituted

porphyrins have appeared in the literature^[3]due to the un-

availability of the functionalised heteroporphyrin building

blocks. Heteroporphyrins with one functional group at the

meso position are ideal building blocks for the synthesis of

covalently linked unsymmetrical porphyrin dimers. To the

best of our knowledge, there are only two methods available

in the literature to synthesise monofunctionalised hetero-

atom-substituted porphyrin building blocks. Lindsey and

co-workers^[4]have developed a novel and efficient method

to prepare monofunctionalised 21-thia- and 21-oxaporphy-

rins with ethyne and iodo functional groups at the para po-

sition of the meso-phenyl groups, as shown in Scheme 1. As

noted in Scheme 1, the two key precursors involved in the

synthesis are not easily available, and the method involves

multi-step synthesis, extensive chromatography and vacuum

distillations to purify the precursors. We have recently de-

veloped^[5]a rapid, one-pot synthetic route (Scheme 2) to

prepare monofunctionalised 21-thia- and 21-oxaporphyrins

from 2-(arylhydroxymethyl)thiophene or -furan (thiophene

or furan mono-ol). In this mono-ol method, two equiva-

lents of thiophene or furan mono-ol containing the func-

tionalised aryl group are condensed with two equivalents

of aldehyde and three equivalents of pyrrole under acid-

catalysed conditions followed by simple column chromatog-

raphy to give the desired monofunctionalised 21-thia- or

Introduction

Unsymmetrical porphyrin dimers that consist of two dif-

ferent porphyrin sub-units are suitable models for mimick-

ing electron- and energy-transfer processes of photosynthe-

sis. In the recent past attention has been directed towards

synthesising covalently linked unsymmetrical dimers such

as porphyrin-chlorin, porphyrin-corrole, porphyrin-pheo-

phorbide and porphyrin-phthalocyanine to study the pho-

tosynthesis processes.^[1]A common feature among the vari-

ous unsymmetrical dimers mentioned above is that they all

have similar pyrrole nitrogens as donor atoms. Unsymmet-

rical porphyrin dimers containing two dissimilar cores hav-

ing different donor atoms are expected to possess interest-

ing structural and electronic properties. However, this area

of porphyrin chemistry has largely remained unexplored

due to the unavailability of suitable functionalised porphy-

rin building blocks. The replacement of one or two inner

pyrrole nitrogens of porphyrin with heteroatoms such as S,

O, Se and Te gives heteroatom-substituted porphyrins

which possess quite different properties from normal por-

phyrins (N₄core) in terms of both aromatic character and

their ability to stabilize metals in unusual oxidation states.^[2]

The assembly of such a heteroatom-substituted porphyrin

(N₃S, N₃O, N₂S₂, N₂O₂, N₂SO etc) and normal porphyrin

[a] Department of Chemistry, Indian Institute of Technology,

Bombay, Powai, Mumbai 400076, India

E-mail: ravikanth@chem.iitb.ac.in

Supporting information for this article is available on the

WWW under http://ww w .eurjoc.org or from the author.

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DOI: 10.1002/ejoc.200400887

Eur. J. Org. Chem. 2005, 2500–2517

Monofunctionalised 21-Thia-, 21,23-Dithia-, and 21-Thia-23-oxaporphyrins

FULL PAPER

21-oxaporphyrins (Scheme 2). Although the mono-ol A₂B₂type). In addition to the synthesis of 21-thiaporphyr-

method is very simple, the yields of porphyrins are quite ins, the symmetrical thiophene diols have been explored for

low (2–6%). Furthermore, using this method, one can syn- the synthesis of several novel macrocycles.^[7]There was no

thesise only the monofunctionalised 21-thia- and 21-oxa- method available based on thiophene diols to synthesise

porphyrins. Hence we have developed an alternate method monofunctionalised 21-thiaporphyrins until our recent

using unsymmetrical thiophene diols^[5b]to improve the communication,^[5b]in which we used an unsymmetrical

yields of monofunctionalised 21-thiaporphyrins. The un- thiophene diol in place of the symmetrical thiophene diol

symmetrical diol method is based on the well-established and synthesised for the first time a series of monofunction-

synthetic strategy used for the synthesis of 21-thiaporphyr- alised 21-thiaporphyrins. In this paper, we describe in detail

ins. The 21-thiaporphyrins can be synthesised^[6]by condens- the further importance of the unsymmetrical thiophene di-

ing 2,5-bis(arylhydroxymethyl)thiophene (symmetrical thio- ols as key synthons to synthesise the desired monofunction-

phene diol) with an aldehyde and pyrrole under standard alised heteroporphyrins with three different types of hetero-

porphyrin-forming conditions (Scheme 3). The symmetrical atom-substituted cores (N₃S, N₂S₂and N₂SO). We elabo-

thiophene diol method^[6]is useful to prepare 21-thiaporphy- rate the synthesis and characterisation of a series of unsym-

rins bearing only one type of meso substituent (A₄type) or metrical thiophene diols and a series of monofunctionalised

two types of meso substituents in a cis configuration (cis- 21-thia- (N₃S), 21,23-dithia- (N₂S₂) and 21-thia-23-oxapor-

Scheme 1. Synthetic scheme of Lindsey and co-workers for the preparation of monofunctionalised 21-thia- and 21-oxaporphyrins.

Scheme 2. Mono-ol method for the synthesis of monofunctionalised 21-thia- and 21-oxaporphyrins.

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Scheme 3. Symmetrical and unsymmetrical thiophene diol methods for the preparation of functionalised 21-thiaporphyrins.

phyrin (N₂SO) building blocks. This method is simple and the additional minor spot observed above the major spot

could be due to its diastereomer.^[8]We collected only the

major spot in all diol reactions and used the compound

isolated for the porphyrin reactions. Because the chirality is

lost on porphyrin formation,^[8]no attempts were made to

characterise the very minor spot. We varied the number of

nBuLi equivalents to optimise the conditions for unsym-

metrical thiophene diols. The reaction requires a minimum

of two equivalents of nBuLi to get decent yields of unsym-

metrical thiophene diols because the hydroxyl group of the

thiophene mono-ol is also lithiated during the reactions. Al-

though the yields of unsymmetrical thiophene diols are

moderate (Scheme 4), large quantities of unsymmetrical di-

ols can be prepared easily by this method. Furthermore,

since the aryl group containing the functional group is in-

troduced at the unsymmetrical thiophene diol stage, this al-

lows an easy access to prepare monofunctionalised hetero-

porphyrins containing a desired functional group. The un-

symmetrical thiophene diols 1–14 were characterised by

NMR and IR spectroscopy, mass spectrometry and elemen-

tal analysis. The unsymmetrical nature of the diols is clearly

versatile and the required monofunctionalised heteropor-

phyrin building blocks with N₃S, N₂S₂or N₂SO cores can

be prepared in 100 mg batches in a one-pot reaction. We

also show the use of the monofunctionalised heteroporphy-

rins in the synthesis of the first examples of three covalently

linked diarylethyne-bridged unsymmetrical dimers with dif-

ferent combinations of porphyrin cores such as N₂S₂-N₄,

N₂S₂-N₃S and N₂S₂-N₂SO.

Results and Discussion

Synthesis of Unsymmetrical Thiophene Diols 1–14

The required thiophene mono-ols 2-(phenylhy-

droxymethyl)thiophene and 2-(p-tolylhydroxymethyl)thio-

phene were prepared in 65–70% yields by treating thio-

phene with 1.2 equivalents of nBuLi followed by 1.2 equiva-

lents of benzaldehyde or p-tolualdehyde in THF at 0 °C and

subsequent purification by silica-gel column chromatog-

raphy.^[5a]The unsymmetrical thiophene diols 1–14 were pre-

pared by treating the 2-(phenyl or p-tolylhydroxymethyl)-

thiophene with two equivalents of nBuLi followed by the H NMR spectra, which generally appear as a singlet

1.2 equivalents of functionalised aromatic aldehyde in THF in 2,5-bis(arylhydroxymethyl)thiophene (symmetrical diol),

at 0 °C (Scheme 4). TLC analysis of the crude reaction mix- appear as a multiplet or two sets of doublets in diols 1–14.

ture showed two fast moving minor spots corresponding to Furthermore, the presence of a broad singlet at around δ =

1

evident in their H NMR spectra: the thiophene protons in

1

the unchanged aldehyde and mono-ol, respectively, fol- 2.00–5.00 ppm in the NMR spectrum and a very strong

lowed by one very minor and one major spot which were broad peak at about 3400 cm^–1in the spectra IR indicate

close to each other and correspond to the desired thiophene the presence of hydroxyl groups. The ES mass spectra of 1–

diol. Since the unsymmetrical diols have two chiral centres, 14 show [M⁺], [M⁺– OH] or [M⁺+ Na] peaks, thus con-

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Eur. J. Org. Chem. 2005, 2500–2517

Monofunctionalised 21-Thia-, 21,23-Dithia-, and 21-Thia-23-oxaporphyrins

FULL PAPER

Scheme 4. Synthesis of unsymmetrical thiophene diols 1–14.

firming the identities of the unsymmetrical thiophene diols. the low solubility of the aldehydes under our reaction con-

The elemental analyses were also in agreement with the ditions. Some of these monofunctionalised 21-thiaporphyr-

composition of the diols 1–14.

ins were recently prepared by us^[5a]using the “mono-ol

method”. However, the yields of the monofunctionalised21-

thiaporphyrin building blocks from the “mono-ol method”

are quite low. Although we have not demonstrated the un-

symmetrical diol method with several examples of mono-

functionalised 21-thiaporphyrins, we note that the unsym-

metrical diol method is much superior and more versatile

than than the mono-ol method for preparing the desired

monofunctionalised 21-thiaporphyrins in decent yields.

Furthermore, separation of the mixture of porphyrins is

very straightforward. Absorption spectroscopy is the best

technique to follow the purification of porphyrins on silica

gel column and also to identify the desired 21-thiaporphy-

rin fraction easily, since the absorption spectrum of 21-thia-

porphyrin is quite different from that of H₂TPP and 21,23-

dithiaporphyrin.^[11]We have not made any attempts to sepa-

rate the cis and trans mixture of 21,23-dithiaporphyrin.

Allporphyrin condensation reactions work well under either

Lindsey’s or Adler’s reaction conditions, and no scram-

blingor any other additional porphyrin products were noted

in these reactions.

Synthesis of Monofunctionalised 21-Thiaporphyrins

The monofunctionalised 21-thiaporphyrins were synthe-

sised by condensing one equivalent of the appropriately

functionalised unsymmetrical thiophene diol with two

equivalents of benzaldehyde and three equivalents of pyr-

role under Lindsey’s^[9]or Adler’s^[10]porphyrin-forming con-

ditions (Scheme 5). The condensation is expected to result

in the formation of a mixture of four porphyrins:

5,10,15,20-tetraphenylporphyrin (H₂TPP), the desired

monofunctionalised 21-thiaporphyrin and a cis and trans

mixture of difunctionalised 21,23-dithiaporphyrins.^[5b]The

TLC analysis clearly showed three spots corresponding to

H₂TPP, the desired 21-thiaporphyrin and the cis and trans

mixture of 21,23-dithiaporphyrins. The mixture of porphy-

rins was separated by silica gel column chromatography; the

desired monofunctionalised 21-thiaporphyrin was always

obtained as the second band. Two chromatographic purifi-

cations were required to separate the mixture of porphyrins,

and the pure porphyrins 15–19 were afforded in 2–10%

The porphyrins 15–19 were characterised by NMR and

yields. The low yields in the case of 18 and 19 are due to absorption spectroscopy, mass spectrometry and elemental

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S. Punidha, N. Agarwal, M. Ravikanth

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Scheme 5. Synthesis of monofunctionalised heteroporphyrins 15–31.

analysis. All porphyrins show the [M⁺] ion peak in the ES generally appear as a singlet in the symmetrically substi-

mass spectra and the elemental analyses confirm the com- tuted 21-thiaporphyrin^[2]5,10,15,20-tetraphenyl-21-thiapor-

position of the monofunctionalised 21-thiaporphyrins. In phyrin (STPPH), appear as two sets of signals or a complex

the ¹H NMR spectra, the two thiophene protons, which multiplet in 15–19 due to the unsymmetrical substitution of

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Monofunctionalised 21-Thia-, 21,23-Dithia-, and 21-Thia-23-oxaporphyrins

FULL PAPER

monofunctionalised 21-thiaporphyrins. The absorption Synthesis of Monofunctionalised 21-Thia-23-oxaporphyrins

spectra of 15–19 show four Q-bands and one Soret band

To the best of our knowledge, there is no report of un-

whose peak positions closely match those of STPPH.^[2]

symmetrical porphyrin arrays containing 21-thia-23-oxa-

porphyrin as one of the sub-units. This may be because of

the unavailability of suitable 21-thia-23-oxaporphyrin build-

ing blocks. In general, the reports of heteroporphyrins hav-

Synthesis of Monofunctionalised 21,23-Dithiaporphyrins

ing two different heteroatoms such as S and O in the core

Interestingly, there are very few reports of unsymmetrical

are too few to be able to understand the physico-chemical

porphyrin arrays containing 21,23-dithiaporphyrin as one

properties of such systems.^[14]We have used the unsymmet-

of the sub-units. In 2001, we reported the first synthesis

rical thiophene diols to synthesise for the first time three

of a covalently linked unsymmetrical porphyrin pentamer

monofunctionalised 21-thia-23-oxaporphyrin building

containing one 21,23-dithiaporphyrin unit and four normal

blocks 29–31. The condensation of one equivalent of the

porphyrin units using the tetra-functionalised 21,23-dithia-

appropriate unsymmetrical thiophene diol with one equiva-

porphyrin building block and demonstrated an efficient en-

lent of 16-oxatripyrrane^[14b]under Adler’s or Lindsey’s por-

ergy transfer from a peripheral normal porphyrin unit to

phyrin-forming conditions gave the desired 21-thia-23-oxa-

the central 21,23-dithiaporphyrin unit.^[3c]Recently, we syn-

porphyrin building blocks as the sole product. Since no

thesised a series of mono meso-pyridyl 21,23-dithiaporphy-

other porphyrin was formed due to scrambling, a simple

rin building blocks^[12]and used them for the synthesis of

silica gel column chromatography was used to purify the

non-covalent unsymmetrical dimers. However, there are no

porphyrins. The porphyrins 29–31 were isolated in 6–10%

monofunctionalised 21,23-dithiaporphyrin building blocks

yields and characterised by various spectroscopic tech-

available for the synthesis of covalently linked unsymmetri-

niques. The [M⁺] ion in the ES mass spectra and acceptable

cal porphyrin dimers. We have shown here the use of un-

elemental analysis confirmed the nature of the porphyrins

symmetrical thiophene diols in the synthesis of nine mono-

29–31. In the ¹H NMR spectra of 29–31, the protons corre-

functionalised 21,23-dithiaporphyrin building blocks having

sponding to both thiophene and furan rings are present at

a range of functionalities such as iodo, hydroxy, bromo, cy-

δ = 9.65–9.80 and δ = 9.19–9.26 ppm, respectively, further

ano, ethynyl and nitrophenyl groups at the meso position.

confirming the identity of the compounds. The furan and

The condensation of one equivalent of the appropriate un-

thiophene protons in 5,10,15,20-tetraphenyl-21-thia-23-

symmetrical thiophene diol with one equivalent of known

oxaporphyrin^[2](OSTPP) appear as singlets. However, in

16-thiatripyrrane^[13]under Lindsey’s^[9]or Adler’s^[10]porphy-

monofunctionalised 21-thia-23-oxaporphyrins 29–31 the fu-

rin-forming conditions resulted in the formation of the de-

ran protons appear as a singlet but the thiophene protons

sired monofunctionalised 21,23-dithiaporphyrin as a single

appear always as two sets of signals or a complex multiplet

product (Scheme 5). TLC analysis of the crude reaction

due to the unsymmetrical substitution around the thio-

mixture clearly showed a single spot corresponding to the

phene ring. The pyrrole protons in 29–31, also appear as

required monofunctionalised 21,23-dithiaporphyrin and lot

three sets of doublets or multiplets due to this unsymmetri-

of polymeric material at the base. After standard work-up

cal substitution. The absorption spectra of 29–31 show four

of the reaction mixture, the crude porphyrins were purified

Q-bands and one Soret band with peak positions matching

by one simple silica gel column chromatography and af-

those of OSTPP.^[2]

forded 21,23-dithiaporphyrins 20–28 in 8–19% yields. No

scrambling was noted in these reactions as we did not ob-

serve the formation of any other porphyrin other than the

required monofunctionalised 21,23-dithiaporphyrins. Thus,

Covalently Linked Unsymmetrical Porphyrin Dimers

the present method of using unsymmetrical thiophene diols

The monofunctionalised 21-thia-, 21,23-dithia- and 21-

gives an easy access to any desired monofunctionalised thia-23-oxaporphyrins are suitable building blocks to syn-

21,23-dithiaporphyrin building block in very decent yields. thesise a variety of unsymmetrical porphyrin dimers. As

The porphyrins 20–28 were characterised by NMR and ab- mentioned above, there have been very few reports^[3]of un-

sorption spectroscopy, mass spectrometry and elemental symmetrical dimers containing heteroporphyrins as one of

1

analysis. In the H NMR spectra, unlike the symmetrically the sub-units, and this has limited our understanding of the

substituted 5,10,15,20-tetraphenyl-21,23-dithiaporphyrin^[2]physico-chemical properties of these systems. Recently, we

(S₂TPP), which shows a singlet each for the thiophene and reported the synthesis of five covalently linked unsymmetri-

pyrrole protons, the monofunctionalised 21,23-dithiapor- cal porphyrin dimers containing mainly 21-thia- and 21-

phyrins show two or more signals for the thiophene and oxaporphyrin subunits.^[5a]Interestingly, there is no report

pyrrole protons due to the unsymmetrical substitution of covalently linked dimers containing 21,23-dithia- or 21-

pattern. All porphyrins show an [M⁺] ion peak in the ES thia-23-oxaporphyrins as one of the sub-units. We therefore

mass spectra and the elemental analyses are in agreement synthesised for the first time three covalently linked unsym-

with the composition of the porphyrins 20–28. The absorp- metrical dimers (34–36) having two different porphyrin sub-

tion spectra of 20–28 show the typical four Q-bands and units − dimer 34 contains N₂S₂and N₄sub-units, dimer 35

one Soret band with peak positions matching those of contains N₂S₂and N₃S sub-units and dimer 36 contains

S₂TPP.^[2]

N₂S₂and N₂SO porphyrin sub-units − from the monofunc-

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S. Punidha, N. Agarwal, M. Ravikanth

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tionalised heteroporphyrins synthesised in this report. chromatography with petroleum ether/dichloromethane as

These three diphenylethyne-bridged dimers were synthe- eluent. The excess AsPh₃and the small amounts of unre-

sised using Lindsey’s conditions^[15]for the Sonogashira acted starting monomeric porphyrins were removed with

coupling of an ethynylphenyl porphyrin and an iodophenyl petroleum ether/dichloromethane (80:20) as eluent and the

porphyrin. Under these conditions, the coupling of an equi- desired dimer, with a small amount of impurities, was col-

molar quantity of ethynylphenyl porphyrin and iodophenyl lected with petroleum ether/dichloromethane (65:35) as elu-

porphyrin in dilute conditions can be carried out at very ent. The impure dimer was subjected to a second silica gel

low temperature and in the absence of copper. The low tem- column chromatography with the same solvent mixture to

perature conditions are needed to prevent side reactions, give the pure dimer 34 as a purple solid in 57% yield. Simi-

such as the formation of ethyne oligomerisation products, larly, the N₂S₂-N₃S dimer 35 was prepared by the coupling

and the absence of copper is important since the free-base of 21a and 33, and the N₂S₂-N₂SO dimer 36 by coupling

porphyrins are easily metallated.

of 21a and 29 under the same coupling conditions as used

The required ethynylphenyl porphyrin building block for dimer 34. All three dimer reactions worked smoothly

with an N₂S₂core (21a) was prepared by deprotection of and required two straightforward silica gel column chroma-

21 with KOH in benzene/methanol at 80 °C.^[16]The 5-(4- tographic purifications. Dimers 34–36 are highly soluble in

iodophenyl)-10,15,20-tri(p-tolyl)zinc(ii) porphyrin^[16]32 and all common organic solvents and were characterised by

5-(4-iodophenyl)-10,15,20-tri(p-tolyl)-21-monothiaporphyr- NMR and absorption spectroscopy, mass spectrometry and

in^[5a]33 were prepared by literature methods. The N₂S₂-N₄elemental analysis.

34 dimer was synthesised by coupling of 21a and 32 in tolu-

The ES mass spectra show the expected [M⁺] ion peak

ene/triethylamine at 35 °C in the presence of a catalytic and the elemental analyses closely match the expected com-

amount of Pd₂(dba)₃/AsPh₃(Scheme 6). TLC monitoring positions of the dimers 34–36. The ¹H NMR spectra of

after 12 h showed two very minor spots corresponding to dimers 34–36 are very clean and the resonances of the di-

the starting materials and one major spot corresponding to mers were assigned on the basis of the spectra observed for

the required dimer 34. After standard work-up, the crude the corresponding monomers taken independently. A repre-

reaction mixture was subjected to silica gel column sentative spectrum of dimer 36, along with the spectra of

Scheme 6. Synthesis of unsymmetrical covalent dimer 34 and the structures of dimers 35 and 36.

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Monofunctionalised 21-Thia-, 21,23-Dithia-, and 21-Thia-23-oxaporphyrins

FULL PAPER

the corresponding monomers, are shown in Figure 1. In the ing to the ZnN₄porphyrin sub-unit, appear as four sets of

¹H NMR spectra of the dimers, the resonances correspond- overlapping signals in the δ = 8.69–9.07 ppm region. The

ing to both the porphyrinic sub-units and the bridging ortho and meta protons of the meso tolyl groups and the

groups are present. In the N₂S₂-N₄dimer 34, the four thio- bridging phenyl groups appear in the region δ = 7.42–

phene protons appear as one multiplet resonance in the re- 8.32 ppm and the methyl groups appear at around δ =

gion δ = 9.73–9.76 ppm. The twelve pyrrole protons, four 2.70 ppm. Dimers 35 and 36 were also characterised by

1

belonging to the N₂S₂porphyrin sub-unit and eight belong- comparing the H NMR spectra with their corresponding

monomeric porphyrin units. In N₂S₂-N₃S dimer 35, the four

thiophene protons of the N₂S₂porphyrin unit appeared as

a multiplet in the region δ = 9.68–9.78 ppm and the two

thiophene protons of the N₃S porphyrin sub-unit also ap-

pear as a multiplet in the region δ = 9.48–9.51 ppm. The

ten pyrrole protons of both the porphyrin units appear as

two sets of signals. A broad singlet at δ = 8.94 ppm was

assigned to two pyrrole protons and a complex multiplet in

the region δ = 8.58–8.72 ppm was assigned to eight pyrrole

protons. The aryl protons appear in the region δ = 7.32–

8.28 ppm and the inner NH proton of the N₃S porphyrin

sub-unit appears as a broad singlet at δ = –2.65 ppm. In

¹H NMR spectrum of N₂S₂-N₂SO dimer 36, two multiplet

resonances in the region δ = 9.70–9.73 ppm and δ = 9.61–

9.64 ppm are observed for four and two thiophene protons

of the N₂S₂and N₂SO porphyrin sub-units, respectively.

The two furan protons of the N₂SO porphyrin sub-unit ap-

pear as a singlet at δ = 9.18 ppm. The eight pyrrole protons,

four belonging to the N₂S₂porphyrin sub-unit and the

other four belonging to the N₃S porphyrin sub-unit, appear

as six sets of signals at δ = 8.73 (d, 1 H), 8.70 (s, 2 H), 8.64

(d, 1 H), 8.55 (d, 1 H), 8.51 (d, 1 H) and 8.40–8.43 ppm

(m, 2 H). The aryl protons appear in the region δ = 7.50–

8.18 ppm. A comparison of the chemical shifts of the vari-

ous protons of dimers 34–36 with those of the correspond-

ing individual monomeric porphyrin units indicate only

minor differences, which suggests that the two porphyrin

sub-units in the dimers interact very weakly. This is consis-

tent with earlier reports on covalently linked tetraphen-

ylporphyrin dimers.^[17]

Absorption and Fluorescence Properties of Dimers 34–36

The absorption spectra of dimers 34–36 and the corre-

sponding monomers in toluene were measured at room

temperature; the results are tabulated in Table 1. A com-

parison of the absorption spectra of dimers 34–36 along

Figure 1. ¹H NMR spectra of 21a (a) 29 (b) and 36 (c) recorded in

CDCl₃.

Table 1. Absorption data of dimers 34–36 and their corresponding monomers recorded in toluene.

Porphyrin

Soret band

Absorption Q-bands

λ [nm] (ε×10^–4)

λ [nm] (ε×10^–3)

21a

32

33

29

34

35

36

437 (22.3)

423 (40.6)

431 (27.0)

432 (18.2)

425 (22.9), 439 (20.7)

432 (38.7)

435 (44.3)

514 (22.0), 548 (8.0), 634 (1.6), 697 (4.0)

550 (16.6), 588 (1.9)

515 (20.9), 550 (6.9), 617 (2.8), 677 (5.4)

512 (23.7), 545 (5.4), 645 (1.6), 710 (6.0)

516 (18.9), 551 (13.7) 592 (3.1), 636 (1.6), 699(3.4)

514 (33.3), 548 (9.7), 619 (2.6), 633 (2.1), 678 (3.6), 697 (3.5)

514 (51.0), 547 (13.4), 639 (3.1), 696 (6.6), 708 (8.8)

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S. Punidha, N. Agarwal, M. Ravikanth

FULL PAPER

with their corresponding monomers is shown in Figure 2 corresponding monomers. Thus, the absorption spectral

(see a–c). Dimer 34, which contains N₂S₂porphyrin and studies of dimers 34–36 indicate a weak interaction between

ZnN₄porphyrin sub-units, shows a split Soret band at 425 the two moieties and the two chromophores mostly retain

and 439 nm and Q-bands at 516, 551, 592, 636 and 699 nm. their individual identities.

This spectrum is essentially a linear combination of the

The fluorescence properties of dimers 34–36 and the ap-

spectra of the corresponding monomers with only minor propriate reference compounds were recorded in toluene at

differences in wavelength maxima and band shapes. The So- room temperature. The emission spectra of dimer 34 and

ret band in dimer 34 is split because of the large difference a 1:1 mixture of the corresponding monomers 21a and 32

between the Soret absorption peak maxima of the corre- recorded at 550 nm are shown in Figure 3. As is evident

sponding monomers. Similarly, the absorption spectra of from this figure, in the dimer 34, excitation at 550 nm,

other two dimers 35 and 36 are nearly the sum of the two where the ZnN₄porphyrin sub-unit absorbs strongly (φ =

corresponding monomers. The Soret absorption peak max- 0.033 for ZnTPP), the emission of the ZnN₄porphyrin sub-

ima of these two dimers is not split but appears as a broad unit is quenched by 93.5% (φ = 0.00213) and the strong

band due to the overlap of the Soret band maxima of the emission from the N₂S₂porphyrin sub-unit is observed.

However, when a 1:1 mixture of 21a and 32 was irradiated

at 550 nm, a strong emission was observed mainly from the

ZnN₄porphyrin sub-unit (Figure 3). These results indicate

that there is an efficient energy transfer from the ZnN₄por-

phyrin sub-unit to the N₂S₂porphyrin sub-unit in dimer 34.

The energy transfer that occurs in 34 is independent of the

excitation wavelength. The excitation spectrum recorded for

34 at λ_em= 730 nm matches exactly with the absorption

spectrum, further confirming the efficient energy transfer

between the sub-units. However, in the case of dimers 35

and 36, it is difficult to study the energy-transfer properties

since the porphyrin sub-units of 35 (N₂S₂and N₃S porphy-

rin sub-units) and 36 (N₂S₂and N₂SO porphyrin sub-units)

exhibit overlapping emission spectra, hence no further stud-

ies were carried out on these dimers.

Figure 3. Comparison of emission spectra of dimer 34 (----) and a

1:1 mixture of 21a and 32 (·····) recorded at an excitation wave-

length of 550 nm in toluene. The excitation spectrum of dimer 34

() recorded at an emission wavelength of 750 nm is also shown.

We realized from the steady-state fluorescence study of

dimer 34 that there is an efficient energy transfer between

Figure 2. Q-band absorption spectra of: (a) 21a (), 32 (----), 34 (····);

the sub-units, hence we carried out time-resolved fluores-

(b) 21a (), 33 (-·-·-), 35 (-··-··-); (c) 21a (), 29 (-

ء

-

ء

-), 36 (-

ءء

-

ءء

-)

cence measurements on dimer 34 and its reference com-

recorded in toluene. Their corresponding Soret band absorption

pounds ZnTPP and 21a by exciting at λ = 406 nm in tolu-

spectra are shown in the insets. The concentrations used for Q-

band spectra was 5×10^–5m and for Soret band was 5×10^–6m.

ene at room temperature. The lifetimes of monomers

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Monofunctionalised 21-Thia-, 21,23-Dithia-, and 21-Thia-23-oxaporphyrins

FULL PAPER

ZnTPP (τ = 2.1 ns) and 21a (τ = 1.26 ns) were measured at

Conclusions

600 and 700 nm, respectively, and the observed lifetimes

were closely matched with the reported literature values.^[2]

The fluorescence lifetime of dimer 34 was measured by

monitoring the decay at 600 nm as well as 700 nm corre-

sponding to the ZnN₄and N₂S₂porphyrin sub-units,

respectively. When the emission decay of dimer 34 is moni-

tored at 700 nm the decay is monophasic and exhibits a

lifetime (τ = 1.27 ns) which matches closely that of 21a.

However, when the decay of dimer 34 is monitored at

600 nm, the fluorescence decay curve is biphasic (Figure 4).

The shorter lifetime component (142 ps) accounts for the

major emission of decay (96%) along with the minor

longer-component decay at 2.1 ns. The minor lifetime com-

ponent at 2.1 ns is attributed to the ZnN₄porphyrin impu-

rity present in the dimer 34, and the major component at

142 ps is the decreased lifetime of the ZnN₄porphyrin sub-

unit because of the transfer of energy to N₂S₂porphyrin

sub-unit. From the measured lifetime of the ZnN₄porphy-

rin sub-unit in dimer 34 (τ_{donor–acceptor}) and the lifetime of

In summary, a series of unsymmetrical thiophene diols

have been synthesised in two steps by modifying a known

synthetic strategy. The unsymmetrical thiophene diols,

which can easily be synthesised in 5–7 g batches, were used

as key synthons to prepare the monofunctionalised 21-thia-

(five porphyrins) 21,23-dithia- (nine porphyrins) and 21-

thia-23-oxaporphyrins (three porphyrins) upon condensa-

tion with readily available appropriate precursors under

standard porphyrin-forming conditions. The unsymmetrical

thiophene diol method is versatile and applicable to the syn-

thesis of monofunctionalised 21-thia-, 21,23-dithia- and 21-

thia-23-oxaporphyrins containing a required functional

group such as iodophenyl, ethynylphenyl, nitrophenyl, bro-

mophenyl, hydroxyphenyl and pyridyl groups at the meso

position. To demonstrate the importance of the monofunc-

tionalised heteroporphyrins, we synthesised three novel co-

valently linked unsymmetrical porphyrin dimers containing

two different porphyrin cores. Thus, the unsymmetrical diol

method reported in this paper gives an access to a variety of

unsymmetrical porphyrin dimers containing two different

porphyrin cores. The metallation, optical, electrochemical

and photophysical properties of these dimers should be

interesting and such studies are currently in progress in our

laboratory.

ZnTPP (τ_donor), the rate constant for energy transfer (K_ENT

)

and the yield of energy transfer (φ_ENT) from the ZnN₄por-

phyrin sub-unit to the N₂S₂porphyrin sub-unit can be cal-

culated from Equations (1) and (2).^[17c]

K_ENT= 1/τ_{donor–acceptor}– 1/τ_donor

(1)

Experimental Section

φ_ENT= K_ENT×τ_{donor–acceptor}

(2)

General: ¹H and ¹³C NMR spectra were recorded on a Varian

400 MHz spectrometer using tetramethylsilane as an internal stan-

dard and are reported in δ (ppm) relative to the residual ¹H (of

residual proton; δ = 7.26 ppm) and ¹³C (δ = 77.0 ppm) signals of

CDCl₃. Absorption and fluorescence spectra were obtained with

Perkin–Elmer Lambda 35 and Perkin–Elmer Lambda 55 models,

respectively. IR spectra were recorded on a Nicolet Impact-400 FT-

IR spectrometer and the ES mass spectra were recorded with a Q-

Tof micro (YA-105) mass spectrometer. Elemental analyses were

conducted with a Thermo Finnigan Flash EA 1112. Diethyl ether,

n-hexane, THF and toluene were obtained from S.D Fine chemi-

cals, India, and dried with sodium benzophenone ketyl and distilled

prior to use. Triethylamine was dried over CaH₂and distilled prior

to use. BF₃·OEt₂, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

(DDQ) and N,N,NЈ,NЈ-tetramethylethylenediamine (TMEDA)

were used as obtained from Sigma–Aldrich Chemical Co. All other

chemicals used for the synthesis were reagent grade, unless other-

wise specified. Column chromatography was performed on silica

(Merck, 60–120 mesh) obtained from Sisco Research Laboratories,

India. The mono-ols 2-[hydroxy(phenyl)methyl]thiophene [mono-

ol (a)] and 2-[hydroxy(p-tolyl)methyl]thiophene [mono-ol (b)]^[1]and

the symmetrical tripyrranes 15,17-dihydro-5,10-ditolyl-16-thiatrip-

yrrane (16-thiatripyrrane)^[2]and 15,17-dihydro-5,10-ditolyl-16-ox-

atripyrrane (16-oxatripyrrane)^[2]were synthesised by the reported

methods.

Figure 4. Fluorescence decay profile and the weighted residuals dis-

tribution fit of dimer 34. The excitation wavelength used was

406 nm and emission was detected at 600 nm.

For dimer 34, the rate of excitation energy transfer, K_ENT

,

is 152 ps and the yield of energy transfer, φ_ENT, is 93%.

These results supports the energy transfer from the ZnN₄

porphyrin sub-unit to N₂S₂porphyrin sub-unit. However,

compared to other diarylethyne-bridged porphyrin dimers

reported in the literature,^[17]the rate of energy transfer in

dimer 34 is slow. This may be due to the presence of two

sulfur atoms in one of the porphyrin sub-unit of the dimer,

which enhances the contribution of non-radiative decay

channels.

2-[(4-Bromophenyl)hydroxymethyl]-5-[hydroxy(phenyl)methyl]thio-

phene (1): Freshly distilled dry diethyl ether (20 mL) was added

to a three-necked, round-bottomed flask equipped with a rubber

septum, gas inlet and gas outlet tube. A positive pressure of nitro-

gen was maintained and, after purging nitrogen for 15 min, mono-

ol (a) (0.57 g, 2.91 mmol) was added to it. The temperature of the

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2509

S. Punidha, N. Agarwal, M. Ravikanth

FULL PAPER

reaction flask was maintained at 0 °C. TMEDA (0.88 mL,

5.81 mmol) followed by nBuLi (3.63 mL of ca. 15% solution in

hexane) were added dropwise over 10 min to the stirred solution.

The reaction mixture was allowed to stir for 30 min at 0 °C. An

ice-cold solution of 4-bromobenzaldehyde (0.65 g, 3.49 mmol) in

dry THF (15 mL) was added from another round-bottomed flask

using a siphon apparatus. The mixture was stirred for 15 min and

an ice-cold solution of NH₄Cl (50 mL, ca. 1 m) was added to

quench the excess nBuLi. The organic layer was separated from the

aqueous layer and the aqueous layer was extracted several times

with diethyl ether. All the organic layers were combined and

washed with water and brine and dried with anhydrous Na₂SO₄.

The solvent was removed on a rotary evaporator under reduced

pressure to afford the crude compound. TLC analysis showed three

major spots corresponding to the unreacted mono-ol, unreacted 4-

bromobenzaldehyde, and the desired diol 1. In addition to the

major spot of the diol, we also noted one minor spot just above

the major diol spot, which was not characterised. The aldehyde,

the mono-ol and the minor unidentified fractions were removed by

silica gel column chromatography with petroleum ether/ethyl ace-

tate (90:10) as eluent as eluent, and the major diol fraction 1 was

collected with petroleum ether/ethyl acetate (85:15) as eluent. The

solvent was removed on a rotary evaporator under reduced pressure

to afford the diol 1 as an off-white solid (0.44 g, 40%). M.p. 106–

411.1 (100) [M⁺+ Na], 413.05 (92), 371.1 (98) [M⁺– 17], 373.06

(91). C₁₉H₁₇BrO₂S (389.3): calcd. C 58.62, H 4.40, S 8.24; found C

58.41, H 4.31, S 8.32.

2-{Hydroxy[4-(3-hydroxy-3-methylbut-1-ynyl)phenyl]methyl}-5-

[hydroxy(phenyl)methyl]thiophene (3): Dry diethyl ether (20 mL)

was placed in a three-necked, round-bottomed flask. After purging

nitrogen for 15 min, mono-ol (a) (0.57 g, 2.91 mmol) was added

and stirred for 15 min while maintaining a positive pressure of ni-

trogen. TMEDA (0.88 mL, 5.81 mmol) followed by nBuLi

(3.62 mL of ca. 15% solution in hexane) were then added dropwise

over 10 min and the reaction mixture was allowed to stir for 30 min

at 0 °C. An ice-cooled solution of 4-(3-hydroxy-3-methylbut-1-ynyl)

benzaldehyde (0.66 g, 3.49 mmol) in dry THF (15 mL) was added

and the mixture was stirred for 15 min. The reaction was quenched

by adding an ice-cold NH₄Cl (50 mL, ca. 1 m) solution. After stan-

dard work up, all organic layers were combined and washed several

times with water and brine and dried with anhydrous Na₂SO₄. The

crude compound was subjected to silica gel column chromatog-

raphy and the desired diol 3 collected with petroleum ether/ethyl

acetate (80:20) as eluent. After removal of the solvent on a rotary

evaporator under vacuum the pure diol 3 was isolated as a white

solid (0.18 g, 16 %). M.p. 170–175 °C. IR (KBr film): ν =

˜

3421 cm^–1, 2942, 2868, 2110, 1480, 1484, 1266, 1123, 1077, 827,

705. ¹H NMR (400 MHz, CDCl₃): δ = 1.56 (s, 6 H, CH₃), 2.04 (br.

s, 3 H, OH), 5.94 (s, 1 H, CH), 5.97 (s, 1 H, CH), 6.68–6.70 (m, 2

H, thiophene), 7.29–7.43 (m, 9 H, aryl) ppm. ¹³C NMR (100 MHz,

CDCl₃): δ = 31.45, 65.67, 71.86, 81.93, 94.02, 122.25, 125.09,

125.66, 126.22, 127.70, 131.78, 143.18, 147.71, 151.21 ppm. ES-MS:

m/z (%) = 378.5 (18) [M⁺], 361.4 (100) [M⁺– 17]. C₂₃H₂₂O₃S

(378.5): calcd. C 72.99, H 5.86, S 8.47; found C 73.43, H 5.77, S

8.30.

107 °C. IR (KBr film): ν = 3414 cm^–1, 3010, 2960, 1596, 1489, 1403,

˜

1266, 1123, 1077, 1021, 827, 705, 690. ¹H NMR (400 MHz,

CDCl₃): δ = 2.34 (br. s, 2 H, OH), 5.92 (s, 1 H, CH), 5.97 (s, 1 H,

CH), 6.70–6.74 (m, 2 H, thiophene), 7.28–7.48 (m, 9 H, aryl) ppm.

¹³C NMR (100 MHz, CDCl₃): δ = 121.92, 124.54, 124.73, 126.31,

127.17, 127.47, 128.15, 128.66, 131.67, 141.90, 142.85 ppm. ES-MS

for C₁₈H₁₅BrO₂S (375.3): m/z (%) = 356.99 (48) [M⁺– 17], 359.02

(50). C₁₈H₁₅BrO₂S (375.3): calcd. C 57.61, H 4.03, S 8.54; found C

57.89, H 3.83, S 8.50.

2-{Hydroxy[4-(3-hydroxy-3-methylbut-1-ynyl)phenyl]methyl}-5-

[hydroxy(p-tolyl)methyl]thiophene (4): TMEDA (1.48 mL,

9.79 mmol) and nBuLi (6.12 mL of ca. 15% solution in hexane)

were added, under the same experimental conditions as mentioned

above, to a three-necked, 250-mL, round-bottomed flask contain-

ing mono-ol (b) (1.00 g, 4.90 mmol) in diethyl ether (30 mL). An

ice-cold solution of 4-(3-hydroxy-3-methylbut-1-ynyl)benzaldehyde

(1.10 g, 5.87 mmol) in dry THF (30 mL) was added slowly to the

reaction mixture. The reaction was worked up in the standard way

and the crude compound was purified by silica gel chromatography.

The desired compound 4 was collected with petroleum ether/ethyl

acetate (81:19) as eluent and the solvent was removed on a rotary

evaporator under vacuum to afford pure diol 4 as a white solid in

2-[(4-Bromophenyl)hydroxymethyl]-5-[hydroxy(p-tolyl)methyl]-

thiophene (2): Dry, distilled diethyl ether (30 mL) was placed in a

dry, 250-mL, three-necked, round-bottomed flask fitted with a rub-

ber septum, gas inlet and gas outlet tube and a positive pressure

of nitrogen was maintained. After purging nitrogen for 15 min,

mono-ol (b) (1.00 g, 4.90 mmol) followed by TMEDA (1.48 mL,

9.79 mmol) and nBuLi (6.12 mL of ca. 15% solution in hexane)

were added at 0 °C and stirring was continued for 1 h. Then, an

ice-cold solution of 4-bromobenzaldehyde (1.09 g, 5.87 mmol) in

dry THF (30 mL) was added to the stirred solution. The reaction

mixture was stirred at 0 °C for a further 15 min and then brought

to room temperature. The reaction was quenched by adding an ice-

cold NH₄Cl solution (50 mL, ca. 1 m). The organic layer was

washed with water and brine solution and dried with anhydrous

Na₂SO₄. The solvent was removed on a rotary evaporator under

reduced pressure to afford the crude compound. The crude com-

pound was subjected to silica gel column chromatography for puri-

fication. The unreacted starting materials and the minor unidenti-

fied fractions were removed with petroleum ether/ethyl acetate

(92:8) and the major diol fraction 2 was collected with petroleum

ether/ethyl acetate (84:16) as eluent. The solvent was removed on

a rotary evaporator under vacuum to afford pure diol 2 as a light-

46% yield (0.88 g). M.p. 122–123 °C. IR (KBr film): ν = 3372 cm^–1,

˜

1

3010, 2960, 2870, 2115, 1486, 1436, 1050, 810, 750, 690. H NMR

(400 MHz, CDCl₃): δ = 1.60 (s, 6 H, CH₃), 2.03 (s, 3 H, CH₃), 2.80

(br. s, 3 H, OH), 5.81–5.83 (m, 2 H, CH), 6.78 (m, 2 H, thiophene),

7.27 (m, 4 H, aryl), 7.52 (d, J = 8.2 Hz, 2 H, aryl), 7.80 (d, J =

8.2 Hz, 2 H, aryl) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.81,

25.83, 31.73, 70.67, 70.82, 81.73, 100.29, 124.40, 124.51, 125.51,

128.17, 129.35, 133.20, 134.52, 136.00, 136.55, 140.21, 146.04,

146.42, 146.47, 148.20, 150.71, 152.20 ppm. ES-MS: m/z (%) =

415.2 (22) [M⁺+ Na], 375.2 (55) [M⁺– 17]. C₂₄H₂₄O₃S (392.51):

calcd. C 73.44, H 6.16, S 8.17; found C 73.41, H 6.32, S 8.32.

yellow liquid (0.76 g, 40%). IR (neat): ν = 3457 cm^–1, 3059, 2964,

˜

2856, 1600, 1486, 1436, 1050, 810, 750, 690, 574. ¹H NMR 2-[Hydroxy(4-nitrophenyl)methyl]-5-[hydroxy(phenyl)methyl]thio-

(400 MHz, CDCl₃): δ = 2.23 (s, 3 H, CH₃), 2.80 (br. s, 2 H, OH), phene (5): TMEDA (0.88 mL, 5.81 mmol) and nBuLi (3.63 mL of

5.90–5.98 (m, 2 H, CH), 6.72 (m, 2 H, thiophene), 7.22–7.25 (m, 4

ca. 15% solution in hexane) were added to a three-necked, 250-

mL, round-bottomed flask containing mono-ol (a) (0.57 g,

H, aryl), 7.44 (d, J = 8.2 Hz, 2 H, aryl), 7.60 (d, J = 8.2 Hz, 2 H,

aryl) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.52, 70.60, 71.83, 2.91 mmol) in diethyl ether (20 mL). An ice-cold solution of 4-ni-

120.33, 124.20, 124.55, 126.38, 126.57, 128.11, 129.37, 134.59,

136.00, 136.14, 140.22, 142.11, 142.45 ppm. ES-MS: m/z (%) =

trobenzaldehyde (0.40 g, 3.49 mmol) in dry THF (15 mL) was

added slowly to the reaction mixture. Standard workup and

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Monofunctionalised 21-Thia-, 21,23-Dithia-, and 21-Thia-23-oxaporphyrins

FULL PAPER

chromatography on silica with petroleum ether/ethyl acetate (85:15)

cold solution of 3-bromobenzaldehyde (1.09 g, 5.87 mmol) in dry

THF (30 mL) was added to it and the reaction mixture was stirred

for additional 15 min. An ice-cold NH₄Cl solution (50 mL ca.1 M)

as eluent afforded the desired diol 5 as a white solid (0.29 g, 29%).

M.p. 145–148 °C. IR (KBr film): ν = 3348 cm^–1, 3083, 2859, 1642,

˜

1596, 1525, 1454, 1352, 1275, 1204, 1011, 850, 706. ¹H NMR was added to quench the reaction. After standard workup, the

(400 MHz, CDCl₃): δ = 2.62 (br. s, 2 H, OH), 6.20–6.22 (m, 2 H,

crude compound was purified by silica gel column chromatography

CH), 6.90–6.92 (m, 2 H, thiophene), 7.42–8.16 (m, 9 H, aryl) ppm. using petroleum ether/ethyl acetate (84:16) as eluent to give the diol

ES-MS: m/z (%) = 341.0 (20) [M⁺], 324.3 (100) [M⁺– 17].

C₁₈H₁₅NO₄S (341.4): calcd. C 63.33, H 4.43, N 4.10, S 9.39; found

C 63.61, H 4.27, N 4.36, S 9.20.

8 as a yellow oily liquid (0.72 g, 38%). IR (neat): ν = 3456 cm^–1,

˜

3057, 2856, 1484, 1432, 1050, 810, 750, 690, 570. ¹H NMR

(400 MHz, CDCl₃): δ = 2.22 (s, 3 H, CH₃), 5.50 (s, 2 H, OH), 5.73

(s, 1 H, CH), 5.78 (s, 1 H, CH), 6.52 (d, J = 4.4 Hz, 1 H, thio-

phene), 6.58 (d, J = 4.4 Hz, 1 H, thiophene), 7.02–7.04 (m, 3 H,

aryl), 7.18–7.20 (m, 2 H, aryl), 7.38–7.40 (m, 1 H, aryl), 7.52–7.54

(m, 1 H, aryl), 7.60 (s, 1 H, aryl) ppm. ¹³C NMR (100 MHz,

CDCl₃): δ = 21.32, 70.60, 70.89, 124.22, 124.54, 126.84, 127.00,

128.15, 129.34, 132.55, 133.20, 134.59, 136.11, 136.23, 140.22,

142.72, 143.7 ppm. ES-MS: m/z (%) = 411.1 (100) [M⁺+ Na], 413.1

(98), 371.1 (60) [M⁺– 17], 373.06 (57). C₁₉H₁₇BrO₂S (389.3): calcd.

C 58.62, H 4.40, S 8.24; found C 58.40, H 4.33, S 8.13.

2-{[4-(5,5-Dimethyl-1,3-dioxan-2-yl)phenyl]hydroxymethyl}-5-[hy-

droxy(phenyl)methyl]thiophene (6): Mono-ol (a) (0.38 g,

1.94 mmol), TMEDA (0.58 mL, 3.87 mmol) and nBuLi (2.42 mL

of ca. 15% solution in hexane) were added successively to dry dis-

tilled diethyl ether (20 mL) in a three-necked, round-bottomed

flask under nitrogen, and the reaction mixture was stirred for

30 min at 0 °C. An ice-cold solution of 4-(5,5-dimethyl-1,3-dioxan-

2-yl)benzaldehyde (0.51 g, 2.32 mmol) in dry THF (15 mL) was

then added and the mixture was stirred for 15 min. Ice cold NH₄Cl

(50 mL, ca. 1 m) was added to quench the reaction. After standard

work-up, the crude compound was purified by silica gel column

chromatography with petroleum ether/ethyl acetate (90:10) as elu-

ent to afford diol 6 as a white solid (0.28 g, 35%). M.p. 141–143 °C.

2-[Hydroxy(4-iodophenyl)methyl]-5-[hydroxy(p-tolyl)methyl]thio-

phene (9): TMEDA (1.48 mL, 9.79 mmol) and nBuLi (6.12 mL of

ca. 15% solution in hexane) were added under the same experimen-

tal conditions to a three-necked, 250-mL, round-bottomed flask

IR (KBr film): ν = 3383 cm^–1, 3011, 2936, 2869, 1480, 1494, 1246, containing mono-ol (b) (1.00 g, 4.90 mmol) in diethyl ether

˜

1047, 827, 705. ¹H NMR (400 MHz, CDCl₃): δ = 0.90 (s, 3 H, (30 mL). 4-Iodobenzaldehyde (1.36 g, 5.87 mmol) in dry THF

CH₃), 0.88 (s, 3 H, CH₃), 3.24 (br. s, 2 H, OH), 3.64 (s, 2 H, OCH₂), (30 mL) was added slowly to the reaction mixture followed by

3.74 (s, 2 H, OCH₂), 5.49–5.53 (m, 2 H, CH), 5.60 (s, 1 H, CH),

6.50–6.54 (m, 2 H, thiophene), 7.31–7.47 (m, 9 H, aryl) ppm. ¹³C

NMR (100 MHz, CDCl₃): δ = 15.35, 22.00, 23.18, 36.64, 101.69,

workup and chromatography on silica with petroleum ether/ethyl

acetate (82:18) as eluent to afford the desired diol 9 as a white solid

(0.77 g, 36 %). M.p. 117–118 °C. IR (KBr film): ν = 3450 cm^–1

,

˜

124.26, 125.23, 126.25, 127.43, 129.17, 130.07, 135.84, 138.08, 3059, 2852, 1484, 1432, 1050, 810, 750, 690, 574. ¹H NMR

141.65, 146.13, 147.49, 148.63 ppm. ES-MS: m/z (%) = 393.5 (100)

[M⁺– 17]. C₂₄H₂₆O₄S (410.5): calcd. C 70.22, H 6.38, S 7.81; found

C 70.65, H 6.51, S 7.60.

(400 MHz, CDCl₃): δ = 1.62 (br. s, 2 H, OH), 2.30 (s, 3 H, CH₃),

5.90 (s, 1 H, CH), 5.93 (s, 1 H, CH), 6.72–6.75 (m, 2 H, thiophene),

7.18 (m, 4 H, aryl), 7.24 (d, J = 8.1 Hz, 2 H, aryl), 7.71 (d, J =

8.1 Hz, 2 H, aryl) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.85,

70.62, 70.85, 101.00, 105.32, 124.44, 124.57, 128.13, 129.33, 134.56,

136.04, 136.58, 140.29, 143.71, 146.00, 146.42, 146.91 ppm. ES-MS:

m/z (%) = 459.0 (100) [M⁺+ 23], 419.0 (98) [M⁺– 17]. C₁₉H₁₇IO₂S

(436.3): calcd. C 52.30, H 3.93, S 7.35; found C 52.41, H 3.01, S

7.32.

5-[Hydroxy(phenyl)methyl]-2-[hydroxy(4-pyridyl)methyl]-

thiophene (7): The mono-ol (a) (0.57 g, 2.91 mmol) and nBuLi

(3.63 mL of ca. 15% solution in hexane) were added successively

to freshly distilled dry diethyl ether (20 mL) and stirred for 15 min

under nitrogen at 0 °C. An ice-cold solution of 4-pyridinecarboxal-

dehyde (0.33 mL, 3.49 mmol) in dry THF (15 mL) was then added.

The mixture was stirred for 15 min and ice-cold NH₄Cl (50 mL, ca.

1 m) was added. The aqueous layer was separated, washed with

diethyl ether and mixed with the organic layer. All the organic lay-

ers were combined and washed several times with water and brine

and dried with anhydrous Na₂SO₄. The crude compound was puri-

fied by silica gel column chromatography with dichloromethane/

methanol (97:3) to give the diol 7 as a white solid (0.26 g, 30%).

2-[Hydroxy(4-hydroxyphenyl)methyl)]-5-[hydroxy(p-tolyl)methyl]-

thiophene (10): The diol 10 was prepared following the same

method by adding TMEDA (1.48 mL, 9.79 mmol) and nBuLi

(6.12 mL of ca. 15% solution in hexane) to mono-ol (b) (1.00 g,

4.90 mmol) in diethyl ether (30 mL) followed by an ice-cold solu-

tion of 4-hydroxybenzaldehyde (0.72 g, 5.87 mmol) in dry THF

(30 mL). Purification of the crude product by silica gel column

chromatography with petroleum ether/ethyl acetate (74:26) as elu-

M.p. 79–80 °C. IR (KBr film): ν = 3362 cm^–1, 3011, 2860, 1596,

˜

1

1429, 1403, 1021, 827, 705. H NMR (400 MHz, CDCl₃): δ = 3.70 ent gave the desired diol 10 as a dark-yellow oily liquid (0.51 g,

(br. s, 2 H, OH), 5.82 (s, 1 H, CH), 6.02 (s, 1 H, CH), 6.70 (d, J =

5.2 Hz, 1 H, thiophene), 6.92 (d, J = 5.2 Hz, 1 H, thiophene), 7.21–

7.29 (m, 5 H, aryl), 7.60 (d, J = 7.8 Hz, 2 H, pyridyl), 8.38 (d, J =

7.8 Hz, 2 H, pyridyl) ppm. ¹³C NMR (100 MHz, CDCl₃): δ =

32%). IR (neat): ν = 3380 cm^–1, 3058, 2850, 1486, 1436, 1050, 810,

˜

750, 690. ¹H NMR (400 MHz, CDCl₃): δ = 2.25 (s, 3 H, CH₃),

3.00 (s, 2 H, OH), 5.82–5.85 (m, 2 H, CH), 6.62–6.65 (m, 2 H,

thiophene), 7.16 (d, J = 7.8 Hz, 2 H, aryl), 7.27 (d, J = 7.8 Hz, 2

70.41, 71.87, 121.38, 124.03, 126.25, 126.31, 126.44, 129.10, 129.43, H, aryl), 7.78 (d, J = 8.2 Hz, 2 H, aryl), 8.42 (d, J = 8.2 Hz, 2 H,

137.41, 140.33, 146.26, 148.63, 149.77, 153.22 ppm. ES-MS: m/z

(%) = 298.1 (10) [M⁺], 280.1 (100) [M⁺– 17]. C₁₇H₁₅NO₂S (297.4):

calcd. C 68.66, H 5.08, N 4.71, S 10.78; found C 68.75, H 5.22, N

4.59, S 10.60.

aryl) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 22.53, 70.51, 71.55,

120.12, 124.33, 124.54, 128.17, 129.30, 134.57, 136.00, 139.45,

140.22, 143.73, 145.36, 146.07, 156.92 ppm. ES-MS: m/z (%) =

309.3 (65) [M⁺– 17]. C₁₉H₁₈O₃S (326.4): calcd. C 58.62, H 4.40, S

8.24; found C 70.01, H 5.41, S 9.62.

2-[(3-Bromophenyl)hydroxymethyl]-5-[hydroxy(p-tolyl)-

methyl]thiophene (8): Mono-ol (b) (1.00 g, 4.90 mmol), TMEDA

(1.48 mL, 9.79 mmol) and nBuLi (6.12 mL of ca. 15% solution in

hexane) were added successively to dry, distilled diethyl ether

(30 mL) in a three-necked, round-bottomed flask under nitrogen

and the reaction mixture was stirred for 30 min at 0 °C. An ice-

2-[(4-Cyanophenyl)hydroxymethyl]-5-[hydroxy(p-tolyl)methyl]thio-

phene (11): Diol 11 was prepared by adding TMEDA (1.48 mL,

9.79 mmol) and nBuLi (6.12 mL of ca. 15% solution in hexane) to

mono-ol (b) (1.00 g, 4.90 mmol) in diethyl ether (30 mL) followed

by an ice-cold solution of 4-cyanobenzaldehyde (0.77 g, 5.87 mmol)

Eur. J. Org. Chem. 2005, 2500–2517

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2511

S. Punidha, N. Agarwal, M. Ravikanth

FULL PAPER

in dry THF (30 mL) under the same experimental conditions. Puri-

fication of the crude product by silica gel column chromatography

with petroleum ether/ethyl acetate (81:19) as eluent gave the desired

diol 11 as a white solid (0.66 g, 40%). M.p. 133–135 °C. IR (KBr

leum ether/ethyl acetate (73:27) as eluent gave the desired diol 14

as a white solid (0.85 g, 44%). M.p. 120–122 °C. IR (KBr film): ν

˜

= 3370 cm^–1, 3008, 2954, 2870, 2110, 1484, 1432, 1050, 807, 750,

1

692. H NMR (400 MHz, CDCl₃): δ = 1.61 (s, 6 H, CH₃), 2.23 (s,

film): ν = 3457 cm^–1, 3059, 2856, 1486, 1436, 1050, 810, 750, 690.

3 H, CH₃), 2.80 (s, 2 H, OH), 5.80–5.83 (m, 2 H, CH), 6.60 (d, J

= 4.6 Hz, 1 H, thiophene), 6.74 (d, J = 4.6 Hz, 1 H, thiophene),

7.17 (d, J = 7.8 Hz, 2 H, aryl), 7.36–7.38 (m, 4 H, aryl), 7.78–7.80

(m, 1 H, aryl), 7.88 (s, 1 H, aryl) ppm. ¹³C NMR (100 MHz,

CDCl₃): δ = 21.83, 25.80, 61.57, 70.67, 70.81, 81.73, 100.20, 124.44,

124.50, 125.52, 128.11, 129.34, 133.26, 134.59, 136.07, 136.51,

˜

¹H NMR (400 MHz, CDCl₃): δ = 2.24 (s, 3 H, CH₃), 4.00 (br. s, 2

H, OH), 5.80–5.83 (m, 2 H, CH), 6.72–6.75 (m, 2 H, thiophene),

7.16 (d, J = 7.8 Hz, 2 H, aryl), 7.30 (d, J = 7.8 Hz, 2 H, aryl), 7.61

(d, J = 8.2 Hz, 2 H, aryl), 8.28 (d, J = 8.2 Hz, 2 H, aryl) ppm. ¹³C

NMR (100 MHz, CDCl₃): δ = 21.50, 70.55, 70.82, 111.01, 117.38,

124.34, 124.53, 128.16, 129.33, 134.51, 136.00, 136.56, 139.43, 140.25, 146.08, 146.40, 148.30, 149.74, 152.84, 155.02 ppm. ES-MS:

140.25, 143.71, 145.35, 146.00, 147.45, 147.92 ppm. ES-MS: m/z

(%) = 318.1 (100) [M⁺– 17]. C₂₀H₁₇NO₂S (335.4): calcd. C 71.62,

H 5.11, N 4.18, S 9.56; found C 71.41, H 5.31, N 4.11, S 9.32.

m/z (%) = 376.1 (100) [M⁺– 17]. C₂₄H₂₄O₃S (392.5): calcd. C 73.44,

H 6.16, S 8.17; found C 73.20, H 6.21, S 8.30.

5-(4-Bromophenyl)-10,15,20-triphenyl-21-monothiaporphyrin (15):

Diol 1 (0.34 g, 0.90 mmol), benzaldehyde (0.20 mL, 1.98 mmol)

and pyrrole (0.20 mL, 2.88 mmol) were dissolved in dichlorometh-

ane (120 mL) in a 250-mL, round-bottomed flask and nitrogen was

purged for 10 min. BF₃·OEt₂(0.06 mL of a 2.5 m stock solution)

was added to catalyze the reaction and the stirring was continued

for 1 h. DDQ (0.21 g, 0.92 mmol) was added to oxidize the porphy-

rinogen to porphyrin and stirring was continued for an additional

hour in air. TLC analysis indicated the formation of a mixture of

four porphyrins: tetraphenylporphyrin (H₂TPP), the desired 21-thi-

aporphyrin 15 and cis and trans mixture of 21,23-dithiaporphyrins.

The crude compound containing this mixture of four porphyrins

was subjected to silica gel column chromatography and the desired

N₃S porphyrin 15 with a small amount of impurities was obtained

as the second band with petroleum ether/dichloromethane (75:25)

as eluent. It was further subjected to a second chromatographic

separation with the same solvent mixture to afford pure 15 as a

purple solid (0.07 g, 10%). M.p. Ͼ 300 °C. ¹H NMR (400 MHz,

CDCl₃): δ = –2.70 (s, 1 H, NH), 7.70–7.80 (m, 9 H, aryl), 7.92 (d,

J = 7.2 Hz, 2 H, aryl), 8.10 (d, J = 7.2 Hz, 2 H, aryl), 8.17–8.24

(m, 6 H, aryl), 8.60–8.62 (m, 2 H, β-pyrrole), 8.64 (d, J = 4.8 Hz,

1 H, β-pyrrole), 8.68 (d, J = 4.8 Hz, 1 H, β-pyrrole), 8.92 (s, 2 H,

β-pyrrole), 9.68 (d, J = 5.5 Hz, 1 H, β-thiophene), 9.74 (d, J =

5.5 Hz, 1 H, β-thiophene) ppm. ¹³C NMR (100 MHz, CDCl₃): δ =

122.80, 124.14, 126.77, 127.70, 128.05, 129.75, 130.88, 132.90,

133.37, 134.03, 134.53, 137.74, 135.65, 139.21, 140.07, 141.05,

147.21, 154.66, 157.11, 157.65 ppm. ES-MS: m/z (%) = 710.1 (97)

[M⁺], 712.1 (100%). C₄₄H₂₈BrN₃S (710.7): calcd. C 74.36, H 3.97,

N 5.91, S 4.51; found C 74.82, H 5.14, N 5.75, S 4.41. UV/Vis

(toluene): λ_max(ε) = 430 nm (363 078 m^–1cm^–1), 514 (28 840), 548

(7286), 617 (3631), 677 (5012).

2-[Hydroxy(3-nitrophenyl)methyl]-5-[hydroxy(p-tolyl)methyl]thio-

phene (12): In a three-necked, 250-mL, round-bottomed flask, a

solution of the mono-ol (b) (1.00 g, 4.90 mmol) in diethyl ether

(30 mL) was treated with nBuLi (6.12 mL of ca. 15% solution in

hexane) in the presence of TMEDA (1.48 mL, 9.79 mmol) under

the same experimental conditions. An ice-cold solution of 3-ni-

trobenzaldehyde (0.68 g, 5.87 mmol) was added slowly to the reac-

tion mixture followed by workup and chromatography on silica

with petroleum ether/ethyl acetate (79:21) as eluent to afford the

desired diol 12 as an oily yellow liquid (0.71 g, 41%). IR (neat): ν

˜

= 3457 cm^–1, 3059, 2856, 1520, 1486, 1436, 1346, 1050, 852, 810,

750, 690. ¹H NMR (400 MHz, CDCl₃): δ = 2.30 (s, 3 H, CH₃),

2.81 (s, 2 H, OH), 5.88–6.01 (m, 2 H, CH), 6.68 (d, J = 4.4 Hz, 1

H, thiophene), 6.80 (d, J = 4.4 Hz, 1 H, thiophene), 7.15 (d, J =

7.8 Hz, 2 H, aryl), 7.22–7.25 (m, 4 H, aryl), 7.62 (t, J = 8.1 Hz, 1

H, aryl), 8.10 (s, 1 H, aryl) ppm. ¹³C NMR (100 MHz, CDCl₃): δ

= 21.81, 70.53, 70.60, 124.32, 124.56, 128.17, 129.4, 134.55, 136.08,

136.52, 140.29, 143.74, 145.33, 146.07, 147.80, 148.44, 150.91 ppm.

ES-MS: m/z (%) = 338.4 (100) [M⁺– 17]. C₁₉H₁₇NO₄S (355.4):

calcd. C 64.21, H 4.82, N 3.94, S 9.02; found C 64.41, H 4.71, N

4.08, S 9.22.

2-[Hydroxy(4-pyridyl)methyl]-5-[hydroxy(p-tolyl)methyl]thiophene

(13):^[12]Diol 13 was prepared by the same method from diethyl

ether (30 mL), nBuLi (6.12 mL of a 15% solution in hexane) and

mono-ol (b) (1.00 g, 4.90 mmol) to give the 2,5-dilithiothiophene

salt, which was added to an ice-cold solution of 4-pyridinecarbox-

aldehyde (0.63 g, 5.87 mmol) in dry THF (20 mL). The crude diol

was purified by column chromatography on silica with dichloro-

methane/methanol (96:4). The solvent was removed to afford the

desired diol 13 as a white solid (0.68 g, 45%). M.p. 125–126 °C. IR

5-[4-(3-Hydroxy-3-methylbut-1-ynyl)phenyl]-10,15,20-triphen-

yl-21-monothiaporphyrin (16): One equivalent of diol 3 (0.88 g,

2.31 mmol), two equivalents of benzaldehyde (0.55 mL, 5.39 mmol)

and three equivalents of pyrrole (0.55 mL, 7.93 mmol) were dis-

solved in warm propionic acid (100 mL) and the temperature was

increased slowly to reflux. The reaction mixture was refluxed for

2 h. The propionic acid was distilled off under reduced pressure

and the crude solid was washed several times with water to remove

any traces of acid. A dark slurry was then prepared by dissolving

the crude solid in dichloromethane and loaded onto a silica gel

column with dichloromethane as eluent. The N₄porphyrin

(H₂TPP) eluted as the first band and the desired N₃S porphyrin 16

as the second band in dichloromethane/methanol (98:2). The sol-

vent was removed to afford 16 as a purple solid (0.15 g, 9%). M.p.

(KBr film): ν = 3457 cm^–1, 3060, 2858, 1484, 1430, 1050, 810, 750,

˜

690. ¹H NMR (400 MHz, CDCl₃): δ = 2.27 (s, 3 H, CH₃), 4.81 (br.

s, 2 H, OH), 5.82–5.85 (m, 2 H, CH), 6.59 (d, J = 5.2 Hz, 1 H,

thiophene), 6.62 (d, J = 5.2 Hz, 1 H, thiophene), 7.06 (d, J =

8.8 Hz, 2 H, pyridyl), 7.21–7.25 (m, 4 H, aryl), 8.18 (d, J = 8.8 Hz,

2 H, pyridyl) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.14, 70.42,

71.88, 121.38, 123.11, 124.38, 124.68, 126.31, 129.43, 137.41,

140.73, 146.21, 146.46, 148.63, 149.77, 153.22 ppm. ES-MS: m/z

(%) = 294.1 (100) [M⁺– 17]. C₁₈H₁₇NO₂S (311.4): calcd. C 69.43,

H 5.50, N 4.50, S 10.30; found C 69.28, H 5.41, N 4.30, S 10.18.

2-{Hydroxy[3-(3-hydroxy-3-methylbut-1-ynyl)phenyl]methyl}-5-[hy-

droxy(p-tolyl)methyl]thiophene (14): Diol 14 was prepared by add-

ing TMEDA (1.48 mL, 9.79 mmol) and nBuLi (6.12 mL of ca. 15%

solution in hexane) to mono-ol (b) (1.00 g, 4.90 mmol) in diethyl

ether (30 mL) followed by an ice-cold solution of 3-(3-hydroxy-3-

methylbut-1-ynyl)benzaldehyde (1.10 g, 5.87 mmol) in dry THF

(30 mL) under the same experimental conditions. Purification of

the crude product by silica gel column chromatography with petro-

1

Ͼ 300 °C. H NMR (400 MHz, CDCl₃): δ = –2.70 (s, 1 H, NH),

1.75 (s, 6 H, CH₃), 7.70–7.80 (m, 9 H, aryl), 7.92 (d, J = 7.2 Hz, 2

H, aryl), 8.10 (d, J = 7.2 Hz, 2 H, aryl), 8.17–8.24 (m, 6 H, aryl),

8.59–8.61 (m, 2 H, β-pyrrole), 8.64 (d, J = 4.8 Hz, 1 H, β-pyrrole),

8.68 (d, J = 4.8 Hz, 1 H, β-pyrrole), 8.92 (s, 2 H, β-pyrrole), 9.68

2512

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Eur. J. Org. Chem. 2005, 2500–2517

Monofunctionalised 21-Thia-, 21,23-Dithia-, and 21-Thia-23-oxaporphyrins

FULL PAPER

(d, J = 5.2 Hz, 1 H, β-thiophene), 9.74 (d, J = 5.2 Hz, 1 H, β-

thiophene) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 122.80, 124.14,

thiophene), 9.77 (d, J = 5.2 Hz, 1 H, β-thiophene) ppm. ES-MS:

m/z (%) = 633.3 (50) [M⁺]. C₄₃H₂₈N₄S (632.8): calcd. C 81.62, H

126.77, 127.70, 129.75, 130.88, 132.90, 133.37, 134.03, 134.53, 4.46, N 8.84, S 5.01; found C 81.95, H 4.69, N 8.59, S 5.20. UV/

137.74, 135.65, 139.21, 140.07, 141.05, 147.21, 154.66, 157.11, Vis (toluene): λ_max(ε) = 428 nm (95 499 m^–1cm^–1), 513 (8318), 547

157.65 ppm. ES-MS: m/z (%) = 714.4 (100) [M⁺]. C₄₉H₃₅N₃SO

(713.9): calcd. C 82.44, H 4.94, N 5.89, S 4.49; found C 82.76, H

5.16, N 5.62, S; 4.30. UV/Vis (toluene): λ_max(ε) = 430 nm

(186 209 m^–1cm^–1), 514 (15 488), 549 (5370), 617 (2399), 678 (3020).

(3236), 615 (1549), 675 (2512).

5-[4-(5,5-Dimethyl-1,3-dioxan-2-yl)phenyl]-10,15,20-triphenyl-21-

monothiaporphyrin (19): Diol 6 (0.25 g, 0.61 mmol), benzaldehyde

(0.14 mL, 1.34 mmol) and pyrrole (0.14 mL, 1.95 mmol) were con-

5-(4-Ethynylphenyl)-10,15,20-triphenyl-21-monothiaporphyrin (16a): densed in dichloromethane (100 mL) in the presence of BF₃·OEt₂

Porphyrin 16 (0.12 g, 0.l7 mmol) was dissolved in benzene/meth-

anol (3:1, 40 mL) and an excess of potassium hydroxide (0.02 g)

was added. The reaction mixture was refluxed at 80 °C overnight

in a Dean–Stark apparatus. TLC analysis showed the completion

of reaction after 12 h. The crude compound was subjected to silica

gel column chromatography with a petroleum ether/dichlorometh-

(0.03 mL of a 2.5 m stock solution) under nitrogen for 1 h. DDQ

(0.21 g, 0.99 mmol) was added and reaction mixture was stirred for

an additional hour in air. The solvent was removed on a rotary

evaporator under vacuum and the crude solid was purified by col-

umn chromatography. The desired N₃S porphyrin 19 eluted with

petroleum ether/dichloromethane (35:65) as eluent and the solvent

ane mixture (50:50) as eluent to afford the pure desired porphyrin was removed to afford 19 as a purple solid (0.01 g, 2%). M.p. Ͼ

1

16a as a purple solid (0.09 g, 80%). H NMR (400 MHz, CDCl₃): 300 °C. ¹H NMR (400 MHz, CDCl₃): δ = –2.69 (s, 1 H, NH), 0.99

δ = –2.71 (s, 1 H, NH), 3.32 (s, 1 H, CH), 7.76–7.95 (m, 11 H,

aryl), 8.20–8.24 (m, 8 H, aryl), 8.66 (m, 4 H, β-pyrrole), 8.93 (s, 2

H, β-pyrrole), 9.73–9.76 (m, 2 H, β-thiophene) ppm. ES-MS: m/z

(%) = 656.2 (100) [M⁺]. C₄₆H₂₉N₃S (655.8): calcd. C 84.24, H 4.46,

N 6.41, S 4.89; found C 84.57, H 4.71, N 6.26, S 4.70. UV/Vis

(toluene): λ_max(ε) = 430 nm (281 838 m^–1cm^–1), 514 (23 442), 548

(6607), 618 (2884), 677 (3981).

(s, 6 H, CH₃), 3.90 (s, 4 H, OCH₂), 5.65 (s, 1 H, CH), 7.72–7.80

(m, 11 H, aryl), 8.18–8.26 (m, 8 H, aryl), 8.66 (d, J = 4.2 Hz, 2 H,

β-pyrrole), 8.83 (s, 2 H, β-pyrrole), 8.92–8.94 (m, 2 H, β-pyrrole),

9.72 (m, 2 H, β-thiophene) ppm. ES-MS: m/z (%) = 746.1 (100)

[M⁺] C₅₀H₃₉N₃O₂S (745.9): calcd. C 80.51, H 5.27, N 5.63, S 4.30;

found C 80.69, H 5.41, N 5.76, S 4.11. UV/Vis (toluene): λ_max(ε)

= 439 nm (104 713 m^–1cm^–1), 513 (10 965), 551 (2951), 619 (2818),

680 (3388).

5-(4-Nitrophenyl)-10,15,20-triphenyl-21-monothiaporphyrin (17):

Diol 5 (0.25 g, 0.73 mmol), benzaldehyde (0.16 mL, 1.61 mmol)

and pyrrole (0.16 mL, 2.30 mmol) were dissolved in dry dichloro-

methane (80 mL) in a 250-mL round-bottomed flask. After 10 min

purging with nitrogen, BF₃·OEt₂(0.05 mL of a 2.5 m stock solu-

tion) was added to initiate the reaction. After 1 h stirring, DDQ

(0.17 g, 0.74 mmol) was added and stirring was continued in air for

an additional hour. The crude compound was subjected to silica gel

chromatography and the desired N₃S porphyrin 17 was collected as

the second band with petroleum ether/dichloromethane (65:35) as

eluent. The solvent was removed to afford 17 as a purple solid

(0.60 g, 12%). M.p. Ͼ 300 °C. ¹H NMR (400 MHz, CDCl₃): δ =

–2.68 (s, 1 H, NH), 7.22–7.80 (m, 9 H, aryl), 8.17–8.24 (m, 6 H,

aryl), 8.38 (d, J = 7.4 Hz, 2 H, aryl), 8.56 (d, J = 4.8 Hz, 1 H, β-

pyrrole), 8.60–8.64 (m, 4 H, β-pyrrole and aryl), 8.68 (d, J = 4.8 Hz,

1 H, β-pyrrole), 8.94 (s, 2 H, β-pyrrole), 9.60 (d, J = 5.4 Hz, 1 H, β-

thiophene), 9.77 (d, J = 5.4 Hz, 1 H, β-thiophene) ppm. ¹³C NMR

(100 MHz, CDCl₃): δ = 122.74, 124.45, 124.84, 126.78, 127.73,

5-(4-Bromophenyl)-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin (20):

A solution of diol 2 (0.50 g, 1.29 mmol) and 16-thiatripyrrane

(0.54 g, 1.29 mmol) in dichloromethane (130 mL) was placed in a

250-mL, one-necked, round-bottomed flask fitted with a nitrogen

gas bubbler. After purging nitrogen gas for 15 min, condensation

of diol and tripyrrane was initiated at room temperature by the

addition of a catalytic amount of BF₃·OEt₂(0.05 mL of a 2.5 m

stock solution). The reaction mixture was stirred at room tempera-

ture for 1 h under nitrogen. DDQ (0.29 g, 1.10 mmol) was added

and the reaction mixture was stirred in air for an additional hour.

The progress of the reaction was checked by absorption spec-

troscopy, which showed bands characteristic of the desired porphy-

rin. TLC analysis showed the formation of the required compound

as the sole product. The solvent was removed under reduced pres-

sure and the crude compound was purified by silica gel column

chromatography with petroleum ether/dichloromethane (63:37) as

eluent to afford the desired porphyrin 20 as a purple solid (0.10 g,

128.13, 129.30, 129.43, 132.33, 133.29, 134.48, 134.82, 135.13, 10%). M.p. Ͼ 300 °C. IR (KBr film): ν = 3072 cm^–1, 2930, 2864,

˜

135.94, 136.28, 139.24, 139.40, 142.25, 146.74, 146.90, 147.76, 1456, 970, 790, 585. ¹H NMR (400 MHz, CDCl₃): δ = 2.71 (s, 9

147.93 ppm. ES-MS: m/z (%) = 677.4 (100) [M⁺]. C₄₄H₂₈N₄O₂S

(676.8): calcd. C 79.09, H 4.17, N 8.28, S 4.74; found C 79.34, H

4.29, N 8.11, S 4.60. UV/Vis (toluene): λ_max(ε) = 432 nm

(316 228 m^–1cm^–1), 515 (29 512), 550 (9333), 616 (4365), 676 (5248).

H, CH₃), 7.60 (d, J = 7.8 Hz, 6 H, aryl), 7.72 (d, J = 8.1 Hz, 2 H,

aryl), 7.92 (d, J = 8.1 Hz, 2 H, aryl), 8.11 (d, J = 7.8 Hz, 6 H, aryl),

8.62 (d, J = 4.5 Hz, 1 H, β-pyrrole), 8.68–8.70 (m, 3 H, β-pyrrole),

9.61 (d, J = 5.1 Hz, 1 H, β-thiophene), 9.66–9.70 (m, 3 H, β-thio-

phene) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.64, 122.54,

123.05, 123.47, 124.09, 124.42, 127.67, 128.81, 129.04, 131.22,

133.16, 135.09, 136.53, 138.44, 141.29, 144.65, 145.53, 147.65,

148.26 ppm. ES-MS: m/z (%) = 769.4 (85) [M⁺], 771.3 (100%).

C₄₇H₃₃BrN₂S₂(769.8): calcd. C 73.33, H 4.32, N 3.64, S 8.33;

found C 73.00, H 4.50, N 3.70, S 8.10. UV/Vis (toluene): λ_max(ε)

= 437 nm (223 938 m^–1cm^–1), 515 (21 561), 548 (7138), 634 (1583),

697 (4104).

10,15,20-Triphenyl-5-(4-pyridyl)-21-monothiaporphyrin (18): A solu-

tion of diol 7 (0.50 g, 1.67 mmol), benzaldehyde (0.40 mL,

3.92 mmol) and pyrrole (0.38 mL, 5.48 mmol) in hot propionic acid

(70 mL) was refluxed for 2 h. The propionic acid was then removed

under vacuum and the crude compound was loaded onto a silica

gel chromatography column with dichloromethane as eluent. The

N₄porphyrin (H₂TPP) eluted as the first band and the desired

N₃S porphyrin 18 eluted as the second band with dichloromethane/

methanol (98:2) as eluent. The solvent was removed on a rotary

evaporator to afford 18 as a purple solid (0.02 g, 2 %). M.p. Ͼ

300 °C. ¹H NMR (400 MHz, CDCl₃): δ = –2.70 (s, 1 H, NH), 7.71–

7.82 (m, 9 H, aryl), 8.16–8.20 (m, 6 H, aryl), 8.25 (d, J = 7.6 Hz,

5-[4-(3-Hydroxy-3-methylbut-1-ynyl)phenyl]-10,15,20-tri(p-tolyl)-

21,23-dithiaporphyrin (21): A solution of 4 (0.50 g, 1.28 mmol) and

16-thiatripyrrane (0.54 g, 1.28 mmol) in 125 mL of propionic acid

was refluxed for 3 h. The progress of the reaction was checked by

2 H, pyridyl), 8.60–8.69 (m, 4 H, β-pyrrole), 8.94 (s, 2 H, β-pyrrole), absorption spectroscopy, which showed bands characteristic of the

9.02 (d, J = 7.6 Hz, 2 H, pyridyl), 9.65 (d, J = 5.2 Hz, 1 H, β- desired porphyrin. The excess propionic acid was removed under

Eur. J. Org. Chem. 2005, 2500–2517

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2513

S. Punidha, N. Agarwal, M. Ravikanth

FULL PAPER

vacuum and the resultant black solid was washed several times with

warm water and dried in an oven at 100 °C. The crude product was

then purified by silica gel column chromatography with petroleum

ether/dichloromethane (15:85) as eluent to afford the desired por-

phyrin 21 as a purple solid (0.19 g, 19%). M.p. Ͼ 300 °C. IR (KBr

1.15 mmol) were condensed in 115 mL of dichloromethane under

nitrogen in the presence of a catalytic amount of BF₃·OEt₂

(0.05 mL of a 2.5 m stock solution) for 1 h under nitrogen followed

by oxidation with DDQ (0.26 g, 1.15 mmol) in air for an additional

hour. The crude mixture was purified by silica gel column

chromatography with petroleum ether/dichloromethane (70:30) as

eluent. The desired porphyrin was collected as a purple solid

film): ν = 3360 cm^–1, 3070, 2942, 2860, 1520, 1456, 1050, 972, 790.

˜

¹H NMR (400 MHz, CDCl₃): δ = 1.44 (s, 6 H, CH₃), 2.73 (s, 9 H,

CH₃), 7.62 (d, J = 7.2 Hz, 6 H, aryl), 7.86 (d, J = 8.0 Hz, 2 H,

aryl), 8.12 (d, J = 7.2 Hz, 6 H, aryl), 8.21 (d, J = 8.0 Hz, 2 H, aryl),

8.63 (d, J = 4.6 Hz, 1 H, β-pyrrole), 8.72 (m, 3 H, β-pyrrole), 9.63

(d, J = 4.6 Hz, I H, β-thiophene), 9.69–9.72 (m, 3 H, β-thiophene)

ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.61, 29.79, 31.68, 65.90,

(0.13 g, 14%). M.p. Ͼ 250 °C. IR (KBr film): ν = 3070 cm^–1, 2942,

˜

1

2860, 1456, 972, 790, 555. H NMR (400 MHz, CDCl₃): δ = 2.68

(s, 9 H, CH₃), 7.60 (d, J = 7.6 Hz, 6 H, aryl), 7.94 (d, J = 7.8 Hz,

2 H, aryl), 8.10 (d, J = 7.6 Hz, 6 H, aryl), 8.38 (d, J = 7.8 Hz, 2

H, aryl), 8.63 (d, J = 4.4 Hz, 1 H, β-pyrrole), 8.68–8.70 (m, 3 H,

121.6, 123.2, 127.1, 128.32, 130.80, 132.75, 134.21, 134.75, 135.01, β-pyrrole), 9.61 (d, J = 4.4 Hz, 1 H, β-thiophene), 9.68–9.70 (m, 3

135.63, 137.97, 138.27, 141.34, 148.06, 155.90, 156.41 ppm. ES-MS:

H, β-thiophene) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.62,

m/z (%) = 773.5 (100) [M⁺]. C₅₂H₄₀N₂OS₂(773.0): calcd. C 80.80, 100.51, 123.00, 123.44, 123.62, 124.09, 127.45, 128.05, 129.56,

H 5.22, N 3.62, S 8.30; found C 80.90, H 5.32, N 3.51, S 8.52. UV/ 131.23, 133.12, 136.06, 137.53, 138.37, 142.28, 145.13, 146.58,

Vis (toluene): λ_max(ε) = 438 nm (265 964 m^–1cm^–1), 515 (24 193), 149.24 ppm. ES-MS: m/z (%) = 817.2 (100) [M⁺]. C₄₇H₃₃IN₂S₂

549 (8949), 635 (1870), 698 (4830).

(816.8): calcd. C 69.11, H 4.07, N 3.43, S 7.85; found C 69.30, H

4.40, N 3.20, S 7.68. UV/Vis (toluene): λ_max(ε) = 437 nm

(212 508 m^–1cm^–1), 514 (19 313), 548 (5837), 633 (1356), 697 (3473).

5-(4-Ethynylphenyl)-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin

(21a): Porphyrin 21 (0.05 g, 0.07 mmol) was dissolved in benzene/

methanol (3:1, 40 mL) in a 250-mL, round bottomed flask and

excess potassium hydroxide (0.02 g) was added. The reaction mix-

ture was refluxed at 80 °C in a Dean–Stark apparatus. TLC analysis

confirmed completion of the reaction after 12 h. The excess solvent

was removed under vacuum and the crude compound was sub-

jected to silica gel column chromatography with petroleum ether/

dichloromethane (60:40) as eluent to afford the pure desired por-

phyrin 21a as a purple solid (0.05 g, 80%). M.p. Ͼ 300 °C. IR (KBr

5-(4-Hydroxyphenyl)-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin

(24): Diol 10 (0.50 g, 1.53 mmol) was condensed with 16-thiatripyr-

rane (0.65 g, 1.53 mmol) in propionic acid (125 mL) and the mix-

ture was refluxed for 2 h. The crude compound was purified by

silica gel column chromatography with petroleum ether/dichloro-

methane (15:85) as eluent to afford porphyrin 24 as a purple solid

(0.09 g, 8%). M.p. Ͼ 300 °C. IR (KBr film): ν = 3372 cm^–1, 3070,

˜

2942, 2860, 1456, 1220, 1050, 972, 790. ¹H NMR (400 MHz,

CDCl₃): δ = 2.73 (s, 9 H, CH₃), 7.64 (d, J = 7.4 Hz, 6 H, aryl),

7.96 (d, J = 8.0 Hz, 2 H, aryl), 8.14 (d, J = 7.4 Hz, 6 H, aryl), 8.44

(d, J = 8.0 Hz, 2 H, aryl), 8.66 (d, J = 4.8 Hz, 1 H, β-pyrrole),

8.72–8.74 (m, 3 H, β-pyrrole), 9.63 (d, J = 4.8 Hz, I H, β-thio-

phene), 9.71–9.73 (m, 3 H, β-thiophene) ppm. ¹³C NMR

(100 MHz, CDCl₃): δ = 21.65, 123.67, 124.08, 127.44, 128.08,

130.00, 134.29, 135.16, 136.02, 137.51, 138.31, 142.26, 146.27,

147.55, 149.19, 152.24, 154.28 ppm. ES-MS: m/z (%) = 707.2 (100)

[M⁺]. C₄₇H₃₄N₂OS₂(706.9): calcd. C 79.85, H 4.85, N 3.96, S 9.07;

found C 79.95, H 4.70, N 4.10, S 9.05. UV/Vis (toluene): λ_max(ε)

= 438 nm (144 369 m^–1cm^–1), 514 (16 150), 549 (5626), 634 (1180),

698 (2245).

film): ν = 3311 cm^–1, 3070, 2942, 2860, 2120, 1520, 1456, 1240,

˜

1050, 972, 790, 630. ¹H NMR (400 MHz, CDCl₃): δ = 2.70 (s, 9

H, CH₃), 7.61 (d, J = 7.2 Hz, 6 H, aryl), 7.94 (d, J = 8.0 Hz, 2 H,

aryl), 8.12 (d, J = 7.2 Hz, 6 H, aryl), 8.20 (d, J = 8.0 Hz, 2 H, aryl),

8.64 (d, J = 4.4 Hz, 1 H, β-pyrrole), 8.69–8.71 (m, 3 H, β-pyrrole),

9.62 (d, J = 4.4 Hz, I H, β-thiophene), 9.68–9.71 (m, 3 H, β-thio-

phene) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.61, 78.59,

121.95, 128.31, 131.29, 132.54, 134.18, 134.55, 134.92, 135.75,

135.93, 138.32, 141.98, 147.52, 147.80, 148.19, 155.95, 156.54,

156.60, 156.67 ppm. ES-MS: m/z (%) = 715.2 (100) [M⁺].

C₄₉H₃₄N₂S₂(714.9): calcd. C 82.31, H 4.79, N 3.92, S 8.97; found C

82.40, H 4.62, N 3.91, S 8.92. UV/Vis (toluene): λ_max(ε) = 437 nm

(222 831 m^–1cm^–1), 514 (21 966), 548 (7963), 633 (1603), 697 (4002).

5-(4-Cyanophenyl)-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin (25):

Porphyrin 25 was prepared by the [3+1] condensation of diol 11

(0.50 g, 1.49 mmol) with 16-thiatripyrrane (0.63 g, 1.49 mmol) in

dry dichloromethane (150 mL) in the presence of a catalytic

amount of BF₃·OEt₂(0.06 mL of a 2.5 m stock solution) for 1 h

under nitrogen followed by oxidation with DDQ (0.34 g,

1.49 mmol) in air for an additional hour. The crude product was

purified by silica gel column chromatography with petroleum ether/

dichloromethane (50:50) as eluent to give 25 as a purple solid in

5-(3-Bromophenyl)-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin (22):

Diol 8 (0.50 g, 1.29 mmol), 16-thiatripyrrane (0.54 g, 1.29 mmol),

BF₃·OEt₂(0.05 mL of a 2.5 m stock solution) and DDQ (0.29 g,

1.41 mmol) in 130 mL of dichloromethane under similar reaction

conditions as mentioned above gave 22 as a purple lustrous solid

(0.14 g, 11%). M.p. Ͼ 250 °C. IR (KBr film): ν = 3069 cm^–1, 2928,

˜

1

2860, 1456, 972, 790, 580. H NMR (400 MHz, CDCl₃): δ = 2.71

(s, 9 H, CH₃), 7.58 (d, J = 7.6 Hz, 6 H, aryl), 7.62 (m, 1 H, aryl),

7.86 (m, 2 H, aryl), 8.11 (d, J = 7.6 Hz, 6 H, aryl), 8.39 (s, 1 H,

aryl), 8.64 (d, J = 5.2 Hz, 1 H, β-pyrrole), 8.68–8.70 (m, 3 H, β-

pyrrole), 9.61 (d, J = 5.2 Hz, I H, β-thiophene), 9.69–9.70 (m, 3 H,

β-thiophene) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.62,

122.54, 123.08, 123.43, 124.08, 124.49, 127.60, 128.85, 129.09,

131.22, 133.15, 135.00, 136.56, 138.48, 141.22, 144.65, 145.58,

147.69, 148.24 ppm. ES-MS: m/z (%) = 769.1 (74) [M⁺], 771.1

(100%). C₄₇H₃₃BrN₂S₂(769.82): calcd. C 73.33, H 4.32, N 3.64, S

8.33; found C 73.10, H 4.42, N 3.62, S 8.11. UV/Vis (toluene):

λ_max(ε) = 437 nm (231 705 m^–1cm^–1), 514 (22 366), 548 (6708), 633

(1553), 697 (4060).

12% yield (0.13 g). M.p. Ͼ 250 °C. IR (KBr film): ν = 3068 cm^–1,

˜

1

2960, 2858, 2220, 1454, 972, 760. H NMR (400 MHz, CDCl₃): δ

= 2.72 (s, 9 H, CH₃), 7.62 (d, J = 7.2 Hz, 6 H, aryl), 7.90 (d, J =

7.6 Hz, 2 H, aryl), 8.12 (d, J = 7.2 Hz, 6 H, aryl), 8.34 (d, J =

7.6 Hz, 2 H, aryl), 8.54 (d, J = 4.6 Hz, 1 H, β-pyrrole), 8.70–8.72

(m, 3 H, β-pyrrole), 9.52 (d, J = 4.8 Hz, 1 H, β-thiophene), 9.70–

9.72 (m, 3 H, β-thiophene) ppm. ¹³C NMR (100 MHz, CDCl₃): δ

= 21.66, 123.64, 124.08, 127.49, 128.00, 130.06, 134.72, 135.91,

136.50, 137.75, 138.63, 142.82, 146.32, 147.75, 149.51, 152.82,

154.62 ppm. ES-MS: m/z (%) = 716.2 (100) [M⁺]. C₄₈H₃₃N₃S₂

(715.9): calcd. C 80.52, H 4.65, N 5.87, S 8.96; found C 80.30, H

5-(4-Iodophenyl)-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin (23): 4.50, N 5.60, S 8.68. UV/Vis (toluene): λ_max(ε) = 438 nm

Diol 9 (0.50 g, 1.15 mmol) and 16-thiatripyrrane (0.48 g,

(220 808 m^–1cm^–1), 515 (21 454), 549 (7247), 634 (1597), 697 (4045).

2514

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Eur. J. Org. Chem. 2005, 2500–2517

Monofunctionalised 21-Thia-, 21,23-Dithia-, and 21-Thia-23-oxaporphyrins

FULL PAPER

5-(3-Nitrophenyl)-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin (26):

Diol 12 (0.50 g, 1.41 mmol) and 16-thiatripyrrane (0.59 g,

1.41 mmol) were condensed in the presence of BF₃·OEt₂(0.06 mL

of a 2.5 m stock solution) in 140 mL of dichloromethane under

nitrogen for 1 h followed by oxidation with DDQ (0.32 g,

1.41 mmol) in air. Column chromatography on silica with petro-

leum ether/dichloromethane (45:55) as eluent gave pure 26 as a

purple lustrous solid (0.10 g, 10%). M.p. Ͼ 250 °C. IR (KBr film):

nitrogen in the presence of a catalytic amount of BF₃·OEt₂

(0.05 mL of a 2.5 m stock solution) for 1 h followed by the oxi-

dation with DDQ (0.26 g, 1.15 mmol). Purification on a silica gel

chromatography column with petroleum ether/dichloromethane

(65:35) as eluent afforded the required porphyrin 29 as a purple

solid (0.07 g, 8%). M.p. Ͼ 250 °C. IR (KBr film): ν = 3070 cm^–1,

˜

1

2940, 2868, 1456, 972, 791, 558. H NMR (400 MHz, CDCl₃): δ =

2.72 (s, 9 H, CH₃), 7.53 (d, J = 7.6 Hz, 4 H, aryl), 7.61 (d, J =

7.6 Hz, 2 H, aryl), 7.94 (d, J = 7.6 Hz, 2 H, aryl), 8.10 (d, J =

7.6 Hz, 6 H, aryl), 8.07 (d, J = 7.6 Hz, 2 H, aryl), 8.52 (d, J =

4.6 Hz, 2 H, β-pyrrole), 8.57 (d, J = 4.6 Hz, 2 H, β-pyrrole), 9.19

ν = 3074 cm^–1, 2962, 2852, 1520, 1454, 1340, 970, 850, 762. ¹H

˜

NMR (400 MHz, CDCl₃): δ = 2.71 (s, 9 H, CH₃), 7.62 (d, J =

7.5 Hz, 6 H, aryl), 7.78–7.80 (m, 2 H, aryl), 8.13 (d, J = 7.5 Hz, 6

H, aryl), 8.54–8.56 (m, 1 H, aryl), 8.60 (d, J = 4.4 Hz, 1 H, β- (s, 2 H, β-furan), 9.65 (d, J = 4.8 Hz, 1 H, β-thiophene), 9.73 (d, J

pyrrole), 8.72–8.75 (m, 3 H, β-pyrrole), 9.81 (s, 1 H, aryl), 9.58 (d,

J = 5.1 Hz, 1 H, β-thiophene), 9.74–9.78 (m, 3 H, β-thiophene)

= 4.8 Hz, 1 H, β-thiophene) ppm. ¹³C NMR (100 MHz, CDCl₃):

δ = 21.62, 22.00, 122.00, 128.26, 131.32, 132.49, 134.78, 135.73,

ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.65, 123.66, 124.08, 138.06, 138.32, 142.03, 147.47, 147.76, 148.00, 148.15, 156.07,

127.49, 128.00, 130.05, 134.28, 135.17, 136.02, 137.51, 138.34, 156.58, 156.66, 156.72 ppm. ES-MS: m/z (%) = 801.2 (100) [M⁺].

142.22, 146.27, 147.54, 149.15, 152.22, 154.28 ppm. ES-MS: m/z

(%) = 736.17 (100) [M⁺]. C₄₇H₃₃N₃O₂S₂(735.92): calcd. C 76.70,

H 4.52, N 5.71, S 8.71; found C 76.60, H 4.50, N 5.60, S 8.58. UV/

C₄₇H₃₃IN₂OS (800.8): calcd. C 70.49, H 4.15, N 3.50, S 4.00; found

C 70.20, H 4.02, N 3.62, S 4.11. UV/Vis (toluene): λ_max(ε) =

432 nm (181 906 m^–1cm^–1), 512 (23 664), 545 (5396), 645 (1584),

Vis (toluene): λ_max(ε) = 437 nm (179 311 m^–1cm^–1), 514 (16 825), 710 (5963).

548 (5115), 634 (1167), 697 (3050).

5-(3-Bromophenyl)-10,15,20-tri(p-tolyl)-21-thia-23-oxaporphyrin

5-(4-Pyridyl)-10,15,20-tri(p-tolyl)-21,23-dithiaporphyrin (27):^[12]

Condensation of diol 7 (0.37 g, 1.18 mmol) with 16-thiatripyrrane

(0.50 g, 1.18 mmol) in propionic acid (125 mL) at refluxing tem-

perature for 2 h followed by standard work up and chromatography

on silica with dichloromethane/methanol (96:4) as eluent gave the

desired porphyrin 27 as a purple solid (0.09 g, 11 %). M.p. Ͼ

(30): A catalytic amount of BF₃·OEt₂(0.05 mL of a 2.5 m stock

solution) was added to a solution of diol 8 (0.50 g, 1.29 mmol) and

16-oxatripyrrane (0.52 g, 1.29 mmol) in 130 mL of dichlorometh-

ane under nitrogen to initiate the condensation. After 1 h, DDQ

(0.29 g, 1.41 mmol) was added and stirred in air for an additional

hour. The crude compound was subjected to silica gel column

chromatography with petroleum ether/dichloromethane (60:40) as

eluent to give the desired compound 30 as a purple lustrous solid

300 °C. IR (KBr film): ν = 2930 cm^–1, 2860, 1455, 982, 798. ¹H

˜

NMR (400 MHz, CDCl₃): δ = 2.69 (s, 9 H, CH₃), 7.61–7.63 (m, 6

H, aryl), 8.12–8.14 (m, 6 H, aryl), 8.18–8.19 (m, 2 H, pyridyl) 8.60

(d, J = 4.8 Hz, 1 H, β-pyrrole), 8.69 (s, 2 H, β-pyrrole), 8.73 (d, J

= 4.8 Hz, 1 H, β-pyrrole), 9.07 (br. s, 2 H, pyridyl), 9.57 (d, J =

5.2 Hz, 1 H, β-thiophene), 9.72–9.74 (m, 3 H, β-thiophene) ppm.

¹³C NMR (100 MHz, CDCl₃): δ = 21.59, 128.03, 129.49, 133.61,

134.71, 134.93, 135.14, 135.73, 136.13, 138.02, 146.90, 147.61,

148.53, 148.68, 149.75, 150.87, 155.11, 156.63, 157.01 ppm. ES-MS:

m/z (%) = 692.3 (100) [M⁺]. C₄₆H₃₃N₃S₂(691.9): calcd. C 79.82, H

4.92, N 6.07, S 9.25; found C 79.71, H 4.77, N 6.28, S 9.10. UV/

Vis (toluene): λ_{m ax}(ε) = 437 nm (375 029 m^{– 1}cm^{– 1}), 515

(321 942 m^–1cm^–1), 549 (9637), 634 (2430), 697 (5661).

(0.07 g, 7%). M.p. Ͼ 250 °C. IR (KBr film): ν = 3069 cm^–1, 2930,

˜

2863, 1454, 972, 790, 577. ¹H NMR (CDCl₃): δ = 2.72 (s, 9 H,

CH₃), 7.56–7.59 (m, 6 H, aryl), 7.94–7.96 (m, 2 H, aryl), 8.06–8.10

(m, 8 H, aryl), 8.52–8.56 (m, 2 H, β-pyrrole), 8.60–8.62 (m, 2 H,

β-pyrrole), 9.26 (s, 2 H, β-furan), 9.70 (d, J = 4.8 Hz, 1 H, β-thio-

phene), 9.80 (d, J = 4.8 Hz, 1 H, β-thiophene) ppm. ¹³C NMR

(100 MHz, CDCl₃): δ = 22.10, 22.60, 122.11, 125.44, 129.54,

130.12, 131.99, 132.49, 134.78, 134.85, 135.63, 137.56, 138.22,

140.63, 142.03, 147.47, 148.00, 149.58, 154.72, 156.33, 156.58,

156.66, 156.72 ppm. ES-MS: m/z (%) = 753.2 (83) [M⁺], 755.2

(100%). C₄₇H₃₃BrN₂OS (753.8): calcd. C 74.89, H 4.41, N 3.72, S

4.25; found C 74.70, H 4.42, N 3.62, S 4.11. UV/Vis (toluene):

λ_max(ε) = 432 nm (166 254 m^–1cm^–1), 512 (21 894), 545 (4709), 645

(1480), 709 (4481).

5-[3-(3-Hydroxy-3-methylbut-1-ynyl)phenyl]-10,15,20-tri(p-tolyl)-

21,23-dithiaporphyrin (28): Condensation of diol 14 (0.50 mg,

1.28 mmol) with 16-thiatripyrrane (0.54 g, 1.28 mmol) in propionic

acid (125 mL) at refluxing temperature for 2 h followed by standard

work up and purification on silica gel column chromatography with

petroleum ether/dichloromethane (15:85) as eluent gave the desired

porphyrin 28 as a purple solid (0.16 g, 16%). M.p. Ͼ 300 °C. IR

5-(3-Nitrophenyl)-10,15,20-tri(p-tolyl)-21-thia-23-oxaporphyrin (31):

Diol 12 (0.50 g, 1.41 mmol) and 16-oxatripyrrane (0.57 g,

1.41 mmol) in 140 mL of dichloromethane were condensed in the

presence of BF₃·OEt₂(0.06 mL of a 2.5 m stock solution) under

nitrogen for 1 h. DDQ (0.32 g, 1.41 mmol) was then added and

stirred in air for an additional hour. After standard work up, the

crude compound was purified by silica gel column chromatography

with petroleum ether/dichloromethane (15:85) as eluent to give

pure 31 as a purple lustrous solid (0.06 g, 6%). M.p. Ͼ 250 °C. IR

(KBr film): ν = 3360 cm^–1, 3071, 2942, 2860, 1520, 1457, 1050, 972,

˜

1

792. H NMR (400 MHz, CDCl₃): δ = 1.43 (s, 6 H, CH₃), 2.72 (s,

9 H, CH₃), 7.60 (d, J = 7.6 Hz, 6 H, aryl), 7.78–7.80 (m, 1 H, aryl),

7.98–8.00 (m, 2 H, aryl), 8.10 (d, J = 7.6 Hz, 6 H, aryl), 8.11 (s, 1

H, aryl), 8.50 (m, 1 H, β-pyrrole), 8.59–8.61 (m, 3 H, β-pyrrole),

9.79–9.81 (m, 4 H, β-thiophene) ppm. ¹³C NMR (100 MHz,

CDCl₃): δ = 21.70, 121.59, 123.26, 125.77, 127.06, 129.25, 129.38,

131.39, 131.56, 132.11, 132.00, 135.16, 137.79, 146.07, 147.00 ppm.

ES-MS: m/z (%) = 773.5 (100) [M⁺]. C₅₂H₄₀N₂OS₂(773.0): calcd.

C 80.80, H 5.22, N 3.62, S 8.30; found C 80.62, H 5.15, N 3.61, S

8.45. UV/Vis (toluene): λ_max(ε) = 437 nm (237 785 m^–1cm^–1), 515

(38 606), 548 (11 698), 634 (2726), 698 (7048).

(KBr film): ν = 3069 cm^–1, 2930, 2863, 1454, 972, 790, 577. ¹H

˜

NMR (400 MHz, CDCl₃): δ = 2.72 (s, 9 H, CH₃), 7.58–7.60 (m, 6

H, aryl), 7.78–7.80 (m, 1 H, aryl), 8.00–8.05 (m, 8 H, aryl), 8.20 (s,

1 H, aryl), 8.66–8.68 (m, 2 H, β-pyrrole), 8.71–8.73 (m, 2 H, β-

pyrrole), 9.22 (s, 2 H, β-furan), 9.70–9.78 (m, 2 H, β-thiophene)

ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.64, 22.14, 122.11,

124.87, 126.55, 127.34, 128.36, 130.56, 132.52, 133.78, 135.73,

138.05, 138.32, 142.03, 145.10, 147.47, 147.76, 148.44, 148.15,

150.73, 154.78, 155.20, 156.66, 156.72 ppm. ES-MS: m/z (%) =

720.3 (100) [M⁺]. C₄₇H₃₃N₃O₃S (719.9): calcd. C 78.42, H 4.62, N

6.67, S 4.45; found C 78.50, H 4.42, N 6.62, S 4.11. UV/Vis (tolu-

5-(4-Iodophenyl)-10,15,20-tri(p-tolyl)-21-thia-23-oxaporphyrin (29):

Diol 9 (0.50 g, 1.15 mmol) and 16-oxatripyrrane (0.47 g,

1.15 mmol) were condensed in 115 mL of dichloromethane under

Eur. J. Org. Chem. 2005, 2500–2517

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2515

S. Punidha, N. Agarwal, M. Ravikanth

FULL PAPER

ene): λ_max(ε) = 432 nm (154 973 m^–1cm^–1), 512 (20 722), 545 (4664),

645 (1406), 710 (4638).

(%) = 1388.4 (50) [M⁺+ H]. C₉₆H₆₇N₅S₃(1386.8): calcd. C 83.15,

H 4.87, N 5.05, S 6.94; found C 83.10, H 4.62, N 5.12, S 7.01. UV/

Vis (toluene): λ_max(ε) = 432 nm (387 067 m^–1cm^–1), 514 (33 331),

548 (9652), 619 (2624), 633 (2079), 678 (3596), 697 (3477).

5-(4-Iodophenyl)-10,15,20-tri(p-tolyl)porphyrinzinc(II

)

(32): This

porphyrin was prepared by a literature method.^[4]

N₂S₂-N₂SO Dimer 36: A solution of N₂S₂porphyrin 21a (0.02 g,

0.03 mmol) and 29 (0.02 g, 0.03 mmol) in dry toluene/triethylamine

(3:1, 30 mL) was purged with nitrogen for 15 min. AsPh₃(0.01 g,

0.03 mmol) and Pd₂(dba)₃(0.004 g, 0.01 mmol) were added to this

solution, and stirred at 35 °C for 15 h. Formation of the dimer was

confirmed by the appearance of a new spot in the TLC as well as

from the characteristic splitting pattern of bands observed in the

UV/Vis spectrum. The crude compound was purified by silica gel

column chromatography and the desired dimer 36 was collected

with petroleum ether/dichloromethane (25:75) as eluent and ob-

5-(4-Iodophenyl)-10,15,20-tri(p-tolyl)-21-monothiaporphyrin (33):

This porphyrin was prepared as reported previously.^[1]

N₂S₂-N₄Dimer 34: A solution of N₂S₂porphyrin 21a (0.02 g,

0.03 mmol) and 32 (0.02 g, 0.03 mmol) in dry toluene/triethylamine

(3:1, 30 mL) was placed in a 100-mL, two-necked, round-bottomed

flask. The flask was fitted with a reflux condenser, gas inlet and gas

outlet tubes for nitrogen purging. The reaction vessel was placed in

an oil bath preheated to 35 °C. After purging nitrogen for 15 min,

AsPh₃(0.01 g, 0.03 mmol) and Pd₂(dba)₃(0.004 g, 0.01 mmol) were

added successively and the reaction was stirred at 35 °C for 12 h.

TLC analysis of the reaction mixture indicated the virtual disap-

pearance of spots corresponding to starting materials and the ap-

pearance of a new spot corresponding to the dimer. The solvent

was removed under vacuum and the crude compound was purified

by silica gel chromatography with petroleum ether/dichlorometh-

ane (80:20) as eluent to remove the excess AsPh₃and the small

amounts of monomeric porphyrins. The desired dimer 34 was then

collected with petroleum ether/dichloromethane (65:35) as eluent.

The solvent was removed on a rotary evaporator under vacuum to

afford dimer 34 as a violet solid (0.02 g, 57%). M.p. Ͼ 300 °C. IR

tained as a purple solid (0.02 g, 40%). M.p. Ͼ 300 °C. IR (KBr

1

film): ν = 3065 cm^–1, 2920, 2860, 2112, 1454, 990, 750. H NMR

˜

(400 MHz, CDCl₃): δ = 2.70 (s, 18 H, CH₃), 7.55 (d, J = 8.0 Hz, 4

H, aryl), 7.62 (d, J = 7.2 Hz, 10 H, aryl), 7.95 (d, J = 8.0 Hz, 4 H,

aryl), 8.04 (d, J = 7.2 Hz, 4 H, aryl), 8.14–8.18 (m, 10 H, aryl),

8.40–8.43 (m, 2 H, β-pyrrole), 8.51 (d, J = 4.8 Hz, 1 H, β-pyrrole),

8.55 (d, J = 4.8 Hz, 1 H, β-pyrrole), 8.64 (d, J = 4.8 Hz, 1 H, β-

pyrrole), 8.70 (s, 2 H, β-pyrrole), 8.73 (d, J = 5.0 Hz, 1 H, β-pyr-

role), 9.18 (s, 2 H, β-furan), 9.61–9.64 (m, 2 H, β-thiophene), 9.70–

9.73 (m, 4 H, β-thiophene) ppm. ES-MS: m/z (%) = 1388.5 (50)

[M⁺]. C₉₆H₆₆N₄OS₃(1387.8): calcd. C 83.09, H 4.79, N 4.04, S

6.93; found C 83.33, H 4.62, N 4.01, S 7.04. UV/Vis (toluene): λ_max

(ε) = 435 nm (443 457 m^–1cm^–1), 514 (50 982), 547 (13 422), 639

(3115), 696 (6550), 708 (8834).

(KBr film): ν = 3069 cm^–1, 2930, 2863, 2110, 1453, 980, 750. ¹H

˜

NMR (400 MHz, CDCl₃): δ = 2.72 (s, 18 H, CH₃), 7.42–7.43 (m,

4 H, aryl), 7.61–7.63 (m, 8 H, aryl), 7.81 (d, J = 8.0 Hz, 4 H, aryl),

8.06–8.16 (m, 12 H, aryl), 8.32 (d, J = 8.0 Hz, 4 H, aryl), 8.69–8.71

(m, 4 H, β-pyrrole), 8.75 (s, 2 H, β-pyrrole), 8.93–8.96 (m, 2 H,

β-pyrrole), 9.04–9.07 (m, 4 H, β-pyrrole), 9.73–9.76 (m, 4 H, β-

thiophene) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 21.14, 21.64,

128.32, 128.88, 129.80, 130.98, 132.36, 134.32, 135.0, 137.95,

138.37, 141.92, 144.63, 147.93, 148.60, 148.66, 150.53 ppm. ES-MS:

m/z (%) = 1433.2 (60) [M⁺]. C₉₆H₆₆N₆S₂Zn (1433.1): calcd. C

80.46, H 4.64, N 5.86, S 4.47; found C 80.20, H 4.42, N 5.72, S

4.40. UV/Vis (toluene): λ_max(ε) = 425 nm (229 043 m^–1cm^–1), 439

(206 668 m^–1cm^–1), 516 (18 962), 551 (13 737), 592 (3125), 636

(1558), 699 (3375).

Supporting Information: The NMR and mass spectra of com-

pounds 1, 2, 4, 8–13, 15–17, 20–31, and 34–36 and mass spectra of

18 and 19 (33 pages).

Acknowledgments

This work was supported by a grant from the Department of Sci-

ence and Technology and Council of Scientific & Industrial Re-

search (CSIR), Government of India. NMR and mass spectra were

obtained at the Department of Chemistry, IIT-Bombay. SP thanks

the CSIR for a fellowship.

N₂S₂-N₃S Dimer 35: A solution of N₂S₂porphyrin 21a (0.02 g,

0.03 mmol) and 33 (0.02 g, 0.03 mmol) in dry toluene/triethylamine

(3:1, 30 mL) was purged with nitrogen for 15 min. The coupling

was initiated by adding AsPh₃(0.01 g, 0.03 mmol) and Pd₂(dba)₃

(0.004 g, 0.01 mmol) and the reaction mixture was then stirred at

35 °C for 12 h. TLC analysis indicated the appearance of new spot

apart from the corresponding monomeric spots. The crude reaction

mixture was purified by silica gel chromatography with petroleum

ether/dichloromethane as eluent. The excess AsPh₃and small

amounts of unreacted monomers were removed with petroleum

ether/dichloromethane (80:20) as eluent and the desired dimer was

then collected with petroleum ether/dichloromethane (50:50) as elu-

ent. The solvent was removed on a rotary evaporator under vacuum

to give dimer 35 as a purple solid (0.02 g, 54%). M.p. Ͼ 300 °C.

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˜

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2516

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Monofunctionalised 21-Thia-, 21,23-Dithia-, and 21-Thia-23-oxaporphyrins

FULL PAPER

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Received: December 16, 2004

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Article Doi

A simple route to prepare monofunctionalised 21-thia-, 21,23-dithia-, and 21-thia-23-oxaporphyrins from unsymmetrical thiophene diols and their use in the synthesis of covatently linked unsymmetrical porphyrin dimers

DOI: 10.1002/ejoc.200400887

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