Synthesis and characterization of salen-type ligands functionalized with pyrrole derivative pendant arms

Article abstract of DOI:10.1002/poc.924

Several salen-type ligands functionalized with two pyrrole derivative pendant arms were prepared. These Schiff base ligands, which differ in the imine bridge, were prepared by a multi-step procedure that includes (i) synthesis of 3-pyrrol-1-ylpropanoic acid, (ii) transformation of the latter compound into the mixed carboxylic-carbonic anhydride (MCCA) intermediate followed by reaction with 2,3-dihydroxybenzaldehyde to give (3-formyl-2-hydroxyphenyl) 3-(pyrrol-1-yl)propanoate and finally (iii) Schiff condensation of the different 1,2-diamines with (3-formyl-2-hydroxyphenyl) 3-(pyrrol-1-yl)propanoate. The key step in the Schiff base ligand preparation is the functionalization of the 2,3-dihydroxybenzaldehyde at the C-3 hydroxyl group without protection of the C-2 hydroxyl group, by a regiospecific acylation of the ortho-hydroxyl group via esterification with the mixed carboxylic-carbonic anhydride of 3-pyrrol-1-ylpropanoic acid. The compounds were characterized by elemental analyses, ¹H and ¹³C NMR spectroscopy, mass spectrometry and FTIR and UV-visible spectrophotometry. Copyright

Full text of DOI:10.1002/poc.924

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2005; 18: 935–940
Published online 5 April 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/poc.924
Synthesis and characterization of salen-type ligands
functionalized with pyrrole derivative pendant arms
1
1
2
1
´
Mariana Andrade, Carla Sousa, Jose Enrique Borges and Cristina Freire *
1
´
ˆ
REQUIMTE, Departamento de Quımica, Faculdade de Ciencias, Universidade do Porto, 4169-007 Porto, Portugal
2
´
ˆ
CIQ, Departamento de Quımica, Faculdade de Ciencias, Universidade do Porto, 4169-007 Porto, Portugal
Received 15 September 2004; revised 03 February 2005; accepted 21 February 2005
ABSTRACT: Several salen-type ligands functionalized with two pyrrole derivative pendant arms were prepared.
These Schiff base ligands, which differ in the imine bridge, were prepared by a multi-step procedure that includes (i)
synthesis of 3-pyrrol-1-ylpropanoic acid, (ii) transformation of the latter compound into the mixed carboxylic–
carbonic anhydride (MCCA) intermediate followed by reaction with 2,3-dihydroxybenzaldehyde to give (3-formyl-2-
hydroxyphenyl) 3-(pyrrol-1-yl)propanoate and finally (iii) Schiff condensation of the different 1,2-diamines with
(3-formyl-2-hydroxyphenyl) 3-(pyrrol-1-yl)propanoate. The key step in the Schiff base ligand preparation is the
functionalization of the 2,3-dihydroxybenzaldehyde at the C-3 hydroxyl group without protection of the C-2 hydroxyl
group, by a regiospecific acylation of the ortho-hydroxyl group via esterification with the mixed carboxylic–carbonic
1
anhydride of 3-pyrrol-1-ylpropanoic acid. The compounds were characterized by elemental analyses, H and 13C
NMR spectroscopy, mass spectrometry and FTIR and UV–visible spectrophotometry. Copyright # 2005 John Wiley
& Sons, Ltd.
KEYWORDS: Salen-type ligands; regiospecific acylation; functionalized ligands; pyrrole derivatives; salicylaldehyde
INTRODUCTION
sensors based on salen-type ligands to receptors with
mixed O,N coordinating atoms, to extend their recogni-
tion properties to softer cations (Cd, Zn and Hg) and to
allow for anion interactions. Although crown ethers and
other macrocycles are known for their ability to act as
efficient and selective hosts for representative cations,4–7
the homologous open-chain derivatives containing donor
atoms can also be extremely effective in this respect.8,9
In this paper, we report the preparation of new salen-
type ligands functionalized at the C-3 of the aldehyde
moieties with pendant arms derived from pyrrole. These
ligands have two mixed N,O-type coordination sites: one
that comprises the N2(imine)O2 coordination sphere that
is well suited for coordination of transition metal cations,
and the other that is composed by the coordinating atoms
within the pyrrole derivative pendant arms, which can
potentially act as a receptor site for representative ca-
tions, lanthanides and also anions. To follow on our work
on the design of molecular receptors based on salen
complexes, these ligands will be used to complex transi-
tion metals and the resulting compounds will be screened
as molecular receptors for cations and anions.
The design of functionalized receptors for the develop-
ment of potential molecular chemosensors is a field
of active research; the sensing function is generally
achieved by coupling selective binding sites and signal-
ling subunits.1–3 Salen-type ligands constitute one of the
most promising building blocks for the preparation of
multifunctional ligands as they are easy to functionalize
with receptor groups (crown ethers, calixarenes and
cryptands)4–6 and can coordinate a great variety of
transition metal cations which can act as signalling units.
Owing to the intrinsic spectroscopic and redox properties
of transition metal cations, these functionalized salen-
type complexes can act as molecular sensors for charged
and neutral guests.
We have been interested in the preparation of salen-
type ligands and N2O/N2O2 Schiff base ligands functio-
nalized with crown ether groups (dibenzo-18-crown-6
and benzo-15-crown-5), which, after transition metal
coordination, have acted as hosts for alkali and alkaline
earth metal and lanthanide ions in solution7–9 or as
polymeric films deposited on Pt and ITO electrodes.10
We are now pursuing our work on the design of molecular
The pyrrole-based salen ligands were prepared using a
multi-step procedure that involves a key step, the func-
tionalization of the 2,3-dihydroxybenzaldehyde at C-3
via a regiospecific acylation using a pyrrole-based mixed
carboxylic–carbonic anhydride (MCCA) intermediate;
within this synthetic approach the C-3 hydroxyl group
of 2,3-dihydroxybenzaldehyde could be functionalized
without protection of the C-2 hydroxyl group.
*Correspondence to: C. Freire, REQUIMTE, Departamento de
´
ˆ
Quımica, Faculdade de Ciencias, Universidade do Porto, Rua do
Campo Alegre, 4169-007 Porto, Portugal.
E-mail: acfreire@fc.up.pt
ˆ
Contract/grant sponsor: Fundac¸a˜o para a Ciencia e Tecnologia (FCT).
Contract/grant number: POCTI/QUI/32831/2000.
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 935–940

936
M. ANDRADE ET AL.
1
The preparation of MCCA intermediates from the
The precursor compound I was characterized by H
NMR spectroscopy to confirm its structure and the
functionalized salicylaldehyde II was characterized by
1H NMR and mass spectrometry (EI). The new pyrrole-
based salen ligands III–V were characterized by elemen-
corresponding carboxylic acids and alkyl haloformates
is a common method in peptide synthesis11 and in the
preparation of alcohols by reduction using soft condi-
tions.12 MCCA are useful mediators in soft esterification
leading to high product yields, as for example in the
preparation of esters of N-protected ꢀ-amino acids with-
out loss of optical activity.13 In this work, we prepared the
MCCA intermediate from 3-pyrrol-1-ylpropionic acid
and reacted it with 2,3-dihydroxybenzaldehyde to obtain
a mono-O-acylated ester.
In previous work, functionalization of 2,3-dihydroxy-
benzaldehyde at the C-3 hydroxyl group was performed
with protection of the C-2 hydroxyl group by regioselec-
tive mono-O-alkylation to prevent multi-substitutions;14
this procedure used 1 equiv. of NaH and allyl bromide
and depended on the experimental conditions, such as
pH (alkaline), solvent and alkylating agent.14,15 In the
present work, the C-3 functionalization of the same
salicylaldehyde was effected under mild conditions,
using a straightforward methodology, with no need for
C-2 hydroxyl protection, by using regiospecific mono-O-
acylation via an MCCA pyrrole based intermediate.
tal analyses, H and 13C NMR spectroscopy, mass spec-
trometry [fast atom bombardment (FAB)] and FTIR and
UV–visible spectrophotometry. All data are summarised
in the Experimental section.
The mass spectrum [electron ionization (EI)] of (3-
formyl-2-hydroxyphenyl) 3-(pyrrol-1-yl)propanoate (II)
reveals the presence of an intense peak corresponding
to the molecular ion Mþ , whereas for those of Schiff
base ligands (III–V) (FAB) a peak due to [M þ H]þ was
observed. The mass spectra of II and those of III–V
reveal similar fragmentation profiles: the spectrum of
1
II evidences
a peak at m/z 122 due to the
C4H4NCH2CH2CO fragment and the spectra of III–V
show peaks corresponding to [M ꢀ C4H4NCH2CH2CO þ
H]þ and [M ꢀ 2C4H4NCH2CH2CO þ H]þ . The high-
resolution mass spectra of the Schiff base ligands confirm
the proposed structures.
The presence of a resolved singlet with ꢁ between
—
8.67 and 8.10 ppm assigned to the two C(H) N protons
—
1
in the H NMR spectra of III–V confirms the Schiff
RESULTS AND DISCUSSION
condensation reaction between the diamines and the
aldehyde group of (3-formyl-2-hydroxyphenyl) 3-(pyr-
rol-1-yl)propanoate (II). For III–V, a singlet due to the
C-2 OH proton is observed in the range 13.57–
12.87 ppm; it is worth noting that the OH chemical shift
is strongly increased in these compounds compared with
II, suggesting the presence of hydrogen bonding with the
oxygen atoms of the pendant arms.
For all compounds the pyrrole aromatic protons con-
stitute an AA0XX0 system and therefore ꢁ values
were measured at the middle of each multiplet.18 The
protons in the ꢀꢀ0 position with respect to N (ꢁ in the
range 6.67–6.74 ppm) are more deshielded than those
in the ꢂꢂ0 position (ꢁ in the range 6.14–6.22 ppm); III
shows the highest ꢁ value and V the lowest. The CH2CH2
group in each pendant arm gives two triplets, with
the group in the ꢀꢀ0 position with respect to N being
more deshielded (ꢁ in the range 4.40–4.26 ppm) than that
in ꢂꢂ0 position (ꢁ in the range 3.14–3.00 ppm); as
observed before, III shows the highest ꢁ value and V
the lowest.
Salen-type ligands with two OC(O)CH2CH2NC4H4 pen-
dant arms were prepared in a multi-step procedure as
depicted in Scheme 1. In the first step, the pyrrole
precursor derivative 3-pyrrol-1-ylpropanoic acid (I),
was prepared by reaction of 3-pyrrol-1-ylpropionitrile
with sulfuric acid in presence of sodium hydroxide. This
compound was converted into the corresponding MCCA
intermediate by treatment with triethylamine and ethyl
chloroformate following the methodology described by
Kim et al.;13 the MCCA intermediate, which was not
isolated, was reacted directly with 2,3-dihydroxybenzal-
dehyde, giving (3-formyl-2-hydroxyphenyl) 3-(pyrrol-1-
yl)propanoate in 60% yield.16,17 No protection of the C-2
hydroxyl group was needed to prevent its functionaliza-
tion, as the MCCA intermediate induces the regiospecific
acylation of the C-3 hydroxyl group; moreover, the
predicted keto–enol tautomerism involved in 2,3-dihy-
droxybenzaldehyde also contributed to a more effective
functionalization at C-3 due to the higher nucleophilic
character of this hydroxyl group compared with the more
hindered C-2 hydroxyl group.
Schiff condensation of (3-formyl-2-hydroxyphenyl) 3-
(pyrrol-1-yl)propanoate with the diamines meso-1,2-
diphenylethylenediamine, 4,5-dimethyl-1,2-phenylene-
diamine and 4,5-dichloro-1,2-phenylenediamine gives
the corresponding ligands H2-[1,2-diphenylethylene-
bis(3-oxyethylpyrrole)salicylideneimine] (III), H2-[1,
2-(4,5-dimethyl)phenylenebis(3-oxyethylpyrrole)salicy-
lideneimine] (IV) and H2-[1,2-(4,5-dichloro)phenylene-
bis(3-oxyethylpyrrole)salicylideneimine] (V).
As regards the phenyl group substituted in at position 1
—
—
by CH O or CH N (II and III–V, respectively), at
—
position 2 by OH and at position 3 by an OCO pendant
—
group, H-5 behaves as a real triplet and is the more
—
—
—
shielded, H-6 [ortho to CH O (II) or to CH N (III–V)
—
is the more deshielded and H-4 (ortho to the OCO
pendant group) is at an intermediate position;18 both H-
4 and H-6 give a doublet of doublets. Compound II when
compared with III–V shows all the ꢁ at higher values,
indicating that the Schiff condensation with the diamines
has introduced some electron density within the phenyl
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 935–940

SYNTHESIS AND CHARACTERIZATION OF SALEN-TYPE LIGANDS
937
Scheme 1. Multi-step procedure used in the preparation of salen-type ligands functionalized with pyrrole derivative pendant
arms
moieties. On comparing the Schiff bases, III shows the
more shielded H-4–H-6 protons.
of the phenyl imine bridge appear at 7.30, para protons at
7.00 ppm and the methine protons at 4.70 ppm.
For the aromatic protons in the imine bridge, a singlet
is expected for IV and V at 7.06 and 7.33 ppm, respec-
tively; the two different values are a consequence of the
electron-donating properties of the methyl groups (lower
ꢁ) in opposition to the withdrawing properties of the
chloride atoms (higher ꢁ). In III, ortho and meta protons
The 13C NMR spectra of the Schiff base ligands (III–
V) also confirm the structure of the synthesized com-
pounds. From the comparison of the three spectra it is
possible to make some peak assignments, especially for
the resonances at the two limits of the spectra: those
which are in the most deshielded region and those 13C
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 935–940

938
M. ANDRADE ET AL.
—
There is a decrease in the frequency of C N(imine)
—
which are more shielded, which in these compounds
correspond to aromatic carbon atoms linked to electro-
negative atoms (O and N) and aliphatic carbons, respec-
tively.18 In this context we propose the following peak
bond stretching vibration on going from III to V; this
variation suggests a decrease in the electronic density of
—
the C N(imine) bond, induced by the electronic proper-
—
ties of the different imine bridges.
13
—
assignments for III–V:— C O resonance ꢁ at 169.0–
—
169.1 ppm, ꢁ N 13CH in the range 165.5–162.6 ppm,
Electronic spectra of the functionalized Schiff base
ligands (III–V) show high-intensity bands in the range
ꢃ ¼ 260–370 (" ¼ 29 000–8000 dm3 molꢀ1 cmꢀ1) and a
medium-intensity shoulder at ꢃ ¼ 410–460 nm (" ¼
340–350 dm3molꢀ1cmꢀ1), which are assigned to ꢄ* ! n
and to ꢄ* ! ꢄ transitions within the aromatic moieties.20
As observed in the IR spectra, there is a small shift of all
bands towards lower energies on going from III to V, a
consequence of the electronic effects of the different
imine bridge substituents.
—
—
ꢁ13C2–OH at 152.7–153.1 ppm, 13Cꢂꢂ0 pyrrole at 108.4–
108.5 ppm, in the CH2CH2 group of the pendent arm
the C in the ꢀꢀ0 position with respect to N is more
13
deshielded (ꢁ in the range 44.9–44.8) than that in the ꢂꢂ0
position (ꢁ in the range 36.3–36.5). For III the
13CH—13CH group in the imine bridge has a resonance
peak at 79.8 ppm and IV has a resonance peak at
19.6 ppm that can be assigned to 13CH3 in the phenyl
group of the imine bridge.
In pursuing the assignments of aromatic carbons near
electronegative atoms, the peak that appear in IVand Vat
the same value, ꢁ 138.7 ppm, and 138.8 ppm for III, can
CONCLUSIONS
13
be tentatively assigned to C3—O—C O, as the 13C
—
—
is far from the direct influence of the imine bridge,
leading to similar values for all three compounds. The
next resonance peaks in the range 139.1–141.2 for IV
and V can be tentatively assigned to 13Cf in the aromatic
imine bridge and the peak at 138.4 ppm for III can be
tentatively assigned to 13Cb in the phenyl ring of the
imine bridge.
Three new salen-type ligands functionalized with pyrrole
derivative arms, which differ in the imine bridge, were
prepared using a new and facile methodology that in-
volves the C-3 hydroxyl functionalization of 2,3-dihy-
droxybenzaldehyde with pyrrole derivatives without any
protection step for the C-2 hydroxyl group of the same
aldehyde moiety.
One more tentative assignment can be made consider-
ing the relative intensity of some peaks. In fact, in all
three compounds the pyrrole carbons that are ꢂꢂ0 with
respect to N are unambiguously assigned at 108.5, 108.4
and 108.5 ppm; four equivalent carbons contribute to
these signals. However, in IV and V there is only one
other signal originating from four equivalent carbons,
which corresponds to the pyrrole carbons that are ꢀꢀ0
with respect to N and its intensity must be very similar to
those of the 108.4 and 108.5 ppm signals and, therefore,
higher than all other signals of these compounds, which
originate from two equivalent carbons. In this context,
the peaks with the highest intensity, that match that of
13Cꢂꢂ0-pyrrole, appear at exactly the same value for both
compounds, 120.6 ppm, and can be tentatively assigned
The spectroscopic characterization of the ligands has
shown that the different imine bridges, which have dif-
ferent electronic properties, have an effect on the electro-
nic density distribution within the ligand. This aspect is
of great importance for the ultimate goal of these com-
pounds, which is to act as hosts for representative cations,
lanthanides and anions, after their complexation by
transition metal ions. Their electronic/structural proper-
ties will be enhanced by coordination of transition metal
complexes and will determine the extent of interaction
between the target species and the host, thus determining
their efficiency and selectivity as molecular chemosen-
sors. We are now preparing and characterizing their
respective transition metal complexes.
13
to Cꢀꢀ0-pyrrole. Once these assignments have been
made, the corresponding signal in III can be assigned
since it will appear at a very similar position: 120.7 ppm.
Finally, the other peaks that appear in the range 135–
105 ppm can not be unambiguously assigned separately
and include all the others aromatic carbons.
EXPERIMENTAL
All solvents were obtained from Merck and all other
reagents from Aldrich; all were used as received. Ele-
mental analyses (C, H, N) were performed at the Micro
Analytical Laboratory, Department of Chemistry, Uni-
versity of Manchester (UK), and EI and FAB mass
—
The IR spectra of III–V show the C O (pendant arm)
—
—
and C N(imine) bond stretching vibrations in the re-
—
gions 1762–1756 and 1628–1614 cmꢀ1 respectively;19
the latter values are similar to those observed for other
salen-type ligands with similar imine bridges.7–9 It is also
possible to observe one band due the C–H out-of-plane
spectra were measured at the Facultad de Quımica,
´
Universidad de Santiago de Compostela (Spain), using
3-nitrobenzylalcohol (NBA) as matrix (FAB). 1H and 13
NMR spectra were recorded in CDCl3 with a Bruker
C
bending of pyrrole in the range 730–723 cmꢀ1 19
.
No
DRX-300 instrument at the Departamento de Quımica,
´
bands due to NH2 stretching vibrations are present, thus
confirming that Schiff condensation took place between
the diamines and functionalized salicylaldehyde.
Universidade de Aveiro (Portugal); chemical shifts are
reported in ppm referred to TMS as internal standard. IR
spectra in the 400–4000 cmꢀ 1 region were recorded on a
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 935–940

SYNTHESIS AND CHARACTERIZATION OF SALEN-TYPE LIGANDS
939
Biorad FTS 155 instrument using KBr pellets or Nujol
mulls. UV–visible spectra were recorded with a Unicam
UV-2 instrument in the range 250–600 nm, using quartz
cells with a 1 cm optical path; acetonitrile solutions of
the Schiff base ligands with concentration between
1.00 ꢁ 10ꢀ3 and 4.00 ꢁ 10ꢀ5 mol dmꢀ3 were used.
5.65; N, 7.88% MS (FAB) m/z (%): 695 (Mþ , 20%); high
resolution: 695, C4113CH38N4O6, found 695.283506;
1
calc. 695.282490. H NMR (CDCl3, ppm): ꢁ 13.54 (s;
—
2H; HO), 8.10 (s; 2H; N CH), 7.30 (m, 2H, C6-H), 7.04
—
(m; 2H; C4-H), 7.30 (m, 8H, Cc,d-H), 7.00 (m, 2H, Ce-
H), 6.83 (t, 2H, C5-H), 6.79 (m; 4H; ꢀꢀ0-pyrrole), 6.22
(m; 4H; ꢂꢂ0-pyrrole), 4.75 (s, 2H, Ca-H), 4.40 (t; 4H;
C20H2), 3.14 (t; 4H; C10H2). 13C NMR (CDCl3, ppm): ꢁ
13
Syntheses
169.1 (s;
C
O), 165.5 (s; N 13CH), 152.7 (s; arom
—
—
—
—
13C2-OH), 138.8 (s, arom 13C3-OCO), 138.4 (s, arom
13Cb), 129.2 (s, arom 13C), 128.7 (s, arom 13C), 128.1 (s,
arom 13C), 128.0 (s, arom 13C), 125.7 (s, arom 13C), 120.7
3-Pyrrol-1-yl-propanoic acid (I): 3-pyrrol-1-ylpropioni-
trile (11.83 g; 0.098 mol) and a solution of NaOH
(5 mol dmꢀ3) in water (79 cm3) were stirred for 8 h, at
room temperature, under an argon atmosphere. Concen-
trated sulfuric acid was added to the mixture until pH3.
The mixture was extracted with diethyl ether and the
extract dried over MgSO4. The resulting solution was
concentrated and n-hexane was added. After cooling, 3-
pyrrol-1-ylpropionic acid (I) was obtained as yellow
crystals, which were washed with n-hexane and dried
under vacuum. Yield 10.92 g (80.1%). 1H NMR (CDCl3):
ꢁ 6.68 (m; 2H; ꢀꢀ0-pyrrole), 6.16 (m; 2H; ꢂꢂ0-pyrrole),
4.22 (t; 2H; C20H2), 2.84 (t; 2H; C10H2).
(s, Cꢀꢀ0-pyrrole), 119.8 (s, arom 13C), 118.2 (s, arom
13
13C), 108.5 (s, Cꢂꢂ0-pyrrole), 79.8 (s, 13Ca), 44.9 (s,
13
13C20H2), 36.4 (s, C10H2). IR (KBr) ꢅ (cmꢀ1): 3463
13
(br), 3135, 3103, 3055, 3025, 2930, 2895, 1754, 1628,
1586, 1498, 1463, 1422, 1365, 1343, 1283, 1269, 1234,
1200, 1149, 1092, 1073, 1034, 982, 928, 876, 854, 823,
787, 769, 750, 727, 705, 606, 577, 551, 530, 506, 434.
UV–visible (CH3CN) ꢃmax (nm) (" (dm3 molꢀ1 cmꢀ 1)):
260 (28 220), 320 (8050), 414 sh (340).
H2-[1,2-(4,5-dimethyl)phenylenebis(3-oxyethylpyrro-
le)salicylideneimine] (IV): this compound was prepared
using the procedure described for III, but using a metha-
nolic solution of 4,5-dimethyl-1,2-phenylenediamine
(0.44 g; 0.0033 mol) and a solution of (3-formyl-2-
hydroxyphenyl) 3-(pyrrol-1-yl)propanoate (II) (1.69 g;
0.0065 mol) in CHCl3. The resulting light-orange solid
was collected by filtration, recrystallized from methanol,
washed with diethyl ether and dried under vacuum. Yield
0.81 g (40.0%). Anal. Calcd for C36H34N4O6: C, 69.89;
H, 5.54; N, 9.06. Found: C, 69.68; H, 5.75; N, 8.86%. MS
(FAB) m/z (%): 619 ([M þ H]þ , 100%); high resolution:
(3-Formyl-2-hydroxyphenyl) 3-(pyrrol-1-yl)propano-
ate (II): under an argon atmosphere, triethylamine
(8.0 cm3, 0.057 mol) was added to 3-pyrrol-1-ylpropa-
noic acid (I) (8.79 g; 0.063 mol) in dried CH2Cl2 at
ꢀ17 ꢂC. Ethyl chloroformate (5.4 cm3; 0.056 mol) in
dried CH2Cl2 was added slowly to the solution, under
an argon atmosphere, with stirring, at ꢀ17 ꢂC during
30 min; then a solution of 2,3-dihydroxybenzaldehyde
(7.15 g; 0.052 mol) in dried CH2Cl2 was added. The
mixture was kept between ꢀ17 and ꢀ13 ꢂC for 1 h, at
ꢀ3 ꢂC during 1.5 hours and finally at room temperature,
with stirring, for 20 h under an argon atmosphere. The
mixture was extracted with water and the organic layer
was washed with a saturated aqueous solution of
NaHCO3. The organic layer was dried with MgSO4, the
solvent was evaporated and the solid (3-formyl-2-hydro-
xyphenyl) 3-(pyrrol-1-yl)propanoate (II) was obtained.
Recrystallization from acetone afforded the expected
white solid. Yield 6.72 g (50.0%). MS (EI) m/z (%):
619, C36H35N4O6, found 619.257389; calc. 619.255660.
1
—
—
H NMR (CDCl ): ꢁ 13.57 (s; 2H; OH), 8.67 (s; 2H; N
3
CH), 7.32 (m, 2H, C6-H), 7.11 (m; 2H; C4-H), 7.06 (s,
2H, Cg-H), 6.92 (t, 2H, C5-H), 6.75 (m; 4H; ꢀꢀ0-
pyrrole), 6.18 (m; 4H; ꢂꢂ0-pyrrole), 4.31 (t; 4H;
C20H2), 3.05 (t; 4H; C10H2), 2.36 (s, 6H, CH3). 13C
13
—
O), 162.6 (s;
—
NMR (CDCl3, ppm): ꢁ 169.0 (s;
—
C
N
13CH), 153.1 (s; arom 13C2-OH), 139.1 (s, arom
—
13Cf), 138.7 (s, arom 13C3-OCO), 136.8 (s, arom 13C),
1
259 (Mþ , 50%). H NMR (CDCl3): ꢁ 11.13 (s; 2H;
129.9 (s, arom 13C), 126.1 (s, arom 13C), 121.1 (s, arom
13
HO), 9.93 (s; 2H; CHO), 7.49 (m, 2H, C6-H), 7.25
(m; 2H; C4-H), 7.02 (t, 2H, C5-H), 6.74 (m; 2H; ꢀꢀ0-
pyrrole), 6.18 (m; 2H; ꢂꢂ0-pyrrole), 4.35 (t; 2H; C20H2),
3.09 (t; 2H; C10H2).
13C), 120.6 (s, Cꢀꢀ0-pyrrole), 120.5 (s, arom 13C),
118.4 (s, arom 13C) 108.4 (s, Cꢂꢂ0-pyrrole), 44.8 (s,
13
13C20H2), 36.3 (s, C10H2), 19.6 (s, 13CH3). IR (KBr) ꢅ
13
(cmꢀ1): 3453 (br), 3096, 2919, 1762, 1746, 1617, 1574,
1496, 1450, 1410, 1382, 1363, 1283, 1230, 1187, 1144,
1088, 1068, 1043, 1015, 978, 925, 879, 853, 831, 777,
750, 735, 723, 701, 614, 564, 482, 425. UV–visible
(CH3CN) ꢃmax (nm) (" (dm3 molꢀ1 cmꢀ1): 268 (17 015),
332 (14 530), 368 (9635), 455 sh (345).
H2-[1,2-(4,5-dichloro)phenylenebis(3-oxyethylpyrrole)
salicylideneimine] (V): this compound was synthesized
following the procedure described for III, but using a
methanolic solution of 4,5-dichloro-1,2-phenylenedia-
mine (0.73 g; 0.0041 mol) and a solution of (3-formyl-
H2-[1,2-diphenylethylenebis(3-oxyethylpyrrole)salicy-
lideneimine] (III): to a solution of meso-1,2-dipheny-
lethylenediamine (1.38 g; 0.0065 mol) in methanol was
added a solution of (3-formyl-2-hydroxyphenyl) 3-(pyr-
rol-1-yl)propanoate (II) (3.37 g; 0.013 mol) in CHCl3.
The resulting yellow solution was refluxed for 1.5 h to
afford a yellow solid, which was filtered under reduce
pressure, recrystallized from acetone and dried under
vacuum. Yield 3.98 (88.1%). Anal. Calcd for C42H38
N4O6: C, 72.60; H, 5.51; N, 8.07. Found: C, 71.90; H,
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 935–940

940
M. ANDRADE ET AL.
2-hydroxyphenyl) 3-(pyrrol-1-yl)propanoate (II) (2.14 g;
0.0082 mol) in CHCl3. The resulting brown solid was
collected by filtration, recrystallized from acetonitrile and
dried under vacuum. Yield 0.93 g (34.2%). Anal. Calcd
for C34H28N4O6Cl2: C, 61.92; H, 4.28; N, 8.49. Found: C,
61.31; H, 4.22; N, 8.46% MS (FAB) m/z (%): 659
([M þ H]þ , 45%); high resolution: 659, C34H29N4O6Cl2,
5678/2001). We acknowledge Professor N. Platzer for
helpful comments on NMR analysis.
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(s; N 13CH), 153.0 (s; arom 13C2-OH), 141.2 (s, arom
—
—
13Cf), 138.7 (s, arom 13C3-OCO), 131.3 (s, arom 13C),
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118.9 (s, arom 13C), 108.5 (s, Cꢂꢂ0-pyrrole), 44.8 (s,
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13
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1092, 1069, 1012, 985, 972, 955, 924, 887, 874, 851, 785,
763, 738, 730, 716, 679, 616, 557, 535, 424. UV–visible
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338 (23 220).
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Acknowledgments
The work was partial funded by Fundac¸a˜o para a
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Ciencia e Tecnologia (FCT), Portugal, through the pro-
ject POCTI/QUI/32831/2000. C.S. thanks the Social
European Fund and FCT for a fellowship (SFRH/BPD/
Copyright # 2005 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2005; 18: 935–940