Synthesis and characterization of linear and macrocyclic ligands with multiple hemisalen pockets

Article abstract of DOI:10.1080/00397911.2011.579382

Procedures for the convenient preparation of new ligands possessing multiple metal binding sites are presented. Among those, a Schiff base macrocycle exhibiting three outward hemisalen pockets was synthesized using a one-pot reduction/condensation reactio

Full text of DOI:10.1080/00397911.2011.579382

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Synthesis and Characterization of Linear
and Macrocyclic Ligands with Multiple
Hemisalen Pockets
Samuel Guieu a
a Department of Chemistry, University of Aveiro, Aveiro, Portugal
Accepted author version posted online: 10 Jan 2012.
To cite this article: Samuel Guieu (2012): Synthesis and Characterization of Linear and Macrocyclic
Ligands with Multiple Hemisalen Pockets, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 42:21, 3177-3186
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Synthetic Communications1, 42: 3177–3186, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.579382
SYNTHESIS AND CHARACTERIZATION OF LINEAR
AND MACROCYCLIC LIGANDS WITH MULTIPLE
HEMISALEN POCKETS
Samuel Guieu
Department of Chemistry, University of Aveiro, Aveiro, Portugal
GRAPHICAL ABSTRACT
Abstract Procedures for the convenient preparation of new ligands possessing multiple
metal binding sites are presented. Among those, a Schiff base macrocycle exhibiting three
outward hemisalen pockets was synthesized using a one-pot reduction/condensation reac-
tion. These ligands are promising building blocks for supramolecular architectures such
as metal–organic frameworks or polyhedra.
Keywords Hemisalen; macrocycle; Schiff base ligands
INTRODUCTION
Schiff base condensation has been widely used to create sophisticated organic
structures, including multidentate ligands,[1] conjugated polymers,[2] and macro-
cycles.[3] Because of its selectivity and reversibility, imine formation has proved to
be a useful reaction for macrocyclization. Numerous macrocycles with salen or hemi-
salen pockets pointing toward the interior of the molecule have been synthesized
using this approach,[4] and these have been used to complex transition-metal ions[5]
or to stabilize multimetallic clusters.[6] Hemisalen ligands can be used as grafting
points in supramolecular architectures (Fig. 1), two of them being linked through
a transition-metal ion,[7] or one can be linked to pyridine through platinum ions.[8]
To develop the potential of this supramolecular link, new ligands bearing more than
one hemisalen pocket are required. Macrocycles with outward complexing sites are
Received April 1, 2011.
Address correspondence to Samuel Guieu, Department of Chemistry, University of Aveiro, Aveiro
3810-193, Portugal. E-mail: sguieu@ua.pt
3177

3178
S. GUIEU
Figure 1. Example of a hemisalen ligand and the corresponding transition-metal complexes.
rare,[9] and to the best of our knowledge, no Schiff base macrocycles possessing out-
ward hemisalen complexing sites have been synthesized to date.
Herein is presented a new type of Schiff base macrocycle bearing three hemi-
salen pockets pointing outward, obtained through a one-pot reductive imination
of a single precursor bearing both formyl and nitro groups.
RESULTS AND DISCUSSION
Precursor 2 was obtained by the diformylation of 4,40-biphenol 1, using mag-
nesium chloride, triethylamine, and formaldehyde in refluxing tetrahydrofuran
(Scheme 1). Other formylation reactions we tried, such as Duff formylation, did
not significantly improve the yield.
Dinitration of the 4,40-biphenol 1 using 70% nitric acid in glacial acetic acid
gave compound 3 (Scheme 1). The diamino precursor 4 was obtained by reduction
of the nitro groups using sodium dithionite (Na2S2O4) in a refluxing mixture of etha-
nol and water.
We expected that the condensation of diformyl-substituted compound 2 with a
diamine would give a Schiff base macrocycle (Scheme 2). When compound 2 was
treated with 1 equivalent of 1,3-phenylenediamine in refluxing ethanol, a red solid
was obtained. Proton NMR spectroscopy of the product showed that multiple spe-
cies were formed, and analysis of the sample by matrix-assisted laser desorption
ionization time-of-flight (MALDI-TOF) mass spectrometry revealed that the pro-
duct was indeed a mixture of open oligomers, with no evidence for macrocycle.
Changing the solvent to methanol, chloroform, or acetonitrile, as well as varying
Scheme 1. Synthesis of diformyl and diamino precursors 2 and 4.

MULTIHEMISALEN LIGANDS
3179
Scheme 2. Proposed synthesis of a [2 þ 2] Schiff base macrocycle.
the concentration, did not give the desired cyclic compound. Assuming that the
geometry of the diamine was not suitable, we tried the same reaction with 1,2-
phenylenediamine and 1,4-phenylenediamine, but no macrocycles were obtained.
Diamino-substituted precursor 4 was heated at reflux in ethanol for 12 h with 1
equivalent of 4,6-dihydroxyisophthalaldehyde, and we expected that a [2 þ 2] Schiff
base macrocycle would selectively form (Scheme 3). A reddish solid was collected by
filtration after the reaction mixture was cooled to room temperature. Analysis of 1H
NMR and MALDI-TOF mass spectra of the crude product revealed that only a mix-
ture of open oligomers was obtained. When diamino-substituted biphenyl 4 was
reacted with 2,3-dihydroxyterephthalaldehyde or 4,5,6-trihydroxyisophthalaldehyde,
again only mixtures of oligomeric species were obtained, even at very low
concentrations.
To determine whether the absence of macrocyclic product was due to a lack of
reactivity of the building blocks, two model compounds were synthesized (Scheme 4).
Ditopic ligand L1 was obtained in good yield after refluxing compound 2 with 2
equivalents of o-aminophenol overnight in ethanol. The same reaction conditions
applied to compound 4 and salicylaldehyde gave ditopic ligand L2 in good yield.
Clearly, both biphenyl building blocks are reactive enough to form Schiff base
ligands. It is then reasonable to think that the dihedral angle in the biphenyl building
blocks prevents the oligomeric species from adopting the correct orientation for
macrocyclization.
Scheme 3. Proposed synthesis of a [2 þ 2] Schiff base macrocycle.

3180
S. GUIEU
Scheme 4. Synthesis of ditopic ligands L1 and L2.
Knowing that the building blocks are sufficiently reactive and that only the
geometry prevents the cyclization, we changed the design for a unique building block
bearing both the aldehyde and the amino group (Scheme 5). Schiff base macrocycles
are usually formed by the condensation of two precursors: one bearing two alde-
hydes or ketones, and the other two amino groups. This allowed the synthesis of
two-, three-, four-, and six-fold symmetric macrocycles.[10] In a few examples, a sin-
gle precursor possessing both the aldehyde and the amino groups, one of them being
protected, has been used.[11]
Monoformylation of 4,40-biphenol 1 using magnesium chloride, formaldehyde,
and triethylamine gave monoformyl compound 5 in 21% yield (Scheme 5), which was
subsequently mononitrated using 70% nitric acid in glacial acetic acid.
Several methods have been used to selectively reduce nitro groups in the pres-
ence of formyl or imine groups, the most common being iron or zinc with dilute
HCl.[12] The major by-product of these reactions is transition-metal ions, which in
our case would complex into the hemisalen pockets and could not be easily removed.
Instead, sodium dithionite (Na2S2O4) was used as a reducing agent.[13] When nitro-
formyl compound 6 was heated at reflux with 6 equivalents of Na2S2O4 in a mixture
of ethanol and water, a dark purple solid formed rapidly. The purple solid was
collected by filtration and subjected to column chromatography over neutral alu-
mina to remove the salts. After removal of the solvent, a red powder was obtained.
Scheme 5. Synthesis of macrocycle L3.

MULTIHEMISALEN LIGANDS
3181
Figure 2. Section of the 1H NMR spectrum of macrocycle L3 in DMSO-d6.
The 1H NMR spectrum of the product in dimethylsulfoxide (DMSO-d6) shows a sin-
gle imine signal at 9.31 ppm and two hydroxyl signals at 13.39 and 9.94 ppm, respect-
ively (Fig. 2). These peaks indicate the formation of a highly symmetric compound
and not a mixture of oligomers. The large downfield shift of the phenol resonance at
13.39 ppm is characteristic of strong hydrogen bonding to an imine group. Six aro-
matic signals can be seen, divided into two sets of protons coupling together in an
AA0X fashion. The MALDI-TOF mass spectrum shows only one peak (at
m=z ¼ 634.8) that corresponds to the three-fold symmetric macrocycle L3 plus a
proton (Fig. 3). No evidence for open oligomers was found.
In conclusion, bis-aminophenol 4 and bis-salicylaldehyde 2 have been prepared
and characterized. Condensation studies showed that they do not form Schiff base
macrocycles with aromatic diformyl- or diamino-substituted aromatics, but they
can be used to synthesize ditopic ligands. Moreover, a new three-fold symmetric
Figure 3. Section of the MALDI-TOF mass spectrum of macrocycle L3. Inset: Experimental (left) and
simulated (right) isotope distribution patterns for the protonated ion.

3182
S. GUIEU
Schiff base macrocycle L3 has been synthesized and characterized. It is readily
accessible through a selective reduction=condensation one-pot reaction. The com-
plexation of different metals and the insertion of ditopic ligands L1, L2 and macro-
cycle L3 into three-dimensional architectures are currently under investigation.
EXPERIMENTAL
All reactions were carried out under air unless otherwise stated. Tetrahydro-
furan (THF) was distilled from sodium=benzophenone under nitrogen. Acetonitrile,
methanol, and triethylamine were purged with nitrogen gas and dried over molecular
sieves before use. Deuterated solvents were obtained from Cambridge Isotope
Laboratories, Inc. All reagents were used as received unless otherwise stated.
1H NMR (300 MHz) and 13C NMR (75.5 MHz) spectra were recorded on a
Bruker AV-300 spectrometer. 1H NMR (400 MHz) and 13C NMR (100.6 MHz) spec-
tra were recorded on a Bruker AV-400 spectrometer. Mass spectra and elemental
analyses were obtained at the UBC Microanalytical Services Laboratory. MALDI
mass spectra were obtained in a dithranol matrix (1:1 analyte–matrix, solvent free)
at the UBC Microanalytical Services Laboratory on a Bruker Biflex IV TOF mass
spectrometer equipped with a MALDI ion source. Electrospray ionization (ESI)
mass spectra were obtained on a Bruker Esquire-LC ion trap mass spectrometer
equipped with an electrospray ion source. Elemental analyses were obtained on
a Carlo Erba elemental analyzer EA 1108. Melting points were obtained on
a Fisher-John melting-point apparatus. Infrared (IR) spectra were obtained neat
using a Thermo Scientific Nicolet 6700 Fourier transform (FT)–IR spectrometer
equipped with a diamond attenuated total reflectance instrument.
4,4’-Dihydroxybiphenyl-3,3’-dicarbaldehyde 2 and
4,4’-Dihydroxybiphenyl-3-carbaldehyde 5
Et3N (4 eq., 19.4 mmol, 2.7 mL) was added dropwise to a solution of
4,40-dihydroxybiphenyl 1 (1 eq., 4.8 mmol, 900 mg), MgCl2 (4 eq., 19.4 mmol,
1.84 g), and (CH2O)n (4.5 eq., 21.8 mmol, 654 mg) in dry THF (20 mL) under a nitro-
gen atmosphere. After heating at reflux for 24 h, dilute HCl was added at rt until the
precipitate dissolved. Most of the THF was removed by rotary evaporation, and
then the aqueous phase was extracted with CH2Cl2 (3 ꢀ 25 mL). The combined
organic phases were dried over MgSO4, filtered, and then concentrated under
reduced pressure. Silica-gel flash column chromatography (eluent: CH2Cl2) of the
residue gave the monoformyl 5 (220 mg, 21%) as a pale yellow solid and the diformyl
2 (50 mg, 5%) as a pale yellow solid.
4,4’-Dihydroxybiphenyl-3,3’-dicarbaldehyde 2[14]
1H NMR (300 MHz, CDCl3, 25 ꢁC): d ¼ 11.02 (s, 2H, OH), 10.00 (s, 2H,
13
3
CH ¼ O), 7.76–7.73 (m, 4H, aromatic CH), 7.11 (d, JH-H 9.6 Hz, 2H, aromatic
ꢁ
=
CH); C NMR (75 MHz, CDCl3, 25 C): d ¼ 195.1 (CH O), 161.9 (C-OH), 134.2
(aromatic CH), 130.7 (aromatic quaternary C), 129.8 (aromatic CH), 120.5
(aromatic quaternary C), 117.5 (aromatic CH); ESI-MS (methanol): m=z ¼ 241.3

MULTIHEMISALEN LIGANDS
3183
[M ꢂ H]- (calcd. 241.1); IR (neat): v ¼ 2865, 1645, 1588, 1470, 1372, 1276, 1183, 1161,
1047, 1003, 911, 882, 833, 769, 734, 711, 690 cmꢂ1. Anal. calcd. for C14H10O4: C,
69.42; H, 4.16. Found: C, 69.25; H, 4.52. Mp 220–222 ꢁC.
4,4’-Dihydroxybiphenyl-3-carbaldehyde 5[15]
1H NMR (300 MHz, CDCl3, 25 ꢁC): d ¼ 10.97 (s, 1H, OH), 9.98 (s, 1H,
3
CH ¼ O), 7.74–7.71 (m, 2H, aromatic CH), 7.44 (d, JH-H 8.4 Hz, 2H, aromatic
13
3
CH), 7.06 (d, JH-H 8.7 Hz, 1H, aromatic CH), 6.93 (d, JH-H 8.4 Hz, 2H, aromatic
3
ꢁ
=
CH), 4.82 (s, 1H, OH); C NMR (75 MHz, CDCl3, 25 C): d ¼ 196.3 (CH O),
159.8 (C-OH), 156.7 (C-OH), 134.9 (aromatic CH), 133.0 (aromatic quaternary
C), 130.6 (aromatic CH), 130.1 (aromatic quaternary C), 127.2 (2 aromatic CH),
120.4 (aromatic quaternary C), 117.5 (aromatic CH), 115.7 (2 aromatic CH);
ESI-MS (methanol): m=z ¼ 213.3 [MꢂH]- (calcd. 213.1); IR (neat): v ¼ 3233, 1681,
1645, 1610, 1583, 1519, 1484, 1453, 1418, 1379, 1318, 1296, 1264, 1228, 1174,
1162, 1034, 1010, 907, 890, 845, 826, 770, 739, 691, 659, 630 cmꢂ1. Anal. calcd. for
C13H10O3: C, 72.89; H, 4.71. Found: C, 72.53; H, 4.81. Mp 177–179 ꢁC.
3,3’-Bis((E)-(2-hydroxyphenylimino)methyl)biphenyl-4,4’-diol L1
Diformyl 2 (1 eq., 41 mmol, 10 mg) and o-aminophenol (2 eq., 83 mmol, 9 mg)
were heated at reflux in EtOH (10 mL) for 5 min, and the solution was stirred at
rt for 12 h. The solid was collected by filtration, washed with EtOH, and dried under
1
vacuum. The hemisalen proligand L1 was obtained as a red solid (12 mg, 69%). H
NMR (400 MHz, DMSO-d6, 25 ꢁC): d ¼ 13.74 (s, 2H, OH), 9.76 (s, 2H, OH), 9.06 (s,
4
4
2H, CH ¼ N), 7.96 (d, JH-H 2.2 Hz, 2H, aromatic CH), 7.71 (dd, JH-H 2.2 Hz,
3JH-H 8.0 Hz, 2H, aromatic CH), 7.37 (d, JH-H 8.0 Hz, 2H, aromatic CH), 7.14
3
3
(dd, JH-H 7.0 Hz, JH-H 8.4 Hz, 2H, aromatic CH), 7.04 (d, JH-H 8.4 Hz, 2H, aro-
3
3
3
matic CH), 6.97 (d, JH-H 8.0 Hz, 2H, aromatic CH), 6.90 (dd, JH-H 7.0 Hz,
3
3JH-H8.0 Hz, 2H, aromatic CH); C NMR (100 MHz, DMSO-d6, 25 ꢁC): d ¼ 161.5
13
=
(CH N), 159.9 (C-OH), 151.2 (C-OH), 134.9 (aromatic quaternary C), 130.6 (aro-
matic CH), 130.2 (aromatic quaternary C), 129.6, 128.2 (aromatic CH), 119.8 (aro-
matic quaternary C), 119.7, 119.6, 117.3, 116.6 (aromatic CH); ESI-MS (methanol):
m=z ¼ 423.2 [M ꢂ H- (calcd. 423.1), 425.2 [M þ H]þ (calcd. 425.2); IR (neat):
v ¼ 2359, 1614, 1504, 1455, 1372, 1263, 1210, 1156, 1113, 1031, 928, 860, 819, 787,
757, 739, 669 cmꢂ1. Anal. calcd. for C26H12N2O4: C, 73.57; H, 4.75; N, 6.60. Found:
C, 73.85; H, 4.83; N, 6.22. Mp 278–280 ꢁC.
3,3’-Dinitro-[1,1’-biphenyl]-4,4’-diol 3
Nitric acid (70%, 2 mL) was added dropwise at rt to a solution of
4,40-dihydroxybiphenyl 1 (1 eq., 5.4 mmol, 1.0 g) in 20 mL of glacial AcOH. After
stirring for 10 min, water (10 mL) was added, and the solid was collected by filtration
and washed with water and EtOH. The dinitro product 3 was obtained as an orange
1
solid (380 mg, 25%). H NMR (300 MHz, DMSO-d6, 25 ꢁC): d ¼ 11.13 (s, 2H, OH),
4
8.15 (d, JH-H 2.4 Hz, 2H, aromatic CH), 7.87 (dd, JH-H 2.4 Hz, JH-H 8.7 Hz, 2H,
4
3
3
aromatic CH), 7.20 (d, JH-H 8.7 Hz, 2H, aromatic CH); 13C NMR (75 MHz,

3184
S. GUIEU
DMSO-d6, 25 ꢁC): d ¼ 151.2 (C-OH), 137.4 (aromatic quaternary C), 132.7 (aromatic
CH), 129.1 (aromatic quaternary C), 122.4, 119.6 (aromatic CH); ESI-MS (meth-
anol): m=z ¼ 275.3 [MꢂH]- (calcd. 275.0); IR (neat): v ¼ 3240, 3083, 1267, 1519,
1471, 1403, 1309, 1234, 1174, 1149, 1078, 1041, 870, 836, 818, 761, 666 cmꢂ1. Anal.
calcd. for C12H8N2O6: C, 52.18; H, 2.92; N, 10.14. Found: C, 52.62; H, 3.02; N, 9.70.
Mp 245–247 ꢁC.
3,3’-Diamino-[1,1’-biphenyl]-4,4’-diol 4
This compound is commercially available, but we synthesized it using the fol-
lowing procedure: Sodium dithionite (12 eq., 4.35 mmol, 760 mg) was added to a sol-
ution of dinitro 3 (1 eq., 362 mmol, 100 mg) in water (10 mL) and EtOH (20 mL).
After refluxing for 5 min, the yellow color disappeared, and the solvent was removed
under reduced pressure. The solid was washed with water and EtOH to afford the
1
diamino compound 4 as a white solid (40 mg, 51%). H NMR (300 MHz, DMSO-
4
d6, 25 ꢁC): d ¼ 8.93 (s, 2H, OH), 6.75 (d, JH-H 2.1 Hz, 2H, aromatic CH), 6.64 (d,
4
3JH-H 8.1 Hz, 2H, aromatic CH), 6.53 (dd, JH-H 2.1 Hz, 3JH-H 8.1 Hz, 2H, aromatic
CH), 4.61 (bs, 4H, NH2); ESI-MS (methanol): m=z ¼ 217.3 [M þ H]þ (calcd. 217.1).
3,3’-Bis((E)-(2-hydroxybenzylidene)amino)-[1,1’-biphenyl]-4,4’-diol
L2[16]
Diamino 4 (1 eq., 185 mmol, 40 mg) and salicylaldehyde (2 eq., 370 mmol, 45 mg)
were refluxed in EtOH (20 mL) for 5 min, and the solution was stirred at rt for 12 h.
The solid was collected by filtration, washed with EtOH, and dried under vacuum.
1
The hemisalen proligand L2 was obtained as a red solid (68 mg, 87%). H NMR
(400 MHz, DMSO-d6, 25ꢁC): d ¼ 13.82 (s, 2H, OH), 9.80 (s, 2H, OH), 9.10 (s, 2H,
4
4
3
CH ¼ N), 7.68 (d, JH-H 2.4 Hz, 2H, aromatic CH), 7.63 (dd, JH-H 1.6 Hz, JH-H
4
7.4 Hz, 2H, aromatic CH), 7.46 (dd, JH-H 2.4 Hz, JH-H 8.4Hz, 2H, aromatic CH),
3
4
3
3
3
7.40 (ddd, JH-H 1.6 Hz, JH-H 8.0 Hz, JH-H 8.0 Hz, 2H, aromatic CH), 7.02 (d, JH-H
3
3
8.4 Hz, 2H, aromatic CH), 6.96 (dd, JH-H 7.4 Hz, JH-H 8.0Hz, 4H, aromatic CH);
ESI-MS (methanol): m=z ¼ 423.3 [M ꢂ H]- (calcd. 423.1), 425.3 [M þ H]þ (calcd. 425.2).
4,4’-Dihydroxy-3’-nitrobiphenyl-3-carbaldehyde 6
Nitric acid (70%, 300 mL) was added slowly to
a
solution of
4,40-dihydroxybiphenyl-3-carbaldehyde 5 (150 mg, 701 mmol) in glacial AcOH
(10 mL). After stirring at rt for 5 min, water was added to the reaction, and the pre-
cipitate was collected by filtration and washed with water and methanol to give com-
1
pound 6 as an orange solid (190 mg, 99%). H NMR (300 MHz, CDCl3, 25 ꢁC):
4
d ¼ 11.07 (s, 1H, OH), 10.59 (s, 1H, OH), 10.01 (s, 1H, CH¼O), 8.30 (d, JH-H
3
2.7 Hz, 1H, aromatic CH), 7.81 (dd, JH-H 9.0, JH-H 3.7 Hz, 1H, aromatic CH),
4
4
7.76–7.73 (m, 2H, aromatic CH), 7.29 (d, JH-H 2.1 Hz, 1H, aromatic CH), 7.13
3
13
(d, JH-H 9.3 Hz, 1H, aromatic CH); C NMR (75 MHz, CDCl3, 25 ꢁC): d ¼ 194.0
=
(CH O), 159.9 (C-OH), 151.9 (C-OH), 140.1 (aromatic quaternary C), 137.3 (aro-
matic quaternary C), 133.9 (aromatic CH), 133.6 (aromatic CH), 130.6 (aromatic
quaternary C), 129.0 (aromatic CH), 121.2 (aromatic CH), 120.5 (aromatic

MULTIHEMISALEN LIGANDS
3185
quaternary C), 119.6 (aromatic CH), 117.3 (aromatic CH); ESI-MS (methanol): m=
z ¼ 258.3 [M ꢂ H]- (calcd. 258.0). IR (neat): v ¼ 3292, 3079, 2849, 1657, 1645, 1630,
1590, 1567, 1494, 1474, 1435, 1356, 1330, 1295, 1259, 1232, 1169, 1132, 1078, 1047,
970, 931, 876, 832, 764, 691 cmꢂ1. Anal. calcd. for C13H9NO5: C, 60.24; N, 5.40; H,
3.50. Found: C, 59.97; N, 5.48; H, 3.53. Mp 204–206 ꢁC.
[3 þ 0] Schiff Base Macrocycle L3
Sodium dithionite (Na2S2O4, 6 eq., 3.47 mmol, 600 mg) was added to a solution
of 4,40-dihydroxy-30-nitrobiphenyl-3-carbaldehyde 6 (1 eq., 579 mmol, 150 mg) in
MeOH (30 mL) and water (10 mL) at rt under air. After refluxing for 2 h, the solid
was isolated by centrifugation in MeOH=H2O to give the macrocycle as a dark pur-
ple powder. Purification by flash column chromatography (neutral alumina, eluent
1
CH2Cl2=MeOH) gave macrocycle L3 (147 mg, 99%) as a dark red solid. H NMR
(300 MHz, DMSO-d6, 25 ꢁC): d ¼ 13.39 (s, 3H, OH), 9.94 (s, 3H, OH), 9.31 (s, 3H,
4
4
CH ¼ N), 8.21 (d, JH-H 2.1 Hz, 3H, aromatic CH), 7.90 (d, JH-H 2.1 Hz, 3H, aro-
3
matic CH), 7.81 (dd, JH-H 8.7, JH-H 2.1 Hz, 3H, aromatic CH),7.60 (dd, JH-H
4
3
4
3
8.7, JH-H 2.1 Hz, 3H, aromatic CH),7.07 (d, JH-H 8.7 Hz, 3H, aromatic CH),
3
13
7.06 (d, JH-H 8.7 Hz, 3H, aromatic CH); C NMR (75 MHz, DMSO-d6, 25 ꢁC):
=
d ¼ 161.4 (CH N), 159.5 (C-OH), 151.0 (C-OH), 135.3 (aromatic quaternary C),
130.24 (aromatic quaternary C), 130.17 (aromatic CH), 130.07 (aromatic quaternary
C), 130.05 (aromatic CH), 125.1 (aromatic CH), 119.7 (aromatic quaternary C),
117.3 (aromatic CH), 117.1 (aromatic CH), 115.4 (aromatic CH); ESI-MS (meth-
anol): m=z ¼ 632.3 [M ꢂ H]- (calcd. 632.2); MALDI-TOF-MS: m=z ¼ 634.8 [M þ H]þ
(calcd. 634.2); IR (neat): v ¼ 3363, 1622, 1495, 1455, 1385, 1283, 1084, 860, 809 cmꢂ1
mp ꢃ 300 ꢁC (decomposition).
;
ACKNOWLEDGMENT
The author thanks Pr Mark J. MacLachlan (University of British Columbia,
Canada) for his help during the achievement of this work.
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