Synthesis of tri-and disalicylaldehydes and their chiral schiff base compounds

Article abstract of DOI:10.1080/00397910903040252

A suitable procedure for convenient preparation of 1,3,5-tris(4-hydroxy-5- formylphenyl)benzene (6) was exploited via 5-bromosalicylaldehyde as starting reactant. Among the obtained products, compound 6, 4-methoxy-3- formylphenylboronic acid (9), 1,3,5-tris(4-methoxy-5-formylphenyl)benzene (10), and 4-methoxy-4'-hydroxyl-3,3'-diformyl-1,1'-diphenyl (11) had not been reported previously. Two new chiral Schiff base ligands, L1 and L2, were obtained from the tri-or disalicylaldehydes.

Full text of DOI:10.1080/00397910903040252

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Synthesis of Tri- and Disalicylaldehydes
and Their Chiral Schiff Base Compounds
Hai-Bin Liu a b , Mei Wang a , Ying Wang a , Lin Wang a & Li-Cheng Sun
a c
a State Key Laboratory of Fine Chemicals, Dalian University of
Technology, Dalian, Liaoning, China
b Department of Biology and Chemical Engineering, Liaoning
Institute of Science and Technology, Benxi, Liaoning, China
c School of Chemical Science and Engineering, Royal Institute of
Technology, Stockholm, Sweden
Published online: 04 Mar 2010.
To cite this article: Hai-Bin Liu , Mei Wang , Ying Wang , Lin Wang & Li-Cheng Sun (2010) Synthesis of
Tri- and Disalicylaldehydes and Their Chiral Schiff Base Compounds, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 40:7, 1074-1081, DOI:
10.1080/00397910903040252
To link to this article: http://dx.doi.org/10.1080/00397910903040252
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Synthetic Communications1, 40: 1074–1081, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903040252
SYNTHESIS OF TRI- AND DISALICYLALDEHYDES AND
THEIR CHIRAL SCHIFF BASE COMPOUNDS
Hai-Bin Liu,1,2 Mei Wang,1 Ying Wang,1 Lin Wang,1 and
Li-Cheng Sun1,3
1State Key Laboratory of Fine Chemicals, Dalian University of Technology,
Dalian, Liaoning, China
2Department of Biology and Chemical Engineering, Liaoning Institute of
Science and Technology, Benxi, Liaoning, China
3School of Chemical Science and Engineering, Royal Institute of Technology,
Stockholm, Sweden
A suitable procedure for convenient preparation of 1,3,5-tris(4-hydroxy-5-formylphenyl)-
benzene (6) was exploited via 5-bromosalicylaldehyde as starting reactant. Among the
obtained products, compound 6, 4-methoxy-3-formylphenylboronic acid (9), 1,3,5-tris(4-
methoxy-5-formylphenyl)benzene (10), and 4-methoxy-40-hydroxyl-3,30-diformyl-1,10-
diphenyl (11) had not been reported previously. Two new chiral Schiff base ligands, L1
and L2, were obtained from the tri- or disalicylaldehydes.
Keywords: 5-Bromosalicylaldehyde; disalicylaldehyde; Schiff base ligands; trisalicylaldehyde
INTRODUCTION
Salicylaldehydes and their derivatives can be transformed to Schiff bases and
salen compounds, which are important ligands and have been widely used in asym-
metric catalysis.[1] Transition-metal complexes containing chiral Schiff bases or salen
ligands can catalyze many enantioselective reactions, such as asymmetric oxidation
of sulfides,[2] epoxidation of olefins,[3] cyclopropanation of styrene,[4] and asymmetric
hetero-Diels–Alder reactions.[5] Monosalicylaldehydes and their Schiff base ligands
have been widely studied, for example, 3-aryl-5-butylsalicylaldehydes were prepared
in our group by the Suzuki–Miyaura coupling reaction, as well as 10 new Schiff base
ligands,[6] which were applied to the asymmetric oxidation of aryl methyl sulfides to
give good to excellent ee values (up to 90% ee).[7]
However, there are few reports concerning the synthesis of tri- or disalicylalde-
hydes and the catalytic reactions using their Schiff base ligands. In 2007, Suresh and
coworkers prepared chiral Schiff base ligands 1 and 2 by condensation of two
Received March 24, 2009.
Address correspondence to Hai-Bin Liu, State Key Laboratory of Fine Chemicals, Dalian
University of Technology, Dalian 116012, Liaoning, China. E-mail: haibin0616@163.com
1074

SALICYLALDEHYDES AND SCHIFF BASES
1075
Scheme 1. Schiff base ligands 1 and 2.
trisalicylaldehydes and chiral aminoalcohol, which catalyzed the asymmetric
oxidation of thioanisole with good ee values (Scheme 1).[8]
In this article, we describe the synthesis of trisalicylaldehyde by hydroxyl
protection and formyl protection, forming arylboronic acid, followed by Suzuki–
Miyaura coupling reaction and hydroxyl deprotection. Moreover, disalicylaldehyde
was prepared via the same method as the synthesis of trisalicylaldehyde.
RESULTS AND DISCUSSION
At first, we attempted to prepare trisalicylaldehyde 6 through the simple
synthetic route as outlined in Scheme 2: 1,3,5-tribromobenzene transformed to
1,3,5-tribronic acid benzene 4 first, and then the Suzuki–Miyaura coupling reaction
of 4 with 5-bromosalicylaldehyde 5 gave trisalicylaldehyde 6. Unfortunately, all
attempts at forming arylboronic acid 4 were unsuccessful, presumably because of
the instability of the intermediate of 3 with n-BuLi.
Therefore, another synthetic route was designed to obtain trisalicylaldehyde 6,
shown in Scheme 3. Because phenol hydroxyl and formyl groups would be destroyed
in the presence of a strong base, they need to be protected. Compound 7 was
conveniently prepared in acetone for 10 h, and then it was reacted with triethylortho-
formate in absolute EtOH and a catalytic amount of ZrCl4 to obtain compound 8.
Lithiation of compound 8 with 1.2 equiv. of n-BuLi in tetrahydrofuran (THF) at
ꢀ78 ꢁC followed by reaction with 2.0 equiv. of B(OnBu)3 and acidic hydrolysis
Scheme 2. The simple synthetic route of preparing trisalicylaldehyde 6.

1076
H.-B. LIU ET AL.
Scheme 3. Preparation of Schiff base L1.
produced arylboronic acid 9 in 94% yield as a yellow needle crystal. Refluxing a
solution of 9 and 1,3,5-tribromobenzene in mixed ethylene glycol dimethyl ether
(DME) and water (3=1, v=v) in the presence of 15 mol% Pd(PPh3)4 and K2CO3
(6 equiv.) for 48 h provided trialdehyde 10 in 38% yield. Compound 10 was reacted
with BBr3 in CH2Cl2 at ꢀ78 ꢁC and then hydrolyzed to obtain trisalicylaldehyde 6.
In this step, the resulting mixture needed to be slowly and carefully added into
chilled water and stirred continuously until two liquid layers formed. Therefore, tri-
salicylaldehyde 6 was transformed to the corresponding Schiff base L1 in 36% yield
as a salmon-pink solid by condensation with (S)-valinol.
According to the literature, there are some reports of the synthesis of disalicy-
laldehydes.[9] Using the method of preparing trisalicylaldehyde 6 as a base, we
succeeded in synthesizing disalicylaldehyde 12 and its chiral Schiff base ligand L2.
The synthesis of chiral Schiff base ligand L2 is summarized in Scheme 4.
Compound 11 was obtained in 78% yield by taking advantage of the Suzuki–
Miyaura coupling reaction with 5-bromosalicylaldehyde 5 (1 equiv.) and arylboronic
acid 9 (1.2 equiv.) as reactants in mixed DME and water (3:1) at 90 ꢁC for 6 h.
Compound 11 was reacted with BBr3 in CH2Cl2 at ꢀ15 ꢁC and then hydrolyzed
to obtain disalicylaldehyde 12 as a light green solid in 67% yield. Thus, 2 equiv. of
(S)-valinol and disalicylaldehyde 12 were dissolved in an appropriate volume of
anhydrous ethanol and stirred for 12 h at 60 ꢁC. After flash-column chromatography
and drying in vacuo, the chiral Schiff base ligand L2 was obtained in 56% yield.
In conclusion, trisalicylaldehyde 6 and disalicylaldehyde 12 were successfully
synthesized via 5-bromosalicylaldehyde as starting reactant. Among the obtained
compounds, 6, 9, 10, and 11 have not been reported previously. Two new chiral
Schiff base ligands, L1 and L2, have also been prepared. The application of the

SALICYLALDEHYDES AND SCHIFF BASES
1077
Scheme 4. Preparation of Schiff base L2.
two new chiral Schiff base ligands is currently being explored for asymmetric
oxidation of sulfides.
EXPERIMENTAL
General Procedures
Catalysts Pd(PPh3)4
and (S)-valinol[11] were obtained by literature proce-
[10]
dures. Anhydrous THF was dried prior to use by distillation over sodium=benzophe-
˚
none ketyl. Absolute ethanol was predried by 4-A molecular sieves for 1 day and
then distilled over sodium=diethyl phthalate. A mixture of DME=water was
degassed before use for Suzuki–Miyaura coupling reactions. Melting points were
measured on an XRc-1 melting-point apparatus and are uncorrected. NMR, mass
spectroscopy (MS), and high-performance liquid chromatography (HPLC) spectra
were recorded on Unity Inova 400-MHz or Brucker 400-MHz (with tetramethyl-
silane as internal standard), Hewlett 5973 or HP 1100 MSD, and Waters instru-
ments, respectively. High-resolution mass spectra (HRMS) were obtained on a
Micromass GCT-TOF mass spectrometer.
5-Bromo-2-methoxybenzaldehyde (7)
Dimethylsulfate (1.51 g, 12 mmol) was added to a mixture of 5-bromosalicylal-
dehyde (5) (2.0 g, 10 mmol) and solid K2CO3 (2.76 g, 20 mmol) in acetone (30 mL).
The mixture was stirred at room temperature for 10 h before being quenched with
H2O (15 mL) and concentrated under reduced pressure. The residue was extracted
with CH2Cl2 (3 ꢂ 20 mL) and dried with anhydrous MgSO4. Evaporation of the sol-
vent afforded the title compound as a white solid (2.0 g, 93%); mp 107–109 ꢁC (lit.[12]
:
113.5–116.5 ꢁC); 1H NMR (400 MHz, CDCl3): d 3.37 (s, 3H, OCH3), 6.88 (d,
J ¼ 8.8 Hz, 1H), 7.61 (dd, J ¼ 2.4, 2.8 Hz, 1H), 7.89 (d, J ¼ 2.8 Hz, 1H), 10.36 (s, 1H,
CHO). EI-HRMS (C8H7BrO2): calcd. 213.9629; found 213.9634.
4-Bromo-2-(diethoxymethyl)-1-methoxybenzene (8)
Triethylorthoformate (5.92 g, 40 mmol) and anhydrous ZrCl4 (0.02 g,
0.1 mmol) were added to a suspension of 5-bromo-2-methoxybenzaldehyde (7)

1078
H.-B. LIU ET AL.
(4.28 g, 20 mmol) in absolute EtOH (20 mL). The mixture was stirred at room tem-
perature for several minutes until the solid was dissolved. The resulting mixture was
purified by chromatography (petroleum ether=EtOAc, 2.5=1) to give the title com-
1
pound as a light green liquid (5.64 g, 98%). H NMR (400 MHz, CDCl3): d 1.22
[t, J ¼ 4.4 Hz, 6H, (OCH2CH3)2], 3.59 [m, 4H, (OCH2CH3)2], 3.81 (s, 3H, OCH3),
5.72 [s, 1H, CH(OCH2CH3)2], 6.74 (d, J ¼ 8.8 Hz, 1H), 7.36 (dd, J ¼ 2.4, 2.4 Hz, 1H),
7.67 (d, J ¼ 2.4 Hz, 1H); GC mass: 288.
4-Methoxy-3-formylphenylboronic Acid (9)
A
solution of protected aldehyde 4-bromo-2-(diethoxymethyl)-1-
methoxybenzene (8) (5.76 g, 20 mmol) in THF (30 mL) was cooled to ꢀ78 ꢁC under
argon. n-BuLi (2.9 M in hexanes, 8.3 mL, 24 mmol) was added dropwise over 30 min.
The solution was stirred at ꢀ78 ꢁC for 1 h before being quenched with B(OnBu)3
(9.2 g, 40 mmol). The yellow resulting solution was stirred at ꢀ78 ꢁC for 2 h, allowed
to warm slowly to room temperature, and was stirred overnight. The mixture was
quenched with HCl (20 mL, 1 M) and extracted with Et2O (3 ꢂ 20 mL). The organic
layer was washed twice with H2O (20 mL) and once with brine (15 mL) and dried
with anhydrous Na2SO4. The solvent was evaporated, and the crude product was
purified by recrystallization from ethanol to obtain 3.39 g of yellow solid in a yield
of 94%. Mp 206–208 ꢁC; 1H NMR [400 MHz, CD3C(O)CD3]: d 3.11 [s, 2H,
B(OH)2], 4.0 (s, 3H, OCH3), 7.19 (d, J ¼ 8.8 Hz, 1H), 8.13 (dd, J ¼ 2.0, 2.0 Hz,
1H), 8.28 (d, J ¼ 3.6 Hz, 1H), 10.45 (s, 1H, CHO); 13C NMR [CD3C(O)CD3]: d
55.6, 111.5, 124.3, 134.4, 142.4, 163.8, 189.1, 206.1. EI-HRMS (C8H9O4B): calcd.
180.0590; found 180.0594.
1,3,5-Tris(4-methoxy-5-formylphenyl)benzene (10)
1,3,5-Tribromobenzene (0.78 g, 2.5 mmol), 4-methoxy-3-formylphenylboronic
acid (9) (2.7 g, 15 mmol), K2CO3 (2.07 g, 15 mmol), and Pd(PPh3)4 (0.73 g,
0.37 mmol, 15 mol%) were added to a Schlenk flask with a stirring bar. The mixture
was purged with argon. Degassed solvent of DME=water (3=1, v=v, 100 mL) was
then added. The mixture was refluxed with stirring in the dark at 90 ꢁC for 48 h under
the protection of argon. The organic layer was then separated, and the water layer
was extracted with CH2Cl2 (3 ꢂ 30 mL). The combined organic layers were washed
with brine and dried over anhydrous Na2SO4, and then the solvent was removed
under reduced pressure. The residue was purified by chromatography on silica gel,
eluting with CH2Cl2 to give the title compound as a white solid (0.46 g, 38%). Mp
257–258 ꢁC;1H NMR (400 MHz, CDCl3): d 3.95 (s, 9H, OCH3), 7.06 (d, J ¼ 8.4 Hz,
3H), 7.65 (s, 3H), 7.84 (dd, J ¼ 2.8, 2.4 Hz, 3H), 8.08 (d, J ¼ 2.0 Hz, 3H), 10.48 (s, 3H,
CHO). EI-HRMS (C30H24O6): calcd. 480.1573; found 480.1577.
1,3,5-Tris(4-hydroxy-5-formylphenyl)benzene (6)
BBr3 (1 M in CH2Cl2, 3.2 mL, 3.2 mmol) was added at ꢀ78 ꢁC under nitrogen
to
a suspension of 1,3,5-tris(4-methoxy-5-formylphenyl)benzene (10) (0.3 g,
0.63 mmol) in dry CH2Cl2 (6 mL). After 10 min, the external temperature was raised

SALICYLALDEHYDES AND SCHIFF BASES
1079
to ꢀ15 ꢁC, and the dark brown suspension was stirred for 1 h. The resulting mixture
was slowly poured into chilled water (10 mL) and stirred continuously until two
liquid layers were formed. The aqueous phase was extracted with Et2O (3 ꢂ 20 mL).
The combined organic layers were washed with brine, dried with MgSO4, and
concentrated under reduced pressure. Purification by column chromatography (CC)
(silica gel, CH2Cl2=MeOH, 100=1) afforded the title compound as a pale white solid
(0.18 g, 66%); mp > 300 ꢁC; 1H NMR (400 MHz, DMSO): d 7.15 (d, J ¼ 8.4 Hz, 3H),
7.81 (s, 3H), 8.07 (d, J ¼ 9.6 Hz, 3H), 8.11 (s, 3H), 10.35 (s, 3H, CHO), 10.93 (s, 3H,
OH); 13C NMR (DMSO): d 117.9, 122.5, 123.0, 127.6, 131.4, 135.2, 140.5, 160.5,
191.8. EI-HRMS (C27H18O6): calcd. 438.1103; found 438.1096.
Chiral Schiff Base Ligand L1
(S)-Valinol (0.48 g, 0.47 mmol) and 1,3,5-tris(4-hydroxy-5-formylphenyl)ben-
zene (6) (0.8 g, 0.12 mmol) were dissolved in 4 mL of EtOH. The solution was stir-
red overnight at 60 ꢁC. After the solvent was evaporated under reduced pressure,
the residue was subject to flash-column chromatography on silica gel using
CH2Cl2=CH3OH (95=5) as eluent to give the title compound as a salmon-pink solid
21
(0.27 g, 36%). Mp 129–132 ꢁC; ½aꢃ589 ¼ ꢀ284:5ꢁ (c 0.2, CH2Cl2); 1H NMR
(400 MHz, CDCl3): d 0.98 [t, 18H, CH(CH3)2], 1.98–1.91 [m, 3H, CH(CH3)2],
3.21–3.08 (m, 3H, N-CH), 3.94–3.70 (m, 6H,CH2OH), 7.91 (s, 3H, CH¼N), 7.28
(s, 3H), 6.63–6.61 (m, 9H), 14.15 (s, 3H, OH). EI-HRMS (C42H51N3O6): calcd.
693.3778; found 693.3771.
4-Methoxy-40-hydroxyl-3,30-diformyl-1,10-diphenyl (11)
5-Bromosalicylaldehyde (5) (0.76 g, 3.80 mmol), 3-formyl-4-methoxyphenyl-
boronic acid (9) (0.82 mg, 4.56 mmol), K2CO3 (0.79 g, 5.7 mmol), and Pd(PPh3)4
(0.22 g, 0.19 mmol, 5 mol%) were added to a Schlenk flask with a stirring bar.
The mixture was purged with argon. Degassed solvent of DME=water (3=1, v=v,
35 mL) was then added. The mixture was refluxed with stirring at 90 ꢁC for 6 h under
the protection of argon. The organic layer was then separated, and the water layer
was extracted with CH2Cl2 (3 ꢂ 15 mL). The combined organic layers were washed
with brine and dried over anhydrous MgSO4, and then the solvent was removed
under reduced pressure. The residue was purified by chromatography on silica gel,
eluting with CH2Cl2 to give the title compound as a light green solid (0.76 g,
78%). 1H NMR (400 MHz, CDCl3): d 3.93 (s, 3H, OCH3), 7.00–7.04 (m, 2H),
7.68–7.71 (m, 3H), 7.97 (d, J ¼ 2.4 Hz, 1H), 9.91 (s, 1H, CHO), 10.46 (s, 1H,
CHO), 10.94 (s, 1H, OH); EI-HRMS (C15H12O4): calcd. 256.0736; found 256.0732.
4,40-Diol-3,30-diformyl-1,10-diphenyl (12)
BBr3 (1 M in CH2Cl2, 13.6 mL, 13.6 mmol) was added at ꢀ15 ꢁC under nitro-
gen to a solution of 4-methoxy-40-hydroxy-3,30-biformyl-1,10-biphenyl (11) (0.87 g,
3.4 mmol) in dry CH2Cl2 (10 mL). The dark brown suspension was stirred for 1 h.
The resulting mixture was slowly poured into chilled water (30 mL) and stirred con-
tinuously until two liquid layers were formed. The aqueous phase was extracted with

1080
H.-B. LIU ET AL.
Et2O (3 ꢂ 20 mL). The combined organic layers were washed with water (2 ꢂ 20 mL)
and brine, dried with MgSO4, and concentrated under reduced pressure. Purification
by CC (silica gel, CH2Cl2=MeOH, 95=5) afforded the title compound as a yellow
solid (0.55 g, 67%). 1H NMR (400 MHz, CDCl3): d 7.04 (d, J ¼ 9.6 Hz, 2H),
7.66–7.68 (m, 4H), 9.93 (s, 2H, CHO), 10.95 (s, 2H, OH). EI-HRMS (C14H10O4):
calcd. 242.0579; found 242.0576.
Chiral Schiff Base Ligand L2
(S)-Valinol (0.21 g, 2 mmol) and 4,40-diol-3,30-diformyl-1,10-diphenyl (12)
(0.24 g, 1 mmol) were dissolved in 4 mL of EtOH. The solution was stirred for 12 h
at 60 ꢁC. After the solvent was evaporated under reduced pressure, the residue was
subject to flash-column chromatography on silica gel using petroleum ether=ethyl
acetate (1=5) as eluent to give the title compound as a salmon-pink solid (0.23 g,
21
1
56%). Mp 88–90 ꢁC; ½aꢃ589 ¼ ꢀ51:7ꢁ (c 0.2, CH2Cl2); H NMR (400 MHz, CDCl3):
d 0.92 (t, J ¼ 6.8 Hz, 12H), 1.87–1.95 (m, 2H), 3.04–3.09 (m, 2H), 3.78–3.86 (m,
13
4H), 6.82 (d, J ¼ 8.4 Hz, 2H), 7.04 (s, 2H), 7.28 (d, J ¼ 8.4 Hz, 2H), 8.17 (s, 2H,
=
CH¼N), 13.91 (s, 2H); C NMR (CDCl3): 165.8 (CH N), 161.5 (C-OH), 130.8,
130.6, 129.3, 118.4, 117.8, 77.8 (CH-N), 64.7 (CH2OH), 30.4 [CH(CH3)2], 20.0 and
18.8 [2C, CH(CH3)2]. MS (API-ES): calcd. m=z 412.3, found 413.3 [M þ H]þ,
435.2 [M þ Na]þ.
ACKNOWLEDGMENTS
We are grateful to the Chinese National Natural Science Foundation (Grant
Nos. 20471013 and 20633020), the Swedish Energy Agency, the Swedish Research
Council, and the K&A Wallenberg Foundation for financial support of this work.
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