Synthesis of new chiral schiff bases containing bromo- and iodo-functionalized hydroxynaphthalene frameworks

Article abstract of DOI:10.1080/00397911.2010.486505

Two series of chiral Schiff bases 3a-g and 4a-g containing bromo- and iodo-functionalized hydroxynaphthalene frameworks were conveniently prepared in acceptable to moderate yields by controlled halogenation of hydroxynaphthaldehyde and then condensation of the corresponding mono-, di-, and trihalohydroxynaphthaldehyde with the chiral amino alcohol. Except for 4d, the Schiff bases 3a-g, 4a-c, and 4e-g prepared in the present work have not been reported in literature so far, and they might be used as effective chiral inducers in some asymmetrically synthetic reactions.

Full text of DOI:10.1080/00397911.2010.486505

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Synthesis of New Chiral Schiff
Bases Containing Bromo- and Iodo-
Functionalized Hydroxynaphthalene
Frameworks
a
a
a
a
a b
Ying Wang , Mei Wang , Yu Wang , Yuee Chen & Licheng Sun
a
State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education
and Research Center on Molecular Devices , Dalian University of
Technology , Dalian , China
b
Department of Chemistry, Royal Institute of Technology ,
Stockholm , Sweden
Published online: 30 Mar 2011.
To cite this article: Ying Wang , Mei Wang , Yu Wang , Yuee Chen & Licheng Sun (2011) Synthesis of
New Chiral Schiff Bases Containing Bromo- and Iodo-Functionalized Hydroxynaphthalene Frameworks,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 41:9, 1381-1393, DOI: 10.1080/00397911.2010.486505
To link to this article: http://dx.doi.org/10.1080/00397911.2010.486505
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1
Synthetic Communications , 41: 1381–1393, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.486505
SYNTHESIS OF NEW CHIRAL SCHIFF BASES
CONTAINING BROMO- AND IODO-FUNCTIONALIZED
HYDROXYNAPHTHALENE FRAMEWORKS
1
Ying Wang, Mei Wang, Yu Wang, Yuee Chen, and
1
1
1
1,2
Licheng Sun
1
State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and
Research Center on Molecular Devices, Dalian University of Technology,
Dalian, China
2
Department of Chemistry, Royal Institute of Technology,
Stockholm, Sweden
GRAPHICAL ABSTRACT
Abstract Two series of chiral Schiff bases 3a–g and 4a–g containing bromo- and iodo-
functionalized hydroxynaphthalene frameworks were conveniently prepared in acceptable
to moderate yields by controlled halogenation of hydroxynaphthaldehyde and then conden-
sation of the corresponding mono-, di-, and trihalohydroxynaphthaldehyde with the chiral
amino alcohol. Except for 4d, the Schiff bases 3a–g, 4a–c, and 4e–g prepared in the present
work have not been reported in literature so far, and they might be used as effective chiral
inducers in some asymmetrically synthetic reactions.
Keywords Chiral schiff base; condensation; controlled halogenation; halohydroxy-
naphthaldehyde
Received December 9, 2009.
Address correspondence to Mei Wang, State Key Laboratory of Fine Chemicals, DUT-KTH Joint
Education and Research Center on Molecular Devices, Dalian University of Technology, Dalian 116012,
China. E-mail: symbueno@dlut.edu.cn
1
381

1382
Y. WANG ET AL.
INTRODUCTION
Chiral Schiff bases play important roles in various asymmetric syntheses.
Transition-metal complexes of chiral Schiff bases have been widely used as catalysts
[
in asymmetric reactions, such as asymmetric Strecker reaction, ring opening of
1]
[
2,3]
[4–8]
[9–11]
epoxides,
sulfoxidations.
epoxidation of olefins,
[12–18]
hetero-Diels–Alder reactions,
The structures of chiral Schiff base ligands can be easily
and
modified to improve the activity and enantioselectivity of Schiff base–coordinate
metal catalysts.
For chiral Schiff base ligands derived from salicylaldehyde and chiral amino
[
12,15]
[12,16]
alcohol, introduction of different substituents such as tert-butyl,
[
nitro,
to the 3- and=or 5-position of the salicylidenyl moiety of
17]
[18,19]
bromo,
and iodo
a Schiff base has an important influence on asymmetric catalytic reactions. It was
found that the transition metal–based catalysts of 3,5-dibromo- and 3,5-diiodo-
functionalized chiral Schiff bases displayed obviously better enantioselectivity in
the asymmetric oxidation of sulfides as compared to other analogous Schiff
bases. For example, in the case of the oxidation of thioanisole using the catalyst
ꢀ
system of VO(acac) and 3,5-diiodo (S)-1 or (R)-1 with H O as oxidant at 0 C,
2
2
2
Figure 1. Structures of some effective chiral Schiff bases used for asymmetric oxidation of sulfides.
Figure 2. Structures of chiral Schiff bases 3a–g and 4a–g prepared in this work.

HALO-FUNCTIONALIZED CHIRAL SCHIFF BASES
1383
the enantioselectivities of the reaction were up to 90.0–96.7% ee with 70–81% yield of
chiral methyl phenyl sulfoxide (Fig. 1).
[15,17]
In attempt to extend the scope of high-
performance, low-cost, and conveniently prepared chiral Schiff base ligands, we
prepared two series of chiral Schiff bases (3a–g and 4a–g) containing bromo- and
iodo-functionalized hydroxynaphthalene frameworks (Fig. 2) in acceptable to
moderate yields by controlled halogenation of hydroxynaphthaldehyde and then
condensation of the corresponding mono-, di-, and trihalohydroxynaphthaldehyde
with the chiral amino alcohol.
RESULTS AND DISCUSSION
3
-Hydroxy-2-naphthaldehyde (5) was conveniently prepared from 2-naphthol
[
20]
and dimethylformamide (DMF) according to the literature procedure. The other
starting compound, 1-hydroxy-2-naphthaldehyde (7), was synthesized by two steps:
first, oxidation of 1-naphthaldehyde by m-chloroperbenzoic acid (MCPBA) and then
by rearrangement of the formyl group from the oxygen atom to the 2-position of the
[21,22]
naphthalene ring.
Mono-, di-, and tribromohydroxynaphthaldehydes were available by controlled
bromination of 3-hydroxy-2-naphthaldehyde and 1-hydroxy-2-naphthaldehyde
(Schemes 1 and 2). The number of the Br atom(s) introduced to the naphthalene ring
depended on the reaction conditions, such as the ratio of Br to hydroxynaphthalde-
2
hyde, reaction temperature, reaction period, solvents, and the absence or presence of
iron powder as catalyst (Table 1). Bromination of 3-hydroxy-2-naphthaldehyde and
1
-hydroxy-2-naphthaldehyde with 1.5 equiv of Br at room temperature in CHCl for
2 3
4 h gave the corresponding monobromohydroxynaphthaldehyde 6a in 75–85% yields
and 8a in 45–50% yields,
[23]
respectively, as sole products. Compound 8a was
obtained in a lower yield than 6a because it was more strongly adsorbed on silica
gel when it was purified by chromatography. Introduction of the second Br atom
to the naphthalene ring is more difficult. Dibromination of 3-hydroxy-2-naphthalde-
ꢀ
hyde was carried out with addition of 3.0 equiv of Br in acetic acid at 70 C for 24 h.
2
Product 6b was isolated in an acceptable yield (55%) by flash chromatography.
Scheme 1. Bromination and iodination of 3-hydroxy-2-naphthaldehyde. Reagents and conditions: (a) Br
ꢀ
2
(
1.5 equiv), CHCl
0.54 equiv), CHCl
3
, rt, 4 h; (b) Br
ꢀ
2
(3.0 equiv), AcOH, 70 C, 24 h; (c) Br
2
(4.5 equiv), iron powder
PO (1:1:1, v=v=v),
(
rt, 6 h.
3
, 50 C, 24 h; (d) I
2
(0.5 equiv), KIO
3
(0.5 equiv), EtOH=AcOH=H
3
4

1384
Y. WANG ET AL.
Scheme 2. Bromination and iodination of 1-hydroxy-2-naphthaldehyde. Reagents and conditions: (a) Br
2
ꢀ
(
(
1.5 equiv), CHCl , rt, 4 h; (b) Br
3
2
(3.0 equiv), iron powder (0.36 equiv), CHCl
ꢀ
3
, 50 C, 24 h; (c) Br
(0.5 equiv), EtOH=
2
4.5 equiv), iron powder (0.54 equiv), CHCl
PO (1:1:1, v=v=v), rt, 6 h.
3
, 50 C, 24 h; (d) I
2
(0.5 equiv), KIO
3
AcOH=H
3
4
Compound 8b was prepared by treating 1-hydroxy-2-naphthaldehyde with 3.0 equiv
ꢀ
of Br in the presence of iron powder in CHCl at 50 C for 24 h. Tribromonated
2
3
hydroxynaphthaldehydes 6c and 8c were prepared with 5 and 7 as starting com-
pounds, respectively, in a hydroxynaphthaldehyde=Br =Fe ratio of 1:4.5:0.54 in
2
ꢀ
CHCl at 50 C for 24 h.
3
Introduction of an iodo group to ortho- and para-positions of the OH group of
-hydroxy-2-naphthaldehyde and 1-hydroxy-2-naphthaldehyde was carried out,
3
respectively, using I and potassium iodate as iodating reagent in a mixed solvent
2
of ethanol, acetic acid, and orthophosphoric acid in a ratio of 1:1:1 at room tempera-
ture for 6 h. Iodohydroxynaphthaldehydes 6d and 8d were obtained in 65–70% yields
(Schemes 1 and 2). Both of them have not been previously reported in literature.
Diiodination of naphthalene ring is more difficult. Our attempts to prepare diiodo-
substituted hydroxynaphthaldehydes from 5 and 7 by a procedure similar to that for
the preparation of 6d and 8d with a large excess of I and potassium iodate were not
successful.
2
Condensation of bromo- and iodo-functionalized hydroxynaphthaldehydes,
a–d and 8a–d, with chiral amino alcohols, for example, (S)-tert-leucinol and
6
(S)-valinol, gave two series of chiral Schiff bases, 3a–g and 4a–g. The condensation
reactions were carried out with equivalent amounts of hydroxynaphthaldehydes and
Table 1. Reaction conditions for bromination of hydroxynaphthaldehydes 5 and 7
Br
(equiv)
2
Temp.
ꢀ
Reaction
time (h)
Iron powder
(equiv)
Yield
a
(%)
Entry
Reactant
Product
( C)
Solvent
1
2
3
4
5
6
5
5
5
7
7
7
6a
6b
6c
8a
8b
8c
1.5
3.0
4.5
1.5
3.0
4.5
rt
70
50
rt
4
24
24
4
CHCl
AcOH
3
––
––
75–85
55
71
CHCl
CHCl
CHCl
CHCl
3
3
3
3
0.54
––
45–50
38
33
50
50
24
24
0.36
0.54
a
Isolated yield.

HALO-FUNCTIONALIZED CHIRAL SCHIFF BASES
1385
Scheme 3. Condensation of bromo- and iodo-functionalized hydroxynaphthaldehydes and chiral amino
alcohols. Reagents and conditions: (a) dry MeOH, reflux, 4 h.
chiral amino alcohols in anhydrous methanol solution at reflux for 4 h (Scheme 3).
The desired Schiff base ligands were obtained in acceptable to moderate yields after
flash chromatography and drying in vacuo or recrystallization from ethanol. Chiral
1
13
Schiff bases were characterized by mass spectroscopy (MS), H and C NMR
spectroscopy, and their optical rotations.
In summary, two series of mono-, di-, tribromo-, and monoiodohydroxy-
naphthaldehydes, 6a–d and 8a–d, were prepared in 33–85% yields by controlled
halogenation of 3-hydroxy-2-naphthaldehyde and 1-hydroxy-2-naphthaldehyde,
respectively, under different reaction conditions. Fourteen chiral Schiff bases, 3a–g
and 4a–g, were sequentially prepared from condensation of the corresponding
bromo- and iodo-functionalized hydroxynaphthaldehydes with chiral amino
[
19]
alcohols. To our knowledge, except for 4d,
the other 13 chiral Schiff bases have
not been reported so far. These new chiral Schiff bases containing bromo- and
iodo-functionalized hydroxynaphthalene frameworks may act as effective chiral
inducers in some asymmetrically synthetic reactions.
EXPERIMENTAL
Chiral amino acids, (S)-tert-leucine and (S)-valine, were purchased from Aldrich
and GL Biochem (Shanghai) Ltd., respectively. 2-Naphthol, 1-naphthaldehyde, and
other starting compounds of reagent grade were obtained from local suppliers and
used as received. 3-Hydroxy-2-naphthaldehyde (5) was prepared as yellow solid in
[
20]
65% yield by formylation of 2-naphthol according to the literature procedure.
Chiral amino alcohols were prepared by reduction of corresponding amino acids.
[
24]
Melting points were measured on an XRc-1 melting-point apparatus and were
1 13
uncorrected. The H and C NMR spectra were recorded on an Unity Inova 400

1386
Y. WANG ET AL.
NMR spectrometer with tetramethylsilane (TMS) as internal standard. Mass spectra
were performed by electrospray ionization (ESI) on an HP 1100 MSD instrument.
Elemental analyses were performed with a Thermoquest-Flash EA 1112 elemental
analyzer. Optical rotations were measured at 589 nm with a Jasco P-1010 digital
polarimeter.
1-Bromo-2-hydroxy-3-naphthaldehyde (6a)
Compound 6a was prepared by monobromination of 5 according to the litera-
1
[
23]
ture procedure.
ArH), 7.72 (t, 1H, ArH), 7.9 (d, 1H, ArH), 8.18 (s, 1H, ArH), 8.23 (d, 1H, ArH),
1
Yellow solid; yield: 75–85%. H NMR (CDCl ): d ¼ 7.46 (t, 1H,
3
ꢁ
0.05 (s, 1H, HC=O), 11.06 (s, 1H, ArOH). API-ES: m=z ¼ 248.9 [M ꢁ H] .
[23]
1,6-Dibromo-2-hydroxy-3-naphthaldehyde (6b)
A solution of Br (0.47 g, 3 mmol in 10 mL acetic acid) was added dropwise to
2
the solution of 3-hydroxy-2-naphthaldehyde (0.17 g, 1.0 mmol) in 20 mL acetic acid
ꢀ
for 30 min. After the mixture was stirred at 70 C for 24 h, a NaHSO saturated
3
aqueous solution (20 mL) was added. The mixture was extracted with CH Cl
2
2
(
3 ꢂ 15 mL). The organic layer was washed with brine and dried over anhydrous
Na SO . The solvent was then removed under reduced pressure and the product
2
4
was purified by flash chromatography on silica gel with petroleum ether=CH Cl
2
2
1
(
1:1, v=v) as eluent. Yellow solid; yield: 55%. H NMR (CDCl ): d ¼ 7.76 (d, 1H,
3
ArH), 8.07 (s, 1H, ArH), 8.08 (s, 1H, ArH), 8.11 (d, 1H, ArH), 10.05 (s, 1H,
HC=O), 11.06 (s, 1H, ArOH). API-ES: m=z ¼ 326.9 [M ꢁ H] .
ꢁ
1,5,6-Tribromo-2-hydroxy-3-naphthaldehyde (6c)
Iron powder (30 mg) was added to the CHCl solution (20 mL) of 3-hydroxy-2-
3
naphthaldehyde (0.17 g, 1.0 mmol), followed by dropwise addition of Br (0.71 g,
2
ꢀ
4
2
.5 mmol in 10 mL CHCl ) for 30 min. After the mixture was stirred at 50 C for
3
4 h, a NaHSO saturated aqueous solution (20 mL) was added. The following
3
1
workup was essentially identical with that for 6b. Yellow solid; yield: 71%. H
NMR (CDCl ): d ¼ 7.83 (d, 1H, ArH), 8.11 (d, 1H, ArH), 8.68 (s, 1H, ArH),
3
ꢁ
1
0.12 (s, 1H, HC=O), 11.18 (s, 1H, ArOH). API-ES: m=z ¼ 405.0 [M ꢁ H] .
1
-Iodo-2-hydroxy-3-naphthaldehyde (6d)
Iodine (0.25 g, 1.0 mmol) and KIO3 (0.21 g, 1.0 mmol) were added to the
solution of 3-hydroxy-2-naphthaldehyde (0.34 g, 2.0 mmol) in a mixed solvent
1.5 mL) of ethanol, acetic acid, and orthophosphoric acid (1:1:1, v=v=v). After the
(
mixture was stirred for 6 h at room temperature, a NaHSO saturated aqueous
3
solution (20 mL) was added. The following workup was essentially identical with
1
that for 6b. Yellow solid; yield: 70%. H NMR (CDCl ): d ¼ 7.44 (t, 1H, ArH),
3
7
.69 (t, 1H, ArH), 7.86 (d, 1H, ArH), 8.16 (d, 1H, ArH), 8.18 (s, 1H, ArH), 9.98
ꢁ
(
s, 1H, HC=O), 11.35 (s, 1H, ArOH). API-ES: m=z ¼ 296.9 [M ꢁ H] .

HALO-FUNCTIONALIZED CHIRAL SCHIFF BASES
1387
1-Hydroxy-2-naphthaldehyde (7)
[21]
First, 1-naphthylformate was prepared by a modified procedure. m-Chloro-
perbenzoic acid (0.19 g, 1.2 mmol) was added to the solution of 1-naphthaldehyde
(0.16 g, 1.0 mmol) in dry CH Cl (50 mL). The solution was stirred at room tempera-
ture under an N atmosphere for 12 h until 1-naphthaldehyde could not be detected
2 2
2
by thin-layer chromatographic (TLC) analysis. After filtration, a NaHCO saturated
3
aqueous solution (20 mL) was added. The following workup was essentially identical
with that for 6b. 1-Naphthylformate was isolated as a colorless oil in 75% yield and
þ
characterized by GC-MS (m=z ¼ 172.0 [M] ). Compound 7 was further prepared by
[
rearrangement of the formyl group according to the literature procedure. Yellow
22]
1
solid; yield: 42%. H NMR (CDCl ): d ¼ 7.37 (d, 1H, ArH), 7.50 (d, 1H, ArH), 7.54
3
(
t, 1H, ArH), 7.65 (t, 1H, ArH), 7.83 (d, 1H, ArH), 8.44 (d, 1H, ArH), 9.98 (s, 1H,
HC=O), 12.67 (s, 1H, ArOH). API-ES: m=z ¼ 171.1 [M ꢁ H] .
ꢁ
4-Bromo-1-hydroxy-2-naphthaldehyde (8a)
A solution of Br (0.24 g, 1.5 mmol in 10 mL CHCl ) was added dropwise to the
2
3
solution of 1-hydroxy-2-naphthaldehyde (0.17 g, 1.0 mmol) in CHCl (20 mL) for
3
3
rated aqueous solution (20 mL) was added. The following workup was essentially
0 min. After the mixture was stirred at room temperature for 4 h, a NaHSO satu-
3
1
identical with that for 6b. Yellow solid; yield: 45–50%. H NMR (CDCl ): d ¼ 7.64
3
(
t, 1H, ArH), 7.79 (t, 1H, ArH), 7.81 (s, 1H, ArH), 8.18 (d, 1H, ArH), 8.48 (d, 1H,
ArH), 9.92 (s, 1H, HC=O), 12.61 (s, 1H, ArOH). API-ES: m=z ¼ 248.9 [M ꢁ H] .
ꢁ
4,8-Dibromo-1-hydroxy-2-naphthaldehyde (8b)
Iron powder (20 mg) was added to the CHCl solution (20 mL) of 1-hydroxy-2-
3
naphthaldehyde (0.17 g, 1.0 mmol), followed by dropwise addition of Br (0.47 g,
2
ꢀ
3
.0 mmol in 10 mL CHCl ) for 30 min. After the mixture was stirred at 50 C for
3
2
workup was essentially identical with that for 6b. Yellow solid; yield: 38%. API-ES:
4 h, a NaHSO saturated aqueous solution (20 mL) was added. The following
3
ꢁ
m=z ¼ 326.9 [M ꢁ H] . The TLC analysis shows that product 8b was contaminated
with a small amount of unknown by-products of similar polarity, which are neither
8
a nor 8c. The crude product 8b was directly used for further preparation.
4,5,8-Tribromo-1-hydroxy-2-naphthaldehyde (8c)
Compound 8c was prepared by a procedure similar to that for 6c, using 1-hydroxy-
-naphthaldehyde in place of 3-hydroxy-2-naphthaldehyde. Yellow solid; yield: 33%.
API-ES: m=z ¼ 404.8 [Mꢁ H] . The TLC analysis shows that product 8c was contami-
nated with a small amount of unknown by-products of similar polarity, which are
neither 8a nor 8b. The crude product 8c was directly used for further preparation.
2
ꢁ
4-Iodo-1-hydroxy-2-naphthaldehyde (8d)
Compound 8d was prepared by a procedure similar to that for 6d, using
-hydroxy-2-naphthaldehyde in place of 3-hydroxy-2-naphthaldehyde. Yellow solid;
1

1388
Y. WANG ET AL.
1
yield: 65%. H NMR (CDCl ): d ¼ 7.60 (t, 1H, ArH), 7.75 (t, 1H, ArH), 8.03 (d, 1H,
3
ArH), 8.07 (s, 1H, ArH), 8.43 (d, 1H, ArH), 9.91 (s, 1H, HC=O), 12.60 (s, 1H,
ArOH). API-ES: m=z ¼ 297.0 [M ꢁ H] .
ꢁ
General Procedure for the Preparation of Ligands 3a–g and 4a–g
A chiral amino alcohol (1.2 mmol) and bromo- or iodo-substituted hydroxy-
naphthylaldehyde (1.0 mmol) were dissolved in dry methanol (20–50 mL) under a
nitrogen atmosphere. The solution was refluxed for 4 h, and then the solvent was
removed under reduced pressure to give a crude product, which was purified by flash
chromatography on silica gel with CH Cl =methanol (100:1, v=v) as eluent for 3a,
2
2
4a–g, and with CH Cl as eluent for 3d, 3f, 3g, or by recrystallization from ethanol
2 2
for 3b, 3c, and 3e.
3-((E)-((S)-1-Hydroxy-3-methylbutan-2-ylimino)methyl)-1-
bromonaphthalen-2-ol (3a)
2
1
ꢀ
1
Waxy red solid; yield: 50%; ½aꢃ ¼ ꢁ19.1 (c ¼ 0.01 mol=L, CH Cl ). H NMR
589
2
2
(
CDCl ): d ¼ 0.98 (d, 6H, HC(CH ) ), 1.56 (s br, 1H, CH OH), 1.98–2.03 [m, 1H,
3
3 2
2
HC(CH ) ], 3.16–3.21 (m, 1H, C=NꢁCH), 3.78 (dd, 1H, CH OH), 3.89 (dd, 1H,
3
2
2
CH OH), 7.35 (t, 1H, ArH), 7.59 (t, 1H, ArH), 7.77 (d, 1H, ArH), 7.83 (s, 1H,
2
1
3
ArH), 8.17 (d, 1H, ArH), 8.52 (s, 1H, HC=N), 14.14 (s br, 1H, ArOH). C NMR
(
1
[
[
CDCl ): d ¼ 165.23 (CH=N), 153.98 (CꢁOH), 133.85, 132.66, 129.42, 128.82,
3
27.62, 125.43, 124.04, 120.45, 106.27, 77.08 (CHꢁN), 64.31 (CH OH), 30.09
2
CH(CH ) ], 19.84 and 18.52 [2C, CH(CH ) ]. API-ES: m=z ¼ 336.0 and 338.0
3
2
3 2
þ
M þ H] .
3-((E)-((S)-1-Hydroxy-3-methylbutan-2-ylimino)methyl)-1,6-
dibromonaphthalen-2-ol (3b)
ꢀ
21
Red solid; yield: 73%; mp: 190–193 C; ½aꢃ ¼ ꢁ17.2 (c ¼ 0.01 mol=L,
ꢀ
5
89
1
CH Cl ). H NMR (CDCl ): d ¼ 0.99 [d, 6H, HC(CH ) ], 1.55 (s br, 1H, CH OH),
2
2
3
3 2
2
1
3
.97–2.03 (m, 1H, HC(CH ) ), 3.18–3.22 (m, 1H, C=NꢁCH), 3.78 (dd, 1H, CH OH),
2
3
2
2
.90 (dd, 1H, CH OH), 7.63 (d, 1H, ArH), 7.72 (s, 1H, ArH), 7.94 (s, 1H, ArH), 8.06
(
4
d, 1H, ArH), 8.51 (s, 1H, HC=N), 14.26 (s br, 1H, ArOH). API-ES: m=z ¼ 412.0,
ꢁ
14.0, and 416.0 [M ꢁ H] .
3-((E)-((S)-1-Hydroxy-3-methylbutan-2-ylimino)methyl)-1,5,6-
tribromonaphthalen-2-ol (3c)
ꢀ
1
Red solid; yield: 71%; mp: 215–216 C. H NMR (CDCl ): d ¼ 1.00 [d, 6H,
3
HC(CH ) ], 1.55 (s br, 1H, CH OH), 1.99–2.03 [m, 1H, HC(CH ) ], 3.22–3.27
3 2
3
2
2
(
m, 1H, C=NꢁCH), 3.78 (dd, 1H, CH OH), 3.92 (dd, 1H, CH OH), 7.67 (d, 1H,
2
2
ArH), 7.97 (d, 1H, ArH), 8.30 (s, 1H, ArH), 8.58 (s, 1H, HC=N), 14.60 (s br, 1H,
1
3
ArOH). C NMR (CDCl ): d ¼ 165.58 (CH=N), 155.27 (CꢁOH), 132.93, 132.86,
3
1
26.94, 126.29, 125.28, 121.87, 121.15, 106.87, 77.59 (CHꢁN), 64.35 (CH OH),
2

HALO-FUNCTIONALIZED CHIRAL SCHIFF BASES
1389
3
4
1.06 [CH(CH ) ], 20.06 and 18.72 [2C, CH(CH ) ]. API-ES: m=z ¼ 490.0, 492.0,
ꢁ
3
2
3 2
93.9, and 496.0 [M ꢁ H] .
3-((E)-((S)-1-Hydroxy-3,3-dimethylbutan-2-ylimino)methyl)-1-
bromonaphthalen-2-ol (3d)
2
1
ꢀ
1
Waxy red solid; yield: 34%; ½aꢃ ¼ ꢁ19.1 (c ¼ 0.01 mol=L, CH Cl ). H NMR
589
2
2
(
CDCl ): d ¼ 1.01 [s, 9H, C(CH ) ], 1.57 (s br, 1H, CH OH), 3.05–3.08 (m, 1H,
3
3 3
2
C=NꢁCH), 3.74 (dd, 1H, CH OH), 3.97 (dd, 1H, CH OH), 7.32 (t, 1H, ArH),
2 2
7
(
1
7
.57 (t, 1H, ArH), 7.73 (d, 1H, ArH), 7.80 (s, 1H, ArH), 8.13 (d, 1H, ArH), 8.50
13
s, 1H, HC=N), 14.24 (s br, 1H, ArOH). C NMR (CDCl ): d ¼ 165.31 (CH=N),
3
54.14 (CꢁOH), 132.87, 131.82, 129.60, 128.98, 125.27, 124.23, 120.70, 106.41,
7.70 (CHꢁN), 62.31 (CH OH), 33.39 [C(CH ) ], 27.19 [3C, C(CH ) ]. API-ES:
2
3 3
3 3
þ
m=z ¼ 350.0 and 352.0 [M þ H] .
3-((E)-((S)-1-Hydroxy-3,3-dimethylbutan-2-ylimino)methyl)-1,6-
dibromonaphthalen-2-ol (3e)
ꢀ
21
Orange solid; yield: 42%; mp: 254–255 C; ½aꢃ ¼ ꢁ24.7 (c ¼ 0.01 mol=L,
ꢀ
5
89
1
CH Cl ). H NMR (CDCl ): d ¼ 1.02 [s, 9H, C(CH ) ], 1.57 (s br, 1H, CH OH),
2
2
3
3 3
2
3
7
(
1
7
.07–3.10 (m, 1H, C=NꢁCH), 3.74 (dd, 1H, CH OH), 4.00 (dd, 1H, CH OH),
2
2
.62 (d, 1H, ArH), 7.71 (s, 1H, ArH), 7.90 (s, 1H, ArH), 8.00 (d, 1H, ArH), 8.49
1
3
s, 1H, HC=N), 14.35 (s br, 1H, ArOH). C NMR (CDCl ): d ¼ 165.43 (CH=N),
3
54.52 (CꢁOH), 132.54, 131.66, 130.60, 127.43, 125.64, 124.31, 121.11, 106.53,
7.68 (CHꢁN), 62.41 (CH OH), 33.37 [C(CH ) ], 27.21 [3C, C(CH ) ]. API-ES:
2
3 3
3 3
ꢁ
m=z ¼ 426.0, 428.0 and 430.0 [M ꢁ H] . Anal. calcd. for C H Br NO : C, 47.58;
1
7
19
2
2
H, 4.46; N, 3.26. Found: C, 47.85; H, 4.40; N, 3.19.
3-((E)-((S)-1-Hydroxy-3-methylbutan-2-ylimino)methyl)-1-
iodonaphthalen-2-ol (3f)
1
Waxy red solid; yield: 35%. H NMR (CDCl ): d ¼ 0.98 [d, 6H, HC(CH ) ],
3
3 2
1
.60 (s br, 1H, CH OH), 1.97–2.02 [m, 1H, HC(CH ) ], 3.16–3.21 (m, 1H, C=Nꢁ
CH), 3.78 (dd, 1H, CH OH), 3.89 (dd, 1H, CH OH), 7.34 (t, 1H, ArH), 7.57 (t,
2 2
2
3 2
1
H, ArH), 7.74 (d, 1H, ArH), 7.84 (s, 1H, ArH), 8.10 (d, 1H, ArH), 8.46 (s, 1H,
1
3
HC=N), 14.32 (s br, 1H, ArOH). C NMR (CDCl ): d ¼ 165.09 (CH=N), 156.97
3
(
7
CꢁOH), 138.85, 136.53, 134.30, 130.62, 130.04, 129.19, 128.07, 124.28, 120.16,
2 3 2 3 2
7.70 (CHꢁN), 64.50 (CH OH), 30.24 [CH(CH ) ], 19.96 and 18.82 (2C, CH[CH ) ].
ꢁ
API-ES: m=z ¼ 382.0 [M ꢁ H] .
3-((E)-((S)-1-Hydroxy-3,3-dimethylbutan-2-ylimino)methyl)-1-
iodonaphthalen-2-ol (3g)
1
Waxy red solid; yield: 30%. H NMR (CDCl ): d ¼ 1.01 [d, 9H, C(CH ) ], 1.59
3
3 3
(
1
s br, 1H, CH OH), 3.06–3.09 (m, 1H, C=NꢁCH), 3.75 (dd, 1H, CH OH), 3.98 (dd,
2
2
H, CH OH), 7.32 (t, 1H, ArH), 7.55 (t, 1H, ArH), 7.71 (d, 1H, ArH), 7.82 (s, 1H,
2
1
3
ArH), 8.07 (d, 1H, ArH), 8.44 (s, 1H, HC=N), 14.38 (s br, 1H, ArOH). C NMR

1390
Y. WANG ET AL.
(
1
2
CDCl ): d ¼ 165.06 (CH=N), 156.92 (CꢁOH), 136.30, 134.28, 130.45, 129.88,
3
29.08, 127.90, 124.18, 120.01, 77.72 (CHꢁN), 62.28 (CH OH), 33.32 [C(CH ) ],
2
3 3
ꢁ
7.15 [3C, C(CH ) ]. API-ES: m=z ¼ 396.0 [M ꢁ H] .
3
3
2-((E)-((S)-1-Hydroxy-3-methylbutan-2-ylimino)methyl)-4-
bromonaphthalen-1-ol (4a)
ꢀ
21
Yellow solid; yield: 65%; mp: 137–138 C; ½aꢃ ¼ ꢁ184.8 (c ¼ 0.01 mol=L,
ꢀ
5
89
1
CH Cl ). H NMR (CDCl ): d ¼ 1.01 [t, 6H, HC(CH ) ], 1.62 (s br, 1H, CH OH),
2
2
3
3 2
2
1
CH OH), 3.90 (dd, 1H, CH OH), 7.43 (t, 1H, ArH), 7.54 (d, 1H, ArH), 7.56 (s,
.98–2.03 [m, 1H, HC(CH ) ], 3.23–3.24 (m, 1H, C=NꢁCH), 3.77 (dd, 1H,
2 2
3
2
1
1
1
H, ArH), 7.65 (t, 1H, ArH), 7.93 (d, 1H, ArH), 8.32 (s, 1H, HC=N), 13.24 (s br,
1
3
H, ArOH). C NMR (CDCl ): d ¼ 177.38 (CH=N), 161.70 (CꢁOH), 135.70,
3
31.30, 130.46, 127.55, 125.89, 125.26, 109.12, 106.58, 70.99 (CHꢁN), 64.17
(
CH OH), 29.64 [CH(CH ) ], 19.87 and 18.31 [2C, CH(CH ) ]. API-ES: m=
2
3 2
ꢁ
3 2
z ¼ 334.0 and 336.0 [M ꢁ H] .
2-((E)-((S)-1-Hydroxy-3-methylbutan-2-ylimino)methyl)-4,8-
dibromonaphthalen-1-ol (4b)
ꢀ
21
Yellow solid; yield: 50%; mp: 159–160 C; ½aꢃ ¼ ꢁ148.6 (c ¼ 0.01 mol=L,
ꢀ
5
89
1
CH Cl ). H NMR (CDCl ): d ¼ 1.04 [d, 6H, HC(CH ) ], 1.58 (s br, 1H, CH OH),
2
2
3
3 2
2
2
CH OH), 3.94 (dd, 1H, CH OH), 7.00 (s, 1H, ArH), 7.71 (t, 1H, ArH), 7.73 (d,
.02–2.07 [m, 1H, HC(CH ) ], 3.30–3.31 (m, 1H, C=NꢁCH), 3.78 (dd, 1H,
2 2
3
2
1
3
1
H, ArH), 7.79 (d, 1H, ArH), 8.50 (s, 1H, HC=N), 13.27 (s br, 1H, ArOH).
C
NMR (CDCl ): d ¼ 176.03 (CH=N), 161.83 (CꢁOH), 134.26, 134.17, 132.19,
3
1
2
30.98, 129.25, 128.09, 120.25, 109.51, 105.66, 70.95 (CHꢁN), 64.03 (CH OH),
2
9.65 [CH(CH ) ], 19.87 and 18.40 [2C, CH(CH ) ]. API-ES: m=z ¼ 411.9, 413.9,
3
2
3 2
ꢁ
and 415.9 [M ꢁ H] .
2-((E)-((S)-1-Hydroxy-3-methylbutan-2-ylimino)methyl)-4,5,8-
tribromonaphthalen-1-ol (4c)
ꢀ
21
Yellow solid; yield: 46%; mp: 190–193 C; ½aꢃ ¼ ꢁ117.4 (c ¼ 0.01 mol=L,
ꢀ
5
89
1
CH Cl ). H NMR (CDCl ): d ¼ 1.06 [d, 6H, HC(CH ) ], 1.55 (s br, 1H, CH OH),
2
2
3
3 2
2
2
3
(
1
1
.04–2.11 [m, 1H, HC(CH ) ], 3.35–3.37 (m, 1H, C=NꢁCH), 3.81 (dd, 1H, CH OH),
3
2
2
.94 (dd, 1H, CH OH), 7.69 (d, 1H, ArH), 7.92 (d, 1H, ArH), 8.48 (s, 1H, ArH), 8.51
2
1
3
s, 1H, HC=N), 13.71 (s br, 1H, ArOH). C NMR (CDCl ): d ¼ 176.44 (CH=N),
3
64.49 (CꢁOH), 135.11, 134.37, 131.74, 130.77, 128.52, 125.63, 121.30, 110.76,
09.20, 70.63 (CHꢁN), 63.92 (CH OH), 29.68 [CH(CH ) ], 19.83 and 18.50 [2C,
2
3 2
ꢁ
CH(CH ) ]. API-ES: m=z ¼ 489.9, 491.9, 493.9, and 495.9 [M ꢁ H] .
3
2
2-((E)-((S)-1-Hydroxy-3,3-dimethylbutan-2-ylimino)methyl)-4-
bromonaphthalen-1-ol (4d)
ꢀ
1
Yellow solid; yield: 53%; mp: 190–192 C. H NMR (CDCl ): d ¼ 1.07 [s, 9H,
3
C(CH ) ], 1.62 (s br, 1H, CH OH), 3.16 (m, 1H, C=NꢁCH), 3.77 (dd, 1H, CH OH),
3
3
2
2

HALO-FUNCTIONALIZED CHIRAL SCHIFF BASES
1391
4
.09 (dd, 1H, CH OH), 7.48 (t, 1H, ArH), 7.55 (d, 1H, ArH), 7.60–7.65 (m, 2H,
2
1
3
ArH), 7.95 (d, 1H, ArH), 8.27 (s, 1H, HC=N), 13.28 (s br, 1H, ArOH). C NMR
(
1
[
CDCl ): d ¼ 177.12 (CH=N), 162.02 (CꢁOH), 135.68, 131.27, 131.02, 130.40
3
27.62, 125.92, 125.25, 109.14, 106.69, 74.97 (CHꢁN), 62.11 (CH OH), 33.26
2
ꢁ
C(CH ) ], 26.97 [3C, C(CH ) ]. API-ES: m=z ¼ 348.0 and 350.0 [M ꢁ H] .
3
3
3 3
2-((E)-((S)-1-Hydroxy-3,3-dimethylbutan-2-ylimino)methyl)-4,8-
dibromonaphthalen-1-ol (4e)
ꢀ
21
Yellow solid; yield: 66%; mp: 90–95 C; ½aꢃ ¼ ꢁ242.4 (c ¼ 0.01 mol=L,
ꢀ
5
89
1
CH Cl ). H NMR (CDCl ): d ¼ 1.07 [s, 9H, C(CH ) ], 1.59 (s br, 1H, CH OH),
2
2
3
3 3
2
3
1
.18 (m, 1H, C=NꢁCH), 3.73 (dd, 1H, CH OH), 4.08 (dd, 1H, CH OH), 6.82 (s,
2
2
H, ArH), 7.66 (t, 1H, ArH), 7.71 (d, 1H, ArH), 7.79 (d, 1H, ArH), 8.48 (s, 1H,
1
3
HC=N), 13.46 (s br, 1H, ArOH). C NMR (CDCl ): d ¼ 175.87 (CH=N), 162.19
3
(
7
CꢁOH), 134.22, 134.09, 132.07, 130.90, 129.30, 128.01, 120.16, 109.44, 105.60,
2 3 3 3 3
4.82 (CHꢁN), 61.94 (CH OH), 33.23 [C(CH ) ], 26.93 [3C, C(CH ) ]. API-ES:
ꢁ
m=z ¼ 426.0, 428.0, and 430.1 [M ꢁ H] .
2-((E)-((S)-1-Hydroxy-3-methylbutan-2-ylimino)methyl)-4-
iodonaphthalen-1-ol (4f)
ꢀ
1
Yellow solid; yield: 60%; mp: 127–129 C. H NMR (CDCl ): d ¼ 1.03 [d, 6H,
3
HC(CH ) ], 2.01–2.05 [m, 1H, HC(CH ) ], 3.35 (s br, 1H, CH OH), 3.36 (m, 1H,
3
2
3 2
2
C=NꢁCH), 3.78 (dd, 1H, CH OH), 3.95 (dd, 1H, CH OH), 7.29 (s, 1H, ArH),
2
2
7
.47 (t, 1H, ArH), 7.63 (t, 1H, ArH), 7.78 (d, 1H, ArH), 7.79 (d, 1H, ArH), 8.39
13
(
1
s, 1H, HC=N), 13.12 (s br, 1H, ArOH). C NMR (CDCl ): d ¼ 177.98 (CH=N),
3
61.66 (CꢁOH), 138.26, 137.41, 132.54, 131.64, 130.99, 125.96, 125.28, 110.68,
1.01 (CHꢁN), 64.17 (CH OH), 29.67 [CH(CH ) ], 19.89 and 18.33 [2C, CH(CH ) ].
7
2
3 2
3 2
ꢁ
API-ES: m=z ¼ 382.0 [M ꢁ H] .
2-((E)-((S)-1-Hydroxy-3,3-dimethylbutan-2-ylimino)methyl)-4-
iodonaphthalen-1-ol (4g)
ꢀ
1
Yellow solid; yield: 79%; mp: 94–97 C. H NMR (CDCl ): d ¼ 1.06 [s, 9H,
3
C(CH ) ], 3.15 (m, 1H, C=NꢁCH), 3.74 (dd, 1H, CH OH), 4.07 (dd, 1H, CH OH),
3
3
2
2
6
1
.88 (s, 1H, ArH), 7.43 (t, 1H, ArH), 7.54 (d, 1H, ArH), 7.61 (t, 1H, ArH), 7.80 (d,
H, ArH), 8.22 (s, 1H, HC=N), 13.35 (s br, 1H, ArOH). C NMR (CDCl3):
1
3
d ¼ 177.76 (CH=N), 161.98 (CꢁOH), 138.09, 137.38, 132.65, 131.59, 130.84,
1
25.92, 125.18, 110.57, 74.94 (CHꢁN), 62.06 (CH OH), 33.32 [C(CH ) ], 26.94
ꢁ
3 3 17 20 2
2
3 3
[
3C, C(CH ) ]. API-ES: m=z ¼ 396.0 [M ꢁ H] . Anal. calcd. for C H INO : C,
5
1.40; H, 5.07; N, 3.53. Found: C, 52.50; H, 5.51; N, 3.48.
ACKNOWLEDGMENTS
We gratefully acknowledge support from the National Natural Science Foun-
dation of China (Grant No. 20973032), the Program for Changjiang Scholars and

1392
Y. WANG ET AL.
Innovative Research Team in University (IRT0711), and the K & A Wallenberg
Foundation of Sweden.
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2