Balakrishnan and Velmathi Chirally Functionalized SBA-15 as Efficient Heterogeneous Catalyst for Asymmetric Ketone Reduction
2.2. Synthesis of Chiral Amine 1 from 5-Chloro
Salicylaldehdye and (1R, 2S)-(-)-Norephedrine
2.5. Immobilization of Modified Chiral
Amine Ligand on SBA-15 (3)
Calcined SBA-15 (1 g) was added to the toluene solution
of above synthesized 2 and the suspension was allowed
to stir at reflux temperature under nitrogen atmosphere for
48 h. After cooling, the powder was collected by filtra-
tion, washed successively with dry toluene, and then dried
under vacuum. Dried material was subjected to soxhlet-
extraction with dichloromethane for 24 hꢀ. Finally the
sample was dried under vacuum at 45–50 C. IR (KBr)
cm−1: 3340, 2950, 2857, 1635, 1439, 1251, 964, 807, 796
and 558.
Chiral amine 1 was synthesized based on the method
589
ꢀ
reported by us earlier.26 Melting point: 52–54 C. ꢅꢂꢆ35
=
+11ꢇ1 (c = 0ꢇ2, CHCl3ꢈ. FTIR (cm−1ꢈ: 3630 (–OH), 3340
1
(–NH), 3098 (ar–CH), 1238 (C–O). H NMR (300 MHz,
CDCl3ꢀ25 ꢀC): ꢉ = 1ꢇ01 (d, 3 H), 2.9 (q, 1 H), 3.15
(s, 1 H), 4.0 (dd, 2 H), 4.8 (d, 1 H), 6.7–7.4 (Ar–H, 8 H)
ppm. 13C NMR, CDCl3ꢀꢉ ppm: 14, 49, 57, 75, 117.8,
123.5, 124.2, 126.2, 127.8, 127.9, 128.4, 128.5, 141.2, 157.
220. Elemental Anal. Calcd: C, 65.86; H, 6.22; N, 4.8.
Found: C, 64.38; H, 6.63; N, 4.79.
2.6. Synthesis of Trimethylsilyl Capped Chiral
Ligand Immobilized SBA-15 (4)
2.3. Synthesis of SBA-15
Highly ordered mesoporous SBA-15 support was synthe-
sized by the procedure previously reported by Zhao et al.27
under hydrothermal conditions using a triblock organic
copolymer as a template. In a typical synthesis, triblock
copolymer (4 g), poly(ethylene oxide)–poly(propylene
oxide)–poly(ethylene oxide) (EO20–PO70–EO20ꢈ (Pluronic
P123, MW 5800) was dispersed in double-distilled water
(40 g) followed by the addition of 2 M aqueous HCl
Under extremely dry condition, a suspension of above
synthesized 3 (1 g) and hexamethyl disiloxane (HMDS)
(0.1 ml) was refluxed overnight with stirring under nitro-
gen atmosphere. The solvent was removed under reduced
pressure in a rotary evaporator and the dry powder was
washed two or three times with dry ethanol (10 ml) by
ꢀ
centrifugation and finally dried under vacuum at 80 C
for 8 h. Material recovery was ≥ 98%. TMS capping of
chiral amine immobilized SBA-15 was confirmed by IR
spectroscopy.
ꢀ
(120 ml) under stirring at ambient temperature (35 C) for
3 h. Finally, tetraethyl orthosilicate (4 g) was added to
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the homogeneous solution under stirring to form a gel at
IP: 185.50.250.40 On: Mon, 20 Jun 2016 04:44:01
ꢀ
40 C for 24 h. The resultant gel was allowed to stand
2.7. Asymmetric Borane Reductin of Prochiral
Ketone Using SBA-15 Immobilized Catalyst (4)
Copyright: American Scientific Publishers
for crystallization under static hydrothermal condition at
100 ꢀC for 48 h in a Teflon Parr reactor. The white colored
solid product was filtered off, washed with warm distilled
water several times, and dried at 100 ꢀC overnight. The as-
synthesized solid product was calcined at 540 ꢀC in air for
24 h to remove the organic template. The calcined mate-
rial was characterized using low angle powder XRD, BET
isotherm and SEM technique.
The chiral amine ligand 1 immobilized SBA-15 (4)
(320 mg, 30 mol%) was dissolved in dry toluene. Borane
dimethyl sulfide (BMS) (0.03, 0.3 mmol) was added drop
wise and then the reaction mixture was refluxed for half an
hour followed by the drop wise addition of acetophenone
(0.025, 0.1 mmol). The reaction mixture was continuously
refluxed for 12 hours, cooled to room temperature, and fil-
tered. To the filtrate, 2 N HCl was added and extracted
with dichloromethane. (R)-1-phenyl ethanol was separated
by column chromatography with silica gel as an adsorbent
and 98:2 hexane:ethyl acetate as an eluant.
2.4. Synthesis of 2-((1-hydroxy-1-phenylpropan-
2-ylamino)methyl)-5-(3-(trimethoxysilyl)
propyl)Phenol(2)
Coupling of the chiral amine 1 with 3-Cl propyl tri-
methoxysilane and immobilising on SBA-15 was done
similar to the procedure reported elsewhere.28–30 1H-NMR
3. RESULTS AND DISCUSSION
3.1. Synthesis of Immobilised Chiral Ligand
3
(300 MHz, CDCl3ꢈ: ꢉ = 0ꢇ75 (t, J = 4ꢇ5 Hz, 2 H, Si–
CH2–), 1.17 (d, 3J = 6ꢇ5 Hz, 3 H, CH–CH3ꢈ, 1.21 (q, 3J =
Chiral amine ligand 1 was synthesized by the condensation
of 5-chloro salicylaldehyde and (1R, 2S)-(-)-norephedrine.
The imine formed was reduced to the corresponding amine
using NaBH4/Methanol (Scheme 1). This chiral catalyst 1
was reported by us for asymmetric ketone reduction26 and
asymmetric carbon–carbon addition31 under homogeneous
(in solution phase) conditions with very good enantiomeric
excess and yield. On seeing the merits of the catalyst, we
focused our attention to immobilize this ꢁ-amino alcohol
3
4ꢇ3 Hz, 2 H, CH2–CH2–CH2ꢈ, 1.9 (t, J = 4ꢇ1 Hz, 2 H,
CH2–CH2–), 2.05 (s, 1 H, CHNH), 2.5 (b, s, 1 H, CH–
OH), 3.4 (sep, 3J = 7ꢇ5 Hz, 1 H, CH–CH3ꢈ, 3.8 (dd, 3J =
2 Hz, 2 H, CH2–NH), 4.3 (d, 2.1 Hz, 1 H, CH–OH),
5.3 (s, 9 H, OCH3ꢈ, 5.4 (s, 1 H, Ph–OH), 6.9 (d, 1 H,
Phenyl H), 7.0 (d, 1 H, phenyl H), 7.1 (d, 1 H, phenyl H),
589
35
7.24–7.34 (m, 5 H, Ar–H) ppm. [ꢂꢆ = +25ꢇ3 (c = 0ꢇ1
in methanol).
J. Nanosci. Nanotechnol. 13, 3079–3086, 2013
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