Studies of the Henry reaction catalyzed by Cu-O and Zn-O complexes with dimethoxysilane-bridged derivatives

Article abstract of DOI:10.1007/s11164-010-0128-3

Dimethyldimethoxysilane, methylphenyldimethoxysilane, and diphenyldimethoxysilane have been synthesized by a one-step, simple method and used as catalysts in the Henry reaction with Cu(OAc)₂.H₂O and Zn(OAc)₂.2H₂O, affording 60-96% conversion under the optimum catalytic conditions. Springer Science+Business Media B.V. 2010.

Full text of DOI:10.1007/s11164-010-0128-3

Res Chem Intermed (2010) 36:181–191
DOI 10.1007/s11164-010-0128-3
Studies of the Henry reaction catalyzed by Cu–O
and Zn–O complexes with dimethoxysilane-bridged
derivatives
•
Luo Mei Han Bing Yang Shu Song
•
Received: 5 May 2009 / Accepted: 24 November 2009 / Published online: 12 March 2010
Ó Springer Science+Business Media B.V. 2010
Abstract Dimethyldimethoxysilane, methylphenyldimethoxysilane, and diphenyldi-
methoxysilane have been synthesized by a one-step, simple method and used as catalysts
in the Henry reaction with Cu(OAc)2ÁH2O and Zn(OAc)2Á2H2O, affording 60–96%
conversion under the optimum catalytic conditions.
Keywords Dimethyldimethoxysilane Á Methylphenyldimethoxysilane Á
Diphenyldimethoxysilane Á Co-catalysts Á Henry reaction
Introduction
The Henry reaction, or the nitroaldol reaction, is an important organic reaction involving
formation of C–C bonds. The product of this reaction is a b-nitroalcohol which can be
converted to a variety of products, for example ketones, b-aminoalcohols, and
nitroalkenes after oxidation, reduction, and dehydration reactions, then denitration [1–3].
L. Mei (&) Á H. B. Yang Á S. Song
Department of Chemical Engineering, Hefei University of Technology, 230009 Hefei, China
e-mail: luomei@pku.edu.cn; lmhh5523385@yahoo.cn
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In the last decade many research groups, for example the Shibasaki group [4, 5],
the Corey group [6], the Evans Group [7], the Jorgensen group [8], and the Trost
group [1, 9], have made great contributions to the Henry reaction. Inspired by their
work, we have performed careful research on the Henry reaction, and achieved
moderate to excellent conversion.
Results and discussion
First, we synthesized dimethyldimethoxysilane, methylphenyldimethoxysilane, and
diphenyldimethoxysilane ligands (Fig. 1) by reaction of dichlorodimethylsilane,
methylphenyldichlorosilane, and diphenyldichlorosilane with methanol, with pyr-
idine as dehydrochlorination agent [1]. These compounds were all characterized by
NMR.
We did not obtain the crystal structure of the complexes, and IR can give some
explanation. Figure 2 shows the IR of complexes 2a and 2b and the dimethyldi-
methoxy ligand. From the comparison, the m (Cu–O, Zn–O) vibration was reported
in the range 900–400 cm-1, strong absorption was observed within this range in the
spectra of Cu–O and Zn–O.
Next they were used with Cu(OAc)2ÁH2O and Zn(OAc)2Á2H2O to catalyze the
Henry reaction. Catalysts 1a, 1b, 2a, and 2b, and catalysts 3a and 3b were obtained
separately (Fig. 1). Comparison of their catalytic activity in the Henry reaction
showed catalyst 2a resulted in better reactivity during 24 h reaction time at room
temperature (Table 1).
We also examined the effect of solvents on the conversion of the reaction
(Table 2). Methanol was found to provide the best conversion. This is because
methanol is more polar than CH2Cl2, toluene, and hexane.
In order to achieve the highest conversion in the Henry reaction we prolonged the
reaction time to 48 h; conversion was increased to 74%.
Consequently, the best reaction conditions were determined to involve of the use
of 30 mol% catalyst 2a in THF solvent at room temperature for 2 days.
Catalyst 2a resulted in moderate to excellent conversion to various prochiral
aldehydes including both aromatic and aliphatic aldehydes (Table 3); this is closely
connected with the combination of P–p conjugate effects, electron effects, and steric
OCH3
OCH3
OCH3
OCH3
OAc
OAc
R1
R2
OAc
OAc
R1
R2
Cu
Si
Si
Zn
catalyst 1b:
R1, R2: CH3, Ph
catalyst 1a:
R1, R2: CH3, Ph
catalyst 2a: R1, R2:
catalyst 3a: R1, R2:
catalyst 2b: R1, R2:
catalyst 3b: R1, R2:
CH3C, H3
CH3,CH3
Fig. 1 The synthetic route to catalysts 1a–3a and 1b–3b
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183
Complex 2b
Complex 2a
100
80
60
40
20
0
100
80
60
40
20
0
-20
Ligand 2a
100
80
60
3500
3000
2500
2000
1500
1000
500
v/cm-1
Fig. 2 Comparison of the IR spectra of the ligand and complexes 2a and 2b
Table 1 Effect of catalysts
Catalyst
Conv. (%)a
1a
2a
1b
2b
3a
3b
12
51
20
48
20
50
Reactions were carried out on 1 mmol PhCHO with 0.2 mL CH3NO2, in 4 mL methanol at room
temperature (10–20 °C)
a
The conv.% was measured by 1HNMR
effects. For example, because of the steric hindrance effect conversion of 1-naphthyl
aldehyde is lowest.
The mechanism that can be proposed is that the C=O bond is activated by metal
ion, followed by nucleophilic attack of –CH2NO2, leading to the smooth reaction.
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Table 2 Effect of solvents
OH
O
H
NO2
30 mol% catalyst 2a
solvent , r.t., 24h
H
+
CH3NO2
Solvent
Conv. (%)a
Time
Toluene
Hexane
CH3OH
Ether
32
38
51
49
36
48
74
24
24
24
24
24
24
48
THF
CH2Cl2
CH3OH
Reactions were carried out on 1 mmol PhCHO with 0.2 mL CH3NO2, in 4 mL solvents, for 24 h, at room
temperature (10–20 °C)
a
The conv.% was measured by 1H NMR
Conclusions
In summary, we have developed the Henry reaction catalyzed by Cu–O and Zn–O
complexes involving dimethoxysilane-bridged derivatives. The novelty of this
methodology can be summarized as follows:
1
we first synthesized a series of ligands and Cu–O and Zn–O complexes by use of
simple, easy to operate methods;
we reported a novel catalytic method in the Henry reaction at room temperature.
2
Further efforts will be devoted to applying the catalysts to other organic
reactions, for example the Baylis–Hillman reaction, the aldol reaction, etc.
Experimental
General procedures
All Henry reactions were performed at room temperature. Dichlorodimethylsilane,
dichloromethylphenylsilane, dichlorodiphenylsilane, Cu(OAc)2ÁH2O, Zn(OAc)2Á2H2O,
aldehydes, and nitromethane were purchased from Acros, Aldrich, and Fluka. Reactions
were monitored by thin-layer chromatography. Flash column chromatography was
performed using E. Merck silica gel 60 (particle size 0.02–0.03 mm), Chemical
conversion was measured by 1H NMR. 1H and 13C NMR spectra were obtained using
Bruker AM-300 and Bruker AM-400 spectrometers. Proton chemical shifts are reported in
ppm (d) with the solvent relative to tetramethylsilane (TMS) employed as the internal
standard (CDCl3, d 7.26 ppm). The following abbreviations were used to designate
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Studies on Henry reaction catalyzed by Cu–O, Zn–O complexes
185
Table 3 Catalytic Henry reaction of aldehydes
O
OH
H
30mol%catalyst 2a
H
NO2
+
CH3NO2
CH3OH, 48h
R
R
Entry
1
Products
Conv. (%)a
74
OH
NO2
2
3
88
72
OH
NO2
CH3
OH
NO2
OCH3
4
5
6
85
59
81
OH
F
NO2
OH
Br
NO2
OH
NO2
H3
C
7
8
84
66
OH
NO2
H3CO
OH
NO2
F
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Table 3 continued
Entry
Products
Conv. (%)a
93
9
OH
OH
OH
NO2
NO2
NO2
Cl
10
11
12
96
72
69
Br
O2
N
HO
NO2
Reactions were carried out on 1 mmol PhCHO with 0.2 mL CH3NO2, in 4 mL solvent, for 24 h, at room
temperature (10–20 °C)
a
The conv.% was measured by 1H NMR
chemical shift mutiplicities: s = singlet, d = doublet, t = triplet, m = multiplet.
Infrared spectra were recorded on a Mattson Galaxy Series FTIR 3000 Spectrometer;
peaks are reported in cm-1, High-resolution mass spectra (HRMS) were obtained on a
Micro GCT-MS equipped with an EI ion source.
1. Preparation of catalyst 1
(1) Preparation of methylphenyldimethoxysilane
A 250 mL Schlenk flask equipped with a pressure-equalizing dropping funnel, was
charged with a solution of dichlorodimethylsilane 8.2 mL (50 mmol) in 30 mL dry
methanol and 20 mL benzene. A dropping funnel was charged with 25 mL benzene
and 8 mL pyridine and this was added dropwise to the flask at about -5 to 0 °C
while stirring. After 20 min, white pyridine hydrochloric acid was obtained. The
mixture was carefully filtered at room temperature and the solvent was evaporated
in vacuo using a rotary evaporator. The residue was then washed with 10 mL H2O
and extracted with 2 9 30 mL CH2Cl2. The extract was dried with NaSO4, yielding
of 9.0 g (36.8 mmol, 71%).b.p.: 106–108 °C (10 mmHg), 1H NMR (500 MHz,
CDCl3, 27 °C), d (ppm) = 7.63–7.64 (d, J = 7.0 Hz, 2H, aromH), 7.40–7.42 (m,
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3H, aromH), 3.58 (s, 6H), 0.38 (s, 3H). 13C NMR, -5.09, 50.60 (92), 127.99 (92),
130.26 (92), 134.04 (92).
(2) Preparation of catalyst 1a
A solution of 0.1314 g (0.6 mmol) Zn(OAc)Á2H2O and 0.13 mL (0.6 mmol)
methylphenyldimethoxysilane in 4 mL methanol was heated under reflux for 1 h.
The resulting solution was concentrated under vacuum and dried to give catalyst 1a.
(3) Preparation of catalyst 1b
A solution of 0.1198 g (0.6 mmol) Cu(OAc)ÁH2O and 0.13 mL (0.6 mmol)
methylphenyldimethoxysilane in 4 mL methanol was heated under reflux for 1 h.
The resulting solution was concentrated under vacuum and dried to give catalyst 1b.
2. Preparation of catalyst 2
(1) Preparation of dimethyldimethoxysilane
The procedure described in 1(1), above, was followed.
1
b.p.: 80–82 °C (10 mmHg) H NMR (300 MHz, CDCl3, 27 °C), d (ppm) =
0.073(s, 6H, CH3), 3.45(s, 6H, OCH3). 13C NMR, -4.26 (92), 49.94 (92).
(2) Preparation of catalyst 2a
A solution of 0.1314 g (0.6 mmol) Zn(OAc)Á2H2O and 0.08 mL (0.6 mmol)
dimethyldimethoxysilane in 4 mL methanol was heated under reflux for 1 h. The
resulting solution was concentrated under vacuum and dried to give catalyst 2a. IR
(KBr): 3128, 2375, 1560, 1027, 692.
(2) Preparation of catalyst 2b
A solution of 0.1198 g (0.6 mmol) Cu(OAc)ÁH2O and 0.08 mL (0.6 mmol)
dimethyldimethoxy silane in 4 mL methanol was heated under reflux for 1 h. The
resulting solution was concentrated under vacuum and dried to give catalyst 2b.
3. Preparation of catalyst 3
(1) Preparation of diphenyldimethoxysilane
The procedure described in 1(1), above, was followed.
b.p.: 150–152 °C (10 mmHg), 1H NMR (300 MHz, CDCl3, 27 °C), d
(ppm) = 7.78–7.80 (m, 4H, aromH), 7.50–7.54 (m, 6H, aromH), 3.59(s, 6H).13C
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NMR: 51.04 (92), 128.06 (92),130.52 (92), 132.27 (92), 134.72 (92), 134.94
(92).
(2) Preparation of catalyst 3a
A solution of 0.1314 g (0.6 mmol) Zn(OAc)Á2H2O and 0.14 mL (0.6 mmol)
diphenyldimethoxysilane in 4 mL methanol was heated under reflux for 1 h, The
resulting solution was concentrated under vacuum and dried to give catalyst 3a.
(2) Preparation of catalyst 3b
A solution of 0.1198 g (0.6 mmol) Cu(OAc)ÁH2O and 0.14 mL (0.6 mmol)
methylphenyldimethoxysilane in 4 mL methanol was heated under reflux for 1 h,
The resulting solution was concentrated under vacuum amd dried to give catalyst
3b.
4. 2-Nitro-1-phenylethanol
Catalyst 2 (0.6 mmol), benzaldehyde 0.20 mL (1.972 mmol), and nitromethane
(0.20 mL, 3.702 mmol) were successively added at room temperature. After 48 h, the
reaction was quenched. Further purification was performed by silica gel chromatog-
raphy (petroleum–dichloromethane 4:1).The title compound was obtained as a
colorless oil, conv.% = 74%, 1H NMR (300 MHz, CDCl3), 7.28–7.32 (m, 5H, Ar–H),
5.32–5.35 (d, J = 9.18 Hz, 1H, –CH), 4.38–4.56 (m, 2H, –CH2), 3.38 (br, 1H, –OH).
13C NMR (75 MHz, CDCl3) 138.30, 128.92 (92), 128.82, 125.98 (92), 81.16, 70.91.
5. 1-(2-Methylphenyl)-2-nitroethanol
The procedure described in 4, above, was followed.
Conv.% = 88%, 1H NMR (500 MHz, CDCl3) 7.51–7.52 (d, J = 7 Hz, 1H,
Ar–H), 7.18–7.27 (m, 3H, Ar–H), 5.75 (d, 1H), 4.44–4.53 (m, 2H, –CH2), 2.93
(br, 1H, –OH), 2.38 (s, 3H, –CH3). 13C NMR (75 MHz, CDCl3) 136.30, 134.50,
130.90, 128.75, 126.84, 125.68, 80.30, 67.96. Conv.% = 88%.
6. 1-(2-Methyloxyphenyl)-2-nitroethanol
The procedure described in 4, above, was followed.
Conv.% = 72%, 1H NMR (500 MHz, CDCl3), 7.32–7.44 (m, 2H, Ar–H), 6.89–7.02
(m, 2H, Ar–H), 5.61–5.62 (d, J = 5 Hz, 1H), 4.54–4.65 (m, 2H, –CH2), 3.88 (s, 3H,
–OCH3), 3.28 (br, 1H, –OH). 13C NMR (125 MHz, CDCl3) 156.02, 129.85, 127.24,
125.99, 121.19, 110.55, 79.89, 67.86, 55.46. HRMS (EI):m/z (%):Anal calcd for
C9H11NO4: 197.0688; found: 197.0686
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7. 1-(2-Fluorophenyl)-2-nitroethanol
The procedure described in 4, above, was followed.
1
Conv.% = 85%, H NMR (500 MHz, CDCl3), 7.56 (t, J = 0.5 Hz, 1H, Ar–H),
7.34–7.36 (m, 1H, Ar–H), 7.22 (t, 1H, Ar–H), 7.08 (t, J = 0.5 Hz, 1H, Ar–H), 5.75
(t, 1H, –CH), 4.59–4.62 (m, 2H, –CH2), 3.08–3.09 (d, J = 4.5 Hz, 1H, –OH). 13C
NMR (125 MHz, CDCl3), 160.32, 158.36, 130.54, 130.47, 127.61, 124.89, 115.74,
115.56, 79.70, 65.44. HRMS (EI):m/z (%):Anal calcd for C8H8NO3F: 185.0488;
found: 185.0480.
8. 1-(2-Bromophenyl)-2-nitroethanol
The procedure described in 4, above, was followed.
1
Conv.% = 59%, H NMR (500 MHz, CDCl3) 7.64–7.65 (d, J = 7.5 Hz, 1H,
Ar–H), 7.48–7.51 (d, J = 8 Hz, 1H, Ar–H), 7.39 (t, 1H, Ar–H), 7.22 (t, 1H, Ar–H),
5.78–5.80 (d, J = 9.5 Hz, 1H, –CH), 4.41–4.68 (m, 2H, –CH2), 3.25 (br, 1H, –OH).
13C NMR (125 MHz, CDCl3) 137.12, 133.01, 130.32, 128.26, 127.84, 121.47,
79.42, 70.06. Conv.% = 73%, HRMS (EI):m/z (%):Anal calcd for C8H8NO3Br:
181.0739; found: 181.0734.
9. 1-(4-Methylphenyl)-2-nitroethanol
The procedure described in 4, above, was followed.
1
Conv.% = 81%, H NMR (500 MHz, CDCl3) 7.19–7.28 (m, 4H, Ar–H), 5.38–
5.41 (dd, J = 2.5, 2.5 Hz, 1H, Ar–H), 4.45–4.61 (m, 2H, –CH2), 2.89 (br, 1H,
–OH), 2.36 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3) 138.92, 135.28, 129.71 (92),
125.93 (92), 81.32, 70.93, 21.22 HRMS (EI):m/z (%):Anal calcd for C9H11NO3:
181.0739; found: 181.0734.
10. 1-(4-Methyloxyphenyl)-2-nitroethanol
The procedure described in 4, above, was followed.
1
Conv.% = 84%, H NMR (500 MHz, CDCl3) 7.28–7.29 (d, J = 8.5 Hz, 2H,
Ar–H), 6.88–6.89 (d, J = 8.5 Hz, 2H), 5.36–5.38 (m, 1H, –CH), 4.42–4.59 (m, 2H,
–CH2), 3.78 (s, 3H, –CH3), 3.43 (br, 1H, –OH). 13C NMR (125 MHz, CDCl3)
160.06, 130.26, 127.32 (92), 114.42 (92), 81.32, 70.70, 55.40, HRMS (EI):m/z
(%):Anal calcd for C9H11NO4: 197.0688; found: 197.0687
11. 1-(4-Fluorophenyl)-2-nitroethanol
The procedure described in 4, above, was followed.
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1
Conv.% = 66%, H NMR (500 MHz, CDCl3) 7.37–7.42 (m, 2H, Ar–H), 7.10
(t, J = 0.5 Hz, 2H, Ar–H), 5.45 (m, 1H, –CH), 4.51–4.58 (m, 2H, –CH2), 2.88 (br,
1H, –OH). 13C NMR (125 MHz, CDCl3) 164.20, 161.74, 134.09, 127.89, 116.17,
115.95, 81.23, 70.40, HRMS (EI):m/z (%):Anal calcd for C8H8NO3F: 185.0488;
found: 185.0486.
12. 1-(4-Chlorophenyl)-2-nitroethanol
The procedure described in 4, above, was followed.
Conv.% = 93%, 1H NMR (300 MHz, CDCl3) 7.41–7.42 (m, 4H, Ar–H),
5.47–5.52 (dd, J = 5, 2.5 Hz, 1H, –CH), 4.52–4.62 (m, 2H, –CH2), 2.72 (br, 1H,
–OH). 13C NMR (125 MHz, CDCl3) 136.57, 134.84, 129.25, 127.38, 81.04, 70.33,
HRMS (EI):m/z (%):Anal calcd for C8H8NO3Cl: 201.0193; found: 201.0196.
13. 1-(4-Bromophenyl)-2-nitroethanol
The procedure described in 4, above, was followed.
1
Conv.% = 96%, H NMR (500 MHz, CDCl3) 7.62–7.66 (d, J = 13.5 Hz, 2H,
Ar–H), 7.38–7.40 (d, J = 14 Hz, 2H, Ar–H), 5.52–5.56 (dd, J = 5, 5 Hz, 1H,
–CH), 4.61–4.67 (m, 2H, –CH2), 3.18 (br, 1H, –OH). 13C NMR (125 MHz, CDCl3)
137.10, 132.21, 127.68, 122.98, 80.98, 70.38, Conv.% = 96%, HRMS (EI):m/z
(%):Anal calcd for C8H8NO3Br: 244.9688; found: 201.9694.
14. 2-Nitro-1-(4-nitrophenyl)ethanol
The procedure described in 4, above, was followed.
1
Conv.% = 72%, H NMR (300 MHz, CDCl3) 8.22–8.24 (d, J = 8.7 Hz, 2H,
Ar–H), 8.22–8.24 (d, J = 8.7 Hz, 2H, Ar–H), 5.58 (m, 1H), 4.54–4.57 (m, 2H), 3.24
(br, 1H). 13C NMR (75 MHz, CDCl3) 148.12, 145.06, 126.99 (92), 124.23 (92),
80.66, 69.99.
15. 1-(Naphthalen-1-yl)-2-nitroethanol
The procedure described in 4, above, was followed.
1H NMR (300 MHz, CDCl3) 8.12–8.16 (d, J = 13.5 Hz, 2H, Ar–H), 7.94–7.98
(dd, J = 12.5, 13.5 Hz, 2H, Ar–H), 7.84–7.86 (d, J = 11.5 Hz, 1H, Ar–H),
7.61–7.70 (m, 3H, Ar–H), 6.32–6.36 (dd, J = 7.5, 7.5 Hz, 1H, –CH), 4.74–4.78
(m, 2H, –CH2), 3.14 (br, 1H, –OH). 13C NMR (75 MHz, CDCl3) 133.72, 133.66,
129.56, 129.36, 127.12, 126.16 (92), 125.58, 123.90, 121.89, 80.86, 68.32
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