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Acetic acid assisted cobalt methanesulfonate catalysed chemoselective diacetylation of aldehydes
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Chinese Chemical Letters 19 (2008) 897–900 www.elsevier.com/locate/cclet
Acetic acid assisted cobalt methanesulfonate catalysed chemoselective diacetylation of aldehydes Min Wang a,*, Zhi Guo Song b, Hong Gong c, Heng Jiang c a
College of Chemistry and Chemical Engineering, Bohai University, Jinzhou 121000, China b Center for Science & Technology Experiment, Bohai University, Jinzhou 121000, China c Liaoning Shihua University, Fushun 113001, China Received 25 February 2008
Abstract Cobalt methanesulfonate in combination with acetic acid catalysed the chemoselective diacetylation of aldehyde with acetic anhydride at room temperature under solvent free conditions. After reaction, cobalt methanesulfonate can be easily recovered and reused many times. The reaction was mild and efficient with good to high yields. # 2008 Min Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Gem-diacetate; Aldehyde; Acetic anhydride; Cobalt methanesulfonate; Acetic acid
Selective protection of carbonyl compounds is an important transformation in organic synthesis. Due to the remarkable stability of gem-diacetaes (acylals) in neutral and basic media, they have been widely used as protecting groups for aldehydes [1]. Acylals are conventionally prepared from aldehyde, acetic anhydride, and an acidic catalyst such as protonic acid [2], metal halide [3], metal tetrafluoroborate [4], metal triflate [5], metal perchlorate [6], supported heterogeneous catalyst [7], and heteropolyacid [8]. However, many of these methods suffer from one or more of the following disadvantages: using strong acid, high temperature, moisture sensitive reagent, large excess of Ac2O, expensive catalysts and harmful organic solvents. Recently, Brønsted assisted Lewis acid as a combined catalyst for organic synthesis has been well documented. Kobayashi and co-workers combined Sc(O3SC12H25)3 with HCl in a 1:1 ratio to produce a very active catalyst for the Aldol reaction [9]. Aspinall et al. reported a successful acceleration in a La(OTf)3/PhCO2H catalysed allylation reaction [10]. We also reported Cu(CH3SO3)24H2O/HOAc can catalyse the diacetylation and tetrahydropyranylation efficiently [11,12]. Both Lewis acid and Brønsted acid are indispensable for these conversions. Those procedures used 2 mol% of Cu(CH3SO3)24H2O and 12 mmol HOAc as catalysts. We now report that the use of Co(CH3SO3)24H2O as Lewis acid can decrease the amount of HOAc to 9 mmol for diacetoxylation in high yields at room temperature under solvent-free conditions (Scheme 1). The new catalytic system enlarges the scope of reactants. Two new compounds were synthesized.
* Corresponding author. E-mail address: [email protected] (M. Wang). 1001-8417/$ – see front matter # 2008 Min Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.05.045
898
M. Wang et al. / Chinese Chemical Letters 19 (2008) 897–900
Scheme 1.
1. Experimental Typical procedure for the synthesis of 1,1-diacetates: a mixture of aldehyde (15 mmol), Ac2O (30 mmol), Co(CH3SO3)24H2O (2 mol%), and HOAc (9 mmol) was stirred magnetically at ambient temperature for an appropriate time (monitored by GC). After the reaction, most of the mixture solidified gradually, and 30 mL CH2Cl2 was added to dissolve the solid product. The organic layer was washed twice with saturated NaHCO3 solution (20 mL), dried (Na2SO4), and evaporated to yield the almost-pure product. The product was purified further by crystallization from cyclohexane or by column chromatography on silica gel (ethyl acetate/hexane, 1:9 as the eluent). All the acylals were characterized by IR, 1H NMR and elemental analysis. The data were compared with literature ones and found to be identical with the authentic samples [11]. Analytical data for new compounds: 1,1-Diacetoxyheptane (Table 2, Entry 12): colorless liquid. IR (KBr, cm 1): 3029, 2961, 1761, 1463, 1378, 1248, 1113, 1016, 968; 1H NMR (300 MHz, CDCl3, d ppm): 6.77 (t, J = 5.6 Hz, 1H, CH), 2.07 (s, 6H, 2OCOCH3), 1.64– 1.80 (m, 2H, CH2), 1.23–1.41 (br, 8H, 4CH2), 0.92 (t, 3H, J = 6.8 Hz, CH3). Anal. calcd. for C11H20O4: C, 61.09; H, 9.32. Found: C, 61.12; H, 9.31. 1,1-Diacetoxyoctane (Table 2, Entry 13): colorless liquid. IR (KBr, cm 1): 3027, 2926, 2854, 1760, 1461, 1247, 1115, 1012, 967; 1H NMR (300 MHz, CDCl3, d ppm): 6.75 (t, 1H, J = 5.2 Hz, CH), 2.09 (s, 6H, 2OCOCH3), 1.61– 1.78 (m, 2H, CH2), 1.24–1.41 (br, 10H, 5CH2), 0.87 (t, 3H, J = 6.4 Hz, CH3); Anal. calcd. for C12H22O4: C, 62.58; H, 9.63. Found: C, 62.61; H, 9.62. 2. Results and discussion First, the optimization of the amount of Co(CH3SO3)24H2O and HOAc was investigated in a model reaction of benzaldehyde with acetic anhydride (Table 1). Only Co(CH3SO3)24H2O or HOAc could not catalyse the conversion efficiently (entries 1 and 6). A remarkable acceleration was found when the amount of HOAc was increased from 3 mmol to 9 mmol in the presence of 2 mol% Co(CH3SO3)24H2O, the yields of the product improved and an 98% yield was obtained (entries 2–4). It seemed that 9 mmol HOAc was sufficient to drive the reaction completely. After reaction, Co(CH3SO3)24H2O can be easily recovered by filtration and can be reused four times without distinct loss of activity. However, the yield of product decreased when the amount of Co(CH3SO3)24H2O was less than 2 mol% (entry 5). The results combined with previous reports clearly show that HOAc assisted Co(CH3SO3)24H2O forms a synergistic catalytic system that catalysed the diacetylation of aldehydes efficiently. For the synergistic catalytic system, Lewis acid Co2+ and protonic acid H+ coordinated with aldehyde together, which resulted in the formation of a ternary complex of cobalt methanesulfonate–acetic acid–aldehyde. In the complex, the ‘‘double activation’’ of Brønsted assisted Lewis acid catalysis on the aldehyde would facilitate electrophilic attack into the aldehyde. The diacetylation of series of aromatic, heteroaromatic, unsaturated, and aliphatic aldehydes to 1,1-diacetates was tested in Table 2. Aromatic aldehyde carrying both electron-donating group and electron-withdrawing group all reacted smoothly. Steric hindrance seems to have effects on the efficiency of this transformation, shown in entries 2–4. Table 1 Effect of amount of Co(CH3SO3)24H2O and HOAc Entry
Co(CH3SO3)24H2O (mol%)
HOAc (mmol)
Time (h)
Isolated yield (%)
1 2 3 4 5 6
2 2 2 2 1 0
0 3 6 9 9 9
1.3 1.3 1.3 1.3 1.3 10
35 69 83 98, 96, 87, 73a 64 0
a
Co(CH3SO3)24H2O reused four times.
M. Wang et al. / Chinese Chemical Letters 19 (2008) 897–900
899
Table 2 Preparation of acylals catalysed by Co(CH3SO3)24H2O and HOAc Entry
Aldehyde
Time (h)
Product
Isolated yield (%)
1
1.3
98
2
4
93
3
7
62
4
13
67
5
3
90
6
8
70
7
5
91
8
4
94
9
12
52
10
9
62
11
8
66
12
15
53
13
15
52
14
10
0
15
10
0
16 a
3
92 + 0
a
Equimolar mixture of benzaldehyde and acetophenone, the percentage of the products in the reaction mixtures were determined by GC analysis.
900
M. Wang et al. / Chinese Chemical Letters 19 (2008) 897–900
The sensitive heteroaromatic furfural, crotonaldehyde and cinnamaldehyde were converted to the corresponding 1,1diacetates without any side products, which were normally observed under the strongly acidic conditions (entries 7–9). The protection of aliphatic aldehydes proceeded sluggishly with long time in low yields (entries 10–13). pDimethylaminobenzaldehyde and cyclohexanone failed to give the corresponding 1,1-diacetates (entries 14 and 15). The chemoselective protection of aldehyde with Ac2O in the presence of ketone was achieved successfully (entry 16). We also investigated the catalytic activity of Co(NO3)26H2O and CoCl26H2O in the diacetylation of benzaldehyde under the same conditions. Whether they used alone or they combined with HOAc, the yields of products were less than 70%. Therefore, in view of the excellent catalytic activity, observed chemoselectivity, easy availability, inexpensive cost, and ready recovery, HOAc assisted Co(CH3SO3)24H2O was proved to be an efficient synergistic catalytic system for the diacetylation. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
K.S. Kochhar, B.S. Bal, R.P. Deshpande, et al. J. Org. Chem. 48 (1983) 1765. F. Freeman, E.M. Karchefski, J. Chem. Eng. Data 22 (1977) 355. A. Saini, S. Kumar, J.S. Sandhu, Synth. Commun. 38 (2008) 106. N. Sumida, K. Nishioka, T. Sato, Synlett (2001) 1921. J.W.J. Bosco, A.K. Saikia, Synth. Commun. 38 (2008) 77. A. Ziyaei, N. Azizi, M.R. Saidi, J. Mol. Catal. A: Chem. 238 (2005) 138. A.R. Hajipour, A. Zarei, A.E. Ruoho, Tetrahedron Lett. 48 (2007) 2881. M.M. Heravi, K. Bakhtiari, F.F. Bamoharram, Catal. Commun. 7 (2006) 499. K. Manabe, S. Kobayashi, Tetrahedron Lett. 40 (1999) 3773. H.C. Aspinall, J.S. Bissett, N. Greeves, et al. Tetrahedron Lett 43 (2002) 319. M. Wang, H. Gong, H. Jiang, et al. Synth. Commun. 36 (2006) 1953. M. Wang, Z.G. Song, H. Gong, et al. Chin. Chem. Lett. 18 (2007) 799.
Chinese Chemical Letters 19 (2008) 897–900 www.elsevier.com/locate/cclet
Acetic acid assisted cobalt methanesulfonate catalysed chemoselective diacetylation of aldehydes Min Wang a,*, Zhi Guo Song b, Hong Gong c, Heng Jiang c a
College of Chemistry and Chemical Engineering, Bohai University, Jinzhou 121000, China b Center for Science & Technology Experiment, Bohai University, Jinzhou 121000, China c Liaoning Shihua University, Fushun 113001, China Received 25 February 2008
Abstract Cobalt methanesulfonate in combination with acetic acid catalysed the chemoselective diacetylation of aldehyde with acetic anhydride at room temperature under solvent free conditions. After reaction, cobalt methanesulfonate can be easily recovered and reused many times. The reaction was mild and efficient with good to high yields. # 2008 Min Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Gem-diacetate; Aldehyde; Acetic anhydride; Cobalt methanesulfonate; Acetic acid
Selective protection of carbonyl compounds is an important transformation in organic synthesis. Due to the remarkable stability of gem-diacetaes (acylals) in neutral and basic media, they have been widely used as protecting groups for aldehydes [1]. Acylals are conventionally prepared from aldehyde, acetic anhydride, and an acidic catalyst such as protonic acid [2], metal halide [3], metal tetrafluoroborate [4], metal triflate [5], metal perchlorate [6], supported heterogeneous catalyst [7], and heteropolyacid [8]. However, many of these methods suffer from one or more of the following disadvantages: using strong acid, high temperature, moisture sensitive reagent, large excess of Ac2O, expensive catalysts and harmful organic solvents. Recently, Brønsted assisted Lewis acid as a combined catalyst for organic synthesis has been well documented. Kobayashi and co-workers combined Sc(O3SC12H25)3 with HCl in a 1:1 ratio to produce a very active catalyst for the Aldol reaction [9]. Aspinall et al. reported a successful acceleration in a La(OTf)3/PhCO2H catalysed allylation reaction [10]. We also reported Cu(CH3SO3)24H2O/HOAc can catalyse the diacetylation and tetrahydropyranylation efficiently [11,12]. Both Lewis acid and Brønsted acid are indispensable for these conversions. Those procedures used 2 mol% of Cu(CH3SO3)24H2O and 12 mmol HOAc as catalysts. We now report that the use of Co(CH3SO3)24H2O as Lewis acid can decrease the amount of HOAc to 9 mmol for diacetoxylation in high yields at room temperature under solvent-free conditions (Scheme 1). The new catalytic system enlarges the scope of reactants. Two new compounds were synthesized.
* Corresponding author. E-mail address: [email protected] (M. Wang). 1001-8417/$ – see front matter # 2008 Min Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.05.045
898
M. Wang et al. / Chinese Chemical Letters 19 (2008) 897–900
Scheme 1.
1. Experimental Typical procedure for the synthesis of 1,1-diacetates: a mixture of aldehyde (15 mmol), Ac2O (30 mmol), Co(CH3SO3)24H2O (2 mol%), and HOAc (9 mmol) was stirred magnetically at ambient temperature for an appropriate time (monitored by GC). After the reaction, most of the mixture solidified gradually, and 30 mL CH2Cl2 was added to dissolve the solid product. The organic layer was washed twice with saturated NaHCO3 solution (20 mL), dried (Na2SO4), and evaporated to yield the almost-pure product. The product was purified further by crystallization from cyclohexane or by column chromatography on silica gel (ethyl acetate/hexane, 1:9 as the eluent). All the acylals were characterized by IR, 1H NMR and elemental analysis. The data were compared with literature ones and found to be identical with the authentic samples [11]. Analytical data for new compounds: 1,1-Diacetoxyheptane (Table 2, Entry 12): colorless liquid. IR (KBr, cm 1): 3029, 2961, 1761, 1463, 1378, 1248, 1113, 1016, 968; 1H NMR (300 MHz, CDCl3, d ppm): 6.77 (t, J = 5.6 Hz, 1H, CH), 2.07 (s, 6H, 2OCOCH3), 1.64– 1.80 (m, 2H, CH2), 1.23–1.41 (br, 8H, 4CH2), 0.92 (t, 3H, J = 6.8 Hz, CH3). Anal. calcd. for C11H20O4: C, 61.09; H, 9.32. Found: C, 61.12; H, 9.31. 1,1-Diacetoxyoctane (Table 2, Entry 13): colorless liquid. IR (KBr, cm 1): 3027, 2926, 2854, 1760, 1461, 1247, 1115, 1012, 967; 1H NMR (300 MHz, CDCl3, d ppm): 6.75 (t, 1H, J = 5.2 Hz, CH), 2.09 (s, 6H, 2OCOCH3), 1.61– 1.78 (m, 2H, CH2), 1.24–1.41 (br, 10H, 5CH2), 0.87 (t, 3H, J = 6.4 Hz, CH3); Anal. calcd. for C12H22O4: C, 62.58; H, 9.63. Found: C, 62.61; H, 9.62. 2. Results and discussion First, the optimization of the amount of Co(CH3SO3)24H2O and HOAc was investigated in a model reaction of benzaldehyde with acetic anhydride (Table 1). Only Co(CH3SO3)24H2O or HOAc could not catalyse the conversion efficiently (entries 1 and 6). A remarkable acceleration was found when the amount of HOAc was increased from 3 mmol to 9 mmol in the presence of 2 mol% Co(CH3SO3)24H2O, the yields of the product improved and an 98% yield was obtained (entries 2–4). It seemed that 9 mmol HOAc was sufficient to drive the reaction completely. After reaction, Co(CH3SO3)24H2O can be easily recovered by filtration and can be reused four times without distinct loss of activity. However, the yield of product decreased when the amount of Co(CH3SO3)24H2O was less than 2 mol% (entry 5). The results combined with previous reports clearly show that HOAc assisted Co(CH3SO3)24H2O forms a synergistic catalytic system that catalysed the diacetylation of aldehydes efficiently. For the synergistic catalytic system, Lewis acid Co2+ and protonic acid H+ coordinated with aldehyde together, which resulted in the formation of a ternary complex of cobalt methanesulfonate–acetic acid–aldehyde. In the complex, the ‘‘double activation’’ of Brønsted assisted Lewis acid catalysis on the aldehyde would facilitate electrophilic attack into the aldehyde. The diacetylation of series of aromatic, heteroaromatic, unsaturated, and aliphatic aldehydes to 1,1-diacetates was tested in Table 2. Aromatic aldehyde carrying both electron-donating group and electron-withdrawing group all reacted smoothly. Steric hindrance seems to have effects on the efficiency of this transformation, shown in entries 2–4. Table 1 Effect of amount of Co(CH3SO3)24H2O and HOAc Entry
Co(CH3SO3)24H2O (mol%)
HOAc (mmol)
Time (h)
Isolated yield (%)
1 2 3 4 5 6
2 2 2 2 1 0
0 3 6 9 9 9
1.3 1.3 1.3 1.3 1.3 10
35 69 83 98, 96, 87, 73a 64 0
a
Co(CH3SO3)24H2O reused four times.
M. Wang et al. / Chinese Chemical Letters 19 (2008) 897–900
899
Table 2 Preparation of acylals catalysed by Co(CH3SO3)24H2O and HOAc Entry
Aldehyde
Time (h)
Product
Isolated yield (%)
1
1.3
98
2
4
93
3
7
62
4
13
67
5
3
90
6
8
70
7
5
91
8
4
94
9
12
52
10
9
62
11
8
66
12
15
53
13
15
52
14
10
0
15
10
0
16 a
3
92 + 0
a
Equimolar mixture of benzaldehyde and acetophenone, the percentage of the products in the reaction mixtures were determined by GC analysis.
900
M. Wang et al. / Chinese Chemical Letters 19 (2008) 897–900
The sensitive heteroaromatic furfural, crotonaldehyde and cinnamaldehyde were converted to the corresponding 1,1diacetates without any side products, which were normally observed under the strongly acidic conditions (entries 7–9). The protection of aliphatic aldehydes proceeded sluggishly with long time in low yields (entries 10–13). pDimethylaminobenzaldehyde and cyclohexanone failed to give the corresponding 1,1-diacetates (entries 14 and 15). The chemoselective protection of aldehyde with Ac2O in the presence of ketone was achieved successfully (entry 16). We also investigated the catalytic activity of Co(NO3)26H2O and CoCl26H2O in the diacetylation of benzaldehyde under the same conditions. Whether they used alone or they combined with HOAc, the yields of products were less than 70%. Therefore, in view of the excellent catalytic activity, observed chemoselectivity, easy availability, inexpensive cost, and ready recovery, HOAc assisted Co(CH3SO3)24H2O was proved to be an efficient synergistic catalytic system for the diacetylation. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]
K.S. Kochhar, B.S. Bal, R.P. Deshpande, et al. J. Org. Chem. 48 (1983) 1765. F. Freeman, E.M. Karchefski, J. Chem. Eng. Data 22 (1977) 355. A. Saini, S. Kumar, J.S. Sandhu, Synth. Commun. 38 (2008) 106. N. Sumida, K. Nishioka, T. Sato, Synlett (2001) 1921. J.W.J. Bosco, A.K. Saikia, Synth. Commun. 38 (2008) 77. A. Ziyaei, N. Azizi, M.R. Saidi, J. Mol. Catal. A: Chem. 238 (2005) 138. A.R. Hajipour, A. Zarei, A.E. Ruoho, Tetrahedron Lett. 48 (2007) 2881. M.M. Heravi, K. Bakhtiari, F.F. Bamoharram, Catal. Commun. 7 (2006) 499. K. Manabe, S. Kobayashi, Tetrahedron Lett. 40 (1999) 3773. H.C. Aspinall, J.S. Bissett, N. Greeves, et al. Tetrahedron Lett 43 (2002) 319. M. Wang, H. Gong, H. Jiang, et al. Synth. Commun. 36 (2006) 1953. M. Wang, Z.G. Song, H. Gong, et al. Chin. Chem. Lett. 18 (2007) 799.