RSC Advances
Page 4 of 6
DOI: 10.1039/C4RA09851J
for the selective oxidation of benzylic and allylic alcohols to
aldehydes and phenones under ambient air atmosphere. A wide
(5 × 250 mL). The combined nꢀpentane phase was concentrated
in vacuo. The yield was determined by GC using tridecane as an
range of substrates which even contained phenolic hydroxyl, 65 internal standard and the residue was purified by vacuum
amino, and methylthio functional groups could be transformed
into corresponding aldehydes with no trace of over oxidized
carboxylic acids. The aerobic oxidative imine synthesis from
benzyl alcohol and amines were achieved by employing the
newly developed catalyst system. 100 gꢀscale reactions for
aldehyde and imine formation were achieved in higher than 90%
10 yield with low catalyst loading in 36 hours. To our best of
knowledge, this is the most convenient way to synthesize these
kinds of compounds in lab. The more detailed mechanism and
synthetic applications of this new developed catalyst system are
currently under investigation.
distillation to afford benzaldehyde (87% isolated yield).
5
Procedures for synthesis of N-Benzylideneaniline on mole-
scale
70
A mixture of benzyl alcohol (1 mol, 1.0 eq), aniline (1.2 mol,
1.2 eq), Cu(OAc)2 (900 mg, 0.005 eq), DMAP (1200 mg, 0.01 eq)
and TEMPO (750 mg, 0.005 eq) in a 500 mL roundꢀbottomed
flask (under air atmosphere) was heated at 110 oC with a decantor
75 for 36 hours before it was quenched by NH4Cl (250 mL, sat. aq.).
The layers were separated and the aqueous layer was extracted
with EtOAc (3 × 250 mL). The combined ethyl acetate phase was
concentrated in vacuo. The yield was determined by GC using
tridecane as an internal standard and the residue was purified by
80 recrystallization (ethyl acetate/ nꢀpentane, three times) to afford
Nꢀbenzylideneaniline (80% isolated yield).
15 Experimental
General
All the chemicals and solvents were obtained from commercial
sources and used without further purification. Column
20 chromatography purifications were performed using 300–400
mesh silica gel. Reactions were monitored by thinꢀlayer
chromatography (TLC) carried out on 0.2 mm huanghai silica gel
plates (HSGFꢀ254) using UV light as visualizing agent. NMR
spectra were recorded on Bruker DRX–400 instruments and
25 calibrated using residual solvent peaks as internal reference.
Acknowledgements
85 This research was financially supported by the financial support
from the Natural Science Foundation of Jiangsu Province of
China (L210903913), and a startꢀup fund (Q410901212) from
Soochow University for support of this work. The PAPD and
Qing Lan Project are also gratefully acknowledged.
90
General procedures for synthesis of aldehydes
A mixture of alcohol (1 mmol, 1.0 eq), Cu(OAc)2 (1.8 mg, 0.01
30 eq), DMAP (2.4 mg, 0.02 eq) and TEMPO (1.5 mg, 0.01 eq) in a
15 mL glass tube (under air atmosphere) was heated and stirred at
25 C for 24 hours. The reaction mixture was cooled to rt, and
concentrated in vacuo. The resulting residue was purified by
Notes and references
o
1 (a) R. A. Sheldon, J. K. Kochi, Metal-Catalysed Oxidations of
Organic Compounds, Academic Press: New York, 1981; (b) R. C.
Larok, Comprehensive organic transformations, John Wiley & Sons,
New York, 2nd Ed, 1999.
95
column chromatography on silica gel to give the aldehyde.
35
2 (a) J. W. Ladbury, C. F. Cullis, Chem. Rev., 1958, 58, 403; (b) A. J.
Fatiadi, Synthesis, 1976, 65; (c) R. J. K. Taylor, M. Reid, J. Foot, S.
A. Raw, Acc. Chem. Res., 2005, 38, 851.
Benzaldehyde(1a) 1H NMR (400 MHz, CDCl3) δ = 10.01 (s, 1H),
7.90 – 7.84 (m, 2H), 7.65 – 7.59 (m, 1H), 7.52 (dd, J = 7.9, 7.1 Hz, 2H).
13C NMR (101 MHz, CDCl3) δ = 192.49, 136.47, 134.55, 129.82, 129.08.
100 3 (a) E. J. Corey, J. W. Suggs, Tetrahedron Lett., 1975, 16, 2647; (b) R.
J. K. Taylor, M. Reid, J. Foot, S. A. Raw, Acc. Chem. Res., 2005, 38,
851.
40 General procedures for synthesis of imines
4 (a) K. E. Pfitzner, J. G. Moffatt, J. Am. Chem. Soc., 1963, 85, 3027; (b)
A. J. Mancuso, S. L. Huang, D. Swern, J. Org. Chem., 1978, 43,
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Frigerio, M. Santagostino, Tetrahedron Lett., 1994, 35, 8019; (c) Y.
Jiang, W. Chen, W. Lu, Tetrahedron, 2013, 69, 3669.
6 (a) S. Wertz and A. Studer, Green Chem., 2013, 15, 3116; (b) M. C.
López, G. Royal, C. Philouze, P. Y. Chavant and V. Blandin, Eur. J.
Org. Chem., 2014, 4884; (c) R. Prebil, G. Stavber and S. Stavber, Eur.
J. Org. Chem. 2014, 395.
7 (a) K. Yamaguchi, K. Mori, T. Mizugaki, K. Ebitani, K. Kaneda, J.
Am. Chem. Soc., 2000, 122, 7144; (b) R. A. Sheldon, I. W. C. E.
A mixture of alcohol (1 mmol, 1.0 eq), amine (1.2 mmol, 1.2
eq), Cu(OAc)2 (1.8 mg, 0.01 eq), DMAP (2.4 mg, 0.02 eq) and 105
TEMPO (1.5 mg, 0.01 eq) in a 15 mL glass tube (under air
45 atmosphere) was heated and stirred at 110 C for 24 hours. The
reaction mixture was cooled to rt, and concentrated in vacuo. The
o
resulting residue was purified by column chromatography on
silica gel to give the imine. The silica gel column was leached
110
by= eluent (PE : Et3N = 100:1) at first.
50
N-Benzylideneaniline (4a) 1H NMR (400 MHz, CDCl3) δ = 8.45
(s, 1H), 7.91 (dd, J=6.5, 3.1 Hz, 2H), 7.51 – 7.44 (m, 3H), 7.40 (dd,
J=10.6, 4.9 Hz, 2H), 7.27 – 7.17 (m, 3H). 13C NMR (101 MHz, CDCl3) δ
= 160.56, 152.20, 136.33, 131.51, 129.28, 128.94, 128.90, 126.07, 120.99.
115
120
125
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55
Procedures for synthesis of benzaldehyde on mole-scale
A mixture of benzyl alcohol (1 mol, 1.0 eq), Cu(OAc)2 (900
mg, 0.005 eq), DMAP (1200 mg, 0.01 eq) and TEMPO (750 mg,
60 0.005 eq) in a 250 mL roundꢀbottomed flask (under air
o
atmosphere) was heated at 80 C for 36 hours. After the reaction
was finished, the reaction mixture was extracted with nꢀpentane
4
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