Oxidative deprotection of oximes using pyridinium fluorochromate and hydrogen peroxide

Article abstract of DOI:10.1081/SCC-100104075

A simple convenient procedure of oxidative deoximation has been developed using pyridinium fluorochromate (PFC), in combination with 30% hydrogen peroxide. The method has been found to be effective for a wide range of aliphatic and aromatic oximes, and may be used for selective cleavage of aldoximes in the presence of ketoximes.

Full text of DOI:10.1081/SCC-100104075

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OXIDATIVE DEPROTECTION
OF OXIMES USING PYRIDINIUM
FLUOROCHROMATE AND
HYDROGEN PEROXIDE
Nemai C. Ganguly a , Arun K. Sukai a , Sripada De a
& Prithwiraj De a
a Department of Chemistry , University of
Kalyani , Kalyani, W.B., 741 235, India
Published online: 02 Aug 2010.
To cite this article: Nemai C. Ganguly , Arun K. Sukai , Sripada De & Prithwiraj De
(2001) OXIDATIVE DEPROTECTION OF OXIMES USING PYRIDINIUM FLUOROCHROMATE
AND HYDROGEN PEROXIDE, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 31:10, 1607-1612, DOI:
10.1081/SCC-100104075
To link to this article: http://dx.doi.org/10.1081/SCC-100104075
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SYNTHETIC COMMUNICATIONS, 31(10), 1607–1612 (2001)
OXIDATIVE DEPROTECTION OF OXIMES
USING PYRIDINIUM FLUOROCHROMATE
AND HYDROGEN PEROXIDE
Nemai C. Ganguly,* Arun K. Sukai, Sripada De,
and Prithwiraj De
Department of Chemistry, University of Kalyani,
Kalyani–741 235, W.B. India
ABSTRACT
A simple convenient procedure of oxidative deoximation
has been developed using pyridinium fluorochromate (PFC),
in combination with 30% hydrogen peroxide. The method has
been found to be effective for a wide range of aliphatic and
aromatic oximes, and may be used for selective cleavage of
aldoximes in the presence of ketoximes.
Deprotection of oximes has evoked considerable interest in recent
years1–23 because the functional group transformations involving aldehydes
and ketones play an important role in many organic syntheses. Apart from
their usefulness as protecting groups of aldehydes and ketones,24 oximes
synthesized from noncarbonyl sources25–27 may be utilized as precursors of
carbonyl compounds. A plethora of oxidative deoximation procedures1–20
are enumerated in the literature. It is significant that some of the methods
are specific for the cleavage of ketoximes11,16,21 and cannot be used for
* Corresponding author.
1607
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

1608
GANGULY ET AL.
the regeneration of aldehydes from aldoximes. Therefore, efforts have been
focused on developing newer efficient general protocols of deoxi-
mation involving cheap readily available reagents. In view of the reported
formation of strongly oxidizing diperoxo oxochromium (VI) species
[CrVIO(O2)2OH]À5 on treatment of potassium dichromate with hydrogen
peroxide in neutral or slightly acidic conditions, we became interested to
examine the scope of the versatile oxochromium (VI) reagent, pyridinium
fluorochromate (PFC) in combination with 30% hydrogen peroxide as a
reagent for oxidative deoximation in general. Herein we describe a simple
method of regeneration of carbonyl compounds with this reagent from a
wide range of aldoximes and ketoximes with varying structural and steric
parameters. The results of some representative transformations are
presented in Table 1.
Regeneration of carbonyl compounds from aldoximes and aliphatic
ketoximes (entries 1–7) was very fast. However, some overoxidation to
the corresponding carboxylic acids (10–30%) was observed for aldoximes,
particularly for those with electron-releasing ortho-/para-substituents
(entries 1–6). However, overoxidation was considerably minimized by
slow addition of 30% hydrogen peroxide to a mixture of oxime and pyr-
idinium fluorochromate at À10ꢀC. Aromatic ketoximes and conjugated
oximes displayed lower levels of reactivity and required longer reaction
time. The optimized reaction conditions for the cleavage of 1 mmol of
oxime were determined to be 2 mmol of pyridinium fluorochromate and
0.5 mL of 30% hydrogen peroxide. However, application of the optimized
reaction conditions to sterically hindered oximes (e.g., camphor oxime,
1-tetralone oxime) led to slow deprotection. Addition of an extra amount
of the reagent (4 mol equivalent of pyridinium fluorochromate, 1 mL 30%
hydrogen peroxide) improved the yield and considerably shortened the
reaction time (entries 19, 20). Conjugated or unconjugated carbon-carbon
double bonds (entries 6, 10, 11), ester (entry 21), and methylene-
dioxy functions (entry 5) were not affected during the cleavage process.
The deactivating effect of electron-withdrawing group (entry 9) and steric
congestion factor (entries 19, 20) were demonstrated clearly. The remark-
able reactivity differential of aldoximes and ketoximes is potentially useful for
chemoselective deprotection in a situation where both the functions exist.
In a model experiment, exposure of an equimolar mixture of syn-benzalde-
hyde oxime and benzophenone oxime to the reagent (2 mol equivalent

OXIME DEPROTECTION
1609
Table 1. Oxidation of Oximes with Pyridinium Fluorochromale and 30% Hydrogen
Peroxide
Reaction
time
Yielda of carbonyl
compound (%)
Entry
Substrate
1.
2.
3.
4.
5.
syn-Benzaldehyde oxime
2-Methoxybenzaldehyde oxime
2,4-Dimethoxybenzaldehyde oxime
4-Dimethylaminobenzaldehyde oxime
3,4-Methylenedioxybenzaldehyde
oxime
20 min
10 min
10 min
10 min
15 min
74 (83b)
64 (86b)
54 (89b)
68 (90b)
70 (80b)
6.
7.
8.
Citral oxime
15 min
20 min
1.5 h
5 h
3 h
4 h
4 h
6 h
5 h
6.5 h
6 h
4 h
3 h
78 (95b)
98
97
Isobutyl methyl ketone oxime
t-butyl methyl ketone oxime
4-Nitrobenzaldehyde oxime
Cinnamaldehyde oxime
Mesityl oxide oxime
9.
89
88
92
92
94
98
96
90
10.
11.
12.
13.
14.
15.
16.
Acetophenone oxime
2-Chloroacetophenone oxime
Benzophenone oxime
Anthrone oxime
(a) Z-Benzil monoxime
(b) E-Benzil monoxime
Cyclohexanone oxime
Cyclopentanone oxime
1-Tetralone oxime
92
98
96
17.
18.
19.
20.
21.
2.5 h
24 h (18 hc)
30 h (20 hc)
8 h
78 (92c)
88 (96c)
86
Camphor oxime
4-Carbethoxy-3-methyl-2-cyclo-
hexen-1-one oxime
(Hagemann’s ester oxime)
aYields refer to chromatographically isolated pure products; the products were fully
characterized by their physical properties (m.p./b.p.), spectral characteristics
1
(IR, H NMR), and comparison with authentic samples;
bValues in parentheses indicate yields when the reaction was carried out at À10ꢀC;
cTypical reaction conditions: To a well-stirred solution of camphor oxime (1.19 mmol)
in acetone (10 mL) was added pyridinium fluorochromate (4.8 mmol) in three
portions; 30% hydrogen peroxide (1.2 mL) was then added dropwise, maintaining
the room temperature, and the reaction mixture was stirred for 20 h at room tem-
perature.
pyridinium fluorochromate, 0.5 mL 30% hydrogen peroxide) at À10ꢀ for
20 min led to the isolation of benzaldehyde and unreacted benzophenone
oxime only. The slower deoximation of Z-benzil monoxime, in comparison
with the E-oxime, may be attributed to the engagement of oxime hydroxy

1610
GANGULY ET AL.
group in hydrogen bonding with suitably disposed syn-benzoyl group in
the former, thereby preventing the formation of chromate ester intermedi-
ate. The necessity of a free hydroxy group for successful deoximation was
further confirmed by the complete failure of acetophenone O-methyl oxime
to react.
In summary, a simple method of deoximation based on pyridinium
fluorochromate and 30% hydrogen peroxide has been developed. This
protocol is found to be effective for a wide variety of aliphatic, aromatic,
and cyclic oximes and may be used for selective deoximation of aldoximes
in the presence of ketoximes by proper choice of reaction conditions.
EXPERIMENTAL
Representative Procedure for the Deoximation with Pyridinium
Fluorochromate and 30% Hydrogen Peroxide
Toawell-stirredsolutionofpyridiniumfluorochromate(5.97 g,30 mmol)
and benzophenone oxime (2.95 g, 15 mmol) in acetone (30 mL), a 30%
hydrogen peroxide solution (7.5 mL) was added dropwise maintaining the
temperature to 0ꢀÀ10ꢀC. The reaction was stirred for 5 h (TLC-monitored)
and then acetone was slowly removed under reduced pressure. The residue
was extracted with ether (3 Â 25 mL) after addition of water (10 mL). The
combined ethereal extract was washed successively with 5% sodium sulphite
solution (10 mL), 1 N HCl, and water (15 mL). The washed and dried
(Na2SO4) extract gave crude product after removal of solvent.
Chromatography over silica gel (60–120 mesh, 20 g) afforded benzophenone
(2.67 g, 98%).
Deprotection of Aldoximes with Pyridinium Fluorochromate and
30% Hydrogen Peroxide Under Controlled Condition
To
a well-stirred mixture of syn-benzaldehyde oxime (0.48 g,
4 mmol) and pyridinium fluorochromate (1.6 g, 8 mmol) in acetone
(20 mL) in a two-neck flask, was added 30% hydrogen peroxide
solution (2 mL) dropwise over a period of 10 min, maintaining the
temperature at À10ꢀC. After the addition was complete, the mixture
was stirred at À10ꢀC for another 10 min. Removal of acetone in
vacuo, usual work-up, and chromatographic purification gave benzaldehyde
(0.35 g, 83%).

OXIME DEPROTECTION
ACKNOWLEDGMENTS
1611
One of the authors (AKS) is thankful to the University of Kalyani for
a research fellowship.
REFERENCES AND NOTES
1. Pines, S.H.; Chemerda, J.M.; Kozlowski, M.A. J. Org. Chem. 1966,
31, 3446.
2. Araujo, H.C.; Ferriera, G.A.L.; Mahajan, J.R. J. Chem. Soc., Perkin
Trans. 1 1974, 2257.
3. Maloney, J.R.; Lyle, R.E.; Saavedra, J.E.; Lyle, G.G. Synthesis
1978, 212.
4. Drabowicz, J. Synthesis 1980, 125.
5. Barton, D.H.R.; Lester, D.J.; Ley, S.V. J. Chem. Soc., Perkin Trans. 1
1980, 1212.
6. Donaldson, R.E.; Saddler, J.C.; Byrn, S.; McKenzie, A.T.; Fuchs, P.L.
J. Org. Chem. 1983, 48, 2167.
7. Rao, C.G.; Radhakrishna, A.S.; Singh, B.B.; Bhatnagar, S.P. Synthesis
1983, 808.
8. Aizpurua, J.M.; Juaristi, M.; Lecea, B.; Palomo, C. Tetrahedron 1985,
41, 2903.
9. Shim, S.B.; Kim, K.; Kim, Y.H. Tetrahedron Lett. 1987, 28, 645.
10. Lee, J.G.; Kwak, K.H.; Hwang, J.P. Tetrahedron Lett. 1990, 31, 6677.
11. Olah, G.A.; Liao, Q.; Lee, C.S.; Surya Prakash, G.K. Synlett 1993, 427.
12. Barhate, N.B.; Garjare, A.S.; Wakharkar, R.D.; Sudalai, A.
Tetrahedron Lett. 1997, 38, 653.
13. Verma, R.S.; Mesharam, H.M. Tetrahedron Lett. 1997, 38, 5427.
14. Demir, A.S.; Tanyeli, C.; Altinel, E. Tetrahedron Lett. 1997, 38, 7267.
15. Bandgar, B.P.; Kunde, L.B.; Thote, J.L. Synth. Commun. 1997,
27, 1149.
16. Bose, D.S.; Srinivas, P. Synth. Commun. 1997, 27, 3835.
17. Verma, R.S.; Dahiya, R.; Saini, R.K. Tetrahedron Lett. 1997, 38, 8819.
18. Chaudhuri, S.S.; Akamanchi, K.G. Tetrahedron Lett. 1998, 39, 3209.
19. Zhang, G.; Yang, D.; Chen, M. Synth. Commun. 1998, 28, 3721.
20. Mitra, A.K.; De, A.; Karchaudhuri, N. Synlett. 1998, 1345.
21. Ranu, B.C.; Sarkar, D.C. J. Org. Chem. 1988, 53, 878.
22. Curran, D.P.; Brill, J.F.; Rakiewicz, D.M. J. Org. Chem. 1984,
49, 1654.
23. Corey, E.J.; Hopkins, P.B.; Kim, S.; Yoo, S.; Nambier, K.P.;
Falck, J.R. J. Am. Chem. Soc. 1979, 101, 7131.

1612
GANGULY ET AL.
24. Greene, T.W.; Wuts, P.G.M. Protective Groups in Organic Synthesis,
2nd Ed.; John Wiley & Sons, Inc.: Toronto, 1991; 214.
25. Kabalka, G.W.; Pace, R.D.; Wadgaonkar, P.P. Synth. Commun. 1990,
20, 2453.
26. Barton, D.H.R.; Beaton, J.M. J. Am. Chem. Soc. 1961, 83, 4083.
27. Barton, D.H.R.; Beaton, J.M.; Geller, L.E.; Pechet, M. J. Am. Chem.
Soc. 1961, 83, 4086.
28. Bartlett, B.L.; Quane, D. Inorg. Chem. 1973, 12, 1925.
29. Cotton, F.A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th Ed.;
John Wiley & Sons, Inc.: New York, 1988; 696.
30. Pyridinium fluorochromate was prepared by the reported procedure:
Bhattacharjee, M.N.; Chaudhuri, M.K.; Dasgupta, H.S.; Roy, N.;
Khathing, D.T. Synthesis 1982, 588.
31. syn-Benzaldehyde oxime was prepared by the reported procedure:
Harwood, L.M.; Moody, C.J. Experimental Organic Chemistry,
1st Ed.; Blackwell Scientific Publications: London, 1989; 647.
32. Other oximes were prepared by the standard methods: Vogel, A.I.
A Textbook of Practical Organic Chemistry, 3rd Ed.; ELBS and
Longman Group Ltd.: London, 1973.
33. Pyridinium fluorochromate, like other chromium (VI) oxidants, is toxic
and chromium-induced damages might be related to the concentration
of biological reductants. However, the toxicological properties,
particularly genotoxicity levels of halogenochromates CrO3XÀ, have
not been ascertained: Cieslak-Golonska, M. Polyhedron 1996, 15,
3667.
Received in Japan May 15, 2000