Quinolium dichromate adsorbed on alumina: A mild, convenient, and inexpensive reagent for cleavage of C=N under nonaqueous conditions

Article abstract of DOI:10.1080/00397910500213047

Oximes, hydrazones, and semicarbazones are converted to the corresponding carbonyl compounds using quinolium dichromate adsorbed on alumina (QDC/alumina) under nonaqueous conditions. Copyright Taylor & Francis, Inc.

Full text of DOI:10.1080/00397910500213047

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Quinolium Dichromate
Adsorbed on Alumina: A Mild,
Convenient, and Inexpensive
Reagent for Cleavage of C˭N
Under Nonaqueous Conditions
Surya Kanta De a
a Department of Medicinal Chemistry and Molecular
Pharmacology, School of Pharmacy, Purdue Cancer
Center , Purdue University , West Lafayette,
Indiana, USA
Published online: 22 Aug 2006.
To cite this article: Surya Kanta De (2005) Quinolium Dichromate Adsorbed on
Alumina: A Mild, Convenient, and Inexpensive Reagent for Cleavage of C˭N Under
Nonaqueous Conditions, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 35:20, 2641-2644
To link to this article: http://dx.doi.org/10.1080/00397910500213047
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Synthetic Communicationsw, 35: 2641–2644, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500213047
Quinolium Dichromate Adsorbed
on Alumina: A Mild, Convenient,
and Inexpensive Reagent for Cleavage of
C55N Under Nonaqueous Conditions
Surya Kanta De
Department of Medicinal Chemistry and Molecular Pharmacology,
School of Pharmacy, Purdue Cancer Center, Purdue University,
West Lafayette, Indiana, USA
Abstract: Oximes, hydrazones, and semicarbazones are converted to the correspond-
ing carbonyl compounds using quinolium dichromate adsorbed on alumina (QDC/
alumina) under nonaqueous conditions.
Keywords: Quinolium dichromate, alumina, oximes, hydrazones, semicarbazones,
carbonyl compounds
Derivatives of carbonyl compounds such as oximes, hydrazones, and semi-
carbazones have played an important role in the protection of carbonyl
compounds,[1] because they are very crystalline and stable compounds.
Because oximes can be prepared from noncarbonyl compounds, the regener-
ation of carbonyl compounds from oximes is an alternative method for the
preparation of aldehydes and ketones.[2] Interest in regeneration of carbonyl
compounds from their derivatives under mild conditions has been growing
in synthetic organic chemistry. The classical acid-hydrolytic method
requires strong mineral acids, often results in low yields, and is not suitable
for acid-sensitive compounds.[3] Several oxidative deoximation methods
Received in the USA May 18, 2005
Address correspondence to Surya Kanta De, Department of Medicinal Chemistry
and Molecular Pharmacology, School of Pharmacy, Purdue Cancer Center, Purdue
University, West Lafayette, IN 47907, USA. Fax: 765-494-1414; E-mail: skd125@
pharmacy.purdue.edu
2641

2642
S. K. De
have been reported that have some advantages over the classical acid-
hydrolysis method.[4–13] Recently, some microwave techniques have been
developed that are valuable from a synthetic standpoint but extreme precau-
tions have to be taken because these reactions were performed under
microwave irradiation with an oxidant.[14,15] Little attention has been paid
to oxidative cleavage of hydrazones and semicarbazones.[6,16] Thus, there is
still a need to develop a new and facile procedure for the regeneration of
carbonyl compounds from oximes, hydrazones, and semicarbazones.
Quinolium dichromate is an inexpensive reagent and was previously
reported as an oxidizing agent.[17] Quinolium dichromate-adsorbed alumina
is stable and easily prepared by adding alumina to a solution of quinolium
dichromate in water. In recent years, the organic reactions on solid
supports have attracted much attention because of their enhanced selectivity,
milder reaction conditions, and associated ease of manipulation.[18] In this
communication, I report a convenient and efficient method for the
cleavage of carbon–nitrogen double bonds using QDC/alumina under
nonaqueous conditions. Several oximes were deoximated to their corre-
sponding aldehydes and ketones in good to excellent yields. Overoxidation
of aldehydes to their carboxylic acids was not observed. In contrast, deoxi-
mation with PCC suffers from long reaction times (12–94 h);[4] PCC-
hydrogen peroxide,[5] PDC-tert-butyl hydroperoxide,[12] and TBHP[6] alone
are not suitable for aldoximes, and overoxidation products are usually
produced. QDC/alumina heterogeneous system is successfully used for
cleavage of semicarbazones and phenylhydrazones. The reagent has the
ability to tolerate a variety of substrates. Without alumina support,
oxidative cleavage takes longer to complete the reaction (Scheme 1).
In summary, the method has advantages in terms of yield, heterogeneous
nature, cost and availability of reagents, reaction time, and workup.
EXPERIMENTAL
All of the products are known compounds and were checked by comparison of
1
their spectral data (IR, H NMR) and physical properties with an authentic
Scheme 1. 2a, R1 ¼ R2 ¼ C6H5; 2b, R1 ¼ C6H5, R2 ¼ Me; 2c, R1 ¼ p–MeOC6H4,
R2 ¼ H; 2d, R2 ¼ H; 2e, R1 ¼ R2 ¼ –(CH2)5–; 2f, R1 ¼ R2 ¼ –(CH2)4–; 2g,
R1 ¼ C6H5, R2 ¼ H; 2h, R1 ¼ p–ClC6H4, R2 ¼ Me; 2i, R1 ¼ p–ClC6H4, R2 ¼ Me;
2j, R1 ¼ p–MeOC6H4, R2 ¼ Me.

Quinolium Dichromate on Alumina
2643
Table 1. Oxidative deprotection of oximes, hydrazones, and semicarbazones with
QDC/alumina in refluxing acetonitrile
Product Time Yield
(2)
Mp/bp(8C)
lit.a/obs.
Entry
Substrate (1)
(min)
(%)
1
2
3
Benzophenone oxime
Acetophenone oxime
4-Methoxybenzaldehyde
oxime
2a
2b
2c
18
22
15
89
92
93
48–49/46–47
202/200–202
248/245–247
4
4-Bromobenzaldehyde
oxime
2d
10
90
55–58/55–57
5
6
7
8
Cyclohexanone oxime
Cyclopentanone oxime
Benzaldehyde oxime
4-Chloroacetophenone
oxime
2e
2f
28
27
15
25
93
87
95
87
155/150–152
130–131/128–129
178–179/179–180
232/228–230
2g
2h
9
10
11
12
13
14
15
16
17
Benzophenone
semicarbazone
2a
2d
2h
2e
2b
2a
2h
2d
2j
10
15
18
23
20
27
27
16
27
92
90
92
81
92
79
83
92
91
48–49/46–47
55–57/55–57
233/228–231
155/150–151
202/200–201
48/47–49
4-Bromobenzaldehyde
semicarbazone
4-Chloroacetophenone
semicarbazone
Cyclohexanone
semicarbazone
Acetophenone
semicarbazone
Benzophenone
phenylhydrazone
4-Chloroacetophenone
phenylhydrazone
4-Bromobenzaldehyde
phenylhydrazone
4-Methoxyacetophenone
phenylhydrazone
231/228–230
57/56–58
36–38/34–35
aAvailable from Aldrich Chemical Company.
sample. The progress of the reaction was monitored by thin-layer chromato-
graphy on silica gel. All yields refer to isolated products.
Preparation of Quinolium Dichromate Adsorbed on Alumina
To a solution of quinolium dichromate (11.90 g) in water (25 mL) was added
alumina (12.75 g). The reaction mixture was stirred at 508C for 1 h. After
evaporation on a rotary evaporator, the yellow solid was dried in vacuum at
508C for 2 h. The reagent may be kept for several months in air at room
temperature without losing its activity.

2644
S. K. De
General Procedure for Cleavage of C55N with QDC/Alumina
A mixture of substrate (oxime or hydrazone or semicarbazone, 1 mmol) and
QDC/alumina (1.5 equiv of oxidant, QDC) in acetonitrile (10 mL) was
refluxed for the specified time (Table 1). After completion of the reaction,
the reaction mixture was filtered, and the solid material was washed with
acetonitrile several times. The combined filtrate was evaporated and residue
was chromatographed over silica gel (eluted hexane–ethyl acetate, 8/2) to
give the pure product in good to excellent yields. All of the products are
known compounds and were identified by their spectral data and physical
properties (bp or mp) with those of authentic samples.
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