A mild and efficient method for cleavage of C=N using imidazolium dichromate

Article abstract of DOI:10.1081/SCC-200026210

Oximes, hydrazones, and semicarbazones are converted to their corresponding carbonyl compounds by using imidazolium dichromate (IDC).

Full text of DOI:10.1081/SCC-200026210

SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 15, pp. 2751–2755, 2004
A Mild and Efficient Method for Cleavage of
C55N Using Imidazolium Dichromate
*
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 their corres-
ponding carbonyl compounds by using imidazolium dichromate (IDC).
Key Words: Imidazolium dichromate; Oximes; Hydrazones; Semicarba-
zones.
INTRODUCTION
Oximes, hydrazones, and semicarbazones are useful intermediates in
organic chemistry and are utilized for purification and characterization of
*
Correspondence: Surya Kanta De, Department of Medicinal Chemistry and Molecular
Pharmacology, School of Pharmacy, Purdue Cancer Center, Purdue University,
West Lafayette, IN 47907, USA; E-mail: skd125@yahoo.com.
2751
DOI: 10.1081/SCC-200026210
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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De
carbonyl compounds. They are also used as protecting groups for carbonyl
compounds.[1] Their synthesis from noncarbonyl compounds[2] provides an
alternative pathway to aldehydes and ketones. Therefore, the regeneration
of carbonyl compounds from their oximes has received much attention.[3]
Some chlorochromate derivatives are also used for this purpose [4–9] Although
some of the known methods are carried out under mild conditions, most of
them require drastic conditions, such as high temperature, long reaction
times, expensive, toxic, or not readily available reagents, and they
need to be freshly prepared with tedious work-up procedures. Little
attention has been paid to oxidative cleavage[5,6,10] of hydrazones and semi-
carbazones. In this communication, author wishes to report a convenient
and an efficient method for the regeneration of carbonyl compounds from
oximes, hydrazones, and semicarbazones by using imidazolium dichromate
(IDC).
2a, R1 ¼ R2 ¼ C6H5; 2b, R1 ¼ C6H5, R2 ¼ Me; 2c, R1 ¼ p-MeOC6H4,
R2 ¼ H; 2d, R1 ¼ p-BrC6H4, 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 Ph–CH55CH,
R2 ¼ H; 2i, R1 ¼ p-ClC6H4, R2 ¼ Me; 2j, R1 ¼ p-MeOC6H4, R2 ¼ Me.
IDC is an inexpensive reagent, which has been used as an oxidizing
agent.[11] Author believes this is the first report of using IDC as the reagent
for the deprotection of oximes, hydrazones, and semicarbazones. Several
oximes were deoximated to their corresponding aldehydes and ketones in a
good to excellent yields. Over-oxidation of aldehydes to their carboxylic
acid was not observed. In contrast, deoximation with PCC suffers from
long reaction times (12–94 hr).[4] Also, PCC-hydrogen peroxide,[12] PDC-
TBHP,[13] or TBHP[14] alone are not suitable for aldoximes, over-oxidation
products are usually produced. The reagent IDC has the ability to tolerate a
variety of substrates. Aromatic and aliphatic oximes were deoximated with
IDC. Acid sensitive methoxy group remained intact and a,ß-unsaturated,
cinnamaldoxime was deoximated without any difficulty. Several phenyl
hydrazones and semicarbazones were deprotected by using IDC to give the
corresponding carbonyl compounds in excellent yields.

Cleavage of C55N Using IDC
2753

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De
Mildness of reaction condition, efficiency of the reagent, ease of work-up
procedure and high yields of products are among the outstanding advantages
of this new method.
EXPERIMENTAL
All products are known compounds and were identified by comparison of
their spectral data (IR, 1H NMR) and physical properties with those of auth-
entic samples. The progress of reaction was monitored by thin layer chromato-
graphy on silica gel. All yields refer to isolated products.
General Procedure for Regeneration of Carbonyl Compounds
from Oximes, Hydrazones, and Semicarbazones with IDC
To a solution of substrate (oxime or hydrazone or semicarbazone,
5 mmol) in acetonitrile (25 mL) IDC (7.5 mmol) was added. The reaction
mixture was refluxed for the specified time (Table 1). After completion of
the reaction (TLC), the solvent was evaporated on rotary evaporator and the
residue was chromatographed over silica gel, eluted hexane–ethyl acetate
system to afford a pure product.
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2755
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Received in the USA March 31, 2004

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