A mild and efficient oxidation of alcohols to aldehydes and ketones with periodic acid catalyzed by chromium(III) acetylacetonate

Article abstract of DOI:10.1016/S0040-4039(03)00283-1

Chromium(III) acetylacetonate was found to be an efficient catalyst (10 mol%) for the oxidation of alcohols to aldehydes and ketones with periodic acid (1.5 equiv.) in acetonitrile at room temperature.

Full text of DOI:10.1016/S0040-4039(03)00283-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 2553–2555
A mild and efficient oxidation of alcohols to aldehydes and
ketones with periodic acid catalyzed by chromium(III)
acetylacetonate
b
a,
Liang Xu and Mark L. Trudell *
a
Department of Chemistry, University of New Orleans, New Orleans, LA 70148, USA
St Charles Pharmaceuticals, Inc., PO Box 850185, New Orleans, LA 70185, USA
b
Received 8 January 2003; revised 29 January 2003; accepted 30 January 2003
Abstract—Chromium(III) acetylacetonate was found to be an efficient catalyst (10 mol%) for the oxidation of alcohols to
aldehydes and ketones with periodic acid (1.5 equiv.) in acetonitrile at room temperature. © 2003 Elsevier Science Ltd. All rights
reserved.
4
The oxidation of alcohols to the corresponding alde-
hyde or ketone is one of the most important functional
group transformations in organic synthesis. Despite the1
availability of many reagents for this transformation,
there still exists a need for mild and efficient methods.
Chromium-based reagents play a vital role in organic
chemistry as oxidants for alcohols but such transforma-
tions are most frequently accomplished by using highly
toxic Cr(VI)-based reagents. These transformations typ-
ically employ a minimum of a stoichiometric amount of
chromium reagent and in some systems require large
of the corresponding ketones. Herein, we report a mild
and efficient oxidation of alcohols to the corresponding
aldehydes and ketones with periodic acid catalyzed by
Cr(acac) in acetonitrile at room temperature (Scheme
3
1).
The results for the oxidation of a variety of alcohols are
summarized in Table 1. Benzyl alcohols with either
electron donating groups (entries 1–3) or electron with-
drawing groups (entry 4) were oxidized smoothly to the
corresponding aldehydes in high yields with 1.5 equiv.
of periodic acid (H IO ) catalyzed by 10 mol% of
2
excesses to obtain complete conversion. Chromium-
5
6
catalyzed oxidations are therefore of particular interest
due to concerns of functional group selectivity and
Cr(acac) . As expected, secondary alcohols were oxi-
3
dized more quickly than primary alcohols. Most oxida-
tions of secondary alcohols were completed within one
hour and gave the corresponding ketones cleanly.
3
environmental factors.
Chromium(III) acetylacetonate [Cr(acac) ] was first
3
reported to be an active catalyst for oxidation of sec-
ondary alcohols to ketones using t-BuOOH as co-oxi-
dant. However, high reaction temperatures and long
reaction times were required affording only low yields
The Cr(acac) /H IO oxidation system was tolerant of a
3
5
6
variety of other functional groups. The 2-naphthalene-
methanol was oxidized to 2-naphthaldehyde in 91%
yield (entry 5). Under these conditions the naphthyl
ring was not affected even when the reaction mixture
was stirred at room temperature for 18 h in the pres-
ence of two or more equivalents of periodic acid. This
is in contrast to CrO -catalyzed oxidations in which the
3
aromatic ring has been reported to be easily oxidized to
5
a quinone. In addition, the carbonꢀcarbon triple bond
of 1-phenylpropargyl alcohol (entry 9) and the cyclo-
Scheme 1.
propyl ring of a-cyclopropyl-benzylalcohol (entry 11)
were compatible with the Cr(acac) /H IO system. One
Keywords: oxidation; alcohols; periodic acid; chromium(III) acetyl-
3
5
6
limitation of this system appears to be the oxidation of
allylic alcohols which gave complex mixtures of by-
products. The oxidation of cinnamyl alcohol (entry 12)
acetonate.
*
Corresponding author. Tel.: +1-504 280-7337; fax: +1-504-280-6860;
e-mail: mtrudell@uno.edu
0
040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)00283-1

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554
L. Xu, M. L. Trudell / Tetrahedron Letters 44 (2003) 2553–2555
a
6
Table 1. Oxidation of alcohols with Cr(acac) /H IO
3
5
with Cr(acac) /H IO afforded cinnamaldehyde in 20%
of the alcohol. It is also noteworthy that none of the
corresponding enone that would result from isomeriza-
tion of the terminal carbonꢀcarbon double bond was
observed. Finally, the 3-pyridylcarbinol was oxidized to
nicotinaldehyde (entry 14) in 82% yield. The basic
nitrogen atom of the pyridine ring did not adversely
3
5
6
yield after chromatography. However, the oxidation of
homoallylic alcohol, 4-phenyl-1-buten-4-ol afforded the
corresponding ketone (entry 13) in 88% yield. In this
example a higher yield was obtained if the Cr(acac)3/
H IO solution was stirred for 15 min prior to addition
5
6

L. Xu, M. L. Trudell / Tetrahedron Letters 44 (2003) 2553–2555
2555
affect the catalytic activity of the Cr(acac) /H IO sys-
tem.
temperature. sec-Phenethyl alcohol (610 mg, 5.0 mmol)
was then added and stirring was continued at room
temperature for 1 h. The reaction mixture was diluted
with ethyl acetate (150 mL), washed, respectively, with
water, saturated aqueous Na SO solution, brine, and
3
5
6
As part of an effort to explore the scope of substrate
alcohols that could be oxidized with this system several
functional groups were identified to be not compatible
2
3
then dried over MgSO . After removal of the solvent,
4
with the Cr(acac) /H IO system. Alcohols that con-
3
5
6
the residue was purified by silica gel flash chromatogra-
tained a sulfide or sulfoxide group suffered from com-
phy (SiO , EtOAc:hexanes, 1:8) to afford acetophenone
2
petitive oxidation at sulfur to give mixtures of
(
580 mg, 96%).
1
0
sulfoxides and sulfones. In addition, alcohols that
contained silyl ethers (OTMS and OTBS), N-t-butoxy-
carbonyl (N-Boc) and phenolic groups gave poor yields
or intractable product mixtures.
In summary, the Cr(acac) was found to be an efficient
3
catalyst for the oxidation of alcohols to aldehydes and
ketones by using periodic acid as a co-oxidant. This
new procedure is very simple and cleanly affords the
desired carbonyl compounds in high yields.
Based on preliminary studies, Cr(acac) appears to be
3
the reagent of choice for this catalytic process. Other
Cr(III) substrates, including chromium(III) chloride
hexahydrate, chromium(III) acetate hydroxide and
chromium(III) oxide, were inferior as catalysts at the
same loading concentrations. Although the mechanism
of this oxidation is not fully understood at this time,
the actual oxidant is probably a Cr(IV), Cr(V) or
Cr(VI) species, since neither Cr(acac) nor H IO inde-
References
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5
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–9
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Representative experimental procedure: Periodic acid
1998, 39, 5323.
(
1.7 g, 7.5 mmol) and Cr(acac) (175 mg, 0.50 mmol,
3
10. Xu, L.; Cheng, J.; Trudell, M. L. J. Org. Chem. 2003
purchased from Aldrich Chemical Co. Milwaukee, WI)
were added to acetonitrile (30 mL) and stirred at room
(manuscript submitted).