Novel cerium(IV) ammonium nitrate mediated transformation of styrenes to α-methoxy acetophenones

Article abstract of DOI:10.1246/cl.2000.584

Styrenes when treated with a methanolic solution of CAN underwent a novel transformation to α-methoxy acetophenones presumably via a radical cation.

Full text of DOI:10.1246/cl.2000.584

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Chemistry Letters 2000
Novel Cerium(IV) Ammonium Nitrate Mediated Transformation of
Styrenes to α-Methoxy Acetophenones
Vijay Nair,* Latha G. Nair, Sreeletha B. Panicker, V. Sheeba, and Anu Augustine
Organic Chemistry Division, Regional Research Laboratory (CSIR), Trivandrum 695 019, India
(Received January 20, 2000; CL-00062)
Styrenes when treated with a methanolic solution of CAN
underwent a novel transformation to α-methoxy acetophenones
presumably via a radical cation
Recently it has been observed that alkoxy styrenes undergo
facile cerium(IV) ammonium nitrate (CAN) mediated dimeriza-
1
-3
tion resulting in a variety of interesting compounds. In this
context it was of interest to investigate the reaction of CAN
with styrenes devoid of alkoxy groups on the benzene ring. It
has been reported by Baciocchi that the reaction of styrene with
4
CAN in acetonitrile led to the exclusive formation of dinitrate.
A different reactivity pattern was anticipated in methanol and
our preliminary results validating the assumption are presented
here.
tion with the formation of esters via Wolff rearrangement.
In a prototype experiment, a methanolic solution of styrene
a when treated with CAN afforded α-methoxy acetophenone
a. Similar results were obtained with other substituted
Other methods for the synthesis of α-alkoxy and α-hydroxy
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1
2
ketones involve the reaction of alkenes with peracetic acid,
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10
catalytic system of OsO /Ni(II) complex and permanganate
4
1
1
styrenes (1b-1d) and these are summarized in Table 1.
Interestingly, stilbenes (1f, 1g) also underwent the transforma-
/CuSO reagent combination. The reaction reported herein is
4
simple, direct and uses the inexpensive styrene as starting mate-
rial. The details of the reaction and its mechanistic implications
are currently under investigation.
6
tion to afford the corresponding benzoin methyl ethers. Also
noteworthy is the reaction of β-methoxystyrene (1e) to the
dimethyl acetal of phenyl glyoxal in high yield.
General Experimental Procedure: To a methanolic solution
of the styrene (1 mmol) was added a solution of CAN (2.3
mmol) in methanol with stirring. The reaction mixture after the
decolorization was diluted with water (20 mL) and then extract-
ed with dichloromethane (5x20 mL). The combined organic
extracts were washed with water, brine and dried over sodium
sulfate. The solvent was evaporated off. The residue on column
chromatography using silica gel (5% ethyl acetate-hexane mix-
ture) afforded the corresponding methoxy acetophenone deriva-
tive.
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Spectral data for (2b) IR (CCl ): 2940, 2835, 1715, 1625
4
-
1 1
cm . H NMR (CDCl ): δ 7.83 (d, 2Η, ΑrH), 7.25 (d, 2H,
ArH), 4.68 (s, 1H, CH ), 3.50 (s, 3H, OCH ), 2.41 (s, 3H, CH );
C NMR (CDCl ): 195.80, 144.45, 132.41, 129.40, 127.96,
5.24, 59.42, 21.71.GC-MS m/z (%): 164(M )(2) 134(5),
3
2
3
3
1
3
3
+
7
1
19(65), 91(45), 86 (48), 84(75), 51(35), 49(100).
LGN, SBP, VS and AA thank CSIR, New Delhi for the
award of research fellowships and Ms. Soumini Mathew for
NMR spectra.
References and Notes
Although the mechanistic details of the reaction are not
clear, a tentative rationalization involving a radical cation can
be suggested to account for the formation of the product
1
2
3
V. Nair, J. Mathew, P. P. Kanakamma, S. B. Panicker,
V. Sheeba, S. Zeena, and G. K. Eigendorf, Tetrahedron
Lett., 38, 2191 (1997).
V. Nair, V. Sheeba, S. B. Panicker, Tesmol G. George, R.
Rajan, L. Balagopal, M. Vairamani, and S. Prabhakar,
Tetrahedron, in press.
(
Scheme 1).7
It may be pointed out that the conventional method for the
synthesis of α-methoxy acetophenones consists of the BF ·OEt
3
2
5
,8
catalyzed reaction of diazoketones and alcohols, in competi-
For a recent review of CAN mediated reactions see, V.
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
585
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