Microwave-assisted selenium dioxide mediated selective oxidation of 1-tetralones to 1,2-naphthoquinones

Article abstract of DOI:10.1016/j.tetlet.2008.10.068

We report an improved procedure for the selective transformation of substituted 1-tetralones to 1,2-naphthoquinones by microwave-assisted selenium dioxide oxidation. The reaction time is effectively reduced from hours to seconds without any loss of yield (40-70%) or selectivity.

Full text of DOI:10.1016/j.tetlet.2008.10.068

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Tetrahedron Letters 50 (2009) 39–40
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Microwave-assisted selenium dioxide mediated selective
oxidation of 1-tetralones to 1,2-naphthoquinones
*
Danny M. Gelman, Patrick Perlmutter
School of Chemistry, Monash University, Victoria 3800, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
We report an improved procedure for the selective transformation of substituted 1-tetralones to 1,2-
naphthoquinones by microwave-assisted selenium dioxide oxidation. The reaction time is effectively
reduced from hours to seconds without any loss of yield (40–70%) or selectivity.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 9 September 2008
Revised 8 October 2008
Accepted 14 October 2008
Available online 18 October 2008
As part of our programme directed towards the total synthesis
of steroids, we required access to variously substituted 1,2-naph-
thoquinones.1 Of the methods available to synthesise 1,2-naphtho-
quinones,2,3 the procedure of Kishi, modified by Bekaert, appeared
an attractive approach.4–6 Thus, selenium dioxide was reported to
oxidise 1-tetralones in glacial acetic acid at 60–70 °C in 4–7 h pro-
viding 1,2-naphthoquinone products in good yields (Scheme 1, 60–
70%). In our hands, the oxidation generally required longer reaction
times and it was necessary to use finely ground selenium dioxide
powder.
Recently, it was reported that the synthesis of 1,2-dicarbonyl
compounds by selenium dioxide oxidation was greatly accelerated
by closed-vessel microwave (CVMW) irradiation.7,8 Even the diffi-
cult oxidation of camphor to its corresponding 1,2-diketone was
greatly accelerated. Indeed, it was reported that the selenium
was better converted into selenium black and purification was
simplified. In this Letter, we report the extension of CVMW-
assisted selenium dioxide oxidations to include the conversion of
1-tetralones to 1,2-naphthoquinones.
was also found that very short hold times were required (Table
1, entry 6) and were superior as less decomposition was observed
(Table 1, entry 2) than for longer hold times.
The generality of this new accelerated procedure was assessed
by subjecting substituted 1-tetralones 1b–f to our optimised con-
ditions (Table 2). In all cases, the corresponding 1,2-naphtho-
quinones were successfully obtained, including the previously
unreported 5,7-dimethyl-1,2-naphthoquinone. In each case, com-
plete conversion of starting material was confirmed by 1H NMR
analysis of the crude reaction mixture. Simple filtration to remove
the precipitated selenium gave a crude material of approximately
85–90% purity. Where higher purity material was required, the
crude material was purified by flash chromatography. In these
cases, this chromatography was accompanied by significant prod-
uct decomposition.
In most cases, closed-vessel microwave irradiation greatly
accelerates the selenium dioxide promoted conversion of tetral-
ones 1a–f to 1,2-naphthoquinones 2a–f. Yields and selectivities
were comparable to those obtained employing traditional oil-bath
heating.
The temperature and microwave hold time were varied in order
to optimise the conversion of 1-tetralone 1a into 1,2-naphthoqui-
none 2a. Only reactions in glacial acetic acid were successful. It
Table 1
Optimisation of conversion of 1a–2a
Hold timea
Equivalents of SeO2
Conversionb
O
O
Entry
Temp. (°C)
R4
R3
R4
R3
O
1
2
3
4
5
6
7
8
70
70
15 min
1 h
5 min
5 min
1 min
1 s
2
2
2
2
2
2
1
1.5
20
SeO2, AcOH
65c
82
120
150
150
150
150
150
Reflux (refs 4-6)
100
100
100
0
Microwave (this work)
R2 R1
R2 R1
1a-f
2a-f
1 s
1 s
68
Scheme 1. Selective selenium dioxide oxidation of 1-tetralones to 1,2-naphtho-
quinones.
a
Hold time is the time the microwave reactor holds the set temperature. In all
cases, the reaction reaches the set temperature in less than 5 min and is allowed to
cool over 20 min by standing at room temperature.
b
* Corresponding author. Tel.: +61 3 99054522; fax: +61 3 99054597.
E-mail address: Patrick.Perlmutter@sci.monash.edu.au (P. Perlmutter).
Determined by 1H NMR spectroscopy.
c
Extensive decomposition observed.
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.10.068

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
40
D. M. Gelman, P. Perlmutter / Tetrahedron Letters 50 (2009) 39–40
Table 2
compound (112 mg, 60%) as a red-brown solid. Mp 119–122 °C.
1H NMR (CDCl3, 500 MHz) d 7.77 (br s, 1H, ArH), 7.70 (d,
J = 10 Hz, 1H, H4), 7.26 (br s, ArH, 1H), 6.35 (d, J = 10 Hz, 1H, H3),
2.44 (s, 3H, CH3), 2.36 (s, 3H, CH3). 13C NMR (CDCl3, 125 MHz) d
181.2, 179.9, 142.0, 141.5, 138.6, 137.8, 132.3, 130.2, 129.5,
Oxidations of substituted 1-tetralones
Entry
Tetralone
R1
R2
R3
R4
Product
Isolated Yield (%)
1
2
3
4
5
6
1a
1b
1c
1d
1e
1f
H
H
H
H
Me
H
H
H
OMe
H
H
H
OMe
H
OMe
H
H
H
H
H
OMe
H
2a
2b
2c
2d
2e
2f
44a
64
56
126.2, 21.3, 18.8. IR (CDCl3)
m 2958, 2928, 2872, 1678, 1663,
38a
71
1469, 1261 cmÀ1. ESI-MS (M+Na)+ = 209 m/z. Microanalysis Calcd
(C12H10O2) C, 77.40; H, 5.41. Found: C, 76.97; H, 5.26.
Me
Me
60
a
Extensive decomposition occurred during chromatographic purification on
Acknowledgement
silica gel.
D.M.G. is grateful to the Australian Government for the
provision of an Australian Post-Graduate Award.
All reactions were run on a CEM Discover laboratory microwave
reactor. 4-Methyl-1-tetralone was synthesised, according to the
literature procedure.9 All previously reported compounds matched
literature spectral data and full characterisation of new com-
pounds follows.5,10
References and notes
1. Gelman, D. M.; Mayes, P. A.; Mulder, R.; Perlmutter, P. Tetrahedron: Asymmetry
2006, 17, 3341–3350.
General procedure: 5,7-Dimethyl-1,2-naphthoquinone (2f). To
an oven dried microwave vessel equipped with a magnetic stirrer
was added 5,7-dimethyl-1-tetralone (174 mg, 1 mmol), finely
ground selenium dioxide (220 mg, 2 mmol) and glacial acetic acid
(1 mL). The vessel was then sealed and irradiated with microwave
heating to 150 °C with a maximum of 300 W holding for 1 s. The
vessel was allowed to cool to RT prior to dilution with 3 mL CH2Cl2
and filtering through Celite (4.25 Â 10 cm plug) eluting with
CH2Cl2. The volatile solvents were removed in vacuo before
purification by flash chromatography (40% ethyl acetate/hexanes
with 1% acetic acid and N2 as pressurising gas) to yield the title
2. Owton, W. M. J. Chem. Soc., Perkin Trans. 1 1999, 2409–2420.
3. Fieser, L. Org. Synth. 1937, 17, 68.
4. Bekaert, A.; Andrieux, J.; Plat, M.; Brion, J.-D. Tetrahedron Lett. 1997, 38, 4219–
4220.
5. Vicker, N.; Burgess, L.; Chuckowree, I. S.; Dodd, R.; Folkes, A. J.; Hardick, D. J.;
Hancox, T. C.; Miller, W.; Milton, J.; Sohal, S.; Wang, S.; Wren, S. P.; Charlton, P.
A.; Dangerfield, W.; Liddle, C.; Mistry, P.; Stewart, A. J.; Denny, W. A. J. Med.
Chem. 2002, 45, 721–739.
6. Nagaoka, H.; Schmid, G.; Iio, H.; Kishi, Y. Tetrahedron Lett. 1981, 22, 899–902.
7. Belsey, S.; Danks, T.; Wagner, G. Synth. Commun. 2006, 36, 1019–1024.
8. Goswami, S.; Adak, A. K. Synth. Commun. 2003, 33, 475–480.
9. Ansell, M. F.; Whitfield, G. F. Tetrahedron Lett. 1968, 26, 3075–3077.
10. Babu, B. H.; Rau, N. V. S. Proc. Indian Acad. Sci. Sect. A 1967, 66, 301–305.