4038
R. M. Young, M. T. Davies-Coleman / Tetrahedron Letters 52 (2011) 4036–4038
Figure 2. Conversion of compounds 1a (empty diamonds e); 1c (filled circles d); 1d (filled squares j) and 1e (empty squares h) into the corresponding aryl glyoxals 2a and
2c–e, respectively.
Table 3
MeOH (10 mL). The combined organic filtrate was concentrated
under reduced pressure and the organic residue subsequently
stirred in boiling H2O (6 mL) and filtered hot to remove any insol-
uble precipitate. The aqueous filtrate was cooled on ice to afford
crystals of the glyoxal monohydrate product which were collected
under vacuum filtration, washed with cold H2O, and dried in a vac-
uum desiccator.
Percentage conversiona of 1a–f into 2a–f under standardized microwave conditionsb
and the isolated yields of 3a–f after crystallization from water
Substrate
% Conversion
Product
Isolated yield (%)
1a
1b
1c
1d
1e
1f
100
100
99
100
95
3a
3b
3c
3d
3e
3f
84
89
81
85
63
84
Acknowledgments
100
a
The % conversion was calculated from quantitative GC analysis.
Hold time of 15 min at 100 °C and using 2.7 equiv of SeO2.
This research was supported by Rhodes University, the South
African National Research Foundation (NRF) and the Medical
Research Council (MRC). A post-graduate bursary from Deutscher
Akademischer Austauschdienst (DAAD), awarded to R.M.Y., is
gratefully acknowledged. Drs. Kevin Lobb and Ernst Ferg of Rhodes
University and Nelson Mandela Metropolitan University are
thanked for their assistance with the kinetic studies and TGMS,
respectively.
b
the relative concentrations of 2a and 3a to ensure no deviations in
the peak intensities.
Microwave reactions were carried out using a CEM Discover
single-mode laboratory microwave reactor (producing controlled
irradiation at 2450 MHz) using 10 mL microwave glass pressure
vials. The glyoxal monohydrates, 3a–f, are all known compounds
and the melting points, spectroscopic data (NMR, IR and MS) of
all these compounds matched the physical and spectral data re-
ported in the literature.3,9
References and notes
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lowing microwave irradiation the reaction solution was rapidly
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was filtered through Celite, in order to remove Se, and washed with
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