3
14
15
16
2-furanyl (1n)
12
14
12
10
65
55
66
70
(3n)
(3o)
(3p)
5-methyl-2-furanyl (1o)
2-thiophenyl (1p)
2-naphthyl (1q)
17
(3q)
aIsolated yields
bProducts were fully characterized by recording their 1H, 13C NMR, IR, Mass and elemental analyses.
The advantages and limitations of this methodology were
investigated by reacting triethylorthoformate (2) with various
substituted aryl methyl ketones (1a-q) in the presence of 0.7
equiv of H2SeO3 and BF3·Et2O (1.5 mL) to give 2,2-diethoxy-1-
phenylethanones (3a-q, Scheme 1).
nucleophilic attack by the lone pair of oxygen atom of the
triethylorthoformate leading to the formation of the product (3).
In summary, we have devised a one-pot method for the
synthesis of α-ketoacetals via the intermediary of H2SeO3 and
BF3·Et2O. The reaction proceeds efficiently at ambient
temperature and ordinary reaction conditions. In the present
methodology we were able to highlight a viable alternative
method involving the use of H2SeO3 and BF3·Et2O in a neat
reaction to furnish the 2,2-diethoxy-1-phenylethanones in good
yields in comparison to some of the earlier reported methods
involving expensive metal catalysts14,16 and strong bases.1,10
From the results obtained it may be noted that irrespective of
the presence of electron withdrawing or releasing substituents in
the ortho-, meta- or para-positions, the reactions proceeded fairly
smoothly to afford the desired products in good to excellent
yields (Table 2, 3a–q). Interestingly, electron poor aromatic
ketones such as 3-nitrobenzaldehyde (1h), and 4-
nitrobenzaldehyde (1i) also furnished 2,2-diethoxy-1-
phenylethanones (3h-i) in high yields (Table 2, entries 8-9). The
scope of this methodology was further extended to the reaction of
heteroaryl or fused aromatic methyl ketones with
triethylorthoformate (2). The same reaction trend was observed in
the case of 1-(2-furanyl)ethanone (1n), 5-methyl-(2-
furanyl)ethanone (1o), 1-(2-thiophenyl)ethanone (1p) to give the
corresponding 2,2-diethoxy-1-(heteroaryl)ethanones (3n-p, 55-
66%) while 1-(2-naphthyl)ethanone (1q) afforded 2,2-diethoxy-
1-(naphthalen-2-yl)ethanones (3q) in 70% yields (Table 1,
entries 14-17).
Acknowledgments
I.K. thanks the University Grants Commission for Rajiv
Gandhi National Fellowship, SAIF NEHU, CDRI Lucknow and
IISC Bangalore for spectral analysis. The author gratefully
acknowledges financial assistance from the Council of Scientific
and Industrial Research, Government of India (Project No.
02(0102)/12/EMR-II)
References and notes
Notably, substituted acetophenones bearing the N-acetyl
group at meta- and para-positions (1l, 1m) also furnished the
product in good yields (Table 1, entries 12-13). The reaction goes
to completion in each case as the starting ketone is completely
consumed. Besides the isolated product, no other products could
be isolated except for the usual unidentifiable impurities. All the
products obtained were fully characterized by 1H NMR, 13C
NMR, IR, Mass and elemental analyses.
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O
O
O
H
Se
BF3 Et2O
HO
OH
R
R
R
Se OBF3
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4
H
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Se
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R
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3
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Scheme 2. Probable Mechanism
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electrophilic centre at the α-carbon of
6 resulting in a