ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 8, pp. 1252–1253. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © N.V. Pchelintseva, O.V. Fedotova, Ya.G. Kolevatova, A.M. Burov, M.A. Men’shova, 2008, published in Zhurnal Organicheskoi
Khimii, 2008, Vol. 44, No. 8, pp. 1263–1264.
SHORT
COMMUNICATIONS
Chemistry of 1,5-Diketones. A New Synthetic Approach
to Unsaturated 1,5-Diketones
N. V. Pchelintseva, O. V. Fedotova, Ya. G. Kolevatova, A. M. Burov, and M. A. Men’shova
Chernyshevskii Saratov State University, ul. Astrakhanskaya 83, Saratov, 410012 Russia
e-mail: KolevatovaJG@mail.ru
Received February 7, 2008
DOI: 10.1134/S1070428008080290
It is known that substituted pent-2-ene-1,5-diones
IIa and IIb and their fused analogs IId and IIe can be
obtained by base hydrolysis of pyrylium and dihydro-
benzochromenium slats [1, 2]. Opening of the pyryli-
um ring by the action of sodium acetate smoothly
afforded aryl-substituted pent-2-ene-1,5-diones IIa and
IIb in 92–96% yield [3]. The hydrolysis of 4-(3-ni-
trophenyl)-2,6-diphenylpyrylium and 2,4-diphenyl-
and 4-(4-methoxyphenyl)-2-phenyldihydrobenzochro-
menium tetrafluoroborates Ic–Ie in aqueous alcohol in
the presence of sodium acetate gave the corresponding
unsaturated 1,5-diketones IIc–IIe in 31–52% yield [4].
Opening of the labile heteroring in alkyl/aryl-substi-
tuted pyrylium salts with formation of unsaturated
1,5-diketones also occurred during thin-layer chroma-
tography (TLC) on aluminum oxide or weakly basic
sorbents [5].
the C–O bond in the heteroring, thus favoring its
opening with formation of unsaturated diketone.
Initial pyrylium tetrafluoroborates Ia–Ic were syn-
thesized according to the procedure reported in [6],
and salts Id and Ie were prepared as described in [7].
General procedure for the hydrolysis of pyryli-
um and dihydrobenzochromenium salts. A suspen-
sion of 11 mmol of tetrafluoroborate Ia–Ie and
55 mmol of Al2O3 in 40 ml of ethanol was heated to
70–80°C under stirring, a solution of 66 mmol of
sodium acetate in 15 ml of water was added, and the
mixture was kept for 24 h. The precipitate was filtered
off and washed with chloroform, the filtrate was evap-
orated, and the crystalline product was separated and
dried.
1,3,5-Triphenylpent-2-ene-1,5-dione (IIa). Yield
We were the first to accomplish hydrolysis of pyr-
ylium salts Ia–Ic and dihydrobenzochromenium salts
Id and Ie in aqueous ethanol in the presence of 5 equiv
of sodium acetate and 6 equiv of powdered aluminum
oxide as catalyst. The yields of unsaturated diketones
IIa–IIe were 75–98%. Pentenedione IIc was isolated
as cis-s-cis isomer; diketone IIe was a mixture of cis
and trans isomers (according to the GC–MS data).
Presumably, aluminum oxide promotes polarization of
98%, mp 118–119°C [1].
3-(4-Methoxyphenyl)-1,5-diphenylpent-2-ene-
1,5-dione (IIb). Yield 97%, mp 121–122°C (from
ethanol) [7].
3-(3-Nitrophenyl)-1,5-diphenylpent-2-ene-1,5-di-
one (IIc). Yield 81%, yellow crystals, mp 126–127°C
(from ethanol). IR spectrum, ν, cm–1: 1686 (C1=O),
1664 (C5=O), 1580 (C=C). 1H NMR spectrum, δ, ppm:
Ar
Ar
Ph
R2
AcONa, Al2O3, EtOH
R2
BF4
O
R1
O
Ph
O
R1
Ia–Ie
IIa–IIe
R1 = Ar = Ph, R2 = H (a); R1 = Ph, R2 = H, Ar = 4-MeOC6H4 (b); R1 = Ph, R2 = H, Ar = 3-O2NC6H4 (c); R1R2 = o-(CH2)2C6H4,
Ar = Ph (d); R1R2 = o-(CH2)2C6H4, Ar = 4-MeOC6H4 (e).
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