Chemistry of 1,5-diketones: I. Halogenation of aryl-substituted pent-2-ene-1,5-diones, pentane-1,5-diones, and their fused analogs

Article abstract of DOI:10.1134/S1070428007090059

Halogenation of 3-(4-methoxyphenyl)-1,5-diphenylpent-2-ene-1,5-dione, 3-(4-methoxyphenyl)-1,5-diphenylpentane-1,5-dione, and 2-[1-(4-methoxyphenyl)-3- oxo-3-phenylpropyl)-1,2,3,4-tetrahydroaphthalen-one with bromine, chlorine, and dichloro(phenyl)-λ³

Full text of DOI:10.1134/S1070428007090059

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2007, Vol. 43, No. 9, pp. 1285–1290. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © N.V. Pchelintseva, D.A. Tsimbalenko, O.V. Fedotova, 2007, published in Zhurnal Organicheskoi Khimii, 2007, Vol. 43, No. 9,
pp. 1292–1296.
Chemistry of 1,5-Diketones:
I. Halogenation of Aryl-Substituted Pent-2-ene-1,5-diones,
Pentane-1,5-diones, and Their Fused Analogs
N. V. Pchelintseva, D. A. Tsimbalenko, and O. V. Fedotova
Chernyshevskii Saratov State University, ul. Astrakhanskaya 83, Saratov, 410012 Russia
e-mail: KolevatovaJG@mail.ru
Received December 6, 2006
Abstract—Halogenation of 3-(4-methoxyphenyl)-1,5-diphenylpent-2-ene-1,5-dione, 3-(4-methoxyphenyl)-1,5-
diphenylpentane-1,5-dione, and 2-[1-(4-methoxyphenyl)-3-oxo-3-phenylpropyl)-1,2,3,4-tetrahydronaphthalen-
1-one with bromine, chlorine, and dichloro(phenyl)-λ3-iodane leads to formation of the corresponding mono-
bromo-, dichloro-, or trichloro-substituted 1,5-diketones, depending on the conditions. Halogenation of the
aliphatic chain and methoxyphenyl substituent can be accompanied by heterocyclization to give pyrylium salts.
DOI: 10.1134/S1070428007090059
Among numerous chemical transformations of cy-
clic and semicyclic 1,5-diketones, their heterocycliza-
tions in reactions with nucleophiles have been studied
most thoroughly [1, 2]. The halogenation of phenyl-
substituted pent-2-ene-1,5-dione, pentane-1,5-dione,
and 2-(3-oxopropyl)tetrahydronaphthalen-1-one with
chlorine and bromine was reported in [3–6]. Introduc-
tion of a halogen atom into diketone molecules opens
new facilities in synthesizing functionalized dicarbonyl
and heterocyclic compounds [2, 7].
In continuation of our systematic studies on halo-
genation of dioxo compounds, in the present work we
examined reactions of 3-(4-methoxyphenyl)-1,5-di-
phenylpent-2-ene-1,5-dione (I), 3-(4-methoxyphenyl)-
1,5-diphenylpentane-1,5-dione (II), and 2-[1-(4-meth-
oxyphenyl)-3-oxo-3-phenylpropyl]-1,2,3,4-tetrahydro-
naphthalen-1-one (III) with chlorine, bromine, and di-
chloro(phenyl)-λ3-iodane with a view to find out how
the substituent nature, degree of saturation, conjuga-
tion pattern, and reaction conditions affect the direc-
tion of transformation of 1,5-diketones.
by the action of bromine or chlorine in carbon tetra-
chloride at 0–20°C or of dichloro(phenyl)-λ3-iodane
(V) in chloroform at room temperature. Saturated
diketone II remained unchanged on treatment with
chlorine or bromine under analogous conditions. The
reaction of 1,5-diketone II with chlorine in carbon
tetrachloride at 75–80°C (reaction time 30 h) gave
dichloropentanedione VII.
We succeeded in obtaining monobromo- and di-
and trichloropentenediones X–XII only by treatment
of compound I with bromine and chlorine, respec-
tively, in carbon tetrachloride in the presence of so-
dium acetate as reagent suppressing salt formation.
Bromodiketone X was formed at 0°C, and dichloro-
diketone XI, at 20°C. Introduction of three chlorine
atoms into the substrate molecule required elevated
temperature (70°C).
No chlorination of diketone III occurred in carbon
tetrachloride, benzene, and acetic acid; this is consist-
ent with published data on the chlorination of acyclic
1,5-diketones [6, 9]. Compound III readily reacted
with bromine at room temperature to give a mixture of
2-bromo-2-[2-bromo-1-(4-methoxyphenyl)-3-oxo-3-
phenylpropyl]-1,2,3,4-tetrahydronaphthalen-1-one and
2-bromo-2-[2-bromo-1-(3-bromo-4-methoxyphenyl)-
3-oxo-3-phenylpropyl]-1,2,3,4-tetrahydronaphthalen-
1-one [6]. Although (dichloro-λ3-iodanyl)benzene is
known to act as effective electrophilic chlorinating
agent in polar solvents and is successfully used to
Unsaturated diketone I and its saturated analog II
failed to undergo bromination on heating with bromine
in boiling acetic acid (Scheme 1); instead, hetero-
cyclization of these substrates occurred to give pyryli-
um bromide IV, in keeping with published data for the
corresponding triphenyl-substituted diketones [2, 8].
Heteroaromatization of diketone I to pyrylium salts IV
and VI was also observed under mild conditions, i.e.,
1285

PCHELINTSEVA et al.
1286
Scheme 1.
Ar
Ar
Ar
Br2, AcOH, 118°C
or Br2, Cl2, CCl4, 20°C
or PhICl2 (V), CHCl3, 20°C
Br2, AcOH, 118°C
X–
Ph
Ph
Ph
Ph
Ph
O
Ph
O
O
O
O
I
IV, VI
II
Ar
Br
Br2, 0°C
Ph
Ph
O
O
X
Ar
Ar
Cl
Cl
Cl
Cl
AcONa, CCl4 Cl2, 20°C
I
Cl2, CCl4, 75–80°C
II
Ph
Ph
Ph
Ph
O
O
O
O
O
XI
VII
Ar
Cl
Cl
Cl
Cl2, 70°C
Ph
Ph
O
XII
IV, X = Br; VI, X = Cl; Ar = 4-MeOC6H4.
introduce chlorine atoms into 1,5-dicarbonyl com-
pounds [9], chlorination of the methoxyphenyl group
was observed only in the reaction with diketone III.
Treatment of III with compound V in acetic acid gave
dichloro derivative VIII in 1 h. When the reaction time
was increased to 4 h, three chlorine atoms were intro-
duced into the substrate molecule to produce com-
pound IX (Scheme 2). Analogous results were ob-
tained by carrying out the chlorination in a simpler
way: a solution of diketone III in acetic acid in the
presence of iodobenzene (PhI-to-III molar ratio ~1:3)
was saturated with chlorine; in this case, dichloro-
(phenyl)-λ3-iodane is generated in situ, and iodoben-
zene acts as chlorine carrier.
Scheme 2.
O
Ph
Cl
O
Cl2, PhI, AcOH, 1 h
Cl
OMe
O
Ar
O
VIII
Ph
O
Cl
O
Ph
III
Cl
Cl2, PhI, AcOH, 4 h
Cl
OMe
IX
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 9 2007

CHEMISTRY OF 1,5-DIKETONES: I.
1287
Halogenation of 1,5-diketones I–III
Substrate
Reagent
Br2
Solvent
Reaction time, h
Temperature, °C
Product
Yield, %
AcOH
CCl4
0.5
1.0
118
020
020
020
000
020
070
118
96
88
86
81
63
78
72
84
55
59
57
I
I
I
I
I
I
I
II
II
III
III
IV
IV
VI
VI
X
XI
XII
IV
VII
VIII
IX
Br2
Cl2
CCl4
1.0
PhICl2 (V)
Br2/AcONa
Cl2/AcONa
Cl2/AcONa
Br2
CHCl3
CCl4
1.0
1.0
CCl4
2.0
CCl4
2.0
AcOH
CCl4
1.0
Cl2
30.00
1.0
75–80
020
020
AcOH
AcOH
V
V
4.0
The conditions and results of halogenation of
1,5-diketones I–III are collected in table. We can con-
clude that halogenation of diketones I–III under mild
conditions (in carbon tetrachloride or acetic acid at
room or slightly elevated temperature) is not accom-
panied by transformation of the substrate skeleton
(compounds VII–XII); moreover, the double C=C
bond in the aliphatic chain of pentenedione I remains
intact (compounds X–XII).
VIII and IX, the carbonyl band appears at a higher
frequency (1680–1685 cm–1). Introduction of a chlo-
rine atom into the α-position with respect to the
carbonyl group in the aliphatic chain increases the
carbonyl stretching vibration frequency (νC=O). In this
case, the molecule has an eclipsed conformation with
respect to the chlorine and carbonyl oxygen atoms.
The presence of a halogen atom in the methoxyphenyl
group of diketones VIII and IX gives rise to two bands
in the region 878–838 cm–1 due to bending vibrations
(δC–H) of 1,2,4-substituted benzene ring.
The structure of halogen derivatives VII–XII was
1
confirmed by the IR and H and 13C NMR data. The
1
position and intensity of IR bands arising from stretch-
ing vibrations of conjugated C=O and C=C bonds
could provide information on mutual arrangement of
these bonds in α,β-unsaturated ketones [10]. The dif-
ferences between the stretching vibration frequencies of
the double C=O and C=C bonds in initial pentenedione
I (62 cm–1) and bromodiketone X (66 cm–1), as well as
the intensity ratios of the C=O and C=C bands (0.8 and
0.7, respectively), indicate cis configuration of the
double C=C bond in molecule X. In the IR spectra of
di- and trichloro-substituted pentenediones XI and
XII, the corresponding difference is 36 cm–1, and
the intensity ratio is equal to 3.6–3.9; therefore, these
compounds may be assigned s-trans configuration as
shown below.
In the H NMR spectra of compounds X and XI,
the one-proton singlet from 4-H (δ 6.60 and 6.58 ppm,
respectively) is displaced downfield relative to the 4-H
signal of initial pentenedione I (δ 4.86 ppm) owing to
deshielding effect of the halogen atom. Likewise, di-
chloropentanedione VII is characterized by downfield
shift of the 2-H signal relative to 4-H (δ 6.52 ppm;
Δ δ = 0.8 ppm) and of C4 relative to C2 (Δ δC =
7.56 ppm) in the 13C NMR spectrum. The reason is
that the oxygen and chlorine atoms are spatially close
to each other; as a result of additional shielding, the
carbonyl carbon signals shift upfield. Similar chemical
shifts of 4-H, C4, and C5 in dichloro diketones VII, XI,
and XII suggest eclipsed configuration of the C4–Cl
and C5=O bonds in their molecules [11].
The strong absorption band at 1674 cm–1 in the IR
spectrum of III belongs to stretching vibrations of the
C=O groups; in the spectra of chlorinated diketones
The shape and intensity of signals in the H NMR
1
spectra of dichloro diketones VIII and IX are consist-
1
ent with the assumed structures. The H NMR spectra
H
Cl
Cl
Cl Cl
O
Br
Cl
H
H
H
Cl
Ph
O
Ph
Ph
O
O
Ph
H
Ar
Ar
H
O
Ph
O
Ar
O
Ph
Ar
XI
Ph
O
VII
IX
X
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 9 2007

PCHELINTSEVA et al.
1288
of diketones VIII and IX contained multiplet signals
from aromatic and alicyclic protons at δ 6.88–8.29 and
2.04–3.12 ppm, respectively, and a singlet from pro-
tons in the methoxy group at δ 3.94 ppm; the latter is
displaced downfield relative to the corresponding
signal of diketones I–III and halogenated acyclic
diketones VII and X–XII, indicating that the chlorine
atom is located in the ortho position with respect to the
methoxy group.
were measured on Varian FT-80A and Bruker MSL-
400 instruments from solutions in chloroform-d and
DMSO-d6 using TMS as internal reference.
3-(4-Methoxyphenyl)-1,5-diphenylpent-2-ene-1,5-
dione (I) was synthesized by alkaline hydrolysis of
3-(4-methoxyphenyl)-2,6-diphenylpyrylium perchlo-
rate [12], 3-(4-methoxyphenyl)-1,5-diphenylpentane-
1,5-dione (II) was prepared according to the procedure
described in [1], and 2-[1-(4-methoxyphenyl)-3-oxo-3-
phenylpropyl]-1,2,3,4-tetrahydronaphthalen-1-one
(III) was synthesized by the Michael reaction as
reported in [13].
The facts that the chlorination of compound I
changes the geometry of the conjugated C=O and C=C
bonds and that the s-cis configuration of the initial
unsaturated diketone is conserved in the bromination
process suggest that its transformation follows two
concurrent pathways: (1) electrophilic addition of chlo-
rine with subsequent elimination of hydrogen chloride
which favors enolization of intermediate pentenedi-
ones, and (2) substitutive bromination.
Gaseous chlorine was prepared by treatment with
dilute sulfuric acid of a mixture of sodium chloride and
manganese dioxide at a ratio of 1:2 and was dried by
passing through concentrated sulfuric acid [14].
4-(4-Methoxyphenyl)-2,6-diphenylpyrylium
bromide (IV). a. A solution of 2.1 g (13 mmol, 0.7 ml)
of bromine in 10 ml of acetic acid was added under
stirring at 20°C to a solution of 3.2 g (9 mmol) of
diketone I in 40 ml of glacial acetic acid. The mixture
was heated for 0.5 h at 118°C, cooled, and poured into
150 ml of diethyl ether. The crystalline product was
filtered off and dried. Yield 3.7 g (96%), yellow crys-
tals; the product was characterized as 3-(4-methoxy-
phenyl)-2,6-diphenylpyrylium tetrafluoroborate [12].
The chlorination of saturated diketones II and III
involves initial enolization, attack by chlorine on the
double C=C bond thus formed, and elimination of
hydrogen chloride. The presence of an aryl substituent
on C3 favors approach of chlorine molecule from the
rear side (with respect to the aryl group) of the enol
C=C bond. Attack by the second chlorine molecule on
the C=C bond appearing as a result of enolization of
the second phenacyl fragment is likely to be deter-
mined by electrostatic interaction between electronic
orbitals of the chlorine molecule and chlorine atom in
the chloro diketone. Therefore, the reaction gives
threo-dichloropentanedione VII in which the last intro-
duced chlorine atom is distant from that introduced
first, and it occupies eclipsed position with respect to
the carbonyl oxygen atom.
b. A solution of 2.1 g (13 mmol) of bromine in
25 ml of carbon tetrachloride was added at 20°C to
a suspension of 3.2 g (9 mmol) of diketone I in 30 ml
of carbon tetrachloride. The mixture was stirred for 1 h
at 20°C, washed with water, dried over magnesium
sulfate, and evaporated. The crystals were filtered off
and dried. Yield 3.4 g (88%).
c. A solution of 2.7 g (17 mmol) of bromine in
10 ml of acetic acid was added to a solution of 4.8 g
(12 mmol) of diketone II in 50 ml of glacial acetic
acid. The mixture was heated for 1 h at 118°C and
evaporated, and the residue was treated with 150 ml of
diethyl ether. The crystals were filtered off and dried.
Yield 4.4 g (84%).
The chlorination of diketone III in the presence of
iodobenzene involves electrophilic (by the result) re-
placement of hydrogen atoms in the α-positions with
respect to the carbonyl groups and in the meta position
of the methoxyphenyl substituent (ortho position with
respect to the methoxy group). The major product is
threo isomer IX. As follows from the results of halo-
genation of compound III, obtained in 1 and 4 h, the
chlorination occurs first at the alicyclic carbon atom
(C2) and only then the side-chain carbon atom is
involved.
4-(4-Methoxyphenyl)-2,6-diphenylpyrylium
chloride (VI). a. A solution of 7.0 g (22 mmol) of
pentenedione I in 70 ml of carbon tetrachloride was
saturated with chlorine for 2 h at 20°C. The precipitate
was filtered off, washed with diethyl ether, and dried.
Yield 7.3 g (86%); the product was characterized as
3-(4-methoxyphenyl)-2,6-diphenylpyrylium tetra-
fluoroborate [12].
EXPERIMENTAL
The IR spectra were recorded on a Specord M-80
spectrometer from samples dispersed in mineral oil or
b. A mixture of 3.5 g (11 mmol) of diketone I, 6.0 g
(22 mmol) of dichloro(phenyl)-λ3-iodane [15], and
1
hexachlorobutadiene. The H and 13C NMR spectra
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 9 2007

CHEMISTRY OF 1,5-DIKETONES: I.
1289
40 ml of chloroform was stirred for 1 h at 20°C. The
mixture was evaporated, the residue was treated with
150 ml of diethyl ether, and the precipitate was filtered
off, washed with diethyl ether, and dried. Yield 3.3 g
(81%).
bromine in 25 ml of carbon tetrachloride was added
over a period of 1 h to a suspension of 2.8 g (8 mmol)
of diketone I and 2.5 g (36 mmol) of sodium acetate in
30 ml of carbon tetrachloride, stirred at 0°C. When the
reaction was complete, excess bromine was removed
by purging with an inert gas, the mixture was washed
with water and dried over MgSO4, the solvent was
distilled off, and the crystalline product was filtered off
and dried. Yield 2.2 g (63%), yellow crystals, mp 101–
102°C. IR spectrum, ν, cm–1: 1718, 1648, 1582, 822,
2,4-Dichloro-3-(4-methoxyphenyl)-1,5-diphenyl-
pentane-1,5-dione (VII). Chlorine was passed over
a period of 30 h through a solution of 3.6 g (10 mmol)
of diketone II in 30 ml of carbon tetrachloride, heated
to 75–80°C. The solvent was distilled off under re-
duced pressure, and the crystalline product was filtered
off, washed with ethanol, and dried. Yield 2.3 g (55%),
colorless crystals, mp 124.5–125°C. IR spectrum, ν,
1
746, 700. H NMR spectrum (400 MHz, DMSO-d6,
20°C), δ, ppm: 6.60 s (1H, 4-H), 3.85 s (3H, CH3).
13C NMR spectrum (400 MHz, CDCl3, 20°C), δC,
ppm: 191.10 (C5), 189.32 (C1), 138.66 (C3), 123.84
(C2), 61.71 (C4), 55.24 (CH3). Found, %: C 66.10;
H 4.21; Br 18.16. C24H19BrO3. Calculated, %: C 66.21;
H 4.37; Br 18.39.
1
cm–1: 1680, 1673, 823, 750, 706. H NMR spectrum
(400 MHz, DMSO-d6, 20°C), δ, ppm: 6.52 d (1H,
4-H), 5.72 d (1H, 2-H), 4.27 d.d (1H, 3-H), 3.85 s (3H,
13
CH3). C NMR spectrum (400 MHz, CDCl3, 20°C),
δC, ppm: 191.60 (C5), 191.11 (C1), 63.90 (C4), 56.34
(C2), 54.91 (CH3), 49.38 (C3). Found, %: C 64.34;
H 4.80; Cl 16.71. C24H20Cl2O3. Calculated, %:
C 67.45; H 4.72; Cl 16.59.
2,4-Dichloro-3-(4-methoxyphenyl)-1,5-diphenyl-
pent-2-ene-1,5-dione (XI). A suspension of 2.8 g
(8 mmol) of diketone I and 2.6 g (32 mmol) of sodium
acetate in 30 ml of carbon tetrachloride was saturated
with chlorine for 2 h at 20°C. The mixture was filtered,
the filtrate was evaporated, and the crystals were
filtered off, washed with ethanol, and dried. Yield 2.7 g
(78%), pale yellow crystals, mp 122–123°C (from
EtOH). IR spectrum, ν, cm–1: 1720, 1675, 1640, 820,
2-Chloro-2-[1-(3-chloro-4-methoxyphenyl)-3-
oxo-3-phenylpropyl]-1,2,3,4-tetrahydronaphthalen-
1-one (VIII). A mixture of 5 g (13 mmol) of diketone
III, 0.5 g (2.5 mmol) of iodobenzene, and 80 ml of
acetic acid was saturated with chlorine over a period of
1 h. The crystals were filtered off and washed with
ethanol. Yield 3.5 g (59%), colorless crystals, mp 190–
191.5°C (from EtOH–CHCl3, 1:1). IR spectrum, ν,
cm–1: 1680, 878, 860, 840, 800, 786, 767, 690.
1H NMR spectrum (400 MHz, DMSO-d6, 20°C), δ,
ppm: 8.20–6.88 m (Harom), 3.94 s (3H, CH3), 3.12–
2.04 m (Halicycl). Found, %: C 68.39; H 4.44; Cl 16.01.
C26H22Cl2O3 . Calculated, %: C 68.88; H 4.89;
Cl 15.64.
1
748, 704. H NMR spectrum (400 MHz, DMSO-d6,
20°C), δ, ppm: 6.58 s (1H, 4-H), 3.83 s (3H, CH3).
13C NMR spectrum (400 MHz, CDCl3, 20°C), δC,
ppm: 191.36 (C5), 189.46 (C1), 139.34 (C3), 133.50
(C2), 63.42 (C4), 55.30 (CH3). Found, %: C 66.97;
H 4.06; Cl 16.25. C24H18Cl2O3. Calculated, %:
C 67.76; H 4.24; Cl 16.71.
2,4,4-Trichloro-3-(4-methoxyphenyl)-1,5-di-
phenylpent-2-ene-1,5-dione (XII) was synthesized as
desribed above for compound XI using 2.8 g (8 mmol)
of diketone I, 3.3 g (40 mmol) of sodium acetate, and
30 ml of carbon tetrachloride at 70°C (2 h). Yield 2.6 g
(72%), colorless crystals, mp 152–153°C (from EtOH).
Found, %: C 62.14; H 3.44; Cl 22.98. C24H17Cl3O3.
Calculated, %: C 62.67; H 37.00; Cl 23.18.
2-Chloro-2-[2-chloro-1-(3-chloro-4-methoxy-
phenyl)-3-oxo-3-phenylpropyl]-1,2,3,4-tetrahydro-
naphthalen-1-one (IX). A mixture of 5 g (13 mmol)
of diketone III, 0.5 g (2.5 mmol) of iodobenzene, and
80 ml of acetic acid was saturated with chlorine over
a period of 4 h. The crystals were filtered off and
washed with ethanol. Yield 3.6 g (57%), colorless crys-
tals, mp 170–171°C (from i-PrOH). IR spectrum, ν,
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 06-03-32667a).
1
cm–1: 1685, 876, 838, 752, 738, 702. H NMR spec-
trum (400 MHz, DMSO-d6, 20°C), δ, ppm: 8.29–
6.84 m (Harom), 3.94 s (3H, CH3), 2.88–2.16 m (Halicycl).
Found, %: C 66.51; H 3.96; Cl 22.28. C26H21Cl3O2 .
Calculated, %: C 64.02; H 4.34; Cl 21.80.
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 9 2007

PCHELINTSEVA et al.
1290
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