Synthesis and properties of Z-1, 3-bis- (aryl)-4-bromo-2-buten-1-ones

Article abstract of DOI:10.1007/s10593-010-0405-5

Bromination of 1, 3-bis(aryl)-2-buten-1-ones by N-bromosuccinimide in anhydrous carbon tetrachloride gives Z-1, 3-bis(aryl)-4-bromo-2-buten-1-ones. The effect of the nature of substituent in the benzene ring on the course of a reaction with nucleophiles h

Full text of DOI:10.1007/s10593-010-0405-5

Chemistry of Heterocyclic Compounds, Vol. 45, No. 10, 2009
SYNTHESIS AND PROPERTIES OF Z-1,3-BIS-
(ARYL)-4-BROMO-2-BUTEN-1-ONES
L. M. Potikha1*, A. R. Turelik1, and V. A. Kovtunenko1
Bromination of 1,3-bis(aryl)-2-buten-1-ones by N-bromosuccinimide in anhydrous carbon tetrachloride
gives Z-1,3-bis(aryl)-4-bromo-2-buten-1-ones. The effect of the nature of substituent in the benzene ring
on the course of a reaction with nucleophiles has been studied. Heating an alcohol solution of these
ketones (Ar = 4-MeOC6H4, 4-ClC6H4) in the presence of acid or in the presence of base (Ar = Ph) gave
2,4-bis(aryl)furans. Treatment of 1,3-bis(aryl)-4-bromo-2-buten-1-ones with thioacetamide gave
2,4-bis(aryl)thiophenes. The oxidation of the halo-substituted dypnones with H2O2/NaOH gave
(3-bromomethyl-3-aryl-2-oxiranyl)(aryl)methanones. The reaction of halo-substituted dypnones with
aryl hydrazines gave 1,3,5-triaryl-1,6-dihydropyridazines or 1,3,5-triarylpyridazinium bromides
depending on the structure of the reagents.
Keywords: 2,4-bis(aryl)thiophene, 2,4-bis(aryl)furan, γ-bromodypnone, α-bromodiphenacyl, 1,3,5-tri-
aryl-1,6-dihydropyridazine.
γ-Halocarbonyl compounds are convenient building blocks for the synthesis of different carbo- and
heterocyclic compounds [1]. Amongst these, γ-halo-substituted unsaturated ketones (α-halo ketone vinylogs) are
difficult to obtain and so have been little studied. In a number of cases the vinylogous homologation [2, 3] of
α-halo ketones can lead to an unexpected reaction course and to the appearance of products totally
uncharacteristic of the starting compounds. Data in the literature for the reactions of γ-halo-substituted
unsaturated ketones points to the existence of a marked structural effect on the course of their reaction with
different nucleophiles [4, 5]. The aim of this work was to determine the effect of the nature of the substituent in
the benzene ring of the 1,3-bis(aryl)-4-bromo-2-buten-1-ones 1a-d on their reactivity towards several nucleo-
philes (previously studied in the case of the 4-bromo-1,3-diphenyl-2-buten-1-one (γ-bromodypnone, 1b, [5-8])).
According to our data problems of this type are not covered in the literature.
The preparation of the 1,3-bis(aryl)-4-bromo-2-buten-1-ones 1a,c,d used the procedure developed
before for the synthesis of the γ-bromodypnone 1b [8]. Bromination of the 1,3-bis(aryl)-4-bromo-2-buten-1-ones
2a,c,d using N-bromosuccinimide in anhydrous carbon tetrachloride gave the target products 1a,c,d in good
yields (55-75%). The presence of a substituent in the benzene ring did not have a marked effect on the method
of preparing compound 1 but an increase in the electron acceptor properties of the substituent showed a
tendency towards the decreasing formation of side reaction products.
_______
* To whom correspondence should be addressed, e-mail: potikha_l@mail.ru.
1 Taras Shevchenko National University, Kiev 01033, Ukraine.
__________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No.10, pp. 1478-1484, October, 2009.
Original article submitted August 9. 2008; revision submitted April 29, 2009.
1184
0009-3122/09/4510-1184©2009 Springer Science+Business Media, Inc.

Ar
Ar
Ar
Ar
O
S
H2N
Me
4a–d
3a–d
S
Ar
H2O2/NaOH
PhNHNH2
O
NBS
Ar
Ar
Br
Br
COAr
Me
COAr
2a–d
COAr
5b–d
1a–d
Ar1NHNH2
Ar
Ar
Ar
Ar
+
N
N
N
N
_
Ar 1
Ph
Br
6a,b
7a,b
1–5 a Ar = 4-MeOC6H4, b Ar =Ph, c Ar = 4-ClC6H4, d Ar = 4-BrC6H4;
6 a Ar = 4-ClC6H4, Ar1 = 4-O2NC6H4, b Ar = 4-BrC6H4, Ar1 =Ph;
7 a Ar = 4-ClC6H4, b Ar = 4-BrC6H4
The structure of γ-bromodypnone 1b as the Z-isomer was reliably established previously [8, 9] through
its chemical and spectroscopic properties. It is apparent that, using the same conditions, the Z-isomers would
also be expected in the case of the substituted ketones 2. In order to verify this proposal the UV spectra of the
novel compounds 1a,c,d were recorded. Their methanol solutions showed a characteristic maximum absorption
for the Z-γ-bromodypnone 1b [9] at 286-302 nm with ε 19,500-24,000. As in the case of 1b, short irradiation
(5-7 min, mercury lamp) of the solutions of compounds 1a,c,d gave a hypsochromic shift for the long
wavelength band of 30-50 nm caused by conversion of Z- to E-isomers [9]. Attempts to separate the latter
proved unsuccessful, evaporation of solvent giving the Z-structured starting compounds.
The cis orientation of the functional groups in the 1,3-bis(aryl)-4-bromo-2-buten-1-ones 1 results in
ready formation of cyclic products. Intramolecular cyclization of compounds 1a-d gives the 2,4-bis(aryl)furans
3a-d and can take place upon heating solutions of compound 1 in neutral (ethanol), acid (ethanol + HCl), or base
(ethanol + Na2CO3) medium. The substituent in the benzene ring of starting compound 1 proved to have a
marked effect on the rate of formation of the product 3. Hence, when carrying out the reaction without catalyst
the conversion of compounds 1a to 3a occurs over 30-40 min. The preparation of furan 3b needs longer heating
(3 h) [10] but the halo-substituted dypnones 1c,d proved stable under these conditions. In the presence of acid or
base the conversion of compounds 1 to furans 3 occurs more rapidly with preservation of the overall tendency of
decreasing reactivity from 1a to 1d. In addition, in the case of compounds 1a,b the reaction is accompanied by
the formation of a large amount of side products. The furan 3c was obtained in satisfactory yield by heating an
alcohol solution of compound 1c in the presence of acid. With the use of the p-bromo-substituted
γ-bromodypnone 1d the furan 3d is formed only with prolonged heating in the presence of base (Na2CO3).
We have previously found [6] that heating the γ-bromodypnone 1b with thioacetamide in ethanol gives
the 2,4-diphenylthiophene (4b). The 2,4-bis(aryl)thiophenes 4a,c,d were obtained from compounds 1a,c,d
1185

under the same conditions. In this case the rate of formation of the reaction products 4 follows the same
dependence with an increase in the electronegativity of the substituent in the benzene ring correlating with an
increase in the time for heating the reaction mixture from 10 min for 1a to 2 h for 1d.
α,β-Unsaturated ketones readily form epoxy derivatives via direct oxidation with hydrogen peroxide in
the presence of base [11]. In the case of the γ-bromodypnone 1b this reaction had been studied in detail
previously [8, 9]. We have shown that the halo-substituted dypnones 1c,d can also be converted to the
corresponding (3-aryl-3-bromomethyl-2-oxiranyl)(aryl)methanones 5c,d in the conditions indicated. However,
in contrast to the γ-bromodypnone 1b, the preparation of oxiranes 5c,d needs heating of the reaction mixtures.
Compound 1a gives a complex mixture of products upon treatment with strong bases, even with cooling. A
comparison of the melting points of the oxiranes 5c,d prepared with literature data [12, 13] points to the
formation of trans isomers.
We have previously shown [14] that the formation of arylhydrazones as a characteristic of ketones
occurs with greater complexity for the γ-bromodypnone 1b and can lead to acylhydrazone or cyclic products
depending on the conditions and the structure of the hydrazine. The reaction of γ-bromo ketones 1c,d with
arylhydrazines gives exclusively cyclic 1,3,5-triarylpyridazine products. Independently of the structure of the
arylhydrazine and the reaction conditions, compound 1a gives furan 3a.
A factor determining the result of the reaction is the nature of the substituent in both reagents. As in the
example of the γ-bromodypnone 1b [14], heating compound 1c with 4-nitrophenylhydrazine in alcohol gives a
1,6-dihydropyridazine derivative which is 3,5-bis(4-chlorophenyl)-1-(4-nitrophenyl)-1,6-dihydropyridazine
(6a). The more inert p-bromo-substituted γ-bromodypnone 1d reacts very slowly with 4-nitrophenylhydrazine
hence prolonged (24 h) heating gives a complex mixture containing mainly the starting ketone.
By contrast with compound 1b, compounds 1c,d react with phenylhydrazine exclusively upon heating.
Compound 1c gives the 1-phenyl-3,5-bis(4-chlorophenyl)pyridazin-1-ium bromide (7a) and compound 1d gives
the 3,5-bis(4-bromophenyl)-1-phenyl-1,6-dihydropyridazine (6b). In the latter case a solid product was also
obtained from the reaction mixture and this proved to be a mixture which contained 40% of the 3,5-bis-
(4-bromophenyl)-1-phenylpyridazin-1-ium salt (7b). It should be noted that the it is possible to stop reaction of
the γ-bromo ketone 1b with phenylhydrazine at an earlier reaction stage to give the 1,3,5-triphenyl-1,6- and
1,3,5-triphenyl-1,4-dihydropyridazine arylhydrazone [14]. An increase in the length of heating the reaction
mixture or the presence of a strong acid leads to aromatization of the product.
The observed results of the reaction of bromo ketones 1c,d with arylhydrazines can be explained in the
following way. Introduction of electron acceptor substituents into the 1,6-dihydropyridazine system lowers its
basicity and increases the stability towards oxidation [14, 15]. On the other hand, the lowered reactivity of the
γ-bromo ketones 1c,d leads to an increase in the reaction mixture heating time and this offers the right
conditions for further oxidation to the pyridazinium salt 7. In the case of the γ-bromo ketone 1d the low
solubility of the reaction product 6b in alcohol removes the major part of it from the reaction mixture and avoids
its subsequent oxidation.
The conclusions regarding the structure of the reaction products 6, 7 were made on the basis of their 1H
NMR spectroscopic data. In this case, the criteria for assigning the structure are the presence and position of a
signal for the methylene group protons. The spectra of compounds 6a,b show a two proton singlet at 4.85 (6a)
and 4.70 ppm (6b) in the region characteristic of 1,6-dihydropyridazines [14]. The absence of signals in the
aliphatic part of the spectrum of product 7a and the presence of one proton singlets at 10.64 (H-6) and 9.53 ppm
(H-4) point to the formation of the aromatic 1,3,5-trisubstituted pyridazinium system.
Hence we can conclude that the reactivity of the 1,3-bis(aryl)-4-bromo-2-buten-1-one system depends
on the nature of the substituent in the benzene ring. For reactions carried out in a protonic solvent (alcohol)
lowering of the donor properties of the substituent leads to a decrease in reactivity which correlates with the
Hammett σ constant for the para substituent [16]. The result of introducing electron acceptor substituents into
the 1,3-bis(aryl)-4-bromo-2-buten-1-one structure is an increase in their stability and decreased tendency to
1186

form products of intramolecular cyclization upon heating in the presence of base. The introduction of donor
substituents leads to a reversed effect which lowers the likelihood of forming the target products in reactions
with nucleophiles.
In order to assess the biological potential of the 1,3-bis(aryl)-4-bromo-2-buten-1-ones reported in this
work a spectrum of their biological activity was calculated. The PASS (Prediction of Activity Spectra for
Substances) [17-19] program was used in these calculations. Basically the selection of active compounds
involves a multilevel assessment of the closest environment of the atoms and comparison of the calculated 2D
descriptors with a set of those corresponding to likely appearance of either high compound activity or of
inactivity. The final result of the program is a schedule of the likely appearance of compound activity (pa) or
inactivity (pi) in fractional units. A spectrum of more than 3000 types of activity was calculated for each
compound with the activity threshold set at pa > 0.9 and pi < 0.02. Amongst the activity characterizing
compounds 1a-d there is observed the prediction of an efficient inhibition of the synthesis of protein structures
in terms of non specific inhibition of the enzyme systems: prolyl aminopeptidases, phosphoenolpyruvate protein
phosphotransferases, (-)-(4S)-limonene synthases, and threonine aldolases.
EXPERIMENTAL
1
IR spectra were recorded on a Pye-Unicam SP3-300 instrument for CsI tablets. H NMR spectra were
taken on a Varian Mercury 400 (400 MHz) instrument using DMSO-d6 with TMS as internal standard. UV
spectra were obtained in methanol on a Lambda 20 UV/VIS spectrometer. Irradiation of compounds 1a-d was
carried out using a PRK-4 mercury lamp. Monitoring of the reaction course and the purity of the compounds
obtained was carried out using TLC on Silufol UV-254 plates.
1,3-Bis(aryl)-2-buten-1-ones 2a,c,d were prepared by method [20].
Compound 2a. Yield 60%; mp 94-96ºC (EtOH), mp 95ºC [21].
Compound 2c. Yield 75%; mp 74-76ºC (EtOH), mp 79ºC [22].
Compound 2d. Yield 70%; mp 105-106ºC (EtOH), mp 107ºC [23].
Z-1,3-Bis(aryl)-4-bromo-2-buten-1-ones 1a,c,d. N-Bromosuccinimide (8.9 g, 50 mmol) was added to
a solution of the 1,3-bis(aryl)-2-buten-1-ones 2a,c,d (50 mmol) in anhydrous carbon tetrachloride (50 ml). The
mixture was heated to reflux, benzoyl peroxide (0.3 g) was added, and the product was refluxed for 1-1.5 h. It
was cooled and succinimide filtered off. The solvent was evaporated and the residue was recrystallized from
2-propanol.
Compound 1a. Yield 9.93 g (55%); mp 92-93ºC (from 2-propanol). IR spectrum, ν, cm-1: 1640 (C=O),
1600, 1570, 1485, 1297, 1265, 1220, 1178 (C–O); 1030 (C–O); 828. UV spectrum (MeOH), λmax, nm (ε×10-3):
1
3
226 (22.28), 286 (19.55). H NMR spectrum, δ, ppm (J, Hz): 8.06 (2H, d, J = 8.5, H-2',6'); 7.77 (2H, d,
3J = 8.5, H-2'',6''); 7.41 (1H, s, H-2); 7.05 (2H, d, J = 8.5, H-3',5'); 7.02 (2H, d, 3J = 8.5, H-3'',5''); 5.07 (2H, s,
3
H-4); 3.85 (3H, s, 4'-OCH3); 3.82 (3H, s, 4''-OCH3). Found, %: C 59.80; H 4.65; Br 22.15. C18H17BrO3.
Calculated, %: C 59.85; H 4.74; Br 22.12.
Compound 1c. Yield 13.88 g (75%); mp 107-108ºC (2-propanol). IR spectrum, ν, cm-1: 1698 (C=O),
1
1595, 1490, 1410, 1215, 820. UV spectrum (MeOH), λmax, nm (ε×10-3): 226 (23.48), 298 (22.69). H NMR
3
3
3
spectrum, δ, ppm (J, Hz): 8.09 (2H, d, J = 8.0, H-2',6'); 7.84 (2H, d, J = 8.0, H-2'',6''); 7.61 (2H, d, J = 8.0,
3
H-3',5'); 7.55 (2H, d, J = 8.0, H-3'',5''); 7.48 (1H, s, H-2); 5.02 (2H, s, H-4). Found, %: C 51.84; H 2.92; Br
21.61; Cl 19.19. C16H11BrCl2O. Calculated, %: C 51.93; H 3.00; Br 21.59; Cl 19.16.
Compound 1d. Yield 16.06 g (70%); mp 117-119ºC (2-propanol). IR spectrum, ν, cm-1: 1705 (C=O),
1585, 1210, 1070, 1055, 1010, 995, 825. UV spectrum (MeOH), λmax, nm (ε×10-3): 230 (25.32), 274 (25.10),
1
3
3
302 (24.00). H NMR Spectrum, δ, ppm (J, Hz): 7.99 (2H, d, J = 8.0, H-2',6'); 7.71 (2H, d, J = 8.0, H-2'',6'');
3
3
7.68 (2H, d, J = 8.0, H-3',5'); 7.60 (2H, d, J = 8.0, H-3'',5''); 7.40 (1H, s, H-2); 5.01 (2H, s, H-4). Found, %:
C 41.79; H 2.33; Br 52.24. C16H11Br3O. Calculated, %: C 41.87; H 2.42; Br 52.23.
1187

2,4-Bis(4-methoxyphenyl)furan (3a). A solution of compound 1a (0.4 g, 1.1 mmol) in ethanol (10 ml)
was refluxed for 40 min. After cooling the precipitate was filtered off, washed with ethanol and crystallized
from ethanol. Yield 0.25 g (80%); mp 190-192ºC, mp 192ºC [24].
2,4-Bis(4-chlorophenyl)furan (3c). Conc. HCl (1 ml) was added to a solution of compound 1c (0.4 g,
1.08 mmol) in ethanol (10 ml) and refluxed for 1 h. After cooling the precipitate was filtered off, washed with
ethanol, and crystallized from ethanol. Yield 0.17 g (56%); mp 127-129ºC, mp 128ºC [24].
2,4-Bis(4-bromophenyl)furan (3d). Na2CO3 (0.1 g, 1.0 mmol) was added to a solution of compound 1d
(0.4 g, 0.87 mmol) in ethanol (20 ml) and refluxed for 3 h. After cooling, the precipitate was filtered off,
thoroughly washed with water and ethanol, and recrystallized from nitromethane to give the product (0.13 g,
40%) with mp 159-160ºC and mp 160ºC [24].
2,4-Bis(aryl)thiophenes 4a,c,d. Thioacetamide (0.15 g, 2.0 mmol) was added to a solution of
compound 1a,c,d (2.0 mmol) in ethanol (30 ml) and the mixture obtained was refluxed for 10 min (in the case of
compound 1a), 50 min (compound 1c), or 2 h (compound 1d). The product was cooled and the precipitate was
filtered and washed with alcohol.
Compound 4a. Yield 0.30 g (51%); mp 219-220ºC (EtOH), mp 221ºC [25].
Compound 4c. Yield 0.38 g (62%); mp 139-140ºC (MeNO2), mp 140ºC [26].
Compound 4d. Yield 0.44 g (56%); mp 173-175ºC (MeNO2), mp 174.5ºC [26].
[(2R,3S)-3-Aryl-3-bromomethyl-2-oxiranyl](aryl)methanones 5c,d. H2O2 (30%, 2 ml) and NaOH
solution (1N, 1 ml) were added with stirring to a solution of compound 1c,d (0.65 mmol) in ethanol (10 ml) and
the mixture was stirred at 40-50ºC for 1 h. Water (30 ml) was added and the precipitate was filtered, thoroughly
washed with water and alcohol, and recrystallized from 2-propanol.
Compound 5c. Yield 0.14 g (54%); mp 131-132ºC (2-propanol), mp 131ºC [12].
Compound 5d. Yield 0.20 g (65%); mp 119-120ºC (2-propanol), mp 119ºC [13].
3,5-Bis(4-chlorophenyl)-1-(4-nitrophenyl)-1,6-dihydropyridazine (6a). A mixture of compound 1c
(0.4 g, 1.08 mmol) and 4-nitrophenylhydrazine (0.2 g, 1.08 mmol) in ethanol (20 ml) was refluxed for 3 h,
cooled, and the precipitate formed was filtered off and washed with alcohol. Yield 0.27 g (60%); mp 250-253ºC
(decomp., MeNO2). IR spectrum, ν, cm-1: 1580, 1495, 1320, 1280, 1165, 1085, 810. 1H NMR spectrum, δ, ppm
(J, Hz): 8.20 (2H, d, 3J = 9.0, H-3',5'); 8.01 (2H, d, 3J = 8.0, H-2'',6''); 7.96 (2H, d, 3J = 8.0, H-2''',6'''); 7.66 (2H,
d, 3J = 9.0, H-2',6'); 7.48 (2H, d, 3J = 8.0, H-3'',5''); 7.44 (2H, d, 3J = 8.0, H-3''',5'''); 7.33 (1H, s, H-4); 4.85 (2H,
s, H-6). Found, %: C 62.21; H 3.49; Cl 16.75; N 9.91. C22H15Cl2N3O2. Calculated, %: C 62.28; H 3.56;
Cl 16.71; N 9.90.
3,5-Bis(4-bromophenyl)-1-phenyl-1,6-dihydropyridazine (6b). A mixture of compound 1d (0.4 g,
0.87 mmol) and phenylhydrazine (0.01 ml, 1 mmol) in ethanol (20 ml) was refluxed for 1 h. The product was
cooled and the precipitate was filtered off, washed with alcohol, and recrystallized from nitromethane to give
1
0.27 g (67%) with mp 143-145ºC (nitromethane). IR spectrum, ν, cm-1: 1600, 1595, 1210, 1080, 1010, 805. H
3
NMR spectrum, δ, ppm (J, Hz): 7.88 (2H, d, 3J = 8.0, H-2'',6''); 7.79 (2H, d, J = 8.0, H-2''',6'''); 7.62-7.47 (6H,
m, H-2',6', H-3'',5'', H-3''',5'''); 7.34 (2H, t, 3J = 8.0, H-3',5'); 7.24 (1H, s, H-4); 6.98 (1H, t, 3J = 8.0, H-4'); 4.70
(2H, s, H-6). Found, %: C 56.37; H 3.39; Br 34.18; N 6.00. C22H16Br2N2. Calculated, %: C 56.44; H 3.44;
N 5.98.
3,5-Bis(4-chlorophenyl)-1-phenylpyridazin-1-ium Bromide (7a). A mixture of compound 1c (0.4 g,
1.08 mmol) and phenylhydrazine (0.11 ml, 1.08 mmol) in ethanol (20 ml) was refluxed for 2 h. Solvent was
evaporated and the residue was treated with methyl tert-butyl ether (10 ml). The precipitate formed was filtered
off and washed with ether to give 0.24 g (48%) with mp 321-323ºC (decomp., 2-propanol). IR spectrum, ν, cm-1:
1595, 1390, 1090, 820, 752. 1H NMR spectrum, δ, ppm (J, Hz): 10.64 (1H, s, H-6); 9.53 (1H, s, H-4); 8.50 (4H,
m, H-2',6', H-2'',6''); 8.29 (2H, m, H-2''',6'''); 7.79 (3H, m, H-3'-H-5'); 7.71 (4H, m, H-3'',5'', H-3''',5'''). Found, %:
C 57.63; H 3.28; Br 17.45; Cl 15.46; N 6.14. C22H15BrCl2N2. Calculated, %: C 57.67; H 3.30; Br 17.44;
Cl 15.48; N 6.11.
1188

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