Synthesis of 1,3-diketones from 3-(4-R-phenyl)propionic acids

Article abstract of DOI:10.1134/S1070428014040022

Self-acylation of 3-(4-R-phenyl)propionic acids (R = H, Br, 1-adamantyl) in trifluoroacetic anhydride catalyzed by trifluoromethanesulfonic acid provides a simple and efficient synthesis of 1,3-diketones. Indan-1-ones formed in the first step undergo acylation to give the corresponding 2-(3-phenyl-1-oxopropyl) indan-1-ones as the major products. One-pot synthesis of polysubstituted pyrazoles directly from 3-(4-R-phenyl)propionic acids is described.

Full text of DOI:10.1134/S1070428014040022

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2014, Vol. 50, No. 4, pp. 464–468. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © D.K. Kim, E.A. Shokova, V.A. Tafeenko, V.V. Kovalev, 2014, published in Zhurnal Organicheskoi Khimii, 2014, Vol. 50, No. 4,
pp. 479–483.
Synthesis of 1,3-Diketones from 3-(4-R-Phenyl)propionic Acids
D. K. Kim, E. A. Shokova, V. A. Tafeenko, and V. V. Kovalev
Faculty of Chemistry, Moscow State University, Leninskie gory 1, Moscow, 119991 Russia
e-mail: kovalev@petrol.chem.msu.ru
Received January 22, 2014
Abstract—Self-acylation of 3-(4-R-phenyl)propionic acids (R = H, Br, 1-adamantyl) in trifluoroacetic
anhydride catalyzed by trifluoromethanesulfonic acid provides a simple and efficient synthesis of 1,3-di-
ketones. Indan-1-ones formed in the first step undergo acylation to give the corresponding 2-(3-phenyl-1-oxo-
propyl)indan-1-ones as the major products. One-pot synthesis of polysubstituted pyrazoles directly from
3-(4-R-phenyl)propionic acids is described.
DOI: 10.1134/S1070428014040022
1,3-Diketones constitute one of the most important
classes of organic compounds; they are widely used as
key building blocks in organic synthesis and exhibit
various kinds of biological activity, including anti-
tumor, antiviral, anti-inflammatory, antioxidant, and
antimicrobial; they also show a broad spectrum of
ionophoric properties [1–3].
activator readily converts carboxylic acids into mixed
anhydrides, acyl trifluoroacetates, which are efficient
acylating agents [11], while the presence of trifluoro-
methanesulfonic acid favors enolization and enhances
the acylating power of acyl trifluoroacetates.
Scheme 1.
R
(1) TFAA, TfOH, Δ
1,3-Diketones are traditionally synthesized by the
Claisen condensation which in a general case includes
C-acylation of the α-position of a ketone taken as
enolate, enamine, or silyl enol ether. Acid halides,
esters (including formates and oxalates), and anhy-
drides, dialkyl carbonates, methoxymagnesium methyl
carbonate, N-acyl imidazoles, acyl cyanides, and acyl-
benzotriazoles are commonly used as acylating agents
[4]. Despite numerous modifications of this method
[1, 2], in particular recent ones [5–9], none of them
ensure direct synthesis of β-diketones from acids and
ketones with simultaneous activation of both carbonyl
and methylene components immediately during the
reaction.
(2) NuH
OH
Nu
R
R
O
O
O
R = 1-adamantyl, t-Bu, i-Pr; NuH = H2O, ROH, R′R″NH.
In this work we studied the transformations of
ω-phenylalkanoic acids Ia–Id in the acylating system
TFAA–TfOH (see table). Unlike phenylacetic acid
which underwent polymerization under these condi-
tions [10], β-phenylpropionic acid Ia in a mixture of
TFAA and methylene chloride in the presence of
0.25 equiv of TfOH at room temperature was convert-
ed into 2-(3-phenyl-1-oxopropyl)indan-1-one (IIIa) in
~55% yield (Scheme 2). Diketone IIIa is the product
of acylation of intermediate indan-1-one (IIa). Com-
pound IIa was isolated from the reaction mixture in
a small amount (<2%), and 40% of initial acid Ia was
recovered (see table, run no. 2). The yield of IIIa in-
creased to 80% when 0.5 equiv of TfOH was used (run
no. 3). By contrast, γ-phenylbutyric acid (Id) under
analogous conditions (run nos. 12, 13) was quanti-
tatively converted into tetralone (IV).
In this article we describe a simple and efficient
method for the synthesis of 1,3-diketones via intra- and
intermolecular self-acylation of β-phenylpropionic
acids in the system trifluoroacetic anhydride–trifluoro-
methanesulfonic acid (TFAA–TfOH). We previously
found [10] that self-acylation of aliphatic carboxylic
acids in trifluoroacetic anhydride, catalyzed by tri-
fluoromethanesulfonic acid, provides a convenient
synthetic approach to 2,4-dialkyl-substituted aceto-
acetic acids and their derivatives (Scheme 1). Tri-
fluoroacetic anhydride used as a reaction medium and
Acid-catalyzed intramolecular cyclization of 3-aryl-
propanoic and 4-arylbutanoic acids into indan-1-ones
464

SYNTHESIS OF 1,3-DIKETONES FROM 3-(4-R-PHENYL)PROPIONIC ACIDS
465
Scheme 2.
R
O
O
O
TFAA, TfOH
CH2Cl2, 20°C
R
R
O
( )n
OH
+
( )n
R
Ia–Id
IIa–IIc, IV
IIIa–IIIc
R = H (a, d), Br (b), 1-Ad (c); Ia–Ic, IIa–IIc, n = 1; Id, IV, n = 2.
and tetrahydronaphthalen-1-ones is well known
[12–16]; however, in no case further acylation with
formation of β-diketones was observed. As far as we
know, both intra- and intermolecular acylation with
formation of indan-1-one together with an appreciable
amount of diketone IIIa was reported only for activat-
ed 3-phenylpropanoyl perchlorate (prepared from
3-phenylpropanoyl chloride and silver perchlorate) in
nitromethane solution [17].
increase of the amount of TfOH in the reaction with
3-phenylpropionic acid (Ia) led to sharp decrease of
the yield of diketone IIIa and increase of the yield of
indan-1-one (IIa), which attained 94% in the presence
of 1.5 equiv of TfOH (see table; run nos. 4, 5).
The reaction of 3-(4-bromophenyl)propionic acid
(Ib) with TFAA in the presence of 0.5 equiv of TfOH
was chemoselective, and the only product was di-
ketone IIIb (~67%, run no. 7); the highest yield of
IIIb was obtained using 1 equiv of TfOH (~78%, run
no. 8). Raising the amount of TfOH to 3 equiv made
indanone IIb the major product (67%, run no. 10);
simultaneously, the amount of unreacted acid Ib in-
creased (13 and 24%, respectively). From 3-[4-(1-ada-
mantyl)phenyl]propionic acid (Ic) we obtained 48% of
ketone IIc and 35% of diketone IIIc (run no. 11). We
believe that the lower yield of diketone IIIc is related
to the poor solubility of 6-(1-adamantyl)indan-1-one
(IIc) in the reaction medium. Obviously, the intra- and
intermolecular acylation of 3-phenylpropionic acids is
sensitive to both the nature of substituent in the phenyl
Acyl trifluoroacetates generated in situ from car-
boxylic acids and TFAA were used to acylate arenes
in the presence of acid catalysts (H3PO4 or TfOH)
[18–20]. For example, the system TFAA–TfOH was
applied to prepare aryl alkyl ketones from aromatic
compounds and carboxylic acids, but no formation of
1,3-diketones was observed [20]. The difference be-
tween our results and those reported in [20] may be
rationalized by the fact that in the latter case consider-
ably larger amount of superacid (TfOH) was used
(4 equiv against 0.25–0.5 equiv in our experiments), so
that the acylation of ketones slowed down. In fact,
Self-acylation of ω-phenylalkanoic acids Ia–Id
Run no.
Initial acid no.
Molar ratio I–TFAA–TfOH
Reaction time, h
Product, yield,a %
IIIa, <2
01
02
03
04
05
06
07
08
09
10
11
12
13
Ia
Ia
Ia
Ia
Ia
Ib
Ib
Ib
Ib
Ib
Ic
Id
Id
1:6:0
2.0
2.0
2.0
2.0
0.5
2.0
2.0
2.0
2.0
2.0
3.0
1.5
1.5
1:6:0.25
1:6:0.5
1:6:1.0
1:6:1.5
1:6:0.25
1:6:0.5
1:6:1.0
1:6:1.5
1:6:3.0
1:6:0.5
1:6:0.25
1:6:0.5
IIa, <2; IIIa 55 (50)
IIa, 23 (20); IIIa, 80 (75)
IIa, 81; IIIa, 16
IIa, 96 (94); IIIa, <1
IIIb, 27
IIIb, 67 (47)
IIb, 9 (8); IIIb, 78 (70)
IIb, 28; IIIb, 58
IIb, 67 (62); IIIb, <1
IIc (48); IIIc (35)
IV, 96 (89)
IV, 89
a
The yields were determined on the basis of the 1H NMR data; the yields of the products isolated by silica gel chromatography are given
in parentheses.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 4 2014

KIM et al.
466
Scheme 3.
O
O
N
NH
R'
TFAA, TfOH
CH2Cl2, 20°C
N2H4·H2O
EtOH, Δ
R
R
O
OH
R'
R
Ia, Ib
IIIa, IIIb
Va, Vb
R = H, R′ = PhCH2CH2 (a); R = Br, R′ = 4-BrC6H4CH2CH2 (b).
fragment and the amount of trifluoromethanesulfonic
acid added.
elemental compositions. Diketones IIIa–IIIc in CDCl3
solution exist mainly in the enol form, as follows from
the presence in their 13C NMR spectra of a strong
signal at δC ~110 ppm, which belongs to the α-olefinic
quaternary carbon atom in the C(OH)=C–C(O) frag-
ment. The minor diketone tautomer characteristically
displays a multiplet signal at δ ~3.9 ppm in the
1H NMR spectrum due to the C(O)CHC(O) proton,
and the corresponding carbon signal is located at
δC ~61 ppm in the 13C NMR spectrum.
1,3-Diketones are very popular intermediate prod-
ucts in the synthesis of various heterocyclic com-
pounds. For example, the most widely used method for
the synthesis of pyrazoles is based on the reaction of
1,3-diketones with hydrazine derivatives [21, 22]. With
a view to extend the synthetic potential of the
described reaction, we tried to obtain pyrazoles Va and
Vb from 3-phenylpropionic acids Ia and Ib in a one-
pot process. For this purpose, the reaction mixtures
containing diketones IIIa and IIIb (run nos. 3, 8) were
evaporated under reduced pressure, the residue was
dissolved in ethanol, hydrazine hydrate was added to
the solution, and the mixture was heated under reflux.
As a result, we isolated pyrazoles Va and Vb in 69 and
62% yield, respectively (Scheme 3).
To conclude, we have shown for the first time that
self-acylation of 3-phenylpropionic acids in the system
trifluoroacetic anhydride–trifluoromethanesulfonic
acid–methylene chloride gives β-diketones as the
major products. The described reaction makes it
possible to synthesize substituted pyrazoles directly
from 3-phenylpropionic acid via a one-pot process
where diketones are formed as intermediate products.
Studies on the synthetic potential of this procedure will
be continued.
The structure of pyrazole Vb was determined by
X-ray analysis (CCDC 950017) [23]. Molecules Vb in
crystal form centrosymmetric dimers through inter-
molecular hydrogen bonds N1–H1···N2′ (see figure).
EXPERIMENTAL
The structure of the newly synthesized compounds
was confirmed by their H and C NMR spectra and
1
The H and 13C NMR spectra were recorded on
1
13
a Bruker Avance-400 spectrometer at 400 and 100 MHz,
respectively, using CDCl3 as solvent; the chemical
shifts were determined relative to the solvent signals.
The X-ray diffraction data for compound Vb were
acquired on an Enraf Nonius CAD4 diffractometer at
295 K (CuKα radiation, graphite monochromator,
ω-scanning). Analytical thin-layer chromatography
was carried out on Merck DC Alufolien Kieselgel
60 F254 plates; spots were detected under UV light
(λ 254 nm). Silica gel Merck Kieselgel 40/60 was used
for preparative column chromatography. Trifluoro-
acetic anhydride was distilled over P2O5 prior to use.
C5
C6
C7
C4
C10
Br1
C12
C2 C1
C8
C15
C9
C14
C13
C11
N2
Br2
C16
C17
C3
N1
C18
N2′
N1′
Self-acylation of 3-(4-R-phenyl)propionic acids
Ia–Ic (general procedure). A solution of acid Ia–Ic
and trifluoroacetic anhydride in 1 mL of methylene
chloride was stirred for 15 min, a required amount of
trifluoromethanesulfonic acid was added, and the mix-
ture was stirred for a time indicated in table (TLC).
The mixture was evaporated, the residue was treated
Structure of centrosymmetric dimer formed by molecules of
7-bromo-3-[2-(4-bromophenyl)ethyl]-1,4-dihydroindeno-
[1,2-c]pyrazole (Vb) in crystal according to the X-ray dif-
fraction data.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 4 2014

SYNTHESIS OF 1,3-DIKETONES FROM 3-(4-R-PHENYL)PROPIONIC ACIDS
467
1
with water (3 mL) and dissolved in methylene chloride
(15 mL), the solution was washed with a 5% solution
of NaHCO3 (2×3 mL) and water (2×3 mL) and dried
over MgSO4, the solvent was distilled off under
reduced pressure, and the residue was purified by
chromatography on silica gel using hexane–methylene
chloride as eluent.
red powder, mp 147–148°C. H NMR spectrum, δ,
ppm (ketone–enol ratio 15:85); enol: 2.72 t (2H, CH2,
J = 7.2 Hz), 2.99 t (2H, CH2, J = 7.2 Hz), 3.36 s (2H,
CH2), 7.10 d (2H, Harom, J = 8 Hz), 7.31 d (1H, Harom
J = 7.6 Hz), 7.40 d (2H, Harom, J = 8 Hz), 7.63 d (1H,
Harom, J = 7.6 Hz), 7.91 s (1H, Harom). C NMR spec-
trum, δC, ppm: 29.46 (CH2), 30.40 (CH2), 36.45 (CH2),
110.53 [C=C(OH)], 119.77 (Carom), 121.09 (Carom),
125.66 (CHarom), 126.74 (CHarom), 129.72 (CHarom),
131.20 (CHarom), 135.00 (CHarom), 139.11 (Carom),
139.47 (Carom), 145.16 (Carom), 180.72 [C=C(OH)],
187. 95 (CO). Found, %: C 51. 01; H 3. 23.
C18H14Br2O2. Calculated, %: C 51.22; H 3.34.
,
13
Indan-1-one (IIa) was synthesized by reaction of
150 mg (1 mmol) of acid Ia with 0.85 mL (6 mmol) of
TFAA in the presence of 0.133 mL (1.5 mmol) of
TfOH. Yield 124 mg (94%), mp 37–40°C; published
data [17]: mp 39–42°C.
6-Bromoindan-1-one (IIb) was synthesized by
reaction of 229 mg (1 mmol) of acid Ib with 0.85 mL
(6 mmol) of TFAA in the presence of 0.265 mL
(3.0 mmol) of TfOH. Yield 130 mg (62%), mp 111–
115°C; published data [24]: mp 109–110°C.
6-(1-Adamantyl)-2-{3-[4-(1-adamantyl)phenyl]-
1-oxopropyl}indan-1-one (IIIc) was synthesized from
284 mg (1 mmol) of acid Ic using 0.85 mL (6 mmol)
of TFAA and 0.044 mL (0.5 mmol) of TfOH. Yield
155 mg (35%), grey powder, mp 177–178°C. 1H NMR
spectrum, δ, ppm (ketone–enol ratio 5:95); enol: 1.70–
1.90 m (24H, Ad), 2.05–2.15 m (6H, Ad), 2.72 t (2H,
CH2), 3.01 t (2H, CH2), 3.35 s (2H, CH2), 7.19 d (2H,
6-(1-Adamantyl)indan-1-one (IIc) was synthe-
sized from 284 mg (1 mmol) of acid Ic using 0.85 mL
(6 mmol) of TFAA and 0.044 mL (0.5 mmol) of TfOH.
Yield 128 mg (48%), white crystals, mp 164–165°C.
1H NMR spectrum, δ, ppm: 1.60–1.80 m (6H, Ad),
1.91 br.s (6H, Ad), 2.09 br.s (3H, Ad), 2.66 m (2H,
CH2), 3.07 m (2H, CH2), 7.40 d (1H, Harom, J =
H
arom, J = 8 Hz), 7.28 d (2H, Harom, J = 8 Hz), 7.39 d
(1H, Harom, J = 7.9 Hz), 7.58 d (1H, Harom, J = 7.9 Hz),
7.82 br.s (1H, Harom). 13C NMR spectrum, δC, ppm:
28.48 (CH), 28.53 (CH), 29.02 (CH2), 30.93 (CH2),
35.49 (C), 35.97 (C), 36.28 (CH2), 36.37 (CH2), 110.51
[C=C(OH)], 119.02 (CHarom), 124.60 (CHarom), 124.87
(CHarom), 127.64 (CHarom), 129.70 (CHarom), 137.34
(Carom), 137.73 (Carom), 144.75 (Carom), 149.04 (Carom),
150.63 (Carom), 178.24 [C=C(OH)], 192.00 (CO).
Found, %: C 84.44; H 8.33. C18H14Br2O2. Calculated,
%: C 84.12; H 8.65.
7.8 Hz), 7.61 d (1H, Harom, J = 7.8 Hz), 7.73 d (1H,
13
H
arom, J = 2 Hz). C NMR spectrum, δC, ppm: 25.28
(CH2), 28.78 (CH), 36.24 (C), 36.58 (CH2), 43.13
(CH2), 119.76 (CHarom), 126.19 (CHarom), 131.90
(CHarom), 136.94 (Carom), 150.96 (Carom), 152.58 (Carom),
207.35 (CO). Found, %: C 85.32; H 8.04. C19H22O.
Calculated, %: C 85.67; H 8.32.
2-(3-Phenyl-1-oxopropyl)indan-1-one (IIIa) was
synthesized from 150 mg (1 mmol) of acid Ia using
0.85 mL (6 mmol) of TFAA and 0.044 mL (0.5 mmol)
of TfOH. Yield 75% (100 mg), red powder, mp 65–
1,2,3,4-Tetrahydronaphthalen-1-one (IV) was
synthesized from 164 mg (1 mmol) of acid Id using
0.85 mL (6 mmol) of TFAA and 0.133 mL (1.5 mmol)
of TfOH. Yield 130 mg (89%), oily substance.
1
66°C; published data [17]: mp 68–69°C. H NMR
Pyrazoles Va and Vb (general procedure). A solu-
tion of acid Ia or Ib in a mixture of trifluoroacetic
anhydride and 1 mL of methylene chloride was stirred
for 15 min, a required amount of trifluoromethanesul-
fonic acid was added, and the mixture was kept for 2 h
and evaporated under reduced pressure. The residue
was dissolved in 5 mL of ethanol, 0.05 mL (1 mmol)
of hydrazine hydrate was added, and the mixture was
heated for 2 h under reflux. The solvent was distilled
off, the oily residue was dissolved in 15 mL of meth-
ylene chloride, the solution was washed with a 5% so-
lution of NaHCO3 and water, dried over MgSO4, and
evaporated, and the residue was purified by chroma-
spectrum, δ, ppm (ketone–enol ratio 20:80): enol:
2.73 t (2H, CH2, J = 8 Hz), 3.04 t (2H, CH2, J = 8 Hz),
3.40 s (2H, CH2), 7.15–7.32 m (5H, Harom), 7.33–
7.55 m (3H, Harom), 7.80 d (1H, Harom, J = 7.6 Hz).
13C NMR spectrum, δC, ppm: 29.91 (CH2), 31.64
(CH2), 36.79 (CH2), 110.50 [C=C(OH)], 123.02
(CHarom), 125.60 (CHarom), 126.25 (CHarom), 127.21
(CHarom), 128.29 (CHarom), 128.45 (CHarom), 132.65
(Carom), 138.05 (Carom), 140.64 (Carom), 147.44 (Carom),
179.70 [C=C(OH)], 191.06 (CO).
6-Bromo-2-[3-(4-bromophenyl)-1-oxopropyl]-
indan-1-one (IIIb) was synthesized from 229 mg
(1 mmol) of acid Ib using 0.85 mL (6 mmol) of TFAA tography on silica gel using methylene chloride–
and 0.088 mL (1 mmol) of TfOH. Yield 148 mg (70%),
methanol (50:1) as eluent.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 50 No. 4 2014

KIM et al.
468
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zole (Va) was synthesized from 150 mg (1 mmol) of
acid Ia, 0.85 mL (6 mmol) of TFAA, 0.044 mL
(0.5 mmol) of TfOH, and 0.05 mL (1 mmol) of hy-
drazine hydrate. Yield 90 mg (69%), brown powder,
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1
mp 108–110°C. H NMR spectrum, δ, ppm: 3.04 m
(4H, CH2), 3.42 s (2H, CH2), 7.14 m (2H, Harom), 7.17–
7.40 m (4H, Harom), 7.44 d (1H, Harom, J = 6.4 Hz),
7.71 d (1H, Harom, J = 6.4 Hz). 13C NMR spectrum, δC,
ppm: 27.54 (CH2), 28.36 (CH2), 34.78 (CH2), 119.91
(CH), 121.64 (C), 122.73 (CH), 125.83 (CH), 126.28
(CH), 126.43 (2CH), 128.36 (CH), 128.54 (CH),
134.72 (C), 137.93 (C), 140.81 (C), 148.67 (C). Found,
%: C 82.67; H 6.35; N 10.37. C18H16N2. Calculated, %:
C 83.05; H 6.19; N 10.76.
7-Bromo-3-[2-(4-bromophenyl)ethyl]-1,4-dihy-
droindeno[1,2-c]pyrazole (Vb) was synthesized from
229 mg (1 mmol) of acid Ib, 0.85 mL (6 mmol) of
TFAA, 0.088 mL (1 mmol) of TfOH, and 0.05 mL
(1 mmol) of hydrazine hydrate. Yield 150 mg (72%),
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red crystals, mp 172–174°C. H NMR spectrum, δ,
ppm: 2.92–3.08 m (4H, CH2), 3.36 s (2H, CH2), 7.01 d
(2H, Harom, J = 8 Hz), 7.45–7.28 m (3H, Harom), 7.82 s
(1H, Harom), 8.50 br.s (1H, NH). 13C NMR spectrum,
δC, ppm: 26.86 (CH2), 27.70 (CH2), 33.68 (CH2),
119.81 (C), 120.46 (C), 122.73 (CH), 126.78 (CH),
129.00 (CH), 129.64 (2CH), 131.15 (C), 131.23
(2CH), 135.94 (C), 138.98 (C), 146.76 (C). Found, %:
C 52.27; H 3.30; N 6.46. C18H14Br2N2. Calculated, %:
C 51.71; H 3.37; N 6.70.
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