(CF3CO)2O/CF3so3H-mediated synthesis of 1,3-diketones from carboxylic acids and aromatic ketones

Article abstract of DOI:10.3762/bjoc.10.236

A very simple and convenient reaction for 1,3-diketone preparation from carboxylic acids and aromatic ketones in TFAA/TfOH system is described. When the β-phenylpropionic acids were used as starting materials, they initially gave 1-indanones and then underwent further acylation with the formation of 2-(β-phenylpropionyl)-1-indanones as the main reaction products. In addition, the application of the proposed protocol allowed for the synthesis of selected polysubstituted pyrazoles in a one-pot procedure directly from acids and ketones.

Full text of DOI:10.3762/bjoc.10.236

(CF3CO)2O/CF3SO3H-mediated synthesis of 1,3-diketones
from carboxylic acids and aromatic ketones
JungKeun Kim, Elvira Shokova, Victor Tafeenko and Vladimir Kovalev*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2014, 10, 2270–2278.
Laboratory of Macrocyclic Receptors, Department of Chemistry,
Moscow State University, Lenin’s Hills, Moscow 119991, Russia
doi:10.3762/bjoc.10.236
Received: 22 April 2014
Email:
Accepted: 01 September 2014
Published: 26 September 2014
Vladimir Kovalev* - kovalev@petrol.chem.msu.ru
* Corresponding author
Associate Editor: T. P. Yoon
Keywords:
© 2014 Kim et al; licensee Beilstein-Institut.
License and terms: see end of document.
Claisen condensation; 1,3-diketones; heterocycles; triflic acid;
trifluoroacetic acid anhydride
Abstract
A very simple and convenient reaction for 1,3-diketone preparation from carboxylic acids and aromatic ketones in TFAA/TfOH
system is described. When the β-phenylpropionic acids were used as starting materials, they initially gave 1-indanones and then
underwent further acylation with the formation of 2-(β-phenylpropionyl)-1-indanones as the main reaction products. In addition, the
application of the proposed protocol allowed for the synthesis of selected polysubstituted pyrazoles in a one-pot procedure directly
from acids and ketones.
Introduction
1,3-Diketones represent one of the most important class of [5-11], it is noticeable that none of these techniques imple-
organic compounds, since they are applied as key structural ments a direct synthesis of β-diketones from acids and ketones
blocks in organic syntheses, exhibit different kinds of bio- with an immediate activation of both carbonyl and methylene
logical activities, and display a broad range of ionophoric prop- components in the course of the reaction.
erties [1-3]. The method most frequently used for 1,3-diketone
synthesis is the Claisen condensation, which comprises the Herein, we would like to describe a direct and operationally
C-acylation of the α-position of ketones in the form of their simple TFAA/TfOH-mediated synthesis of 1,3-diketones from
metal enolates, enamines or silyl ethers, with or without a cata- unmodified carboxylic acids and ketones.
lyst. To appear as an acylating agent one of the following com-
pounds could be required: acyl halides and acid esters, Results and Discussion
including formates and oxalates, and acid anhydrides, dialkyl Initially, an unusual transformation of the β-phenylpropionic
carbonates, methoxymagnesium methyl carbonate, N-acylimi- acids was observed by us in a TFAA/TfOH/CH2Cl2 system
dazoles, acyl cyanides, and acylbenzotriazoles [4]. Though (Table 1), which gave the impulse for this research. Surpris-
recently many modifications of this method have been proposed ingly, it turned out that β-phenylpropionic acid (1a) in a TFAA/
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Table 1: TFAA/TfOH-mediated self-acylation of ω-phenylalkanoic acids 1a–ca.
Entry
1
TfOH (equiv)
Time (h)
Yield, %b
2
3
1
1a
1a
1a
1a
1b
1b
1b
1b
1b
1c
1c
0.25
0.5
2
2a, <2
3a, 55, (51)c
2
2
2a, 19, (16)
2a, 81
3a, 79, (75)
3a, 16
3
1.0
1
4
1.5
0.5
2
2a, 96, (94)
2b, 0
3a, <1
5
0.25
0.5
3b, 27
6
2
2b, 0
3b, 67, (59)
3b, 78, (70)
3b, 58
7
1.0
2
2b, 9, (8)
2b, 28
8
1.5
2
9
3.0
2
2b, 67, (62)
2с, 98, (96)
2с, 96
3b, <1
10
11
0.25
0.5
1.5
1
a Reactions were performed by the addition of TfOH to a solution of 1a–c (1.0 mmol) and TFAA (6 mmol) in 1.0 mL of dry CH2Cl2 at rt; byield deter-
mined by1H NMR; cyield of individual product, purified by using silica gel column chromatography, is given in parentheses.
CH2Cl2 medium in the presence of TfOH (0.25 equiv, Table 1, of phenylpropionic acid 1а. Here, the yield of the diketone 3a
entry 1) gave 2-(β-phenylpropionyl)-1-indanone (3а) in 51% decreased with an increase of the quantity of TfOH, whereas the
yield as the major product, even though we expected yield of 1-indanone (2a) increased and reached 94% with
1-indanone (2а, <2%). When 0.5 equiv of TfOH was applied, 1.5 equiv of TfOH (Table 1, entry 4).
3а and 2a were obtained in 75 and 16% yield, respectively
(Table 1, entry 2). Evidently, in this reaction, 1-indanone (2а), In the case of β-(4-bromophenyl)propionic acid (1b) with
which was initially formed as the result of an intramolecular 0.5 equiv of TfOH, the reaction chemoselectively proceeds to
cyclization of 1a, underwent a further acylation with the forma- give the only diketone 3b (59%, Table 1, entry 6). The maximal
tion of 1,3-diketone 3a. In contrast, γ-phenylbutanoic acid (1c) yield of the diketone 3b is obtained with 1 equiv of TfOH
was quantitatively transformed only to the tetralone 2с (Table 1, (70%, Table 1, entry 7), and a further increase of the TfOH
entries 10 and 11).
quantity to 3 equiv results in the indanone 2b as the only prod-
uct (62%, Table 1, entry 9). Evidently, the intra- and intermole-
The acid-catalyzed cyclization of 3-arylpropanoic and 4-arylbu- cular acylation of β-phenylpropionic acids in this reaction is
tanoic acids to 1-indanones and 1-tetralones is well-known [12- dependent on the used TfOH quantity and the nature of the
18], but it appears that the further acylation and β-diketone for- substituent in the phenyl moiety.
mation has not been reported yet. While the use of acyl trifluo-
roacetates, generated in situ from a carboxylic acid and TFAA, On the basis of the above results, we supposed that the acyla-
for the aromatic acylation catalyzed by acid (H3PO4 [19-22] or tion of ketones with carboxylic acids in a TFAA/TfOH/CH2Cl2
TfOH [23-25]) has been reported, the 1,3-diketone formation system could be applied as an effective method for the syn-
has not been observed yet.
thesis of β-diketone. It turned out that the acylation of different
alkyl aryl ketones 2a–k (indanones, tetralone, acetophenones,
We concluded that in the work of reference [25], an apparently 2-acetylthiophene and methyl benzyl ketone) with alkanoic
larger quantity of the super acidic TfOH was employed (4 equiv acids RCOOH 1d–h (where R = 1-adamantylmethyl, neopentyl,
vs 0.25–1.5 equiv in our work), which possibly slowed down isopropyl, methyl, phenyl) gave the corresponding β-diketones
the reaction of ketone acylation. This is corroborated in the case 3c–t in 37–86% yields (Table 2).
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Table 2: TFAA/TfOH-mediated acylation of aromatic ketones with alkanoic acidsа.
Entry
1
Acid 1, R
Ketone
1,3-Diketone
Yield,%
79
1-AdCH2
1d
1e
1f
2a
2a
3c
3d
3e
3f
2
3
4
5
t-BuCH2
74
50
iPr
2a
2a
2a
Me
1g
1h
77b
66c
Ph
3g
6
1-AdCH2
t-BuCH2
Me
1d
1e
1g
1e
1d
(65)d
57
2c
2c
3h
3i
7
8
2c
53b
86
3j
9
t-BuCH2
1-AdCH2
2d
2e
3k
3l
10
47
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Table 2: TFAA/TfOH-mediated acylation of aromatic ketones with alkanoic acidsа. (continued)
11
12
t-BuCH2
t-BuCH2
1e
1e
2e
69b
3m
61
2f
2f
3n
13
14
15
Me
1g
1d
1d
41b,c
3o
1-AdCH2
1-AdCH2
48
2g
2h
3p
37
3q
16
17
1-AdCH2
1-AdCH2
1d
1d
49
2i
2j
3r
43
3s
18
1-AdCH2
1d
64
2k
3t
aReaction conditions: ketone (1 mmol), acid (1 mmol), TFAA (6 mmol), TfOH (0.5 mmol) in 1 mL CH2Cl2, 2–4 h, rt; b2 mmol of acid was used;
c1.5 mmol of TfOH was used; dyield determined by 1H NMR.
In most cases reactions were carried out at the molar ratios of reactions. An excess of the acid 1e (2 equiv vs 1 equiv) in the
acid:ketone:TFAA:TfOH = 1:1:6:0.5. For the reaction of acylation of acetophenone (2e) only modestly increase the yield
1-indanone (2а) and 1-adamantylacetic acid (1d) it was shown of diketone 3d from 64 to 69% (Table 2, entry 11), and usually
that in the absence of TfOH the yield of diketone 3c signifi- we added equimolecular quantities of an acid and a ketone. An
cantly dropped (<2%). With 0.25–1.5 equiv of TfOH the yield excess of acetic acid in acylation reactions (Table 2, entries 4, 8
of the diketone 3c reached its maximal value (~80%) and and 13) was employed considering that this acid was partially
decreased with a greater excess (3 equiv) of TfOH (57%). self-acylated under the reaction conditions. A probable mecha-
Apparently, the reduction of the TFAA excess (from 6 to nism of the reaction of ketone acylation by acids in TFAA/
3 equiv) slightly lowered the yield of the diketone 3c to 68%, TfOH media may be that after the acyl trifluoroacetates are
although the quantity of TFAA was not optimized for these generated in situ, triflic acid becomes involved in the enoliza-
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tion of ketones and increases the acylating ability of acyl triflu- The acylation of the methyl benzyl ketone (2k) by 1-adamantyl-
oroacetates. However, with an increase of the TfOH quantity acetic acid (1d) proceeded with regioselectivity at the α-СН2-
(>1.5 equiv) a retardation of the ketone acylation is observed, group and gave the diketone 3t in good yield (Table 2, entry
presumably as a result of its protonation.
18), which is apparently associated with the enolization ability
of 2k in the benzyl fragment of the molecule.
Since the γ-phenylbutanoic acid (1c) was quantitatively
converted to 1-tetralone (2c) under the acylation conditions, the To enhance the application of the considered reaction, we
diketone 3h (Table 2, entry 6) was also obtained by a two-stage investigated the acylation of the ketones by several functionally
one-pot approach, i.e., the intramolecular cyclization of the acid substituted carboxylic acids. Whereas glycine did not react with
1c (to form the tetralone 2c) and the following acylation with the ketones, β-alanine (1i) reacting with 1-indanone, 1-tetralone
1-adamantylacetic acid (1d) (Scheme 1).
and acetophenone formed the corresponding trifluoroacylated
β-aminodiketones 3u–w (reaction 1 in Scheme 2). A fuller
acylation for 2a and 2c was achieved when 1.5 equiv of the acid
1i and 1 equiv of TfOH were used, whereas the yield of dike-
tone 3w still remained low under these conditions. The hydrol-
ysis of trifluoroacetates 3u, 3v under reflux in dilute HCl was
followed by the intramolecular cyclization and led to the
unknown heterocycles 4а,b.
Unambiguous evidence for the structure of heterocycle 4a was
Scheme 1: One-pot synthesis of diketone 3h from acids 1d and 1c.
obtained by X-ray diffraction analysis [26]. The crystal struc-
Scheme 2: Scope and limitations.
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ture of 4a is mediated by hydrogen bonds with a cation, a chlo-
ride anion and a solvating water molecule as participants
(Figure 1).
Figure 1: The molecular structure of 4a.
By acylation of 1-indanone (2a) with (diphenylphos-
phoryl)acetic acid (1j), the self-acylation of the acid 1j already
occurred at room temperature, which complicated the sep-
Scheme 3: One-pot synthesis of pyrazoles 6.
aration of the desired dicarbonyl compound. When the acid 1j The products were identified by 1H and 13C NMR spec-
was heated under the conditions of TFAA/TfOH-mediated self- troscopy, microanalysis and by spectral comparison with the
acylation of alkanoic acids recently reported by us [27] and known compounds. The molecular structures of compounds 3с,
decarboxylation was subsequently carried out, 1,3-diphenyl- 3u, 4a, 6b were confirmed by X-ray diffraction [26]. The
phosphorylated acetone 5 could be obtained (reaction 2 in obtained diketones were mainly present in the enol form in
Scheme 2).
CDCl3 solution. The enol structures of the β-diketones 3 were
supported by 1H/13C NMR spectra, which showed a set of
The two-stage one-pot reaction of γ-phenylbutanoic acid (1c) singlets at δ 5.9–6.2 corresponding to the α-olefinic protons for
and 3-hydroxy-1-adamantylacetic acid (1k) gave as a result the 3l–3r, 3s and 3w, signals at δ 106.5–116.1 and at δ 96.1–102.7
trifluoroacetylated hydroxydiketone 3x, which could be were assigned to the α-olefinic carbon for 3a–3k, 3u, 3v, 3x–3z
hydrolyzed to the corresponding alcohol 3y (reaction 3 in and 3l–3r, 3s, 3w, respectively. The minor keto tautomers
Scheme 2). The acylation of 1-indanone (2а) with 2,2’- (2–30%) were characterized by 1H multiplets or singlets
(adamantane-1,3-diyl)diacetic acid (1l) gave the tetraketone 3z. between δ 3.6 and 4.2 (4.70 for 3t) and 13C NMR signals
between δ 59.0 and 61.5.
Finally, we used our method in a two-stage one-pot syntheses of
pyrazoles, which find extensive use in the pharmaceutical Conclusion
industry [8,28]. Diketones 3a–c,f, essential for synthesis of the In summary, we proposed a simple and effective synthetic ap-
pyrazoles 6a–d, were obtained by one of the three routes proach to 1,3-diketones based on the TFAA/TfOH-mediated
(Scheme 3). The one-pot intra- and intermolecular acylation of acylation of ketones with carboxylic acids. Advantages of this
β-phenylpropionic acids 1а,b gave 3а,b. The acylation of the approach are the ready availability of the starting materials, the
1-indanone (2а) by acetic acid (1g) yielded 3f. The selective simple operational procedure, and the possibility to realize the
intramolecular cyclization of acid 1а was used to obtain the one-pot immediate syntheses of 1,3-diketones and pyrazoles
intermediate ketone 2а, which was further acylated by the acid directly from acids and ketones. Moreover, 1,3-diketones and
1d to finally give 3c. Upon the formation of the diketones, the pyrazoles can be obtained from unmodified β-phenylpropionic
reaction mixtures were evaporated in vacuum, the residues were acids. Given the importance of 1,3-dicarbonyl compounds in
dissolved in ethanol, and the following reaction with hydrazine general, we expect that this reaction has a wide application in
hydrate gave the pyrazoles 6a–d in 62–76% yield.
the realm of synthetic chemistry.
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Experimental
solvent was evaporated, the product was washed with diethyl
General procedure for the synthesis of diketones: A solution ether and hexane and dried.
of carboxylic acid (1 mmol), ketone (1 mmol, if required) and
TFAA (0.85 mL, 6 mmol) in dichloromethane (1 mL) was 1-Hydroxy-4-aza-2,3-dihydrofluorene hydrochloride (4a):
stirred for 15 min at rt. The required quantity of triflic acid Obtained from diketone 3u (299 mg, 1 mmol) in 95% (210 mg)
(usually 44 μL, 0.5 mmol) was then added, and the resulting yield as a brown solid. Mp 110–112 °С; 1H NMR (400 MHz,
solution was stirred at rt for 1–4 h (24 h for 3v and 3w) under methanol-d4) δ 7.97 (d, J = 7.8 Hz, HAr, 1H), 7.69 (t, J = 7.5
the conditions indicated in Scheme 1, Scheme 2, Table 1, and Hz, HAr, 1H), 7.59 (d, J = 7.7 Hz, HAr, 1H), 7.56 (t, J = 7.5 Hz,
Table 2 (TLC monitoring). The reaction mixture was evapo- HAr, 1H), 3.99 (t, J = 8.5 Hz, CH2, 2H), 3.79 (s, CH2, 2H), 2.91
rated under reduced pressure, and after quenching with water, (t, J = 8.5 Hz, CH2, 2H); 13С NMR (100 MHz, methanol-d4) δ
the residue was redissolved in dichloromethane (10 mL), 173.7 (C), 173.2 (C), 149.5 (C), 135.1 (CH), 132.0 (C), 127.4
washed with 5% NaHCO3 (2 × 3 mL), water (2 × 3 mL), and (CH), 126.1 (CH), 123.8 (CH), 105.9 (C), 41.1 (CH2), 30.7
dried over MgSO4. The solvent was removed in vacuum, and (CH2), 27.3 (CH2); Anal. calcd for C12H11NO·HCl: C, 65.02;
the crude reaction mixture was purified by silica gel chromatog- H, 5.46; N, 6.32; found: C, 64.72; H, 5.61; N, 6.24.
raphy (n-hexane/CH2Cl2/MeOH).
1,3-Bis(diphenylphosphoryl)acetone (5): A solution of
As illustrative examples, compounds 3a and 3c are prepared as diphenylphosphorylacetic acid (260 mg, 1 mmol) in a mixture
follows.
of TFAA (1.95 mL, 13.8 mmol) and TfOH (0.05 mL,
0.57 mmol) was kept at 60–65 °C for 1.5 h. The solvent was
2-(3-Phenylpropionyl)-1-indanone (3a): Obtained from evaporated under reduced pressure, the obtained residue was
β-phenylpropionic acid (1a, 150 mg, 1 mmol), TFAA (0.85 mL, stirred in a water (4 mL)/EtOH (4 mL) solution under reflux for
6 mmol) and TfOH (44 μL, 0.5 mmol) in 75% (100 mg) yield 2 h, cooled and concentrated. The residue was adjusted to pH
as a red solid. Mp 65–66 °C (Lit. [29]: mp 68–69 °C); 1H NMR 7.5 with 1 N NaHCO3, the solid formed was filtered, washed
(400 MHz, CDCl3) keto-enol (20:80); enol tautomer: δ 7.80 (d, with water, and dried. The product was purified by column
J = 7.6 MHz, HAr, 1H), 7.55–7.33 (m, HAr, 3H), 7.32–7.15 (m, chromatography (eluent: CH2Cl2/MeOH 50:1). Yield: 44%
HAr, 5H), 3.40 (s, CH2Ind, 2H), 3.04 (t, J = 7.7 Hz, CH2, 2H), (101 mg), white solid; mp 173–175 °С (Lit. [30]: mp
2.73 (t, J = 7.7 Hz, CH2, 2H); 13С NMR (100 MHz, CDCl3) δ 175–176 °C); 1H NMR (400 MHz, CDCl3) δ 7.80–7.68 (m,
191.1 (CO), 179.7 (C=C(OH)), 147.4 (CAr), 140.6 (CAr), 138.1 HAr, 8H), 7.57–7.41 (m, HAr, 12H), 3.97 (d, J = 14.3 Hz, CH2,
(CAr), 132.7 (CAr), 128.5 (CHAr), 128.3 (CHAr), 127.2 (CHAr), 4H); 13С NMR (100 MHz, CDCl3) δ 195.6 (CO), 132.2 (CHAr),
126.3 (CHAr), 125.6 (CHAr), 123.0 (CHAr), 110.5 (C=C(OH)), 131.2 (CAr), 130.9 (d, J = 10.6 Hz, CHAr,), 128.7 (CHAr, J =
36.8 (CH2), 31.6 (CH2), 29.9 (CH2).
12.7 Hz), 48.2 (d, J = 55.7, CH2, Hz); 31P NMR (CDCl3) δ
27.1.
2-[2-(1-Adamantyl)acetyl]-1-indanone (3c): Obtained from
1-adamantylacetic acid (1d, 194 mg, 1 mmol), 1-indanone (2a, The synthesis of pyrazoles 6. As an illustrative example, com-
132 mg, 1 mmol), TFAA (0.85 mL, 6 mmol) and TfOH (44 μL, pound 6a is prepared as follows. A solution of β-phenylpropi-
0.5 mmol) in 79% (240 mg) yield as a red solid. Mp 154 °C; onic acid (1a, 150 mg, 1 mmol) and TFAA (0.85 mL, 6 mmol)
1H NMR (400 MHz, CDCl3) keto-enol (2:98), enol tautomer: δ in 1 mL CH2Cl2 was stirred for 15 min at rt. Then TfOH
7.81 (d, J = 7.6 Hz, HAr, 1H), 7.52 (t, J = 7.4 Hz, HAr, 1H), (44 μL, 0.5 mmol) was added, and the reaction mixture was
7.46 (d, J = 7.5 Hz, HAr, 1H), 7.38 (t, J = 7.4 Hz, HAr, 1H), kept for 2 h. On completion of the reaction, the solvent was
3.58 (s, CH2Ind, 2H), 2.18 (s, CH2Ad, 2H), 1.98 (bs, CHAd, removed under reduced pressure. The crude 3a was dissolved in
3H,), 1.75–1.59 (m, CH2Ad, 12H); 13С NMR (100 MHz, 5 mL ethanol and heated under reflux with hydrazine hydrate
CDCl3) δ 193.6 (CO), 177.1 (C=C(OH)), 148.0 (CAr), 138.5 (0.1 mL, 2 mmol). After 2 h the solvent was evaporated, and the
(CAr), 132.9 (CHAr), 127.2 (CHAr), 125.6 (CHAr), 123.2 remaining oil was dissolved in CH2Cl2, washed with 5%
(CHAr), 111.7 (C=C(OH)), 48.6 (CH2Ad), 43.0 (CH2Ad), 36.7 NaHCO3, water, and dried over MgSO4. The product was puri-
(CH2Ad), 35.1 (CAd), 30.7 (CH2), 28.7 (CHAd); Anal. calcd for fied by means of column chromatography (SiO2 60, eluent:
C21H24O2: C, 81.78; H, 7.84; found: C, 82.23; H 7.67.
CH2Cl2/MeOH 50:1). Yield: 69% (90 mg), brown solid; mp
108–110 °С; 1H NMR (400 MHz, CDCl3) δ 7.71 (d, J = 7.2 Hz,
Typical procedure for the synthesis of heterocycles 4a,b: A HAr, 1H), 7.44 (d, J = 7.2 Hz, HAr, 1H), 7.40–7.17 (m, HAr,
solution of diketone 3u or 3v (1 mmol) in an ethanol (20 mL)/ 4H), 7.14 (d, J = 6.8 Hz, HAr, 2H), 3.42 (s, CH2, 2H), 3.04 (m,
water (4 mL)/HClconc (4 mL) mixture was heated under reflux CH2, 4H); 13С NMR (100 MHz, CDCl3) δ 148.7 (C), 140.8 (C),
for 6 h. After the reaction was completed (TLC control) the 137.9 (C), 134.7 (C), 128.5 (CH), 128.4 (CH), 126.4 (2CH),
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Crystallographic information for compound 4a.
[http://www.beilstein-journals.org/bjoc/content/
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Crystallographic information for compound 6b.
[http://www.beilstein-journals.org/bjoc/content/
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Acknowledgements
This investigation was supported by the Russian Foundation of
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