Detrifluoroacetylation of 4,4,4-trifluoro-3,3-dihydroxy-2-(hydroxyimino)butan-1-ones as a convenient synthetic strategy for acyl cyanides Dedicated to Academician Valery N. Charushin on his 65th birthday.

Article abstract of DOI:10.1016/j.jfluchem.2016.04.009

A reaction reinvestigation of fluorinated 1,3-dicarbonyl compounds with NaNO₂ in acidic conditions revealed the formation of corresponding 1,1,1-trifluoro-3-hydroxyimino-butan-2,4-diones which predominantly isolated as hydrates. A novel synthesis of ethoxy-, alkyl-, (het)aryl substituted carbonylcyanides via acid-catalyzed detrifluoroacetylation of obtained 2-hydroxyimino derivatives of 1,3-dicarbonyl compounds was described.

Full text of DOI:10.1016/j.jfluchem.2016.04.009

Journal of Fluorine Chemistry 186 (2016) 28–32
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Detrifluoroacetylation of 4,4,4-trifluoro-3,3-dihydroxy-2-
(hydroxyimino)butan-1-ones as a convenient synthetic strategy for
acyl cyanides
*
Denis N. Bazhin , Yulia S. Kudyakova, Natalia A. Nemytova, Yanina V. Burgart,
Victor I. Saloutin
Postovsky Institute of Organic Synthesis, the Ural Branch of the Russian Academy of Sciences, 22 S. Kovalevskoy Str., 620990, Ekaterinburg, Russian Federation
A R T I C L E I N F O
A B S T R A C T
Article history:
A reaction reinvestigation of fluorinated 1,3-dicarbonyl compounds with NaNO2 in acidic conditions
revealed the formation of corresponding 1,1,1-trifluoro-3-hydroxyimino-butan-2,4-diones which
Received 16 March 2016
Received in revised form 12 April 2016
Accepted 14 April 2016
predominantly isolated as hydrates.
A novel synthesis of ethoxy-, alkyl-, (het)aryl substituted
Available online 16 April 2016
carbonylcyanides via acid-catalyzed detrifluoroacetylation of obtained 2-hydroxyimino derivatives of
1,3-dicarbonyl compounds was described.
Dedicated to Academician Valery N. Char-
ushin on his 65th birthday.
ã 2016 Elsevier B.V. All rights reserved.
Keywords:
Detrifluoroacetylation
1,3-Dicarbonyl compounds
NaNO2
Carbonylcyanides
1. Introduction
a-amino esters and a-aminoketones [4d]. The base or nucleophile
action on the trifluoroacetyl derivatives resulting in CF3C(O) group
elimination is one of the main features in most cases thus far
studied.
Trifluoroacetyl group is one of widely used functionalities in
organic synthesis and plays a significant role in the construction of
fluorinated building blocks, such as enones, 1,3-diketones,
heterocyclic derivatives [1]. The electron-withdrawing properties
of CF3 group enhanced the electrophilicity of carbonyl carbon atom
thereby promoting the nucleophilic attack by different N,O,C-
reagents [2]. In contrast to nonfluorinated analogs, the ability of
the trifluoromethyl group to stabilize acetals, hydrates or aminals
is well known for trifluoroacetyl derivatives [3].
The loss of the CF3C(O) moiety is usually an unexpected result
which is rarely reported in the literature [1b,4]. Recently, much
attention has been devoted to detrifluoroacetylation approaches of
some 1,1,1-trifluoro-2,4-dione derivatives. Applications of this
methodology as a convenient route to in situ difluoro(fluoro)
enolate generation for reactions with different electrophiles have
been reviewed [1b] (Fig. 1). The elimination of the trifluoroacetyl
group after functionalization of 1,1,1-trifluoro-2,4-diones has been
Among fluorinated 2-functionalized 1,3-dicarbonyl com-
pounds, 2-hydroxyimino derivatives 2 are less studied (Fig. 1)
[5]. To the best of our knowledge, only a few reports have been
described applications of such derivatives in pyrazoles, [5b–f]
benzodiazepines [5e,f] and aminoacids [5g] preparation. In most
cases hydroxyimino derivatives 2 have been used without isolation
as in situ prepared intermediates. From this point, their applica-
tions are still limited. It has been mentioned, that some of 2 could
not be isolated from the reaction mixture probably due to their low
stability [5a,f]. For almost two last decades, only two examples of
trifluorinated hydroxyimino derivatives 2 were characterized by IR
and 1H NMR spectra [5f,g].
Hence, our motivation in this work was to explore the
peculiarities of trifluorinated 2-hydroxyimino-1,3-dicarbonyl
compound preparation and their isolation in pure form, which
would provide the opportunities for broad investigation of their
properties and applications. Herein, we wish to report on acid-
catalyzed detrifluoroacetylation of 4,4,4-trifluoro-3,3-dihydroxy-
2-(hydroxyimino)butan-1-ones to yield carbonylcyanides under
mild conditions.
used in the synthesis of hardly available
a,b-unsaturated ketones
[4a], -nitroketones [4b], -diazoketones [4c], N-substituted
g
a
* Corresponding author.
E-mail address: dnbazhin@gmail.com (D.N. Bazhin).
http://dx.doi.org/10.1016/j.jfluchem.2016.04.009
0022-1139/ã 2016 Elsevier B.V. All rights reserved.

D.N. Bazhin et al. / Journal of Fluorine Chemistry 186 (2016) 28–32
29
in case of the gram scale preparation of 3, GC–MS analysis of the
reaction mixture revealed the formation of non-fluorinated by-
products (5–10%) as acyl nitriles and their derivatives. To facilitate
the product 3 purification and avoid detrifluoroacetylation process
caused by acetic acid we attempted to apply acid with low
solubility in organic media.
The use of citric acid (2 equiv) in the reaction of 1,3-dicarbonyl
compounds (1 equiv) with NaNO2 (1.2 equiv) allowed us to avoid
neutralization step due to the high solubility of this organic acid in
water. As a result, the yields of isolated products have increased
and reaction wastes reduced (Table 1). It should be noted that
detrifluoroacetylative products were not observed in the reaction
mixtures under such conditions (according to GC–MS analysis).
The developed synthesis is reproducible and scalable to allow the
target compounds to be easily prepared in gram quantities (up to
5 g of compounds at one synthesis run).
The NMR spectra of obtained compounds confirmed that these
products exist predominantly as 4,4,4-trifluoro-3,3-dihydroxy-2-
(hydroxyimino)butan-1-ones (3a–h). A characteristic feature of
their 1H NMR spectra (DMSO-d6) is the appearance of the 2 singlets
at d 11.70–12.08 and 6.4–7.78 ppm for NOH and CF3C(OH)2 protons,
respectively. In the 19F NMR spectra of 3a–h the signal of CF3 group
attached to the sp3-hybridized carbon atom is exhibited as the
singlet at dF from À82.7 to À81.7 ppm. In the 13C NMR spectra of
Fig. 1. The examples of 3-functionalized 1,1,1-trifluorobutan-2,4-diones.
2
3a–h the CF3-C was identified by spin-spin coupling constant
2. Results and discussion
JCF ꢁ 37 Hz. This quartet is appeared at dC ꢁ 92 ppm. The signals of
diketo form (2g,h) in NMR spectra are up-shielded in contrast to
that of hydrate forms (3g,h). Dehydrated form 2g,h has been easily
identified by the presence of signals at dF from À71.6 to À71.5 ppm
in the 19F NMR spectra.
We commenced our study with the nitrozation of trifluorinated
1,3-diketones 1a–k with NaNO2 in aqueous AcOH accordingly to
our previous study. In contrast to non-fluorinated analogs the
formation of hydrates 3a–h of expected 2-hydroxyimino-1,3-
diketones 2 was observed (checked by reaction mixture 19F NMR
spectra monitoring) (Scheme 1). In case of trifluoroacetoacetone
hydrate 3k was identified by 19F NMR spectra of reaction mixture
but all attempts of the product 3k isolation were failed.
The products 3a–h are white solids, insoluble in chloroform,
stable at store for months at ambient conditions. However, to
achieve a complete removal of solvent under products 3g,h
isolation the vacuum evaporation on a water bath at 60 ꢀC was
required. It resulted in a partial dehydration of obtained products
3g,h and formation of a mixture containing diketo form 2g,h in
addition to target compounds 3g,h (see Table 1).
Next, we focused on the preparation of acyl cyanides 4 from
obtained hydroxyimino derivatives 3. We found that the reaction
of compounds 3a–h with acetic anhydride in CHCl3 under reflux
gave corresponding carbonylcyanides 4a–d,f–h in moderate yields
(Table 2,Scheme 2). For compound 3e only the mixture of
decomposition products was obtained. This reaction proceeded
with clear solution formation after heating of the starting
suspension for 10–15 min. Further product isolation by column
chromatography or distillation was required because of by-
products formation derived from reactive acyl cyanides 4a–d,f–
h (checked by GC–MS analysis and 1H NMR data). We also found
that the acetic acid action on compounds 3a-h resulted in acyl
cyanides 4a–d,f–h in good yields.
It is important to note that this simple procedure represents a
convenient synthetic approach to acyl nitriles that are versatile
multifunctional intermediates [6]. The classical methods of acyl
cyanides synthesis usually require the metal cyanides use at a high
reaction temperature while the alternative ways mostly involve
the several steps, including cyanosilylation, cyanohydrin forma-
tion, and oxidation [7]. However, the process described here does
not require the use of hazardous chemicals or harsh reaction
conditions. Furthermore, the detrifluoroacetylation occurs in the
absence of common bases that are usually employed for the
trifluoroacetic group elimination.
It should be mentioned that the traces of acetic acid in isolated
products were identified even after several neutralization steps.
Acidic impurities can result in by-products formation under the
further transformations of 3 as starting compounds. For example,
We can assume that the proposed mechanism is realized via
either acylation or protonation of hydroxyimino moiety of 3 with
the formation of intermediates A or B respectively (Scheme 2). It
should be noted that acylation of non-fluorinated 2-hydroxyimino
analogs of 2 proceeds smoothly under the same conditions [8].
In case of compounds 3, the formation of A or B resulted in
the elimination of trifluoroacetic and acetic acids to yield
compounds 4.
In conclusion,
a practical approach for 2-hydroxyimino
derivatives of trifluorinated 1,3-dicarbonyl compounds was
elaborated. Detrifluoroacetylation of products obtained was
demonstrated to be an acid-catalyzed process. Another possible
Scheme 1. The nitrozation of trifluorinated 1,3-diketones.

30
D.N. Bazhin et al. / Journal of Fluorine Chemistry 186 (2016) 28–32
Table 1
Scope of 4,4,4-trifluoro-3,3-dihydroxy-2-(hydroxyimino)butan-1-ones 3.
Entry
1
Dicarbonyl
compound
R
Reaction
Yieldb, %
Ratio of 3:2
Mp, ꢀC
conditionsa
1a
AcOH/H2O
Citric acid/H2O
55
84
100:0
100:0
83–84
2
1b
AcOH/H2O
Citric acid/H2O
49
78
100:0
100:0
86–87
3
4
1c
AcOH/H2O
Citric acid/H2O
52
87
100:0
100:0
87–88
90–91
1d
AcOH/H2O
Citric acid/H2O
51
85
100:0
100:0
5
6
7
1e
1f
1g
CF3
OEt
Citric acid/H2O
Citric acid/H2O
Citric acid/H2O
71
100:0
100:0
10:6
30–31
32–33
149–150
78
84c
8
1h
1k
Citric acid/H2O
89c
20:7
180–181
9
Me
AcOH/H2O
Citric acid/H2O
0
0
a
Reaction conditions: dicarbonyl compound 1a–k (30 mmol), NaNO2 (2.48 g, 36 mmol), acid (60 mmol), H2O (20 ml), r.t.
Yields of isolated products.
Overall yield for a mixture of 2 and 3.
b
c
applications of obtained 2-hydroxyimino derivatives of trifluori-
nated 1,3-diketones are underway now in our laboratory.
water was added. Reaction mixture was stirred for 1 h. Then
obtained solution was extracted with Et2O (2 Â 20 ml) and the
organic fractions were dried over MgSO4 and concentrated under
vacuum to afford hydroxyimino derivatives 3a–h, 2 g,h.
3. Experimental part
All reagents and solvents are commercially available and were
used without further purification. The 1H (500 MHz), 19F
(470 MHz), 13C (125 MHz) NMR spectra were recorded on a Bruker
AVANCE-500 spectrometer with TMS and C6F6 as internal stand-
ards. 19F chemical shifts have been reported relative to CFCl3 as an
external standard. Melting points were obtained on a Stuart
SMP3 apparatus in open capillaries. Reactions were monitored by
thin layer chromatography (TLC) with 0.20 mm Alugram Sil G/
UV254 pre-coated silica gel plates (60 F254). GC–MS analysis was
carried out by using Agilent GC 7890A MS 5975C Inert XL EI/CI GC–
MS spectrometer with a quadrupole mass-spectrometric detector
with electron ionization (70 eV) and scan over the total ionic
current in the range m/z = 20–1000 and a quartz capillary column
HP-5MS (30 m–0.25 mm, film thickness 0.25 mm).
3.2. 4,4,4-Trifluoro-3,3-dihydroxy-2-(hydroxyimino)-1-phenylbutan-
1-one (3a)
1H NMR (500 MHz, DMSO-d6):
d= 7.55 (m, 2H, Ph), 7.66 (m, 1H,
Ph), 7.87 (m, 2H, Ph), 7.88 (s, 2H, 2 OH), 11.86 (s, 1H, NOH) ppm. 19
F
NMR (470 MHz, DMSO-d6):
(125 MHz, DMSO-d6):
d
= À81.8 (s, CF3) ppm. 13C NMR
d
= 91.63 (q, CF3, J = 32 Hz), 122.66 (q,
J = 290 Hz), 128.69, 128.98, 133.87, 135.06, 154.18, 192.26 ppm. MS
(EI) m/z 244.90 [M-H2O]+.
3.3. 6,6,6-Trifluoro-5,5-dihydroxy-4-(hydroxyimino)-2,2-
dimethylhexan-3-one (3b)
1H NMR (500 MHz, DMSO-d6):
d= 1.12 (s, 9H, 3 Me), 7.78 (s, 2H,
2 OH), 11.74 (s, 1H, NOH) ppm. 19F NMR (470 MHz, DMSO-d6):
d
3.1. General method of the nitrozation of 1,3-dicarbonyl compounds
= À81.6 (s, CF3) ppm. 13C NMR (125 MHz, DMSO-d6):
d= 25.93,
42.27, 91.07 (q, CF3, J = 34 Hz), 122.67 (q, J = 290 Hz), 155.84,
To a mixture of 1a–k (20 mmol) and citric acid (40 mmol) in
10 ml of water sodium nitrite 1.65 g (24 mmol) dissolved in 8 ml of
210.27 ppm. MS (EI) m/z 225.56 [M-H2O]+.

D.N. Bazhin et al. / Journal of Fluorine Chemistry 186 (2016) 28–32
31
Table 2
J = 288 Hz), 128.80, 135.68, 136.25, 142.48, 153.64, 183.95 ppm.
MS (EI) m/z 250.87 [M-H2O]+.
Scope of carbonylcyanides 4 via detrifluoroacetylation of compounds 3.
Entry
1
Starting
compound
R
Reaction
Yield of 4b,
%
conditionsa
3.5. 1-(2,4-Dimethylphenyl)-4,4,4-trifluoro-3,3-dihydroxy-2-
(hydroxyimino)butan-1-one (3d)
3a
Ac2O
AcOH
85
79
1H NMR (500 MHz, DMSO-d6):
Me), 7.14 (m, 2H, Ph), 7.66 (m,1H, Ph), 7.78 (s, 2H, 2 OH),11.70 (s,1H,
NOH) ppm. 19F NMR (470 MHz, DMSO-d6):
= À81.8 (s, CF3) ppm.
13C NMR (125 MHz, DMSO-d6):
= 21.01, 21.28, 91.49 (q, CF3,
d= 2.33 (s, 3H, Me), 2.49 (s, 3H,
d
2
3b
Ac2O
AcOH
55
44
d
J = 32 Hz), 122.67 (q, J = 289 Hz), 126.52, 131.40, 132.40, 132.44,
133.31, 138.92, 142.96, 155.12 ppm. MS (EI) m/z 272.94 [M-H2O]+.
3.6. 1,1,1,5,5,5-Hexafluoro-4,4-dihydroxy-3-(hydroxyimino)pentan-2-
one (3e)
3
4
3c
Ac2O
AcOH
76
63
1H NMR (500 MHz, DMSO-d6):
d= 8.45 (s, 2H, 2 OH), 12.95 (s,
1H, NOH) ppm. 19F NMR (470 MHz, DMSO-d6):
d
= À82.7 (s, CF3),
À77.2 (s, CF3) ppm. MS (EI) m/z 236.86 [M-H2O]+.
3d
Ac2O
AcOH
81
75
3.7. Ethyl 4,4,4-trifluoro-3,3-dihydroxy-2-(hydroxyimino)butanoate
(3f)
1H NMR (500 MHz, DMSO-d6):
(q, 2H, CH2, J = 7 Hz), 7.85 (s, 2H, 2 OH), 12.08 (s, 1H, NOH) ppm. 19
F
d= 1.22 (t, 3H, Me, J = 7 Hz), 4.20
5
6
7
3e
CF3
OEt
Ac2O
AcOH
Ac2O
AcOH
Ac2O
AcOH
0
0
48
42
78
71
NMR (470 MHz, DMSO-d6):
d
= À82.3 (s, CF3) ppm. MS (EI) m/z
3f
212.93 [M-H2O]+.
3g (+2g)
3.8. 4,4,4-Trifluoro-1-(furan-2-yl)-3,3-dihydroxy-2-(hydroxyimino)
butan-1-one (3g)
1H NMR (500 MHz, DMSO-d6):
Ar), 7.84 (s, 2H, 2 OH), 8.04 (m, 1H, Ar), 11.95 (s, 1H, NOH) ppm. 19
NMR (470 MHz, DMSO-d6):
= À82.0 (s, CF3) ppm.
d= 6.75 (m, 1H, Ar), 7.34 (m, 1H,
8
3h (+2h)
Ac2O
AcOH
79
72
F
d
3.9. 4,4,4-Trifluoro-1-(furan-2-yl)-2-(hydroxyimino)butan-1,3-dione
(2g)
a
Reaction conditions: 3a–h (20 mmol), acidic reagent (20 mmol), CHCl3, reflux.
Yields of isolated products.
b
1H NMR (500 MHz, DMSO-d6):
Ar), 8.17 (m, 1H, Ar), 14.52 (s, 1H, NOH) ppm. 19F NMR (470 MHz,
DMSO-d6):
= À71.6 (s, CF3) ppm.
d= 6.83 (m, 1H, Ar), 7.58 (m, 1H,
d
OAc
N
3.10. 4,4,4-Trifluoro-3,3-dihydroxy-2-(hydroxyimino)-1-(pyridin-4-
yl)butan-1-one (3h)
i
F3C
R
OH
O
N
N
HO OH
R
O
1H NMR (500 MHz, DMSO-d6):
2 OH), 8.86 (m, 2H, Ar), 12.13 (s, 1H, NOH) ppm. 19F NMR (470 MHz,
DMSO-d6):
= À82.1 (s, CF3) ppm.
d= 7.75 (m, 2H, Ar), 8.07 (s, 2H,
F3C
R
A
H
O+
O
HO OH
d
ii
N
H
4a-d,f-h, 42-85%
3a-h
F3C
R
3.11. 4,4,4-Trifluoro-2-(hydroxyimino)-1-(pyridin-4-yl)butan-1,3-
dione (2h)
HO OH
O
B
1H NMR (500 MHz, DMSO-d6):
Ar), 14.66 (s, 1H, NOH) ppm. 19F NMR (470 MHz, DMSO-d6):
= À71.6 (s, CF3) ppm.
d= 7.78 (m, 2H, Ar), 8.92 (m, 2H,
i : Ac2O (1 eq), CHCl3, reflux; ii: AcOH (1 eq), CHCl3, reflux.
d
Scheme 2. Detrifluoroacetylation of 4,4,4-trifluoro-3,3-dihydroxy-2-(hydroxyi-
mino)butan-1-ones.
3.12. Acyl nitriles 4 (general procedure)
Compound 3 (20 mmol) and Ac2O (20 mmol) in 20 ml of CHCl3
was refluxed for 1 h. Then 25 mL of water was added to quench the
reaction. Organic layer was washed with brine and dried over
anhydrous MgSO4. After removal of the solvent under reduced
pressure the residue was purified by column chromatography on
silica gel (eluent CHCl3/hexane = 3:1). Spectral data (1H NMR
spectra) and physico-chemical properties (mp or bp) were in
accordance with the literature [7].
3.4. 4,4,4-Trifluoro-3,3-dihydroxy-2-(hydroxyimino)-1-(thien-2-yl)
butan-1-one (3c)
1H NMR (500 MHz, DMSO-d6):
d= 7.28 (m, 1H, Ar), 7.77 (m, 1H,
Ar), 7.89 (s, 2H, 2 OH), 8.07 (m, 1H, Ar), 11.95 (s, 1H, NOH) ppm. 19
F
NMR (470 MHz, DMSO-d6):
(125 MHz, DMSO-d6):
d
= À81.9 (s, CF3) ppm. 13C NMR
d
= 91.49 (q, CF3, J = 32 Hz), 122.62 (q,

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D.N. Bazhin et al. / Journal of Fluorine Chemistry 186 (2016) 28–32
Slepukhin, M.L. Isenov, V.I. Saloutin, V.N. Charushin, Eur. J. Org. Chem. (2015)
Acknowledgments
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