Synthesis of β-(trifluoromethyl)furans and spiro-gem- dichlorocyclopropanes from cyclic 1,3-dicarbonyl compounds and α-(trihaloethylidene)nitroethanes

Article abstract of DOI:10.1016/j.tetlet.2013.05.129

While 1,3-dicarbonyl compounds react with (E)-1,1,1-trifluoro-3-nitrobut-2- ene in the presence of sodium acetate to produce the target β- (trifluoromethyl)furans, their reaction with (E)-1,1,1-trichloro-3-nitrobut-2- ene, under the same conditions, took an entirely different course and gave spiro-gem-dichlorocyclopropanes bearing a 1-nitroethyl moiety, with high diastereoselectivity and in good yields.

Full text of DOI:10.1016/j.tetlet.2013.05.129

Accepted Manuscript
Synthesis of β-(trifluoromethyl)furans and spiro-gem-dichlorocyclopropanes
from cyclic 1,3-dicarbonyl compounds and α-(trihaloethylidene)nitroethanes
Alexey Yu. Barkov, Vladislav Yu. Korotaev, Vyacheslav Ya. Sosnovskikh
PII:
S0040-4039(13)00920-9
DOI:
http://dx.doi.org/10.1016/j.tetlet.2013.05.129
TETL 43029
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
17 April 2013
13 May 2013
24 May 2013
Please cite this article as: Barkov, A.Y., Korotaev, V.Y., Sosnovskikh, V.Y., Synthesis of β-(trifluoromethyl)furans
and spiro-gem-dichlorocyclopropanes from cyclic 1,3-dicarbonyl compounds and α-
(trihaloethylidene)nitroethanes, Tetrahedron Letters (2013), doi: http://dx.doi.org/10.1016/j.tetlet.2013.05.129
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Graphical abstract
________________________________________________________________________________
Synthesis of β-(trifluoromethyl)furans and spiro-gem-dichlorocyclopropanes from cyclic 1,3-dicarbonyl
compounds and α-(trihaloethylidene)nitroethanes
Alexey Yu. Barkov, Vladislav Yu. Korotaev, Vyacheslav Ya. Sosnovskikh*
________________________________________________________________________________________________________________________
∗ Corresponding author. Fax: +7 343 261 59 78;
e-mail: vyacheslav.sosnovskikh@usu.ru

2
Synthesis of β-(trifluoromethyl)furans and spiro-gem-dichlorocyclopropanes
from cyclic 1,3-dicarbonyl compounds and α-(trihaloethylidene)nitroethanes
Alexey Yu. Barkov, Vladislav Yu. Korotaev, Vyacheslav Ya. Sosnovskikh*
Department of Chemistry, Ural Federal University, pr. Lenina 51, 620000 Ekaterinburg, Russia
ABSTRACT
While 1,3-dicarbonyl compounds react with (E)-1,1,1-trifluoro-3-nitrobut-2-ene in the presence of
sodium acetate to produce the target β-(trifluoromethyl)furans, their reaction with (E)-1,1,1-
trichloro-3-nitrobut-2-ene, under the same conditions, took an entirely different course and gave
spiro-gem-dichlorocyclopropanes bearing a 1-nitroethyl moiety, with high diastereoselectivity and
in good yields.
Keywords:
β-(Trifluoromethyl)furans;
α-(Trihaloethylidene)nitroethanes;
1,3-Dicarbonyl
compounds; Michael addition; Spiro-cyclopropanation.
Conjugated nitroolefins are widely used in organic synthesis due to the high electrophilicity of
the double bond.1 As a result, partially fluorinated nitroalkenes have attracted attention as excellent
building blocks for the preparation of various RF-containing compounds.2 In particular,
polyfluoroalkylated nitroalkenes react with enamines of cycloalkanones and methyl ketones to give
β-polyfluoroalkyl-γ-nitroketones,3 nitro alkylated enamines and 1,2-oxazine N-oxides,4 as well as 1-
pyrroline N-oxides.5 At the same time, very little information is available on the reactions of
trihalomethylated conjugated nitroalkenes with 1,3-dicarbonyl compounds. Only one paper is
known reporting the reaction of 3,3,3-trifluoro-1-nitropropene with 1,3-dicarbonyl compounds to
give the corresponding addition products.6 Recently, we reported that 1,1,1-trifluoro-3-nitrobut-2-
ene (1a) reacted with 1,3-diketones and primary aliphatic amines to give substituted β-
(trifluoromethyl)pyrroles via the Grob cyclization.7
On the other hand, it is well-known that β-diketones and β-ketoesters add to nitroalkenes to form
substituted dihydrofurans or furans depending on the number and nature of the substituents at the

3
nitroalkene double bond.8 In this furan synthesis, nitroalkenes are commonly employed because the
nitro group can act as both a powerful stabilizer of the intermediate anion and as a good leaving
group in the aromatization forming a furan ring. In the case of 1,1,1-trifluoro-3-nitrobut-2-ene (1a)
and 1,1,1-trichloro-3-nitrobut-2-ene (1b), it would be reasonable to assume the possibility of an
intramolecular Nef reaction occurring with formation of the β-(trihalomethyl)furan core. In this
context, and in connection with our interest in the development of CX3-nitroolefin (X = F, Cl)
chemistry,4,5,7 a method for the preparation of the β-(trihalomethyl)furan system based on the Nef
reaction, in a one-pot procedure, attracted our attention. The present communication describes the
dramatic effect of the trihalomethyl group on the pathway of the reactions between α-
(trihaloethylidene)nitroethanes 1a,b with 1,3-dicarbonyl compounds.
Although a number of methods have been developed for the construction of β-
(trifluoromethyl)furans,9 which are versatile intermediates in synthetic organic chemistry,10 their
simple and convenient synthesis still remains an attractive goal. Furthermore, benzofuran
derivatives bearing a trifluoromethyl group at the 3-position have, surprisingly, been poorly
investigated, probably due to the few methods available for their preparation.11
We found that the reaction of CF3-nitrobutene 1a with 1,3-cyclohexanedione, dimedone, or 5-
phenyl-1,3-cyclohexanedione
resulted
in
the
formation
of
2-methyl-3-
(trifluoromethyl)dihydrobenzo[b]furan-4-ones 2a–c. The procedure is simple and the products were
obtained in 41–67% yields, merely by standing a mixture of the reactants and NaOAc (as the base)
in ethanol at room temperature for seven days. A plausible pathway leading to the formation of
these compounds via intermediates A and B is outlined in Scheme 1. In a similar manner, reaction
with benzoylacetone gave an 83:17 mixture of isomeric furans 2d and 2'd in 41% yield. When ethyl
acetoacetate was allowed to react with nitrobutene 1a, compound 2e was obtained in 66% yield as a
single regioisomeric product. This approach represents a new synthesis of β-(trifluoromethyl)furans
and has advantages with regard to ease of operation and the ready availability of the starting
materials. However, Meldrum’s acid and its derivatives did not react with 1,1,1-trifluoro-3-nitrobut-

4
2-ene (1a) under the same conditions. We believe that this difference arises from the absence of the
enolic form of Meldrum’s acid in solution.12 In the 19F NMR spectra of furans 2a–e, the
5
trifluoromethyl group appeared as a quartet at δ 104.4–106.1 ppm (CDCl3, C6F6) with JF,H = 2.0–
2.4 Hz.
O
O
O
CF3 OH
N
F3C
Me
1a
NO2
O
R1
R2
R1
R2
Me
OH
NaOAc
OH
A
O
CF3
CF3
Me
Me
R1
R2
R1
R2
N
OH
-H2O,
-HNO
O
O
OH
B
2a: R1 = R2 = H (45%)
2b: R1 = R2 = Me (67%)
2c: R1 = H, R2 = Ph (50%)
O
O
O
CF3
Me
2d:2'd = 83:17 (41%)
CF3 EtO
Me
CF3
Me
Ph
Me
Me
Ph
Me
O
O
O
2e (66%)
Scheme 1. Reactions of CF3-nitroalkene 1a with 1,3-dicarbonyl compounds.
Next, and taking into account the above results, it was of interest to evaluate the behavior of
1,1,1-trichloro-3-nitrobut-2-ene (1b) in this reaction with cyclic 1,3-dicarbonyl compounds. In this
case, formation of the desired β-(trichloromethyl)furans 2', involving the enolic hydroxyl and the
aci-form, did not occur. As the reactions of the cyclic diketones, such as 1,3-cyclohexanedione and
dimedone, with nitroalkenes, having a good leaving group, usually afford tetrahydrocoumaran
derivatives,13 we envisaged that the reaction of 1b with these 1,3-diketones would produce
compounds 3. However, in contrast to the literature data, there was a marked difference in the
propensity towards ring-closure, and interesting results were obtained. Thus, when CCl3-nitrobutene
1b was allowed to react with 1,3-cyclohexanedione and dimedone under the conditions described
above, the reaction unexpectedly provided spirocyclopropanes 4a,b, which precipitated from the

5
ethanol solution as the sole products, with the stereochemistry as shown, instead of affording the
expected tetrahydrocoumarans 3. A similar reaction with 5-phenyl-1,3-cyclohexanedione gave a
mixture of trans-4c and cis-4'c isomers (Scheme 2). Their ratio (55:45) was easily determined by
1H NMR analysis.
O
O
O
CCl3
Me
Cl3C
Me
1b
NO2
X
R
R
R
R
NaOAc
O
O
2'
1b
-AcOH
AcO
Me
NO2
O
CCl3
Me
S*
R*
Cl
Cl
X
-Cl
R
NO2
R
R
O
O
R
A
3
-Cl
Me
Cl
Cl
H
O
S*
R*H
NO2
H
R
R
Cl
O
O
NO2
Me
S*
R*
Cl
H
O
R
R
4a: R = H (21%)
4b: R = Me (48%)
O
O
H
H
Cl
Cl
Cl
H
Ph
Ph
H
NO2
Me
NO2
Me
Cl
H
H
O
O
4c:4'c = 55:45 (51%)
Scheme 2. Reactions of CCl3-nitroalkene 1b with 1,3-cyclohexanediones.
In order to determine the scope of this reaction, we tested Meldrum’s acid under the same
reaction conditions. To our delight, replacement of 1,3-cyclohexanediones with Meldrum’s acid and
its 2-substituted derivatives resulted in direct and efficient cyclopropanation to give compounds 4d–
g in 28–88% yields (Figure 1).14 As expected, spirocyclopropane 4g was obtained as a mixture of
two geometric isomers in an 86:14 ratio, which was affected by steric factors. The structures of
1
compounds 4a–g were established by elemental analysis, and IR, Н, and 13C NMR spectroscopy.
1
In the H NMR spectra, protons H-2 and H-1' appeared as a doublet and a doublet of quartets at δ

6
3.30–3.55 and δ 5.25–5.42 ppm, respectively (3J = 10.5, 7.0 Hz). In addition, to determine the
relative configuration of these compounds, single crystal X-ray analysis of 4b, as a representative
example, was performed (Figure 2).15 The stereochemistry was assigned unambiguously as
(2R*,1'S*) and by analogy to the other spirocyclopropane derivatives.
O
4
5O
H
Me
Me
Cl
6
3
2
NO2
1
Cl
7O
Me
H 1'
8
2'
O
4d (88%)
O
O
O
O
O
O
O
O
H
H
Cl
Cl
Cl
Cl
NO2
Me
NO2
Me
H
H
4e (43%)
4f (58%)
O
O
O
O
H
H
Cl
Cl
Cl
t-Bu
Me
Me
t-Bu
NO2
Me
NO2
Me
O
O
Cl
H
H
O
O
4g:4'g = 84:16 (28%)
Figure 1. Products 4d–g prepared by cyclopropanation of various Meldrum’s acid derivatives.
Figure 2. X-ray crystal structure of 4b (ORTEP drawing, 50% probability level).
Thus, the reactions of cyclic 1,3-dicarbonyl compounds with CF3-nitroalkene 1a produced β-
(trifluoromethyl)furans 2, whereas similar reactions with CCl3-nitroalkene 1b, due to the good
leaving ability of the chlorine, lead to gem-dichlorocyclopropanes 4, and no furan or dihydrofuran

7
derivatives (e.g. 2' and 3). This result is of particular interest because all the important practical
methods of synthesizing gem-dichlorocyclopropanes consist of the addition of dichlorocarbene to
an appropriate alkene.16
The simplest explanation for this outcome is a Michael addition followed by cyclisation with
displacement of chloride from the trichloromethyl group. Such reactions are defined as Michael-
initiated ring closure (MIRC) reactions.17 The first step of the process involves the
diastereoselective formation18 of a new C–C bond in the key intermediate A generated via
nucleophilic addition with a concomitant [1,3]-H shift, in which the ambident enolate anion can
react with the CCl3 group producing a cyclic compound, which can be either a dihydrofuran 3 or a
cyclopropane 4, as a result of formal [3+2] or [1+2] cycloadditions, respectively. In our case, the
cyclization process leads to the stereoselective preparation of spiro-gem-dichlorocyclopropanes 4
with a 1-nitroethyl moiety on the cyclopropane ring, and proves that the enolate anion reacts with
the CCl3 group acting as a C-nucleophile (Scheme 2). To our knowledge, cyclopropanation based
on the reaction between a trichloromethyl group and an internal C-nucleophile has not been
described previously. As dihalocyclopropanes are very useful in organic synthesis16 this reaction is
noteworthy.
A methyl substituent at the α-position of CCl3-nitrobutene 1b appears to be a prerequisite for
cyclopropane formation and influences the course of the cyclization since the reaction of 3,3,3-
trichloro-1-nitropropene gave none of the desired products. It should also be noted that active
methylene compounds such as diethyl malonate, ethyl cyanoacetate, acetylacetone, and 1,3-
indanedione did not give positive results under the above experimental conditions. This indicates
that the presence of the 6-membered ring in the 1,3-dicarbonyl compounds is necessary for
nucleophilic attack at the CCl3 group.
In conclusion, we have shown, for the first time, that the reactions of α-
(trihaloethylidene)nitroethanes with 1,3-dicarbonyl compounds affords [3+2] or [1+2] cycloadducts
depending on the nature of the trihalomethyl group. In the case of CF3-nitrobutene 1a, a new

8
synthesis of β-(trifluoromethyl)furan derivatives was found, while reactions of CCl3-nitrobutene 1b
proceeded with participation of the trichloromethyl group to give spiro[2.5]octane-4,8-diones. The
ready accessibility of the starting materials, good yields, and simple manipulation make the
described methods for furan and spirocyclopropane syntheses very useful. Further studies on related
reactions are now in progress.
Acknowledgment
This work was supported financially by the Russian Foundation for Basic Research (Grant 11-
03-00126).
References and notes
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9
7. Korotaev, V. Y.; Barkov, A. Y.; Kotovich, I. V., Sosnovskikh, V. Y. J. Fluorine Chem. 2012, 138, 42.
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14. General procedure for the synthesis of compounds 2 and 4. To a solution of the corresponding 1,3-dione
(1.5 mmol) and NaOAc (0.12 g, 1.5 mmol) in EtOH (7.0 mL) was added CX3-nitrobutene 1a or 1b (1.5
mmol), and the resulting mixture stirred at room temperature for 7 d. The mixture was concentrated under
reduced pressure, chromatographed on silica gel (eluting with CHCl3), and the solid formed was
recrystallized from CH2Cl2–hexane (1:2) to give compounds 2 (colorless needles) or 4 (white powders).

10
2,6,6-Trimethyl-3-(trifluoromethyl)-6,7-dihydro-1-benzofuran-4(5H)-one (2b). Yield 0.25 g (67%), mp
1
90−91 °C. IR (KBr): 1681, 1628, 1595, 1463, 1363 cm–1; H NMR (400 MHz, CDCl3) δ 1.14 (s, 6H,
2Me), 2.39 (s, 2H, CH2), 2.44 (q, J = 2.3 Hz, 3H, Me), 2.71 (s, 2H, CH2); 19F NMR (471 MHz, CDCl3) δ
104.5 (q, J = 2.3 Hz, CF3); 13C NMR (126 MHz, CDCl3) δ 12.9, 28.4 (2Me), 34.9, 37.1, 52.4, 109.0 (q,
2JC,F = 38.4 Hz, C-3), 117.5 (C-3a), 122.4 (q, 1JC,F = 267.4 Hz, CF3), 153.7 (q, 3JC,F = 4.2 Hz, C-2), 165.2
(C-7a), 191.0 (C=O). Anal. Calcd for C12H13F3O2: С, 58.54; Н, 5.32. Found: С, 58.45; Н, 5.23.
2-Methyl-6-phenyl-3-(trifluoromethyl)-6,7-dihydro-1-benzofuran-4(5H)-one (2c). Yield 0.22 g (50%),
mp 85−86 °C. IR (KBr): 1690, 1631, 1593, 1457, 1351 cm–1; 1H NMR (400 MHz, CDCl3) δ 2.47 (q, J =
2.2 Hz, 3H, Me), 2.73−2.83 (m, 2H, CH2), 3.03 (dd, J = 17.2, 11.0 Hz, 1H, CHH), 3.15 (dd, J = 17.2, 5.1
Hz, 1H, CHH), 3.55 (m, 1H, CH), 7.23−7.40 (m, 5H, Ph); 19F NMR (471 MHz, CDCl3) δ 104.4 (q, J =
2.2 Hz, CF3); 13C NMR (126 MHz, CDCl3) δ 12.9 (q, 4JC,F = 1.1 Hz, Me), 31.0, 40.8, 45.3, 109.2 (q, 2JC,F
= 38.5 Hz, C-3), 118.5 (C-3a), 122.3 (q, 1JC,F = 267.5 Hz, CF3), 126.7, 127.4, 129.0, 142.0, 153.9 (q, 3JC,F
= 4.6 Hz, C-2), 165.3 (C-7a), 190.2 (C=O). Anal. Calcd for C16H13F3O2: С, 65.31; Н, 4.45. Found: С,
65.18; Н, 4.58.
(2R*)-1,1-Dichloro-6,6-dimethyl-2-[(1'S*)-1'-nitroethyl]spiro[2.5]octane-4,8-dione (4b). Yield 0.22 g
(48% in the presence of NaOH), mp 135−136 °C. IR (KBr) 1734, 1705, 1552, 1467, 1445, 1413, 1361
1
cm–1; H NMR (400 MHz, CDCl3) δ 1.00 (s, 3H, Me), 1.25 (s, 3H, Me), 1.84 (d, J = 7.0 Hz, 3H, Me),
2.62 (dd, J = 15.1, 2.3 Hz, 1H, He), 2.65 (d, J = 15.1 Hz, 1H, Ha), 2.69 (d, J = 15.1 Hz, 1H, Ha), 2.76 (dd,
J = 15.1, 2.3 Hz, 1H, He), 3.30 (d, J = 10.5 Hz, 1H, H-2), 5.26 (dq, J = 10.5, 7.0 Hz, 1H, H-1'); 13C NMR
(126 MHz, CDCl3) δ 20.5, 26.9, 30.1, 30.5, 38.7, 53.8, 53.9, 55.5, 63.3, 77.4, 196.4 (C=O), 199.6 (C=O).
Anal. Calcd for C12H15Cl2NO4: С, 46.77; Н, 4.91; N, 4.55. Found: С, 46.70; Н, 4.84; N, 4.44.
(2R*)-1,1-Dichloro-6,6-dimethyl-2-[(1'S*)-1'-nitroethyl]-5,7-dioxaspiro[2.5]octane-4,8-dione
(4d).
1
Yield 0.41 g (88%), mp 190−191 °C. IR (KBr) 1786, 1755, 1553, 1417, 1404, 1387, 1359 cm–1; H
NMR (400 MHz, CDCl3) δ 1.85 (s, 3H, Me), 1.91 (d, J = 7.1 Hz, 3H, Me), 1.93 (s, 3H, Me), 3.56 (d, J =
10.4 Hz, 1H, H-2), 5.42 (dq, J = 10.4, 7.1 Hz, 1H, H-1'); 13C NMR (126 MHz, CDCl3) δ 19.7, 27.67,
27.71, 41.7, 42.0, 64.8, 76.8, 106.4, 160.18 (C=O), 160.21 (C=O). Anal. Calcd for C10H11Cl2NO6: С,
38.48; Н, 3.55; N, 4.49. Found: С, 38.49; Н, 3.35; N, 4.49.
(2R*)-1,1-Dichloro-2-[(1'S*)-1'-nitroethyl]-5,12-dioxadispiro[2.2.5.2]tridecane-4,13-dione (4f). Yield
0.31 g (58%), mp 185−186 °C. IR (KBr): 1784, 1755, 1551, 1451, 1414, 1366 cm–1; 1H NMR (500 MHz,
CDCl3) δ 1.49−1.59 (m, 2H, CH2), 1.76 (quin, J = 6.0 Hz, 2H, CH2), 1.82 (quin, J = 6.0 Hz, 2H, CH2),
1.90 (d, J = 7.0 Hz, 3H, Me), 1.99−2.16 (m, 4H, 2CH2), 3.55 (d, J = 10.4 Hz, 1H, H-2), 5.42 (dq, J = 10.4,
7.0 Hz, 1H, H-1'); 13C NMR (126 MHz, CDCl3) δ 19.6, 21.6, 22.4, 23.8, 36.0, 37.0, 41.7, 42.2, 64.9, 76.8,
107.3, 160.1 (C=O), 160.2 (C=O). Anal. Calcd for C13H15Cl2NO6: С, 44.34; Н, 4.29; N, 3.98. Found: С,
44.43; Н, 4.11; N, 3.76.
15. X-Ray diffraction study of compound 4b. Diffraction data were collected at 295 K on an Xcalibur 3
automatic single-crystal diffractometer (graphite-monochromated MoKα radiation, ω-scan). The structure
was solved by direct methods and refined by the full-matrix least-squares method using the SHELX-97

11
program package.19 The H atoms were located geometrically using the riding model. Crystal data for 4b:
C12H15Cl2NO4, M = 308.15, triclinic crystals, space group P−1, a = 7.6112(9), b = 9.3563(10), c =
10.4839(5) Å, α = 98.561(8), β = 90.887(9), γ = 91.007(9)°, V = 738.03(12) Å3, Z = 2, ρcalcd = 1.387
g/cm3, μ = 0.448 mm–1, F(000) = 320. Crystallographic data for compound 4b (CCDC deposition number
934298) have been deposited at the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK.
16. (a) Fedoryński, M. Chem. Rev. 2003, 103, 1099; (b) Wong, H. N. C.; Hon, M.-Y.; Tse, C.-W.; Yip, Y.-C.;
Tanko, J.; Hudlicky, T. Chem. Rev. 1989, 89, 165.
17. (a) Lebel, H.; Marcoux, J.-F.; Molinaro, C.; Charette, A. B. Chem. Rev. 2003, 103, 977; (b) Maghsoodlou,
M. T.; Khorassani, S. M. H.; Heydari, R.; Charati, F. R.; Hazeri, N.; Lashkari, M.; Rostamizadeh, M.;
Marandi, G.; Sobolev, A.; Makha, M. Tetrahedron Lett. 2009, 50, 4439.
18. Barkov, A. Y.; Korotaev, V. Y.; Slepukhin, P. A.; Kodess, M. I.; Sosnovskikh, V. Y. Izv. Akad. Nauk Ser.
Khim. 2012, 1548.
19. Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.