A simple nitration of electrophilic alkenes with tetranitromethane in the presence of triethylamine. Synthesis of functionalized β-nitroalkenes

Article abstract of DOI:10.1016/j.tetlet.2011.04.012

A convenient method for the preparation of functionalized β-nitroalkenes based on the nitration of α,α-di- and α,α,β-trisubstituted unsaturated aldehydes, ketones and esters with tetranitromethane in the presence of triethylamine is described. Series of s

Full text of DOI:10.1016/j.tetlet.2011.04.012

Tetrahedron Letters 52 (2011) 2910–2913
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A simple nitration of electrophilic alkenes with tetranitromethane in the
presence of triethylamine. Synthesis of functionalized b-nitroalkenes
Yulia A. Volkova a, Elena B. Averina a,b, , Yuri K. Grishin a, Victor B. Rybakov a, Tamara S. Kuznetsova a,b
,
⇑
Nikolai S. Zefirov a,b
a Lomonosov Moscow State University, Department of Chemistry, Leninskie Gory, 1-3, Moscow 119992, Russia
b IPhaC RAS, Severnyi Proezd, 1, Chernogolovka, Moscow Region 142432, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
A convenient method for the preparation of functionalized b-nitroalkenes based on the nitration of
a,a-
Received 14 February 2011
Revised 18 March 2011
Accepted 1 April 2011
Available online 9 April 2011
di- and ,b-trisubstituted unsaturated aldehydes, ketones and esters with tetranitromethane in the
a,a
presence of triethylamine is described. Series of substituted b-nitroalcohols and b-nitroalkenes are
obtained in good yields under mild conditions.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Tetranitromethane
Electrophilic alkenes
b-Nitroalcohols
b-Nitroalkenes
Functionalized nitroalkenes are a highly reactive and versatile
class of electron-poor alkenes that readily undergo conjugate addi-
tion reactions with nucleophiles1 and react as dienophiles in
Diels–Alder reactions.2 These processes may be used to assemble
molecules, including fragments of natural substances and biologi-
cally active compounds.2b,c,3 Also, nitroalkenes are known to be use-
ful precursors to diverse functionalized compounds. Nitroalkenes
may be reduced to provide oximes, hydroxylamines, imines, amines
and can also be converted into carbonyl compounds.3a,b,4 Conju-
gated nitroalkenes including functionalized examples are generally
prepared by nitration of the corresponding alkenes or by dehydra-
tion of nitroalcohols formed via the Henry reaction.3a,b,5 Fuming ni-
tric acid, dinitrogen tetraoxide, nitryl or nitrosyl chlorides, and
NaNO2 or AgNO2 in the presence of I2 have been employed for the
nitration of alkenes.3a,b,5 However, these methods have limitations
in view of their low regioselectivity or volatility of some reagents.
A more convenient method for the synthesis of nitroalkenes based
on the nitration of various alkenes with NaNO2–ceric ammonium ni-
trate has been reported.6
nitrates,8 respectively. This reagent has also been employed for
heterocyclization of mono- and ,b-disubstituted electrophilic al-
a
kenes under mild conditions affording difficult to access 3-nitrois-
oxazoles.9 In continuation of our investigations on the synthetic
potential of TNM–Et3N, we have found that
a,a-di- and a,a,b-tri-
substituted electrophilic alkenes can be nitrated to afford the
corresponding nitroalcohols and nitroalkenes.
A brief study to optimize the nitration conditions on methyl
methacrylate 1a as a model compound indicated that complete
conversion of the starting olefin into both nitration products
(nitroalcohol 2a and nitroalkene 3a) could be achieved by using
the alkene, TNM and Et3N in a 1:2.5:2 molar ratio, and heating
the reaction mixture in 1,4-dioxane at 70 °C (procedure A).10 If
the reagents were used in a 1:1:1 molar ratio, only b-nitroalcohol
2a was obtained in 64% yield. Conversion of nitroalcohols into
the corresponding nitroalkenes (procedure B)10 was performed
via their mesylates using a modified McMurry method.6c,11 We
noted that according to procedure A, b-nitroalkene 3a was ob-
tained preferably in E-configuration while dehydration of com-
pound 2a via its mesylate gave a mixture of E and Z-isomers in
nearly equal ratio. The stereochemistry of nitroalkene 3a was as-
signed unambiguously by the NOE enhancements only observed
for isomer Z-3a due to a dipolar interaction between the olefinic
C(3)H proton and the protons of C(2)Me group. The 13C NMR chem-
ical shifts confirmed the stereochemical assignments of the olefins.
The carbon atoms of the Me groups of E-isomers were more
Herein we report a novel synthetic approach to nitroalkenes via
direct nitration of electrophilic alkenes using tetranitromethane
(TNM) in the presence of triethylamine. Recently, we reported that
the TNM–Et3N system may be regarded as a specific and efficient
reagent which was used for the ring-opening of oxiranes and
N-tosylaziridines yielding b-hydroxy nitrates7 and b-tosylamino
shielded (ca. 4 ppm) due to the known steric
The above-mentioned conditions were successfully applied to a
variety of substituted ,b-unsaturated esters, aldehydes and
c
-effect.12
⇑
Corresponding author. Tel.: +7 495 9393969; fax: +7 495 9393969.
E-mail address: elaver@org.chem.msu.ru (E.B. Averina).
a
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.04.012

Y. A. Volkova et al. / Tetrahedron Letters 52 (2011) 2910–2913
2911
Table 1
Reactions of
a
,a
-di- and
a,
a
,b-trisubstituted electrophilic alkenes with TNM in the presence of triethylamine
COR3
R2
R1
R2
R1
COR3
OH
R1
TNM-Et3N
+
1,4-dioxane
(procedure A)
COR3
R2
O2N
O2N
1
2
3
MsCl/Et3N
(procedure B)
Entry
Alkene 1
R2
Nitroalcohol 2
Yield (A)a (%)
Nitroalkene 3
Yielda (%), E/Zb
R1
H
R3
37 (A), 10/1
75 (B), 1/1
CO2Me
OH
CO2Me
Me
a
b
c
d
e
f
Me
Me
Me
Me
Me
Me
OMe
38
40
40
36
O2N
O2N
O2N
O2N
O2N
Me
CO2Bu
OH
Me
CO2Bui
OH
Me
CO2( -Hex)
OH
Me
O2N
O2N
38 (A), 10/1
73 (B), 1/1
CO2Bu
H
H
H
H
H
OBu
Me
CO2Bui
35 (A), 4/1
76 (B), 1/1
OBui
O2N
O2N
O2N
Me
CO2( -Hex)
c
c
32 (A), 7/1
75 (B), 5/1
O(c-Hex)
O(CH2)2OH
O(CH2)2Cl
Me
CO2CH2CH2OH
OH
Me
CO2CH2CH2OH
c
—
22 (A), 1/0
Me
CO2CH2CH2Cl
CO2CH2CH2Cl
OH
Me
47
35 (A), 10/1
O2N
Ph
O2N
Ph
Me
CO2Me
OH
CO2Me
d
g
Ph
Me
OMe
Me
—
63d
O2N
Me
O2N
O2N
O2N
Me
h
(CH2)4
44
24
30 (A)
OH
O2N
O2N
COMe
CHO
COMe
20 (A)
64 (B)
i
(CH2)4
H
OH
CHO
a
Isolated yield after chromatographic purification. The synthetic procedure A or B10 is given in brackets.
The ratio of stereoisomers was determined by 1H NMR spectroscopy. Combined yield of both isomers.
Compound 2e was not identified from NMR spectra.
b
c
d
Reaction conditions: 1,4-dioxane/chlorobenzene = 1:1, 100 °C, 30 h, conversion of starting olefin was 80%. Compound 2g was not formed in the reaction. The configu-
ration of compound 3g cannot be defined by NMR spectra.
3
ketones to provide functionalized b-nitroalkenes with
a-carbonyl
The large values of the JHH coupling constants for the proton of
groups in good isolated yields (Table 1).10,13
the CHNO2 groups (11.5–12.6 Hz)10 show that the equilibrium for
We found that the reactions of unsaturated esters 1a–g with
TNM–Et3N, according to procedure A, resulted in the formation
of a mixture of b-nitroalkenes 3a–g, preferably in E-configuration,
along with the corresponding b-nitroalcohols 2a–d,f, which were
readily separated by column chromatography. Treatment of the
nitroalcohol with mesyl chloride followed by triethylamine led to
nitroalkenes 3 in E- and Z-configurations of different ratios. Nitra-
tion of a-methyl cinnamic ester 1g and ester 1e under conditions A
led to E-nitroalkenes 3g and 3e as the sole products in good yields
(Table 1).
The general character of this nitration reaction was demon-
strated for trisubstituted unsaturated ketone 1h and aldehyde 1i
(Table 1). The nitro alcohols 2h,i and alkenes 3h,i were obtained
in good yields. Cyclic nitroalcohols 2h and 2i were obtained as
mixtures of two stereoisomers in 5:1 and 3:1 ratios, respectively.
Figure 1. X-ray crystal structure of compound 2h (ORTEP-3).13

2912
Y. A. Volkova et al. / Tetrahedron Letters 52 (2011) 2910–2913
C(NO2)4
NO2 C(NO2)3
,
+ Et3N
Et N
Et3N·NO2
C(NO2)3
,
3
O
O
O
O
NO2
HNO2
+
2HNO2
NO2 + NO + H2O
COR3
R2
R1
R2
C(NO2)4
R1
R1
R2
COR3
R1
R2
COR3
NO2
Et3N
-H+
COR3
O2N
NO2 C(NO2)3
,
O2N
O2N
1
I
II
3
H2O
C(NO2)3
COR3
-HC(NO2)3
R1
R1
COR3
OH
ON=C(NO2)2
R2
O2N
R2
O2N
O
2
III
Scheme 1. Proposed reaction mechanism.
both isomers of compounds 2h and 2i was shifted to conformers
with the NO2-group in the equatorial position. The trans-diequato-
rial position of the nitro and carbonyl groups in minor isomer 2i
was confirmed by NOE measurements; this structural conforma-
tion was also established by X-ray analysis of minor isomer 2h (
Fig. 1).14
Supplementary data
Supplementary data (representative procedures and NMR spec-
tra of products) associated with this article can be found, in the on-
line version, at doi:10.1016/j.tetlet.2011.04.012.
The mechanism of this reaction requires further investigation,
however, we assume that nitration of the functionalized alkene
can proceed via formation of radicals. According to the literature15
and our previous investigations,7–9 the proposed mechanism for
this reaction is outlined in Scheme 1. It is likely that an NO2 radical,
formed upon a redox process with TNM,15 adds to the b-carbon of
the electrophilic alkene giving intermediate I which undergoes oxi-
dation by TNM to carbocation II. Due to the high stereoselectivity
during formation of the b-nitroalkene we assume that a trinitrom-
ethyl anion participated in O-alkylation of intermediate II affording
unstable nitronate III which underwent further transformation
into b-nitroalkene 3 via elimination of trinitromethane. The forma-
tion of 3 may also proceed through elimination of a proton from
intermediate II. Hydrolysis of carbocation II by water, generated
from the reaction of 1,4-dioxane with TNM,16 can lead to b-nitroal-
cohol 2.
To sum up, we have developed a preparative and efficient meth-
od for the synthesis of functionalized b-nitroalkenes which are of
potential synthetic and pharmacological interest. High regio- and
stereoselectivity, good yields of target products, the simplicity of
the procedure and readily available starting reagents are the main
advantages of this method making it an interesting alternative to
other syntheses of b-nitroalkenes.
References and notes
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Hermekenes, P. H. H.; Sliedregt, L. A. J. M.; Scheeren, H. W.; Futjes, F. P. J. T.
Tetrahedron 2009, 65, 5393–5401; (c) Martin, N. J. A.; Cheng, X.; List, B. J. Am.
Chem. Soc. 2008, 130, 13862–13863; (d) Swiderska, M. A.; Stewart, J. D. Org.
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5794–5795.
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V. V.; Lipina, E. S.; Berestovitskaya, V. M.; Efremov, D. A. In Nitroalkenes:
Conjugated Nitro Compounds; Feuer, H., Ed.; Wiley-VCH: Chichester, 1994; p
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Caution: Although we have not experienced any problems in han-
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Acknowledgements
7. Volkova, Yu. A.; Ivanova, O. A.; Budynina, E. M.; Averina, E. B.; Kuznetsova, T. S.;
Zefirov, N. S. Tetrahedron Lett. 2008, 49, 3935–3938.
8. Volkova, Yu. A.; Averina, E. B.; Kuznetsova, T. S.; Zefirov, N. S. Tetrahedron Lett.
2010, 51, 2254–2257.
9. Volkova, Yu. A.; Averina, E. B.; Grishin, Y. K.; Bruheim, P.; Kuznetsova, T. S.;
Zefirov, N. S. J. Org. Chem. 2010, 75, 3047–3052.
10. Procedure A: alkene nitration: Et3N (0.28 mL, 2 mmol) was added dropwise to a
solution of tetranitromethane (0.30 mL, 2.5 mmol) in 1,4-dioxane (2 mL) at
0 °C (ice bath). The mixture was stirred for 5 min after which the alkene
We thank the Division of Chemistry and Materials Science RAS
(Program N 4), the President’s grant ‘Support of Leading Scientific
School’ N 65546.2010.3 (academician N.S. Zefirov), and the Russian
Foundation for Basic Research (Project 11-03-01040-a) for finan-
cial support of this work. We thank Dr. Chizhov A.O. for HRMS
spectra which were recorded at the Department of Structural Stud-
ies of the Zelinsky Institute of Organic Chemistry, Moscow.

Y. A. Volkova et al. / Tetrahedron Letters 52 (2011) 2910–2913
2913
(1 mmol) was added in one portion. The mixture was stirred at 70 °C for 4 h.
TLC and NMR spectra were used to monitor the progress of the reaction. The
solvent was removed under reduced pressure and the product was isolated by
column chromatography (petroleum ether–EtOAc, 10:1).
12. Günther, H. NMR Spectroscopy. Basic Principles, Concepts, and Applications in
Chemistry; Feuer, H., 2nd ed.; Wiley-VCH: Chichester, 1995; p 503.
13. In attempts to apply the nitration procedure (NaNO2–ceric ammonium
nitrate)6c to compounds 1a,b,f we obtained mixtures of the corresponding 3-
nitro-2-hydroxy substituted esters and 3-nitro-2-nitrooxy substituted esters in
nearly equal ratios.
14. Two polymorphous modifications of the minor isomer of compound 2h were
obtained upon crystallization with monoclinic P21/n and triclinic P(-1) space
groups (CCDC-794925, CCDC-794926).
Procedure B: dehydration of nitroalcohols:6c To a stirred solution of nitroalcohol
(1 mmol) in dry CH2Cl2 (5 mL) was added dropwise MsCl (0.2 mL, 3 mmol) at
À20 °C. The mixture was stirred for 15 min and Et3N (0.4 mL, 3 mmol) was
added. The resulting mixture was warmed to room temperature over 1 h and
stirred for an additional 5 h. The mixture was quenched with ice-water and
extracted with CH2Cl2 (3 Â 5 mL), the combined organics washed with 5% HCl
(5 mL), brine (2 Â 5 mL) and H2O (5 mL), and dried over anhydrous MgSO4. The
solvent was removed under reduced pressure and the product was isolated by
column chromatography (petroleum ether–EtOAc, 4:1).
Crystal data: molecular formula C8H13NO4, Mr = 187.19.
Cell parameters a = 12.3220(12) Å, b = 5.7927(5) Å, c = 13.6791(13) Å,
b = 108.190(10)°, V = 927.59(15) Å3, Dc = 1.340 g  cmÀ3
,
Z = 4. Space group
a
monoclinic P21/n. Crystal size 0.2 Â 0.2 Â 0.2 mm,
l
Cu K = 0.913 mmÀ1. (b)
Spectral and analytical data of representative products:
Data
collection:
temperature
295(2) K,
hmax = 74.87°,
reflections
1-(1-Hydroxy-2-nitrocyclohexyl)ethanone (2h): Brown solid; mp 68 °C; Rf 0.10
(petroleum ether–EtOAc, 5:1); mixture of two isomers A:B = 5:1; 1H NMR
(400 MHz, CDCl3): d 1.27–1.41 (m, 2H+2H, c-Hex), 1.55–1.75 (m, 2H+2H, c-
Hex), 1.93–1.98 (m, 1H+1H, c-Hex), 2.14–2.17 (m, 1H+1H, c-Hex), 2.34 (s, 3H,
CH3, for isomer A), 2.36–2.40 (m, 1H+1H, c-Hex), 2.42 (s, 3H, CH3, for isomer B),
2.49–2.53 (m, 1H+1H, c-Hex), 4.07 (br s, 1H, OH, for isomer B), 4.33 (dd,
3J = 11.5, 5.5 Hz, 1H, CHNO2, for isomer A), 4.43 (br s, 1H, OH, for isomer A),
4.86 (dd, 3J = 12.4, 4.5 Hz, 1H, CHNO2, for isomer B); 13C NMR (100 MHz, CDCl3)
for isomer A: d 20.8, 23.8 (CH2, c-Hex), 25.3 (CH3), 27.8, 34.4 (CH2, c-Hex), 78.9
(C), 90.1 (CHNO2), 209.4 (CO); 13C NMR (100 MHz, CDCl3) for isomer B: d 19.4
(CH2, c-Hex), 23.7 (CH3), 23.9, 25.9, 34.4 (CH2, c-Hex), 79.1 (C), 86.5 (CHNO2),
measured = 1701. (c) Refinement: independent observed reflections with
I P2
r(I) = 1106, No. of parameters in L.S. = 119, R1 = 0.0444, wR2 = 0.0686.
Residual electron density (
Cell parameters a = 8.263(3) Å, b = 10.893(3) Å, c = 11.262(4) Å,
b = 110.34(2)°,
D
q)
max = 0.141 eÅÀ3, (
D
q
)
min = À0.164 eÅÀ3
.
a
= 101.04(2)°,
c
= 97.69(2)°, V = 910.5(6) Å3, Dc = 1.366 g  cmÀ3, Z = 4. Space
group triclinic P(À1). Crystal size 0.2 Â 0.2 Â 0.2 mm,
l .
Ag K = 0.067 mmÀ1
a
(b) Data collection: temperature 295(2) K, hmax = 22.97°, reflections
measured = 5148. (c) Refinement: independent observed reflections with
I P2
r(I) = 1780, No. of parameters in L.S. = 237, R1 = 0.0502, wR2 = 0.1203.
Residual electron density (
D
q)
max = 0.225 eÅÀ3, (
D
q
)
min = À0.195 eÅÀ3
.
15. (a) Altukhov, K. V.; Perekalin, V. V. Usp. Khim. 1976, 45, 2050. Chem. Abstr. 1977,
86, 71774s.; (b) Nielsen, A. T. In Nitrocarbons; Feuer, H., Ed.; Wiley-VCH: New
York, 1995; pp 6–66.
209.5 (CO); IR (film):
C, 51.33; H, 7.00; N, 7.48. Found: C, 51.15; H, 7.11; N, 8.00.
m
3480, 1740, 1570, 1360 cmÀ1; Anal. Calcd for C8H13NO4:
1-(2-Nitrocyclohex-1-enyl)ethanone (3h): Pale yellow liquid; Rf 0.21 (petroleum
ether–EtOAc, 5:1); 1H NMR (400 MHz, CDCl3): d 1.66–1.71 (m, 2H, c-Hex),
1.75–1.81 (m, 2H, c-Hex), 2.33 (s, 3H, CH3), 2.35–2.41 (m, 2H, c-Hex), 2.54–2.60
(m, 2H, c-Hex); 13C NMR (100 MHz, CDCl3): d 20.6 (CH2), 21.5 (CH2), 24.0 (CH2),
16. In the NMR spectra of the reaction mixtures of the alkenes with TNM-Et3N, we
observed signals which presumably can be attributed to monosubstituted 1,4-
dioxanes, unfortunately these could not be isolated due to their lability.
Analogous processes have been described in the literature,15b and in our
previous work using THF17 or 1,4-dioxane7,8 as solvents.
17. Volkova, Yu. A.; Ivanova, O. A.; Budynina, E. M.; Averina, E. B.; Kuznetsova, T. S.;
Zefirov, N. S. Izv. Akad. Nauk, Ser. Khim. 2008, 1999–2000; Volkova, Yu. Russ.
Chem. Bull. 2008, 57, 2034–2035.
27.5 (CH2), 28.1 (CH3), 143.6 (C), 147.5 (C), 202.4 (CO); IR (film):
m 3125, 1740,
1645, 1560, 1540, 1370 (s) cmÀ1; HRMS-ESI calcd for C8H12NO3 (M+H)+:
170.0812. Found: 170.0816.
11. Melton, J.; McMurry, J. E. J. Org. Chem. 1975, 40, 2138–2139.