SRN1 reactions in the nitrobenzo[1,3]dioxole series

Article abstract of DOI:10.1023/B:COHC.0000003513.53760.fb

5-Chloromethyl-6-nitrobenzo[1,3]dioxole has been shown to react with 2-nitropropane anion to give C-alkylation by an S_RN1 mechanism. The reaction was extended to various aliphatic, cyclic, and heterocyclic nitronate anions, leading to a new series of nitrobenzo[1,3]dioxole derivatives.

Full text of DOI:10.1023/B:COHC.0000003513.53760.fb

Chemistry of Heterocyclic Compounds, Vol. 39, No. 8, 2003
S
RN1 REACTIONS IN THE NITRO-
BENZO[1,3]DIOXOLE SERIES
J. Meuche-Albeny, P. Rathelot, M. P. Crozet, and P. Vanelle
5-Chloromethyl-6-nitrobenzo[1,3]dioxole has been shown to react with 2-nitropropane anion to give
C-alkylation by an SRN1 mechanism. The reaction was extended to various aliphatic, cyclic, and
heterocyclic nitronate anions, leading to a new series of nitrobenzo[1,3]dioxole derivatives.
Keywords: nitrobenzo[1,3]dioxole, nitronate anion, C-alkylation, SRN1 reaction.
SRN1 reactions have been studied extensively on aza- and thiaheterocycles [1-7]. Works relating the
reactivity with such a mechanism on O-heterocycles are rarer. In the nitrofuran series, while the C-alkylation of
2-chloromethyl-5-nitrofuran has been well known since 1951 [8], it was only proved to succeed via an SRN1
mechanism in 1980 [9]. Then, Beadle and Bowman published a complete study on the reactivity of the
2-nitropropane anion with various 2-substituted 5-nitrofuran derivatives [10].
This work presents the reactivity of 5-chloromethyl-6-nitrobenzo[1,3]dioxole (1) with various nitronate
anions.
The target compound 1 was easily prepared in one step from the 6-nitropiperonyl alcohol.
Scheme 1
NO2
OH
O
O
NO2
Cl
SOCl2
O
O
CH2Cl2, Et3N
1
96%
In order to study the reactivity of 1 with 2-nitropropane anion (2a), various operating conditions were
used as shown in Table 1. The reaction led to several compounds in yields which depended on experimental
conditions.
The C-alkylation of 1 was sensitive to the solvent, and the yields of C-alkylated products 3a and 4a were
higher when an aprotic solvent was used (DMF, DMSO). These results were in complete agreement with the
works of Bowman [11] and Russell [12]. The best yields were observed with DMSO as solvent (entries 6-11) in
Kornblum conditions [13]. Most of the published works have reported that an anion excess led to higher yields
in C-alkylated compounds [5, 14]. In this series, an anion excess enhanced yields of 3a + 4a either in DMF
(entry 2 versus entry 1) or DMSO (entry 7 versus entry 6) up to more than 90% excess for 3 equivalents of
anion 2a (entries 7 and 8). Above such an excess, the yields decreased (entries 9-11). The ethylenic compound
4a was formed via the C-alkylated product 3a by base-promoted nitrous acid elimination. Even if such an
elimination reaction can occur spontaneously in the reaction mixture, in the benzo[1,3]dioxole series it only
occurred after a 120 h reaction time (entry 8).
__________________________________________________________________________________________
Laboratoire de Chimie Organique, UMR CNRS 6517, Faculte de Pharmacie, 13385 Marseille, France;
e-mail: patrice.vanelle@pharmacie.univ-mrs.fr. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 8,
pp. 1139-1147, August, 2003. Original article submitted July 25, 2002.
0009-3122/03/3908-0989$25.00©2003 Plenum Publishing Corporation
989

Scheme 2
Me
Me
+
NO2
M –
NO2
Me
O
+
1
2a
O
Me
NO2
3a
NO2
NO2
NO2
O
O
O
O
O
O
+
+
+
Me
Me
CHO
O
O
4a
5
O2N
6
Investigation of the mechanism of the reaction requires the use of classical inhibitors [15]. The best
operating conditions (entry 7) were used to perform the inhibition experiments (entries 12-20). The results
reported in Table 1 show that the C-alkylation rate strongly decreased while the formation of 6-nitropiperonal 5,
the product of the competitive O-alkylation reaction due to the ambident character of 2a, was increased. The
formation of a side product, the 1,2-bis[(6-nitrobenzo[1,3]dioxol-5-yl)ethylene] (6), was observed (entries 16
and 17). A similar compound was observed in nitrothiophene [16] and in the nitrothiazole [17] series. Two
possible mechanisms were suggested to explain the formation of 6. In the first one, the carbanion obtained by
reduction of the intermediate radical could react with the 6-nitropiperonal 5; the resulting alcohol may be
dehydrated into the alkene 6.
Scheme 3
NO2
NO2
O
O
O
O
5
– H2O
O
_
6
CH2
HO
O
O2N
In the second one, the carbanion resulting from attack of the anion 2a (as a base) on the chloride 1 could
react with 1 leading to 6 after dehydrohalogenation of the intermediate condensation product.
Scheme 4
NO2
NO2
O
O
O
O
– HCl
1
6
_
CHCl
O
O
Cl
O2N
Thus, using the same operating conditions except to replace 2a by a stronger base, we obtained 6 in 60%
yield and 6-nitropiperonylalcohol (7) simultaneously.
990

TABLE 1. Influence of Experimental Conditions in the Reaction of Compound 1 with 2a*
Yields, %
C-alkylation
2a,
Scavenger,
mol. eq.
Entry
Solvent
mol. eq.
1
5
6
3a
4a
1
2
3
4
5
6
2
3
3
3
3
2
3
3
4
5
6
3
3
3
3
3
3
3
3
3
DMF
DMF
CH3OH
CH2Cl2/H2O
C6H5CH3/H2O
DMSO
—
—
—
—
—
—
—
—
—
22
—
—
—
—
—
—
—
—
—
—
—
—
—
—
3
30
54
42
Traces
Traces
80
88
63
82
80
73
45
45
21
45
25
36
10
—
—
—
—
—
—
4
29
—
—
—
—
—
—
—
—
—
—
—
—
—
—
12
—
—
—
5
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
10
5
7
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
8*2
9
5
—
—
—
11
52
52
17
45
29
45
45
53
10
11
12
13
14
15
16
17
18
19
20
—
—
Dark
O2 bubbling
O2 bubbling + Dark
CuCl2 (0.1 eq.)
CuCl2 (1 eq.)
p-DNB (0.1 eq.)
p-DNB (1 eq.)
TEMPO (0.1 eq.)
TEMPO (1 eq.)
5
15
14
5
—
—
—
20
5
_______
* All the reactions were performed under nitrogen and irradiation with two 60-W fluorescent tungsten lamps for 24 h.
*2 The reaction was performed for 120 h.

TABLE 2. C-Alkylated Compounds Synthesized via the SRN1 Reaction of 1 with 2b-g*
1
R
Anion
1
Reaction time, h
3
Compound
4
Formula*2
5
Yield, %
6
E/Z ratio
. .
2
O2N
O2N
R
2
7
62
19
48
—
—
—
3b
4b
3c
BD
NO2
24
60
2b
2c
BD
BD
NO2
20
—
4c
O2N
BD

TABLE 2 (continued)
1
2
3
4
5
6
7
40
—
3d
BD
O N
2
48
2d
O N
2
14
16
—
—
4d
3e
BD
BD
NO
2
48
2e
2f
O2N
42
90/10
4e
BD
CH3
CH3
59
13
—
3f
4f
BD
CH
3
NO2
CH
24
48
CH
3
O N
2
3
70/30
CH
3
BD
BD
CH3
CH3
CH
CH
3
O
O
69
—
2g
3g
O
3
O
O N
2
NO2
_______
* All the reactions were performed under nitrogen and irradiation with two 60-W fluorescent tungsten lamps for 24 h,
using 3 eq of anion.
*2 BD for nitrobenzo[1,3]dioxole.

Scheme 5
NO2
OH
O
O
NaOH
+
1
6
7
Such a result was consistent with the second hypothesis for the formation of compound 6.
The results of the inhibition experiments reported in Table 1 were in complete agreement with an SRN1
mechanism [18] for the C-alkylation of 1.
Electron-transfer reactions might provide a versatile access to new benzo[1,3]dioxole derivatives.
Therefore, we have synthesized various nitronate anions obtained from commercially available nitroalkanes or
from oxidation of the corresponding amines with m-chloroperoxybenzoic acid [19]. As observed for the reaction
of 1 with 2a, the reactions led to a mixture of C-alkylated product and its ethylenic derivative. When the latter
was unsymmetrical, the E-isomer was the main product (Table 2).
Thus, in this series, the SRN1 mechanism appears to be a convenient pathway for the formation of a C–C
bond under mild operating conditions.
EXPERIMENTAL
Melting points were determined on a Büchi B-540 apparatus and are uncorrected. 1H NMR spectra were
1
determined on a Bruker ARX 200 spectrometer. The H chemical shifts were reported as ppm downfield from
Me4Si. Column chromatography was performed using silica gel 60 (Merck, particle size 0.063-0.200 mm,
70-230 mesh ASTM) as adsorbent. Microanalyses for C, H, N were performed by the Microanalytical Section of
St-Jerome Faculty, Aix-Marseille III University, France.
5-Chloromethyl-6-nitrobenzo[1,3]dioxole (1). Triethylamine (0.61 g) was added to a solution of
6-nitropiperonyl alcohol (0.99 g, 5 mmol) in dichloromethane (40 ml). After cooling at 0°C, cool anhydrous
thionyl chloride (0.44 ml, 6 mmol) was added dropwise. The reaction mixture was stirred for 1 h at 0°C and 2 h
at room temperature. Then it was poured over crushed ice and extracted with dichloromethane. The organic
layer was washed with water, dried over anhydrous MgSO4, and evaporated. The crude oil was purified by
chromatography on a silica gel column, eluting with dichloromethane, to give 1 in 96% yield (1.03 g). Yellow
1
solid; mp 76°C (ethanol–chloroform, 1:1) (78-80°C [20]). H NMR (CDCl3), δ, ppm (J, Hz): 4.90 (2H, s,
CH2Cl); 6.10 (2H, s, H(2)); 7.05 (1H, s, H(4)); 7.56 (1H, s, H(7)). Found, %: C 44.30; H 2.70; N 6.43. C8H6ClNO4.
Calculated, %: C 44.57; H 2.81; N 6.50.
2-Nitropropane Lithium Salt (2a) was prepared from 2-nitropropane as previously described [21].
S
General Procedure for RN1 Reactions
A. Kornblum Conditions. Chloride 1 (200 mg, 0.92 mmol) was added to a solution of 2a (1.8 or
2.7 mmol) in 30 ml of dry DMF (entries 1-2, Table 1) or to a solution of 2a (1.8 to 5.4 mmol) in 30 ml of dry
DMSO (entries 6-11, Table 1) under nitrogen and anhydrous conditions. The reaction mixture was then
irradiated with two 60-W fluorescent lamps. After stirring at room temperature for 24 h (except for entry 8:
120 h) under nitrogen, it was poured into water and extracted with toluene (3 × 50 ml) and ether (1 × 50 ml).
The organic layer was washed with water, dried over anhydrous MgSO4, and evaporated under reduced
pressure. Purification by chromatography on a silica gel column, eluting with dichloromethane, gave
5-(2-methyl-2-nitropropyl)-6-nitrobenzo[1,3]dioxole (3a) and 5-(2-methylpropenyl)-6-nitrobenzo[1,3]dioxole
(4a) in various yields depending on reaction time and anion excess (see Table 1).
994

5-(2-Methyl-2-nitropropyl)-6-nitrobenzo[1,3]dioxole (3a). Yellow solid; mp 105°C (ethanol–water,
1
1:1). H NMR (CDCl3), δ, ppm (J, Hz): 1.61 (6H, s, 2CH3); 3.75 (2H, s, CH2); 6.18 (2H, s, H(2)); 6.55 (1H, s,
H(4)); 7.49 (1H, s, H(7)). Found, %: C 49.77; H 4.54; N 10.39. C11H12N2O6. Calculated, %: C 49.66; H 4.51;
N 10.44.
5-(2-Methylpropenyl)-6-nitrobenzo[1,3]dioxole (4a). Yellow solid; mp 73°C (ethanol–water, 1:1).
1H NMR (CDCl3), δ, ppm (J, Hz): 1.72 (3H, s, CH3); 1.95 (3H, s, CH3); 6.14 (2H, s, H(2)); 6.49 (1H, s, ethylenic
H); 6.72 (1H, s, H(4)); 7.56 (1H, s, H(7)). Found, %: C 59.70; H 4.88; N 6.30. C11H11NO4. Calculated, %: C 59.73;
H 5.01; N 6.33.
B. Norris Conditions. Under nitrogen atmosphere, a solution of 2-nitropropane (245 mg, 2.76 mmol) in
40% tetrabutylammonium hydroxide in water (1.8 ml, 2.76 mmol) was stirred at room temperature for 1 h. Then
a solution of 1 (200 mg, 0.92 mmol) in 30 ml of dichloromethane (entry 4) or toluene (entry 5) was added. The
mixture was stirred for 24 h at room temperature under nitrogen and irradiated with two 60-W fluorescent
lamps. The organic layer was separated and the aqueous layer was extracted with dichloromethane (3 × 30 ml).
The combined organic layers were evaporated under reduced pressure. The crude residue was dissolved in 40 ml
of benzene, washed with water, dried over anhydrous MgSO4, and evaporated. The NMR data of the crude
residue showed only trace amounts of 3a.
C. Experiment Performed in Methanol. Entry 3 was performed in the Kornblum operating conditions
but using methanol as solvent and gave 3a and 5 in 42 and 12% yields, respectively.
6-Nitropiperonal (5): mp 93°C (Acros Organics mp 93-94°C).
D. Inhibition Experiments (Entries 12-20). These experiments were performed with the operating
conditions of entry 7 and carried out in the dark, bubbling dioxygen in the reaction mixture, or adding the
required amount of cupric chloride, p-dinitrobenzene (p-DNB), or 2,2,6,6-tetramethyl-1-piperidinyl oxyl
(TEMPO). Yields of 3a, 4a and 5 are reported in Table 1.
Using 1 eq. of CuCl2 (entry 16) or 0.1 eq. of p-DNB (entry 17), a side product, 1,2-bis[(6-
nitrobenzo[1,3]dioxol-5-yl)-ethylene] (6), was isolated in 10 and 5% yields, respectively. Yellow solid;
1
mp 81°C (ethanol). H NMR (CDCl3), δ, ppm (J, Hz): 4.48 (2H, s, CH=CH); 6.19 (4H, s, 2H(2)); 7.16 (2H, s,
2H(4)); 7.72 (2H, s, 2H(7)). Found, %: C 53.79; H 2.67; N 7.77. C16H10N2O8. Calculated, %: C 53.64; H 2.81;
N 7.82.
Preparation of the Nitroalkanes and Their Lithium Salts. The nitrolkanes were commercially
available or prepared from the secondary amines by oxidation with m-chloroperoxybenzoic acid [19, 22] in
refluxed 1,2-dichloroethane for 3 h (2b-f). 2,2-Dimethyl-5-nitro-1,3-dioxane (2g) was obtained as previously
described [23].
A lithium methoxide solution was prepared by careful addition of lithium (175 mg, 0.025 at. g) to
methanol (15 ml). After the solution had become clear, the nitroalkane (25 mmol) was added. The solution was
stirred at room temperature for 2 h and concentrated under vacuum. When the solution became viscous, about
300 ml of ether was added to cause precipitation. The lithium salt was filtered off, washed with ether, and kept
under oil-pump vacuum for 24 h.
S
All the reactions were performed with the Kornblum
RN1 Reactions with Various Lithium Salts.
conditions of entry 7, using (200 mg, 0.92 mmol) of the chloride 1 and 3 eq. of the lithium salt 2b-g. The crude
residues were treated like those of entry 7 to give the required compounds. The silica gel column was eluted by
chloroform for the reactions performed with anions 2c-e,g and was eluted by chloroform–cyclohexane, 3:2, for
the anions 2b and 2f.
5-Nitro-6-(1-nitrocyclopentylmethyl)benzo[1,3]dioxole (3b). Yellow solid, yield 62%; mp 84°C
1
(i-PrOH). H NMR (CDCl3), δ, ppm (J, Hz): 1.60-1.70 (4H, m, 2CH2); 1.71-1.79 (4H, m, 2CH2); 3.69 (2H, s,
allylic CH2); 6.01 (2H, s, H(2)); 6.45 (1H, s, H(4)); 7.36 (1H, s, H(7)). Found, %: C 53.06; H 4.72; N 9.43.
C13H14N2O6. Calculated, %: C 53.06; H 4.80; N 9.52.
995

1
5-Cyclopentylidenemethyl-6-nitrobenzo[1,3]dioxole (4b). Oil, yield 19%. H NMR (CDCl3), δ, ppm
(J, Hz): 1.70-1.73 (4H, m, 2CH2); 2.26 (2H, t, J = 5.3, allylic CH2); 2.41 (2H, t, J = 5.3, allylic CH2); 6.01 (2H,
s, H(2)); 6.54 (1H, s, ethylenic H); 6.77 (1H, s, H(4)); 7.39 (1H, s, H(7)). Found, %: C 62.95; H 5.36; N 5.64.
C13H13NO4. Calculated, %: C 63.15; H 5.30; N 5.67.
5-Nitro-6-(1-nitrocyclohexylmethyl)benzo[1,3]dioxole (3c). Yellow solid, yield 48%; mp 105°C
1
(ethanol). H NMR (CDCl3),δ, ppm (J, Hz): 1.12-1.22 (2H, m, CH2); 1.41-1.53 (6H, m, 3CH2); 2.30-2.37 (2H,
m, CH2); 3.48 (2H, s, allylic CH2); 6.01 (2H, s, H(2)); 6.36 (1H, s, H(4)); 7.35 (1H, s, H(7)). Found, %: C 54.50;
H 5.21; N 9.05. C14H16N2O6. Calculated, %: C 54.54; H 5.23; N 9.09.
1
5-Cyclohexylidenemethyl-6-nitrobenzo[1,3]dioxole (4c). Oil, yield 20%. H NMR (CDCl3), δ, ppm
(J, Hz): 1.40-1.59 (6H, m, 3CH2); 2.02 (2H, t, J = 5.6, allylic CH2); 2.18 (2H, t, J = 5.6, allylic CH2); 6.12 (2H,
s, H(2)); 6.31 (1H, s, ethylenic H); 6.55 (1H, s, H(4)); 7.43 (1H, s, H(7)). Found, %: C 64.39; H 5.68; N 5.46.
C14H15NO4. Calculated, %: C 64.36; H 5.79; N 5.36.
5-Nitro-6-(1-nitrocycloheptylmethyl)benzo[1,3]dioxole (3d). Yellow solid, yield 40%; mp 115°C
(ethanol). 1H NMR (CDCl3), δ, ppm (J, Hz): 1.47-1.53 (8H, m, 4CH2); 1.72 (2H, dd, J = 11.0, J = 5.0, β-H(3') and
β-H(8')); 2.24 (2H, dd J = 11.0, J = 5.0, α-H(3') and α-H(8')); 3.60 (2H, s, allylic CH2); 6.00 (2H, s, H(2)); 6.36 (1H,
s, H(4)); 7.35 (1H, s, H(7)). Found, %: C 55.93; H 5.54; N 8.65. C15H18N2O6. Calculated, %: C 55.90; H 5.63; N 8.69.
1
5-Cycloheptylidenemethyl-6-nitrobenzo[1,3]dioxole (4d). Oil, yield 14%. H NMR (CDCl3), δ, ppm
(J, Hz): 1.43-1.60 (8H, m, 4CH2); 2.12 (2H, t, J = 5.1, allylic CH2); 2.31 (2H, t, J = 5.1, allylic CH2); 6.02 (2H,
s, H(2)); 6.34 (1H, s, ethylenic H); 6.60 (1H, s, H(4)); 7.43 (1H, s, H(7)). Found, %: C 65.41; H 6.15; N 5.03.
C15H17NO4. Calculated, %: C 65.44; H 6.22; N 5.09.
5-Nitro-6-(2-nitrobicyclo[2.2.1]hept-2-ylmethyl)benzo[1,3]dioxole (3e). Yellow solid, yield 16%; mp
1
102°C (ethanol–water, 1:1). H NMR (CDCl3), δ, ppm (J, Hz): 1.09-1.22 (2H, m, CH2); 1.35-1.55 (4H, m,
2CH2); 1.75-1.76 (1H, m, H(3') exo); 2.19-2.21 (1H, m, H(4')); 2.29-2.30 (1H, m, H(3') endo); 2.57-2.58 (1H, m,
H(7')); 3.63 (1H, d, J = 15.7, α-H(1')); 3.81 (1H, d, J = 15.7, β-H(1')); 6.01 (2H, s, H(2)); 6.37 (1H, s, H(4)); 7.38 (1H,
s, H(7)). Found, %: C 56.19; H 4.90; N 8.75. C15H16N2O6. Calculated, %: C 56.25; H 5.04; N 8.75.
5-Bicyclo[2.2.1]hept-2-ylidenemethyl-6-nitrobenzo[1,3]dioxole (4e). Oil, yield 42%. E-isomer:
1H NMR (CDCl3), δ, ppm (J, Hz): 1.16-1.39 (6H, m, 3CH2); 1.96-2.16 (2H, m, allylic CH2); 2.34 (1H, br. s,
CH); 2.77 (1H, br. s, allylic CH); 5.98 (2H, s, H(2)); 6.52 (1H, s, ethylenic H); 6.78 (1H, s, H(4)); 7.34 (1H, s,
1
H(7)). Z-isomer: H NMR (CDCl3), δ, ppm (J, Hz): 1.51-1.66 (6H, m, 3CH2); 1.96-2.16 (2H, m, allylic CH2);
2.25 (1H, br. s, CH); 2.78 (1H, br. s, allylic CH); 5.98 (2H, s, H(2)); 6.51 (1H, s, ethylenic H); 6.78 (1H, s, H(4));
7.34 (1H, s, H(7)). Found, %: C 65.88; H 5.49; N 5.11. C15H15NO4. Calculated, %: C 65.92; H 5.53; N 5.13.
5-(2-Methyl-2-nitropentyl)-6-nitrobenzo[1,3]dioxole (3f). Yellow solid, yield 59%; mp 101°C
1
(ethanol). H NMR (CDCl3), δ, ppm (J, Hz): 0.96 (3H, t, J = 6.7, CH2CH3); 1.21-125 (2H, m, CH2CH3); 1.40
(3H, s, CCH3); 1.83-1.85 (1H, m, α-H(3')); 2.12-2.13 (1H, m, β-H(3')); 3.55 (1H, d, J = 14.6, α-H(1')); 3.90 (1H, d,
J = 14.6, β-H(1')); 6.12 (2H, s, H(2)); 6.54 (1H, s, H(4)); 7.52 (1H, s, H(7)). Found, %: C 52.55; H 5.38; N 9.41.
C13H16N2O6. Calculated, %: C 52.70; H 5.44; N 9.46.
1
5-(2-Methylpent-1-enyl)-6-nitrobenzo[1,3]dioxole (4f). Oil, yield 13%. E-isomer: H NMR (CDCl3),
δ, ppm (J, Hz): 0.71 (3H, t, J = 7.3, CH2CH3); 1.34 (2H, sextuplet, J = 7.3, CH2CH3); 1.78 (3H, d, J = 1.3,
CCH3); 1.90 (2H, t, J = 7.3, allylic CH2); 6.01 (2H, s, H(2)); 6.35 (1H, br. s, ethylenic H); 6.56 (1H, s, H(4)); 7.43
1
(1H, s, H(7)). Z-isomer: H NMR (CDCl3), δ, ppm (J, Hz): 0.87 (3H, t, J = 7.3, CH2CH3); 1.51 (2H, sextuplet,
J = 7.3, CH2CH3); 1.57 (3H, d, J = 1.2, CCH3); 2.07 (2H, t, J = 7.3, allylic CH2); 6.01 (2H, s, H(2)); 6.35 (1H,
br. s, ethylenic H); 6.60 (1H, s, H(4)); 7.43 (1H, s, H(7)). Found, %: C 62.59; H 6.14; N 5.63. C13H15NO4.
Calculated, %: C 62.64; H 6.07; N 5.62.
5-(5,5-Dimethyl-2-nitro-1,3-dioxan-2-ylmethyl)-6-nitrobenzo[1,3]dioxole (3g). Yellow solid,
1
yield 69%; mp 173°C (ethanol–water, 1:1). H NMR (CDCl3), δ, ppm (J, Hz): 1.38 (3H, s, CH3); 1.50 (3H, s,
CH3); 3.58 (2H, s, CH2); 4.37 (2H, d, J = 12.7, CH2O); 4.90 (2H, d, J = 12.7, CH2O); 6.15 (2H, s, H(2)); 6.56
(1H, s, H(4)); 7.53 (1H, s, H(7)). Found, %: C 49.31; H 4.67; N 8.15. C14H16N2O8. Calculated, %: C 49.41; H 4.74;
N 8.23.
996

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