Synthesis of 3-alkyl-4-aminofurazans

Article abstract of DOI:10.1007/s11172-005-0352-y

A "one-pot" method for the synthesis of 3-alkyl-4-aminofurazans from ethyl β-alkyl-β-oxopropionates was developed. The multistep process involves hydrolysis of the ester, nitrosation at the activated methylene group, and treatment of the resulting intermediate with an alkaline solution of hydroxylamine in the presence of urea.

Full text of DOI:10.1007/s11172-005-0352-y

1032
Russian Chemical Bulletin, International Edition, Vol. 54, No. 4, pp. 1032—1037, April, 2005
Synthesis of 3ꢀalkylꢀ4ꢀaminofurazans*
A. B. Sheremetev,ꢀ Yu. L. Shamshina, and D. E. Dmitriev
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Eꢀmail: sab@ioc.ac.ru
A "oneꢀpot" method for the synthesis of 3ꢀalkylꢀ4ꢀaminofurazans from ethyl βꢀalkylꢀβꢀ
oxopropionates was developed. The multistep process involves hydrolysis of the ester, nitrosation
at the activated methylene group, and treatment of the resulting intermediate with an alkaline
solution of hydroxylamine in the presence of urea.
Key words: alkylfurazans, aminofurazans, glyoximes, oximes, nitrosation, cyclization.
Aminofurazans (aminoꢀ1,2,5ꢀoxadiazoles) have found
a wide use in organic synthesis.1,2 Although 3ꢀaminoꢀ4ꢀ
methylfurazan (1a)3 was first obtained more than 80 years
ago, its homologs with longer alkyl substituents have not
been synthesized to date. Reactions affecting the methyl
group of compound 1a remain unknown so far. At the
same time, the chemistry of its amino group have been
studied in detail.1,2
Scheme 1 illustrates the strategy that was used for the
first synthesis of amine 1a.3 The total yield of the product
was ~3%. This multistep process started from commerꢀ
cially inaccessible 2ꢀchloroꢀ1ꢀmethylglyoxime (2). Acyꢀ
lation of glyoxime 3 gave O,O´ꢀdiacyl derivative 4, which
underwent cyclization into 1,2,4ꢀoxadiazole 5. When
treated with HCl, oxadiazole 5 rearranged into Nꢀacetyl
derivative 6, which was in situ deacylated to give the target
amine 1 in low yield. Later versions of this process,4,5 as
well as direct cyclization of 1ꢀaminoꢀ2ꢀmethylglyoxime
(3) into furazan 1,6 did not increase its yield noticeably.
An original solution to the problem was a "oneꢀpot"
method7 and its modified versions8 for the conversion of
isonitrosoacetone (7a) into furazan 1a. According to the
procedure, oxo oxime 7a was treated with hydroxylamine
in the presence of an alkali (Scheme 2) to give aminoꢀ
furazan 1a in 10% yield. Later,9 its yield was increased to
63% by carrying out the reaction in the presence of urea.
The detailed mechanism of the transformation of comꢀ
pound 7a into aminofurazan 1a and the roles and effects
of different factors on the reaction outcome have not
been discussed hitherto.
The goal of the present study was to develop an effiꢀ
cient method for the synthesis of 3ꢀalkylꢀ4ꢀaminofurazans.
Scheme 2 is obviously attractive as a basic route to this
group of compounds. However, to extend the area of its
* Dedicated to Corresponding Member of the Russian Acadꢀ
emy of Sciences E. P. Serebryakov on the occasion of his
70th birthday.
Scheme 1
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 1007—1012, April, 2005.
1066ꢀ5285/05/5404ꢀ1032 © 2005 Springer Science+Business Media, Inc.

Synthesis of 3ꢀalkylꢀ4ꢀaminofurazans
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
1033
Scheme 2
application, one should distinctly conceive of the chemism
of the conversion 7a → 1a and the factors affecting the
reaction at different steps. Analysis and detailing of these
separate steps were essential parts of this study.
Obviously, this reaction involves a sequence of transꢀ
formations, which can be described, by analogy with the
literature data and our previous results,10—13 by Scheme 3.
Note that the feasibility of some of these transformations
was mentioned earlier.9,14
Previously,10—13 in the study of oneꢀpot syntheses of
aminofurazans, we found that cyclization of glyoximes
into the corresponding furazans is most difficult to occur
in such processes as shown in Scheme 2. The ability of the
oxime groups to participate in cyclization is determined
by their configurations.
The configurations of both the glyoximes shown in
Scheme 3 are known. For instance, glyoxime 8 exists in
two sufficiently easily interconvertible isomers (E,E´
and Z,E´).18 Because of this, glyoxime 8 is involved in
subsequent transformations and is not detected in the
final reaction mixture. Aminoglyoxime 3 exists exclusively
as the unfavorable Z,Z´ꢀform,19,20 which necessitates its
preisomerization.
Unsymmetrically substituted glyoximes can exist as
four geometrical isomers, depending on the configuraꢀ
tions of the oxime groups.15—17
The intramolecular hydrogen bond in the amphiꢀform
fixes both oxime groups on the same side of the C—C
bond, which is favorable for cyclization.
Indeed, the formation of the furazan ring implies an
intramolecular attack of an anionic center (formed in
an alkaline medium at the O atom of one oxime group)
on the N atom of the other oxime group (Scheme 4),
which is possible only for the amphiꢀconfiguration of the
glyoxime. Other conformers must be isomerized into the
amphiꢀform before cyclization.
As a rule, the transition of one conformer into another
is hindered.15—17 To initiate it, high temperatures are reꢀ
quired in some cases and base or acid catalysis, in others.
According to the method proposed8 (see Scheme 2),
a mixture of αꢀhydroxyiminoacetone 7a, KOH, and
NH2OH•HCl in the molar ratio 1 : 5 : 2.5 is refluxed for
6 h to give amine 1a in 10% yield. We found that 1ꢀaminoꢀ
2ꢀmethylglyoxime 3, which is a precursor of amine 1a
(see Scheme 3), is fairly resistant to dehydration/cyclizaꢀ
tion. A fourfold extension of the refluxing time (~24 h)
increased the yield of amine 1 only to 15%. The reaction
mixture always contained aminoglyoxime 3, which could
be isolated in 20 to 48% yield. It should be noted that
heating in an alkaline medium causes reported9 hydrolyꢀ
sis of important intermediates in Scheme 3. The major
hydrolysis products 11—14 21,22 are found in the reaction
mixture as salts.
It turned out that the percentages of byꢀproducts inꢀ
crease with an increase in the reaction time.
Scheme 3

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Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
Sheremetev et al.
Scheme 4
Scheme 5
than do glyoximes themselves.1,2 According to Scheme 4,
hydroxyl is a leaving group in intramolecular nucleophilic
substitution resulting in ring formation. In Oꢀacylglyꢀ
oxime, the acyloxy group is displaced (Scheme 6). Here,
requirements to the glyoxime conformation are also subꢀ
stantial.
Scheme 6
We believed that the synthesis of aminofurazan 1a
could be intensified by optimization of the ratio of the
reagents, as well as by addition of various additives.
For instance, according to Scheme 3, even catalytic
amounts of an alkali are sufficient for the cyclization to
occur since it is not consumed in this process. The presꢀ
ence of an alkali ensures intermediate generation of the
oxime anion. Moreover, an alkali excess can give rise to a
dianion15 as the result of simultaneous deprotonation of
both oxime groups of the glyoxime, which is not favorable
for cyclization into the furazan ring. Indeed, a decrease in
the alkali amount by one and a half (to 3 equiv.) provided
a nearly doubled yield (up to 18%). Replacement of KOH
by NaOH increased the yield to 21%.
The formation of aminofurazan 1a proved to be deꢀ
pendent on the hydroxylamine excess: the use of an
1.5—2 excess of NH2OH made it possible to reduce the
reaction time by half (3 h), the same yield being reached.
However, a further increase in the amount of NH2OH
was ineffective.
Apparently, the presence of hydroxylamine facilitates
the E/Zꢀisomerization of the oximes. We assumed that
NH2OH adds to the C=N bond of the oxime to form an
intermediate with geminal hydroxyamino groups, which
is converted into another oxime isomer by loss of a
hydroxylamine molecule (Scheme 5). This process is obꢀ
viously reversible.
Since the isomer involved in the formation of the
furazan ring is consumed in subsequent cyclization, this
equilibrium is shifted in the desired isomerization diꢀ
rection.
Because the electronic stabilization of the acyloxy anꢀ
ion is much higher than that of the hydroxide anion,
detachment of the former should occur more easily, thus
making ring closure more efficient. Clearly, a catalytic
amount of an alkali is insufficient in this case, because the
resulting carboxylate is brought out of the reaction cycle.
It should be noted that acylation of aminoglyoximes is
often accompanied by cyclization of another type (see
Scheme 1) that yields 1,2,4ꢀoxadiazole derivatives. When
heated with an acid or an alkali, they become rearranged
into Nꢀacylated aminofurazans;3,23 subsequent deacylaꢀ
tion is possible only in an acidic medium.
We found that addition of strong acylating reagents to
the reaction mixture, which is a complex multicompoꢀ
nent system, is inefficient. For this reason, less reactive
acylating reagents should be used (e.g., isocyanic acid
derivatives, which change oximes into Oꢀcarbamoyl deꢀ
rivatives22,24—26). Urea is most attractive in this group of
reagents. Urea is known as a dehydrating agent that alꢀ
lows cyclization of glyoximes into furazans.9,27 The plauꢀ
sible mechanism of the action of urea is shown in
Scheme 7.
Thermal decomposition of urea produces two species
necessary for the transformation of glyoxime into furazan:
isocyanic acid acts as an acylating reagent, while ammoꢀ
nia provides the formation of an anionic center at the
oxime group, thus promoting the cyclization. No less than
It has long been known that Oꢀacyl derivatives of
glyoximes undergo cyclization into furazans more easily

Synthesis of 3ꢀalkylꢀ4ꢀaminofurazans
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
1035
Table 1. Effects of the reaction conditions on the yield of aminofurazan 1a
Entry
Ratio of the starting reagents (mol)
τ/h
Yield
(%)
Compound 7a
NH2OH•HCl
NaOH OC(NH2)2
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
3
2
2
2
3
0.5
1
1
1
1
1
1
1
1
2
2
4
2
4
2
4
2
2
2
3
3
38
45
51
57
60
67
69
72
75
78
81
69
3
3
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.6
3.7
3.8
3.8
4.5
9
10
11
12
1
1
1
Scheme 7
slow addition of a solution of an alkali to an aqueous
solution of compound 7a and NH2OH•HCl, heating of
the reaction mixture, addition of urea, and refluxing for a
certain period of time. Selected data illustrating the obꢀ
served trends are given in Table 1.
Apparently, the enhanced nucleophilicity of the
oximate anion in the presence of a small alkali excess is
+
due to an exchange reaction (replacement of the NH4
cation by Na+; see Scheme 7). This increases the yield of
furazan 1a. Finally, we attained an 81% yield of the tarꢀ
get product.
Thus, use of an excess of hydroxylamine and alkali in
the presence of an equimolar amount of urea is efficient
for the oneꢀpot syntheses of aminofurazans.
The starting isonitrosoacetone 7a in Scheme 2 was
easily prepared from ethyl acetoacetate 15a 28 by hydrolyꢀ
sis to sodium acetoacetate 16, nitrosation at the methylꢀ
ene group, and decarboxylation in an acidic medium. The
yield of compound 7a was 80% (Scheme 8).
Treatment of the reaction mixture containing comꢀ
pound 7a (without its isolation in the individual state)
with an alkaline solution of hydroxylamine and urea in
the aforementioned ratio allowed amine 1a to be obtained
in 50 to 55% total yield with respect to the starting esꢀ
ter 15a. Thus, we developed a simple and efficient oneꢀ
pot method for the synthesis of amine 1a.
an equimolar amount of urea is required for successful
completion of the reaction.
We studied the effects of the ratio of reagents
(7a/NH2OH•HCl/NaOH/urea) and the reaction time on
the outcome of the process. A typical procedure involved
An analogous procedure was used to obtain for the
first time homologs of compound 1a with larger alkyl
Scheme 8

1036
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
Sheremetev et al.
bined extracts were washed with water (2×200 mL), 5% sodium
carbonate (200 mL), and water (200 mL) and dried with MgSO4.
The solvent was removed and the residue was recrystallized from
CHCl3—light petroleum (3 : 1).
The yield of 3ꢀaminoꢀ4ꢀmethylfurazan (1a) was 39 g (51%),
small colorless crystals, m.p. 72.8—73.8 °C (cf. Refs: m.p. 72 °C,9
72—73 °C3). Its IR29 and NMR spectra30 were identical with the
published ones.
substituents. As with compound 1a, 3ꢀalkylꢀ4ꢀaminoꢀ
furazans 1b—d and 3ꢀ(adamantꢀ1ꢀyl)ꢀ4ꢀaminofurazan
(1e) were synthesized from the corresponding βꢀalkylꢀβꢀ
oxo esters 15b—e (Scheme 9) in ten sequential steps (see
Schemes 3, 7, and 8). This methodology afforded alkylꢀ
furazans and adamantylfurazan in satisfactory yields.
Compounds 1b—e were synthesized analogously.
Scheme 9
3ꢀAminoꢀ4ꢀethylfurazan (1b), yield 49%, m.p. 71.3—71.6 °C
(hexane). Found (%): C, 42.51; H, 6.22; N, 37.09. C4H7N3O.
M = 113.12. Calculated (%): C, 42.47; H, 6.24; N, 37.15.
IR (KBr), ν/cm–1: 3408, 3368, 3344, 3288, 3264, 1648, 1600,
1536, 1448, 1216, 968, 872. MS, m/z: 113 [M]+, 83 [M – NO]+.
1H NMR (CDCl3), δ: 1.29 (t, 3 H, Me, J = 6.7 Hz); 2.59 (q,
2 H, CH2, J = 6.7 Hz); 4.38 (br.s, 2 H, NH2). 13C NMR
(CDCl3), δ: 10.9 (Me); 16.1 (CH2); 148.7 (N=C—CH2);
154.8 (CNH2).
R = Et (b), Pr (c), But (d), Ad (e)
3ꢀAminoꢀ4ꢀpropylfurazan (1c), yield 57%, m.p. 31.4—31.9 °C
(light petroleum). Found (%): C, 47.30; H, 7.12; N, 33.01.
C5H9N3O. M = 127.15. Calculated (%): C, 47.23; H, 7.13;
N, 33.05. IR (KBr), ν/cm–1: 3428, 3332, 2964, 2936, 2876,
1632, 1532, 1468, 1452, 1380, 1212, 1096, 992, 876. MS, m/z:
Thus, 3ꢀalkylꢀ4ꢀaminofurazans can be obtained by the
developed oneꢀpot method from ethyl βꢀalkylꢀβꢀoxoꢀ
propionates. The process involves a sequence of steps
such as hydrolysis of the ester, nitrosation at the activated
methylene group, and treatment with an alkaline solution
of hydroxylamine in the presence of urea. Apparently,
this methodology is of the general character.
1
127 [M]+, 97 [M – NO]+. H NMR (CDCl3), δ: 0.91 (t, 3 H,
Me, J = 6.4 Hz); 1.67 (m, 2 H, CH2Me); 2.53 (t, 2 H,
N=C—CH2, J = 5.7 Hz); 4.58 (br.s, 2 H, NH2). 13C NMR
(CDCl3), δ: 13.3 (Me); 19.8 (CH2Me); 24.1 (N=C—CH2); 147.5
(N=C—CH2); 155.0 (CNH2).
3ꢀAminoꢀ4ꢀtertꢀbutylfurazan (1d), yield 42%, m.p.
101—104 °C (light petroleum). Found (%): C, 51.11; H, 7.88;
N, 29.71. C6H11N3O. M = 141.17. Calculated (%): C, 51.05;
H, 7.85; N, 29.77. IR (KBr), ν/cm–1: 3452, 3348, 3252, 3216,
2972, 2968, 2940, 2908, 1640, 1516, 1468, 1424, 1376, 1300,
1148, 1028, 984, 888. MS, m/z: 141 [M]+, 111 [M – NO]+, 84
Experimental
Melting points were determined with a Gallenkamp unit
(Sanyo Co.). Naturalꢀisotope 1H and 13C NMR spectra were
recorded on Bruker AMꢀ300 (300.13 and 75.7 MHz, respectively)
and Bruker DRXꢀ500 spectrometers (500.13 and 125.7 MHz,
respectively). Chemical shifts are given in the δ scale with a
solvent as the internal standard. Mass spectra were recorded on
Finnigan MAT INCOSꢀ50 and Varian MAT CHꢀ111 instruꢀ
ments (EI, 70 eV). IR spectra were recorded on a Specord IR75
spectrometer in pellets with KBr for solids and in a thin film for
liquids. The course of the reaction was monitored and the purity
of the products was checked by TLC on Silufol UVꢀ254 plates;
spots were visualized with UV irradiation. βꢀAlkylꢀβꢀoxo esters
were purchased from Reakhim Co.
Oneꢀpot synthesis of 3ꢀalkylꢀ4ꢀaminofurazans (general proꢀ
cedure). Freshly distilled ethyl acetoacetate (100 mL, 0.78 mol)
was added at 10 °C to a solution of NaOH (35.6 g, 0.89 mol) in
water (300 mL). The resulting emulsion was stirred for 12 h to
homogenization and NaNO2 (58.7 g, 0.85 mol) was dissolved.
Then 20% HClO4 (1.74 mol) was slowly added dropwise at 10
to 15 °C. The reaction mixture was stirred while warming it to
room temperature and then left for ~14 h. Sodium hydroxide
(1 g) was added; a solution of NH2OH•HCl (166 g, 2.4 mol) in
water (300 mL) was then added dropwise with vigorous stirring.
After half the solution of hydroxylamine was added, a solution
of NaOH (108 g, 2.7 mol) in water (200 mL) was simultaneously
added dropwise from a second dropping funnel at a temperature
no higher than 30 °C. The mixture was heated to 95 °C for 1.5 to
2 h and urea (40 g, 0.67 mol) was added in one portion. The
resulting reaction mixture was refluxed for 3 h and cooled and
the product was extracted with CH2Cl2 (5×200 mL). The comꢀ
1
[M – But]+. H NMR (DMSOꢀd6), δ: 1.32 (s, 9 H, Me); 5.93
(br.s, 2 H, NH2). 13C NMR (DMSOꢀd6), δ: 27.5 (Me); 30.9
(CMe3); 153.9 (CBut); 155.0 (CNH2).
4ꢀAdamantꢀ1ꢀylꢀ3ꢀaminofurazan (1e), yield 31%, m.p.
158—159 °C (CCl4). Found (%): C, 65.77; H 7.82; N, 19.14.
C
12H17N3O. M = 219.29. Calculated (%): C, 65.73; H, 7.81;
N, 19.16. IR (KBr), ν/cm–1: 3468, 3324, 3232, 2904, 2852,
1624, 1508, 1456, 1344, 1272, 1100, 992. MS, m/z: 219 [M]+.
1H NMR (CDCl3), δ: 1.70, 2.05 (both br.s, 6 H each, CH2); 2.10
(br.s, 3 H, CH); 4.33 (br.s, 2 H, NH2). 13C NMR (CDCl3), δ:
27.7 (CH); 36.4 (CH2); 39.1 (N=C—C); 39.7 (N=C—C—CH2),
153.4 (N=C—Ad), 154.2 (CNH2).
This work was financially supported in part by the
Russian Foundation for Basic Research (Project No. 01ꢀ
03ꢀ32944a) and the Federal Target Program "Integration
of Science and Higher Education in Russia for 2002
to 2006" (State Contract No. I0667).
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Synthesis of 3ꢀalkylꢀ4ꢀaminofurazans
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Received June 28, 2004;
in revised form February 2, 2005