Preparation and characterisation of N,N-disubstituted 2-amino-5H- selenophenes

Article abstract of DOI:10.1515/znb-2004-0412

The reaction of N,N′-persubstituted selenoacrylamides with alkyl bromoacetates gives rise to the formation of alkyl derivatives of N,N-disubstituted 2-aminoselenophene-5-carboxylates which can be transformed by saponification into corresponding 5-carboxylic acids. These compounds decompose by heating under formation of hitherto unknown N,N-disubstituted 2-amino-5H-selenophenes their spectral and chemical properties were outlined.

Full text of DOI:10.1515/znb-2004-0412

Preparation and Characterisation of N,N-Disubstituted
2-Amino-5H-selenophenes*
Ines Zug and Horst Hartmann
University of Applied Sciences, Geusaer Straße, D-06217 Merseburg, Germany
Reprint requests to Prof. Dr. H. Hartmann. Fax: +49 (0)3461-462192.
E-mail: Horst.Hartmann@cui.fh-merseburg.de
Z. Naturforsch. 59b, 439 – 442 (2004); received January 28, 2004
Dedicated to Prof. Willi Kantlehner on the occasion of his 60th birthday
The reaction of N,N’-persubstituted selenoacrylamides with alkyl bromoacetates gives rise to the
formation of alkyl derivatives of N,N-disubstituted 2-aminoselenophene-5-carboxylates which can be
transformed by saponification into corresponding 5-carboxylic acids. These compounds decompose
by heating under formation of hitherto unknown N,N-disubstituted 2-amino-5H-selenophenes their
spectral and chemical properties were outlined.
Key words: 2-Aminoselenophenes, Heterocyclisation, Decarboxylation, Heterocyclic Azo Dyes,
Methine Dyes
In the last three decades N,N-disubstituted 2-amino-
thiophenes 2 and 2-amino-1,3-thiazoles 3 received a
lot of interest. As heterocyclic analogues of the well-
known N,N-disubstituted anilines 1, which are impor-
tant starting compounds for the synthesis of organic
Scheme 1.
dyes [1], they have also been used as versatile precur-
sors for the preparation of different types of organic
dyes. Thus, N,N-disubstituted 2-aminothiophenes 2
could by successfully transformed, especially if un-
substituted at their 5-position, into, e. g., azo dyes [2],
methine [3] and azomethine dyes [4], or squarylium
[5] and croconium dyes [6]. Recently these hetero-
cycles were used for the preparation of a variety of
stilbenoid dyes with high non-linear optical proper-
ties [7]. Analogously, N,N-disubstitued 2-aminothia-
zoles 3 [8] have been transformed into correspond-
ing azo dyes [9], methine and azamethine dyes [4], as
well as into squarylium dyes [10]. Very recently N,N-
disubstitued 2-aminoselenazoles 5 have also found at-
tention as starting materials for the synthesis of differ-
ent types of dyes [11], namely azo dye [9], methinum
dyes [4], and squarylium dyes [12] (Scheme 1).
to these compounds was an important precondi-
tion. Usually these amines could be prepared from
simple thioacetamides, thiourea or selenourea pre-
cursors, respectively, and halomethyl ketones using
the well-known Hantzsch route [13, 14]. For the
N,N-disubstituted 2-aminothiophenes 2 a route start-
ing from secondary amines and 2-mercaptothiophene
[15] or 2-bromothiophene [16] was also con-
venient.
We found, however, that both methods could not
be applied for the synthesis of N,N-disubstituted 2-
aminoselenophenes 4. Therefore, these seleno-con-
taining heterocyclic amines are unknown as yet and
constitute the missing link in the series of hetero-
cylic aniline analogues 2 – 5. Only few N,N-disub-
stituted 2-aminoselenophenes substituted with strong
electron acceptor moieties in their 5-position have
been prepared very recently by starting from N,N’-
persubstituted selenoacrylamides 6 [17]. These com-
pounds which were easily available from N,N’-persub-
For the use of the mentioned heterocyclic amines
2, 3, and 5 as dye precursors, a simple access
* Presented in part at the 6th Conference on Iminium Salts stituted 1-chlorovinamidinium salts by reaction with
(ImSAT-6), Stimpfach-Rechenberg (Germany), September
16 – 18, 2003
sodium selenide [18] were allowed to react with accep-
tor-substituted halomethyl compounds 7 to yield N,N-
c
0932–0776 / 04 / 0400–0439 $ 06.00 ꢀ 2004 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com
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440
I. Zug – H. Hartmann · N,N-Disubstituted 2-Amino-5H-selenophenes
Entry R1R2N
Yield M. p.
1H NMR, δ-values, measured in [D6]-DMSO
Table 1. Melting points and
1H NMR data of the com-
(%)
87
(◦C)
for 10 and in CDCl3 for 11 (ppm)
pounds 10 and 11 prepared.
10a
10b
10c
10d
10e
Dimethylamino
122 – 124 2.99 (s, 6H, NCH3), 5.86 (d, 1H, CH), 7.62
(d, 1H, CH), 11.67 (s, 1H, OH)
Morpholino
88
87
72
90
150 – 152 3.18 (t, 4H, NCH2), 3.73 (t, 4H, OCH3), 5.86
(d, 1H, CH), 7.62 (d, 1H, CH), 11.76 (s, 1H, OH)
149 – 151 6.33 (d, 1H, CH), 7.25 (m, 6H, CH), 7.40 (m, 4H,
CH), 7.62 (d, 1H, CH), 12.49 (s, 1H, OH)
137 – 139 6.13 (d, 1H, CH), 7.21 (m, 4H, CH), 7.41 –
7.51 (m, 5H, CH), 7.81 – 7.94 (m, 3H, CH)
138 – 142 6.77 (d, 1H, CH), 7.18 – 7.24 (m, 2H, CH), 7.29 –
7.35 (m, 2H, CH), 7.37 – 7.42 (m, 4H, CH),
7.73 (d, 1H,CH)
Diphenylamino
1-(N-Phenyl)-
naphthylamino
Phenothiazinyl
11a
11b
Dimethylamino
Morpholino
64
62
oil
2.94 (s, 6H, NCH3), 5.89 (dd, 1H, CH), 6.99
(q, 1H, CH), 7.09 (dd, 1H, CH)
3.10 (t, 4H, NCH2), 3.82 (t, 4H, OCH2), 6.19
(dd, 1H, CH), 7.02 (q, 1H, CH), 7.26 (dd, 1H,
CH)
oil
11c
11d
Diphenylamino
70
78
108 – 110 6.77 (dd, 1H, CH), 7.04 – 7.12 (m, 7H, CH),
7.28 – 7.34 (m, 4H, CH), 7.79 (dd, 1H, CH)
1-(N-Phenyl)-
naphthylamino
88 – 91
6.72 (dd, 1H, CH), 6.87 – 6.95 (m, 3H, CH),
7.01 (q, 1H, CH), 7.16 – 7.21 (m, 2H, CH), 7.44 –
7.60 (m, 6H, CH), 7.67 (dd, 1H, CH), 7.91 –
8.01 (m, 3H, CH)
11e
Phenothiazinyl
94
90 – 94
6.20 (dd, 2H, CH), 6.96 (m, 2H, CH), 7.05 –
7.14 (m, 4H, CH), 7.30 – 7.35 (m, 2H, CH),
8.23 (dd, 1H)
aqueous/methanolic sodium hydroxide and subsequent
addition of mineral acid into the corresponding car-
boxylic acids 10 from which the hitherto unknown
N,N-disubstituted 2-amino-5H-selenophenes 11 were
available by heating at their melting points. Ana-
logously to the behaviour of the N,N-disubstituted
2-aminothiophene-5-carboxylic acids [20], these car-
boxylic acids 10 [21] decompose under elimination
of carbon dioxide to give rise to the formation of
the desired compounds 11 in mostly moderate yield.
The N,N’-disubstituted 2-amino-5H-selenophenes 11
so prepared (see Table 1) are colourless or pale yellow
coloured solids which can be stored in a closed vessel
under nitrogen without decomposition. Their consti-
tution was confirmed by means of elemental analyses
and spectroscopic data. Thus, the N,N’-disubstituted 2-
Scheme 2.
1
aminoselenophenes 11 exhibit in their H NMR spec-
disubstituted 2-aminoslenophenes of the general struc-
ture 8 [19].
tra characteristic signals at δ = 2.9 − 3.9 and 5.9 −
8.0 ppm. Whereas the signals in the first range arise
Now we found that the 5-methoxycarbonyl deriva- from the protons at the N-alkyl groups, the signals in
tives 9 of such 2-aminoselenophenes, prepared by re- the second range can be attributed to the protons at
action of the N,N’-persubstituted selenoacrylamides 6 their selenophene and, as far as present, at their N-aryl
with methyl bromoacetate as described in ref. [19], moieties.
can be used to prepare the 5H-substituted parent com-
It is worth mentioning that there is a significant
pound. To this end, these methyl 2-aminoselenophene- difference between the spectral pattern of the N,N’-
5-carboxylates 9 were transformed by reaction with disubstituted 2-aminoselenophenes 11 and their 5-
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I. Zug – H. Hartmann · N,N-Disubstituted 2-Amino-5H-selenophenes
Experimental Section
441
Melting points: Boetius heating-table, uncorrected.
1H NMR: Varian 300 Gemini (300 MHz). Elemental
analyses: LECO CHNS 932.
Preparation of N,N-disubstituted 2-aminoselenophenes 11
and their 5-carboxylic acid precursors 10 (General proce-
dure)
Scheme 3.
carboxylic acid precursors 10. Whereas the carboxylic
acids 10 exhibit, analogously to their alkyl carboxy-
lates 9 [16], two characteristic doublets at about 6.0
and 7.7 ppm with coupling constants J = 4.5 Hz, the
5H-substituted 2-aminoseleophenes 11 exhibit three
multiplets between 5.9 and 7.9 ppm with coupling con-
stants J = 1.2, 3.9, and 6.0 Hz. Although in the 2-
aminoselenophenes 11 one of these multiplets is super-
imposed by the multiplets of the aryl protons, it can be
recognised that the chemical shifts of the selenophene
protons are significantly influenced by the type of
amino substituents. Thus, for the N-alkyl-substituted
2-aminoselenophenes 11a and 11b these multiplets
were found between 5.9 and 7.3 ppm whereas for
the N-aryl-substituted 2-aminoselenophenes 11c and
11d these multiplets were found at considerably lower
fields. This fact indicates that the electron-donating ef-
fect of the arylamino substituents on the selenophene
moiety is significantly smaller than the one of the N-
alkyl substituents.
The methyl derivative of
a N,N-disubstituted 2-
aminoselenophene-5-carboxylate 9 (0.01 mol), prepared
according to ref. [19], was refluxed in methanol (50 ml) con-
taining a concentrated aqueous sodium hydroxide solution
(0.015 mol) for 30 min. After cooling at room temperature
the mixture was filtrated and, subsequently acidified with
diluted HCl. The 2-aminoselenophene-5-carboxylic acid 10
precipitated was isolated by filtration and dried at 50 ◦C. By
heating at its melting point the acids 10 decompose to yield
the corresponding N,N-disubstituted 2-aminoseleophenes 11
as oils which crystallise after cooling at room temperature
and triturating with some methanol or diethyl ether. Physical
data of compounds 10 and 11 are given in Table 1.
Compound 11a: C6H9NSe (175.0): calcd. C 41.39,
H 5.21, N 8.05; found: C 41.03, H 5.33, N 8.08.
Compound 11b: C8H11NOSe (216.1): calcd. C 44.46,
H 5.13, N 6.48; found: C 44.09, H 5.22, N 6.66.
Compound 11c: C16H13NSe (299.0): calcd. C 64.43,
H 4.39, N 4.70; found: C 64.64, H 4.42, N 4.58.
Compound 11d: C20H15NSe (349.0): calcd. C 68.97,
H 4.34, N 4.02; found: C 69.39, H 4.34, N 4.15.
As expected, the new N,N-disubstituted 2-amino-
Compound 11e: C16H11NSSe (229.0): calcd. C 58.54,
selenophenes 11 and their carboxylic acid precur- H 3.38, N 4.27; found: C 59.02, H 3.28, N 4.25.
Methyl
2-[(N-phenyl-1-naphthylamino]selenophene-
sors 10 can be used as versatile starting materials
for the preparation of organic dyes. Thus, with arene
diazonium salts or reactive formyl derivatives they
can be transformed, as exemplified by compounds 12
and 13, into deeply coloured compounds. Details on
these reactions, which were performed accordingly
to reported methods for preparing corresponding 2-
aminothiophene dyes [2, 4], and on the properties of
the compounds so obtained will be published in a forth-
coming paper soon.
5-carboxylate (9d), the precursor of compound 10d, has
the following physical data: m.p. 98 – 100 C. – 1H NMR
◦
(CDCl3): δ = 3.07 (s, 3H, OCH3), 6.42 (d, 1 H, CH),
7.27 – 7.38 (m, 6 H, CH), 7.62 (m, 2 H, CH), 7.66 – 7.73 (m,
4H, CH).
Acknowledgement
The authors thanks the Deutsche Forschungsgemeinschaft
for financial support.
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