1,3-Dipolar cycloaddition of ethyl propiolate to 4,4-dimethyl- 4,5-dihydro-1,2-dithiolo-[5,4-c]quinoline-1-thiones

Article abstract of DOI:10.1023/A:1020913328392

The interaction of ethyl propiolate with 4,4-dimethyl-4,5-dihydro-2,3-dithiolo[3,4-c]quinoline-1-thiones leads to 1,3-dithiol-2-ylidenes, 1,6,6a(λ⁴)-trithiapentalene, or thiino[2,3-c]quinolines depending on the conditions.

Full text of DOI:10.1023/A:1020913328392

Chemistry of Heterocyclic Compounds, Vol. 38, No. 8, 2002
1,3-DIPOLAR CYCLOADDITION
OF ETHYL PROPIOLATE TO 4,4-DIMETHYL-
4,5-DIHYDRO-1,2-DITHIOLO-
c
[5,4- ]QUINOLINE-1-THIONES
S. M. Medvedeva, Kh. S. Shikhaliev, G. I. Ermolova, A. S. Solov'ev, and G. V. Shatalov
The interaction of ethyl propiolate with 4,4-dimethyl-4,5-dihydro-2,3-dithiolo[3,4-c]quinoline-1-thiones
leads to 1,3-dithiol-2-ylidenes, 1,6,6a(λ4)-trithiapentalene, or thiino[2,3-c]quinolines depending on the
conditions.
Keywords:
1,3-dithiol-2-ylidene,
2,3-dithiolo[3,4-c]quinoline-1-thione,
thiino[2,3-c]quinoline,
1,6,6a(λ4)-trithiapentalenes, 1,3-dipolar cycloaddition.
As a continuation of studies on the heterocyclization reaction in condensed 1,2-dithiol-3-
thionedihydroquinolines [1] we have carried out the interaction of 4,4-dimethyl-4,5-dihydro-2,3-dithiolo[3,4-c]-
quinoline-1-thiones 1a,b with ethyl propiolate.
It is known that simple 1,2-dithiol-3-thiones may react with dipolarophiles both with opening of the
1,2-dithiol ring by a 1,3-dipolar cycloaddition and by fission of the thioketone bond by a [2+2] cycloaddition
with subsequent recyclization [2-4]. The direction, the character of the cycloaddition, the form, and the number
of products formed depends on the reaction conditions.
We have established that the cycloaddition of ethyl propiolate to compounds 1a,b, depending on the
conditions used (solvent, temperature), may proceed fairly selectively in any of the directions indicated. Thus on
boiling equimolar quantities of the reactants in chloroform the reaction takes place as the usual 1,3-dipolar
cycloaddition with opening of the 1,2-dithiol ring and the formation of 4-(4-carbethoxy-1,3-dithiol-2-ylidene)-
2,2-dimethyl-6-R-1,2,3,4-tetrahydroquinoline-3-thiones 2a,b, the structures of which were confirmed by data of
1H NMR and mass spectroscopy.
1
Signals appeared in the H NMR spectrum of compound 2a (Table 1), together with quinoline ring
signals, for the ethoxy group as a triplet at 1.48 and a quintet at 4.46 ppm, and also a signal for the one
quasiaromatic proton of the 1,3-dithiol ring at 8.02 and 8.34 ppm. Splitting of the latter into two singlets is
evidently caused by the existence of compounds 2a,b as E and Z isomers (Table 2).
High temperature interaction of ethyl propiolate with thiones 1a,b in boiling xylene occurs with fission
of the thioketone bond and subsequent recyclization with the formation of 5-R-2(3)-carbethoxy-9,9-dimethyl-
8,9-dihydroquino[3,4-b]-1,6,6a(λ4)-trithiapentalenes 3a,b.
__________________________________________________________________________________________
Voronezh State University, Voronezh 394693, Russia; e-mail: shikh@online.ru. Translated from
Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1056-1059, August, 2002. Original article submitted
December 17, 1999; revision submitted September 19, 2000.
918
0009-3122/02/3808-0918$27.00©2002 Plenum Publishing Corporation

TABLE 1. 1H NMR Spectra of Compounds 2-4
Chemical shifts, δ, ppm
Com-
Н arom.,
m (Σ H)
CMe2,
ArMe,
COOCH2CH3
NH
pound
C=CH, s
(s, 6Н) (s, 3H)
(s, 1H)
CH3, t
CH2
1.49
1.46
1.51
1.48
1.41
1.48
—
2.32
—
1.48
(3H)
4.46
5.98
5.49
6.02
5.86
6.01
5.69
6.3-7.6
8.02; 8.34, (1Н)
2а
2b
3а
3b
4a
4b
(m, 2Н)
(4Н)
1.39
4.36
6.31-7.58 7.98; 8.39, (1Н)
(3H)
1.36
(3H)
(m, 2H)
(3Н)
4.35
6.82-7.64
9.01 (1Н)
9.08 (1Н)
(m, 2H)
(4Н)
2.34
—
1.38
4.32
6.84-7.49
(3H)
(m, 2H)
(3Н)
0.85; 1.32 3.95, q; 4.18, q
6.6-7.1
7.48; 7.88
(2 × 3H)
(2 × 2Н)
(4Н)
(2Н)
2.21
0.89; 1.29 3.93, q; 4.21, q
6.5-7.0
7.35; 7.77
(2 × 3Н)
(2 × 2Н)
(3Н)
(2Н)
S
S
S
R
Me
Me
N
H
1a,b
2
HC CCOOEt
∆, xylene, 50 h
HC CCOOEt
∆, chloroform,
HC CCOOEt
∆, toluene, 20 h
20 h
COOEt
EtOOC
EtOOC
R
S
COOEt
HC CCOOEt
∆, toluene,
S
S
S
Me
Me
S
S
xylene
S
S
Me
Me
∆, 20 h
S
R
R
10 h
Me
Me
N
H
N
H
N
H
3a,b
4a,b
2a,b
1–4 a R = H, b R = Me
The presence of a 1,6,6a(λ4)-trithiapentalene structure in products 3a,b was confirmed unequivocally by
1
1
data of H NMR and mass spectroscopy. In the H NMR spectra of compounds 3a,b, in difference to thiones
2a,b, the signal for the quasiaromatic proton of the trithiapentalene ring is displaced into the low field region to
9.0-9.2 ppm, which is characteristic of the structure proposed. The mass spectra of compounds 3a,b also have a
characteristic fragmentation, differing from the mass spectra of adducts 2a,b [5]. In the latter there are ions
formed by fission of a molecule of the dipolarophile, which are absent from the former.
Boiling dihydrodithioloquinolinethiones 1a,b with ethyl propiolate in toluene leads to a mixture of
products 2 and 3, from which they were isolated successfully in pure form only in insignificant yield by column
chromatography.
It was shown by additional investigations that pentalenes 3a,b may be obtained by boiling thiones 2a,b
in xylene. It is evident that such a rearrangement is possible on catalysis by various sulfur-containing
compounds (elementary sulfur, the initial 1,2-dithiol-3-thione, etc) and occurs by the mechanism described
previously through the stage of radical addition of sulfur at the polarized methylene bond [6].
919

TABLE 2. Characteristics of Compounds 2-4
Found, %
——————
Com-
pound
Empirical
formula
Yield,
%
Calculated, %
mp, °С
C
H
N
S
C17H17NO2S3
C18H19NO2S3
C17H17NO2S3
C18H19NO2S3
C22H23NO4S3
C23H25NO4S3
56.32
56.20
4.71
4.68
3.89
3.86
27.69
26.45
126-127
131-132
181-182
149-150
122-123
151-152
65
67
53
48
71
78
2а
2b
3а
3b
4а
4b
57.15
4.97
3.68
26.03
57.29
5.04
3.71
25.46
56.28
56.20
4.64
4.68
3.79
3.86
26.52
26.45
57.24
5.03
3.79
25.38
57.27
5.07
3.71
25.48
57.34
57.27
4.90
4.99
3.01
3.04
20.89
20.82
58.26
5.27
2.89
20.26
58.11
5.26
2.95
20.21
It was established that compounds 2a,b, having a free α,β-unsaturated thioketone fragment, unlike
compounds 3a,b, participate in the diene synthesis reaction. On boiling them in toluene with an equimolar
amount of ethyl propiolate 2,2-dimethyl-4'(5'),9(10)-dicarbethoxy-1',3'-dithiol-2'-spiro-8-(2,3-dihydro-8H-
thiino[2,3-c]quinolines) 4a,b were formed, which were also obtained directly from 1,2-dithiole-3-thiones 1a,b
on boiling the latter with a twofold excess of ethyl propiolate. The structure of adducts 4a,b was confirmed by
their 1H NMR spectra, in which, unlike the 1H NMR spectra of compounds 2a,b, there were two sets of signals
for two carbethoxy groups and two singlets for the quasiaromatic protons.
EXPERIMENTAL
A check on the progress of reactions and the homogeneity of the substances obtained was effected by
1
TLC on Silufol UV 254 plates, eluent was chloroform. The H NMR spectra were taken on a Bruker AC-300
(300 MHz) instrument in DMSO-d6, internal standard was TMS. Mass spectra were taken on an LKB 9000
instrument, energy of ionizing electrons was 70 eV.
4-(4-Carbethoxy-1,3-dithiol-2-ylidene)-2,2-dimethyl-6-R-1,2,3,4-tetrahydroquinoline-3-thiones 2a,b.
Ethyl propiolate (0.01 mol) was added to a solution of compound 1 (0.01 mol) in chloroform (30 ml), and the
mixture was boiled for 20 h. The solvent was then removed, and the residue crystallized from isopropanol.
b
λ4
5-R-2(3)-Carbethoxy-9,9-dimethyl-8,9-dihydroquino[3,4- ]-1,6,6a( )-trithiapentalenes 3a,b.
A.
Ethyl propiolate (0.01 mol) was added to a solution of compound 1 (0.01 mol) in xylene (30 ml), and the
mixture boiled for 50 h, after which the solvent was distilled off, and the residue crystallized from isopropanol.
B. Compound 2 (0.005 mol) in xylene (30 ml) was boiled for 20 h. The solvent was then distilled off,
and the residue crystallized from isopropanol.
c
4'(5'),9(10)-Diethoxycarbonyl-2,2-dimethyl-1',3'-dithiolo-2'-spiro-8-(2,3-dihydro-8H-thiino[2,3- ]-
quinolines) 4a,b. A. Ethyl propiolate (0.01 mol) was added to a solution of compound 1 (0.01 mol) in toluene,
and the mixture boiled for 10 h. The solvent was then distilled off, and the residue crystallized from
isopropanol.
B. A mixture of compound 1 (0.01 mol) and ethyl propiolate (0.02 mol) in toluene was boiled for 20 h,
the solvent was distilled off, and the residue crystallized from isopropanol.
920

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