4-Aryl-2-Imino-1,3-Dithiolanes from the Room Temperature Coupling of Sodium Dithiocarbamates with Sulfonium Salts

Article abstract of DOI:10.1002/ejoc.202100124

A series of 4-aryl-2-imino-1,3-dithiolanes was synthesized by means of a straightforward strategy starting from readily available precursors: reactions of dithiocarbamates and arylsulfonium salts, at room temperature in water/CH₂Cl₂ as biphasic medium, afforded the five-membered cyclic products in good yields. The reaction mechanism was investigated by DFT calculations.

Full text of DOI:10.1002/ejoc.202100124

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Very Important Paper
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4-Aryl-2-Imino-1,3-Dithiolanes from the Room Temperature
Coupling of Sodium Dithiocarbamates with Sulfonium Salts
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Giulio Bresciani,[a, b] Fabio Marchetti,[a, b] Gianluca Ciancaleoni,*[a, b] and Guido Pampaloni*[a, b]
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A series of 4-aryl-2-imino-1,3-dithiolanes was synthesized by
means of a straightforward strategy starting from readily
available precursors: reactions of dithiocarbamates and arylsul-
fonium salts, at room temperature in water/CH2Cl2 as biphasic
medium, afforded the five-membered cyclic products in good
yields. The reaction mechanism was investigated by DFT
calculations.
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Introduction
salts, as nitrogen and sulfur source,[22,23] with sulfonium reagents
[Me2SCH(Ar)CH2Br]Br acting as C2-synthon. This class of sulfo-
nium salts has aroused interest due to the presence of
fragments with an enhanced leaving ability, facilitating the
functionalization of complex substrates.[24] Inter alia, aryl-
sulfonium bromide salts have been employed as traditional,
convenient precursors to aryl-aziridines by combination with
amines,[25,26] and in the synthesis of aryl-oxazolidinones under
mild conditions.[27]
2-Imino-1,3-dithiolanes are five-membered heterocyclic com-
pounds containing two sulfur atoms adjacent to the iminium
function, which display interesting activities as insecticides,[1,2]
and pharmaceuticals against several diseases.[3–6] Furthermore,
this class of molecules has been also incorporated as ligands in
metal complexes.[7,8]
Some documented synthetic methods to access 2-imino-
1,3-dithiolanes require starting materials difficult to handle due
to their physical nature or their toxicity and corrosive
character.[9–12] Furthermore, substituted 2-imino-1,3-dithiolanes Results and Discussion
(or the corresponding iminium cations) have been obtained
from dithiocarbamate salts and epoxides in the presence[13] or
A series of sodium dithiocarbamate salts, Na[1a–e], was
not[14] of BF3 ·OEt2 as catalyst (Scheme 1A) or from the diiodine-
prepared in almost quantitative yield from the exothermic
reaction of carbon disulfide with primary amines in diethyl
ether in the presence of sodium hydroxide, Equation 1.[28] The
use of an excess of isopropylamine led to the ammonium
induced
cyclization
of
S-allyl
dithiocarbamates
(Scheme 1B).[4,15,16] Regioselective [3+2]-cycloaddition of 2-aryl/
alkylthiiranes with isothiocyanates mediated by Pd catalysts in
combination with a phosphine ligand,[17] a boron Lewis acid,[9]
or triethylamine in hot DMF[18] has also been used to yield the
2-imino-dithiolane frameworks (Scheme 1C). On the other hand,
a more simple strategy employing sodium dithiocarbamates in
combination with 1,2-dihaloalkanes as C2-synthons was re-
ported in several papers,[19–21] however the procedures required
the use of reflux conditions and additives such as K2CO3, NEt3,
or Br2 (Scheme 1D). The one-pot synthesis of 2-imino-1,3-
dithiolanes starting from allyl chloride, N-alkylamines, and CS2
was recently described (Scheme 1E).[3]
i
dithiocarbamate [NH3 Pr][1b], Equation 2.[29]
(1)
(2)
i
The air-stable products Na[1a–e] and [NH3 Pr][1b] were
Here, we report a new reaction leading to the synthesis of a
series of unprecedented N-alkyl-4-phenyl-2-imino-1,3-dithio-
lanes, carried out in dichloromethane/water medium at room
temperature, consisting in the assembly of dithiocarbamate
previously described.[30] Yields and reaction conditions for the
synthesis of these compounds are reported in Table 1.
The spectroscopic characterization of the compounds, being
rather sparse in the literature, has been performed for all the
compounds described in the paper and it is detailed in the
Experimental section. The IR spectra (solid state) display an
absorption assigned to the {CS2} moiety in the range 984–
949 cmÀ 1,[31] while the thioureide {NÀ CS2} carbon-nitrogen bond
stretching is observed in the interval 1526–1479 cmÀ 1, suggest-
ing a bond order in between a single (1350–1250 cmÀ 1) and a
double one (1690–1640 cmÀ 1).[32,33] Resonances around 210 ppm
due to the {CS2} carbon are observed in the 13C NMR spectra (in
CDCl3).
[a] Dr. G. Bresciani, Prof. F. Marchetti, Prof. G. Ciancaleoni, Prof. G. Pampaloni
Dipartimento di Chimica e Chimica Industriale
Università di Pisa
Via G. Moruzzi 13, 56124 Pisa, Italy
E-mail: gianluca.ciancaleoni@unipi.it
guido.pampaloni@unipi.it
[b] Dr. G. Bresciani, Prof. F. Marchetti, Prof. G. Ciancaleoni, Prof. G. Pampaloni
CIRCC
Via Celso Ulpiani 27, 70126 Bari, Italy
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejoc.202100124
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Table 1. Synthesis of N-alkyldithiocarbamates from carbon disulfide,
amine, and sodium hydroxide.
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]
R
Yield [%][a]
[b]
CH3
CH(CH3)2
Na[1a]
Na[1b]
[NH3 Pr][1b]
Na[1c]
Na[1d]
Na[1e]
98
88
98
97
97
98
[b]
[c]
i
CH(CH3)2
tBu=CMe3
[b]
Bn=CH2Ph[b]
[b]
Cy=C6H11
[a] Yields referred to isolated products. [b] Reaction conditions: Et2O 25 mL,
T=0 C, t=24 h, amine (17 mmol), CS2 (17 mmol), NaOH (17 mmol) in
MeOH (5 mL); [c] Reaction conditions: Et2O 25 mL, T=0 C, t=4 h, amine
°
°
(42 mmol), CS2 (16.6 mmol).
Table 2. Synthesis of 2-imino-1,3-dithiolanes from (2-bromo-1-arylethyl)
dimethylsulfonium bromide and sodium dithiocarbamates.
X
R
Yield [%][a]
2
3
H
CH3
7a
7b
7c
7d
54
56
49
57
CH(CH3)2
tBu=CMe3
Bn=CH2Ph
CH3
CH3
8a
8b
8d
63
74
74
CH(CH3)2
Bn=CH2Ph
5
6
F
CH3
10a
10d
72
47
Bn=CH2Ph
CO2Me
CH3
11a
76
[a] Yields referred to isolated products. Reaction conditions: H2O 30 mL,
CH2Cl2 15 mL, T=25 C, t=20 h, 2–6 (2.15 mmol), 1a–d (2.15 mmol).
°
Scheme 1. Preparation routes to 2-imino-1,3-dithiolanes (or to the corre-
sponding iminium cations).
The possible formation of thiazolidine-2-thiones (cyclic dithio-
carbamates) was ruled out by 13C NMR. Note that cyclic
dithiocarbamates are isomers of dithiolanes and their {SC=S}
Sulfonium salts can be easily obtained from styrene and
ring-substituted derivatives, and are versatile reagents in
organic chemistry, providing a C2 unit.[24] Thus, compounds
[Me2SCH(Ar)CH2Br]Br, 2–6, reacted with Na[1a–d] in water/
CH2Cl2 biphasic medium at ambient temperature, affording 7–
11 which were isolated in good yields after work-up, Table 2.
group is typically featured by
a
13C resonance at ca.
200 ppm,[32–36] whereas a diagnostic signal was found around
165 ppm in products spectra and assigned to the C=N moiety
of dithiolanes.[9,16] All the IR spectra of prepared 2-amino-1,3-
dithiolanes display an intense absorption from 1590 to
1605 cmÀ 1 due to the C=N stretching.
i
The use of [NH3 Pr][1b] in the place of Na[1b] for the synthesis
of 7b led to a comparable outcome. Isolated products were
characterized by elemental analysis, IR, and NMR spectroscopy.
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As for other synthetic procedures, the products were
to this, a weak hydrogen bond between a CH of 2 and a sulfur
of 1a (H…S distance=2.309 Å) further stabilizes TS6 with
respect to the others (Figure 1).
1
2
3
obtained as a mixture of E/Z isomers in an almost 1:1
ratio..[9,15–17,19]
In order to elucidate the mechanism of the reaction
between dithiocarbamate and sulfonium salts, a DFT study
(B3LYP-D3/def2-TZVP level of theory) was carried out on the
model reaction of 1a with 2 leading to 7a. The solvent effect
was considered with the conductor-like polarizable continuum
model, CPCM, as implemented in ORCA (solvent=water).
As 1a comprises two nucleophilic centers (i.e., N and S),
while two electrophilic sites are present in 2 (i.e., the carbon
bound to S, C1, and the carbon bound to Br, C2), in principle
four coupling reactions may be envisaged (see paths TS1, TS4,
TS6 and TS9 in Scheme 2). After the first attack, the cyclization
can take place. Three different isomers can be finally generated,
i.e. the experimentally observed 1,3-dithiolane 7a, 3-methyl-4-
phenylthiazolidine-2-thione (Prod-NS), and 3-methyl-5-phenyl-
thiazolidine-2-thione (Prod-SN). The latter two are accessible
from the initial nucleophilic addition by nitrogen (TS4, TS9),
whereas all of the three compounds are theoretically obtainable
In the intermediate species Int6b, either the nitrogen of the
thiocarbamate (TS7) or the other sulfur atom (TS8) is potentially
able to attack C1 (Scheme 2). The DFT-computed activation
energies for these processes are 31.6 and 15.8 kcalmolÀ 1,
respectively (Figure 2). Also, in this case, the attack of the
nitrogen involves a more sterically hindered transition state
because of the methyl substituent on the nitrogen, which is not
present on the sulfur. Obviously, bulkier substituents will even
amplify the difference, explaining why only 7a (and dithiolanes
in general) are experimentally found. Noteworthy, 7a is a
kinetic product, since ProdNS is thermodynamically more stable
by 9 kcalmolÀ 1. The large difference of energy between TS7
and TS8 implies that cyclic dithiocarbamates are quite difficult
to obtain through this procedure, which remains extremely
chemoselective.
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through TS1 and TS6. In particular, the formation of 7a appears Conclusion
the result of two consecutive S-attacks to 2.
The reactant complex (RC1) is not stable with respect to the
isolated reactants (ΔG= +6.9 kcalmolÀ 1), but it is easily acces-
sible at room temperature. The following transition states (TSs)
for the different nucleophilic additions have been optimized:
TS1 (S!C1), TS4 (N!C1), TS6 (S!C2), and TS9 (N!C2). The
corresponding Gibbs energies are 23.1, 34.8, 15.9, and
27.8 kcalmolÀ 1, respectively, indicating that the attack of sulfur
to C2 (TS6) is much more favorable than the others. This is
probably due to the less steric hindrance around S and C2, and
to the fact that, in water, a bromide is a better leaving group
A series of 4-aryl-2-imino-1,3-dithiolanes has been prepared in
good yields by using a novel and straightforward synthetic
strategy, consisting of the reaction between dithiocarbamates
and aryl-sulfonium salts at room temperature in water/CH2Cl2 as
a biphasic medium. A plausible reaction mechanism has been
outlined by DFT calculations, evidencing that the products are
selectively obtained instead of possible heterocyclic isomers
essentially due to kinetic reasons.
than SMe2 because it is more stabilized by solvation. In addition Experimental Section
Methods and materials. Organic reactants (Merck or TCI Europe)
were of the highest purity available and were stored under N2
atmosphere as received. Compounds [Me2SCH(Ar)CH2Br]Br, 3–7,
were prepared according to the literature.[27,37] Infrared spectra of
solid samples were recorded on a Perkin Elmer Spectrum One FT-IR
spectrometer equipped with a UATR sampling accessory (4000-
400 cmÀ 1 range) and were processed with Spectragryph software.[38]
NMR spectra were recorded at 298 K on a Bruker Avance II DRX400
instrument equipped with a BBFO broadband probe. Chemical
shifts (expressed in parts per million) are referenced to the residual
solvent peaks (1H, 13C).[39] NMR signals due to a second isomeric
form (where it has been possible to clearly distinguish them) are
Scheme 2. Theoretically possible reaction paths for the reaction of 1a with
2.
Figure 1. DFT-optimized geometry of TS6.
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Figure 2. DFT-computed energy paths for the reaction between 1a and 2.
1
italicized. NMR spectra were assigned with the assistance of H-13C
Sodium tert-butyldithiocarbamate, Na[1c].[44] Pale-pink solid, from
NH2 Bu and CS2. Yield: 2.82 g, 97%. Anal. Calc. for C5H10NNaS2: C,
(gs-HSQC and gs-HMBC) correlation experiments.[40] Elemental
analyses were performed on an Elementar Vario MICRO cube
instrument.
t
35.07; H, 5.89; N, 8.18; S, 37.45. Found: C, 35.16; H, 5.78; N, 8.04; S,
37.56. IR (solid state): ν=3335vs, 2978 m, 2122w, 1625m, 1476w-m,
1446w-m, 1393m, 1363m, 1349m, 1241w-m, 1201w-m, 1046w-m,
1
969 m, 925w-m, 882w-m, 756w, 679w cmÀ 1. H NMR (D2O) δ=1.47
(s, 9H, CH3) ppm. 13C{1H} NMR (D2O) δ=210.1 (SCS); 56.2 (NC); 27.4
Synthesis and characterization of sodium
N-alkyl-dithiocarbamates, Na[S2CNHR] (Na[1a–e])
(CH3) ppm.
Sodium N-benzyldithiocarbamate, Na[1d].[45] Pale pink solid, from
NH2Bn and CS2. Yield: 3.38 g, 97%. Anal. Calc. for C8H8NNaS2: C,
46.81; H, 3.93; N, 6.82; S, 31.24. Found: C, 46.65; H, 3.98; N, 6.68; S,
31.32. IR (solid state): ν=3313 m, 3244 m, 3058w-m, 3025w-m,
2927w-m, 1955w, 1617w, 1604w-m, 1503s, 1451m, 1429w-m,
1370w-m, 1331m, 1321m, 1298m, 1262m, 1233m, 1194w-m, 1155w,
1084m, 1066m, 1045m, 1028m, 984w-m, 968m, 933s, 915s, 893m-s,
The title compounds were prepared by modification of published
procedures.[30]
General procedure. A round bottom flask was filled with 25 mL of
diethyl ether, the selected amine (17 mmol), and carbon disulfide
°
(17 mmol), in the order given. The system was cooled to 0 C, thus a
solution of NaOH (1 eq.) in MeOH (5 mL) was added. The mixture
was stirred for 24 hours, then the resulting precipitate was
separated, washed with Et2O (2 x 15 mL), and dried under vacuum.
1
885s, 816w, 743w-m, 728m-s, 692s, 656w cmÀ 1. H NMR (D2O): δ=
7.42–7.31 (m, 5H, Ph), 4.75 (s, 2H, CH2) ppm. 13C{1H} NMR (D2O): δ=
Sodium N-methyldithiocarbamate, Na[1a].[41] Colourless solid, from
NH2Me and CS2. Yield: 2.15 g, 98%. Anal. Calc. for C2H4NNaS2: C,
18.60; H, 3.12; N, 10.84; S, 49.64. Found: C, 18.52; H, 3.20; N, 10.93; S,
49.42. IR (solid state): ν =3372s, 3282m-s, 3174s, 3016 m, 2111w-m,
1643w-m, 1625 m, 1526s, 1426w-m, 1338m-s, 1163m, 1019w-m,
949vs, 929vs, 755 m, 672w cmÀ 1. 1H NMR (D2O): δ=3.01 (s, 3H, CH3)
ppm. 13C{1H} NMR (D2O): δ=210.9 (SCS), 34.5 (CH3) ppm.
211.7 (SCS); 138.8, 128.8, 127.9, 127.1 (Ph); 51.0 (CH2) ppm.
Sodium N-cyclohexyldithiocarbamate, Na[1e].[46,47] Colourless solid,
from NH2Cy and CS2. Yield: 3.29 g, 98%. Anal. Calc. for C7H12NNaS2:
C, 42.61; H, 6.13; N, 7.10; S, 32.51. Found: C, 42.75; H, 6.18; N, 7.01; S,
32.40. IR (solid state): v=3334 vs, 3262vs, 2949w-m, 2932m, 2854w-
m, 2131vw, 1636m, 1609m, 1491m, 1447 w, 1367 w-m, 1353w,
1337m, 1246w, 1153w, 1091w, 976m-s, 945m, 885m, 795 w, 756w
cmÀ 1. 1H NMR (D2O): δ=4.08 (m, 1H, CH); 1.93 (m, 2H, CH2); 1.73 (m,
2H, CH2); 1.63–1.16 (m, 6H, CH2) ppm. 13C{1H} NMR (D2O): δ=207.9
(SCS); 57.3 (CH); 31.2, 24.9, 24.6 (CH2) ppm.
Sodium N-isopropyldithiocarbamate, Na[1b].[42,43] Colourless solid,
i
from NH2 Pr and CS2. Yield: 2.35 g, 88%. Anal. Calc. for C4H8NNaS2: C,
30.55; H, 5.13; N, 8.91; S, 40.79. Found: C, 30.38; H, 5.18; N, 9.02; S,
40.65. IR (solid state): ν =3362m-s, 2967w-m, 2112w, 1627w-m,
1479 m, 1449 m, 1387w-m, 1356 m, 1329w-m, 1298w-m, 1167m,
1123m, 1050w-m, 1001w, 967vs, 937m-s, 864w, 832w-m, 699w,
666w-m cmÀ 1. 1H NMR (D2O): δ=4.38 (m, 3JHH =6.7 Hz, 1H, CH); 1.19
Synthesis and characterization of isopropylammonium N-isopro-
i
i
pyldithiocarbamate, [NH3 Pr][S2CNH iPr] ([NH3 Pr][1b])[29]
Isopropylamine (3.4mL, 42mmol) was added to a solution of CS2
3
(d, JHH =6.6 Hz, 6H, CH3) ppm. 13C{1H} NMR (D2O): δ=208.1 (SCS);
°
(1.00mL, 16.6mmol) in Et2O (25mL), at 0 C. The mixture was stirred
50.2 (CH); 20.2 (CH3) ppm.
for 4 hours, and the resulting colourless precipitate was separated,
washed with cold Et2O (3×10mL) and dried under vacuum. Yield
3.16 g, 98%. Anal. Calc. for C7H18N2S2: C, 43.26; H, 9.33; N, 14.41; S,
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33.00. Found: C, 43.16; H, 9.22; N, 14.50; S, 33.04. IR (solid state): ν=
1123m, 985w, 904s, 820w, 767m, 695vs cmÀ 1. H NMR (CDCl3): δ=
7.54–7.33 (m, 5H, Ph); 5.10, 4.98 (m, 1H, C1H); 3.73–3.39 (m, 3H, C2H2
+CHMe2); 1.30-1.23 (m, 6H, CHMe2) ppm. Isomer ratio=1.1. 13C{1H}
NMR (CDCl3): δ=164.3, 163.7 (C3); 137.0, 136.7, 129.0, 128.9, 128.7,
128.6, 127.7, 127.6 (Ph); 60.7, 59.8 (CHMe2); 58.1, 54.3 (C1); 43.8, 40.7
(C2); 23.1, 23.0, 22.9, 22.8 (CHMe2) ppm.
1
2
3
4
5
6
7
8
3304m, 2966m, 2770m, 2699m, 2582w, 2502w, 1578w, 1481s,
1386m, 1282m, 1159s, 966 vs, 943s, 834s, 658 vs cmÀ 1
.
1H NMR
3
(D2O): δ=4.26 (m, 3JHH =6.5 Hz, 1H, CH, anion); 3.39 (m, JHH
=
3
6.5 Hz, 1H, CH, cation); 1.19 (d, JHH =6.5 Hz, 6H, CH3, anion); 1.07(d,
3JHH =6.5 Hz, 6H, CH3, cation) ppm. 13C{1H} NMR (D2O): δ=208.1
(SCS); 50.0 (CH, anion); 44.0 (CH, cation); 20.6 (CH3, anion); 19.8 (CH3,
cation) ppm.
N-(tert-butyl)-4-phenyl-1,3-dithiolan-2-imine, 7c
Synthesis and characterization of
9
N-alkyl-4-aryl-2-imino-1,3-dithiolanes
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General procedure. The appropriate reagents, respectively 2–6
i
(2.15 mmol) and [Na][1a-d] or [NH3 Pr][1b] (2.15 mmol), were
introduced into a round bottom flask containing 30 mL of H2O.
After 20 minutes of stirring, 15 mL of CH2Cl2 were added to the
system and the resulting mixture was stirred vigorously for
20 hours. After separation of the organic and aqueous phases, the
latter phase was further extracted with dichloromethane (2 x
10 mL). The organic liquors were collected together and dried with
anhydrous MgSO4, then the volatiles were removed under vacuum
affording an oily product. This oil was purified by flash chromatog-
raphy on Al2O3 using a dichloromethane/hexane mixture (4/1 v/v).
Yellow Oil. Yield 0.265 g, 49%. Anal. Calc. for C13H17NS2: C, 62.10; H,
6.82; N, 5.57; S, 25.51. Found: C, 61.92; H, 6.75; N, 5.67; S, 25.41. IR
(solid state): ν =2968m, 1593vs, 1453m, 1361s, 1203s, 986w, 893s,
695vs cmÀ 1. 1H NMR (CDCl3): δ=7.51–7.36 (m, 5H, Ph); 5.18, 4.93 (m,
1H, C1H); 3.78-3.76, 3.54–3.42 (m, 2H, C2H2); 1.39, 1.37 (s, 9H, CMe3)
ppm. Isomer ratio=1.3. 13C{1H} NMR (CDCl3): δ=160.2, 159.2 (C3);
137.2, 137.0, 129.0, 128.7, 128.5, 128.0, 127.8, 127.7 (Ph); 60.6
(CMe3); 58.1, 53.2 (C1); 46.4, 39.9 (C2); 28.6 (CMe3) ppm.
N-methyl-4-phenyl-1,3-dithiolan-2-imine, 7a
N-benzyl-4-phenyl-1,3-dithiolan-2-imine, 7d
Yellow oil. Yield 0.256 g, 54%. Anal. Calc. for C10H11NS2: C, 57.38; H,
5.30; N, 6.69; S, 30.64. Found: C, 57.22; H, 5.20; N, 6.76; S, 30.51. IR
(solid state): ν =3028w, 2925w, 1600vs, 1452m, 1395m, 1224w,
1158w, 997m, 903s, 767m, 695vs cmÀ 1 1H NMR (CDCl3): δ=7.49-
.
7.29 (m, 5H, Ph); 5.15, 5.03 (m, 1H, C1H); 3.76-3.65, 3.61-3.49 (m, 2H,
C2H2); 3.26, 3.25 (s, 3H, Me) ppm. Isomer ratio=1.1. 13C{1H} NMR
(CDCl3): δ=168.6, 168.0 (C3); 136.8, 136.5, 129.0, 128.9, 128.7, 128.6,
127.6, 127.5 (Ph); 58.2, 54.8 (C1); 45.2, 44.4 (Me); 43.9, 41.3 (C2) ppm.
Yellow Oil. Yield 0.359 g, 57%. Anal. Calc. for C16H15NS2: C, 67.33; H,
5.30; N, 4.91; S, 22.47. Found: C, 67.21; H, 5.30; N, 5.01; S, 22.54. IR
(solid state): ν =3028w, 2917w, 1578s, 1452s, 1308m, 1222m,
1
1073w, 1002m, 934s, 694vs cmÀ 1. H NMR (CDCl3) δ=7.55–7.34 (m,
10H, Ph); 5.19, 5.08 (m, 1H, C1H); 4.72–4.56 (m, 2H, CH2Ph); 3.80-3.71,
3.65–3.52 (m, 2H, C2H2) ppm. Isomer ratio=1.1 13C{1H} NMR (CDCl3)
δ=168.0, 167.5 (C3); 138.9, 138.8, 136.7, 136.5, 129.0, 128.9, 128.7,
128.6, 128.5, 128.4, 128.1, 127.8, 127.6, 127.5, 127.0 (Ph); 62.7, 61.9
(CH2Ph); 58.4, 54.8 (C1); 44.1, 41.1 (C2) ppm.
N-isopropyl-4-phenyl-1,3-dithiolan-2-imine, 7b
Yellow Oil. Yield 0.285 g, 56%. Anal. Calc. for C12H15NS2: C, 60.71; H,
6.37; N, 5.90; S, 27.02. Found: C, 60.58; H, 6.42; N, 5.82; S, 27.09. IR
(solid state): ν =2966m, 2868w, 1592vs, 1452m, 1338m, 1229w,
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Yellow Oil. Yield 0.418 g, 65%. Anal. Calc. for C17H17NS2: C, 68.19; H,
N-methyl-4-(p–tolyl) À 1,3-dithiolan-2-imine, 8a
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5.72; N, 4.68; S, 21.41. Found: C, 68.21; H, 5.70; N, 4.61; S, 21.48. IR
(solid state): ν =3027w, 2919w, 1596s, 1512m, 1452m, 1344w-m,
1185w, 1089w, 1019m, 908m, 814s, 695vs cmÀ 1. 1H NMR (CDCl3) δ=
7.44–7.31 (m, 9H, Ph+C6H4); 5.20, 5.06 (m, 1H, C1H); 4.62 (m, 2H,
CH2Ph); 3.75–3.53 (m, 2H, C2H2) ppm. Isomer ratio=1.1 13C{1H} NMR
(CDCl3) δ=167.9, 167.3 (C3); 139.0, 138.6, 138.5, 133.7, 133.5, 129.6,
128.4, 127.9, 127.5, 127.0 (Ph+C6H4); 62.8, 61.9 (CH2Ph); 58.4, 54.6
(C1); 44.1, 41.2 (C2); 21.2 (Me) ppm.
9
4-(4-chlorophenyl)-N-methyl-1,3-dithiolan-2-imine, 9a
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Yellow oil. Yield 0.326 g, 68%. Anal. Calc. for C11H13NS2: C, 59.15; H,
5.87; N, 6.27; S, 28.71. Found: C, 59.03; H, 5.75; N, 6.42; S, 28.85. IR
(solid state): ν =2967m, 2868w, 1711w, 1594vs, 1512m, 1455w,
1361m, 1220w, 1126m, 986w, 906s, 816vs, 736w cmÀ 1 1H NMR
.
(CDCl3): δ=7.37–7.34, 7.19-7.17 (m, 4H, C6H4); 5.10, 4.98 (m, 1H,
C1H); 3.69–3.48 (m, 2H, C2H2); 3.24, 3.23 (s, 3H, NMe); 2.36, 2.35 (s,
3H, C6H4Me) ppm. Isomer ratio=1.0. 13C{1H} NMR (CDCl3): δ=168.1,
167.5 (C3); 138.7, 138.5, 134.0, 133.6, 129.6, 127.6, 127.5 (C6H4); 58.2,
54.7 (C1); 45.4, 44.6 (NMe); 44.0, 41.3 (C2); 21.2 (C6H4Me) ppm.
N-isopropyl-4-(p–tolyl) À 1,3-dithiolan-2-imine, 8b
Yellow oil. Yield 0.330 g, 63%. Anal. Calc. for C10H10ClNS2: C, 49.27;
H, 4.13; N, 5.75; S, 26.31. Found: C, 49.16; H, 4.22; N, 5.71; S, 26.42. IR
(solid state): ν =3176w, 2918w, 2763vw, 1604vs, 1490vs, 1395m,
1226w, 1162w, 1088vs, 1013s, 905s, 822vs, 734s cmÀ 1 1H NMR
.
(CDCl3): δ=7.42–7.39, 7.35–7.32 (m, 4H, C6H4); 5.09, 4.96 (m, 1H,
C1H); 3.75–3.59, 3.53–3.49 (m, 2H, C2H2); 3.23 (s, 3H, Me) ppm.
Isomer ratio=1.0. 13C{1H} NMR (CDCl3): δ=167.7, 167.0 (C3); 135.8,
135.6, 129.2, 129.1, 129.0 (C6H4); 57.4, 53.9 (C1); 45.5, 44.8 (Me); 44.0,
41.3 (C2) ppm.
4-(4-chlorophenyl)-N-ispropyl-1,3-dithiolan-2-imine, 9b
Yellow Oil. Yield 0.378 g, 70%. Anal. Calc. for C13H17NS2: C, 62.10; H,
6.82; N, 5.57; S, 25.51. Found: C, 62.21; H, 6.72; N, 5.69; S, 25.45. IR
(solid state): ν =3022vw, 2919w, 1710w, 1602vs, 1513m, 1395m,
1221w, 1161vw, 998m, 905s, 816vs, 716w cmÀ 1. 1H NMR (CDCl3): δ=
7.36--7.33, 7.19–7.16 (m, 4H, C6H4); 5.06, 4.94 (m, 1H, C1H); 3.68–3.38
(m, 3H, C2H2 +CHMe2); 2.35, 2.34 (s, 3H, C6H4Me); 1.24, 1.22 (s, 6H,
CHMe2) ppm. Isomer ratio=1.1. 13C{1H} NMR (CDCl3): δ=165.3,
164.6 (C3); 138.6, 138.5, 133.8, 133.5, 129.6, 127.6, 127.5 (C6H4); 60.7,
59.7 (CHMe2); 58.0, 54.4 (C1); 43.9, 40.9 (C2); 23.1, 23.0 (CHMe2); 21.2
(C6H4Me) ppm.
Yellow Oil. Yield 0.432 g, 74%. Anal. Calc. for C12H14ClNS2: C, 53.02;
H, 5.19; N, 5.15; S, 23.59. Found: C, 53.09; H, 5.26; N, 5.01; S, 23.46. IR
(solid state): ν =3161vw, 2967m, 2868w, 1594vs, 1490vs, 1380m,
N-benzyl-4-(p–tolyl) À 1,3-dithiolan-2-imine, 8d
1
1089vs, 1013s, 907s, 821vs, 735m cmÀ 1. H NMR (CDCl3): δ=7.40–
7.37 (m, 4H, C6H4); 5.05, 4.92 (m, 1H, C1H); 3.69–3.58, 3.46–3.36 (m,
3H, C2H2 +CHMe2); 1.20 (m, 6H, CHMe2) ppm. Isomer ratio=1.0. 13C
{1H} NMR (CDCl3): δ=163.6, 162.9 (C3); 135.8, 135.6, 134.9, 134.4,
129.1, 129.0, (C6H4); 61.0, 60.1 (CHMe2); 57.1, 53.3 (C1); 43.9, 40.7 (C2);
23.2, 23.1, 23.1, 23.0 (CHMe2) ppm.
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Yellow Oil. Yield 0.306 g, 47%. Anal. Calc. for C16H14FNS2: C, 63.34; H,
4.65; N, 4.62; S, 21.13. Found: C, 63.21; H, 4.60; N, 4.71; S, 21.18. IR
4-(4-chlorophenyl)-N-benzyl-1,3-dithiolan-2-imine, 9d
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9
(solid state): ν =3028w, 2918w, 1598s, 1507vs, 1452m, 1341w-m,
1223s, 1159m, 1094w, 1014w, 930m, 834s, 695vs cmÀ 1 1H NMR
.
(CDCl3) δ=7.50–7.07 (m, 9H, Ph+C6H4); 5.18, 5.04 (m, 1H, C1H); 4.57
(m, 2H, CH2Ph); 3.77–3.64, 3.55–3.50 (m, 2H, C2H2) ppm. Isomer
ratio=1.0 13C{1H} NMR (CDCl3) δ=167.6, 166.9 (C3); 164.0 (d), 161.5
(d), 138.9, 129.4, 129.3, 128.5, 127.9, 127.1, 116.1, 116.0, 115.9, 115.8
(Ph+C6H4); 62.9, 62.0 (CH2Ph); 57.6, 53.9 (C1); 44.3, 41.3 (C2) ppm.
19F NMR (CDCl3): δ=À 112.5, À 112.8 (s, 1F) ppm
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Methyl-4-(2-(methylimino)-1,3-dithiolan-4-yl)benzoate, 11a
Yellow Oil. Yield 0.509 g, 74%. Anal. Calc. for C16H14ClNS2: C, 60.08;
H, 4.41; N, 4.38; S, 20.05. Found: C, 60.11; H, 4.30; N, 4.31; S, 20.14. IR
(solid state): ν =3028w, 2917w, 1595s, 1490vs, 1453m, 1348w,
1
1262w, 1080s, 1013s, 930m, 821s, 695vs cmÀ 1. H NMR (CDCl3) δ=
7.44–7.33 (m, 9H, C6H4 + Ph); 5.13, 5.01 (m, 1H, C1H); 4.54 (m, 2H,
CH2Ph); 3.76–3.64, 3.55 (m, 2H, C2H2) ppm. Isomer ratio=1.0 13C{1H}
NMR (CDCl3) δ=167.3, 166.7 (C3); 138.9, 135.7, 136.7, 135.4, 134.8,
134.6, 129.3, 129.1, 128.9, 128.6, 128.0, 127.2 (C6H4 +Ph); 63.0, 62.3
(CH2Ph); 57.7, 54.0 (C1); 44.3, 41.2 (C2) ppm.
4-(4-fluorophenyl)-N-methyl-1,3-dithiolan-2-imine, 10a
Yellow oil. Yield 0.437 g. 76%. Anal. Calc. for C12H13NO2S2: C, 53.91;
H, 4.90; N, 5.24; S, 23.99. Found: C, 53.82; H, 4.82; N, 5.36; S, 24.05. IR
(solid state): ν =2949w, 1716s (C=O), 1604s, 1434m, 1361m,
1
1274vs, 1181m, 1104sw, 905m, 773m, 704m cmÀ 1. H NMR (CDCl3):
δ=8.04–7.99, 7.59–7.53 (m, 4H, C6H4); 5.17, 5.05 (m, 1H, C1H); 3.91
(s, 3H, OMe); 3.81-3.64, 3.58–3.55 (m, 4H, C2H2); 3.23 (s, 3H, NMe)
ppm. Isomer ratio=1.0. 13C{1H} NMR (CDCl3): δ=168.4, 167.7 (C3);
166.4, 166.3 (C=O); 142.1, 142.0, 130.5, 130.4, 130.2, 130.2, 127.7,
127.6 (C6H4); 57.5, 54.2 (C1); 52.3 (OMe); 45.3, 44.6 (NMe); 43.8, 41.1
(C2) ppm.
Colourless oil. Yield 0.352 g, 72%. Anal. Calc. for C10H10FNS2: C,
52.84; H, 4.43; N, 6.16; S, 28.21. Found: C, 52.71; H, 4.51; N, 6.31; S,
28.31. IR (solid state): ν =2924w, 1601s, 1507vs, 1396m, 1296w,
DFT calculations
All geometries were optimized with ORCA 4.0.1.2,[48] using the
b3lyp functional in conjunction with a triple-ζ quality basis set
(def2-TZVP). The dispersion corrections were introduced using the
Grimme D3-parametrized correction and the BeckeÀ Johnson
damping to the DFT energy.[49] Most of the structures were
confirmed to be local energy minima (no imaginary frequencies).
The solvent was considered through the Continuum-like Polarizable
Continuum Model (C-PCM, water).
1222s, 1159m-s, 1095w, 997m, 905m, 833s, 718w cmÀ 1 1H NMR
.
(CDCl3): δ=7.48–7.45, 7.10–7.04 (m, 4H, C6H4); 5.14, 5.03 (m, 1H,
C1H); 3.77–3.53 (m, 2H, C2H2); 3.25, 3.24 (s, 3H, Me) ppm. Isomer
ratio=1.1. 13C{1H} NMR (CDCl3): δ=168.9, 168.2 (C3); 162.8 (d), 162.7
(d), 132.6 (d), 132.5 (d), 129.5 (d), 129.4 (d), 116.0 (d), 115.9 (d)
(C6H4); 57.5, 54.2 (C1); 45.2, 44.4 (Me); 44.1, 41.6 (C2) ppm. 19F{1H}
NMR (CDCl3): δ=À 112.5, À 112.7 (s, 1F) ppm.
4-(4-fluorophenyl)-N-benzyl-1,3-dithiolan-2-imine, 10d
Acknowledgements
We gratefully thank the University of Pisa for financial support
(Fondi di Ateneo 2019).
Conflict of Interest
The authors declare no conflict of interest.
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Keywords: Carbon disulfide · Cyclization · Dithiocarbamates ·
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Manuscript received: February 2, 2021
Revised manuscript received: February 15, 2021
Accepted manuscript online: February 23, 2021
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