Electrogenerated base promoted synthesis of N-substituted-4-hydroxy-4- methylthiazolidine-2-thione derivatives

Article abstract of DOI:10.3184/030823409X12572506562749

Electrochemically-generated basic species from the reduction of acetonitrile assisted the condensation of carbon disulfide, primary arylmethylamines and chloroacetone to yield the corresponding N-substituted-4-hydroxy-4-methylthiazolidine-2-thione derivat

Full text of DOI:10.3184/030823409X12572506562749

710 RESEARCH PAPER
NOVEMBER, 710–712
JOURNAL OF CHEMICAL RESEARCH 2009
Electrogenerated base promoted synthesis of N-substituted-4-hydroxy-
4-methylthiazolidine-2-thione derivatives
Khalil Tissaoui, Noureddine Raouafi* and Khaled Boujlel
Laboratoire de Chimie Analytique et Electrochimie, Faculté des Sciences de Tunis, Université Tunis El-Manar,
Campus Universitaire 2092 Tunis, Tunisia
Electrochemically-generated basic species from the reduction of acetonitrile assisted the condensation of carbon
disulfide, primary arylmethylamines and chloroacetone to yield the corresponding N-substituted-4-hydroxy-
4-methylthiazolidine-2-thione derivatives. In some cases, dehydration reaction led to the N-substituted-4-
methylthiazole-2(3H)-thione analogues. The effect of the electrogenerated base amount on the reaction yield was
also studied.
Keywords: electrogenerated bases/anions, carbamodithioates, electrosynthesis, cyclisation, thiazolidine-2-thione, thiazole-
2-thione
Numerous new regulations and policies such the EPA
standards for polluting contaminants and European program
REACH for hazardous chemical registration are aimed to limit
and eventually to banish the use of polluting and hazardous
solvents and corrosive reagents from chemical processes.1-4
Alternative methods for organic compounds preparation
are therefore widely solicited. Recently, an efficient and
convenient one-pot electrosynthesis of tetrahydro-1-benzo[b]
pyran derivatives starting from malononitrile, aryl aldehydes
and dimedone without involvement of an added base was
reported.5 Feroci et al. reported numerous preparations and
synthetic applications of carbamates and oxazolinones under
mild conditions by cyanomethyl in situ electrogenerated
base (EGB).6,7 One of the most striking advantages of
electrochemical methods is the excellent control of the base
strength depending on the choice of the solvent acidity.
Furthermore, the amount of the electrogenerated base is a
function of the applied current densities and the duration of
the electrolysis which also could be also tuned.8
It is well established that the electrochemical reduction of
dry acetonitrile with, or without, the addition of a probase
such as azobenzene or cyanomethyl anion precursors like
cyanomethyl triphenylphosphonium9 in the presence of
quaternary ammonium salt as a supporting electrolyte produces
the corresponding cyanomethyl anion, a strong base entity,
with a pKa value of 31.3,10 which is strong enough to remove
weak acidic protons and is also able to act as a nucleophile.11,12
The anion could be easily stabilised as Grignard-type species
by association with the anodically-generated cation from the
oxidation of a sacrificial metal anode.13
versatile chiral auxiliaries for asymmetric synthesis,16 and as
intermediates for organic synthesis.17,18
Using an undivided electrochemical cell, fitted with a
magnesium rod as a sacrificial anode and a stainless steel
grid cathode and maintained under inert atmosphere of
argon, the electrolysis of anhydrous acetonitrile, under
galvanostatic conditions, yielded cyanomethyl anions/bases.
The electrolysis of acetonitrile was stopped when the desired
amount of base was formed. The amount was calculated
with respect to the quantity of amine to be introduced. Once
the electrolysis finished, the amine was introduced in the
basic medium followed by the addition of carbon disulfide
provoking a dramatic change in colour of the solution from
yellowish to dark-red. Finally, chloroacetone was added,
the solution was allowed to reach room temperature and
kept under continuous stirring overnight. Final work-up and
column chromatography over silica gel afforded the products
2 and 3 (Table 1) in good yields (Scheme 1).
A stabilised carbamodithioate intermediate was formed
during the reaction of carbon disulfide and the amine
promoted by the electrogenerated cyanomethyl and amino-
crotonitrile anions/bases.13,14 The carbamodithioate anion was
probably stabilised by ion-pairing with the electrogenerated
magnesium cations from the sacrificial magnesium anode.
Alkylation of the intermediate with chloroacetone gave
the acyclic intermediate which immediately underwent
ring closure to give product 2. Attempts failed to isolate
the acyclic intermediate even if 0.5 equivalents EGB were
used with respect to the amine. For all the studied amines,
the highest reaction yields were obtained for an amount of
electrogenerated base equal to 2.2 equivalents. In some cases,
the product 2 underwent dehydration reaction favoured by the
excess of formed EGB to give the product 3. The formation of
compound 3 from 2 has been confirmed by treating substrate
2 by EGB which gave product 3 in high yields. A series of
products 2 and 3 was synthesised by applying the latter
conditions i.e. consumption of 2.2 Faradays, to form the same
amount of EGB, followed by a subsequent addition of amine,
carbon disulfide and chloroacetone (Table 1).
In the last few years, we have devoted much effort to develop
an alternative synthesis of carbamodithioate derivatives from
primary and secondary amines and carbon disulfide using an
in situ electrogenerated base.14 We report here the synthesis
of
N-substitued-4-hydroxy-4-methylthiazolidine-2-thione
derivatives starting from various arylmethylamines, carbon
disulfide and chloroacetone promoted by electrochemically
generated bases. These products possess a large spectrum
of applications such as a subunit for material design
through charge transfer complexes formation,15 as a class of
Ar
Ar
S
S
N
N
1) 2.2 eq. EGB
H2N
Ar
+
2) 1.1 eq. CS2
S
S
OH
3) ClCH2-COCH3
1
2
3
Scheme 1
* Correspondent. Noureddine.raouafi@gmail.com//rdnnin@fst.rnu.tn
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JOURNAL OF CHEMICAL RESEARCH 2009 711
Table 1 Synthesised N-substituted-4-hydroxy-4-methylthiazolidine-2-thione 2 and N-substituted-4-methylthiazole-2-thione 3
Entry
Starting amine R–CH2–NH2; R =
Qa
2b/%
3b/%
a
b
c
d
e
f
Phenyl
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
85
68
53
46
79
54
65
72
11
c
Pyridin-2-yl
–
2-Chlorophenyl
4-Methylphenyl
4-Fluorophenyl
4-Methoxyphenyl
4-Chlorophenyl
3-Piperonyl
9
32
c
–
c
–
c
g
h
–
–
c
aThe consumed quantity of electricity represents the number of Faradays per mole of amine (F mol-1).
bThe yield was calculated in regard to the starting amine.
cProduct not isolated.
Comparatively to our previous preparation method for the
carbamodithioate14 using a two-compartment electrochemical
cell, inox steel grid as cathode and carbon graphite as anode,
improvement of the reaction yield was noticed that could
be mainly attributed to two factors: (i) the replacement of a
divided electrochemical cell by an undivided one allowed
the application of a higher current densities since the ohmic
drop was less important; and (ii) unlike the magnesium
anode, the oxidation of graphite carbon did not produce any
stabilising cations for the electrogenerated anonic species.
Note that when a small quantity of the same amine was used,
the electrolysis time of acetonitrile was shortened and less
basic species were re-protonated affording higher yields of
compound 2a (see Tables 1 and 2).
The number of Faradays with respect to the quantity
of amine, i.e. consumed amount of electrons during the
electrolysis of acetonitrile being proportional to the number
of mole of the electrogenerated base, affected the yield of the
reaction. This influence was studied in a typical procedure
using benzylamine as model compound. The standardised
procedure consisted of the electrolysis of the acetonitrile by
passing through the desired number of Faradays, and then
benzylamine was introduced, followed half an hour later by
carbon disulfide and finally chloroacetone. The solution was
stirred overnight and followed by a standard workup to yield
product 2a (Table 2).
The yield of the reaction increased with the amount of the
used electrogenerated base i.e. the number of Faradays. For an
amount of the base equal to 2.0–2.5 equivalents with respect
to benzylamine, the yield reached 85–87% which was a good
compromise between the reaction time and the consumed
energy and the Faradic yield i.e. chemical yield divided by
number of used Faradays was ca 40%. Furthermore, when a
five-fold excess of base was used per mole of amine, the yield
was only improved ca 7% and the Faradic yield decreased
to ca 19%.
As compared to classical synthetic methods, the present
one using electrogenerated bases shows several advantages
such as: (i) no additional base was required because of the
in situ base generation; (ii) milder reaction conditions and
use of cheap and readily available reagents; (iii) fair to very
good yields; (iv) no hazardous chemicals and polluting by-
products resulting from the addition of base or probase;
(v) no sophisticated electrochemical instrumentation and cell
needed; and (vi) an easy work-up procedure.
Experimental
Melting points were determined with an Electrothermal 9100
apparatus. 1H NMR and 13C NMR spectra were recorded using
a Bruker Advance 250 or 300 MHz spectrometer in CDCl3 with
tetramethylsilane as internal standard. IR spectra were measured
using Bruker Alpha ATR spectrometer; samples were dissolved in
CHCl3. High resolution mass spectra were performed by the ICSN,
Gif-sur-Yvette, Paris, France. Only products 2a and 3a have been
previously described19 and others similar compounds have also
been reported.20,21 Anhydrous acetonitrile (10 ppm, anhydroscan®)
was purchased from Labscan and dried over activated alumina.
All chemicals were purchased from Sigma-Aldrich and are used
without further purification.
Electroorganic synthesis of N-substituted-4-hydroxy-4-methyl
thiazolidine-2-thione 2
In a typical reaction, 90 mL dry acetonitrile solution of tetrabutyl-
ammonium tetrafluoroborate (0.01 M) as supporting electrolyte
in an undivided cell fitted with a sacrificial magnesium rod as an
anode and a stainless steel grid (20 cm2) as cathode was subjected to
electrolysis at a constant current density (I = 80 mA cm-2, 7.0 h, 2.2 F
mole-1 with respect to the quantity of amine to be added). The cell
was cooled to –20°C by immersing it in Lauder refrigerating system.
During the electrolysis, the system was maintained under inert
atmosphere by continuous bubbling of argon. The electrolysis was
stopped after the formation of 2.2 equivalents of cyanomethyl anion
with respect to the amine; 10.0 mmol of the amine was introduced
first and, one hour later, 2.2 equivalents of carbon disulfide were
added, and the solution turned immediately from pale yellow to
dark red. For the second set of experiments summarised in Table 2,
5.0 mmol of benzylamine, 11.0 mmol of CS2 and 11.0 mmol of
chloroacetone were used, respectively. After one hour of stirring,
2.2 equivalents of chloroacetone were added. The cooling bath was
removed and the solution was allowed to reach room temperature
and kept under continuous stirring overnight to ensure the tandem
alkyation–cyclisation reaction where it is possible. The excess of
acetonitrile was removed in rotatory evaporator and the residue was
diluted in 50 mL of water and extracted three times with 20 mL of
diethyl ether. The organic layer was washed with 20 mL of water and
dried over anhydrous magnesium sulfate. The solvent was removed
and the residue was purified by column chromatography on silica
gel 60. A mixture of ethyl acetate/hexanes (3:7) was used as eluant.
The resulting yellowish solid was filtered and recrystallised from
chloroform. All the products are known and were characterised by
1H NMR and 13C NMR spectroscopy, IR spectroscopy, melting point,
in some cases, HRMS and elemental analysis.
Table 2 Variation of the yield of 2a as a function of the
consumed number of Faradays in respect to the quantity of
amine
3-benzyl-4-hydroxy-4-methylthiazolidine-2-thione (2a): M.p. 106–
107°C (lit. 102–103); yield: 85%. IR (cm-1, CHCl3) n: 3570 (OH);
3120–2985 (CH); 1605 (C=C); 1210 (C=S). 1H NMR (300 MHz,
CDCl3) d: 1.28 (d, 3H, CH3, J = 10.7); 2.14 (br, 1H, OH); 3.47 (dd,
2H, CH2, J = 12.0 Hz); 5.11 (dd, 2H, CH2, J = 15.4 Hz); 7.24–7.40
(m, 5H, Harom.). 13C NMR (75 MHz, CDCl3) d: 25.8; 42.1; 48.8; 97.6;
126.6; 127.3; 127.5; 128.7; 128.9; 136.9; 197.2 (C=S). GC-MS:
m/z = 239 (M+); 221 (M+-H2O); 188 (M+-H2O-HS); 91 (C7H7+); 77
(C6H5+). HRMS Calcd for C11H13NOS2: 239.0439. Found 239.0475.
4-hydroxy-4-methyl-3-[(pyridin-2-yl)methyl]thiazolidine-2-thione
(2b): M.p. 112–113°C; yield: 68%. IR (cm-1, CHCl3) n: 3575 (OH);
Entry
Q/F mol−1
Yield of 2a/%
1
2
3
4
5
6
7
8
0.5
1.0
1.5
2.0
2.5
3.0
4.0
5.0
61
71
82
85
87
89
92
93
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712 JOURNAL OF CHEMICAL RESEARCH 2009
3125–2980 (CH); 1610 (C=C); 1214 (C=S). 1H NMR (300 MHz,
CDCl3) d: 1.74 (s, 3H, CH3); 2.30 (br, 1H, OH); 3.41 (dd, 2H, CH2,
J = 12.1 Hz); 5.12 (dd, 2H, CH2, J = 15.7 Hz); 7.26 (t, 1H, CHarom.);
7.52 (d, 1H, CHarom.); 7.73 (t, 1H, CHarom.); 8.44 (d, 1H, CHarom.).
13C NMR (75 MHz, CDCl3) d: 25.8; 43.1; 49.4; 96.8; 122.9; 124.5;
138.1; 148.2; 154.5; 196.2 (C=S). GC-MS: m/z = 240 (M+); 222
(M+-H2O); 189 (M+-H2O-HS); 92 (C6H6N+). HRMS Calcd for
C10H12N2OS2: 240.0391. Found 240.0404.
3-(2-chlorobenzyl)-4-methylthiazole-2(3H)-thione (3c): M.p. 98–
99°C; yield: 9%. IR (cm-1, CHCl3) n: 3100–2975 (CH); 1604 (C=C);
1175 (C=S).1H NMR (300 MHz, CDCl3) d: 2.11 (s, 3H, CH3); 5.53
(s, 2H, CH2); 6.26 (s, 1H, CH); 7.07–7.26 (mu, 4H, CHarom.). 13C
NMR (75.0 MHz, CDCl3) d: 15.2; 50.0; 106.1; 126.6; 127.8; 128.5;
128.8; 134.8; 140.3; 189.0 (C=S). HRMS Calcd for C11H10ClNS2:
254.9943. Found 254.9987.
4-methyl-3-(4-methylbenzyl)thiazole-2(3H)-thione (3d): M.p. 121–
122°C; yield: 32%. IR (cm-1, CHCl3) n: 3107–2990 (CH); 1605
(C=C); 1171 (C=S). 1H NMR (300 MHz, CDCl3) d: 2.08 (s, 3H,
CH3); 5.45 (s, 2H, CH2); 6.17 (s, 1H, CH); 6.96–7.09 (mu, 4H,
CHarom.). 13C NMR (75.0 MHz, CDCl3) d: 15.6; 21.1; 59.7; 106.0;
126.7; 129.5; 131.8; 137.6; 140.1; 189.2 (C=S). HRMS Calcd for
C12H13NS2: 235.0489. Found 235.0535.
3-(2-chlorobenzyl)-4-hydroxy-4-methylthiazolidine-2-thione (2c):
M.p. 115–116°C; yield: 53%. IR (cm-1, CHCl3) n: 3565 (OH); 3110–
1
2985 (CH); 1604 (C=C); 1206 (C=S). H NMR (300 MHz, CDCl3)
d: 1.45 (s, 3H, CH3); 3.11 (br, 1H, OH); 3.36 (dd, 2H, CH2, J = 12.0
Hz); 4.97 (dd, 2H, CH2, J = 15.4 Hz); 6.71–7.25 (4H, CHarom.). 13C
NMR (75 MHz, CDCl3) d: 23.8; 41.2; 59.2; 97.0; 128.8; 129.5;
133.3; 135.8; 160.2; 197.2 (C=S). HRMS Calcd for C11H12ClNOS2:
273.0049. Found 273.0083.
The authors thank the Tunisian MESRST for financial support
(Lab CH-02). Bernd Schöllhorn is also acknowledged for his
valuable help during the preparation of the manuscript.
4-hydroxy-4-methyl-3-(4-methylbenzyl)-thiazolidine-2-thione (2d):
M.p. 138–139°C; yield: 46%. IR (cm-1, CHCl3) n: 3574 (OH); 3124–
1
2982 (CH); 1601 (C=C); 1213 (C=S). H NMR (300 MHz, CDCl3)
d:1.53(s,3H,CH3);2.32(s,3H,CH3);3.31(dd,2H,CH2,2JH-H=11.7Hz);
4.94 (dd, 2H, CH2, dd, J = 16.6 Hz); 7.17 (dd, 4H, J = 3.0 Hz;
CHarom.). 13C NMR (75 MHz, CDCl3) d: 15.6; 21.1; 29.7; 49.9;
106.1; 126.6; 129.5; 131.8; 137.6; 140.1; 189.2 (C=S). HRMS Calcd
for C12H15NOS2: 253.0595. Found 240.0613.
Received: 16 August 2009; accepted 28 October 2009
Paper 09/0741 doi: 10.3184/030823409X12572506562749
Published online: 17 November 2009
3-(4-fluorobenzyl)-4-hydroxy-4-methylthiazolidine-2-thione (2e):
1
M.p. 122–123°C; yield: 79%. H IR (cm-1, CHCl3) n: 3557 (OH);
References
3111–2981 (CH); 1603 (C=C); 1217 (C=S). NMR (300 MHz,
CDCl3) d: 1.50 (s, 3H, CH3); 3.34 (dd, 2H, CH2, J = 12.4 Hz); 4.98
(dd, 2H, CH2, dd, J = 16.0 Hz); 6.96 (mu, 2H, CHarom.); 7.32 (mu,
2H, CHarom.). 13C NMR (75 MHz, CDCl3) d: 25.8; 42.1; 47.4;
97.6; 115.7; 128.6; 138.1; 160.5; 197.2 (C=S). HRMS Calcd for
C11H12FNOS2: 257.0344. Found 257.0356.
4-hydroxy-3-(4-methoxybenzyl)-4-methylthiazolidine-2-thione
(2f): M.p. 154–155°C; yield: 54%. IR (cm-1, CHCl3) n: 3576 (OH);
3110–2984 (CH); 1607 (C=C); 1223 (C=S). 1H NMR (300 MHz,
CDCl3) d: 1.47 (s, 3H, CH3); 3.33 (dd, 2H, CH2, J = 11.4 Hz); 3.81 (s,
3H, CH3); 5.02 (dd, 2H, CH2, J = 15.5 Hz); 6.72 (d, 2H, J = 8.5 Hz,
CHarom.); 7.26 (d, 2H, J = 8.5 Hz, CHarom.). 13C NMR (75.0 MHz,
CDCl3) d: 26.1; 42.1; 47.7; 49.8; 55.4; 97.8; 106.5; 114.1; 114.3;
128.3; 129.0; 140; 159.1; 196.9. HRMS Calcd for C12H15NO2S2:
269.0544. Found 269.0578.
1
2
3
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3-(4-chlorobenzyl)-4-hydroxy-4-methylthiazolidine-2-thione (2g):
9
J.H. Wagenknecht and M.M. Baizer, J. Org. Chem., 1966, 31, 3885.
M.p. 111–112°C; yield: 65%. IR (cm-1, CHCl3) n: 3572 (OH); 3112–
10 W.S. Matthews, J.E. Bares, J.E. Bartmess, F.G. Bordwell, F.J. Cornforth,
G.E. Drucker, Z. Margolin, R.J. McCallum, G.J. McCollum and N.R.
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14 M. Toumi, N. Raouafi, K. Boujlel, I. Tapsoba, J.P. Picard and M. Bordeau,
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1
2983 (CH); 1602 (C=C); 1214 (C=S). H NMR (300 MHz, CDCl3)
d: 1.51 (s, 3H, CH3); 3.42 (dd, 2H, CH2, J = 11.1 Hz); 5.01 (dd, 2H,
CH2, J = 16.6 Hz); 7.22 (2H, J = 8.1 Hz, CHarom.); 7.40 (2H, J = 8.1 Hz,
CHarom.). 13C NMR (75 MHz, CDCl3) d: 23.8; 41.7; 58.6; 98.4;
128.2; 129.1; 132.9; 135.8; 160.2; 196.6 (C=S). HRMS Calcd for
C11H12ClNOS2: 273.0049. Found 273.0085.
[(1,3-benzodioxol-5-yl)methy)]-4-hydroxy-4-methylthiazolidine-2-
thione (2h): M.p. 144–145°C; yield: 72%. IR (cm-1, CHCl3) n: 3565
(OH); 3113–2982 (CH); 1608 (C=C); 1211(C=S). 1H NMR (300 MHz,
CDCl3) d: 1.50 (s, 3H, CH3); 2.17 (br, 1H, OH); 3.35 (dd, 2H, CH2,
J= 10.8 Hz); 4.97 (dd, 2H, CH2, J = 14.5 Hz); 5.91 (s, 2H, CH2); 6.75–
6.94 (mu, 3H, CHarom.). 13C NMR (62.9 MHz, CDCl3) d: 25.7; 42.1;
47.8; 97.6; 101.1; 108.3; 120.8; 130.7; 147.0; 147.9; 197.1 (C=S).
HRMS Calcd for C12H13NO3S2: 283.0337. Found 273.0405.
18 A.J. Moore and M.R. Bryce, Synthesis 1997, 407-409.
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3-benzyl-4-methylthiazole-2(3H)-thione (3a): M.p. 88–89°C
(lit. 86–87°C); yield: 11%. IR (cm-1, CHCl3) n: 3105–2982 (CH);
1
1611 (C=C); 1184 (C=S). H NMR (300 MHz, CDCl3) d: 2.09 (s,
3H, CH3); 5.47 (s, 2H, CH2); 6.22 (s, 1H, CH); 7.18–7.34 (mu, 5H,
CHarom.). 13C NMR (75.0 MHz, CDCl3) d: 15.5; 50.4; 106.1; 126.8;
127.7; 128.2; 134.8; 147.1; 189.1 (C=S).
21 C.K. Bradsher, F.C. Bown and E.F. Sinclair, J. Am. Chem. Soc., 1956, 78,
6189.
PAPER: JC090741