An unprecedented synthesis of eight-membered-ring cyclic thioimidic esters by a three-component reaction

Article abstract of DOI:10.1055/s-0029-1216886

The three-component reaction of the isocyanides and dialkyl acetylenedicarboxylates or dibenzoylacetylene (DBA) in the presence of elemental sulfur is described. The reaction afforded the corresponding eight-membered cyclic thioimidic esters in good yield

Full text of DOI:10.1055/s-0029-1216886

PAPER
2733
An Unprecedented Synthesis of Eight-Membered-Ring Cyclic Thioimidic
Esters by a Three-Component Reaction
E
ight-Membered-R
b
ingCyclic
T
d
hioimidic
E
o
sters lali Alizadeh,* Reza Hosseinpour
Department of Chemistry, Tarbiat Modares University, P. O. Box 14115-175, Tehran 18716, Iran
Fax +98(21)88006544; E-mail: abdol_alizad@yahoo.com; E-mail: aalizadeh@modares.ac.ir
Received 13 April 2009; revised 23 April 2009
with O–H, N–H, and C–H acids has been widely stud-
ied,13–17 trapping of the initially formed 1:1 intermediate
with elemental sulfur has not been reported.
Abstract: The three-component reaction of the isocyanides and di-
alkyl acetylenedicarboxylates or dibenzoylacetylene (DBA) in the
presence of elemental sulfur is described. The reaction afforded the
corresponding eight-membered cyclic thioimidic esters in good
yields.
As part of our current studies18–21 on the development of
new routes to heterocyclic system we wish to report a sim-
ple one-pot three-component reaction between dialkyl
acetylenedicarboxylates or dibenzoylacetylene and isocy-
anides in the presence of elemental sulfur to yield cyclic
thioimidic esters. The thioimidates are useful intermedi-
ates,22 and recently a preparation was reported that uses
imidoyltriphenylphosphonium methylides.23
Key words: three-component reaction, acetylenic compound, ele-
mental sulfur, cyclic thioimidic ester, eight-membered ring
There has been a great interest in the sulfur containing
compounds because of their potential biological activity
and pharmaceutical significance.1 On the other hand, or-
ganosulfur compounds are also versatile reagents in or-
ganic synthesis.2 There are many methods available for
the synthesis of such compounds,3 among which a number
of sulfur-transfer reagents have also been reported.3,4
The reaction of alkyl isocyanides 1 with acetylenic esters
2 in the presence of elemental sulfur, proceeded spontane-
ously without activation of elemental sulfur at room tem-
perature in anhydrous dichloromethane–carbon disulfide
mixture (1:10) and was over within six hours to produce
cyclic thioimidic esters 3 in 80–92% yields (Table 1).
Utilization of elemental sulfur is a challenging synthetic
methodology for the preparation of organosulfur com-
pounds. Conventional methods, however, in general re-
quire harsh conditions. It was considered that transition
metal catalyzed activation of elemental sulfur could be an
interesting approach to control sulfuration reaction.5 The
abundance of sulfur, its low cost, and its almost nonodor-
ous nature is highly desirable in industrial or academic
processes.6 However, few such insertions involving ele-
mental sulfur as the intervening species have been de-
scribed.7 We now wish to incorporate elemental sulfur in
the area of isocyanide-based multicomponent reactions
(IMCRs).
Table 1 Reaction of Isocyanides 1 with Acetylenedicarboxylates 2
in the Presence of Elemental Sulfur
R2OC
S
COR2
NR1
COR2
+
CS2, CH2Cl2
r.t., 6 h
1
R1
N
C +
2
S8
/
2
4
S
R1N
R2OC
COR2
COR2
1
2
3
Entry
R1
t-Bu
R2
Product
Yield (%)a of 3
1
2
3
4
5
6
7
OMe
OMe
OEt
3a
3b
3c
3d
3e
3f
90
87
85
92
84
82
80
Isocyanide-based multicomponent reactions now occupy
a position of importance in synthetic organic chemistry,
mainly due to the contributions of Ugi and co-workers.8,9
In addition to many variations of the classical Ugi four-
component condensation (U-4CC), other IMCRs have en-
tered the arena in recent years.10 One such class, the reac-
tivity of nucleophilic carbenes such as isocyanides toward
dimethyl acetylenedicarboxylate (DMAD), is well docu-
mented.11 The reaction of isocyanides with C≡C bonds
occurs in a stepwise manner through a zwitterionic inter-
mediate, the ultimate fate of which appears to be dictated
by the nature of the original triple-bonded substrate.12
c-Hex
t-Bu
c-Hex
t-Bu
OEt
Ot-Bu
Ot-Bu
Ph
c-Hex
t-Bu
3g
a Isolated yield.
Although the trapping of the 1:1 intermediates formed be-
tween dialkyl acetylenedicarboxylates and isocyanides
The structures of compounds 3a–g were deduced from
1
their elemental analyses, IR, and high-field H and 13C
NMR spectra. The mass spectrum of 3a displayed the mo-
lecular ion (M+) peak at m/z 514, which is consistent with
the tetramethyl 2,6-bis(tert-butylimino)-2H,6H-1,5-
dithiocine-3,4,7,8-tetracarboxylate structure. The IR
SYNTHESIS 2009, No. 16, pp 2733–2736
x
x.
x
x
.
2
0
0
9
Advanced online publication: 07.07.2009
DOI: 10.1055/s-0029-1216886; Art ID: Z07009SS
© Georg Thieme Verlag Stuttgart · New York

2734
A. Alizadeh, R. Hosseinpour
PAPER
recorded on a Shimadzu IR-460 spectrometer. Chromatography
columns were prepared from Merck silica gel (230–240 mesh).
spectrum of 3a exhibited absorption band due to the car-
bonyl groups of esters and imines at 1681 and 1638 cm–1,
respectively.
Tetramethyl 2,6-Bis(tert-butylimino)-2H,6H-1,5-dithiocine-
3,4,7,8-tetracarboxylate (3a); Typical Procedure
1
The H NMR spectrum of 3a, exhibited three sharp sin-
To a magnetically stirred solution of dimethyl acetylenedicarboxy-
late (0.28 g, 2 mmol) and S8 (0.512 g, 2 mmol) in anhyd CH2Cl2–
CS2 mixture (1:10, 10 mL) was added dropwise a solution of tert-
butyl isocyanide (0.166 g, 2 mmol) in anhyd CH2Cl2 (2 mL) at
25 °C over 15 min. The reaction mixture was stirred for 6 h. The sol-
vent was removed under reduced pressure, and the residue was pu-
rified by column chromatography over silica gel (Merck 230–240
mesh) using a hexane–EtOAc mixture (5:1) as eluent; yield: 0.46 g
(90%); yellow powder; mp 95–97 °C.
glets readily recognized as arising from tert-butyl group
(d = 1.62), and two methoxy groups (d = 3.65 and 4.51).
The 1H decoupled 13C NMR spectrum of 3a showed 9 dis-
tinct resonances in agreement with the tetramethyl 2,6-
bis(tert-butylimino)-2H,6H-1,5-dithiocine-3,4,7,8-tetra-
1
carboxylate structure. The H and 13C NMR spectra of
compounds 3b–g are similar to those of 3a, except for N-
alkyl and the esters groups, which exhibit characteristic
signals with appropriate chemical shifts (see experimen-
tal).
IR (KBr): 1737 (C=O of ester), 1575 (C=N), 1689 (C=C), 1289 and
1248 cm–1 (C–O of ester).
1H NMR (500.13 MHz, CDCl3): d = 1.91 (s, 18 H, 2 t-C4H9), 3.91
(s, 6 H, 2 CO2CH3), 3.96 (s, 6 H, 2 CO2CH3).
Although we have not established the mechanism of the
reaction between the isocyanides and the acetylenic esters
in the presence of the elemental sulfur in an experimental
manner, a possible explanation is proposed in Scheme 1.
On the basis of the well-established chemistry of isocya-
nides,24 it is reasonable to assume that compounds 3 result
from initial addition of alkyl isocyanides to the acetylenic
esters and concomitant addition to elemental sulfur lead-
ing to charge transfer from negative carbon atom of zwit-
terions 4 onto sulfur atom that provide new zwitterions 5
and subsequent dimerization to produce cyclic thioimidic
esters (Scheme 1).
13C NMR (125.7 MHz, CDCl3): d = 27.67 [2 C(CH3)3], 53.39 (2
CO2CH3), 53.73 (2 CO2CH3), 65.90 (2 CMe3), 138.57 (2 C=C),
140.42 (2 C=C), 159.18 (2 CO2Me), 162.61 (2 CO2Me), 183.56 (2
C=N).
MS: m/z (%) = 514 (M+, 2), 484 (3), 234 (1), 168 (3), 101 (4), 58
(33), 43 (100).
Anal. Calcd for C22H30N2O8S2 (514.60): C, 51.35; H, 5.88; N, 5.44.
Found: C, 51.40; H, 5.80; N, 5.50.
Tetramethyl 2,6-Bis(cyclohexylimino)-2H,6H-1,5-dithiocine-
3,4,7,8-tetracarboxylate (3b)
Yield: 0.50 g (87%); yellow powder; mp 125–127 °C.
R2O2C
CO2R2
CO2R2
IR (KBr): 1745 (C=O of ester), 1572 (C=N), 1689 (C=C), 1279 and
1247 cm–1 (C–O of ester).
R1
N
C
+
C
N
R1
1H NMR (500.13 MHz, CDCl3): d = 1.01–2.29 (m, 20 H, 10 CH2 of
cyclohexyl), 3.84 (s, 6 H, 2 CO2CH3), 3.87 (s, 6 H, 2 CO2CH3), 4.93
(m, 2 H, 2 CH of cyclohexyl).
CO2R2
4
13C NMR (125.7 MHz, CDCl3): d = 24.94 (2 CH2), 25.33 (4 CH2),
32.66 (4 CH2), 53.33 (2 CO2CH3), 53.80 (2 CO2CH3), 59.21 (2
NCH), 137.20 (2 C=C), 141.25 (2 C=C), 158.92 (2 CO2Me), 162.49
(2 CO2Me), 182.80 (2 C=N).
R2O2C
CO2R2
S8
5
3
C
S
N
R1
MS: m/z (%) = 566 (M+, 2), 521 (22), 362 (27), 339 (6), 135 (5), 103
(10), 57 (30), 43 (100).
5
Scheme 1 Plausible reaction mechanism for the generation of
thioimidate derivatives from alkyl isocyanides 1 and acetylenic esters
2 in the presence of elemental sulfur
Anal. Calcd for C26H34N2O8S2 (566.68): C, 55.11; H, 6.05; N, 4.94.
Found: C, 55.10; H, 6.10; N, 4.85.
Tetraethyl 2,6-Bis(tert-butylimino)-2H,6H-1,5-dithiocine-
3,4,7,8-tetracarboxylate (3c)
Yield: 0.48 g (85%); yellow powder; mp 105–107 °C.
In summary, the present method carries the advantage
that, not only is the reaction performed under neutral con-
ditions, but also the substrates can be mixed without any
activation or modification.
IR (KBr): 1733 (C=O of ester), 1572 (C=N), 1689 (C=C), 1290 and
1242 cm–1 (C–O of ester).
1H NMR (500.13 MHz, CDCl3): d = 1.34 (t, 3JH,H = 7.1 Hz, 6 H, 2
OCH2CH3), 1.40 (t, 3JH,H = 7.1 Hz, 6 H, 2 OCH2CH3), 1.90 (s, 18 H,
Dimethyl, diethyl, and di(tert-butyl) acetylenedicarboxylates, tert-
butyl and cyclohexyl isocyanides were obtained from Merck (Ger-
many) and Fluka (Switzerland) and were used without further puri-
fication. Dibenzoylacetylene was prepared according to the
literature procedure.11 Melting points were measured on an Electro-
thermal 9100 apparatus. Elemental analyses for C, H, and N were
performed using a Heraeus CHN-O-Rapid analyzer. Mass spectra
were recorded on a Finnigan Matt 8430 mass spectrometer operat-
3
2 t-C4H9), 4.36 (q, JH,H = 7.1 Hz, 4 H, 2 OCH2CH3), 4.44 (q,
3JH,H = 7.1 Hz, 4 H, 2 OCH2CH3).
13C NMR (125.7 MHz, CDCl3): d = 13.98 and 14.08 (4 OCH2CH3),
27.71 [2 C(CH3)3], 62.53 and 63.26 (4 OCH2CH3), 65.76 (2 CMe3),
138.95 (2 C=C), 140.29 (2 C=C), 158.85 (2 CO2Et), 162.20 (2
CO2Et), 183.72 (2 C=N).
MS: m/z (%) = 570 (M+, 2), 386 (2), 317 (90), 272 (6), 215 (100),
187 (52), 145 (38), 84 (13), 57 (96).
1
ing at an ionization potential of 70 eV. H and 13C NMR spectra
were recorded (CDCl3 solution) on a Bruker DRX-500 Avance
spectrometer at 500.1 and 125.8 MHz, respectively. IR spectra were
Anal. Calcd for C13H19NO4S (570.71): C, 54.72; H, 6.71; N, 4.91.
Found: C, 54.68; H, 6.80; N, 4.85.
Synthesis 2009, No. 16, 2733–2736 © Thieme Stuttgart · New York

PAPER
Eight-Membered-Ring Cyclic Thioimidic Esters
2735
Tetraethyl 2,6-Bis(cyclohexylimino)-2H,6H-1,5-dithiocine-
3,4,7,8-tetracarboxylate (3d)
Yield: 0.58 g (92%); yellow powder; mp 120–122 °C.
13C NMR (125.7 MHz, CDCl3): d = 27.96 [2 C(CH3)3], 65.89 (2
CMe3), 128.57 (4 CH of C6H5), 128.81 (4 CH of C6H5), 129.03 (4
CH of C6H5), 129.57 (4 CH of C6H5), 133.64 (2 CH of C6H5),
134.43 (2 CH of C6H5), 136.00 (2 Cipso), 136.42 (2 Cipso), 144.33 (2
C=C), 146.46 (2 C=C), 184.35 (2 PhC=O), 186.37 (2 PhC=O),
190.05 (2 C=N).
IR (KBr): 1742 (C=O of ester), 1564 (C=N), 1688 (C=C), 1278 and
1247 cm–1 (C–O of ester).
1H NMR (500.13 MHz, CDCl3): d= 1.15–2.21 (m, 20 H, 10 CH2 of
MS: m/z (%) = 698 (M+, 2), 365 (3), 302 (4), 285 (4), 279 (5), 265
(9), 217 (16), 167 (10), 105 (38), 77 (36), 57 (83), 43 (100).
3
cyclohexyl), 1.32 (t, JH,H = 7.1 Hz, 6 H, 2 OCH2CH3), 1.37 (t,
3JH,H = 7.1 Hz, 6 H, 2 OCH2CH3), 4.35 (q, 3JH,H = 7.1 Hz, 4 H, 2
OCH2CH3), 4.42 (q, 3JH,H = 7.1 Hz, 4 H, 2 OCH2CH3), 5.00–5.03
(m, 2 H, 2 CH of cyclohexyl).
Anal. Calcd for C42H38N2O4S2 (698.89): C, 72.18; H, 5.48; N, 4.01.
Found: C, 72.10; H, 5.40; N, 4.10.
13C NMR (125.7 MHz, CDCl3): d = 13.95 and 14.04 (4 OCH2CH3),
25.06 (2 CH2), 25.41 (4 CH2), 32.78 (4 CH2), 59.13 (2 NCH), 62.60
and 63.38 (4 OCH2CH3), 137.28 (2 C=C), 141.64 (2 C=C), 158.71
(2 CO2Et), 162.15 (2 CO2Et), 183.18 (2 C=N).
References
(1) (a) Tanner, D. Angew. Chem., Int. Ed. Engl. 1994, 33, 599.
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Hanson, P. R. Chem. Rev. 2004, 104, 2239.
MS: m/z (%) = 622 (M+, 2), 256 (30), 155 (62), 99 (78), 81 (56), 64
(100), 54 (58).
Anal. Calcd for C30H42N2O8S2 (622.79): C, 57.86; H, 6.80; N, 4.56.
Found: C, 57.80; H, 6.75; N, 4.45.
(2) Cremlyn, R. J. An Introduction to Organosulfur Chemistry;
Wiley: Chichester, 1996.
Tetra(tert-butyl) 2,6-Bis(tert-butylimino)-2H,6H-1,5-dithiocine-
3,4,7,8-tetracarboxylate (3e)
Yield: 0.57 g (84%); yellow powder; mp 115–117 °C.
(3) (a) Pedersen, C. T. Sulfur Rep. 1995, 16, 173. (b) Pedersen,
C. T. Adv. Heterocycl. Chem. 1982, 31, 63. (c) McKinnon,
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IR (KBr): 1729 (C=O of ester), 1574 (C=N), 1689 (C=C), 1289 and
1251 cm–1 (C–O of ester).
1H NMR (500.13 MHz, CDCl3): d = 1.54 (s, 18 H, 2 CO2t-C4H9),
1.62 (s, 18 H, 2 CO2t-C4H9), 1.90 (s, 18 H, 2 t-C4H9).
13C NMR (125.7 MHz, CDCl3): d = 27.78 [2 C(CH3)3], 28.05 and
28.21 [2 CO2C(CH3)3], 65.29 (2 CMe3), 83.72 and 85.38 (2
CO2CMe3), 139.71 (2 C=C), 140.41 (2 C=C), 157.75 (2 CO2CMe3),
161.11 (2 CO2CMe3), 184.13 (2 C=N).
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MS: m/z (%) = 682 (M+, 2), 436 (3), 373 (6), 317 (2), 261 (4), 243
(3), 205 (24), 143 (4), 57 (100).
Anal. Calcd for C34H54N2O8S2 (682.93): C, 59.80; H, 7.97; N, 4.10.
Found: C, 59.70; H, 7.90; N, 4.00.
Tetra(tert-butyl) 2,6-Bis(cyclohexylimino)-2H,6H-1,5-dithio-
cine-3,4,7,8-tetracarboxylate (3f)
Yield: 0.60 g (82%); yellow powder; mp 110–112 °C.
(6) Kerverdo, S.; Fernandez, X.; Poualin, S.; Gingras, M.
Tetrahedron Lett. 2000, 41, 5841.
IR (KBr): 1732 (C=O of ester), 1566 (C=N), 1688 (C=C), 1273 and
1249 cm–1 (C–O of ester).
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1H NMR (500.13 MHz, CDCl3): d = 1.10–2.15 (m, 20 H, 10 CH2 of
cyclohexyl), 1.53 (s, 18 H, 2 CO2t-C4H9), 1.61 (s, 18 H, 2 CO2t-
C4H9), 5.00–5.04 (m, 2 H, 2 CH of cyclohexyl).
13C NMR (125.7 MHz, CDCl3): d = 25.04 (2 CH2), 25.44 (4 CH2),
28.02 and 28.20 [4 CO2C(CH3)3], 32.81 (4 CH2), 58.73 (2 NCH),
83.92 and 85.58 (4 CO2CMe3), 137.48 (2 C=C), 142.44 (2 C=C),
157.63 (2 CO2CMe3), 161.10 (2 CO2CMe3), 183.55 (2 C=N).
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MS: m/z (%) = 735 (M+, 2), 399 (3), 317 (6), 287 (8), 270 (5), 256
(92), 237 (14), 192 (13), 160 (13), 128 (32), 96 (23), 64 (100), 57
(74).
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Anal. Calcd for C38H58N2O8S2 (735.00): C, 62.10; H, 7.95; N, 3.81.
Found: C, 62.00; H, 7.90; N, 3.75.
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Phenyl[4,7,8-tribenzoyl-2,6-bis(tert-butylimino)-2H,6H-1,5-
dithiocine-3-yl]methanone (3g)
Yield: 0.56 g (80%); yellow powder; mp 145–147 °C.
IR (KBr): 1664 (C=O), 1594 (C=N), 1650 cm–1 (C=C).
1H NMR (500.13 MHz, CDCl3): d = 1.99 (s, 18 H, 2 t-C4H9), 7.34–
7.76 (m, 20 H, 20 CH of 4 C6H5).
Synthesis 2009, No. 16, 2733–2736 © Thieme Stuttgart · New York

2736
A. Alizadeh, R. Hosseinpour
PAPER
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Synthesis 2009, No. 16, 2733–2736 © Thieme Stuttgart · New York