Nef-isocyanide-Perkow synthesis of new polarized olefins containing 2-dicyanomethylene-2,3-dihydrothiazole and 2-dicyanomethylene-1,3-dithiole moieties

Article abstract of DOI:10.1016/j.tet.2013.01.023

Imidoyl chlorides (generated from isocyanides and acyl chlorides) reacts with triisopropyl phosphite, in a Perkow-type reaction, to produce 1-alkoxycarbonyl-2-(alkylimino)vinyl diisopropyl phosphate, which undergo a smooth reaction with bidentate nucleoph

Full text of DOI:10.1016/j.tet.2013.01.023

Tetrahedron 69 (2013) 2462e2467
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Nef-isocyanideePerkow synthesis of new polarized olefins
containing 2-dicyanomethylene-2,3-dihydrothiazole and
2-dicyanomethylene-1,3-dithiole moieties
,
a
a
a
Issa Yavari a , Reza Hosseinpour , Ramin Pashazadeh , Ehsan Ghanbari ,
*
Stavroula Skoulika b
a Department of Chemistry, Tarbiat Modares University, PO Box 14115-175, Tehran, Iran
b Laboratory of Physical Chemistry, Department of Chemistry, The University of Ioannina, 45110 Ioannina, Greece
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 October 2012
Received in revised form 19 December 2012
Accepted 8 January 2013
Available online 12 January 2013
Imidoyl chlorides (generated from isocyanides and acyl chlorides) reacts with triisopropyl phosphite, in
a Perkow-type reaction, to produce 1-alkoxycarbonyl-2-(alkylimino)vinyl diisopropyl phosphate, which
undergo a smooth reaction with bidentate nucleophilic intermediates obtained from the reaction be-
tween malononitrile and heterocumulenes, such as arylisothiocyanates or carbon disulfide to produce
polarized olefins containing 2-dicyanomethylene-2,3-dihydrothiazole and 2-dicyanomethylene-1,3-
dithiole moieties.
Keywords:
Ó 2013 Elsevier Ltd. All rights reserved.
Polarized olefins
Keteneimine
Dithiole
Dihydrothiazole
1. Introduction
isocyanides forming imidoyl chlorides.8 Also Nef-type reactions
could be obtained with highly electrophilic acid derivatives, such as
The concept of polarized (or pushepull) olefinic systems has
played an important role in organic chemistry for several decades.
Substitution of one carbon atom of the double bond with electron-
donating groups and of the other with electron-withdrawing
groups diminishes the double bond order by charge separa-
tion.1e3 The polarized structure of the double bond is discernible by
13C NMR due to the extreme deshielded position of the alkenyl
carbon on the donor side and the contrasting shielded position of
the carbon atom on the acceptor side of the pushepull alkene.
Polarized olefinic systems permit an intramolecular charge transfer,
which is relevant to notable electronic properties; for example,
optical nonlinearity.4,5
The unique properties of the isocyano group, which may func-
tion both as electrophile and nucleophile, have turned these com-
pounds into useful reagents. Beyond classical multicomponent
reactions,6 the most important applications of isocyanides are in
the synthesis of various heterocycles.7 A number of isocyanide re-
actions have seen their potential largely unexplored. It is probably
trifluoroacetic anhydride9 or acyl bromides, which are more re-
active than the corresponding chlorides.10,11 Intramolecular trap-
pings of the Nef adduct with various nucleophiles have been
reported.12e15 The scope of the Nef reaction could be further ex-
tended by adding external trapping agents prone to induce new
cascades.
One of the main problems of the Nef-isocyanide reaction is the
selectivity of the nucleophilic attack on the Nef adducts; either the
imidoyl or the carbonyl function can be attacked, which may lead to
isocyanide elimination. We anticipated that the use of the a-car-
boalkoxy substituent would make the ketone more electrophilic
and reduce the chance of elimination of the isocyanide and con-
sequent formation of trivial acylation derivatives. This modification
was found to be successful.
Ketenimines, the heterocumulenes that are structurally similar
to ketenes and carbodiimides, have numerous synthetic potenti-
alities.16 For instance, cycloaddition reactions of ketenimines have
become useful protocols for the construction of cyclic com-
pounds.17,18 Furthermore, addition reactions constitute another
important feature of ketenimines. Depending on the nature of
substituents attached to the cumulated double bonds, ketenimines
are known to act either as electrophiles to react with nucleophilic
reagents19 or act as nucleophiles toward electrophilic spicies.20
the case with the Nef reaction, the a-addition of acyl chlorides onto
* Corresponding author. Tel.: þ98 21 82883465; fax: þ98 21 82883455; e-mail
address: yavarisa@modares.ac.ir (I. Yavari).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.01.023

I. Yavari et al. / Tetrahedron 69 (2013) 2462e2467
2463
2. Results and discussion
As part of our current studies on the development of new routes to
polarized carbonecarbon double bonds,21e25 we studied the reaction
between keteneimines and the bidentate nucleophilic intermediates
obtained from malononitrile and carbon disulfide or isothiocyanates.
These reactions led to the synthesis of new polarized olefinic
systems containing 2-dicyanomethylene-2,3-dihydrothiazole and
2-dicyanomethylene-1,3-dithiole moieties (Table 1). These structures
possess highly polarized pushepull double bonds.
Table 1
Reaction of ethyl chloroglyoxalate (1a), cyclohexyl isocyanide (2a), triisopropyl
phosphite (3a), and malononitrile (4a) in the presence of phenyl isothiocyanate (5a)
or carbon disulfide at room temperaturea
Fig. 1. X-ray crystal structure of 6a. ORTEP-III Plot;26 arbitrary atom numbering.
deduced from the crystallographic experiment, by analogy can be
applied to the other products on account of their NMR-
spectroscopic similarities. For details of the structure de-
termination and refinement, see the Experimental part.
With the suitable reaction conditions in hand, we next explored
the protocol with alkyl chloroglyoxalates 1, isocyanides 2, triiso-
propyl phosphite 3, malononitrile or ethyl cyanoacetate (4), and
isothiocyanate in the presence of Et3N in MeCN. As shown in
Table 2, the reaction afforded the corresponding alkyl 3-aryl-2-
dicyanomethylene-4-alkylamino-2,3-dihydrothiazole-5-
carboxylates 6 in 40e65% yields.
Entry
Solvent
Base
Time (h)b
Yieldc (%) of
6a
7a
1
2
3
4
5
6
7
8
9
THF
THF
THF
EtOH
EtOH
EtOH
MeCN
MeCN
MeCN
Et3N
DBU
KOH
Et3N
DBU
KOH
Et3N
DBU
KOH
8
8
7
8
7
8
8
8
7
60
64
27
34
47
44
65
56
53
45
56
35
22
42
38
72
64
65
Table 2
Synthesis of functionalized 2,3-dihydrothiazole
a
General conditions: 1 (1 mmol), 2a (1 mmol), 3a (1 mmol), 4a malononitrile
(1 mmol), phenylisothocyanate (5a) or carbon disulfide (1 mmol) and base
(2 mmol).
b
Reaction time for consuming all of the starting materials.
Yields of isolated products.
c
We began our study by looking at the reaction of ethyl chlor-
oglyoxalate (1a), cyclohexyl isocyanide (2a), triisopropyl phosphite
(3a), and malononitrile (4a) in the presence of phenyl iso-
thiocyanate (5a), at room temperature in different solvent systems,
and the results are shown in Table 1. The desired product 6a could
be obtained in 27e65% yield using THF, EtOH, and MeCN as solvent
(Table 1). Common bases, such as Et3N, DBU, and KOH can catalyze
this reaction with low to moderate yields (Table 1, entries 1e9).
However, Et3N/MeCN system was the best combination of the
systems screened (see Table 1, entry 7). The same reaction was
carried out using carbon disulfide instead of 5a.
Entry
R
R0
Ar
Yield (%)a
of 6
a
b
c
d
e
f
Et
Me
Et
Et
Et
Et
Et
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
1,1,3,3-Tetramethylbutyl
Cyclohexyl
1,1,3,3-Tetramethylbutyl
Ph
Ph
65 (6a)
54 (6b)
58 (6c)
63 (6d)
46 (6e)
40 (6f)
46 (6g)
4-FeC6H4
2,4-Cl2eC6H3
2,4-Cl2eC6H3
4-O2NeC6H4
4-O2NeC6H4
g
a
Yields of isolated products.
The polarized nature of the double bond in 6a is discernible
from its 13C NMR shifts. The 13C NMR peak for the donor substituted
side of the pushepull alkene is 162.8 ppm, while the 13C NMR peak
for the acceptor side is 65.0 ppm. The 1H and 13C NMR spectra of
compounds 6bef are similar to those of 6a, except for the sub-
stituent on the 1,3-dithiole ring, which show characteristic signals
in the appropriate regions of the spectra.
To extend our knowledge of this transformation, we performed
the same reaction with carbon disulfide instead of isothiocyanate.
These reactions led to the formation of alkyl 5-alkylamino-2-
dicyanomethylene-1,3-dithiole-4-carboxylates and a nearly 1:1
mixture of the E/Z isomers of alkyl 2-(1-cyano-2-ethoxy-2-
oxoethylidene)-5-alkylamino-1,3-dithiole-4-carboxylates
7
in
Unambiguous evidence for the structure and stereochemistry of
compound 6a was obtained from a single-crystal X-ray analysis. An
ORTEP26 diagram of 6a is shown in Fig. 1. There are four molecules
of 6a in the unit cell. The molecular structure is further stabilized by
an intramolecular hydrogen bond of the type Nꢀ4eH/O2, with
40e72% yields (see Table 3). Compounds 7 were again fully char-
acterized with their IR, 1H NMR and 13C NMR spectra.
Although the detailed mechanism of this reaction remains to be
fully clarified, the formation of compounds 6 and 7 could be
explained by the reaction sequence in (Scheme 1). The addition of
isocyanides to acyl chlorides (Nef-isocyanide reaction) leads to
ꢀ
d(N4/O2)¼2.851(3) A and 4(N4eH/O2)¼128(2) . The structure

2464
I. Yavari et al. / Tetrahedron 69 (2013) 2462e2467
Table 3
Electrothermal-9100 apparatus. IR Spectra: Shimadzu IR-460
spectrometer; in cmꢁ1. 1H and 13C NMR Spectra: Bruker DRX-500
AVANCE instrument; in CDCl3 at 500.1 and 125.7 MHz, resp.; in
Synthesis of functionalized 1,3-dithiole
d
parts per million, J in Hertz. EIMS: Finnigan-MAT-8430 mass
spectrometer, at 70 eV; in m/z. Elemental analyses: Heraeus CHN-
O-Rapid analyzer.
3.2. Compounds 6aeg: general procedure
Entry
R
R0
Z
Yielda (%)
of 7
A mixture of alkyl chloroglyoxalate (1, 1 mmol) and alkyl iso-
cyanide (2, 1 mmol) was stirred at room temperature for 10 min.
Then, triisopropyl phosphite (0.208 g, 1 mmol) was added. The
reaction mixture was stirred for 5 min. Then, a solution of malo-
nonitrile (0.062 g, 1 mmol), Et3N (0.202 g, 2 mmol), and aryliso-
thiocyanate (5, 1 mmol) in MeCN (5 mL) was added in one portion.
After 3 h, the solvent was removed under reduced pressure and the
residue was purified by silica gel (Merck 230e240 mesh) column
chromatography using a hexane/EtOAc mixture 5:1 as eluant.
a
b
c
d
e
f
Me
Et
Me
Et
Me
Et
Cyclohexyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
t-Bu
t-Bu
CN
CN
CO2Et
CO2Et
CN
72 (7a)
67 (7b)
65 (7c)
62 (7d)
42 (7e)
46 (7f)
43 (7g)
48 (7h)
40 (7i)
45 (7j)
48 (7k)
47 (7l)
CN
g
h
i
j
k
l
Me
Et
Me
Et
Me
Et
t-Bu
t-Bu
CO2Et
CO2Et
CN
CN
CO2Et
CO2Et
1,1,3,3-Tetramethylbutyl
1,1,3,3-Tetramethylbutyl
1,1,3,3-Tetramethylbutyl
1,1,3,3-Tetramethylbutyl
3.2.1. Ethyl 2-dicyanomethylene-4-cyclohexylamino-2,3-dihydro-3-
phenylthiazole-5-carboxylate (6a). Yellow solid; (0.26 g, 65%); mp
172e174 ꢀC; [found: C, 63.82; H, 5.73; N, 14.12. C21H22N4O2S 394.49
requires C, 63.94; H, 5.62; N, 14.20%]; Rf (20% EtOAc/hexane) 0.80;
a
Yields of isolated products.
nmax (KBr): 3379 (NH), 2201 (CN), 1675 (C]O) cmꢁ1
; dH (500 MHz,
CDCl3) 7.69 (1H, t, 3J 7.5 Hz, 1 CH), 7.60 (2H, t, 3J 7.5 Hz, 2 CH), 7.42
(2H, d, 3J 7.5 Hz, 2 CH), 6.44 (1H, d, 3J 9.7 Hz, NH), 4.29 (2H, 3J 7.1 Hz,
CH2O), 2.39e2.44 (1H, m, CH), 1.33 (3H, t, 3J 7.1 Hz, Me), 0.87e1.57
(10H, m, 5 CH2); dC (125 MHz, CDCl3) 167.4 (C]O), 162.8 (C), 153.1
(C), 134.3 (C), 132.5 (CH), 130.4 (2 CH), 129.2 (2 CH), 116.3 (CN), 111.7
(CN), 84.7 (C), 65.0 (C), 61.3 (CH2O), 53.8 (CH), 33.9 (2 CH2), 24.9 (2
CH2), 24.3 (CH2), 14.3 (Me); m/z (EIMS) 394.2 (36 Mþ), 312 (25), 278
(18), 212 (10), 168 (33), 139 (31), 91 (72), 69 (89), 55 (100%).
3.2.1.1. X-ray crystal structure determination of 6a. Structure
determination and refinement data: formula, C21H22N4O2S; Mr
394.49; monoclinic, space group P2(1)/c, a¼9.262(1) b¼21.150(1),
3
ꢀ
ꢀ
c¼11.500(1) A,
a
¼90ꢀ,
b
¼113.26(1)ꢀ,
g
¼90 ; Z¼4, V¼2069.7(3) A ,
ꢀ
3
ꢀ
Dcalcd.¼1.266 Mg/m ; MoKa radiation (0.71073 A); T¼293(2) K. 4081
reflections collected on a Bruker P4 diffractometer, 3625 unique
(Rint¼0.0415). All heavy atoms have been located by difference
Fourier maps and refined anisotropically. The five ‘free’ carbon atoms
of the cyclohexane ring appeared to be disordered and have been
refined over two positions with occupations factors 0.6 and 0.4.
During refinement the bond distances and angles of the ring have
been fixed by using DFIX and DANG. All hydrogen atoms except that
of the NH group, have been placed on calculated positions and re-
finedisotropically by using the riding model. The NH proton has been
located by difference Fourier maps and refined isotropically. Final
Scheme 1. A plausible mechanism for the formation of compounds 6 and 7.
imidoyl chlorides, which can later be treated with triisopropyl
phosphite to afford ketenimines in a Perkow-type reaction.13 Then,
the reaction of triethylammonium salts of 8 with ketenimine give
intermediate 9, which is converted to intermediate 10 by proton
transfer reaction. This intermediate undergoes removal of phos-
phate with intramolecular cyclization and tautomerization to
products 6 and 7 (Scheme 1).
In summary, utilizing 1-alkoxycarbonyl-2-(alkylimino)vinyl dii-
sopropyl phosphate (the ketenimine intermediate) we have dem-
onstrated two efficient and practical methods to synthesis of 2,3-
dihydrothiazole-4-amino-5-carboxylate and 1,3-dithiole-5-amino-
4-carboxylate in moderate yields. In addition, the mild and simple
reaction conditions of these procedures (no high temperature or
inert atmosphere) make them suitable for the generation of such
derivatives. Further application of Nef-isocyanideePerkow adducts
to synthesis of libraries compounds is in progress in our laboratory.
indices for 1517 reflections with I>2s(I): R1¼0.0733, wR2¼0.1374,
GOF¼979. The crystallographic data of 6a have been deposited with
the Cambridge Crystallographic Data Centre as supplementary
publication number CCDC-875116. Copies of the data can be ob-
tained, free of charge, via the internet (http://www.ccdc.cam.ac.uk/
data_request/cif), e-mail (data_request@ccdc.cam.ac.uk), or fax
(þ44-1223-336033).
3.2.2. Methyl 2-dicyanomethylene-4-cyclohexylamino-2,3-dihydro-
3-phenylthiazole-5-carboxylate (6b). Yellow solid; (0.21 g, 54%); mp
168e170 ꢀC; [found: C, 63.21; H, 5.35; N, 14.68. C20H20N4O2S 380
requires C, 63.14; H, 5.30; N, 14.73%]; Rf (20% EtOAc/hexane)
3. Experimental
3.1. General
0.84; nmax (KBr): 3343 (NH), 2205 (CN), 1678 (C]O) cmꢁ1
; dH
(500 MHz, CDCl3) 7.56 (1H, t, 3J 7.4 Hz, 1 CH), 7.41 (2H, t, 3J 7.4 Hz, 2
CH), 7.35 (2H, d, 3J 7.4 Hz, 2 CH), 7.30 (1H, d, 3J 9.5 Hz, NH), 3.33 (3H,
s, Me), 2.70e2.75 (1H, m, CH), 0.84e1.60 (10H, m, 5 CH2); dC
(125 MHz, CDCl3) 165.4 (C]O), 162.0 (C), 148.2 (C), 132.8 (C), 130.6
(CH), 130.0 (2 CH), 124.6 (2 CH), 114.3 (CN), 114.1 (CN), 85.5 (C), 64.2
Isocyanides 1, alkyl cyanoacetates 2, triisopropyl phosphite (3),
malononitrile (4), arylisothiocyanates 5, and CS2 were obtained
from Merck and used without further purification. Mp:

I. Yavari et al. / Tetrahedron 69 (2013) 2462e2467
2465
(C), 59.7 (MeO), 59.0 (CH), 32.2 (2 CH2), 24.8 (2 CH2), 24.7 (CH2); m/
z (EIMS) 380 (2 Mþ), 330 (32), 302 (17), 240 (47), 186 (43), 168 (38),
136 (23), 93 (42), 77 (95), 55 (100%).
nmax (KBr): 3413 (NH), 2205 (CN), 1642 (C]O) cmꢁ1
;
dH (500 MHz,
CDCl3) 8.50 (1H, br s, NH), 8.21 (2H, d, 3J 7.3 Hz, 2 CH), 7.55 (1H, d,
3J 7.3 Hz, 2 CH), 4.65 (2H, 3J 7.2 Hz, CH2O),1.42 (6H, s, CMe2),1.31 (2H,
s, CH2), 1.24 (9H, s, CMe3), 0.98 (3H, t, 3J 7.1 Hz, Me); dC (125 MHz,
CDCl3) 167.1 (C]O), 153.5 (C), 152.0 (C), 142.3 (C), 125.3 (C), 125.1 (2
CH),120.4 (2 CH),117.6 (CN),112.3 (CN), 86.2 (C), 68.1 (C), 66.3 (CH2O),
55.1 (CMe2), 51.6 (CMe3), 31.4 (CH2), 29.7 (CMe3), 29.3 (CMe2), 14.1
(Me); m/z (EIMS) 469 (2 Mþ), 412 (10), 331 (5), 290 (15), 226 (100),
198 (72), 165 (93), 138 (45), 108 (52), 92 (17), 58 (64%).
3.2.3. Ethyl 2-dicyanomethylene-4-cyclohexylamino-3-(4-
fluorophenyl)-2,3-dihydrothiazole-5-carboxylate (6c). Yellow oil;
(0.24 g, 58%); [found: C, 60.78; H, 5.24; N, 13.48. C21H21FN4O2S 412
requires C, 61.15; H, 5.13; N,13.58%]; Rf (20% EtOAc/hexane) 0.83; nmax
(KBr): 3438 (NH), 2196 (CN),1669 (C]O) cmꢁ1
; dH (500 MHz, CDCl3)
7.40e7.45(2H, m, 2 CH), 7.25e7.31 (2H, m, 2 CH), 6.43 (1H, d, 3J 9.6Hz,
NH), 4.28 (2H, 3J 7.2 Hz, CH2O), 2.40e2.44 (1H, m, CH), 1.32 (3H, t, 3J
7.2 Hz, Me), 0.82e1.70 (10H, m, 5 CH2);dC (125MHz, CDCl3) 167.6 (C]
O),164.2 (d,1JCF 253.9 Hz, C),162.6 (C),153.1 (C),131.3 (d, 3JCF 9.3 Hz, 2
CH), 130.2 (d, 4JCF 3.4 Hz, C), 117.7 (d, 2JCF 23.1 Hz, 2 CH), 116.1 (CN),
111.8 (CN), 85.4 (C), 68.1 (C), 61.4 (CH2O), 54.0 (CH), 31.9 (2 CH2), 29.3
(2 CH2), 22.7 (CH2), 14.3 (Me); m/z (EIMS) 412 (21 Mþ), 330 (15), 279
(36), 210 (10), 167 (84), 149 (100), 113 (34), 83 (36), 71 (45), 57 (52%).
3.3. Compounds 7ael: general procedure
A mixture of alkyl chloroglyoxalate (1, 1 mmol) and alkyl iso-
cyanide (2, 1 mmol) was stirred at room temperature for 10 min.
Then, triisopropyl phosphite (0.208 g, 1 mmol) was added. The
reaction mixture was stirred for 5 min. Then, a solution of the active
methylene compound (4, 1 mmol), Et3N (0.202 g, 2 mmol), and CS2
(2 mmol) in MeCN (5 mL) was added in one portion. After 2 h, the
solvent was removed under reduced pressure and the residue was
purified by silica gel (Merck 230e240 mesh) column chromatog-
raphy using a hexane/EtOAc mixture 5:1 as eluant.
3.2.4. Ethyl 3-(2,4-dichlorophenyl)-2-dicyanomethylene-4-
cyclohexylamino-2,3-dihydrothiazole-5-carboxylate
(6d). Yellow
oil; (0.29 g, 63%); [found: C, 54.58; H, 4.26; N, 12.23 C21H20Cl2N4O2S
462 requires C, 54.43; H, 4.35; N, 12.09%]; Rf (20% EtOAc/hexane)
0.82; nmax (KBr): 3319 (NH), 2204 (CN), 1675 (C]O) cmꢁ1
;
dH
3.3.1. Ethyl 2-dicyanomethylene-5-cyclohexylamino-1,3-dithiole-4-
carboxylate (7a). Yellow solid; (0.24 g, 72%); mp 152e154 ꢀC;
[found: C, 53.71; H, 5.11; N, 12.53 C15H17N3O2S2 335 requires C,
53.64; H, 5.18; N, 12.43%]; Rf (20% EtOAc/hexane) 0.72; nmax (KBr):
(500 MHz, CDCl3) 7.66 (1H, s, CH), 7.46 (1H, s, CH), 7.43 (1H, d, 3J
7.0 Hz, CH), 6.33 (1H, d, 3J 9.5 Hz, NH), 4.30 (2H, 3J 7.1 Hz, CH2O),
2.53e2.57 (1H, m, CH), 1.30 (3H, t, 3J 7.1 Hz, Me), 1.10e1.78 (10H, m,
5 CH2); dC (125 MHz, CDCl3) 166.9 (C]O), 162.5 (C), 152.6 (C), 139.7
(C),135.7 (C),131.9 (CH),130.6 (C),130.6 (CH),128.8 (CH),115.6 (CN),
111.4 (CN), 86.1 (C), 71.5 (C), 61.5 (CH2O), 54.8 (CH), 31.8 (2 CH2),
29.6 (2 CH2), 29.3 (CH2), 14.1 (Me); m/z (EIMS) 462 (10 Mþ), 412
(12), 380 (10), 330 (5), 309 (10), 261 (4), 220 (7), 186 (12), 149 (15),
111 (24), 84 (75), 71 (95), 57 (90%).
3436 (NH), 2205 (CN), 1664 (C]O), 1575 (C]C), 1452 (C]C) cmꢁ1
;
dH (500 MHz, CDCl3) 8.00 (1H, br s, NH), 4.25 (2H, 3J 7.1 Hz, CH2O),
3.12e3.16 (1H, m, CH), 1.19e2.00 (10H, m, 5 CH2), 1.32 (3H, t, 3J
7.1 Hz, Me); dC (125 MHz, CDCl3) 173 (C]O), 162.5 (C), 157.3 (C),
113.6 (CN), 112.8 (CN), 89.9 (C), 62.6 (C), 61.5 (CH2O), 58.6 (CH), 33.2
(2 CH2), 24.9 (CH2), 24.2 (2 CH2), 14.3 (Me); m/z (EIMS) 335 (68 Mþ),
252 (65), 224 (42), 206 (25), 180 (7), 145 (15), 109 (22), 99 (16), 83
(48), 73 (36), 64 (22), 55 (100%).
3.2.5. Ethyl 4-(2,4,4-trimethylpentan-2-ylamino)-3-(2,4-dichloro-
phenyl)-2-dicyanomethylene-2,3-dihydrothiazole-5-carboxylate
(6e). Yellow oil; (0.23 g, 46%); [found: C, 55.74; H, 5.24; N, 11.23
C23H26Cl2N4O2S 492 requires C, 55.98; H, 5.31; N, 11.35%]; Rf (20%
EtOAc/hexane) 0.75; nmax (KBr): 3326 (NH), 2204 (CN), 1634 (C]O)
3.3.2. Methyl 2-dicyanomethylene-5-cyclohexylamino-1,3-dithiole-
4-carboxylate (7b). Yellow solid; (0.21 g, 67%); mp 148e150 ꢀC;
[found: C, 52.32; H, 4.70; N, 13.07 C14H15N3O2S2 321 requires C,
52.41; H, 4.76; N, 13.15]; Rf (20% EtOAc/hexane) 0.76; nmax (KBr):
cmꢁ1 dH (500 MHz, CDCl3), 7.39 (1H, s, CH), 7.18 (1H, d, 3J 7.0 Hz, CH),
;
6.86 (1H, br s, NH), 6.83 (1H, d, 3J 7.0 Hz, CH), 4.50 (2H, 3J 7.2 Hz, CH2O),
1.52 (6H, s, CMe2), 1.24 (2H, s, CH2), 0.99 (9H, s, CMe3), 0.97 (3H, t, 3J
7.2 Hz, Me); dC (125 MHz, CDCl3) 166.5 (C]O), 158.2 (C), 156.4 (C),
141.9 (C), 141.2 (C), 129.8 (C), 129.7 (CH), 127.7 (CH), 123.8 (CH), 115.6
(CN), 115.4 (CN), 87.1 (C), 67.0 (C), 62.2 (CH2O), 55.2 (CMe2), 51.7
(CMe3), 31.5 (CMe3), 30.9 (CH2), 29.7 (CMe2), 14.2 (Me); m/z (EIMS)
492 (2 Mþ), 412 (14), 330 (10), 247 (15), 186 (31), 149 (48), 113 (43), 85
(52), 71 (95), 57 (100%).
3442 (NH), 2207 (CN), 1662 (C]O), 1572 (C]C), 1449 (C]C) cmꢁ1
;
dH (500 MHz, CDCl3) 8.00 (1H, br s, NH), 3.80 (3H, s, MeO),
3.12e3.17 (1H, m, CH), 1.21e2.00 (10H, m, 5 CH2); dC (125 MHz,
CDCl3) 172.9 (C]O), 162.6 (C), 157.3 (C), 113.4 (CN), 112.6 (CN), 89.0
(C), 62.6 (C), 58.6 (MeO), 52.1 (CH), 33.1 (2 CH2), 24.8 (CH2), 24.1 (2
CH2); m/z (EIMS) 321 (54 Mþ), 238 (84), 206 (18), 180 (5), 131 (15),
109 (20), 99 (18), 83 (52), 73 (30), 64 (17), 55 (100%).
3.3.3. Ethyl 2-(E and Z)-1-cyano-2-ethoxy-2-oxoethylidene-5-
cyclohexylamino-1,3-dithile-4-carboxylate (7c). Yellow oil; (0.25 g,
65%); [found: C, 53.47; H, 5.66; N, 7.24 C17H22N2O4S2 382 requires C,
53.38; H, 5.80; N, 7.32%]; Rf (20% EtOAc/hexane) 0.78; nmax (KBr):
3.2.6. Ethyl 2-dicyanomethylene-4-cyclohexylamino-2,3-dihydro-3-
(4-nitrophenyl)thiazole-5-carboxylate (6f). Yellow solid; (0.17 g,
40%); mp 158e160 ꢀC; [found: C, 57.46; H, 4.71; N, 15.82
C21H21N5O4S 439 C, 57.39; H, 4.82; N, 15.94%]; Rf (20% EtOAc/hex-
3276 (NH), 2203 (CN),1659 (C]O),1578 (C]C),1448 (C]C) cmꢁ1
; dH
ane) 0.78; nmax (KBr): 3389 (NH), 2209 (CN), 1673 (C]O) cmꢁ1
;
dH
(400 MHz, CDCl3) 7.98 (2H, br s, 2 NH), 4.28 (2H, m, CH2O), 3.73e3.80
(2H, m, CH2O), 3.31e3.41 (1H, m, CH), 3.17e3.24 (1H, m, CH),
1.20e2.10 (20H, m, 10 CH2), 1.12e1.37 (12H, m, 4 Me); dC (100 MHz,
CDCl3) 170.6 and 169.8 (2 C]O), 165.1 and 164.5 (6 C), 163.3, 163.1,
160.1,156.4,116.3 and 115.4 (2 CN), 82.7 and 82.2 (2 C), 68.0 (2 C), 61.1
and 61.0 (4 CH2O), 58.2, 57.3, 52.6 and 52.5 (2 CH), 33.4 and 33.3 (10
CH2), 25.6, 25.1, 25.0, 24.3,14.5 and 14.4 (4 Me); m/z (EIMS) 382 (Mþ,
5), 368 (100), 321 (14), 286 (98), 258 (90), 240 (57), 214 (12),182 (15),
142 (96), 125 (18), 97 (17), 83 (80), 71 (19), 55 (99%).
(500 MHz, CDCl3) 8.20 (2H, d, 3J 7.1 Hz, 2 CH), 7.56 (2H, d, 3J¼7.1 Hz,
2 CH), 6.84 (1H, d, 3J¼9.5 Hz, NH), 4.63 (2H, 3J¼7.2 Hz, CH2O),
2.89e2.94 (1H, m, CH), 1.28 (3H, t, 3J¼7.2 Hz, Me), 0.91e1.80 (10H,
m, 5 CH2); dC (125 MHz, CDCl3) 167.2 (C]O), 156.2 (C), 154.0 (C),
142.8 (C), 125.2 (C), 124.9 (2 CH), 120.5 (2 CH), 117.7 (CN), 111.2 (CN),
88.7 (C), 71.2 (C), 67.9 (CH2O), 51.3 (CH), 33.5 (CH2), 29.2 (2 CH2),
25.63 (2 CH2), 14.1 (Me); m/z (EIMS) 440 (2 Mþþ1), 368 (5), 226
(100), 198 (82), 165 (83), 138 (61), 108 (84), 92 (34), 65 (23%).
3.2.7. Ethyl 4-(2,4,4-trimethylpentan-2-ylamino)-2-dicyanomethylene-
2,3-dihydro-3-(4-nitrophenyl)thiazole-5-carboxylate (6g). Yellow oil;
(0.23 g, 46%); [found: C, 58.69; H, 5.72; N, 14.83 C23H27N5O4S 469
requires C, 58.83; H, 5.80; N, 14.91%]; Rf (20% EtOAc/hexane) 0.80;
3.3.4. Methyl 2-(E and Z)-1-cyano-2-ethoxy-2-oxoethylidene-
5-cyclohexylamino-1,3-dithiole-4-carboxylate
(7d). Yellow
oil;
(0.23 g, 62%); [found: C, 52.27; H, 5.34; N, 7.42 C16H20N2O4S2 368
requires C, 52.15; H, 5.47; N, 7.60%]; Rf (20% EtOAc/hexane) 0.75;

2466
I. Yavari et al. / Tetrahedron 69 (2013) 2462e2467
nmax (KBr): 3278 (NH), 2204 (CN), 1661 (C]O), 1575 (C]C), 1449
(C]C) cmꢁ1
dH (500 MHz, CDCl3) 7.94 (2H, br s, 2 NH), 3.85 and
[found: C, 54.67; H, 6.02; N, 11.95 C16H21N3O2S2 351 requires C,
;
54.72; H, 6.11; N, 11.82%]; Rf (20% EtOAc/hexane) 0.74; nmax (KBr):
3.84 (6H, s, 2 MeO), 3.80e3.77 (4H, m, 2 CH2O), 3.37e3.30 (1H, m,
CH), 3.20e3.12 (1H, m, CH), 2.10e1.27 (20H, m, 10 CH2), 1.30e1.18
(6H, m, 2 Me); dC (125 MHz, CDCl3) 170.5 and 169.7 (2 C]O), 165.0
and 164.4 (6 C), 163.6, 163.4, 160.3, 156.6, 116.2 and 115.2 (2 CN),
91.9 and 91.8 (2 C), 82.5 and 82.8 (2 C), 58.2 and 57.3 (2 CH2O), 52.6
and 52.4 (2 MeO), 51.8 and 51.7 (2 CH), 33.4 and 33.2 (10 CH2), 25.2,
25.0, 24.8, 24.7, 14.0 (2 Me); m/z (EIMS) 368 (5 Mþ), 354 (100), 330
(11), 297 (10), 272 (78), 239 (18), 215 (25), 204 (32), 183 (12), 142
(55), 131 (13), 110 (10), 98 (22), 83 (52), 71 (20), 55 (98%).
3419 (NH), 2205 (CN), 1640 (C]O), 1560 (C]C), 1456 (C]C) cmꢁ1
;
dH (400 MHz, CDCl3) 8.65 (1H, br s, NH), 3.70 (3H, s, MeO), 1.60 ( 2H,
s, CH2), 1.40 (6H, s, CMe2), 1.01 (9H, s, CMe3); dC (100 MHz, CDCl3)
167.3 (C]O), 164.2 and 155.7 (2 C), 116.2 and 113.9 (2 CN), 78.5 (C),
67.9 (C), 54.9 (MeO), 53.5 (CMe2), 52.0 (CMe3), 31.4 (CMe3), 31.3
(CH2), 29.6 (CMe2); m/z (EIMS) 351 (5 Mþ), 329 (42), 289 (10), 245
(68), 217 (78), 205 (80), 177 (28), 158 (58), 134 (100), 134 (100), 113
(36), 97 (67), 84 (20), 69 (35), 55 (85%).
3.3.10. Ethyl
2-dicyanomethylene-5-(1,1,3,3-tetramethylbuthyl)
3.3.5. Methyl 5-tert-butylamino-2-dicyanomethylene-1,3-dithiole-4-
carboxylate (7e). Yellow oil; (0.12 g, 42%); [found: C, 48.67; H,
4.53; N, 14.19 C12H13N3O2S2 295 requires C, 48.79; H, 4.44; N,
14.23%]; Rf (20% EtOAc/hexane) 0.79; nmax (KBr): 3255 (NH), 2208
amino-1,3-dithiole-4-carboxylate (7j). Yellow oil; (0.16 g, 45%);
[found: C, 55.76; H, 6.27; N, 11.62 C17H23N3O2S2 365 requires C,
55.86; H, 6.34; N, 11.50%]; Rf (20% EtOAc/hexane) 0.76; nmax (KBr):
3438 (NH), 2205 (CN), 1662 (C]O), 1570 (C]C), 1451 (C]C) cmꢁ1
;
(CN), 1663 (C]O), 1567 (C]C), 1453 (C]C) cmꢁ1
;
dH (400 MHz,
dH (400 MHz, CDCl3) 8.64 (1H, br s, NH), 4.27 (3H, q, 3J 7.2 Hz, CH2O),
1.70 (2H, s, CH2), 1.49 (6H, s, CMe2), 1.02 (9H, s, CMe3), 1.01e0.96
(3H, m, Me), dC (100 MHz, CDCl3) 173.3 (C]O), 162.6 and 155.5
(2 C), 113.7 and 113.0 (2 CN), 90.1 (C), 61.8 (C), 61.6 (CH2O), 58.4
(CMe2), 52.0 (CMe3), 31.7 (CH2), 31.3 (CMe3), 29.7 (CMe2), 14.3 (Me);
m/z (EIMS) 365 (66 Mþ), 294 (27), 252 (72), 224 (54), 206 (32), 178
(15), 134 (34), 112 (63), 97 (73), 69 (45), 57 (100%).
CDCl3) 8.50 (1H, br s, NH), 3.78 (3H, s, MeO), 1.25 (9H, s, CMe3); dC
(100 MHz, CDCl3) 167.0 (C]O), 156.0 (C), 155.7 (C), 113.5 and 113.1
(2 CN), 90.5 (C), 62.0 (C), 54.8 (CMe3), 52.4 (MeO), 29.7 (CMe3); m/z
(EIMS) 295 (63 Mþ), 252 (14), 238 (84), 206 (42), 179 (10), 149 (11),
131 (15), 109 (28), 99 (25), 83 (21), 71 (27), 57 (100%).
3.3.6. Ethyl 5-tert-butylamino-2-dicyanomethylene-1,3-dithiole-4-
carboxylate (7f). Yellow oil; (0.14 g, 46%); [found: C, 50.37; H,
4.96; N, 13.43 C13H15N3O2S2 309 requires C, 50.46; H, 4.89; N,
13.58%]; Rf (20% EtOAc/hexane) 0.71; nmax (KBr): 3255 (NH), 2208
3.3.11. Methyl 2-(E and Z)-1-cyano-2-ethoxy-2oxoethylidene-5-
(1,1,3,3-tetramethylbuthyl)amino-1,3-dithiole-4-carboxylate
(7k). Yellow oil; (0.19 g, 48%); [found: C, 54.33; H, 6.47; N, 7.11
C18H26N2O4S2 398 requires C, 54.25; H, 6.58; N, 7.03%]; Rf (20%
EtOAc/hexane) 0.74; nmax (KBr): 3266 (NH), 2204 (CN), 1671 (C]O),
(CN), 1663 (C]O), 1567 (C]C), 1453 (C]C) cmꢁ1
; dH (400 MHz,
CDCl3) 8.55 (1H, br s, NH), 4.40e4.25 (2H, m, CH2O), 1.47 (9H, s,
CMe3), 1.40e1.25 (3H, m, Me); dC (100 MHz, CDCl3) 173.4 (C]O),
162.6 (C), 155.7 (C), 113.6 and 113.1 (2 CN), 90.6 (C), 62.0 (C), 61.7
(CH2O), 54.8 (CMe3), 29.3 (CMe3), 14.4 (Me); m/z (EIMS) 309 (52
Mþ), 252 (82), 240 (50), 224 (64), 212 (66), 183 (45), 165 (50), 155
(12), 138 (30), 109 (36), 99 (25), 84 (22), 71 (21), 57 (100%).
1566 (C]C), 1452 (C]C) cmꢁ1
; dH (400 MHz, CDCl3) 8.60 and 8.57
(2H, br s, 2 NH), 4.34e4.20 (4H, m, 2 CH2O), 3.82 and 3.81 (6H, s, 2
MeO), 1.73 and 1.77 (4H, s, 2 CH2), 1.54 and 1.50 (12H, s, 2 CMe2),
1.02 and 0.99 (18H, s, 2 CMe3), 1.01e0.96 (6H, m, 2 Me); dC
(100 MHz, CDCl3) 170.4, 169.6, 164.5 and 164.1 (4 C]O), 163.8,
163.6, 159.2 and 154.8 (4 C), 116.2 and 115.5 (2 CN), 93.0and 87.3 (2
C), 62.5 and 61.9 (2 C), 61.8 and 61.7 (2 CH2O), 55.9 and 55.8 (2
CMe2), 51.9 and 51.8 (2 CMe3), 31.5 and 31.6 (2 CH2), 31.4 and 31.3 (2
CMe3), 30.0 and 29.8 (2 CMe2), 14.3 and 13.9 (2 Me); m/z (EIMS) 398
(12 Mþ), 343 (15), 329 (19), 285 (84), 259 (27), 245 (50), 231 (45),
217 (54), 181 (21), 147 (60), 133 (85), 112 (83), 97 (88), 84 (38), 69
(59), 57 (100%).
3.3.7. Methyl 5-tert-butylamino-2-(E and Z)-1-cyano-2-ethoxy-2-
oxoethylidene-1,3-dithiole-4-carboxylate (7g). Yellow oil; (0.15 g,
43%); [found: C, 49.21; H, 5.19; N, 8.27 C14H18N2O4S2 342 requires C,
49.10; H, 5.30; N, 8.18%]; Rf (20% EtOAc/hexane) 0.78; nmax (KBr):
3434 (NH), 2204 (CN), 1670 (C]O), 1569 (C]C), 1452 (C]C) cmꢁ1
;
dH (400 MHz, CDCl3) 8.50 and 8.48 (2H, br s, 2 NH), 4.39e4.29 (4H,
m, 2 CH2O), 3.88 and 3.84 (6H, s, 2 MeO), 1.51 and 1.48 (18H, s, 2
CMe3), 1.33e140 (6H, m, 2 Me); dC (100 MHz, CDCl3) 170.4, 170.2,
170.1 and 169.9 (4 C]O), 163.8, 163.6, 159.4 and 155.1 (4 C), 116.2
and 115.5 (2 CN), 87.8 and 87.6 (2 C), 76.7 (2 C), 61.8 and 61.7 (2
CH2O), 54.5 and 54.4 (2 CMe3), 51.9 and 52.0 (2 MeO), 29.5 and 29.3
(2 CMe3), 14.4 (2 Me); m/z (EIMS) 342 (2 Mþ), 286 (100), 272 (24),
258 (95), 241 (48), 226 (83), 214 (35), 182 (26), 156 (37), 142 (20),
128 (98), 110 (30), 99 (50), 84 (51), 72 (84), 59 (24%).
3.3.12. Ethyl 2-(E and Z)-1-cyano-2-ethoxy-2oxoethylidene-5-
(1,1,3,3-tetramethylbuthyl)amino-1,3-dithiole-4-carboxylate
(7l). Yellow oil; (0.19 g, 47%); [found C, 55.43; H, 6.73; N, 6.82
C19H28N2O4S2 412 requires C, 55.31; H, 6.84; N, 6.79%]; Rf (20%
EtOAc/hexane) 0.71; nmax (KBr): 3260 (NH), 2204 (CN), 1669 (C]O),
1567 (C]C), 1456 (C]C) cmꢁ1
; dH (400 MHz, CDCl3) 8.63 and 8.58
(2H, br s, 2 NH), 4.35e4.18 (8H, m, 4 CH2O), 1.76 and 1.73 (4H, s, 2
CH2), 1.54 and 1.47 (12H, s, 2 CMe2), 1.04 and 1.02 (18H, s, 2 CMe3),
1.10e0.98 (12H, m, 4 Me); dC (100 MHz, CDCl3) 170.6, 169.8, 164.6
and 164.3 (4 C]O), 163.6, 163.3, 159.0 and 154.7 (4 C), 116.3 and
115.6 (2 CN), 93.4, 87.7, 82.9 and 70.8 (4 C), 61.8, 61.7, 61.2 and 61.1
(4 CH2O), 55.8 and 54.6 (2 CMe2), 52.4 and 52.2 (2 CMe3), 31.8 and
31.6 (2 CH2), 31.4 and 31.3 (2 CMe3), 30.1 and 29.8 (2 CMe2), 14.5 and
14.3 (4 Me); m/z (EIMS) 412 (23 Mþ), 371 (20), 330 (18), 300 (90),
283 (27), 270 (45), 226 (50), 201 (54), 188 (88), 160 (100), 145 (92),
128 (53), 116 (44), 83 (72), 57 (87%).
3.3.8. Ethyl 5-tert-butylamino-2-(E and Z)-1-cyano-2-ethoxy-2-
oxoethylidene-1,3-dithiole-4-carboxylate (7h). Yellow oil; (0.16 g,
yield 48%); [found: C, 50.65; H, 5.82; N, 7.94C15H20N2O4S2 356 re-
quires C, 50.54; H, 5.66; N, 7.86%]; Rf (20% EtOAc/hexane) 0.73; nmax
(KBr): 3433 (NH), 2203 (CN), 1668 (C]O), 1567 (C]C), 1456 (C]
C) cmꢁ1
; dH (400 MHz, CDCl3) 8.52 and 8.47 (2H, br s, 2 NH),
4.22e4.36 (8H, m, 4 CH2O), 1.50 and 1.47 (18H, s, 2 CMe3), 1.30e140
(12H, m, 4 Me); dC (100 MHz, CDCl3) 170.6, 170.2, 164.5 and 164.2 (4
C]O).163.5,163.2,159.2 and 154.9 (4 C),115.6 and 115.5 (2 CN), 92.0
and 88.3 (2 C), 62.1, 61.8, 61.7 and 61.1 (4 CH2O), 54.3 and 54.2 (CMe3),
29.5 and 29.3 (2 CMe3),14.4 and 14.3 (4 Me); m/z (EIMS) 356 (77 Mþ),
300 (100), 286 (95), 272 (71), 258 (52), 240 (45), 226 (34), 200 (15),
158 (74), 142 (78), 128 (47), 99 (25), 84 (24), 71 (53), 57 (53%).
References and notes
€
1. Sandstrom, J.; Wenoerbeck, I. Acta Chem. Scand. 1970, 24, 1191.
€
2. Sandstrom, J. Top. Stereochem. 1983, 14, 83.
3. Kalinowski, H.-O.; Kessler, H. Top. Stereochem. 1973, 7, 303.
4. Marder, S. R.; Gorman, C. B.; Meyers, F.; Perry, J. W.; Bourhill, G.; Bredas, J.-L.;
3.3.9. Methyl
2-dicyanomethylene-5-(1,1,3,3-tetramethylbuthyl)
ꢁ
amino-1,3-dithiole-4-carboxylate (7i). Yellow oil; (0.14 g, 40%);
Pierce, B. M. Science 1994, 265, 632.

I. Yavari et al. / Tetrahedron 69 (2013) 2462e2467
2467
5. Andreu, R.; Blesa, M. J.; Carrasquer, L.; Garín, J.; Orduna, J.; Villacampa, B.;
Alcala, R.; Casado, J.; Delgado, M. C. R.; Navarrete, J. T. L.; Allain, M. J. Am. Chem.
14. Coffinier, D.; El Kaim, L.; Grimaud, L. Synlett 2010, 2474.
15. Mossetti, R.; Pirali, T.; Tron, G. C.; Zhu, J. Org. Lett. 2010, 12, 820.
16. Krow, G. R. Angew. Chem., Int. Ed. Engl. 1971, 10, 435.
ꢁ
Soc. 2005, 127, 8835.
€
6. (a) Domling, A. Chem. Rev. 2006, 106, 17; (b) Suginome, M.; Ito, Y. In Science of
17. Giera, H.; Huisgen, R.; Polborn, K. Eur. J. Org. Chem. 2005, 3781.
Synthesis; Murahashi, S.-I., Ed.; Thieme: Stuttgart, 2004; Vol. 19, p 445.
7. (a) Adlington, R. M.; Barrett, A. G. M. Tetrahedron 1981, 37, 3935; (b) Chen, J. J.;
Deshpande, S. V. Tetrahedron Lett. 2003, 44, 8873.
8. (a) Lygin, A. V.; Meiere, A. D. Angew. Chem., Int. Ed. 2010, 49, 9094; (b) Livinghouse,
T. Tetrahedron 1999, 55, 9947; (c) Van Wangenen, B. C.; Cardenilla, J. H. Tetrahe-
dron Lett. 1989, 30, 3605.
18. Alajarin, M.; Vidal, A.; Tovar, F.; Sanchez-Andrada, P.; Bautista, D. Tetrahedron
2003, 59, 9913.
19. Sung, K.; Huang, P.-M.; Chiang, S.-M. Tetrahedron 2006, 62, 4795.
20. Fromont, C.; Masson, S. Tetrahedron 1999, 55, 5405.
21. Yavari, I.; Zonouzi, A.; Hekmat-Shoar, R. Tetrahedron Lett. 1998, 39, 3841.
22. Yavari, I.; Hazeri, N.; Maghsoodlou, M. T.; Moradi, A. J. Chem. Res. 2001, 272.
23. Yavari, I.; Ghazanfarpour-Darjani, M.; Solgi, Y.; Ahmadian, S. Helv. Chim. Acta
2011, 94, 639.
9. Nef, J. U. Justus Liebigs Ann. Chem. 1892, 270, 267.
ꢁ
10. El Kaim, L.; Pinot-Perigord, E. Tetrahedron 1998, 54, 3799.
11. Westling, M.; Smith, R.; Livinghouse, T. J. Org. Chem. 1986, 51, 1159.
12. Lee, C. H.; Westling, M.; Livinghouse, T.; Williams, A. C. J. Am. Chem. Soc. 1992,
114, 4089.
24. Yavari, I.; Pashazadeh, R.; Hosseinpour, R. Helv. Chim. Acta 2012, 95, 169.
25. Yavari, I.; Hosseinpour, R.; Pashazadeh, R. Synlett 2012, 1662.
26. Burnett, A. M. N.; Johnson, C. K. Oak Ridge National Laboratory Report ORNL-
6895; Oak Ridge National Laboratory: Tennessee, 1996.
13. Coffinier, D.; El Kaim, L.; Grimaud, L. Org. Lett. 2009, 11, 1825.