One-pot synthesis of selenocarbamates from isocyanates and diselenides using the Zn/AlCl3 system

Article abstract of DOI:10.1016/j.cclet.2013.01.050

Several N-alkyl/aryl-Se-alkyl/(aryl)selenocarbamates were prepared from various isocyanates and diselenides by reductive cleavage of SeSe bond with the Zn/AlCl₃ system in dry acetonitrile at 80 °C.

Full text of DOI:10.1016/j.cclet.2013.01.050

Chinese Chemical Letters 24 (2013) 192–194
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Chinese Chemical Letters
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Original article
One-pot synthesis of selenocarbamates from isocyanates and diselenides using
the Zn/AlCl3 system
*
Barahman Movassagh , Mona Moradi
Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 16315-1618, Tehran, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Several N-alkyl/aryl-Se-alkyl/(aryl)selenocarbamates were prepared from various isocyanates and
diselenides by reductive cleavage of Se–Se bond with the Zn/AlCl3 system in dry acetonitrile at 80 8C.
ß 2013 Barahman Movassagh. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights
reserved.
Received 29 November 2012
Received in revised form 9 January 2013
Accepted 16 January 2013
Available online 7 March 2013
Keywords:
Selenocarbamates
Diselenides
Isocyanates
Zinc selenolate
Zn/AlCl3 system
1. Introduction
methodologies necessitate the development of more convenient
methods. Ishihara and co-workers reported the synthesis of N-alkyl-
Over the last three decades, organoselenium chemistry has not
only been of constant scientific interest but also used intensively [1].
Recently, many synthetic methods for the compounds containing
selenium have been studied and reported due to their interesting
reactivity [2] and potential pharmaceutical importance [3]. Among
the selenium compounds, selenocarbamates are an important class
of compounds whose biological, especially antiviral activity, have
been investigated[4]. These compounds have alsobeenemployedas
an efficient source of acyl radicals by homolytic cleavage of the Se–
Se-alkylselenocarbamates by the reaction of isocyanates with
LiAlHSeH, followed by addition of alkyl halides [12], This method,
however, requires an argon atmosphere, and also the reagent,
LiAlHSeH, has to be made in situ prior to the reaction. It was also
limited to the preparation of Se-alkylselenocarbamates.
2. Experimental
Chemicals were purchased from Merck or Aldrich. Yields
referred to the yields of isolated products. IR spectra were obtained
using an ABB FTLA 2000 instrument. NMR spectra were recorded
using a Bruker DRX-500 Avance spectrometer with a nominal
frequency of 500 MHz for proton and 125 MHz for carbon (13C),
respectively, in CDCl3 using TMS as an internal standard. Mass
spectra were recorded with a Hewlett-Packard model 5973
instrument.
CO bond [5], and for the construction of a-alkylidene lactams [6].
There are a limited number of reports of selenocarbamate synthesis
including treatment of a N-tosylamine with triphosgene followed by
addition of phenylselenol [7], reaction of an amine and carbon
monoxide with elemental selenium followed by treatment with an
alkyl halide [8], treatment of diselenides with lithium triethylbor-
ohydride followed by a reaction with diethylcarbamyl chloride [9],
reactions of selenocarboxylic acids with aryl isocyanates [10], and
treatment of bis[N,N-dimethylcarbamoyl] diselenides with NaH or
NaBH4, followed by reacting with various alkylating agents [11].
However, some disadvantages such as synthetic inconvenience,
unavailability of starting materials and reagents, needs of an inert
atmosphere and low temperatures encountered in the reported
2.1. Typical procedure for the preparation of N-cyclohexyl-Se-
phenylselenocarbamate (3a)
A mixture of diphenyl diselenide (0.20 g, 0.64 mmol), Zn dust
(0.23 g, 3.5 mmol), finely ground anhydrous AlCl3 (0.43 g,
3.2 mmol), and dry CH3CN (10 mL) was stirred at 80 8C for 1 h
until the zinc powder had almost disappeared. Then, cyclohexyl
isocyanate (0.20 g, 1.6 mmol) was added in one portion to the
solution and stirring was continued at that temperature for 0.5 h in
* Corresponding author.
E-mail address: bmovass1178@yahoo.com (B. Movassagh).
1001-8417/$ – see front matter ß 2013 Barahman Movassagh. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.01.050

B. Movassagh, M. Moradi / Chinese Chemical Letters 24 (2013) 192–194
193
O
air atmosphere. After completion of the reaction as indicated by
Zn/AlCl 3
dry CH3CN, 80oC
R1SeSeR1
R2-N=C=O
TLC analysis, the solution was filtered, and the filtrate was
evaporated, EtOAc (20 mL) was added and washed with water
(3 ꢀ 10 mL) and dried over anhydrous Na2SO4. The solvent was
evaporated to give the crude product, which upon addition of
petroleum ether (30 mL), the pure N-cyclohexyl-Se-phenylseleno-
carbamate (3a, 0.23 g, 64%) solidified as colorless crystals. Mp 95–
NHR2
+
R1Se
1
2
3
Scheme 1. Reaction of diselenides 1 and isocyanates 2 in the presence of Zn/AlCl3
system.
97 8C; IR (KBr, cmꢁ1): nmax 1660, 3297; 1H NMR (CDCl3):
d 1.11–
Table 1
1.19 (m, 3H), 1.33–1.39 (m, 2H), 1.56–1.62 (m, 3H), 1.88–1.92 (m,
2H), 3.72–3.79 (m, 1H), 5.27 (br s, 1H), 7.41–7.46 (m, 3H), 7.72–
Synthesis of various N-alkyl(aryl)-Se-alkyl(aryl)selenocarbamates.
7.75 (m, 2H); 13C NMR (CDCl3):
d 24.8, 25.7, 33.1, 51.3, 127.6, 129.7,
Entry
R1
R2
Time (h)
Product
Yield (%)a,b
130.1, 131.9, 136.9, 161.9; MS: m/z (%) 284 [M+2]+ (100), 282 [M+]
(52), 225 (20), 158 (68), 156 (75), 83 (54), 55 (61), 41 (38).
Selective data: 3c: Colorless crystals, mp 116–118 8C; IR (KBr,
1
2
3
4
5
6
7
8
9
Ph
c-C6H11
Ph
3.5
0.5
0.5
0.5
1
3a
3b
3c
3d
3e
3f
64
Ph
89 [15]
35
Ph
4-ClC6H4
4-MeC6H4
c-C6H11
4-MeC6H4
c-C6H11
Ph
cmꢁ1):
n
max 1674, 3260; 1H NMR (CDCl3):
d
7.15 (br s, 1H), 7.23–
7.28 (m, 4H), 7.43–7.50 (m, 3H), 7.75 (d, 2H, J = 6.2 Hz); 13C NMR
(CDCl3): 120.9 (br), 126.8, 129.6, 130.38, 130.43, 136.3, 137.2,
Ph
56
4-ClC6H4
4-ClC6H4
PhCH2
PhCH2
4-MeC6H4
68
0.75
2
32
d
3g
3h
3i
22 [12b]
48 [12b]
65
161.9; MS: m/z (%) 314 [M+4]+ (3), 312 [M+2]+ (6), 310 [M+] (4), 158
(88), 156 (42), 155 (32), 153 (100), 125 (45), 90 (34), 78 (78), 63
(17), 51 (16). 3d: Colorless crystals, mp 93–95 8C; IR (KBr, cmꢁ1):
2
Ph
0.5
a
Isolated yield.
b
max 1669, 3282; 1H NMR (CDCl3):
d
2.34 (s, 3H), 7.10–7.14 (m, 3H),
7.23 (d, 2H, J = 8.3 Hz), 7.46–7.51 (m, 3H), 7.78 (d, 2H, J = 6.9 Hz);
13C NMR (CDCl3):
21.3, 119.5 (br), 127.2, 130.04, 130.12, 130.3,
References for known compounds.
n
d
134.9 (br), 137.1, 162.2; MS: m/z (%) = 292 [M+2]+ (68), 290 [M+]
(35), 158 (100), 156 (51), 133 (58), 106 (48), 91 (30), 77 (52), 51
(30). 3e: Light pink crystals, mp 116–118 8C; IR (KBr, cmꢁ1): nmax
H
2
5
Se
7
N
1
3
4
C
1653, 3323; 1H NMR (CDCl3):
d 1.12–1.22 (m, 3H), 1.33–1.41 (m,
2H), 1.62–1.69 (m, 3H), 1.93–1.95 (m, 2H), 3.77–3.79 (m, 1H), 5.25
(br s, 1H), 7.39 (d, 2H, J = 8.3 Hz), 7.63 (d, 2H, J = 8.3 Hz); 13C NMR
O
6
(CDCl3):
d 24.9, 25.7, 33.2, 51.6, 125.5, 130.2, 136.1, 138.1, 160.9;
MS: m/z (%) 320 [M+4]+ (13), 318 [M+2]+ (30), 316 [M+] (15), 194
(49), 192 (100), 190 (50), 156 (24), 112 (45), 83 (90), 67 (39), 55
(47), 41 (43). 3f: Pale yellow crystals, mp 110–112 8C; IR (KBr,
Scheme 2. s-Trans form of compound 3b.
cmꢁ1):
n
max 1658, 3304; 1H NMR (CDCl3):
d
2.35 (s, 3H), 7.12–7.16
(m, 3H), 7.27 (d, 2H, J = 8.4 Hz), 7.42 (d, 2H, J = 8.4 Hz), 7.67 (d, 2H,
J = 7.8 Hz); 13C NMR (CDCl3):
21.3, 119.9 (br), 125.1, 130.1, 130.3,
facilitates the attack by the selenolate anion. The disappearance
of zinc powder during the preliminary treatment of diselenides
with Zn/AlCl3 is attributed to the formation of zinc selenolate
intermediate [14a–e], which further undergoes nucleophilic attack
to the isocyanate to afford the selenocarbamates. The structures of
all the products were established by analyzing their analytical and
spectral (IR, 1H and 13C NMR, and Ms) data. Reactions of four
diselenides with four different isocyanates gave various N-
alkyl(aryl)-Se-alkyl(aryl)selenocarbamates (Table 1). The highest
yield was obtained for N-phenyl-Se-phenylselenocarbamate 3b
(89%, entry 2, Table 1), and the lowest for N-cyclohexyl-Se-
benzylselenocarbamate 3g (22%, entry 7, Table 1).
d
135.1 (br), 136.5, 138.2; MS: m/z (%) 328 [M+4]+ (1), 326 [M+2]+
(2), 324 [M+] (1), 194 (31), 192 (62), 190 (34), 133 (100), 112 (23),
104 (38), 91 (15), 77 (25), 51 (21). 3i: Pale yellow crystals, mp 100–
102 8C; IR (KBr, cmꢁ1):
n
max 1652, 3239; 1H NMR (CDCl3):
d
2.46 (s,
3H), 7.12–7.15 (m, 2H), 7.29–7.34 (m, 6H), 7.68 (d, 2H, J = 8.0 Hz);
13C NMR (CDCl3):
d 21.8, 119.7 (br), 123.6, 125.2 (br), 129.5, 131.3,
137.2, 137.8, 140.7, 161.8; MS: m/z (%) 291 [M+2]+ (3), 289 [M+] (1),
172 (71), 170 (36), 119 (44), 91 (100), 77 (19), 65 (25), 51 (11).
3. Results and discussion
In the 13C NMR spectrum of 3b in CDCl3, an interesting spectral
feature was observed. A significant line broadening was observed
Recently, transition-metal selenolates or complexes have been
widely used in the synthesis of organoselenium compounds [13],
but reports exploring zinc selenolates are rare [14]. As a part of our
interest in zinc chemistry, we are constantly searching for novel
applications of zinc selenolates in chemical reactions. In the present
study we describe the use of zinc metal–aluminum chloride (Zn/
AlCl3) system for the cleavage of diselenides and in situ addition of
selenolate anion to isocyanates to give the corresponding N-
alkyl(aryl)-Se-alkyl(aryl)selenocarbamates (Scheme 1).
The experiments were initially conducted using cyclohexyl
isocyanate and diphenyl diselenide, as a model reaction, at various
molar ratios, solvents, and temperatures under an aerial atmo-
sphere. It was found that the reaction proceeded quantitatively
with a molar ratio of diselenide:Zn:AlCl3:isocyanate = 1:5.5:5:2.5
in dry acetonitrile at 80 8C. The presence of aluminum chloride is
essential in both steps (Se–Se bond cleavage and addition to
isocyanate). In the absence of this Lewis acid, the reaction slows
down considerably. This Lewis acid acts as a catalyst by its
coordination with the oxygen atom in isocyanates, hence,
for the peaks of C1, C2, C4, C6, and C7 at
and 161.6, respectively, while those of C3 and C5 (both at
d
137.7, 119.8, 125.2, 119.8,
129.6)
d
were, as usual, observed as sharp peaks at +25 8C (Scheme 2). The
broad signals became sharper when the spectrum was measured at
ꢁ25 8C. As reported earlier by Koketsu et al. [12b], the full
conjugation of the nitrogen lone pair electrons with the entire
p-
system of the phenyl ring of the major s-trans form led to these
interesting observations in the 13C NMR spectrum. As a result of
this conjugation, some alterations in the chemical shifts of the
carbon atoms in the phenyl ring were observed especially for C2, C4,
and C6.
4. Conclusion
In conclusion, we have developed a novel, efficient and simple
protocol for the synthesis of selenocarbamates. This method has
the advantages of operational simplicity, mild reaction conditions,
fast reaction rates, simple reaction work-up, lack of toxicity, and
low costs.

194
B. Movassagh, M. Moradi / Chinese Chemical Letters 24 (2013) 192–194
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