Zinc-mediated cleavage of diselenides: A novel synthesis of selenoformates in aqueous media

Article abstract of DOI:10.1007/s00706-007-0642-1

An efficient procedure was developed for the preparation of selenoformates by means of an one-pot zinc-mediated reaction of diaryl diselenides and chloroformates in aqueous media.

Full text of DOI:10.1007/s00706-007-0642-1

Monatshefte fu¨r Chemie 138, 863–865 (2007)
DOI 10.1007/s00706-007-0642-1
Printed in The Netherlands
Zinc-Mediated Cleavage of Diselenides: A Novel Synthesis
of Selenoformates in Aqueous Media
Barahman Movassagh1;2;ꢀ and Azadeh Fazeli1;2
1
Department of Chemistry, K.N. Toosi University of Technology, Tehran, Iran
2
Kermanshah Oil Refining Company, Kermanshah, Iran
Received February 13, 2007; accepted (revised) February 28, 2007; published online June 4, 2007
# Springer-Verlag 2007
Summary. An efficient procedure was developed for the
borohydride [4], sodium [5], samarium diiodide [6],
preparation of selenoformates by means of an one-pot zinc-
mediated reaction of diaryl diselenides and chloroformates in
aqueous media.
lithium aluminum hydride [7], reaction of Grignard
reagents with selenium [8], and of selenol with sodi-
um hydride or even with aqueous sodium hydroxide
under certain conditions [9].
Keywords. Selenoformates; Zinc selenolate; Diselenides;
Chloroformates.
In the last decade, organometallic reactions in
aqueous media have attracted considerable attention
in organic synthesis [10]. Transition metal selenolates
or complexes have been widely used in the synthesis
of organoselenium compounds [11–13], but reports
exploring zinc selenolates are rare [14].
In connection with our ongoing work in aqueous
organometallic reactions [14a–e], we report herein
that zinc powder promotes the cleavage of the Se–Se
bond of diselenides 1 to form a selenide anion
(RSeꢁ), which then reacts with different chlorofor-
mates 2 to give selenoformates 3 in CH3CN–H2O
mixture as solvent at 70ꢂC (Scheme 1).
Introduction
There is no doubt that selenium-containing organic
molecules have played and continue to play an im-
portant role in biology and medicine. A wide range
of organic selenides are now accepted as useful an-
tibiotics, antiinflammatory agents, antioxidants, and
antiviral agents [1]. Although numerous reports on
the synthesis of organoselenium compounds have
already been published [2], most of them, with the
exception of two recent reports [3], require the hand-
ling of unstable reagents, strongly acidic or basic
reaction conditions, and two-step procedures. Hence,
the development of a one-step synthesis method using
stable reagents under neutral conditions is in demand.
Among the methods for the introduction of a sele-
nium moiety into organic molecules, the use of sele-
nide anions is especially convenient and common.
In general, the methods for the preparation of sele-
nide anions include reductive cleavage of the Se–Se
bond by various reducing agents such as sodium
Results and Discussion
Among a few reported methods for the preparation
of selenoformates, we can cite those involving the
treatment of phenylselenotris(trimethylsilyl)silane
ꢀ
Scheme 1
Corresponding author. E-mail: bmovass1178@yahoo.com

864
B. Movassagh and A. Fazeli
with chloroformates in benzene and in the presence
of tetrakis(triphenylphosphine)palladium(0) [15],
the reaction of phenylselenol with chloroformates in
benzene and in the presence of pyridine [16], the
reaction of sodium phenylselenoate – prepared by
the reduction of diphenyl diselenide with sodium
borohydride – with chloroformates [17], and water
accelerated Sm=TMSCl reductive cleavage of the
Se–Se bonds followed by subsequent reaction with
methylchloroformate [18]. These methods suffer from
laborious removal of by-products, such as diaryl di-
selenides, or in some cases, hardly to obtain reagents.
We now introduce another procedure for the pre-
paration of selenoformates from various chlorofor-
mates and aryl diselenides by reductive cleavage of
Se–Se bond promoted by cheap and reactive metal-
lic zinc powder. The effects of several solvents were
examined and the best results were obtained with the
acetonitrile-water (5:1) system. The consumption
of zinc powder during the preliminary treatment of
diselenide 1 with zinc is attributed to the formation
of the zinc selenolate intermediate I, which further
undergoes nucleophilic displacement with chlorofor-
mate 2 to afford the selenoformates 3 (Scheme 2) in
65–78% yield as shown in Table 1.
Experimental
1H (300 MHz) and 13C (75 MHz) NMR spectra were recorded
using a Bruker AQS-300 Avance spectrometer. IR spectra
were obtained using an ABB FTLA 2000 instrument. Mass
spectra were recorded with a Hewlett-Packard model 5973
instrument.
General Procedure for the Synthesis of Selenoformates
In a 50cm3 round bottom flask, fitted with a reflux condenser,
were placed 3.2mmol Zn powder, 0.64 mmol diselenide,
20cm3 CH3CN, and 4 cm3 H2O. The mixture was stirred at
70ꢂC for 2 h. Then 3.2 mmol chloroformate 2 were added at
once and stirring was continued at that temperature for the
appropriate time (Table 1) in ambient atmosphere. After com-
pletion of the reaction, the solution was filtered, MeCN was
evaporated, diethyl ether (20 cm3) was added, the mixture was
washed with H2O (3ꢃ20cm3), and the organic layer was dried
(Na2SO4). The solvent was evaporated in vacuo to give the
corresponding selenoformate, which was purified by prepara-
tive TLC (silica gel, eluent n-heptane:EtOAc¼ 10:1). Products
3a–3f were shown to be identical with those described in
Refs. [17, 18] by means of their spectroscopic data.
n-Butyl (4-chlorophenylseleno)formate (3g, C11H13ClO2Se)
;
1H NMR
Yellow oil; IR (neat): ꢀꢀ¼ 1725 (C¼O) cmꢁ1
(CDCl3): ꢁ ¼ 0.89 (t, J ¼ 6.8 Hz, CH3), 1.36 (sex, J ¼ 6.8 Hz,
CH2CH3), 1.68 (quint, J ¼ 6.9 Hz, OCH2CH2), 4.26 (t,
J ¼ 6.9 Hz, OCH2), 7.26 (d, J ¼ 8.4 Hz, Ph), 7.55 (d, J ¼
8.4 Hz, Ph) ppm; 13C NMR (CDCl3): ꢁ ¼ 13.6, 18.9, 30.7,
68.5, 124.3, 129.5, 135.6, 137.1, 166.4 ppm; MS: m=z
(%) ¼ 293 ((M þ 2)þ, 28), 291 (Mþ, 75), 192 (7), 190 (22),
156 (20), 57 (100), 41 (69), 29 (65).
To conclude, an efficient one-pot synthesis meth-
od of selenoformates was developed based on the
zinc-mediated reaction of diselenides with chloro-
formates. The present method has the advantages
of operational simplicity, neutral, and mild reaction
conditions, lack of toxicity, and low costs.
2-Methyl-1-propyl (4-chlorophenylseleno)formate
(3h, C11H13ClO2Se)
Yellow oil; IR (neat): ꢀꢀ¼ 1722 (C¼O) cmꢁ1
;
1H NMR
(CDCl3): ꢁ ¼ 0.85 (d, J ¼ 6.7 Hz, 2ꢃCH3), 1.89 (m, CHMe2),
3.98 (d, J ¼ 6.6 Hz, OCH2), 7.26 (d, J ¼ 9.1 Hz, Ph), 7.48 (d,
J ¼ 9.1 Hz, Ph) ppm; 13C NMR (CDCl3): ꢁ ¼ 18.9, 27.9, 74.5,
124.3, 129.5, 135.6, 137.1, 166.4ppm; MS: m=z (%) ¼ 293
((M þ 2)þ, 18), 291 (Mþ, 52), 192 (8), 190 (23), 156 (19),
57 (100), 41 (91), 29 (53).
Scheme 2
Table 1. Synthesis of selenoformates 3 from diselenides 1 and chloroformates 2 (Scheme 2)
Entry
R
R0
Reaction time=h
Product
Isolated yield=%
1
2
3
4
5
6
7
8
9
10
Ph
Ph
Ph
Ph
CH3
2.5
1.8
3.3
3
1
4
5.5
4.25
3.3
2
3a
3b
3c
3d
3e
3f
3g
3h
3i
74
73
73
71
78
72
68
65
68
73
CH3(CH2)2CH2
(CH3)2CHCH2
CH3(CH2)6CH2
Ph
Ph
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
CH3
CH3(CH2)2CH2
(CH3)2CHCH2
CH3(CH2)6CH2
Ph
3j

Zinc-Mediated Cleavage of Diselenides
865
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n-Octyl (4-chlorophenylseleno)formate (3i, C15H21ClO2Se)
1
Pale yellow oil; IR (neat): ꢀꢀ¼ 1721 (C¼O), 1116 cmꢁ1; H
NMR (CDCl3): ꢁ ¼ 0.76 (t, J ¼ 6.9 Hz, CH3), 1.07–1.21 (m,
5ꢃCH2), 1.53 (quint, J ¼ 6.7 Hz, OCH2CH2), 4.13 (t, J ¼
6.6 Hz, OCH2), 7.20 (d, J ¼ 8.2 Hz, Ph), 7.41 (d, J ¼ 8.2 Hz,
Ph) ppm; MS: m=z (%) ¼ 349 ((M þ 2)þ, 4), 347 (Mþ, 11),
192 (34), 190 (100), 156 (47), 128 (15), 112 (11), 71 (69), 57
(78), 43 (53), 41 (32), 29 (11).
Phenyl (4-chlorophenylseleno)formate (3j, C13H9ClO2Se)
;
13C NMR
Yellow oil; IR (neat): ꢀꢀ¼ 1725 (C¼O) cmꢁ1
(CDCl3): ꢁ ¼ 121.3, 123.9, 126.5, 129.67, 129.77, 136.1,
137.2, 151.7, 165.8 ppm; MS: m=z (%) ¼ 313 ((M þ 2)þ, 7),
311 (Mþ, 20), 285 (29), 283 (91), 192 (35), 190 (100), 156
(42), 77 (41), 65 (35), 51 (12), 39 (23).
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Acknowledgements
The authors thank the K.N. Toosi University of Technology
Research Council and Kermanshah Oil Refining Company for
financial assistance.
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