Remarkable alkene-to-alkene and alkene-to-alkyne transfer reactions of selenium dibromide and phsebr. Stereoselective addition of selenium dihalides to cycloalkenes

Article abstract of DOI:10.3390/molecules25010194

The original goal of this research was to study stereochemistry of selenium dihalides addition to cycloalkenes and properties of obtained products. Remarkable alkene-to-alkene and alkene-to-alkyne transfer reactions of selenium dibromide and PhSeBr were discovered during this research. The adducts of selenium dibromide with alkenes or cycloalkenes easily exchange SeBr₂ with other unsaturated compounds, including acetylenes, at room temperature, in acetonitrile. Similar alkene-to-alkene and alkene-to-alkyne transfer reactions of the PhSeBr adducts with alkenes or cycloalkenes take place. The supposed reaction pathway includes the selenium group transfer from seleniranium species to alkenes or alkynes. It was found that the efficient SeBr₂ and PhSeBr transfer reagents are Se(CH₂CH₂Br)₂ and PhSeCH₂CH₂Br, which liberate ethylene, leading to a shift in equilibrium. The regioselective and stereoselective synthesis of bis(E-2-bromovinyl) selenides and unsymmetrical E-2-bromovinyl selenides was developed based on the SeBr₂ and PhSeBr transfer reactions which proceeded with higher selectivity compared to analogous addition reactions of SeBr₂ and PhSeBr to alkynes under the same conditions.

Full text of DOI:10.3390/molecules25010194

molecules
Article
Remarkable Alkene-to-Alkene and Alkene-to-Alkyne
Transfer Reactions of Selenium Dibromide and
PhSeBr. Stereoselective Addition of Selenium
Dihalides to Cycloalkenes
Vladimir A. Potapov *, Maxim V. Musalov, Evgeny O. Kurkutov, Vladimir A. Yakimov,
Alfiya G. Khabibulina, Maria V. Musalova, Svetlana V. Amosova, Tatyana N. Borodina and
Alexander I. Albanov
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of the Russian Academy of Sciences, 1 Favorsky
Str., Irkutsk 664033, Russia; musalov_maxim@irioch.irk.ru (M.V.M.); kurkutov@irioch.irk.ru (E.O.K.);
yakimov@irioch.irk.ru (V.A.Y.); almah@irioch.irk.ru (A.G.K.); musalova@irioch.irk.ru (M.V.M.);
amosova@irioch.irk.ru (S.V.A.); borodina@irioch.irk.ru (T.N.B.); albanov@irioch.irk.ru (A.I.A.)
* Correspondence: v.a.potapov@mail.ru
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
Academic Editor: Francesca Marini
Received: 24 November 2019; Accepted: 31 December 2019; Published: 3 January 2020
ꢀꢁꢂꢃꢄꢅꢆ
Abstract: The original goal of this research was to study stereochemistry of selenium dihalides
addition to cycloalkenes and properties of obtained products. Remarkable alkene-to-alkene and
alkene-to-alkyne transfer reactions of selenium dibromide and PhSeBr were discovered during
this research. The adducts of selenium dibromide with alkenes or cycloalkenes easily exchange
SeBr2 with other unsaturated compounds, including acetylenes, at room temperature, in acetonitrile.
Similar alkene-to-alkene and alkene-to-alkyne transfer reactions of the PhSeBr adducts with alkenes
or cycloalkenes take place. The supposed reaction pathway includes the selenium group transfer
from seleniranium species to alkenes or alkynes. It was found that the efficient SeBr2 and PhSeBr
transfer reagents are Se(CH2CH2Br)2 and PhSeCH2CH2Br, which liberate ethylene, leading to a shift
in equilibrium. The regioselective and stereoselective synthesis of bis(E-2-bromovinyl) selenides and
unsymmetrical E-2-bromovinyl selenides was developed based on the SeBr2 and PhSeBr transfer
reactions which proceeded with higher selectivity compared to analogous addition reactions of SeBr2
and PhSeBr to alkynes under the same conditions.
Keywords: 1-alkenes; alkynes; cycloalkenes; 2-bromoethyl selenides; 2-bromovinyl selenides;
phenylselenenyl bromide; selenium dibromide; selenium dihalides; transfer reactions
1. Introduction
Selenium is an essential trace element nutrient that functions as cofactor for glutathione
peroxidase and certain forms of thioredoxin reductase in humans [
exhibit various biological activities, including antitumor, antibacterial, antifungal, anti-inflammatory,
and glutathione peroxidase-like actions [ ]. Selenium-containing reagents and organoselenium
compounds play an important role in modern organic synthesis [ 14]. Application of novel
1–4]. Organoselenium compounds
1–9
7–
selenium-containing reagents which allow carrying out regioselective and stereoselective introduction
of the selenium atom into organic molecules is an important function.
Efficient electrophilic selenium-containing reagents, selenium dichloride and dibromide, were
first introduced in synthesis of organoselenium compounds in 2003 [15,16]. It has been demonstrated
that selenium dichloride [17] and dibromide [15] (generated in situ from elemental selenium and
sulfuryl chloride or bromine) can be successfully used for selective introduction of the selenium atom
Molecules 2020, 25, 194; doi:10.3390/molecules25010194
www.mdpi.com/journal/molecules

Molecules 2020, 25, 194
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into organic molecules [15
,
16]. Since then, novel chemistry of selenium dihalides has been intensively
developed [18–55].
The addition of selenium dichloride and dibromide to double bonds was studied in the reactions
with divinyl sulfide [29 31], divinyl selenide [32 36], and divinyl sulfone [37 41], affording novel
heterocyclic compounds. The transannular addition of selenium dihalides to cis,cis-cycloocta-1,5-diene
gave 2,6-dihalo-9-selenabicyclo[3.3.1]nonanes in high yields [42 44]. The reactions of selenium
dichloride with allyl and propargyl phenyl ethers afforded annulated products in high yields [45 47].
Recently we studied the addition of selenium halides to 1-alkenes 1a 1c 48 49]. It has been
found that the reactions led to anti-Markovnikov adducts, bis(1-haloalk-2-yl) selenides 2a 2c and
3a 3c (kinetic products), which underwent rearrangement to thermodynamically stable Markovnikov
adducts, bis(2-haloalkyl) selenides 4a 4c and 5a 5c (Scheme 1). The rearrangement was supposed to
proceed via intermediate seleniranium species.
–
–
–
–
–
–
[ ,
–
–
–
–
R
X
R
X
R
X
R
X
R
R
R
R
R
SeX2 + 2
R
Se
X
Se
Se
R
Se
X
X
Se
X
X
X
4a-c
5a-c
1a-c
2a-c
3a-c
X = Cl (2, 4), Br (3, 5); R = C4H9 (a), C5H11 (b), C6H13 (c)
Scheme 1. The reactions of selenium dihalides with 1-alkenes.
Stereoselectivity of the addition of selenium halides to unsaturated compounds has been
basically studied for acetylenes [45 50 56]. The reactions of selenium dichloride and dibromide
,
–
with acetylene occurred stereoselectively as anti-addition affording (E,E)-bis(2-halovinyl) selenides
in high yields [50]. The addition of selenium dihalides to mono-substituted acetylenes, as a rule,
proceeded in a regioselective and stereoselective mode, giving anti-Markovnikov products with
(E)-stereochemistry [45,51,52].
In spite of sufficient progress in application of selenium dihalides in synthesis of organoselenium
compounds [18–55], the stereochemistry of the addition of these novel electrophilic reagents to the
double bond was not examined and required careful studying. Besides, the reactions of selenium
dichloride and dibromide with cycloalkenes were not described in the literature. However, studying
these reactions may make it possible to determine syn or anti process takes place on the addition of
selenium dihalides to the double bond. We endeavored to study these reactions and stereochemistry of
the addition.
2. Results and Discussion
We found that reactions of selenium dihalides with cycloalkenes 6a,b proceeded stereoselectively
as anti-addition giving hitherto unknown trans,trans-bis(2-halocycloalkyl) selenides 7a,b and 8a,b in
quantitative yields (Scheme 2).
Favorable conditions for efficient chemoselective and stereoselective reaction consist in addition
of selenium dichloride or dibromide to a solution of cycloalkenes 6a at
78 ◦C in methylene chloride
,
b
−
or chloroform. These reactions can be carried out at room temperature; however, the selectivity was
decreased in this case, and the formation of some by-products in 2–5% yields was observed.
The reliable evidence of the anti-addition could be obtained by X-ray studying the adducts of
selenium dihalides with cycloalkenes. However, the selenides 7a
In order to obtain crystals suitable for X-ray analysis, the halogenation of selenides 7a
,
b
and 8a
,
b
are liquid substances.
and 8a , with
,
b
,b
bromine and sulfuryl chloride, was carried out. We found that the halogenation reaction occurred
efficiently in hexane at 0 ◦C. Under these conditions, the reaction was accompanied by precipitation of
the target products, which can be easily isolated.

Molecules 2020, 25, 194
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n
n
n
n
n
n
CH2Cl2 (CHCl3)
-78 oC, 5 h
n
SeX2
2
Se
Se
Se
X
X
X
X
X
X
6a,b
7a,b, 8a,b
~100%
two diastereomers
C6H14
0 oC
SO2Cl2
or Br2
C6H14
0 oC
SO2Cl2
or Br2
X = Cl (7, 9), Br (8, 10)
n = 1 (a), 2 (b)
n
n
n
n
n
n
Se
Se
Se
X
X
X
X
X
X
X
X
X
X
X
X
9a,b, 10a,b
96-99%
two diastereomers
Scheme 2. Synthesis of compounds 7a,b and 8a,b and halogenated products 9a,b and 10a,b.
4-selanes 9a
,b and 10a,b
Using this method, we obtained trans,trans-dihalo[bis(2-halocycloalkyl)]-
λ
in 96–99% yields (Scheme 2). The materials suitable for single-crystal X-ray diffraction were obtained
from selanes 9a and 10a. The X-ray analysis of selanes 9a and 10a exhibited trans,trans-configuration
(Figure 1). The structural assignment of trans,trans-configuration of selenides 7a,b and 8a,b was also
proved by NMR spectroscopy, including NOESY experiments (see Supplementary Materials), which
indicated trans-disposition of the protons in the group SeCH-CHCl (no cross-peaks between these
protons were observed in 1H 2D NOESY spectra). Each of compounds 7a
,b, 8a,b, 9a,b, and 10a,b has
trans,trans-configuration and consist of two diastereomers (Scheme 2), which manifest in the NMR
spectra. In the 13C-NMR spectra of these compounds, every carbon atom appears as two close signals
which correspond to two diastereomers.
We failed to obtain pure products from the reaction of selenium dihalides and cyclooctene.
We supposed that equilibrium may take place between starting compounds and the product in the
reaction of selenium dibromide with cyclooctene or other alkenes. The reaction with cyclooctene was
carried out in chloroform or methylene chloride, using a 1:2 ratio of the reagents, at room temperature.
However, some amount of cyclooctene always remained in the reaction mixture, and the reaction
was not accomplished to the end. Adding acetonitrile to the reaction mixture increased conversion
and led to halogenation of the double bond, accompanied by the elemental selenium precipitation
(Scheme 3). The selenium precipitation led to the shift of the equilibrium, and the formation of
1,2-dibromocyclooctane (11) (~40% yield) was observed. It was noted in [57] that the adduct of PhSeCl
with cyclooctene was found to be relatively unstable and suffered decomposition over the course of
several hours at room temperature.
The anchimeric assistance effect, also known as neighboring-group participation, is usually
considered mainly as a factor accelerating the rate of nucleophilic substitution reaction. In the present
study, we are facing the new property of this effect, consisting in discovery of remarkable selenium
dibromide and organylselenenylbromide transfer reactions.
Figure 1. ORTEP molecular structure of selanes 9a and 10a (50% thermal ellipsoid probability).

Molecules 2020, 25, 194
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MeCN
RT
+
+ Se
SeBr2
+
Br
Se
Br
Br
Br
11
Scheme 3. The reaction of selenium dibromide with cyclooctene.
Mixing compounds 5a–5c or 8a,b (or their solutions) with alkene or alkyne leads to the formation
of new adducts of selenium dibromide. Possible options of the alkene-to-alkene transfer reactions of
selenium dibromide are presented in the Scheme 4.
The selenides 5a–5c and 8a,b are believed to exist in equilibrium with seleniranium cations and
the transfer reactions proceed via these intermediate species. The driving force for the generation
of seleniranium cations is high anchimeric assistance effect of the selenium atom. It was found that
this effect is more than one order of magnitude greater than the effect of the sulfur atom [42]. The
anchimeric assistance effects of selenium and sulfur atoms have been quantitatively estimated based
on the determination of the absolute and relative rates of nucleophilic substitution of chlorine in
2,6-dichloro-9-selena- and -thiabicyclo[3.3.1]nonanes obtained by the transannular addition of selenium
or sulfur dichloride to cis,cis-1,5-cyclooctadiene [42].
We found that a useful reagent to carry out the selenium dibromide transfer reaction is
bis(2-bromoethyl) selenide (12). The reactions of selenide 12 with 1-alkenes 1a,c or cyclohexene
(a 1:2 molar ratio of selenide 12 and the alkene) were monitored by NMR spectroscopy (Scheme 5).
The reagents were mixed in CDCl3 solution and closed NMR tubes were left at room temperature. The
1H and 13C-NMR spectra of the samples were recorded at regular intervals. In the case of cyclohexene,
a molar ratio of the compounds 12:13:8b was 34:51:15 after 10 days. The appearance of the intensive
signal of ethylene (5.36 ppm) is noteworthy. The complete conversion of 12 was observed after
~1 month with the formation of compounds 13 and 8b in approximately equimolar ratio. The reaction
of selenide 12 with 1-hexene was faster. The molar ratio of the compounds 12
:14a:5a was 18:50:32 after
four days, and the complete conversion of 12 was observed after two weeks.
R'
n
R'
R'
R
R
R
n
R
R
Se
Se
Se
Se
Se
Se
+
+
+
+
+
+
R
R
R'
Br
Br
Br
Br
Br
Br
Br
Br
n
n
R
n
Se
Br
Br
Br
Br
Br
n
n
R
R
n
R
Se
+
+
+
+
+
R
Se
Br
Br
Br
Br
m
Br
Br
n
n
m
n
m
m
n
+
Se
Se
Se
Br
Br
Br
Br
Br
R, R' - organyl; n, m = 1, 2
Scheme 4. The alkene-to-alkene transfer reactions of selenium dibromide.

Molecules 2020, 25, 194
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CDCl3
CDCl3
Br
Br
C2H4
+
+
Br
Br
Br
2
2
+
+
Se
Se
Se
Br
Br
Br
Br
6b
13
8b
12
R
R
R
Br
Se
C2H4
+
Se
5a,c
+
Se
R
Br
Br
1a,c
12
14a,c
R = C4H9 (a), C6H13 (c)
Scheme 5. The 1H-NMR monitoring of the alkene-to-alkene transfer reactions of SeBr2.
Alkynes were involved in the selenium dibromide transfer reactions. The reactions of selenide
12 with 1-hexyne and 3-hexyne (a 1:2 molar ratio of selenide 12 and the alkyne) were also monitored
by NMR spectroscopy at room temperature, using CDCl3 solutions in closed NMR tubes (Scheme 6).
The reactions led to unsymmetrical selenides 15a,b and 16a,b. The complete conversion of selenide 12
was observed after ~15 days in the reaction with 3-hexyne (~90% yield of selenide 16a). For the same
period of time, the conversion of compound 12 was 60% (~55% yield of selenide 15a) in the reaction
with 1-hexyne.
We found that the transfer reactions are considerably accelerated by using acetonitrile as a solvent.
Acetonitrile is a polar aprotic solvent with a high dielectric constant (~38), exhibiting the ability to
accelerate ionic reactions. The reactions of selenide 12 with terminal (1-hexyne and 1-heptyne) and
internal (3-hexyne and 4-octyne) alkynes were carried out in acetonitrile in closed flasks, using a 1:3
molar ratio of selenide 12 and the alkyne (Scheme 6). The complete conversion of selenide 12 and
the formation of products 16a
,b in 91–93% yield were observed in the reactions with internal alkynes
(3-hexyne or 4-octyne) after overnight stirring (14 h) at room temperature. In the case of terminal
alkynes (1-hexyne and 1-heptyne), the reactions gave compound 15a,b in 90–92% yield after 30 h of
stirring at room temperature.
With the goal to purify the product, selenide 16b was subjected to column chromatography (Al2O3,
hexane hexane/chloroform 4:1). However, instead of compound 16b, hydroxyl derivative 17 was
→
isolated in 70% yield (Scheme 7). Obviously, the bromine atom in compound 16b was substituted by
the hydroxyl group due to traces of moisture on the alumina. It is worth noting that the bromine atom
in the 2-bromoethylselenide group is very reactive with respect to nucleophilic substitution due to
high anchimeric assistance effect of the selenium atom [42].
Taking into account that selenides containing 2-bromoethyl moiety may decompose on purification
by column chromatography, the bromine atom was substituted by methoxy group in compound
15a by reaction with methanol in the presence of NaHCO3 at room temperature (Scheme 7). The
target product, (1E)-1-bromo-2-[(2-methoxyethyl)selanyl]hex-1-ene (18), was isolated in 71% yield by
column chromatography (Al2O3, hexane
demonstrate the possibility for selective preparation of unsymmetrical selenides of the type 15a,b–18
→
hexane/chloroform 9:1). The reactions (Schemes 6 and 7)
based on selenium dibromide transfer reactions.
The reaction of selenide 12 with 4-octyne (a 1:2 molar ratio) was also monitored by NMR
spectroscopy at room temperature, using CD3CN solution in a closed NMR tube. The decrease of
the content of starting selenide 12 with proportional increasing the contents of compound 16b and
bis[(E)-2-bromo-1-propyl-1-pentenyl] selenide (19b) was observed. The formation of symmetrical
selenide 19b occurred by the reaction of compound 16b with 4-octyne. After 145 h, the molar ratio of
the compounds 12:16b:19b was 34:51:15 (see Supplementary Materials).
When the reactions were carried out in open-air flasks, there was a better possibility for ethylene
evolution compared to closed NMR tubes, and the reactions proceeded faster in the open-air flasks.
The use of excess alkyne with respect to bis(2-bromoethyl) selenide was also useful for shifting the
equilibrium. When the reaction of selenide 12 with 4-octyne (a 1:3.3 molar ratio) was carried out in a

Molecules 2020, 25, 194
6 of 17
closed flask in acetonitrile at room temperature, pure selenide 19b was obtained in quantitative yield
in 90 h (Figure 2).
R
MeCN
Br
Br
Br
Br
Br
Br
R
H2C=CH2
+
+
+
Se
Se
(CDCl3)
12
15a,b
90-92%
R = C4H9 (a), C5H11 (b)
R
MeCN
Br
Br
R
R
H2C=CH2
+
Se
Se
12
(CDCl3)
R
16a,b
91-93%
R = Et (a), Pr (b)
Scheme 6. Synthesis of unsymmetrical selenides 15a,b and 16a,b.
Pr
Pr
Al2O3
(H2O)
Br
Br
Br
HO
Br
Se
16b
Se
Pr
Pr
17
70%
Bu
Bu
MeOH/NaHCO3
RT
MeO
Br
Br
Se
Se
18
15a
71%
Scheme 7. Synthesis of compounds 17 and 18.
Pr
Pr
Pr
Pr
Pr
Pr
Pr
Br
Br
Br
Br
Br
Br
Se
Se
19b
Se
MeCN
MeCN
Pr
Pr
Pr
12
16b
Figure 2. The 1H-NMR monitoring of the 16b and 19b formation from selenide 12 in MeCN.
When the flasks were equipped with a tube containing drying agent (CaCl2) in order to allow
ethylene releasing without moisture access in the flask, the complete conversion of 12 in the reaction

Molecules 2020, 25, 194
7 of 17
with internal alkynes was observed after overnight stirring, and pure divinyl selenides 19a
,b
were
obtained in quantitative yields (Scheme 8).
R
R
MeCN
RT
Br
Br
Br
Br
Br
Br
2
R
R
H2C=CH2
+
+
+
Se
Se
(excess)
R
R
12
19a,b
~100%
R = Et (a), Pr (b)
Bu Bu
Se
MeCN
RT
Br
Br
H2C=CH2
2
Bu
(excess)
+
Se
20
12
~100%
Scheme 8. The alkene-to-alkyne transfer reactions of selenium dibromide.
In the case of 1-hexyne, 40 h stirring at room temperature was required in order to complete the
reaction and to produce selenide 20 in a quantitative yield (Scheme 8). The reaction occurred in a
regioselective and stereoselective mode affording anti-Markovnikov product of (E,E)-stereochemistry.
The fastest version of these reactions consisted in carrying out the process with inert gas bubbling
(argon or nitrogen) into the mixture, in order to remove ethylene. The reactions of selenide 12 with
excess internal alkynes (3-hexyne and 4-octyne) in acetonitrile were accomplished in 1 h, and the
reaction with 1-hexyne was completed in 2 h at room temperature. However, the yields (90–96%) and
purity (90–95%) of the crude products 19a
,b and 20 were slightly lower compared to those achieved by
reactions proceeding in flasks (Scheme 8).
We also studied the direct reactions of selenium dibromide with 3-hexyne and 4-octyne under the
same conditions as in Scheme 8. These reactions proceeded in acetonitrile faster than the reactions of
compound 12 with 3-hexyne and 4-octyne but less selectively and the formation of some by-products
was observed. Changing acetonitrile for methylene chloride as a solvent and decreasing temperature
of the reaction to 0 ◦C allowed to increase the selectivity of the reactions of selenium dibromide with
3-hexyne and 4-octyne and to obtain pure products 19a,b in near quantitative yields.
We supposed that similar transfer reactions may also occur with addition products of
organylselenenyl bromides to alkenes. We obtained 2-bromoethyl, 2-bromocyclopentyl and
2-bromocyclohexyl phenyl selenides 21
cyclopentene and cyclohexene (Scheme 9) and studied the PhSeBr transfer reactions of these reagents
with some alkenes, cycloalkenes, and alkynes. Indeed, compounds 21 23 participated in the
–23 by addition of phenylselenenyl bromide to ethylene,
–
phenylselenenyl bromide transfer reactions, which proceeded smoothly at room temperature in
acetonitrile. Preliminary results demonstrate that the PhSeBr transfer reactions occur faster compared
to the SeBr2 transfer reactions with the same alkenes or alkynes under the same conditions.
Br
Br2
H2C=CH2
PhSe
PhSeSePh
PhSeBr
CH2Cl2
RT
CH2Cl2
RT
21
99%
c-C5H8
c-C6H10
PhSeBr
PhSe
PhSe
CH2Cl2
RT
CH2Cl2
RT
Br
Br
23
22
~100%
~100%
Scheme 9. Synthesis of compounds 21–23.
The reactions of selenide 21 with excess 1-hexyne, 3-hexyne, and 4-octyne were carried out
by stirring the reagents in acetonitrile overnight at room temperature in the flasks equipped with

Molecules 2020, 25, 194
8 of 17
a tube containing a drying agent (CaCl2). The reactions proceeded in a stereoselective mode, as
anti-addition giving products with (E)-stereochemistry 24 and 25a in quantitative yields (Scheme 10).
,
b
The regioselective formation of anti-Markovnikov adduct 24 was observed in the reaction with
1-hexyne. The addition of PhSeBr to 1-hexyne under the same conditions in acetonitrile was less
selective compared to the PhSeBr transfer reaction giving some by-products (5–7%) along with the
target compound 24.
Bu
MeCN
Br
H2C=CH2
Bu
+
+
Br
PhSe
PhSe
24
RT
21
~100%
R
Br
MeCN
RT
Br
H2C=CH2
PhSe
PhSe
+
+
R
R
R
R
R
21
25a,b
~100%
R
MeCN
RT
Br
+
PhSe
+
R
PhSe
Br
25a,b
22
~100%
Scheme 10. The alkene-to-alkyne transfer reactions of PhSeBr.
Surprisingly, adduct 22 can also serve as the efficient PhSeBr transfer reagent liberating
cyclopentene (bp 44 ◦C), which is evaporated during 40 h stirring (Scheme 10).
The alkene-to-alkene PhSeBr transfer reactions also occurred easily at room temperature in
acetonitrile. Examples of the alkene-to-alkene PhSeBr transfer (the reactions of selenide 21 with
cycloalkenes and 1-hexene) are presented in Scheme 11. The reactions (Schemes 10 and 11) proceeded
very fast (~1 h) when inert gas (argon or nitrogen) was slowly bubbled into the mixture in order to
remove ethylene.
Two possible pathways of the SeBr2 or PhSeBr transfer reactions can be discussed. If the selenides
containing the 2-bromoethyl moiety exist in some equilibrium with the starting compounds, generated
SeBr2 or PhSeBr may add to other unsaturated compound (pathway
A is depicted in Scheme 12
on the example of compounds 12 21, and 1-hexyne). Another reaction pathway is based on the
,
assumption that the intermediates involved in the transfer reactions are seleniranium species (pathway
B, Scheme 12).
n
n
Br
Br
MeCN
RT
+
H2C=CH2
H2C=CH2
+
PhSe
PhSe
PhSe
Br
Br
21
21
6a,b
22, 23
95-97%
MeCN
RT
Bu
+
PhSe
+
Bu
26
92%
Scheme 11. The alkene-to-alkene transfer reactions of PhSeBr.

Molecules 2020, 25, 194
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A
Se
Br
SeBr
R
SeBr2 + C2H4
Br
H2C=CH2
+
Se
Br
Se
Br
Br
Br
Br
12
A
R
B
R
R
R
R
R
B
Br
Br
R
Br
Se
Se
C2H4
+
Se
Br
Br
Se
Br
Br
Br
R
R
A
R
Br
Ph
H2C=CH2 + PhSeBr
Br
PhSe
Se
Br
PhSe
21
B
R
R
Ph
C2H4
+
Br
R
Br
Se
PhSe
R = Bu
Scheme 12. The possible pathways (
A and B) of the alkene-to-alkyne transfer reactions of SeBr2 and
PhSeBr on the example of reactions of compounds 12 and 21 with 1-hexyne.
Seleniranium species have been discussed for a long time as reactive intermediates in addition
reactions of selenium-centered electrophiles to the double bond [57
–74]. Some of them have been
detected or isolated [57 59 71 74]. Recently, Poleschner and Seppelt isolated and fully characterized
–
, –
series of moderately stable seleniranium and telluriranium salts [73]. The seleniranium ions have
been found to play a key role in the process of chirality transfer in asymmetric synthesis reactions
studied by Wirth, Santi, Back, and others [60
alkene-to-alkene transfer of selenenium cations in the asymmetric reactions [60
of Russian scientists [58 59], the enthalpic barrier for seleniranium ion–alkene transfer has been
–
67]. Wirth and co-workers have postulated facile
,
63]. In the reports
,
computationally evaluated and found to be considerably lower compared to that of thiiranium
ion–alkene transfer. Denmark and co-workers have experimentally observed direct selenium group
transfer from phenyl- and butylseleniranium ions to alkenes [57]. The transfer occurred instantaneously
at low temperature (
are more likely to follow the pathway
−
70 ◦C) in these experiments. We think that the SeBr2 and PhSeBr transfer reactions
, taking into account the ease of the selenium group transfer
B
from seleniranium species to unsaturated bonds. Regiochemistry and stereochemistry of the SeBr2
and PhSeBr transfer reactions are determined by the formation of seleniranium species. For example,
in the case of monosubstituted acetylene (e.g., 1-hexyne), the attack of bromide anion occurs at
the unsubstituted carbon atom of the seleniranium cation leading to anti-Markovnikov products
(Scheme 12, pathway B). The formation of seleniranium species also determines the reaction course as
anti-addition.
3. Materials and Methods
3.1. General Information
X-ray diffraction experiments were carried out on a Bruker D8 Venture Photon 100 CMOS
diffractometer with Mo-Kα radiation (λ = 0.71073 Å). X-ray crystallographic data for compounds
9a (CCDC 1965943) and 10a (CCDC 1502244) are shown in Supplementary Materials. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html. We recorded 1H
(400.1 MHz) and 13C (100.6 MHz) NMR spectra on a Bruker DPX-400 spectrometer, in 5–10% solution
in CDCl3. Of note, 1H and 13C chemical shifts (
the residual solvent peak of CDCl3 (
δ
) are reported in parts per million (ppm), relative to
δ
= 7.27 and 77.00 ppm in 1H- and 13C-NMR, respectively). Mass

Molecules 2020, 25, 194
10 of 17
spectra were recorded on a Shimadzu GCMS-QP5050A, with electron impact (EI) ionization, at 70 eV.
Elemental analysis was performed on a Thermo Flash EA 1112 Elemental Analyzer (USA).
3.2. Synthesis of Compounds 7a,b–10a,b
trans,trans-Bis(2-chlorocyclopentyl) selenide (7a). Typical Procedure. A sol◦ution of selenium dichloride
(2.5 mmol) in CH2Cl2 (20 mL) was added dropwise to a cooled ( 78 C) solution of cyclopentene
−
(0.347 g, 5.1 mmol) in CH2Cl2 (30 mL). The mixture was stirred at
78 ◦C for 4 h and 1 h at room
−
temperature. The solvent was removed on a rotary evaporator. The residue was dried in vacuum,
giving the product as a yellowish oil. Yield: 0.715 g (quantitative). 1H-NMR (400.1 MHz, CDCl3):
δ
1.70–1.92 (m, 4H, CH2), 1.98–2.17 (m, 4H, CH2), 2.41–2.55 (m, 4H, CH2), 3.58–3.64 (m, 2H, CHSe),
4.41–4.48 (m, 2H, CHCl). 13C-NMR (100.6 MHz, CDCl3):
34.91 (CH2), 47.03 (CHSe, JC-Se = 69 Hz), 47.41 (CHSe, JC-Se = 65 Hz), 66.42, 66.60 (CHCl). Anal.
Calcd for C10H16Cl2Se: C, 41.98; H, 5.64; Cl, 24.78; Se, 27.60. Found, %: C, 42.25; H, 5.83; Cl, 25.08;
Se, 27.29.
δ 22.25, 22.30 (CH2), 31.27, 31.61 (CH2), 34.81,
1
1
trans,trans-Bis(2-chlorocyclohexyl) selenide (7b) was obtained as a yellowish oil (0.785 g) in quantitative
1
yield from selenium dichloride and cyclohexene under the same conditions as compound 7a. H-NMR
(400.1 MHz, CDCl3):
δ 1.44–1.47 (m, 4H, CH2), 1.57–1.81 (m, 8H, CH2), 2.24–2.38 (m, 4H, CH2),
3.25–3.30 (m, 2H, CHSe), 4.23–4.30 (m, 2H, CHCl). 13C-NMR (100.6 MHz, CDCl3): 22.03 (CH2), 22.26
(CH2), 23.58 (CH2), 23.90 (CH2), 30.35 (CH2), 33.07 (CH2), 45.92 (CHSe, 1JC-Se = 66 Hz) 46.53 (CHSe,
1JC-Se = 69 Hz), 63.86 (CHCl), 64.45 (CHCl). Anal. Calcd for C12H20Cl2Se: C, 45.88; H, 6.42; Cl, 22.57;
Se, 25.13. Found, %: C, 46.15; H, 6.61; Cl, 22.87; Se, 24.89.
trans,trans-Bis(2-bromocyclopentyl) selenide (8a) was obtained as a light yellow oil (0.938 g) in quantitative
1
yield from selenium dibromide and cyclopentene under the same conditions as compound 7a. H-NMR
(400.1 MHz, CDCl3):
δ
1.76–1.91 (m, 4H, CH2), 1.96–2.07 (m, 2H, CH2), 2.11–2.18 (m, 2H, CH2), 2.43–2.59
22.39
(m, 4H, CH2), 3.67–3.77 (m, 2H, CHSe), 4.43–4.54 (m, 2H, CHBr). 13C-NMR (100.6 MHz, CDCl3):
δ
(CH2), 22.45 (CH2), 31.22 (CH2), 31.53 (CH2), 35.27 (CH2), 35.41 (CH2), 47.74 (CHSe, 1JCSe = 67 Hz)
48.16 (CHSe, 1JCSe = 64 Hz), 57.18 (CHBr), 57.22 (CHBr). Anal. Calcd for C10H16Br2Se: C, 32.03; H,
4.30; Br, 42.62; Se, 21.08. Found, %: C, 31.85; H, 4.12; Br, 42.98; Se, 20.73.
trans,trans-Bis(2-bromocyclohexyl) selenide (8b) was obtained as a light yellow oil (1.008 g) in quantitative
1
yield from selenium dibromide and cyclohexene under the same conditions as compound 7a. H-NMR
(400.1 MHz, CDCl3):
δ 1.49–1.57 (m, 6H, CH2), 1.74–1.79 (m, 4H, CH2), 1.89–1.93 (m, 2H, CH2), 2.29–2.43
(m, 4H, CH2), 3.38–3.41 (m, 2H, CHSe), 4.53–4.58 (m, 2H, CHBr). 13C-NMR (100.6 MHz, CDCl3):
δ
22.41 (CH2), 23.36 (CH2), 23.57 (CH2), 30.37 (CH2), 32.90 (CH2), 46.65 (CHSe, 1JCSe = 66 Hz), 47.07
(CHSe, 1JCSe = 67 Hz), 57.73 (CHBr), 58.06 (CHBr). Anal. Calcd for C12H20Br2Se: C, 35.76; H, 5.00; Br,
39.65; Se, 19.59. Found, %: C, 35.48; H, 4.85; Br, 40.03; Se, 19.82.
trans,trans-Dichloro[bis(2-chlorocyclopentyl)]-λ ). A solution of sulfuryl chloride (0.27 g,
4-selane (9a
2 mmol) in hexane (10 mL) was added to a cooled to
in hexane (15 mL) and the mixture was stirred at
temperature. The precipitate was filtered off and dried in vacuum to give the product as a white
powder, mp = 114–115 ◦C. Yield: 0.685 g (96%). The crystals suitable for single-crystal X-ray diffraction
−
0 ◦◦C solution of selenide 7a (0.572 g, 2 mmol)
−
0 C for 8 h and allowed to warm to room
1
were obtained by recrystallization from chloroform. H-NMR (400.1 MHz, CDCl3):
δ 1.98–2.03 (m,
6H, CH2), 2.38–2.42 (m, 4H, CH2), 2.63–2.70 (m, 2H, CH2), 4.59–4.68 (m, 2H, CHSe), 4.98–4.99 (m, 2H,
CHCl). 13C-NMR (100.6 MHz, CDCl3):
23.20 (CH2), 29.49 (CH2), 29.65 (CH2), 36.54 (CH2), 36.71
δ
(CH2), 60.29 (CHCl), 60.35 (CHCl), 77.51 (CHSe), 78.07 (CHSe). Anal. Calcd for C10H16Cl4Se: C, 35.64;
H, 4.52; Cl, 39.72; Se, 22.12. Found, %: C, 35.36; H, 4.33; Cl, 40.05; Se, 21.81.
trans,trans-Dichloro[bis(2-chlorocyclohexyl)]-
conditions as compound 9a as a white powder (0.739 g), mp = 133–135 C. H-NMR (400.1 MHz,
CDCl3): 1.39–1.49 (m, 4H, CH2), 1.76–1.84 (m, 3H, CH2), 1.85–1.93 (m, 3H, CH2), 2.04–2.16 (m, 1H,
λ
4-selane (9b) was obtained in 96% yield under the same
◦
1
δ

Molecules 2020, 25, 194
11 of 17
CH2), 2.29–2.33 (m, 1H, CH2), 2.40–2.44 (m, 2H, CH2), 2.47–2.55 (m, 1H, CH2), 2.85–2.88 (m, 1H, CH2),
4.24–4.36 (m, 2H, CHSe), 4.50–4.63 (m, 2H, CHCl). 13C-NMR (100.6 MHz, CDCl3):
25.22, 25.39 (CH2),
δ
25.75, 25.97 (CH2), 30.24, 30.41 (CH2), 38.23, 38.60 (CH2), 58.67 (CHCl), 79.03 (CHSe). Anal. Calcd for
C12H20Cl4Se: C, 37.43; H, 5.24; Cl, 36.83; Se, 20.51. Found, %: C, 37.34; H, 5.41; Cl, 37.18; Se, 20.87.
trans,trans-Dibromo[bis(2-bromocyclopentyl)]-λ ). A solution of bromine (0.32 g, 2 mmol) in
4-selane (10a
hexane (10 mL) was added to a cooled to 0 ◦C solution of selenide 10a (0.75 g, 2 mmol) in hexane (15 mL),
and the mixture was stirred at 0 ◦C for 4 h and allowed to warm to room temperature. The precipitate
was filtered off and dried in vacuum, to give the product as a yellow powder, mp = 101–102 ◦C. Yield:
1.06 g (99%). The crystals suitable for single-crystal X-ray diffraction were obtained by recrystallization
from chloroform. 1H-NMR (400.1 MHz, CDCl3): 2.03–2.06 (m, 4H, CH2), 2.21–2.23 (m, 2H, CH2),
2.46–2.54 (m, 4H, CH2), 2.70–2.73 (m, 2H, CH2), 4.65–4.74 (m, 2H, CHSe), 5.07–5.08 (m, 2H, CHBr).
13C-NMR (100.6 MHz, CDCl3):
δ 23.71 (CH2), 23.80 (CH2), 30.66 (CH2), 30.95 (CH2), 37.73 (CH2), 38.00
(CH2), 50.50 (CHBr), 50.53 (CHBr), 75.34 (CHSe), 76.06 (CHSe). Anal. Calcd for C10H16Br4Se: C, 22.46;
H, 3.02; Br, 59.76; Se, 14.76. Found, %: C, 22.18; H, 2.87; Br, 60.13; Se, 15.05.
trans,trans-Dibromo[bis(2-bromocyclohexyl)]-
conditions as compound 10a as a yellow powder (1.103 g), mp = 95–96 C. H-NMR (400.1 MHz,
λ
4-selane (10b) was obtained in ◦98% yield under the same
1
CDCl3):
δ 1.44–1.57 (m, 4H, CH2), 1.75–1.84 (m, 2H, CH2), 1.90–1.98 (m, 2H, CH2), 2.02–2.11 (m, 2H,
CH2), 2.17–2.27 (m, 2H, CH2), 2.31–2.35 (m, 2H, CH2), 2.51–2.58 (m, 2H, CH2), 2.66–2.76 (m, 2H, CH2),
2.92–2.95 (m, 2H, CH2), 4.23–4.38 (m, 2H, CHSe), 4.75–4.87 (m, 2H, CHBr). 13C-NMR (100.6 MHz,
CDCl3):
δ 25.00 (CH2), 26.10 (CH2), 31.84, 31.96 (CH2), 39.18, 39.66 (CH2), 53.21, 55.37 (CHBr), 72.95,
75.41 (CHSe). Anal. Calcd for C12H20Br4Se: C, 25.61; H, 3.58; Br, 56.78; Se, 14.03. Found, %: C, 25.33;
H, 3.39; Br, 57.19; Se, 13.82.
3.3. Synthesis of Compounds 17–26
(4E)-4-Bromo-5-[(2-hydroxyethyl)selanyl]oct-4-ene (17). A solution of 4-octyne (0.11 g, 1 mmol) in MeCN
(1 mL) was added to a solution of selenide 12 (0.1 g, 0.34 mmol) in MeCN (1.5 mL), and the mixture
was stirred in a 200 mL round-bottomed closed flask overnight (14 h) at room temperature. The solvent
was removed by a rotary evaporator. The residue contained compounds 16b (0.117 g, 91% yield)
and 19b in a 20:1 molar ratio (the NMR data). The residue was subjected to column chromatography
(Al2O3, hexane
→
hexane/chloroform 4:1). Instead of compound 16b, hydroxyl derivative 17 (0.068 g,
1
70% yield based on compound 16b) was isolated as a colorless oil. H-NMR (400 MHz, CDCl3):
3.78–3.75 (m, 2H), 2.91–2.84 (m, 4H), 2.53–2.49 (m, 2H), 1.65–1.54 (m, 4H), 0.98–0.92 (m, 6H). 13C-NMR
δ
(100.6 MHz, CDCl3): δ: 129.50, 126.83, 61.62, 43.21, 40.32, 30.03, 21.88, 21.36, 13.52, 13.01. MS (EI): m/z
(%) 314 (20) [M+·], 207 (9), 149 (9), 109 (50), 67 (100), 41 (64). Anal. Calcd. For C10H19BrOSe (314.12):
C, 38.24; H, 6.10; Br, 25.44; Se, 25.14%. Found, %: C, 38.52; H, 5.98; Br, 25.19; Se, 24.87%.
(1E)-1-Bromo-2-[(2-methoxyethyl)selanyl]hex-1-ene (18). A solution of 1-hexyne (0.082 g, 1 mmol) in
MeCN (1 mL) was added to a solution of selenide 12 (0.1 g, 0.34 mmol) in MeCN (1.5 mL), and the
mixture was stirred in a 200 mL round-bottomed closed flask for 30 h at room temperature. The solvent
was removed by a rotary evaporator. The residue contained compounds 15a (0.107 g, 90% yield) and
unconverted selenide 12 in a 9:1 molar ratio (the NMR data). The residue was dissolved in chloroform
(1 mL) and methanol (0.3 mL) and NaHCO3 (0.084 g, 1 mmol) were added. The mixture was stirred
for 24 h at room temperature and then filtered; solvents were removed by a rotary evaporator. The
residue was subjected to column chromatography (Al2O3, hexane
compound 18 (0.065 g, 71% yield based on compound 15a) as a colorless oil. 1H-NMR (400 MHz,
CDCl3): 6.33 (s, 1H) 3.63–3.59 (m, 2H), 3.38 s, 2.90–2.87 (m, 2H), 2.48–2.44 (m, 2H), 1.55–1.51 (m, 2H),
1.41–1.35 (m, 2H), 0.97–0.93 (m, 3H). 13C-NMR (100 MHz, CDCl3):
134.56, 103.64, 71.71, 58.67, 35.17,
→
hexane/chloroform 9:1), giving
δ
δ
29.81, 25.44, 22.16, 13.93. MS (EI): m/z (%) = 300 (20) [M+·], 242(10), 202 (22), 163 (33), 108 (21), 79 (57),
59 (100). Anal. Calcd. for C9H17BrOSe (300.09): C, 36.02; H, 5.71; Br, 26.63; Se, 26.31%. Found, %: C,
35.75; H, 5.56; Br, 26.39; Se, 26.11%.

Molecules 2020, 25, 194
12 of 17
Bis(E-2-bromo-1-ethyl-1-butenyl) selenide (19a). A solution of 3-hexyne (0.14 g, 1.7 mmol) in MeCN (1 mL)
was added to a solution of selenide 12 (0.1 g, 0.34 mmol) in MeCN (1 mL). The mixture was stirred in a
100 mL round-bottomed flask equipped with a tube containing a drying agent (CaCl2) overnight (18 h)
at room temperature. The solvent was removed by a rotary evaporator, and the residue was dried in
1
vacuum, giving compound 19a (0.137 g) as a light-yellow oil in quantitative yield. H-NMR (400 MHz,
CDCl3):
δ 2.85 (q, J = 7.3 Hz, 4H), 2.41 (q, J = 7.3 Hz, 4H), 1.12 (t, J = 7.3 Hz, 6H), 1.07 (t, J = 7.3 Hz, 6H).
13C NMR (100 MHz, CDCl3): δ 129.84 (1JC-Se = 108.7 Hz), 129.49, 35.06 (2JC-Se = 10.6 Hz), 32.57, 13.42,
12.00. Anal. Calcd. For C12H20Br2Se (403.06): C, 35.76; H, 5.00; Br, 39.65; Se, 19.59%. Found: C, 36.04;
H, 4.87; Br, 39.42; Se, 19.87%.
Bis(E-2-bromo-1-propyl-1-pentenyl) selenide (19b) was obtained in quantitative yield as a light-yellow
oil (0.156 g) from 4-octyne and selenide 12 in acetonitrile under the same conditions as compound
1
19a. H-NMR (400 MHz, CDCl3):
δ
2.83 (t, J = 7.5 Hz, 4H), 2.38 (t, J = 7.5 Hz, 4H), 1.64–1.53 (m, 8H),
129.79, 128.38, 43.04, 40.79, 21.89, 21.10, 13.56, 12.95.
0.95–0.90 (m, 12H). 13C-NMR (100 MHz, CDCl3):
δ
Anal. Calcd. For C16H28Br2Se (459.16): C, 41.85; H, 6.15; Br, 34.80; Se, 17.20%. Found: C, 42.14; H, 5.98;
Br, 35.07; Se, 17.03%.
Bis[(1E)-1-bromohex-1-en-2-yl] selenide (20). A solution of 1-hexyne (0.137 g, 1.67 mmol) in MeCN (1 mL)
was added to a solution of selenide 12 (0.065 g, 0.22 mmol) in MeCN (1 mL). The mixture was stirred
in a 100 mL round-bottomed flask equipped with a tube containing a drying agent (CaCl2) for 40 h at
room temperature. The solvent was removed by a rotary evaporator, and the residue was dried in
1
vacuum, giving compound 20 (0.089 g) as a light-yellow oil in quantitative yield. H-NMR (400 MHz,
CDCl3):
δ
6.45 (s, 2H), 2.46–2.42 (m, 4H), 1.56–1.48 (m, 4H), 1.41–1.32 (m, 4H), 0.96–0.93 (m, 6H).
134.97, 107.40, 34.77, 29.68, 22.12, 13.90. Anal. Calcd. for C12H20Br2Se
13C NMR (100 MHz, CDCl3):
δ
(403.06): C, 35.76; H, 5.00; Br, 39.65; Se, 19.59%. Found, %: C, 35.91; H, 4.89; Br, 39.42; Se, 19.33%.
2-Bromoethyl phenyl selenide (21). Dry ethylene was bubbled to a flask containing CH2Cl2 (10 mL) with
stirring for 10 min at room temperature. A solution of PhSeBr [(4 mmol), prepared from Ph2Se2 (0.624 g,
2 mmol) and bromine (0.320 g, 2 mmol) in CH2Cl2 (15 mL)] was added dropwise to the flask for
30 min with stirring. The ethylene bubbling (~30 mL/min) was continued during the PhSeBr addition
and 40 min after the addition. The mixture was stirred additionally for 1 h at room temperature and
filtered. The solvent was removed in vacuum, giving selenide 21 (1.046 g, 99% yield) as a light-yellow
1
oil. H-NMR (400 MHz, CDCl3):
δ
7.56–7.53 (m, 2H), 7.32–7.30 (m, 3H), 3.59–3.55 (m, 2H), 3.30–3.26
133.25, 129.20, 128.11, 127,57, 30.58, 28.55. Anal. Calcd. for
(m, 2H). 13C-NMR (100 MHz, CDCl3):
δ
C8H9BrSe (264.02): C, 36.39; H, 3.44; Br, 30.26; Se, 29.91%.
2-Bromocyclopentyl phenyl selenide (22). A solution of PhSeBr [(2 mmol), prepared from Ph2Se2 (0.312 g,
1 mmol) and bromine (0.16 g, 1 mmol) in CH2Cl2 (10 mL)] was added dropwise to a solution of
cyclopentene (0.15 g, 2.2 mmol) in CH2Cl2 (10 mL), at such a rate that discoloration of the reaction
mixture occurred after each drop. The mixture was stirred for 1 h at room temperature, and the solvent
was removed on a rotary evaporator. The residue was dried in vacuum, giving the product as a
1
light-yellow oil. Yield: 0.608 g (quantitative). H-NMR (400 MHz, CDCl3):
δ 1.80–1.89 (m, 2H, CH2),
2.02–2.17 (m, 2H, CH2), 2.51–2.59 (m, 2H, CH2), 4.08–4.10 (m, 1H, CHSe), 4.50–4.51 (m, 1H, CHBr),
7.32–7.33 (m, 3H, CHAr), 7.57 (m, 2H, CHAr). 13C-NMR (100.6 MHz, CDCl3):
δ 22.30 (CH2), 29.93
(CH2), 34.80 (CH2), 50.40 (CHSe, 1JC-Se = 65 Hz), 58.58 (CHBr), 127.49 (CHAr), 129.19 (CHAr), 131.36
(CHAr), 133.40 (CHAr). Anal. Calcd for C11H13BrSe: C, 43.45; H, 4.31; Br, 26.28; Se, 25.97. Found, %: C,
43.67; H, 4.49; Br, 26.48; Se, 26.21.
2-Bromocyclohexyl phenyl selenide (23) was obtained in quantitative yield as a light-yellow oil (0.636 g)
from PhSeBr and cyclohexene in CH2Cl2 under the same conditions as compound 22. 1H-NMR
(400.1 MHz, CDCl3):
2.39–2.47 (m, 2H, CH2), 3.73–3.74 (m, 1H, CHSe), 4.55 (m, 1H, CHBr), 7.27–7.33 (m, 3H, CHAr), 7.61–7.63
(m, 2H, CHAr). 13C-NMR (100.6 MHz, CDCl3):
22.32 (CH2), 22.38 (CH2), 23.14 (CH2), 29.05 (CH2),
δ 1.52–1.67 (m, 3H, CH2), 1.81–1.85 (m, 2H, CH2), 1.96–1.97 (m, 1H, CH2),
δ

Molecules 2020, 25, 194
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29.08 (CH2), 29.09 (CH2), 32.30 (CH2), 32.33 (CH2), 48.90 (CHSe, 1JC,Se 64 Hz), 56.57 (CHBr), 127.57
(CHAr), 128.92 (CHAr), 131.16 (CHAr), 134.35 (CHAr). Anal. Calcd for C12H15BrSe: C, 45.31; H, 4.75; Br,
25.12; Se, 24.82. Found, %: C, 43.05; H, 4.93; Br, 24.86; Se, 25.09.
(1E)-1-Bromohex-1-en-2-yl phenyl selenide (24). A solution of 1-hexyne (0.091 g, 1.1 mmol) in MeCN
(1 mL) was added to a solution of selenide 21 (0.073 g, 0.28 mmol) in MeCN (1 mL). The mixture was
stirred in a 100 mL round-bottomed flask equipped with a tube containing a drying agent (CaCl2)
for 30 h at room temperature. The solvent was removed by a rotary evaporator, and the residue was
1
dried in vacuum, giving compound 24 (0.089 g) as a light-yellow oil in quantitative yield. H-NMR
(400 MHz, CDCl3):
δ
7.52–7.50 (m, 2H), 7.32–7.27 (m, 3H), 6.39 (s, 1H), 2.45–2.41 (m, 2H), 1.58–1.51 (m,
136.59, 133.58, 129.38, 129.02,
2H), 1.37–1.30 (m, 2H), 0.93–0.89 (m, 3H). 13C-NMR (100 MHz, CDCl3):
δ
127.91, 105.98, 34.69, 29.78, 22.08, 13.88. Anal. Calcd. for C12H15BrSe (318.11): C, 45.31; H, 4.75; Br,
25.12; Se, 24.82%. Found, %: C, 45.17; H, 4.58; Br, 24.85; Se, 25.09%.
(3E)-4-Bromohex-3-en-3-yl phenyl selenide (25a). A solution of 3-hexyne (0.091 g, 1.1 mmol) in MeCN
(1 mL) was added to a solution of selenide 21 (0.1 g, 0.38 mmol) in MeCN (1 mL). The mixture was
stirred in a 100 mL round-bottomed flask equipped with a tube containing a drying agent (CaCl2)
overnight (14 h) at room temperature. The solvent was removed by a rotary evaporator, and the
residue was dried in vacuum, giving compound 25a (0.12 g) as a light-yellow oil in quantitative yield.
1H-NMR (400 MHz, CDCl3):
2H), 1.16–1.12 (m, 3H), 1.07–1.03 (m, 3H). 13C NMR (100 MHz, CDCl3):
δ
7.43–7.41 (m, 2H), 7.29–7.27 (m, 3H), 2.95–2.89 (m, 2H), 2.50–2.45 (m,
131.99, 130.64, 130.62, 129.83,
δ
129.23, 127.08, 35.37, 32.69, 13.48, 12.34. Anal. Calcd. for C12H15BrSe (318.11): C, 45.31; H, 4.75; Br,
25.12; Se, 24.82%. Found, %: C, 45.58; H, 4.61; Br, 25.31; Se, 25.11%.
(4E)-5-Bromooct-4-en-4-yl phenyl selenide (25b) was obtained in quantitative yield as a light-yellow oil
(0.131 g) from 4-octyne and selenide 21 in acetonitrile under the same conditions as compound 25a
1H-NMR (400 MHz, CDCl3):
7.43–7.41 (m, 2H), 7.29–7.27 (m, 3H), 2.93–2.89 (m, 2H), 2.45–2.41 (m,
2H), 1.67–1.53 (m, 4H), 0.96–0.92 (m, 3H), 0.90–0.86 (m, 3H). 13C-NMR (100 MHz, CDCl3):
132.11,
.
δ
δ
130.59, 129.50, 129.20, 129.15, 127.07, 43.30, 40.66, 21.86, 21.28, 13.44, 13.00. Anal. Calcd. for C14H19BrSe
(346.16): C, 48.58; H, 5.53; Br, 23.08; Se, 22.81%. Found: C, 48.34; H, 5.38; Br, 22.81; Se, 23.04%.
The experiment under Ar. A solution of 4-octyne (0.11 g, 1 mmol) in MeCN (1 mL) was added to a
solution of selenide 21 (0.066 g, 0.25 mmol) in MeCN (1 mL), and argon was bubbled into the mixture
for 1 h. The solvent was removed by a rotary evaporator and the residue was dried in vacuum, giving
compound 25b (0.084 g, 97% yield) as a light-yellow oil (~95% purity).
2-Bromohexyl phenyl selenide (26). A solution of 1-hexene (0.185 g, 2.2 mmol) in MeCN (1 mL) was
added to a solution of selenide 21 (0.074 g, 0.28 mmol) in MeCN (1.5 mL), and the mixture was stirred
in a 200 mL round-bottomed closed flask for 24 h at room temperature. The solvent was removed
by a rotary evaporator. The residue (0.089 g) was dried in vacuum, giving the product 25 (~92%
1
purity) as a light-yellow oil. Yield: 92%. H-NMR (400 MHz, CDCl3):
δ 7.55–7.53 (m, 2H), 7.31–7.27
(m, 3H), 4.21–4.14 (m, 1H), 3.58–3.53 (m, 1H), 3.35–3.29 (m, 1H), 2.16–2.08 (m, 1H), 1.84–1.75 (m, 1H),
1.54–1.27(m, 4H), 0.93–0.89 (m, 3H). 13C-NMR (100 MHz, CDCl3):
36.97, 36.35, 29.26, 21.94, 13.87.
δ 133.21, 129.26, 128.10, 127.49, 55.34,
4. Conclusions
Remarkable alkene-to-alkene and alkene-to-alkyne transfer reactions of selenium dibromide and
PhSeBr have been discovered. The compounds containing the 2-bromoethylselanyl moiety easily
exchange SeBr2 or RSeBr with alkenes, cycloalkenes, and alkynes at room temperature. The efficient
SeBr2 and PhSeBr transfer reagents are bis(2-bromoethyl) selenide and 2-bromoethyl phenyl selenide,
which liberate ethylene, leading to a shift in equilibrium. The favorable conditions include the use
of acetonitrile as a solvent and removing the formed alkene (e.g., ethylene or cyclopentene). The
regioselective and stereoselective synthesis of E-2-bromovinyl selenides 15–20, 24, and 25a,b in up to

Molecules 2020, 25, 194
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quantitative yields was developed based on the SeBr2 and PhSeBr transfer reactions, which proceeded
with higher selectivity compared to analogous addition reactions of SeBr2 and PhSeBr to alkynes under
the same conditions. High selectivity, quantitative yields, mild-reaction conditions, and very simple
work-up procedures are important features of this approach.
The reactions of selenium dihalides with cycloalkenes proceed stereoselectively as anti-addition,
affording hitherto unknown trans,trans-bis(2-halocycloalkyl) selenides 7a
,b and 8a,b in quantitative
yields (Scheme 2). The reliable evidence of the anti-addition has been obtained by X-ray analysis
of dihalo[bis(2-halocycloalkyl)]-λ
4-selanes 9a and 10a, as well as by NMR spectroscopy studies of
selenides 7a,b and 8a,b.
Supplementary Materials: The following are available online, synthesis of compounds 12–16a,b and monitoring
data, Figure S1, examples of 1H- and 13C-NMR spectra of the obtained compounds, X-ray crystallographic data of
compounds 9a and 10a.
Author Contributions: Conceptualization and the paper preparation, V.A.P.; methodology and data curation,
M.V.M. (Maxim V. Musalov); research experiments, E.O.K. and A.G.K.; supervision, S.V.A.; investigation, V.A.Y.
and M.V.M. (Maria V. Musalova); X-ray studies, T.N.B.; NMR experiments, A.I.A. All authors have read and
agreed to the published version of the manuscript.
Funding: This research was funded by Russian Science Foundation, grant number 18-13-00372.
Acknowledgments: The authors thank Baikal Analytical Center SB RAS for providing the instrumental equipment
for structural investigations.
Conflicts of Interest: The authors declare no conflict of interest.
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