Addition of selenium(II) bromide to arylalkynylamides - a route to hypervalent T-shaped 10-Se-3 systems

Article abstract of DOI:10.1016/j.tetlet.2015.06.026

Abstract A route for the generation of hypervalent T-shaped 10-Se-3 systems is described involving an interaction between in situ prepared selenium(II) bromide and an aryl alkynyl amide derivative. The existence of hypervalent selenium in both the solid and solution states has been supported by X-ray analysis and ⁷⁷Se NMR data.

Full text of DOI:10.1016/j.tetlet.2015.06.026

Accepted Manuscript
Addition of selenium(II) bromide to arylalkynylamides – a route to hypervalent
T-shaped 10–Se–3 systems
Edgars Paegle, Sergey Belyakov, Gilbert Kirsch, Pavel Arsenyan
PII:
S0040-4039(15)01019-9
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.06.026
TETL 46418
Reference:
Tetrahedron Letters
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Revised Date:
Accepted Date:
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2 June 2015
9 June 2015
Please cite this article as: Paegle, E., Belyakov, S., Kirsch, G., Arsenyan, P., Addition of selenium(II) bromide to
arylalkynylamides – a route to hypervalent T-shaped 10–Se–3 systems, Tetrahedron Letters (2015), doi: http://
dx.doi.org/10.1016/j.tetlet.2015.06.026
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Edgars Paegle, Sergey Belyakov, Gilbert Kirsch, Pavel Arsenyan*

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Addition of selenium(II) bromide to arylalkynylamides – a route to hypervalent
T-shaped 10–Se–3 systems
Edgars Paegle,a Sergey Belyakov,a Gilbert Kirsch,b Pavel Arsenyan*,a
a Latvian Institute of Organic Synthesis, Aizkraukles 21, LV-1006, Riga, Latvia. e-mail: pavel.arsenyan@lycos.com,
Phone: +(371)29849464, Fax: +(371) 67550338
b
Université de Lorraine 1, SRSMC UMR 7565, boulevard Arago, 57070, Metz, France
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A route for the generation of hypervalent T–shaped 10-Se-3 systems is described involving an
interaction between in situ prepared selenium(II) bromide and an aryl alkynyl amide derivative.
The existence of hypervalent selenium in both the solid and solution states has been supported
by X-ray analysis and 77Se NMR data.
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
oxazole
hypervalent
selenium
selenium bromide
10-Se-3 system
Selenium is able to form highly versatile organic and
inorganic hypervalent compounds due to its wide range of
oxidative states and its unoccupied valence d orbitals.1 Trivalent
selenium compounds bearing a formal positive charge on the
selenium atom have been extensively described,1 but much less is
known about the negatively charged T-shaped trivalent selenium
groups. These type of compounds, which feature a linear X–Se–
X or X–Se–Y moiety (X = Cl, Br, I; Y = CN), are frequently
designated as a 10–Se–3 system, which means that 10 electrons
are associated with the central selenium atom but only six (3
pairs) are involved in bonding.2 The most widely used method for
the formation of T-shaped selenium moieties containing a C–Se
bond involve an oxidative addition of halogens (Cl2,3 Br2,3a,c,4
I23a,c,4a,5), interhalogens (IBr),6 or pseudohalogens (ICN)7 to the
selenium atom of the corresponding selone derivative. However,
generation of such a system has also been accomplished by the
addition of selenium halides to an N-heterocyclic carbene8 or by
reaction of diaryldiselenide derivatives with an excessive amount
of the corresponding dihalogen.9 Herein, we report an alternative
method for the synthesis of a new type of oxazolinium derived
hypervalent T-shaped 10–Se–3 system utilizing the addition of
selenium(II) bromide to the triple bond of the corresponding N-
aryl(hetaryl)alkynyl pyrrolidinone.
due to their stability and relatively simple preparation. The initial
alkynyl amides 3a-g were prepared by a two-step procedure
(Scheme 1). Benzaldehydes 1a-f and thiophene-2-carbaldehyde
(1g)
dibromovinylbenzenes(thiophene) 2a-g by the Corey–Fuchs11
protocol. Subsequent CuI/DMEDA (N,N’-
were
converted
to
the
corresponding
dimethylethylenediamine) catalyzed coupling12 of 2a-g with
pyrrolidin-2-one led to the desired alkynyl amides 3a-g. Next,
alkynyl amides 3a-g were treated with in situ prepared
selenium(II) bromide13 in CHCl3. Unexpectedly, the reaction of
phenylethynyl amide 3a with SeBr2 failed to yield the
corresponding 3-bromobenzo[b]selenophene derivative, instead
generating a new type of 10–Se–3 system 4a. Since selenirenium
species have been widely14 postulated as the key intermediates in
reactions of selenium electrophiles with C≡C triple bonds, we
propose that the reaction begins with the coordination of SeBr2 to
the triple bond of 3a, forming selenirenium type adduct A, which
induces an intramolecular nucleophilic attack of oxygen onto the
carbon of the triple bond to form a five-membered cycle. The
intramolecular nucleophilic attack of the carbonyl oxygen seems
to be favored over the expected selenobromination. Product 4a
began to precipitate as a yellow amorphous solid during the
addition of alkynyl amide 3a to the selenium(II) bromide
solution. Complete consumption of the starting material was
observed in 15 min (TLC), then the reaction was left to stir
overnight to achieve complete precipitation of the product, which
was isolated in 50 % yield after filtration. In a similar manner, a
series of hypervalent selenium compounds 4b-g were prepared in
moderate to high yields. It was concluded that electron-rich
substrates were generally more suitable for these reactions, thus
enabling the desired products to be obtained in higher yields.
As the selenohalogenation of aryl(thienyl)alkynes10 is one of
the most straightforward synthetic pathways for the preparation
of benzo[b]selenophenes and selenophenothiophenes, we were
inspired to further expand the existing protocol. Because almost
nothing was known about the selenohalogenation of aryl alkyne
derivatives bearing heteroatoms directly attached to the triple
bond, we decided to pursue this research direction. Aryl alkynyl
amides were found to be suitable substrates for this investigation

2
Tetrahedron
This was exemplified by the low yield obtained for o-
by crystallization from an oversaturated solution in acetone, but
in the cases of 4b, e, g, acetonitrile was used as a solvent. In the
crystal structures of 4a and 4g, strong intermolecular σ-hole
interactions between the T-shaped selenium atom and the
bromine of another molecule were observed. By means of these
fluorosubstituted 3f and quantitative yield using trimethoxy
substituted 3d. A modified isolation procedure was required to
obtain 4c, d, f as these products did not precipitate directly from
the reaction mixture, even after stirring for 24 h. Thus, the
reaction mixture was evaporated under reduced pressure after
stirring for 15 min at 0 °C, and the corresponding product was
successfully precipitated by stirring in a mixture of petroleum
ether and CHCl3. The modified procedure also worked well for
the other products, but highly pure compounds were more easily
obtained by direct precipitation from the reaction mixture. To the
best of our knowledge, this is a new route for preparation of
zwitterionic T-shaped trivalent selenium derivatives.
interactions,
centrosymmetric
molecular
pseudodimers
containing square-planar coordinated selenium atoms were
formed. The corresponding intermolecular Se…Br distances are
equal to 3.4439(8) Å and 3.3374(5) Å for 4a and 4g,
respectively. A perspective view of the molecular pseudodimer
of the thiophene derivative 4g is illustrated in Figure 1A. Similar
centrosymmetric pseudodimers formed by Se…Br σ-hole
interactions have also been observed in previously reported
crystal structures;15 however, the same interactions were weaker,
and their lengths fell in the range of 3.491-3.610 Å. Unlike the
crystal structures of phenyl derivative 4a and thienyl analogue 4g
(Figure 1A), the Se…Br σ-hole interactions in 4-fluorophenyl
substituted 4e did not lead to the formation of analogous
centrosymmetric pseudodimers (Figure 1B). Because of the
elevated electronegativity of C-5, strong intermolecular CH…F
type hydrogen bonds are present, leading to the formation of
molecular chains along the screw axes 21 parallel to the lattice
parameter a (space group is Pbca). In this case, the distance of
the intermolecular Se…Br interaction is 3.556(1) Å, and the
length of the hydrogen bonds is 2.948(9) Å. A similar type of
packing for the 10-Se-3 system has been shown by Mugesh4a and
co-workers in the crystal structure of dibromo(1-methyl-3-
a
Br
b
Ar
Ar
Ar
N
O
1a-g
58-88%
21-79%
Br
2a-g
3a-g
c
O
Br2
Se
Br
Se
N
Br
Ar
N
O
Ar
4a-g
A
O
Br
Se
Br
Se
Br
Se
Br
Se
N
Br
N
Br
N
Br
N
O
Br
MeO
MeO
MeO
O
benzylimidazolium-2-yl)selenide.
This
compound forms
O
O
Ph
molecular chains along the screw axes 21 parallel to the lattice
parameter b (space group Pbca) supported by the corresponding
Se…Br σ-hole interactions with a distance equal to 3.507(1) Å.
MeO
4b (82%)d
4a (50%)d
4c (57%)
OMe
4d (quant.)
Br
Se
Br
Se
Br
Se
N
O
In contrast to the crystal structures of 4a, 4e, and 4g, no
shortened intermolecular Se…Br contacts were found in the
crystal structure of 4b. Instead, the selenium atom formed a
moderate intermolecular Se…O σ-hole bond (3.232(5) Å) with the
oxygen atom of the methoxy group, which leads to the
continuation of molecular chains along the crystallographic
direction [101] (Figure 1C). As a result, similar to 4-fluorophenyl
substituted 4e, no centrosymmetric pseudodimers were observed
in the crystal structure of 4-methoxyphenyl derivative 4b.
Considering that the crystal structure of 4b belongs to space
group Pn, non-centrosymmetric physical properties described by
third-rank tensors (piezoelectricity, second harmonic generation,
etc.) could be expressed. Due to their symmetry, all components
of the third-rank tensors for centrosymmetric crystals are zero.16
The main geometric parameters characterizing the square-planar
coordination of selenium in compounds 4a, 4e, and 4g are listed
in Table 1. It should be noted that the length of the Se…Br σ-hole
interaction in thienyl derivative 4g is the shortest among all
known hypervalent T-shaped 10-Se-3 systems. However, it
seems that the nature of the substituent has a slight influence on
the σ-hole interaction length. This length is most strongly
affected by the crystal packing effect and temperature.17 The
packing coefficients for 4a, 4b, 4e, and 4g were calculated based
on Kitaigorodsky’s18 approach (Table 1). A consistent correlation
between the packing coefficient and the length of the Se…Br σ-
hole interaction in 4a, 4b, and 4g was observed, meaning that
denser crystal structures yield weaker intermolecular interactions.
In the structures studied, the atomic lines Br15−Se14−Br16 have
considerable angles with the oxazolinium plane. Overall, the
tricyclic systems in the molecular structures are nearly planar; the
carbon atom of C6 insignificantly deviates from the oxazolinium
planes. The dihedral angles between the aryl rings and the
oxazolinium planes are as follows: 1.6(4)° (4a), 14.4(5)° (4b),
Br
N
Br
N
Br
O
O
S
F
F
4e (60%)d
4g (77%)d
4f (16%)
Scheme 1. Synthetic procedure for the preparation of hypervalent T-shaped
compounds 4a-g. (a) 1a-g (1.0 equiv.), CBr4 (1.5 equiv.), PPh3 (3.0 equiv.),
CH2Cl2, 0 °C, 2 h; (b) 2a-g (1.0 equiv.), pyrrolidin-2-one (1.0 equiv.), CuI
(12 mol%), DMEDA (18 mol%), Cs2CO3 (4.0 equiv.), dioxane, 60 °C, 24 h;
(c) 3a-g (1.0 equiv.), SeBr2 (1.0 equiv.), CHCl3, 0 °C, 15 min. d To achieve
complete precipitation of the corresponding products 4a, b, e, g the reaction
mixture was stirred at room temperature for an additional 24 h.
The chemical shift values in the 77Se NMR spectra for known
analogous trivalent systems are found in the range of
approximately 300 to 400 ppm,3a,4b,c showing considerably higher
shielding than in the case of the corresponding divalent PhSeBr
system (888 ppm in dioxane). The 77Se chemical shifts for the
new derivatives 4a-g ranged from 344 ppm for 4g to 374 ppm for
4d. These results suggest the hypervalent state of selenium in
solution. Compounds 4a-g were relatively stable and could be
stored in a closed system at room temperature for several months
without any signs of decomposition, however, the slow
appearance of red selenium was observed in the presence of air.
These compounds are insoluble in nonpolar organic solvents but
slightly soluble in acetonitrile and acetone. In highly polar
solvents (DMSO, DMF, and water), these substances quickly
decompose which was accompanied by the precipitation of
amorphous selenium. Because of their thermal instability, no
melting points were obtained. In general, upon heating above
100 °C, compounds 4a-g decompose, as evidenced by a color
change.
The structures of 4a, b, e, g were unambiguously confirmed
by X-ray analysis (Figure 1). Monocrystals of 4a were obtained

3
25.1(5)° (4e) and 4.4(3)° (4f). It should be noted that the crystal
structure 4f features static disorder in the thienyl group.
containing heteroatoms directly attached to the triple bond is in
progress.
An alternative method for the generation of zwitterionic
hypervalent T–shaped 10-Se-3 systems via the treatment of N-
ethynylpyrrolidinones with SeBr2 in moderate to high yields has
been described. The existence of hypervalent selenium in both
the solid state and solution has been unambiguously confirmed
by X-ray analysis and 77Se NMR data. Future research dedicated
to studying the reactions of aryl alkynyl amides with other
selenium halides and the use of other aryl alkynyl derivatives
Supporting Information
Supporting information containing full experimental data,
copies of the 1H, 19F, and 13C NMR spectra of all compounds, and
crystallographic data for compounds 4a, 4b, 4e and 4g19 can be
found, in the online version, at http://dx.doi.org/
Figure 1. A: view of molecular pseudodimers formed by 4g, showing the atom-numbering scheme; B: projection of the crystal structure of 4e along
crystallographic direction [100], showing the screw axes of second order, unit cell outlines, σ-hole and hydrogen bonds; C: Partial crystal structure of
4b, showing the formation of a σ-hole interaction and unit cell outlines. Displacement ellipsoids are drawn at 50% probability level and H atoms are
shown as small spheres of arbitrary radii.
Table 1. Geometrical parameters of square-planar coordinated selenium in 4a, 4b, 4e, and 4g
4a
4b
4e
4g
C3−Se14, Å
Se14−Br15, Å
Se14−Br16, Å
1.906(3)
2.6356(8)
2.5569(8)
3.4439(8)
173.5(1)
63.2(1)
0.152(5)
0.713
1.904(5)
2.534(1)
2.637(1)
3.232(5)[a]
164.4(3)[b]
85.1(2)
0.244(6)
0.709
1.870(5)
2.586(1)
2.600(1)
3.556(1)
156.6(2)
81.9(2)
0.070(5)
0.677
1.894(3)
2.6199(5)
2.5724(5)
3.3374(5)
168.5(1)
65.6(1)
0.256(4)
0.736
Se14···Br15, Å
C3−Se14···Br15#1,°
Br15−Se14−Br16,°
C6 deviation, Å
Packing coefficient
[a] Se14···O17 σ-hole bond length; [b] C3−Se14···O17 angle.
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Acknowledgments
The financial support for this work provided by the Latvian
Council of Science (447/2012) is gratefully acknowledged. This
research was partially supported by EC 7th Framework
Programme project REGPOT-CT-2013-316149-InnovaBalt.
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The crystal structures were solved by direct methods and refined
by full-matrix least squares. The main crystallographic data and
refinement parameters of the crystal structures are listed in the
ESI. For further details, the crystallographic data for 4a (CCDC
1047477), 4b (CCDC 1045665), 4e (CCDC 1045663), and 4f
(CCDC 1045664) is deposited with the Cambridge
Crystallographic Data Centre as Supplementary Publications.
Copies of the data can be obtained, free of charge, on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK.