Preparation of selenofunctionalized heterocycles via iodosobenzene-mediated intramolecular selenocyclizations of olefins with diselenides

Article abstract of DOI:10.1016/j.cclet.2021.02.050

An intramolecular selenocyclizations of olefins mediated by a commercially available hypervalent iodine(III) reagent, PhIO, was developed. This method provided access to a wide range of selenenylated heterocycles under ambient conditions. The striking advantages of this protocol over all previous methods include mild reaction conditions, easy operation, good yields, high levels of functional group compatibility, large–scale application and suitability for the late-stage functionalization of complex molecules of biological importance.

Full text of DOI:10.1016/j.cclet.2021.02.050

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Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Communication
Preparation of selenofunctionalized heterocycles via
iodosobenzene-mediated intramolecular selenocyclizations of olefins
with diselenides
*
*
Peng-Fei Wang, Wei Yi, Yong Ling, Liang Ming, Gong-Qing Liu , Yu Zhao
School of Pharmacy, Nantong University, Nantong 226001, China
A R T I C L E I N F O
A B S T R A C T
Article history:
An intramolecular selenocyclizations of olefins mediated by a commercially available hypervalent iodine
(III) reagent, PhIO, was developed. This method provided access to a wide range of selenenylated
heterocycles under ambient conditions. The striking advantages of this protocol over all previous
methods include mild reaction conditions, easy operation, good yields, high levels of functional group
compatibility, large–scale application and suitability for the late-stage functionalization of complex
molecules of biological importance.
Received 6 January 2021
Received in revised form 20 February 2021
Accepted 23 February 2021
Available online xxx
Keywords:
Selenocyclizations
Olefins
© 2021 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.
Published by Elsevier B.V. All rights reserved.
Heterocycles
Iodosobenzene
Diselenides
Selenenylated molecules have widespread applications in
the fields of pharmaceuticals and materials science because of
their interesting biological activities [1] and suitable fluores-
cence properties [2]. Furthermore, organoselenium com-
pounds have been widely used as convenient intermediates
or reagents and catalysts in organic synthesis [3]. Thus,
significant efforts have been made to develop various strate-
gies for the incorporation of selenium functional groups into
organic molecules [4].
On the other hand, the difunctionalization of readily accessible
alkenes has become a powerful tool for the construction of highly
functionalized skeletons in organic synthesis [5]. In this context,
selenocyclizations of unsaturated amines are a useful concept for
the preparation of selenenylated and nitrogenated heterocycles,
which could provide an excellent opportunity for medicinal
chemists in drug discovery. Additionally, the simultaneous
incorporation of synthetically versatile seleno and nitro moieties
has enabled further elaboration of these products as intermediates
in syntheses of structurally diverse molecules. Accordingly, over
the years, substantial efforts have been devoted to advance this
topic, and numerous elegant procedures have been developed as a
result. Early reports on these reactions usually involved electro-
philic selenium species-induced cyclizations with organoselenium
reagents, e.g., phenylselenenyl halides have been reported with
olefinic amines [6], (sulfon)amides [7], oximes [8], thiazolines [9],
carbamates [10], imines [11], imidates [12], hydrazines [13] and
hydrazine [14] (Scheme 1a). Typically, this selenoamination of
olefins occurs via intramolecular nucleophilic attack onto sele-
niranium ion 3 to form nitrogen-containing heterocycles with the
aid of additives, such as Lewis acids [8a], Brønsted acids [7a,13], or
silica gel [7e,10b–10e]. However, the presence of nucleophilic
halides often causes some undesirable processes, such as the
incorporation of halogens, which decrease the selectivity [15].
Additionally, the addition adducts sometimes can further react
with phenylselenenyl halides to afford the deselenenylated
products [16]. Furthermore, these procedures are usually incom-
patible with a large number of important functional groups due to
the formation of hydrogen halide as a side-product during the
course of the reaction.
Diselenide is preferable as an alternative selenylation agent in
this transformation because it is bench-stable, readily available
and easy to handle during the synthesis process. For example,
Tiecco et al. reported the reaction of unsaturated amines with
phenylselenenyl sulfate, generated from the oxidation of diphenyl
diselenide with ammonium persulfate in the presence of
trifluoromethanesulfonic acid, to afford phenylseleno-substituted
N-heterocyclics (Scheme 1b) [17]. Again, these cyclization
reactions were carried out in acidic conditions, and substrates
bearing acid-sensitive functional group, such as silyl ethers or
ketones, were not tolerated under these reaction conditions.
* Corresponding authors.
E-mail addresses: gqliu@ntu.edu.cn (G.-Q. Liu), zhaoyu@ntu.edu.cn (Y. Zhao).
https://doi.org/10.1016/j.cclet.2021.02.050
1001-8417/© 2021 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.
Please cite this article as: P.-F. Wang, W. Yi, Y. Ling et al., Preparation of selenofunctionalized heterocycles via iodosobenzene-mediated
intramolecular selenocyclizations of olefins with diselenides, Chin. Chem. Lett., https://doi.org/10.1016/j.cclet.2021.02.050

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in this transformation, as no reaction occurred in the absence of
PhIO (entry 12).
With these optimized reaction conditions, we turned our
attention to investigating the substrate scope of the title
transformation with a diverse range of N-alkenyl sulfonamides
using 2a as the selenium source. As indicated in Scheme 2, both N-
aryl and N-alkylsulfonamides produced the corresponding 2-
phenylselenomethylpyrrolidines with good to excellent isolated
yields (3b-3j). The structural skeleton of 2-phenylselenomethyl-
pyrrolidine was confirmed by an X-ray diffraction experiment
performed with compound 3b (CCDC: 2022145). As shown in the
ORTEP drawing, 3b bore an envelope chair conformation with two
phenyl groups at both axial and equatorial positions, the phenyl-
seleno moiety and Ts group also stayed at equatorial positions.
Notably, p-nitrobenzenesulfonamide resulted in the correspond-
ing pyrrolidine derivative 3d with moderate yield. This is most
likely because of the low nucleophilicity of sulfonamide caused by
the strong electron-withdrawing nitro group at the para position of
the benzene ring. Reactions of substrates bearing different
substituents on the main chain proceeded well to produce their
corresponding products 3k–3q with good yields. It is noteworthy
that the Thorpe–Ingold effect was not required in the current
cyclization, and selenoaminated products 3n and 3p were isolated
with 90% and 95% yields, respectively.
Importantly, the protocol of the present reaction was very
simple: the alkene, PhIO and diselenide were stirred in simple
glassware under ambient conditions. Thus, this reaction could be
applied to a large-scale synthesis without any difficulties. For
instance, when the reaction of 1p (1.16 g, 5 mmol) was performed
with Ph2Se2 (1.56 g, 5 mmol) and PhIO (1.10 g, 5 mmol) under the
optimized reaction conditions, the desired product 3p was
obtained with 83% yield (1.60 g) after recrystallization.
N-Tosyl o-allyl aniline 1r worked well in this transformation,
and the corresponding indoline 3r was obtained with good yield.
Reaction of 1-sulfonamido-5-hexene substrate gave lower isolated
yield of seleno piperidine (3s), although a lower yield was
obtained, possibly due to unfavorable entropy of the current
Scheme 1. Intramolecular selenoamination.
Despite these advances, general methods for the preparation of
various arylselenopyrrolidines and alkylselenopyrrolidines in
particular are still limited. Our goal was to develop an efficient
and operationally simple selenoamination, in which readily
available, inexpensive, and easy-to-handle reagents were
employed. In continuation of our interest in hypervalent iodine
chemistry [18], we conjectured that diselenides would be oxidized
in the presence of a commercially available hypervalent iodine(III)
reagent to form electrophilic selenium species (RSe+), which would
participate in the electrophilic selenocyclization of olefins
(Scheme 1c).
We started our investigation with the optimization of the
reaction conditions using N-(2,2-diphenylpent-4-en-1-yl)-4-
methylbenzenesulfonamide (1a) as a model substrate due to its
ease of preparation and UV-absorption property, which facilitates
the monitoring of the reaction progress. The preliminary results
are summarized in Table 1.
Based on our previous results [18a], we first employed iodine
pentoxide (I2O5) as reaction promoter and diphenyl diselenide
(Ph2Se2) (2a) as selenium source. However, only a trace amount of
selenoamination product 3a was obtained (Table 1, entry 1). Other
promoters, such as oxone, K2S2O8, O2, PhI(OAc)2 and PhIO were
tested to further improve the yield, and PhIO produced the best
result (entries 2–6). The effect of the solvents on the course of the
reaction was also noteworthy (entries 7–10), and CH2Cl2 was the
most suitable solvent for the reaction. Decreasing the amount of
Ph2Se2 to 0.5 equiv. led to a decrease in the conversion (entry 11).
Control experiments indicated that PhIO played an important role
cyclization [19]. Substituents on the C C double bonds showed a
¼
low impact on the reaction. Di- and trisubstituted terminal
alkenes, such as 1t and 1u, were efficiently converted into their
corresponding pyrrolidines with satisfactory yields. More complex
bicyclic and bridged ring systems were also accessible using this
protocol (3v-3y). The relative configuration of the phenylseleno
unit and amino group in 3x and 3y was assigned to trans, as
expected for a selenoamination via an intermediate seleniranium
ion. The desymmetrization of diene 1z delivered seleno-pyrroli-
dine 3z with 80% yield as a mixture of diastereomers. Substrates
bearing one substitute on the main chain also underwent high
cyclization to produce the corresponding pyrrolidines 3aa-3ac
with a good isolated yield but low diastereoselectivity. The
resulting disubstituted pyrrolidines can serve as useful precursors
for the synthesis of biological hexahydro-1H-pyrrolizines and
octahydroindolizines [20]. The relative stereochemistry of trans-
3ac was established by an X-ray diffraction experiment (CCDC:
2022148). Finally, we further applied this methodology to
architecturally complex sulfonamide substrates. In this regard, a
glibenclamide precursor-derived sulfonamide smoothly engaged
in this selenoamination and afforded acceptable yields of 3ad. The
sulfonamide 1ae derived from celecoxib, which is a nonsteroidal
anti-inflammatory drug, worked well under the standard con-
ditions, delivering the corresponding products 3ae with good
yields.
Table 1
Optimization of the reaction conditions.a
Entry
Promoter
Solvent
Yield (%)b
1
2
3
4
5
6
7
8
I2O5
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
hexane
MeOH
DMF
trace
80
43
NR
85
91
46
53
63
31
44
–
oxone
K2S2O8
O2
PhI(OAc)2
PhIO
PhIO
PhIO
PhIO
9
10
11c
12
PhIO
PhIO
DMSO
CH2Cl2
CH2Cl2
Next, we examined the generality of this transformation with
respect to different diselenides, and the results are summarized in
Scheme 3. As depicted in Scheme 3, the dialkyl diselenides were
suitable reaction partners under the reaction conditions, and provided
a
Reaction conditions: 1a (0.2 mmol), 2a (0.2 mmol), promoter (0.2 mmol),
solvent (2 mL), r.t., 20 h.
b
Isolated yields.
0.1 mmol of 2a was used.
c
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Scheme 2. Scope of the intramolecular selenoamination. Reaction conditions: 1 (0.2 mmol,1.00 equiv.), 2a (0.2 mmol,1.00 equiv.), PhIO (0.2 mmol,1.00 equiv.), DCM (2 mL), r.
a
t., the numbers in the parentheses are the diastereomeric ratios determined by 1H NMR. 5 mmol scale.
In consideration of the remarkably broad substrate scope
accessible from this transformation, the current procedure was
applied to the preparation of other seleno-containing heterocycles.
As shown in Scheme 4, a series of seleno oxazolines were produced
successfully under optimal conditions (6aa-6ad). The generality of
the title procedure has also been demonstrated by a series of
unsaturated carboxylic acids furnishing the corresponding phenyl-
selenolactones in good yield (6ba-6bd). Additionally, using the
alkenoic alcohols as substrates, we observed the construction of
five- and six-membered cyclic ethers in high yields (6ca-6cd).
Subsequently, we continued to investigate the generality of this
transformation with respect to different olefinic dicarbonyl
compounds. As we expected, different seleno dihydrofurans
(6da-6de) could be obtained in acceptable isolated yields under
Scheme 3. Scope of diselenides. Reaction conditions: 1a (0.2 mmol, 1.00 equiv.), 2
(0.2 mmol, 1.00 equiv.), PhIO (0.2 mmol, 1.00 equiv.), DCM (2 mL), r.t.
standard conditions. Finally, preparation of isoxazolidine 6ea was
also possible using N-alkenoxyl sulfonamide derivative 5ea as the
starting material.
Mechanistic studies were then performed to gain knowledge
regarding the reaction pathway. Initially, no dramatic decline in the
yield was observed after the addition of 2.0 equiv. of 2,2,6,6-
tetramethyl-1-piperidinyloxy (TEMPO) to the reaction mixture
(Scheme 5a), which indicated that a radical process likely did not
occur. PhIO was insoluble in CH2Cl2 because it displays a zigzag
polymeric chain structure according to X-ray powder diffraction
and EXAFS studies [21]. It, however, could be mostly dissolved
when Ph2Se2 was added to the CH2Cl2 solution (Fig. S1 in
Supporting information). This result indicated that PhIO can react
with Ph2Se2 to generate new reactive species in the current
reaction system. This phenomenon was in accordance with NMR
observations, which showed that the signal pattern for the
aromatic protons of Ph2Se2 changed significantly after the addition
of PhIO, indicating the mutual interaction between Ph2Se2 and
the corresponding products with good yields (4a-4c). Thus, this
newly developed PhIO-promoted selenoamination provides, for
the first time, a feasible way to access alkylselenopyrrolidines.
Different diaryl diselenides with an electron-withdrawing group or
electron-donating group at the para position all showed good
reactivity in the procedure (4d-4h). Additionally, naphthyl dis-
elenide was successfully reacted with 1a to produce the respective
2-selenomethylpyrrolidine 4i with 77% yield. Finally, heteroaryl
diselenides, such as dithienyl diselane were subjected to the
procedure, and the selenation product (4k) was isolated with 73%
yields. Unfortunately, other dichalcogenides, such as diphenyl
disulfide(Ph2S2)anddiphenylditelluride(Ph2Te2), failedtoproduce
the desired products in this transformation, presumably because
Ph2S2 and Ph2Te2 cannot be oxidized to the corresponding
electrophilic species under the present conditions.
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Scheme 4. Selenocyclization of different olefins. Reaction conditions: 5 (0.2 mmol, 1.00 equiv.), Ph2Se2 (0.2 mmol, 1.00 equiv.), PhIO (0.2 mmol, 1.00 equiv.), DCM (2 mL), r.t.
In summary, we developed an iodosobenzene-mediated
intramolecular selenocyclization of olefins, which produced
selenenylated heterocycles with good yields and excellent
functional group compatibility. Preliminary mechanistic studies
indicate that the title reaction takes place via an active
electrophilic selenium intermediate generated in situ from PhIO
and diselenide. We believe that the developed methodology can be
applied to potential operational procedures for the synthesis of
nitrogen- and selenium-containing molecules due to its good
isolated yields, high functional group tolerance, mild conditions
and operational simplicity. Efforts are in progress to elucidate the
mechanistic details of this reaction by means of DFT-calculations
Scheme 5. Experiments for mechanistic studies.
and to disclose its scope and limitations.
PhIO and, thus, resulting in changes in the electronic environment
surrounding the phenyl groups in Ph2Se2 (Fig. S2 in Supporting
information).
Declaration of competing interest
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
When the reaction was performed in acetone under otherwise
identical conditions, α-phenylselenenylated ketone 7 was obtained
unexpectedly instead of the selenoamination product (Scheme 5b).
Compound 7 was probably a result of an electrophilic attack of the
phenylselenenyl cation (PhSe+) to the enol form of acetone [22].
Furthermore, 2 equiv. of indole was added to the reaction mixture
under optimal conditions to capture any possible PhSe+ formed
during the reaction. Indole was employed as a competitive
substrate based on the fact that it could be easily selenenylated
by PhSe+ [23]. As expected, indolyl selenide 8 was detected with
15% isolated yield (Scheme 5c).
Acknowledgments
This study was supported by the Natural Science Foundation of
Jiangsu Province (No. BK20170439), Science and Technology Plan
Projects of Nantong (Nos. JC2019102 and JC2020072).
Appendix A. Supplementary data
According to the aforementioned information and previous
reports [24], a possible reaction pathway for this transformation is
outlined in Scheme 6. First, diselenide is oxidized by PhIO to
generate RSe+, which serves as a reactive electrophilic intermedi-
ate to induce the title selenocyclization.
Supplementarymaterialrelatedtothisarticlecanbefound, inthe
online version, at doi:https://doi.org/10.1016/j.cclet.2021.02.050.
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5